| With the scientific and technological development, people have become increasingly demanding structural parts, which called for a higher strength, excellent weldability, low-temperature anti-fracture ability to improve the ductility and formability. From the economic considerations, we also need to get as much as possible to use fewer raw materials. However, the existing steel variety and quality has been far from the standard to meet the rapid development of economic and social demands, the future high-rise buildings, large-span bridges, offshore oil platforms, large-scale engineering machinery, large-scale high-performance ships, light energy-saving cars and so on are all we need to improve the strength and service life of steel.B700L is a new type of low-alloy high strength steel, which adds a lot of micro-alloying elements ,produced by baosteel. In the automotive and shipbuilding industries it has broad application prospects,.Domestic high-strength steel plate of some high-power laser welding technology research is still in its early stages. Therefore, high-strength steel plate to carry out high-power laser welding technology research is of great significance. Through its laser welding, to explore an appropriate set of laser welding technology for the future of such high-strength steel to provide a basis for laser welding.This article mainly related to 8mm thick B700L laser welding technology of micro-alloyed steel, through the laser power, welding speed, gas flow, defocus length, gap and other parameters on the impact of comparative weld to determine the appropriate process parameters,in-depth discussion on weld metal, heat affected zone as well as their mechanical properties .Through the design of orthogonal parameter table, observating process parameters which have an impact on the welding and in the subsequence by changing the different parameters and study their impact on penetration, weld width, area and other effects. Between 8kw to 12kw, with the laser power increases, penetration ,weld width, heat affected zone width are showing an increase. In the case of a fixed laser power, with the increase of welding speed, weld width decreases, penetration depth increases, the line energy 3KJ/cm is the critical point whether the weld will penetrate. Changing defocus length ,we found under -2mm condition,we can get the greatest width.Under the premise of the penetration, gap changing from 0.1mm to 0.5mm, weld width and penetration has not changed significantly. With the increase in heat input,weld size, heat-affected area of the joint increase in a direct proportion way from a platform to another higher platform, but the area of coarse and fine grain does not increase as the line energy ever-increasing .Weld metal is composed mainly of acicular ferrite , granular bainite and a small amountof martensite. Fusion zone is mainly composed of granular bainite + martensite, relatively coarse grain size, heat affected zone is mainly ferrite + pearlite + carbide composition. Weld metal zone are mostly acicular ferrite which can improve the weld zone toughness. Weld heat affected zone near the fusion line exists a certain hardening phenomenon, a width of about 0.25mm, a certain degree of softening region is between the fine-grained and two-phase region , with the line energy increases, the softening zone is gradually expanded.
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