Microstructure And Properties Of High Heat Input Welding HAZ Of EH420 Offshore Plate Steel

In recent years,with the increase in size and strength of components,in order to improve production efficiency and reduce production costs,some high-efficiency welding techniques have been gradually applied in the field of marine engineering manufacturing.High-efficiency high input energy welding process,because the welding heat input is high during the welding thermal cycle,and the residence time in the high temperature region is too long,resulting in uneven microstructure after welding and poor impact toughness.Therefore,improving the quality and safety of large-scale structural steel and using steel plates for high input energy welding has become the key in the field of high-intensity marine engineering.This project relies on the "13th Five-Year" national key R&D project "High-strength,large-size,easy-weld marine engineering steel and application",using EH420 high heat energy welding marine engineering steel to transform from the cooling of the heat affected zone systematic research on the properties of welding heat affected zone,inclusion nucleation mechanism,actual large-line energy welding,etc.The main research work and results of this thesis are as follows:(1)Through the Formastor-? phase change instrument,the continuous cooling phase transformation behavior and microstructure change of EH420 offshore steel produced by Ti-Mg deoxidation process were studied,and the SH-CCT curve was established.(2)Through the MMS-300 thermal simulation test machine,the EH420 offshore steel is tested.The EH420 offshore steel has a line energy range of 20kJ/cm?600kJ/cm,and the impact energy at-20? is gradually reduced.The impact energy is 186J when the online energy is 400kJ/cm.,and the impact energy value is much larger than the classification society standard 47J.(3)High-temperature confocal experiments show that the inclusions of EH420 experimental steel effectively promote the nucleation of intragranular cross-interlocking acicular ferrite and grow around when the input input line energy is 200kJ/cm.The austenite grains were pinned at high temperatures,and the average grain size was 104?m.(4)The inert interface mechanism can well explain the phenomenon that non-metallic inclusions promote multi-dimensional nucleation of acicular ferrite.The type of inclusion in EH420 offshore steel produced by Ti-Mg deoxidation process is(Ti-Mg-Ca-Al-O)+MnS complex phase inclusions,and the inclusion size is mainly distributed in the range of 0.2-0.6?m.(5)For the EH420 experimental steel with the line energy of 196kJ/cm submerged arc welding and 206kJ/cm electric vertical welding,the impact energy of the fusion line is 110J and 157J respectively at-20?,and it is considered that Ti-Mg is utilized by analysis.The EH420 steel sheet produced by the deoxidation process has the ability to maintain high temperature impact toughness under large-line energy welding.