42CrMo钢零件的气体渗氮

Gas Nitriding of 42CrMo Steel Parts

42CrMo钢制小件内齿圈和小齿轮需进行气体渗氮，要求的表面硬度和渗层深度分别为≥550HV1、0．2～0．4mm和≥600HVl、≥0．25mm。对这两种零件采用两段工艺进行了渗氮，即515℃×6h、分解率20％和515℃×11h、分解率40％。结果，表面硬度和渗层深度均未达到要求。随后进行了补渗处理，工艺为515℃×6h、分解率20％和515℃×6h、分解率40％，结果表面硬度和渗层深度达到了要求。

Two types of small-scale part made of 42CrMo steel, i.e., inner rim and pinion, have to be gas nitrided to surface hardness of not less than 550 HV1 and case depth of 0.2 to 0.4 mm for the former, and to surface hardness of not less than 600 HV1 and case depth of not less than 0.25 mm for the latter. These parts were double- stage nitrided at 515 ℃ for 6 h with 20% dissociation, then at 515 ℃ for 11 h with 40% dissociation. As a result, both the surface hardness and the case depth of the parts are failure to conform with the requirements. Subsequently, both the inner rim and the pinion were again nitrided at 515 ℃ for 6 h with 20% dissociation, then at 515 ℃ for 6 h with 40% dissociation, with these parts obtaining desirable surface hardness and case depth.