1996 Volume 45 Issue 2 Pages 90-96
Austenitic/ferritic duplex stainless steels, which contain 22-25% Cr-3%Mo-5-7%Ni-0.15%N, show excellent corrosion resistance in many corrosive environments. When duplex stainless steels were heat-treated, Cr carbo-nitride which was Cr nitride including C was formed. In this paper, effect of Cr carbo-nitride on corrosion resistance of duplex stainless steels was studied. Cr carbo-nitride affected intergranular corrosion resistance of duplex stainless steels in the Huey and the Streicher tests. Cr depleted zone formed with Cr carbo-nitride will lead to intergranular corrosion in such tests. In the Huey test, sigma phase behave as protective even when a large quantity of Cr carbo-nitride precipitated. Cr carbo-nitride did not affect intergranular corrosion resistance in the Strauss test and general corrosion resistance. On the other hand, Cr carbo-nitride a little affected pitting corrosion resistance. As a result, the Streicher test was the most sensitive method in detecting Cr carbo-nitride. Reducing C, Si, Mn, P and S of duplex stainless steels lead to prevention of Cr carbo-nitride precipitation and improve intergranular corrosion resistance of heat-treated materials.
