Dot matrix hardening of steels using a fiber optic coupled pulsed Nd:YAG laser

This paper describes a novel process called "Dot Matrix Hardening" as applied to O1, D2 and AISI 4340 steels. This process uses a pulsed laser (particularly an Nd:YAG laser) to create a uniform distribution of transformation-hardened spots to cover only a certain percentage of the desired surface. Due to significantly reduced energy input, wear resistance can be imparted to thin and intricate parts without distortion. In addition, with the use of a coupled fiber optic beam delivery system, this process provides greater flexibility compared to conventional CO2 laser hardening for a number of applications. The use of an Nd:YAG laser also eliminates the need of absorptive coating required for hardening with a CO2 laser. With optimized processing parameters, a relatively uniform hardened layer is obtained within the hardened spot, with a thickness of about 60 mu m and hardness values around 800 HV100. The sliding wear test results show that the wear resistance of O1 samples with only 20 - 40% area coverage of laser-hardened spots is similar to the 100% covered laser dot hardened sample as well as the furnace hardened (Rc 60) sample.