纳米晶/超细晶奥氏体不锈钢奥氏体稳定性与形变机理的关联性研究

Austenitic stainless steels have been restricted in structural application because of low yield strength. Nanograined/ultrafine-grained (NG/UFG) austenitic stainless steels obtained by an ingenious approach that involves controlled phase-reversion annealing of strain-induced martensite formed from cold-deformation austenite have excellent yield strength and possess boundless prospect. However, the stability of austenite increases precipitously with decrease in grain size from coarse gained structure to NG/UFG structure and deformation mechanism and ductility will be changed. The objective of this proposed research is to fundamentally understand austenite stability dependence on deformation mechanisms in austenitic stainless steel. Meanwhile, the strain hardening behavior in NG/UFG austenitic stainless steels with different stability and TRIP/TWIP effect regions during staining will be analyzed, respectively. The effect of grain refinement and crystallographic orientation of austenite on formation of strain-induced martensite/deformation twinning also be studied. This research not only enrich the effect of austenite stability on deformation mechanism in NG/UFG austenitic stainless steels, but also provide the theoretical guidance for the large scale production of NG/UFG austenitic stainless steels with high yield strength-high ductility combination.

奥氏体不锈钢屈服强度较低，限制了使用。大压下冷变形结合退火工艺获得的纳米晶/超细晶奥氏体不锈钢具有极高的屈服强度和十分广阔的市场前景。然而奥氏体晶粒细化到纳米晶/超细晶时稳定性会急剧提高，形变机制会发生改变并影响塑性。本项目拟研究具有不同奥氏体稳定性的奥氏体不锈钢形变机制，确立奥氏体稳定性与形变机制之间的内在关联；分析纳米晶/超细晶奥氏体不锈钢应变过程中应变硬化行为特性，解析应变过程中TRIP/TWIP效应区间；明确晶粒细化及奥氏体晶体学取向对应变过程中形变马氏体/形变孪晶形成的影响规律。这不仅揭示纳米晶/超细晶奥氏体不锈钢中奥氏体稳定性与形变机制的关系，还为开发高屈服强度高塑性纳米晶/超细晶奥氏体不锈钢提供理论指导。

奥氏体不锈钢屈服强度较低，限制了使用。大压下冷变形结合退火工艺获得的纳米晶/超细晶奥氏体不锈钢具有极高的屈服强度和较好的塑性匹配以及十分广阔的市场前景。然而冷变形和退火过程中组织演变特征、获得的纳米晶/超细晶奥氏体不锈钢的力学性能和塑性变形机理还需要进一步深入的研究。本项目采用18Cr-8Ni奥氏体不锈钢开展研究，采用10%-90%冷变形，发现形变过程中马氏体含量逐渐增加到46%，马氏体形态也由板条状逐步演变为胞状结构。随后对不同冷轧样品进行不同温度和时间的退火处理，发现90%冷轧后再900℃保温2分钟获得组织为无缺陷晶粒的超细晶奥氏体不锈钢。在拉伸过程中这些超细晶奥氏体晶粒转变为孪晶而不全是马氏体，导致应变硬化行为和断裂行为发生改变，其屈服强度高达994MPa的同时延伸率还保持在40%。形变机制的改变归因于晶粒细化到纳米晶/超细晶时奥氏体稳定性急剧提高，形变马氏体难以形成转而形成机械孪晶并影响塑性。这揭示纳米晶/超细晶奥氏体不锈钢中奥氏体稳定性与形变机制的关系，还为开发高屈服强度高塑性纳米晶/超细晶奥氏体不锈钢提供理论指导。