The influence of pre-heat treatment and laser hardening on the steel structure formation

Abstract

Efficiency of application of laser hardening is a significant increase in strength and wear-resistance parts, which is provided by forming on the surface of the part with a hardened layer structure, which differs from the metal structure obtained by classical methods of volumetric hardening. The aim of this work is to study the effect of different types of thermal pre-treatment and regimes of laser hardening on structure formation hardened zone of the steel. The test material is high quality structural carbon steel 40. For experimental studies was used for continuous Nd: YAG Laser, "DY044" produced by "ROFІN-SІNAR". The microstructure was investigated by optical microscopy on the microscope MIM-8 by the standard method at different magnifications. The microhardness of the samples was determined on the device PMT-3 according to standard methods. Ultrafast laser heating of the annealed steel with a pronounced structural components in the initial state does not allow to obtain a homogeneous final structure. The main feature of laser machining pre-hardened steel is a mandatory manifestation of structural heredity during heating. This fact is explained by the oriented formation of austenite. Also a decisive influence on the oriented nucleation of austenite, leading to structural heredity, has not only the original steel structure, but also a high heating rate during laser processing. On the formation of laser hardened zone is influenced by such factors as the processing speed of the laser beam and laser power. With the power increase, the depth of the hardened layer is increased, and the increase in processing speed is of the opposite character. The best way to pre-heat treatment of steel before the laser annealing is improved. This method of hardening the surface layer contributes to the formation of adequate areas with high values of hardness (7 GPA) with a smooth transition to a core that further positive effect during operation of the part