Duplex stainless steel alloy and use of this alloy

Abstract

The present invention relates to a duplex stainless steel alloy containing in weight-%: C max 0.03%, Si<0.30%, Mn 0-3.0%, P max 0.030%, S max 0.050%, Cr 25-29%, Ni 5-9%, Mo 4.5-8%, W 0-3%, Cu 0-2%, Co 0-3%, Ti 0-2%, Al 0-0.05%, B 0-0.01%, Ca 0-0.01%, and N 0.35-0.60%, balance Fe and normal occurring impurities, wherein the ferrite content is 30-70 volume-%, and wherein each weight-% of Mo above may optionally be replaced by two (2) weight-% W.

Description

TECHNICAL FIELD OF THE INVENTION[0001]The present invention relates to a duplex stainless steel alloy, which is a steel alloy having a ferritic-austenitic matrix and especially high resistance to corrosion in combination with good structural stability and hotworkability. The ferrite content is 30-70 volume-% and such steel alloys have a well balanced composition, which imparts the material corrosion properties, which make it suitable for use in for instance chloride-containing environments, such as in the sea.BACKGROUND OF THE INVENTION AND PRIOR ART[0002]Over the recent years, the environments in which corrosion resistant metallic materials were used became more aggressive and the requirements on the corrosion properties as well as on their mechanical properties increased. Duplex steel alloys, which were established as an alternative to other steel grades used until then, for example high alloyed austenitic steels, nickel-base alloys or other high alloyed steels, were also a part o...

AI Technical Summary

Benefits of technology

[0010]The object of the present invention is to provide a duplex stainless steel alloy of the type defined above and especially in the European patent 0 683 241, which has improved properties, especially ductility and toughness, with respect to such an alloy already known while maintaining at least similar levels of corrosion resistance as such an alloy. The alloy should have a good hotworkability.

[0012]It has been found that a duplex stainless steel alloy with this composition has especially an increased ductility and toughness with respect to the alloy according to EP 0 683 241, and it has also an increased corrosion resistance. By reducing the Si content to be below 0.30 weight-% a significant reduction in sigma phase precipitation is achieved, which is the key to the increased ductility and toughness of the steel alloy according to the invention. Thus, it has been found that when using a comparatively high content of Mo it is highly efficient to reduce the content of Si for reducing the risk for intermetallic precipitations.

[0013]According to an embodiment of the invention the content of Si is max 0.25 weight-%, which makes the steel alloy even less prone to sigma-formation for increasing the ductility and toughness of the material. It is expected that the same would be valid if Molybdenum would be partly or entirely replaced by Tungsten.

Problems solved by technology

However, this alloy as well as the alloys discussed above is highly susceptible to intermetallic precipitation, especially sigma phase precipitation, which makes the material hard and brittle.

Accordingly, the production of a material with good ductility by use of the duplex stainless steel alloy according to EP 0 683 241 is made very difficult.

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