JP2001234278A - Cold tool steel excellent in machinability - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide cold tool steel excellent in toughness, furthermore excellent in machinability as-annealed at a hardness of about 90 to 105 HRB and also excellent in machinability even in a region in which hardness after quenching and temperature lies in 45 to 50 HRC. SOLUTION: This cold tool steel excellent in machinability has a composition containing, by weight, 0.5 to 1.5% C, <=3.0% Si, 0.2 to 3.0% Mn, <=4.0% Ni, 0.25 to 15.0% Cr, Mo and W alone or in combination so as to satisfy 2Mo+W: 0.2 to 8.0%. 0.03 to 0.4% S and 0.0002 to 0.02% Ca, and the balance substantially Fe, in which also MnS has the average particle size of <=10 μm equivalent to a circle and is dispered in the in the range of 0.5 to 3.0% by area ratio, and, moreover, the aspect ratio of MnS after cogging.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a cold work tool steel excellent in machinability used in a pre-hardened state or the like.

[0002]

2. Description of the Related Art Conventionally, cold tools such as press dies have been manufactured by JI.
S SKD11 (C: 1.40 to 1.60%, Si:
0.40% or less, Mn: 0.6% or less, P: 0.030
%, S: 0.030% or less, Cr: 11.00 to 1
3.00%, Mo: 0.80 to 1.20%, V: 0.2
0 to 0.50%, with the balance being Fe). However, since the steel of SKD11 has a high C content and a high annealing hardness, the machinability is poor, and further, the C content is high and the weldability is poor, and the workability after quenching and tempering is also poor. In other words, low-temperature tempering to increase the hardness,
Since a large amount of austenite remains, there is a problem that electric discharge machining causes cracks.

[0003] As a cold mold steel which has improved the disadvantages of the steel of SKD11, C: 0.9 to 1.3%, Si: 0.5%.
-2.0%, Mn: 0.1-2.0%, Cr: 5.0-
11.0%, Mo: 1.3-4.0% and V: 0.1
0 to 0.35%, and if necessary, S: 0.
20% or less, Pb: 0.4% or less, Bi: 0.50% or less, and Ca: 0.002 to 0.010%. An inter-die steel (JP-B-64-5100) is known.

[0004] After quenching at a high temperature, the cold mold steel is tempered at a high temperature to remove residual stress during quenching, thereby stabilizing the structure and increasing the secondary hardening hardness. It has excellent hardness and toughness, does not cause galling when used as a tool, and does not crack when heat is generated in the tool due to electric discharge machining etc., extending the tool life and improving workability. It will be greatly improved. However, this cold mold steel has poor machinability after annealing, and hardness (HRC) after quenching and tempering.
(Approximately 62), it is difficult to correct the deformation after quenching and tempering, and the weldability is not sufficient.

[0005] Then, the present inventors, C: 0.70 ~
0.80%, Si: 0.10 to 0.60%, Mn: 0.
10 to 1.00%, Ni: 4.0% or less, Cr: 6.5
0 to 7.50%, Mo and W alone or in combination, 2Mo +
W: 1.00 to 3.00%, S: 0.03 to 0.40
%, Ca: 0.0002 to 0.02%, O: 0.000
2 to 0.02%, and if necessary, V: 0.0
5 to 3.0%, Nb: 0.02 to 2.0% and Ta:
One or more of 0.02 to 2.0%, and if necessary, Te: 0.01 to 0.06%, Pb:
0.03-0.10% and Bi: 0.02-0.10
%, And the balance was made up of Fe and inevitable impurities, and a patent application was filed (Japanese Patent Application No. 10-368852).

[0006] The hardness of the steel for cold mold after quenching and tempering is about HRC 56 to 62 (the annealing hardness is HRB95).
), Which is suitable for manufacturing a mold for cold working a large number of products, but is hard to machine because of its hardness. Also,
Since the size and area ratio of MnS were not considered, the toughness was not sufficient.

[0007]

The present invention has excellent toughness, excellent machinability in an annealed state of about 90 to 105 HRB, and hardness after quenching and tempering of the above patent application. It is an object of the present invention to provide a cold tool steel excellent in machinability even in a lower hardness range of about HRC 45 to 60.

[0008]

Means for Solving the Problems In order to solve the above problems, the present inventors have focused on MnS of cold tool steel and studied its size, area ratio, and the like.
Addition of MnS makes the morphology of MnS at the time of casting spherical, and increases the deformation resistance of MnS, thereby making it possible to suppress an increase in the aspect ratio of MnS after forging and toughness due to the addition of S. And the like, while minimizing the decrease in the S, and improving the machinability as compared with the case where S alone is added. The present invention has been made based on the above findings.

That is, in the cold work tool steel of the present invention having excellent machinability, C: 0.5-1.5%, Si: 3.0.
%, Mn: 0.2 to 3.0%, Ni: 4.0% or less, Cr: 0.25 to 15.0%, Mo and W alone or in combination, 2Mo + W: 0.2 to 8.0 %, S: 0.03
０．４0.4% and Ca: 0.0002-0.02%, the balance being substantially Fe, MnS equivalent to a circle having an average particle size of 10 μm or less, and an area ratio of 0 .5
To 3.0%, and the MnS after forging has an aspect ratio of 1 to 30.

In the cold work tool steel of the present invention having excellent machinability, C: 0.5-1.5%, Si: 3.0% or less, Mn: 0.2-3.0%. , Ni: 4.0% or less, C
r: 0.25 to 15.0%, Mo and W alone or in combination, 2Mo + W: 0.2 to 8.0%, S: 0.03 to 0.
4% and Ca: 0.0002-0.02%,
Further, if necessary, V: 0.05 to 3.0%, Nb: 0.
02-2.0%, Ta: 0.02-2.0% and T
i: contains one or more of 0.01 to 2.0%,
If necessary, Te: 0.005 to 0.05%, P
b: 0.05 to 0.50%, Bi: 0.015 to 0.1
5%, REM: 0.01% or less and Se: 0.02-
0.20% of one or more kinds, the balance being substantially Fe, and MnS having an average particle diameter of 10
μm or less, the area ratio is dispersed in the range of 0.5 to 3.0%, and the aspect ratio of MnS after forging is 1 to 3%.
0.

Further, the cold work tool steel of the present invention having excellent machinability is used for HRC45 or more, preferably HR.
It is a pre-hardened state having a hardness of C60 or less, that is, a pre-hardened state which can be processed in a quenched and tempered state.

[0012]

Next, the reasons why the component composition, MnS size, and the like of the cold work tool steel excellent in machinability of the present invention are limited as described above will be described. C: 0.5 to 1.5% C is an element contained to increase the hardness of the matrix and to form a secondary carbide by tempering to secure wear resistance. 0.5%, preferably 0% If it is less than 0.7%, the required hardness cannot be ensured, and if it is contained more than 1.5%, preferably more than 1.2%, coarse primary carbides are formed and the toughness is reduced. In addition, the machinability also decreases, so the content is set to 0.5 to 1.5%. The preferred range is 0.7-1.2%.

Si: 3.0% or less Si is an element contained to improve the quenching properties of pearlite and bainite and to increase the tempering hardness. In order to obtain these effects, 0.3% or more is required. Is preferably contained in an amount of more than 3.0%, preferably more than 1.0%, since the toughness decreases, so the content is set to 3.0% or less. The preferred range is 0.3 to 1.2.
% Or less.

Mn: 0.2-3.0% Mn is an element contained for improving the quenching properties of pearlite and bainite and producing MnS.
If it is less than 2%, preferably less than 0.4%, the amount of MnS produced will be small and the machinability cannot be improved, and if it exceeds 3.0%, preferably more than 2.5%, the residual will remain. Austenite formation is caused and toughness is also reduced, so the content is made 0.2 to 3.0%. The preferred range is 0.4-2.5%.

Ni: 4.0% or less (excluding 0%) Ni is an element contained for improving hardenability.
In order to obtain these effects, it is preferable to contain 0.1% or more, and if it exceeds 4.0%, preferably 2.5%, retained austenite increases and it is difficult to secure necessary hardness. And the toughness also decreases, so the content is set to 4.0% or less. The preferred range is 0.1-2.
5%. Cr: 0.25 to 15.0% Cr is an element contained for improving the hardenability, and its effect is small when it is less than 0.25%, preferably 1.0%, and 15.0%, preferably If the content exceeds 8.0%, the amount of high-hardness carbides increases, thereby reducing the machinability. Therefore, the content is set to Cr: 0.25 to 15.0%.
And A preferred range is 1.0-8.0%.

2 Mo + W: 0.2 to 8.0% Mo and W are elements contained for improving the bainite hardenability and increasing the tempering hardness, and are 0.2%, preferably 1.0%. If the amount is less than the above, bainite hardenability cannot be sufficiently improved and the secondary hardening cannot be performed by tempering. If the amount is more than 8.0%, preferably more than 5.0, hardly soluble primary carbides increase and quenching occurs. Since the temperature is increased and the toughness is decreased, the content is set to 0.2 to 8.0%. A preferred range is 1.0-5.0%. S: 0.03 to 0.4% S is an element contained to improve machinability.
If it is less than 0.03%, preferably less than 0.05%, machinability is not improved, and if it exceeds 0.4%, preferably 0.35%, toughness, hardness and hot workability are reduced. The content is set to 0.03 to 0.4%. The preferred range is 0.05-0.35%.

Ca: 0.0002-0.02% Ca forms a solid solution in MnS and forms MnS or Mn as an oxide.
It is an element to be included for dispersing MnS uniformly and finely by becoming a core of S, spheroidizing MnS, increasing the deformation resistance of MnS, suppressing the decrease in toughness, and improving the machinability. . If the content is less than 0.0002%, preferably 0.0008%, these effects are not obtained, and 0.02%, preferably 0.02%.
If it exceeds 12%, the toughness decreases, so the content is made 0.0002 to 0.02%. The preferred range is 0.
0008 to 0.012%.

V: 0.05 to 3.0% V is an element contained for improving the high-temperature tempering hardness and preventing the crystal grains from becoming coarse. If the content exceeds 3.0%, preferably 1.0%, hardly soluble primary carbides increase to increase the quenching temperature and decrease the toughness and machinability. To 3.0%. The preferred range is from 005 to
1.0%.

Nb and Ta: 0.02-2.0%, T
i: 0.01 to 2.0% Nb, Ta and Ti are elements to be contained in order to suppress the growth of crystal grains, and Nb and Ta are 0.02%, preferably 0.05%, and Ti is , 0.01%, preferably less than 0.05%, there is no effect of suppressing the growth of crystal grains,
If the content exceeds 2.0%, preferably 1.0, the amount of hardly soluble primary carbides increases, raising the quenching temperature and reducing the toughness and machinability. 0
2 to 2.0%, and 0.01 to 2.0% for Ti. The preferred ranges are all 0.05 to 1.0%.

Te: 0.005 to 0.05% Te is an element contained to form MnTe and improve machinability. If less than 0.005%, this effect is not obtained, and 0.05% If it exceeds 0.005%, toughness and hot workability deteriorate, so the content range is set to 0.05 to 0.05%. Pb: 0.05 to 0.50% Pb is an element contained for improving machinability.
If it is less than 0.05%, this effect is not obtained, and if it exceeds 0.50%, the hot shock resistance is reduced.
05 to 0.50%.

Bi: 0.015 to 0.15% Bi is an element contained for improving machinability.
Less than 0.015% does not have this effect, and 0.15%
When the content exceeds 0.01%, the toughness is reduced.
To 0.10%. REM: 0.01% or less REM is an element contained for improving machinability, and if it exceeds 0.01%, toughness is reduced. Therefore, the content is made 0.01% or less. Se: 0.02 to 0.20% Se is an element contained for improving machinability.
If it is less than 0.02%, this effect is not obtained, and if it exceeds 0.20%, the toughness is reduced.
0.20%.

Next, in the present invention, the average particle size of MnS equivalent to a circle is 10 μm or less, and the area ratio is 0.5 to
Dispersion in the range of 3.0% and further setting the aspect ratio of MnS after forging to 1 to 30 will be described. Mn
S has an average particle size of 10 μm or less, preferably 5
The reason why the thickness is set to 10 to 10 μm is that if it is smaller than 5 μm, the machinability decreases, and if it exceeds 10 μm, the toughness decreases. Further, the area ratio of MnS is set to 0.5 to 3.0.
%, Preferably 2.0 to 3.0%, is 0.5%
%, Preferably less than 2.0%, results in reduced machinability, and more than 3.0% results in reduced toughness. Further, the aspect ratio of MnS after forging was 1-3.
The reason why it is set to 0, preferably 5 to 10 is that it is difficult to make it smaller than 1 and preferably smaller than 5, and that if it exceeds 30, preferably 10 the toughness is reduced.

In the present invention, the hardness after the heat treatment of quenching and tempering is set to HRC 45 or more because of HRC
If it is lower than 45, the hardness required for a cold tool such as a mold will not be obtained. Further, if the hardness is too high, it becomes difficult to perform machining by mechanical cutting to obtain a product such as a mold. Therefore, it is preferable to set the HRC to 60 or less. This hardness can be achieved by heating to 800 to 1000 ° C., air cooling, and then air cooling at 400 to 650 ° C.

The cold work tool steel having excellent machinability according to the present invention can reduce the content of Ca to 0.0050% or less, for example.
By preventing the generation of O and suppressing the generation of CaS by suppressing Al to 0.030% or less, Mn is reduced.
It can be manufactured by controlling the form of MnS by dispersing Ca in S. further,
The cold work tool steel with excellent machinability according to the present invention can be used by machining a die or the like in a pre-hardened state, or can be used for machining in a die or the like in an annealed state. After processing, quenching and tempering may be performed, followed by finishing if necessary. Further, the use of the cold work tool steel having excellent machinability of the present invention includes the use of the conventional cold work tool steel such as a press die, a bending die, a punch die, a drawing die, a die, a punch, and a rolling die. It can be used as well.

[0025]

DESCRIPTION OF THE PREFERRED EMBODIMENTS The present invention will be described below with reference to embodiments.

EXAMPLES Example 1 Steels of Examples and Comparative Examples of the present invention having the component compositions shown in Table 1 below were melted by a normal method using a high-frequency induction furnace, and formed into ingots by a normal casting method. A steel material was manufactured by a normal processing method. The steel materials of these Examples and Comparative Examples were heated at 830 ° C. × 3 hr, cooled to 600 ° C. at a cooling rate of 15 ° C./h, and then subjected to spheroidizing annealing under air-cooling conditions. A test piece for measurement of size, a machinability test piece and an impact test piece are cut out, and these test pieces are roughly processed into a rough-processed test piece, and have a hardness of HRC 45 to 60 under the conditions shown in Table 2 below. It was quenched and tempered so as to obtain. The hardness was measured using a hardness test piece among these test pieces, and the size of MnS was measured using a test piece for measurement such as the size of MnS by the following method.
The area ratio and the aspect ratio were measured, and the results are shown in Table 2 below.

[0026]

[Table 1]

Measuring method of MnS size, area ratio and aspect ratio: 40% per steel type using image analyzer
The evaluation was performed with a visual field of 0 × and a total measurement area of 5 × 10 ⁶ μm ² . Impact test: The quenched and tempered machinability test piece and the impact test piece are finely processed and are 50 mm wide and 40 m thick.
A machinable test piece of mx 200 mm in length and an impact test piece of 10R notch were used. Using the machinability test piece, a machinability test was performed by the following method to measure the life of the cutting tool, and the results are shown in Table 2 below. A Charpy impact test was performed using the impact test piece, and the results are shown in Table 2 below.

Machinability test method: Cutting was performed under the following cutting conditions, the cutting length was measured until the flank wear became 0.3 mm, and Comparative Example No. 12 which was a material containing neither S nor Ca was used.
The value was expressed as an index with the value of 100 as 100. Tool: Carbide end mill (UTi20T), 1 blade Cutting width: 4.0mm Cutting depth: 1.0mm Cutting speed: 100m / min Feed: 0.035mm / tooth Cutting oil: Dry type

[0029]

[Table 2]

Example 2 Examples No. 10 and No. 11 and Comparative Example No. 17 of the steel materials of Examples and Comparative Examples of the present invention produced in Example 1 above.
And No. 18 at 830 ° C under the same conditions as in Example 1 above.
After heating for 3 hours, the sample was cooled to 600 ° C. at a cooling rate of 15 ° C./h and then spheroidized under the condition of air cooling, but a hardness test piece, a test piece for measuring MnS size, etc., machinability The test piece and the impact test piece were cut out, and these test pieces were roughly processed to obtain rough-processed test pieces. The size, area ratio and aspect ratio of MnS were measured by the following method using a test piece for measuring hardness and MnS size using a roughened hardness test piece, and the results were shown in Table 3 below.
Shown in Further, the machinability test piece and the impact test piece were precision-processed to obtain a machinability test piece of 50 mm width × 40 mm thickness × 200 mm length and a 2 mm V notch JIS No. 3 impact test piece. Using the machinability test piece, a machinability test was performed by the following method to measure the life of the cutting tool, and the results are shown in Table 3 below. A Charpy impact test was performed using the impact test piece, and the results are shown in Table 3 below.

[0031]

[Table 3]

According to these results, the spheroidized annealed and quenched and tempered ones of the present invention were found to have Mn
The size of S is 2.56 to 4.96 μm, the area ratio of MnS is 0.30 to 2.97%, and the aspect ratio is 5.2 to 2.
In addition, the cutting tool life of Comparative Example No. 12 (which differs from the present invention in that it does not contain Ca and that the total amount of carbides is large) is defined as 100 and 151 to 31.
7 and a Charpy impact value of 15.6 to 22.8.
J / cm ² .

The spheroidized annealed embodiment of the present invention has a MnS size of 3.72 μm and 3.6 MnS.
6 μm, the area ratio of MnS is 1.76% and 1.31%, the aspect ratio is 18.4 and 16.8, and the cutting tool life is comparative example No. 17 (in comparison with the present invention, Ca-free point). And the total amount of carbides is large.) And 362 and 286, respectively, and the Charpy impact values were 106.4 J / cm ² and 127.6 J / cm ² .

On the other hand, the spheroidized annealed and quenched and tempered steel of the comparative example had a MnS size of 3.23 to 3.23.
5.16 μm, MnS area ratio is 0.39 to 2.75
% And an aspect ratio of 31.4 to 46.2, and a cutting tool life of Comparative Example No. 12 (which differs from the present invention in that Ca is not contained and the total amount of carbide is large) is 100. Was 63 to 130, and the Charpy impact value was 7.3 to 27.8 J / cm ² . Also,
The spheroidized-annealed comparative examples had MnS sizes of 4.28 μm and 3.87 μm and an MnS area ratio of 1.28 μm.
53% and 0.74%, aspect ratio 46.2 and 31.
4, and the cutting tool life was 100 and 91, with 100 being the case of Comparative Example No. 17 (which differs from the present invention in that Ca is not contained and the total amount of carbides is large), and the Charpy impact value. Of 82.3 J / cm ² and 96.
It was 1 J / cm ² .

[0035]

The cold work tool steel of the present invention is excellent in machinability without hardly reducing the toughness even in the region where the hardness of quenching and tempering is about HRC 45 to 60, so that it can be easily prepared in a pre-hardened state. This has an excellent effect that the cutting can be performed more easily, and the cutting can be more easily performed in the annealed state.

Claims (5)

[Claims] C .: 0.5 to 1% by weight (the same applies hereinafter)
1.5%, Si: 3.0% or less, Mn: 0.2 to 3.0
%, Ni: 4.0% or less, Cr: 0.25 to 15.0
%, Mo and W alone or in combination, 2Mo + W: 0.2 to
8.0%, S: 0.03-0.4% and Ca: 0.0
002-0.02%, the balance being substantially Fe, and MnS having an average particle diameter equivalent to a circle of 10 μm or less and an area ratio of 0.5 to 3.0%. A cold work tool steel excellent in machinability, wherein the aspect ratio of MnS after dispersing and forging is 1 to 30. 2. C: 0.5-1.5%, Si: 3.0%
Hereinafter, Mn: 0.2 to 3.0%, Ni: 4.0% or less,
Cr: 0.25 to 15.0%, Mo and W alone or in combination, 2Mo + W: 0.2 to 8.0%, S: 0.03 to
0.4% and Ca: 0.0002-0.02%, V: 0.05-3.0%, Nb: 0.02-
2.0%, Ta: 0.02 to 2.0% and Ti: 0.1%
One or two or more of the same are contained in an amount of 0.1 to 2.0%, the balance is substantially Fe, and MnS has an average particle diameter of 10 μm or less in a circle equivalent, and an area ratio of 0.5 to 3.0%, and the MnS after forging has an aspect ratio of 1
A cold work tool steel excellent in machinability, characterized by having a size of from 30 to 30. 3. C: 0.5-1.5%, Si: 3.0%
Hereinafter, Mn: 0.2 to 3.0%, Ni: 4.0% or less,
Cr: 0.25 to 15.0%, Mo and W alone or in combination, 2Mo + W: 0.2 to 8.0%, S: 0.03 to
0.4% and Ca: 0.0002-0.02%, Te: 0.005-0.05%, Pb: 0.0
5 to 0.50%, Bi: 0.015 to 0.15%, RE
M: 0.01% or less and Se: 0.02 to 0.20%
And the balance is substantially Fe, and MnS has an average particle size of 10 μm or less in a circle equivalent, and an area ratio of 0.5 to 3.0%. Characterized by having an aspect ratio of MnS after forging of 1 to 30 and having excellent machinability. 4. C: 0.5-1.5%, Si: 3.0%
Hereinafter, Mn: 0.2 to 3.0%, Ni: 4.0% or less,
Cr: 0.25 to 15.0%, Mo and W alone or in combination, 2Mo + W: 0.2 to 8.0%, S: 0.03 to
0.4% and Ca: 0.0002-0.02%, V: 0.05-3.0%, Nb: 0.02-
2.0%, Ta: 0.02 to 2.0% and Ti: 0.1%
0.1 to 2.0% of one or more kinds.
e: 0.005 to 0.05%, Pb: 0.05 to 0.5
0%, Bi: 0.015 to 0.15%, REM: 0.0
1% or less and one or more of Se: 0.02 to 0.20%, the balance being substantially Fe and M
The average particle diameter of nS is equivalent to a circle of 10 μm or less, the area ratio is dispersed in a range of 0.5 to 3.0%, and the aspect ratio of MnS after forging is 1 to 30. Cold work tool steel with excellent machinability. 5. The use of the cold work tool steel having excellent machinability is for a pre-hardened steel which can be machined in a pre-hardened state having a hardness of HRC 45 or more. A cold work tool steel excellent in machinability according to any one of the preceding claims.