*2.2. Materials' Characterization*

Examinations were performed on samples from 12 wear-resistant hardfaced composite plates (Table 1) produced by different arc hardfacing processes. The selected surfacing technologies differed in the metal deposition rate, penetration depth, surfacing speed, surfacing overlay quality, and the final cost of the product. For a given product type and quality requirements, quality assurance is mainly determined by the coating application process, the technique and technological conditions of coating application, and the type of additional material.


**Table 1.** Hardfaced composite wear-resistant plates with an arc hardfaced layer by T Fe15 and T Fe16 alloys.


**Table 1.** *Cont.*


**Table 1.** *Cont.*

Remarks: <sup>1</sup> Surface layer manufactured in a three-pass process; <sup>2</sup> surface layer manufactured in a one-pass process; 3 chemistry composition proprietary to its own copyright patent [31].

The advantages of the manual metal arc deposition process are its versatility and the availability of a wide range of hardfacing alloys. The set-up time is short, making the process ideal for small jobs and short production runs. For a working surface, the manual metal arc deposition process has lower deposition rates than the flux-cored arc welding (FCAW) deposition processes, which use a higher current. The process has a low operator duty cycle, with the operator spending significant time changing electrodes and chipping slag. These two factors combine to limit the application of this process, especially if high production rates are required.

The flux-cored arc welding gas-shielded (FCAW-GS) deposition process has the advantage of deeper penetration and a higher charging rate than the manual metal arc process. Thus, the welding process is becoming more economical for jobs in welding workshops. Flux-cored arc welding self-shielded (FCAW-SS) filler metal eliminates the need for external shielding gas and tolerates stronger wind conditions without causing porosity.

The compositions of nine layers contain alloys from group T Fe15, and three layers contain alloys from group T Fe16 (including a hardfaced plate with the name PHWP). The obtained results were compared to the reference abrasion-wear-resistant steel plate (Table 2).

The wear-resistant plate with the name PHWP was obtained by the arc welding process with a tubular electrode 4 mm in diameter. The metallic core of the electrode has a patented metallic composition with a rutile cover. A cross-sectional view of the electrode is presented in Figure 1.

**Name of the Abrasion‐ Resistant Steel**

PHWP Patented hardfacing wear plate <sup>2</sup>

Remarks: <sup>1</sup> Surface layer manufactured in a three‐pass process; <sup>2</sup> surface layer manufactured in a one‐

**Table 2.** Characteristics of the abrasion‐resistant steel.

pass process; <sup>3</sup> chemistry composition proprietary to its own copyright patent [31].

pipes, shovel wear packages, cutter rings, primary and secondary crusher teeth, grouser risers, and other mining applications Industry: cement, agriculture, quarries, mining, ceramic, and power

T Fe16 C (5.0%), Cr (23.0%), Mo (xx%), Nb (xx%), Si (xx%), B (xx%), W (xx%), V (xx%), Fe (Balance) <sup>3</sup> Manual metal arc welding (MMA) with patented cover tubular electrode Potential applications: screeners, blast furnace hoppers, extractor fans Industry: iron and steel, power, quarries, and cement

**Steel in Accordance with EN 10029 [32] Element Contents Metal Hardness**

C (0.32%), Si (0.7%), Mn (1.6%), P (0.025%), S (0.01%), Cr (1.4%), Ni (1.5%), Mo (0.6%), B (0.004%), Fe (Balance) 38–44 HRC (372–435 HV)

**Figure 1.** Macrostructure view of the cross‐section of the new patented tubular electrode [31]. **Figure 1.** Macrostructure view of the cross-section of the new patented tubular electrode [31].


*2.3. Methodology of Research* **Table 2.** Characteristics of the abrasion-resistant steel.

2.3.1. Nondestructive Testing: Visual Testing The samples were cut from the inner regions of the examined hardfaced composite wear-resistant plates and reference material.

#### Visual testing of the wear plates was performed in accordance with the procedures, materials, and equipment from the ISO 17637 standard [33]. Visual testing was based on a direct inspection of *2.3. Methodology of Research*

the antiabrasive wear of the hardfaced layer procedure. Before testing, the surface subjected to observation was cleaned. For each examined sample, a visual test (VT) on the sample surface was performed to identify potential unacceptable welding defects, such as cracks directed longitudinally to the hardfaced seam, other discontinuities, porosity, irregularity of shape, and lack of fusion. Metal-mineral wear resistance was determined by strictly adhering to the procedure disclosed in the ASTM G65 standard [28]. The determination of surface layer structure and other properties was based on metallographic macroand microscopic examinations, measuring the base material content in the hardfaced layer and the hardness tests on the working surface.

#### 2.3.1. Nondestructive Testing: Visual Testing

Visual testing of the wear plates was performed in accordance with the procedures, materials, and equipment from the ISO 17637 standard [33]. Visual testing was based on a direct inspection of the antiabrasive wear of the hardfaced layer procedure. Before testing, the surface subjected to observation was cleaned.

#### 2.3.2. Hardness Measurements

The hardness testing of the reference material (Hardox 400 steel) and the hardfaced layer was performed using the Rockwell method Scale C (HRC) on the Nexus 610 RS stationary hardness tester (Innovatest Europe BV, Maastricht, Netherlands). Hardness testing was performed according to ISO 6508 [29]. The test load used was 150 kgf (total test force of 1.471 kN). Hardness tests were performed in five test points on the surface, finished by grinding selected layers manufactured by the arc hardfacing process. The way the measurement points were located on the wear-resistant layer surface is presented in Figure 2.

is presented in Figure 2.

2.3.2. Hardness Measurements

2.3.2. Hardness Measurements

examinations were performed in conformity to the ISO 6507‐1:2018 standard [34].

The hardness testing of the reference material (Hardox 400 steel) and the hardfaced layer was performed using the Rockwell method Scale C (HRC) on the Nexus 610 RS stationary hardness tester (Innovatest Europe BV, Maastricht, Netherlands). Hardness testing was performed according to ISO 6508 [29]. The test load used was 150 kgf (total test force of 1.471 kN). Hardness tests were performed in five test points on the surface, finished by grinding selected layers manufactured by the arc hardfacing process. The way the measurement points were located on the wear‐resistant layer surface

The carbide's microhardness measurement was made with the Vickers method at the polished cross‐section of the samples. A Sunpoc SMV‐1000X (Guizhou Sunpoc Tech Industry Co., Ltd., Guizhou, China) microhardness tester with a diamond pyramidal indenter was used. The load could

The hardness testing of the reference material (Hardox 400 steel) and the hardfaced layer was performed using the Rockwell method Scale C (HRC) on the Nexus 610 RS stationary hardness tester

*Materials* **2020**, *12*, x FOR PEER REVIEW 7 of 25

in five test points on the surface, finished by grinding selected layers manufactured by the arc

**Figure 2.** Measurement points location on the wear‐resistant layer surface. **Figure 2.** Measurement points location on the wear-resistant layer surface.

2.3.3. Abrasive Wear Test The metal‐mineral wear resistance of all test samples and the reference material (Hardox 400 steel) was carried in accordance with ASTM G 65‐00: Standard Test Method for Measuring Abrasion Using the Dry Sand/Rubber Wheel Apparatus, Procedure A (Figure 3) [28]. The carbide's microhardness measurement was made with the Vickers method at the polished cross-section of the samples. A Sunpoc SMV-1000X (Guizhou Sunpoc Tech Industry Co., Ltd., Guizhou, China) microhardness tester with a diamond pyramidal indenter was used. The load could be varied from 5 to 500 g in fixed steps. The duration was kept at 25 s throughout the study. The examinations were performed in conformity to the ISO 6507-1:2018 standard [34]. **Figure 2.** Measurement points location on the wear‐resistant layer surface.

#### 2.3.3. Abrasive Wear Test 2.3.3. Abrasive Wear Test

The metal-mineral wear resistance of all test samples and the reference material (Hardox 400 steel) was carried in accordance with ASTM G 65-00: Standard Test Method for Measuring Abrasion Using the Dry Sand/Rubber Wheel Apparatus, Procedure A (Figure 3) [28]. The metal‐mineral wear resistance of all test samples and the reference material (Hardox 400 steel) was carried in accordance with ASTM G 65‐00: Standard Test Method for Measuring Abrasion Using the Dry Sand/Rubber Wheel Apparatus, Procedure A (Figure 3) [28].

sand with a grain size of 50–70 mesh (0.300–0.212 mm). The abrasive is fed from a gravity hopper **Figure 3.** Schematic diagram of ASTM G65, Procedure A: abrasive wear resistance test (**a**) and apparatus overview (**b**) [35]. **Figure 3.**Schematic diagram of ASTM G65, Procedure A: abrasive wear resistance test (**a**) and apparatus overview (**b**) [35].

The rubber wheel test outlined in ASTM G65, first introduced in 1980, is the most widely applied method in determining material wear resistance. The abrasive used in the test procedure is quartz sand with a grain size of 50–70 mesh (0.300–0.212 mm). The abrasive is fed from a gravity hopper The rubber wheel test outlined in ASTM G65, first introduced in 1980, is the most widely applied method in determining material wear resistance. The abrasive used in the test procedure is quartz sand with a grain size of 50–70 mesh (0.300–0.212 mm). The abrasive is fed from a gravity hopper with a 250–350 g/min feed rate. The counterface in the test is rubberized by a hard wheel compound with a total dimension of φ 228 mm × 12.7 mm. The specimen under investigation is pressed to the counterface by forces of, depending on the procedure chosen, 45 N or 135 N. The test length is determined by the number of wheel revolutions of the counterface and is contained in the range of 100–6000 revolutions (wheel speed of 200 r/min). The measured results comprised the volume of wear and an examination of the worn surface. According to Hejwowski, under the test condition, the worn material is transferred to the surface of the abrasive grains [36]. In the rubber wheel test, the abrasive

grains may rotate in the friction zone or temporarily attach to the rubber material. The movement and interaction of the abrasive material are dependent not only on the test parameters (abrasive flux and type, test force, and counterface revolution speed) but also on the hardness of the sample under investigation. The rolling of abrasive grains is facilitated by a low test force and the limited tested sample hardness. For high test forces and an elevated sample hardness, the sliding movement of the abrasive grains is promoted. grains may rotate in the friction zone or temporarily attach to the rubber material. The movement and interaction of the abrasive material are dependent not only on the test parameters (abrasive flux and type, test force, and counterface revolution speed) but also on the hardness of the sample under investigation. The rolling of abrasive grains is facilitated by a low test force and the limited tested sample hardness. For high test forces and an elevated sample hardness, the sliding movement of the abrasive grains is promoted.

and an examination of the worn surface. According to Hejwowski, under the test condition, the worn material is transferred to the surface of the abrasive grains [36]. In the rubber wheel test, the abrasive

*Materials* **2020**, *12*, x FOR PEER REVIEW 8 of 25

with a 250–350 g/min feed rate. The counterface in the test is rubberized by a hard wheel compound with a total dimension of ϕ 228 mm × 12.7 mm. The specimen under investigation is pressed to the counterface by forces of, depending on the procedure chosen, 45 N or 135 N. The test length is determined by the number of wheel revolutions of the counterface and is contained in the range of

In order to determine the wear resistance of the selected wear-resistant composite plates, two samples (75 mm × 25 mm × 10 mm) were cut from the inner area of the plate. During the test procedure, the counterface wheel made 6000 revolutions, samples were pressed with the force of 130 N, and the abrasive materials' (A. F. S. Testing Sand 50–70 mesh) expense was 335 g/min (Figure 4). The ASTM G65-00 wear test time was 30 min. In order to determine the wear resistance of the selected wear‐resistant composite plates, two samples (75 mm × 25 mm × 10 mm) were cut from the inner area of the plate. During the test procedure, the counterface wheel made 6000 revolutions, samples were pressed with the force of 130 N, and the abrasive materials' (A. F. S. Testing Sand 50–70 mesh) expense was 335 g/min (Figure 4). The ASTM G65‐00 wear test time was 30 min.

**Figure 4.** View of the abrasive material particles (A.F.S Testing Sand 50–70) used in ASTM G65‐00, Procedure A: abrasive wear resistance test: (**a**) a quartz sand grain fraction, (**b**) a single grain of quartz sand, (**c**) the surface structure of quartz sand grain. **Figure 4.** View of the abrasive material particles (A.F.S Testing Sand 50–70) used in ASTM G65-00, Procedure A: abrasive wear resistance test: (**a**) a quartz sand grain fraction, (**b**) a single grain of quartz sand, (**c**) the surface structure of quartz sand grain.

Before and after the test procedure, the samples subjected to wear testing were weighed on a laboratory scale with an accuracy of 0.0001 g. The mean density of the tested hardfaced layers and reference Hardox steel was determined by measuring the weight of three specimens in air and during submersion in liquid at room temperature (Table 3). The measured mass loss during the test procedure, in conjunction with the determined mean density, was used to calculate volumetric loss according to Formula (1). A similar fraction and distribution of the matrix reinforcing phase over the entire cross‐section of the surface layer worn during the 30 min test period were assumed. Before and after the test procedure, the samples subjected to wear testing were weighed on a laboratory scale with an accuracy of 0.0001 g. The mean density of the tested hardfaced layers and reference Hardox steel was determined by measuring the weight of three specimens in air and during submersion in liquid at room temperature (Table 3). The measured mass loss during the test procedure, in conjunction with the determined mean density, was used to calculate volumetric loss according to Formula (1). A similar fraction and distribution of the matrix reinforcing phase over the entire cross-section of the surface layer worn during the 30 min test period were assumed.

$$\text{Volume loss} \left[ \text{mm}^3 \right] = \frac{\text{mass loss} \left[ \text{g} \right]}{\text{density} \left[ \frac{\text{g}}{\text{cm}^3} \right]} \times 1000 \tag{1}$$

The abrasive wear mechanism was assessed in accordance with the criterion, which was the quotient of the cross‐sectional area of the sum of the two‐sided upsets of the material next to the deepest crack F1 and crack cavity F2 [37–39]. The loss of material in the surface layer during abrasive wear was classified as: The abrasive wear mechanism was assessed in accordance with the criterion, which was the quotient of the cross-sectional area of the sum of the two-sided upsets of the material next to the deepest crack F<sup>1</sup> and crack cavity F<sup>2</sup> [37–39]. The loss of material in the surface layer during abrasive wear was classified as:




Remarks: 1 Mass loss in 30 min; 2 relative abrasive wear resistance to Hardox 400 steel; 3 surface layer manufactured in a three-pass process; 4 surface layer manufactured in a one-pass process.

**3. Results and Discussion**

**3. Results and Discussion**

*3.1. Nondestructive Testing: Visual Testing Results*

*3.1. Nondestructive Testing: Visual Testing Results*

direction and surface spatter (602) were found, as presented in Figure 7.

direction and surface spatter (602) were found, as presented in Figure 7.

*Materials* **2020**, *12*, x FOR PEER REVIEW 9 of 25

**Figure 5.** The abrasive wear mechanism criterion: az—groove depth; m‐m—reference line. **Figure 5.** The abrasive wear mechanism criterion: az—groove depth; m-m—reference line. **Figure 5.** The abrasive wear mechanism criterion: az—groove depth; m‐m—reference line.

2.3.4. Metallographic Examination and X‐ray Diffraction Analysis 2.3.4. Metallographic Examination and X-ray Diffraction Analysis

Microscopic examinations were performed on standard metallographic specimens. The etchant chemical composition and etching parameters were determined individually for each hardfaced layer. The observation and acquisition of the macro‐ and microstructure of the specimens were performed using the Olympus SZX7 (Olympus Corporation, Tokyo, Japan) stereoscopic microscope, the Olympus GX 71 inverse metallographic microscope (Olympus Corporation, Tokyo, Japan), the Zeiss Smartproof 5 confocal microscope (Carl Zeiss AG, Oberkochen, Germany), and the Zeiss Supra 25 scanning microscope (Carl Zeiss AG, Oberkochen, Germany). Precise determination (surface and volumetric) of the surfaced layer chemical composition was performed by means of energy‐ dispersive spectroscopy (EDS). Microscopic examinations were performed on standard metallographic specimens. The etchant chemical composition and etching parameters were determined individually for each hardfaced layer. The observation and acquisition of the macro- and microstructure of the specimens were performed using the Olympus SZX7 (Olympus Corporation, Tokyo, Japan) stereoscopic microscope, the Olympus GX 71 inverse metallographic microscope (Olympus Corporation, Tokyo, Japan), the Zeiss Smartproof 5 confocal microscope (Carl Zeiss AG, Oberkochen, Germany), and the Zeiss Supra 25 scanning microscope (Carl Zeiss AG, Oberkochen, Germany). Precise determination (surface and volumetric) of the surfaced layer chemical composition was performed by means of energy-dispersive spectroscopy (EDS). 2.3.4. Metallographic Examination and X‐ray Diffraction Analysis Microscopic examinations were performed on standard metallographic specimens. The etchant chemical composition and etching parameters were determined individually for each hardfaced layer. The observation and acquisition of the macro‐ and microstructure of the specimens were performed using the Olympus SZX7 (Olympus Corporation, Tokyo, Japan) stereoscopic microscope, the Olympus GX 71 inverse metallographic microscope (Olympus Corporation, Tokyo, Japan), the Zeiss Smartproof 5 confocal microscope (Carl Zeiss AG, Oberkochen, Germany), and the Zeiss Supra 25 scanning microscope (Carl Zeiss AG, Oberkochen, Germany). Precise determination (surface and volumetric) of the surfaced layer chemical composition was performed by means of energy‐

The obtained macroscopic images enabled the determination of surface layer thickness as well as the base material content in the hardfaced layer. The dilution of weld metal, U, was calculated according to Formula (2), as the ratio between FBM, the area of the fusion‐based metal and a sum of FBM and FR, the area of reinforcement, Figure 6. The obtained macroscopic images enabled the determination of surface layer thickness as well as the base material content in the hardfaced layer. The dilution of weld metal, U, was calculated according to Formula (2), as the ratio between FBM, the area of the fusion-based metal and a sum of FBM and FR, the area of reinforcement, Figure 6. dispersive spectroscopy (EDS). The obtained macroscopic images enabled the determination of surface layer thickness as well as the base material content in the hardfaced layer. The dilution of weld metal, U, was calculated according to Formula (2), as the ratio between FBM, the area of the fusion‐based metal and a sum of

$$\mathbf{U} = \frac{\mathbf{F\_{BM}}}{\mathbf{F\_R} + \mathbf{F\_{BM}}} \times 100\% \tag{2}$$

hR—height of the bead reinforcement; hBM—base metal penetration depth; FR—area of reinforcement; FBM—area of base metal melted. **Figure 6.** Geometrical parameters of the stringer and weave bead deposits: B—width of the bead face; hR—height of the bead reinforcement; hBM—base metal penetration depth; FR—area of reinforcement; FBM—area of base metal melted. **Figure 6.** Geometrical parameters of the stringer and weave bead deposits: B—width of the bead face; hR—height of the bead reinforcement; hBM—base metal penetration depth; FR—area of reinforcement; FBM—area of base metal melted.

**Figure 6.** Geometrical parameters of the stringer and weave bead deposits: B—width of the bead face;

The X‐ray diffraction phase examinations were carried on X'Pert Pro PANalytical (Malvern Panalytical Ltd., Malvern, UK) diffractometer with Cu lamp (λ = 1.54056 nm). The samples were examined in a Bragg–Brentano geometry. The X‐ray diffraction phase examinations were carried on X'Pert Pro PANalytical (Malvern Panalytical Ltd., Malvern, UK) diffractometer with Cu lamp (λ = 1.54056 nm). The samples were examined in a Bragg–Brentano geometry. The X-ray diffraction phase examinations were carried on X'Pert Pro PANalytical (Malvern Panalytical Ltd., Malvern, UK) diffractometer with Cu lamp (λ = 1.54056 nm). The samples were examined in a Bragg–Brentano geometry.

During the visual tests of selected hardfaced composite wear‐resistant plates produced by the automated FCAW and MMA methods, imperfections of cracks (100) perpendicular to the hardfacing

During the visual tests of selected hardfaced composite wear‐resistant plates produced by the automated FCAW and MMA methods, imperfections of cracks (100) perpendicular to the hardfacing
