JPH06212253A - Production of cold tool steel - Google Patents

Abstract

PURPOSE:To remarkably improve the service life of cold tool steel and its discharge machinability by subjecting tool steel in which the compositional range of each component is specified to high temp. tempering treatment at a temp. of specified value or above. CONSTITUTION:Steel contg., by weight, 0.75 to 1.75% C, 0.5 to 3.0% Si, 0.1 to 2.0% Mn, 5.0 to 11.0% Cr, 1.3 to 5.0% Mo and 0.1 to 5.0% V or furthermore contg. one or >= two kinds among 0.001 to 0.5% rare earth metals, 0.1 to 2.0% Cu, 0.2 to 2.0% Ni, 0.1 to 3.0% W, 0.1 to 5.0% Co, 0.01 to 3.0% Nb, >=2% Ti and <=2.0% Zr and/or <=0.20% S, <=0.40% Pb, <=0.30% Se, <=0.50% Bi, <=0.30% Te and 0.002 to 0.010% Ca, an the balance Fe with impurities is tempered at >=450 deg.C.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a cold tool having a high hardness and a high toughness which is particularly suitable for use in cold working under severe working conditions or electric discharge machining such as wire cutting when working into a tool. Manufacturing method.

[0002]

2. Description of the Related Art Conventionally, cold forging dies and punches,
As an alloy tool steel for cold working used for die cutting applications, etc.
JIS SKD11 is widely used. These SKD11 are generally used as a heat treatment method after quenching from 1000 to 1050 ° C, tempering at 150 to 200 ° C, and HRC61 or higher. However, although these conventional SKD11 have high hardness, they do not have sufficient toughness, and due to the recent severeness of cold working methods or the spread of electric discharge machining methods such as wire cutting, SKD11 may not be able to cope with them. It is increasing. For example, a die for cold forging has a problem that the tool life is shortened by seizure, and a die is cracked during electric discharge machining due to the wire cutting. For such a situation, various cold work tool steels have been proposed, such as adding various components based on the composition of SKD11. However, it is difficult to say that these have sufficient hardness and toughness as a tool used for severe cold working or electric discharge machining as described above.

[0003]

DISCLOSURE OF THE INVENTION The present invention is sufficiently hard to cope with the recent severe conditions of use, and has a high hardness which enables stable use for a long period of time without causing strength deterioration or cracking. An object of the present invention is to provide a method for producing a cold work tool steel having high toughness and excellent electric discharge machinability.

[0004]

Means for Solving the Problems The present inventors have made various studies for the purpose of solving the above problems. As a result, while maintaining an appropriate balance between carbon and carbide-forming elements to reduce the amount of primary eutectic carbides, the toughness is enhanced, and the composition range of each component is specified.
The present invention has been found out that the life and the electric discharge machinability of the cold work tool steel are significantly improved by performing the high temperature tempering treatment at a temperature of ℃ or more to increase the secondary hardening hardness.

In the present invention, C: 0.75 to 1.75%, Si: 0.5 to 3.0
%, Mn: 0.1 to 2.0%, Cr: 5.0 to 11.0%, Mo: 1.3 to 5.0
%, V: 0.1-5.0%, or further RE
M: 0.001-0.5%, Cu: 0.1-2.0%, Ni: 0.2-2.0%,
W: 0.1-3.0%, Co: 0.1-5.0%, Nb: 0.01-3%, T
i: 2.0% or less, Zr: 2.0 or less, one or more, and / or S: 0.20% or less, Pb: 0.40% or less,
Se: 0.30% or less, Bi: 0.50% or less, Te: 0.30% or less, C
a: A steel material containing one or more of 0.002 to 0.010% (each weight%) and the balance Fe and impurities is 450
A method for producing a cold work tool steel characterized by tempering at a temperature of ℃ or more.

The reasons for limiting the composition range of each component in the present invention are as follows. C: C is an essential element that enhances the hardness of martensite, forms special carbides by high temperature tempering and contributes to secondary hardening, and further forms carbides with Cr, Mo, V to contribute to wear resistance. Is. This C content correlates with the Cr content, but is 0.75%
If it is less than (weight), the quenching and tempering hardness is low, and the wear resistance is reduced. Conversely, if it exceeds 1.75% (weight), toughness is reduced, so it is 0.75 to 1.75% (weight). Si: Si is effective in increasing the high temperature temper hardness, and also improves the toughness without lowering the hardness. In order to obtain these effects, it is necessary to contain it in an amount exceeding 0.5%, but if it exceeds 3.0% (by weight), hot workability and toughness deteriorate. Mn: Mn acts as a deoxidizing and desulfurizing agent, improving the cleanliness of steel and improving hardenability. for that reason,
Although it is contained in an amount of 0.1% (weight) or more, if it exceeds 2% (weight), workability is impaired. Cr: Cr forms a solid solution in the matrix during quenching to enhance hardenability and form Cr carbides, improving wear resistance, but 5%
If it is less than (weight), such effect is small, and conversely it is 11%.
If it exceeds (weight), toughness is deteriorated. Mo: Mo is an element effective in forming a solid solution in the matrix during quenching and forming carbides to improve wear resistance and enhance quenching and tempering resistance. It is necessary to contain 1.3% (by weight) or more in order to exert such effects, and in particular to obtain high hardness of HRC62 or more by high temperature tempering.
Even if it exceeds% (weight), the increase in the effect is not so great and the hot workability deteriorates. V: V prevents coarsening of the austenite-based crystal grains of the matrix, forms fine carbides, and contributes to improvement of wear resistance and hardenability. These effects cannot be expected when less than 0.1% (weight), and workability deteriorates when more than 5.0%. REM, Cu, Ni, W, Co, Nb, Ti, Zr: Each of these elements contributes to the improvement of strength and toughness, but if contained in a large amount, they deteriorate hot workability and toughness.
REM: 0.001 to 0.5%, Cu: 0.1 to 2.0%, Ni: 0.2 to 2.0
%, W: 0.1 to 3.0%, Co: 0.1 to 5.0%, Nb: 0.01 to 3
%, Ti: 2.0% or less, Zr: 2.0 or less (each weight%).
Each of these elements may be contained alone or in combination of two or more. S, Pb, Se, Bi, Te, Ca: All of these elements are effective in improving machinability, and workability during finishing after machining and plastic working (forging, etc.) However, if too much, the hot workability and toughness deteriorate, so S: 0.20% or less, Pb: 0.40% or less, Se: 0.
30% or less, Bi: 0.50% or less, Te: 0.30% or less, Ca: 0.00
2 to 0.010% (each weight%). These elements may be contained in one kind or in two or more kinds.

The manufacturing method of the present invention is carried out by annealing the steel materials having the above respective compositions, post-quenching, and then tempering at a high temperature of 450 ° C. or higher. The quenching temperature at this time is preferably at a high temperature within 1000 to 1060 ° C, and the tempering temperature in the subsequent stage is preferably 450 to 550 ° C. The cold work tool steel thus produced is used for cold dies, punches, die cutting, and the like. The present invention is manufactured by this method, and by high temperature tempering, residual stress during quenching is removed to form a stable structure and secondary hardening hardness is increased, and both hardness and toughness are excellent, and it is used as a tool. When a tool is galvanized over time or heat is generated in the tool due to electric discharge machining or the like, the tool life is extended without cracking and the workability is greatly improved. Furthermore, the surface treatment property when TiC or the like is physically vapor-deposited on the tool surface is also improved. These advantages of high temperature tempering cannot be fully exhibited at tempering temperatures below 450 ° C.

[0008]

EXAMPLES The present invention will now be described in detail with reference to Examples.
A steel material having the composition shown in Table 1 is quenched at the quenching temperature shown in Table 2,
Then, it is tempered at the tempering temperature shown in Table 2 to obtain the cold work tool steel of the present invention. JIS SKD11, SKD12, etc., which have been conventionally used as comparative steels, were melted and the hardness, Charpy impact value, bending resistance, seizure load, specific wear amount, residual stress and Tested for wire cutability. Table 2 shows the test results of those characteristic values. Charpy impact value is 15 × 15 × 60mm for φ30mm material
It is cut into and quenched (oil-cooled) and tempered (air-cooled),
A central notch having a depth of 2 mm, a surface roughness of 0.25 or less, and a 10 mm R notch were formed to obtain a test piece. Residual stress is φ200 × 300mml
The material is hardened (holding at the heating temperature for 15 minutes, air cooling) and tempered (holding at the heating temperature for 2 hours, air cooling x 2 times), and the center of the surface layer is electrolytically polished to a 20 mm square and a depth of 0.5 mm. Was measured by the X-ray method (longitudinal direction), and the other test conditions are as follows. (B) Bending strength: For a test piece of φ8 × 130 mm, the distance between fulcrums is 100 mm, and the load is one point at the center. (B) Specific wear amount ... Mating material by Ogoshi-type rapid friction tester
SCM415 (HB190), friction speed 2.9m / sec, friction distance 200m
m, friction load 6.5 kg. (C) Seizure load: SCM415 (annealed) as mating material
, Friction speed 30-100mm / sec, contact surface pressure 5-50kgf / m
m ² and fat-based oil as the lubricating oil. (D) Wire cutability: 10 mm due to wire cut
The length is cut, and the number of cracks of 100 μm or longer on the cut surface is shown.

[0009]

[Table 1]

[0010]

[Table 2]

From Table 2, all the steels manufactured according to the present invention are
It can be seen that it has hardness of HRC62 or higher and high toughness, and is excellent in wear resistance, seizure load, and wire cut property.

Next, test materials No. 1, 7 and 16 (SKD11)
The effect of tempering temperature after high temperature quenching on the secondary hardening hardness and Charpy impact value was investigated by using. The results are shown in Table 3.

[0013]

[Table 3]

From Table 3, the No. related to the production according to the present invention is shown.
In 1 and No. 7, the tempering temperature was 200 ℃, 300 ℃, 4
The secondary hardening hardness at 00 ℃ is not enough, it reaches the desired hardness at 500 ℃, and the impact value at 500 ℃ is slightly lower than that at 400 ℃, but it still has high toughness. There is. From these facts, it can be said that the tempering temperature must be 450 ° C or higher in order to provide both high hardness and high toughness. On the other hand, it can be seen that the conventional material is considerably inferior to the steel of the present invention in hardness and impact value even when subjected to high temperature tempering.

[0015]

The tool steel manufactured according to the present invention has excellent hardness, high toughness and electrical discharge machinability that can be used stably for a long period of time without severe deterioration of strength and cracking, even under severe conditions. It is cold tool steel.

Claims (4)

[Claims] 1. C: 0.75 to 1.75%, Si: 0.5 to 3.0%, M
n: 0.1-2.0%, Cr: 5.0-11.0%, Mo: 1.3-5.0%,
V: A method for producing a cold work tool steel, which comprises tempering a steel material containing 0.1 to 5.0% (each weight%) and consisting of balance Fe and impurities at a temperature of 450 ° C. or higher. 2. C: 0.75 to 1.75%, Si: 0.5 to 3.0%, M
n: 0.1-2.0%, Cr: 5.0-11.0%, Mo: 1.3-5.0%,
V: 0.1-5.0%, REM: 0.001-0.5%, C
u: 0.1-2.0%, Ni: 0.2-2.0%, W: 0.1-3.0%, C
o: 0.1-5.0%, Nb: 0.01-3%, Ti: 2.0% or less and
Zr: A method for producing a cold work tool steel, which comprises tempering a steel material containing one or more kinds of 2.0 or less (each weight%) and having the balance Fe and impurities at a temperature of 450 ° C. or more. 3. C: 0.75 to 1.75%, Si: 0.5 to 3.0%, M
n: 0.1-2.0%, Cr: 5.0-11.0%, Mo: 1.3-5.0%,
V: 0.1 to 5.0%, S: 0.20% or less, Pb:
0.40% or less, Se: 0.3% or less, Bi: 0.50% or less, Te: 0.3
Cold containing 0% or less and Ca: 0.002 to 0.010% (each weight%) of 1 or 2 or more and tempering a steel material composed of the balance Fe and impurities at a temperature of 450 ° C. or more Tool steel manufacturing method. 4. C: 0.75 to 1.75%, Si: 0.5 to 3.0%, M
n: 0.1-2.0%, Cr: 5.0-11.0%, Mo: 1.3-5.0%,
V: 0.1-5.0%, REM: 0.001-0.5%, C
u: 0.1-2.0%, Ni: 0.2-2.0%, W: 0.1-3.0%, C
o: 0.1-5.0%, Nb: 0.01-3%, Ti: 2.0% or less and
Zr: 2.0 or less, 1 or 2 or more, S: 0.20%
The following contains Pb: 0.40% or less, Se: 0.3% or less, Bi: 0.5% or less, Te: 0.30% or less and Ca: 0.002 to 0.010% (each weight%), and one or more kinds, and the balance. A method for producing a cold work tool steel, which comprises tempering a steel material comprising Fe and impurities at a temperature of 450 ° C or higher.