Predicting case depth in tempered steels hardened via laser processing

Abstract

Surface transformation hardening of several Cr–Mo steels, namely, AISI 4140, 4130, and 4118, was carried out using a CO₂ laser. The influence of processing variables and tempering conditions of the specimens on the case depth Z_c of laser hardened zones was analysed. The ease of formation of a hardened layer in tempered steels during laser treatment was represented by a parameter M, which is simply a function of the specimen hardness. An empirical equation was developed to describe quantitatively the superheating effect in the laser hardening process. The superheating ∆T above Ac₃ was then related to the M value for the specimen and the heating rate in the laser treating process. Using the experimental results of the as quenched specimen as calibrated standards, Z_c versus M curves could be constructed for each steel. These diagrams are useful in predicting the case depth of tempered steels in the laser hardening process.

MST/1834