The Production of Marine Iron Objects in Europe Following the First Industrial Revolution: The Akko Tower Shipwreck Test Case

Abstract

Four ferrous objects, a winch, a heart-shaped shackle, a deadeye strap with a futtock plate, and a stud-link chain controller, that were retrieved from the Akko Tower shipwreck were studied by different methods, including conventional metallography, light microscopy, scanning electron microscopy with energy-dispersive spectroscopy, optical emission spectroscopy, microhardness measurements, and the novel field multi-focal metallography (FMM), in order to determine their composition, microstructure, and manufacturing methods. The results of FMM agree well with conventional destructive metallography. The winch drum was made of grey cast iron and its shaft was wrought iron; the heart-shaped shackle and the deadeye strap with a futtock plate were wrought iron; and the stud-link chain controller was grey cast iron similar in composition and microstructure to the winch. All the wrought iron items revealed a similar composition and microstructure. Based on the composition, microstructure, and manufacturing processes of the four items, it is suggested that they were manufactured in the mid-nineteenth century. The high quality of these items indicates that they were produced using controlled processes, probably in the same workshop.

1. Introduction

1.1. The Akko Tower Shipwreck

Waves lap the walls of Akko (Acre, St. Jean d’Acre), once a bustling port in the northern part of Haifa Bay, Israel. At the entrance to the harbour, 35 m north of the Tower of Flies, in 4.4 m of water, lies the Akko Tower shipwreck. The shipwreck was discovered in 1966 and was surveyed in 1975 by Avner Raban, and in 1981, an underwater excavation workshop of the shipwreck was directed by J. Richard Steffy [1,2,3]. A full-scale underwater excavation of the shipwreck took place over four seasons (2012, 2013, 2015, and 2016) by the Leon Recanati Institute for Maritime Studies of the University of Haifa (IAA permits G-23/2012, G-78/2013, G-16/2015, and G-25/2016) [1].

The area covered by the remains of the ship, oriented northeast to southwest, was 17.8 m long and a maximum of 6.4 m wide. A preliminary study of the hull remains revealed a French construction tradition using British metal rigging and fasteners. Dendrochronology, 14C wiggle-matching, and Bayesian chronological modelling indicate that the ship was probably built in the mid-1850s [4].

Raban’s 1975 survey produced four well-preserved ferrous objects: a winch, a heart-shaped shackle, a deadeye strap with a futtock plate, and a stud-link chain controller. The wooden deadeye itself did not survive. These items were received from the Israel Antiquities Authority (IAA) after cleaning and removal of encrustation and concretion layers. They are the subject of this multidisciplinary approach to the study of the production of naval iron objects in Europe following the Industrial Revolution.

1.2. Descriptions of the Ferrous Objects

The winch (Figure 1a and Supplementary Material Figure S1a) is a mechanical winding device that allows adjusting the tension of, or extending or retracting, a rope, wire, or cable [5,6]. The total weight of this winch was 11.5 kg. Its drum was 149 mm long, with a maximum diameter of 146 mm and an average diameter of 112 mm. The shaft was 296 mm long and 20 to 24 mm thick.

Heart-shaped shackle (Figure 1b and Supplementary Material Figure S2a) is a primary connecting link in the rigging system, with a bolt and pin made of iron, allowing fast connection and disconnection of rigging elements, such as chain cables [7,8]. The heart shape of the shackle enables the connection of lines, chains, or ropes at different angles. This shackle weighed 3.2 kg. Its link was 281 mm long, with an average thickness of 18 mm. It was 153 mm long by 55–63 mm wide and had an average thickness of 19 mm. The bolt diameter was 27.5 mm.

Deadeye strap with futtock plate (Figure 1c and Supplementary Material Figure S2b). Deadeyes were part of the standing rigging system of a sailing ship. A typical deadeye was made of a circular hardwood block with groves for ropes. They were used in pairs to set the tension of stays (ropes, wires, or shafts located on the bow and stern of the vessel) and shrouds (sets of ropes providing lateral support to the ship’s masts). They secured the lower end of the shroud to a metal chain plate fastened to the ship’s hull. The main metal parts of such deadeyes included a strap wrapped around the wooden block, a loop forge-welded around a bolt, a securing element below the loop, a futtock plate, and a shackle that connected the futtock plate to an iron chain with a bolt [8,9,10,11]. The strap weighed 1.7 kg. Its internal diameter was 139 mm and its external diameter was 164 mm. The strap itself was 51 mm wide and 12 mm thick. The futtock plate was 381 mm long, 65 mm wide, and 9.5 mm thick. The bolt diameter was 29 mm.

Stud-link chain controller (Figure 1d and Supplementary Material Figure S1b) was possibly used to support the anchor stud-link chain [12]. This item weighed 12 kg and was 405 mm long, 81 mm wide, and 135 mm high; the arc thickness varied between 40 and 70 mm. The circular hole, which was apparently for the handle (e.g., [13]) had an internal diameter of 42 mm and an external diameter of 33 mm. The chain passageway was 35 mm wide.

2. Metallurgical Background of Research

Wrought iron and cast iron, two seemingly similar, yet very different materials, were used during the eighteenth century according to their properties. Wrought iron, being more plastic and workable, was used for the production of small plates, shafts, and other forged objects, whereas cast iron was used for the production of parts too large to forge, such as military and civilian structural material components. The production of cast iron street furniture, such as streetlamps, balconies, fountains, and sculptures, was mainly due to technological progress in the iron and steel industries during the First Industrial Revolution (1760–1840) and improved the quality of life in evolving urban regions [14]. By the end of the eighteenth century, cast iron was used in general construction and bridge building. Wrought iron was more suited for some large objects, such as anchors, due to its superior mechanical properties and corrosion resistance [15].

2.1. Wrought Iron

Before the seventeenth century, iron was produced in Europe and the Middle East by the direct single-stage solid-state smelting process called ‘bloomery’, where the iron ore was fed into a furnace at a temperature below the melting point of iron (1538 °C) in a reducing atmosphere [16,17,18]. The characteristic microstructure of wrought iron items produced by the direct smelting process is heterogeneous and includes almost pure ferrite, Widmanstätten ferrite, Widmanstätten ferrite–pearlite, and pure pearlite, as well as slag inclusions oriented in the direction of the forging process. The process is usually performed in relatively small batches, and hence, when producing large objects, it is necessary to forge-weld several batches together, further increasing the heterogeneous character of the microstructure [19].

In the indirect smelting technique, the iron ore was reduced in two stages and carried out in separate furnaces [9,19,20]. In the first stage, iron ore and fuel reacted in a blast furnace to produce molten pig iron that included about 4 wt% carbon (C) and some other elements, including silicon (Si), phosphorus (P), and manganese (Mn). In the second stage, the pig iron was refined through a decarburisation process [21].

In 1784, Henry Cort developed an indirect smelting technique called ‘puddling’ to refine the pig iron into wrought iron [22]. The puddling process made it possible to satisfy the growing demand for iron and enabled increasing the capacity of wrought iron production by replacing charcoal fuel with coal and preventing contact between the metal and harmful impurities (mainly sulphur) in the fuel [9,16,23]. The stirring of molten pig iron during the puddling process, which was held isolated from the charcoal fire in the furnace, exposed the metal homogeneously to the elevated temperature of burning gas, reducing iron oxide and oxidizing carbon. This reduced the carbon content in the alloy, raised the melting temperature of the metal, and caused the formation of small quantities of semi-solid iron in the liquid material, which were collected and worked into larger pieces [19,23].

The characteristic microstructure of wrought iron items produced by the ‘puddling’ technique contains elongated slag inclusions surrounded by a ferritic iron matrix. The preferred orientation of slag inclusions indicates the direction of plastic deformation in the forging process [9,12,19]. Until the development of the Bessemer process in 1856, wrought iron was produced either by the direct or the indirect smelting technique [16,19,24,25,26].

2.2. Cast Iron

A blast furnace had been used for the production of cast iron in China since 500 BCE [16]. Blast furnaces, fed by hot air blown into the lower part of the furnace, could reach temperatures about 1450 °C for smelting. The partially molten cast iron was fed into sand moulds, generating ‘pigs’ that could be re-melted [14]. The first blast furnace arrived in Britain from continental Europe [14] towards the end of the fifteenth century; during the sixteenth century, blast furnaces spread to most of western Europe. The first documented serious effort to use pig iron as ballast in the Royal Navy’s warships was in the late 1720s [27,28]. The modern European blast furnace was a large construction, consuming a considerable amount of charcoal, and it needed a continuous water power supply for operating the bellows [29]. Charcoal was replaced by coke as the fuel in blast furnaces from 1750 to 1770, and by 1770, coke furnaces were already common [30].

Grey cast iron (ternary iron–carbon–silicon alloys) is characterised by the content of more than 2 wt% C as graphite particles, the increased carbon content reducing the melting temperature of the alloy [28,31,32]. Cast iron objects are often cast in a sand mould containing a cavity of the desired shape, consisting of cope and drag (top and bottom parts) with an upper pouring space (cup and sprue), as well as a vent and riser [33] (p. 102, Figure 6). At the end of the casting procedure, the sand mould was broken, and the cast item was retrieved. To reduce shrinkage porosity during the process, a feeder was frequently used, and a thermal sleeve was commonly added around the feeder for adding molten metal during the solidification of the metal [33,34].

The main difference between white cast iron and grey cast iron is in the silicon content. White cast iron contains less than 1 wt% Si, whereas grey cast iron normally contains 1–3 wt%. Si is a graphite stabiliser that causes carbon to precipitate as dark graphite flakes, surrounded by ferrite and pearlite grains [28,31,35]. It also contains smaller concentrations of other elements, including P, sulphur (S), and Mn. The high concentration of manganese in cast objects (>0.5 wt% Mn) results in high-quality products with only a small amount of porosity defects attributable to the sand casting. The presence of manganese in cast iron products, to prevent the formation of gas holes and porosity, indicates a post-1839 manufacturing date [31,32,33].

Cast iron has good fluidity and castability, as well as good hardness; however, it tends to be brittle (strong in compression and brittle in tension). Grey cast iron has good machinability and wear resistance; however, the graphite flakes cause low strength and low ductility [31,36,37]. The primary motivation for cast iron production was probably the military, such as the production of cannons and cannonballs [31]. The production of cast iron increased gradually from the sixteenth century onwards, reaching a yearly production of 250,000 tons in England alone at the beginning of the nineteenth century [26] (p. 124). The production of modern grey cast iron with metallurgical control started in Europe between 1810 and 1815 following the development of new equipment and improved manufacturing processes [33].

3. Materials and Methods

The four ferrous objects examined in this study were characterised by the metallurgical methods described below (

Table 1. Description of the ferrous objects and their characterisation method. The winch, the heart-shaped shackle, the deadeye with a futtock plate, and the stud-link chain controller were currently studied, whereas deadeye 163B, deadeye 164 chain links [9,19], and the anchor chain link and stud [12] were studied previously. The + sign represents tests that were performed and the − sign represents tests that were not.

Artefact	Material	Characterisation Method
		VT	XRF	Field Multi-Focal Metallography (FMM)	Conventional Metallography	HV	SEM-EDS	OES
Winch drum	Grey cast iron	+	+	+	+	+	+	−
Winch shaft	Wrought iron	+	+	+	+	+	+	−
Heart-shaped shackle link	Wrought iron	+	+	+	+	+	+	−
Heart-shaped shackle	Wrought iron	+	+	+	+	+	+	−
Futtock plate	Wrought iron	+	+	+	+	+	+	+
Deadeye strap	Wrought iron	+	−	+	+	+	+	−
Stud-link chain controller	Grey cast iron	+	+	+	+	+	+	−
Deadeye 163B futtock plate	Wrought iron	+	+	−	−	−	−	−
Deadeye 163B loop	Wrought iron	+	+	−	+	+	+	+
Deadeye 163B bolt	Wrought iron	+	+	−	+	+	+	+
Deadeye 164 chain links	Wrought iron	+	−	−	+	+	+	−
Anchor chain shaft	Wrought iron	+	+	−	+	+	+	−
Anchor chain link	Wrought iron	+	+	−	+	+	+	+
Anchor chain stud	Grey cast iron	+	+	−	+	+	+	+

):

(a)

Visual testing (VT) inspection to identify visible macroscopic defects related to the manufacturing process.

(b)

Chemical analysis, after grinding the surface and removing the oxide layer, was performed with a calibrated handheld X-ray fluorescence (XRF) instrument, fitted with a 45 kV Rh target X-ray tube. Each area examined was about 20 mm². Oxygen and carbon could not be detected with this tool due to instrumental limitations.

(c)

Optical emission spectroscopy (OES) analysis determined carbon content with a detection limit of less than 0.1% [19].

(d)

For the conventional metallographic examination of the objects, samples of approximately 5 mm in length were cut from the items and positioned in a planar section (P-section), a longitudinal cross-section (L-CS), and a transverse cross-section (T-CS), according to ASTM E3–11 standard [38], and were mounted in Bakelite. The surface of the samples was ground with 80–4000 silicon carbide grit papers, polished with a 1 μm aluminium oxide (Al₂O₃) polishing suspension, and then with a 0.04 μm colloidal silica suspension. The samples were cleaned with ethanol between these steps to remove contaminants and then etched with Nital (97% alcohol, 3% HNO₃). Following the metallographic sample preparation, the microstructure was examined with a light microscope (LM).

(e)

Chemical analysis was carried out on the conventional metallographic samples using a scanning electron microscope (SEM) with an energy-dispersive spectroscope (EDS), equipped with a silicon drift detector using a Zeiss Supra 40 SEM instrument with Quantax 200 EDS, equipped with a silicon drift Brucker XFlash 4010 detector with EDS resolution of 129 eV, to determine the microstructure and bulk composition of the four samples with an approximate error of 0.1–1%.

(f)

Vickers microhardness of the ground and polished metallographic specimens was measured with a 200 gf load for 15 s, according to the ASTM E384–99 standard [39].

(g)

Minimally destructive field multi-focal metallography (FMM) was performed on a selected surface of each item. The FMM surface preparation comprised the following steps: (1) locating the appropriate external area to be examined; (2) grinding the chosen surface area of each object with a conventional handheld grinder/polisher with 80, 120, 240, 400, and 600 grit SiC paper; (3) polishing the surface with a handheld grinder/polisher with a polishing cloth using a 9, 3, and 1 μm polishing compound; and (4) etching the surface with Nital (97% alcohol, 3% HNO₃) etchant. The surface was systematically cleaned with ethanol between these steps. A layer of less than 1 mm of metal was removed in the grinding process. At the last stage of this procedure, the etched surface was examined with a HIROX RH-2000 digital 3D multi-focal LM equipped with various lenses, a high-intensity LED lighting source, and advanced 3D software.

4. Results

Although the surface of all four objects was covered with corrosion products, their general shape was well-preserved. Cast defects, such as rounded cavities and interdendritic porosity, were observed by VT on the surface of the winch drum and the stud-link chain controller, indicating that these two items were cast products [31,33]. Straight parallel lines were observed by VT on the external surface of the winch shaft, the heart-shaped shackle, and the deadeye strap with a futtock plate, showing that these items were wrought iron products worked by plastic deformation [12] (p. 215, Figure 3).

The XRF chemical analysis results of the four items are presented in Table 2. The microstructure and the elemental mapping of the winch drum are presented in Figure 2, Figure 3, Figure 4 and Figure 5 and in the Supplementary Material Figures S3–S6. The SEM-EDS chemical analysis results of the four objects are presented in Table 3. The microstructure and the elemental mapping of the winch shaft are presented in Figure 6 and Figure 7 and in the Supplementary Material Figures S7–S10. The microstructure and the elemental mapping of the heart-shaped shackle (including its link) are presented in Figure 8, Figure 9, Figure 10 and Figure 11 and in the Supplementary Material Figures S11–S19. The microstructure and the elemental mapping of the deadeye with futtock plate are presented in Figure 12 and Figure 13 and in the Supplementary Material Figures S20–S23. The microstructure and the elemental mapping of the stud-link chain controller are presented in Figure 14 and Figure 15 and in the Supplementary Material Figures S24–S27.

4.1. Winch

The XRF analysis of the winch drum revealed that the grey cast alloy was composed mainly of iron (95.1–96.3 weight percentages (wt%) Fe), with a low percentage of silicon (2.6–3.8 wt% Si) (ground metal, Table 2). The presence of 0.5–0.9 wt% Mn and up to 0.5 wt% of P and Ti were also detected (Table 2).

Table 2. The XRF chemical analysis of the four ferrous items (wt%) after rough grinding to expose the core metal. At least two measurements were taken for each point. Carbon and oxygen could not be detected with this XRF instrument.

Measured Area	Composition (wt%)
	Fe	Si	P	S	Mn	Ti
Cast winch drum, area 1, upper part (Figure 1a and Supplementary Material Figure S1a, T-CS)	95.1	3.8	0.5	-	0.5	0.1
Cast winch drum, area 2, upper part (Figure 1a and Supplementary Material Figure S1a, T-CS)	96.3	2.6	0.4	-	0.5	0.2
Cast winch drum, area 3, centre of the drum (Figure 1a and Supplementary Material Figure S1a, L-CS)	96.2	2.7	0.2	-	0.9	-
Winch shaft, upper part, area 1 (Figure 1a and Supplementary Material Figure S1a, T-CS)	99.9	-	-	-	-	0.1
Winch shaft, upper part, area 2 (Figure 1a and Supplementary Material Figure S1a, T-CS)	99.9	-	-	-	-	0.1
Heart-shaped shackle, area 1 (Figure 1b and Supplementary Material Figure S2a, L-CS)	99.8	-	-	-	-	0.2
Heart-shaped shackle, area 2 (Figure 1b and Supplementary Material Figure S2a, L-CS)	99.4	0.5	-	0.1	-	-
Heart-shaped shackle, centre of the link, area 1 (Figure 1b and Supplementary Material Figure S2a, L-CS)	99.6	0.4	-	-	-	-
Heart-shaped shackle, centre of the link, area 2 (Figure 1b and Supplementary Material Figure S2a, L-CS)	98.6	0.8	0.3	0.1	-	0.2
Heart-shaped shackle, centre of the link, area 3 (Figure 1b and Supplementary Material Figure S2a, L-CS)	98.8	0.7	0.3	-	0.2	-
Futtock plate, upper part, area 1 (Figure 1c and Supplementary Material Figure S2b)	99.2	0.7	-	-	-	0.1
Futtock plate, upper part, area 2 (Figure 1c and Supplementary Material Figure S2b)	98.9	0.7	0.3	-	-	0.1
Futtock plate, upper part, area 3 (Figure 1c and Supplementary Material Figure S2b)	99.3	0.5	0.1	0.1	-	-
Futtock plate, centre, area 4 (Figure 1c and Supplementary Material Figure S2b)	99.5	0.5	-	-	-	-
Futtock plate, centre, area 5 (Figure 1c and Supplementary Material Figure S2b)	99.4	0.3	0.2	-	-	0.1
Cast stud-link chain controller, side wall, area 1 (Figure 1d,e and Supplementary Material Figure S1b, L-CS)	96.0	1.9	1.5	-	0.4	0.2
Cast stud-link chain controller, side wall, area 2 (Figure 1d,e and Supplementary Material Figure S1b, L-CS)	96.5	1.9	1.0	-	0.4	0.2
Cast stud-link chain controller, side wall, area 3 (Figure 1d,e and Supplementary Material Figure S1b, L-CS)	97.0	1.2	1.3	-	0.3	0.2
Cast stud-link chain controller, side wall, area 3 (Figure 1d,e and Supplementary Material Figure S1b, T-CS)	96.7	2.3	0.7	-	0.3	-
Cast stud-link chain controller, side wall, area 3 (Figure 1d,e and Supplementary Material Figure S1b, L-CS)	97.6	2.0	0.4	-	-	-

Table 2. The XRF chemical analysis of the four ferrous items (wt%) after rough grinding to expose the core metal. At least two measurements were taken for each point. Carbon and oxygen could not be detected with this XRF instrument.

Measured Area	Composition (wt%)
	Fe	Si	P	S	Mn	Ti
Cast winch drum, area 1, upper part (Figure 1a and Supplementary Material Figure S1a, T-CS)	95.1	3.8	0.5	-	0.5	0.1
Cast winch drum, area 2, upper part (Figure 1a and Supplementary Material Figure S1a, T-CS)	96.3	2.6	0.4	-	0.5	0.2
Cast winch drum, area 3, centre of the drum (Figure 1a and Supplementary Material Figure S1a, L-CS)	96.2	2.7	0.2	-	0.9	-
Winch shaft, upper part, area 1 (Figure 1a and Supplementary Material Figure S1a, T-CS)	99.9	-	-	-	-	0.1
Winch shaft, upper part, area 2 (Figure 1a and Supplementary Material Figure S1a, T-CS)	99.9	-	-	-	-	0.1
Heart-shaped shackle, area 1 (Figure 1b and Supplementary Material Figure S2a, L-CS)	99.8	-	-	-	-	0.2
Heart-shaped shackle, area 2 (Figure 1b and Supplementary Material Figure S2a, L-CS)	99.4	0.5	-	0.1	-	-
Heart-shaped shackle, centre of the link, area 1 (Figure 1b and Supplementary Material Figure S2a, L-CS)	99.6	0.4	-	-	-	-
Heart-shaped shackle, centre of the link, area 2 (Figure 1b and Supplementary Material Figure S2a, L-CS)	98.6	0.8	0.3	0.1	-	0.2
Heart-shaped shackle, centre of the link, area 3 (Figure 1b and Supplementary Material Figure S2a, L-CS)	98.8	0.7	0.3	-	0.2	-
Futtock plate, upper part, area 1 (Figure 1c and Supplementary Material Figure S2b)	99.2	0.7	-	-	-	0.1
Futtock plate, upper part, area 2 (Figure 1c and Supplementary Material Figure S2b)	98.9	0.7	0.3	-	-	0.1
Futtock plate, upper part, area 3 (Figure 1c and Supplementary Material Figure S2b)	99.3	0.5	0.1	0.1	-	-
Futtock plate, centre, area 4 (Figure 1c and Supplementary Material Figure S2b)	99.5	0.5	-	-	-	-
Futtock plate, centre, area 5 (Figure 1c and Supplementary Material Figure S2b)	99.4	0.3	0.2	-	-	0.1
Cast stud-link chain controller, side wall, area 1 (Figure 1d,e and Supplementary Material Figure S1b, L-CS)	96.0	1.9	1.5	-	0.4	0.2
Cast stud-link chain controller, side wall, area 2 (Figure 1d,e and Supplementary Material Figure S1b, L-CS)	96.5	1.9	1.0	-	0.4	0.2
Cast stud-link chain controller, side wall, area 3 (Figure 1d,e and Supplementary Material Figure S1b, L-CS)	97.0	1.2	1.3	-	0.3	0.2
Cast stud-link chain controller, side wall, area 3 (Figure 1d,e and Supplementary Material Figure S1b, T-CS)	96.7	2.3	0.7	-	0.3	-
Cast stud-link chain controller, side wall, area 3 (Figure 1d,e and Supplementary Material Figure S1b, L-CS)	97.6	2.0	0.4	-	-	-

Based on VT, LM, and SEM observations, the material of the drum was identified according to ASTM A247-67 [40] as type B grey cast iron (Figure 2, Figure 3, Figure 4 and Figure 5) with a carbon content of above 2 wt% C. The drum’s conventional metallographic (Figure 2c) and FMM (Figure 3a and Supplementary Material Figure S3a, respectively) metallographic observations showed dendritic morphology with a heterogeneous microstructure containing areas of ferrite (matrix), perlite, iron phosphide (Fe₃P) eutectic (bright areas), graphite flakes (black thin elongated particles), and flower-like graphite rosettes (round clusters of black graphite flakes arranged perpendicular to a central point) (Figure 2, Figure 3, Figure 4 and Figure 5 and Supplementary Material Figures S3–S6).

Figure 2. Conventional metallographic light microscope (LM) images of the winch drum (L-section): (a,b) grey cast iron with dendritic pattern containing black graphite flakes and graphite rosettes (before etching); (c,d) grey cast iron with black graphite flakes surrounded by ferrite grains and pearlite at ferrite grain boundaries and iron phosphide eutectic (after etching).

Figure 2. Conventional metallographic light microscope (LM) images of the winch drum (L-section): (a,b) grey cast iron with dendritic pattern containing black graphite flakes and graphite rosettes (before etching); (c,d) grey cast iron with black graphite flakes surrounded by ferrite grains and pearlite at ferrite grain boundaries and iron phosphide eutectic (after etching).

Figure 3. Field multi-focal metallography (FMM) LM images of the winch drum (upper part of the drum, L-CS, area 1, after etching): (a,b) general view of grey cast iron with dendritic pattern; (c,d) higher magnifications showing black graphite flakes surrounded by ferrite grains and pearlite at grain boundaries and iron phosphide eutectic.

Figure 3. Field multi-focal metallography (FMM) LM images of the winch drum (upper part of the drum, L-CS, area 1, after etching): (a,b) general view of grey cast iron with dendritic pattern; (c,d) higher magnifications showing black graphite flakes surrounded by ferrite grains and pearlite at grain boundaries and iron phosphide eutectic.

Figure 4. Conventional metallographic SEM images of the winch drum after grinding, polishing, and etching (L-section): (a) general view of grey cast iron—areas in squares analysed by EDS; (b) typical area of grey cast iron containing black graphite flakes; and (c,d) ferrite matrix, graphite flakes (black), iron phosphide eutectic (bright microstructure)—areas in squares analysed by EDS.

Figure 4. Conventional metallographic SEM images of the winch drum after grinding, polishing, and etching (L-section): (a) general view of grey cast iron—areas in squares analysed by EDS; (b) typical area of grey cast iron containing black graphite flakes; and (c,d) ferrite matrix, graphite flakes (black), iron phosphide eutectic (bright microstructure)—areas in squares analysed by EDS.

Figure 5. SEM-EDS elemental mapping of the winch drum, an area (shown in Figure 4c) of graphite flakes surrounded by ferrite grains and iron phosphide eutectic (conventional metallographic sample), showing the presence of elements (bright dots) (a) iron; (b) carbon; (c) phosphorus; (d) manganese; (e) sulphur; (f) titanium.

Figure 5. SEM-EDS elemental mapping of the winch drum, an area (shown in Figure 4c) of graphite flakes surrounded by ferrite grains and iron phosphide eutectic (conventional metallographic sample), showing the presence of elements (bright dots) (a) iron; (b) carbon; (c) phosphorus; (d) manganese; (e) sulphur; (f) titanium.

The SEM-EDS analysis of the conventional metallographic samples of the drum revealed that the grey cast alloy (Figure 4a, areas 1 and 2, and Figure 4d, area 1) was mainly composed of iron (95.0–96.0 wt% Fe) with low percentages of silicon (2.6–2.8 wt% Si). Other elements were also detected, including 0.9–1.1 wt% manganese (Mn), 0.2–1.0 wt% phosphorus (P), and up to 0.2 wt% of titanium (Ti), sulphur (S), and copper (Cu) (Table 3 and Supplementary Material Figure S4). The SEM-EDS analysis of single black flakes showed that they were composed of 100 wt% carbon. Manganese sulphide (MnS) precipitations were also observed (Figure 4c, area 1), with a composition of 59.2 wt% Mn and 36.9 wt% S (Table 3). Areas of iron phosphide were also observed (Figure 4d, area 2), composed of 83.5–83.7 wt% Fe and 13.7–13.8 wt% P. The presence of 2.0–2.3 wt% Mn, and 0.1 wt% of Ti and chromium (Cr) were also detected in the Fe₃P eutectic morphology (Table 3).

Table 3. The SEM-EDS chemical analysis of the four ferrous objects (wt%) after grinding, polishing, and etching.

Measured Area	Composition (wt%)
	Fe	Si	O	P	S	Mn	Ti	Cu	Cr	Al	Ca	Mg	V
Winch drum, grey cast iron (Figure 4a, area 1 of ferrite matrix with graphite flakes, scanned area 200 µm × 200 µm)—carbon peaks omitted	95.2	2.7	-	0.6	0.1	1.1	0.1	0.2	-	-	-	-	-
Winch drum, grey cast iron (Figure 4a, area 2 of ferrite matrix with graphite flakes, scanned area 200 µm × 200 µm)—carbon peaks omitted	95.0	2.6	-	1.0	0.1	1.1	0.2	-	-	-	-	-	-
Winch drum, area of MnS (Figure 4c, area 1, and Supplementary Material Figure S6, scanned area 10 µm × 10 µm)	2.9	-	0.3	0.5	36.9	59.2	0.2	-	-	-	-	-	-
Winch drum, grey cast iron (Figure 4d, area 1 of ferrite matrix, scanned area 20 µm × 20 µm)	96.0	2.8	-	0.2	-	0.9	-	0.1	-	-	-	-	-
Winch drum, area of Fe3P (Figure 4d, area 2, scanned area 20 µm × 20 µm)	83.7	0.3	-	13.8	-	2.0	0.1	-	0.1	-	-	-	-
Winch shaft, wrought iron, iron matrix (Figure 6e, scanned area 1200 µm × 800 µm)	99.5	0.1	-	0.3	0.1	-	-	-	-	-	-	-	-
Winch shaft, wrought iron, iron matrix (Figure 6f, area 1, scanned area 40 µm × 40 µm)	99.3	0.2	-	0.4	0.1	-	-	-	-	-	-	-	-
Winch shaft, wrought iron, iron matrix (Figure 6f, area 2, scanned area 40 µm × 40 µm)	99.8	-	-	0.2	-	-	-	-	-	-	-	-	-
Heart-shaped shackle link, wrought iron (scanned area 800 µm × 500 µm)	96.3	0.6	2.3	0.6	0.2	-	-	-	-	-	-	-	-
Heart-shaped shackle link, area rich in inclusions (Supplementary Material Figure S12a, scanned area 300 µm × 240 µm)	49.6	6.2	34.8	3.7	2.0	2.1	0.2	-	-	0.7	0.5	0.2	-
Heart-shaped shackle link, in typical glassy inclusion (scanned area 20 µm × 20 µm)	47.0	8.9	37.0	1.0	1.7	2.7	0.2	-	0.1	0.6	0.5	0.1	0.2
Heart-shaped shackle link, in typical two-phase inclusion (Figure 8d, Supplementary Material Figure S14b, scanned area 30 µm × 30 µm)	66.0	2.2	26.8	2.9	0.8	1.0	-	-	-	0.1	-	0.2	-
Heart-shaped shackle link, typical ferrite grain (Supplementary Material Figure S12b, scanned area 40 µm × 40 µm)	99.2	0.5	0.2	-	-	0.1	-	-	-	-	-	-	-
Heart-shaped shackle, wrought iron (scanned area 1200 µm × 900 µm)	97.0	0.5	1.8	0.4	0.1	0.2	-	-	-	-	-	-	-
Heart-shaped shackle, in typical glassy inclusion No. 1 (Figure 9c, scanned area 20 µm × 20 µm)	51.2	10.3	33.8	0.4	-	3.4	-	-	-	0.2	0.2	0.5	-
Heart-shaped shackle, in typical glassy inclusion No. 2 (Figure 9c, scanned area 10 µm × 10 µm)	54.3	10.3	31.0	0.9	-	2.8	-	-	-	0.2	-	0.4	0.1
Heart-shaped shackle, in typical two-phase inclusion No. 3 (Figure 9c, scanned area 20 µm × 20 µm)	74.1	0.4	24.2	0.3	0.6	0.4	-	-	-	-	-	-	-
Heart-shaped shackle, typical ferrite matrix (Figure 9c, area 4, scanned area 20 µm × 20 µm)	99.7	0.1	-	0.2	-	-	-	-	-	-	-	-	-
Futtock plate, wrought iron (Supplementary Material Figure S21a, scanned area 600 µm × 400 µm)	96.2	0.4	2.8	0.2	0.1	0.3	-	-	-	-	-	-	-
Futtock plate, wrought iron (Supplementary Material Figure S21b, scanned area 160 µm × 120 µm)	97.4	0.4	1.7	0.2	0.1	0.2	-	-	-	-	-	-	-
Futtock plate, wrought iron (scanned area 120 µm × 80 µm)	99.5	-	-	0.2	-	0.2	-	0.1	-	-	-	-	-
Deadeye strap, wrought iron (Supplementary Material Figure S21a, scanned area 1000 µm × 800 µm)	96.8	0.5	1.7	0.6	0.1	0.3	-	-	-	-	-	-	-
Deadeye strap, wrought iron (scanned area 600 µm × 400 µm)	99.4	-	-	0.4	-	0.2	-	-	-	-	-	-	-
Deadeye strap, in typical two-phase slag inclusion (scanned area 10 µm × 10 µm)	51.0	8.6	34.3	2.2	-	2.9	0.1	-	0.1	0.6	0.1	0.1	-
Stud-link chain controller grey cast iron (Supplementary Material Figure S25a, scanned area 500 µm × 400 µm)—carbon peaks omitted	95.7	1.6	0.2	1.3	0.1	0.9	0.1	-	-	-	-	-	0.1
Stud-link chain controller grey cast iron (Figure 14c, scanned area 100 µm × 80 µm)—carbon peaks omitted	96.9	2.2	0.1	0.3	-	0.5	-	-	-	-	-	-	-
Stud-link chain controller, ferrite matrix (Supplementary Material Figure S25b, scanned area 20 µm × 20 µm)	96.4	1.5	0.9	0.4	-	0.8	-	-	-	-	-	-	-
Stud-link chain controller, area of Fe3P (Supplementary Material Figure S25c, scanned area 20 µm × 20 µm)	88.9	0.5	-	10.2	-	-	-	-	0.2	-	-	-	0.2

Table 3. The SEM-EDS chemical analysis of the four ferrous objects (wt%) after grinding, polishing, and etching.

Measured Area	Composition (wt%)
	Fe	Si	O	P	S	Mn	Ti	Cu	Cr	Al	Ca	Mg	V
Winch drum, grey cast iron (Figure 4a, area 1 of ferrite matrix with graphite flakes, scanned area 200 µm × 200 µm)—carbon peaks omitted	95.2	2.7	-	0.6	0.1	1.1	0.1	0.2	-	-	-	-	-
Winch drum, grey cast iron (Figure 4a, area 2 of ferrite matrix with graphite flakes, scanned area 200 µm × 200 µm)—carbon peaks omitted	95.0	2.6	-	1.0	0.1	1.1	0.2	-	-	-	-	-	-
Winch drum, area of MnS (Figure 4c, area 1, and Supplementary Material Figure S6, scanned area 10 µm × 10 µm)	2.9	-	0.3	0.5	36.9	59.2	0.2	-	-	-	-	-	-
Winch drum, grey cast iron (Figure 4d, area 1 of ferrite matrix, scanned area 20 µm × 20 µm)	96.0	2.8	-	0.2	-	0.9	-	0.1	-	-	-	-	-
Winch drum, area of Fe3P (Figure 4d, area 2, scanned area 20 µm × 20 µm)	83.7	0.3	-	13.8	-	2.0	0.1	-	0.1	-	-	-	-
Winch shaft, wrought iron, iron matrix (Figure 6e, scanned area 1200 µm × 800 µm)	99.5	0.1	-	0.3	0.1	-	-	-	-	-	-	-	-
Winch shaft, wrought iron, iron matrix (Figure 6f, area 1, scanned area 40 µm × 40 µm)	99.3	0.2	-	0.4	0.1	-	-	-	-	-	-	-	-
Winch shaft, wrought iron, iron matrix (Figure 6f, area 2, scanned area 40 µm × 40 µm)	99.8	-	-	0.2	-	-	-	-	-	-	-	-	-
Heart-shaped shackle link, wrought iron (scanned area 800 µm × 500 µm)	96.3	0.6	2.3	0.6	0.2	-	-	-	-	-	-	-	-
Heart-shaped shackle link, area rich in inclusions (Supplementary Material Figure S12a, scanned area 300 µm × 240 µm)	49.6	6.2	34.8	3.7	2.0	2.1	0.2	-	-	0.7	0.5	0.2	-
Heart-shaped shackle link, in typical glassy inclusion (scanned area 20 µm × 20 µm)	47.0	8.9	37.0	1.0	1.7	2.7	0.2	-	0.1	0.6	0.5	0.1	0.2
Heart-shaped shackle link, in typical two-phase inclusion (Figure 8d, Supplementary Material Figure S14b, scanned area 30 µm × 30 µm)	66.0	2.2	26.8	2.9	0.8	1.0	-	-	-	0.1	-	0.2	-
Heart-shaped shackle link, typical ferrite grain (Supplementary Material Figure S12b, scanned area 40 µm × 40 µm)	99.2	0.5	0.2	-	-	0.1	-	-	-	-	-	-	-
Heart-shaped shackle, wrought iron (scanned area 1200 µm × 900 µm)	97.0	0.5	1.8	0.4	0.1	0.2	-	-	-	-	-	-	-
Heart-shaped shackle, in typical glassy inclusion No. 1 (Figure 9c, scanned area 20 µm × 20 µm)	51.2	10.3	33.8	0.4	-	3.4	-	-	-	0.2	0.2	0.5	-
Heart-shaped shackle, in typical glassy inclusion No. 2 (Figure 9c, scanned area 10 µm × 10 µm)	54.3	10.3	31.0	0.9	-	2.8	-	-	-	0.2	-	0.4	0.1
Heart-shaped shackle, in typical two-phase inclusion No. 3 (Figure 9c, scanned area 20 µm × 20 µm)	74.1	0.4	24.2	0.3	0.6	0.4	-	-	-	-	-	-	-
Heart-shaped shackle, typical ferrite matrix (Figure 9c, area 4, scanned area 20 µm × 20 µm)	99.7	0.1	-	0.2	-	-	-	-	-	-	-	-	-
Futtock plate, wrought iron (Supplementary Material Figure S21a, scanned area 600 µm × 400 µm)	96.2	0.4	2.8	0.2	0.1	0.3	-	-	-	-	-	-	-
Futtock plate, wrought iron (Supplementary Material Figure S21b, scanned area 160 µm × 120 µm)	97.4	0.4	1.7	0.2	0.1	0.2	-	-	-	-	-	-	-
Futtock plate, wrought iron (scanned area 120 µm × 80 µm)	99.5	-	-	0.2	-	0.2	-	0.1	-	-	-	-	-
Deadeye strap, wrought iron (Supplementary Material Figure S21a, scanned area 1000 µm × 800 µm)	96.8	0.5	1.7	0.6	0.1	0.3	-	-	-	-	-	-	-
Deadeye strap, wrought iron (scanned area 600 µm × 400 µm)	99.4	-	-	0.4	-	0.2	-	-	-	-	-	-	-
Deadeye strap, in typical two-phase slag inclusion (scanned area 10 µm × 10 µm)	51.0	8.6	34.3	2.2	-	2.9	0.1	-	0.1	0.6	0.1	0.1	-
Stud-link chain controller grey cast iron (Supplementary Material Figure S25a, scanned area 500 µm × 400 µm)—carbon peaks omitted	95.7	1.6	0.2	1.3	0.1	0.9	0.1	-	-	-	-	-	0.1
Stud-link chain controller grey cast iron (Figure 14c, scanned area 100 µm × 80 µm)—carbon peaks omitted	96.9	2.2	0.1	0.3	-	0.5	-	-	-	-	-	-	-
Stud-link chain controller, ferrite matrix (Supplementary Material Figure S25b, scanned area 20 µm × 20 µm)	96.4	1.5	0.9	0.4	-	0.8	-	-	-	-	-	-	-
Stud-link chain controller, area of Fe3P (Supplementary Material Figure S25c, scanned area 20 µm × 20 µm)	88.9	0.5	-	10.2	-	-	-	-	0.2	-	-	-	0.2

SEM-EDS elemental mapping of the conventional metallographic samples of the drum revealed that the grey cast iron matrix was mainly composed of iron (Figure 5a and Supplementary Material Figure S5a); however, the black flake particles were composed of pure carbon (Figure 5b and Supplementary Material Figure S5b). Other elements, including Si, P, Mn, S, and Ti, were also detected in the grey cast iron matrix (Figure 5c–f and Supplementary Material Figure S5c–f).

The LM and SEM observations of the winch shaft showed that it was made of wrought iron with preferentially oriented elongated slag inclusions surrounded by an iron ferrite matrix (Figure 6a and Supplementary Material Figures S7 and S8a). Small ferrite grains of 10–100 µm in diameter and large ferrite grains of 100–500 µm in diameter were observed (Figure 6e and Supplementary Material Figure S8).

Figure 6. Conventional metallographic images of the winch shaft (L-CS): (a) general view of preferentially oriented slag inclusions surrounded by an iron ferrite matrix (LM, before etching); (b) elongated two-phase inclusion (LM, before etching); (c,d) preferentially oriented slag inclusions surrounded by iron ferrite grains (LM, after etching); (e) small ferrite grains, 10–100 µm in diameter, and large ferrite grains, 100–500 µm in diameter (SEM, after etching); (f) preferentially oriented slag inclusions surrounded by iron ferrite grains (SEM, after etching).

Figure 6. Conventional metallographic images of the winch shaft (L-CS): (a) general view of preferentially oriented slag inclusions surrounded by an iron ferrite matrix (LM, before etching); (b) elongated two-phase inclusion (LM, before etching); (c,d) preferentially oriented slag inclusions surrounded by iron ferrite grains (LM, after etching); (e) small ferrite grains, 10–100 µm in diameter, and large ferrite grains, 100–500 µm in diameter (SEM, after etching); (f) preferentially oriented slag inclusions surrounded by iron ferrite grains (SEM, after etching).

The XRF analysis of the winch shaft showed that the wrought iron was mainly composed of iron (99.9 wt% Fe) and 0.1 wt% Ti (ground metal, Table 2). The SEM-EDS element analysis showed it was mostly made of iron, with the presence of Si, P, and S (Supplementary Material Figure S8b).

The SEM-EDS analysis of the conventional metallographic samples of the winch shaft revealed a composition of 99.3–99.8 wt% Fe, up to 0.2 wt% Si, 0.2–0.4 wt% P, and up to 0.1 wt% S (Table 3). Its SEM-EDS elemental mapping showed it was made of a wrought iron matrix (Figure 7a and Supplementary Material Figures S9a and S10a). The slag inclusions were mostly composed of silicon oxide (Figure 7b,c and Supplementary Material Figures S9b,c and S10b,c). Phosphorus (Figure 7d and Supplementary Material Figures S9d and S10d) and sulphur (Figure 7e), were also detected in the slag inclusions.

Figure 7. SEM-EDS elemental mapping of the winch shaft, an area (shown in Figure 6f) of preferentially oriented slag inclusions surrounded by iron ferrite grains (conventional metallographic sample), showing the presence of elements (bright dots) (a) iron; (b) silicon; (c) oxygen; (d) phosphorus; (e) sulphur; (f) carbon.

Figure 7. SEM-EDS elemental mapping of the winch shaft, an area (shown in Figure 6f) of preferentially oriented slag inclusions surrounded by iron ferrite grains (conventional metallographic sample), showing the presence of elements (bright dots) (a) iron; (b) silicon; (c) oxygen; (d) phosphorus; (e) sulphur; (f) carbon.

4.2. Heart-Shaped Shackle

The XRF analysis of the heart-shaped shackle revealed that it was made of a wrought iron alloy, with a composition of 98.6–99.8 wt% Fe and up to 0.8 wt % of Si, P, S, Mn, and Ti (ground metal, Table 2). LM observation of the conventional metallographic sample of the link before etching (Supplementary Material Figure S11) and after etching (Figure 8a,b) detected slag inclusions surrounded by an iron ferrite matrix. The ferrite grain size was 10–200 µm (Figure 8a,b). Some of the inclusions were small, several micrometres in diameter, whereas other inclusions were large, up to several hundred micrometres long (Figure 8b and Supplementary Material Figure S11). The SEM observation analysis of the link detected slag inclusions (Figure 8c,d, respectively, and Supplementary Material Figure S12).

Figure 8. Conventional metallographic images of the heart-shaped shackle link, L-CS, after etching): (a) general view of the wrought iron microstructure with preferentially oriented slag inclusions surrounded by an iron ferrite matrix (LM); (b) higher magnification showing ferrite grains and two-phase slag inclusions (LM); (c,d) slag inclusions surrounded by iron ferrite grins (SEM).

Figure 8. Conventional metallographic images of the heart-shaped shackle link, L-CS, after etching): (a) general view of the wrought iron microstructure with preferentially oriented slag inclusions surrounded by an iron ferrite matrix (LM); (b) higher magnification showing ferrite grains and two-phase slag inclusions (LM); (c,d) slag inclusions surrounded by iron ferrite grins (SEM).

The SEM-EDS analysis of the link revealed that it was made of iron, with impurities of Si, O, P, and S (Supplementary Material Figure S12a). The SEM-EDS elemental mapping of the conventional metallographic samples of the link showed that the wrought iron was mainly composed of iron, with the presence of Si, O, P, S, and Mn impurities (Supplementary Material Figure S13a–f). Different types of slag inclusions were observed by SEM, such as glassy slag inclusions, the two-phase slag inclusion of a wüstite (FeO) phase surrounded by a glassy phase, and slag inclusions with fayalite (Fe₂SiO₄) laths (Supplementary Material Figure S14). The SEM-EDS elemental mapping of the link revealed that a typical one-phase slag inclusion was composed of Si, O, P, S, and Mn, and a typical two-phase slag inclusion was composed of Fe, Si, O, P, and S (Supplementary Material Figure S15a–f). The SEM-EDS elemental mapping of a typical two-phase slag inclusion detected the presence of Fe, Si, O, P, S, and C (Supplementary Material Figures S14b and S16a–f), which was typical of the wüstite (FeO) phase surrounded by a glassy phase matrix [19] (p. 110).

The SEM-EDS analysis of the conventional metallographic samples of the link’s wrought iron (Supplementary Material Figures S12 and S13) revealed a composition of 96.3–99.2 wt% Fe, 0.5–0.6 wt% Si, and 0.2–2.3 wt% O (Table 3). Other elements were also detected, including up to 0.6 wt% P, up to 0.2 wt% S, and up to 0.1 wt% Mn (Table 3).

The SEM-EDS analysis of a typical glassy single-phase inclusion in the link showed a composition of 47.0 wt% Fe, 8.9 wt% Si, and 37.0 wt% O (Table 3). Other elements were also detected, including 1.0 wt% P, 1.7 wt% S, 2.7 wt% Mn, and less than 1.0 wt% of Ti, Cr, Al, Ca, Mg, and V (Table 3). The SEM-EDS analysis of a typical two-phase slag inclusion inside the link showed that it comprised 66.0 wt% Fe, 2.2 wt% Si, 26.8 wt% O, 2.9 wt% P, 1.0 wt% Mn, and less than 1.0 wt% of S, Al, and Mg (Table 3).

LM observation of conventional samples of the shackle revealed slag inclusions surrounded by an iron ferrite matrix (Figure 9a,b and Supplementary Material Figure S17), where the size of the ferrite grains and slag inclusions was similar to that observed in the metallographic sample of the link (Figure 8a,b). The small ferrite grains were 20–80 µm across, and the large ferrite grains were 100–400 µm across (Figure 9a,b). The FMM observation of both the link and shackle revealed a microstructure similar to that observed by conventional metallography observation, with slag inclusions surrounded by an iron ferrite matrix (Figure 10).

Figure 9. Conventional metallographic images of the heart-shaped shackle (T-CS, after etching): (a,b) circular slag inclusions surrounded by large and small iron ferrite grains (LM); (c,d) slag inclusions surrounded by iron ferrite grains (SEM).

Figure 9. Conventional metallographic images of the heart-shaped shackle (T-CS, after etching): (a,b) circular slag inclusions surrounded by large and small iron ferrite grains (LM); (c,d) slag inclusions surrounded by iron ferrite grains (SEM).

Figure 10. FMM LM images of the heart-shaped shackle (L-CS, after etching): (a) general view of preferentially oriented slag inclusions surrounded by the iron matrix (area 1); (b) higher magnifications of bright ferrite grains and dark inclusions (area 1); (c) general view of preferentially oriented slag inclusions surrounded by the iron matrix (area 2); (d) higher magnifications of dark preferentially oriented slag inclusions and bright ferrite grains (area 2).

Figure 10. FMM LM images of the heart-shaped shackle (L-CS, after etching): (a) general view of preferentially oriented slag inclusions surrounded by the iron matrix (area 1); (b) higher magnifications of bright ferrite grains and dark inclusions (area 1); (c) general view of preferentially oriented slag inclusions surrounded by the iron matrix (area 2); (d) higher magnifications of dark preferentially oriented slag inclusions and bright ferrite grains (area 2).

The SEM-EDS analysis of the shackle revealed it was mostly made of iron; however, the presence of Si, O, P, S, and Mn was also detected (Supplementary Material Figure S18a,b). The SEM-EDS elemental mapping of the shackle detected Fe, Si, O, P, S, and Mn (Figure 11 and Figure S19a–e). The presence of Al was also detected (Supplementary Material Figure S19f). The wrought iron ferrite matrix was mostly composed of iron, and the slag inclusions were composed of Si, O, P, S, and Mn (Figure 11 and Supplementary Material Figure S19).

The SEM-EDS analysis of the conventional metallographic sample of the shackle’s wrought iron revealed a composition of 97.0 wt% Fe, as well as 0.5 wt% Si, 1.8 wt% O, and less than 0.5 wt% of P, S, and Mn (Table 3); whereas the composition of a typical ferrite matrix (Figure 9c, area 1) was 99.7 wt% Fe, 0.1 wt% Si, and 0.2 wt% P (Table 3).

The SEM-EDS analysis of a typical glassy single-phase inclusion (Figure 9c, areas 1 and 2) inside the shackle was composed of 51.2–54.3 wt% Fe, 10.3 wt% Si, 31.0–33.8 wt% O, 2.8–3.4 wt% Mn, and less than 1.0 wt% of P, Al, Ca, Mg, and V (Table 3). The SEM-EDS analysis of a typical two-phase slag inclusion (Figure 9c, area 3) inside the shackle was composed of 74.1 wt% Fe, 24.2 wt% O, and less than 1.0 wt% of Si, P, S, and Mn (Table 3).

Figure 11. SEM-EDS elemental mapping of the heart-shaped shackle (T-CS, conventional metallographic sample), slag inclusions surrounded by the iron ferrite matrix, showing the presence of elements (bright dots) (a) iron; (b) silicon; (c) oxygen; (d) phosphorus; (e) sulphur; (f) manganese.

Figure 11. SEM-EDS elemental mapping of the heart-shaped shackle (T-CS, conventional metallographic sample), slag inclusions surrounded by the iron ferrite matrix, showing the presence of elements (bright dots) (a) iron; (b) silicon; (c) oxygen; (d) phosphorus; (e) sulphur; (f) manganese.

4.3. Deadeye Strap with Futtock Plate

The XRF analysis of the deadeye strap with a futtock plate showed that it was a wrought iron alloy, with a composition of 98.9–99.5 wt% Fe and up to 0.7 wt % of Si, P, S, and Ti (ground metal, Table 2). LM observation of the metallographic samples revealed an iron ferrite matrix with preferentially oriented elongated slag inclusions in the futtock plate and strap (Supplementary Material Figures S20a,b and S20c,d, respectively). Large and small grains were observed in both the futtock plate and the strap; the small grains were 10–100 µm across and the large grains were 100–400 µm across (Figure 12a–d and Supplementary Material Figure S20b,d). Different types of slag inclusions were observed by SEM, including one-phase glassy fayalite slag inclusions, two-phase slag inclusions with a wüstite phase surrounded by a glassy phase matrix, and three-phase slag inclusions of wüstite and fayalite laths surrounded by a glassy phase matrix, where both small inclusions, a few micrometres in diameter, and large inclusions, several hundred micrometres in diameter, were observed (Figure 12 and Supplementary Material Figure S20).

Figure 12. Conventional metallographic images of the deadeye with futtock plate (LM, L-CS, after etching): (a,b) a futtock plate with slag inclusions surrounded by large and small iron ferrite grains, where the small grains are 10–100 µm across and the large grains are 100–300 µm across; (c,d) a strap with preferentially oriented slag inclusions surrounded by large and small iron ferrite grains.

Figure 12. Conventional metallographic images of the deadeye with futtock plate (LM, L-CS, after etching): (a,b) a futtock plate with slag inclusions surrounded by large and small iron ferrite grains, where the small grains are 10–100 µm across and the large grains are 100–300 µm across; (c,d) a strap with preferentially oriented slag inclusions surrounded by large and small iron ferrite grains.

The SEM-EDS analysis of the futtock plate detected Fe, Si, O, P, S, Mn, and Al (Supplementary Material Figure S21). The wrought iron composition of the futtock plate was 96.2–99.5 wt% Fe, up to 2.8 wt% O, and less than 0.5 wt% Si, P, S, Mn, and Cu (Table 3). The SEM-EDS elemental mapping of the metallographic samples of the iron ferrite matrix with slag inclusions of the futtock plate revealed that the iron matrix was mostly composed of Fe, and the slag inclusions were composed of Si, O, P, S, and Al (Supplementary Material Figure S22a–f).

The SEM-EDS analysis of the deadeye strap revealed that it was mostly composed of iron, with Si, O, P, S, and Mn impurities (Supplementary Material Figure S23). The wrought iron composition of the strap was 96.8–99.4 wt% Fe, up to 1.7 wt% O, and less than 1.0 wt% Si, P, S, and Mn (Table 3). The composition of a typical two-phase slag inclusion inside the strap revealed 51.0 wt% Fe, 8.6 wt% Si, 34.3 wt% O, 2.2 wt% P, and 2.9 wt% Mn. In addition, 0.6 wt% Al and up to 0.1 wt% of Ti, Cr, Ca, and Mg were detected (Table 3). The SEM-EDS elemental mapping of the strap’s metallographic sample and the area of the iron ferrite matrix with preferentially oriented elongated slag inclusions showed that the wrought iron was mostly composed of Fe, and the slag inclusions were composed of Si, O, and P (Figure 13). The OES analysis of the deadeye strap revealed that it was mostly composed of iron (98.6 wt%) with the presence of other elements, including 0.5 wt% Si, 0.3 wt% P, 0.1 wt% C, 0.1 wt% S, and 0.2 wt% Mn, which was typical of wrought iron products.

Figure 13. SEM-EDS elemental mapping of the deadeye strap (conventional metallographic sample), showing preferentially oriented slag inclusions surrounded by iron ferrite grains and the presence of elements (bright dots) (a) iron; (b) silicon; (c) oxygen; (d) phosphorus; (e) sulphur; (f) manganese.

Figure 13. SEM-EDS elemental mapping of the deadeye strap (conventional metallographic sample), showing preferentially oriented slag inclusions surrounded by iron ferrite grains and the presence of elements (bright dots) (a) iron; (b) silicon; (c) oxygen; (d) phosphorus; (e) sulphur; (f) manganese.

4.4. Stud-Link Chain Controller

The XRF analysis of the stud-link chain controller showed that it was made of a wrought iron alloy, with a composition of 96.0–97.6 wt% Fe, 1.2–2.3 wt% Si, 0.4–1.5 wt% P, and less than 0.5 wt % of Mn and Ti (ground metal, Table 2). The stud-link chain controller was characterised by LM observation of the conventional metallographic sample, according to ASTM A247-67 [40] as type B grey cast iron with a dendritic pattern (Supplementary Material Figure S24). Black graphite flakes and areas of graphite rosettes surrounded by the ferrite matrix, perlite microstructure, and bright iron phosphide eutectic were observed by LM and SEM (Figure 14 and Supplementary Material Figures S25 and S26). The FMM observation of the chain controller revealed a microstructure similar to that observed by conventional metallography observation, with graphite flakes surrounded by ferrite and perlite (Figure 15).

Figure 14. Conventional metallographic images of the stud-link chain controller (P-section, after etching): (a,b) grey cast iron containing black graphite flakes (LM); (c) black graphite flakes surrounded by the ferrite matrix, perlite, and white iron phosphide eutectic (SEM); (d) elemental mapping (SEM-EDS).

Figure 14. Conventional metallographic images of the stud-link chain controller (P-section, after etching): (a,b) grey cast iron containing black graphite flakes (LM); (c) black graphite flakes surrounded by the ferrite matrix, perlite, and white iron phosphide eutectic (SEM); (d) elemental mapping (SEM-EDS).

Figure 15. FMM LM images of the stud-link chain controller (side wall, P-section, after etching) grey cast iron (L-CS, after etching): (a,b) general view; (c,d) higher magnifications.

Figure 15. FMM LM images of the stud-link chain controller (side wall, P-section, after etching) grey cast iron (L-CS, after etching): (a,b) general view; (c,d) higher magnifications.

The SEM-EDS analysis of the metallographic samples of the chain controller ferrite matrix with graphite flakes detected the presence of Fe, Si, O, P, S, Mn, Ti, and V (Supplementary Material Figure S25a). The EDS analysis of the grey cast iron ferrite matrix with phosphide eutectic areas revealed the presence of Fe, Si, O, P, and Mn (Supplementary Material Figures S25b and S25c, respectively). The SEM-EDS elemental mapping of grey cast iron metallographic samples of the chain controller revealed the presence of Fe, C, Si, O, P, S, Mn, Ti, and V (Supplementary Material Figures S26d and S27a–i).

The SEM-EDS analysis results of the metallographic samples of the stud-link chain controller after omitting carbon peaks have shown that the grey cast iron composition was 95.7–96.9 wt% Fe and 1.5–2.2 wt% Si, as well as less than 1.0 wt% of O, P, S, Mn, Ti, and V (Table 3). The SEM-EDS analysis results of a typical area of Fe3P eutectic morphology (Figure S25c) revealed a composition of 88.9 wt% Fe, 0.5 wt% Si, 10.2 wt% P, and 0.2 wt% of Cr and V (Table 3).

5. Discussion

Analysis of the elemental composition and microstructure of metals and alloys may assist in differentiating between diverse manufacturing technologies and is a valuable tool for understanding the period, and in some cases, the origin, of ancient metal objects [9]. The metallurgical methodology used in the current research contributes to the understanding of the manufacturing technologies of four ferrous objects, categorised as rigging elements, which were retrieved from the nineteenth-century Akko Tower shipwreck. Based on the current analysis results, the type of alloy and manufacturing process of these objects is divided into two main groups following engineering considerations: (1) the winch drum and the stud-link chain controller (Figure 1a,d) were manufactured from type B grey cast iron (formed by the casting), which is a relatively brittle and hard material with low tensile strength since these two objects were not designed to withstand tensile stresses; while (2) the winch shaft, shackle, and deadeye strap were manufactured from wrought iron (heated and worked by plastic deformation), which is a highly malleable and ductile material with high tensile strength (Supplementary Material Figure S1a and Figure 1b,d). This difference in material selection was apparently based on different requirements: the grey cast iron was chosen for its good compressive strength and its low cost, while the wrought iron was chosen for its excellent plasticity, good tensile strength, impact resistance, and weldability [41].

A minimally destructive FMM method was applied here for the first time on ancient ferrous objects (Figure 3, Figure 10 and Figure 15 and Supplementary Material Figures S3 and S7). This method was previously applied on a bronze powder chamber retrieved from an underwater excavation and demonstrated that the FMM method agrees well with conventional metallography [42]. The FMM method is an improvement in field metallurgical replication (FMR) metallography. The FMR method involves the preparation of a curved or irregular surface by locally grinding, polishing, and then etching the external surface of the object by swabbing without cross-sectioning it. Next, a thin plastic film is pressed against the etched surface, producing a ‘negative’ replication of the microstructure, which is then observed by LM. The minimally destructive testing (MDT) FMR metallography does not always produce the high-quality micrographs attained by conventional destructive metallography. The FMM is a powerful MDT method that involves the preparation of a curved or irregular surface in a similar way as the FMR method, and then observing the surface by a multi-focal light microscope instead of a standard optical light microscope, omitting the plastic film replication step used in the FMR method and directly observing the microstructure of the surface, as well as identifying microscopic defects related to the manufacturing process on-site after proper preparation, producing a high-quality image without having to cut samples and destroy unique archaeological objects [42]. The current observation of the objects by using the novel FMM method produced metallographic images comparable in quality to the images obtained by conventional metallography of destructively obtained samples set in Bakelite.

In a future study, it could be useful to perform Raman spectroscopy on the four ferrous objects retrieved from the Akko Tower shipwreck (on the surface areas of the objects that were not ground and polished). However, this is beyond the scope of the current study. Incorporating Raman spectroscopy into the research of ancient ferrous objects can offer several advantages. For example, it can provide information about the organic and inorganic components present on the surface. It can also assist in identifying long-term corrosion products, processes, and coatings, providing insights into the historical use and preservation of the objects.

The winch drum and stud-link chain controller were identified as being made of grey cast iron with dendritic morphology and a microstructure containing areas of ferrite, perlite, iron phosphide eutectic, graphite flakes, and graphite rosettes (Figure 2, Figure 3, Figure 4, Figure 14 and Figure 15 and Supplementary Material Figures S5, S6 and S24–S27). Microhardness testing obtained average hardness values of 353 ± 80 HV for the winch drum and 369 ± 75 HV for the chain controller (Supplementary Material Table S1). For comparison, the average microhardness value of the stud-link chain stud was 411.7 ± 49.8 HV [12]. The grey cast iron items were probably produced by casting the molten alloy in a two-part casting die. A similar microstructure was observed in the metallographic sample of the anchor chain link stud retrieved from the Akko Tower shipwreck [12]. The XRF analysis of the winch drum and the stud-link chain controller revealed that they were mainly composed of iron (95.1–97.6 wt% Fe), with up to few wt% of other elements, including Si, P, Mn, and Ti (Table 2). For comparison, the average composition of the grey cast iron anchor chain stud was 97.2 wt% Fe, 1.9 wt% Si, 0.4 wt% P, 0.2 wt% S, 0.2 wt% Mn, and 0.1 wt% Ti based on the XRF analysis [12]. The SEM-EDS analysis of the winch drum and the stud-link chain controller after omitting the carbon peaks revealed similar results to the XRF analysis, with a composition of 95.0–96.9 wt% Fe and up to few wt% of Si, P, S, Mn, and Ti (Table 3). For comparison, the average composition of the grey cast iron anchor chain stud was 94.4–96.1 wt% Fe, 2.0–2.7 wt% Si, 0.3–2.0 wt% P, up to 0.1 wt% S, 0.9–1.3 wt% Mn, and up to 0.1 wt% of Ti and V, according to the SEM-EDS analysis after omitting the carbon peaks [12]. The presence of about 2 wt % Si (Table 3), which was added deliberately as a graphite stabiliser element, was characteristic of grey cast iron [12,43,44]. The manganese was probably added in order to improve the quality of the casting by reducing gas porosity [12,21].

The microhardness testing of the winch shaft, heart-shaped shackle, and the deadeye strap with a futtock plate revealed average hardness values of 164 ± 19 HV for the deadeye strap with a futtock plate and 182 ± 10 HV for the shackle (Supplementary Material Table S1). For comparison, the stud-link chain links showed an average microhardness of 152.4 ± 3.3 HV [12]. The existence of equiaxed ferrite grains combined with preferentially oriented elongated slag inclusions in the L-CS and P-section (Figure 6, Figure 7, Figure 10, Figure 12 and Figure 13 and Supplementary Material Figures S7–S9, S20 and S23) and the microhardness values of the objects (Supplementary Material Table S1) indicate that the winch shaft, heart-shaped shackle, and the deadeye strap with a futtock plate were made of ductile wrought iron produced by the indirect smelting ‘puddling’ method, which was extensively used in Europe at the middle of the nineteenth century [23,34,45]. These wrought iron items were shaped by hot-forging, and the strap components were joined by forge welding and riveting processes [19]. The preferentially oriented elongated slag inclusions observed in the L-CS and P-section (Figure 6, Figure 7, Figure 10, Figure 12 and Figure 13 and Supplementary Material Figures S7–S9, S20 and S23) show the direction of plastic deformation during the forging process [12]. The components of deadeyes No. 163B and 164 retrieved from the Akko Tower shipwreck, which were made of wrought iron, were also joined by forge welding [9,19]. A similar microstructure of ferrite equiaxed grains combined with preferentially oriented slag inclusions was also observed in the metallographic samples of wrought iron deadeye No. 163B [9] and the wrought iron chain link [12] retrieved from the Akko Tower shipwreck.

The XRF analysis of the winch shaft, the heart-shaped shackle, and the deadeye strap with a futtock plate, has shown that they were wrought iron products mainly composed of iron (98.8–99.9 wt% Fe), with small additions of other elements, including less than 1 wt% of Si, P, S, Mn, and Ti (Table 2). For comparison, the wrought iron deadeye No. 163B revealed a composition of 97.6–99.5 wt% Fe, up to 1.3 wt% Si, 0.3–0.9 wt% P, up to 0.6 wt% S, up to 0.7 wt% Al, and up to 0.2 wt% Cu and Mn [9]. The wrought iron ship’s bolt examined by Cohen et al. (2017) was composed of 98.5–99.3 wt% Fe, 0.3–0.9 wt% Si, up to 0.5 wt% P, up to 0.1 wt% S, and up to 0.2 wt% Cu and Mn [9]. The wrought iron anchor chain links also revealed a similar composition [12]. The SEM-EDS analysis of the winch shaft, the heart-shaped shackle, and the deadeye strap with a futtock plate, detected similar results to the XRF analysis, with a composition of 96.3–99.8 wt% Fe and less than 1 wt% of Si, P, S, and Mn (Table 3). For comparison, the composition of a typical wrought iron link with embedded inclusion particles (part of the anchor chain segment), according to the SEM-EDS analysis, was 95.6 wt% Fe, 2.9 wt% O, 0.5 wt% Si, 0.3 wt% P, 0.4 wt% Mn, 0.2 wt% Ca, and 0.1 wt% Mg [12]. SEM observation of the wrought iron objects revealed the presence of one-phase glassy fayalite slag inclusions, two-phase slag inclusions of the wüstite phase surrounded by a glassy phase matrix, and three-phase slag inclusions of wüstite and fayalite laths surrounded by a glassy phase matrix (Figure 6, Figure 7, Figure 8, Figure 9, Figure 10, Figure 11, Figure 12 and Figure 13 and Supplementary Material Figures S11, S14–S16, S19 and S22). Similar inclusions were also observed in the metallographic samples of the wrought iron deadeye No. 163B [9,19], deadeye 164 chain links [19], and the wrought iron anchor chain links [12], which were all retrieved from the Akko Tower shipwreck.

The winch drum, the stud-link chain controller, and the anchor chain link stud were all made of grey cast iron with a similar elemental composition and microstructure, which indicates high-quality production and standardisation of the raw material. The microstructure and composition are comparable to pig iron produced using the coke-fuelled blast furnace in Europe in the nineteenth century [46]. The winch shaft, heart-shaped shackle, deadeye strap with a futtock plate, deadeye No. 163B [9], and the chain link [12] were all made of wrought iron made by refining pig iron, with a similar elemental composition and microstructure, which again indicates a high-quality production and standardisation of the raw metal. The need for metal standardisation arose during the First Industrial Revolution [47]. Most structural ferrous systems during the mid-nineteenth century used a combination of wrought iron and cast iron based on engineering considerations to resist compressive and tensile stresses as appropriate [46]. Wrought iron was chosen because of its weldability, plasticity, and impact resistance [12]. Based on the composition, microstructure, and manufacturing technologies of the grey cast iron and wrought iron objects retrieved from the Akko Tower shipwreck, it is proposed that they were manufactured in the middle of the nineteenth century [12,45,46]. This dating agrees well with the dating of the ship [1]. The high quality of the ferrous items retrieved from this shipwreck and their microstructures and compositions indicated that they were all manufactured according to controlled processes and standards at the same workshop and belonged to the original ship.

6. Conclusions

Four ferrous objects retrieved from the Akko Tower shipwreck were divided into two main groups based on engineering considerations: (1) wrought iron objects and (2) type B grey cast iron objects. The wrought iron items were made of alloy produced by the ‘puddling’ process and forged (plastically deformed) to their final shape; their components were joined by forge welding. The grey cast iron items were most probably produced by a coke-fuelled blast furnace, casting the molten alloy in a two-part casting die. Based on the composition, microstructure, and manufacturing processes of these four items, it is suggested that they were manufactured in the mid-nineteenth century, which agrees well with the dating of the ship. The high quality of all of the ferrous items retrieved from the Akko Tower shipwreck and their microstructures and compositions indicated that they were produced by controlled processes according to high standards, probably in one workshop. Good agreement was achieved between the novel FMM in situ minimally destructive testing method and the conventional destructive metallography observations. The FMM technique can be used to reveal the microstructure of ancient metallic objects without damaging them and contribute to a better understanding of their manufacturing techniques.