Search Results (632)

Structural applications that use High-Strength Low-Alloy (HSLA) steels require detailed microstructural analysis to manufacture welded components that combine strength and weldability. The balance of these properties depends on both the chemical composition and the welding parameters. Moreover, in multi-pass welds, thermal cycling results in a complex Heat-Affected Zone (HAZ), characterized by sub-regions with a multitude of microstructural constituents, including brittle phases. This study investigates the influence of Vanadium addition on the microstructure and performance of the HAZ. Multi-pass welded joints were manufactured on 15 mm thick S355 steels with different Vanadium contents using a robotic GMAW process. A steel variant containing both Vanadium and Niobium was also considered, and the results were compared to those of standard S355 steel. Moving through the different sub-regions of the welded joints, the results show a heterogeneous microstructure characterized by ferrite, bainite and martensite/austenite (M/A) islands. The presence of Vanadium reduces carbon solubility during the phase transformations involved in the welding process. This results in the formation of very fine (average size 11 ± 4 nm) and dispersed precipitates, as well as a lower percentage of the brittle M/A phase, in the variant with a high Vanadium content (0.1 wt.%), compared to the standard S355 steel. Despite the presence of the brittle phase, the micro-alloyed variants exhibit strengthening without loss of ductility. The combined presence of both hard and soft phases in the HAZ provides stress-damping behavior, which, together with the very fine precipitates, promises improved resistance to crack propagation under different loading conditions. Full article

The influence of cold rolling deformation degree (15%, 30%, 45%, 60%, 75%, and 90%) on the microstructural evolution and the mechanical properties of type 347H austenitic heat-resistant steel was investigated using optical microscopy, X-ray diffraction, magnetic hysteresis loop measurement, transmission electron microscopy, and a hardness test. Two types of martensite formed in the deformed specimens, as thin ε-martensite in the cold-rolled steels when the deformation degree was less than 60%, and α′-martensite in the heavily cold-rolled steels when the deformation degree ranged from 60% to 90%. Furthermore, the amount of α′-martensite increases rapidly with the increase in the cold rolling deformation degree. Hence, 60% is considered as the critical point of cold rolling reduction for the formation of α′-martensite. If the specimen experienced a cold rolling reduction of 90%, ε-martensite was hardly observed, while the volume faction of the α′-martensite amounts to 25%. It is verified by the TEM observations that the α′-martensite is transformed from the austenitic matrix as well as the preformed ε-martensite. Full article

In this work, small amounts of Fe or Cr were added to Ni₄₇Co₃Mn_36.5In_13.5 alloy (x = 0) to produce five-component alloys with nominal compositions of Ni₄₇Co₃Mn_35.5In_13.5Fe₁, Ni₄₇Co₃Mn_33.5In_13.5Fe₃, Ni₄₇Co₃Mn_35.5In_13.5Cr₁, and Ni₄₇Co₃Mn_33.5In_13.5Cr₃, which are denoted as Ni₄₇Co₃Mn_36.5−xIn_13.5Fe_x/Cr_x (x = 1, 3 at.% Cr/Fe) series or as Mn-series (due to the addition of alloying elements instead of Mn), and Ni₄₇Co₃Mn_36.5In_12.5Fe₁, Ni₄₇Co₃Mn_36.5In_10.5Fe₃, Ni₄₇Co₃Mn_36.5In_12.5Cr₁, and Ni₄₇Co₃Mn_36.5In_10.5Cr₃, denoted as Ni₄₇Co₃Mn_36.5In_13.5−x (x = 1, 3 at.% Cr/Fe) series or In-series (due to the addition of alloying elements instead of In). The polycrystalline alloys were produced using the vacuum arc melting technique. The as-received alloys were characterized in structure, homogeneity, phase composition, martensitic transformation, and microhardness. The results showed that the addition of 1 at.% of Cr or Fe positively impacted the microstructure of the alloys. The quaternary alloy exhibited a single-phase coarse-grained structure. The addition of Fe and Cr (1 at.%) caused microstructure refinement with small Fe/Cr- and Co-rich γ particles appropriately distributed in the matrix, while the addition of 3% Fe or Cr resulted in γ formation in a dendritic form distributed more randomly. The addition of 1 at.% and 3 at.% of Cr or Fe significantly influenced the martensitic transformation temperatures. The microhardness increased by 21% in the Ni₄₇Co₃Mn_33.5In_13.5Fe₃ alloy compared to the quaternary alloy. Full article

Friction stir welding (FSW) is a leading technique for joining high-strength steel. This study investigates the relationship between weld power, heat generation (HG), cooling medium, and parent austenite grain (PAG) size during both FSW and submerged FSW (SFSW) processes on 11Cr-1.6W-1.6Ni Martensitic Stainless Steel. Weld power and HG were determined by measuring plunge force and tool torque at various tool rotation rates (350–550 rpm). Additionally, the PAG size and microstructural phases in the base metal (BM), thermo-mechanically affected zone (TMAZ), and stir zone (SZ) were examined using scanning electron microscopy (SEM), electron backscattered diffraction (EBSD), and X-ray diffraction (XRD). The results indicated that the SFSW of martensitic steel required a plunge force twice that of the FSW process, along with greater weld power. The heat generated during SFSW was 130% higher than in FSW at 550 rpm. Despite this, the peak temperatures in the SZ were lower in SFSW as a result of the surrounding water’s high heat absorption. This difference in thermal behavior significantly affected the microstructure. While FSW resulted in a complete phase transformation to fine PAG, SFSW showed only minimal or partial transformation and a higher strain rate. Consequently, the SZ and TMAZ in SFSW exhibited a higher hardness than in FSW. Full article

Strain-induced deformations and phase evolutions are two hidden factors that may influence cytocompatibility of Gum Metal alloys during processing for relevant implant applications. In the present research, changes in cell viability of a new Gum Metal Ti-Nb-Zr alloy in its cold-rolled state and after heat treatments (at 700, 850, and 900 °C) were investigated by a comprehensive study of microstructural phases and their role in deformation mechanisms as well as mechanical properties. In its cold-rolled state, the alloy showed a lamellar microstructure along with stress-induced α″ martensite and ω phases, as confirmed by optical microscopy (OM) and X-ray diffractometry (XRD) analysis. The instability in the β phase led to a strain-induced martensitic (SIM) transformation from β to α′/α″ phases, causing lower viability of MG-63 cells compared with commercially pure titanium. MG-63 cell viability was significantly higher (p < 0.0001) in the alloy heat-treated at 900 °C compared with those heat-treated at 700 and 850 °C. This can be directly attributed to the increased portion of the stable and dominant β phase. The stabilized β phase greatly improved the alloy’s cellular response by reducing harmful phase interactions and maintaining mechanical compatibility with bone (admissible strain of 1.3%). Importantly, heat treatment at high temperatures (between 850 and 900 °C) effectively converted the stress-induced α″ and ω phases back into a stable β phase matrix as the dominant phase. Full article

The crystal structure, texture, martensitic transformation, and magnetic properties of magnetic shape-memory Heusler alloys of Ni_51−xMn_33.4In_15.6V_x (x = 0; 0.1; 0.3; 0.5; 1) were investigated. Experimental studies of the magnetic properties and meta-magnetostructural transition (martensitic transition—MT) confirm the main sensitivity of the martensitic transition temperature to vanadium doping and to an applied magnetic field. This makes this family of shape-memory alloys promising for use in numerous applications, such as magnetocaloric cooling and MEMS technology. Diffuse electron scattering was analyzed, and the structures of the austenite and martensite were determined, including the use of TEM in situ experiments during heating and cooling for an alloy with a 0.3 at.% concentration of V. In the austenitic state, the alloys are characterized by a high-temperature-ordered phase of the L2₁ type. The images show nanodomain structures in the form of tweed contrast and contrast from antiphase domains and antiphase boundaries. The alloy microstructure in the temperature range from the martensitic finish to 113 K consists of a six-layer modulated martensite, with 10 M and 14 M modulation observed in local zones. The morphology of the double structure of the modulated martensite structure inherits the morphology of the nanodomain structure in the parent phase. This suggests that it is possible to control the structure of the high-temperature austenite phase and the temperature of the martensitic transition by alloying and/or rapidly quenching from the high-temperature phase. In addition, attention is paid to maintaining fine interface structures. High-resolution transmission electron microscopy showed good coherence along the austenite–martensite boundary. Full article

Decarbonizing the steel industry relies on a transition from carbon-intensive blast furnace technology to scrap-based secondary steelmaking using electric arc furnaces. This transition introduces tramp elements and leads to their gradual accumulation, which can significantly influence the functional properties of chemically sensitive steel grades. In this study, the combined impact of several tramp element contents on the phase transformations, microstructure and mechanical properties of a 0.3 wt.% C low-alloyed steel was investigated. To achieve this, a reference alloy was produced using the conventional blast furnace production route. It was then compared with two trial alloys, which contained intentionally elevated levels of tramp elements and were produced through an experimental melting route designed to simulate scrap-based electric arc furnace production. The experimental characterization included light optical and electron microscopy, electron back-scatter diffraction, in situ synchrotron high-energy X-ray diffraction coupled with dilatometry, and Vickers hardness testing. The results revealed the formation of displacive transformation products such as martensite and showed that austenite was retained in the tramp element-enriched trial alloys. The combination of solid solution strengthening and martensitic transformation led to a gradual increase in hardness. These findings underscore the critical role of tramp elements in determining the microstructural and mechanical response of steels produced from scrap-based feedstock. Full article

Cu–Al–Ni shape memory alloys (SMAs) are attractive for structural and functional applications due to their cost-effectiveness and shape memory behavior. This study systematically investigated the effect of beryllium (Be) addition on the phase stability, microstructure, transformation temperatures, mechanical hardness, corrosion resistance, and wear behavior of Cu–Al–Ni alloys. Alloys with Be contents ranging from 0 to 1.5 wt.% were fabricated via arc melting and subjected to thermal treatment. Characterization techniques included dilatometry, X-ray diffraction (XRD), microhardness testing, potentiodynamic polarization, and pin-on-flat wear testing. The results showed that Be additions ≤ 0.4 wt.% stabilized the martensitic β′ phase, while higher concentrations favored the formation of austenitic β phase with a BCC structure. Hardness increased with Be content, especially in austenitic samples. Corrosion tests revealed that while the 0.2 wt.% Be alloy exhibited the most positive corrosion potential (Ecorr), it also had a higher corrosion rate. Overall, corrosion resistance declined with Be concentrations ≥ 0.6 wt.%. Wear tests demonstrated improved resistance in martensitic alloys, attributed to pseudoplastic deformation. These findings highlight the dual role of Be in modifying phase stability and functional properties, offering useful guidance for designing Cu-based SMAs with tailored performance. Full article

Thermo-mechanical fatigue remains one of the more difficult phenomena to analyze due to the interplay between temperature, mechanical properties, and microstructural features of the material. For austenitic stainless steel, thermo-mechanical fatigue plays a particularly critical role—temperature changes the affinity of $\gamma$ austenite to transform into ${\alpha }^{\prime }$ martensite under overcritical deformation. This paper presents the results of an in situ study of $\gamma \to {\alpha }^{\prime }$ deformation-induced transformation kinetics at elevated temperatures in AISI 347. Fatigue tests were conducted in the temperature range of 20 to 320 °C. A uniaxial magnetic balance was used to directly measure the change in ferromagnetic volume fraction of the fatigue specimens as the fatigue load was applied. From this data, an empirical mathematical model was found. This model describes the kinetics of $\gamma \to {\alpha }^{\prime }$ transformation as an exponential function of temperature, where the rate of phase transformation decreases with temperature, asymptotically approaching zero but never actually reaching it. Full article

This study investigates the microstructural and mechanical evolution of Ti6Al4V alloy surfaces modified through laser surface alloying (LSA) with antimicrobial elements silver (Ag) and copper (Cu) to enhance surface performance for biomedical applications. The as-received Ti6Al4V exhibited a typical equiaxed $\alpha \text{-}\beta$ microstructure with baseline hardness. Following LSA treatment using a 1000 W pulsed laser, distinct transformations were observed in the melt zone (MZ) and heat-affected zone (HAZ), influenced by the specific alloying element. Ag incorporation led to the development of ultrafine acicular martensitic structures and a higher fraction of high-angle grain boundaries, resulting in moderate hardness improvement. In contrast, Cu alloying promoted the formation of Ti₂Cu intermetallic phases, dendritic morphologies, and pronounced solute segregation, leading to a more significant increase in hardness. Electron Backscatter Diffraction(EBSD) and Energy Dispersive Spectroscopy (EDS) analyses revealed grain refinement, texture evolution, and elemental redistribution across the modified regions, while X-ray Diffraction XRD confirmed the presence of new phases. The comparative analysis highlights that although both Ag and Cu improve microstructural complexity and hardness, Cu-modified zones exhibited higher hardness values than Ag-modified zones, suggesting a stronger surface strengthening effect under the tested conditions. These findings contribute valuable insights into the structure–property relationships of LSA-modified Ti alloys, supporting their potential for durable and antimicrobial biomedical implants. Full article

Martensitic stainless steel is a commonly used stainless steel, and is widely used in daily production and life, but its high content of alloy elements increases its cost. This study aimed to develop low-cost martensitic stainless steel with excellent seawater corrosion resistance by using Zr-Ti combined deoxidation with molten iron from low-priced laterite nickel ore as raw material, taking advantage of the corrosion-resistant elements Cr and Ni, abundant in laterite nickel ore. The characteristics of corrosion-active inclusions in steel, such as their density and electrostatic potential saturation-current density, were observed and studied using scanning electron microscopy and electrochemical testing methods. The intentionally added composite deoxidizing elements (Zr, Ti) form highly stable oxide particles at high temperatures. During the solidification of the molten steel and subsequent solid-state phase transformation, the highly corrosion-active MnS nucleates and disperses on the oxide particles already formed in the liquid phase, while TiN continues to precipitate and coat the MnS particles. This significantly reduces the saturation-current density of locally corrosion-active inclusions, resulting in a marked improvement in seawater corrosion resistance. Full article

The reduced ductility caused by the brittle needle-like α′ martensite limits the application of TC4 alloys produced by selective laser melting (SLM). Appropriate heat treatment can improve the microstructures and properties of SLM-fabricated TC4 alloys. In this work, SLM-fabricated TC4 alloys underwent stress relief annealing at 600 °C and high-temperature annealing at 800 °C. The effects of heat treatment temperature on phase composition, microstructural morphology, grain orientation, and mechanical properties were investigated. Meanwhile, the microstructural evolution and fracture mechanisms during the heat treatment process were analyzed. The results indicate that after annealing at 600 °C, the needle-like α′ phase transforms into elongated α, and nano-β phase increases. When annealed at 800 °C, the α′ phase completely transforms into a more stable lath-shaped α phase and a short rod-shaped β phase, with the nano-β phase disappearing. The texture orientation gradually shifts from <0001> towards <01-10>, where slip systems are more active. Additionally, heat treatment promotes the transition of grain boundaries to high-angle grain boundaries, thereby alleviating stress concentration and enhancing solid-solution strengthening. After heat treatment, the ultimate tensile strength of the material slightly decreases, but the elongation significantly increases. As the annealing temperature increased, the elongation (EL) improved from 5.22% to 11.43%. Following high-temperature annealing at 800 °C, necking and larger dimples appear on the fracture surface, and the fracture mechanism shifts from a mixed brittle–ductile fracture to a ductile fracture. This work provides a theoretical basis for improving the microstructures and properties of SLM-fabricated TC4 alloys through heat treatment. Full article

The induction quenching–tempering process typically enhances the surface strength and core toughness of alloy steels by utilizing the skin effect. However, the impact of parameters like quenching current and heating time on the microstructure and mechanical property of 34CrNiMo6 steel crankshafts remains unclear. In this work, the microstructure of 34CrNiMo6 steel after induction quenching exhibits three distinct zones: a martensite hardened layer; a transition zone of martensite and tempered sorbite; and a matrix of tempered sorbite. As the induction current (400, 500, and 600 mA) and heating time (3, 5, and 7 s) increase, the hardened layer thickness enhances (up to 3.21 mm). Under the 600 mA and 7 s, the hardened layer reaches peak hardness and residual stress values of 521.48 HV and −330.12 MPa, showing a decreasing trend from surface to core. After tempering at 330 °C for 2 h, the hardened layer mainly consists of tempered martensite, and the surface hardness and residual stress decrease to 417.94 HV and −12.33 MPa. The temperature gradient from quenching balances after tempering, with martensitic phase transformation and stress redistribution reducing hardness and residual stress. Furthermore, the induction quenching–tempering process enhances the toughness of 34CrNiMo6 steel when compared to the untreated specimen, boosting its tensile yield strength, elongation, and tensile strength by 15.3%, 14.9%, and 19.5%, respectively. This work deepens the understanding of induction quenching–tempering process and provides valuable insights for designing alloy steels with excellent mechanical properties. Full article

To address the central cracking problem in continuous casting slabs of 38CrMoAl steel, high-temperature tensile tests were performed using a Gleeble-3800 thermal simulator to characterize the hot ductility of the steel within the temperature range of 600–1200 °C. The phase transformation behavior was computationally analyzed via the Thermo-Calc software, while the microstructure, fracture morphology, and precipitate characteristics were systematically investigated using a metallographic microscope (MM), a field-emission scanning electron microscope (FE-SEM), and transmission electron microscopy (TEM). Additionally, the effects of different holding times and cooling rates on the microstructure and precipitates of 38CrMoAl steel were also studied. The results show that the third brittle temperature region of 38CrMoAl steel is 645–1009 °C, and the fracture mechanisms can be classified into three types: (I) in the α single-phase region, the thickness of intergranular proeutectoid ferrite increases with rising temperature, leading to reduced hot ductility; (II) in the γ single-phase region, the average size of precipitates increases while the number density decreases with increasing temperature, thereby improving hot ductility; and (III) in the α + γ two-phase region, the precipitation of proeutectoid ferrite promotes crack propagation and the dense distribution of precipitates at grain boundaries causes stress concentration, further deteriorating hot ductility. Heat treatment experiments indicate that the microstructures of the specimen transformed under water cooling, air cooling, and furnace cooling conditions as follows: martensite + proeutectoid ferrite → bainite + ferrite → ferrite. The average size of precipitates first decreased, then increased, and finally decreased again with increasing holding time, while the number density exhibited the opposite trend. Therefore, when the holding time was the same, reducing the cooling rate could increase the average size of the precipitates and decrease their number density, thereby improving the hot ductility of 38CrMoAl steel. Full article

This study aims to determine the optimal low-temperature stress relieving heat treatment that minimizes residual stresses while preserving corrosion resistance in Laser Powder Bed Fusion (L-PBF) processed Ti6Al4V alloy. Specifically, it investigates the effects of stress relieving at 400 °C, 600 °C, and 800 °C on microstructure, residual stress, and electrochemical performance. Specimens were characterized using X-ray diffraction (XRD), scanning electron microscopy (SEM), and electrochemical techniques. A novel microcapillary electrochemical method was employed to precisely assess passive layer stability and corrosion behaviour under simulated oral conditions, including fluoride contamination and tensile loading. Results show that heat treatments up to 600 °C effectively reduce residual stress with minimal impact on corrosion resistance. However, 800 °C treatment leads to a phase transformation from α′ martensite to a dual-phase α + β structure, significantly compromising passive film integrity. The findings establish 600 °C as the optimal stress-relieving temperature for balancing mechanical stability and electrochemical performance in biomedical and aerospace components. Full article