Ferritic stainless steel for exhaust gas passage member

Abstract

Provided is a stainless steel for exhaust gas path members, which has a composition including, in terms of % by mass, at most 0.03 % of C, at most 1 % of Si, at most 1.5 % of Mn, at most 0.6 % of Ni, from 10 to 20 % of Cr, from more than 0.5 to 0.7 % of Nb, from 0.05 to 0.3 % of Ti, from more than 1 to 2 % of Cu, at most 0.2 % of V, at most 0.03 % of N, from 0.0005 to 0.02 % of B, and optionally at most 0.1 % of Al, and further optionally at least one of Mo, W, Zr and Co in an amount of at most 4 % in total, with a balance of Fe and inevitable impurities, and which has a texture where the Cu phase and the Nb compound phase having a major diameter of at least 0.5 [mu]m are controlled to be in an amount of at most 10 grains / 25 [mu]m 2 each. The stainless steel exhibits excellent thermal fatigue resistance when applied to exhaust gas path members of both cases where the maximum ultimate temperature is high and low, and has excellent low-temperature toughness.

Description

[0001] This application is a divisional application of an invention patent application with an application date of January 31, 2008, an application number of 200880003793.5, and an invention title of "ferritic stainless steel for exhaust passage components". technical field [0002] The present invention relates to ferritic stainless steel used for exhaust passage components represented by exhaust manifolds, catalytic converter cases (casings), front pipes, and center pipes, and automobile exhaust passage components using them. Background technique [0003] Exhaust passage components such as exhaust manifolds, catalytic converter housings, front pipes, center pipes, etc. are mostly made of SUS444 series materials with good heat resistance. Also, Patent Documents 1 and 2 disclose ferritic stainless steel to which about 1 to 2% by mass of Cu is added as a material for improving high temperature oxidation resistance and high temperature strength in a high temperature range excee...

AI Technical Summary

Problems solved by technology

However, according to detailed investigations by the present inventors, the thermal fatigue properties of the Cu-containing steels of Patent Documents 1 and 2 are good when the maximum attainable temperature is high (for example, 200 to 900° C.). The thermal fatigue characteristics under high temperature conditions (such as 200-750°C) are sometimes slightly worse than those of SUS444 series materials

Therefore, the steels of Patent Documents 1 and 2 are advantageous for applications to vehicles equipped with high-output engines with high exhaust temperatures, but are not suitable for applications to vehicles equipped with small engines with relatively low exhaust temperatures.

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