PRECIPITATION AND CREEP BEHAVIOUR OF AISI TYPE 321 STEEL.

The creep strength of AISI type 321 steel is influenced by factors such as solution-treatment temperature, grain size, excess titanium content, cold work and delta-ferrite content. The excess titanium content depends not only on the amounts of titanium and carbon but also on other elements such as nitrogen, sulphur, nickel and silicon, due to the possible precipitation of TiN, Ti//4C//2S//2 and G-phase. It is shown that the current British Standard Specification of a minimum titanium content of five times the carbon content does not always guarantee excess titanium for long-term high temperature applications.