The effect of carbon and titanium on the hot workability of 25Cr-6Ni stainless steels

Abstract

A structural investigation has heen conducted to explain variations in the hot working characteristics of 25 pct Cr-6 pct Ni stainless steels over a broad range of temperatures. The difficulties in hot working flat products previously associated with a two phase ferriteaustenite structure are shown to be related to the formation of a cellular aggregate of chromium carbide and austenite at ferrite-austenite interfaces. These difficulties may be avoided in two ways. 1) Starting hot working at temperatures where the structure of the steel is substantially all ferrite. 2) Limiting the formation of the cellular aggregate of chromium carbide and austenite either by melting to carbon contents less than 0.03 pct or by adding stoichiometric amounts of a strong carbide forming element such as titanium to combine with excess carbon. This compositional control allows hot working of flat products over a broad range of starting temperatures. There appears to be no criticality in carbon control for successful hot working of bar products over the broad range of starting temperatures.