Characterization of laser treated steels using instrumented indentation by cylindrical flat punch

The aim of the present work is to assess the possibility of predicting the thickness of the hardened layers produced by High Power Diode Laser (HPDL) heat treatment. Instrumented indentation by cylindrical flat punch was carried out in order to evaluate the effectiveness of the surface-hardening heat treatments on milled AISI 1040 steel substrates by varying laser operational parameters as well as the morphology of steel substrates. In particular, the trend in load-penetration depth were obtained, supporting the identification of the depth at which the hardened layer starts transferring the deformation to the softer substrate, that is, the Critical Transition Depth (CTD) in addition to identifying the overall degree of hardening reached by the laser treated material. On the other hand, hardness profiles and the thickness of hardened layers were also monitored by using combination of Vickers micro-hardness tests and standard metallographic characterizations. Analytical examinations and simple mathematical simulations of the experimental results coming from indentation tests and conventional testing procedures showed good correlation between the extent of the heat affected zone (HAZ), hardness and CTD. In conclusion, this study demonstrates that indentation tests are an effective, sensitive, fast, and low-cost characterization technique for heat treated steels. (C) 2007 Elsevier B.V. All rights reserved.