Microstructure and Properties of JG4246A Superalloy Revert Purified by Vacuum Horizontal Continuous Casting
With the gradual development of industries such as aerospace,the demand for cast superalloy products is increasing.During the casting process,due to the needs of design,there are often a large number of cast systems,which makes the yield of parts relatively low,often accounting for 40％.If thin-walled parts are cast,the yield will be lower,often accounting for 20％.At the same time,there are cast scrap rates,all above will result in many cast superalloys forming reverts,and the number of reverts is staggering with increasing number of cast superalloy products.This results in a large accumulation of cast superalloy reverts,leading to a massive waste of strategic resources.Non-metallic inclusions and harmful gases are the main obstacles affecting the reuse of cast superalloy returned materials,the existence of inclusions will seriously affect the preparation cost and service performance of cast superalloys,especially the fatigue properties of alloys.The effective removal of the inclusions and reduction of harmful gas content are the main tasks when purifying cast superalloy reverts.According to the alloy composition and the inclusion characteristics of the reverts,the returned materials of casting superalloys are divided into three categories:(1)high Hf content cast superalloy,the inclusions in the reverts are mainly composed of a large amount of high specific gravity HfO2;(2)high Cr content casting superalloy,the N content in the revert is relatively higher,and there are many N-rich inclusions in the reverts;(3)high Al and Ti content casting superalloy,the reverts contain a large amount of low-specific gravity inclusions,such as Al-rich inclusions and Ti-rich inclusions.JG4246A alloy is a cast Ni3Al-based high temperature structural material with Al,Ti,Hf content as high as 10％,it is the representative of high Al and Ti content cast superalloys,and it has been used in batches.Since the alloy castings are all complex thin-walled parts,the preparation is very difficult,and the yield of the castings is low.Those have resulted in the formation of many reverts,and the need for recycling and reuse of the reverts are urgent.As a representative of high Al and Ti system casting superalloys,JG4246A alloys are easy to form dense oxide films,which makes the processing of reverts difficult,and a common key technology is urgently needed to solve the existing bottleneck.First,the types of inclusions on the surface of different types of JG4246A revert alloy were analyzed,and shot blasting or alkaline washing+shot blasting treatment were carried out for different types of JG4246A revert alloy.And then the surface inclusions of JG4246A revert alloy after cleaning were analyzed,which were dominated by Al-and Si-rich inclusions,and there was a small amount of HfO2 and Zr-and Si-rich oxides.And then,the vacuum horizontal continuous casting equipment with a furnace capacity of 800 kg was used to purify JG4246A revert alloy with addition proportion 100％.Since the density of most inclusion particles in the reverts was lower than that of the superalloy melt,the inclusions floated to the top surface of the melt.Therefore,they were far away from the continuous casting filling area at the bottom of the crucible.And then through the continuous casting bottom casting process technology,the floating inclusions were eliminated.The casting billet was directly formed in the water-cooled copper crucible mold,thus avoiding the secondary contamination caused by contacting with sprue cup and the pouring trough.At last,the returns master alloy bars purified and prepared by vacuum horizontal continuous casting possess high cleanliness.The O,N and S total contents of the returns master alloy bars were not higher than 12 × 10-6,and inclusion contents were not higher than 0.46 mg/10 kg.All above verified that the cleanliness of returns master alloy reached the advanced level of domestic new materials.JG4246A revert alloy rods were cast into mechanical properties test rods,and the microstructure and morphology of mechanical properties test rod were basically the same as the new material test rod with the same casting process.And the tensile strengths at room temperature,600,800 and 1000 ℃ reached 808,843,902 and 539 MPa,respectively.The stress rupture lives at 800 ℃/490 MPa and 1100 ℃/60 MPa were 212 h and 104.2 h.The high cycle fatigue lives under different stress states had reached the level of new materials,especially the high cycle fatigue lives at 850 ℃/461 MPa and 850 ℃/229 MPa increased several times over the median value of fresh alloy,and no inclusions were found in the high cycle fatigue fracture.The researches showed that JG4246A revert alloy purified by vacuum horizontal continuous casting technology had reached the level of new material.
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