Influence of Carbides and Strain-induced Martensite on Wear Resistance of Austenitic Medium Manganese Steels

The abrasive wear behaviour of austeniticmedium manganese steels was studied under weakcorrosion-abrasive wear simulating the linerplate in wet metallic ore bail mill undernon-severe impact-loading working condition.Results show that the work-hardening mechanismand the wear resistance of high carbon austeniticmedium manganese steels differ from those ofmedium carbon austenitic medium manganese steel.Under non-severe impact and weakcorrosion-abrasive wear,the wear resistancesof high carbon and medium carbon austeniticmedium manganese steels are 50-90% and 20-40%higher than that of Hadfield steel respectively.     

Influence of Nb and N on microstructure and work-hardening properties of medium manganese Austenitic Steel

The form of existance of Nb and N in medium manganese steel and influence of Nb and N on microstuctures and work-hardening properties have been researched The mechanism of work hardening of austenitic Mn steel has been conducted Experimental results show that when trace Nb and N are added into the steel, they can form carbide, nitride of Nb(Nbc, NbN, Nb(N · C)), and become heterogeneous nuclei of r-Fe. When addition contents of Nb and N are from 0.15% to 0.25% and 0.03% to 0.05% respectively, grain size can be 6–7 Grade Through ageing treatment, grained and dispersed secondary phases were obtained Nb and N can decrease the stacking faults energy. Under no-severe impact loading conditions, the structures of Mn 7 is high density dislocation, tangled dislocation, stacking fault and strain-induced martensite. So that the work hardening of Mn 7 is the combined results of dislocation strengthening and the formation of straininduced martensite.     

A novel high manganese austenitic steel with higher work hardening capacity and much lower impact deformation than Hadfield manganese steel

To tackle the problem of poor work hardening capacity and high initial deformation under low load in Hadfield manganese steel, the deformation behavior and microstructures under tensile and impact were investigated in a new high manganese austenitic steel Fe18Mn5Si0.35C (wt.%). The results show that this new steel has higher work hardening capacity at low and high strains than Hadfield manganese steel. Its impact deformation is much lower than that of Hadfield manganese steel. The easy occurrence and rapid increase of the amount of stress-induced ε martensitic transformation account for this unique properties in Fe18Mn5Si0.35C steel. The results indirectly confirm that the formation of distorted deformation twin leads to the anomalous work hardening in Hadfield manganese steel.     

Thermodynamic Analyses of Strain-induced Martensite Transformation in Fe-7Mn-1.2C Alloy

Research Notes1. ~odT.he ability Of work-hardenillg of medium manganese steel (Fe-7Mn-1.2C) can be brought into action under non-severe impact loading condition withthe surface hardness from HB224 to HB67411] t and thestrain-induced martensite has been found in the workhardening \Inyer[2]. But t)he mechanism of the martensite transformation is still in question. In this \paper,the Ms temperat-"re, AGe-", aC7-M and mechanical energy have been calculated by means of XU'SFe-X-C model. An…     

Effects of Al addition on high strain rate deformation of fully austenitic high Mn steels

The effects of Al addition on dynamic flow response of the fully austenitic high Mn steel were investigated by conducting high strain rate compression tests on Fe-22Mn-xAl-0.6C steels (x = 0, 3, 6 in wt.%). While dynamic yield strength of the 0 Al steel and the 3 Al steel were comparable, the 6 Al steel exhibited the highest one. Meanwhile, strain hardenability of the 0 Al steel was the highest and that of other two steels was nearly same. Under the present dynamic loading, no obvious dynamic recrystallization by adiabatic heating was observed in all steels. Fully compressed microstructures revealed (a) ?-martensite and mechanical twin bands for the 0 Al steel, (b) multi-layer deformation bands and mechanical twin bands for the 3 Al steel, and (c) a variety of dislocation configurations such as the directional slip traces, tangled dislocations, and incomplete dislocation cells for the 6 Al steel. These findings inform that dynamic flow of the 0 Al steel was associated with both TRIP and TWIP, and that of other two steels was dominated by dislocation gliding - mainly, planar glide for the 3 Al steel and the combination of both planar glide and wavy glide for the 6 Al steel. The dynamic flow response of the present steels was discussed in terms of the stacking fault energy affected by the Al content and adiabatic heating during dynamic loading and of the strain rate effect on the critical stress for mechanical twinning.     

低温时效对6Mn2Cr钢耐磨性的影响

低温时效处理明显提高６Ｍｎ２Ｃｒ介稳奥氏体钢抗高冲击功的耐磨性，穆斯堡尔谱分析不韧处理试样的磨面诱发出无碳马氏体和合金马氏体。经低温时效处理试样的磨面为韧性罗合金奥氏体和无碳氏体两相组织，并在随后的磨损过程中产生的强烈的加工硬化，致使低温对时效处理试样的磨面兼有高韧性和高硬度。     

Nickel-free austenitic steels for cryogenic applications: The Fe-23% Mn-5% Al-0.2% C alloys

A study has been made of the influence of carbon and aluminium additions on the mechanical properties under uniaxial tensile loading and by Charpy V notch impact tests at room temperature and ?196°C on the Fe-24 % Mn alloys. It is concluded that the Fe-24 % Mn-5 % Al-0.2 % C appears as a new nickel-free iron-based alloy which is particularly interesting for cryogenic applications. In these alloys, both additions of carbon and aluminium contribute to the stability of the austenitic phase by suppressing the γ → ? martensitic transformation of the binary Fe-24 % Mn and to the solution hardening of the manganese-rich austenitic alloy.     

Corrosion-resistant analogue of Hadfield steel

The concept of alloying austenitic steels with carbon + nitrogen is used for the development of a corrosion-resistant austenitic CrMn steel having an impact wear resistance close to that of the Hadfield steel. A higher stabilization of the austenitic phase by C + N, as compared to carbon or nitrogen alone, is substantiated by ab initio calculation of the electron structure, measurements of the concentration of free electrons and calculations of the phase equilibrium. Based on these results, the compositions (mass%) Cr18Mn18C0.34N0.61 and Cr18Mn18C0.49N0.58 were melted and tested along with Hadfield steel Mn12C1.2. Mechanical tests have shown that, as compared to the Hadfield steel, the experimental steels possess a higher strength, plasticity, hardness and the same resistance to impact wear. TEM studies of the surface layer after impact treatment revealed a mixture of the amorphous phase, nanocrystals and fine-twinned austenite. At the same time, using Mössbauer spectroscopy of conversion electrons, the ferromagnetic ordering was found in the surface layer of up to 10 μm in depth, which is the sign of the strain-induced martensitic phase. The hypothesis of a transition from the low-spin to the high-spin state of the iron atoms within the thin twins in austenite was proposed in order to interpret the discrepancy between TEM and Mössbauer studies. Potentiodynamic measurements and immersion tests show that the CrMnCN steels possess a significantly higher pitting potential and resistance to general corrosion in comparison with Hadfield steel.     

耐酸性高Mn奥氏体钢的实验研究

为适应特殊油气开采环境的复杂工况条件,提高设备的使用寿命和安全性,降低开采成本,不同于常规管线钢低C低Mn的合金设计思路,采用高C高Mn成分体系获得了综合性能优异的新型耐酸性奥氏体钢.通过拉伸实验、冲击试验以及氢致开裂实验等方法对其综合性能进行研究,并利用光学显微镜、扫描电镜、透射电镜等手段对高Mn奥氏体钢的组织进行了观察分析.研究结果表明:实验钢抗拉强度达到1 153 MPa,屈强比仅为0.46,伸长率高达50%,-40℃冲击功达到123 J,同时A溶液条件下经96 h浸泡未发现氢鼓泡及裂纹.实验钢显微组织为单相奥氏体组织,组织中存在大量位错、层错以及孪晶.与常规管线钢相比较,实验钢具有低屈强比、高均匀塑性变形的优点.此外,奥氏体组织的溶氢能力极强,本实验钢具有优良的抗氢致开裂腐蚀性能.     

Microstructure and tensile properties of the laser welded TWIP steel and the deformation behavior of the fusion zone

Microstructure and tensile properties of the laser welded joint of Fe–18.8Mn–0.6C TWIP steel were investigated in this research. The microstructure of fusion zone (FZ) was characterized by means of X-ray diffraction (XRD), transmission electron microscope (TEM) and scanning electron microscope (SEM). TEM and in-situ SEM observation were employed to investigate the microstructural evolution and strengthening mechanism of FZ during deformation. The welded joint with a fully austenitic structure was obtained by the laser welding. The granular divorced eutectic phases (Fe, Mn)₃C and inclusions formed in the interdendritic regions during the solidification of FZ. The fully austenitic structure and coarse dendrite grains were responsible for the fracture at the weld seam. The FZ exhibited a good combination of strength (e.g. tensile strength up to 1000 MPa) and ductility (e.g. total elongation up to 73%). The microstructural evolution revealed that dislocation slip was the main deformation mechanism at low strains of FZ, while at relatively high strains, mechanical twinning was the domain deformation mechanism and played an important role in improving the strength and ductility as well as the work-hardening effect of FZ.     

Microstructure characterization of austenitic Fe–25Mn–22Cr–2Si–0.7N alloy processed by twin roll strip casting

Near net shape casting of austenitic stainless steel containing high Mn and N was explored by using a twin roll strip caster. Microstructural observation and analysis of the as-cast strip by XRD, SEM, and TEM demonstrated that the formation of δ-ferrite and carbides had been prohibited due to the high solidification cooling rate of more than 14,000 K/s during strip casting. Tensile tests indicated that the as-cast strip possessed reasonably good mechanical properties, with a yield strength of 500 MPa and elongation of about 15%. The elastic modulus of the as-cast strip was higher than that of solution treated steel by about one order of magnitude. From the TEM observations, it was found that the as-cast strip contained more dislocations and numerous interstitial elements (N and C) dissolved in grains than the solution treated material, in which dislocations were scarcely observed and precipitates were formed along grain boundaries. Fracture morphology indicates that the as-cast strip has undergone ductile rupture during tensile testing. Deformation twins were observed in the deformed region of the sample by the in-situ tensile test under SEM and TEM observations. The formation of deformation twins were believed to be responsible for high plasticity of the as-cast strip.     

Initial wear characteristics of aging-treated ZG120Mn13 steel under steel shot at high-velocity impact

The initial wear of high manganese steel parts in practical use is related to their original hardness, external loading, surface machining accuracy, and the change of shape and dimension. The paper studies the size and coverage percentage of impact scars on the ZG120Mn13 high carbon high manganese steel surface, as well as the variation of weight loss under high-velocity steel shot by changing aging treatment process. Meanwhile, the relationship between the hardness of aging ZG120Mn13 steel and its initial wear characteristics is discussed. The results show that after 5 seconds, the size and coverage percentage decreased with the increment of hardness. However, in any different period, the wear mass losses of the steel increase with increment of hardness, and increase rapidly first, then slowly. Therefore, under high-velocity impact loading, the increment of hardness is beneficial to improving initial wear-resistance from the perspective of the deformation, but is conducive to improving the resistance from the mass loss. Consequently, we should not only emphasize the high hardness merely, but also consider the changing law of weight loss and initial deformation comprehensively, so that we can achieve the best initial wear resistance when the high manganese steel has the appropriate hardness.     

奥氏体不锈钢滞回本构模型研究

准确的材料滞回本构模型是保证弹塑性地震反应预测准确性的基本前提,如果本构模型选取不当,会对计算结果产生较大影响。为此该文提出了奥氏体不锈钢考虑循环强化作用的单轴滞回本构模型,包括骨架准则及滞回准则。建立数学模型描述奥氏体不锈钢在循环荷载作用下的受力性能。根据提出的理论模型并利用ABAQUS用户材料子程序UMAT,采用Fortran语言二次开发了能够进行循环荷载下奥氏体不锈钢计算分析的程序。通过与试验结果进行对比,表明提出的模型能够准确描述奥氏体不锈钢材料的滞回行为,兼顾计算精度和效率,为奥氏体不锈钢结构体系强震分析提供有力工具。     

Modulated structures of Fe–10Mn–2Cr–1.5C alloy

In Fe–10Mn–2Cr–1.5C alloy the superlattice diffraction spots and satellite reflections have been observed by transmission electron microscopy, these results show that the ordering structure and modulated structure have taken place in this alloy. X-ray diffraction proved that austenitic steel in this alloy is more stable than in traditional austenitic manganese steel. Based on this investigation, we consider that the C–Mn ordering clusters were existing in austenitic manganese steel and the chromium could strengthen this effect by linking the weaker C–Mn couples together. These structures may play an important role in the work hardening of austenitic manganese steel.     

Hydrogen-induced change in microstructure and properties of steels: 18Cr10Mn–0.4N vis-à-vis 18Cr10Ni

ABSTRACT

Cr–Mn–N stainless steels have a cost and strength advantage over conventional Cr–Ni stainless steels. In this study microstructure and mechanical property of hydrogen-charged 18Cr10Mn-0.4N was compared with 18Cr10Ni austenitic stainless steel. This is the first such study for 18Cr10Mn–0.4N austenitic stainless steel. Electron microscopy was used to compare the deformed microstructure of the uncharged and hydrogen-charged specimens. The results are discussed in view of the current knowledge on hydrogen embrittlement. The 18Cr10Mn–0.4N steel suffered higher embrittlement mainly because it absorbed moref hydrogen.     

Martensitic transformation under impact with high strain rate

This paper deals with the quantitative prediction of the volume fraction of martensitic transformation in a austenitic steel that undergoes impact with high strain rate. The coupling relations between strain, stress, strain rate, transformation rate and transformed fraction were derived from the OTC model and modified Bodner–Partom equations, where the impact process was considered as an adiabatic and no entropy-increased process (pressure⩽20 GPa). The one-dimensional results were found to model and predict various experimental results obtained on 304 stainless steel under impact with high strain rate.     

Microhardness profile prediction of a graded steel by strain gradient plasticity theory

In the present study, the Vickers microhardness profile of functionally graded steel austenitic steel produced by electroslag remelting process has been investigated. To produce functionally graded steels, two different slices from plain carbon steel and austenitic stainless steels were spot welded and used as electroslag remelting electrode. Functionally graded steel containing graded layers of austenite may be fabricated via diffusion of alloying elements during remelting stage. Vickers microhardness profile of the specimen has been obtained experimentally and modeled with mechanism-based strain gradient plasticity theory. In this regard, the density of the statistically stored dislocations and that of geometrically necessary dislocations was related to the Vickers microhardness profile of each layer. The experimental results are in good agreement with those obtained from the theory.     

舰船高温排烟管腐蚀机理分析及高温腐蚀研究

目前国内外使用的舰船排烟管材料大多为20钢，20Mn、16Mn钢，15CrMo钢，奥氏体合金钢等，海水对高温排烟管腐蚀严重。对舰船高温排烟管腐蚀机理进行了详细分析，研究了几种不同级别的材料在高温和海水交替作用下的腐蚀机理。     

Effect of prior austenite on reversed austenite stability and mechanical properties of low carbon medium manganese steel heavy plate

The effect of prior austenite on reversed austenite stability and mechanical properties of Fe‐0.06C‐0.2Si‐5.5Mn‐0.4Cr (wt.%) annealed steels was elucidated. With the decrease of austenitizing temperature from 1250 °C to 980 °C, the prior austenite changed from complete recrystallization to partial recrystallization, and the average austenite size was reduced. The volume fraction of reversed austenite was increased from 26.32 % to 30.25 % because of high density of grain boundaries and dislocations. The martensite transformation temperature of annealed steels was increased from ～115 °C to ～150 °C, and both of thermal and mechanical stability of reversed were reduced. There was no significant different in tensile properties, however, the impact toughness was enhanced from 100 J to 180 J at ?60 °C. The excellent impact toughness in annealed steel (austenitized at 980 °C) was obtained because of higher density of high misorientation grain boundaries, more volume fraction of reversed austenite and reduced segregation at grain boundaries.     

Time-dependent fracture of type 316L(N) steel at ambient temperature

Experimental data on tensile and compact geometry (CT) specimens of austenitic Type 316L(N) steel were obtained under sustained load conditions at room temperature. Time‐dependent crack growth, in some cases leading to failure, occurred in many of the CT specimens, dependent on the load level. However, rupture of the uniaxial specimens occurred only at stresses very close to the material's ultimate strength. The data validate the approach to assessing sustained loading effects in the R6 defect assessment procedure. In particular, sustained load effects in austenitic steel may be neglected for values of the R6 L_r parameter less than unity. Uniaxial sustained load tests were also performed at 100 °C and 200 °C. The measured strain rates decreased with increasing temperature, becoming negligible at 200 °C. This is consistent with the advice in R6 that sustained load effects in austenitic steel can be neglected at temperatures between 200 °C and the high‐temperature creep range.