Visual Information Extraction Of S690QL Laser Welding Process And Analysis Of Microstructure And Properties Of Its Welded Joints

With the development of marine industry,shipbuilding industry is particularly important.S690 QL has been widely used in shipbuilding industry,construction,bridge and other fields with its high strength.In the application process of S690 QL,the most important problem is welding.With the requirements of industry,the performance of the welded joint is improved continuously.Most of the plates can meet the strength requirements.However,the traditional welding method is inefficient and the joint performance is poor.Therefore,it is urgent to improve the welding efficiency and joint performance of S690 QL.With the improvement of AI performance and the laser equipment in recent years,it is possible to realize intelligent laser welding of S690 QL.The premise of realizing S690 QL intelligent welding is information extraction,and visual information is the most important information in welding.In order to understand S690 QL laser welding better,we need to make an in-depth analysis of the microstructure and properties of the joint.Therefore,this paper has deeply study the Visual information extraction of S690 QL laser welding process and Analysis of microstructure and properties of its welded joints.The main research contents are as follows:(1)A flexible fixture suitable for extracting visual information in laser welding process is designed and the hardware platform of the system is built.The connection between the industrial camera and Open CV is realized on the VS platform.The format conversion of the digital image captured by the Daheng imgvision is successful,which adapts to the direct processing of image information by the Open CV library function.Based on the MFC interface platform,a series of visual information extraction modules for welding process were developed,and the visual information of all the welding progress can be extracted.(2)The S690 QL was welded directly by different welding processes without filling materials,after welding the samples were analyzed.Brinell hardness test,Vivtorinox hardness test and low temperature impact test were carried out.According to the test results and microstructure morphology analysis,the change of grain size and microstructure is the fundamental reason for the hardness change of welded joint.The existence of porosity and other defects as well as the formation and nonuniform distribution of martensite found in weld seam are the fundamental reasons for mixed fracture of welded joints.(3)The microstructure of the weld metal was analyzed by optical microscope,scanning electron microscope,XRD diffractometer,EDS analyzer and transmission electron microscope.It was found that bainite with different morphology and coarse M were formed in the weld metal,and the cementite and retained austenite were found in the base metal and weld beam of S690 QL.According to the experimental results,it is found that the S690 QL laser welded joint has good metallurgical bonding.Compared with double-sided welding,single-sided welded joint has better weld forming and impact toughness,so the single-sided welding process is chosen as far as possible on the premise of ensuring penetration.(4)STE-EDS analysis of the joints showed that more Mn elements were found in the area of martensite formation.The ferrite structure in BF is strengthened due to the precipitation of ultrafine grains and dislocation stacking at grain boundaries.From these results,it is concluded that the strengthening and hardenability of the S690 QL joints is mainly caused by grain boundary dislocations,segregation of the BF,and the grain coarsening of the laths of bainite and M.