GH2909 alloy is an important engineering material for advanced aero-engine clearance control technology. It is mainly used to manufacture clearance control parts such as turbine casing, bearing ring and honeycomb support ring for fourth-generation engines to reduce air leakage loss, improve efficiency and reduce fuel consumption rate. GH2909 is developed by increasing Si content and adjusting heat treatment process on the basis of GH2907 alloy. GH2909 is Fe - Ni - Co base age hardening new low expansion, high temperature alloy under 650 ℃ with high strength and plasticity, low thermal expansion coefficient, almost constant elastic modulus and good oxidation resistance and comprehensive mechanical properties, such as cold and hot fatigue can reduce the gap between the rotating components and stationary parts, achieve clearance control, save energy and reduce consumption, It is an ideal superalloy material for aviation and aerospace engines to increase engine thrust, so it has been widely used in aircraft engines.
For MANY years, due to the limitation of forging equipment conditions: there are only 2000 tons of fast forging press, so the production of large specification high-temperature alloy forging bar is the short board of the development of high-temperature alloy in a company. The main problems of GH2909 alloy bar are as follows :(1) the structure is coarse and uneven, which leads to high ultrasonic clutter and even serious attenuation of bottom wave; (2) The performance test data fluctuates greatly. With the improvement of forging equipment conditions: 4500 tons fast forging press and 1800 tons fine forging press were put into operation, and in order to improve and improve the quality of GH2909 alloy large forging material, the influence of forging process on the microstructure and properties of GH2909 alloy large bar was studied.
GH2909 alloy smelting process route is vacuum induction + vacuum arc remelting, will Φ 440mm electrode vacuum arc remelting Φ 508mm steel ingot, steel ingot after uniform heat treatment, forging to produce large size superalloy forging material.
The forging process of step by step cooling and large deformation is adopted, and the deformation of each fire is more than 30%. Heating temperature of final forging: 1000℃; Most deformation temperatures: ≤ 955℃, final forging temperature: ≥ 870 ℃; Three forging methods were adopted :(1) direct drawing of the whole ingot of 2000 tons fast forging press + middle section + forging with one fire respectively; (2) For the whole ingot, 4500 tons of fast forging press with two upsetting and two drawing + middle cutting + one fire of fine forging machine with 1,800 tons of each; (3) 4500 tons of fast forging press the whole branch drawing length + two ends of the clamp mouth + middle cutting section + using the leakage disc two upsetting two drawing +1800 tons of one fire fine forging machine forming material; Then, the center, 1/2R, edge tissue and transverse property samples were taken from the bar, and the microstructure and mechanical properties were observed by optical microscopy, and the finished products were tested by ultrasonic flaw detection after polishing. The test results show that:
(1) The tonnage limitation of 2000 tons fast forging press equipment is obvious.
(2) In Method 2, there is a small amount of mixed crystal structure in the center and 1/2R of the bar cross section after forging, and the edge grain reaches 8 grade, and the structure is uniform and fine.
(3) Method 3 After forging, the center, 1/2R and edge of the bar cross section are uniform, and the grain size of each part is relatively consistent, and the grain size is about grade 6. Compared with method 1, the yield strength and tensile strength of method 3 at room temperature increased by more than 70MPa, and the tensile plasticity at room temperature also increased by more than 3%. The yield strength and tensile strength at high temperature are increased by more than 20MPa, and the tensile plasticity at high temperature is decreased. The durable life is reduced, and the durable plasticity is equal. The performance test results of method 3 are comparable to those of method 2.
Therefore, method 3, that is, the whole drawing length of 4500 tons of press + two ends of the clamp mouth + middle cutting section + leakage disc respectively heading and two drawing +1800 tons of one fire precision forging machine can make GH2909 alloy large size bar uniform and fine structure, and obtain good comprehensive performance to meet the requirements of standard indexes.