To enhance the wear resistance of carburized M50NiL steel, this study introduces a method for refining the grains in carburized layer to a micro/nano-scale. The method involves extending the carburization time to ensure the formation of large MC carbides at grain boundaries, and adjusting the quenching temperature to facilitate the particle-stimulated nucleation (PSN). The process promoted the recrystallization of the residual austenite (RA), together with the subgrains unexpectedly discovered, successfully achieving the grain refinement. In this paper, the formation mechanism of recrystallization and subgrains are discussed based on interfacial energy model and first principles calculation. The results indicate that recrystallization is driven by the release of energy at the interface between MC carbides and the matrix during quenching, while the formation of subgrain boundaries is due to the reduction of fault energy in the RA, which caused by the increase of C content, promotes the dislocation movement and entanglement. Furthermore, the effects on hardness and wear resistance of micro/nano-crystalline region (MNCR) were investigated. The results show that MNCR after complete carburizing heat treatment has abundant dispersed carbides and refined martensite, which led to an approximate 15HV increase in the hardness, and exhibited nearly a 50% reduction in wear loss.

中文翻译：

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M50NiL渗碳钢微/纳米晶层的制备及力学性能

为了提高渗碳M50NiL钢的耐磨性，本研究介绍了一种将渗碳层晶粒细化至微/纳米尺度的方法。该方法包括延长渗碳时间以确保在晶界处形成大的MC碳化物，并调整淬火温度以促进颗粒刺激成核（PSN）。该过程促进了残余奥氏体（RA）的再结晶，以及意外发现的亚晶，成功实现了晶粒细化。本文基于界面能模型和第一性原理计算，讨论了再结晶和亚晶的形成机制。结果表明，再结晶是由淬火过程中MC碳化物与基体界面处的能量释放驱动的，而亚晶界的形成是由于C含量增加导致RA中断层能的减少。 ，促进位错运动和纠缠。此外，还研究了微/纳米晶区（MNCR）对硬度和耐磨性的影响。结果表明，完全渗碳热处理后的MNCR具有丰富的弥散碳化物和细化的马氏体，硬度提高了约15HV，磨损量减少了近50%。