Study on electroslag remelting furnaces' desulfurization

Desulfurization experiment of electric slag furnace

The harm and action mechanism of sulfur in nickel base superalloy were summarized, indicating the necessity of further controlling the sulfur content in the alloy. In order to further improve the desulfurization efficiency of electroslag remelting nickel base superalloy in electroslag remelting furnace, the desulfurization effect of electroslag remelting process of GH4169 under different remelting conditions was experimentally studied, and the experimental results were thermodynamically analyzed and discussed.

The electrode material GH4169 used in the experiment is smelted in a 200kg vacuum induction furnace. The diameter of the original electrode is 100mm and the length is 500mm. The composition (mass fraction) of caf60 is 20% Cao, 20% Al2O3 and 60% CaF2. The primary electrode of the same furnace is remelted in a 50kg electroslag remelting furnace. The diameter of the crystallizer is 160mm and the amount of slag is 8kg.

Three different processes were designed:

Experiment 1: electroslag remelting process was carried out when the protective cover was opened and the slag surface was completely exposed to the atmosphere;

Experiment 2: during electroslag remelting, the protective cover is sealed with the mold and high-purity argon is introduced to fully protect the slag surface by argon;

Experiment 3: on the basis of Experiment 2, metal calcium was continuously added to the slag in the same amount during remelting (3kg metal calcium was added per 1t alloy remelted).

Experimental results of desulfurization in electroslag remelting furnaces

During the experiment of each furnace, the Remelting Ingot of seamless steel pipe www.tcpipes.combd shall suck the slag sample every 30mm. After remelting, three remelting ingots shall be cut along the diameter and height direction respectively, and the chemical analysis samples shall be taken along the height direction at 1/2 of the radius. The contents of Ca and s in remelted ingots were analyzed by ICP-AES (nacis/C h011:2005) and infrared absorption method (GB/T 20123-2006). The content of S in slag samples is analyzed by combustion iodometry (GB/T 5195.5-2006). The results are as follows:

1. With the increase of sulfur content, the grain boundary strength weakens continuously, which deteriorates the tensile plasticity, rupture life and creep properties of the alloy at high temperature, and finally reduces the service life of the alloy;

2. At high temperature, the sulfur on the surface of the alloy substrate will spontaneously segregate to the surface, reduce the adhesion and peel off of the oxide film on the alloy surface, resulting in further oxidation and deepening of cracks on the substrate surface. Reducing the sulfur content in the matrix as much as possible is an important measure to improve the service life of nickel base superalloy;

3. Take w [S] as 18×GH4169 of 10-6 is the original electrode, and w [S] in the alloy obtained by electroslag remelting in atmosphere is stable at 6×10-6； W [S] in the alloy obtained at the beginning of electroslag remelting under inert gas protection is reduced to 7×10-6, w [S] in the alloy increases to 9 at the end of remelting×10-6; The addition of metal calcium can improve the inert atmosphere, protect the electroslag remelting desulfurization conditions, and continuously reduce w [S] in the alloy to 3×10-6；

4. The initial w [S] in the slag of seamless steel pipe used in the experiment is 0.03%. In the process of electroslag remelting in atmosphere, the sulfur in the slag is removed by gasification, and the w [S] in the slag basically remains 0.03%; W [S] in the slag of electroslag remelting under inert atmosphere increased continuously, reaching 0.04%; After adding metal calcium, w [S] in electroslag remelting slag under atmosphere protection further increased to 0.047%;

5. The calculation results of [Ca] - [S] thermodynamic equilibrium in GH4169 alloy show that the equilibrium trend of w [Ca], w [S] in the alloy is consistent with the theoretical calculation, which is close to the [Ca] - [S] thermodynamic equilibrium line at 1743k.