Ferritic Stainless Steel for Use as Conduit Members for Emission of Automotive Exhaust Gas

Abstract

A ferritic stainless steel useful as conduit members for emission of automotive exhaust gas consists of C up to 0.03 mass %, Si up to 1.0 mass %, Mn up to 1.5 mass %, Ni up to 0.6 mass %, 10-20 mass % of Cr, Nb up to 0.50 mass %, 0.8-2.0 mass % of Cu, Al up to 0.03 mass %, 0.03-0.20 mass % of V, N up to 0.03 mass % and the balance being Fe except inevitable impurities with a provision that at least 90% of Cu contained is dissolved in a steel matrix and that Nb□8(C+N). The steel may further contain 0.05-0.30 mass % of Ti and / or 0.0005-0.02 mass % of B. Mo as an inevitable impurity is controlled to be less than 0.10 mass %. The steel has excellent formability, low-temperature toughness and weldability as well as the same heat-resistance as Nb, Mo-alloyed steel.

Description

CROSS REFERENCE TO RELATED APPLICATIONS[0001]This application is a Continuation-in-Part of co-pending U.S. patent application Ser. No. 13 / 042,542, filed on Mar. 8, 2011, which is a continuation of U.S. patent application Ser. No. 12 / 689,824 filed Jan. 19, 2010, now abandoned, which is a continuation of U.S. patent application Ser. No. 12 / 233,122 filed Sep. 18, 2008, now abandoned, which is a continuation of U.S. patent application Ser. No. 10 / 482,718 filed Jan. 2, 2004, now abandoned, which is a national phase of International Patent Application No. PCT / JP02 / 06768 filed Jul. 4, 2002, which claims priority to Japanese Patent Application No. JP 2001-204444 filed Jul. 5, 2001, all of which are incorporated herein by reference in their entirety.BACKGROUND OF THE INVENTION[0002]1. Field of the Invention[0003]The present invention relates to a ferritic stainless steel, which is excellent in heat-resistance, low-temperature toughness and weldability, useful as conduit members, e.g., exhaus...

AI Technical Summary

Benefits of technology

The present invention provides a ferritic stainless steel that can be used as conduit members for emission of exhaust gas. The steel does not contain expensive Mo, but has similar heat-resistance to Nb, Mo-alloyed steel. Additionally, the steel has excellent formability, low-temperature toughness, and weldability.

Problems solved by technology

Conduit members of automobiles for emission of exhaust gas are directly exposed to a high-temperature atmosphere containing exhaust gas during driving automobiles, and subjected to thermal stress caused by repetition of driving and stopping as well as vibration during driving.

However, poor formability and inferior low-temperature toughness are disadvantages of the Nb, Mo-alloyed steel.

Although a few reports are published on improvement of formability and low-temperature toughness, the improvement is still insufficient for the purpose.

Consumption of expensive Mo at a high ratio is also a disadvantage of the Nb, Mo-alloyed steel.

By the way, high-temperature strength (e.g., resistance to thermal fatigue failure) and high-temperature oxidation-resistance (evaluated as a critical temperature of abnormal oxidation) are not necessarily balanced at high level for some parts or members.

However, the Nb, Mo-alloyed steel is necessarily used for such a part or member with emphasis on heat-resistance regardless of poor formability, inferior low-temperature toughness and expensiveness.

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