Development of High-Heat-Resistant High-Nitrogen Containing Austenitic Stainless Steel for Exhaust Gasket

SUS301-EH is widely used as a material for exhaust system gaskets, however, at temperatures in excess of 400°C, it can not be used as gas-seal ability of the material declines due to its reduced hardness. The following methods were found to be effective in controlling the softening of stainless steel at high temperatures: (1) The addition of a nitrogen component; (2) Stabilization of the austenite structure; (3) The addition of a molybdenum component. The addition of 0.5% nitrogen to austenitic stainless steel containing molybdenum has enabled the speed of softening at high temperatures to be significantly reduced, due to strain aging by solid nitrogen below 600°C and the combined effects of precipitation hardening and control of growth of recrystallized grains through the precipitation of fine Cr₂N on the dislocations and the grain boundary above 600°C. A high-heat-resistant spring material has been developed which shows no reduction in hardness up to at 600°C, which is higher by 200°C or more compared to conventional materials. The application of this material to exhaust gaskets has enabled the achievement of excellent seal performance even in tightened sections in high-temperature environments of 400°C and above, which was problematic for conventional gasket materials.