The characterisation of work-hardened austenitic stainless steel by NDT micro-magnetic techniques

Abstract

It is accepted that the work-hardening of austenitic stainless steels during machining or cold-working results in two main products: the appearance of α′-martensite and increased dislocation densities within the host material. In machining, this results in many difficulties (poor surface finish, poor machinability and high tool wear). Non-destructive sensing is essential in today's high volume production environments because of its ease of use, speed and non-invasive sensing. Non-destructive magnetic measurement techniques have been employed to characterise the work-hardening of an austenitic stainless steel grade (SS404) due to room-temperature plastic tensile loading. These techniques include the use of magnetic Barkhausen noise, ferromagnetic phase measurement and coercivity measurement. It was found that the dislocation density, rather than the α′-martensite phase, to be the cause of material work-hardening. It is suggested that the use of coercivity measurement is a useful quantitative and non-destructive method for characterising work-hardening of the studied alloy in relation to the amount of its plastic deformation (work-hardening).