The thermal stability and microstructure evolution of a new die casting steel containing 1％(mass fraction)nickel and without nickel were comparatively studied.Two kinds of steels were quenched in the same process,following by several times of tempering to achieve similar hardness.The thermal stability experiment of the materials was carried out at 600 ℃.SEM(scanning electron microscopy)and TEM(transmission electron microscopy)were employed to compare the microstructure evolution of the two materials during the thermal stability test,in order to explore the effect of Ni on microstructure of the material.The results showed that in the process of austenitizing,Ni retarded the dissolution of carbides,and the undissolved carbides at the grain boundaries prevented the growth of the austenite effectively,so that the quenching temperature could be increased.When quenched at the same temperature,the carbides in SDYZ1 could not dissolve in the matrix adequately,which reduced the precipitation strengthening effect of secondary carbides,and then resulting in a sharp decline of the hardness in the early stage of the thermal stability experiment.The advantage of Ni to improve the thermal stability of the material may need to be reflected at a much higher quenching temperature.%对比研究了含镍1％(质量分数)和不含镍的新型压铸模具钢的热稳定性能及微观组织演变情况.两种材料采取相同的淬火工艺,再经多次回火达到相似的硬度,然后于600 ℃进行热稳定性实验,并采用SEM(扫描电子显微镜)和TEM(透射电子显微镜)对比分析了两种材料的淬火态及热稳过程中的微观组织的变化情况,探索了Ni元素的添加对材料热稳定性的影响.实验结果表明:Ni元素能够阻碍碳化物向基体中溶解,未溶的碳化物颗粒在晶界处能有效阻止原始奥氏体的长大,从而使材料允许的淬火加热温度提高.在相同的淬火条件下,Ni使得SDYZ1钢中的碳化物无法充分地固溶于基体,因而在回火过程中减弱了二次碳化物的析出强化效果,导致在热稳前期SDYZ1钢的硬度降低较快;Ni提高材料热稳定性能的优势可能需要在较高淬火温度下才能体现.
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