Chen Wu, He Xiaofei, Yu Wenchao, Shi Jie, Wang Maoqiu, Yao Kefu
School of Materials Science and Engineering, Tsinghua University, Beijing 100084, PR China; NCS Testing Technology Co., Ltd., No.13 GaoLiangQiao XieJie, Beijing 100081, PR China.
Institute of Special Steel, Central Iron and Steel Research Institute, No.76 XueYuanNanLu, Beijing 100081, PR China.
Micron. 2021 May;144:103028. doi: 10.1016/j.micron.2021.103028. Epub 2021 Feb 2.
The microstructure and hardness of case-hardened steel were investigated after carburizing and austenitizing at 820-900 °C, and oil quenching and tempering at 180 °C. The carburized case had a multiphase microstructure consisting of martensite, carbides, and retained austenite, and the maximum content of the retained austenite was 30%; the particle size range was 2-3 μm. The nano-hardness decreased from about 12 GPa near the surface to about 7 GPa in the core, and the microhardness decreased from 800 HV to 450 HV. The in-depth distribution of the microhardness and nano-hardness showed a similar trend, and the ratio of nano-hardness to microhardness was about 15. The results were attributed to the fine particle size of the retained austenite and its even distribution in the martensite matrix and it could not lower the nano-hardness. The nano-hardness was relatively low in areas of the retained austenite (about 5.5 GPa), and pop-in effects were observed, indicating the phase transformation of the retained austenite during nanoindentation loading.
对渗碳钢在820 - 900°C进行渗碳和奥氏体化，然后在180°C进行油淬和回火后的微观结构和硬度进行了研究。渗碳层具有由马氏体、碳化物和残余奥氏体组成的多相微观结构，残余奥氏体的最大含量为30%；粒径范围为2 - 3μm。纳米硬度从表面附近的约12 GPa降至芯部的约7 GPa，显微硬度从800 HV降至450 HV。显微硬度和纳米硬度的深度分布呈现相似趋势，纳米硬度与显微硬度之比约为15。这些结果归因于残余奥氏体的细粒度及其在马氏体基体中的均匀分布，且其不会降低纳米硬度。在残余奥氏体区域纳米硬度相对较低（约5.5 GPa），并且观察到压入效应，表明在纳米压痕加载过程中残余奥氏体发生了相变。
