Evolution Behavior Of Pinning Particles In Mg Treated Shipbuilding Steel Under Large Heat Input Welding

In order to meet the growing demand for shipbuilding,large heat input welding technology has begun to be widely used.The precipitation temperature,the amount of precipitation and the mutual binding behavior of the secondary precipitation pinning particles during the large heat input welding process will determine whether the pinning particles can play a role in pinning.Therefore,evolution behavior of pinning particles in Mg treated shipbuilding steel under large heat input welding was studied by theoretical calculation,statistical analysis of pinned particles and molecular dynamics simulation.The experimental steel is DH36 Mg treated shipbuilding steel.It can be seen from theoretical calculations that the dissolution temperature of Al₂O₃,Ti N,and Mn S is higher than 1350°C,which does not dissolve under large heat input welding conditions.However,due to the low content of Al₂O₃in the steel,Mn S is easy to segregate and precipitate at the grain boundary,so the stable pinning particles should be mainly Ti N particles.The misfit between Ti N and Mg O is extremely low,and they are likely to adhere to each other at high temperature to play a more stable pinning role.By comparing the metallographic structure of the HAZ under different welding heat input,the results show that the metallographic structure is the smallest when the welding heat input is 200 k J/cm.The second-phase particles in the HAZ were observed by transmission electron microscope,and the results showed that it was mostly irregular composite particle with a particle size of less than 100 nm.The matrix is dominated by rectangular Ti N particles with Nb C and Mg O particles attached to the surface.The diffusion model of elements in molten steel was established by using molecular dynamics software,and the migration behavior of each atom in the system was analyzed.The results show that the Mg and Si atoms in the system begin to have obvious clustering phenomenon at 1050℃,and the clustering phenomenon becomes more and more obvious with the increase of temperature,which provides the possibility for Mg atoms to reduce Si O₂and is conducive to the formation of fine particles in the steel.Mg O pinned particles.Figure 79;Table 16;Reference 60...