Abstract It is a big challenge to identify whether or not a high temperature rise at high strain rate is a prerequisite for shear instability in crystalline materials. In contrast to the prevailing report of shear instability at high strain rate loading, the shear band (SB) was generated at quasi-static loading in a martensite steel. This gives strong evidence that the high temperature rise is not essential as the quasi-static loading is not able to generate enough heat to initiate the shear instability. Different from the conventional narrow SB at high strain rate loading, a large patch of SB was firstly observed. Considerably localized melting occurred due to the abrupt fracture of SB. SB displays different TEM microstructures at melting and no-melting places. This indicates the significance of distinguishing the microstructure formed during shear instability from the one affected by the fracture of SB. The result suggests that the strain localization mechanism in this material is attributed to the microstructural change instead of the thermal softening. The findings provide a new insight into understanding the formation mechanism of SB from the perspective of microstructural evolution in crystalline materials.

中文翻译：

---

准静态压缩中的剪切不稳定性和相当大的局部熔化

摘要 确定高应变速率下的高温升高是否是晶体材料剪切不稳定性的先决条件是一个很大的挑战。与在高应变率载荷下剪切不稳定性的普遍报道相反，剪切带 (SB) 是在马氏体钢中在准静态载荷下产生的。这提供了强有力的证据，表明高温上升不是必需的，因为准静态载荷不能产生足够的热量来引发剪切不稳定。与在高应变率载荷下的常规窄 SB 不同，首先观察到大块 SB。由于 SB 的突然断裂，发生了相当大的局部熔化。SB 在熔化和非熔化位置显示不同的 TEM 微观结构。这表明区分剪切不稳定期间形成的微观结构与受 SB 断裂影响的微观结构的重要性。结果表明，该材料中的应变局部化机制归因于微观结构变化而不是热软化。这些发现为从晶体材料的微观结构演化的角度理解 SB 的形成机制提供了新的见解。