Precipitation Phenomena in Stainless Steels and Weld Metals

Abstract

As shown by the constitution diagrams which characterize metallurgical equilibrium, stainless steels possess at ambient temperature a very low solubility for carbon (see Chapter 1). Due to the high affinity of the major alloying constituent chromium towards carbon, there is a strong tendency towards carbide formation. The ranges of intermetallic phases, e.g. sigma phase, will often reach under equilibrium conditions far into the alloying ranges of stainless steels (see, for example, the iron-chromium system in Fig. 1 (page 2). Therefore we must expect the precipitation of these phases associated with the normal cooling rates experienced when working stainless steels, e.g. after rolling or forging. In most cases, however, they are undesirable because of their negative influence on both the corrosion resistance and the mechanical properties of the alloy.