氮强化高锰奥氏体低温钢的拉伸应变硬化行为

Tensile strain hardening behaviours of nitrogen strengthening high manganese austenitic cryogenic steel

采用低温拉伸、SEM和TEM等方法,对32Mn-7Cr-1Mo-0.3N奥氏体钢进行表征,研究了它的拉伸应变硬化行为.结果表明,32Mn-7Cr-1Mo-0.3N奥氏体钢的真应力与真应变不遵循Hollomon 的线性关系,应变硬化指数n随着真应变的增大而提高,但当ε>0.2后,77 K下的dn/dε值明显高于其它温度的值.在77 K真应变ε>0.2后材料的d2σ/dε2变为正值.dn/dε与d2σ/dε2这一特殊变化趋势导致77 K下应变硬化率和延伸率的提高.其微观机制是,孪晶的形成速率以及孪晶与位错之间的相互作用与硬化率相协调,进而延迟了颈缩的产生,导致较高的均匀变形能力.

The strain hardening behavior of 32Mn-7Cr-1Mo-0.3N austenitic steels was investigated and characterized. The results show that Hollomon relationship is inapplicable. The value of n increases with increasing true strain e. However, after the value of true strain is larger than 0.2, the value of dn/de at 77 K is obviously higher than that at other temperatures, and the value of d2σ/dΕ2 at 77 K becomes positive, which results in the high strain hardening rate and elongation increasing at 77 K. The micro mechanisms are proposed to be the coordination of the forming rates of twins and the interactions between twins and dislocations with strain hardening rates. Subsequently, the necking is delayed and the ability of uniform deformation is obtained.