JP2965865B2 - Spraying method to metal extrusion die - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a thermal spraying method suitable as a wear-resistant coating means for metal dies for hot extrusion.

[0002]

2. Description of the Related Art Dies for hot extrusion of iron or stainless steel are required to have high temperature hardness and high thermal shock resistance. Therefore, the die material is C: 0.25 to 1.2.
%, W: 5 to 10%, based on which an alloy steel containing Cr, Mo and V as appropriate is used, and the steel is subjected to a secondary hardening to obtain a Rockwell hardness of about 45 to 63. Is used. In addition, there are also semi-high-speed steel having a composition close to that of high-speed steel and Cr-Mo-V steel in which the Cr alloy content is increased from 13% to 25% in order to eliminate the low thermal fatigue characteristics of W. It shows good results (for example, the 48th plastic working studies course outline collection 1991.7.
10-12, p. 119-).

In order to further increase the high-temperature hardness, a technique for forming a sprayed coating having high hardness at the contact portion between the die material and the extruded material has been developed. In the extrusion of a high melting point metal such as Mo, alumina or zirconia is applied to the die surface. May be used (“Spraying Technology”, Yokendo 1969, P269)
~). However, these ceramic materials have a problem in brittleness. Therefore, a Co-based alloy having high high-temperature strength and hardness, particularly stellite (trade name) has already been used by overlaying on the surface of a die or a roll. This material has slightly different properties depending on the contained components, but has a Vickers hardness of 200 or more even at a high temperature of 1000 ° C.

[0004] As a method of forming the thermal spray coating, there are a method of overlaying, plasma spraying, and flame spraying. Recently, a plasma in which a high-frequency plasma and a DC plasma capable of forming a dense coating are superimposed (hereinafter abbreviated as hybrid plasma spraying). ) A thermal spraying method has also been developed, and a method for forming a dense film of zirconia, Ti, and Ni has been reported (for example, PlasmaSo
urces Technol. 1 (1992) p195-201, T. Yoshida).

[0005]

The steel used for the dies has a high hardness, but the hardness decreases rapidly at a high temperature of 800 ° C. or higher. Excessive damage and replacement required. As a surface hardening method, in the case of stellite-based Co alloy cladding, the material is melted to form a film, so even if the film thickness is 3.2 mm, the film contains about 30% of the material component, and the high-temperature hardness of the film Is not enough. On the other hand, conventional plasma spraying and flame spraying have many pores inside the coating and have low adhesion strength, so that it is difficult to form the coating.

Accordingly, an object of the present invention is to form a thick Co-based alloy such as stellite having excellent high-temperature hardness on the surface of a die, and to form a thick film which does not contain any material and has high adhesion strength.

[0007]

The gist of the present invention is as follows. (1) A part or the whole of a die surface where a die and an extruded material are in contact with each other has a thickness of 3.5 to 20 mm and a weight%. C:
1.0 to 3.0%, W: 4 to 25%, Cr: 25 to 32
%, The balance being Co and an unavoidable impurity, a Co-based alloy is sprayed under atmospheric pressure by a plasma in which high-frequency plasma and DC plasma are superimposed. The inner diameter of the torch is 50 to 80 mm, the distance between the spray torch and the surface of the base material is 100 to 200 mm, and the high frequency output is 150 mm.
After heating the base material at 100 to less than the melting point of the base material at ~ 250 kW, the Co-based alloy having a particle size of 60-500 µm is sprayed at a supply rate of 10-100 g / min (1). The method is for spraying a metal extrusion die.

[0008]

[Function] Regarding the thickness of the coating, the heat affected depth at the time of extrusion is not less than 3.5 mm from the die surface, that is, high temperature hardness and strength are required in the area of 3.5 mm from the surface. It is necessary to set the thickness to 3.5 mm or more, and to increase the thickness to 20 mm or less because the effect of residual stress generated during film formation increases as the thickness increases.

As a thermal spraying material, a stellite-based Co-based alloy is an effective material because of its high temperature hardness and high strength. This composition is limited for the following reasons.

C is added in order to form carbides such as WC, Cr ₃ C ₂ and Cr ₇ C ₃ to secure hardness, but this amount is set to 1.0% or more in order to increase the hardness. .
If it exceeds 0%, the brittleness deteriorates, so the content is made 1.0 to 3.0%.

W is added to increase the hardness by forming WC, but if it is less than 4%, the hardness is insufficient.
If it exceeds 5%, the brittleness is extremely deteriorated, and the thermal fatigue property is lowered.

[0012] Cr forms a carbide having excellent high-temperature hardness. This carbide has better thermal fatigue properties than WC. If the Cr content exceeds 32%, the brittleness decreases, and if it is less than 25%, the hardness is low, so that the Cr content is set to 25 to 32%.

[0013] Other than the above, impurities such as oxygen mixed during the production of the powder are preferably set to 0.02% or less to prevent embrittlement. Co is used for the matrix because creep characteristics and strength at high temperatures are superior to those of Fe and Ni.

The use of hybrid plasma spraying is preferred because compared to other spraying methods, the particles can be completely melted and larger-sized particles can be used, so that a coating having high density strength can be formed. In this hybrid plasma spraying, the inner diameter of the spraying torch is set to 80 mm or less to increase the oscillation efficiency, and 5 mm to increase the spraying area.
It is preferable to set it to 0 mm or more. The distance between the torch and the base material is preferably 100 mm or more so as not to melt the base material, and 200 mm or less to re-melt the film.

Further, the higher the temperature of the base material before thermal spraying, the higher the adhesion strength between the base material and the coating. When the base material is an iron alloy, the base material temperature dependence of the adhesion strength particularly between room temperature and 400 ° C. Is high. The required adhesion strength varies depending on the application, but 60MP
In order to obtain the adhesion strength of a or more, it is necessary to heat the base material to 100 ° C. or higher, and to lower the melting point of the base material so as not to melt the base material. For the above-mentioned reason, it is preferable to increase the temperature within a range where thermal deformation or deterioration of the base material does not occur.

Here, when spraying a stellite-based Co alloy, the size of the sprayed material should be 60 μm or more to increase the adhesion strength between the base material and the coating, and the particle size should be 500 μm or less to stably supply the powder. Need to be The high frequency output of the hybrid plasma is set to 150 kW or more for melting the powder, and 250 kW or less for preventing the powder from evaporating during thermal spraying. The gas flow rate and output of DC plasma are set to 2
The output must be less than 500 A (5 V) below 0 LPM. Also, the gas flow rate should be 1 to prevent damage to the DC gun.
More than 0 LPM is required (when the output is 0, high-frequency plasma is generated, and plasma stability is poor).

The relationship between the particle diameter (D) of the stellite Co alloy, the high-frequency output (Pm) required for melting, and the high-frequency output (Pv) required for evaporation is Pm (kW) = D / 5 (μm).
m), Pv (kW) = 2D / 5 (μm). Plasma gas with high frequency output of 150 to 250 kW is Ar = 80 to
150 LPM, nitrogen = 30-200 LPM, hydrogen = 5-50
LPM. Each gas flow rate needs to be lower than the upper limit so that the plasma does not extinguish, and lower than the lower limit so that the plasma does not expand and damage the torch. At this time, the powder supply rate is 10 g / mi for stable powder supply.
n or more and 100 g / min or less for complete melting of the particles in the plasma.

[0018]

DESCRIPTION OF THE PREFERRED EMBODIMENTS SKD61 of φ265 × t25 mm shown in FIG.
Table 2 shows the hybrid plasma spray conditions of the stellite-based Co alloy (Table 1) on the surface of the die that comes into contact with the extruded material. As a result of using this die, the conventional SKD61
(0.5C-5Cr-Fe, after forging, quenching, tempering, the hardness is about Hv450) The wear weight of the die after one hot extrusion process is less than 1/2. And the life was improved more than twice.

[0019]

[Table 1]

[0020]

[Table 2]

[0021]

According to the thermal spraying method of the present invention, the amount of wear of the die is reduced to one half of that of the conventional method, and the life is extended.

[Brief description of the drawings]

FIG. 1 is a perspective view of a sprayed die according to the present invention.

Continued on the front page (72) Inventor Nobutaka Yurioka 20-1 Shintomi, Futtsu-shi, Chiba Nippon Steel Corporation Technology Development Division (72) Inventor Fuyasu Yamamoto 20-1 Shintomi, Futtsu-shi, Chiba Made in New Japan (72) Inventor Shoichi Aratani 20-1 Shintomi, Futtsu City, Chiba Prefecture Nippon Steel Corporation Technology Development Headquarters (72) Inventor Mikio Kanamori 3434 Shimada, Hikari-shi, Yamaguchi Prefecture Address Nippon Steel Corporation Hikari Works (72) Inventor Satoshi Araki 3434 Oshima Shimada, Hikari-shi, Yamaguchi Prefecture Nippon Steel Corporation Hikari Works (72) Inventor Yoshihiro Inmaki 20 Shintomi, Futtsu City, Chiba Prefecture -1 Nippon Steel Corporation Technology Development Division (72) Inventor Masahiro Ohara 20-1 Shintomi, Futtsu City, Chiba Prefecture Nippon Steel Corporation Technology Development Division (58) Fields surveyed (Int.Cl. ⁶ , DB name) C23C 4/12 C23C 4/06

Claims (2)

(57) [Claims] 1. A part or the whole of a die surface where a die and an extruded material are in contact with each other, a thickness of 3.5 to 20 mm, C: 1.0 to 3.0% by weight%, W: 4 to 25% by weight. %, Cr: 25 to 32%, the balance being Co and an unavoidable impurity,
A method for spraying onto a processing die for metal extrusion, wherein spraying is performed by plasma obtained by superimposing high-frequency plasma and DC plasma under atmospheric pressure. 2. The plasma spraying torch has an inner diameter of 50 to 80 mm, and the distance between the spraying torch and the surface of the base material is 100 to 100 mm.
200mm, high frequency output of 150-250kW and one base material
After heating to a temperature of less than the melting point of the base material, the particle size is
The supply rate of the Co-based alloy of 500 μm is 10 to 100 g /
The method for spraying a metal extrusion die according to claim 1, wherein the thermal spraying is performed at min.