Ferritic Stainless steel material for automobile exhaust gas passage components

Abstract

To provide a ferritic stainless steel material for automobile exhaust gas passage components usable in a high-temperature range over 900° C. and even over 950° C. The ferritic stainless steel material has excellent heat resistance and low-temperature toughness and has a composition comprising, in terms of % by mass, at most 0.03% of C, at most 1% of Si, from 0.6 to 2% of Mn, at most 3% of Ni, from 10 to 25% of Cr, from 0.3 to 0.7% of Nb, from more than 1 to 2% of Cu, from 1 to 2.5% of Mo, from 1 to 2.5% of W, at most 0.15% of Al, from 0.03 to 0.2% of V, and at most 0.03% of N, and optionally containing any of B, Co, W, Ti, Zr, REM and Ca with a balance of Fe and inevitable impurities, and the composition satisfies restrictive formulae 1.2Nb+5Mo+6Cu≧11.5 and 15Nb+2Mo+0.5Cu≧10.5. The steel material has a texture where the total amount of Nb and Mo existing as a precipitation phase is at most 0.2% by mass.

Description

BACKGROUND OF THE INVENTION[0001]The present invention relates to a ferritic stainless steel material for use as automobile exhaust gas passage components, in particular to a ferritic stainless steel material for use as automobile exhaust gas passage components, which has excellent heat resistance and low-temperature toughness favorable for exhaust gas upstream passage components where the material temperature may be over 900° C. or further over 950° C., for example, exhaust manifolds, catalyst converters, front pipes and the like.[0002]Heretofore, two typical ferritic steel species are used properly for automobile exhaust gas passage components, depending on the service temperature range of the components. One is a steel species such as typically SUS429 steel mainly applied to the components of which the maximum ultimate temperature of the material may be on a level of 750° C.; and the other is a steel species such as typically SUS444 steel mainly applied to the components of which...

AI Technical Summary

Benefits of technology

[0019]An object of the present invention is to provide a ferritic stainless steel material for automobile exhaust gas passage components, which simultaneously satisfies 0.2% yield strength at high temperature of 1000° C., thermal fatigue resistance, low-temperature toughness and workability all on a high level and which, even when used under the condition where the material temperature actually reaches a high-temperature range of higher than 900° C. and even higher than 950° C., still exhibits excellent durability.

[0024]According to the invention, there is provided a ferritic stainless steel material for automobile exhaust gas passage components, which satisfies all the requirements of high-temperature strength durable to exposure to high temperature of 1000° C., good thermal fatigue resistance, good workability and good low-temperature toughness. The material meets the recent tendency in the art toward elevated exhaust gas temperatures and brings about an broadened latitude in planning exhaust gas passage upstream components.

Problems solved by technology

With the increase in various devices to be fitted in an engine room, the limitation to the housing space for exhaust gas components is increasing more than before.

However, this has no description relating to 0.2% yield strength, and in this, the measures for sufficiently securing the durability in a case where the material temperature has actually risen up to 1000° C. or so could not be said to be always satisfactory.

However, this shows nothing relating to 0.2% yield strength, and in this, it is not certain as to whether or not the material could be actually durable to exposure to about 1000° C. or so.

However, there is taken no intention of improving the high-temperature strength of the material in a temperature range of about 1000° C. or so.