In-situ X-ray diffraction study of load partitioning and microyielding for the super duplex stainless steel SAF2507 (UNS S32750)

The deformation behaviour of the super duplex stainless steel SAF2507 (UNS S32750) under successive uniaxial tensile loading-unloading was investigated with respect to load sharing and inter-phase interactions. The steel consists of 58% austenite and 42% ferrite in volume. By insitu X-ray diffraction experiment the evolution of phase-specific stresses with applied load was monitored for three successive loading-unloading cycles with the maximum total strains being 0.34%, 0.75% and 1.63%, respectively. It was found that yielding occurred earlier in the austenitic phase than in the ferritic phase during the first loading cycle. In the followed loading cycles, both phases yielded under larger but similar applied stresses. Due to a similar behavior of the phases in the elasto-plastic regime inter-phase interactions were relatively weak. Low microstresses induced by the plastic straining resulted in somewhat larger stresses in the ferritic phase.