JPS5845338A - Alloy remelting method - Google Patents

Abstract

(57) [Summary] This bulletin contains application data before electronic filing, so abstract data is not recorded.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention provides a substantially uniform distribution of components (i.e., chemical elements) that tend to be unevenly segregated in macroscopic areas of the ingot in conventional solidification methods. The present invention relates to a remelting method for producing alloy ingots.

Composite alloys and alloys with active elements are usually produced by -order melting methods, such as vacuum induction melting (CVIM), in order to obtain excellent melt composition control and also high-grade purity. The molten metal is poured from the VIM crucible into large molds in a relatively short period of time.

Thus, most of the solidification occurs after the mold is filled.

Many of these alloys have wide solidification ranges (ie, the temperature difference between solidus and liquidus) and have different solubilities in solid versus liquid solvents. Thus, the first metal to solidify may have a much different chemical composition than the later solidified gold 1.4, resulting in chemical segregation throughout the ingot.

- from the above-mentioned macrosegregation (and also structural defects such as shrinkage cavities and pores) resulting from secondary melting and casting methods;
In order to produce ingots with desirable chemical and physical uniformity and texture, the ingots need to be refined by secondary remelting techniques such as vacuum arc remelting (VAR) or electric slag remelting (ESR). arise. V
The IM casting is remelted in a cold crucible as a consumable electrode in these methods. (Chemical uniformity of the resulting ingot is improved by zone refining while the size of the molten metal pool is limited by the amount controlled remelting step). As the metal solidifies in these methods, solute is rejected into the melt pool above the solid-liquid interface while more liquid is added to the melt pool from the melting electrode. In this way, the composition of the liquid above the solid-liquid interface remains approximately equal to the exact electrode composition during the entire remelting process, and overall ingot drift is reduced. The gradual directional solidification that occurs in cold crucibles also improves the physical uniformity of the ingot by reducing the area of voids caused by shrinkage of the material during solidification.
Let it be.

Another type of macrosegregation often occurs in composite and active alloys that are secondary remelted by VAR and ESR techniques. Solidification occurs primarily through columnar dendrite growth. These dendrites are finger-like solid projections that grow into the liquid from the solidified ingot. A mass of material in which liquid and solid coexist at a certain time during solidification is called ``ma/izone'' (m
The movement of the liquid or solid in the mushy zone causes the growth of dendrites (
Note 1) Partial segregation zones can be created by confinement of liquid or solid between [Note 1: framing, solid processing (Flemings, 5solid
Processing ) ).

Motion of liquid metal can result from thermal contraction, solidification contraction, and density differences in the liquid. During V'AR, F, and SR operations, fluid flow between unstable dendrites often occurs in the ingot.
This results in channel-shaped segregations called ``freckles'' and solute stratification or ``banding''. To minimize macrosegregation, measures such as electromagnetic stirring are used during vacuum arc remelting. Previous attempts to control liquid flow during secondary remelting have been unsuccessful, often resulting in increased ingot segregation (Notes 2, 6).

[Note 2 Nidorance Action, International Nomikyumu Metal Ji Conférance 1967゜Throw 6
95 Buer Ant McCauley.

(Trans, Int, Vaq, Met
, C:onf, 1967, Pg, 695
Buehl & McCauly) Note 3: Id. 196.7. Eazi 599 J Dazzlew Troutman.

(' 1968+ Pgo, 599 J, W,
Materials such as uranium-niobium alloys tend to be highly segregated in small diameter (8 inch) VAR ingots due to substantial differences in their atomic weights and melting points. Differences in liquid density and unstable flow in the mashy zone are somewhat arbitrary in the banding system, as described by Jessen.
is defined as a stratified chemical heterogeneity in which the segregation appears on the radiograph as a continuous gradient of niobium (0
, 1% by weight of niobium solidifies from the bottom to the top). Flemings et al. (note 1) show that for unidirectional solidification there is a quantitative correlation between the fluid flow in the mashy zone and the thermal environment between the growing dendrites. Abrupt changes in heat transfer rates result in solute-rich or solute-poor layers.

Zanner et al. (Note 4) recently analyzed the vacuum arc remelting of uranium-niobium alloys by quantitative experimental methods to reduce macrosegregation through improved process control. , "Consumable Ant Excremental Analysis/U-6w10N'b Bacium Consumable Remerite Ingot (Zanner et al.
, ”Computational and Expe.
rimentalAnalysis of a U-
6W10 Nb Vacuum Consumable
eArc Remelted Ingot”).

The rigid complexity of the physics of the VAR method, which has a consumable electrode remelting step with an electric arc in close contact with the superheated liquid metal, also limits the degree of process control and macro-segregation control that can be achieved.

In the remelting method of the present invention, 6 banding” (and “fleck/
Q”) Alloying elements that tend to form macrosegregations (such as uranium-niobium or copper-aluminum alloys)
An alloy ingot can be produced that has a substantially uniform distribution of . Compared to prior art methods of solidifying these alloys from superheated holes circulating over columnar dendrites growing from the surface of the ingot, the method of the present invention produces milkshake-like solidification with any circulation of liquid being negligible. 7. It relies on solidifying most of the liquid by homogeneous nucleation creating a mashy zone consisting of discrete solid nuclei with liquid metal having a C consistency.

Since the homogeneous mixture of solid particles and liquid effectively retards the movement of solidification, there is virtually no liquid circulation (and therefore no sudden changes in liquid convection in the mashy zone). Solidification takes place before the liquid can segregate, and there is no sudden change in the rate of heat transfer, because the solid particles throughout the body absorb at least the state of the heat of fusion so that they are not overheated, and there is no sudden change in the rate of heat transfer. Solidification proceeds even more rapidly than in VAR and ESR because there is no source of liquid. Droplets that fall onto the ingot from the melting ingot contain solid cores and aggregate to form a mashy zone on top of the ingot itself. The practice of the invention thus consists of the following steps: holding at least one expendable ingot in the upper part of the mold, which ingot has the composition of the ingot to be produced in the mold; are characterized by substantially different specific gravities and substantially different melting points.
A portion of the ingot is heated to a temperature between the solidus temperature and the liquidus temperature of the alloy composition to partially solidify and form droplets. forming a droplet and causing it to fall to form a goose-like body consisting of a large number of droplets on the surface of the ingot in the mold;
and a step of coagulating the residual liquid portion of the porridge.

As a definition, 'mush' used in the present invention
The term y) describes an alloy at a temperature between the in-phase and liquidus temperatures. These temperatures can be accurately measured by differential thermal analysis; articles describing this technique include, for example, Lilliam Shinnyhosh et al., Examining Superalloy Reactions by Differential Thermal Analysis, Metal Progress, October 1975 ( William J., Boe
sch, et al,, Differentia
l The-rmal Analysis Detect
5upperal], oy Reactions.

METALS PROGRESS, ○ctober 1
975. ). The process of the present invention is suitable for systems characterized by reverse segregation, i.e. 1 with a relatively high melting point.
It may be particularly useful in connection with cases where the components also have a relatively low specific gravity, or where one component with a relatively low melting point also has a relatively high specific gravity.

The invention can be described more fully with reference to an embodiment of the invention, preferably illustrated by means of a schematic diagram. As shown by this diagram, at least one consuming electrode 10 is placed above a mold (or crucible) 24. A more detailed preferred practice and drawings are described in U.S. Pat. No. 4,261,412, which is incorporated herein by reference. It is listed here as a reference.

The expendable ingot 10 can be pre-alloyed and have the nominal composition of the ingot to be cast, or in rare cases the ingot may contain alternating strips of metal creating an alloy system. There may also be two ingots, both of which can be consumed as shown in the drawings. There may also be multiple combinations of ingots that are consumed simultaneously. Arc Process VCjJI] Additionally, one or more ingots can also be melted (as described below) by electron beam, plasma arc, or similar methods.

A VIM prealloyed 4,'5 weight Pi% copper-aluminum ingot of diameter 20.3 crn (3 inches) was melted in accordance with the present invention and made into a diameter 15
．． A remelted ingot was made into a 2rm (6 inch) long 65.6 m (14 inch) ingot. This ingot has a nominal current of 4
00077” 726-28 volts for 1 minute 3.1
It was melted at a rate of 5Kr (7 pounds). The temperature of the formed ingot was measured using seven square thermocouples spaced 5 cm (2 inches) apart along the sidewalls of the mold 24. According to the method of the invention, a portion of the spent ingot 10 is heated to a temperature between the solidus and liquidus temperatures of the nominal composition of the ingot formed in the underlying mold. A second ingot (in this case the spent ingot) 12 having the same composition is located near the first ingot 10 with a gap 14 between their respective adjacent ends. ingots 10 and 1
An electric arc was discharged into the gap 14 between the two adjacent ends.

When the temperature of ingots 10 and 12 exceeds the solidus temperature,
The partially solidified droplet 20 is placed inside the mold 24.
'Mushy body' begins to fall on top of 6
form. 4.6 The maximum temperature of the weight-bound copper-aluminum ingot 260 to the porridge 27 is 642.8°C (
A thermocouple in the wall of the mold 24 indicated the temperature change from 1189F to 1205F. According to differential thermal analysis, the solidus temperature and liquidus temperature of this composition are 602.8°C (11177;') and 6678°C (
1234F). The condition is that systems such as these copper-aluminum compositions (i.e., containing less than about 26% copper by weight) tend to segregate because the solidifying alloy tends to be lighter than the remaining liquid. From the diagram. The relative specific gravity of these components (copper 8.92 and aluminum 2.70) indicates that segregation tends to occur in bands.

The porridge 27 on top of the ingot 26 solidified with no liquid pond forming. A 15.2 tM (6 inch) diameter ingot was cut lengthwise and chemically etched to examine the microstructure. The particle size of the ingot is 1
．． It had a uniform crystal structure with less than 6 ran (% inches). There were no three foundations for Pandeink.

In the electric arc furnace shown in the drawings, the expended ingots 10 and 1 are used to promote even melting and to prevent the partially solidified droplets from being significantly overheated.
2 is reciprocated by any suitable means 16 and 18. Furthermore, the mold 24 itself can be formed into a variety of shapes and shapes according to the desired product, including not only conventional intermediate molds such as billets, but also the shape and shape of the final product.

The figure shows a rotary mold driven by means 28 of a rotating shaft to equalize the distribution of droplets 20 across the surface of the ingot. The mold 24 may also be provided with means for pulling down the inject when it is formed. The furnace must have a controlled atmosphere, such as a vacuum created by some suitable means, such as a pump 22 as shown.

Uranium-niobium (such as niobium-uranium alloy by weight 6)
and other systems prone to banding macrosegregation, such as lithium-aluminum systems, can be rebroken into substantially uniform ingots in accordance with the present invention. In addition, reinforcing particles, such as fibers such as Ittriya or Torya or silicon carbide, are added to the droplet 2 as it falls onto the oyster.
It can be injected into the flow of o.

[Brief explanation of the drawing]

The drawings schematically show embodiments of the invention. 10.12: Consumption ingot, 14: Gap between ingots> 16. is: round trip means, 2o:
i drop, 22: pump, 24 nil acupoint mataha mold, 26: ingot, 27: gourd body (mu
shybOdy).

Claims (1)

[Scope of Claims] (1) A remelting process for producing an alloy ingot having a substantially uniform distribution of components with a tendency to form band-like macrosegregation, comprising the steps of: holding at least one consumable ingot in the mold, provided that the ingot has the composition of the ingot to be produced in the mold, and the composition has a substantially different specific gravity and a substantially different melting point. heating a portion of said ingot to a temperature between the solidus and liquidus temperatures of said alloy composition to form a partially solidified liquid; Step of forming droplets and allowing them to fall to form a slag-like body consisting of a large number of droplets on the surface of the ingot in the mold:
and a step of solidifying the remaining liquid portion in the porridge. (2) heating a plurality of consumed ingots above the mold;
A method according to claim 1. 3. The method of claim 1, wherein the ingot heated above the mold is first prealloyed. (4) The method according to claim 1, wherein the ingot is heated by an electric arc. (5) The method according to claim 1, wherein the ingot is heated by an electron beam. (6) The method according to claim 1, wherein the ingot is heated by a plasma arc. (7) the composition consists of at least two components, the first component having a melting point substantially higher than the melting point of the second component;
2. The method of claim 1, wherein the second component has a specific gravity that is substantially greater than the specific gravity of the first component. (8) The melting point of the first component is at least 1000° C. higher than the melting point of the second component, and the specific gravity of the second component is less than (both twice) that of the first component. (9) Claim 8, wherein the first component is niobium.
The method described in section. (10) The method according to claim 9, wherein the second component is uranium. 11. The method of claim 10, wherein the Qi) a component comprises about 6 wt. niobium in uranium. (121) The method of claim 1, wherein the composition consists of at least two components, the first component having a melting point and specific gravity substantially greater than the melting point and specific gravity of the second component. 13) The melting point of the first component is at least 600° C. higher than the melting point of the second component, and the specific gravity of the first component is at least twice that of the second component.
The method described in section. (14) Claim 12, wherein the first component is copper.
The method described in section. (15) The method of claim 14, wherein the second component is aluminum. (16) The composition is about 4.3% by weight copper in aluminum.
17) An alloy ingot produced by the method of claim 1, having a substantially uniform distribution of components that tend to form band-like macrosegregations.