JP2003321749A - Surface treatment tool and parts - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a tool which is used by working cold tool steel, and thereafter subjecting the steel to penetration diffusion treatment for the purpose of increasing its seizure resistance, galling resistance and wear resistance, and to provide parts. <P>SOLUTION: Cold tool steel having a composition containing, by mass, >0.9 to 1.1% C, 0.1 to 2.0% Si, 0.1 to 1.5% Mn, 5.0 to 7.0% Cr, one or two kinds of metals selected from Mo and W of 3.0 to 4.5% in terms of Mo+1/2W and one or two kinds of metals selected from V and Nb of 0.5 to 1.0% in terms of V+1/2Nb, and the balance Fe with inevitable impurities is subjected to quenching and tempering by penetration diffusion treatment so as to be dipped into a molten salt bath heated at 980 to 1,030°C, so that high hardness of 62 to 64 HRC can be obtained in the surface treatment tool. The parts are obtained by using the surface treatment tool. <P>COPYRIGHT: (C)2004,JPO

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a tool and a part which are used after cold working tool steel is processed and then subjected to a permeation diffusion treatment for enhancing seizure resistance, galling resistance and wear resistance.

[0002]

2. Description of the Related Art Conventionally, with the progress of plastic working technology, the load on the mold has been increased due to the net shape of parts and the higher strength of the work material. In order to apply to such a severe use environment that the conventional SKD 11 cannot deal with, improvements have been made by reviewing the mold material and performing various surface treatments. For example, JP-A-9-3
In Japanese Patent No. 16601, a cold work tool steel suitable for a surface treatment in which a high hardness of 63 to 66 HRC is obtained by high temperature tempering after the surface treatment at 400 ° C. or higher is proposed.

Further, Japanese Patent Application Laid-Open No. 9-194992 proposes a tool steel for improving the surface adhesion of a high speed tool steel by PVD method or CVD method.
Further, in JP-A-2000-129398, it is used for a cutting tool, a plastic working tool or the like having a hard coating layer formed on the surface thereof which has excellent adhesion to the coating layer and maintains high high temperature hardness and high wear resistance. Tool steel has been proposed. further,
Japanese Patent Application Laid-Open No. 2000-73142 proposes a high hardness cold tool steel, a die and a tool thereof, which can be used for a forging die, a forming roll, a rolling die and the like and which can obtain a high temperature tempering hardness of 64 HRC or more. .

[0004]

However, the above-mentioned JP-A-9-316601 and JP-A-9-19.
The 4992 publication is not V and Nb-added steel, and
It is not based on quenching or tempering by a permeation diffusion treatment of immersing in a molten salt bath at 980 to 1030 ° C. for 1 to 15 hours to form a carbide layer of 5 to 15 mm on the surface of the material to be treated. Further, Japanese Patent Laid-Open No. 2000-129398 discloses Co, Ti.
It is an added steel, which is expensive and inferior in toughness.
On the other hand, Japanese Patent Laid-Open No. 2000-73142 discloses 1000 ° C.
In contrast to low temperature quenching in the vicinity, the present invention provides
Quenching is performed by a permeation diffusion treatment in which a molten salt bath at 1030 ° C. is immersed for 1 to 15 hours to form a carbide layer of 5 to 15 mm on the surface of the material to be treated.

In this case, since the quenching condition is a temperature slightly lower than the standard quenching temperature of 1030 ° C. of the conventional steel SKD11 and the like, the matrix hardness of the SKD11 and its improved steel is 56 after tempering. Only about 60 HRC can be obtained. Further, the portion immediately below the hard film becomes a C supply source when the hard carbide layer is formed, and is decarburized and slightly softened. Therefore, the adhesion between the hard surface film and the matrix is poor, and there is a problem that the mold life is reached due to early peeling during use. This problem can be solved by the low temperature quenching in the diffusion process 62
˜64 HRC, and further tempered at a high temperature to obtain a matrix hardness of 62 to 64 HRC.

[0006]

In order to solve the above-mentioned problems, the inventors of the present invention have earnestly developed the result, and as a result, even in the low temperature quenching condition by a molten salt bath at 980 to 1030 ° C. in the permeation diffusion treatment. Not only high matrix hardness of 62 to 64 HRC is obtained, but also control of carbide improves adhesion of surface hard film and matrix, suppresses delamination of hard film, and tool and mold with significantly improved life. The purpose is to provide. The gist of the invention is (1) mass%, C: more than 0.9% to 1.1%, Si:
0.1-2.0%, Mn: 0.1-1.5%, Cr:
5.0-7.0%, Mo + 1 or 2 kinds of Mo and W
1 / 2W: 3.0 to 4.5%, one or two of V and Nb
A cold work tool steel containing V + 1 / 2Nb: 0.5-1.0%, the balance being Fe and inevitable impurities,
A surface-treated tool characterized in that a high hardness of 62 to 64 HRC is obtained by tempering after quenching by a permeation diffusion treatment of immersing in a molten salt bath at 0 to 1030 ° C.

(2) In the steel described in (1) above, S: 0.
A surface-treating tool characterized by adding 01 to 0.10% to improve workability. (3) The carbide size in the steel according to (1) or (2) above is 20 μm or less, and the size of the carbide agglomerated portion is 1.
A surface treatment tool having a diameter of not more than 00 μm. (4) A component characterized by using the surface treatment tool as described in (1) to (3) above.

The present invention will be described in detail below. The present invention has clarified that the cause of early peeling of the surface hard film of the mold as described above is as follows. (1) Cracks are generated in the hard film by using the coarse carbide and carbide agglomerates directly under the hard film as a stress concentration source. (2) If the matrix hardness is insufficient, the amount of plastic deformation when a high load is applied to the mold is large, and the hard film cannot follow the deformation and cracks occur. (3) When the matrix hardness is insufficient due to the amount of C in the matrix, a softened layer due to decarburization is formed immediately below the hard film, and cracks are generated for the same reason as above. (4) When the surface finish of the die material is poor, the hard film is locally stressed when subjected to a high load, and cracks occur.

In order to prevent the above-mentioned cracks from occurring, it is necessary to secure the amount of C. That is, if the amount of C in the matrix is low, it is softened by decarburization immediately below the hard film, leading to early peeling. In addition, when there are carbides and their agglomerates directly under the hard film, they act as a stress concentration source and cause cracks in the surface hard film, leading to early delamination, so it is necessary to suppress the primary carbide size and the carbide agglomerate size. Furthermore, by finely dispersing the hard carbide, the hardness of the matrix by the hard carbide is increased, which is the cause of the peeling of the hard film, because the deformation of the matrix when subjected to repeated high load is relaxed, The deformation of the hard film is reduced, and the occurrence of cracks is suppressed. In addition, such control of carbide improves the surface roughness during finishing and enhances the adhesion of the hard film.

[0010]

BEST MODE FOR CARRYING OUT THE INVENTION Next, the reasons for limiting the component composition of the present invention will be described. C: more than 0.9% to 1.1% C is an element for ensuring a sufficient quenching and tempering hardness, and a hard film having a sufficient thickness is obtained by the permeation diffusion treatment. It is necessary to exceed 0.9% in order to suppress softening of the base material due to decarburization immediately below. However, if it exceeds 1.1%, the amount of retained austenite at the time of quenching increases and the hardness decreases. Therefore, the range is set to more than 0.9% to 1.1%.

Si: 0.1 to 2.0% Si is added for the deoxidizing effect in steel making and hardenability, but if it is less than 0.1%, the deoxidizing effect is insufficient. The upper limit was set to 2.0% because it suppresses the agglomeration of carbides during tempering and promotes secondary hardening. Mn: 0.1-1.5% Mn is added for hardenability, but 0.1
If less than 1.5%, the effect is insufficient, and if more than 1.5%, the workability decreases, so the range is set to 0.
It was set to 1 to 1.5%.

Cr: 5.0-7.0% Cr is added for hardenability, but 5.0
If it is less than 0.1%, the effect is insufficient, and if it is added in excess, coarsening of primary carbides and formation of carbide agglomerated portions are likely to occur, resulting in deterioration of surface treatment adhesion. Therefore, the range is set to 5.0 to 7.0%. One or two kinds of Mo and W are Mo + 1 / 2W: 3.0-
4.5% Mo and W improve hardenability, and also form fine precipitated carbides during tempering to contribute to secondary hardening. However, if added excessively, the surface treatment property is deteriorated, so Mo + 1 / 2W was set to 3.0 to 4.5%.

One or two of V and Nb is V + 1 / 2N
b: 0.5 to 1.0% V and Nb form fine and hard precipitated carbides during tempering and contribute to secondary hardening. However, if added excessively, the surface treatment property is deteriorated, so V + 1 / 2Nb
Was set to 0.5 to 1.0%. S: 0.01 to 0.10% S is an element necessary for ensuring free-cutting property. However, if it is less than 0.01%, the effect cannot be obtained, and excessive addition lowers the hot workability and toughness, so the upper limit was made 0.10%.

Carbide size is 20 μm or less, and carbide agglomerate size is 100 μm or less. The formation of coarse carbides and agglomerated carbides is reduced, and fine and hard precipitated carbides are dispersed in the matrix, thereby making it possible under a high load environment. By suppressing stress concentration and plastic deformation, it is possible to avoid premature peeling of the hard surface film when using a mold. However, the carbide size exceeds 20 μm, and the size of the carbide agglomerate is 1
If it exceeds 00 μm, there is no effect, so the upper limit was set to 20 μm for the carbide size and 100 μm for the size of the carbide agglomerated portion.

[0015]

EXAMPLES The present invention will be specifically described below with reference to examples. As test materials, each steel having the chemical composition shown in Table 1 was melted and forged in a 100 kg vacuum induction melting furnace.
It was annealed and used as a test material. The results are shown in Table 2.
In the scratch test, an indenter was pressed against the surface hard film of the test piece, scratching was performed while increasing the load, and the critical load at which cracking of the hard film occurred was measured. In addition, Table 3 shows cold pilger mandrels and automobile parts bending presses as examples of actual application. In the actual machine test, both were subjected to permeation diffusion treatment as a measure against die seizure. The osmotic diffusion treatment is a kind of surface hard film formation process in which a VC hard film having a thickness of about 10 μm is obtained by immersing in a V-based salt bath. The cold pilger processing method involves inserting a tapered mandrel into a mother tube and performing cold rolling from the outside with a roll die having a special hole shape. In this actual machine test, SUJ2 was rolled at a surface reduction rate of 75%, and the die life was evaluated by the number of rolled raw tubes at the stage when the transfer of scratches to the inner surface of the product tube due to the peeling of the hard film on the mandrel surface was confirmed. In addition, a bending die for automobile parts was manufactured and the thickness of the work piece was 5
The life of the mold was evaluated by the number of shots until the surface hard film was peeled off when the SPCC of mm was bent by a 1000 t press machine.

[0016]

[Table 1]

[0017]

[Table 2]

[0018]

[Table 3]

As shown in Table 2, No. Nos. 1 to 4 are examples of the present invention. 5-8 is a comparative example. Comparative Example No.
5 and No. The composition of 6 is high in C and Cr, and M
The value of o + 1 / 2W is low, and the value of V + 1 / 2Nb is No. No. 5 is low, and No. 5 is high. Moreover, No. In the case of No. 5, since the size of the carbonaceous material and the size of the agglomerated portion of the carbide are large, the scratch critical load is small and the mold life in the actual machine test is short. Comparative Example No. 7
As for the component composition, since Cr is low, the value of Mo + 1 / 2W is low, and the value of V + 1 / 2Nb is high, the scratch critical load is small and the mold life in the actual machine test is short.

Comparative Example No. The composition of 8 is high in Cr,
In addition, since the value of Mo + 1 / 2W and the value of V + 1 / 2Nb are low, and the size of the carbon material and the size of the agglomerated portion of the carbide are large, the scratch critical load is small and the mold life in the actual machine test is short. Further, it can be seen that the matrix hardness is 61 HRC or less. On the other hand, the present invention example No. It is understood that in each of 1 to 4, the matrix hardness is 62 HRC or more, and the scratch critical load and the mold life in the actual machine test are long.

[0021]

As described above, by improving the adhesion of the surface hard film by the permeation diffusion treatment according to the present invention, the life of the mold, which had been scrapped due to the early peeling of the hard film, was significantly improved. Therefore, it greatly contributes to productivity improvement and cost reduction, and exerts an extremely excellent effect industrially.

─────────────────────────────────────────────────── ─── Continuation of front page (51) Int.Cl. ⁷ Identification code FI theme code (reference) C21D 9/00 C21D 9/00 M

Claims (4)

[Claims] 1. In mass%, C: more than 0.9% to 1.1%, Si: 0.1 to 2.0%, Mn: 0.1 to 1.5%, Cr: 5.0 to. 7.0%, 1 type or 2 types of Mo and W are Mo + 1 / 2W: 3.0-
4.5%, one or two of V and Nb is V + 1 / 2N
b: A cold tool steel containing 0.5 to 1.0% and the balance being Fe and unavoidable impurities is quenched by an infiltration diffusion treatment of immersing in a molten salt bath at 980 to 1030 ° C., and then tempered. A surface treatment tool having a high hardness of 62 to 64 HRC. 2. The steel according to claim 1, wherein S: 0.01 to
A surface-treated tool characterized by improving workability by adding 0.10%. 3. A surface treatment tool, wherein the carbide size in the steel according to claim 1 or 2 is 20 μm or less, and the size of the carbide agglomerated portion is 100 μm or less. 4. A part comprising the surface treatment tool according to any one of claims 1 to 3.