Grain Refining Effects Of Mg,Mo And Ni At High Temperature And Development Of High Strength Shipbuilding Steel

As the main process of thick plate processing,with the increase of welding line energy,the grain size in the heat affected zone of traditional hull steel will increase rapidly,and its toughness will decrease sharply.In recent years,how to improve the toughness of HAZ under the condition of large line energy welding has become the focus of domestic and foreign scholars.With the development of the research,oxide metallurgy technology came out,that is to introduce a large number of micro inclusions into the steel by using micro alloy.These micro inclusions dispersed in the steel and precipitated on the austenite grain boundary as pinning particles,which hindered the grain growth.During the cooling process after welding,these fine particles act as nucleating particles,induce IAF nucleation,further refine the grains,and significantly improve the toughness of HAZ region.The in-situ observation of the microstructure changes of hull steel with different alloying elements(Mg,Ni,Mo)was carried out by high temperature laser confocal microscope.The results show that Mg element can refine the inclusions in the steel effectively,the pinning effect on austenite grains is more stable,and the induction rate of acicular ferrite can be guaranteed.For Mg treated steel,with the extension of holding time,the welding line energy increases continuously,and the nucleation capacity of acicular ferrite increases first and then decreases,which is the best when holding for 300 s.Compared with the addition of Ni and Mo,the stability of micro particles in steel is better and the pinning effect is more significant.Therefore,Mg and Mo alloy are added to the test steel,and industrial production test is carried out.Through the actual welding,impact and relevant analysis of the industrial test production steel plate,it is found that the impact results of all positions at-20 ? and-40 ? are significantly higher than those required by the national standard,indicating that the toughness of the heat affected zone of the industrial test steel is good.Figure 57;Table 7;Reference 60...