Duplex stainless steel and cast article thereof

Abstract

A generally Mo-free, ferrite-austenite duplex stainless steel has a ferrite phase area ratio of about 20 to about 60% and a composition containing, in mass %, not more than about 0.08% of C, about 0.5 to about 1.5% of Si, not more than about 1.0% of Mn, about 4.0 to about 8.0% of Ni, about 23 to about 27% of Cr, about 2.0 to about 6.0% of Cu, about 0.05 to about 0.3% of N, and the balance being Fe and generally unavoidable impurities.

Description

CROSS-REFERENCE TO RELATED APPLICATIONS[0001]This application claims foreign priority benefits under 35 USC § 119(a)-(d) from Japanese Patent Application No. 2007-012845, filed on Jan. 23, 2007, which is hereby incorporated by reference in its entirety.BACKGROUND OF THE INVENTION[0002]1. Field of the Invention[0003]The present invention generally relates to a duplex stainless steel having a ferrite phase and an austenite phase and also relates to a cast article of the duplex stainless steel.[0004]2. Description of the Related Art[0005]A two-phase stainless steel having a ferrite phase and an austenite phase, also referred to as duplex stainless steel, is now used as a raw material of various members because of its excellent corrosion resistance.[0006]JP-B-3270498 proposes a two-phase stainless steel for a large-sized article. The proposed stainless steel is composed of up to 0.02 mass % of C, up to 2.0 mass % of Si, up to 2.0 mass % of Mn, up to 0.04 mass % of P, up to 0.04 mass % o...

AI Technical Summary

Benefits of technology

The present invention provides a duplex stainless steel that is free of Mo, uses a reduced number of elements, and shows satisfactory mechanical strength and corrosion resistance. The duplex stainless steel has a wide temperature range over which the melt has suitable fluidity for easily producing cast articles with thinner portions. The duplex stainless steel has a melting point of not higher than about 1,450° C and is used as a casting material for cast articles, such as propeller blades for small watercrafts.

Problems solved by technology

However, Mo is not only expensive but also tends to adversely affect mechanical properties, such as toughness of the stainless steel, as the content thereof increases.

When the difference between the pouring temperature and the melting point of the stainless steel is small, therefore, the melt cannot flow sufficiently into the thinner portion forming section.

This is likely to cause defects, such as incomplete filling, in the cast product.

If the pouring temperature is increased to ensure a sufficient difference from the melting point to reduce the likelihood of incomplete filling, then the temperature of the melt introduced into the mold will be also increased correspondingly, resulting in application of a great thermal load to the mold and generation of a gas during casting operation.

The use of such a high temperature melt is therefore disadvantageous.

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