JPS59143079A - Manufacture of material for pipe forming tool - Google Patents

Abstract

PURPOSE:To obtain the titled material having superior wear resistance even at high temp. by nitriding a cast steel contg. a specified amount of Nb or V besides prescribed amounts of C, Si, Mn, Cr and Ni after shaping and by forming oxide scale. CONSTITUTION:A molten steel contg., by weight, 0.020-2.0% Nb and/or 0.020- 2.0% V besides 0.20-0.60% C, 0.10-2.0% Si, 0.30-2.0% Mn, 1.0-6.0% Cr and 0.50-6.0% Ni is cast. The cast steel is finished to a prescribed shape, the surface of the cast steel is nitrided at 500-1,100 deg.C up to >=10mum depth, and oxide scale is formed on the nitrided surface at 900-1,250 deg.C. Thus, the wear resistance of the material for a pipe forming tool at high temp. can be remarkably improved, and the life of the material can be considerably prolonged.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a method of manufacturing tool materials for pipe making, and in particular to forming plugs such as piercers, elongators and reelers used in the manufacture of seamless steel pipes, as well as mandrel bars and guide shoes. The present invention seeks to advantageously improve the high-temperature wear resistance of various tool materials.

The manufacturing method for seamless steel pipes involves punching a round copper piece or square steel piece using the Mannesmann method or press method to create a hollow material, and then elongating this hollow material using a rolling machine such as an elongator, plug mill, or mandrel mill. The method is common.

In each step of manufacturing such seamless steel pipes, tool materials such as forming plugs and guide shoes are exposed to severe abrasive environments at high temperatures.

Therefore, improving the wear resistance of this type of tool material and extending its life is one of the most important issues in the production of seamless steel pipes using the above process. In recent years, the importance of aluminum alloys has become more and more important as increased production and higher alloys are desired.

The present invention meets the above-mentioned requirements and aims to propose an advantageous method for manufacturing a pipe-making tool material that has excellent wear resistance even under high temperatures.

By the way, the most common means to improve the wear resistance of materials at high temperatures is to increase the high temperature strength of the materials, and for this purpose C1Cr, Mo and W
It is known that addition of alloying elements such as However, when these alloying elements are added, as the amount of addition increases, the thermal conductivity of the material generally deteriorates and the melting point decreases, so it is necessary to apply a treatment to improve high-temperature strength by adding alloying elements to pipe-making tool materials. There were limits to this.

In other words, if a product such as a plug for molding is used in constant contact with a high-temperature processed material and has poor thermal conductivity, the heat input from the processed material will be concentrated on the surface, causing the temperature of only the surface to decrease. If the melting point increases significantly and the melting point decreases, the surface tends to soften, resulting in severe surface wear. For this reason, the amount of alloying elements added was limited, and therefore there was a limit to the increase in high temperature strength.

In particular, in piercers and elongators, although the rolling load is smaller than that in plug mills,
The deformation temperature of the treated material is high (and the thickness of the treated material that comes into contact with the plug during 7 holes or expansion is larger than the plug diameter, so the amount of heat input to the plug is large.

Therefore, current plug materials for piercers and elongators are focused on not reducing thermal conductivity rather than high-temperature strength, and therefore have low alloy compositions.

However, as mentioned above, such current materials do not have sufficient high-temperature strength and also have poor surface scale supporting properties, so they are not suitable for the recent production efficiency improvement and high alloying of seamless steel pipes for oil wells. It is becoming impossible to deal with it any longer.

Therefore, the inventors conducted extensive research to develop a new tool material in consideration of the above points, and found that a predetermined amount of C, S
In addition to i, Mn, Cr and N1, Nb or V
After finishing the cast steel to which an appropriate amount of at least one selected from among these is added, it is subjected to nitriding treatment and oxide scaling treatment to (1) solid solution harden with N, Cr, Nb, and (2) The surface layer is hardened without deteriorating thermal conductivity due to the precipitation hardening effect with / or We have found that this is an improvement over the case where oxide scale treatment is applied alone.

This invention is derived from the above findings.

In other words, in this invention, C: 0.20 to 0.60% by weight, Si: 0.10 to 2.0% by weight, Mn: 0.80 to 2.0% by weight! -%, Cr: 1.
(1 to 6.0% by weight and Ni: 0.50 to 6.0
Nb: 0.020 to 2.0 wt% and V: 0
．． Molten steel containing at least one selected from 0.020 to 2.0% by weight is cast, and then finished into a predetermined shape.
The above-mentioned problem is solved by performing a surface nitriding treatment to give a nitriding depth of 10 μm or more in a temperature range of 900°C to 1250°C, and then performing an oxide scale formation treatment in a temperature range of 900 to 1250°C.

This invention will be specifically explained below.

First, the reason why the basic components in this invention are limited to the above range will be explained.

C: 0.20-0660% by weight (hereinafter simply expressed as %)
C is useful as an element that improves high-temperature wear resistance by forming carbides, but if it is less than 0.20%, the effect is small, while if it exceeds 0.60%, the melting point decreases and the wear resistance is adversely affected. Since it deteriorates properties, it is limited to a range of 0.20 to 0.60%.

Si: 0.10% to 0.0% Si effectively contributes to the generation of scale with good adhesion to the base metal alloy, but 0.10% to 0.0% If it is less than 10%, the effect will be small, while if it exceeds 2.0%, the high temperature strength will decrease, so it was limited to a range of 0°10 to 2.0%.

Mn: 0.80-2.0% Mn effectively contributes to increasing high temperature strength, but 0.80% to 2.0% Mn effectively contributes to increasing high temperature strength.
If it is less than 80%, the effect will be small, while if it exceeds 2.0%, the thermal conductivity will deteriorate and the high temperature wear resistance will deteriorate, so the lower limit was set to 0.80% and the upper limit was set to 2.0%.

Cr: 1.0 to 6.0% Cr produces scale on the surface that has good adhesion to the base metal alloy and has good heat insulation properties, and also forms Cr carbides to increase high-temperature strength and further undergo nitriding treatment. Sometimes it forms Cr nitride and contributes effectively to hardening the surface layer, but 1.0
If it is less than 1.0%, the effect will be poor, while if it exceeds 6.0%, the amount of scale generated will decrease, and the thermal conductivity will deteriorate, leading to deterioration of high-temperature wear resistance. limited to a range.

Nb, V: 0.020-2.0% Nb and ■
Both are particularly important in this invention because they increase high-temperature strength by forming carbides and effectively contribute to forming nitrides and significantly hardening the surface layer during nitriding treatment, but if it is less than 0.020%, the 0.0 because it is not effective
20% or more is required, but if it exceeds 2.0%, the effect is saturated and it is also expensive, so the upper limit was set at 2.0%.

In addition, the above-mentioned C, Si, Mn, Cr, Ni,
In addition to Nb and one or two of the basic components, this invention further contains Zr and Ca as required.

A combination with one or two of Mg and Y, or one or more selected from Mo, W, Co, Cu1he, B and S can be simultaneously contained within the following range. can. The reasons for limiting these additive elements are as follows.

Zr: 0.050-5.0% Zr has good adhesion to the steel base and has good heat insulation and resistance by adding one or more selected from the following Ca + Mg and Y. It is useful as an element that generates an oxide scale containing stabilized zirconia that has excellent wear resistance, but its effect is small if it is less than 0.050%.
On the other hand, if it exceeds 5.0%, the amount of scale formed will decrease significantly and high temperature wear resistance and purity will deteriorate, so 0.050 to 5.0%
% range.

Ca, Mg, Y: 0.003<Ca/Zr
<:0.06.

0.002 < Mg/Zr <0.04, 0.00
5 <y/zr <0.10Ca, Mg, Y is 1. As mentioned above, when added in combination with Zr, it effectively contributes as an element that generates oxide scale that has good adhesion to the base steel and has excellent heat insulation and wear resistance, but the amount of these additions is ca/zr (0
,00B, Mg/Zr (0,002, Y/Zr (0
,005, it is difficult to obtain a scale with good adhesion to the base steel, and also Ca/Zr) o, oe, Mg/Zr)
0.04, y/zr:> o, to, the adhesion tends to decrease, and these are also expensive, so o, ooa≦Ca/Zr≦0.006.0, respectively.
002≦Mg/Zr≦0.04.0.005≦Y/Zr
The range was limited to ≦0.10.

Mo: 0.50-5.0% Mo is added as an element that increases high-temperature strength through solid solution hardening and carbide formation, but if it is less than 0.50%, the effect is poor, so the lower limit is set at 0.50%. On the other hand, 5.0%
If it exceeds 5.0%, the amount of scale formed will decrease significantly and high-temperature wear resistance will deteriorate, so the upper limit was limited to 5.0%.

W: 0.50-5.0% W effectively contributes to increasing high-temperature strength through solid solution hardening and carbide formation, but less than 0.50%, the effect is small, while more than 0.0% Since coarse carbides are formed and the toughness is deteriorated, the content is limited to 0.50 to 5.0%.

Co: 0.50-5.0% Co is useful for increasing high-temperature strength through solid solution hardening, making the scale denser, and improving the adhesion between the scale and the steel base, but less than 0.50%. However, if it exceeds 5.0%, the amount of scale generated tends to decrease and high-temperature wear resistance tends to deteriorate, and it is also expensive, so it is limited to a range of 0.50 to 5.0%. did.

Cu: 0.10-3.0% Cu effectively contributes to improving the adhesion between the scale and the steel base, but if it is less than 0.10%, it has no effect (,
On the other hand, if it exceeds 8.0%, a Cu-enriched layer will form on the surface layer, lowering the melting point of this part and deteriorating high-temperature wear resistance.
．． It was limited to a range of 10 to 3.0%.

Ae: 0.020 to 2.0% l effectively contributes to producing scale that has good adhesion to the steel base and has excellent heat insulation properties, but 0.020%
If it is less than 2.0%, the effect will be small, whereas if it exceeds 2.0%, the amount of scale formed will be significantly reduced and high temperature wear resistance will be deteriorated, so the content was limited to a range of 9.020 to 2.0%.

B: 0.0020-0.50% B is a useful element that increases high-temperature strength and improves surface lubricity by forming BN in the nitriding treatment after final forming, but if it is less than 0.0020%, The effect is small, and if it exceeds 0.50%, thermal shock cracking will occur, so the content was limited to a range of 0.0020 to 0.50%.

S: 0.020-0.80% S contributes effectively to increasing surface lubricity through the formation of sulfides, but less than 0.020%, the effect is poor, while more than 0.80% Since thermal shock cracking is likely to occur, it is limited to a range of 0.020 to 0.80%.

Next, a description will be given of the nitriding treatment and the oxide scale formation treatment, which are performed after the cast steel adjusted to the above-mentioned appropriate component composition is finished into a predetermined shape.

In this invention, Nb and/or 1-containing steel is subjected to nitriding treatment, followed by oxide scale formation treatment.
The surface layer is hardened by solid solution hardening and precipitation hardening of Cr%Nb and V, and a dense and adhesive oxide scale is formed on the N-enriched surface to improve wear resistance at high temperatures. Although the purpose is to extend tool life, if the thickness of the nitrided layer by nitriding treatment, that is, the nitriding depth, is less than 10 μm, the improvement effect is poor, so the nitriding depth needs to be 10 μm or more. Any of the gas nitriding methods, gas soft nitriding methods, liquid nitriding methods, and ion nitriding methods can be used as such desaturation methods, but in order to perform good nitriding, the treatment temperature should be 500 to 11
The temperature was limited to 00°C.

Following nitriding treatment (in oxide scale breaking treatment, if the heating temperature is less than 90°C, the amount of school produced is small, while if it exceeds 1250°C, many voids are generated in the scale, resulting in poor adhesion to the base alloy). decreases, so the processing temperature is 9
The temperature was limited to a range of 00 to 1250°C.

In addition, the thickness of the oxide scale layer containing Cr, which has good adhesion to the steel base, must be reduced to 2 to maintain satisfactory insulation properties.
It is advantageous to set the thickness to 0 μm or more, and for this purpose, it is desirable to maintain the temperature at an appropriate temperature for 80 minutes or more.

Embodiments of this invention will be described below.

Each cast steel having the chemical composition shown by symbols A-P in Table 1,
After being formed into a piercer plug, it was nitrided in an atmosphere of 3 g of NH under the conditions shown in Table 1, and then Co
3% CO2, 10% CO2, 4% CO2, and the balance N2, the oxide scale treatment was carried out under the same conditions shown in Table 1. Which nitriding depth is 40-160μm
Moreover, the thickness of the dense oxide scale layer containing Cr near the base iron was 200 to 250 μm.

Then, using each plug obtained, c: 0.25%
, Si: 0.25%, Mn: 1.28%, Ti
: tl, 020%, B: 0.0028%, remainder F
The drilling life of each plug when continuously drilling a carbon steel billet with a diameter of 207 mm with a composition of It is also listed in Table 1.

As is clear from the results shown in Table 1, all of the piercer plugs (coded A to O) obtained according to the present invention had an improvement of 8. It had ~4 times better drilling life.

In the above embodiments, the present invention was mainly applied to the manufacture of piercer plugs, but the same effects can be obtained when the present invention is applied to the manufacture of elongator gloves, mandrel bars, etc. It's confirmed.

Thus, according to the present invention, in the production of construction tool materials, wear resistance at high temperatures is significantly improved by increasing the hardness of the bottom surface of the material and forming an oxide scale with excellent heat insulation and adhesion. This can significantly extend the life of tool materials.

Claims (1)

[Claims] LC: 0.20 to 0.60% by weight, Si:
0.10-2.0% by weight, Mn: 0.30-2.0g%, Cr: 1
．． 0 to 6.0 wt% and Ni: 0.50 to 6
．． ．． 0% by weight, Nb: (1,020-2.0% by weight, and V:
Molten steel containing at least one selected from 0.020 to 2.0% by weight is cast, then finished into a predetermined shape, and then
1. A method for manufacturing a pipe-making tool material, which comprises performing a surface nitriding treatment to give a desired depth of 10 μm or more in a temperature range of 900 to 1250°C, and subsequently performing an oxide scale formation treatment in a temperature range of 900 to 1250°C.