The tests were carried out on two newly developed high-manganese steel grades (27Mn-4Si-2Al-Nb and 24Mn-3Si-1.5Al-Nb-Ti). The developed chemical composition of the tested steels ensured obtaining an austenitic matrix. In order to determine the technological plasticity of the tested steels, the SICO (Strain Induced Crack Opening) test was carried out using samples with a diameter of 6 mm and a length of 76 mm. The tests were performed on a Gleeble 3800 thermomechanical simulator. The samples were deformed in the temperature range from 1180 ℃ to 1240 ℃ in steps of 20 ℃, at a strain rate of 0.1 s−1, 1 s−1 and 10 s−1. Based on the tests performed, the values ​​of critical circumferential strains (for the applied deformation parameters) were determined, i.e. the smallest circumferential strains that cause the sample to crack. The SICO tests performed showed that with the increase of temperature and strain rate, the determined values ​​of circumferential strain increase, with higher values ​​for steel 24Mn-3Si-1.5Al-Nb-Ti. Samples made of steel 27Mn-4Si-2Al-Nb deformed at 1240℃ were completely destroyed, regardless of the applied strain rate.

The hot deformation behavior and activation energy were investigated in three medium-Mn steels of various Mn concentration (3, 4 and 5 wt.%) through continuous compression tests using a Gleeble 3800 thermomechanical simulator. The electron backscatter diffraction (EBSD) technique was used to reveal the prior austenite grains (PAGs) and to assess the effectiveness of recrystallization process. The experimental procedure was performed in a temperature range of 1173-1373 K at different strain rates of 0.05, 0.5, and 5 s-1. The recorded compression curves were analyzed to determine flow stress values and calculate the activation energy of plastic deformation (Q) using Arrhenius-type and Trimble constitutive models. The comparison and validation results demonstrated that both models show high predictive accuracy. The correlation coefficient ranged from 0.993 to 0.997, while the average absolute relative error varied between 2.4% and 3.8%, confirming the models' accuracy and reliability. The determined average values of activation energy of plastic deformation were relatively high, reaching 382, 400, and 393 kJ/mol for the 3Mn, 4Mn and 5Mn steels, respectively. The average Q value of 4Mn steel was 17 KJ/mol higher than that of 3Mn steel. However, increasing the Al content from 0.55% in 4Mn steel to 1% in 5Mn steel, while eliminating Mo, Ti, and V microadditions, reduced the average Q value by about 7 KJ/mol showing the complex hot deformation behavior of this new type of advanced high-strength steels.

The current study aims to investigate the effect of Cu and Mo, commonly found in steel scrap, on the kinetics of isothermal phase transformations in medium-Mn steels designed for the quenching and partitioning (QP) process. Three steels were designed with a base steel composition of 0.18C–4Mn-0.8Al- 0.5Si (wt.%). The second steel contained an additional 0.3 wt% Mo, while the third one included both 0.3 wt% Mo and 1.0 wt% Cu. The phase transformation kinetics at different isothermal temperatures (ranging from 480 to 210°C) were analysed using the JMatPro software and experimentally verified by a high-resolution Baehr DIL805 dilatometer. As a result, the shorter bainite incubation time was predicted by JMatPro as compared to dilatometric experiments. This discrepancy is probably associated with software databases lacking the kinetic parameter corrections accounting for the Mo-and Cu-induced solute drag effect in the investigated multi-alloyed medium-Mn steels. The determined time–temperature–transformation (TTT) diagrams showed that Mo and Cu additions shifted the bainitic transformation to longer times. Microstructural analysis revealed mixed martensitic–bainitic structures with varying proportions, whereas martensite was more dominant in Mo- and Mo + Cu-alloyed steels. Subsequently, QP treatments were optimized and verified using dilatometry. Quenching at 270°C and partitioning at 400°C for 120-1800 s were used to cover different time scenarios during the heat treatment. SEM evidenced details of a tempered martensite morphology and RA films. The microscopic studies were completed by hardness measurements, with the highest hardness registered for the Mo + Cu steel (∼391 HV) at short and intermediate partitioning times.

In the context of increasing circularity in steel recycling and the connected increasing build-up of residual elements in the steel industry, the present study investigates the influence of Mo, Cu, and hot plastic deformation on critical temperatures and phase transformation kinetics of 4 wt

The effects of intercritical annealing (IA) temperature and manganese content on austenite formation and stability in medium-Mn steels were investigated using combined computational and experimental approaches. Three steels containing 3, 4, and 5 wt

The increasing reliance and usage of recycled steel in the global steel industry brings the need for a scientific assessment of alloying concepts that remain robust against recycling-induced variations in steel composition. In this study, the influence of elevated Mo and Cu concentrations, representing exaggerated recycling-induced alloying elements, on the microstructure and mechanical performance of cost-effective air-hardening ductile (AHD) forging steels is systematically investigated. The results show that both elements improve the hardenability of the steels by delaying diffusional and bainitic transformations, increasing the maximum possible thickness of forging components that can be produced via air cooling. Cu alloying significantly controls the prior austenite grain size, most likely through a solute drag effect in solid solution. Among the achieved microstructures, the fully martensitic state exhibits the most favorable mechanical property profile, combining the highest strength under static and cyclic loading, adequate ductility, and the highest impact toughness. However, multiphase microstructures, containing bainite and martensite, display inconsistent trends in tensile ductility and impact toughness. Overall, the results suggest that recycling-induced Mo and Cu alloying can improve the mechanical performance of the AHD forging steels as long as Cu-induced hot shortness can be avoided during processing.

Steel recycling is fundamental for advancing a circular economy and green steel mission, as producing steel from scrap substantially reduces energy consumption and CO 2 emissions compared with ore‐based steelmaking. However, the uncontrolled retention of residual Cu in recycled steels poses a significant challenge known as copper contamination. During hot working, Cu enrichment at surfaces and near‐surface grain boundaries can lead to the formation of low‐melting Cu‐rich liquid films, which result in hot shortness and surface cracking. Moreover, depending on Cu content, precipitate size, and processing conditions, Cu segregation and precipitation of Cu‐rich phases during cooling or aging may cause embrittlement and reduced toughness. In contrast, when Cu incorporation is carefully controlled and combined with appropriate alloy design and processing parameters, it can enhance mechanical properties through nanoscale precipitate strengthening, improve corrosion resistance via the formation of protective patina layers, and impart antibacterial functionality in specific steel grades and environments. This work reviews the dual role of Cu as both a detrimental residual element and a beneficial alloying addition in steels and provides important considerations for the design of high‐performance, sustainable, and multifunctional Cu‐bearing steels with potential applications in automotive, construction, marine, pipeline, medical, food, and sanitary sectors.

Theoretical and experimental critical temperatures as well as phase transition phenomena during continuous cooling in 4 mass.

This study investigates the bainite transformation kinetics, microstructural evolution, and mechanical properties of Al-alloyed 3MnNb and 4MnNb multiphase steels subjected to a novel hybrid heat treatment. Dilatometric analysis revealed that bainite formation in the 3MnNb steel initiates more rapidly during isothermal holding, while the 4MnNb steel exhibits accelerated transformation kinetics in later stages, resulting in distinct final bainite fractions. Thermodynamic calculations, including T0 curves, underscore the roles of Mn and Al in modifying the Gibbs free energy landscape and influencing the potential for nanobainite formation. Micro-structural characterization identified a lath-type ferritic matrix comprising bainite, retained austenite (RA), and, in some cases, fresh martensite. Lower intercritical annealing temperatures (IATs) favored the formation of coarse ferrite laths and residual martensite, whereas higher IATs promoted microstructural refinement. Although 3MnNb achieved 10-15 % nanobainite, further transformation was limited by the stability of RA and sluggish carbon diffusion at 200 degrees C. In contrast, the 4MnNb steel displayed enhanced grain refinement, increased hardness, and a higher fraction of stabilized RA, which impeded the progression of nanobainite formation.

Ferritic lightweight steels are an emerging class of low-density steels (LDSs) with promising mechanical properties. The study aimed to develop two ferritic lightweight steels with different Mn concentrations. Al was incorporated to achieve the lightweighting effect due to its relatively low atomic mass of substitutional solutions. The C concentration was kept at a minimum level to avoid the precipitation of carbides and the Mn addition was intended to increase solid solution strengthening. Thermodynamic calculations (Thermo-Calc) were employed to design the composition, analyze the phase constituents, and predict the phase transformation behavior. Microstructural investigation and hardness tests were conducted to experimentally verify the calculations. Both produced alloys exhibited a fully ferritic microstructure. Compared to industrially produced DP980 steel, a density reduction of about 7.2% and 8.3% was attained for the Fe-0.04C-5.5Al-1.6Mn-0.075Nb and Fe-0.04C-5.6Al-5.5Mn-0.08Nb steels, respectively. The steel with the higher Mn content showed increased hardness attributed to its solution strengthening effect. An increase in the hardness values was also measured with the progress in hot-rolling thickness reductions for both alloys. The alloying elements influenced the microstructural characteristics, phase transformation behavior, density, and hardness of the newly designed lightweight steels.

In this study, the hot deformation behavior of novel 0.17C-3.92Mn-1.02Si-0.53Al-0.22Mo-0.032Ti-0.069V steel during continuous compression was predicted using numerical simulation, providing a reference for optimizing the process. Medium-Mn steels have not been applied for forgings yet. Therefore, their industrial application requires detailed investigations on their hot deformability. Results of finite element (FEM) simulations will be used for further optimization of the press forging process. The material model parameters used in the FEM method were identified based on stress-strain curves registered during hot compression tests carried out using a Gleeble thermomechanical simulator. The numerical simulation and physical investigations were performed at temperatures of 900, 1000 and 1100 °C to reflect a range of temperatures occurring during press forging. The influence of strain rates of 0.05, 0.5 and 5 s-1 on the flow behavior of steel was also investigated. Colored maps of the plastic strain distribution in a sample volume were obtained as a result of the numerical research. The maps allowed for the identification of differently strengthened zones as a result of varied plastic strain. Results of FEM analysis were experimentally validated by hardness measurements. A good correlation between the hardness and plastic deformation zones was obtained. An increase in the material hardness was identified in the zones characterized by the highest plastic strain.

Medium manganese steels provide a good combination of tensile strength and ductility due to their multiphase microstructure produced during the multi-step heat treatment process. This study primarily focused on testing and analyzing the tensile properties of 0.17C-5Mn-0.76Al-0.9Si-Nb medium manganese quenching and partitioning (QP) steel using both the experimental and finite element method (FEM) in the multilinear isotropic hardening material model. The 7 mm and 12 mm thick plates exhibited a similar microstructure of tempered primary martensite, lath-type retained austenite, and secondary martensite. The experiments measured tensile strengths of 1400 MPa for 12 mm round specimens and 1325 MPa for 7 mm flat specimens, with total elongations of 15% for round specimens and 11% for flat specimens. The results indicated that the sample’s geometry has some effect on the UTS and ductility of the studied medium-Mn QP steel. However, the more important is the complex relationship between the plate thickness and yield stress and ductility, which are affected by finishing hot rolling conditions. The FEM results showed that the von Mises stresses for flat and round specimens were 1496 MPa and 1514 MPa, respectively, and were consistent with the calculated true stresses of experimental results. This shows that numerical modeling, specifically a multilinear isotropic hardening material model, properly describes the material properties beyond the yield stress and accurately predicts the plastic deformation of the investigated multiphase QP steel.

Manufacturing including intercritical processing of medium-Mn sheet steels is usually a multi-hour batch-type annealing with low environmental and economic indicators. It additionally influences severe variability of mechanical properties of steel depending on a distance from the center of the coil, and thus material waste. For this reason, car body elements with high quality requirements cannot be effectively manufactured in such a process. There is a research gap and an industry need for a sustainable time- and cost-effective production process that can be implemented on a large scale in industry, using existing installations. For this reason, the process of designing and optimizing the conditions of heat treatment of medium-Mn steel in a continuous-annealing mode was performed, which assumes soaking in less than 120 s. During the research, heating conditions were developed that can be achieved using a conventional electric furnace. To experimentally and time-effectively optimize the temperature–time conditions in terms of mechanical properties, a novel method of “rapid investigation” of heat treatment was proposed and implemented. This method using a dilatometer allows for high-precision, time-efficient and waste-reducing optimization of heat treatment of newly designed steels. The research showed the full possibility of introducing continuous annealing into the heat treatment of advanced medium-Mn steel. A slight change in thermal parameters allowed formation of lath like microstructures with different thickness and stability of RA and thus a wide control of both the strength (YS, UTS) and plasticity of steel (TEl) up to the UTS x TEl threshold of 37 GPa%. This suggests the possibility of applying the presented heat treatment conditions to the industrial production of steel for various applications.

The toughness of steel is a critical material property that represents the ability to absorb energy at fracture, particularly in ultra-high-strength steels. The optimal balance between high strength and ductility depends on the complexity of the microstructure formed during heat treatment, which influences the toughness of the steel. In this study, a numerical modeling approach was used to investigate the Charpy impact behavior of medium manganese Q&P (quenching and partitioning) steel with a focus on toughness and stress distribution. ANSYS Explicit Dynamics was used for numerical modeling to simulate stress distribution and energy absorption in Charpy specimens. The Johnson–Cook model approach was used to describe the material behavior for such dynamic conditions. The results showed that ductility and toughness decreased with increasing partitioning time from 300 s to 900 s. The simulation results also showed that the stress distribution was more pronounced near the notch radius. The absorbed energy of the samples increased slightly as the notch radius increased from 0.1 mm to 0.25 mm, and it significantly increased as the plate thickness increased from 7 mm to 12 mm.

Studies on the intercritical annealing of medium-Mn steel sheets mostly focus on batch annealing conditions, a multi-hour process with low economic and technological efficiency. The literature on continuous annealing of these steels, which is crucial for their large-scale industrial production, is limited and primarily focuses on specific aspects of the process like annealing temperature or time. The following study comprehensively addresses all of the most important parameters of continuous annealing of Al-added medium-Mn steels. A broad range of soaking temperatures (700-760 degrees C) and times (2-120 s) was analyzed for heating (3 degrees C/s) and cooling (1 degrees C/s) conditions that are favorable for retaining austenite stability and feasible for industrial production. The effects of these conditions on the chemical and mechanical stability of retained austenite were examined. The resulting microstructures were correlated with the mechanical properties of the heat-treated steel. This allowed to determine the technological window for continuous annealing of medium-Mn steels. Moreover, the fractions and stability of retained austenite in a range from 18 to 34 %, for all applied thermal cycles, were linked to changes in the steel's mechanical properties. This confirmed that a high fraction of retained austenite alone is insufficient for achieving high plasticity. The key factor is the optimal mechanical stability of the austenite phase, as evidenced by the significantly better plasticity observed in a sample with 32 % RA compared to one containing 41 % RA. Furthermore, the relationship between global and local plasticity changes significantly as the stability of retained austenite decreases.

Depending on the alloy composition, intercritical annealing may provide different phases in the microstructure. For low-alloyed dual-phase (DP) steels it is usually ferrite and martensite, while for medium-Mn steels retained austenite is also formed. In a present study, a wide intercritical temperature range was applied to a 5% Mn steel to investigate possible microstructure combinations: ranging from fully ferritic, through ferritic-austenitic, multiphase, to fully martensitic, which were next investigated in terms of mechanical properties to clarify the behavior of this type of material. The obtained results together with technological issues and economic indicators were next compared to mechanical properties of typical DP steels in order to assess the possibility of replacing this material in car production. The mechanical properties were evaluated using static tensile and hardness tests. The phase composition was determined qualitatively and quantitatively using dilatometry, X-ray diffraction measurements, and electron backscatter diffraction analysis. The results suggest that both initial austenite and martensite fractions have a decisive influence on the yielding and elongation of steel; however, the tensile strength depends mainly on the sum of martensite initially present in the microstructure and the strain-induced martensite formed from the plastically deformed austenite regardless of the initial retained austenite—martensite ratio. The results indicate superior total elongation of medium-Mn steels reaching 30% compared to DP steels with a similar strength level in the range between 900 and 1400 MPa. However, medium-Mn steels could be a significant competitor to dual phase steels only if some technological problems like discontinuous yielding and serrations are significantly reduced.

The study addresses the design and optimization of chemical composition and processing routes of new quenching and partitioning medium-Mn alloy using theoretical and experimental approaches. The thermodynamic calculations using Thermo-Calc and JMatPro software were carried out to characterize the influence of Mn, Si and Al contents on cementite formation and precipitation processes. The evolution of individual phases as a function of temperature under thermodynamic equilibrium conditions was estimated. The investigations included the determination of continuous cooling transformation (CCT) and the time–temperature transformation (TTT) diagrams of a model 4Mn alloy. The calculated equilibrium diagrams were compared with the experimental diagrams determined using dilatometric tests. Microstructural observations were carried out to verify the results of dilatometric measurements. The results of thermodynamic calculations and experimental tests showed the moderate agreement. It is related to the inaccuracy of currently available models in the used software and/or non-equilibrium conditions of experimental tests.

This study addresses the characterization of the particular microstructural constituents of multiphase transformation-induced plasticity (TRIP)-aided steels belonging to the first and third generations of Advanced High Strength Steels (AHSS) to explore the possibilities of the EBSD method. Complex microstructures composed of ferrite, bainite, retained austenite and martensite were qualitatively and quantitatively assessed. Microstructural constituents with the same crystal structure were distinguished using characteristic EBSD parameters like confidence index (CI), image quality (IQ), kernel average misorientation (KAM) and specific crystallographic orientation relationships. A detailed linear analysis of the IQ parameter and misorientation angles was also performed. These tools are very helpful in linking different symmetric or asymmetric features of metallic alloys with a type of their structure and morphology details. Two types of samples were investigated: thermomechanically processed and subjected to 10% tensile strain to study the microstructural changes caused by plastic deformation.

The objective of this study was to analyze the thermodynamic feasibility of forming nanobainite in Al-alloyed medium-Mn steels through intercritical annealing (IA) and subsequent heat treatments. The research aimed to determine the influence of IA temperature and Mn content on the stability of austenite, the Ms temperature, and the resulting bainite plate thickness (BPT). Our findings indicate that the IA temperature range of 780–860 °C effectively decreased the Ms temperature, facilitating the formation of nanobainite. The results demonstrated that a higher Mn content increases an austenite fraction during IA, thus enhancing the potential for nanobainite formation. For the 3MnNb steel, the IA temperature of 860°C was sufficient to achieve bainitic plates thinner than 100 nm, whereas the 4MnNb steel required lower IA temperatures due to its higher Mn content. The transformation kinetics was found to be faster in 3MnNb steel, with a complete transformation time of 300 min, compared to approximately 600 min for the 4MnNb steel. Dilatometric analysis confirmed that the real austenite fractions were approximately 20

The influence of different microstructures on the plastic stability of an air‐hardened industrially produced medium‐manganese steel is presented. For this matter, heat treatment parameters before and during intercritical annealing (IA) are varied, to achieve different microstructures. The resulting duplex microstructure is consecutively tested by tensile tests, which are monitored by digital image correlation (DIC) to obtain information on the local plastic deformation. The tests are accompanied by microstructure investigations using optical, scanning electron, and transmission electron microscopy. Finally, X‐ray and electron backscatter diffraction experiments are performed before and after deformation, to describe the altering phase fractions. It is demonstrated that the effect of the deformation temperature prior to IA treatment has a significant influence on the duplex microstructure, as it changes the austenite morphology from lamellar to globular and increases the phase fraction. The change in austenite phase fraction and morphology results in a higher yield strength (≈100 MPa), as well as higher uniform and total elongations (+2% and +5%, respectively). The DIC and tensile tests reveal that these differences in the austenite phase lead to a complete change in the strain hardening behavior, from continuous flow to discontinuous serrated flow, with clearly visible deformation bands during plastic deformation.