Study On The Effect Of Rare-earth Y On The Performance Of Ship Plate Steel And Its High Heat Input Welding Tissue

With the rapid development of society and economy,efficiency is the top priority in actual large-scale production.While ensuring efficiency,quality control cannot be ignored.Due to the increasing size of marine ships,the thickness of ship plate steel has increased,but the efficiency of shipbuilding by conventional welding processes is low,so high heat input welding technology has emerged at the historic moment,which can significantly improve work efficiency.The structure of the weld zone of high-line energy welding is complex.The high welding heat input causes the temperature near the welding fusion line to rise instantaneously,causing the coarse-grained heat affected zone(CGHAZ)to stay longer at high temperatures,slower cooling speed,and The formation of coarse widmanstatten structure with poor toughness becomes a weak part in the entire weld zone.The fusion zone(HFZ)undergoes a more specific solid-liquid-solid transition,with less related research,and its mechanical properties are still not very clear.Therefore,it is particularly important to study how to improve the quality of the weld zone.Rare earth Y has excellent properties such as microalloying and spheroidizing inclusions,but its role in the high heat input welding process has not yet been determined.In this paper,the simulation of high heat input welding of ship plate steel with a single component of high-purity rare earth Y is carried out.Testing machine,impact tester and other equipment to analyze and test the experimental steel,including the effect of rare earth Y on the acicular ferrite nucleation position and grain orientation of ship plate steel during the solid phase transformation,and the coarse grains under different heat input The influence of the morphology,existence location and existence form of rare earth inclusions in the zone and the fusion zone,and the effect of rare earth Y on the properties of the coarse grain zone and the fusion zone,etc.The research results are as follows:During the process of heating the austenitizing temperature of the steel containing rare earth Y,there are more uniform dispersed particles.During the phase change cooling process,increasing the number of acicular ferrites will not only generate acicular ferrites in the same direction,but also produce new,finer secondary needles in different directions at the top of the formed acicular ferrites.At the same time,acicular ferrite also forms acicular ferrite that grows from the grain boundary into the crystal,and intersects the acicular ferrite in the crystal to make the structure more uniform.The existence of rare-earth Y in hot-rolled experimental steel is: solid solution inthe crystal in atomic form;segregation in grain boundaries;existence of spherical inclusions of rare-earth sulfur oxides,sulfides and oxides in grain boundaries and grain in.After high heat input welding,the size and shape of the spherical inclusions of rare earth Y in the coarse grain region did not change much,but the O content in the composition decreased with the increase of heat input value.In the fusion zone,the S element in the rare-earth Y-containing inclusions disappears,and the inclusions in the fusion zone only exist in the form of rare-earth oxides.The rare earth Y in ship plate steel can reduce the hardness of the fusion zone after high heat input welding.Under the heat input of 100 k J/cm,200 k J/cm,500 k J/cm,the hardness of Y-V test steel is lower than that of V test steel.