RU2851153C1 - METHOD FOR PRODUCING HEAT-RESISTANT ALLOY INGOT “ВЖ 718” WITH DIAMETER OF MORE THAN 400 mm - Google Patents

Abstract

FIELD: electrometallurgy.

SUBSTANCE: invention relates to the production of ingots from heat-resistant alloy “ВЖ 718” with a diameter of more than 400 mm. The ingot is smelted in a vacuum induction furnace (VIF) and cooled for 4 hours in a vacuum, then remelted in an electroslag furnace (ESF) at a melting rate of 3.4 to 6.0 kg/min and cooled with the furnace for 2 hours, then in a thermostat for 24 hours, the resulting ingot is remelted in a vacuum arc furnace (VAF) at a melting rate of 3.0 to 4.0 kg/min, followed by thermostatting for 24 hours, then the ingot is subjected to plastic deformation, with forging carried out on a hydraulic press at a deformation temperature of 1180° C, then the resulting intermediate consumable electrode is remelted in a VAF at a melting rate of 3.0 to 4.0 kg/min.

EFFECT: improvement in the quality of the ingot in terms of minimising defects in its macrostructure.

1 cl, 3 dwg, 1 ex

Description

Field of technology.

Gas turbine parts, including turbine disks, are made from the VZh718 alloy.

State of the art.

Analog. A known method for producing an ingot from a heat-resistant alloy (CN 113444889 A, priority dated May 19, 2021) consists of initially forming the ingot by melting an electrode in a vacuum induction furnace, remelting the electrode into an electrode blank using electroslag remelting, and then subjecting the electrode blank to a second electroslag remelting.

This method produces an ingot with a uniform distribution of aluminum and titanium. However, a drawback of this method is that it does not account for the need to form a defect-free structure for large-sized ingots for alloys with a wide crystallization range. However, it does not eliminate the possibility of individual chipping particles falling off, as this can lead to the formation of a discontinuous electrode blank.

Prototype. A method is known for producing an ingot from a heat-resistant nickel alloy (RU 2272083 C2, priority dated 25.02.2002) by producing an electrode in a vacuum induction furnace, remelting it in an electroslag furnace to form an electroslag electrode, reforging the electroslag electrode, and remelting the resulting blank in a vacuum arc furnace.

A disadvantage of this method is the inability to completely eliminate the formation of localized structural and/or chemical heterogeneity defects in the final VAR ingot. Specifically, this method does not eliminate the formation of "white spot" structural defects for nickel and iron-nickel alloys alloyed with niobium at 4% or more by weight. This is due to the low ductility of the electrode after electroslag remelting, and cracks may form during the reforging process, which can lead to particle spalling during subsequent VAR.

The essence of the invention.

Parts made of VZh718 alloy must possess high mechanical properties and be free of discontinuities (such as pores, cracks, and cavities), nonmetallic inclusions, and segregation. The structure of such parts must be uniform. These requirements can only be met by producing ingots free of discontinuities, with a uniform chemical composition and a homogeneous macrostructure.

A common method for producing ingots from the VZh718 alloy is “triple remelting,” which involves producing a consumable electrode by vacuum induction melting (VIM) and pouring the metal into a crystallizer, remelting the resulting electrode using the electroslag method (ESM), and subsequent vacuum arc melting (VAM).

With this production method, vacuum induction melting allows for the chemical composition to be averaged throughout the ingot by stirring the melt with a magnetic field. Subsequent electroslag remelting reduces the amount of harmful impurities such as sulfur and phosphorus, resulting in a denser material with fewer shrinkage defects.

When smelting large-diameter ingots from heat-resistant nickel and iron-nickel alloys, macro- and microstructural defects may occur. Certain defects are common to all alloys and are primarily associated with the formation characteristics of the ingots during VAR and ESR. These defects include off-axis and radial inhomogeneities ("cord" and "spotted" segregation), light contours, "crowns," shrinkage porosity, non-metallic inclusions, etc.

In addition to obvious macrostructural defects, ingot smelting using the VIP plus VAR, VIL plus ESR, and VIL plus ESR plus VAR processes can result in the formation of unregulated zones that are not formally considered defects but are nonetheless unfavorable for subsequent deformation. For example, these zones may include wider areas of the central equiaxed grain, areas with columnar crystals asymmetrical relative to the ingot axis, etc. Such structural features are associated with the temporary departure of the actual remelting process from a quasi-steady-state regime.

At the same time, some alloys may exhibit structural defects that are unique to them. For example, iron-nickel alloys (e.g., VZh718) containing niobium at a concentration of 3 percent or more (by weight) exhibit a macrostructural defect called a "white spot."

The formation of a white spot is caused by the entry of individual solid particles of the original electrode into the liquid metal pool during VAR welding. When in contact with the liquid phase, these particles become somewhat depleted of niobium, which has a higher positive segregation coefficient (toward the liquid phase) than other alloying elements. Due to this depletion, such a particle appears as a lighter ("white") spot of arbitrary shape during macrostructure inspection. An example of a "white spot" defect is shown in Fig. 1.

The source of white spots during VAR are particles that crumble from the consumable electrode if it has a non-continuous structure (contains shrinkage cavities, looseness, etc., cracks without reaching the surface, etc.), which fall into the liquid bath of the forming ingot and remain undissolved.

The present invention relates to the field of metallurgy, namely to the improvement of the technology for smelting ingots from the VZh718 alloy of large diameter (more than 400 mm) and the elimination of the formation of “white spot” type defects in the ingot.

The proposed method eliminates shrinkage phenomena within the consumable electrode by forging the electrode. During the forging process, the electrode material is compacted, preventing particles from chipping off and entering the liquid metal pool during VAR ingot formation, thereby eliminating the causes of "white spot" defects.

To improve the quality of ingots made from heat-resistant nickel and iron-nickel alloys and prevent the formation of localized structural and/or chemical heterogeneity defects in the final VAR ingot, a method for producing an ingot is proposed. The ingot is melted in a vacuum induction furnace, an electroslag furnace, and a vacuum arc furnace. The resulting intermediate consumable electrode is subjected to plastic deformation and vacuum arc remelting. The resulting ingot is free of structural defects.

The proposed method is distinguished by the intermediate consumable electrode for the final VAR process being produced by triple remelting in a vacuum induction furnace, electroslag furnace, and vacuum arc furnace, followed by plastic deformation. Producing an electrode blank for subsequent forging by triple remelting (VIR + ESR + VAR) ensures high ductility during forging of the intermediate consumable electrode. Furthermore, with this method of producing the intermediate consumable electrode, possible defects of local structural and/or chemical heterogeneity, in particular "white spots," will be partially crushed during plastic deformation and, during the final VAR, melted during melting of the electrode and homogenized in the liquid metal bath of the forming ingot.

Implementation of the invention.

Using this method, ingots from the heat-resistant iron-nickel alloy VZh718 were produced at JSC SMK. The resulting ingots were free of localized structural and/or chemical heterogeneity defects such as "white spots."

A 405 mm diameter electrode was melted in a vacuum induction furnace and poured into a 410 mm diameter cast iron chill mold. The electrode was cooled for 4 hours in a vacuum, remelted in an electroslag furnace in a 470/500 mm diameter crystallizer at a melting rate of 3.4 to 6.0 kg/min, cooled in the furnace for 2 hours, then in a thermostat for 24 hours, and the ingot was remelted in a vacuum arc furnace in a 520 mm crystallizer at a melting rate of 3.0 to 4.0 kg/min. Subsequently, thermostatting for 24 hours was carried out on the ingot. Then, plastic deformation was performed on a hydraulic press to a diameter of 450 mm at a deformation temperature of 1180°C. The resulting intermediate consumable VAR electrode was then ground to a diameter of 445 mm and subjected to vacuum arc remelting in a 520 mm crystallizer at a melting rate of 3.0 to 4.0 kg/min. This process resulted in a ground ingot with a diameter of 485 mm. The ingot was then forged to a diameter of 230 mm.

The absence of defects was determined on forged rods obtained from this ingot by examining the macrostructure. Inspection of the forged rod's macrostructure revealed the absence of defects. The rod's macrostructure is shown in Fig. 3.

Claims (1)

A method for producing an ingot from heat-resistant alloy VZh 718 with a diameter greater than 400 mm, characterized in that the ingot is melted in a vacuum induction furnace (VIF) and cooled for 4 hours in a vacuum, then remelted in an electroslag furnace (ESF) with a melting rate of 3.4 to 6.0 kg/min and cooled with the furnace for 2 hours, then in a thermostat - for 24 hours, remelted the resulting ingot in a vacuum arc furnace (VAR) with a melting rate of 3.0 to 4.0 kg/min with subsequent thermostatting for 24 hours, then the ingot is subjected to plastic deformation, wherein forging is carried out on a hydraulic press at a deformation temperature of 1180 °C, then the resulting intermediate consumable electrode is remelted in a VAR with a melting rate of 3.0 to 4.0 kg/min.