Microstructure of laser boronized nodular iron

Nodular iron was laser boronized by a CO2 molecular laser with a continuous wave. Parameters of laser treatment have been selected in an appropriate way to achieve different cooling rates for the melting zone. The surface layer microstructure of nodular iron after laser boronizing has been investigated by optical microscopy, scanning electron microscopy and X-ray diffraction. Different microstructures in melted zones have been observed for different cooling rates. The polygonal shape of the Fe2B phase (typical for Fe2B after laser boronizing) has been found in the melted zone cooled at 103 °C/s. Fe2B borides have been confirmed by X-ray diffraction. An ultra-fine microstructure has been found in the melted zone cooled at the rate of 8 × 103 °C/s in contrary to the previous one. In this case, the X-ray diffraction revealed higher amounts of hard phases such as Fe2B and Fe3C. The microhardness of the melted zone cooled at 8 × 103 °C/s was approximately 1300 HV0.1 while in the case of 103 °C/s the cooling rate microhardness was lower— approximately 1100 HV0.1.