| Selective hardening of AISI 1045 steel has been achieved by using a Nd:Yag laser under different process parameters. The maximum surface hardness of {dollar}sim{dollar}780 Hv has been achieved. The highest hardness of the laser surface hardened layer increases with power density of laser, up to a certain level. Pre-processing surface treatments like etching, and graphite coating improve the coupling of laser energy significantly.; The highest hardness, which can be obtained by laser transformation hardening of AISI 1018 steel is {dollar}sim{dollar}450 Hv. The higher hardness of 1050 Hv has been achieved in this steel by laser carburizing. Incorporation of higher carbon concentration, through fine ledeburitic microstructure in surface layers, produces such high hardness. Further increase in hardness can be obtained by laser boriding. Laser boriding of AISI 1018 steel produces hardness ranging from 1350 to 2200 Hv (can be compared with the hardness of SiC {dollar}sim{dollar} 2300 HV). FeB phase was found to be the hardest phase in the laser borided surfaces of AISI 1018 steel, having hardness of {dollar}sim{dollar}2200 Hv.; A simple analytical heat transfer model, using Green's functions, was developed to predict the temperature distribution on a workpiece during laser surface treatment. This model demonstrates a new approach to formulate heat transfer problems, involving high energy sources. The model can be used to predict the case depth during laser hardening. The results obtained by the analytical model compare fairly well with the results, obtained by the commercial FEM package ANSYS. The simulation of moving laser, in ANSYS, showed that maximum hardness achieved at the surface of a workpiece is shifted towards the trailing end. The above analytical model has been modified to implement the laser traverse speed.; Few problems have been encountered with laser carburizing of AISI 1018 steel. In some cases, cracks and porosity have been found in the laser treated surface. The cracks produced were found to be of two kinds: straight cracks and wiggly cracks. The cracks formed were due to a combination of various factors such as shrinkage, thermal stresses, surface brittleness and low melting point, interdendritic liquid phase. (Abstract shortened with permission of author.)... |
