Simulation Research On The Solidification Process Of Mn18Cr18N Hollow Ingot

In recent years,with the rapid development of nuclear power and petroleum chemical industry,the manufacturing technology of hollow parts have been got more and more attention of the people.Compared with the traditional manufacturing process of hollow parts with solid ingots,the manufacturing technology for hollow parts with hollow ingots is material-saving,power-saving and free from upsetting and punching operations.With the improvement of the numerical simulation of solidification and the development of the casting software,large hollow ingot solidification process could be analyzed in the laboratory.The influence factors on the hollow ingot solidification process can be explored.It ensures high quality of hollow ingots in the actual production.The main contents can be drawn as follows.(1)The solidification process of a hollow ingot with 65 t weight was simulated by ProCAST.The influence of different boundary conditions on the final solidification position has been analyzed.The boundary conditions were obtained when the actual final solidification position located at 35% wall thickness far from the core.(2)By using the same ingot cases,gating system and boundary conditions with 65 t solidification process,the solidification process of a Mn18Cr18 N hollow ingot with 4.2t weight was simulated also.The influences of pouring temperature and pouring velocity on solidification processes have been analyzed.The results indicate that some axial micro-porosities close to internal surfaces under the root of riser have been observed in the hollow ingot.The micro-porosities increased with the increase of pouring temperature and pouring velocity.The pouring temperature of 1415? and the pouring velocity of 25kg/s is the reasonable pouring process,which is called “low temperature and slow injection”.For reasonable pouring process,the temperature field,solid fraction line and shrinkage were analyzed.(3)Under the different boundary conditions,the solidification process of aMn18Cr18 N hollow ingot with 4.2t weight was simulated.The micro-porosities inside the hollow ingot were analyzed.The results indicate that,when the internal and outside boundary conditions are the same,some discontinuous micro-porosities have been observed in the core location of hollow ingot.The distance between micro-porosities and the root of riser is 54 mm.Its degree was significantly less than that under different the internal and outside boundary conditions.When the boundary conditions are change,compared with the constant boundary conditions,both the degree and distribution area were similar.(4)Under the conventional casting,the microstructure of a Mn18Cr18 N hollow ingot was simulated.It is found that the main nucleation parameters affecting the CET columnar-equiaxed transition is volume nucleation rate Nv;The primary dendrite arm space of columnar is changed by surface nucleation rate Ns;?TV,max and ?TS,max have little effects on microstructure;Both Nv and??Tv will affect grain size,but the main factor is Nv;With the increase of Ns and??Ts,the primary dendrite spacing of the columnar crystal will increase and there is no obvious change of CET transformation.When the growth kinetics coefficient and the pouring temperature increased,CET transformation was delayed and transition gradually slow.The length of columnar was mainly affected by the constant boundary condition.The changing boundary conditions will accelerate the CET transformation.(5)Under the electro-slag re-melting,the microstructure of a Mn18Cr18 N ingot was simulated.The simulation results have been compared to the experimental results.The results indicate that,on the longitudinal section,the microstructure of electro-slag ingot is composed of columnar crystal.The columnar crystal at the bottom of ingot grows along the axial direction.The inside of ingot is composed of an inverted V columnar crystal zone.Columnar crystal is 60 degree with the axial direction.On the cross section,the surface of electro-slag ingot is composed of fine grains.The more close to the core,the cross-sectional area of the grain is larger.Compared to the experimental results,the simulation solidification characteristics is very close to that in experimental results,which is verified the rationality of ESR model.