JPH0866705A - Composite film forming tool for hot working - Google Patents

Abstract

PURPOSE: To obtain a composite film forming tool for hot working having excellent characteristics in both terms of wear resistance and thermal crack resistance which normally contradict from each other by forming a metal-carbide composite film on the surface of a base material by using carbon particles having a specific average grain size and volumetric ratio. CONSTITUTION: The metal-carbide composite film contg. the carbide particles having the average grain size of 65 to 135μm at the volumetric ratio of 20 to 50% is formed on the surface of the base material for the composite film forming tool for hot working. This composite film forming tool for hot working has the excellent high-temp. wear resistance and thermal impact resistance in combination. Particularly excellent performance is obtainable therewith by using niobium carbide as the carbide. The tool having an excellent tool life is thus obtd. A plug life is greatly prolonged and a pipe making cost is reduced when this tool is applied particularly to the plug for a plug mill at the time of producing a hot worked seamless steel pipe. In addition, the product having the excellent inside surface quality of the product and dimensional accuracy is obtd.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION The present invention relates to a seamless pipe or sheet rolling,
The present invention relates to a tool used in hot plastic working such as shaped steel, bar steel, and wire rod rolling, and particularly to a composite film forming tool for hot working excellent in wear resistance and heat crack resistance.

[0002]

2. Description of the Related Art Tools used in hot plastic working such as seamless pipe and plate rolling, shaped steel, bar steel and wire rolling suffer from severe friction while being in direct contact with a hot work material. The surface layer temperature rises extremely, which causes considerable wear.
In addition, these tools are repeatedly rubbed intermittently with the work material, and the surface is cooled by water cooling or air cooling when not in contact with the work material. The rapid heating due to and the rapid cooling due to cooling are likely to cause cracks due to thermal shock and thermal fatigue, which may cause surface flaws on the work material, may cause breakage and become unusable, or in extreme cases. It may cause rolling trouble and damage the equipment. Therefore, a tool for hot working is required to have wear resistance and heat crack resistance at the same time.

[0003] For example, in plug mill rolling, which is one of the steps of hot-manufacturing seamless pipes, a pair of hole-shaped rolls that feed in the axial direction while restraining the outer surface of the raw pipe and the inner surface of the raw pipe are restrained. Rolling is performed with the plug
At that time, the plug undergoes complete sliding friction under high surface pressure while being in contact with the inner surface of the base material at a high temperature of 1000 to 1200 ° C., so that it easily wears, and immediately after rolling, it is rapidly cooled by water cooling, Furthermore, since rapid heating and rapid cooling are repeated, cracks occur due to thermal shock and thermal fatigue.

Conventionally, a plug used in such a situation is 1.0 to 1.5% C-25% Cr-3%.
High C-high Cr cast steels such as Ni steel and 1.0-1.5% C-17% Cr-2% W steel are used.

[0005]

[Problems to be Solved by the Invention] Seamless pipe and sheet rolling,
For shaped steel, bar steel, wire rod rolling, etc., rationalization of manufacturing cost and improvement of product surface quality and dimensional accuracy are strongly desired, but for example, conventional plugs used for manufacturing seamless pipes are As described above, wear and thermal cracks occur early and reach the end of their lives, and these damages cause defects on the inner surface of the product and poor dimensional accuracy, so the development of tools with excellent wear resistance and heat crack resistance is desired. .

However, in general, it is necessary to increase the strength of the tool surface layer in order to improve wear resistance, while it is necessary to improve the ductility and toughness of the tool in order to suppress the occurrence and development of thermal cracks. However, since these are usually contradictory properties, a tool having both wear resistance and heat crack resistance has not yet been developed.

In JP-A-1-148405, a metal matrix of a specific component is added in a weight ratio of 50-8.
A guide pipe for hot-rolled seamless pipe with a composite build-up coating in which 0% niobium carbide is dispersed has been proposed. Although it has good wear resistance, it is prone to thermal cracking, The current situation is that the tool life cannot be extended.

The present invention has been made in view of the above circumstances, and provides a composite coating forming tool for hot working which has excellent properties in both wear resistance and heat crack resistance, which are usually contradictory properties. It is the one we are trying to provide.

[0009]

The composite film forming tool for hot working according to the present invention has an average particle size of 65 to 1 on the surface of the base material.
A metal-carbide composite coating containing 20 to 50% by volume of 35 μm carbide particles is formed, and the carbide particles in the metal-carbide composite coating are niobium carbides. .

[0010]

The base steel in the present invention is required not to be deformed during rolling or to be cracked to the inside so as not to cause cracking. The temperature and deformation resistance of the work material, rolling conditions, etc. May be selected as appropriate. Generally, stainless steel, carbon steel, or alloy steel such as SKD is used. Carbon steel, low alloy steel, etc. can be used as long as the load conditions applied to the base material are not particularly severe.

As the carbide of the metal-carbide composite coating in the present invention, there are various niobium carbides, tungsten carbides, titanium carbides, vanadium carbides, chromium carbides, and the like, and the metal (marix metal) has a high temperature strength and toughness to some extent. Martensitic and austenitic stainless steels having

In the present invention, the average grain size of carbide in the metal-carbide composite coating is limited to 65 to 135 μm.
The reason is as follows. That is, the carbide particle size in the metal-carbide composite coating formed on the surface of the base material is generally 50 to 50.
It is usually about 200 μm, but it has a significant influence on the wear resistance and heat crack resistance of the hot working tool,
There is an optimum particle size range that makes both properties compatible,
It became clear from the test results conducted by the present inventor.

FIG. 1 is a diagram showing the influence of the grain size of carbides on the high temperature wear characteristics which was clarified from the test results conducted by the present inventor, and is the result obtained by the friction test method conducted under the following conditions. is there.

<Friction test conditions> Specimen material: Conventional plug material (1.0 to 1.5C-17C)
r-2W cast steel) composite coating (carbide: niobium carbide 40) in which the grain size of carbide is changed by plasma powder overlaying method
%, Matrix metal: SUS304) formed. Specimen size: length 20 mm x width 20 mm x thickness 10 mm
(Friction surface is 20 mm x 10 mm) Mating material: 2.25% Cr-1Mo steel Mating material dimension: 100 mm diameter x 30 mm thickness Mating temperature: 1000 ° C (high frequency induction heating) Mating speed: 100 rpm Load: 100 kgf (load to press the test material against the outer peripheral surface of the mating material) Test time: 10 minutes Evaluation method: The volume of the wear mark was measured and evaluated as the relative wear degree when the conventional plug was used as a reference.

As shown in FIG. 1, if the average particle size of the carbide in the metal-carbide composite coating is small, it is likely to wear, while on the other hand, if the carbide becomes too large, the amount of wear tends to increase, and the relative degree of wear is the highest. The average particle size of carbides is 6
It was found to be 5 to 135 μm.

The results of a thermal crack test conducted to investigate the effect of the carbide grain size in the metal-carbide composite coating on the thermal crack characteristics of the base material are shown below.

As a test method, a cylindrical test piece (material:
S45C, dimensions: diameter 30 mm x length 30 mm) metal-carbide composite coating (carbide: niobium carbide 40%, with varying average carbide particle size by plasma powder overlay method)
Matrix metal: SUS304) was formed, the outer surface was cut to finish into a predetermined shape, and this test piece and a test piece cut out from a conventional plug material (1.0 to 1.5C-17Cr-2W cast steel) were subjected to high frequency Heating (heating temperature 100
After 0 ° C.), the step of cooling with water was defined as one cycle, and this was repeated 100 times. As an evaluation method, the cross section of the test material after the test was microscopically observed, the crack lengths were totaled, and evaluated as the relative crack length based on the conventional plug material. The result is shown in FIG.

As shown in FIG. 2, regarding the thermal crack resistance, it was found that the crack length gradually increased as the average grain size of the carbides increased, but when it exceeded 135 μm, the crack length drastically increased. On the other hand, the smaller the lower limit of the carbide average particle size, the shorter the crack length,
If the carbide average particle size is less than 65 μm, the wear resistance is reduced as is apparent from the data shown in FIG. 1, so the lower limit of the carbide average particle size needs to be 65 μm.

From the above results, in the present invention, the grain size of carbide in the metal-carbide composite coating is limited to 65 to 135 μm as a range in which both the wear resistance and the heat crack resistance are good.

Next, the reason why the content of the carbide particles in the metal-carbide composite coating is limited to 20 to 50% by volume will be described below. That is, the carbide particles dispersed in the metal have the effect of increasing the strength of the coating from normal temperature to high temperature and suppressing wear, and the effect of preventing seizure, and in order to make these effects work effectively, At least 20% by volume is necessary. On the other hand, if the content exceeds 50%, not only the effect cannot be expected to increase, but also the amount of metal that retains carbides decreases, making it difficult to form a film. Since the thermal crack resistance is also reduced, the content of the carbide particles is limited to 20 to 50% by volume.

Further, in the present invention, niobium carbide is specified as the carbide particles in the metal-carbide composite coating, and the carbide particles having the effect of improving the wear resistance by being dispersed in the coating are described above. In addition to niobium carbide, there are various types such as tungsten carbide, titanium carbide, vanadium carbide, and chromium carbide. However, when niobium carbide is dispersed in the coating, the best wear resistance and heat crack resistance can be obtained.

As a method for forming a metal-carbide composite coating containing carbide particles, a method of enclosing mixed powder of metal and carbide between a base material and a capsule and hot isostatic pressing (HIP method), a surface of the base material A method of partially melting and solidifying by irradiating a laser after applying the above powder to the above (laser cladding) is also possible, but as a simpler method of forming a composite coating, the electrode and the base material are There is a plasma powder build-up method in which the powder is fed into the plasma generated between and built up on the surface of the base material, and in addition to excellent adhesion to the base material and denseness of the coating, It is also advantageous in terms of cost. The thickness of the metal-carbide composite coating containing the carbide particles is not particularly limited, but in order to secure sufficient surface strength in the range from normal temperature to high temperature, it is necessary to have a thickness of at least 1 mm or more. preferable.

The metal-carbide composite coating forming tool of the present invention has both excellent high-temperature wear resistance and thermal shock resistance as described above, and particularly when niobium carbide is used as the carbide, particularly excellent performance can be obtained. And has an excellent tool life.

[0024]

【Example】

Example 1 For a plug used in a plug mill, using S45C steel as a base material, in addition to a metal-niobium carbide mixed powder having various contents of niobium carbide on its surface, a metal-tungsten carbide mixed powder, a metal-titanium The carbide mixed powder, the metal-vanadium carbide mixed powder, and the metal-chromium carbide mixed powder were overlay welded by the plasma powder overlay method. The metal powder used at that time was SUS30.
It was 4 stainless steel powder, and the build-up thickness was about 2 mm. The surface of each plug was finished by cutting.

The results of plug mill rolling of carbon steel blanks using these plugs are 1.0
Evaluation was made by the life ratio based on the life of a plug made of ~ 1.5% C-17% Cr-2% W steel. The results are shown in Table 2. The dimensions and temperatures of the blank tube are as shown in Table 1.

As a result of this rolling test, a plug having a carbide grain size and a carbide content in the coating within the range of the present invention was
Both had excellent wear resistance and heat crack resistance, and exhibited a life of 2.3 to 3.7 times that of conventional plugs. On the other hand, in the case where the carbide grain size and the carbide content were out of the range of the present invention and the conventional plug, extremely large abrasion was caused or deep cracks were generated, and the life was early.

[0027]

[Table 1]

[0028]

[Table 2]

[0029]

As described above, the composite coating forming tool for hot working of the present invention has excellent high temperature wear resistance and thermal shock resistance together, and in particular, when niobium carbide is used as the carbide, Excellent performance is obtained and excellent tool life. Therefore, especially when applied to a plug mill for plug mills when manufacturing hot seamless pipes, the life of the plugs can be significantly extended, pipe manufacturing costs can be reduced, and the product inner surface quality and dimensional accuracy are excellent. It is possible to obtain a great product, which is very effective. Further, the present invention is not only a plug mill for a plug mill, but also a piercer plug, a mandrel bar for a mandrel mill, a guide shoe, a roll, a pipe end upset processing die and a mandrel,
Not only various hot tools such as rolls for rolling hot-rolled steel sheets, shaped steel, bar steel, and wire rods, but also applicable to hot-roll material transfer rolls and hot-sliding members such as guides. .

[Brief description of drawings]

FIG. 1 is a diagram showing a relationship between an average grain size of carbides in a metal-carbide composite coating and wear characteristics in the present invention.

FIG. 2 is a view showing the relationship between the average grain size of carbide in the metal-carbide composite coating and the thermal cracking property.

Claims (2)

[Claims] 1. An average particle size of 65 to 135 μm on the surface of the base material.
A composite coating forming tool for hot working, wherein a metal-carbide composite coating containing 20 to 50% by volume of carbide particles of m is formed. 2. The composite coating forming tool for hot working according to claim 1, wherein the carbide particles in the metal-carbide composite coating are niobium carbide.