Large-sized high-Nb superalloy ingot and smelting process thereof

A smelting process of a high-Nb superalloy ingot, comprising the following steps of:

• vacuum induction melting (VIM):
• conducting VIM on at least one of pure metal raw material or recycled material as raw material, and pouring to form a plurality of consumable VIM ingots, wherein the plurality of consumable VIM ingots have a same composition;
• and
• electroslag remelting (ESR):
• preparing a same number of electroslag electrodes as that of the plurality of consumable VIM ingots;
• and electroslag remelting all the electroslag electrodes under protection of argon;
• cooling down and demoulding to obtain an ESR ingot;
• conducting consumable vacuum arc remelting (VAR) for a plurality of times:
• performing a first annealing and a second annealing on the ESR ingot and forging by stretching to a predetermined size to obtain a primary consumable electrode, in which the second annealing is performed at a temperature higher than that for performing the first annealing;
• and performing VAR at least twice by using the primary consumable electrode as starting material, in which a resulting VAR ingot obtained after each VAR is used as a consumable electrode to be used in a next VAR, with a diameter of the resulting VAR ingot being increased after each VAR until fluctuation of a melting rate during a last VAR falls within ±10% of a steady-state melting rate, and a VAR ingot obtained in the last VAR is used to prepare an ingot with a target diameter,
• wherein preparing the electroslag electrodes comprises directly stress-relieve annealing each of the plurality of consumable VIM ingot, in which a temperature is initially raised to 600-800° C., then raised to 800-1000° C. at a rate of 5-45° C./h, kept constant for 4-32 h, lowered to 600-800° C. at a rate of 1-35° C./h and kept constant for 4-32 h;
• air cooling;
• polishing;
• and flattening at a head and a tail to obtain the electroslag electrodes;
• wherein a quaternary slag system having a composition of CaF2—CaO—Al2O3—TiO2 comprising 60-75 wt % CaF2, 10-25 wt % CaO, 10-25 wt % Al2O3, and 1-10 wt % TiO2 is employed;
• the steady-state melting rate of the ESR is controlled to be 5-15 kg/min,
• before exchanging each of the electroslag electrodes, when a remaining weight of one electroslag electrode is 500 kg-1000 kg, the melting rate is increased by a slope of 0.5-2 kg/min to 12-25 kg/min on a basis of the steady-state melting rate and kept stable until the exchanging begins, during which smelting parameters remain the same as those before the exchanging and an exchanging time does not exceed 2 min;
• after the exchanging each of the electroslag electrodes, the melting rate is reduced by a slope of 0.5-2 kg/min to the steady-state melting rate of 5-15 kg/min for continuing the remelting when 100kg-500 kg of a next electroslag electrode is melted, and hot topping is carried out when a remaining weight of a last electroslag electrode is 200-600 kg;
• and
• after the ESR, the cooling down is carried out for 2-10 h and the demoulding is carried out to obtain the ESR ingot;
• wherein in the step of VAR for a plurality of times, the performing the first annealing and the second annealing on the ESR ingot and the forging by stretching to the predetermined size to obtain the primary consumable electrode comprises the following steps of:
• initiating the first annealing to the ESR ingot within 0.5-2 h after the demoulding, in which the temperature is initially raised to 300-550° C., kept constant for 12-32 h for achieving homogeneous temperature distribution, raised to 600-750° C. at a rate of 1-25° C./h, kept constant for 4-32 h, raised to 800-1000° C. at a rate of 5-35° C./h, kept constant for 4-32 h, lowered to 550-750° C. at a rate of 1-35° C./h, and kept constant for 4-32 h, followed by air cooling;
• performing the second annealing on the ESR ingot after the first annealing, in which the temperature is raised to 800-1000° C. at a rate of 5-35° C./h, raised to 1050-1150° C. at a rate of 1-25° C./h, kept constant for 4-32 h, raised to 1150-1250° C. at a rate of 1-25° C./h, kept constant for 24-72 h, lowered to 800-950° C. at a rate of 1-35° C./h, and kept constant for 4-32 h, followed by air cooling;
• forging the ESR ingot after the second annealing, in which the ESR ingot is heated to 1100-1180° C. for 4-12 h before the forging, and subjected to a free forging on a forging press of 3000 tons or above by stretching in one direction, in which a reduction per pass in one direction is 5-30 mm and a final forging temperature is in a range of 850-1000° C.;
• and
• polishing the ESR ingot stretched during the free forging and flattening at a head and a tail to obtain the primary consumable electrode.