Development of Ferritic Stainless Steel YUS 450 with High Heat Resistance for Automotive Exhaust System Components

摘要

To clean the automobiles' exhaust gases and improve fuel economy, measures have been implemented that raise exhaust-gas temperature and reduce body weight. Nippon Steel has developed a low-cost, high-heat resistant ferritic stainless steel, designated YUS 450 (14Cr-0.3Nb-0.1Ti-0.5Mo). According to the finding that adding niobium and titanium can simultaneously prolong thermal fatigue life, the most important property for exhaust manifold materials, and ensure stiffness during high-temperature service, despite thickness reduction, niobium and titanium are added in respective amounts of 0.3% and 0.1% to obtain high-temperature strength and prevent grain growth around 900℃. The chromium content is set at 14% to provide oxidation resistance at temperatures close to 900℃. According to another finding that corrosion thickness loss from hot salt damage can be reduced by a trace addition of 0.5% molybdenum. YUS 450 is superior to the conventional automotive exhaust system stainless steel SUS 430 J1L (YUS 180 with 19Cr-0.4Nb-0.4Cu) in high-temperature properties, such as thermal fatigue life and hot salt damage resistance, and can be produced at low cost by reducing the alloy content.