In present paper, a ladle–tundish–mold CFD model and a macrosegregation model were utilized to investigate the effects of the multiple pouring(MP) process on the macrosegregation in a 438-ton steel ingot. Firstly, the model was partially proved as compared to the measured carbon distributions along the transverse sections in the riser of ingot. Then, the comparison between the single pouring(SP) and MP process has been carried out to study their influences on the macrosegregation in ingot. Besides, the predicted macrosegregation results in MP process which introduced the improved riser fixed with an insulating sleeve were compared with that in traditional MP process. The traditional MP process leads to certain favorable initial carbon distribution in the mold, which has some favorable influence on suppressing the positive segregation in ingot. The holding time of the low carbon in the riser is the main factor to suppress the positive segregation in ingot. Improved insulating sleeve can prolong the holding time of the low carbon in the riser and release the positive segregation in the riser of ingot. Improvement of the insulating effect of the riser is an efficient method to control macrosegregation in large steel ingot.
A ladle-tundish-mould transportation model considering the entire multiple pouring(MP) process is proposed. Numerical simulation is carried out to study the carbon distribution and variation in both the tundish and the mould for making a 292 t steel ingot. Firstly, the fluid flow as well as the heat and mass transfer of the molten steel in the tundish is simulated based on the multiphase transient turbulence model. Then, the carbon mixing in the mould is calculated by using the species concentration at the tundish outlet as the inlet condition during the teeming process. The results show a high concentration of carbon at the bottom and a low concentration of carbon at the top of the mould after a MP process with carbon content high in the first ladle and low in the last ladle. Such carbon concentration distribution would help reduce the negative segregation at the bottom and the positive segregation at the top of the solidified ingot.
We present the results of systematic molecular dynamics simulations of pure aluminium melt with a well-accepted embedded atom potential. The structure and dynamics were calculated over a wide temperature range, and the calculated results(including the pair correlation function, self-diffusion coefficient, and viscosity) agree well with the available experimental observations. The calculated data were used to examine the Stokes–Einstein relation(SER). The results indicate that the SER begins to break down at a temperature T_x(~1090 K) which is well above the equilibrium melting point(912.5 K).This high-temperature breakdown is confirmed by the evolution of dynamics heterogeneity, which is characterised by the non-Gaussian parameter α_2(t). The maximum value of α 2(t), α_(2,max), increases at an accelerating rate as the temperature falls below Tx. The development of α_(2,max) was found to be related to the liquid structure change evidenced by local fivefold symmetry. Accordingly, we suggest that this high-temperature breakdown of SER has a structural origin. The results of this study are expected to make researchers reconsider the applicability of SER and promote greater understanding of the relationship between dynamics and structure.
The effect of solidification cooling rate on the size and distribution of inclusions in 12%Cr stainless steel was investigated. A wide range of solidification cooling rates(from 0.05 to 106 K·s-1) was achieved using various solidification processes, including conventional casting, laser remelting, and melt spinning. The size and distribution of inclusions in the steel were observed and statistically collected. For comparison, mathematical models were used to calculate the sizes of inclusions at different solidification cooling rates. Both the statistical size determined from observations and that predicted from calculations tended to decrease with increasing cooling rate; however, the experimental and calculated results did not agree well with each other at excessively high or low cooling rate. The reasons for this discrepancy were theoretically analyzed. For the size distribution of inclusions, the effect of cooling rate on the number densities of large-sized(> 2 μm) inclusions and small-sized(≤ 2 μm) inclusions were distinct. The number density of inclusions larger than 1 μm was not affected when the cooing rate was less than or equal to 6 K·s-1 because inclusion precipitation was suppressed by the increased cooling rate.
In order to perform numerical simulation of forging and determine the hot deformation processing parameters for 30Cr2Ni4MoV steel,the compressive deformation behaviors of 30Cr2Ni4MoV steel were investigated at the temperatures from 970to 1 270℃and strain rates from 0.001to 0.1s-1 on a Gleeble-3500thermo-mechanical simulator.The flow stress constitutive equations of the work hardening-dynamical recovery period and dynamical recrystallization period were established for 30Cr2Ni4MoV steel.The stress-strain curves of 30Cr2Ni4MoV steel predicted by the proposed model well agreed with experimental results,which confirmed that the proposed equations can be used to determine the hot deformation processing parameters for 30Cr2Ni4MoV steel.
