Thermal and mechanical loading of duplex steels
Hot-forged duplex stainless steels possess a highly anisotropic microstructure consisting of nearly equal volume fractions of ferrite and austenite forming an interwoven network of elongated phase domains. The anisotropy and the different thermal expansion of the two phases can lead to plastic deformation under pure thermal loading (even in the absence of an external meachanical load) if the thermally induced stresses surpass the elasticity limit either of one or of both phases. The structural macroscopic response of entire specimens and the local deformation of traction-free surfaces are investigated experimentally by means of dilatometry experiments and surface roughness measurements. The influence of different alloying concepts and corresponding differences in mechanical properties of the phases are discussed. Microstructural models show the strong influence of material properties on the evolution of residual thermal stresses and their subsequent influence on the macroscopic deformation as well as the local surface roughening.