Simulation And Experimental Research On Stamping Of 9Ni For Steel Large Head Of LNG Tank

Nowadays nation more concern about the low-carbon life have a sustainable future,Liquefied Natural Gas(LNG),which is known as clean energy,has growth very fast last few years,and the requirement has been raised,so it is used for storage.The demand for large-scale LNG storage tanks for transporting liquefied natural gas is also increasing.When manufacturing large storage tanks,the most important and difficult thing is the formation of large heads.When manufacturing traditional storage tank heads,it is necessary to constantly pass experiments and experience to obtain a relatively suitable production process.This is not only time-consuming and labor-intensive,but also the obtained process parameters are not necessarily accurate.Therefore,studying the high-temperature deformation behavior of 9Ni steel and the microstructure evolution law in the microstructure has great academic and engineering value for the formulation of large-scale head forming methods.In order to optimize the stamping and forming process of 9Ni steel large-scale head of LNG tank,this paper used 9Ni steel hot compression true stress-true strain curve and mathematical regression to construct 9Ni steel high temperature constitutive equation,explored 9Ni steel dynamic recrystallization critical conditions and constructed DRX model and conducted comparative verification.In DEFORM-3D,the stamping simulation of the thick plate 9Ni large-scale head was carried out to study the best stamping plan.The main contents were as follows:1.After thermal compression simulation of 9Ni steel,in the true stress-true strain curve of 9Ni steel,as the deformation temperature(770??830?)increases,the peak stress of 9Ni steel decreased,with a minimum of 192MPa;With the increase of rate(0.1333~1?0.2667~1),the peak stress of 9Ni steel increased significantly,up to 243MPa,and then the mathematical regression method was used to construct the high-temperature constitutive equation and DRX model of 9Ni steel.2.The correlation coefficient()and average relative error()between the true stress of 9Ni steel obtained by hot compression and the model prediction results were 0.969 and 6.18%,respectively,indicating the prediction results of the thick plate 9Ni steel high temperature constitutive model proposed in this experiment It was consistent with the experimental value.The9Ni steel high temperature constitutive model was used for DEFORM-3D simulation calculation,and the workpieces had no process defects such as cracks and wrinkles,which were consistent with the actual production workpieces,which proved that the constitutive equation can better reflect the actual deformation state of the workpiece in the simulation calculation.3.The initial grain size of 9Ni steel was 17.03?m,and the minimum grain size after thermal compression was 0.82?m and the maximum was 1.31?m.The thermal compression process of 9Ni steel was simulated in DEFORM-3D,and it was found that the material was unevenly deformed,and the DRX volume fraction decreased in the direction of easy deformation zone,indefinite deformation zone and small deformation zone,and the DRX grain size was in accordance with the directions of easy deformation zone,indefinite deformation zone and small deformation zone increased.In different samples,the equally crystalline grain dimensions were positive correlation to transshape level,transshape temperature and strain speed;DRX crystalline grain dimensions were positive correlation to transshape temperature,but strain speed;DRX bulk fraction were positive correlation to transshape level,transshape temperature and strain speed.4.In the process of stamping and forming simulation of the large-scale9Ni steel head of the thick plate,it was found that the die gap was too small(?32mm),which will cause the workpiece to be thinned significantly and will produce greater stress and strain concentration at the thinning;The faster the speed(?4mm/s),the higher of the punching force and the increase of stress on the material;the higher the punching temperature(>790?),the corresponding punching force will be reduced and the stress concentration will be relieved,but it will Accelerate the service life of the mold and increase the heating and cooling time of the workpiece.Considering comprehensively,the optimal process for stamping large-scale heads of thick 9Ni steel were a stamping speed of 3mm/s,a stamping temperature of 790?,and a die gap of 34mm.After the9Ni steel is solid solution treated,its grain structure is lath martensite and revolving austenite,and there are twins inside.And through CA simulation,it can be found that the DRX model of 9Ni steel is more consistent with the actual structure size.