Ferritic stainless steel sheet with excellent thermal fatigue properties, and automotive exhaust-gas path member

Abstract

Disclosed is a ferritic stainless steel sheet with excellent thermal fatigue properties, including, by mass %, 0.03% or less of C, 1.0% or less of Si, 1.5% or less of Mn, 0.6% or less of Ni, 10˜20% of Cr, 0.05˜0.30% of Ti, 0.51˜0.65% of Nb, 0˜less than 0.10% of Mo, 0.8˜2.0% of Cu, 0˜0.10% of Al, 0.0005˜0.02% of B, 0˜0.20% of V, and 0.03% or less of N, with the balance being Fe and inevitable impurities, having a composition satisfying the following equations (1) and (2) and having a structure in which ε-Cu phase grains each having a long diameter of 0.5 μm or more are present in a density of 10 or less per 25 μm²: Nb−8(C+N)≧0 . . . (1), 10 Si+20 Mo+30 Cu+20(Ti+V)+160 Nb−(Mn+Ni)≧100 . . . (2). The ferritic stainless steel sheet, having a relatively inexpensive component composition, has excellent thermal fatigue properties, and is suitable for use in an automotive exhaust-gas path member, including an exhaust manifold, a catalyst converter, a front pipe, or a center pipe.

Description

BACKGROUND OF THE INVENTION[0001]1. Field of the Invention[0002]The present invention relates to a stainless steel sheet with excellent thermal fatigue properties, and to an automotive exhaust-gas path member using the same, and in particular, to a member that constitutes the upstream part of the exhaust-gas path and is heated to temperatures of 700° C. or higher upon the use of automobiles.[0003]2. Description of the Related Art[0004]Among automotive exhaust-gas path members, an upstream member, which is heated to 700° C. or higher during use thereof, is required to have, first of all, heat resistance in a range of high temperatures exceeding 700° C. In this regard, with the main goal of increasing high-temperature strength in the high-temperature range of 700˜1000° C., characteristic materials therefor have been developed. Further, the automotive exhaust-gas path member undergoes repeated heat cycles, including heating to the high-temperature range and cooling to room temperature,...

AI Technical Summary

Benefits of technology

[0018]According to the present invention, the thermal fatigue properties of the ferritic stainless steel sheet may be considerably improved without the use of expensive elements, including Mo. This steel sheet has a reasonable component design, which obviates the need for an excessive increase in high-temperature strength in the high-temperature range exceeding 700° C., and exhibits excellent durability in end uses, in which heating to the high-temperature range exceeding 700° C. and cooling to room tempera

Problems solved by technology

As mentioned above, however, to increase the high-temperature strength in the wide temperature range from 500° C. to 1000° C. merely depends on component designs in which specific elements are added in large amounts, undesirably resulting in increased material costs.

Moreover, forming workability is poor.

However, the present inventors have conducted intensive inve