Effect of tungsten additions on simulated heat affected zone toughness in 25%Cr base super duplex stainless steels

Abstract

The effect of partial replacement of molybdenum with tungsten in 25%Cr base super duplex stainless steels on simulated heat affected zone (HAZ) properties was investigated using (wt-%) Fe-25Cr-3Mc-7Ni-0.25N, Fe-25 Cr-2Mo-7Ni-0.25N-2W and Fe-25Cr-1.5Mo-7Ni-0.25N-3W alloys. Substitution of tungsten for molybdenum produced enhanced impact toughness for all selected cooling conditions as a result of increased austenite content, decreased intragranular precipitation, and smaller ferrite grain size. All simulated alloys exhibited a dea ease in toughness after fast cooling owing to a higher amount of ferrite and intragranular precipitation. Impact toughness also decreased at slow cooling because of the large ferrite grain size, despite a high austenite content. The peak impact toughness was observed at optimum cooling times of 33 and 171 s for all alloys. It is concluded that the addition of tungsten has a favourable effect on HAZ properties of 25%Cr base super duplex stainless steels. (C) 1998 The Institute of Materials.