中锰钢塑性失稳现象的研究进展及未来研究展望

中锰钢是近年来出现的新型钢铁材料，因为其优异的力学性能被认为是第三代汽车用钢，但是该钢的一个突出特点就是在拉伸变形时会发生塑性失稳，导致材料结构稳定性减弱甚至在某些情况下过早失效，这已然成为限制中锰钢商业化使用的关键问题。塑性失稳包括出现不连续屈服和屈服平台（吕德斯应变）以及流变应力锯齿（PLC效应）。两者都受到成分、晶粒形貌、退火工艺、组织构成等因素的影响，也均与拉伸变形过程中 奥氏体相变转变存在或强或弱的相关性，使得这一塑性失稳现象的机理更为复杂化，因而在近期各种观点迥异的理论解释也相继被提出。本文综述了相关研究中各种因素对吕德斯应变和PLC效应的影响结果及相关理论解释，并着重指出了各理论解释的局限性及未来的研究思路。最后，基于现有研究和预研实验对在保证中锰钢超高强度和优良塑性的前提下消除中锰钢塑性失稳现象的可行途径进行了展望。 

Recent progress and future research prospects on the plastic instability of medium-Mn steels: a review

Lightweight materials are desired for energy saving and emission reduction of automobiles. A promising material for automobile parts is advanced high strength steel (AHSS). A recently developed material called medium-Mn steel, with excellent mechanical properties, has attracted increasing attention as the third-generation AHSS for automotive processing. However, medium-Mn steel is disadvantaged by plastic instability during tensile tests. This plastic instability is usually associated with localized and propagative bands on the material surface, which cause an unexpected surface roughening effect and premature failure in the most unfavorable cases. Therefore, plastic instability has severely impeded the commercialization of medium-Mn steels. The phenomenon manifests as discontinuous yielding followed by a yielding plateau (the Lüders strain), along with flow stress serrations (the Portevin-Le Chatelier (PLC) effect). Both effects are influenced by the composition, annealing process, and microstructure (phase morphology and constituents) of the steel. Both effects are also correlated with the austenite-to-martensite transformation during deformation to a greater or lesser extent, which is rarely observed in metallic materials. Consequently, the mechanisms of both effects are complicated and explainable by diverse theories. This paper reviewed the current research results on the influences of various factors on the Lüders strain and PLC effect, and discussed their corresponding mechanisms. This paper particularly emphasized the limitations of the existing theoretical explanations and proposed future researches to elucidate the existing disputes. Based on the current research and our preliminary experiment, this paper finally suggested ways of eliminating the plastic instability of medium-Mn steel, while guaranteeing ultrahigh strength, and excellent ductility. These improvements will drive the future development of this field.