Fundamental Research On High Performance Laser Forging Composite Arc Repair Of Offshore Fan Structure

The development of offshore wind platforms is a powerful way to advance China's carbon-neutral goals.As the main structure of offshore wind power,pipe parts play an important role.Under the influence of wind,wave,flow load and other harsh environment for a long time,they are prone to wear,crack,corrosion and other failure behaviors,leading to internal leakage of the platform and loss of power generation function.The replacement of pipe parts is faced with problems such as high cost,low efficiency and waste of resources.It is of great significance to adopt reasonable on-site repair means of pipe parts for the sustainable development of resources.In this paper,a new high performance welding repair technology of laser forging composite arc welding is proposed.Different from the traditional repair technology,this technology has many advantages,such as good wear resistance of repair layer,less welding defects and high repair efficiency.In this paper,YD998 welding wire with high hardness and wear resistance was selected as the repair material,and Q235 steel tube was used as the matrix.The repair process of pipe parts was explored by using laser forging composite arc welding technology,and the metallographic structure and hardness properties of pipe repair parts were studied.The typical welding defects were analyzed and preventive measures were put forward.The friction and wear properties and influence mechanism of pipe repair parts before and after laser forging were analyzed.The main research contents and results are as follows:(1)Through the repair process research of pipe parts,the influence of process parameters on the weld morphology was explored,and the optimized process parameters were selected to complete the overall repair work of pipe parts.The results show that when the welding parameters are too large or too small,the defects of the welding seam,such as porosity,incomplete welding,underbite and welding nodule,are easily produced.The welding current has great influence on the welding depth,the welding speed has great influence on the welding height,the arc voltage and the laser frequency have great influence on the welding width.When the working current is 130 A,the arc voltage is 34 V,the welding speed is 160mm/min,and the laser frequency is 10 Hz,the weld quality is good.Laser forging has a great influence on the surface morphology of pipe integral repair parts.Before forging,there are obvious pores on the weld surface,serious splash,and the weld pass transition is concave and convex.After forging,the weld pass surface is smooth and flat,the transition fluctuation is small,and there is no obvious defect on the surface.(2)The influence of different process parameters and laser forging on the microstructure and microhardness of the weld was explored.The typical welding defects were analyzed and the improvement methods were put forward.The results show that the cooling rate in the weld zone is the main factor affecting the microstructure.With the increase of welding current and the decrease of welding speed,the energy of the weld line increases,the cooling rate of the weld decreases,the martensite structure in the fusion zone decreases,and the bainite structure increases.The microstructure of the heat-affected zone is characterized by proeutectoid ferrite and Widmannian structure.With the increase of laser frequency,the size of columnar crystals decreases,the number of columnar dendrites increases,and the microstructure is mainly lamellar martensite.Before and after laser forging,the microstructure of the fusion zone of the tubular repair parts changed greatly.Before forging,the microstructure of the fusion zone was in the shape of coarse columnar crystal,which was composed of acicular martensite and granular bainite.After forging,the microstructure was obviously refined,which was in the shape of fine equiaxed crystal,which was composed of a lot of platelike martensite and acicular martensite.The microstructure composition and grain size of the weld area are the main factors affecting the microhardness value.The higher the martensite content in the microstructure,the smaller the grain size,and the higher the microhardness value.After laser forging,the average hardness value reaches 607.45 HV,which is 8.12% higher than that of unforged,and 3 times higher than that of base metal.The hardness value of heat-affected zone changed little before and after laser forging.The welding defects mainly include porosity,crack,underbite,welding bump,pits,etc.,which can be prevented by process regulation and environmental control.(3)The influence of laser forging on the friction and wear properties in the weld zone of pipe repair parts was explored.The results show that the main wear mechanisms are adhesion wear and contact fatigue wear in the base metal area,contact fatigue wear in the unforged area,and abrasive wear in the forged area.After laser forging,the friction and wear parameters such as friction coefficient,wear mark width and depth,wear quantity and wear rate of pipe repair parts are significantly reduced,and the wear resistance is significantly improved.