In this paper,a colorimetric pyrometer was used to determine the molten pool thermal history parameters in laser welding of 2205 dupleX stainless steel.The cooling rate of solidification under different welding speed was investigated.The effect of molten pool thermal history on the micro structure and microhardness of the joints was studied.The weld morphologies present a“nail”shape.With an increase in welding speed,the width,depth and section area of the joints were found to de- crease,while the cooling rate increases.As a result,the grains were refined obviously.Further,the grain morphology in the center of the weld evolves from eQuiaXed grains to columnar grains.The solid phase cooling rate increases with the welding speed,resulting in a decreasement of the precipitated phase.All the welds are hardened,and the average microhardness increa- ses with the welding speed.