Investigation On Grain Refinement Of Coarse Grain Zone In Heat Affected Zone Of 310S Steel

310S austenitic heat resistant stainless steel for high level waste storage tank materials,in the welding of high discharge waste storage tank welding heat affected zone coarse grain coarse grain(CGHAZ)coarse grain coarsening,resulting in the reduction of its mechanical properties.In order to meet the requirements of strength and toughness of the coarse grain zone in the heat affected zone of the high level waste storage tank,the grain growth is suppressed by the method of micro alloying.In this paper,the microstructure and mechanical properties of CGHAZ steel in 310 S zone of steel were studied by optical microscope,scanning observation,transmission electron microscope and SYSWELD software.The main contents of this paper are as follows:1.310 S single channel steel welding numerical simulationBased on the SYSWELD software to establish a welding heat source model,single channel self fluxing welding experiment,extracted from the CGHAZ area of the welding heat circular curve,lay the foundation for the determination of the mechanical properties of the CGHAZ the next step.2.Phase composition and evolution of precipitates in 310 S steelBased on the thermodynamic calculation of Thermo-Calc software on the phase composition of 310 S steel and alloy elements on phase composition were calculated,and laid the foundation for the later development of aluminized 310 S steel as well as the reasonable range of the solution process,but also provides a reference for the materials of welding heat affected zone temperature.The calculated results show that with the change of Al content(from 0.52% to 1.38%),the microstructure of 310 S steel is changed,but the quantity of AlN precipitates changes.And the AlN precipitate phase is gradually changed from the two phase to the first one.3.Microstructure and precipitation phase of BM and CGHAZ in 310 S steel with different Al and Nb contentsThrough the observation of the microstructure of Al and Nb containing steel.Coarse grain size of coarse grain is found to roughly equal to that of base metal.The effect of Al and Nb elements on the growth of austenite grain in coarse grain region was described.With the increase of Al content,the precipitation of Al N gradually increased.And more 310 S content of Al steel,after casting,forging,hot rolling,the remnants of a AlN phase and its particle size is relatively large,the mechanical properties of the material damage.When the content of Al was 1.38%,the delta ferrite in 310 S steel was precipitated.During the casting process,Al will give priority to the delta ferrite,reducing the content of AlN phase.With the increase of Nb content,the MX phase was increased,and the ability to inhibit the growth of austenite grain in coarse grain region was increased.4.Effect of Al and Nb content on mechanical properties of 310 S steel The study found that AlN during tensile deformation,the deformation will prevent grain,when the content of Al is high(1.38%),3-Fe stretched along the direction of extension,will play a "hard" role,thereby increasing the plastic material.The microhardness of AlN and delta ferrite is higher than that of austenite matrix,which can decrease the toughness of 310 S steel.The tensile strength of the MX phase in 310 S steel is not obvious,and the tensile strength of the base metal and the coarse grain zone of the three kinds of Nb containing steels is roughly equal to that of the tensile strength.The impact of impact is relatively large,with the increase in the content of Nb,the impact of continuous reduction.Before and after the welding thermal cycle,the impact of 0Nb steel significantly decreased,while the same composition of Nb steel,the base material and coarse grain zone impact strength roughly equivalent.