节镍型高锰奥氏体不锈钢逆变与再结晶协同细化机理研究

The martensitic reversion is known to be effective in refining the grain size of metastable austenitic stainless steels. However, severe cold rolling reductions are generally required for this process. The sheets of an austenitic high-Mn low-Ni Fe-Cr-Ni-Mn-C-N stainless steel with and without V alloying were used in the project. The steel sheets were cold rolled to less than 60% thickness reduction. Hence, the cold-rolled structure consists of strain-induced martensite, deformed to various degrees, and also strain-hardened austenite, which can be called deformed retained austenite (RA). Then the cold-rolled samples were annealed at different temperatures for durations to revert the martensite back to austenite and recrystallize the retained austenite. The mechanisms of both the reversion of martensite and the recrystallization of cold deformed RA in stainless steels were investigated to obtain bimodal grain size distribution. The influence of the degree of prior cold rolling and subsequent annealing on the microstructure evolution and mechanical properties of a metastable high-Mn austenitic steel was also studied.

马氏体逆转变是一种有效的细化奥氏体不锈钢的方法，然而该工艺一般要求大压下量的轧制变形，给生产和加工带来困难。本项目以Fe-Cr-Ni-Mn-C-N型节镍奥氏体不锈钢的成分为基础，适当提高Mn含量和增加细化晶粒的合金元素V，通过室温下较小压下量（不高于60%）的轧制变形后得到一定比例的应变诱导马氏体和应变硬化奥氏体双相组织，再改变退火工艺获得细化后的逆转变奥氏体和较粗的再结晶奥氏体，最终得到具有双峰晶粒尺度分布的细晶/超细晶奥氏体不锈钢。通过逆变和再结晶协同细化机理的研究，将微观组织与强度、塑性之间的关系联系起来，揭示两种细化机理作用下的微观组织的形成与演变规律，探讨逆变与再结晶两种机理同时作用下的既提高奥氏体不锈钢的强度而又增加其塑性的科学问题，为材料强韧化新途径奠定理论基础，也为节镍高锰奥氏体不锈钢的塑性变形行为及产业化奠定理论及工艺基础。

随着奥氏体不锈钢主要成份镍的成本上升，节镍型奥氏体不锈钢的生产和研发得到高度重视。节镍奥氏体不锈钢通过冷轧+逆变退火的工艺能够对其组织进行调控，获得细晶奥氏体组织，在保留奥氏体不锈钢良好的塑性的同时，增加不锈钢的强度。. 本项目以1Cr13.2Mn10.3Ni2.4和1Cr14Mn10Ni1.5高锰节镍型奥氏体不锈钢作为研究对象，适当提高Mn含量和增加细化晶粒的合金元素V，再通过逆变退火工艺（退火温度为500℃~1000℃，退火保温时间为10s~1000s）的研究，获得细化后的逆转变奥氏体和再结晶奥氏体，制备出了具有微米/亚微米晶粒尺度分布的细晶奥氏体不锈钢。得到了两个优化后的逆变退火工艺，分别是在50%冷轧变形900℃退火100s和80%冷轧变形850℃退火100s。50%冷轧变形900℃退火100s后，抗拉强度为1345MPa，延伸率为60%；80%冷轧变形850℃退火100s后，抗拉强度为1255MPa，延伸率为63%。50%冷轧变形900℃退火100s后得到的晶粒几乎无亚微米级晶粒，80%冷轧变形850℃退火100s后奥氏体不锈钢中亚微米级晶粒约占28.5%。此二者的晶粒均可通过调控晶粒尺寸分布达到双峰特征，增强其综合力学性能。. 经过冷轧+750ºC保温100s逆变退火的1Cr13.2Mn10.3Ni2.4不锈钢进行不同拉伸速率的单向拉伸试验，发现拉伸速率较低的条件下，不锈钢的强度和塑性较高，应变硬化率较高，表现出明显的TRIP效应，而拉伸速率较高的条件下，不锈钢的TRIP效应不明显。当拉伸速率为2mm/s时，80%冷轧逆变退火不锈钢的抗拉强度为1108.6MPa，延伸率为44.3%，而拉伸速率为0.002mm/s时，80%冷轧逆变退火不锈钢的抗拉强度达到1243.1MPa，延伸率达到49.2%。