Medium Manganese Steel Research Articles

Superior Comprehensive Mechanical Properties of a Low-Carbon Medium Manganese Steel for Replacing AISI 4330 Steel in the Oil and Gas Industry.

A low-carbon medium manganese steel (0.12C-3.13Mn) containing Cr, Ni, Mo, V, and Cu elements was designed to replace the AISI 4330 steel applied in the oil and gas industry. The mechanical properties, microstructures, and fatigue crack growth rate were comparatively analyzed using uniaxial tension tests, microstructure characterization, and compact tension with fatigue crack growth characterization. The results showed that the ductility and -40 °C impact energy of 0.12C-3.13Mn steel were better than AISI 4330 steel (from 115 J to 179 J), while the yield strength of 957 MPa of the former was lower than the latter of 1060 MPa after being subjected to the same tempering process. The microstructure of 0.12C-3.13Mn steel was composed of a mixture of tempered martensite, reversed austenite, and nanosized precipitation particles, while the microstructure of S4330 steel contained ferrite and large-size Fe3C with lath and near-spherical morphologies. Compared to Cr-rich Fe3C, (V, Mo)C and Cu-rich particles have smaller sizes and, thus, provide more strengthening increment, leading to a higher yield ratio. The impressive fatigue-resistance property was obtained in 0.12C-3.13Mn steel because the threshold value was 5.23 MPa*m1/2 compared to the value of 4.88 MPa*m1/2 for S4330 steel. Even if the fatigue crack grew, the stress intensity factor range of 0.12C-3.13Mn steel was obviously wider than that of AISI 4330 steel due to the presence of reversed austenite and secondary cracks. Overall, the AISI 4330 steel could be replaced with the designed 0.12C-3.13Mn steel due to the similar strength and better ductility, low-temperature toughness, and fatigue-resistance property.

Effect of strain rate on the microstructure evolution and tensile behavior of medium manganese steel

• The TRIP effect is predominant at lower strain rates. • An increase in the strain rate facilitates mechanical stability of austenite. • Excellent tensile properties are resulted at lower strain rates. In the present study, the effect of strain rate on the microstructure evolution and tensile behavior of intercritically annealed medium manganese steel is investigated. Tensile tests were performed on the annealed samples at strain rates of 1.33×10 -4 , 0.665×10 -3 and 1.33×10 -3 s -1 . The amount of austenite to martensite transformation and dislocation density decrease with the increase in strain rates. The sample at the strain rate of 1.33×10 -4 s -1 exhibits superior tensile properties due to the synergistic influences of the transformation-induced plasticity (TRIP) effect and high dislocation density.

A systematic study on microstructure evolution, mechanical stability and the micro-mechanical response of tensile deformed medium manganese steel through interrupted tensile test

In the current work, the microstructure evolution, mechanical stability of austenite and the micro-mechanical response of tensile deformed Fe-0.18C-4Al-7Mn (Wt%) steel are investigated. Interrupted tensile tests on the annealed samples (750 °C, 1 h) were performed at a tensile elongation of 5, 10, 20, 30, 40 and 60% to understand the deformation behavior and transformation-induced plasticity (TRIP) effect. Strain-induced martensitic transformation (SIMT) of reverted austenite is explored using X-ray diffraction (XRD), transmission electron microscopy (TEM) and electron backscattered diffraction (EBSD) analysis. The coefficient of mechanical stability of austenite (k-parameter) is quantified through the interrupted tensile tests using XRD analysis. Instrumented nanoindentation test was conducted on individual phases of the interrupted tensile-tested samples to determine their hardness and modulus values. The scanning electron microscopy (SEM) analysis reveals the gradual decrease in width and increase in length of austenite-martensite islands with an increase in the percentage of elongation. Evolution of dislocation lines, dislocation tangles and dislocation accumulations occur at ferrite grain boundaries and martensite lath boundaries during tensile deformation. The volume fraction of austenite decreases, and the transformation of austenite to martensite and dislocation density of austenite increase with the increase in the tensile elongation. Austenite is found to be mechanically more stable at 30% of tensile elongation due to the low austenite transformation ratio. Nanoindentation results show that the hardness increases with an increasing percentage of deformation. Multiple pop-ins are observed in load (P)–indentation depth (h) curves due to dislocation interaction at the interphase boundary.

Forecasting the steelmaking and casting of a medium manganese steel

The steelmaking and casting of medium Mn steels brings some challenges in the production route because of their high alloying content. In this paper, the evaluation of the casting processes for these steel chemistries is assessed with a set of models and laboratory-scale tests, in order to find possible casting conditions. Results evaluation from this study pointed out to the regular conventional slab casting and hot rolling route, so that it can be produced through a conventional production line.

Study on Mechanical Properties and Failure Mechanism of Medium Manganese TRIP Steel / DP590 Dissimilar Steel Resistance Spot Welding Joint

This paper presents the resistance spot welding process test and numerical simulation analysis of medium manganese steel TRIP steel (7MnSteel) and DP590 steel plate. The results show that the failure mode is PF-TT failure, and IF and PF-TT are investigated. At the same time, based on the numerical simulation under the typical welding parameters, the welding plate has the stress concentration at the electrode edge at the beginning of the welding. Along with the welding, there is the stress concentration in the heat-affected zone of the medium manganese TRIP steel, which may also be the reason for the failure of the joint here. The current density is concentrated at the contact surface between the electrode and the weld plate, and the error in the diameter of the nugget measured by simulation and experiment is within 7%, which verifies the accuracy and reliability of the model.

Effect of rolling temperature on microstructure and mechanical properties of medium manganese steel

The effect of rolling temperature on the incomplete recrystallization behavior and the relationship to mechanical properties in 0.06C–4Mn-1.2Cr (wt.%) steel was investigated. Three plates of experimental steel were produced by hot rolling at different temperatures and intercritical annealing processes in this study. The microstructure of experimental steels was examined by optical microscopy (OM), scanning electron microscopy (SEM), X-ray diffraction (XRD), electron backscatter diffraction (EBSD), and transmission electron microscope (TEM). The mechanical properties of test steel were examined by impact test and tensile test. Austenite reversion and cementite precipitation-dissolution was numerically simulated under the assumption of local equilibrium. With the decrease of hot rolling temperature from 1000 °C to 800 °C, the uniform equiaxed prior austenite grains microstructures changed to heterogeneous microstructures of laminated and ultrafine prior austenite grains arranged alternatively. The tensile and impact tests revealed that the medium manganese steels rolling at 800 °C had an excellent combination of mechanical properties. Elongation had a great relationship with retained austenite fraction and stability. The fractography of impact specimens was examined to explore the toughening mechanism of the micro-laminated steels. The steel with uniform equiaxed grain structure exhibited a relatively low tensile strength of 750 MPa and low elongation of ∼20% and an extremely poor low-temperature toughness of ∼40 J at −40 °C. An enhanced low-temperature toughness (∼233 J at −40 °C), as well as an improved tensile strength (823 MPa) and higher elongation of ∼40%, was obtained in the steel with heterogeneous microstructures. The content of austenite in heterogeneous microstructure is twice that in uniform equiaxed grain structure. And cementite dissolved more thoroughly in the heterogeneous microstructure. The high austenite content of heterogeneous microstructures enabled the steel to be significantly stronger and ductile, which contributed to the high tensile strength and elongation to some extent. It is concluded that the effect of interface decohesion resulted in the occurrence of delamination. And the high austenite content and delamination greatly improved the low-temperature toughness of experimental steel.

Effect of a new pretreatment-Q&P process on the microstructure and mechanical properties of light-weight Al-containing medium-Mn steels

This study examines the impact of a new pretreatment-Q&P process on the mechanical properties and microstructure of lightweight Al-containing medium Mn steels. The tested steel is pre-strained (0%, 1%, 2%, and 3%) before going through the Q&P process. The tested steel's microstructure and mechanical properties were examined. And the results revealed that the tested steel was composed of martensite, α-ferrite, δ-ferrite, and retained austenite. After the heat treatment process, the retained austenite in the microstructure is distributed in a dispersed distribution. According to research, the amount of elemental Mn required to maintain a stable presence at room temperature varies depending on the retained austenite morphology. Simultaneously, it was revealed that the process significantly improved martensite/retained austenite/ferrite to accept dislocations. This is because the increase in dislocation channels allows C/Mn/Al/Si elements to diffuse more easily, allowing the block, granular retained austenite to remain moderately stable at room temperature. This facilitates the TRIP effect, which enhances the plasticity of the medium manganese steels. At the same time, when the external stress reaches a certain degree, the sudden opening of dislocations in the microstructure and their mutual cancellation causes stress relaxation and redistribution in the medium manganese steel microstructure. The plasticity of medium manganese steels is greatly enhanced by the combined effect of the TRIP effect and the redistribution of stress between the microstructures.

The synergistic effect of grain refinement and precipitation strengthening on mechanical properties and dry sliding wear behavior of medium manganese steels

The hot rolled medium manganese Ti-bearing and Ti-free steels were solution treated at 1000 ℃ and then aged at 500, 550 and 600 ℃, respectively. The results showed that Ti-bearing steel had refined grain size but higher hardness than Ti-free steel. Moreover, Ti-bearing steel exhibited a superior impact toughness than Ti-free steel, especially when the samples were aged at 500 ℃, which was attributed to the homogeneous distribution of Ti(C, N) precipitates and alloyed cementite in the matrix. In addition, the Ti-bearing steel aged at 500 ℃ exhibited the best wear resistance despite its lower initial hardness, which was primarily attributed to the significant work hardening achieved by ε-martensitic transformation and mechanical twins during wear deformation.

Characterization of precipitation, evolution, and growth of MnS inclusions in medium/high manganese steel during solidification process

MnS as a main manganese-containing inclusion in medium/high manganese steel, which can be determined to the mechanical properties of steel. However, the precipitation and evolution mechanism of MnS in medium/high manganese steel is still unclear due to the special solidification properties and element segregation behavior. Hence, the effects of sulfur content, manganese content and cooling rate on the precipitation, evolution, and growth behavior of MnS inclusions in medium/high manganese are various experimentally characterized and thermodynamically elucidated in the present work. The results of 2D and 3D observation indicated that the morphology of MnS in medium manganese steel were transformed from globular and spindle-like (type I MnS) into large-sized rods (type II MnS) and dendritic (type D MnS), when sulfur content was increased from 78 ppm to 1578 ppm. Particularly, the spatial distribution and structure of MnS inclusions are elaborated in detail through X-ray micro-CT observations, which are discussed by defining the quantitative topography parameters and statistical analysis. Based on in situ CSLM observations, MnS precipitation path in high sulfur medium manganese steel was monitored as L → (L + δ + MnS) → (δ + MnS) → (δ + γ + MnS) → (γ + MnS) → (α + γ + MnS) → (α+MnS). Simultaneously, the Scheil-solidification calculations demonstrated that MnS is precipitated at the interdendritic region where the solid-liquid states are coexisted, which is caused by the segregation of sulfur and manganese. Moreover, increasing sulfur content generates the earlier precipitation, and leads to the significant increase in the number and size of MnS inclusions. Besides, the increase of manganese content promotes the transition of MnS from globular to polyhedral shape, which is attributed to the dissociative eutectic reaction of MnS formation preferentially takes place earlier in case of high manganese steel. It is also found that the decreasing of cooling rate and increasing the manganese content tends to increase the number and size of MnS inclusions, which is resulted from the long growth times of high manganese steel induced by large solid-liquid temperature differences. This work provides a systematic understanding of the precipitation and evolution of MnS inclusions in medium/high manganese steel.

Research on short process hot forming technology of a medium manganese steel

Carbon neutrality and carbon peaking are one of the key tasks of our country in the future. As a major carbon producer, the steel industry played an important role in achieving energy conservation. The feasibility and benefits of rapidly heating (over 100 °C/s) has been proven to be effective for producing press hardening steel, which can also shorten the hot forming process. In this work, we studied the application of short hot forming process in a medium manganese steel. Results shown that the new process can greatly reduce the austenitizing time while ensuring the strength of the materials. In addition, the short-term heating of the material in a non-equilibrium state exacerbated the uneven distribution of alloying elements. Thus, the content of retained austenite in the final microstructure doubled (increased from 8.7% to 18.5%) through the new process, thereby further improving the toughness of the material. The microstructure evolution and mechanical properties of the material under the short process hot forming process was analysed, together with the feasibility of the new process in the future industrialization.

Microstructure evolution and yield strength improvement of a low carbon medium manganese steel experienced intercritical annealing, pre-straining and tempering

The microstructure evolution and mechanical properties of a 0.15C1.2Si10Mn0.5 V medium manganese steel after intercritical annealing, pre-straining and tempering treatment are systematically analyzed. An intercritical annealing yields a microstructure containing ultrafine γ + α coexisting structure while final tempering reduces martensitic supersaturation, which is beneficial to the ductility of the steel. The applied pre-strains between the two processes cause a part of unstable banded austenite in hot rolled state prematurely to transform into lath martensite that divides the coarse banded austenite into smaller ones. When the pre-strain is 0.02, there are about 21% strain-induced martensite produced in the microstructure and the steel exhibits the best comprehensive mechanical properties with the yield strength of 1264 MPa, tensile strength of 1506 MPa and total elongation of 19%. Actually, the increase in yield strength under pre-strains should be ascribed to dislocation strengthening in the strain-induced martensite and the precipitation strengthening of vanadium carbides during the deformation and subsequent tempering.

Simultaneous Occurrence of Twinning and Phase Transformation During Yield Point Elongation in Medium Manganese Steels

Simultaneous Occurrence of Twinning and Phase Transformation During Yield Point Elongation in Medium Manganese Steels

Processing, Properties, and Microstructure Interrelationships in Medium Manganese Steels

Processing, Properties, and Microstructure Interrelationships in Medium Manganese Steels

Alloying and Processing of Medium Manganese Steels for Forging Applications

The processability of medium Mn-containing steels (MMnS) with 4–10% Mn is discussed in light of their continuous casting behavior. Precipitation, phase transformation, extension, or shift of solidification intervals induced by various alloying concepts are decisive in controlling the hot ductility. It turns out that the formation of complex AlN and MnS precipitates as well as δ‑ferrite solidification deteriorates the high temperature ductility. The concept of MMnS has been used to develop air-hardening forging steels with 4% Mn. The alloy design and the heat treatment parameters have been varied with a focus on the prevention of Mn embrittlement as well as the formation of fine austenite grains during intercritical annealing. It is shown that the addition of B and Mo increases the impact toughness, although the effectiveness of each element varies depending on the heat treatment conditions. The impact toughness can be significantly improved by the introduction of a globular metastable austenitic phase. Compared to conventional quenched+tempered steels, an improved cyclic strength for an ultimate tensile strength level of more than 1300 MPa can be achieved.

Cyclic intercritical annealing to improve strength-ductility combinations in medium manganese steels

With the push for superior properties from third-generation advanced high-strength steels, particularly by the automotive industry, medium manganese steels have emerged as a viable candidate. Intercritical annealing of medium manganese steels promotes retention of large austenite fractions (>30%) at room temperature. While prior studies have established strong mechanical property dependence on the amount and mechanical stability of retained austenite, the effect of austenite distribution on mitigating local strain incompatibility has received less attention. The present study proposes a method to alter phase distribution: a novel cyclic intercritical annealing that promotes nucleation and efficient stabilization of retained austenite. Grain sizes were found to be comparable between isothermal- and cyclic-annealed samples, yet bulk neutron diffraction revealed greater austenite fractions in the latter, indicating more extensive austenite nucleation. Combining the cycle with an isothermal hold facilitated austenite growth and enrichment, improving work hardening while maintaining toughness relative to purely isothermal annealing.

The Significant Influence of Cooling Rate and Intercritical Annealing Temperature on Austenite Stability and Relationship to Mechanical Behavior in Medium Manganese Steel

The influence of cooling rate and intercritical annealing temperature on austenite stability and mechanical properties of cold rolled Fe‐11Mn‐4Al‐0.2C steel are elucidated. The samples are intercritical annealed in the range of 700–900 °C for 5 min followed by either water‐quenched or furnace‐cooled. For 700–750 °C samples, the cooling rate has an insignificant influence on the mechanical properties. However, austenite in 800–900 °C water‐quenched samples is characterized by smaller grain size, lower Mn and C content and higher residual stress than the furnace‐cooled samples, which result in lower austenite stability, stronger transformation‐induced plasticity effect and higher ultimate tensile strength in water‐quenched samples. The specific contribution of factors relates to austenite stability is quantified. The contribution of grain size and elements is much higher than the residual stress. However, residual stress becomes a decisive factor because the opposite contribution of grain size and elements is almost offset.

Effect of microstructure on corrosion behavior of medium manganese steel

In this work, the corrosion behavior of medium-manganese steel (MMS), with lamellar and globular microstructure having comparable austenite and ferrite fractions is studied using potentiodynamic polarization and electrochemical impedance spectroscopy techniques. It was observed that lamellar morphology had superior corrosion resistance depicted by ∼44 % lower corrosion current and a greater charge transfer resistance. The superior corrosion resistance of lamellar morphology was attributed to a relatively favorable crystallographic texture and a higher fraction of low energy low angle grain boundaries compared to globular morphology MMS. This work sheds important insights into controlling corrosion resistance of third-generation advanced high-strength MMS through microstructural design.

Investigation of Wear Property and Strengthening Mechanism of Hot-Rolled Medium Manganese Steel on Condition of Slurry Erosion Wear

Abstract In order to further expand the application field of medium manganese steel, its wear property and strengthening mechanism under the slurry erosion wear were studied in this paper. At different erosion angles and velocities, the erosion-wear resistance of medium manganese steel was superior to the martensitic wear-resistant steel. The formation of wear-hardened layer caused by the work-hardening effect was the fundamental reason for wear strengthening. The depth of the wear-hardening layer was nearly 400 µm and surface hardness was above 495 HV. The wear strengthening mechanism was attributed to the combined strengthening, including the martensitic transformation, twin, and dislocation strengthening. The maximum value of erosion wear-rate appeared at 60 deg erosion angle and the minimum value occurred at 90 deg erosion angle. The erosion-wear damage included three aspects of the micro-cutting, erosion peeling caused by the plastic deformation, and local gouging abrasion. The change of erosion angle led to the change of normal and tangential force components of erosion particles on the wear surface, which changed the main wear mechanism of erosion wear. With the change of erosion angle from low to high, the main wear mechanism gradually changed from the micro-cutting wear to the erosion peeling wear and local gouging abrasion.

Occurrence of dynamic strain aging in intercritically annealed low carbon high aluminum medium manganese steels

Medium manganese steel grades heat treated with the quench and partition (Q&P) treatment have shown promising results of strength and formability, but the number of studies on high aluminum medium manganese Q&P steels still remains rather limited. Consequently, this study investigates the mechanical properties, behavior and microstructures of a low carbon-high aluminum medium manganese (3%) steel after intercritical annealing and subsequent Q&P heat treatments with varying heat treatment parameters. Samples that were intercritically annealed above 760 °C showed an ultimate tensile strength (UTS) of around 1500 MPa with uniform elongation values of approximately 10%. On the other hand, the samples annealed at 740 °C showed somewhat lower UTS values (in the range of 1000 … 1200 MPa) but much higher uniform and total elongations, i.e., considerably improved formability. However, the stress-strain curves of the samples annealed at 740 °C showed rather severe serrations that can be connected to the dynamic strain aging (DSA) phenomena, which limits the usability of the steel especially in applications where good surface quality of the deformed (sheet) is required. Therefore, the main focus of this article is on the samples annealed at temperatures close to A1, where DSA serrations tend to appear. The evidence gathered from these investigations leads to the conjecture that the DSA serrations are due to the free carbon and nitrogen originating from the dissolution of M(C,N) and M2(C,N) type carbides, which were formed during the intercritical annealing at temperatures producing less than 50% of the austenite phase. Other reasons for the occurrence of DSA in the current test materials can be the scarcity of martensite and the morphology of the retained austenite.

Plasma Nitriding of an Air-Hardening Medium Manganese Forging Steel

Abstract The impact of plasma nitriding on the microstructure and the hardness of a recently developed 4 wt.-% medium manganese steel are presented. In contrast to standard quench and tempering steels, the investigated material achieves its martensitic microstructure by air-cooling from the forging heat, which enables the reduction of the carbon footprint of the forged components. The influence of nitriding on this grade of steel has not been investigated so far, but fundamental differences in comparison to standard nitriding steels are expected due to the increased manganese concentration. To address this issue, nitriding treatments with different temperatures (350 °C, 580 °C and 650 °C) have been performed, followed by examinations of the microstructure, the phase composition, the obtained hardness profiles and the tensile properties of the bulk material after nitriding, accompanied by thermodynamic equilibrium calculations. It is demonstrated that after nitriding at 580 °C similar hardness profiles like standard nitriding steels are achieved, with a shorter process as austenitization and hardening were omitted, reaching a hardness of approximately 950 HV0.1. Furthermore, it was demonstrated that austenite can be stabilized by manganese and nitrogen partitioning to room temperature during nitriding in the intercritical phase region.