Q235钢密封罐法稀土催渗氮化层的组织与耐蚀性能

针对常规气体渗氮工艺氮原子扩散速度慢的问题,采用密封罐法,以尿素为渗氮剂、稀土做催渗剂,对Q235钢进行570 ℃×4 h渗氮实验.利用金相显微镜、X射线衍射仪和电化学工作站,研究分别加入1、3和5 mL稀土时,渗氮层的组织和耐蚀性能.结果表明：稀土催渗能增加渗氮层中白亮层厚度,并明显改善氮化层的耐蚀性能.但稀土加入较多达5 mL时,组织开始疏松,加3 mL稀土时白亮层组织致密,耐蚀性能较佳.Q235钢渗氮层主要由ε-Fe3N相和γ ＇-Fe4N相组成,与常规氮化相比,加稀土催渗后,氮化层中ε相数量增加.密封罐法可以实现Q235钢的快速渗氮,在尿素渗剂中加入稀土后能明显增加渗氮层厚度,并改善耐蚀性能.

Microstructure and corrosion resistance of RE catalytic nitriding layer of Q235 steel using seal pot method

This paper introduces the seal pot method as an alternative to conventional gas nitriding technology with an inherent drawback, such as a slower diffusion of nitrogen atom. This alternative works better for 570 ℃ × 4 h nitriding experiment on Q235 steel, using the ureophil as the nitriding agent and the rare earth as the catalytic agent. The paper goes further into describing the use of the metallographic microscope, X-ray diffractermeter and electrochemical workstation to investigate the microstrueture and the corrosion resistance performance of the nitriding layer by adding 1,3, and 5 mL rare earth, respec- tively. The results show that despite the ability of the rare earth to give an increased thickness of the white layer in the nitriding layer and a significantly improved corrosion resistance performance, the addi- tion of the rare earth up to 5 mL tends to leave the microstrueture loose and the addition of 3 mL rare earth would likely afford a denser microstrueture of the white layer and a better corrosion resistance. The nitriding layer of Q235 steel composed mainly of e-Fe3N phase and γ＇-FenN phase shows a greater a- mount of e phase than does normal nitriding after the addition of the rare earth. The seal pot method ca- pable of a more rapid nitriding of Q235 steel enables an obviously increased thickness of the nitriding lay- er and a significantly improved corrosion resistance performance due to the addition of rare earth in the ni- triding medium.