RU2557438C1 - Chrome-based heat resisting alloy and method of smelting of chrome-based alloy - Google Patents

Abstract

FIELD: metallurgy.

SUBSTANCE: heat resisting alloy is used which contains, wt %: nickel 31-33, tungsten 1-3, vanadium 0.1-0.4, titanium 0.05-0.3, aluminium + silicon no more than 0.2, oxygen no more than 0.08, nitrogen no more than 0.04, iron no more than 0.5, carbon no more than 0.08, chrome - the rest and having the structure in the cast state containing no eutectic. To provide high quality of the ingot from the named alloy and increase of output of good metal at the expense of exception of subcrustal bubbles on ingot surface and reduction of a shrinkage cavity, and also increased plasticity of the alloy at the subsequent hot plastic deformation the furnace charge consisting of pure initial materials is loaded into the vacuum electric furnace: Electrolytically refined chrome, nickel, tungsten, vanadium, titanium, microalloying additives for deacidification and modifying of the alloy, the furnace charge is melted and the obtained molten metal is poured into moulds at the temperature 1550-1570°C.

EFFECT: hot plasticity improvement.

2 cl, 4 tbl, 6 dwg, 1 ex

Description

The group of inventions relates to the field of metallurgy and can be used for the manufacture of parts from a heat-resistant alloy based on chromium, operating at high temperatures and in aggressive environments, and to special electrometallurgy, namely, vacuum-induction smelting of a heat-resistant alloy.

A heat-resistant alloy based on chromium is known, containing tungsten, zirconium or hafnium, titanium, lanthanide oxide, manganese (RU 2236480 C1, C22C 27/06, 09/20/2004).

The closest analogue of the invention is an alloy based on chromium containing, by weight. %: Ni - 32, W - 1.5, V 0.1-0.4, Ti 0.05-0.25, impurities no more than: C 0.08, O ₂ 0.03, N ₂ 0.04 , Cr - basis (Materials in mechanical engineering. Selection and application. Handbook t. 3, “Special steels and alloys”, under the editorship of Himushin F.F., M., Engineering, 1968, p. 423).

However, this composition does not allow the production of real industrial alloys, since there are no limits on the contents of nickel, tungsten and, accordingly, chromium. In addition, the lack of restrictions on the content of impurities does not allow to obtain an alloy of the required purity, this leads to an increase in the number of non-metallic inclusions and reduces the technological ductility of the alloy. In addition, the requirements for the structure of the alloy in a molten state, in particular for the presence or absence of a eutectic, are not regulated. The presence of a eutectic in the structure reduces the ductility of the alloy, complicating its plastic deformation.

A known method of smelting a high-chromium alloy, comprising loading a charge containing electrolytically unrefined chromium, nickel, slag-forming components and deoxidizers, their melting and casting into molds (RU 2070228 C1, C21C 5/52, 10.12.1996).

The absence in the known method of a regulated temperature for casting the alloy does not allow to consistently obtain high-quality ingots, to have a high yield of metal.

The technical result of the claimed group of inventions is to obtain an alloy with a small number of non-metallic inclusions and not containing a eutectic in the structure, which provides an increase in the technological properties of the alloy, namely hot ductility, as well as ensuring the quality of the ingot and increasing the yield of metal by eliminating subcortical bubbles on the surface ingot and shrinkage reduction.

To achieve a technical result, a heat-resistant alloy based on chromium contains nickel, tungsten, vanadium, titanium, aluminum, silicon, oxygen, nitrogen, iron, carbon in the following ratio of components, wt. %:

nickel 31-33 tungsten 1-3 vanadium 0.1-0.4 titanium 0.05-0.3 aluminum + silicon no more than 0.2 oxygen no more than 0.08 nitrogen no more than 0,04 iron no more than 0.5 carbon no more than 0.08 chromium rest,

having a molten state structure that does not contain eutectics.

Limitations on the content of silicon, aluminum, iron reduces the number of non-metallic inclusions; the nickel content in the alloy is not more than 33 wt. % in accordance with the state diagram of Ni-Cr (Fig. 1) ensures the absence of a eutectic in the structure (Table 1), all this leads to an increase in the ductility of the alloy — elongation (δ) and narrowing (ψ).

In accordance with the state diagram of Ni-Cr alloy with a content of 35% of the mass. Ni contains up to 10% vol. eutectic (Fig. 2); when the content of 34% of the mass. Ni eutectic should not be (Fig. 1). However, due to segregation in real alloys, a eutectic is formed in areas enriched with nickel (Fig. 3).

It is especially important that at elevated temperatures of hot plastic deformation, the ductility indicators of the proposed alloy are one and a half to two times higher (Table 2) due to a change in its chemical composition.

Table 1 The Ni content in the alloy, mass. % The presence of eutectic in the structure 34.9 present (see figure 2) 33.8 traces (see figure 3) 33.0 absent

The decrease in the nickel content in the alloy is less than 31 mass. % leads to an increase in solidus temperature (see Fig. 1), enlargement of the grain and a decrease in mechanical properties and hot ductility.

To achieve a technical result, a method for smelting a chromium-based alloy involves loading a charge into a vacuum electric furnace consisting of pure starting materials: electrolytically refined chromium, nickel tungsten, vanadium, titanium, microalloying additives in the form of cerium and a nickel-magnesium-cerium alloy for deoxidation and modification alloy, their melting and casting of the melt into the molds at a temperature of 1550-1570 ° C.

An example implementation of the method

High-chromium alloy was smelted. For alloy smelting, the following pure charge starting materials were used: refined electrolytic refined chromium of the ERX grade, nickel, tungsten, vanadium, and titanium. The use of pure starting materials is associated with the need to ensure high requirements for limiting the content of gas impurities and impurities of iron, carbon, silicon and aluminum in the alloy. For deoxidation and modification of the alloy, cerium and a nickel-magnesium-cerium alloy were used as microalloying additives.

The use of microalloying additives in the amount of 0.123 (Table 3) for deoxidation and modification of the alloy does not affect the final composition of the alloy.

The calculated content of alloying elements and an example of alloy blending are given in table. 3.

The charge materials are loaded into the crucible of the furnace. Part of the chromium is placed in the basket of the furnace for introduction into the crucible after the main part of the charge is melted. Titanium, vanadium and microadditives are placed in the cells of the dispenser.

After placing the charge, the furnace chamber is sealed and vacuum to a pressure of 10 ^-3 mm Hg. Art., maintained at this pressure for 10-15 minutes to degass the charge, and then neutral argon gas of high purity is introduced into the chamber and a power source is turned on - a high-frequency converter for heating and melting the charge.

The mixture is heated to a temperature of 1600-1620 ° C until it is completely melted, kept at this temperature for 5-10 minutes, and then the temperature is reduced to 1550-1570 ° C and vanadium and titanium are introduced into the melt, and cerium and ligature in 1-2 minutes and then poured into molds with a diameter of 90 mm. From one melting of an alloy weighing ~ 120 kg, 3 ingots weighing ~ 40 kg (with a profitable part) each are made.

A total of 4 melts were smelted, 12 alloy ingots were cast, their composition is given in table. 4, corresponded to TU 1-809-321-87.

When working out the process parameters on individual melts, the casting temperature was varied.

A parameter that significantly affects the quality of the ingot is the temperature of the metal casting.

To study the effect of casting temperature on the quality of the ingot, melts were performed with the metal temperature before casting 1600-1620 ° C, 1550-1570 ° C, 1500-1520 ° C.

The melt temperature above 1600 ° C reliably ensures the casting of all the heat in three molds without cooling the metal in the melting crucible. However, in this case, strong spatter of the metal in the mold was observed. Drops of metal froze on the surface of the mold and led to the formation of an uneven, porous surface of the ingot and subcortical bubbles (Fig. 4).

Such defects reduce the utilization of metal and increase the cost of machining the ingots for further processing.

When casting a metal with a temperature below 1520 ° C, accelerated crystallization of the metal in the mold and a profitable extension was observed, which leads to an increase in the depth of the shrink shell to 1/3 of the ingot height and a decrease in the yield of metal (Fig. 5).

The satisfactory quality of the surface of the ingot and the formation of a small shrink shell at a depth of not more than 50 mm from the profitable part are ensured when casting metal into molds with a melt temperature of 1550-1570 ° C (Fig. 6).

Claims (2)

1. A heat-resistant chromium-based alloy containing nickel, tungsten, vanadium, titanium, aluminum, silicon, oxygen, nitrogen, iron, carbon, in the following ratio, wt.%:
nickel 31-33 tungsten 1-3 vanadium 0.1-0.4 titanium 0.05-0.3 aluminum + silicon no more than 0.2 oxygen no more than 0.08 nitrogen no more than 0,04 iron no more than 0.5 carbon no more than 0.08 chromium rest,
which has a molten state structure that does not contain eutectics. 2. A method of smelting a heat-resistant alloy according to claim 1, comprising loading a charge into a vacuum electric furnace, consisting of pure starting materials, including electrolytically refined chromium, nickel and tungsten, heating the mixture to a temperature of 1600-1620 ° C until it is completely melted, holding for 5- 10 minutes, lowering the temperature to 1550-1570 ° C and introducing vanadium and titanium into the melt, and after 1-2 minutes for deoxidation and modification - microalloying additives, after which the melt is poured into the molds at a temperature of 1550-1570 ° C to ensure that cast condition eutectic-free alloy structure.

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