Ferritic Stainless Steel for Automotive Exhaust Systems--High Heat-Resistant Ferritic Stainless Steel with High Formability for Automotive Exhaust Manifolds: 'JFE-MH1'

摘要

The effects of Mo and Si on formability, high temperature strength, and oxidation resistance of the 15 percent Cr ferritic stainless steel were investigated in order to develop a high heat-resistant, high formability stainless steel suitable for automotive exhaust manifolds. The Mo addition displays a remarkable effect in improving oxidation resistance and high temperature strength. The Si addition is effective in improving oxidation resistance, but was found to have virtually no effect in improving high temperature strength. Based on these findings, a new Mo-added ferritic stainless steel with excellent heat resistance and formability was developed. The new steel, JFE-MHl (l5 percent Cr-0.3 percent Si-0.5 percent Nb-1.6 percent Mo), possesses the combined advantages of two existing steels (high formability type and high heat-resistant type). Specifically, JFE-MHl steel sheets and ERW tubes show form-ability equal to the values of the existing high formability stainless steel, JFE429EX (l5 percent Cr-0.9 percent Si-0.5 percent Nb), and high temperature strength, high temperature fatigue properties, and thermal fatigue properties superior to those of the existing high heat-resistant stainless steel JFE434LN2 (SUS444: 19 percent Cr-0.3 percent Si-0.3 percentNb-1.9 percent Mo).