An efficient model for laser surface hardening of hypo-eutectoid steels

This paper presents a model able to predict the austenization of hypo-eutectoid steels during very fast heat cycle such as laser hardening. Laser surface hardening is a process highly suitable for hypo-eutectoid carbon steels with carbon content below 0.6% or for low alloy steels where the critical cooling rate is reached by means of the thermal inertia of the bulk. As proposed by many authors, the severe heat cycle occurring in laser hardening leads to the pearlite to austenite microstructures transformation happening to a temperature much higher than the eutectoid temperature Ac1 and, afterwards, all the austenite predicted during the heating phase become martensite during quenching. Anyway, all these models usually generate a predicted hardness profile into the material depth with an on–off behavior or very complicated and time consumed software simulators. In this paper, a new austenization model for fast heating processes based on the austenite transformation time parameter Ip→a is proposed. By means of the Ip→a parameter it is possible to predict the typical hardness transition from the treated surface to the base material. At the same time, this new austenization model also reduces the calculation time. Ip→a was determined by experimental tests and it was postulated to be constant for low-medium carbon steels. Several experimental examples are proposed to validate the assumptions and to show the accuracy of the model.