The effects of 0.0001%，0.0018% and 0.0037% S content on the solidification characteristics of K417G alloy were studied by isothermal solidification experiment in the temperature range of 1340-1230 ℃. The results show that S can reduce the solidus temperature of the alloy and enlarge the solid-liquid two phase region. When the S content increases from 0.0001% to 0.0037%， the solidus temperature of the alloy decreases from 1255 ℃ to 1245 ℃. During the solidification process， the S element segregates in the liquid phase and precipitates out as the Y phase in the final solidification zone. And S promotes the enrichment of Al and Cr elements at the solid-liquid interface. At the same isothermal temperature， the increase of S content promotes the increase of the volume fraction of MC carbide，γ+γ΄ eutectic and Y phase， and has little effect on the morphology and precipitation temperature of MC carbide and γ+γ΄ eutectic， but the precipitation temperature of the Y phase is increased from 1230 ℃ to 1240 ℃.

The microstructure and morphology of the alloy were characterized by metallographic microscope and thermasimulation test and other equipment， and the thermal deformation parameters were set at different strain temperatures of 850-1150 ℃ and strain rates of 0. 1-10 s ^-1. It was analyzed by combining the stress-strain curve of thermal simulation compression test and the microstructure morphology， the thermal deformation behavior and microsturcture morphology evolution process of 4J32 super invar alloy （Fe-32Ni-4Co） at high temperature 850-1 150 ℃ were systematically studied. It is found that no dynamic recrystallization occurs during hot deformation of 4J32 super invar alloy below 900 ℃， and there are a lot of deformed grain structures in the alloy. When the thermal deformation temperature is greater than 1 050 ℃， the dynamic recrystallization of the alloy begins， and the faster the strain rate， the higher the dynamic recrystallization degree.The results show that the optimum thermal deformation temperature of super invar alloy is greater than 1100 ℃ and the strain rate is 10 s ^-1.

The increasing service temperature of aero-engine turbine discs makes more stringent requirements for oxidation resistance of the materials. U720Li alloy is a high-strength nickel-based superalloy for turbine discs with a long-term service temperature up to 750 ℃. Clarifying the oxidation behavior at service temperatures of this alloy is of great significance for improving the service life of high-performance turbine discs. In this paper， the oxidation kinetics curve of forged U720Li alloy at 750 ℃ has been determined by the static weight gain method， and the oxide film morphology， structure and element distribution in different oxidation stages were analyzed by XRD and SEM-EDS. The results show that the U720Li alloy has excellent oxidation resistance at its service temperature， and its isothermal oxidation kinetic curve at 750 ℃ basically follows the cubic law， reaching the full anti-oxidant level. It has been analyzed that the loose γ-Cr ₂O ₃ is generated at the early oxidation stage of U720Li alloy. The γ-Cr ₂O ₃ layer spalls continuously as the oxidation proceeds， and the oxide film becomes more continuous and dense and forms a complex multilayer structure. Meanwhile， a γ´ depleted layer is gradually formed within the matrix nearby the oxide film. In the stable oxidation stage， the oxide film becomes more continuous and dense， forming a regular double-layer structure which includes the dense α-Cr ₂O ₃ outer layer and α-Al ₂O ₃ inner layer. The formation of continuous dense α-Cr ₂O ₃ and α-Al ₂O ₃ layers can effectively prevent the internal diffusion of oxygen and external diffusion of alloying elements， which guarantees the excellent oxidation resistance of U720Li alloy.

Low nitrogen content can control the formation of TiN inclusions， thereby improving the metallurgical quality and comprehensive performance of nickel based high-temperature alloys. This article first compared the differences between the standard Gibbs free energy and the interaction coefficient of alloy elements with N， Ti activity in nickel based and iron based metal liquids， it pointed out that two different sets of thermodynamic data from nickel based and iron based metal liquids cannot be mixed.The thermodynamic model for nitrogen removal of IN718 alloy was established based on the existing thermodynamic parameters of nickel based alloys. It was found that reducing temperature and increasing vacuum degree to reduce nitrogen partial pressure while meeting other smelting conditions are the direct means to reduce nitrogen content in the alloy liquid. The addition of different alloying elements has different effects on nitrogen removal. At the same time， the thermodynamic model and segregation model for TiN precipitation were established， and the calculation results showed that under the production temperature of IN718 at 1 450 ℃， the ［N］ content in the alloy liquid was controlled below 43.69×10 ^-6， the solute elements N and Ti are enriched and precipitated in the liquid phase during solidification. The calculated precipitation temperature is 1 468 K， and the solid fraction  is fs 0.829. If we want to control the solid phase fraction  fs to be above 90% or 95% respectively for precipitating TiN inclusions， ［N］ needs to be controlled below 25.00×10- ⁶ and 15.00×10 ^-6 respectively.

GH4710 nickel base alloy ingots， melted by VIM plus VAR， were subjected to trails of two-stage high-temperature homogenizing heat treatments， the microstructure and grain size of the ingots before and after heat treatment were analyzed by metallographic microscop. the distribution and content of alloy element in the ingot before and after heat treatment were evaluated by scanning electron microscope and electron probe， as well as to calculate the segregation index for alloying elements in different positions of ingots. Test result verified that， the two-stage homogenizing heat treatment at （1 150±50）℃×30 h-（1 200±10）℃×50 h， it could significantly eliminate the eutectic phase in the structure of GH 4710 ingot and reduce the element segregation in the ingot，and the mechanical properties of the forged bar are improved significantly. Under the test conditions of 980 ℃， 120 N/mm ²， the persistence performance reached 126 h and 134 h， which was about double improvement compared with 53 h and 74 h of un-homogenizing heat treatment production. The persistent elongation rate has also increased by more than 50%.

In this paper， the main research object is the deformed superalloys that have passed the national acceptance， identification or batch production， which are included in the China Superalloy Manual （2012 edition），through a large number of literature research， the role of Nb in deformed superalloys is summarized. The results show that Nb is not only the main solution strengthening element， but also the main precipitation strengthening element in superalloys. In the solution strengthened superalloy， NbC and Z-（Ni _0.04Cr _0.83Fe _0.13）1.9（W _0.15Mo _0.09Nb _0.76） _3.3 N are mainly Nb formed， which can significantly improve the creep strength of the alloy， reduce the creep rate， and ensure the good welding process performance of the alloy； In precipitation strengthened superalloys γ′- Ni ₃（Al，Ti）、γ″-Ni ₃ Nb、δ-Ni ₃ Nb、ε- Ni ₃（Nb，Ti） and Laves-（FeCoNi） _1.84（NbTiSi） etc are mainly Nb formed， and good comprehensive properties can be obtained by controlling the changes of the size， morphology and distribution of the precipitated phase. At present， nearly 30% of deformed superalloys are strengthened by Nb， and the development of modern superalloy materials has been inseparable from the participation of Nb.

 In this paper ， the microstructure of Inconel 783 alloy 508 mm ingot produced by VIM+VAR process in Daye Special Steel was analyzed by means of optical microscope， SEM， XRD and DSC. The results show that the ingot crown can be divided into two equiaxed crystal zones and two columnar crystal zones， and the shrinkage cavity depth of the ingot crown is about 70 mm. Within 50-100 μm thick area of the ingot surface， there is a large number of phase β precipitation. The average dendrite spacing in the center of the VAR ingot is about 131 μm， and there are a lot of white Nb-rich inter-dendritic phases in the center of the ingot. The solution temperature of the inter-dendritic phase is 1 189.6-1 209.7 ℃. The matrix of the VAR ingots is a typical face-centered cubic structure with a lattice constant of 0.356 9 nm. The melting temperature of the VAR ingots is 1 356.8-1 399.6 ℃.

With regard to the whole production process of N08120 nickel-based thick plate， the precipitation law of material in each process was analyzed by using metallographic microscope， scanning electron microscope and Thermo-Calc software. The results indicate that the main precipitation type in N08120 nickel base alloy thick plate is Z phase， accompanied by dispersed MX precipitation phase， which are distributed in strips along the rolling direction. Besides， σ phase， M ₂₃C ₆ precipitation and transition state from MX to Z phase are also found in ingots and forging billets during production. The analysis reveals that during the mould casting process， the internal heat dissipation of the ingot is slow， which is beneficial to the transformation of NbN to Z phase， and the ingot surface is found to have σ phase precipitation during the die cooling process when it stays at medium and low temperature for a long time. The forging billet and rolling plate are air-cooled after deformation， the main precipitation phase types are Z phase and MX phase. After solution treatment， the species and distribution of precipitated phases in plate have not changed obviously， indicating that Z phase and MX phase have rapid precipitation rate and high thermal stability.

The melting method of nickel-based superalloy is the decisive factor related to the alloy quality. Vacuum induction melting can effectively control the content of O， N， H and other gases and harmful impurities in alloy ingots， and accurately control the alloy composition. On this basis， the remelting of alloy （electroslag remelting and vacuum arc remelting） can further reduce the content of S， P and other harmful impurities， eliminate the defects such as component segregation and shrinkage cavity， and optimize the control of the solidification structure， so as to achieve the melting of large size and high-quality alloy ingots. This paper reviews the progress of the melting process of nickel-based superalloy， and focuses on the principles and characteristics of common melting technologies including vacuum induction melting， electroslag remelting， and vacuum arc remelting. The research progress of "vacuum induction melting + protective atmosphere electroslag remelting"， "vacuum induction melting + vacuum arc remelting" duplex melting process and "vacuum induction melting + protective atmosphere electroslag remelting + vacuum arc remelting" triple melting process in nickel-based superalloy melting are discussed. Finally， some suggestions on the selection and development direction of nickel-based superalloy smelting process are propounded.

The hot reduction deformation behaviors of N08800 Iron-Nickel base alloy (/% ：0.015C , 20.8Cr , 31.2Ni, 0.42A1 , 0.35Ti) are investigated by hot compression tests with Gleeble-3800 simulated machine. The true stress-true strain curves of alloy at 1150-1280℃ with strain rate 1 ~20 s ^-1 are obtained. The a = 0.0092 and n=4.34, and activation energy (Q) =432780 J/mol of high-temperature deformation constants for N08800 alloy are obtained by linear regression of peak stress, the hot deformation peak constitutive equation of N08800 alloy is established. Results show that in hot reduction deformation process at higher temperature with lower strain rate the dynamic recrystallization of the N08800 alloy occures easily, the suitable hot working parameters are 1200-1250℃ and 1-10 s ^-1. Commercial production result shows that of N08800 alloy with roughing pass redution 30%-35% , breakdown at 1 150℃ end rolling at 1000℃ ,the 5-6 mm hot rolled coiledge quality is fine.

The precipitation behavior of δ phase of 1 050 °C 1 h solution-treated GH4169 alloy aging treated at 800 ~980 °C and the dissolution rule of δ phase in alloy after 900 °C 20 h pre-precipitation treatment alloy solution-treating at 980 ~ 1 040 °C are studied. The results indicate that the peak temperature of δ phase precipitation occurred at approximately 900 °C. δ phase precipitates in grain boundary and twin boundary first, and δ phase transforms from granular to short rod and even needle. Intragranular δ phase transforms from γ" phase. Growing up mechanism of δ phase is influenced by temperature. δ phase dissolves during no less than 980 °C solution treated from δ phase boundaries first, and then transforms from needle to short rod and granular. Needle-δ phase in grain boundary dissolves faster, and transforms to short rod or granular. The δ phase shall be completely dissolves by solution-treated at ≥1 020 °C.

The GH2132 alloy (1.90% ~2. 30%Ti) has the problems of large loss of Ti element ( A[Ti]0. 37% ~ 0. 57% ) in ESR process, the Ti content in steel is only 1. 83% ~ 1. 89% in ESR middle and last period. By adopting (/% ) CaF： Al ₂O ₃： CaO： TiO ₂ =75： 15： 5： 5 slag system to replace original CaF270% + Al ₂O ₂0% slag system, the unstable oxide (SiO ₂ + FeO) in the slag is controlled to be less then 0. 6% , and die controlled melting rate of the smelting process decreases from 6. 1 -6. 3 kg/min to 5. 3 -5. 6 kg/min, etc technological measures, as a result, the Ti content in steel at ESR ingot each part is 2. 06% ~2. 21% , and the Ti burning loss A[Ti] decreases to 0. 19% ~0. 34%, ESR ingots are sampled to check the inclusions after forging, and it is found that the inclusions have also been significantly improved after the process adjustment. The class inclusions of D fine system is controlled below rating 0. 5, which meets the requirements.

Nb and Si diffusing rule at 1 190℃ in GH2907 (0.02C,38,20Ni,13.92Co,4. 92Nb,l. 60Ti,0.32Si) alloy ϕ508 mm 3 t ingot is studied by using optical microscope, scanning electron microscope etc. Studies have shown that the dendrite spacing of the GH2907 alloy ϕ508 mm ingot is approximately 110μm, the apparent diffusion coefficients of Nb and Si at 1190℃ are respectively D = (0.704 ±0.041) X 10 ^-14m ²/s and D = (1. 870 ±0.511) x 10 ^-14m ²/s. Theoretical calculation shows that,when Nb diffuses 44.8 ~50.3 h or Si diffuses 14.0~24.5 h at 1 190℃,the residual segregation index δ _i will reach 0.02 respectively.

The microstructure evolution and the hardness change rule of GH2036 alloy Φ150 mm bar solution treatment at 1120~1240 ℃ are studied by optical microscope and SEM and HB hardness testing device. Studies have shown that there are two types of rich Cr and Nb-V carbide in the forging microstructure of GH2036 alloy after forging air cooling, most of carbides are backdissolved and the grain size is basically uniform after 1220 ℃solution treatment. The HB hardness number of the alloy is reduced with the increase of heat treatment temperature, but the HB hardness number increases from 185 to 193 at temperature increasing from 1160 to1200 ℃, this is mainly due to the large amount of carbides solving back to matrix.

The microstructure evolution and hardening behavior of CH2696 alloy with aging hardening by different heat treatment scheme are studied. The results show that the supersaturation of CH2696 alloy matrix increases with the increase of solid solution temperature. In 1100 ℃ 2 h solution-treated CH2696 alloy the γ′phase precipitates adequately in 780 ℃ 16 h aging process, and the hardness increases significantly. The low temperature at 650 ℃ 16 h aging treatment plays the role of supplementary aging, it HBW hardness number is 350.