Multiaxial creep of fine grained 0·5Cr–0·5Mo–0·25V and coarse grained 1Cr–0·5Mo steels

Abstract

To explore the multiaxial creep response of materials used from electrical power generating plant, two steels, a fine grained 0·5Cr–0·5Mo–0·25V steel in a normalised and tempered condition with high creep ductility and a coarse grained 1Cr–0·5Mo steel in a quenched and tempered condition with low uniaxial creep ductility, have been selected. A range of multi axial stress testing techniques which span the stress states that would allow identification of any technique dependent variables has been used. The deformation andfailure of the normalised and tempered 0·5Cr–0·5Mo–0·25V steel for a range of multi axial test techniques and, therefore, stress states may be described by an equivalent stress criterion. The results from the multiaxial tests carried out on the fully bainitic 1Cr–0·5 Mo steel show that the multiaxial stress rupture criterion (MSRC) varies with stress state, at high triaxialit y (notch) , it is controlled by the maximum prinicipal stress, whereas, at low triaxiality (shear), it is dependent on both maximum principal stress and equivalent stress. Furthermore, a simple description of stress state based on maximum principal and equivalent stress does not define this uniquely, since the MSRC derived from uniaxial and torsion testing does not describe the failure of notch, tube, or double shear tests.MST/1390