P R E P A R A T I O N A N D P E R F O R M A N C E S T U D I E S O F S P E C I A L M O R P H O L O G Y T I T A N A T E D I O X I D E A N D U S I N G Its P R E C U R S O R A S T E M P L A T E T O P R E P A R E L I T H I U M T I T A N A T E

Carbon steel is the most consumable metal materials in the world. Fusion welding is one of the most important methods for joining steel structure in engineering and it is widely used in various fields of national economic construction. Fusion welding is a highly non-uniform heating and cooling process. The energy input causes a thermal cycle that drives the grain growth and microstructure transformation in heat affected zone, which seriously influence the mechanical properties of welded joint and even lead to welding structure failure. It has the important theoretical significance and engineering’s application value to study the rules of phase transformation and grain growth process in welding heat affected zone, which can provide basis for optimizing material microstructure, improving joint performance and guiding the welding process.In this paper, typical carbon steel Q235 B, Q345 E, No.45 steel are taken as experimental material and metal active gas plate butt welding experiment, metallographic experiment and quantitative analysis experiment are carried out sequentially. Finally, the volume fraction of carbon steel Q235 B, Q345 E, No.45 steel and the grain size of Q345 E steel in welding heat affected zone coarse crystal are measured.Combining with the actual welding process, adoptting J.Goldak double ellipsoidal power density distribution body heat source and synthesizing heat transfer theory, the welding temperature field model of metal active gas welding is established. Based on Kirkaldy phase transformation kinetics equation and Koistinen-Marburger phase transformation kinetics equation, the complete phase transformation model in welding heat affected zone is established. Through coupling the welding temperature model with phase transformation model,the user subroutine DFLUX and UMATHT are written respectively by means of FORTRAN language. After establishing a appropriate finite element model, the computer simulation of metal active gas welding temperature and phase transformation in the welding heat affected zone can be achieved by the application of ABAQUS three-dimensional finite element analysis software. Simulation results show that simulated weld pool coincide with the actual topography, the width and depth of weld pool are 7.2mm and 4.5mm respectively. The simulation results of the volume fraction of microstructure in HAZ is consistent with the measured results and the deviation within ±10%,thus the reliability of phase transformation model was verified.N.E.Hannerz equation is used to calculate welding thermal cycle. The EDB model is selected to implement the conversion between MC time step and the real time temperature relationship. The grain growth model is established by combing MC method and the grain growth kinetics theory. The computer simulation of grain growth dynamic process in CGHAZ can be realized by means of writing a simulation program with MATLAB software. Simulation results show that the degree of grain growth are vary with the position in Q345 E steel CGHAZ. The nearer the distance to the fusion line is, the larger the diameter of the grain is. The simulation results of the grain size of five positions(the distance to the fusion line is 100, 200, 300, 400 and 500um) in CGHAZ is consistent with the measured results and the deviation within ±10%, thus the reliability of grain growth model was verified.