Abstract
Primary and secondary CO2 laser beam quenching under traveling heat condition are applied to a Cr-Mo steel block with pro-eutectoid ferrite and pearlite structures, and characteristics of hardness and microstructure in heat affected zone are investigated in relation with beam power. Martensite structure with hardness of 700-800HV0.1 is produced to the depth of 1.2mm after primary quenching operation by laser power of 1100W. When the secondary operation by the power of over 600W is made to once-quenched part, hardened martensite is found to transform into three kinds of structure such as secondary martensite, tempered martensite with bainite and reproduced pearlite, while entire region becomes to much hardened secondary martensite by the power of 1000W. From the experiments, it reveals to possibly control the characteristics of hardened zone and microstructure by choosing the proper condition of primary and secondary beam irradiation.
