GCr15马氏体钢剪切试样断口局部熔融研究

本文采用开45?缺口剪切压缩试样, 比较研究GCr15马氏体钢在准静态压缩和高速冲击下样品断裂面的温升机制. 结果显示两种加载状态的断口上都发现了大量的局部熔融, 说明温升均超过1500℃. GCr15马氏体钢的塑性很低, 然而在剪切应力主导的试样上, 两种加载的剪切面均发生了很大塑性应变. 试样断裂瞬时所释放的能量以及裂纹面间的大滑移摩擦导致局部温升超过熔点. 分析结果表明, 两种加载模式下产生的熔融物均由残余奥氏体和孪晶马氏体组成. 受热的影响, 熔融物下面的基体组织经历了动态再结晶, 从而形成马氏体和奥氏体等轴晶. 因此,在剪应力主导的应力状态下, 马氏体钢的剪切断裂机理与加载速率无关, 高速冲击与准静态加载下的断裂模式和机理没有本质区别. 断裂瞬间产生局部温升促使材料熔融, 这是该材料剪切断裂的特性. 本文结论对GCr15马氏体钢剪切主导断裂机理的认识有重要意义.

Localized melting on fracture surface of shear-dominated specimen of GCr15 martensite steel

In this study, quasi-static compression and high-rate impact tests are conducted on shear-compression specimens with 45? notch to investigate the temperature rise mechanism at fracture. The results showed that considerable localized melting is observed on fracture surfaces of two loading cases, indicating the temperature rise over 1500℃. The plasticity of GCr15 martensite steel is very low. However, large plastic strain occurs at the shear plane in the shear-dominated specimens. At fracture, the energy released by crack propagation combined with large sliding friction leads to localized temperature rise up to the melting point. The results show that the melt produced under the two loading modes is composed of residual austenite and twin martensite. Below the melt, the matrix is severely heat-affected and subjected to dynamic recrystallization. It is composed of equiaxed austenite and martensite. It suggests that the shear fracture of this material is independent of loading rates. The fracture mode and mechanism under dynamic loading such as high strain impact makes no difference to the quasi-static loading. Localized melting at the moment of fracture is a common feature in this material. This study is of great significance in understanding the shear-dominated fracture mechanism of GCr15martensite steel.