JPH0570827A - Manufacture of age hardening steel for mold for plastic molding excellent in toughness - Google Patents

Abstract

PURPOSE:To provide an age hardening steel for a mold for plastic molding excellent in mirror finishing properties and crimping workability as well as toughness. CONSTITUTION:At the time of using a mold steel contg., as essential alloy components, by weight, 0.05 to 0.18% C, <=1.0% Si, 0.5 to 2.0% Mn, 2.5 to 3.5% Ni, 0.1 to 0.4% Mo, 0.5 to 1.5% Al and 0.7 to 2.5% Cu and the balance Fe with impurities, subjecting it to forging or rolling, subsequently executing soln. treatment and thereafter subjecting it to aging treatment into a steel for a mold for plastic molding, the above soln. treatment is executed for >= two times, by which the age hardenability steel for a mold for plastic molding excellent in toughness can be manufactured.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a plastic mold steel suitable for use as a material for a mold used for molding a plastic part or a product, and more particularly, it has excellent mirror-finishing and grain-workability. In addition, the present invention relates to a method for producing a plastic die steel suitable for producing an age-hardening die steel which is excellent in toughness.

[0002]

2. Description of the Related Art Plastic molds for resin molding have been used to manufacture various parts such as automobile parts, office equipment parts, precision machine parts, electric parts, etc. At the same time that there is a tendency for small-volume production, strict conditions such as simplification of die manufacturing, cost reduction, and high precision are becoming demanded.

Heretofore, various proposals have been made for plastic mold steels, and there is also a proposal for those used in a pre-hardened state by utilizing age hardening (for example,
(See JP-A-63-183158).

[0004]

However, the plastic mold steels proposed hitherto have a problem that they have low toughness in comparison with hardness and that they are still insufficient in mirror finish and grain workability. There was a problem to solve these problems.

[0005]

DISCLOSURE OF THE INVENTION The present invention has been made in view of the above problems in the prior art, and is a plastic mold steel which is excellent in mirror finish and grain workability as well as in toughness. Is intended to provide.

[0006]

Means for Solving the Problems As a result of a detailed study, the inventors of the present invention decided to carry out solution treatment twice or more when manufacturing age-hardening plastic mold steel, thereby forming a uniform structure. It was found that a die steel can be obtained, and when used as a pre-hardened plastic die steel that utilizes age hardening, it has excellent mirror-finishing properties and grain-workability as well as excellent toughness. The present invention has been completed.

The method for producing a plastic die steel having excellent toughness according to the present invention is as follows: C: 0.05 to 0.18% by weight, Si: 1.0% by weight or less, Mn: 0.5 to 2 0.0 wt%, Ni: 2.5-3.5 wt%, Mo: 0.1
0.4% by weight, Al: 0.5 to 1.5% by weight, Cu:
Using a die steel consisting of 0.7 to 2.5 wt% as a basic alloy component and the balance Fe and impurities, a solution treatment is carried out after forging or rolling, and then an aging treatment is carried out to obtain a plastic die steel. In this case, the solution treatment is performed twice or more. In the embodiment, the cooling rate in the first solution treatment is higher than the cooling rate in the second solution treatment and thereafter. It is characterized by

In addition to the above basic alloy components, the die steel material used here further contains any one or all of the following alloy components (1), (2) and (3). Is also good.

(1) Nb + Ta: 0.3% by weight or less, T
i: 0.5 wt% or less, V: 0.5 wt% or less, Zr:
One or more selected from 0.5% by weight or less.

(2) Pb: 0.01 to 0.30% by weight,
Bi: 0.01 to 0.30% by weight, Se: 001 to 0.
40% by weight, Te: 0.01 to 0.30% by weight, S:
One or more selected from 0.05 to 0.30% by weight.

(3) Cr: 0.1 to 2.5% by weight, W:
0.5 wt% or less, Co: 0.5 wt% or less, Be:
One or two or more selected from 0.5% by weight or less and B: 0.01% by weight or less.

Further, the hydrogen content in the impurities is 3 ppm.
It may be desirable in some cases to reduce the susceptibility to hair splitting and to further stabilize quality by doing the following:

Next, the composition range and structure of the chemical components of the die steel material and the reasons for limitation in the method for producing the age hardening plastic die steel according to the present invention will be described.

C: 0.05 to 0.18% by weight: C keeps the quenching structure as a massive upper bainite structure with good machinability and also brings about a precipitation effect based on the precipitation of carbides during the aging treatment. Since it is an effective element, it is set to 0.05% by weight or more to obtain such an effect. However, when added in a large amount, the matrix is martensitic, and excessive carbides are generated to impair the machinability and reduce the toughness after age hardening. ..

Si: 1.0 wt% or less: Si acts as a deoxidizing agent during steel melting, and is added as a hardness adjusting element in the solution treatment. Since the toughness may decrease, the content is set to 1.0% by weight or less.

Mn: 0.5 to 2.0% by weight: In order to minimize the occurrence of bending during quenching of steel during age hardening treatment, cooling during quenching is preferably performed by air cooling. In order to ensure the desired hardenability even with air cooling, the amount was 0.5% by weight or more. However, if added in too large an amount, workability and toughness are impaired, so the content was made 2.0% by weight or less.

Ni: 2.5 to 3.5% by weight: Ni enhances the bainite hardenability and suppresses the formation of ferrite, precipitating a Ni-Al intermetallic compound during the aging treatment to increase the hardness. Since it is an element effective for increasing the photoetching property and increasing the photoetching property, it is set to 2.5% by weight or more in order to obtain such an effect. However, if contained in a large amount, the bainite transformation temperature is lowered, the bainite structure is refined, and the machinability is lowered.

Mo: 0.1 to 0.4% by weight: Mo is an element effective in improving toughness, and a small amount of Mo produces a uniform microstructure to ensure excellent photoetching property. There are effects, so to ensure these effects,
It was set to 0.1% by weight or more. However, if a large amount is added, the hardness increases and the machinability decreases, which is not preferable as a plastic mold steel, so it was set to 0.4 wt% or less.

Al: 0.5 to 1.5% by weight: Al makes it easier to obtain a desired massive upper bainite structure by increasing the bainite transformation temperature, and Ni-Al during aging treatment.
Since it is an element effective for improving the photoetching property as well as the precipitation effect due to the fine precipitation of the intermetallic compound of the system, it is set to 0.5% by weight or more. However, if the Al content is too high, the alumina-based inclusions increase, impairing the manufacturability, and also impairing the mirror finish and the corrosion resistance.
It was set to 1.5% by weight or less.

Cu: 0.7 to 2.5% by weight: Cu brings about precipitation hardening by finely depositing an Fe-Cu intermetallic compound at the time of aging treatment and, at the same time, is machinable in a solution treatment state. Since it is an element effective to bring about the above improvement, the content was made 0.7% by weight or more in order to bring about these effects. However, if the Cu content is too high, the hot workability is deteriorated and the machinability is impaired.

Cr: 0.1 to 2.5% by weight, W: 0.5
% Or less, Co: 0.5% by weight or less, Be: 0.5% by weight or less, B: 0.01% by weight or less, one or more selected from: Cr, W, Co, Be , B are elements effective for improving hardenability and improving toughness, especially in a large die,
One kind or two or more kinds may be appropriately added. Also,
Since Cr is an element effective for improving the corrosion resistance, it is preferable to contain Cr in an amount of 0.1% by weight or more in order to obtain such an effect. And, by adding these components, it is possible to adjust the solution hardening hardness and the aging hardness, but even if added more than necessary, it is not possible to obtain the improvement in properties commensurate with the increase in cost, Even if it is made, the Cr content is 2.5 wt% or less, and the W, Co and Be contents are 0.
It should be 5% by weight or less, and B should be 0.01% by weight or less.

Nb + Ta: 0.3% by weight or less, Ti:
0.5 wt% or less, V: 0.5 wt% or less, Zr: 0.
One or more selected from 5% by weight or less:
Nb, Ta, Ti, V, and Zr are elements effective not only for refining crystal grains to improve toughness but also for improving notch toughness, but addition of a large amount of them causes solution hardening and aging hardness. Content of Nb + Ta is 0.3% by weight or less and Ti, V, Zr is 0.5% by weight or less. is necessary.

Pb: 0.01 to 0.30% by weight, Bi:
0.01-0.30% by weight, Se: 0.01-0.40
% By weight, Te: 0.01 to 0.30% by weight, S: 0.0
One or more selected from the range of 5 to 0.30% by weight: Pb, Bi, Se, Te, S have the effect of improving machinability. To
Add 0.01 wt% or more for Pb, 0.01 wt% or more for Bi, 0.01 wt% or more for Se, 0.01 wt% or more for Te, 0.05 wt% or more for S. However, if too much is added, the toughness is impaired.
30 wt% or less, Bi about 0.30 wt% or less,
It is preferable that Se is 0.40% by weight or less, Te is 0.30% by weight or less, and S is 0.30% by weight or less.

Hydrogen: 3 ppm or less Since hydrogen cracking susceptibility increases if the hydrogen content in the impurities is too high and hair cracking may occur in extreme cases, the hydrogen content in the impurities is 3 ppm. The following is more preferable, and it is also desirable in some cases to employ special melting such as vacuum melting when reducing the hydrogen content.

In the method for producing an age-hardenable plastic die steel having excellent toughness according to the present invention, the die steel material is melted by electroslag melting, vacuum melting or the like and then cast to obtain a cast piece or a steel piece. On the other hand, it is forged or rolled, then subjected to solution treatment and age hardening treatment two or more times, and supplied as a mold material for plastic molding.

In the solution treatment and the aging treatment in this case, for example, the first solution treatment of heating to 800 to 950 ° C. and then water cooling is performed, and then 800 to 950 ° C.
The second solution treatment is performed by heating to 100 ° C. and then cooling with an air blast, followed by heating to 500 to 600 ° C. and then air cooling to perform an age hardening treatment.

By carrying out the solution treatment at least twice as described above, the mixed grain structure becomes a sizing structure, whereby the toughness is further improved.

In the pre-hardened plastic molding die steel thus subjected to the solution treatment and the age hardening treatment two or more times in this manner, the crystal grain size is 4 to 4 in terms of grain size number.
6, hardness is _H R _C35~40, a tensile strength of 130 to 15
It is 0 kgf / mm ² , and the toughness is excellent with the micro hardness distribution in a narrow range. Although hardness is preferably higher, the hardness exceeds 40 in H _{R C} machining becomes difficult, since problems with the machined surface occurs, hardness solution so as not to exceed 40 in H _{R C} It is desirable to perform aging treatment and age hardening treatment.

[0029]

EXAMPLES The present invention will be described below with reference to examples.

A die steel material having a chemical composition shown in Table 1 for a plastic die is melted by vacuum melting, ingot-casted, and then the steel ingot is peeled, and forged under the forging conditions shown in Table 2. Then, the solution treatment and the age hardening treatment were performed under the solution treatment condition and the age hardening treatment condition also shown in Table 2 to obtain a pre-hardened plastic mold steel. In these pre-hardened plastic die steels, hardness after heat treatment, micro hardness distribution (Hv mix to Hv max) showing uniformity of structure, grain size number, machinability, mirror finish (good: ≤ 8, distorted ≧ 15), textured workability, and hair cracking susceptibility were evaluated. The results are shown in Table 3.

Further, the mechanical properties (tensile strength, elongation, drawing, Charpy impact value) were examined. Further, a mold was prepared and its service life was measured. The results are shown in Table 4.

[0032]

[Table 1]

[0033]

[Table 2]

[0034]

[Table 3]

[0035]

[Table 4]

As is clear from the results shown in Table 1, Table 2 and Table 3, the plastic mold steel obtained by the method of the present invention has an appropriate hardness after heat treatment, and
The micro hardness distribution is narrow, the structure is uniform, and it is recognized that the grain size is close to the grain size. The crystal grain size number is in the range of 4 to 6 and the machinability is good and the mirror surface is good. It was confirmed that the finishing property and the texturing processability were also good, and that the hair cracking sensitivity was small when [H] was 3 ppm or less.

As is clear from the results shown in Table 1, Table 2 and Table 4, the plastic mold steel manufactured by the method of the present invention has good toughness and excellent mechanical properties. It was confirmed that the service life of the plastic molding die made of these materials has been extended.

[0038]

In the method for producing a plastic die steel according to the present invention, since the die steel material having the above chemical composition is subjected to the solution treatment twice or more, the mirror surface is obtained. It is possible to manufacture plastic mold steel with excellent toughness as well as excellent finish and texture workability. By using such plastic mold steel as a material, The remarkable advantage is that long plastic molding dies can be manufactured.

Continuation of front page (51) Int.Cl. ⁵ Identification code Office reference number FI technical display area C22C 38/16

Claims (10)

[Claims] 1. C: 0.05 to 0.18% by weight, Si:
1.0 wt% or less, Mn: 0.5 to 2.0 wt%, N
i: 2.5 to 3.5% by weight, Mo: 0.1 to 0.4% by weight, Al: 0.5 to 1.5% by weight, Cu: 0.7 to 2.
Using a die steel material consisting of 5% by weight as a basic alloy component and the balance Fe and impurities, a solution treatment is carried out after forging or rolling, and then an aging treatment is carried out to obtain a plastic die steel. A process for producing an age-hardening plastic mold steel excellent in toughness, which is characterized by carrying out two or more times. 2. The production of an age hardening plastic die steel having excellent toughness according to claim 1, wherein the cooling rate in the first solution treatment is higher than the cooling rate in the second and subsequent solution treatments. Method. 3. The die steel material comprises C: 0.05 to 0.18% by weight, Si: 1.0% by weight or less, and Mn: 0.5 to 2.0.
% By weight, Ni: 2.5-3.5% by weight, Mo: 0.1
0.4% by weight, Al: 0.5 to 1.5% by weight, Cu:
0.7 to 2.5% by weight as a basic alloy component, and Nb
+ Ta: 0.3 wt% or less, Ti: 0.5 wt% or less,
V: 0.5% by weight or less, Zr: 0.5% by weight or less, one or more selected from, and the balance Fe and impurities, toughness according to claim 1 or 2. An excellent method for producing steel for plastic molds. 4. The die steel material comprises C: 0.05 to 0.18% by weight, Si: 1.0% by weight or less, and Mn: 0.5 to 2.0.
% By weight, Ni: 2.5-3.5% by weight, Mo: 0.1
0.4% by weight, Al: 0.5 to 1.5% by weight, Cu:
0.7 to 2.5% by weight as a basic alloy component, and P
b: 0.01-0.30% by weight, Bi: 0.01-0.
30% by weight, Se: 0.01 to 0.40% by weight, Te:
0.01 to 0.30% by weight, S: containing 0.05 to 0.30% by weight, one or more selected from,
The method for producing an age-hardening plastic mold steel having excellent toughness according to any one of claims 1 to 3, which comprises the balance Fe and impurities. 5. The die steel material comprises C: 0.05 to 0.18% by weight, Si: 1.0% by weight or less, and Mn: 0.5 to 2.0.
% By weight, Ni: 2.5-3.5% by weight, Mo: 0.1
0.4% by weight, Al: 0.5 to 1.5% by weight, Cu:
0.7 to 2.5% by weight as a basic alloy component, and Nb
+ Ta: 0.3 wt% or less, Ti: 0.5 wt% or less,
V: 0.5% by weight or less, Zr: 0.5% by weight or less, one or more selected from, and further P
b: 0.01-0.30% by weight, Bi: 0.01-0.
30% by weight, Se: 0.01 to 0.40% by weight, Te:
0.01 to 0.30% by weight, S: containing 0.05 to 0.30% by weight, one or more selected from,
The method for producing an age-hardening plastic mold steel having excellent toughness according to any one of claims 1 to 4, comprising the balance Fe and impurities. 6. The die steel material comprises C: 0.05 to 0.18% by weight, Si: 1.0% by weight or less, and Mn: 0.5 to 2.0.
% By weight, Ni: 2.5-3.5% by weight, Mo: 0.1
0.4% by weight, Al: 0.5 to 1.5% by weight, Cu:
0.7 to 2.5% by weight as a basic alloy component, and further C
r: 0.1 to 2.5% by weight, W: 0.5% by weight or less, C
o: 0.5 wt% or less, Be: 0.5 wt% or less, B:
The composition contains one or more selected from 0.01 wt% or less, and the balance is Fe and impurities.
6. A method for producing an age-hardening plastic mold steel having excellent toughness according to any one of 1 to 5. 7. The die steel material comprises C: 0.05 to 0.18% by weight, Si: 1.0% by weight or less, and Mn: 0.5 to 2.0.
% By weight, Ni: 2.5-3.5% by weight, Mo: 0.1
0.4% by weight, Al: 0.5 to 1.5% by weight, Cu:
0.7 to 2.5% by weight as a basic alloy component, and further C
r: 0.1 to 2.5% by weight, W: 0.5% by weight or less, C
o: 0.5 wt% or less, Be: 0.5 wt% or less, B:
One or more selected from 0.01 wt% or less, further Nb + Ta: 0.3 wt% or less, Ti:
0.5 wt% or less, V: 0.5 wt% or less, Zr: 0.
The age-hardening plastic mold steel excellent in toughness according to any one of claims 1 to 6, containing one or more selected from 5% by weight or less, and the balance being Fe and impurities. Manufacturing method. 8. The die steel comprises C: 0.05 to 0.18% by weight, Si: 1.0% by weight or less, and Mn: 0.5 to 2.0.
% By weight, Ni: 2.5-3.5% by weight, Mo: 0.1
0.4% by weight, Al: 0.5 to 1.5% by weight, Cu:
0.7 to 2.5% by weight as a basic alloy component, and further C
r: 0.1 to 2.5% by weight, W: 0.5% by weight or less, C
o: 0.5 wt% or less, Be: 0.5 wt% or less, B:
One or more selected from 0.01 wt% or less, Pb: 0.01 to 0.30 as a basic alloy component, and Pb: 0.01 to 0.30 wt%, Bi:
0.01-0.30% by weight, Se: 0.01-0.40
% By weight, Te: 0.01 to 0.30% by weight, S: 0.0
5. One or more selected from 5 to 0.30% by weight is contained, and the balance is Fe and impurities.
8. A method for producing a steel for age-hardening plastic molds having excellent toughness according to any one of 1 to 7. 9. The die steel material comprises C: 0.05 to 0.18 wt%, Si: 1.0 wt% or less, and Mn: 0.5 to 2.0.
% By weight, Ni: 2.5-3.5% by weight, Mo: 0.1
0.4% by weight, Al: 0.5 to 1.5% by weight, Cu:
0.7 to 2.5% by weight as a basic alloy component, and further C
r: 0.1 to 2.5% by weight, W: 0.5% by weight or less, C
o: 0.5 wt% or less, Be: 0.5 wt% or less, B:
One or more selected from 0.01 wt% or less, further Nb + Ta: 0.3 wt% or less, Ti:
0.5 wt% or less, V: 0.5 wt% or less, Zr: 0.
One or more selected from 5% by weight or less,
Further, Pb: 0.01 to 0.30% by weight, Bi: 0.0
1 to 0.30% by weight, Se: 0.01 to 0.40% by weight, Te: 0.01 to 0.30% by weight, S: 0.05 to
9. Age-hardening plastic mold having excellent toughness according to any one of claims 1 to 8, containing one or more selected from 0.30% by weight, and the balance being Fe and impurities. Steel manufacturing method. 10. The method for producing an age-hardening plastic die steel having excellent toughness according to claim 1, wherein the hydrogen content in the impurities is 3 ppm or less.