JP2000005895A - Plug for boring/rolling seamless steel pipe, and its manufacture - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a plug for boring/rolling a seamless steel pipe having an excellent durable life, and a manufacturing method thereof. SOLUTION: A clad layer of an alloy composed of, by mass %, 0.10% or less C, 30-45% Ni, 8-15% Cr, 3-7% Mo, 0.5% or less Al, 2-5% Ti, 0.010-0.050% B, and the balance of Fe and inevitable impurities, is overlaid on a rolling face of a plug for boring/rolling a seamless steel pipe by a plasma powdery welding method.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a seamless steel pipe piercing and rolling plug having an excellent service life and a method for producing the same.

[0002]

2. Description of the Related Art In the production of a seamless steel pipe by a rolling method, a steel blank heated to a predetermined temperature is pierced and rolled by a rolling machine called a piercer to obtain a hollow shell. The hollow shell is further processed into a seamless steel pipe through a process of reducing the wall thickness by a stretching rolling machine such as an elongator and adjusting the outer diameter by a finishing rolling mill.

[0003] A piercer generally includes a roll for rolling a rolled material and a drilling tool called a plug. In the piercing-rolling process, the piercing-rolling plug is surrounded by the rolled material heated to a high temperature, and is constantly pressed against the rolled material at a high pressure to cause friction. Further, since the processing time of piercing and rolling is long, the piercing and rolling plugs are used under severer operating temperature conditions than general hot forging tools, and are liable to wear and melt.

Conventionally, many attempts have been made to improve the life of piercing and rolling plugs by improving the material (for example, Japanese Patent Application Laid-Open Nos. 8-22587 and 9-259).
195002). Further, an oxide layer is formed on the surface of the piercing and rolling plug in advance by heat treatment, and the life of the plug is improved by its lubricating property (for example, Japanese Patent Application Laid-Open No. 8-193241). However,
As the material of the steel pipe to be rolled is further alloyed to have a higher resistance to high-temperature deformation, there is a growing demand for a longer life of the piercing and rolling plug.

[0005]

SUMMARY OF THE INVENTION An object of the present invention is to provide a plug for drilling a seamless steel pipe having an excellent service life and a method of manufacturing the same in view of the above situation.

[0006]

In order to achieve the above object, a seamless steel pipe piercing and rolling plug according to the present invention has a composition in mass%, C: 0.10% or less, and Ni: 30 to 4%.
5%, Cr: 8 to 15%, Mo: 3 to 7%, Al: 0.
5% or less, Ti: 2 to 5%, B: 0.010 to 0.0
It is characterized by having an overlay layer of an alloy consisting of 50%, the balance being Fe and unavoidable impurities.

Further, the method for producing a plug for seamless steel pipe piercing and rolling according to the present invention is characterized in that the rolled surface of the plug for seamless steel pipe piercing and rolling is formed by plasma powder welding to have a composition of mass% and C: 0.10% or less. , Ni: 30 to 45
%, Cr: 8 to 15%, Mo: 3 to 7%, Al: 0.5
%, Ti: 2 to 5%, B: 0.010 to 0.05
It is characterized in that an alloy powder comprising 0%, the balance Fe and inevitable impurities is build-up welded.

[0008]

DESCRIPTION OF THE PREFERRED EMBODIMENTS In a seamless steel pipe piercing and rolling plug according to the present invention, a build-up layer is formed as a rolled surface for piercing and rolling a steel material in direct contact with a steel billet to be rolled. Therefore, the overlay has a very important role in the service life of the piercing and rolling plug. Hereinafter, the reason for limiting the composition of the alloy forming the build-up layer (the build-up alloy) in the seamless steel pipe piercing-rolling plug of the present invention will be described.

C: 0.10% or less C forms a solid solution in the matrix and strengthens the alloy. However, in the present alloy system containing a large amount of elements having a strong tendency to form carbides, such as Ti, Mo, and Cr, carbides are formed due to excessive C content, which not only impairs the cleanliness of the alloy, but also increases the content of the active element in the alloy. Reduce the effect. Therefore, the upper limit of the C content is limited to 0.10%.

Ni: 30 to 45% Ni forms a matrix of the alloy together with Fe and forms a γ phase to impart high-temperature strength to the alloy. Further, an intermetallic compound is formed between Mo and Ti to improve the strength of the alloy. In order to exhibit these effects, it is necessary to contain at least 30% or more of Ni. However, even if it is excessively contained, the effect is saturated and the value of the alloy is simply increased, so the upper limit of the content is set to 45%.

Cr: 8 to 15% Cr is added to form a dense and highly adherent oxide on the surface of the alloy and to increase the oxidation resistance of the alloy. For that purpose, it is necessary to contain at least 8% or more. However, if the content is excessive, the alloy becomes brittle and the build-up layer is peeled off, thereby impairing the useful life of the plug. Therefore, the upper limit of the content is set to 15%.

Mo: 3 to 7% Mo is dissolved in a matrix or added to form an intermetallic compound with Ni to strengthen the alloy. For that purpose, it is necessary to contain at least 3% or more. However, if the content is excessive, the alloy becomes brittle and the build-up layer is peeled off, thereby impairing the service life of the plug.
%.

Al: 0.5% or less Al has an effective role in forming the γ-prime phase of Ni—Ti, and is added at a content of 0.5% or less.

Ti: 2 to 5% Ti is added to combine with Ni to form a γ-prime phase and strengthen the alloy. At least 2% for that
It is necessary to contain the above. However, if the content is excessive, the alloy becomes brittle and the build-up layer is peeled off, thereby impairing the service life of the plug. Therefore, the upper limit of the content is set to 5%.

B: 0.010% to 0.050% B is added to strengthen the grain boundaries of the alloy and increase the toughness of the alloy. For this purpose, it is necessary to contain at least 0.010% or more. However, if the content is excessive, the alloy is rather embrittled and the build-up layer is peeled off, thereby impairing the useful life of the plug. Therefore, the upper limit of the content is set to 0.050%.

With the chemical composition as defined above, the cladding alloy in the seamless steel pipe piercing and rolling plug of the present invention has excellent high-temperature strength. Also,
During use, a dense oxide film is formed on the surface layer of the build-up alloy, which is rich in adhesion and dense. Due to the lubricating action of this oxide film, wear and erosion of the plug for drilling a seamless steel pipe are reduced.

In the seamless steel pipe piercing and rolling plug of the present invention, the overlay layer is formed by plasma powder welding. Here, in the plasma powder welding method, a weld metal powder is blown into a plasma arc of an inert gas, and the weld metal is melted by high heat generated by the plasma arc, and droplets of the weld metal are melted by the pressure of the plasma arc. The material is carried to the build-up surface, where a build-up layer made of the deposited metal is formed. A thick build-up layer can be obtained by forming a multi-layer as needed.

According to this method, there is little dilution of the weld metal due to penetration of the base metal material, and it is easy to obtain a high-performance overlay metal. In addition, since the weld metal is in a powder form, there are advantages such as easy production and supply.

[0019]

EXAMPLE An outer peripheral surface of a 0.3% C-3% Cr-1% Ni steel plug excluding a tip R portion was provided with C: 0.03% by mass, N
i: 43.22% by mass, Cr: 12.01% by mass, M
o: 5.28% by mass, Al: 0.18% by mass, Ti:
A build-up layer was formed by plasma powder welding using an alloy powder having a chemical composition of 2.97% by mass, B: 0.015% by mass, and the balance being mainly Fe.

As the alloy powder, spherical powder of −60 mesh / + 250 mesh produced by the gas atomization method was used. In addition, the plasma powder welding was performed using argon as a plasma gas and a powder carrier gas, and a required overlay was formed by three-layer overlay welding. After the cladding, the plug was machined into a plug having a maximum outer diameter of 200 mm. The thickness of the build-up layer after machining was 8 mm. The plug was subjected to a piercing rolling test on an actual machine.

As a comparative material, 0.3% C-3% Cr-1
A plug having the same shape as that of the example was manufactured using% Ni steel.
In the comparative material, a scale having a thickness of about 500 μm was formed on the surface by heat treatment.

In the piercing and rolling test, the SUS410 steel billet was pierced with an outer diameter of 250 mm using a press roll type piercer.
The rolling was performed by rolling into a hollow shell having an inner diameter of 200 mm and a length of 18 m. Each time one billet was pierced and rolled, the surface of the test plug was inspected for wear, the life of the plug was determined based on erosion, abrasion, chipping, and the like, and the number of piercing and rolling until the plug life was reached was examined.

As a result of the piercing and rolling test, in the comparative material, erosion was caused by the average of six piercings and the steel became unusable. 38 hollow shells could be pierced and rolled without occurrence.

[0024]

As described above, according to the present invention, a plug for drilling a seamless steel pipe having an excellent service life and a method for manufacturing the same can be provided.

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Claims (2)

[Claims] 1. Composition:% by mass, C: 0.10% or less, Ni: 30 to 45%, Cr: 8 to 15%, Mo: 3 to 7%, Al: 0.5% or less, Ti: 2-5%, B: 0.010-0.050%, Plug for seamless steel pipe piercing and rolling characterized by having a build-up layer of an alloy comprising the balance of Fe and unavoidable impurities. 2. The composition having a mass% by plasma powder welding on the rolled surface of a plug for seamless steel pipe piercing and rolling.
And C: 0.10% or less, Ni: 30 to 45%, Cr: 8 to 15%, Mo: 3 to 7%, Al: 0.5% or less, Ti: 2 to 5%, B: 0. A method for producing a plug for piercing and rolling a seamless steel pipe, comprising overlay-welding an alloy powder consisting of 010 to 0.050%, the balance being Fe and unavoidable impurities.