中文摘要：

利用EBSD技术对不同应变速率下单向拉伸高锰TRIP钢中的马氏体相变进行了观察,使用XRD数据计算了奥氏体（γ）,hcp马氏体（ε-M）和bcc马氏体（a′-M）的体积分数,并对γ→ε-M和ε-M→a′-M两阶段相变的变体选择进行了理论计算.结果表明,高速拉伸时TRIP行为仍然具有取向依赖性,这是由不同取向γ晶粒内a′-M变体的机械功差异引起的.应变速率的提高促进ε-M→a′-M转变,但总的马氏体转变量降低,即高速拉伸抑制了TRIP效应.TRIP钢静态拉伸时a′-M变体选择较强,动态拉伸时变体选择减弱.静态拉伸时,〈111〉γ和〈100〉γ晶粒内a′-M变体选择可用局部应力对变体做功来计算.高速拉伸时,需结合应力对a′-M变体做功大小及应变能、界面能来分析这些γ晶粒内的变体选择规律.与1个a′-M变体单独出现相比,一对具有特殊取向关系的变体同时出现,可以降低变体的应变能,使得不利变体能够出现.

英文摘要：

Among the wide variety of recently developed steels, high manganese transformation-induced plasticity （TRIP） steels with low stacking fault energy （SFE） are particularly promising. Outstanding mechanical properties combining a high ductility and a high strength are then obtained. Compared to the static deformation of high manganese TRIP steels, the behaviors of martensitic transformation and mechanical properties of such steels during dynamic deformation may be different. In this work, martensitic transformation of high manganese TRIP steel at different strain rates was characterized by the EBSD technique. The volume fractions of austenite （γ）, hcp martensite （ε-M） and bcc martensite （α＇-M） were calculated based on the XRD data. Meanwhile, variant selections of martensitic transformation in γ→ε-M and ε-M→α＇-M transformation were investigated by theoretical calcula- tion. It is shown that orientation dependence of TRIP effect during tension exists even at high strain rates and can be ascribed to the influence of mechanical work in differently oriented γ grains. The transformation of ε-M→α＇-M was promoted, but the total amount of transformed martensite decreased, which means that TRIP effect was restricted at high strain rates. The α＇-M variant selection is more obvious during static tension and became weaker during dynamic tensile deformation, α＇-M variant selection can be predicted by the calculated mechanical works induced by the local stress in 〈111〉γ and 〈100〉γ grains during static tension. However, during dynamic tension, the mecha- nism of variant selection needs to be explained by analyzing the mechanical works induced by the local stress, the strain energy and the interfacial energy in these grains comprehensively. Compared to the occurrence of a single α＇- M variant, a pair of α＇-M variants having specific orientation relationship reduces the strain energy, then unfavored α＇-M variants appear.