预氮化对Cr-Co-Mo-Ni轴承钢渗碳层组织和性能的影响

化学热处理工艺对轴承钢的服役性能具有重要影响。研究了预氮化工艺对新型Cr-Co-Mo-Ni轴承钢渗碳层组织和性能的影响规律。结果表明,经预氮化处理的渗碳层组织可划分为析出物和针状马氏体区,析出物、针状马氏体和板条马氏体混合区,以及析出物和板条马氏体区,且在原渗氮形成的白亮层位置有数量较多的微小孔洞出现。预氮化全工艺试样表层含铬碳化物析出较少,随渗层深度的增加,次表层析出较多的含铬碳化物且尺寸较大。相较于仅渗碳试样,在表层相同位置,经预氮化处理的试样在回火后,析出物的尺寸更细小。预氮化能够提高渗碳效率,增加渗层硬度,在全工艺试样渗层深度为0.12~0.82 mm,预氮化试样的硬度高于仅渗碳试样,且经渗后热处理的硬度增加程度也显著高于仅渗碳试样。

Effect of preliminary nitriding treatment on microstructure and mechanical properties of carburized layer of Cr-Co-Mo-Ni bearing steel

The process of chemical heat treatment has an important influence on the service performance of bearing steel. Microstructure and mechanical properties of carburized layer of a novel Cr-Co-Mo-Ni bearing steel after preliminary nitriding treatment were investigated. The results show that after preliminary nitriding treatment, the carburized layer can be differentiated as mixed region of precipitates and acicular martensite, mixed region of acicular martensite, lath martensite and precipitates, as well as mixed region of precipitates and lath martensite. A large number of tiny pores were found at the position which was original white light layer formed by nitriding. Less Cr carbides precipitated at the surface layer of the sample during the whole process of preliminary nitriding treatment. With the increase of the depth of the carburized layer, more Cr carbides with largr size precipitated at the subsurface layer. Compared with samples carburizing only, the size of precipitates after tempering was smaller in the preliminary nitriding treatment samples at the same surface position. The preliminary nitriding treatment can improve carburizing efficiency and increase the hardness of carburized layer. The hardness of the preliminary nitriding treatment sample is higher than that with carburizing only from 0.12 to 0.82 mm at carburized layer. The improvement of hardness of heat treatment after carburizing is also significantly higher than that with carburizing only.