Steel wire rods are essential for manufacturing high-strength steel tire cords. Yet, the presence of residual copper (Cu) in recycled steel can cause grain-boundary sensitization, embrittlement, and deterioration of the mechanical performance of the final product. This study introduces a desensitization heat treatment step designed to redistribute Cu away from austenite grain boundaries after sensitization occurs. The treatment consists of a 10 min dwell at 1000 °C in a 5%H2-Ar reducing atmosphere followed by quench. The temperature and hold time were selected based on diffusion calculations to promote solid-state back diffusion of Cu without altering grain morphology. Experimental validation showed that the dwell step reduced the length of Cu-rich sensitized zones of steel wire rod samples containing 0.21 wt.% Cu by approximately 89% and restored the mechanical properties to nearly 95–98% relative to low-Cu baseline steel (0.01 wt.% Cu). Compared with sensitized and as-obtained samples, these results highlight the effectiveness of the proposed method in improving both the microstructure and tensile performance of recycled steel wire rods, enabling their potential application in tire manufacturing.

Effects of prior austenite grain size on hydrogen embrittlement behavior in high-strength martensitic steel

The effect of prior austenite grain size on hierarchical structures of lath martensite in a 22MnB5 steel

Russian 12-% chromium ferritic-martensitic EK-181 steel (RUSFER-EK-181 Fe–12Cr–2W–V–Ta–B) is a promising structural material for power plants. This paper investigates the effect of thermomechanical treatments with plastic deformation in the austenitic region at 1000 °C and 1100 °C on the structural-phase state of EK-181 ferritic-martensitic steel and its microhardness value. The results of the study demonstrated that under these thermomechanical treatments conditions, a microstructure forms characterized by martensitic laths, fine plates of cementite and retained austenite, as well as MX-type carbonitride particles (M – V, Ta, Ti; X – C, N). Under high-temperature tempering (720 °C, 1 h), the thermomechanically treatmented steel exhibits coarsening of structural elements, a reduction in dislocation density, and precipitation of M23C6 carbides (M – Cr, Fe, Mn, W). Meanwhile, MX carbonitrides exhibit high thermal stability and retain their sizes. After tempering, cementite and retained austenite were not detected. A decrease in the deformation temperature leads to an increase in crystal lattice microdistortions and a reduction in coherent scattering regions. The obtained results were compared with the microstructural characteristics of the studied steel after traditional heat treatment (THT). It was demonstrated that plastic deformation in the austenitic region ensures a reduction in the average size of prior austenite grains by 2 times, martensitic laths by 1.5 times, and M23C6 particles by 2 times compared to the THT condition. Furthermore, higher dislocation densities and crystal lattice microdistortion values are observed. After thermomechanical treatments with deformation at 1000 °C and 1100 °C, microhardness values reach 4.6 GPa and 3.9 GPa, respectively. Subsequent high-temperature tempering reduces microhardness to 2.8 GPa and 2.9 GPa, respectively. These microhardness values after thermomechanical treatments and tempering are 10 % higher than values achieved after traditional heat treatment.

The static recrystallization (SRX) behavior of a novel Fe–22Cr–25Ni austenitic heat‐resistant steel is investigated through double hot compression tests. The deformation conditions include interpass holding time (1–200 s), temperature (950–1150 °C), strain rate (0.01–1 s −1 ), and prestrain (10%–22%). Results demonstrate that the SRX volume fraction increases with higher deformation temperature, strain rate, prestrain, and interpass time, but decreases with larger initial austenite grain size. Conversely, the recrystallized grain size increases with elevated temperature, extended interpass time, and coarser initial grains, while decreasing with higher strain rates and prestrain levels. Strain‐induced grain boundary migration is identified as the nucleation mechanism for SRX. Based on experimental data, a kinetics model for SRX is established, the calculated thermal activation energy for SRX is 324.08 kJ mol −1 . Validation shows excellent agreement between predicted and experimental results.

Austempered Ductile Iron (ADI) casting technology is a combination of the smelting process, its post-furnace treatment and the heat treatment of castings. Maintaining the process parameter stability of this innovative high quality cast iron with high Tensile Strength UTS and ductility properties is the aim of a number of studies on the control of graphitization inoculation and inoculation of the metal matrix. The ability to graphitise the liquid alloy decreases with its holding in the furnace, time of pouring into moulds from pouring machines. The tendency to dendritic grains crystallization and the segregation of elements such as Si, Ni and Cu decrease the ductile properties. The austenitizing process can introduce austenite grains growth negatively affecting of the ausferrite morphology. The modifying effect of small amounts of additives on the metal matrix in steel and low alloy cast steel, well known in materials engineering, has been applied to ADI. The addition of cast iron chips, Fe-V and Fe-Nb to the liquid alloy in the first inoculation is an example of a hybrid interaction. The introduction of graphitization nucleus particles and austenite crystallisation nucleus particles resulted in a stabilisation of the ductility of ADI and an increase in mechanical properties. Grains refinement of the primary austenite and precipitation hardening of ausferrite stabilise the mechanical properties of ADI. As a result of graphitization and additive structure inoculation, graphite and ausferrite morphology is improved. The obtained results point the way to further research in the field of hybrid inoculation of Ductile Cast Iron.

A predictive methodology was developed to estimate the pitting growth rate on AISI 304 steel surfaces operating in industrial circulating waters. The approach is based on the observation that most pits formed near oxide inclusions are metastable and repassivate within minutes; therefore, corrosion losses of Cr, Ni, and Fe are attributed primarily to stable pits. Stable pits were identified using selective dissolution coefficients for chromium (ZCr) and nickel (ZNi). Second-order regression models were established to correlate corrosion losses (ΔCr, ΔNi, ΔFe) with steel composition, structural features, and water parameters such as chloride concentration and pH. Results show that ΔCr is mainly influenced by chloride content and microstructural factors, including the number of oxides (1.98–3.95 μm), average austenite grain size, and δ-ferrite volume. Factors reducing ΔFe losses follow the order: chloride concentration < Ni content < acidity < grain size < number of 1.98–3.95 μm oxides; whereas smaller oxides, inter-oxide spacing, and δ-ferrite promote higher losses. ΔNi primarily depends on structural heterogeneity rather than chemical composition or water parameters. The resulting model enables prediction of average pitting growth rates on AISI 304 steel in circulating waters with an accuracy of ±19%, providing a practical tool for assessing corrosion resistance in heat exchanger applications.

Abstract Additive manufacturing can be used to create complex metal parts, free of defects. Extensive research has been conducted to prevent common imperfections like lack of fusion and gas pores by adjusting deposition parameters, including laser power, deposition speed, and powder feed rate. While these imperfections can be present in both single- and multi-material systems, single-material systems have been more thoroughly studied. Additionally, due to the complexity of multi-material additive manufacturing, unique imperfections not seen in single-materials are possible. In this work, AISI H13 tool steel was deposited onto aluminum bronze with laser-based directed energy deposition (DED-LB), with powder as feedstock. The resulting mix between the two materials created a complex structure with several imperfections not usually seen in single-material deposition. The two primary imperfections identified are unmelted particles near the aluminum bronze–steel interface and significant vertical cracks in the steel. The cracks were found to be mainly caused by the segregation of copper to the previous austenite grain boundaries in the steel, leading to hot cracking. The unmelted feedstock particles likely resulted from rapid cooling of the steel, due to the significant difference in thermal properties between the two materials. Despite the improper melting of the steel feedstock near the interface, good cohesion between the two materials was achieved. Graphical Abstract

Cast Hadfield steel is a material with high resistance to abrasion, provided, however, that it is used under the conditions of high dynamic loads. Typically, Hadfield steel starts with a harness value of 200HB after solution heat treatment and can reach values of over 600HB after work hardening. The above characteristics make it an ideal material for manufacturing casting components used in mining, crashing, drilling, steelmaking, naval, automotive and excavation applications. Manganese steel castings require a rapid water quench following the high temperature soak. A slack quench can reduce the toughness of the mterial dramatically. The mechanical properties of manganese steels are greatly enhanced by a fine grain size. Strength and ductility can be as much as 30% greater for fine-grained material. The refinement of the austenitic grain structure in Hadfield's Manganese Steel improves the weldability of the material, especially in cases where repair welding is required, in addition to enhancing the mechanical characteristics of the final products. This paper deals with the effect of heat treatment on casting process on the final properties of the Hadfield steel.

Introduction. When heating with high-frequency currents (HFCs) at high speeds, more significant strengthening effects can be observed compared to using machine generators. Therefore, hardening at high frequencies is more efficient. However, the increase in the generator frequency results in a decrease in the depth of penetration of eddy currents and an increased unevenness of heating across the cross-section. The application of a constant external magnetic field during HFC hardening can increase the depth of eddy current penetration and create more uniform heating. Unfortunately, there is not enough information available on the effect of the external magnetic field on HFC heating processes and phase transformations in steel. Currently, there are no quantitative estimates for the impact of an external magnetic field on changes in the kinetics of electric heating and the penetration depth of eddy currents. In connection with the above, the aim of this paper is to investigate changes in the kinetics of high-frequency heating of iron-carbon alloys when an external constant magnetic field is applied and, and, based on this, to consider the potential for technological applications. Materials and Methods. Theoretical assessment of the influence of an external magnetic field on the change in the kinetics of electric heating and the penetration depth of eddy currents is based on the general theory of induction heating kinetics. An experimental study of the influence of a magnetic field on the kinetics of high-frequency current heating was performed on samples of 45 steel, pearlitic gray (SCh30), and ferritic malleable cast iron (KCh30-6). The temperature distribution over the cross-section of ferromagnetic materials during induction heating with an external magnetic field has been studied using special samples of iron, 45 steel, and SCh30 gray pearlitic cast iron. Electric tempering processes have been investigated on samples of U8A steel using a vacuum tube generator (heating temperature — 450℃, heating rate — 750℃/s). Changes in austenite grain size after high-speed heating with external magnetization have been examined on samples of reduced-hardenability 55PP steel. To study the processes of thermal treatment in a magnetic field during experiments involving heating samples using high-frequency currents, a specially designed electromagnet was created to apply an external constant magnetic field. Results. Theoretical curves were constructed for heating conditions with and without an external constant magnetic field. Experimental data on the effect of an external constant magnetic field on induction heating in the surface layer of various materials were summarized in kinetic diagrams. Evidence that the observed changes were due to increased depth of penetration of eddy currents came from experiments on cylindrical samples of 45 steel with different wall thicknesses. Kinetic curves were provided for estimating the temperature field (at 6 points at different depths) during high-frequency current heating with and without external magnetization. The paper presents experimental data on the micro-hardness distribution across the cross-section of a U8 steel sample after quenching, quenching and electric tempering, quenching and electric tempering with external magnetization, and quenching and bulk tempering. It also includes the results of the study of the austenite grain size of 55PP steel after high-speed heating with external magnetization and conventional (slow) deep heating. Discussion. The application of a high-intensity external constant magnetic field during the first quasi-stationary process resulted in a decrease in the rate of induction heating of the ferromagnetic material and an increase in the depth of its uniform heating. However, above the Curie point, the effect of the magnetic field was negligible due to the low magnetic susceptibility of the material, and the heating rate remained unchanged as if there was no field present. In addition, due to the insignificant difference in the values of magnetic permeability below and above the Curie point during heating in the field, the thermal curve did not exhibit the characteristic inflection typical of kinetic curves observed during the transition of the surface layer to a paramagnetic state. Experiments with electric tempering have demonstrated that by applying an external field, it was possible to temper a material to the desired depth and it could be done on a single high-frequency current setup. The size of the austenite grains after high-speed heating with magnetization was reduced compared to conventional deep heating of steel with low hardenability, eliminating the issue of induction heating for low-hardenability steel. Conclusion. The results of the study demonstrated that the use of an external magnetic field enabled the achievement of strengthening effects during heating at higher frequencies, thereby eliminating the drawbacks of such heating methods.

The influence of solution treatment time on the microstructural and mechanical properties of a super duplex stainless steel was investigated. A solution annealing treatment at 1120 °C was applied to the hot-rolled alloy, with soaking times varying between 10 and 30 min. The microstructural characteristics before and after solution treatment were examined using XRD and EBSD techniques by measuring lattice parameters and micro-strains, weight fraction, average grain size, and maximum misorientation angle. The experimental results showed that the constituent phases are δ-Fe and γ-Fe, regardless of the alloy state. The mechanical properties of the solution-treated alloy were evaluated by tensile testing, measuring the ultimate tensile strength (σUTS), yield strength (σ0.2), fracture strain (εf), and impact toughness (KCV). Increasing the solution treatment time from 10 min to 30 min leads to improved ductility and reduced mechanical strength, with the volume of the ferrite phase increasing, the average austenite grain size decreasing, and the maximum misorientation angle decreasing. This is due to the ability of ferrite to absorb stress and to the greater participation of grains in the deformation process. Important decreases in high elastic strains and residual stress fields after solution treatment were also noted.

On the contrasting effects of parent austenite grain size on athermal and deformation-induced martensitic transformation in an Fe-18Cr-12Ni (wt.%) alloy

Synergistically achieving superior strength and ductility via tailoring prior austenite grain in 11Cr ferritic/martensitic steel

Abstract During production of components using press hardening, the steel will at one point be heated to an austenitic state. Grain growth can occur during this austenitization if the time and temperature are sufficient, where the microstructure becomes increasingly coarse. The final austenite grain size can affect both the phase transformations during quenching and the final mechanical properties of a fully martensitic microstructure. In this work, austenite grain growth was modeled using measurements of the mean grain diameters from isothermal experiments, while the model was validated using non-isothermal experiments. The temperature and time ranges used in the isothermal experiments were 900–960 $$^\circ $$ ∘ C and 1-1200 seconds, respectively. Bending tests according to VDA 238-100 were performed, using samples previously austenitized at 900, 930, and 960 $$^\circ $$ ∘ C and then rapidly quenched. The isothermal grain growth up to 930 $$^\circ $$ ∘ C could be modeled using the average grain size, while at 960 $$^\circ $$ ∘ C the microstructure displayed a more complex growth behavior. The grain growth during the non-isothermal validation experiments could be predicted with the exception of one thermal cycle. No effect of the austenitization temperature on the bending performance was observed when short austenitization times were utilized, and only a minor effect was observed for a longer austenitization time.

The morphology and types of inclusion, as well as the microstructure, fundamentally affect the properties of high-strength peritectic steel. Rare earth elements not only modify inclusions but also act on the transformation of the microstructure. In this paper, the evolution mechanism of yttrium for the inclusions and microstructure in high-strength peritectic steel was investigated through experimental testing and thermodynamic analysis. The results show that yttrium treatment can modify the main large-sized irregular inclusions into spherical or near-spherical rare earth inclusions, accompanied by a reduction in the number density, area fraction, average diameter, and aspect ratio of inclusions. The evolution route for the inclusions follows Al2O3 + MnS + Al2O3-MnS→Y2O3 + Y-O-S + Y-S + Y-O-S-MnS with yttrium addition. The microstructural characteristics of yttrium-free steel show significant differences from those of yttrium-containing steel. Compared to yttrium-free steel, the yttrium-0.015 wt.% steel shows a refined austenite structure with more uniform size distribution and the absence of grain boundary ferrite films. The Y2O3 and Y2O2S inclusions mainly formed in liquid steel were found along the austenite grain boundary to prevent the grain growth and the formation of ferrite films. Additionally, after adding rare earth yttrium, the fraction of high-angle grain boundaries (HAGBs) increases, together with a decrease in the fraction of low-angle grain boundaries (LAGBs) in steel. The research results can provide a theoretical basis for the application of adding rare earth yttrium to high-strength peritectic steel.

Nb Microalloyed 35MnB New Chain Track Link Steel Austenite Grain Growth Behavior and Its Prediction Model

Effect of Solute Atoms and Precipitates on Austenite Grain Growth in Fe – C – Nb Steel

Refining the austenite grain size is a key method for enhancing toughness without compromising strength in eutectoid pearlite rail steels. In this study, the effect of hot deformation parameters on the hot deformation behavior and refinement of prior austenite grains is investigated. The hot deformation behavior and microstructure of samples processed at deformation temperatures of 900, 950, 1000, 1050, 1100, 1150, and 1200 °C, strain rates of 0.01, 0.1, 1, and 5 s −1 , with a true strain of 0.9 are studied. A constitutive model and a processing map are developed to describe the deformation mechanism and microstructure evolution. The derived constitutive equation shows good agreement with experimental values, exhibiting a correlation coefficient ( M ) of 0.983 and an average absolute relative error (AARE) of 7.3%. Processing map indicates that the recommended thermomechanical parameters are temperature above 950 °C and a strain rate of 5 s −1 . The optimal austenite grain refinement effect can be achieved with 18.5 ± 8.9 μm when hot deformation is conducted at a temperature of 950 °C and a strain rate of 5 s −1 . These findings provide valuable insights in the optimization of hot deformation parameters of eutectoid pearlite rail steels.

Revisiting the effect of austenite grain size on hierarchical structure and mechanical properties of high-strength steel

Synergistic effects of V, Ti, and Nb microalloying on prior austenite grain growth kinetics in high-carbon pearlitic steel wire rods