Toyota Jidosha Kabushiki Kaisha

Nippon Steel & Sumikin Stainless Steel Corporation

Yasuhisa Tanaka

Masao Kikuchi

Yoshiharu Inoue

Haruhiko Kajimura

Nobuhiko Hiraide

Yosuke Sumi

A ferrite stainless steel for an automobile exhaust system member superior in thermal fatigue strength comprised of, by wt %, C: 0.020% or less, Si: 0.02 to 0.15%, Mn: 0.05 to 0.20%, P: 0.040% or less, S: 0.010% or less, Al: 0.005 to 0.10%, N: 0.020% or less, Cr: 15 to 18%, Mo: 1.5 to 2.0%, Ti: 3&#xd7;(C+N) to 0.25%, Nb: 0.4 to 0.8%, B: 0.0003 to 0.0050%, the C and N satisfying the relationship of C+N: 0.030% or less, and the Al, Si, and Mn satisfying the relationship of Al&#xd7;(Si+Mn): 0.001 to 0.020, and a balance of Fe and unavoidable impurities. The 0.2% proof stress at 900&#xb0; C. before heat treatment in the atmosphere at 900&#xb0; C. for 300 hours is at least 15 MPa, and a difference of the 0.2% proof stress before and after the heat treatment is not more than 5 MPa.

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Yasuhisa Tanaka