马氏体钢双相区奥氏体组织特征及形成机理

Austenite morphology feature and nucleation mechanism during intercritical reheating of martensite steel

采用双相区再加热-淬火(IQ)工艺,研究了马氏体钢在双相区再加热过程中奥氏体的组织特征及形成机理。结果表明,经890℃奥氏体化900 s后淬火处理获得板条马氏体组织的试验钢,经随后的双相区750℃再加热-淬火处理,在马氏体组织的基础上获得了由亚温铁素体和块状或针状马氏体组成的双相组织。马氏体钢在双相区再加热过程中,针状奥氏体的形成过程可以分为3个阶段:以板条马氏体间碳化物(Fe3C)为奥氏体形核点及C元素在奥氏体内的扩散控制奥氏体在板条界间生长;板条马氏体内C向奥氏体内扩散控制其沿板条方向长大;Mn向奥氏体扩散并控制铁素体-奥氏体两相达到最终的平衡状态。钢在750℃再加热过程中,C、Mn元素由铁素体向奥氏体相中扩散,其扩散过程控制着奥氏体的形核与长大,扩散的结果是C、Mn元素在奥氏体内富集,实现C、Mn元素在两相之间的配分。

The austenite morphology feature and nucleation mechanism during intercritical reheating of the martensite steel were investigated by means of intercritical reheating-quenching（IQ） heat treatment. The results show that lath martensite can be obtained after austenitizing at 890 ℃ for 900 s and quenching. The dual phases contained lath ferrite matrix and needle-like or block martensite in the martensite steel can be gained after the subsequent heat treatment of intercritical reheating at 750 ℃-quenching（IQ）. The transformation of needle-like austenite during intercritieal annealing is divided into three stages when the martensite steel is reheated in the temperature range of the dual-phase region. The first stage consists of nucleation of needle-like austenite at the carbides（ Fe3C） between martensite laths and growth of austenite between martensite laths controlled primarily by carbon diffusion in the austenite. Subsequent growth of the austenite between martensite laths to achieve partial equilibrium is controlled by carbon diffusion in the austenite. At last, the final equilibration of the ferrite and austenite is achieved by Mn diffusion through the austenite. During the intereritical reheating at 750 ℃, C and Mn elements diffuse from ferrite to austenite, which controls the nucleation and growth of austenite. The result of C and Mn diffusion is that they are enriched in austenite, which the partitioning phenomenon of C and Mn between ferrite and anstenite is achievied.