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金属学报  2019, Vol. 55 Issue (2): 191-201    DOI: 10.11900/0412.1961.2018.00081
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一种新型高强度高塑性冷轧中锰钢的组织和力学性能
邵成伟, 惠卫军(), 张永健, 赵晓丽, 翁宇庆
北京交通大学机械与电子控制工程学院 北京 100044
Microstructure and Mechanical Properties of a Novel Cold Rolled Medium-Mn Steel with Superior Strength and Ductility
Chengwei SHAO, Weijun HUI(), Yongjian ZHANG, Xiaoli ZHAO, Yuqing WENG
School of Mechanical, Electronic and Control Engineering, Beijing Jiaotong University, Beijing 100044, China
全文: PDF(7409 KB)   HTML
摘要: 

研究了两相区退火温度对一种新型冷轧中锰钢(0.2C-5Mn-0.6Si-3Al,质量分数,%)显微组织及拉伸性能的影响。结果表明,在退火温度为730 ℃时,冷轧中锰钢可获得优异的强度与塑性配合,即抗拉强度为1062 MPa,总伸长率为58.2%,强塑积为61.8 GPa%。随着退火温度升高,逆转变奥氏体逐渐粗化,且由片层状组织形态逐渐向等轴状组织形态转变,在一定退火温度下可获得奥氏体晶粒尺寸分布较为宽泛的多尺度的组织形态。这种多尺度组织形态的残余奥氏体具有适当的机械稳定性,能够产生连续不断的相变诱发塑性(TRIP)效应。连续不断的TRIP效应与铁素体在变形过程中的良好配合,是冷轧中锰钢获得高强度、高塑性的主要原因。冷轧中锰钢拉伸断裂的裂纹主要萌生于软相的铁素体(δ-铁素体)及超细晶铁素体与形变诱导马氏体(残余奥氏体)的界面处。

关键词 冷轧中锰钢两相区退火微观组织残余奥氏体稳定性    
Abstract

Recently, energy conservation, environmental protection and security are the main factors considered by the automotive manufacturers. Medium-Mn steel with excellent combination of specific strength and ductility have been regarded as the potential candidates for automotive applications. The excellent combination of specific strength and ductility depends on the microstructure under different heat treatment processes of the steels. Therefore, the relationship of the combination of specific strength and ductility and microstructure should be studied in detail. A new alloy system of aluminum-containing medium-Mn steel was developed in this study. The addition of aluminum stabilizes α-ferrite, and facilitates the presence of δ-ferrite during solidification. The addition of Mn and C compensates the effect of aluminum on phase stability and ensures austenite formation. In this investigation, the effects of intercritical annealing temperature on the microstructure and tensile properties of a newly designed cold-rolled aluminum-containing medium-Mn steel (0.2C-5Mn-0.6Si-3Al, mass fraction, %) were investigated by SEM, XRD and uniaxial tensile tests. The tensile results show that an excellent combination of ultimate tensile strength (σb) of 1062 MPa, total elongation (δ) of 58.2% and σb×δ of 61.8 GPa% could be obtained after annealing at 730 ℃. The inverted austenite of the cold-rolled steel coarsenes and gradually changes its morphology from mainly lamellar to mainly equiaxed with increasing intercritical annealing temperature, and a duplex microstructure consisting of multi-scale retained austenite could be obtained at 730 ℃, which possesses suitable mechanical stability and thus presents prolonged transformation-induced plasticity (TRIP) effect during tensile deformation. This kind of sustainable TRIP effect and the cooperative deformation of ferrite are responsible for the superior mechanical properties. The investigation of tensile fracture behavior shows that the nucleation and growth of voids occurred mainly at the interfaces between soft ferrite and hard martensite induced by deformation.

Key wordscold-rolled medium-Mn steel    intercritical annealing    microstructure    retained austenite stability
收稿日期: 2018-03-08      出版日期: 2018-12-11
ZTFLH:  TG111  
基金资助:资助项目 北京交通大学人才基金项目No.M14RC00010
作者简介:

作者简介 邵成伟,男,1988年生,博士

引用本文:

邵成伟, 惠卫军, 张永健, 赵晓丽, 翁宇庆. 一种新型高强度高塑性冷轧中锰钢的组织和力学性能[J]. 金属学报, 2019, 55(2): 191-201.
Chengwei SHAO, Weijun HUI, Yongjian ZHANG, Xiaoli ZHAO, Yuqing WENG. Microstructure and Mechanical Properties of a Novel Cold Rolled Medium-Mn Steel with Superior Strength and Ductility. Acta Metall Sin, 2019, 55(2): 191-201.

链接本文:

http://www.ams.org.cn/CN/10.11900/0412.1961.2018.00081      或      http://www.ams.org.cn/CN/Y2019/V55/I2/191

图1  冷轧态及不同温度退火并回火处理后冷轧中锰钢试样显微组织的SEM像
图2  不同温度退火并回火后冷轧中锰钢中残余奥氏体晶粒尺寸分布及残余奥氏体晶粒尺寸变化
图3  不同温度退火并回火处理后冷轧中锰钢试样拉伸前后的XRD谱及奥氏体含量计算结果
Sample σs / MPa σb / MPa δ / % σb×δ / GPa%
700T 970 1054 25.7 27.1
730T 920 1062 58.2 61.8
750T 865 1140 49.1 56.0
770T 786 1214 40.6 50.9
800T 518 1293 18.3 23.7
850T 746 1379 12.4 17.1
表1  不同温度退火并回火处理后冷轧中锰钢试样的拉伸性能
图4  残余奥氏体的晶粒尺寸(d)与屈服强度之间的关系
图5  700T、730T和770T试样的工程应力-工程应变曲线及其加工硬化率曲线
图6  不同温度退火并回火后冷轧中锰钢试样的k值
Sample Mass fraction of Mn / % Mass fraction of C / %
In RA In F In δ-F In RA
700T 6.34±0.46 5.14±0.53 4.31±0.28 0.772
730T 6.30±0.58 4.89±0.43 4.27±0.35 0.765
750T 6.27±0.50 4.84±0.40 4.27±0.15 0.727
770T 6.25±0.60 4.88±0.38 4.23±0.23 0.701
800T 6.26±0.41 4.68±0.42 4.17±0.15 0.637
850T 6.18±0.29 4.54±0.33 4.11±0.11 0.551
表2  EDS测量及XRD数据计算的组织中Mn和C的含量
图7  700T、730T、770T和850T试样拉伸断裂后纵剖面的SEM像
图8  700T、730T、770T和850T试样拉伸断口附近纵剖面显微组织的SEM像
图9  700T和850T试样拉伸断口的SEM像
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