JPH11181549A - Cold tool made of casting excellent in weldability and its production - Google Patents

Abstract

PROBLEM TO BE SOLVED: To obtain a tool excellent in weldability by composing it of a cast molded body of a steel contg. specified amounts of C, Si, Mn, Cr, Mo, V, and the balance Fe with impurities and regulating the amt. of primary carbides crystallized out at the time of casting to specified one or below. SOLUTION: A steel having a compsn. contg., by weight, 0.5 to 0.8% C, <=1.0% Si, 0.25 to 1.50% Mn, 4.0 to 8.0% Cr, 1.0 to 5.0% Mo and 0.1 to 1.0% V, contg., at need, one or >= two kinds among <=2.5% W, <=2.5% Ni and 0.2 to 2.0% Nb, and the balance Fe with impurities is cast. The cast molded body is subjected to solid solution treatment in an autenitization single phase temp. region of 1,150 to 1,250 deg.C to recyulate the amt. of primary carbides crystallized out at the time of the casting to <=1%, preferably to zero. If required, it is subjected to working such as cutting, grinding, polishing or the like and is thereafter subjected to quenching and tempering. Relating to its weldability, the preheating temp. can be made lower than that in a rolling stock by >=100 deg.C.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a cast cold tool excellent in weldability and a method of manufacturing the same, and more particularly, to a cast cold tool in which a steel cast body is heat-treated to improve weldability and a cast cold tool. It relates to a manufacturing method.

[0002]

2. Description of the Related Art Conventionally, tools used in cold, such as a cold press, a cold die type, a cold header type, a cold upsetter type, etc., that is, cold tools are JIS SKD11.
(C: 1.40-1.60%, Si: ≦ 0.40%, M
n ≦ 0.60%, Cr: 11.0 to 13.0%, Mo:
0.80 to 1.20%, V: 0.20 to 0.50%, balance Fe and impurities) is melted and cast into a steel ingot, and the steel ingot is hot rolled or the like. And hot-worked into a steel material, and the steel material is cut into a predetermined shape, and is manufactured by performing processing such as cutting, grinding, and polishing.

On the other hand, the shape of a cold tool has become more and more complicated in recent years, and when manufactured by the above-mentioned manufacturing method, the yield of materials has been further reduced. In recent years, the development and model change periods of new products have been increasingly shortened, and there has been a demand for shorter delivery times of cold tools. In response to the reduction in the yield and the shortened delivery time of the material, there has been a movement to make the material into a near net shape in order to improve the yield and shorten the delivery time.
As one means for responding to the near net shaping, it has been considered to start from a cast molded body cast into a shape approximate to a desired shape and to manufacture it by adding processing such as cutting, grinding, polishing and the like. .

[0004] However, when a conventional cold steel tool steel component composition is used as it is to form a cast product, there is a problem that the toughness is low and the cast product cannot be used in many cases. The reasons for the low toughness are that the cast material has a non-uniform structure and the toughness tends to be low, and coarse crystallization primary carbides are generated during casting, and the non-uniform and coarse cast structure lowers the toughness. General-purpose cold tool steels have a high C content and, as cast, have low toughness. In addition, welding overlays and castings for repairing molds need to be repaired for welding defects, so they must be materials with good weldability, but the components of conventional cold steel tool steel are used as they are. There was a problem that the cast molding obtained was not good in weldability.

[0005]

SUMMARY OF THE INVENTION The present invention relates to a cold tool manufactured by subjecting a steel ingot to hot working to a steel material manufactured by grinding, polishing and the like, even when manufactured from a cast molded product. It is an object of the present invention to provide a cold tool made of a casting that has the same toughness and wear resistance, and has weldability equal to or higher than the above-mentioned cold tool, and a method of manufacturing the same.

[0006]

Means for Solving the Problems In order to achieve the above object, the present inventors have studied a cold tool made of a casting and a method of manufacturing the same.
% Or more, but 0.6 to
It is about 0.7%, and the remainder is contained in carbides. Therefore, the amount of C may be reduced to the minimum level necessary for securing strength (hardness). Lowering the residual γ generated during welding by reducing the amount of expansion during martensitic transformation that occurs during cooling after welding can be reduced. By adding a solution treatment afterwards, homogenization of the cast structure and solid solution of the primary carbides can be achieved, uneven distribution of residual γ due to non-uniformity of C can be eliminated, and crack sensitivity can be reduced due to improvement in toughness of the base material. The present invention has been made based on the knowledge that, if the toughness is improved, the weld crack resistance can be improved.

That is, in the cast cold tool excellent in weldability of the present invention, C: 0.5 to 0.8%, Si: ≦
1.0%, Mn: 0.25 to 1.50%, Cr: 4.0
-8.0%, Mo: 1.0-5.0%, V: 0.1-
1.0%, if necessary, W: ≦ 2.5%, N
i: ≦ 2.5% and Nb: One or two or more of 0.2 to 2.0% are contained, and the steel is a cast formed body composed of Fe and impurities, and is crystallized during casting. 1% or less, and preferably no primary carbide.

Further, in the method for producing a cast cold tool excellent in weldability of the present invention, C: 0.5 to 0.8%, S:
i: ≦ 1.0%, Mn: 0.25 to 1.50%, Cr:
4.0-8.0%, Mo: 1.0-5.0%, V: 0.
1 to 1.0%, if necessary W: ≦ 2.5%,
Ni: ≦ 2.5% and Nb: Contains one or more of 0.2 to 2.0%, steel containing the balance of Fe and impurities is melted and then cast to form a cast body. This cast body is subjected to a solution treatment in an austenitizing single-phase temperature range such as 1150-1250 ° C. to reduce the primary carbide crystallized at the time of casting to 1% or less, preferably to be completely eliminated. After performing processing such as polishing, quenching and tempering are performed, and finishing processing such as polishing is performed as necessary.

Next, the present invention will be described in detail. In the casting cold tool and the method for producing the same according to the present invention, the component composition of the cast product is the one described above. The reason is as follows. C: 0.5-0.8% C is a basic element for increasing the hardness and strength of steel.
To obtain the required hardness and strength as a cold tool, 0.5
% Or more, and if it exceeds 0.8%, residual γ during welding
Increases the amount of martensitic transformation that expands during cooling to generate tensile stress, increases the likelihood of cracking, and reduces toughness, which further induces cracking during welding cooling. Therefore, its content range is 0.5
To 0.8%.

Si: ≦ 1.0% Si is an element that is usually contained as a deoxidizing agent and to improve tempering softening resistance, abrasion resistance and sag resistance, but exceeds 1.0%. In this case, the toughness of the matrix is reduced, and welding cracks are likely to occur. Mn: 0.25 to 1.50% Mn is an element usually contained as a deoxidizing agent and a desulfurizing agent, and also for improving hardenability and strengthening the matrix.
If it is less than 0.25, the effect is not sufficient, and 1.50
%, The hot workability is impaired, so the content range is 0.25 to 1.50%.

Cr: 4.0 to 8.0% Cr is an element contained in a solid solution in a matrix to increase softening resistance and to improve hardenability to secure hardness and toughness. If less than 0.0%, the effect is not sufficient,
If the content exceeds 8.0%, primary carbides at the time of solidification increase and cracks are easily generated at the time of welding.
To 8.0%. Mo: 1.0 to 5.0% Mo is an element contained for improving the tempering softening resistance. If the content is less than 1.0%, the effect is not sufficient.
More than 5.0% and primary carbides increases formed during solidification, M ₆ during solution treatment C, the solid solution of M ₂ C-type primary carbides becomes difficult, also because impairs weldability, containing the The range is set to 1.0 to 5.0%.

V: 0.1 to 1.0% V is an element contained to improve the wear resistance and seizure resistance and to refine the crystal grains. If the effect is not sufficient, and if it exceeds 1.0%, weld cracks are likely to occur, and primary carbides formed during solidification increase, making it difficult to dissolve MC type primary carbides during solution treatment. Therefore, its content range is 0.1 to
1.0%. W: ≦ 2.5% W is an element contained for improving the tempering softening resistance. However, if it is contained in a large amount, crystallization primary carbides formed at the time of solidification of the cast molded product increase, and solid solution becomes M during processing
₆ C and M ₂ C type primary carbides are difficult to dissolve,
The content is set to 2.5% or less.

Ni: ≤2.5% Ni is an element contained in the matrix to improve the toughness by forming a solid solution in the matrix. However, if it exceeds 2.5%, its effect is small, and the cost is low. Will also be higher,
The content is set to 2.5% or less. Nb: 0.2 to 2.0% Nb improves abrasion resistance and seizure resistance,
It is an element to be contained in order to refine the crystal grains,
If it is less than 0.2%, the effect is not sufficient, and 2.0%
If it exceeds, weld cracks are likely to occur, and the primary carbides formed during solidification increase, resulting in an increase in MC during solution treatment.
Since the solid solution of the primary carbide of the mold becomes difficult, the content range is set to 0.2 to 2.0%.

The cast cold tool of the present invention has a primary carbide crystallized at the time of casting of 1% or less, preferably none, for the following reason. If the primary carbide crystallized at the time of casting exceeds 1%, the toughness is remarkably reduced.
This is because the content is reduced to a value close to the amount of solid solution in the matrix, and insufficient solid solution results in insufficient hardness.

[0015] The method of manufacturing a cold tool for casting according to the present invention is characterized in that: (1) 1% or less of primary carbide crystallized during casting by solution treatment in an austenitizing single-phase temperature range of 1150 to 1250 ° C; , Preferably none, (2)
After that, quenching and tempering are performed. The purpose and conditions are as follows. (1) Solution treatment in austenite single-phase temperature range The solution treatment is to homogenize the cast structure such as resinous crystals crystallized at the time of casting, especially to reduce the primary carbide to 1% or less, and to improve toughness and weldability. The temperature varies depending on the composition of the components and the cooling rate.
It is preferable to heat and hold at 0 to 1250 ° C. 11
If the temperature is lower than 50 ° C., the effect of the solution treatment is small, and long-time processing is required, which is uneconomical. If the temperature exceeds 1250 ° C., the possibility of liquefaction exceeding the liquidus of carbides is high,
In addition, it is uneconomical because furnace damage is increased.

However, the solid solution treatment temperature is preferably about 1150 to 1250 ° C. as described above. However, the liquid phase line of the carbide should be adjusted so that each material subjected to the solid solution treatment does not deviate from the austenite single phase region. It must be determined individually so as not to exceed. The solution treatment time is
It is appropriately determined according to the size of the primary carbide, the dendrite interval, and the like of the cast molded product.

The solution treatment is performed so that the primary carbide crystallized at the time of casting is 1% or less, in order to homogenize the primary carbide, and if it exceeds 1%, the toughness is significantly reduced. In addition, since the amount of C is reduced to a value close to the amount of solid solution in the matrix, if the solid solution of the primary carbide is insufficient, the hardness may be insufficient. Preferably, the primary carbide is completely eliminated by the solution treatment. By performing a solution treatment capable of forming a solid solution of the primary carbide, a cast structure such as a dendrite crystallized at the time of casting can be homogenized at the same time.

(3) Quenching and tempering treatment Quenching and tempering treatment are carried out under the conditions normally used for alloy steels of this kind, that is, quenching is carried out at 1000 times.
Oil quenching is performed at a cooling rate equivalent to oil quenching or oil quenching from 1C to 1150C, and tempering is air cooling from 500 to 650C.

In the method of manufacturing a cold tool for casting according to the present invention, processing is performed as necessary before quenching and tempering. This processing is performed by cutting a cast molded body as cast.
Predetermined shape of products such as molds by grinding, polishing, etc.
This is to make the dimensions and surface condition, and this processing is the same as when manufacturing products such as molds from steel materials manufactured by hot rolling etc., but manufacturing products such as molds from the steel materials The amount of cutting and grinding may be smaller. In addition, after quenching and tempering, processing is performed as necessary, but this processing corrects the deformation when it is deformed by quenching and tempering, and grinds when the surface is oxidized. And so on.

[0020]

According to the cast cold tool of the present invention and the method for producing the same, the strength, hardness, toughness and weldability required for the cold tool can be obtained by using the above component composition. The solution treatment can be performed. Also, by performing the solution treatment, it becomes a cast molded body in which the coarse primary carbides crystallized during casting are dissolved, and this is processed as necessary by cutting, polishing, etc., and then quenched and tempered. Thereby, the strength, hardness, toughness and weldability required for the cold tool can be improved.

[0021]

Next, embodiments of the present invention will be described. Steel raw materials having the component compositions of the present invention material and the comparative material shown in Table 1 below were melted in a high-frequency melting furnace, Charpy test pieces were cast into boat shapes in accordance with JIS G 0307, and welded test pieces were 300 mm thick and wide. 300mm x length 15
The test piece material was collected by casting in a 0 mm casting mold.

[0022]

[Table 1]

Test Material of the Invention Material The material of the invention (No. 1 to 10) of the test piece material was subjected to a solution treatment temperature as shown in Table 2 below ("Solubility temperature" in Table 2).
And a solution treatment time (“solution time” in Table 2), a roughening process (considering removal of a decarburized portion), and then a quenching temperature and a tempering temperature shown in Table 2 below. Was subjected to heat treatment and fine processing to prepare a test piece. Comparative materials No. 11 to 14 of the comparative materials of the above test piece materials consisted of the components of the conventional cold tool steel, of which No. 11 material and No. 13
The as-cast material was rough-processed as cast, the No. 12 material was rough-processed in the horizontal direction of the rolled material, and the No. 14 material was rough-processed from the solution-treated No. 11 material. Thereafter, heat treatment was carried out at the quenching temperature and the tempering temperature shown in Table 2 below, followed by precision processing to prepare a test piece. In addition, No. 15 of the comparative material was the same as No. 1 of the material of the present invention, and was roughly processed as cast, and then heat-treated at the quenching and tempering temperatures shown in Table 2 below. Then, precision processing was performed to prepare a test piece.

[0024]

[Table 2]

Using the test piece thus heat-treated, hardness, residual primary carbide after solution treatment ("after solid solution" in Table 3) or crystallized primary carbide after casting, Charpy impact value, The rate of occurrence of surface cracks in the weld zone was measured for each γ content and preheating temperature, and the results are shown in Table 3 below. In addition, each measurement value was calculated | required using the following methods. The amount of residual or crystallized primary carbide is 10 × 1 as cast or after solution treatment.
A test piece of 0 × 10 mm was cut out and extracted and separated at a current density of 30 mA using a 0.5 N hydrochloric acid aqueous solution as an electrolyte.

The Charpy impact value was obtained by preparing an impact test piece having a length of 10 × 10 × 55 L and a 10R notch by sampling in the longitudinal direction, and conducting a test at room temperature. The rate of occurrence of weld surface cracks is determined by oblique Y-shaped weld crack test (JIS Z 3158)
It was carried out in accordance with. Specimen thickness: 15mm Welding conditions: welding wire; DS2501 (1.2DC / 0.15C-0.8Si-2.3M
n-1.2Cr-055Ca) Welding current; 200 A Welding speed; 25 cm / min Shielding gas; CO ₂ welding crack evaluation method: Cf = Σlf / L × 100% Cf; Surface cracking rate, Δlf; Surface cracking rate, L; Test Beat length

[0027]

[Table 3]

According to these results, the Charpy impact value of the material of the present invention is slightly lower than that of the No. 12 rolled material of the comparative material, though the hardness is almost the same as that of the comparative material. It is much higher than (No. 11, 13-15) of the comparative material, and the toughness is very excellent. Furthermore, while each material of the present invention does not cause welding cracks when preheated to 250 ° C, any of the comparative materials has weld cracks up to 350 ° C, and the welding preheating temperature is higher than that of the comparative material. 100 ℃
About low. Further, since each material of the present invention is subjected to solution treatment after casting, the Charpy impact value is about 1.5 times or more (No. 15 having the same component) as that of the material not subjected to solution treatment (No. 15). (1 is about 3.5 times). Further, each material of the present invention has a C and Cr content of the conventional steel (S
KD11), the Charpy impact value is much higher than that of the conventional heat-treated steel (No. 14), and the welding preheating temperature is also lower by 150 ° C.

[0029]

The casting cold tool and the method for producing the same according to the present invention have the above-mentioned composition and heat treatment.
Not only can the toughness equivalent to that of a cold tool manufactured from a steel material manufactured by hot working a steel ingot be obtained, but also the weldability can be reduced by a preheating temperature of 100 ° C. or higher than that of a rolled material. As a result, not only can the cost be reduced due to the higher material yield compared to cold tools manufactured from steel, and the product can be delivered in a short time due to the reduced amount of machining, Since the preheating temperature in welding can be greatly reduced, the time required for reheating can be shortened, and an excellent effect that productivity can be increased is exhibited.

──────────────────────────────────────────────────続 き Continued on the front page (51) Int.Cl. ⁶ Identification code FI C22C 38/24 C22C 38/24 38/46 38/46

Claims (5)

[Claims] C .: 0.5 to 1% by weight (the same applies hereinafter)
0.8%, Si: ≦ 1.0%, Mn: 0.25 to 1.5
0%, Cr: 4.0 to 8.0%, Mo: 1.0 to 5.0
%, V: 0.1 to 1.0%, and is formed of a cast steel product comprising the balance of Fe and impurities, and the primary carbide crystallized during casting is 1% or less, and has excellent weldability. Cast cold tool. 2. C: 0.5-0.8%, Si: ≦ 1.0
%, Mn: 0.25 to 1.50%, Cr: 4.0 to 8.
0%, Mo: 1.0 to 5.0%, V: 0.1 to 1.0%
And further contains one or more of W: ≤ 2.5%, Ni: ≤ 2.5% and Nb: 0.2 to 2.0%, with the balance being Fe and impurities. A cast cold tool excellent in weldability, comprising a cast steel body, wherein primary carbide crystallized during casting is 1% or less. 3. C: 0.5-0.8%, Si: ≦ 1.0
%, Mn: 0.25 to 1.50%, Cr: 4.0 to 8.
0%, Mo: 1.0 to 5.0%, V: 0.1 to 1.0
%, The steel consisting of the balance Fe and impurities is melted and cast to form a cast body, and the cast body is subjected to a solution treatment in an austenitizing single phase temperature range to reduce the primary carbide crystallized during casting to 1% or less. And a quenching and tempering treatment, followed by a method for manufacturing a cast cold tool excellent in weldability. 4. C: 0.5-0.8%, Si: ≦ 1.0
%, Mn: 0.25 to 1.50%, Cr: 4.0 to 8.
0%, Mo: 1.0 to 5.0%, V: 0.1 to 1.0%
And further contains one or more of W: ≤ 2.5%, Ni: ≤ 2.5% and Nb: 0.2 to 2.0%, with the balance being Fe and impurities. After the steel is melted and cast into a cast compact, the cast compact is subjected to a solution treatment in an austenitizing single-phase temperature range to reduce the primary carbide crystallized during casting to 1% or less, and then quenched and tempered. A method for producing a cast cold tool excellent in weldability, characterized by: 5. The casting-cooling process according to claim 3, wherein the solution treatment in the austenitized single-phase temperature range is performed by heating and maintaining the temperature at 1150 to 1250 ° C. Method of manufacturing intertool steel.