ESSC & DUPLEX 2019

From the viewpoint of initial rust measures of the automotive exhaust system, an application of various type of ferritic stainless steel sheets is carried out. In addition, the replace from C-steel sheet to ferritic stainless steel sheet are promoted from the viewpoint of initial rust characteristics-resistant in the flange part. When the automobile is transported particularly on the sea, the initial rust at the point of appearance of the exhaust system part becomes the problem. From a result of corrosion-resistant examination for C-steel and ferritic stainless steel sheets in consideration of marine transportation, the initial rust characteristics of the 11% Cr ferritic stainless steel are extremely superior than C-steel, and the 17% Cr ferritic stainless steel is superior. However, the thick ferritic stainless steel hot-rolled steel sheets containing Ti with high Cr are have a problem in low-temperature toughness in comparison with C-steel. In this study, from particularly viewpoint of low-temperature toughness Nb-added and Nb and Mo-added 17% Cr ferritic stainless hot-rolled steel sheets have been developed with microstructure control for the exhaust pipe flange. NSSC®430R3M, Nb-added 17% Cr-Low C, N was superior to conventional Ti-added 17%Cr steel sheet in low-temperature toughness and high-temperature strength. NSSC®436LNB-M, Nb and Mo-added 17% Cr-Low C, N, for the part that or the part that the characteristics of high heat resistaince and corrosion resisitance are more necessary in the environment corresponding parts such as EGR flange. NSSC®436LNB-M was superior to conventional Ti and Mo-added 17% Cr steel sheet in low-temperature toughness and high-temperature strength. Furthermore, the low-temperature toughness of the flange part and the flange part welded to an exhaust pipe were estimated by the drop weight test because the ductile-brritle transition temperature in Charpy impact test using the specimen with V-notch may not support with the low-temperature toughness of the real flange part. In this study, the method of drop weight impact test in low-temperature for the flange part and the flange part welded to an exhaust pipe has been developed. From the results of this method, the flange parts using NSSC®430R3M and the parts welded to exhaust pipe showed superior low-temperature toughness at -40°C. Other than the characteristics mentioned above, the developed ferritic stainless hot-rolled steel sheets are superior mechanical properties, corrosion and oxidation resistances. Thanks to various types of characteristics regarding the developed steel sheets, they can be used in automobile exhaust flanges.