Effect of scanning speed on plasma surface quenching of an eutectoid steel

A process using laminar plasma as heat source for surface quenching of an eutectoid steel was studied. The influence of scanning speed of laminar plasma arc on the max depth of hardened layer was researched through theoretical analysis of heat conduction. Microstructure and mechanical properties of the hardened layer were examined by means of scanning electron microscopy and microhardness test. Results show that the max depth of hardened layer decreases with the increasing of the scanning speed. The quantitative relationship between the scanning speed and the max depth of hardened layer is obtained based on the experimental results. The hardened layer mainly consists of lath martensite and acicular martensite, microstructure of the interface of the hardened layer and base steel is composed of pearlite and cryptocrystalline martensite, and it is pearlite for the base steel. The microhardness of hardened layer increases from 350 HV of the base steel to 900-1000 HV.