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Abstract
In this paper, fibre laser is used in welding Q235 steel test. Both properties of metallographic structure and micro-hardness in weld metal and heat-affected zone are analysed separately in air-cooling and water-cooling conditions. The results show that the weld width in water-cooling condition is narrower than the weld width in air-cooling condition. The metallographic structure of weld metal after both air-cooling and water-cooling conditions is composed of ferrite and pearlite. However, the crystal grain is relatively larger with air-cooling and the eutectoid ferrite is separated out as massive texture. In contrast, the columnar crystal in weld metal is long and thin with water-cooling. The eutectoid ferrite is separated out in the form of flakes, and fewer widmanstätten structures appear simultaneously. The weld metal hardness after water-cooling is slightly higher than that of the weld metal after air-cooling.