JPH0847714A - Surface treated tool for hot working - Google Patents

Abstract

PURPOSE:To provide a surface treated toll for hot working having a more excellent coating film by surface treatment in place of hard chromium plating or nitriding. CONSTITUTION:The coating film by surface treatment which satisfies the next requirement is provided on the surface of a base material for tools. The surface hardness of the base material for tools is Vickers hardness of >=350. The surface roughness of the base material for tools is 0.3-4.0mum by center line average roughness (Ra). And the coating film by surface treatment consists of a Ni-base alloy contg. by weight, 30-55% W or 2-15% Cr and 30-50% W.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a surface treatment tool for hot working, particularly a mandrel or die for producing a seamless pipe by a hot extrusion method, and a hot pipe for producing a hot seamless pipe by a Mannesmann method. The present invention relates to a surface treatment tool for hot working such as a mandrel bar, a plug, and a roll for hot rolling.

[0002]

2. Description of the Related Art At present, as a seamless industrial production method, means such as a hot extrusion tube production method and a Mannesmann tube production method (mandrel mill system, plug mill system, etc.) are generally known. The mandrel and die used in the hot extrusion pipe manufacturing method, the mandrel bar and plug used in the Mannesmann method, the hot pipe manufacturing tools such as rolls, etc., have extremely severe operating conditions regardless of surface temperature and surface pressure. Therefore, wear, deformation, and seizure of the tool are likely to occur, and extending the life of the tool has been a major issue. Further, also for rolls used for hot rolling of steel plate, shaped steel, bar steel and the like, similar improvement of tool damage has been an issue.

Among them, the typical example of the Eugene method is a hot extrusion tube manufacturing method that places a heavy load on the tool. First, a heated hollow billet is housed in a container, and a mandrel is placed in the core of the hollow billet. The hollow billet is pushed forward by the stem in the inserted state. A die is set in front of the container, and the tip of the mandrel is inserted into the inside of the die with a predetermined gap. Therefore, the hollow billet pressed forward by the stem is extruded in a tubular shape forward from the annular gap between the die and the mandrel. According to this method, not only stainless steel, but also high alloys having even worse workability can be produced.

The mandrel used here is 1200 ° C.
It is exposed to the severe friction environment of high surface pressure of ^{20 to} 30 kgf / mm ² . Therefore, the hot-alloy tool steel specified in JIS G4404 is used as the material, and this is machined into a mandrel shape, quenched and tempered, and then hard Cr plated on its surface. Hard Cr plating is a treatment for increasing the surface hardness of the mandrel and improving wear resistance. For the same purpose, a mandrel whose surface has been subjected to a nitriding treatment to improve its wear resistance (Japanese Patent Laid-Open No. 5-253613) has also been proposed.

[0005]

By the way, the working environment of the hot extrusion mandrel has become extremely high due to the deterioration of the workability due to the recent high alloying of the extruded material and the high workability for improving the yield. The situation has become severe, and it has become difficult to handle with hard Cr plating and nitriding. In other words, the mandrel coated with these surface-treated coatings has a problem in that the coating is worn out or peeled off early to make it unusable, and this causes adverse effects on the quality and dimensional accuracy of the inner surface of the pipe. there were.

Accordingly, it is an object of the present invention to provide a surface-treating tool for hot working, which is provided with an even better surface-treating coating which replaces the conventional hard Cr plating or nitriding treatment.

[0007]

Therefore, as a result of intensive studies to solve the above problems, the present inventors were able to obtain the following findings.

[0008] In order to prevent damage such as wear and deformation of the mandrel at high temperature, strength at high temperature is required.
The conventional Cr plating and nitriding treatments have a very high Vickers hardness of around 1000 at room temperature, but at 700 ° C
At the above-mentioned high temperatures, the hardness is extremely lowered, and damage such as wear and deformation occurs.

As a result of studying various materials as the surface-treated coatings to replace them, the surface-treated coatings made of the Ni-base alloy containing a specific amount of W have room temperature hardness in Vickers hardness.
It is about 400-500, which is not so high, but it has extremely high hardness in the high temperature range of 700 ° C or higher compared to Cr plating or nitriding coating. That is, when it is used, it is heated to a temperature range of 700 ° C or higher, so that it has a Vickers hardness of 1000.
It hardens to the front and back, and is extremely effective in preventing damage such as wear and deformation of the hot working tool.

When the surface treatment of the above materials is performed, if the base material is too soft, peeling of the coating is likely to occur. In order to prevent peeling, the Vickers hardness of the base must be 350 or more.

Similarly, the surface roughness of the base material affects the peel resistance of the coating. If the surface roughness of the underlayer is too small or too large, film peeling easily occurs, so it is necessary to finish the underlayer to an appropriate roughness.

Although such a composition can be melted as an alloy, if it is left as it is, the segregation of W is remarkable, and as a result, the high temperature strength and the room temperature toughness deteriorate, and it is extremely difficult to use it as a tool.

Here, the gist of the present invention is a surface-treating tool for hot working, which is characterized by comprising a tool base material and a surface-treated coating formed on the surface thereof, and satisfying the following requirements. .

The surface hardness of the tool base material is Vickers hardness
Must be 350 or more. The surface roughness of the tool base material is 0.30μ in terms of center line average roughness (Ra).
m or more and 4.0 μm or less. The surface-treated coating formed on the surface of the tool base material is composed of a Ni-based alloy with a weight ratio of W: 30 to 55% and the balance of Ni. According to a preferred embodiment of the present invention, the Ni-based alloy constituting the surface-treated coating is Cr: 2 to 15%, W: 30 to 50%, and the balance is substantially Ni.

[0015]

Next, the reason why the present invention is limited as described above will be described in detail together with its operation.

[Reason for limiting coating composition] Ni-based alloy: The surface-treated coating provided on the tool according to the present invention has high-temperature strength enhanced by the addition of W. In order to effectively exert its characteristics, The substrate itself must be an alloy with some strength and excellent ductility and toughness. Further, it should not be an alloy that reacts with added W to form a brittle intermetallic compound. The base is Ni to satisfy these properties. In addition to Ni, a component that enhances the toughness of the coating, such as Cr, may be added in the range of 15% or less. Therefore, the composition of the Ni alloy coating film of the present invention may be a Ni-based alloy based on Ni and containing 15% or less of Cr and inevitable impurities.

W: W is a refractory metal and is added to the Ni-based alloy to increase the high temperature strength of the coating. As shown in FIG. 1, a high temperature hardness of W ≧ 30% is obtained. When W is small, the effect is limited to solid solution strengthening, and the hardness improving effect is insufficient. FIG. 1 shows the relationship between the W content and the Vickers hardness at 1000 ° C. with the basic composition of steel type A of the example described later.

That is, when a Ni-based alloy containing 30% or more of W is produced by a normal melting method, W segregates during solidification, and the effect of increasing strength at high temperature is very small, but When a coating film is formed on the surface of the base material by a chemical plating method or a plasma spraying method in which a molten metal is sprayed on the surface of the material to be treated from an ultrahigh temperature range of 2000 ° C or higher, W segregation becomes extremely small After becoming amorphous, and then once heated or exposed to a temperature range of 700 ° C or higher before or during use, W particles (αW) are predominant, and some of them are intermetallic compounds of Ni and W ( As a result of uniformly finely precipitating as Ni ₄ W), it has a Vickers hardness of about 1000 at room temperature and a high hardness even in a high temperature range of 700 ° C or higher, and the ductility of the matrix does not deteriorate. From the dense to the base material Excellent adhesion (peeling resistance). On the other hand, even if it is contained excessively, its effect is saturated, and the ductility and toughness of the coating are impaired, causing cracks,
Peeling easily occurs inside the coating and at the interface with the base material. Therefore, the content of W is limited to 30 to 55% (weight ratio). When Cr, which will be described later, is added, W is preferably 30 to 50%. In any case, the content of W is more preferably 40
~ 50%.

Cr: Cr improves the oxidation resistance and suppresses the precipitation of the intermetallic compound of Ni and W (Ni ₄ W) and the coarsening of the growth thereof, thereby preventing the film-forming alloy of the present invention from becoming brittle. Although it has the effect of preventing it, if it exceeds 15%, the melting point of the alloy decreases, and it becomes impossible to secure high temperature strength. It is desirable to add 2% or more in order to ensure the above effects.
It is preferably 5 to 10%.

[Coating Treatment Method] As a method for forming the surface treatment coating, any method such as a method of electroplating the surface of the base material in a plating bath having a specific composition, a method of spraying powder having the above composition, or the like may be used. However, it is most preferable to use the electroplating method because the coating treatment can be performed at a relatively low cost.

The thickness of the coating film is not particularly limited, but it is generally 10 to 100 μm because it is formed by the electroplating method and the thermal spraying method. If it is too thin, it has no effect, while if it is too thick, it is not sufficient in terms of peeling resistance.

[Reason for Limiting Hardness of Base Tool Base Material] The influence of the hardness of the base base material on the peeling resistance of the coating when the above alloy coating was formed was evaluated by the Nishihara type rolling test.

Material under test Material of base material: SKD61 Hardness of base material: Vickers hardness of 250 ~ by heat treatment
Adjusted to 650 Base material shape: φ30 × 8t, rolling surface curved to R30 Base material roughness: Center line average roughness (Ra) 0.8 μm Surface treatment method: Electroplating coating composition: Ni-50 % W (and unavoidable impurities) The plating conditions were as follows.

Bath composition NiSO ₄ · 7H ₂ O: 30 g / l Na ₂ WO ₄ · 2H ₂ O: 60 g / l Citric acid: 100 g / l pH = 6 Liquid temperature: 50 ° C. Current density: 10 A / dm ² .

Mating material: SUJ2 hardness: Vickers hardness adjusted to 650 by heat treatment Shape: φ30 × 8t, rolling surface curved to R30.

Test conditions Surface pressure: 150 kgf / mm ² Number of revolutions: 800 rpm Slip rate: 10% This test was conducted without lubrication.

Evaluation Method The film peeling condition was visually and microscopically observed every 10,000 rolling cycles, and the peeling resistance was evaluated by the number of rolling occurrences when peeling occurred up to 100,000 cycles. The test results are shown graphically in FIG.

As is apparent from FIG. 2, when the hardness of the base material to be coated is 350 or more in Vickers hardness, a surface-treated coating excellent in peeling resistance can be obtained. When the surface hardness of the base material is less than 350 in Vickers hardness, film peeling occurs when contacting the mating material with a high surface pressure, due to the strength and adhesion of the film This is because deformation occurs and cracks are easily generated and propagated between the coating film and the base material.

[Reason for Limiting Surface Roughness of Base Tool Base Material] The effect of the surface roughness of the base base material on the peeling resistance of the coating when the above alloy coating was formed was evaluated by the Nishihara type rolling test. .

Test material Base material: SKD61 Base material hardness: Vickers hardness adjusted to 400 by heat treatment Base material shape: φ30 × 8t, rolling surface curved to R30 Base material roughness: Processing method Centerline average roughness (Ra)
Adjusted to 0.1 to 5.0 μm Surface treatment method: Electroplating method Coating composition: Ni-40% W-10% Cr (and inevitable impurities) The plating conditions were as follows.

Bath composition NiSO ₄ · 7H ₂ O: 30 g / l Na ₂ WO ₄ · 2H ₂ O: 60 g / l Cr ₂ (SO ₄ ) ₃ · 15H ₂ O: 30 g / l Ethylene glycol: 20 g / l Citric acid: 100 g / l pH = 6 Liquid temperature: 50 ° C. Current density: 10 A / dm ² .

Mating material: SUJ2 hardness: Vickers hardness adjusted to 650 by heat treatment Shape: φ30 × 8t, rolling surface curved to R30.

Test conditions Surface pressure: 150 kgf / mm ² Number of revolutions: 800 rpm Slip rate: 10% This test was carried out without lubrication.

Evaluation Method The film peeling condition was visually and microscopically observed every 10,000 rolling cycles, and the peeling resistance was evaluated by the number of peeling rolling cycles when repeated up to 100,000 cycles. The test results are shown graphically in FIG.

As is apparent from FIG. 3, when the surface roughness of the base base material to be coated is less than 0.30 μm in center line average roughness (Ra) or more than 4.0 μm, the coating Peeling occurred. On the other hand, when the surface roughness is 0.30 μm or more and 4.0 μm or less, a surface-treated coating having excellent peel resistance can be obtained. It is preferably 0.50 to 2.0 μm.

[Material for Tool Base Material] The material for the tool base material is not particularly limited, and any material may be used as long as it has the minimum necessary strength and toughness as the tool base material. Generally, from the viewpoint of its performance and cost, JIS
It is preferable to use hot-alloy tool steels such as SKD6, SKD61, and SKD62 specified in 1. Next, the function and effect of the present invention will be described more specifically with reference to Examples.

[0037]

Example: Eugene extrusion mandrels (rolling section length: 1200 mm, rolling section diameter: 35 mm) on which various surface-treated coatings were formed using a hot alloy tool steel equivalent to SKD61 defined in JIS as a base material Five pieces were prepared and used for hot extrusion of austenitic stainless steel (SUS304) (extrusion temperature: 1220 ° C., extrusion ratio: 40) to evaluate the average life of the mandrel.

Table 1 shows the coating treatment conditions in this example and the evaluation when hot working was carried out in an actual apparatus. The evaluation here is shown as the life ratio of each surface-treated mandrel to the life of the conventional Cr-plated mandrel (the number of pipes manufactured until it becomes unusable due to damage).

[0039]

[Table 1]

As is clear from Table 1, the surface-treated mandrels (A to I) satisfying the conditions of the present invention have a life of about twice as long as that of the conventional Cr-plated or nitrided mandrels. It is understood that there is. On the other hand, in the mandrel surface-treated under the conditions outside the scope of the present invention, the abrasion and peeling of the surface coating occurred at an early stage, and the effect of extending the life could not be obtained.

[0041]

As described above, the surface-treated tool according to the present invention has a high temperature hardness and excellent peeling resistance, and thus has a long service life, and has a great effect on the improvement of the inner surface quality of the pipe. It is something to demonstrate. Further, the surface treatment tool of the present invention, not only the mandrel used in the hot extrusion method, but also the hot extrusion die, the mandrel bar and plug used in the Mannesmann method, the same effect when applied to the rolling rolls and the like. It goes without saying that it will exert its potential.

[Brief description of drawings]

FIG. 1 is a graph showing the relationship between the W content in a Ni-based alloy coating and the high temperature hardness of 1000 ° C.

FIG. 2 is a graph showing the influence of the surface hardness of the base material on the peel resistance of the surface-treated coating.

FIG. 3 is a graph showing the influence of the surface roughness of the base material on the peel resistance of the surface-treated coating.

─────────────────────────────────────────────────── ─── Continuation of the front page (51) Int.Cl. ⁶ Identification code Internal reference number FI technical display location C22C 19/03 J 19/05 D

Claims (2)

[Claims] 1. A surface-treated tool for hot working, comprising a tool base material and a surface-treated coating formed on the surface thereof, and satisfying the following requirements. The surface hardness of the tool base material should be 350 or more in Vickers hardness. The surface roughness of the tool base material is 0.30μ in terms of center line average roughness (Ra).
m or more and 4.0 μm or less. The surface treatment coating formed on the surface of the tool base material is composed of a Ni-based alloy in which W: 30 to 55% by weight and the balance is substantially Ni. 2. The Ni-based alloy constituting the surface-treated coating, by weight ratio, Cr: 2-15%, W: 30-55%, the balance substantially
The surface treatment tool for hot working according to claim 1, which is Ni.