Effect of laser hardening on fracture toughness of steel

Abstract

In our research project, we have tested the impact energy of laser-treated steel bar with the Charpy apparatus. The tested materials were two medium carbon steel materials. Instead of using normal notch on bars, we used the laser hardening line. Laser hardening was done with Nd-YAG lasers.Several different hardening area sizes, depths and cross sections were tested to find the desired behavior. The effects of several laser hardening parameters, such as laser power, shape of beam and traverse speed, were tested. In addition, relations between the laser hardening parameter and fracture toughness were considered in connection with the tests. Also, the effect of laser hardening on hardness was measured.Microstructure and depth of the hardening area were studied by optical microscopy. To achieve accurate analysis and reproducible results, all tested beam shapes and intensity profiles were verified with a power meter and beam analyzer.Some of the findings in the project were that crack initiated at the laser hardening line and reduced the impact energy absorption, and that case depth correlated strongly with fracture toughness, which was affected also by the type of material and previous heat treatments.In our research project, we have tested the impact energy of laser-treated steel bar with the Charpy apparatus. The tested materials were two medium carbon steel materials. Instead of using normal notch on bars, we used the laser hardening line. Laser hardening was done with Nd-YAG lasers.Several different hardening area sizes, depths and cross sections were tested to find the desired behavior. The effects of several laser hardening parameters, such as laser power, shape of beam and traverse speed, were tested. In addition, relations between the laser hardening parameter and fracture toughness were considered in connection with the tests. Also, the effect of laser hardening on hardness was measured.Microstructure and depth of the hardening area were studied by optical microscopy. To achieve accurate analysis and reproducible results, all tested beam shapes and intensity profiles were verified with a power meter and b...