The role of stress state on the creep rupture of 1%Cr1/2%Mo and 12%Cr1%MoVW tube steels

Results of creep tests on uniaxial specimens and tubes of two ferritic steels, 12%Cr 1%MoVW and 1%Cr 1/2%Mo, carried out at a temperature of 848K over a range of stresses are described. The tubes were tested under internal pressure both with and without externally applied axial loads. Optical and electron microscopy are used to examine the microstructural changes which lead to creep failure. The results are examined in terms of the contribution of stress state in the strain controlled rupture of the 12%Cr 1%MoVW steel and the cavitation controlled rupture of the 1%Cr 1/2%Mo steel. The variation of creep life with changing stress state between the uniaxial creep specimens and the tubes is discussed. (author)