Chemical composition analysis on industrial scale ingots and castings of TiAl alloys

The chemical composition variation of the TiAl-4722 alloys was examined in a batch of the industrial scale master ingots,and in the corresponding castings prepared by conventional vacuum arc remelting(VAR)combined with induction skull melting(ISM)and investment casting processes.The content changes of major elements and interstitial elements were evaluated based on the chemical analysis at the top and bottom of the ingots and castings.Results show that the contents of C,N,H,Fe and Si have almost no change in the ingots and castings,suggesting that the chemical analysis on these elements can be based on the batch analysis.The O content keeps almost the same in different ingots,but exhibits relatively large differences in castings,which was probably influenced by the reaction between the shell mold and the molten alloy,and the spalling of face coat of the shell mold during casting.For the major elements of Al,Nb and Cr,the composition difference between the top and the bottom of the ingots is less than that of the castings.But for the O element,the trend is different,especially for the castings,suggesting that the investment casting is a homogenization process for Cr and Nb,but a differentiation process for O.The contents of major elements in castings fluctuate mainly in the same range as that in the ingots,indicating that the contents of the major elements are controllable during investment casting.

Teeming stream protection using an argon shroud during casting of steel ingots

Two kinds of argon shroud protection devices with two different basic structures were designed and investigated. Industrial experiments and numerical simulations were used to examine the protection effect, and the mechanism of air entrapment during the casting of steel ingots was analyzed. The influence of the structure of the argon shroud protection device on the protection effect was investigated. An argon shroud protection device mounted to the nozzle holder on the bottom of the ladle does not provide a good protection effect because air can easily flow into the teeming system and cause reoxidation of molten steel during teeming. By contrast, an argon shroud protection device seated on the top of the central trumpet provides an excellent protection effect, where air has little chance of flowing into the teeming system during casting. The feasibilities of the argon shroud protection devices are discussed.

Investigation of the effect of argon protection behavior in the ingot casting process

With the continuous improvement of product quality and function,the quality control of mold steel is becoming increasingly stricter. Argon protection is essential for ensuring casting quality during ingot casting. The development of argon protection in ingot casting and the production process of enclosed argon protection in 40 t line is discussed,w ith particular focus given the factors affecting the flow of oxygen in the argon protection cover are discussed. The influence of some related factors on the oxygen content is analyzed. On the basis of the online measurements of the oxygen content,the optimized operational approaches for improving the effect of argon protection are developed. This can decrease the liquid steel via secondary oxidation,and improve the quality of the ingots.

Volume-averaged modeling of multiphase solidification with equiaxed crystal sedimentation in a steel ingot

Macrosegregation is a critical factor that limits the mechanical properties of materials.The impact of equiaxed crystal sedimentation on macrosegregation has been extensively studied,as it plays a significant role in determining the distribution of alloying elements and impurities within a material.To improve macrosegregation in steel connecting shafts,a multiphase solidification model that couples melt flow,heat transfer,microstructure evolution,and solute transport was established based on the volume-averaged Eulerian-Eulerian approach.In this model,the effects of liquid phase,equiaxed crystals,columnar dendrites,and columnar-to-equiaxed transition(CET)during solidification and evolution of microstructure can be considered simultaneously.The sedimentation of equiaxed crystals contributes to negative macrosegregation,where regions between columnar dendrites and equiaxed crystals undergo significant A-type positive macrosegregation due to the CET.Additionally,noticeable positive macrosegregation occurs in the area of final solidification in the ingot.The improvement in macrosegregation is beneficial for enhancing the mechanical properties of connecting shafts.To mitigate the thermal convection of molten steel resulting from excessive superheating,reducing the superheating during casting without employing external fields or altering the design of the ingot mold is indeed an effective approach to control macrosegregation.

Research and application of numerical simulation to optimization of ingot casting process

During the ingot casting process, the parametric changes of the molten steel pouring process often cause both ingot surface and internal quality defects. With the increasingly wide application of computers in industrial technology ,numerical simulations of the molten steel pouring process enable predictions of the defects that will arise during the pouring and solidification process, especially for the molten steel flow during the early stages of casting. In addition,using a computer to simulate the casting process of a 40 t ingot and solidification can prevent many defects. The simulation results indicate that controlling the pouring speed to less than 80 kg/s, hanging the casting powder in a mold with the hanging height maintained at 100-150 mm, and controlling the taper angle of the mold brick outlet to a suitable level can reduce the probability of slag entrapment and improve the internal and surface quality of the ingot.

Inclusions in Runner Steel During Ingot Casting

This paper reported the observation of inclusions in the steel of an ingot runner. Thermodynamic modeling was performed to study the formation mechanism and sources of inclusions. CFD modeling on fluid flow, heat transfer, solidification of molten steel was carried out and the entrapment of inclusions in runner steel was predicted and compared with the measurement. Al2O3-based inclusions were the main ones in the steel samples. MgO?Al2O3 mainly stemmed from the lining refractory. The high MnO inclusions in the runner steel came from the runner slag. The effect of natural convection was very important for the cooling and solidification of the steel in the runner. Both the observation and the modeling show that 】 50μm inclusions more accumulated on the upper area in the runner and 【 50μm inclusions dispersed well and more accumulated on the lower area of the runner.

Inclusion Distribution in Ingots Investigated by Dissection

Inclusion distribution in ingots was studied by dissection of a 16.8 t P12 ingot and a 5.0 t H13 ingot, with the analysis of T[O], original position statistic distribution analysis （OPA）, metallographic microscope static analysis and small sample electrolysis. The results showed that the inclusions in ingots were uneven; a positive segregation area was found in the center and lower part of the ingot, while a negative segregation area was present in the central part of ingot top; inclusion segregation in a large size ingot was severer than that in a small one. A new con cept, named inclusion segregation index, was put forward to quantify the segregation degree of inclusion. It was found that the segregation indexes drawn from T[O] analysis and OPA fit well, but they were different from those obtained by metallograpbic microscope static analysis and small sample electrolysis in the investigation of Pl 2 ingot, which contained a higher sulfur content; while the segregation index drawn from T[O] analysis was close to that from metallographic microscope static analysis in the H13 ingot with a lower sulfur content.

Role of radiative and convective heat transfer during heating of an ingot product in a tubular furnace:experiment and simulation

Convective heat transfer and radiative heat transfer are two essential heat transfer modes in the heating process of steel;it is important to understand the role of them during the heating process clearly.The effects of the convective and radiative heat transfer during the heating process of a cast ingot in a tubular furnace have been studied by the designed natural and forced convection experiments and mathematical simulations.The heating time for the center of the ingot to reach the furnace temperature is decreased with the increase in furnace temperature.According to the experimental and simulation results,a model is proposed regarding the role of radiative and convective heat transfer in the heating process.At low temperature,the convective heat transfer plays a dominant role,while at high temperature,the influence of radiative heat transfer is larger.And a critical temperature exists between them.The forced convective heat transfer can enhance the influence of the convective heat transfer.The critical temperature can be shifted to higher temperatures.