在连续退火试验机上, 对一种Mn含量介于中锰和低锰含量之间的C-Si-Mn系(0.14C-2.72Mn-1.3Si, 质量分数, %)超高强钢进行处理, 获得了具有铁素体、淬火马氏体、回火马氏体以及一定量残余奥氏体的多相组织. 利用膨胀仪, SEM, TEM, EBSD和XRD等对实验钢在不同热处理工艺下的微观组织进行了表征. 结果表明, 800 ℃退火实验钢获得最佳综合力学性能, 屈服强度为672 MPa, 抗拉强度为1333 MPa, 总伸长率为13%. 这主要是800 ℃退火钢精细的组织、合适的相比例以及一定量残余奥氏体共同作用的结果. 对实验钢加工硬化行为进行了深入分析, 讨论了实验钢瞬时加工硬化指数n的变化, 采用修正的C-J方法对实验钢多阶段加工硬化行为进行了分析, 探讨了马氏体结构参数\begin{array}{c}\sqrt{f_M/d_M}\end{array}-->(\begin{array}{c}{f}_M\end{array}为马氏体体积分数, \begin{array}{c}dM\end{array}为马氏体等效直径)和铁素体体积分数等对加工硬化的影响. 结果表明, 实验钢颈缩前随真应变增加n快速增加后减小, 但不同温度退火实验钢n减小趋势不同; 由于不同温度退火实验钢马氏体体积分数不同, 经修正后的C-J法分析得到了2阶段和3阶段的加工硬化行为; 铁素体体积分数对马氏体与铁素体共同塑性变形的应变范围△e有显著影响, 低温时共同变形范围小, 高温时范围逐渐增大, 过高温度时可能又减小. 综上, 实验钢高的初始加工硬化率源于各相的配比、形貌和分布等, 是各组织协调配合和各因素共同作用的结果, 有利于提高实验钢的强度和塑韧性.

Multiphase microstructure which contains ferrite, lath martensite, tempered martensite and a specific proportion of retained austenite with chemical composition of Mn between low Mn and medium Mn (0.14C-2.72Mn-1.3Si, mass fraction, %) belong to C-Si-Mn series was produced using continuous annealing simulator. By means of dilatometric simulation, SEM, TEM, EBSD and XRD, microstructures of the steels in different heat treatments were characterized. The results illustrate that the tested steel sheet gained good comprehensive properties with yield strength of 672 MPa, tensile strength up to 1333 MPa, total elongation A₅₀ of 13% after annealing at 800 ℃, which can be explained by the refined microstructure, appropriate proportion of phases and a specific proportion of retained austenite. This work has deeply analyzed the work hardening behavior, discussed the change of instantaneous work hardening rate n. The multi-stage work hardening behavior was studied by modified C-J analysis, and explored the influence of ( is the volume fraction of martensite, is the equivalent diameter of martensite) and fraction of ferrite on it. The results show that n increases with the rise of true strain and then decreases, but has a different feature in the decrease for the different tested steels; the multi-stage work hardening behavior studied by modified C-J analysis shows 2 or 3 stages because of the different martensite volume fraction. The strain scope of combined action of ferrite and martensite △e is affected by the volume fraction of ferrite: △e is small when the temperature is low, and then △e is large when temperature increases, while the △e maybe small when temperature continue to rise. Above all, the high instantaneous work hardening rate which is helpful for the improvement of strength, plasticity and toughness can be attributed to the proportion, morphology and distribution of ferrite and martensite, which is also the consequence of coordination and combination action of each factor.