JPS6213294A - Method for restoring and reutilizing tool for rolling - Google Patents

Abstract

PURPOSE:To reduce the consumption of a high-Mo tool for rolling a seamless steel pipe by subjecting the tool which is worn or damaged after the tool is once used for rolling to surface build-up with a material consisting of the same components and reutilizing the restored tool. CONSTITUTION:The tool for rolling to be restored is assumed to be a plug 1 which consists of an alloy contg. >=70% Mo and is worn or damaged after the tool is once used for rolling. The Mo powder 2 is packed to the surface of the plug 1 and the entire part is subjected to a sealing treatment in a steel plate capsule 3; thereafter, the plug is subjected to diffusion joining by hot hydrostatic molding. Plasma spraying and high energy beam welding are applied to the build-up restoration as necessary. The costly tool for rolling is thus restored and reconditioned, by which the consumption of the tool is reduced.

Description

DETAILED DESCRIPTION OF THE INVENTION (Field of Industrial Application) The present invention relates to a method for repairing and reusing tools such as plugs used in rolling seamless steel pipes.

(Prior art) In a rolling mill that manufactures seamless steel pipes, etc., a plug, a mandrel, etc. are provided inside the steel pipe, and a roll is provided that contacts the outer surface of the steel pipe, and the wall of the steel pipe is rolled by the plug or mandrel and the rolls. Processing is performed.

Therefore, the plug is made to exist inside the steel pipe.

Tools such as mandrels come into direct contact with the rolled material (inner wall surface of steel pipes) at 1000 to 1300°C and are placed under the action of high surface pressure, resulting in significant seizure and wear9 local damage. Localized damage caused by seizure of tools has a direct impact on the quality of rolled products, such as the surface texture and dimensional accuracy, so conventionally, tools were discarded if they fell below a certain control standard.

In particular, when rolling high-alloy steel pipes, plugs, etc.
The rolling of 1-2 steel pipes will force a public prosecutor's investigation. Although it is conceivable to use higher quality tool materials as a means to extend tool life, there is a problem in that as the tool materials become higher grade, the tool consumption rate increases.

The inventors first developed 3C as a means to extend tool life.
r-INi system or 17Cr-2W system (Special Publication 1986-53
No. 863) was developed and is currently widely used.

These tool materials are subjected to heat treatment to form a tight black crust on their surfaces in order to provide them with heat resistance and wear resistance. This black scale is an iron oxide, and when rolling Teitotsu steel, the black scale naturally grows during rolling, so it can provide a long tool life. There is also a technique in which a black scale is formed by thermally spraying iron oxide on the surface of a tool (Japanese Patent Publication No. 1987-IH24).

However, when rolling high-alloy steel, it is impossible to expect the black scale to grow naturally on the tool, and the insulating effect of the black scale cannot be sustained, resulting in excessive heat input to the tool, and the life of the plug ends after several rolls are rolled. Become.

(Problems to be Solved by the Invention) The purpose of this invention is to solve the above-mentioned problem of tool wear and tear in rolling high-alloy steel pipes, as well as the problem of rising tool unit consumption. It was done.

(Means for solving problems) The gist of this invention is as follows.

(1) Mo70 that was once subjected to rolling and was worn out or damaged
A method for repairing and reusing a rolling tool, characterized in that the rolling tool for seamless steel pipes containing % or more is repaired and reused by overlaying the same component material on the surface.

(2) The rolling method according to item i1 above, in which a worn or damaged seamless steel pipe rolling tool containing Mo70$ or more is repaired by diffusion bonding powder of the same composition by hot isostatic pressing. How to repair and reuse tools.

(3) The method for repairing and reusing a rolling tool according to item 1 above, wherein the surface of a worn or damaged rolling tool for seamless steel pipes is overlaid with a material of the same composition by thermal spraying.

(4) The method for repairing and reusing a rolling tool according to item 1 above, wherein the surface of a worn or damaged rolling tool for seamless steel pipes is overlaid with a material of the same composition by welding with a high-energy beam.

This invention will be explained in detail below.

The inventors found that the melting point is high and the coefficient of thermal expansion is low.

Focusing on Mo tools with good thermal conductivity and excellent heat fatigue resistance,
After examining various systems for repairing and recycling tools that had been used for rolling and were worn out, we decided to use hot isostatic pressure acid formation and plasma spraying to replace worn tools.

It has been found that it is possible to completely repair it by electron beam welding, etc., and that a significant reduction in tool consumption can be achieved.

3Cr-INi system or 17C known as rolling tool material
When a tool made of r-2W material is coated with Mo, which has excellent thermal fatigue properties, the base material itself becomes hot due to the good thermal conductivity of Mo, and the strength of the tool decreases rapidly. In addition, the coating layer tends to peel off due to the difference in thermal expansion between the base material and the coating layer, making it difficult to withstand long-term use.

According to the inventors' research, from the above-mentioned point, the base material and
□ It is necessary to have a material with a high melting point and □ a small decrease in strength even in a high temperature range of 1000° C. or higher, and from this point of view, alloys of Mo701 or higher, ceramics, etc. are preferable.

When Mo alloy is used as the base material, Mo 7 (H or less)
□When combined, the melting point is 2000°C or less, and the high temperature strength is also sufficient.

When repairing a plug made of an alloy or ceramic that has been used once, Mo is the best repair material, but there is no problem with Mo alloys.
1, and since the thermal expansion of the base material was small compared to ceramics, no peeling occurred during rolling.

As a result of various studies on the method of repairing plugs using Mo as a repair material, the inventors found that as shown in Fig. For example, it is preferable to use a repair method in which a steel plate capsule 3 is sealed with an electron beam or the like in a vacuum, and then hot isostatic pressing is performed.

When using this repair method, some machining may be required after the surface layer is joined.

The capsule used in the repair process is made from a steel plate with good deep drawability and has a similar shape to the plug.

The conditions for hot isostatic pressing of Mo include a high temperature of 1350°C or higher, and 1.
Good repair was possible due to the synergistic effect of the application of high pressure of 000 Kgf/cra' or more.

Since the bonding between the base material and the restoration material by hot isostatic pressing as described above is diffusion bonding, metal atoms move back and forth at the interface, the base material and the restoration material are completely integrated, and even the growth of metal crystal grains occurs. do. Furthermore, since MO powder can be used as a repair material, it is advantageous in terms of cost.

The inventors investigated other repair methods and found that metal spraying using plasma and overlay welding using electronic heating 1 are also applicable.

The most suitable plasma spraying method was low-pressure plasma spraying, which has a long flame and provides stable spraying. Inventor Kasa adjusts the thickness of the coating layer by thermal spraying to 0.000000000000000 depending on the degree of repair.
As a result of repairing the thickness in the range of 5 to 2.0 mm, good results similar to those obtained by hot isostatic pressing were obtained.

On the other hand, the repair method that uses electron beam overlay processing is
Because the processing was carried out in a vacuum, there were no impurities or pores, and the results were comparable to those achieved by low-pressure plasma spraying. When using this repair method, surface grinding is required after overlay processing.

As mentioned above, good durability has been obtained with each of the repair methods, but which repair method to adopt should be determined by taking into account the state and extent of wear and tear, cost, etc.

(Example) Examples are shown below.

Example 1: (1) Material Mo (solid)/Repair material Mo (
Powder) (2) Hydrostatic pressure conditions for 8 hours Temperature 1350°C 1 Pressure 1200 Kgf/cIIJ,
Time 3) 1r, pressure medium A "gas (3)
2) Thermal spraying method Low-pressure plasma spraying (carrier gas Ha + Nx) (3) Thermal spraying thickness 1.2 mm Example 3: (1) Material Mo (solid) / Overlay material Mo (
2) Overlay method: Electron beam (3) Overlay thickness: 1.5 m+s The repaired plugs that were used once and worn out, as well as the proper plugs (3Cr-INi black scale treatment), were tested under the following test conditions. Model elongator rolling was performed and evaluated.

Test conditions ■Rolled material 5US304 (18Cr-8N
i) ■Bus schedule Jl/75φX14.2
5tX 5001 75φX 5tX 1200J1 ■Plug diameter 60φ Table 1 Test results As is clear from Table 1, the repaired plugs have the same high durability as new plugs.

(Effects of the Invention) As stated above, if repaired and reused as in the present invention, even an expensive MO plug can be recycled repeatedly, achieving the same basic unit as the current proper and having a long life. The effects are significant, such as stabilizing operations and improving internal quality.

[Brief explanation of drawings]

FIG. 1 is a diagram showing the shape of a rolling tool when the method for repairing and reusing a rolling tool according to the present invention is carried out by hot isostatic pressing. ■...Plug, 2...Ma grain powder 3...Capsule.

Claims (4)

[Claims] (1) Mo70 that was once subjected to rolling and was worn out or damaged
A method for repairing and reusing a rolling tool, characterized in that the rolling tool for seamless steel pipes containing % or more is repaired and reused by overlaying the same component material on the surface. (2) A worn or damaged seamless steel pipe rolling tool containing 70% Mo or more is repaired by diffusion bonding powder of the same composition by hot isostatic pressing. Method for repairing and reusing the rolling tools described. (3) A method for repairing and reusing a rolling tool according to claim 1, wherein the surface of a worn or damaged rolling tool for seamless steel pipes is overlaid with a material of the same composition by thermal spraying. (4) A method for repairing and reusing a rolling tool according to claim 1, wherein the surface of a worn or damaged rolling tool for seamless steel pipes is overlaid with a material of the same composition by welding with a high-energy beam.