Laser Hardening of Grey Cast Iron using a High Power Diode Laser E. Kennedy, G. Byrne, R. Byrne The Process ● Rapid cooling by conduction causes self-quenching to form hard martensite on surface Thermal hardening process where high intensity laser radiation heats the workpiece surface above a critical transformation temperature ● 108 Shock Hardening Drilling Laser W/mm2 106 Cutting Melting Vaporisation 104 Welding Irradiance x 50 Heating 102 Alloying Laser beam Transformation Hardening Hardened layer in cast iron Cladding 100 10-8 10-6 10-4 10-2 100 s 102 Interaction time t Hardened track Component Fig.2 Interaction time vs. irradiance for a number of common laser applications Fig.1 Schematic of laser hardening process Thermodynamic modeling Experimental Work Aim: To create a tool for predicting the outputs from the laser hardening process using a high power diode laser, for a given set of input parameters ● Heat transfer problem: Aim: To validate the thermal model and to determine the link between wear resistance of the hardened surface and its material properties Samples of cast iron laser hardened using a range of processing conditions and output characteristics such as hardness profile measured ● Heat flow in 3 dimensions Moving heat source = Variable thermal properties Transient heat conduction Heat transfer solution: Finite element method used to solve (ABAQUS) ● Fig.4 High power diode laser hardening at UCD Abrasive and erosive wear resistance of laser hardened surface experimentally determined ● Hardness Profile for Laser Hardened Cast Iron Sample (HRC) Hardness Fig.3 Visualisation of FEM model using ABAQUS software (µm) ● Heating and cooling rate of various points within the solid calculated Results compared with published metallurgical data to predict resulting surface structures and characteristics Depth below surface ● Fig.5 Typical plot of hardness vs. hardened depth in laser hardening of cast iron