深冷处理对H13钢组织结构和热稳定性的影响

 为了研究深冷处理对H13热作模具钢热稳定性的影响及组织演化规律,利用洛氏硬度计、X射线衍射仪、扫描电子显微镜及透射电子显微镜等对经不同热处理工艺处理后H13热作模具钢的热稳定性及显微组织进行了表征。结果表明,深冷处理促使部分残余奥氏体转变为马氏体,导致深冷处理后试验钢的硬度高于淬火态试验钢的硬度。经深冷处理后试验钢在540 ℃回火20 h过程中其硬度均比常规热处理的试验钢硬度高,深冷处理的试验钢具有更好的热稳定性。与常规热处理的试验钢相比,深冷处理促使钢中碳原子偏聚并在回火过程中以碳化物的形式析出,导致深冷处理的试验钢回火后马氏体基体中碳的质量分数降低。透射电镜结果显示,试验钢在回火过程中析出的大量弥散分布的纳米级M₂₃C₆型碳化物,经长时间回火后碳化物粗化致使试验钢硬度随着回火时间的增加而下降。

Effects of deep cryogenic treatment on microstructure and thermal stability of H13 steel

In order to study the effect of deep cryogenic treatment on the thermal stability and microstructure evolution of H13 hot work mold steel,the thermal stability and microstructure evolution of H13 hot work mold steel treated by different heat treatment processes were characterized by Rockwell hardness tester,X-ray diffractometer,scanning electron microscope and transmission electron microscope. The results show that the deep cryogenic treatment promotes the transformation of the retained austenite to martensite,which resulted in the hardness of the tested steel subjected to deep cryogenic treatment is higher than that of the quenched tested steel. In addition,after deep cryogenic treatment,the hardness of the tested steel during tempering at 540 ℃ for 20 h is higher than that of the conventional heat treatment tested steel,and the cryogenically treated tested steel has better thermal stability too. Compared with the conventional heat-treatment tested steel,the deep cryogenic treatment promotes the segregation of carbon atoms in the steel and precipitates as carbides during the tempering process,thus the carbon content in the martensite matrix after tempering of the cryogenically treated tested steel is less than the conventional heat treatment. Moreover,the results of transmission electron microscopy showed that a large number of dispersed nano-scale M₂₃C₆ carbides precipitated during the tempering process of the tested steel. After a long time of tempering,the carbide coarsening caused the hardness of the tested steel to decrease with the increase of tempering time.