JPH0228401B2 - - Google Patents

Description

[Detailed description of the invention] [Industrial application field]

The present invention is a tool used when manufacturing seamless steel pipes by rolling. Concerning improvement of guide show.

[Conventional technology]

The guide shoe for pipe making is as shown in Figure 1.
In the process of pushing the plug 2 into the steel material 5 to make a hole, the tool 1 presses down the steel material from the outside, which is rotated at high speed by the rolls 3 and 3, so its surface is not only subject to a large amount of friction, but also has a strong A thermal shock is applied. The temperature of the guide shoe is increased to approximately 900°C due to contact with the hot work material, while the temperature of the guide shoe 1 and roll 3
Because it is constantly water-cooled, the temperature drops to approximately 150℃ after the processed material passes through. Steel material 5-1
This temperature change is applied repeatedly each time a piece is processed. Conventionally, the material for this guide shoe was 24Cr-3Ni steel (composition:
1.7C−0.5Si−0.7Mn−3Ni−24Cr), 35Cr−
35Ni steel (1.2C−1.0Si−0.6Mn−5Cu−35Ni−
High alloy steel such as 35Cr-3Mo) is used. However, with the recent trend toward higher alloys of rolled materials and harsher rolling conditions, guide shoes made from these existing materials have become unsatisfactory. The main problems are the lack of wear resistance, the progression of cracks starting from cracks caused by heat checks, that is, thermal shock, and the seizure of the tube material to the guide shoe. Among these, some improvement is possible by optimizing the alloy design of the guide shoe material and heat treatment conditions. However, this is a bigger problem, especially in the current situation where there are many tube materials that are difficult to roll, and seizure tends to occur frequently. If the pipe material seizes on the guide shoe, spiral-shaped flaws will occur on the surface of the steel pipe, resulting in a defective product, so this must be avoided as much as possible.

[Problems to be solved by the invention]

The present invention has been made with the aim of solving these problems, and aims to provide a guide shoe for pipe making that has improved wear resistance and seizure resistance, and has excellent cracking resistance.

[Means to solve the problem]

The guide shoe for pipe making of the present invention has a C content of
Austenite type, ferrite type, less than 0.5%
The base material is heat-resistant steel with a mixed structure, and the surface in contact with the pipe material has a hardness at 900℃.
Manufactured from a material with built-up Co-based alloy of Hv190 or more and 250 or less. The thickness of the build-up is preferably at least 4 mm.

[Effect]

In the course of research toward this objective, the present inventors first discovered that when a heat check occurs due to the above-mentioned thermal shock in a conventional guide shoe, it
I learned that large cracks tend to occur when the cracks develop to a depth of 40 to 50 mm, and that both initial cracks and large cracks progress along primary or eutectic coarse carbides. In order to improve wear resistance, it is effective to use high carbon steel and generate carbides, but this is incompatible with cracking resistance and does not improve tool life. However, materials such as stellite, which is known as a hard alloy, have poor toughness and ductility, and are easily damaged by impact even when used as guide shoes. In view of these facts, the inventors of the present invention came up with the idea of manufacturing the guide shoe, which was conventionally made of a uniform material, for the surface layer that contacts the pipe material and the base material that supports it, using different materials. did. In addition, it was considered appropriate to provide the surface layer by welding overlay onto the base metal. Therefore, in order to determine the material that should carry the surface layer, we conducted a high-temperature wear test at 900°C on the following overlay materials. The test method was conducted in accordance with the Ohkoshi method using a rotating disk-shaped test piece in which build-up material was welded to a rotating disk under the conditions of a load of 3 kg/mm ² and a sliding distance of 500 m.

[Table] The degree of wear of each overlay material is expressed as the rate of decrease in the diameter of the rotating disk, and is shown in relation to its hardness at 900°C as follows.

[Table] From this result, the material for the surface layer should be heated to 900℃.
It was found that wear resistance is sufficient if the hardness is Hv190. The hardness of hard alloys in practical use is up to Hv250, but those within this range may be used. Specifically, “Stellite No. 1, No. 6,
Commercially available Co-based alloys such as No. 12, No. 156, No. 157, and No. F are useful. If carbon steel or low-alloy steel is used as the base material, it will have poor oxidation resistance when exposed to high temperatures, and if stainless steel is used, it will lack rigidity. Although tool steel is expensive, it has poor oxidation resistance. Taking these into consideration, we decided to use heat-resistant steel. Regarding the alloy composition of heat-resistant steel, it is intended to increase the resistance to cracking.
Tests have been conducted to determine the C content that does not form harmful carbides, and it has been found that the upper limit should generally be 0.5%. In the case of two-phase systems that are ferritic, austenitic, or a mixture of these structures, the amount of carbides formed is uniquely determined by the C content, and if it is 0.5% or less, giant carbides that impair toughness will not be formed. This was also confirmed. If the base material is autesnitic, ferrite, or two-phase, a thickness of about 4 mm is sufficient for the build-up. On the other hand, if you try to use martensitic heat-resistant steel as the base material, quench cracking will occur when the temperature reaches the region where it transforms into austenite.
It is necessary to make the meat layer thick so that it does not get heated above 700℃. The built-up surface is given the shape of the guide shoe surface by polishing. Example 1 Base material: C: 0.3%, Si: 1.0%, Mn: 0.8
%, Ni: 18% and Cr: 24% is cast and used as it is, and the surface in contact with the pipe material is undercoated with mild steel underlay material, and then "Stellite" No. .12, that is, C: 1.3%, Si: 0.6%, Mn: 0.6%, Cr:
A heat-resistant cobalt alloy containing 30.3% and 8.1% W, with the remainder being Co, was heated to 5 mm using a gas burner.
Thickly filled with meat. The pipe manufacturing guide shoe manufactured by polishing has high wear resistance and can be used without seizure or large cracks, and is comparable to the current high Ni-high Cr product (C: 1.2%, Si: 1.0%, Mn: 0.6%, Cu: 5%,
Containing Ni: 35%, Cr: 35%, and Mo: 3.2%, the balance being substantially Fe), it exhibited about 5 times the lifespan. Example 2 Base material: C: 0.2%, Si: 0.7%, Mn: 0.8
% and Cr: Austenite containing 25%
Ferrite duplex chromium steel was used as cast, and the overlay materials were C: 1.9%, Si: 0.3%,
Using a band-shaped electrode containing 0.4% Mn, 25.7% Cr, and 8.6% W, with the remainder being Fe, it was built up to a thickness of 4 mm by hand arc welding. This guide shoe also had performance similar to that of Example 1, and exhibited a lifespan approximately 4.5 times longer than that of the current guide shoe.

[Comparative example]

Carbon steel (martensitic) containing C: 0.3%, Si: 0.5% and Mn: 0.6% was cast, and "Stellite" No. 11, that is, C: 1.4, was cast onto the normalized base material. %, Si: 0.8%, Mn: 0.7%,
A cobalt alloy containing 28.4% Cr and 7.9% W with the balance being Co was built up to a thickness of 5 mm using a gas burner. Although this guide shoe had good wear resistance and seizure resistance, quench cracking occurred in the base material.
The lifespan was the same as that of conventional products.

【Effect of the invention】

Since the pipe-making guide shoe of the present invention has a base material part and a surface layer part made of different materials, the surface that contacts the pipe material has good wear resistance and seizure resistance, and the present invention has high cracking resistance. Therefore, it can be used for difficult-to-roll materials and has a longer lifespan than conventional products. Although the manufacturing period is longer, the cost can be reduced because the expensive alloy is limited to the surface layer.

[Brief explanation of drawings]

FIG. 1 is a conceptual cross-sectional view showing a mechanism for manufacturing seamless steel pipes by rolling. FIG. 2 is a sectional view showing the structure of the guide shoe for pipe manufacturing according to the present invention. 1...Guide shoe, 2...Plug, 3...Roll, 5...Steel material, 11...Base metal part, 12...
Meat portion.

Claims (1)

[Claims] 1 Austenitic with a C content of 0.5% or less,
A guide shoe for pipe making made of a base material of heat-resistant steel having a ferrite-based or mixed structure thereof, and a Co-based alloy with a hardness of Hv 190 to 250 at 900°C overlaid on the surface in contact with the pipe material.