预氧化对不同离子渗氮工艺的影响

 利用光学显微镜、显微硬度计、XRD、SEM等分析了预氧化对40CrNiMo钢离子渗氮过程的影响。结果发现:在300℃氧化1 h的40CrNiMo试样,表面生成了厚0. 4～0. 7μm、以Fe₃O₄和Fe₂O₃为主的氧化层。在随后的540℃离子渗氮过程中,当渗氮时间较短（4 h）时,试样出现渗层浅、分布不均和硬度低等缺陷;但随着渗氮时间的延长（8 h）,预氧化表现出了一定的催渗效果,同时渗层中脉状氮化物减少;当渗氮时间延长至16 h时,预氧化的催渗效果更加显著,但渗层的疏松有所增加。

Effect of pre-oxidation on different ion nitriding processes

Effect of pre-oxidation on ion nitriding process of 40 CrNiMo steel was analyzed by means of metallographic microscope,microhardness meter,XRD and SEM. The results show that after pre-oxidation at 300 ℃ for 1 h,an oxide layer with a thickness of 0. 4-0. 7 μm and mainly contains Fe3O4 and Fe2O3 is formed on the surface of the 40 CrNiMo steel. In the subsequent processs of ion nitriding at540 ℃,when the nitriding time is shorter( 4 h),the nitriding layer shows defects such as shallow infiltration,uneven distribution and low hardness. However,as the nitriding time is prolonged to 8 h,the pre-oxidation shows a certain helpful effect on nitriding,while the vein nitride in the layer decreased. Moreover,when the nitriding time is extended to 16 h,the infiltration boosting effect of pre-oxidation is more significant,but the porosity of the layer increased.