JPH093577A - Material for hot extrusion die and its production - Google Patents

Abstract

PURPOSE: To produce a material for hot extrusion die, having long and stable service life. CONSTITUTION: This material is composed of an Ni-base heat resistant alloy having a composition consisting of, by weight, <=0.08% C, <=0.35% Si, <=0.35% Mn, 50.0-55.0% Ni, 17.0-21.0% Cr, 2.80-3.30 Mo, 4.45-5.50% Nb+Ta, 0.65-1.15% Ti, 0.20-0.80% Al, and the balance Fe with inevitable impurities. Further, this material has a structure in which the crystalline grain size, measured by the method for measuring austenitic grain size of steel specified by JIS G 0551, is regulated to grain size No.1 to 4. This material is produced by setting forging finishing temp. to >=950 deg.C or solution heat treatment temp. to 1050-1100 deg.C.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a material for hot extrusion dies and a method for producing the same, and more specifically, a material for hot extrusion dies suitable for hot extrusion of a billet of copper or copper alloy. And the method of manufacturing it.

[0002]

2. Description of the Related Art For example, in hot extrusion of copper, a copper billet heated to 800 to 920 ° C. is inserted into a liner of a hot extruder, a stem is operated, and a die attached to a liner outlet is used. Extruded into an extruded product having a predetermined shape. Each time the hot extrusion of the billet is completed, the die is detached from the liner outlet, the die is cooled by, for example, water cooling, and then the die is attached again to the liner outlet to prepare for the next hot extrusion of the copper billet.

Therefore, the surface of the die is subjected to a heat load of 10 to several tens of seconds in one extrusion operation, and
A rapid cooling load such as water cooling is applied, and it is exposed to a severe heat environment. For this reason, conventionally, as a material forming the copper die, for example, SKD61 or SKD62 is used.
A heat resistant tool steel such as the above, and a Ni-based heat resistant alloy such as Inconel 718 are used. In particular, Inconel 718
Is widely used.

By the way, the above-mentioned Inconel 718 die is manufactured by subjecting an alloy ingot having a predetermined composition to hot forging, solution treatment, and aging treatment in that order, and then processing it into a predetermined shape. . The hot forging at this time is performed at a final forging temperature of about 900 ° C, and the solution treatment is usually performed at a temperature of 1000 ° C or less.

[0005]

However, the Inconel 718 die may be damaged during cooling by water cooling or the like as described above, and its service life is short and the service life often varies depending on the manufacturing lot. It has been pointed out that there is a lack of stability in life.

The present invention has the same composition as Inconel 718, but solves the above problems in the conventional Inconel 718 die, and has a long service life and a stable service life. The purpose is to provide a manufacturing method thereof.

[0007]

Means for Solving the Problems In the process of elucidating the cause of breakage of a conventional Inconel 718 type die manufactured at a forging end temperature of about 900 ° C. and a solutionizing temperature of 1000 ° C. or less, the present inventor Was checked, JIS G
The grain size of the austenite grain size test method (GS method) for steel specified in 0551 was about 8 for grain size number (N), and it was found that the structure was composed of fairly fine grain.

The temperature is 750 ° C. and the load is 26.35 kgf / mm.
^When the minimum creep rate of the above die material was measured under the condition of ² , the value of 0.023 to 0.031% / hr was shown. From the above, the material of the die described above is composed of fine crystal grains with a grain size number of around 8, and its creep deformation resistance is small. Therefore, when a high temperature billet is press-fitted, the die face has a plastic flow of the billet. It was estimated that creep deformation occurred without being able to withstand the induced load, which caused die damage.

[0009] Therefore, the idea that the cause of damage estimated above can be eliminated by making the grain size of the material coarse and increasing the high temperature creep strength was obtained, and as a result of repeated research based on the idea, The invention has led to the development of a material for hot extrusion dies and a method for producing the same. That is, the material for the hot extrusion die of the present invention has C: 0.08% by weight or less and Si:
0.35% by weight or less, Mn: 0.35% by weight or less, Ni: 5
0.0-55.0% by weight, Cr: 17.0-21.0% by weight, M
o: 2.80 to 3.30% by weight or less, Nb + Ta: 4.45 to
5.50% by weight, Ti: 0.65 to 1.15% by weight, Al: 0.
Ni group having 20 to 0.80% by weight, the balance being Fe and inevitable impurities, and having a structure in which the grain size measured by the GS method of JIS G 0551 is in the range of 1 to 4 in grain size number. The first manufacturing method is characterized by comprising a heat-resistant alloy, the step of melting the Ni-based heat-resistant alloy;
And a step of sequentially subjecting the forged product to a solution treatment and an aging treatment, the second step being a forging step at which the grain size is controlled by performing a forging treatment at the above forging end temperature. The manufacturing method of the step is a step of smelting the Ni-base heat-resistant alloy; a step of subjecting the alloy ingot obtained in the step to a forging treatment;
And a step of subjecting the solution to a solution treatment to adjust the crystal grain size; and a step of performing an aging treatment.

In the material of the present invention, first, C is C
It is a component that contributes to increasing the high temperature strength of the die and securing the die strength during hot extrusion by forming carbides by combining with carbide forming elements such as r, Mo, Ti, etc. Then, the toughness and ductility are impaired, the impact value is lowered at high temperature, and a problem such as cracking of the die during hot extrusion occurs,
Its content should be 0.08% by weight or less.

Si is a component that functions as a deoxidizer during melting of the alloy, but if it is contained too much, the toughness and ductility deteriorate and the cracking resistance of the die deteriorates.
Its content should be 0.35% by weight or less. Mn is a component that mainly functions as a deoxidizing agent and a desulfurizing agent at the time of alloy melting, but if it is contained in too much, the toughness and ductility deteriorates and the crack resistance of the die deteriorates. The content is
It should be 0.35 wt% or less.

[0012] Ni is a component that forms a stable austenite structure and contributes to the improvement of the corrosion resistance and heat resistance of the die. If the content is less than 5.0% by weight, the above effect is not sufficiently exhibited, Further, even if it exceeds 55.0% by weight, the above-mentioned effect is not remarkably exhibited and the cost is unnecessarily increased. Therefore, the content thereof is set to 50.0 to 55.0% by weight.

Cr is an effective component for ensuring oxidation resistance and high temperature corrosion resistance, and its content is 17.0 to 21.0.
Set to% by weight. If less than 17.0% by weight,
The above effects are not sufficiently exhibited, and surface oxidation is caused by heat from the high temperature billet. If it exceeds 21.0% by weight, high temperature corrosion resistance is improved, but on the other hand, due to the decrease in toughness and ductility, This is because the impact properties of the die deteriorate and the crack resistance of the die deteriorates.

Mo is a component that contributes to the high temperature tensile strength and high temperature creep strength of the die, and its content is 2.8.
It is set to 0 to 3.30% by weight. If the amount is less than 2.80% by weight, the above-mentioned effects are not sufficiently exhibited, and 3.3
This is because even if it is contained in an amount of more than 0% by weight, the high temperature strength is not significantly improved, and rather the workability is deteriorated and the high temperature impact characteristics are deteriorated.

Nb + Ta is a component that produces carbides and refines the matrix structure to improve the high temperature strength and toughness of the die, and contributes to the improvement of high temperature impact properties without lowering the tensile strength and creep rupture strength at high temperatures. And its content is set to 4.45 to 5.50% by weight.
If it is less than 4.45% by weight, the above effect is not sufficiently exhibited, and if it is more than 5.50% by weight, toughness lowers and workability deteriorates, making it difficult to manufacture dies. Because it causes a problem.

Ti is a component that contributes to the improvement of the high temperature strength of the die, and its content is set to 0.65 to 1.15% by weight. This is because if it is less than 0.65% by weight, the above-mentioned effects are not sufficiently exhibited, and if it is more than 1.15% by weight, there arises a problem that the high temperature characteristics are deteriorated. Al is a component that combines with Ti to form a compound and contributes to age hardening, and the content thereof is 0.20 to 0.8.
It is set to 0% by weight. When the amount is less than 0.20% by weight, the above-mentioned effects are not sufficiently exhibited, and when the amount is more than 0.80% by weight, there is a problem in workability.

The material of the present invention further comprises P, S,
Co may be included, but P is 0.015% by weight
Hereinafter, it is preferable that S is controlled to 0.015% by weight and Co is controlled to 1.00% by weight or less. The crystal grain size in the material of the present invention is the average cross-sectional area (mm ² ) of crystal grains constituting the structure and the grain size number (N) representing the number of crystal grains per unit area 1 (mm ² ) is defined in JIS G 0551. The N value measured by the GS method is in the range of 1 to 4.

That is, the structure of the material is in a state in which crystal grains having a grain size indicated by each grain size number of 1 to 4 are mixed. In the material of the present invention, even the finest crystal grain has a grain size of 4 when indicated by a grain size number. And the whole organization has a grain size number N within the above range,
Even if the temperature is high, the grains are aggregated in a mosaic pattern between the grains with a coarse grain size with a low number and grains with a grain size with a higher number that is finer than that. Slip in the field is unlikely to occur, and it is considered that excellent creep strength is exhibited.

The material of the present invention can be manufactured by the following two methods. In the first method, first, an alloy having the above composition is melted in, for example, an electric furnace, and then an ingot is manufactured. Then, this ingot is hot forged. In this forging process, the forged structure of the ingot is refined, and at the same time, when the solution treatment of the next stage is performed, the crystal grains of the crystal grain size indicated by the grain size numbers N of 1 to 4 are precipitated and mixed. Energy is supplied.

The forging end temperature in this forging process is 95
It is set to 0 ° C or higher. This is because when the final forging temperature is lower than 950 ° C., the desired grain size of grain size number N cannot be obtained when the temperature of the solution treatment in the next stage is set to 1000 ° C. or lower as in the conventional case. Too high a final forging temperature is disadvantageous in terms of thermo-economics and, at the same time, coarsening of crystal grains progresses and cracks often start during forging. ..

At such a final temperature of forging, it is easy to obtain crystal grains having a suitable grain size number N, and also Cr carbides start to precipitate at the grain boundaries of the crystal grains, so that the grain boundary strength can be further improved. become. The forged product is then solution treated. The temperature at that time is 1000
It may be ℃ or less. Specifically, the treatment may be performed at a temperature near 980 ° C. for about 2 to 3 hours.

In this process, a structure is obtained in which the crystal grains having the grain sizes of 1 to 4 are mixed and precipitated. Finally, an aging treatment is applied. The treatment conditions are not particularly limited, but at temperatures of 720 ° C. and 620 ° C., each 8
It should be about an hour. Next, the second manufacturing method will be described.

In this method, first, an ingot having a predetermined composition is manufactured in the same manner as the first method. And
This ingot is hot forged under the same conditions as in the past. Specifically, it is forged at a final forging temperature of about 900 ° C. The obtained forged product is subjected to solution treatment. In this second method, the grain size number N of the grain size is adjusted by controlling the temperature of the solution treatment.

That is, the solution treatment temperature is 1050.
It is set to ˜1100 ° C. If this temperature is lower than 1050 ° C, the precipitated crystal grains become finer because the grain size number N is higher than 4, a structure having sufficient high temperature creep strength cannot be obtained, and if the temperature is higher than 1100 ° C. If this is the case, the crystal grains will be significantly coarsened and the desired high temperature strength will not be obtained. This solution treatment may be performed usually for about 2 to 8 hours.

When the solution treatment is performed at such a high temperature, the aging tends to be delayed. Therefore, the aging treatment in the next stage takes about twice as much time at the high temperature side as the conventional aging treatment. It is preferable. Specifically, it is suitable to carry out at a temperature of about 720 ° C. for about 16 hours.

[0026]

【Example】

Examples 1 to 3 and Comparative Examples 1 and 2 Alloys having the compositions shown in Table 1 were melted in an electric furnace and subjected to forging, solution treatment and aging treatment in the indicated conditions in order to obtain a material for a copper die. did. The minimum creep strength of these materials was measured under the conditions of a temperature of 750 ° C. and a load of 26.35 kgf / mm ² , and the particle size number was measured by the GS method of JIS G 0551.

Copper wrought dies were produced from these materials, a copper alloy billet at a temperature of 900 ° C. was extruded, and after the extruding was completed, the dies were cooled with water and the number of times until the dies were broken was examined. Table 1 summarizes the above results.

[0028]

[Table 1]

[0029]

As is clear from the above description, the material of the present invention has a structure in which coarse grains and fine grains are mixed with each other within the grain size number range of 1 to 4. Therefore, the high temperature creep strength is excellent. This material has a long service life and a stable life, and is very useful as a material for copper dies.

Claims (3)

[Claims] 1. C: 0.08% by weight or less, Si: 0.35% by weight or less, Mn: 0.35% by weight or less, Ni: 5.0-5.
5.0 wt%, Cr: 17.0 to 21.0 wt%, Mo: 2.8
0 to 3.30 wt% or less, Nb + Ta: 4.45 to 5.50 wt%, Ti: 0.65 to 1.15 wt%, Al: 0.20 to 0.
80% by weight, the balance consisting of Fe and inevitable impurities, and the grain size when measured by the austenite grain size test method for steel specified in JIS G 0551, have a grain size number in the range of 1 to 4 A material for a hot extrusion die, characterized by comprising a Ni-based heat-resistant alloy having 2. C: 0.08% by weight or less, Si: 0.35% by weight or less, Mn: 0.35% by weight or less, Ni: 5.0-5.
5.0 wt%, Cr: 17.0 to 21.0 wt%, Mo: 2.8
0 to 3.30 wt% or less, Nb + Ta: 4.45 to 5.50 wt%, Ti: 0.65 to 1.15 wt%, Al: 0.20 to 0.
Ni containing 80% by weight and the balance Fe and inevitable impurities
A step of melting the base heat-resistant alloy; a step of subjecting the alloy ingot obtained in the above step to a forging treatment at a forging end temperature of 950 ° C. or higher to adjust the grain size; and a solution treatment of the forged product. A method for manufacturing a material for a hot extrusion die, comprising a step of sequentially performing a treatment and an aging treatment. 3. C: 0.08% by weight or less, Si: 0.35% by weight or less, Mn: 0.35% by weight or less, Ni: 5.0-5.
5.0 wt%, Cr: 17.0 to 21.0 wt%, Mo: 2.8
0 to 3.30 wt% or less, Nb + Ta: 4.45 to 5.50 wt%, Ti: 0.65 to 1.15 wt%, Al: 0.20 to 0.
Ni containing 80% by weight and the balance Fe and inevitable impurities
A step of melting the base heat-resistant alloy; a step of forging the alloy ingot obtained in the above step;
A method for producing a hot-extrusion die melt material, comprising: a step of performing a solution heat treatment at 50 to 1100 ° C. to adjust a crystal grain size; and a step of performing an aging treatment.