304奥氏体不锈钢低温盐浴渗氮处理

Low temperature salt bath nitriding of 304austenitic stainless steel

采用430℃低温盐浴对304奥氏体不锈钢进行渗氮处理,研究了渗氮时间对渗氮层组织和性能的影响。利用XRD衍射仪、光学显微镜、表面显微硬度计和带能谱仪(EDS)的扫描电镜(SEM)分别分析渗氮层的相组成、厚度、表面硬度和显微组织。结果表明:304奥氏体不锈钢在430℃渗氮不同时间后,渗氮层厚度和表面硬度都随着时间的延长而增加。渗氮时间为1 h时,渗氮层仅为单一的S相,随着渗氮时间的增加,渗氮8 h时开始有少量CrN生成,渗氮16 h时,渗氮层由大量CrN+S相两相混合。用电化学极化的方法评价耐蚀性能的结果表明:盐浴渗氮处理后耐Cl-点蚀性能得到了一定的改善,在430℃渗氮4 h,其耐蚀性能是最好的,优于没经过渗氮的试样,而在所有的渗氮试样中,渗氮8 h、16 h的试样耐点蚀性能较差。

A 304 austenitic stainless steel was nitrided in salt bath at 430 ℃ for different time, and the effects of nitriding time on mierostructure and properties of the nitrided layers were investigated. The phase components, thickness, microhardness and microstructure of the nitrided layers were examined by X-ray diffraction （ XRD ） , optical microscopy, hardness test and scanning electron microscopy （SEM） , respectively. The results show that thickness and hardness of the nitride layers increase with increasing nitriding time. The nitrided layer only contains a single S phase after nitriding for 1 h, and CrN appears in the nitride layer after nitriding for 8 h. With prolonging treating time over 16 h, the nitrided layer is composed of S phase and CrN. Corrosion resistance of the nitrided layers was evaluated by potentiodynamic polarization tests, and the results indicate that the nitriding treatment improves the pitting corrosion resistance of stainless steel. When nitriding time is 4 h, the sample exnibits better corrosion resistance than untreated sample. With prolonging nitriding time over 8 h,the corrosion property of the nitrided sample deteriorates.