Mathematical Approach to #sigma# Phase Precipitation in Austenitic Stainless Steel Welds

摘要

The precipitation behavior of the sigma phase was studied for 8 kinds of austenitic stainless steel weld metals. The obtained results indicate: (1) the sigma phase replaces delta-ferrite in the welds during aging. (2) The sigma formation rate dx/dt in the temperature range 723-1023 K is expressed as follows:dx/dt=H(x_f-x)~2/x_f=H(y-y_f)~2/(l-y_f)X_f-X=X_f/(l+Ht), y-y_t=(1-y_f)/(l +Ht), H=H_0 exp (-Q/RT)where x and y are the ratios of the sigma-phase content and the untransformed ferrite content to the initial ferrite content at aging time 1; X_f and y_f are the x and they after aging for a long time such as 36 Ms; and H is the rate constant. (3) The values of activation energy Q are about 170 kJ/mol for 20Cr-10Ni steels and 220 kJ/mol for 20Cr-10Ni-2Mo or -lNb steels and 30Cr-9Ni steel.