高锰钢爆炸变形孪晶结构调控及其在循环载荷作用下的行为

Nowadays, the current research of material field focuses on the twinning-structure which can remarkably enhance the strength, ductility and toughness. The high-speed railway is the most important strategic project in China and its security has caught the world`s attention. And the crossings, that are used to change the running direction of trains, play a key role on the reliability of the high-speed railway. Hadfield steel and bainitic steel are the main materials used for manufacturing the crossings. A large amount of twinning can be introduced into the microstructure of the Hadfield steel after high strain rate deformation for its low stacking fault energy, which can yield an excellent work hardening effect. In practice, to meet requirements of the high-speed railway, the explosion pre-hardening treatment has been carried out on the Hadfield steel crossing for its low yield strength. However, the research on the mechanism of explosion hardening of Hadfield steel is far behind its application, and no report has been carried out on how to obtain a high density and ultra-fine twinning structure in Hadfield steel via composition designing and the explosion procedure optimizing. In the present project, the conventional and micro-alloyed Hadfield steel become the objects of the study. And the optimum explosion hardening procedure, that can introduce a high density and ultra-fine twinning structure in Hadfield steel, can be obtained via regulating the austenitic stacking fault energy (37 and 48mJ/m2), grain size (50, 200 and 500μm), explosion deformation temperature (-50, 0 and 50℃) and times (1~3) and deformation rate. And then, the microstructure evolution and property change of the deformed Hadfield steel under cyclic loading will be studied in detail. Finally, the relationships between the microstructure and the property of Hadfield steel, the twining structure and the explosion procedure will be revealed, and then the aim of regulating the reliability of Hadfield steel crossing of high-speed railway will be realized.

孪晶可以同时显著提高材料的强塑韧性，成为当今材料界研究热点。目前我国头号重大战略工程是高速铁路，其安全被世界瞩目，改变火车运行方向的辙叉关乎其安全可靠。辙叉用钢主要有高锰钢和贝氏体钢，低层错能高锰钢在超高速率下变形会形成大量孪晶，产生超加工硬化效应。为满足高铁要求，对屈服强度较低的高锰钢辙叉表面采用爆炸预硬化处理。然而其硬化机理研究远落后于其应用，如何通过对高锰钢成分设计和爆炸工艺优化来获得高密度超细孪晶结构未见报道。本项目以传统高锰钢和微合金化高锰钢为研究对象，通过改变奥氏体层错能(37和48mJ/m2)、晶粒尺寸(50、200和500μm)，调整爆炸变形温度(-50、0和50℃)和次数(1、2和3次)及速率，优化高密度超细孪晶高锰钢的爆炸变形工艺，并研究其在循环载荷作用下的结构演变和性能蜕变行为，揭示结构和性能关联性，实现通过调整爆炸工艺调控孪晶结构掌控高速铁路高锰钢辙叉的安全可靠性。

目前，高速铁路是我国重大战略工程，其安全被世界瞩目，改变火车运行方向的辙叉关乎其安全可靠。辙叉用钢主要有高锰钢和贝氏体钢，低层错能高锰钢在超高速率下变形会形成大量孪晶，产生超加工硬化效应。为满足高铁要求，对屈服强度较低的高锰钢辙叉表面采用爆炸预硬化处理。然而其硬化机理研究远落后于其应用，如何通过对高锰钢成分设计和爆炸工艺优化来获得高密度超细孪晶结构未见报道。本项目以传统高锰钢和Cr+N合金化高锰钢为研究对象，研究了不同爆炸硬化条件下高锰钢的组织和力学性能变化。研究表明，化学成分和环境温度对高锰钢的硬化效果和孪生行为影响较大，而晶粒尺寸的影响较小；当炸药总厚度相同时，两次爆炸硬化后高锰钢试样的表面硬度更高，界面硬度降低趋势更加平缓；在变形过程中，高的变形速率有助于高锰钢中形变孪晶的产生。经爆炸硬化处理后，高锰钢的滚动接触疲劳寿命降低，而三点弯曲疲劳性能有所提高。Cr+N合金化高锰钢的强塑性、低周疲劳性能以及耐磨性能都要高于普通高锰钢。 高速重击高锰钢可以在高锰钢表面制备纳米晶，这是由于位错和孪晶发生作用，孪晶界共格特性被破坏导致的。相比于原始态高锰钢和常规变形高锰钢，纳米孪晶高锰钢具有更高的热稳定性和耐蚀性。本项目的研究成果对于高锰钢辙叉的制造和应用具有重要指导意义。