气体渗氮及后续回火工艺对2Cr13钢渗氮层的影响

利用X射线衍射仪、扫描电镜、透射电镜、维氏显微硬度计、摩擦实验机、弯曲实验和浸泡腐蚀实验探究了气体渗氮工艺对2Cr13钢渗氮层的微观组织结构和性能的影响.结果表明：随渗氮温度、时间的增加，渗氮层的总厚度增加，但是表面疏松层也增加.500 ℃渗氮的扩散层组织主要由含有大量位错及位错胞的马氏体和高密度的纳米CrN析出相组成；纳米CrN析出相弥散分布在晶内和位错胞的界面上，位错胞界面上的CrN颗粒数量多且尺寸略大；板条马氏体晶界析出了ε-Fe2-3N或者(Cr,Fe)2N析出相.当渗氮温度升高至550 ℃时，马氏体本身发生了回复，CrN以薄片形式析出，使扩散层组织呈现为由α-Fe和CrN组成的片状珠光体形态.2Cr13钢气体渗氮表面硬度随渗氮温度的升高先升高后下降，在500 ℃达到峰值硬度(1 274 HV0.5).450 ℃ 和 500 ℃渗氮扩散层的硬度可高达1 300 HV0.1以上，但是随渗氮温度进一步升高而明显降低.500 ℃/5 h气体渗氮可同时提高2Cr13钢的耐磨性和抗腐蚀性，但是其弯曲韧性降低.500 ℃渗氮的2Cr13钢试样，不管是水冷还是空冷，或者再进行420 ℃回火2 h处理，其扩散层组织均没有大的改变，因此其硬度没有明显变化，均维持在1 000 HV0.1以上.
The effect of gas nitriding and subsequent ageing on the microstructure and properties of 2Cr13 steel was investigated using X-ray diffractometer, scanning electron microscope, transmission electron microscope, microhardness tester, wear tester, bend test and immersion corrosion test. It was found that with the increase of nitriding temperature and time, both of the thickness of nitrided layers and surface porous layer increased. The diffusion layers of the sample nitrided at 500 ℃ mainly consisted of martensite, a large amount of dislocation and dislocation cell structure, as well as a large amount of CrN nano-precipitates. The CrN nano-precipitates dispersedly distributed in the interior of grains and at the boundaries of dislocation cells, and the CrN nano-precipitates at the boundaries of dislocation cell were denser and larger than those in the grain interior. Further, a large amount of ε-Fe2-3 N or (Cr,Fe)2N were precipitated in the grain boundaries of lath martensite. When the nitriding temperature increased up to 550 ℃, the martensite recovered itself, and the CrN precipitates lined up to form CrN lamellas. The microstructure of the diffusion layers was also transformed into the lamellar pearlite that consists of the α-Fe matrix and CrN phase. The surface hardness of nitrided samples first increased and then declined with the increase of nitriding temperature, where the peak hardness (1 274 HV0.5) reached at 500 ℃. On the other hand, the hardness of diffusion layers formed between 450 ℃ and 500 ℃ was greater than 1 300 HV0.1, and obviously decreased with the nitriding temperature. The wear resistance and corrosion resistance of 2Cr13 steel were improved after nitriding at 500 ℃ for 5 h, but the bend toughness decreased. No matter water cooling or air cooling or subsequent tempering of 420 ℃ for 2 h was applied, the variance of the microstructure at the diffusion layers of 2Cr13 steel nitrided at 500 ℃ was limited, and their hardness was also not changed obviously and was still greater than 1 000