ASTM class 40 gray and 80-55-06 ductile cast irons were surface heat-treated by a 1.2-kW, CO2 laser to study the effects of square and oscillating-gaussian beam modes on case depth, coverage rate, distortion, hardness, and microstructure. The results were compared with that of ring and gaussian beam modes, which were described in Part I. Square and oscillating beams maximized case depth and coverage rate, while ring and gaussian beams minimized distortion. Hardness and microstructure of heat-treated layers were unaffected by the beam mode. For given laser parameters, ductile iron always exhibited larger case depth and coverage rate than gray iron because of the lower thermal diffusivity. Experimental data and theoretical models indicated that thermal response of a material to laser power cannot be described by a simple function as given by heat conduction models and that the best correlating factor for case depth is P/V (P is laser power, V is scan rate).

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