Creep-fatigue failure of SAF 2205 and 316 stainless steels in Ar+3% SO₂ environment at 700 °C

The creep-fatigue behaviour of SAF 2205 duplex stainless steel and 316 austenitic stainless steel was studied under a sulphur-containing environment of an Ar + 3%SO₂ atmosphere at 700°C. The cyclic loading employed creep-tension and plastic compression following the creep-plasticity (cp)-mode of the strain-range partitioning life-prediction method. The results showed that a premature failure was obtained with both SAF 2205 and 316 stainless steels under the combination of creep-fatigue loading and an SO₂-bearing atmosphere. However, SAF 2205 was significantly more resistant than 316 as far as the number of cycles to failure and the sulphidizing attack at the external surface were concerned. In both materials, the creep-fatigue crack propagation was directly controlled by the environmental attack of the SO₂-containing environment at the region ahead of the crack tip.