JP2001172748A - Cold working tool dimension-regulated by heat treatment, and its manufacturing method - Google Patents

Abstract

PROBLEM TO BE SOLVED: To manufacture, in manufacturing a cold working tool requiring high dimensional accuracy, a tool with dimensions close to the desired dimensions by simply applying heat treatment with minimal number of times of treatment without finish working and particularly to provide a manufacturing method suitable for the manufacture of a tool incapable of finish working by providing the surface with a coating of hard film by chemical vapor deposition. SOLUTION: A tool steel, having an alloy composition consisting of, by weight, 0.5-2.6% C, 2.0% Si, 2.0% Mn, one or more kinds among <=1.0% Ni, 0.5-15.0%; Cr, <=5.0% Mo and <=5.0% V, and the balance essentially Fe, is used. The tool steel is formed into a tool shape, quenched to regulate the amount of retained austenite to 5-30% by volume ratio, subjected to subzero treatment consisting of cooling down to 0 to -200 deg.C to regulate the amount of retained austenite, by which dimensional change is controlled. Then tempering at <=500 deg.C is performed to attain the desired dimensions.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a cold tool manufactured by adjusting dimensions by heat treatment without finishing, and includes a manufacturing method thereof.

[0002]

2. Description of the Related Art In recent years, as the demand for dimensional accuracy of a product by cold working has increased, the dimensional accuracy of a tool using cold tool steel has also been forced to increase. For example, outer diameter 200mm x inner diameter 100mm x thickness 50m
In the case of a ring-shaped cold heading tool having a dimension of m and using an inner diameter portion as a tool, the accuracy of the inner diameter is normally required to be ± 0.02 mm. However, when manufacturing a tool by the conventional method, the dimensional change accompanying the heat treatment is large, and large variations are inevitable with respect to the target tool size. I had to.

In the actual work, since a representative of a cold tool is a die, the following description will be made taking a die as an example. First, steel as a tool material is dimensioned in consideration of a dimensional change due to quenching and tempering. Into a mold-shaped material with When this material is quenched, a phase transformation occurs, and the dimensions change accordingly. At this time, since the amount of retained austenite after quenching varies depending on the type of steel, the conditions of the pre-heat treatment, and the shape of the mold, the situation where the dimension after quenching changes accordingly differs. Therefore, in tempering, a desired dimension is realized by controlling the tempering temperature by utilizing the phenomenon that the dimensional change of the material depends on the tempering temperature. FIG. 1 shows the change of the heat treatment temperature in the above operation in the case where the manufacturing of a cold tool includes a CVD (chemical vapor deposition) step often performed.

[0004] This will be described with reference to the graph of FIG. 3 showing the relationship between the tempering temperature and the size reduction ratio.
Where the aspect differs at 0 ° C, the current heat treatment furnace can control the temperature relatively accurately on the high-temperature side, and the high-temperature side has a small dimensional change and is easy to realize fine dimensional changes. Tempering is performed in a temperature range exceeding 500 ° C. At this time, there are the following two cases depending on the relationship between the tempered dimension and the target dimension value.・ Target dimension value <Temperature after tempering: Final adjustment by finish processing> Target dimension value> Temperature dimension: Heat treatment again In the former case, it is almost expected that the tempered dimension will match the target dimension value It is not possible and often requires finishing. In the latter case, an increase in cost due to an increase in the number of heat treatment steps is inevitable. If it can be used even if it is heat treated again, it is still good if it can be used, but for intermediate products with dimensions that are significantly below the target value,
You have to discard and rebuild.

Depending on the mold, as described above, the surface may be coated with a hard film by a chemical vapor deposition method.
In that case, as shown in FIG.
Although tempering is performed, it is not possible to adjust the dimensions in finishing after tempering because of the coating. Therefore, the heat treatment must be repeated until the target dimension value is realized. This heat treatment has a large dimensional change with respect to temperature.
Tempering at around 0 ° C is performed, but in the existing heat treatment furnace, temperature variation of about several ° C is unavoidable, and the intended dimensional change and the realized dimensional change often do not match. It is difficult.

[0006]

SUMMARY OF THE INVENTION It is an object of the present invention to overcome the above-mentioned problems in the art of cold tool steel, and to carry out heat treatment without finishing work. It is an object of the present invention to provide a cold tool adjusted to the required size, and to provide a manufacturing method thereof.

[0007]

According to the cold tool of the present invention, the dimensions of which are adjusted by heat treatment, the basic alloy composition is C: 0.5-2.6% by weight, Si: 2.0% by weight. And M
n: 2.0%, Ni: 1.0% or less, Cr:
0.5 to 15.0%, Mo: 5.0% or less, and V:
A tool steel having an alloy composition of 5.0% or less, with the balance being substantially Fe, and having a hardened state in which retained austenite occupies 5 to 30% by volume, is formed into a tool shape having a hardness of 0%. Sub-zero treatment to cool to a temperature of
This is a cold tool subjected to tempering at a temperature of 500 ° C. or less, omitting finishing, and adjusting the dimensions by heat treatment.

The method of manufacturing a cold tool whose dimensions have been adjusted by the heat treatment according to the present invention is as follows: C: 0.5 to 2.6% by weight, S:
i: 2.0% and Mn: 2.0% in addition to Ni:
1.0% or less, Cr: 0.5 to 15.0%, Mo: 5.
A tool steel having an alloy composition containing 0% or less and V: 5.0% or less, with the balance being substantially Fe, is formed into a tool shape, and quenched to reduce the amount of retained austenite in a volume ratio of 5 to 30. %, And a sub-zero treatment of cooling to a temperature of 0 ° C. to −200 ° C. to control the dimensional change by adjusting the amount of retained austenite. This is a manufacturing method that realizes dimensions and does not require finishing.

[0009]

BEST MODE FOR CARRYING OUT THE INVENTION The tool steel for producing the cold tool of the present invention contains, as an optional additive element, W: 5.0% or less and Nb: 2.0% or less in addition to the basic alloy components described above. Or one or two of the following.

Regardless of which alloy composition is used, in the cold tool of the present invention, a tool steel satisfying the condition of [% Cr] -6.8 [% C] ≧ 0 in each of the specified alloy compositions is used. It is preferred to use.

According to the present invention, since no finishing is performed,
This is particularly significant when applied to a cold tool steel that has been subjected to surface coating treatment by chemical vapor deposition (CVD) prior to quenching. FIG. 2 is a conceptual diagram showing a temperature change in the case of performing the CVD, similar to FIG.

[0012] In the cold work tool steel of the present invention, the function of each alloy component and the reason for limiting the composition range as described above are as follows.

C: 0.5 to 2.6% C is important for securing the hardness and wear resistance required for cold work tool steel. In order to make the amount of retained austenite after quenching 5% or more, the presence of 0.6% or more is necessary. On the other hand, when a large amount of C exceeding 2.6% is present, the amount of retained austenite increases and exceeds the limit of 30%. When performing surface coating by chemical vapor deposition, 0.6% or more of C is required in order to form a stable hard film.

Si: 2.0% Since Si is an element that improves the hardenability,
The appropriate amount is present in the range up to%. If added excessively,
Decreases the toughness of steel.

Mn: 2.0% Mn also improves hardenability. If an excessive amount is added, the amount of retained austenite after quenching increases, so the upper limit is 2.0%.

Ni: 1.0% or less Ni enhances hardenability and toughness, so an appropriate amount is added. However, since it is an austenite forming element,
If the addition exceeds the upper limit of 0%, the amount of retained austenite after quenching becomes excessive.

Cr: 0.5 to 15.0% Cr is an important component in that it forms carbides to strengthen the matrix and provides wear resistance. In order to secure this effect, addition of 0.5% or more is required. Upper limit 15.0
% Exceeds this, the toughness of the steel decreases.

Mo: 5.0% or less Mo, like Cr, also contributes to strengthening the matrix by forming carbides and improving wear resistance. Even if added in excess of 5.0%, the effect saturates and becomes uneconomical.

V: 5.0% or less V, like Cr and Mo, forms carbides to strengthen the matrix and improve wear resistance. If the amount is too large, the toughness is impaired, so the addition is limited to up to 5.0%.

The effects of the elements that can be added arbitrarily and the reasons for limiting the composition range are as follows.

W: 5.0% or less W also contributes to strengthening the matrix by forming carbides and improving wear resistance. However, excessive addition lowers the toughness and increases the cost, so the upper limit is 5.0%.
Was provided.

Nb: 2.0% or less Nb forms fine carbides to make crystal grains finer and helps to improve toughness. This effect saturates at more than 2.0% addition.

The reason that the amount of retained austenite after quenching is in the range of 5 to 30% by volume is that if the amount of retained austenite is too small, the dimensional change that occurs in the subsequent sub-zero treatment is small, and the size of the adjustable size can be adjusted. If the range is narrow and the amount of retained austenite is too large,
This is because the dimensional change is too large to control and it is difficult to reach the target dimensional value.

The production of the cold tool of the present invention is performed by a series of steps of forming into a tool shape, quenching, subzero treatment, and low-temperature tempering. Before quenching,
After quenching, during sub-zero treatment, and after tempering, respectively.

There are the following two cases depending on the result of the dimension measurement after quenching: ・ Target dimension value 1 <dimension after quenching ・ Target dimension value 1> dimension after quenching (“Target dimension value 1” is In order to lead to the target "target dimension value 2", this is the dimension to be reached first.) In the former case, it is out of the target of sub-zero processing, but in the latter case, it is reduced to the target dimension value 1 by sub-zero processing. You can get closer.

The significance of performing the sub-zero treatment is that the curve showing the relationship between the tempering temperature and the size reduction rate shown in FIG. 3 is obtained by performing the sub-zero treatment and selecting a lower temperature as shown in FIG. Above, so that a larger dimensional change can be obtained even at the same tempering temperature. In other words, the realization of the desired dimensional change is made easier by selecting the temperature of the sub-zero treatment. In actual operation, sub-zero processing of relatively shallow cooling (high temperature) is performed, and if the dimensional measurement results show that the dimensional increase based on the dimensional change rate expected at that temperature is insufficient, deeper cooling (low temperature) Sub-zero processing is performed.

The temperature range for the sub-zero treatment is a low temperature that can be easily realized industrially, that is, 0 ° C. (ice), −37 ° C.
Choose an appropriate one from various low temperatures ranging from ℃ (dry ice + methanol), -60 ℃ (dry ice + ethanol), -73 ℃ (dry ice + acetone) to -196 ℃ (liquid nitrogen). . The temperature of sub-zero treatment is
This is advantageous over a heat treatment using a heating furnace, in which the temperature can be easily and accurately controlled, because the temperature tends to vary.

It is within this temperature range that tempering is performed at a relatively low temperature of 500 ° C. or less, as shown in FIGS. The variability is small and thus the temperature range that can be adjusted for the target dimensions is wide. Needless to say, if the range of temperatures that can be applied is wide, it is possible to easily adjust the dimensions of existing heating furnaces that cannot be controlled precisely. Usually, 20
About 0 ° C. is appropriate.

The intermediate product which has reached the target dimension value 1 by the sub-zero process realizes the target dimension value 2 by this tempering. At this time, there are also the following two cases between the tempered dimensions and the following: ・ Target dimension value 2 <dimension after tempering ・ Target dimension value 2> dimension after tempering The former case has already been implemented. The tempering is performed again on the higher temperature side than the tempering, and the target dimension value 2 is obtained. In the latter case, on the contrary, tempering on the lower temperature side also leads to the target dimension value of 2.

The reason that the alloy composition that satisfies the condition of [% Cr] -6.8 [% C] ≧ 0 is preferable is not satisfied, that is, [% Cr] -6.8 [% C] <0.
In the steel having the composition as follows, the bending point of the curve of the sizing ratio with respect to the tempering temperature is 5 as shown in FIGS. 3 and 4.
This is because the tempering temperature is not in the range of 00 to 520 ° C. but is in the vicinity of 250 ° C., so that the selection range of the tempering temperature is small, and it is difficult to adjust the dimensions.

[0031]

EXAMPLE A cold tool steel having an alloy composition shown in Table 1 was melted. In this table, “Residual γ” indicates the amount of retained austenite in volume%, and the column “X” indicates [% C
r] -6.8 [% C].

Table 1 No. Chemical Components (Remainder Fe) Residual γ X C Si Mn Ni Cr Mo V W Nb% Example 1 0.97 0.94 0.41 0.19 8.25 1.92 0.29 − −12 1.65 2 1.42 0.40 0.55 0.03 11.21 1.13 0.31 0.21 0.44 27 1.55 3 0.57 0.59 0.43 0.12 11.29 2.39 0.44 0.88 − 7 7.41 4 1.07 1.98 0.23 0.18 14.56 2.09 0.22 − − 23 7.28 5 0.67 0.82 1.89 0.20 8.47 4.91 4.88 4.78 − 18 3.91 6 0.91 0.87 0.44 0.89 8.54 0.96 0.23 − 1.89 16 2.35 7 1.08 0.45 1.01 0.19 9.30 1.25 1.33 − − 25 1.96 Comparative Example 8 1.58 0.12 0.36 0.24 12.79 0.94 0.27 − − 19 2.05 9 0.98 0.20 0.71 0.18 8.95 0.82 0.38 − − 17 2.29 10 1.67 1.04 0.33 0.33 12.91 0.88 0.86 − 1.44 28 1.55 11 0.13 0.30 0.40 0.33 12.03 2.89 0.27 − − 4 11.15 12 2.93 0.31 0.65 0.22 5.53 0.89 4.32 − 0.39 48 -14.39 13 1.14 1.10 0.47 0.19 16.82 1.91 0.34 − − 22 9.07 14 1.22 0.33 0.24 0.20 8.09 5.89 4.30 − − 24 -0.21 15 1.52 0.19 0.39 0.15 11.38 0.94 0.32--20 1.04 Comparative example No.15 is conventional steel SKD11

Table 2 No. Dimension Heat treatment H temperature SZ temperature T temperature Hardness Target dimension Y (inner diameter adjustment) Pattern degree Degree Method deviation mm ℃ ℃ ℃ HRC mm Example 1 φ200 × φ100 × 50H H → SZ → T 1000 -37 200 61 0.015 ○ 2 φ250 × φ100 × 50H CVD → H → SZ → T 1030 -73 450 58 0.010 ○ 3 φ200 × φ100 × 75H H → SZ → T 1050 0 450 57 0.014 ○ 4 φ150 × φ100 × 50H H → SZ → T 1000 -60 300 60 0.007 ○ 5 φ150 × φ100 × 100H H → SZ → T 1020 -73 200 61 0.009 ○ 6 φ230 × φ100 × 50H CVD → H → SZ → T 1030 0 250 61 0.019 ○ 7 φ180 × φ100 × 50H H → SZ → T 1000 -60 250 62 0.013 ○ Comparative Example 8 φ200 × φ100 × 100H H → SZ → T 1000 -196 520 58 0.144 × 9 φ250 × φ100 × 100H H → T 1000 − 520 57 0.074 × 10 φ200 × φ100 × 100H CVD → H → T 1000 − 250 59 0.075 × 11 φ200 × φ100 × 50H H → SZ → T 1000 -37 300 42 0.099 × 12 φ200 × φ100 × 75H H → SZ → T 1030- 73 150 55 0.121 × 13 φ190 × φ100 × 100H H → SZ → T 1030 -60 2 50 60 0.092 × 14 φ200 × φ100 × 50H H → T 1190 0 400 44 0.019 ○ 15 φ200 × φ100 × 50H H → T 1030-200 61 0.109 × Y: ○, when the dimensional deviation is 0.02mm / 100mm or less, × if exceeded. H: Quenching SZ: Sub-cellular treatment T: Tempering CVD: Chemical vapor deposition

[0034]

According to the cold tool of the present invention, when manufacturing a cold tool that requires high dimensional accuracy, the dimensional adjustment is performed exclusively by heat treatment without finishing work, and the heat treatment is also known. Since the number of processes is smaller than in the case of using the technology, the manufacturing can be performed with a reduced number of processes and a reduced cost as compared with the conventional technology.

The fact that finishing is not performed means that in the production of a cold tool which cannot be finished, such as a tool whose surface is coated with a hard substance such as nitride or carbide by a chemical vapor deposition method. This is a particularly advantageous feature.

[Brief description of the drawings]

FIG. 1 is a diagram conceptually showing a change in a heat treatment temperature in an example of manufacturing a cold tool according to a conventional technique.

FIG. 2 shows an example of the production of a cold tool according to the invention,
The figure similar to FIG. 1 which shows the change of heat processing temperature conceptually.

FIG. 3 is a graph showing the relationship between the temperature of the tempering treatment of cold tool steel and the reduction ratio, taking cold tool steel having a certain alloy composition as an example.

FIG. 4 is a diagram conceptually showing that the curve moves upward by sub-zero processing in the graph of FIG. 3, and that the amount of movement increases as the temperature of sub-zero processing decreases.

──────────────────────────────────────────────────の Continued on the front page (51) Int.Cl. ⁷ Identification symbol FI theme coat ゛ (Reference) C21D 9/00 C21D 9/00 M C22C 38/58 C22C 38/58 C23C 16/30 C23C 16/30

Claims (6)

[Claims] C. 0.5 to 2.6% by weight, Si:
2.0% and Mn: 2.0%, Ni: 1.0% or less,
Cr: 0.5-15.0%, Mo: 5.0% or less, V: 5.0% or less, the balance is substantially Fe, the alloy composition is substantially Fe, and the volume of retained austenite in the quenched state A tool steel occupying 5 to 30% in a ratio is formed into a tool shape, and is subjected to a sub-zero treatment of cooling to a temperature of 0 ° C. to −200 ° C. and a tempering treatment at a temperature of 500 ° C. or less. Adjusted cold tool. 2. In addition to the alloy component according to claim 1,
2. The cold tool according to claim 1, wherein a tool steel having an alloy composition containing one or two of W: 5.0% or less and Nb: 2.0% or less is used. 3. The cold tool according to claim 1, wherein a tool steel satisfying the condition of [% Cr] −6.8 [% C] ≧ 0 is used in the alloy composition defined in claim 1 or 2. 4. The cold tool according to claim 1, wherein a surface of the cold tool is coated with a cured film by a chemical vapor deposition method. 5. The method according to claim 1, wherein C: 0.5 to 2.6% by weight, Si:
2.0% and Mn: 2.0%, and Ni: 1.0%
% Or less, Cr: 0.5 to 15.0%, Mo: 5.0%,
And V: 5.0% or less, with the balance being substantially F
forming a tool steel having an alloy composition of e into a tool shape;
After quenching, the amount of retained austenite is 5 to 5 by volume.
The dimensional change is controlled by adjusting the amount of retained austenite by performing a sub-zero treatment of cooling to a temperature of 0 ° C. to −200 ° C.
A method for manufacturing a cold tool in which finishing processing is omitted and the dimensions are adjusted by heat treatment, which comprises performing a tempering treatment at 0 ° C. or lower to achieve a target dimension. 6. The method for manufacturing a cold tool according to claim 5, further comprising a step of forming a coating of a cured film by a chemical vapor deposition method before quenching.