Abstract
The microstructure and microhardness of AISI 4340 steel melted by a continuous wave ĈÔ2 laser are examined. The parameters investigated are overlap between adjacent passes, laser power, and scanning speed. After melting, three different zones were observed in the treated surface corresponding to the melted zone, the heat affected zone, and the overlapping zone. The melted zone displayed a fine cellular structure, while the other two zones displayed fine martensite or bainite structures. The fine structure and the high microhardness values, which were measured in the melted zone, are evidence of the high quenching rates which follow laser melting. An increase in the scanning speed and a decrease in laser power resulted in afiner microstructure and higher microhardness, and a reduction in the amount of overlap improved the overall microhardness.
MST/1038
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