一种新型盐浴渗氮工艺对K55钢耐蚀性的影响

采用一种新型盐浴对K55石油管线钢进行盐浴渗氮处理,研究了渗层的截面形貌,显微硬度在不同渗层深度上的分布及渗层的耐硫腐蚀性。K55钢经560℃盐浴渗氮处理2h后,表层组织由疏松层、渗氮层及基体扩散层组成。渗层和表面的氧化疏松薄层的厚度分别约为12.48μm和1.54μm,渗层的总深度约为30μm。经渗氮处理的K55钢,其显微硬度明显提高,表面的显微硬度高达695HV,但显微硬度沿渗层深度方向急剧下降。渗氮处理后,K55钢的耐硫腐蚀性能得到明显改善。因此,可利用盐浴渗氮处理来降低油管下井前的腐蚀缺陷。

Effect of a novel salt bath nitriding process on corrosion resistance of K55 steel

K55 pipeline steel was treated by a novel salt bath nitriding process,the cross-sectional morphology,microhardness distribution along the depth direction,and sulfur corrosion resistance of the nitriding layer were studied.The K55 steel nitrided in salt bath at 560℃ for 2 h consists of three layers including loose layer,nitriding layer,and diffusion layer of substrate.The thickness is 12.48μm for the nitriding layer and 1.54μm for the external thin loose oxidation layer.The total penetration depth of nitriding layer is about 30μm.The microhardness of K55 steel is improved remarkably after nitriding and up to 695 HV at the surface,but decreased sharply with increasing penetration depth.The corrosion resistance of K55 steel to sulfur is improved markedly after nitriding.Salt bath nitriding can be used to reduce the corrosion defects of pipelines before their application in oil wells.