| BT22 titanium alloy is an important aerospace structural material,used in the manufacture of aircraft engine blades,landing gear,etc.Its alloying element content is as high as 12.7 %,among which high melting point alloys contain 5 %,easy segregation alloys 2 %,and 5 % low melting point alloys,which are prone to segregation and other quality defects.Therefore,the choice of smelting process is very important.This research uses vacuum consumable electric arc furnace to smelt BT22 titanium alloy.Through trial production and computer simulation of small-sized ingots,the ingot metallurgical quality influencing factors and control measures are studied,and the industrialized production of large-sized ingots is carried out,and the production process is studied.The main research contents of the thesis are as follows:A vacuum melting experiment of a small ingot with a size of Φ622 mm and a weight of 2000 Kg was carried out,and the influence of raw material selection,alloy addition,and melting process on the metallurgical quality was studied.Studies have shown that in order to prepare a monolithic electrode with uniform mixing of materials,high-grade small-grain sponge titanium and a small particle size and uniform size master alloy should be used in the selection of raw materials,the grain size of Cr should be controlled within3 mm;by ensuring that the monolithic electrode mixes uniformly,the welding quality of consumable electrodes is ensured,standardize the cleaning and protection of each process,strengthen the management of the smelting process,can reduce α defects;through the reasonable selection of raw materials and the use of "one small,two large and three moderate" processes,and strict control during electrode preparation and vacuum melting,avoid introducing new pollutants,which can effectively reduce high-density inclusions;through the selection of raw materials,alloy addition methods,electrode preparation,oxygen content control,process parameters(melting power,magnetic field,heat sealing),alloy element segregation behavior and ingot metallurgy The analysis of quality influencing factors puts forward solutions and determines the reasonable production process of BT22 titanium alloy.In the research,through the analysis of electromagnetic field control model,flow field control model,temperature field control model,and molten pool control model,a computer simulation mathematical model of VAR smelting was established,and the smelting process of BT22 ingots with Φ820 mm specifications and a feed volume of 6.8t was simulated.The study found that the depth of the ingot molten pool changes with the input energy.A small molten pool is formed first,then the depth of the molten pool gradually increases,and finally the depth gradually decreases.Using suitable smelting process parameters can reduce the degree of alloying element segregation and obtain ingots with uniform chemical composition.During the smelting process,the bottom begins to cool down first,and then the four walls of the mold begin to cool;thus,a fine crystal zone is formed at the bottom and edges of the ingot,a columnar crystal zone is formed in the middle,and the head is an equiaxed zone and shrinkage cavity position.The simulation results also show that the use of a "small current,low melting rate" smelting process can form a relatively stable and flat liquid molten pool,thereby reducing segregation.On the basis of the above,the trial production of Ф820 mm BT22 ingot was carried out,and the stability of the production process of large-sized ingot was studied.Studies have shown that by selecting 2～12.7 mm small particles of sponge titanium and strong magnetic sieving control,the introduction of high-density substances in the raw materials can be avoided;It can effectively improve the metallurgical quality of the ingot.By accurately measuring the weight of sponge titanium and master alloy,using an automatic mixing cloth system,and performing the electrode block turn-around treatment before welding,the uniformity of the chemical composition of the ingot can be improved.Onetime electrode welding through a vacuum welding box can effectively reduce metallurgical defects such as low-density inclusions caused by oxidation and other reasons.The trial-produced Ф820 mm BT22 ingot has uniform chemical composition.The statistical analysis of the chemical elements of 20 ingots shows that the production process is stable and reliable;the performance test of the Ф400 mm bar after the ingot forging shows that the indicators meet the design and use requirements. |
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