AGING AND CRACKING OF SIMULATED HEAT-AFFECTED ZONES IN 321-STAINLESS-STEEL

The heat affected zone (HAZ) of stabilised austenitic stainless steel welds may exhibit a serious form of intercrystalline cracking during s ervice at high temperature. This type of embrittlement, well known as stress relief cracking, is related to thermal ageing: a fine and abund ant intragranular TI(C,N) precipitation appears near the fusion line d uring service at high temperature and modifies the mechanical behaviou r of the HAZ. To analyse this embrittlement micro mechanism and to ass ess the lifetime of real components, different HAZ were simulated by v arious solution heat treatments, cold rolling and ageing conditions. T he mechanical behaviour of these resulting materials was investigated using creep and tensile tests on smooth bars. Then, creep tests were c arried out and simulated on notched bars by finite element calculation s. A damage model was identified from intergranular damage measurement s made on notched specimens and compared with calculated mechanical fi elds. Further tests on fatigue precracked specimens showed that crack propagation occurred under stress relaxation conditions in simulated H AZ material.