Experimental determination of the constitutive behaviour of a metastable austenitic stainless steel

This article presents measurements to describe the constitutive behaviour of a semi-austenitic precipitation hardenable stainless steel called Sandvik Nanoflex™, during metal forming and hardening. The material is metastable, which causes strain-induced transformation during forming. Depending on the annealing conditions, the material can also transform isothermally as opposed to a-thermal martensite. This transformation can also take place immediately after plastic deformation, as a result of the residual stresses in the material. The martensite phase of this material shows a substantial ageing response (about 1000 N/mm2). In order to understand the behaviour of these transformations, an inductive measurement setup was developed to measure the transformation. This is a known technology, except that calibration of the sensor is complex because the sensor signal is determined by more parameters than only the martensite content. The results of the various measurements to characterize the steel Sandvik Nanoflex™ are discussed here.