Effect of Precipitation on Intergranular Corrosion Resistance of 430 Ferritic Stainless Steel

• Published in: Journal of iron and steel research, international international, 2015-11, Vol.22 (11), p.1062-1068
• Main Authors: HUANG, Xun-zeng, WANG, Dan, YANG, Yi-tao
• Format: Article
• Language: English
• Subjects: 430 ferritic stainless steel; Applied and Technical Physics; carbonitride extraction; double-loop electrochemical potentiokinetic reactivation; Engineering; intergranular corrosion; Machines; Manufacturing; Material; Materials Engineering; Materials Science; Metallic Materials; Physical Chemistry; precipitation; Processes; 动电位再活化; 扫描电子显微镜; 晶间腐蚀; 析出物; 能量色散谱仪; 腐蚀性能; 透射电子显微镜; 铁素体不锈钢
• ISSN: 1006-706X; 2210-3988
• DOI: 10.1016/S1006-706X(15)30113-8

With Nb-Ti-stabilized 430 ferritic stainless steel（NTS430FSS） and SUS 430 ferritic stainless steel（SUS430FSS） as experimental materials, the influence of precipitation on intergranular corrosion resistance was investigated. A series of aging treatment were carried out. The free-exposure corrosion test and double loop electrochemical potentiokinetic reactivation（DL-EPR） test with a scan rate of 1.67 m V/s at 26 °C were applied to evaluate the intergranular corrosion（IGC） resistance. Metallographic observation, scanning electron microscope（SEM）, transmission electron microscope（TEM） with energy dispersive spectroscopy（EDS） and X-ray diffraction（XRD） analysis were conducted. The results show that IGC occurred in SUS430 FSS aged above 700 °C, while it occurred in NTS430 FSS as the temperature was improved to 1 050 °C. The critical degree of sensitization Ir/Ia reaches 0.305 in SUS430 FSS, which is higher than that of NTS430 FSS, i.e. 0.010, aged at 950 °C for 2 h. The TEM, EDS and XRD results show that a large amount of Cr23C6 precipitates with size of 60 nm×22 nm are located at the SUS430 FSS grain boundaries as chains. With the addition of Nb and Ti and reduction of C, the amount of precipitates reduces significantly in NTS430 FSS. A majority of Cr23C6 were replaced by Ti C and Nb C. Only a small amount of spherical Ti C（R=186 nm） and square Ti N（312 nm×192 nm） with Nb and Cr adsorbed are left along grain boundaries. Due to the dual stabilization of Nb and Ti, the precipitation of Cr23C6 is restrained, the chromium depleted region is avoided and accordingly the resistance to the intergranular corrosion is improved.