Characteristics of CO₂ laser welded high carbon steel gauge plate

The welding performance of CO<sub>2</sub> lasers is strongly affected by the clamping geometry andwelding speed. Moreover, the rapid cooling rate associated with laser welding results in an untempered martensitic structure and a transverse variation in the hardness profile. An untempered martensitic structure can lead to brittle welds, and particularly for samples that are subject to cyclic loading, component fatigue and failure. To avoid this problem it is useful to optimize the laser operating parameters to reduce hardness discontinuities throughout the workpiece. An experimental investigation into the weld quality was performed to quantify the effects of clamping and translation velocity by examining the hardness characteristics, weld width and weld depth. A gauge plate, 2 mm thick, was welded with a 1 kW, CW, CO<sub>2</sub> laser for a range of translation velocities between 800 and 1500 mm per min, a He shielding was used at a pressure of 5 × 10<sup>4</sup> Pa. Two weld geometries, namely clamped and unclamped, were considered. The clamped geometry gave improved hardness characteristics and a coarse grainstructure. Whereas for the same operating conditions, the unclamped geometry gave a deeper weld penetration and wider weld width