The deposition of a thin (several tens of microns) protective coating in atmospheric conditions is a challenging task for surface engineering. The structural features and tribological properties of a particle-reinforced metal matrix composite coating synthesized on middle-carbon steel by air pulse-plasma treatments were studied in the present work. The 24–31 µm thick coating of “24 vol.% (TiC + WC)/Hardened steel matrix” was produced by 10 plasma pulses generated by an electro-thermal axial plasma accelerator equipped with a consumable cathode of novel design (low-carbon steel tube filled with “TiC/WC + Epoxy resin” mixture). The study included optical microscopy (OM), scanning electron microscopy (SEM), energy-dispersive X-ray spectroscopy (EDX), X-ray diffraction (XRD, microhardness measurements, and dry “Ball-on-Plate” testing. The carbides were directly plasma-transferred to the substrate (steel of AISI 4145H grade) from the cathode without substantial melting. The hard (500–1044 HV) coating matrix consisted of 57 vol.% austenite (1.43 wt.% C) and 43 vol.% plate martensite was formed via carbon enrichment of steel from plasma flow. Additionally, a minor amount of oxide phases (TiO₂, WO₂, WO₃) were dispersed in the matrix. As compared to substrate, the coating had a lower coefficient of friction; its volumetric wear was decreased by 4.4 times when sliding against hardened steel ball and by 16 times when sliding against SiC ball.

Structural rolled steels are the primary products of modern ferrous metallurgy. Consequently, enhancing the mechanical properties of rolled steel using energy-saving processing routes without furnace heating for additional heat treatment is advisable. This study compared the effect on the mechanical properties of structural steel for different processing routes, like conventional hot rolling, normalizing rolling, thermo-mechanically controlled processing (TMCP), and TMCP with accelerating cooling (AC) to 550 °C or 460 °C. The material studied was a 20 mm-thick sheet of S355N grade (EN 10025) made of low-carbon (V+Nb+Al)-micro-alloyed steel. The research methodology included standard mechanical testing and microstructure characterization using optical microscopy, scanning and transmission electronic microscopies, energy dispersive X-ray spectrometry, and X-ray diffraction. It was found that using different processing routes could increase the mechanical properties of the steel sheets from S355N to S550QL1 grade without additional heat treatment costs. TMCP followed by AC to 550 °C ensured the best combination of strength and cold-temperature resistance due to formation of a quasi-polygonal/acicular ferrite structure with minor fractions of dispersed pearlite and martensite/austenite islands. The contribution of different structural factors to the yield tensile strength and ductile–brittle transition temperature of steel was analyzed using theoretical calculations. The calculated results complied well with the experimental data. The effectiveness of the cost-saving processing routes which may bring definite economic benefits is concluded.

TRIP-assisted C-Si-Mn steels are usually subjected to austempering with a preliminary intercritical annealing that is targeted at the multi-phase structure with 40–60 vol.% of proeutectoid ferrite. The kinetics and the mechanism of phase-structural transformations can be impacted due to the additional alloying of TRIP-assisted steel by the strong carbide forming elements, thus necessitating an alternative approach for the selection of intercritical annealing parameters. This issue is analyzed in the present work, which investigates the effect of the temperature of intercritical annealing on the “Structure/Properties” correlations in 0.2 wt.% C-Si-Mn-Nb steel additionally alloyed by 0.55 wt.% Cr, 0.20% Mo, and 0.11 wt.% V. The annealing temperature ranged from 770 °C to 950 °C, and austempering was performed at 350 °C for 20 min. It was observed that the addition of the (Cr, Mo, and V) complex significantly improved the steel hardenability. However, the annealing of steel at 770 °C (to gain 50 vol.% of proeutectoid ferrite) resulted in the precipitation of coarse cementite lamellas during bainite transformation, thus lowering the amount of retained austenite (RA) and decreasing the strength and ductility of the steel. At higher annealing temperatures, carbide-free bainite was formed, which presented a 2.5–3.5 times increase in the RA volume fraction and a 1.5 times increase in the RA carbon content. The optimal combination of the mechanical properties (UTS of 1040 MPa, TEL of 23%, V-notch impact toughness of 95 J/cm², PSE of 23.9 GPa·%) referred to annealing at a temperature close to the Ac₃ point, resulting in a structure with 5 vol.% ferrite and 9 vol.% RA (the residue was carbide-free bainite). This structure presented an extended manifestation of the TRIP effect with an enhanced strain hardening rate due to strain-induced martensite transformation. The impact of the alloying elements on the carbon activity in austenite served as the basis for the analysis of structure formation.

This study aims to comprehensively assess the suitability of post-processing annealing (at 900–1200 °C) for enhancing the key properties of 316L steel fabricated via laser powder bed fusion (LPBF). It adopts a holistic approach to investigate the annealing-driven evolution of microstructure–property relationships, focusing on tensile properties, nanoindentation hardness and modulus, impact toughness at ambient and cryogenic temperatures (−196 °C), and the corrosion resistance of LPBF 316L. Annealing at 900–1050 °C reduced tensile strength and hardness, followed by a moderate increase at 1200 °C. Conversely, ductility and impact toughness peaked at 900 °C but declined with the increasing annealing temperature. Regardless of the annealing temperature and testing conditions, LPBF 316L steel fractured through a mixed transgranular/intergranular mechanism involving dimple formation. The corrosion resistance of annealed steel was significantly lower than that in the as-built state, with the least detrimental effect being observed at 1050 °C. These changes resulted from the complex interplay of annealing-induced structural transformations, including elimination of the cellular structure and Cr/Mo segregations, reduced dislocation density, the formation of recrystallized grains, and the precipitation of nano-sized (MnCrSiAl)O₃ inclusions. At 1200 °C, an abundant oxide formation strengthened the steel; however, particle coarsening, combined with the transition of (MnCrSiAl)O₃ into Mo-rich oxide, further degraded the passive film, leading to a sharp decrease in corrosion resistance. Overall, post-processing annealing at 900–1200 °C did not comprehensively improve the combination of LPBF 316L steel properties, suggesting that the as-built microstructure offers a favorable balance of properties. High-temperature annealing can enhance a particular property while potentially compromising other performance characteristics.

Additive manufacturing is increasingly used to produce metallic biomaterials, and post-processing is gaining increasing attention for improving the properties of as-built components. This study investigates the effect of work hardening followed by recrystallisation annealing on the tensile and nanoindentation behaviour of laser powder bed-fused (LPBF) 316L stainless steel, with the aim of optimising its mechanical properties. As-built and thermally stabilised (at 900 °C) specimens were prestrained in a uniaxially tensile manner at room temperature (0.12 plastic strain, ~75% of maximum work hardening) and subsequently annealed (at 900 °C or 1050 °C for 1 h). The microstructure and mechanical properties were then characterised by optical microscopy, SEM, EBSD, XRD, nanoindentation, and tensile testing. It was found that prestraining increased yield tensile strength (YTS) 1.2–1.7 times (to 690–699 MPa) and ultimate tensile strength (UTS) ~1.2 times (to 762–770 MPa), but decreased ductility 1.5 times. Annealing led to recovery and partial static recrystallisation, decreasing YTS (to 403–427 MPa), restoring ductility, and increasing the strain hardening rate; UTS and indentation hardness were less affected. Notably, the post-LPBF thermal stabilisation hindered recrystallisation and increased its onset temperature. Mechanical property changes under prestraining and annealing are discussed with respect to microstructure and crystalline features (microstrain, crystal size, dislocation density). All specimens exhibited ductile fractures with fine/ultra-fine dimples consistent with the as-built cellular structure. The combined treatment enhanced tensile strength whilst preserving sufficient ductility, achieving a strength–ductility product of 40.3 GPa·%. This offers a promising approach for tailoring LPBF 316L for engineering applications.

In this paper, enhancing the tribological characteristics of novel cast metallic materials—hybrid multi-component cast irons—by applying a strengthening heat treatment is described. The experimental materials were the cast alloys of a nominal composition (5 wt.% W, 5 wt.% Mo, 5 wt.% V, 10 wt.% Cr, 2.5 wt.% Ti, Fe is a balance) supplemented with 0.3–1.1 wt.% C and 1.5–2.5 wt.% B (total of nine alloys). The heat treatment was oil-quenching followed by 200 °C tempering. The quench temperature (QT) varied in the range of 900–1200 °C, with a step of 50 °C (with a 2-h holding at QT). The correlation of the QT with microstructure and properties was estimated using microstructure/worn surface characterization, differential scanning calorimetry, hardness measurement, and three-body-abrasive wear testing (using Al₂O₃ particles). The as-cast alloys had a multi-phase structure consisting of primary and/or eutectic borocarbide M₂(B,C)₅, carboborides M(C,B), M₇(C,B)₃, M₃(C,B), and the matrix (ferrite, martensite, pearlite/bainite) in different combinations and volume fractions. Generally, the increase in the quenching temperature resulted in a gradual increase in hardness (maximally to 66–67 HRC) and a decrease in the wear rate in most alloys. This was due to the change in the phase-structure state of the alloys under quenching, namely, the secondary carboboride precipitation, and replacing ferrite and pearlite/bainite with martensite. The wear rate was found to be inversely proportional to bulk hardness. The maximum wear resistance was attributed to QT = 1150–1200 °C, when the wear rate of the alloys was lowered by three to six times as compared to the as-cast state. With the QT increase, the difference in the wear rate of the alloys decreased by three times. The highest abrasive resistance was attributed to the alloys with 1.1 wt.% C, which had a 2.36–3.20 times lower wear rate as compared with that of the reference alloy (13 wt.% Cr cast iron, hardness of 66 HRC). The effects of carbon and boron on hardness and wear behavior are analyzed using the regression models developed according to the factorial design procedure. The wear mechanisms are discussed based on worn surface characterization.