PROCESSES FOR PRODUCING SUPERALLOYS AND SUPERALLOYS OBTAINED BY THE PROCESSES

Abstract

The present invention relates to a method (1) of producing a metal superalloy (10) comprising the steps of providing a charge of metal materials (2); melting said charge of metal materials (2) in an electric-arc furnace (3) to obtain a first melt (3A) of said charge of metal materials (2); solidifying (5) said first melt (3A) to obtain first ingots (5A); melting said first ingots (5A) in a V.I.D.P. furnace (6) to obtain a second melt (6A); solidifying (7) said second melt (6A) to obtain second ingots (7A); melting said second ingots (7A) in a V.A.R. furnace (8) to obtain a third melt (8A); solidifying (9) said third melt (8A) to obtain a metal superalloy (10). The method (1) is characterized in that the charge of metal materials (2) has a weight amount ranging from forty to sixty tons, and it includes a step of carrying out an A.O.D. treatment (4) on said first melt (3A) to obtain a decarburized and refined first melt (4A); said melting in the V.I.D.P. furnace (6) and said melting in the V.A.R. furnace (8) are carried out sequentially on said first melt (4A) resulting from said A.O.D. treatment (4).

Claims

1. A method (1) of producing a metal superalloy (10), comprising the steps of: providing a charge of metal materials (2); melting said charge of metal materials (2) in an electric-arc furnace (3) to obtain a first melt (3A) of said charge of metal materials (2); solidifying (5) said first melt (3A) to obtain first ingots (5A); melting said first ingots (5A) in a V.I.D.P. furnace (6) to obtain a second melt (6A); solidifying (7) said second melt (6A) to obtain second ingots (7A); melting said second ingots (7A) in a V.A.R. furnace (8) to obtain a third melt (8A); solidifying (9) said third melt (8A) to obtain a metal superalloy (10); characterized in that said charge of metal materials (2) has a weight amount ranging from forty to sixty tons; and in that it comprises a step of A.O.D. treatment (4) on said first melt (3A) to obtain a decarburized and refined first melt (4A), said melting in the V.I.D.P. furnace (6) and said melting in the V.A.R. Furnace (8) being carried out sequentially on said first and refined decarburized and refined first melt (4A) resulting from said A.O.D. treatment (4).

2. A method as claimed in claim 1, wherein said decarburized and refined first melt (4A) is obtained by carrying out the A.O.D. treatment on said first melt (3A) while the latter is in the molten state as a result of the melting step in said electric-arc furnace (3).

3. Method as claimed in claim 1, wherein said decarburized and refined first melt (4A) undergoing said second melting step in the V.I.D.P. furnace (6) has a weight amount ranging from ten to twenty tons.

4. A method as claimed in claim 1, wherein said step of solidification (7) of said second melt (6A) comprises a step of casting the melt into molds.

5. A method as claimed in claim 1, wherein said steps of solidifying said decarburized and refined first melt (4A) and said second melt (6A) include a step of cooling the melt after casting it into ingot molds.

6. A method as claimed in claim 5, wherein said ingot molds have such a shape that said first and second ingots have a cylindrical shape.

7. A method as claimed in claim 1, wherein said metal superalloy (10) is of the iron- or nickel-based type, comprising variable amounts of Chromium, Cobalt, Niobium, Titanium and/or other elements.

8. A method as claimed in claim 1 wherein, after the step of solidifying (9) said third melt (8A), said superalloy (10) undergoes thermomechanical processing comprising a press forging step.

9. A method as claimed in claim 8 wherein, after the step of solidifying (9) said third melt (8A) and the step of thermomechanical processing comprising a press forging step, said superalloy (10), when thicknesses of less than 250-300 mm are required, undergoes further thermomechanical processing comprising a radial four-die forging step using a hydraulic RUMX machine, and a continuous radial deformation forging step in a rolling plant.

Description

BRIEF DESCRIPTION OF THE FIGURES

[0016] Further features and advantages of the present description will appear more clearly from the illustrative, non-limiting description of a preferred, non-exclusive embodiment of a method of producing superalloys, as well as superalloys obtained with the method as shown in the accompanying FIG. 1, which shows a flowchart of the production of a superalloy according to the present invention.

DETAILED DESCRIPTION

[0017] Even when this is not expressly stated, the individual features as described with reference to the particular embodiments shall be intended as auxiliary to and/or interchangeable with other features described with reference to other exemplary embodiments.

[0018] Referring to the accompanying FIGURE, numeral 1 designates the method of producing a metal superalloy 10, i.e. a metal alloy that is mainly composed of Iron and Nickel with the addition of variable amounts of Chromium, Cobalt, Titanium and other elements.

[0019] In particular, the method 1 is a triple-melt method including, as further explained below, a triple-melt process for melting and remelting a charge of base material 2.

[0020] The method 1 comprises a first step 3 in which the aforementioned charge of materials 2 is provided in an amount ranging from forty to sixty tons, preferably of fifty tons.

[0021] This first step 3 includes melting the aforementioned charge of materials in an electric-arc furnace to obtain a first melt 3A.

[0022] The electric-arc furnace is a conventional furnace and will not be further described.

[0023] Once the first melt 3A of the entire charge of materials 2 has been obtained by means of the electric-arc furnace 3, the same melt, in a liquid state, undergoes an A.O.D. (Argon Oxygen Decarburization) treatment 4, which is known in the art and will not be further described.

[0024] In other words, the first melt 3A molten by the electric furnace 3 undergoes the A.O.D. treatment 4 to obtain a refined first melt 4A.

[0025] According to an advantageous aspect of the present method, the treatment A.O.D. treatment 4 is carried out on the first melt 3A when the first melt 3A is still in the liquid state.

[0026] Namely, the A.O.D. treatment 4 can provide a decarburized and refined melt 4A with minimized impurities such as S, Pb and Sn and extremely high deoxidation.

[0027] It shall be noted that the first melt 4A has the same amount as the charge of materials 2 introduced into the electric furnace 3, that is if the charge of materials 2 is fifty tons then also the first melt 4A. will be fifty tons.

[0028] During the A.O.D. treatment 4, the liquid mass of the first melt 3A is subjected to vigorous stirring due to gases (argon, nitrogen and oxygen in varying proportions depending on the stage of the A.O.D. treatment) blown during treatment, which imparts high homogeneity to the first melt 4A.

[0029] The A.O.D. treatment 4 is followed by a step of solidification 5 of the first melt 4A.

[0030] In one aspect the solidification step 5 comprises a step in which the melt is cast into ingot molds and later cooled to obtain ingots 5A, preferably having a cylindrical shape.

[0031] Then, the ingots 5A undergo melting in a V.I.D.P. (Vacuum Degassing Induction and Pouring) furnace 6 to obtain a second melt 6A.

[0032] At the end of the treatment in the V.I.D.P furnace 6, the second melt 6 undergoes a step of solidification 7, still in the V.I.D.P furnace.

[0033] In one aspect the solidification step 7 comprises a step in which the melt is cast into ingot molds and later cooled to obtain ingots 7A, preferably having a cylindrical shape.

[0034] The ingots 7A as obtained from the solidification step 7 undergo melting in a V.A.R. (Vacuum Arc Remelting) furnace 8 to obtain a third melt 8A.

[0035] Once melting in the V.A.R. furnace 8 is completed, the third melt 8A undergoes a step of solidification 9 in the V.A.R. furnace to obtain the metal superalloy 10.

[0036] The superalloy 10 obtained by the triple-melt 4, 6 and 8 later undergoes homogenization, thermomechanical processing and thermal treatment in prior art plants and with prior art equipment.

[0037] Namely, after the solidification step 9, the superalloy 10 undergoes thermomechanical processing, which comprises a press forging step, preferably with a hydraulic press.

[0038] If a thickness of less than 250-300 mm is desired, after the solidification step and the press forging step, the superalloy 10 undergoes additional thermomechanical processing which comprises a radial four-die forging step using a hydraulic RUMX machine, and a continuous radial deformation forging step in a rolling plant, preferably of hydraulic type.

[0039] This superalloy 10 has a high chemical homogeneity and uniform mechanical, thermal and corrosion-resistance properties, as required for their use.

[0040] The superalloy 10 obtained with the method 1 is found to have high chemical homogeneity, a very high degree of desulfurization with less than 5 ppm residual sulfur, an equally high degree of deoxidation and Bi and Se impurity levels of less than 1 ppm.

[0041] This is believed to result from the fact that the initial charge 2 ranging from forty to sixty tons establishes the chemico-physical conditions required for an effective A.O.D. Treatment 4, leading to a high impurity elimination degree. In addition, the A.O.D. treatment after the first melt 3A is carried out with a high turbulence of the molten mass generated by blowing process gases, which results in a high homogeneity of chemical process reactions, and hence of the chemical composition of the molten alloy.

[0042] According to a variant embodiment of the method of the invention, the charge that leaves the A.O.D. treatment 4, for the subsequent V.I.D.P. and V.A.R. melting steps 6, 7, may be divided into multiple portions depending on the required supply of the alloy 10, thereby ensuring highly homogeneous supplies of the material even after some time.

[0043] Those skilled in the art will obviously appreciate that a number of changes and variants as described above may be made to fulfill particular requirements, without departure from the scope of the invention, as defined in the following claims.