Microstructure and mechanical properties of the hot-rolled Fe16Mn0.6C steel plate

Results presented in this study contribute to investigation of the microstructure and mechanical properties of the hot-rolled Fe16Mn0.6C steel plates.The steel plates have been produced by being hot-rolled at temperatures ranging from 1100℃ to 850℃ in seven passes to 97.5% reduction in thickness and then cooled in a furnace of 650℃.Some plates have been annealed at temperatures ranging from 300℃ to 1100℃ for 5min to 60min,and then followed by water quenching.There are annealing twins in the hot-rolled Fe16Mn0.6C steel.Fe16Mn0.6C steel presents similar ductile behavior as X-IPTM steel,but much higher elongation than commercial martensitic steel (MP) 1000,dual phase (DP) 980,and transformation induced plasticity (TRIP) 980 steels.Fe16Mn0.6C steel experiences γ→ε (-α) transformation in some local regions,but remains mostly austenite during the entire deformation process.Fe16Mn0.6C steel with special mechanical properties can be produced by using the appropriate anneal technology.Twinning induced plasticity(TWIP) effect only occurs in the Fe16Mn0.6C steel annealed at temperature higher than 900℃.     

Effects of High Strain Rate on Properties and Microstructure Evolution of TWIP Steel Subjected to Impact Loading

 The mechanical properties of the TWIP steel subjected to impact loading at various strain rates were analyzed by the Split Pressure Hopkinson Bar. Meanwhile the microstructure of the TWIP steel fore-and-after the dynamic deformation were characterized and analyzed by optical microscopy (OM), X-ray diffraction (XRD), and transmission electron microscope (TEM). The result shows that when the TWIP steel was deformed under dynamic station, the stress, microshardness and work hardening rate increase with the increment of strain and strain rate; there exist stress fluctuation and decline of work hardening rate for adiabatic temperature rising softening. There exist many pin-like deformation twins in the microstructure of the TWIP steel subjected to impact loading, the grain size after deformation is bigger than that before; the interaction of twins with dislocation and twins with twins, especial emergence of high order deformation twins are the main strengthening mechanisms of the TWIP steel. The nucleation mechanism of deformation twins will be “rebound mechanism”; the incomplete deformation twins can be observed when the strain rate is low; when strain rate raises, deformation twins unite together; furthermore, deformation twins become denser because the nucleation rating enhancing with strain rate increasing.     

Microstructure Characteristics of an Fe-Mn-C TWIP Steel After Deformation

The microstructure characteristics of an Fe-Mn-C TWIP steel after deformation are investigated.The results show that the hot-rolled,cold-rolled and then annealed sample of the Fe-Mn-C TWIP steel has excellent mechanical properties,and the true stress-true strain curve from tension tests exhibits repeated serrations.The deformed microstructure exhibits the typical planar glide characteristics such as no cell formation,dislocation pile-ups on a single slip plane,mechanical twins and stacking faults.There are ...     

高碳含铜孪生诱发塑性钢中非金属夹杂物的探讨

高碳含铜孪生诱发塑性(TWIP)钢的纯净化制备对充分发挥其优异性能具有重要性。为了提高高碳含铜TWIP钢的洁净度, 实验利用金相显微镜、扫描电镜及能谱仪等对该TWIP钢经真空感应熔炼、固溶处理后的铸锭和热轧板材中非金属夹杂物进行分析, 找出了钢中夹杂物类型、来源以及不同工序的变化规律。结果表明, TWIP钢中主要存在铁锰氧化物、硅酸盐类夹杂、硫化物和氮化物。在该TWIP钢使用和热加工的温度范围内, 硫化物表现出良好的塑性, 氮化物属硬质脆性夹杂物。硅酸盐类夹杂物和铁锰氧化物变形特性受其成分和温度变化的影响较为明显。     

Study on Microstructures and Mechanical Properties of High Manganese Steels with TRIP/TWIP Effects

In the present work, advanced high strength and high ductility TRIP/TWIP steels with different manganese concentrations were studied. The microstructures of these steels were evaluated prior to and after deformation and the mechanical properties of these steels were determined. The microstructure analysis indicated that both TRIP and TWIP effects appeared in the steel with lower Mn content, while the TWIP effect was the dominant deformation mechanism in the steel with a higher Mn content, with many deformation twins formed during the deformation. In addition, the forming limit diagrams of these steels were recorded and the results showed an excellent formability.     

固溶温度对节约型双相不锈钢TRIP/TWIP行为的影响

 通过微拉伸、电子背散射（EBSD）、透射电子显微镜（TEM）等手段,研究了具有亚稳奥氏体相的节约型双相不锈钢在1 000～1 200 ℃范围内不同固溶温度下的组织与性能的演变规律;探讨了固溶温度对形变诱导塑性（TRIP/TWIP）的作用机制。结果表明,随着固溶温度的升高,抗拉强度与伸长率均先升高后降低,而亚稳奥氏体相比例由74%（1 000 ℃）降低到37%（1 200 ℃）;1 050 ℃固溶时,试验钢表现出最佳综合性能,抗拉强度达到960 MPa,伸长率达到62%,强塑积达到60 GPa·%。在经拉伸变形的微观结构中形变诱导马氏体与形变孪晶共存,表明试验钢中亚稳奥氏体相的变形机制主要受TRIP及TWIP共同控制,从而导致其塑性变形过程呈现多阶段应变硬化特征,而钢中铁素体相的变形机制主要变形为位错的滑移。     

Fe--22Mn--0.7CTWIP钢的热塑性与断裂机制

基于Gleeble-1500热力模拟试验机测定了Fe-22Mn-0.7C TWIP钢和Q235钢700~1300℃范围内的静态拉伸行为.采用光学显微镜、扫描电子显微镜、能谱仪、电子探针微区分析等技术表征两钢种不同温度下的变形特征和断口形貌.通过分析基体化学成分、相体积分数、晶粒尺寸、凝固缺陷等因素探讨TWIP钢铸态热塑性的变化规律及其影响机制.研究结果表明,Fe-22Mn-0.7C TWIP钢700~1250℃范围内的铸态抗拉强度高于Q235,而其断面收缩率低于40%,且断口均以沿枝晶间断裂方式为主.晶粒细化和控制溶质显微偏析有利于提高TWIP钢热塑性,与基体均质性改善有关.此外,增加应变速率TWIP钢拉伸强度和断面收缩率同时增大.      

Development in fundamental research on TWIP steel used in automobile industry

Abstract

This paper tracks the progress in research regarding the use of twinning induced plasticity (TWIP) steel in the automobile industry. The chemical composition of TWIP steel ensures that it has stable austenite and proper stacking fault energy at room temperature, allowing the main deformation mechanism (twinning) to work. The effects of alloying elements on the microstructure and deformation mechanism of TWIP steel are explained in detail, and their properties deformed under static and dynamic conditions are examined. The TWIP steel deformed at a low strain rate shows higher total elongation and strength. When the TWIP steel deforms under dynamic strain conditions, the stress, microhardness and the work hardening rate, all increase along with the increase in strain and the strain rate. The twin characteristics of TWIP steels deformed at various strain rates vary also and the twins generated under a high strain rate exhibit thinner widths and smaller interspaces compared with those formed under a low strain rate. It has also been observed that multisystem twins are able to generate and develop together. The mechanisms of toughening and strengthening in TWIP steels are noted. Finally, some potential application fields have been found for the promising material.     

两种不同层错能TWIP钢的变形行为及组织演变

对两种不同层错能TWIP钢分别在1 100℃进行了固溶处理,观察了实验钢的微观组织,并分析了实验钢的变形行为.结果表明:通过透射电镜观察,发现较低层错能的TW1实验钢内出现层错,而较高层错能的TW2实验钢内层错较少,但发现位错呈有规则排列的组态;TW2实验钢的加工硬化曲线呈现单调下降的趋势,而TW1实验钢的曲线则分为3个阶段.     

Static Tensile Deformation Behaviors of an Fe-30Mn-3Al-3Si TWIP Steel Studied by In-Situ Neutron Diffraction

TWIP (TWinning Induced Plasticity) steel is one of the advanced steels with attractive mechanical properties.The typical composition of TWIP steel includes a large amount of manganese with some aluminum and silicon.Previous study has shown that TWIP steel exhibits high strength with adequate elongation at high strain rates,so that TWIP steel is desired to be applied for automotive use.However,there are few studies concerning the deformation behaviors aimed to make clear the TWIP effect in TWIP steel.In this study,static tensile deformation behaviors of an Fe-30Mn-3Al-3Si TWIP steel and a SUS310S one were studied by in situ neutron diffraction during tensile deformation.In terms of mechanical properties obtained by the static tensile tests,the TWIP steel showed better balance of tensile strength and uniform elongation than the 310S steel.The angular dispersion neutron diffraction with a wavelength of 0.16 nm was performed during stepwise tensile testing by using a neutron diffractometer for residual stress analysis (RESA) at the Japan Atomic Energy Agency.A specimen was extended in a step by step manner and neutron diffraction profiles of (111),(200) and (311) for austenite were obtained at each step.The diffraction peak,lattice plane spacing,lattice plane strain and so on were determined by the profile analysis as a function of applied stress.The changes of lattice plane strain for austenite in the TWIP and 310S steels indicated several deformation stages in the tensile deformation and can be discussed the difference of intergranular stress between the two samples.     

汽车用轻质TWIP钢的组织演变规律研究

研究了中碳-高Mn系TWIP钢在固溶处理后的组织和力学性能。采用OM、XRD、TEM和EBSD分析了TWIP钢形变前后的微观组织演变规律和高强塑性的产生机理。结果表明,形变孪晶密度随着变形程度的增加而增大,形变孪晶渐进产生,细化起到细晶强化和延缓断裂的作用,使TWIP钢具有优异的综合力学性能和成形性能。     

Mechanical Properties and Microstructure Evolution During Deformation of Fe–Mn–C TWIP Steel

The mechanical and deformation microstructure properties of the Fe–Mn–C TWIP steel was investigated by means of tensile experiment, in situ scanning electron microscope (SEM) and transmission electron microscope (TEM).The results showed that the sample has excellent mechanical with tensile strength of the steel is about 1140 MPa and the yield strength is higher than 480 MPa, while the elongation is above 57%, the true stress–strain curve from tension tests exhibited repeated serrations and its strain‐hardening rate is constantly changing. It is found that there were different deformation mechanisms at different deformation stages result in the unique true stress–strain curve. Dislocation slip dominated the initial deformation and with the accumulation of deformation stress concentration reached the twin shear stress resulting in twin shear, which lead to TWIP effect. As the strain capacity increased continually, the parallel twins can no longer rotate and shear deformation occurred, which lead to the forming of shear bands. The intercoordination of slip deformation, twin deformation, and shear deformation mechanism make the TWIP steel show high strength and high plasticity.     

Fe-Mn-Si-Al系和Fe-Mn-C系TWIP钢加工硬化行为

研究了在不同应变量下Fe-Mn-Si-Al系和Fe-Mn-C系孪晶诱导塑性(TWIP)钢的力学性能以及微观组织,分析了TWIP效应在两种不同系列TWIP钢中发挥的作用,阐明了TWIP钢的强化机制.两种系列的TWIP钢都具有高加工硬化能力,但层错能较低的Fe-Mn-C系TWIP钢加工硬化能力更强.两种系列的TWIP钢加工硬化表现为多加工硬化指数行为,这是由多种强化机理在不同阶段起主导作用的结果.微观组织形态与加工硬化强度之间存在着较强的关联性.位错的增殖和形变孪晶的产生对两个系列TWIP钢硬化曲线形态有着明显的影响.在高应变阶段,Fe-Mn-C系TWIP钢大量的第一位向形变孪晶T1和第二位向形变孪晶T2,以及附着在孪晶界旁的高密度位错区域是造成其具有高加工硬化能力的原因,而Fe-Mn-Si-Al系TWIP钢细密的第一位向形变条纹和孪晶片层间的位错是其高加工硬化原因,且其微观组织更为均匀细致.      

异步轧制TWIP钢的力学性能和微观组织

 利用金相显微镜、X射线衍射仪和透射电子显微镜对异步轧制及热处理TWIP钢的力学性能与微观组织进行了研究。结果表明,TWIP钢经500℃异步轧制后强度显著提高,而塑性降低,这是位错与孪晶共同作用的结果。轧制后的热处理降低了位错密度以及变形孪晶数量,导致强度降低,伸长率升高。经600℃和700℃退火后,TWIP钢表现出良好的强度和塑性综合性能。因此,异步轧制后热处理是获得具有优良综合力学性能TWIP钢的可行途径。     

Stretch‐Flangeability of High Mn TWIP steel

The mechanical properties of austenitic high Mn Twinning Inducted Plasticity (TWIP) steel provide an excellent combination of strength and ductility when tested in uni‐axial tension. The performance of TWIP steel during some critical formability tests such as deep drawing, bulge test and cutting edge stretching has not yet been studied extensively. In this contribution, the stretch‐flangeability of Fe18Mn0.6C1.5Al TWIP steel and Ti Interstitial‐Free (IF) steel were studied by means of hole expansion test. In‐situ strain analysis and Infra‐red (IR) thermography were carried out during the test. It was found that TWIP steel, despite having a higher uniform elongation in uniaxial tension, had poorer hole expansion properties than Ti IF steel. Strain distribution analysis revealed that the hole edge deformed in a deep drawing mode which was similar to a tensile deformation. Away from the hole edge, the deformation mode changed gradually from deep drawing to stretch forming mode. The IR‐thermography of TWIP steel revealed a high degree of adiabatic heating which was absent in the case of IF steel. The crack associated with the edge fracture revealed a local temperature increase at the crack tip of up to 92°C. Two types of hole edge preparations were studied. A high quality hole edge finish resulted in a better hole expansion performance. The fractography of the crack plane surface of TWIP steel and Ti IF were also studied by SEM, and revealed a plastic failure mode in both cases.     

碳含量对Fe-Mn-Cu-C系TWIP钢组织和力学性能的影响

 采用真空熔炼法制备Fe-20Mn-3.0Cu-XC系高强度高塑性合金钢,通过X射线衍射（XRD）、光学显微镜（OM）和透射电子显微镜（TEM）观察方法研究了碳含量对该系列合金微观组织和力学性能的影响,分析了合金的拉伸变形微观机制。结果表明：Fe-20Mn-3.0Cu-XC系合金拉伸变形前后均为单相奥氏体组织,未发生马氏体相变。随着碳质量分数的增加,合金的屈服强度、抗拉强度和伸长率均显著提高。Fe-20Mn-3.0Cu-1.41C合金的屈服强度为501.62MPa,抗拉强度为1178.4MPa,具有优异的综合力学性能。Fe-20Mn-3.0Cu-XC系合金具有优异的应变硬化能力。随着碳质量分数增大至1.41%,最大应变硬化指数n值达到0.782。Fe-20Mn-3.0Cu-XC系合金拉伸变形过程中,TWIP效应是主要的塑性变形机制,大量位错的塞积、形变孪晶的形成以及位错与孪晶间的交互作用共同引起材料强度和塑性的提高。     

Fe16Mn0.6C TWIP钢流变应力和临界动态再结晶行为

 利用Thermecmastor-Z热模拟实验机,得到了Fe16Mn0.6C TWIP钢在变形温度850~1150℃,应变速率0.03~30s-1条件下热压缩变形的真应力应变曲线。进而研究了变形温度、应变速率对Fe16Mn0.6C流变应力和临界动态再结晶行为的影响规律。结果表明,850~1150℃范围内Fe16Mn0.6C热变形的峰值应力随温度的升高而降低,随着应变速率的增大而升高;且在应变速率为0.03 s-1和30 s-1出现明显的应力峰值,材料发生了动态再结晶。最后采用线性回归方法计算出Fe16Mn0.6C的高温变形流变应力本构方程,得出热变形激活能为469kJ/mol;并通过应变硬化速率与流变应力曲线求出了该钢种动态再结晶临界条件与Z参数之间的关系。     

析出强化与孪晶强化在Fe--24 Mn--3 Si--3 Al TWIP钢退火过程中的作用机制

对Fe-24Mn-3Si-3Al TWIP钢在不同退火工艺下进行力学性能测试,采用扫描电子显微镜(SEM)、能谱仪(EDS)和透射电子显微镜(TEM)观察钢的微观组织形貌.结果表明:随着退火温度和保温时间的变化,TWIP钢的力学性能并不符合常规的单调上升或下降的规律,而在退火温度为800℃、保温10 min和退火温度为900℃、保温20 min时发生波动.退火温度为800℃、保温10 min条件下,钢的主要强化机制为析出强化,析出相(Fe,Mn)₂₃C₆的增多导致屈服和抗拉强度升高;退火温度为900℃、保温20 min条件下,钢中的析出相并未有明显的变化,而二次孪晶的产生及孪晶相互交割成为抗拉强度增加的主导因素.      

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The low cycle fatigue behaviors of Fe- Mn- C TWIP steels with different Ce contents were studied. The research was done with a total strain amplitude of ??0. 8% during cyclic loading. Microstructure evolutions of TWIP steels after fatigue fracture were observed by SEM and TEM. The experimental results indicate that TWIP steels with Ce and without Ce have the same characteristics of cyclic hardening, cyclic saturating, cyclic softening and final failure. The density of inclusions in the TWIP steel is increased by the addition of rare earth element Ce, which results in the absorption capability of fatigue energy of the TWIP steel is reduced. Therefore, Ce plays a negative role in deformation fatigue of TWIP steel.     

Hot Deformation Behaviors of Fe–30Mn–3Si–3Al TWIP Steel during Compression at Elevated Temperature and Strain Rate

The hot deformation behavior of twinning‐induced plasticity (TWIP) steel was investigated at 973–1373 K and strain rates of 0.01–20 s^?1 by hot‐compression experiments performed on a Gleeble‐3800 thermo‐simulation test system. Microstructural evolution during recrystallization in the hot deformed TWIP steels was investigated by metallurgical analysis. The hot‐flow behavior can be represented by a Zener–Hollomon parameter in the hyperbolic‐sine equation. The hot‐deformation activation energy is 436.813 kJ mol^?1. Deformation bands are initially generated in the deformed austenitic grains during the dynamic recrystallization (DRX) of TWIP steel. With increasing temperature, the recrystallized grains emerge at the boundary junctions after the disappearance of the deformation bands. Subsequently, they gradually spread along the austenitic boundaries and exhibit a necklace shape. The dynamic recrystallized grains continuously grow until they finally reach equilibrium. The DRX mechanism of TWIP steel is a boundary bulge mechanism. The optimum hot‐working technology parameters (especially for rolling) for the TWIP steel is the deformation temperature range of 1223–1323 K, and strain rate range of 1–10 s^?1.