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对经不同深冷处理工艺的Cr8型冷作模具钢SDC99进行了硬度、冲击韧性、摩擦磨损性能测试,并用SEM、XRD、TEM分析了其相组成及显微组织。结果表明,深冷处理使SDC99钢硬度提高,冲击韧性降低,耐磨性提高,1030℃淬火+210℃×2 h回火+(-196℃×24 h)深冷处理+210℃×2 h回火可使SDC99钢获得最优的综合使用性能,其磨损体积较常规热处理工艺减少23.6%。SDC99钢性能提升的主要原因是深冷处理使亚稳态的块状残留奥氏体转变为马氏体及薄膜状残留奥氏体,深冷处理后残留奥氏体体积分数由常规热处理的17.2%下降至5.5%~10.5%,但并未完全转变。薄膜状残留奥氏体分布于孪晶马氏体及二次碳化物的边界处,松弛应力集中,防止微裂纹的产生,因而改善了材料的综合性能。
The hardness, impact toughness and friction and wear properties of Cr8 cold work die steel SDC99 with different cryogenic treatment processes were tested. The phase composition and microstructure were also analyzed by SEM, XRD and TEM. The results showed that the cryogenic treatment enhanced the hardness of SDC99 steel, reduced the impact toughness and improved the wear resistance. The quenching of 1030 ℃ + tempering at 210 ℃ × 2 h + (-196 ℃ × 24 h) SDC99 steel can get the best overall performance, the wear volume than the conventional heat treatment process to reduce 23.6%. The main reason for the improvement of SDC99 steel performance is that the cryogenic treatment transforms the metastable massive retained austenite into martensite and film-like retained austenite. The volume fraction of retained austenite after cryogenic treatment decreased from 17.2% of the conventional heat treatment To 5.5% ~ 10.5%, but not completely changed. Film-like residual austenite distributed in the twin martensite and secondary carbide boundaries, relaxation stress concentration, to prevent the generation of micro-cracks, thus improving the overall performance of the material.