Slag system used for preparing nickel base alloy through electroslag remelting and use method of slag system

Abstract

The invention provides a slag system used for preparing a nickel base alloy through electroslag remelting and a use method of the slag system. The slag system comprises, by mass, 65%-70% of CaF2, 10%-16% of Al2O3, 10%-16% of CaO, 2%-5% of MgO, 2%-5% of TiO2 and not more than 0.8% of impurities. When the slag system is used, prepared slag is baked and then added to an argon-shielded electric slag furnace crystallizer to be melted, then 700 DEG C advanced ultra-supercritical coal fired boiler nickel base alloy is remelted, and slow cooling and mold stripping are conducted after remelting. According to the slag system used for preparing the nickel base alloy through electroslag remelting and the use method of the slag system, burning losses of easily-oxidized elements in the alloy can be effectively reduced, the head and tail distribution of the alloy can be uniform, the segregation degree of elements is reduced, and the surface quality problem of electroslag remelting can be effectively solved.

Description

technical field [0001] The invention relates to an electroslag remelting slag system, in particular to a slag system for electroslag remelting 700°C advanced ultra-supercritical coal-fired boiler nickel-based alloy and a use method thereof. Background technique [0002] The 700°C advanced ultra-supercritical coal-fired boiler requires the steam pressure to reach 35Mpa, and the superheater and reheater temperatures to reach 700°C and 720°C respectively. Therefore, under such harsh conditions, austenitic heat-resistant steels such as Super304H and HR3C for 600°C ultra-supercritical coal-fired boilers can no longer meet the actual requirements, so nickel-based alloy materials must be used in the high-temperature section of the superheater and reheater . [0003] Inconel740, GH4700 and other nickel-based alloys are candidate materials for advanced ultra-supercritical coal-fired boilers at 700 °C. Their purity must be further improved to meet the actual requirements of new boile...

AI Technical Summary

Problems solved by technology

[0004] However, in the process of electroslag remelting of nickel-based alloys in advanced ultra-supercritical coal-fired boilers at 700 °C, problems such as burning loss of easily oxidizable elements such as Al and Ti and uneven distribution of head and tail often occur, and the burning loss rate is generally as high as 15 % or more, it is easy to cause unqualified ingot composition and uneven alloy structure and properties, and it is not conducive to saving resources and reducing costs

At the same time, for nickel-based alloys containing Nb, Ti and other elements that are prone to segregation, the dendrite segregation is more serious during the solidification process, and the maximum value of the segregation coefficient of individual elements may even exceed 4, which often leads to the formation of harmful phases.

In addition, because there are many types of alloys in this kind of nickel-based alloys, the melting point is low. If the slag system is not selected properly, surface quality problems are prone to occur after the steel ingot is cast.

[0005] The slag system plays a vital role in the electroslag remelting process. Currently, the commonly used 70% CaF 2 +30% A1 2 o 3 and 60% CaF 2 +20%A1 2 o 3 +20%CaO and other slags are used in the process of electroslag remelting of nickel-based alloys for advanced ultra-supercritical coal-fired boilers at 700 °C. The above problems have not been effectively solved, so the metallurgical quality is not ideal