JPS5920463A - Manufacture of material for tool for manufacturing seamless steel pipe - Google Patents

Abstract

PURPOSE:To obtain a material for the titled tool having superior wear resistance at high temp. and a remarkably long life, by forming a BN layer on the surface of a worked product of an alloy having a specified composition consisting of C, Si, Mn, Cr, Ni, Mo and Fe. CONSTITUTION:A cast alloy consisting of, by weight, 1.0-2.0% C, 0.10-1.5% Si, 0.30-2.0% Mn, 11-22% Cr, 0.60-8.0% Ni, 0.50-5.0% Mo and the balance Fe with inevitable impurities or further contg. one or more among 0.70-4.0% W, 0.50-5.0% Co, 0.10-2.0% V, 0.10-2.0% Nb, 0.020-2.0% Zr, 0.50-2.0% Al and 0.010-1.0% B is worked and borided to form a borided layer of >=100mum thickness. A nitrogen enriched layer of >=100mum thickness is then formed by surface nitriding to obtain a material for the titled tool having high heat conductivity, high strength at high temp. and surface self-lubricity.

Description

[Detailed description of the invention] The present invention relates to a method for manufacturing a tool material for manufacturing seamless steel pipes,
In particular, the present invention relates to a method for manufacturing a tool material that has excellent wear resistance at high temperatures and has an extremely long life.

The common method for manufacturing seamless steel pipes is to punch round or square steel pieces using the Mannesmann method or press method to create a hollow material, and then stretch this hollow material using a rolling machine such as an elongator, plug mill, or ike mandrel. It is true.

In each step of manufacturing this seamless steel pipe, the forming plug and guide shoe are exposed to severe abrasion conditions at high temperatures. Therefore, manufacturing tools with excellent wear resistance at high temperatures and extending tool life is one of the important issues in the production of seamless steel pipes using the above method. Its importance is becoming even greater when an increase in the amount of steel and high alloying are desired.

Among these, the present inventors have focused on extending the life of plugs for rolling in plug mills and have conducted experimental studies on all types.

In plug mill rolling, the raw tube temperature is usually 950 to 1
The rolling load is about 150°C, the rolling load is about 100 to 2501 degrees, and the rolling speed is about 3 m/sec. At this time, the plug surface contacts the inner surface of the raw tube under high temperature and high pressure, and since the plug itself does not rotate, the plug undergoes complete sliding wear.

Plugs used under such conditions are first required to have high strength at high temperatures.

It is well known as a material with relatively high high temperature strength and low cost (C,
Iron-based alloys containing appropriate amounts of Cr, Mo, W, Nb, V, etc. are typical, and are conventionally used as plug materials for plug mill rolling (1.3-1.5)%C-17%Cr-2. %
W steel or (1,3-1.8)%C-24%Cr-3%N
High carbon steel, high Cr cast steel, etc. are used. However, plugs made of this material cannot cope with the shortening of rolling intervals associated with the recent increase in production of seamless steel pipes for oil wells and the increase in rolling load due to higher alloys, and plug wear becomes a major manufacturing problem. ing.

Ni, W, Co to increase the high temperature strength of tool materials
.

Ni by increasing the amount of Mo, etc., and adding At, Ti, etc.
-At, Ni-Ti intermetallic compounds may be used for precipitation hardening, and Ni-based alloys may also be used. However, the addition of large amounts of these elements causes a significant decrease in thermal conductivity, and when plugs made of these materials are rolled in a plug mill, heat from the deformed raw tube itself and heat generated by rolling flow into the plugs. case,
This heat is difficult to transfer to the inside of the plug, and the temperature of the surface layer increases significantly, resulting in a decrease in strength. In addition, for iron-based alloys or Ni-based alloys such as Cr, Ni%CO%MO, etc., which have a high oxidation scale on the plug surface layer, which works to suppress the inflow of heat from the deformed element tube, heating at high temperatures in an oxidizing atmosphere is sufficient. Not generated. Therefore, during plug mill rolling, plugs made of such alloys are subject to more wear than conventional plugs.

The object of the present invention is to solve the above-mentioned problems of the prior art.

It is an object of the present invention to provide a method for manufacturing a tool material for manufacturing seamless steel pipes that has excellent wear resistance at high temperatures and has a long life.

The inventors of the present invention have repeatedly conducted experiments and found that the characteristics that a plug for plug mill rolling should have are high strength at high temperatures, good thermal conductivity, good oxide scale adhesion at high temperatures, and good lubrication on the surface of the plug. By applying a treatment that imparts surface self-lubricating properties to a material that has the same thermal conductivity and high-temperature strength as conventional materials, we have achieved a significantly longer lifespan than conventional materials. It was possible to produce long tool materials.

The present invention consists of the following two inventions. The gist of the first invention is as follows. In other words, C in terms of weight ratio
: t, o~2.0%% Si: 0.10~1.5%, M
n: 0.30-2.0%, Crtll ~22
1%, Ni: 0.60-8.0%, Mo+0.50-5
．． In the method for producing a tool material for manufacturing a seamless steel pipe from a cast alloy containing 0% Fe and the remainder consisting of Fe and unavoidable impurities, the thickness of the post-forming filler layer of the cast alloy is 10%.
An immersion treatment step to make it 0 μ or more.

Following the immersion treatment step, the thickness of the nitrogen-enriched layer'
1. A method for producing a tool material for producing seamless steel pipes, comprising: a surface nitriding step to increase the thickness to 100μ or more.

The gist of the second invention is that in addition to the same basic composition as the first invention, vv: o, 7o to 4.0%%Co +0.50
~5.0%, V:o, to ~2.0%, Nbjo, 10
~2.0%, Zr: 0.020~2.0%, At=
A cast alloy containing one or more selected from 0.050 to 2.0%, B: o, o1o to 1.0%, and the balance consisting of Fe and inevitable impurities, as in the first invention. This is a manufacturing method in which dipping treatment and nitriding treatment are performed using the method described above.

Next, the reasons for limiting the components of the present invention will be explained.

C: C is added as an element that improves high-temperature wear resistance by forming carbides such as Cr and Mo, but if it is less than 1.0%, the effect is small, and if it exceeds 2.0%, cracking due to thermal shock may occur. Since this tends to occur, it is limited to a range of 1.0 to 2.0%.

Si: Si is added to increase high temperature strength.

If it is less than 0.10%, the effect will be small (if it exceeds 1.5%, the high temperature strength will decrease, so 0.10 to 1.5%)
limited to the range of

Mn: Mn is added to increase high temperature strength.

If it is less than 0.30%, the effect will be small, and if it exceeds 2.0%, the thermal conductivity will deteriorate and the temperature wear resistance will deteriorate, so the lower limit was set to 0.30% and the upper limit was set to 2.0%.

Cr: Cr is added to increase high-temperature strength by forming carbides, but if it is less than 11%, the effect is not sufficient, and 22
If it exceeds 11 to 22%, the high temperature strength will decrease.
% range.

Ni: Ni is added to improve high-temperature strength and toughness, but if it is less than 0.60%, the effect is small, and if it exceeds S and O%, thermal conductivity deteriorates and high-temperature wear resistance deteriorates. It was limited to a range of 0.60 to 8.0%.

MO = MO is effective in increasing high temperature strength through solid solution hardening and carbide formation, but if it is less than 0.50% it has no effect, so the lower limit 'io is set at 50%, and if it exceeds 5.0%, high temperature Since the effect on strength is saturated and it is also expensive, the upper limit was set at 5.0%.

The above-mentioned limited amounts of C, Si, Mn, Cr, Ni, and Mo constitute the basic composition of the tool material for producing seamless steel pipes of the present invention, and additionally W, Co, V, Nb, and Zr.

The object of the present invention can be more effectively achieved even in a rolling tool material containing one or more of At and Bf at the same time within the following limited amounts. The reasons for these limitations are as follows.

W: W has the effect of increasing high-temperature strength through solid solution hardening and carbide formation, but if it is less than 0.70%, the effect is small, and if it exceeds 4.0%, it forms coarse carbides and deteriorates toughness. It was limited to a range of 0.70 to 4.0%.

Co + CO has the effect of increasing high temperature strength, but if it is less than 0.50%, the effect is small, and if it exceeds 5.0%, the effect on high temperature strength is saturated and it is expensive, so it should be 0.50 to 5.0%.
% range.

■ = ■ has the effect of increasing high temperature strength by forming carbides, but if it is less than 0.10%, the effect is saturated, and if it exceeds 2.0%, the effect is saturated and it is also expensive, so 0. 1
It was limited to a range of 0 to 2.0%.

Nb: Nb helps to significantly increase high-temperature strength through carbide formation, but its effect is small when it is less than 0.10%;
0% or more is required, but if it exceeds 2.0%, the effect will be saturated and it will be expensive, so the upper limit was set at tl-2.0%.

Zr: Zr1j has the effect of increasing high temperature strength, but 0.020
If it is less than 2.0%, the effect will be small, and if it exceeds 2.0%, the effect on high temperature strength will be saturated and it will be expensive.
It was limited to a range of 2.0%.

At: Has the effect of increasing high temperature strength through the precipitation of intermetallic compounds of At#'iNi-AL, but if it is less than 0.50%, the effect is small. If it exceeds 2.0%, it will conversely reduce the high temperature strength. Therefore, it was limited to a range of 0.50 to 2.0%.

B: B is added to increase high-temperature strength, but if it is less than 0.010%, its effect will be small, and if it exceeds 1.0%, it will significantly deteriorate thermal shock resistance, so it should be in the range of 0.010 to 1.0%. Limited.

Next, a description will be given of the immersion treatment and subsequent nitriding treatment of a cast alloy having the above-mentioned limited components and molded. Immersion treatment and nitriding treatment include BN' on the plug surface.
(z formation and significantly improves surface lubricity, which is the main focus of the present invention.

Test material AI'li7 with the chemical composition shown in Table 1. Plug mill rolling of a large number of samples with different soaking layer thickness and nitriding layer thickness by changing the soaking treatment and nitriding treatment times shown in Table 1. The lifespan of these plugs was investigated.

On the other hand, for comparison, a plug was also manufactured from sample material A2, which is a conventional material with the chemical composition and processing shown in Table 1, and its lifespan was investigated.

A large number of test materials A1 are used, assuming that the life of the plug of test material A2 is 1.
The relationship between the thickness of the immersion layer, the thickness of the nitrogen enriched layer, and the life ratio of sample material A1 is shown in the attached drawing.

The numbers in the figure indicate the life ratio.

As is clear from the accompanying drawings, when the thickness of the immersion layer and the thickness of the nitrogen enriched layer are less than 100μ.

It is very effective in extending the life of plugs for plug mill rolling.

Therefore, in the present invention, both the thickness of the soaking layer and the thickness of the nitrogen-concentrated layer are limited to 100 μm or more.

The immersion treatment may be either a liquid immersion treatment or a solid immersion treatment using a boride and a reaction accelerator, and the boride and the reaction accelerator are not particularly limited. The nitriding treatment may be gas nitriding, liquid nitriding, or ion nitriding.

EXAMPLE The material of the present invention whose chemical composition is shown in Table 2 was soaked in a mixed molten bath of anhydrous sand and carborundum at 1050°C, and then nitrided in an NH atmosphere at 900°C. The treatment was carried out to produce plugs for plug mill rolling. The thickness of the sinking layer and the thickness of the nitrogen enriched layer are shown in Table 3.

Using a plug made of this invention material, the chemical composition is C:0.
22%, Si+0.25%, Mn:1
．． 30%, Ti: 0.020%, Elo, oozo
%, the lifespan was investigated when a carbon chain blank tube with a diameter of 249 mm and a wall thickness of 12.9 m was continuously rolled in a plug mill to a diameter of 244 m and a wall thickness of 9.9 mm. On the other hand, a comparative material having the chemical composition shown in Table 2 was subjected to oxide scale adhesion treatment and hardening treatment to produce a plug, and was continuously rolled under the same conditions as the above-mentioned inventive material to complete the life of the plug. investigated.

Inventive material A-1, assuming that the life of this comparison material J plug is 1.
The lifespan of the plug is shown and is also shown in Table 3 as a plug lifespan ratio.

As is clear from Table 3, the plug life of the material of the present invention is significantly longer than that of the comparative material.

As is clear from the above examples, the present invention limits the components of the tool material for seamless steel pipe production, and performs a dipping treatment to a thickness of 100 μm or more and a surface nitriding treatment to a thickness of 100 μm or more. We were able to produce a tool material for seamless steel pipe manufacturing that has excellent wear resistance and a significantly long tool life.

The present invention has mainly been described with respect to a plug for plug mill rolling in a seamless steel pipe manufacturing process.

The same process can also be widely applied to piercers, elongator guide shoes, or elongator plugs.

[Brief explanation of the drawing]

The attached drawing is a correlation diagram showing the influence of the thickness of the immersion layer and the thickness of the nitrogen enriched layer on the plug life ratio. Agent Takeshi Nakaji Yuichi is '7) @/) Tsukisaku μ)

Claims (1)

[Claims] (1) Weight ratio: C:1. O~2.0%, Si
: 0.10~1.5%, Mn: 0.30~2.0
%, Cr: 11-22%, Ni+0.60-8.0%,
A method for producing a tool material for seamless steel pipe production from a cast alloy containing Mo + 0.50 to 5.0% and the balance consisting of Fe and unavoidable impurities, the thickness of the post-forming filler layer of the cast alloy An immersion treatment step in which the thickness of the nitrogen-concentrated layer is increased to 1-100 μm or more, and a surface nitriding step in which the nitrogen-concentrated layer is made to have a thickness of 1100 μm or more subsequent to the immersion treatment step. A method for producing a tool material for producing seamless steel pipes, comprising: C) Weight ratio: C:1. O~2.0%, Si:
0.10-1.5%, Mn + 0.30-2.0%
, Cr: 11-22%, NMo, 60-8.0%
, Mo: 0.50 to 5.01%, and W+0.
70-4.0%, Co i O, 50-5.0%, V
F6.10-2.0%, Nb10.10-2.0%, Z
r: 0.020~2.0%, Az: o, so~
A tool material for producing seamless steel pipes from a casting alloy containing one or more selected from 2.0%, s:o, and oto to 1.0%, with the balance consisting of Fe and inevitable impurities. In the manufacturing method, a dipping treatment step in which the thickness of the infiltration layer after forming the cast alloy is made to be 100μ or more, and a nitrogen enriched layer subsequent to the dipping treatment step is made to have a thickness of 100μ or more. A method for producing a tool material for producing seamless steel pipes, comprising: a surface nitriding process.