IN-BEAM CREEP-RUPTURE PROPERTIES OF COLD-WORKED DIN 1.4970 AND AISI-316-L AT 873-K

To compare the helium embrittlement resistance of cold-worked DIN 1.4970 SS and AISI 316 L SS, in-beam creep rupture tests, i.e. in-situ creep rupture tests during helium implantation, were carried out at 873 K with helium concentrations up to 3500 appm. Significant reductions in creep rupture time and in rupture strain by helium were recognized in both materials. AISI 316 L SS was more severely embrittled. SEM fractography showed an increasing tendency for intergranular fracture with increasing helium concentration. Especially, a fairly high fraction of intergranular failure on the rupture surface was observed at low helium concentration in AISI 316 L SS. Quantitative TEM observation revealed that smaller helium bubbles were distributed both in grains and at grain boundaries for DIN 1.4970 SS. The better helium embrittlement resistance of this material can probably be explained by the finer bubbler microstructure.