JPH0369976B2 - - Google Patents

Description

[Detailed description of the invention]

The present invention relates to an electroslag melting (hereinafter referred to as ESR) method for Ni-based alloys containing Ti, Al, and Mg.
Regarding ESR operation method with less yield fluctuation. (Conventional technology and problems) Conventionally, most Ni-based alloys have been manufactured by vacuum arc remelting, but recently it has become possible to add elements that are difficult to add using vacuum arc remelting, such as Mg and Ca. The ESR method has been increasingly used because it improves workability, provides a clean casting surface, requires less maintenance, and naturally has fewer cracks from surface scratches or scratch removal marks, resulting in better yields.
However, even in the ESR method, alloys containing Mg and Ca react with these elements, and Mg in particular has a high vapor pressure, so it cannot be remelted stably and with good yield even in an inert atmosphere. was extremely difficult. In other words, it is difficult to operate with the slag composition initially set without major fluctuations, and as the slag composition changes, the components of the product ingot (Ti, Al, Mg) vary from the bottom (early stage of melting) to the top. was. That is, in the past, the composition of slag was determined by trial and error based on previous experience, which often resulted in large fluctuations, resulting in situations where some or most of the composition of the ingot was off. (Solution Means and Effects) The present invention has been made in view of the above, and the main points are:
In wt% Ti; 1.8-2.7%, Al; 0.9-1.8%, Mg;
In the ESR of Ni-based superalloys containing 0.003 to 0.040%, CaO−MgO with a composition that satisfies formulas (1), (2), and (3)
−Al ₂ O ₃ −TiO ₂ flux or this
This is an ESR method that uses a flux containing CaF ₂ and is carried out under an inert gas atmosphere. 4.5≦3.11log [%Ti] ³ / [%Al] ⁴ −logN ³ _TiO2 /N ² _Al2
O3 ≦5.8……(1) 8.1≦2.01log [%Al] ² / [%Mg] ³ −logN _Al2O3 /N ³ _MgO
≦11.4……(2) 7.6≦2.05log [%Ti] / [%Mg] ² −logN _TiO2 /N ² _MgO ≦
9.2...(3) N _CaO +N _MgO /N _Al2O3 +N _TiO2 ≦1.5...(4) However, [%Ti], etc.: Weight % in the alloy N _TiO2 , etc.: Mole fraction in the slag That is, the present inventors Even in conventional ESR,
Focusing on the fact that relatively stable operation is possible at the end of one melting process, the components of the ingot and slag at this time are mutually expressed by equations (5), (6), and (7) in an inert atmosphere. If the reaction shown occurs and there is an equilibrium relationship, 4[Al] + 3 (TiO ₂ ) = 3 [Ti] + 2 (Al ₂ O ₃ )... (5) 2 [Al] + 3 (MgO) = 3 [Mg] + (Al ₂ O ₃ ) ...(6) 2 [Mg] + (TiO ₂ ) = [Ti] + 2 (MgO) ... (7) When I looked at it and plotted it on the slag, I found that Figure 1~
As shown in FIG. 3, we were able to obtain straight lines, that is, empirical formulas (8) to (10). The present invention is limited to the range indicated by diagonal lines around this, which is expressed by formula (1),
(2) and (3) are summarized as logN ³ _TiO2 /N ² _Al2O3 = 3.11log [%Ti] ³ / [%Al] ⁴ −5
.17……(8) logN _Al2O3 /N ³ _MgO =2.01log[%Al] ² /[%Mg] ³ −9.9
0……(9) logN _TiO2 /N ² _MgO = 2.05log [%Ti] / [%Mg] ² −8.41
...(10) Ru. In other words, if ESR is performed with a slag composition that satisfies Equations (1), (2), and (3), Ti,
It was discovered that Al and Mg exhibit stable yields. Furthermore, in the present invention, oxygen and sulfur, which are extremely harmful elements to Ni-based alloys, are
Focusing on the concentration ratio of MgO and Al ₂ O ₃ + TiO ₂ , we investigated the correlation with this and found that if the shaded range in Figure 4, that is, formula (4) is satisfied, the total amount of oxygen and sulfur can be reduced to 10 ppm. We have found that the following can be done, and have added this to the essential conditions of the present invention. One reason for limiting the alloy components in the present invention is that the data shown in FIGS. 1 to 4, which are the basis of the present invention, were obtained based on alloys in this range, This is because if it is within the range, it is certain that equations (1) to (4) can be applied correctly. This range also includes the range of alloy components standardized by JIS as NCF80A. (Examples) Table 1 shows three examples of the present invention. The flux composition in the table is the value at the start determined by considering the components falling within the shaded range of FIGS. 1 to 4 together with other various conditions, and there was almost no change throughout the dissolution period. Therefore, there was almost no change in the composition of the base metal, ingot, or ingot at the initial, middle, or final stages, and stable operation was possible in all three cases. (Effects) By adopting the present invention, the composition of flux (slag), which was previously determined based on accumulated experience, has been changed.
It is now possible to easily make decisions based on diagrams or formulas without causing any deviations in composition, and it has also become possible to make selections from a much wider range than before, allowing for example flux costs and various operating conditions to be determined. It has become extremely easy to determine the optimal components to consider.

【table】

【table】 [Brief explanation of drawings]

FIGS. 1 to 4 are diagrams showing the relationship between alloy components in an ingot and slag components in ESR of a Ni-based alloy.

Claims (1)

[Claims] 1% by weight: Ti; 1.8 to 2.7%; Al; 0.9 to 1.8%;
In the ESR of Ni-based superalloys containing Mg; 0.003 to 0.040%, CaO− with a composition satisfying formulas (1), (2), and (3)
An ESR method characterized in that it is carried out in an inert gas atmosphere using a MgO-Al ₂ O ₃ -Tio ₂ flux or a flux in which CaF ₂ is added. 4.5≦3.11log [%Ti] ³ / [%Al] ⁴ −logN ³ _TiO2 /N ² _Al2
O3 ≦5.8……(1) 8.1≦2.01log [%Al] ² / [%Mg] ³ −logN _Al2O3 /N ³ _MgO
≦11.4……(2) 7.6≦2.05log [%Ti] / [%Mg] ² −logN _TiO2 /N ² _MgO ≦
9.2...(3) N _CaO +N _MgO /N _Al2O3 +N _TiO2 ≦1.5...(4) However, [%Ti], etc.: Weight % in the alloy N _TiO2 , etc.: Mole fraction in the slag,