Stainless steel sheet for exhaust system part use excellent in intermittent oxidation characteristic and exhaust system part

Abstract

A stainless steel sheet free of surface flaws, having an enhanced high temperature strength and corrosion resistance, not becoming brittle at a high temperature, and further exhibiting a high oxidation resistance enabling it to be suitably used as an inside pipe of a double pipe of an exhaust manifold, a turbocharger part, and other automobile exhaust system parts, which stainless steel sheet has a predetermined composition of chemical components and satisfies Cr+20Mo≧24.0%, and Si+20C+15N≧5.8%. Further, an automobile exhaust system part, excellent in both the oxidation resistances of the base material and weld zone using the above stainless steel sheet, having a gradient of change of sheet thickness between the weld metal and the base material of the above stainless steel sheet of 15 degrees or less.

Description

TECHNICAL FIELD[0001]The present invention relates to a heat resistant stainless steel sheet excellent in intermittent oxidation characteristic and to an exhaust system part. The exhaust system part of the present invention is particularly preferable as a part used in an environment where it is repeatedly heated to a high temperature of 1000° C. or more such as an exhaust manifold or turbocharger part of an automobile engine.BACKGROUND ART[0002]Materials used for the exhaust system parts of automobiles require high thermal fatigue characteristics and are being demanded to be excellent in oxidation resistance and resistance to peeling of oxide scale at a high temperature since the parts are exposed to a high temperature exhaust gas atmosphere and are repeatedly heated and cooled. For example, in the past, SUH409, SUS429, SUS430J1L, SUS436L, SUS444, and other ferritic stainless steels have been used for exhaust manifolds, front pipes, and converter shells. This is because these steels...

AI Technical Summary

Benefits of technology

The present invention improves the oxidation resistance of a stainless steel sheet used in exhaust system parts, making the parts thinner and lighter. This results in better fuel economy for automobiles and reduces surface flaws during production.

Problems solved by technology

These are more expensive compared with ferritic stainless steel.

However, there was the problem that at a temperature over 900° C., with ferritic stainless steel, the strength is insufficient, while with austenitic stainless steel, there is a problem with thermal fatigue and scale peeling and therefore neither can be used.

PLT 2 discloses a material comprised of the ferritic stainless steel SUS444 to which Mo or Nb, Cu, W, etc. is further added to raise the high temperature strength and secure heat resistance at 950° C. However, there was a problem with the workability and manufacturability at room temperature.

There was also a problem when working the steel into complicated shapes such as an exhaust manifold.

Further, there was a problem with sheet breakage etc. when producing sheet.

On the other hand, when applying austenitic stainless steel, there is no problem in terms of strength, but there is a large problem with thermal fatigue.

However, there were the problems that it was difficult to obtain the sheet thickness required for automobile exhaust system parts by hot rolling and the required precision of sheet thickness could not be obtained.

Such a double structure part is expensive but is frequently used in an exhaust manifold where the exhaust gas temperature is 1000° C. or less.

However, these approaches lose effect and a sufficient heat resistance cannot be obtained if the exhaust gas temperature rises to a temperature over 1000° C. For this reason, an exhaust system part having a heat resistance in a 1000° C. or more exhaust gas environment has been sought.

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