Mechanical properties of 8Cr-2WVTa steel aged for 30 000 h

A mill production plate of a reduced activation ferritic steel was thermally aged for up to 30 000 h at 400-650 deg. C. Charpy impact tests, creep rupture tests and hardness tests were conducted. Both Vickers hardness number and creep strength decrease with aging at 650 deg. C. The ductile-brittle transition temperature (DBTT) increases with both aging time and aging temperature. However, the DBTT does not exceed +20 deg. C even after aging at 650 deg. C for 30 000 h. Extracted residues and extraction replicas were analyzed metallurgically. The increase in DBTT is related mainly to the precipitation of Laves phase on the prior austenite grain boundaries. The rather low DBTT after aging is caused by the fine prior austenitic grain size