The effect of specimen thickness on the hardness of plasma surface hardened ASSAB 760 steel specimens

In a previous study, the optimisation of the processing parameters for maximum hardened depth of ASSAB 760 (equivalent to AISI 1045) steel specimens of 6 mm thickness by using a Microplasma-50 plasma arc machine with Taguchi method was conducted. A four-factor three-level L9 orthogonal array was used in the experiment. The maximum depth of hardened zone obtained was 0.36 mm and the maximum hardness observed was 753 Hv. In the present study, experimental work was carried out to study the effect of specimen thickness on the maximum hardness obtained in plasma surface hardening of the same ASSAB 760 steel, with two thickness values of 10 and 20 mm. It was found that the depth, width, hardness and cooling rate of the hardened zones increased as the specimen thickness was increased from 6 to 10 mm due to a better self-quenching effect. However, no increase of these properties was observed when the specimen thickness was further increased from 10 to 20 mm.