Medium Manganese Steel Research Articles

Hot-rolled Al-added medium Mn steel (Fe-8Mn-2.85Al-1Si-0.2C): Microstructural evolution and tensile behavior

In this study, a low Al (<3%) added medium manganese steel has been developed through melting casting route in an open-air induction furnace. The cast steel ingot has been intercritical annealed at 720 °C after hot deformation, that includes hot forging and hot rolling treatment, respectively. Microstructure characterization coupled with X-ray diffraction (XRD) has been performed after each processing step to understand the extent of austenite formation and its subsequent transformation to ferrite/martensite. The processed steel possesses the ultimate tensile strength, yield strength and ductility of 1000±20 MPa,700±10 MPa and 18.5 ± 0.5, respectively. To understand the possible cause of enhanced strength and deformation mode rietveld analysis has been carried out. It reveals that developed (final processed) steel possesses ∼18% (volume%) of austenite that subsequently reduced to ∼6.139% after tensile testing, indicating significant transformation of austenite to martensite (continuous and enhanced TRIP effect). The morphological characteristic of martensite in developed steel has been investigated using transmission electron microscopy (TEM). It reveals lath morphology of martensite due to low carbon content. The TEM and 3D atom probe analysis reveals the precipitation of intergranular type kappa (k) carbide in intercritically annealed specimens due to probable segregation of C and Al. However, volume fraction of the same is low. The SFE of the steel has been found to be ∼16 mJ m− 2, calculated by the modified Olson and Cohen method that also concludes TRIP is the preferred deformation mechanism in the developed steel.

Influence of intercritical annealing temperature on microstructure, microtexture, and tensile behavior of TRIP-assisted medium manganese steel

The present work investigates, the effect of intercritical annealing temperature on the microstructure, microtexture, tensile behavior, and mechanical stability of austenite in thermomechanically processed Fe-0.18C-4Al-7Mn (wt.%) medium manganese steel. The steel is subjected to thermomechanical processing (hot forging and hot rolling) followed by intercritical annealing at various temperatures (700, 750 and 800 °C) for 1 hour. The development of a complex microstructure with blocky and lath-type reverted austenite (RA), fine polygonal and blocky type intercritical ferrite (IF), coarse elongated ferrite (EF), and lath martensite (M) is revealed by the scanning electron microscopy (SEM) and transmission electron microscopy (TEM) analyses. The steel annealed at 750 °C exhibits an excellent ultimate tensile strength (UTS) of 802 MPa and total elongation (TE) of 61% owing to its high RA content, high transformation-induced plasticity (TRIP) effect and low mechanical stability of RA. Further, to understand the dislocation phenomena during tensile deformation, the tensile samples are analyzed using TEM, which reveals dislocation interactions, dislocation tangles, and dislocation accumulations at the IF grain boundaries and martensite lath boundaries. The manifestation of the TRIP effect is elucidated by XRD and EBSD studies. In addition, to study the texture evolution and the role of texture components on the TRIP effect, the orientation distribution function is employed. The major texture component, i.e., Ms Brass {011} 〈211〉 indicates the TRIP effect resulting in the deformation-induced martensitic transformation under tensile deformation. Additionally, Ms Brass component shifts towards G/B (Goss/Brass) twin {011} 〈111〉 component by grain rotation to accommodate the deformation.

Optimization of Hot Forming Temperature to Minimize Liquid Metal Embrittlement Induced Cracking in Resistance Spot Welded Zinc‐Coated Medium Manganese Steel

Herein, an investigation on the influence of the hot press forming (HPF) temperature cycles of a medium manganese, high ductility, zinc‐coated steel with ≈1000 MPa final tensile strength (HPF1000‐GI), with a specific emphasis on the risks of liquid metal embrittlement (LME) induced cracking during resistance spot welding (RSW) is presented. The HPF1000‐GI steel is hot press formed using several temperature cycles, and subsequently the LME sensitivity of the variously hot press formed materials are investigated using both dedicated RSW experiments as well as high‐temperature tensile testing. It is shown that the LME sensitivity of the HPF1000‐GI steel is significantly reduced after hot forming at higher intercritical temperatures, and that this favorable behavior is caused by microstructural changes at the coating‐substrate interface.

TRIP effect detection of medium manganese steel based on the MBN signal

In recent years, m-Mn (medium manganese) steel has gained increasing attention as a promising material for improving the crashworthiness and lightweight of vehicles, owing to its enhanced strength and ductility characteristics. However, the Transformation Induced Plasticity (TRIP) effect makes it challenging to accurately predict the microstructure and mechanical properties of m-Mn steel parts after forming. To overcome this issue, the Magnetic Barkhausen noise (MBN) detection technique is being employed to investigate the mechanism of TRIP effect on m-Mn steel, which could pave the way for the development of a non-destructive testing method for assessing the microstructure and mechanical properties of m-Mn steel parts. By analyzing the variation of MBN peak values of m-Mn steel and dual-phase steel DP1180 during the tensile process, it was found that the peak value of MBN signals increases continuously after the m-Mn steel is yielded due to the TRIP effect. Furthermore, a new strain-transformation model based on the O-C model was proposed to calculate the martensite content of m-Mn steel at all stages of elasticity and plasticity. By combining the detection data of MBN signals during the tensile process of m-Mn steel with the proposed strain-phase transformation model, a non-destructive testing method for the martensite content of m-Mn steel was established and compared with the traditional XRD test method. The results obtained from the testing of the martensite content of the corner of m-Mn steel U-shaped parts after stamping using the MBN testing method (6.56%, 9.94%) and the XRD testing method (7.42%, 9.26%) showed that the error between the two methods is less than 12%.

Microstructure and mechanical properties of medium manganese steel in intercritical annealing

A new type of cold-rolled medium manganese steel was investigated. The test steel was treated by Q&P process. With the increase in annealing temperature, the grain size gradually increases, the carbides dissolve progressively and the fine lath grains transform into massive or equiaxed grains. Both the volume fraction and the stability of the retained austenite are continuously decreasing, which together affect the change of mechanical properties. At the intercritical annealing temperature of 680°C, the specimens have higher retained austenite content and transformation rate. At the same time, due to the discontinuous TRIP effect caused by the retained austenite stability gradient inside the specimen, it exhibits excellent comprehensive mechanical properties, and the product of strength and elongation is 43.5GPa·%.

Influence of aging treatment on mechanical properties and wear resistance of medium manganese steel reinforced with Ti(C,N) particles

AbstractIn this study, the hot rolled medium manganese steel containing titanium was solution treated at 1,000 °C and followed by aging treatment at 500, 550, and 600 °C. The influence of aging treatment on mechanical properties and wear resistance of medium manganese steel reinforced with Ti(C,N) particles was investigated. It was found that the matrix of medium manganese steel was austenite. The austenite grain size was refined, and Ti(C,N) particles were precipitated after aging treatment. Compared to that of the as-hot rolled sample, the initial hardness of 500 °C aged sample increased by 9.5% to 312.86 HV, whose impact energy was more than doubled to 148.5 J. As the aging temperature raised to 600 °C, the initial hardness changed slightly. However, the impact energy dropped significantly to 8 J due to the aggregation of Mn at the grain boundaries. In addition, the main wear mechanisms of the samples were fatigue wear and abrasive wear. It was worth noting that 500 °C aged sample exhibited the best wear resistance under a 300 N applied load, whose wear loss was just half of the as-hot rolled sample. The relationship between wear loss and mechanical properties indicated that the wear resistance of medium manganese steel was independent of the initial hardness. The large difference in the wear resistance was predominately due to the outstanding work hardening ability of 500 °C aged sample, whose strengthening mechanisms were contributed from transformation induced plasticity (TRIP) effect, dislocation strengthening, twinning induced plasticity (TWIP) effect, and precipitation strengthening.

Microstructure and Mechanical Properties of Medium Manganese Steel with Different Aluminum Addition After Very Short Time Intercritical Annealing

Microstructure and Mechanical Properties of Medium Manganese Steel with Different Aluminum Addition After Very Short Time Intercritical Annealing

Effect of Mn Content on the Toughness and Plasticity of Hot-Rolled High-Carbon Medium Manganese Steel

The tensile and impact deformation behavior of three different Mn content test steels, xMn-1.0C-0.25V-1.5Cr-0.3Mo (5, 8 and 13 wt%), were investigated using mechanical properties testing, SEM-EBSD and TEM. The elongation and -20 °C impact energy of the three types of Mn content test steels increased as the Mn content increased. The room temperature tensile elongation was 9%, 23% and 81%, and the -20 °C impact energy was 9 J, 99 J and 241 J, respectively. The fracture morphologies of 5 Mn and 8 Mn were found to be cleavage fractures with secondary cracks and micro-voids. The 13 Mn fracture morphology was a plastic fracture with many coarse dimples. Transverse cracks perpendicular to the tensile direction occurred on the surface of the gauge area of 5 Mn and 8 Mn tensile specimens, reducing plasticity dramatically. This was mainly related to the martensitic transformation produced by stress. We characterized the martensite near the tensile fracture and speculated the main mode of crack propagation. Furthermore, a little amount of sharp-shaped BCC phase was found in the 5 Mn, which was determined to be a hard phase relative to the austenite matrix by nanoindentation test. These steels have stacking fault energies ranging from ~15 to ~29 mJ/m2 with increasing Mn content 13 Mn has high stacking fault energy (SFE) and austenite stability. Twin-induced plasticity (TWIP) was the deformation mechanism.

Effects of Vanadium Microalloying and Intercritical Annealing on Yield Strength–Ductility Trade-Offs of Medium-Manganese Steels

In this paper, we investigate the effects of vanadium on the strength and ductility of medium-manganese steels by analyzing the microstructural evolution and strain hardening rates and performing quantitative calculations. Two significantly different contents of vanadium, 0.05 and 0.5 wt.%, were independently added to model steel (0.12C-10Mn) and annealed at different intercritical temperatures. The results show that higher vanadium addition increases the yield strength but decreases the ductility. The maximum yield strength can increase from 849 MPa to 1063 MPa at low temperatures. The model calculations reveal that this is due to a precipitation strengthening increment of up to 148 MPa and a dislocation strengthening increment of 50 MPa caused by a higher quantity of V4C3 precipitates. However, the high density of vanadium carbides leads them to easily segregate at grain boundaries or phase interfaces, which prevents strain from uniformly distributing throughout the phases. This results in stress concentrations which cause a high strain hardening rate in the early stages of loading and a delayed transformation-induced plasticity (TRIP) effect. Additionally, the precipitates decrease the austenite proportion and its carbon concentrations, rendering the TRIP effect unsustainable. Accordingly, the ductility of high vanadium steels is relatively low.

The Oxide Layer of 10Mn5 Medium Manganese Steel for Wear Protection in High-Temperature Friction during Hot Stamping

A custom-designed high-temperature sliding-on-sheet-strip (SOSS) tribo-tester was used to simulate the high-temperature friction process of 10Mn5 medium manganese steel bare plate under actual hot stamping conditions. To reveal its high-temperature friction mechanism in the hot forming process, the high-temperature friction behavior of 10Mn5 steel and 22MnB5 steel was compared. The scanning electron microscope (SEM), energy spectrum analyzer (EDS) and X-ray diffractometer (XRD) were used to investigate the structure of the oxide layer, composition of physical phase, wear surface morphology and elemental composition. The results show that the average coefficient of friction of 10Mn5 steel is 12.7% lower than that of 22MnB5 steel. The cross-section of both steel consists of an oxide layer, an alloying element-rich layer and the matrix. The oxide layer of 10Mn5 steel is mainly composed of Fe3O4, approximately 63.7%, while that of 22MnB5 is mainly composed of Fe2O3, approximately 66.9%. The complete and less flaking scale of 10Mn5 steel provides good wear protection, and the mechanism is abrasive with slight adhesive wear. Meanwhile, oxide particles and fragments are embedded in the 22MnB5 surface thus increasing the wear, and the mechanism evolves into severe abrasive and adhesive wear. The difference in the mechanism between the two steels is mainly caused by different austenitizing temperatures, which for 10Mn5 is lower than 22MnB5, about 100 °C. This makes the thermal stress of 10Mn5 from the temperature difference between the furnace and the environment not enough to break the scale and decrease abrasion.

Influence of Press‐Hardening in Combination with Quenching and Partitioning Treatment on the Microstructure of Medium Manganese Steel

Press‐hardening of manganese–boron steels is one of the most efficient production processes for high‐strength automotive components. However, the residual formability of these sheet components is greatly limited by the formation of fully martensitic microstructure. Herein, to extend the application of press‐hardened components also to impact energy‐absorptive parts of the vehicle body, the potential of press‐hardening of a medium manganese steel in combination with a quenching and partitioning (Q&amp;P) treatment is analyzed. Therefore, selected heat treatments from prior dilatometer investigations are reproduced in a laboratory‐scale press‐hardening system equipped with a heated hat‐shaped tool. Instead of a complete martensitic microstructure, the Q&amp;P process leads to a multiphase microstructure consisting of fresh and tempered martensite as well as retained austenite with different carbon content each. Since depending on the phase fractions also strongly different mechanical properties are expected, not only the qualitative distinction but also the quantitative determination of the martensitic phases is of extraordinary importance. Herein, it is shown that using phase maps combined with grain‐average band slope of electron backscatter diffraction measurements is a suitable method to distinguish quantitatively fresh and tempered martensite. Validation of the differentiation method is performed using electron‐probe microanalysis.

C-modified stacking-fault networks inducing the excellent strength- plasticity combinations of medium manganese steel by simple two-stage warm rolling without annealing

The medium manganese steel with ultrahigh yield strength of 1421 MPa, a tensile strength of 1575 MPa, and an excellent total elongation of 28.4% was designed by simple two-stage warm rolling without annealing. The improvement of yield strength is mainly attributed to the extensive strengthening defects in the lamellar dual-phase microstructures, which including the high-density dislocations in ferrites and high-density dislocations, nanoscale VC precipitates, stacking faults and Lomer-Cottrell (L-C) locks in austenite (22 Vol.%). In addition, the abnormally enhanced strain-hardening ability benefits from the C-modified stacking-fault networks, whose stability and C-segregated characteristics are precisely clarified by the advanced in-situ heating HRTEM and APT analysis. This special strengthening and plasticizing effects of stacking faults induced by simple two-stage warm rolling can effectively break through the trade-off between strength and plasticity of ultra-strong medium manganese steel.

Properties of medium-manganese steel processed by laser powder bed fusion: The effect of microstructure in as-built and intercritically annealed state on energy absorption during tensile and impact tests

The presented research was aimed at applying laser powder bed fusion (LPBF) technology and TRIP (Transformation Induced Plasticity) steel with medium Mn content to produce thin-walled parts with enhanced crashworthiness. It was expected that the simultaneous use of the excellent combination of strength and ductility of the new type of medium-Mn steel and the advantages of LPBF technology would allow the development of an alternative to the conventional method of manufacturing the energy absorbing components. The energy absorption capability of LPBF-processed Fe-0.15C-7.5Mn-1.8Al steel was evaluated based on its deformation behavior under monotonic and impact loading. Tensile and Charpy V-notch specimens were fabricated by LPBF with layer thicknesses of 30 and 60 μm, using processing windows set established according to the criteria of low porosity (<0.3%) and good surface quality. Specimens were tested in as-built state and after intercritical annealing at a constant temperature (670 °C), but for different holding times and cooling rates to obtain a large fraction (30–50 vol%) of retained austenite capable of strain-induced martensitic transformation. Based on multiscale microstructure examinations (OM, SEM, EBSD, XRD, EDS) the relationships between the morphology of LPBF-specific microstructures before and after intercritical annealing, as well as between their behavior in tensile and impact test, were analyzed and discussed. For both layer thicknesses, the best combination of strength, elongation and impact toughness was obtained after annealing at 670 °C for 6 h followed by argon cooling. LPBF technology has been shown to be suitable for the fabrication of thin-walled energy-absorbing components from medium-manganese TRIP steel with the potential to reduce fabrication time by doubling the layer thickness compared to standard.

The excellent strength and ductility matching of directly warm-rolled V-alloyed medium manganese steel by stacking fault networks

A V-alloyed medium manganese steel with the yield strength of 1107 MPa, tensile strength of 1231 MPa and total elongation of 44.5 % was obtained directly by warm rolling. It is clarified that the high density of dislocations, stacking fault networks, Lomer-Cottrell (L-C) locks and nano-precipitates in the worm-rolled austenite play important roles for the ultrahigh yield strength. The spacing of the stacking faults gradually decreases and the density of L-C locks increases simultaneously during the tensile deformation, resulting in the dynamic refinement of stacking fault networks, which can effectively hinder the movement of dislocations. Thus, the continuous work-hardening ability and excellent total elongation at the ultrahigh yield strength are caused by the combined contribution from the dynamic Hall-Petch effect of stacking fault networks, the dispersed nano-precipitates and the partial TRIP effect. Our results open the way for designing stacking fault- and precipitation-strengthened medium manganese steel with advanced strength, ductility and work-hardening combination.

The effects of hydrogen on dynamic fracture toughness of high-strength low-carbon medium manganese steel

The effect of retained austenite (RA) stability and dislocation density of martensite matrix on low-temperature dynamic fracture toughness and the hydrogen embrittlement (HE) susceptibility was investigated in a high-strength low-carbon medium manganese steel subjected to three different heat treatments, i.e., the inter-critical annealing at 630 °C (QHA), inter-critical annealing at 610 °C (QLA), and direct quenching (DQ). Dynamic cracked three-point bending tests were performed at 20 °C and −40 °C with and without hydrogen charging. The RA volume fraction and the martensite matrix's dislocation density significantly affected the dynamic fracture toughness and HE behavior. All QHA and QLA tested at 20 °C fractured in the ductile mode, but all DQ and QLA tested at −40 °C fractured in the brittle mode. Dynamic fracture toughness decreases with RA volume fraction under the same tested temperature. The HE mechanism in the ductile region is HELP, and that in the brittle region is HEDE.

Modelling of Phase Diagrams and Continuous Cooling Transformation Diagrams of Medium Manganese Steels

The aim of this manuscript was to study the influence of alloying elements on the phase transformation behavior in advanced high-strength multiphase steels. Continuous cooling transformation (CCT) and time–temperature–transformation (TTT) diagrams were calculated to analyze the stability of phases at variable time–temperature processing parameters. The analyzed materials were lean-alloyed transformation induced plasticity (TRIP) medium manganese steels. The simulations of the phase diagrams, the stability of the phases during simulated heat treatments, and the chemical composition evolution diagrams were made using Thermo-Calc and JMatPro material simulation softwares. The influence of alloying elements, i.e., Mn and C, were studied in detail. The computational and modelling results allowed the influence of alloying elements on equilibrium and non-equilibrium phase diagrams and microstructural and chemical composition evolutions to be studied. Good symmetry and correlation between computational softwares were achieved. The study allows for future optimization of the heat-treatment temperature and time conditions of modern medium-Mn automotive sheet steels.

Effects of strain rate and adiabatic heating on mechanical behavior of medium manganese Q&P steels

In this work, the mechanical behavior and properties of four different multiphase steels was studied in tension at strain rates of 10−4, 10−2, 0.5 and 800 s−1. The four materials include a medium manganese (3%) steel grade overcritically and intercritically annealed and Q&P heat treated and two industrially produced TRIP-assisted steels, DH800 and TRIP700 steels, which have different retained austenite morphology. The temperature and strain of the specimens were studied using high speed infrared thermography (IRT) and digital image correlation (DIC). The mechanical response of the Q&P steels had considerably higher tensile strength than the two industrially produced steels. The Q&P steel with a higher austenite volume fraction strain hardened significantly more than the other steels. The DH800 steel and the intercritically annealed Q&P steel heated less with ΔT of 25 °C during uniform deformation than the TRIP700 steel and the overcritically annealed Q&P steel with ΔT of 35 °C. However, the industrially produced steels DH800 and TRIP700 had higher uniform elongation of 0.12 mm/mm and 0.14 mm/mm whereas the Q&P steels reached only 0.09 mm/mm, meaning that the heating rate of the Q&P steels was considerably steeper. In addition, the stronger necking of the DH800 and TRIP700 steels led to much higher maximum temperatures before failure (max. 260 °C) than those observed for the Q&P steels (max. 140 °C). The Taylor-Quinney coefficients of the Q&P steels were large in the beginning of the plastic deformation (0.65–0.95) but decreased as a function of plastic deformation, whereas the Taylor–Quinney Coefficients of the DH800 and TRIP700 steels were lower (0.5–0.6) but increased gradually as a function of plastic deformation.

Ductile 2-GPa steels with hierarchical substructure.

Mechanically strong and ductile load-carrying materials are needed in all sectors, from transportation to lightweight design to safe infrastructure. Yet, a grand challenge is to unify both features in one material. We show that a plain medium-manganese steel can be processed to have a tensile strength >2.2 gigapascals at a uniform elongation >20%. This requires a combination of multiple transversal forging, cryogenic treatment, and tempering steps. A hierarchical microstructure that consists of laminated and twofold topologically aligned martensite with finely dispersed retained austenite simultaneously activates multiple micromechanisms to strengthen and ductilize the material. The dislocation slip in the well-organized martensite and the gradual deformation-stimulated phase transformation synergistically produce the high ductility. Our nanostructure design strategy produces 2 gigapascal-strength and yet ductile steels that have attractive composition and the potential to be produced at large industrial scales.

Effect of Trace Rare-Earth Element Ce on the Microstructure and Properties of Cold-Rolled Medium Manganese Steel

Rare-earth elements have been widely used in the field of functional materials, but their effects on the cold-stamping formability of high-strength automotive steels have rarely been studied. In this paper, the effect of the trace rare-earth element Ce on the microstructure and properties of cold-rolled medium manganese steel after ART (austenite-reverted transformation, ART) annealing was studied. The microstructure of the experimental steel was observed using SEM, and the mechanical properties were tested using a universal tensile testing machine. The volume fraction of the retained austenite and the texture of the steel were measured using XRD. The results showed that the original austenite grain size of the experimental steel was smaller after adding the trace rare-earth element Ce. After ART annealing, the grain size distribution of the experimental steel with rare-earth Ce was more uniform, and the comprehensive mechanical properties were better. Under the conditions of quenching at 800 °C for 5 min and annealing at 645 °C for 15 min, the maximum product of tensile strength and elongation was 28.47 GPa·%.

Strong and ductile medium manganese steel processed by low-temperature partitioning

Conventional medium Mn steels processed by intercritical annealing (IA) demonstrate low yield strength. The present work investigates the effect of low-temperature partitioning (LTP) on the microstructure and tensile properties of medium Mn steel. It is found that medium Mn steel processed by LTP at 300°C possesses ultra-high yield strength of 1683 MPa and proper uniform elongation of 11.3%. The LTP process does not reduce the yield strength but substantially enhances the tensile ductility. The increase of the tensile ductility after LTP treatment can be ascribed to the reduction of the residual stress, martensitic transformation, and the well-developed ductile fracture behaviour. The present LTP process provides an alternative pathway to develop strong and ductile medium Mn steel.