预氧化对密封罐法制备40Cr钢渗氮层组织和性能的影响

Effect of pre-oxidation on microstructure and properties of the nitrided layer of 40Cr steel prepared by seal pot method

通过光学显微镜、X射线衍射仪、洛氏硬度计、摩擦磨损试验机和电化学工作站研究了预氧化温度对40Cr钢渗氮层的组织、硬度、耐磨和耐蚀性能的影响。40Cr钢渗氮前分别在350、400和450℃进行预氧化30 min,随后采用密封钢罐法对40Cr钢渗氮处理,渗氮工艺为600℃×4 h。结果表明:在400~450℃预氧化30 min具有显著的催渗作用,此时渗氮层厚度较厚,达到100~140μm,渗层组织由ε-Fe3N和γ’-Fe4N相组成。此时,40Cr钢渗氮层硬度和耐磨性能明显改善,硬度高达74. 96~76. 80 HRC,摩擦磨损质量损失较小,摩擦因数也较小,在0. 35~0. 65之间波动;400℃预氧化后渗氮层耐腐蚀性能略有改善;450℃时自腐蚀电位显著增大,达到-0. 026 V,但自腐蚀电流密度略有增加。

Effect of pre-oxidation temperature on the microstructure,hardness,wear-resisting property and corrosion resistance of the nitrided layer on 40 Cr steel were studied by optical microscope,X-ray diffractometer,Rockwell hardness tester,friction wear testing machine and the electrochemical workstation.After pre-oxidizing at 350,400,450℃for 30 min,respectively,40 Cr steel was nitridied at 600℃for 4 h by using seal pot method.The results show that pre-oxidation at 400-450℃has a significant catalyst effect on nitriding,resulting in the thicker nitrided layer up to 100-140μm,and the microstructure of nitrided layer consists ofε-Fe3N andγ’-Fe4N phase.At the same time,the hardness and the wear-resisting property are improved obviously,the hardness is up to 74.96-76.80 HRC,with less mass loss and with smaller friction coefficient in the range of 0.35-0.65.The corrosion resistance of the nitrided layer with 400℃pre-oxidation has a slight improvement,and when pre-oxidated at 450℃,the corrosion potential Ecorr increases significantly to-0.026 V,but the corrosion current density icorr increases slightly.