40Cr钢表面纳米化对气体渗氮行为的影响

Effects of surface nanocrystallization pre-treatment on gas-nitriding behavior of 40Cr steel

采用超音速微粒轰击技术对40Cr钢经调质处理后进行单面表面纳米化,使其表面形成晶粒尺寸约10nm的纳米晶层,然后对试样进行不同温度和时间的低温气体渗氮。利用金相法,硬度法和X射线衍射法对试样两面的渗氮层进行分析对比。结果表明:纳米层表面形成氮化物的温度可降至300℃左右,而在450℃时,原始粗晶面气体渗氮才形成连续的氮化物层。主要原因是表面纳米化后大量的晶界为氮原子的扩散提供了通道,同时,晶界和晶内存在的缺陷也可降低氮化物形成的氮势门槛值。

One surface of a 40Cr steel plate which was quenched and tempered was nanocrystallised using supersonic fine particles bombarding method（SFPB）,and the opposite surface was kept to the heat-treated state.The SFPBed specimens were then nitrided at different temperatures for different time.The nitriding layers on both surfaces of each specimen were analyzed with microscope,hardness tester and X-ray diffraction equipment.The results show that sound and continuous nitride layer can be formed at 300℃ on the nanocrystallized surface of the steel plate,instead of at 450℃ on the surface without nanocrystallization pre-treatment.The decrease of nitriding temperature for the nanocrystallized surface of the plate is due to the increase of grain boundary resulting in enhancing nitrogen atomic diffusion.The increased defects produced during bombing within grains and at grain boundary are also very important factor to the nitriding process because the increased defects can reduce the nitriding potential threshold.