JP3497387B2 - Molds and tools made of high hardness cold tool steel - Google Patents

Description

Detailed Description of the Invention

[0001]

The present invention relates to the forging die, the forming rolls, molds 64HRC or more high temperature sintered Modokata is used for thread rolling die and the like is made of high-hardness A steel obtained
And tools.

[0002]

2. Description of the Related Art Conventionally, cold forging dies and punches,
JIS SKD11 is widely used as an alloy tool steel for cold working used for die-cutting applications and the like. These SK
Although D11 is a heat treatment method after quenching from 1000 to 1050 ° C. and then tempering at 150 to 200 ° C. or 500 to 550 ° C., it has a low HRC of about 60, low toughness, and a short tool life. In addition, JIS S which is a high speed tool steel
KH51 has sufficient hardness but low toughness, high material cost and high heat treatment cost, and very poor workability.

Therefore, in recent years, as improvements of these, Japanese Patent Laid-Open Nos. 59-179762, 1-2014442, 6-212253 and 5-156407 are proposed. Has been done. For example, in JP-A-59-179762, 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 to 5.0%
As a basic component, and further, REM, Cu, Ni, W, C
o, Nb, Ti, Zr, S, Pb, Se, Bi, Te,
Disclosed is a cold work tool steel which comprises one or more kinds of Ca, the balance Fe and impurities, and is tempered at a temperature of 450 ° C. or higher.

Further, in Japanese Patent Application Laid-Open No. 1-204442, C: 0.90 to 1.35%, Si: 0.
70-1.40%, Mn: 1.0% or less, S: 0.00
4% or less, Cr: 6.0 to 10.0%, or P: 0.
015% or less, and 1 or 2 kinds of Mo and W are Mo
1.5 to 2.5% at + W / 2, one or two of V and Nb
Seed V + Nb / 2 0.15-2.5%, or Ni +
Co of 0.3 to 1.5%, balance of Fe and impurities, and a hardened and tempered structure of M ₇ C
Disclosed is a steel for a rolling die, which has an area ratio of ₃ type carbides of 2% or more and 9% or less and an area ratio of MC carbides of 2.5% or less.

Japanese Patent Laid-Open No. 6-212253 discloses that
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 to 5.0% as a basic component, and further REM, Cu, Ni, W, Co, N
Steel containing at least one of b, Ti, Zr, S, Pb, Se, Bi, Te, and Ca, and tempering steel consisting of balance Fe and impurities at a temperature of 450 ° C. or higher Disclosed is a method for producing cold working tool steel.

Further, Japanese Patent Laid-Open No. 156407/1993 discloses that
% By weight, C: 0.95 to 1.10%, Si: 0.65
~ 1.20%, Mn: 1.0% or less, Cr: 6.80 ~
7.80%, 1 or 2 kinds of Mo and W (Mo + 1 /
2W) is 2.50 to 3.50%, one or two kinds of V and Nb is (V + 1 / 2Nb) 0.20 to 0.60% as a basic component, and further Co: 1.0 to 4 0.0%, Ni:
Includes one or two of 0.2 to 1.0%, the balance F
e and unavoidable impurities, and after quenching and tempering, M ₇ C ₃ type primary carbides have an area ratio of 4% or less, M
The area ratio of the C-type primary carbides is 0.5% or less, the maximum grain size of the primary carbides is substantially 20 μm or less, and the microstructure is uniformly dispersed in the matrix. Further, from the quenching temperature of 1050 to 1100 ° C., Quenching cooling rate up to ℃ 25 ℃ /
Disclosed is a high-performance rolling die steel capable of obtaining a hardness of HRC 64 or more when quenching as min and tempering at high temperature.

[0007]

As described above, the JI
The high temperature tempering hardness of S-SKD11 is as low as about 60 HRC, and the toughness is low and the tool life is short. In addition, JIS-SKH
Although No. 51 has a hardness of 64 HRC or more, it has a high material unit price, an extremely high proper quenching temperature of 1200 ° C., has many restrictions in terms of heat treatment workability and its cost, and has very poor workability. JP-A-59-179762 and JP-A-1-
Japanese Patent Laid-Open Publication No. Hei 5-1 and No. Hei 5-2153 have a hardness of about 62 to 63 HRC.
In Japanese Patent No. 56407, a steel that can obtain a hardness of 64 HRC or more is proposed, but the quenching temperature is 1050 to 1050.
It is as high as 1100 ° C, and there are many restrictions in terms of heat treatment workability and its cost. Further, it is necessary to limit not only the regulation of the alloy composition but also the application of a special melting method and high temperature diffusion treatment in the manufacturing process, the composition of the primary carbide of the product, the grain size and the precipitation amount.

[0008]

However, due to the recent progress in plastic working technology and the increase in strength of work materials, 64H
There is a need for a tool steel that has a hardness of RC or higher and is rich in toughness. Particularly in applications where abrasion resistance is required, a surface hardening treatment at a treatment temperature of 400 ° C. or higher is performed, so it is necessary to obtain the required hardness in high temperature tempering. Further, from the viewpoint of economy, it is required to be inexpensive and have excellent workability in heat treatment and processing. The gist of the invention is as follows: (1)% by weight, C: 0.8 to 1.1%, Si: 2.0
% Or less, Mn: 1.5% or less, Cr: 4.5 to 8.0
%, 1 type or 2 types of Mo and W, Mo + 1 / 2W (M
o equivalent): 2.0 to 4.5%, one or two of V and Nb
V + 1 / 2Nb (V equivalent): 0.4 to 1.2%, and the balance Fe and unavoidable impurities. The following formula α value is 0.7 to 1.0 and β value is 3.0. Steel having a hardness of 64 HRC or more after being hardened at a quenching temperature of 1020 to 1050 ° C. and then tempered at a high temperature. Mold and tools. However, α value = 0.706 + 0.541C-0.0
63Cr + 0.033Mo equivalent-0.232V equivalent, β
Value = Mo equivalent + 1.9V equivalent

(2) A die and a tool made of a high hardness cold work tool steel, characterized in that the steel according to (1 ) above further contains S: 0.01 to 0.10%.

[0010]

BEST MODE FOR CARRYING OUT THE INVENTION The following is a description of the present invention:
The reason for limiting the composition range of each component will be described in which a steel having a high temperature tempering hardness of 64 HRC or more, high toughness, and excellent adhesion to a hard surface treatment layer can be obtained by quenching at 1050 ° C. C: C gives sufficient matrix hardness by quenching and tempering, and also combines with Cr, Mo, V, Nb and the like to form a carbide, which gives hardness and strength. But,
If it is less than 0.8%, this effect cannot be sufficiently obtained.
If it exceeds 1.1%, coarse carbides are excessively precipitated during solidification, which not only hinders toughness, but also excessive residual austenite remains during quenching, which lowers hardness. Therefore, the range is set to 0.8 to 1.1%. The preferable range is 0.95 to 1.05%.

Si: Si mainly enhances the deoxidizing agent, the oxidation resistance and the hardenability, suppresses the agglomeration of carbides in the tempering process, and promotes the secondary hardening. However, if it exceeds 2.0%, the toughness decreases. Therefore, the range is set to 2.0% or less. Mn: Mn improves the deoxidizing agent and hardenability. But 1.5
%, The hot workability is impaired and the toughness deteriorates.
Therefore, the range is set to 1.5% or less. Cr: Cr enhances hardenability and temper softening resistance. But,
If it is less than 4.5%, the effect cannot be obtained, and if it exceeds 8.0%, it is likely to combine with C during solidification to form a giant primary carbide,
Excessive addition deteriorates toughness. Therefore, the range is set to 4.5 to 8.0%. The preferred range is 5.
It was set to 5 to 6.5%.

Mo + 1 / 2W (Mo equivalent) : Mo and W both form carbides to enhance wear resistance and improve hardenability. During tempering, they precipitate as carbides and undergo strong secondary hardening. It is an element shown. Further, since the atomic weight of W is about twice that of Mo, it is set to (Mo + 1 / 2W) to form fine carbides, contribute to secondary hardening, and improve resistance to softening. It was set to 0.5%. However, if it is less than 2.0%, the effect cannot be obtained, and
%, The toughness decreases and the adhesion with the hard surface layer is hindered. The preferable range is 3.0 to 4.0%.

V + 1 / 2Nb (V equivalent) : V and Nb both form fine carbides, contribute to secondary hardening, improve softening resistance, and are effective for grain refinement and abrasion resistance improvement. is there. To exert these effects, V + 1 / 2Nb
At least 0.4 to 1.2% is required. But,
If it is less than 0.4%, the effect cannot be obtained, and if it exceeds 1.2%, the toughness deteriorates and the adhesion to the hard surface layer is hindered.
The preferable range is 0.6 to 0.9%. S: S is effective for improving machinability,
0.01% is necessary to secure free-cutting property, and if it exceeds 0.10%, toughness and hot workability deteriorate.

The α value is 0.7 to 1.0 and the β value is 3.0.
~ 6.0: If the amount of residual austenite remaining during quenching is too large,
The hardness becomes low, and if it is too small, sufficient secondary hardening cannot be obtained during high temperature tempering. When C, Cr, Mo, and V satisfy the following equation, an appropriate amount of retained austenite is obtained. Therefore, α value = 0.706 + 0.541C−0.063C
r + 0.033Mo equivalent- 0.232V equivalent to 0.7-
It was set to 1.0. That is, in order to provide sufficient matrix hardness and secondary hardening, 0.7 is necessary for that, and if it exceeds 1.0, excessive residual austenite remains during quenching, which lowers the hardness. Let Preferably,
It is set to 0.75 to 0.85.

It is necessary to simultaneously satisfy the above α value and the following β value. When the Mo equivalent and the V equivalent satisfy the following equations, the formation of coarse carbides and agglomerated carbides that inhibit the adhesion to the hard surface layer is suppressed, and sufficient secondary hardening is obtained during high temperature tempering. Therefore, the β value is set to 3.0 to 6.0.
And For that, 3.0 is required, and 6.0
When it exceeds, the adhesion to the hard surface layer is hindered. The preferable range is 4.5 to 5.5. However, β value =
Mo equivalent + 1.9V equivalent

[0016]

EXAMPLES The present invention will be described below based on examples.
As the test material, the steel of the present invention having the composition shown in Table 1 (No. 1 to No. 1)
No. 5), each steel 10 of comparative steels (No. 6 to No. 9)
0 kg was melted in a vacuum induction melting furnace, forged into 50 mm square, and annealed to obtain a test material. Table 2 shows the α value, β value, the quenching temperature, the tempering temperature, and the amount of retained austenite during quenching, which are related to the component composition. At that time, hardness, transverse rupture strength, amount of deflection, scratch critical load, and end mill wear amount were tested. Table 3 shows the test results of those characteristic values. As shown in Table 3, the invention sample No.
Hardness HRCs in 1 to No 5 all show values of 64 or more, bending strength of 4200 N / mm ² or more, deflection amount of 1.0 to 1.7 mm, and scratch critical load of 45 to 48 N. Thus, Comparative Examples No. 6 to No. 9 are all 29 N or less.

Regarding the measurement of the amount of retained austenite,
After holding at 1020 to 1050 ° C. for 30 minutes, it was air-cooled, quenched, and quantified by X-ray diffraction method. In addition, the hardness was measured on a Rockwell C scale at room temperature. In the bending test, a bending strength of 5 mm length × 9 mm width × 60 mm length and the amount of deflection were measured. The scratch test is PVD after quenching and tempering.
After the treatment, an indenter was pressed against the test piece and scratched while increasing the load, and the critical load at which the surface-treated film was peeled off was measured. Furthermore, regarding machinability, annealing after forging, NC milling, φ13 end mill, axial direction 10
mm × 1.2 mm cut, rotation speed 1100 rpm, cutting speed 35 m / min, and end mill wear amount after 5 m machining were measured.

[0018]

[Table 1]

[0019]

[Table 2]

[0020]

[Table 3]

[0021]

As described above, according to the present invention, 64H
It has a high temperature tempering hardness of RC or higher, is inexpensive, is excellent in heat treatment workability and its cost, and has an extremely excellent effect of being able to obtain a high hardness cold tool height particularly suitable for high temperature surface treatment. is there.

─────────────────────────────────────────────────── ─── Continuation of front page (56) Reference JP-A-11-302777 (JP, A) JP-A-5-156407 (JP, A) JP-A-3-134136 (JP, A) JP-A-10- 60596 (JP, A) (58) Fields investigated (Int.Cl. ⁷ , DB name) C22C 38/00-38/60

Claims (2)

(57) [Claims] 1. By weight%, C: 0.8 to 1.1%, Si: 2.0% or less, Mn: 1.5% or less, Cr: 4.5 to 8.0%, Mo and W. No. 1 or two, Mo + 1 / 2W (Mo equivalent): 2.0 to 4.5%, one or two of V and Nb, V + 1 / 2Nb (V equivalent): 0.4 to 1. 2%, and the balance Fe and unavoidable impurities.
A steel satisfying a value of 0.7 to 1.0 and a β value of 3.0 to 6.0 at the same time is hardened at a hardening temperature of 1020 to 1050 ° C. and then high temperature tempered to have a hardness of 64 HRC or more. A mold and tool made of high hardness cold work tool steel characterized by: However, α value = 0.706 + 0.541C−0.063
Cr + 0.033 Mo equivalent-0.232 V equivalent β value = Mo equivalent +1.9 V equivalent 2. The steel according to claim 1, further comprising S: 0.
High hardness cold, characterized by containing 01 to 0.10%
Molds and tools made of inter-tool steel.