Estimation of the Effect of Stress/Phase Transformation Interaction when Calculating Internal Stress during Martensitic Quenching of Steel

Abstract

Usually in the prediction of internal stresses during quenching, in the case of a steel which undergoes phase transformation, a particular effort is made in order to modelize the progress of the transformations. In this work, we try to show in the case of a tool steel (60 NCD 11), which undergoes only martensitic transformation during quenching, how the appearance of internal stresses is modified by taking into account a specific mechanical behaviour of the metal during phase transformation.
The procedure consists in using the experimentally determined dimensional, mechanical and thermal behaviour of the steel in a thermo-elastoplastic model of calculating stresses and strains in cylinders.
The results on the example of water quenching at 80°C show that by considering a stress transformation interaction which induces transformation plasticity the development of the internal stresses during cooling is quite modified.
Indeed, the transformation plasticity phenomenon simulated by a reduction in the yield stress of the steel during its transformation leads to residual stress profiles which are inverse as compared with that of thermal stresses, i.e., the stresses are tensile on the surface and compressive in the centre of the cylinder.