JPS63259021A - Manufacture of nonmagnetic steel for drill collar combining high corrosion resistance with high strength - Google Patents

Abstract

PURPOSE:To manufacture the titled steel having always stable and superior homogeneity, ductility, and toughness by a simplified method, by specifying respective conditions of the rolling, etc., and also of ageing treatment of a steel having a specific composition which contains sufficient amount of Cr and Ni and in which C and N contents are reduced to minimum, respectively. CONSTITUTION:A steel which has a composition consisting of, by weight, <=2.0%, Si, <=2.0% Mn, 25-40% Ni, 18-30% Cr, 0.1-1.5% Al, 1.5-3.0% Ti, 0.0005-0.020% Ca, <=0.020% C, <=0.010% N, and the balance Fe and containing, if necessary, one or 2 >= kinds among <=3.0% Mo and <=0.5% each of Zr, Nb and V is used. This steel is subjected to (a) rolling or forging at <750 deg.C at >=5% draft and then to ageing treatment treatment at 650-850 deg.C, or to (b) rolling or forging at 750-850 deg.C at 5-10% draft and then to ageing treatment at 650-850 deg.C, or to (c) rolling of forging at 750-850 deg.C at <=10% draft.

Description

DETAILED DESCRIPTION OF THE INVENTION [Industrial Application Field] The present invention relates to a method for manufacturing a non-magnetic steel for drill collars that has excellent stress corrosion cracking resistance, strength, and toughness.

[Conventional technology]

A drill collar is a thick-walled steel pipe that is installed directly above a bit (a part equivalent to a drill bit for oil well drilling) to add load to the bit and increase drilling efficiency.An example of its dimensions is an outer diameter of 250 m@, The wall thickness is 70 mm, the length is 1 Om, and the yield strength is 60 mm as a general steel material for drill collars.
~80kyf/mm! A degree of elongation of 25% or more is desired.

In recent years, oil exploration has been moving deeper into the ocean or under harsh environmental conditions such as offshore oil fields, but as the exploration environment becomes more severe, there is a need for steel for drill collars to further improve its resistance to stress corrosion cracking due to chlorine ions. It has come to be.

JP-A-61-130464 is an invention of a non-magnetic steel for use in drill collars with high corrosion resistance and high strength. This class consists of Cr and Ni
, 51 was sufficiently secured, stress corrosion resistance was solved,
Furthermore, in order to eliminate the harmful effects of carbides and nitrides such as Ti, Cr, Mot Nb+V, etc., C and N are limited to extremely low levels, thereby ensuring sufficient ductility, toughness, and homogeneity of the material. This steel is rolled or forged into a round steel, and then subjected to solution treatment and aging treatment to become a high-strength steel for drill collars.

In this aging treatment, the intermetallic compound γ' phase (Ni3(AIl
-Ti)) is finely precipitated, and the so-called precipitation hardening effect of this precipitated phase results in high-strength steel.

Therefore, in JP-A No. 61-130464, the type, amount, and distribution of precipitated phases are extremely important in terms of material quality, and if these can be controlled within a preferable range, the quality will be more stable and desirable. This means that a non-magnetic mesh can be manufactured.

In addition, in JP-A No. 61-130464, solution heat treatment and aging heat treatment are performed, but this heat treatment reduces η, which impairs ductility and toughness.
Phase precipitation cannot be completely avoided, and materials with better ductility and toughness are desired for use in more severe applications.

Furthermore, the manufacturing process is also cumbersome, and in order to reduce manufacturing costs, a simpler heat treatment method is desired.

[Problems to be solved by the invention] The present invention provides a highly corrosion-resistant and high-strength non-magnetic steel for drill collars.
The present invention provides a method of manufacturing with a simpler method than the conventional method, and with always stable and superior ductility and toughness levels.

[Means for solving problems]

The present invention has (1) weight %, Si≦2.0%, Mn≦3.0
%, Ni: 25-40%, Cr: 18-30%,
Al: 0. l ~1.5%, Ti:1.5~3.0%,
Ca: 0.0005 to 0.020χ.

A steel consisting of C50,020%, N≦0.010% and the balance consisting of Fe and unavoidable impurities was processed at a processing rate of 5 at less than 750°C.
% or more rolling or forging, then 650~8
A method for producing a highly corrosion-resistant, high-strength non-magnetic steel for drill collars, which is subjected to aging treatment at 50°C, and (2) in weight%, Si≦2.0%, Mn≦3.0%,
Nl: 25-40%, Cr: 18-30%,
Aji! :0. l ~1.5%, Ti: 1.5
~3.0%, Ca: 0.0005~0.020
χ.

A steel consisting of C50,020%, N≦0.010% and the balance consisting of Fe and unavoidable impurities is rolled or forged at 750 to 850°C with a processing rate of 5% or more and less than 10%, and then rolled or forged at 650 to 850°C. A method for producing a highly corrosion-resistant, high-strength non-magnetic steel for drill collars, which is subjected to aging treatment, and (3) in weight%, Si≦2.0%, Mn≦3.0%,
Ni: 25-40%, Cr: 18-30%, Al
:o, t~1.5%, Ti: 1.5~3.0%,
Ca: O,0O05~0.020χ.

Highly corrosion resistant, high strength non-magnetic material for drill collars made by rolling or forging steel consisting of C50,020%, N≦0.010% with the balance being Fe and unavoidable impurities at 750-850°C with a processing rate of 10% or more. A method for producing steel, and (4) in weight%, Si≦2.0%, Mn≦3.0%,
Ni: 25-40%, Cr: 18-30%, Al: 0.
1-1.5%, Ti: 1.5-3.0%, Ca
: 0.0005-0.020χ.

C50,020%, N≦o, oio%, and Mo≦3
．． 0%.

Zr≦3.5%, Nb≦3.5%, 1 of 750.5%
A high-temperature steel containing one or more of the following, with the balance consisting of Fe and unavoidable impurities, is rolled or forged at a working rate of 5% or more at less than 750°C, and then subjected to aging treatment at 650 to 850°C. A method for producing a corrosion-resistant high-strength non-magnetic steel for drill collars, and (5) Si≦2.0% by weight.
, Mn≦3.0%, Ni:25-40%, Cr:1
8-30%, l: 0.1-1.5%, Ti: 1
．． 5-3.0%, Ca: 0.0005-0.02
0x.

C50,020%, N≦0.010%, and Mo≦3
．． 0%.

Zr≦3.5%, Nb≦3.5%, 1 of 750.5%
A steel containing one or more species, with the remainder consisting of Fe and unavoidable impurities, is rolled or forged at 750° to 850°C with a processing rate of 5% or more and less than 10%, and then 65
A method for producing highly corrosion-resistant, high-strength non-magnetic steel for drill collars, which is subjected to aging treatment at 0 to 850°C, and (6) in weight%, Si≦2.0%, Mn≦3.0%,
Ni: 25-40%, Cr: 18-30%, All,
1-1.5%, Ti: 1.5-3.0%,
Ca: 0.0005-0.020X.

C50,020%, N≦0.010%, and MoS3
．． 0%.

Zr≦3.5%, Nb≦3.5%, 1 of 750.5%
Production of highly corrosion-resistant, high-strength, non-magnetic steel for drill collars, by rolling or forging a steel containing one or more species and the remainder consisting of Fe and unavoidable impurities at a processing rate of 10% or more at 750 to 850°C. It's a method.

[For production]

First, claims Nos. (11, (2), (3)
) term will be explained.

Si is necessary as a deoxidizing agent, but its presence in excess impairs hot workability, so the content is limited to 2.0% or less.

Mn is necessary as a deoxidizing agent, but if it exceeds 2.0%, stress corrosion cracking resistance deteriorates, so it should be kept at 2.0% or less.

Ni coexists with Cr to generate a stable austenite phase that is a prerequisite for nonmagnetism. Further, since the steel of the present invention is a so-called precipitation hardened steel which is made to have high strength by precipitating the intermetallic compound T' phase by aging, Ni is added as a reinforcing element. Furthermore, in order to ensure stress corrosion cracking resistance in a chlorine ion environment, which is a problem with drill collars for deep wells, a content of 25% or more is required. However, the improvement effect on stress corrosion cracking resistance is 40%.
The upper limit was set at 40% because it was saturated.

18% or more of Cr is required to ensure corrosion resistance. However, if it exceeds 30%, heat workability will be impaired and the austenite phase will become unstable, so the upper limit is set at 30%.

Stress 8 in saturated saline water under boiling conditions conducted by the present inventors
In a constant load stress corrosion cracking test at 0 kgf/mn+'', the stress corrosion rupture time was dramatically improved when Cr was 18% or more and Ni was 25% or more.
saturates at 40% for Cr, but 30% for Cr
The effect will still increase even if it exceeds. However, as mentioned above, since hot workability is impaired, the upper limit of Cr is suitably 30%.

Al is the precipitate of the present invention, that is, the intermetallic compound T' phase (N1
It is an element that generates z(Al・Ti). Also, η is a grain boundary reaction type precipitate that has an effect on ductility and toughness.
It has the effect of suppressing phase precipitation. However, when added in excess, the precipitation hardening effect is weakened because the matching strain between the austenite phase and T' is reduced.

Therefore Aj! The appropriate content is 0.1% to 1.5%.

Ti is an intermetallic compound γ' (N15(Af -Ti)
), and its strength increases with the addition of Ti.

In order to ensure high strength, 1.5% or more is required.

However, if it exceeds 3%, hot workability will be significantly impaired. Therefore, its content should be 1.5 to 3%.

Ca is o, ooos as an element that improves hot workability.
% or more, but if it exceeds 0.020%, hot workability will deteriorate. Therefore, the Ca content is 0.00
05 to 0.020%.

C combines with Ti during the solidification process of steel to form coarse Ti carbides, but these coarse carbides are dissolved in solid solution during the subsequent heating/rolling or solution heat treatment process [! It's very difficult. Steel for drill collars must have ductility, toughness, and homogeneity of material, but the undissolved coarse carbides mentioned above not only impair ductility and toughness but also make the material inhomogeneous. In order to prevent such coarse carbides from remaining, it is necessary to limit C1i to 0.020% or less.

Since N is an element that is more likely than C to bond with Ti and form coarse Ti nitrides, it may impair ductility, toughness, and homogeneity, which are necessary properties for drill collars, as in the case of C above. It is necessary to limit the N is more Ti than C
Since it is easy to form compounds with C, the upper limit is set to 0.
It must be set to 010%.

Next, claim paragraphs (4), (5), and (6)
) term will be explained.

The steel of the present invention has the above-mentioned claims (1) to (3) as basic components, and further contains Mo and Zr in order to improve the yield strength for use in high-strength drill collars.

It is effective to contain one or more of Nb and V within a predetermined range.

Mo is an element that has a solid solution strengthening effect and is an effective element for increasing yield strength, but if it is added in an amount of 3% or more, the hot deformation abrasion resistance will be significantly increased, making rolling or forging difficult. Therefore, the content should be 3.0% or less.

Since Zr, Nb, and V are dissolved in the intermetallic compound T' that causes precipitation strengthening, the addition of these elements increases T'
This results in an increase in the amount of precipitation, resulting in an increase in yield strength. However, since excessive addition impairs ductility and toughness, the upper limit was set at 0.5% for each.

In addition, in the present invention, by restricting the content of C and N, the generation of carbides or nitrides such as Ti, Cr, Mo, Nb, Zr, V, etc. is suppressed. Ductility, toughness and homogeneity are ensured.

Next, processing and heat treatment of the present invention will be explained.

The present inventors have studied hot working, solution treatment, and aging treatment for the above-mentioned steel, and have newly obtained the following knowledge.

■ When aging treatment is performed after solution treatment, intermetallic compound γ
' phase (old (Aj -Ti)) precipitates and strengthens the steel, but the γ' phase is an intermediate phase and the equilibrium phase η changes during aging treatment.
The metamorphosis to progresses partially. This η phase mainly precipitates at grain boundaries and causes a decrease in ductility and toughness.

■ Rolling or forging at a working rate of 5% or more at a relatively low temperature and then aging treatment without solution treatment will promote the precipitation of the γ' phase, so it is better to age the solution treated material. The specified strength can also be achieved through low-temperature, short-time aging treatment. Therefore, as a result, precipitation of the η phase that impairs ductility and toughness can be suppressed, and high-strength steel with good ductility and toughness can be manufactured.

■ If rolling or forging is performed at a working rate of 10% or more in the temperature range where γ' phase precipitation occurs, the γ' phase precipitation will be promoted, and the η phase precipitation, which impairs ductility and toughness, can be suppressed. High strength steel with good ductility and toughness can be manufactured.

■ If rolling or forging is performed at a working rate of 5% or more but less than 1O% in the temperature range where γ' phase precipitation occurs, γ' phase precipitation will be small if it is left as is, but aging treatment without subsequent solution treatment will result in less γ' phase precipitation. When this is performed, the precipitation of the γ' phase is promoted, so that the predetermined strength can be achieved by aging treatment at a lower temperature and in a shorter time than by aging the solution-treated material. Therefore, as a result, ductility
Precipitation of the η phase that impairs toughness can be suppressed, and high-strength steel with good ductility and toughness can be manufactured.

The processing and heat treatment of the present invention are based on these new findings.

Processing and heat treatment according to claims 1 and 4 will be explained. This method embodies the above-mentioned new knowledge (1), and FIG. 1 shows an example thereof.

That is, in Figure 1, the steel of the present invention shown in Table 1 is rolled at a working rate of 5% at each temperature shown in the figure, and then rolled at 750°C.
It is a diagram showing the yield strength and total elongation of a steel material subjected to aging for ×4 hours. As shown in FIG. 1, if rolling is performed at a working rate of 5% at a processing temperature of 750° C. or lower, and then aging treatment is performed at 750° C., a high-strength steel material can be obtained without deterioration in ductility and toughness. FIG. 2 is a diagram showing another example of this processing and heat treatment. That is, in Fig. 2, the steel of the present invention shown in Table 1 is rolled at 700°C and at the working rate shown in the figure, and then rolled at 700°C.
This is a diagram showing the yield strength and total elongation of steel material aged for 50"c x 4 hours. As seen in Figure 2, this working rate is 5
% or less, both yield strength and total elongation are low, but when it is 5% or more, a steel material with excellent ductility, toughness, and high strength can be obtained.

Although the aging treatment temperature was limited to 650 to 850°C,
This is because the precipitation of the γ' phase is slow at 850° C., and it becomes difficult for the γ' phase to precipitate if the temperature is too high, exceeding 850°C.

The present invention is a processing and heat treatment method suitable for small drill collar materials and parts, for example, although it is difficult to implement on large drill collar materials because the processing is performed at low temperatures to a degree of 5% or more.

Next, the processing according to claims 3 and 6 will be explained. This method embodies the above-mentioned novel finding (2), and FIG. 3 is an example thereof. That is, Fig. 3 shows the steel of the present invention shown in Table 1 at a processing rate of 15 at each temperature shown in the figure.
It is a figure showing proof strength of the steel material which rolled %. As shown in Figure 3 (15% rolling at 750 to 850°C, high strength steel can be obtained without subsequent solution heat treatment or aging heat treatment. 15% rolling at 750 to 850°C) Even if the temperature is too low, precipitation of the γ′ phase is small if the rolling process is performed, and if the temperature is too high (850°C or higher), the γ′ phase will not precipitate.
Since the temperature exceeds the phase precipitation temperature, high strength cannot be achieved.

FIG. 4 is a diagram showing another embodiment of this processing method. Therefore, Fig. 4 shows that the steel of the present invention shown in Table 1 was heated to 800°C.
FIG. 2 is a diagram showing the yield strength of a steel material that has been rolled at the working rate shown in the figure.

As shown in Fig. 4, if the addition rate is less than 10%, high strength cannot be achieved by rolling as is, but if the addition rate is less than 10%,
Sufficient resistance can be obtained with H. Although the total elongation is not shown in FIGS. 3 and 4, the ductility and toughness of the steel material obtained by this method are at a sufficient level. This method uses 750~
Since 10% or more processing is performed at a high temperature of 850°C, it is easy to apply to general-purpose drill collars, and since no heat treatment is performed after rolling, the process is simple and has a large cost reduction effect.

Next, processing and heat treatment according to claims 2 and 5 will be explained. This method embodies the above-mentioned new knowledge (1) and is a method that applies it to steel materials for large drill collars. That is, when the steel material becomes large, it is difficult to perform processing of 5% or more at temperatures below 750°C, and processing of 5 to 10% is possible at 750 to 850°C, but processing of 10% or more is difficult. In this method, 5-10% at 750-850℃
processing. As shown in Figure 4, the yield strength is low if left as is. However, if the steel is then subjected to aging treatment at 650 to 850° C., precipitation of the T' phase induced by strain is promoted, and high strength can be achieved.

〔Effect of the invention〕

According to the present invention, it is possible to manufacture a highly corrosion-resistant, high-strength non-magnetic steel for drill collars that has consistently excellent material homogeneity, ductility, toughness, and strength.

Furthermore, compared to conventional methods, the present invention is a simpler process because heat treatment can be simplified or omitted, and is also effective in reducing manufacturing costs.

[Brief explanation of drawings]

Fig. 1 is a diagram showing the relationship between processing temperature, yield strength, and total elongation in the inventions claimed in claims 1 and 4; Fig. 2 is a diagram showing the processing rate of the inventions in claims 1 and 4; Figure 3 is a diagram showing the relationship between yield strength and total elongation, Figure 3 is a diagram showing the relationship between processing temperature and yield strength in the inventions of claims 3 and 6,
The figure is a diagram showing the relationship between processing rate and proof stress in the inventions of claims 3 and 6.

Claims (6)

[Claims] (1) In weight%, Si≦2.0%, Mn≦2.0%, N
i: 25-40%, Cr: 18-30%, Al: 0.1
~1.5%, Ti: 1.5-3.0%, Ca: 0.00
05-0.020%, C≦0.020%, N≦0.01
0% steel with the balance consisting of Fe and unavoidable impurities, 7
A method for manufacturing a highly corrosion-resistant, high-strength nonmagnetic steel for drill collars, which comprises rolling or forging at a processing rate of 5% or more at less than 50°C, and then aging treatment at 650 to 850°C. (2) In weight%, Si≦2.0%, Mn≦2.0%, N
i: 25-40%, Cr: 18-30%, Al: 0.1
~1.5%, Ti: 1.5-3.0%, Ca: 0.00
05-0.020%, C≦0.020%, N≦0.01
0% steel with the balance consisting of Fe and unavoidable impurities, 7
A method for producing highly corrosion-resistant, high-strength non-magnetic steel for drill collars, which comprises rolling or forging at 50 to 850°C with a processing rate of 5% to less than 10%, and then aging treatment at 650 to 850°C. . (3) In weight%, Si≦2.0%, Mn≦2.0%, N
i: 25-40%, Cr: 18-30%, Al: 0.1
~1.5%, Ti: 1.5-3.0%, Ca: 0.00
05-0.020%, C≦0.020%, N≦0.01
0% steel with the balance consisting of Fe and unavoidable impurities, 7
A method for producing a highly corrosion-resistant, high-strength nonmagnetic steel for drill collars, which comprises rolling or forging at 50 to 850°C with a processing rate of 10% or more. (4) In weight%, Si≦2.0%, Mn≦2.0%, N
i: 25-40%, Cr: 18-30%, Al: 0.1
~1.5%, Ti: 1.5-3.0%, Ca: 0.00
05-0.020%, C≦0.020%, N≦0.01
0%, further Mo≦3.0%, Zr≦0.5%, Nb≦
0.5%, V≦0.5%, one or more kinds, and the balance is Fe and unavoidable impurities.
A method for manufacturing a highly corrosion-resistant, high-strength nonmagnetic steel for drill collars, which comprises rolling or forging at a processing rate of 5% or more at temperatures below 0.degree. C., followed by aging treatment at 650 to 850.degree. (5) In weight%, Si≦2.0%, Mn≦2.0%, N
i: 25-40%, Cr: 18-30%, Al: 0.1
~1.5%, Ti: 1.5-3.0%, Ca: 0.00
05-0.020%, C≦0.020%, N≦0.01
0%, further Mo≦3.0%, Zr≦0.5%, Nb≦
0.5%, V≦0.5%, one or more kinds, and the balance is Fe and unavoidable impurities.
A method for producing highly corrosion-resistant, high-strength non-magnetic steel for drill collars, which comprises rolling or forging at a temperature of 5% to 850°C with a working ratio of 5% to less than 10%, followed by aging treatment at 650 to 850°C. . (6) In weight%, Si≦2.0%, Mn≦2.0%, N
i: 25-40%, Cr: 18-30%, Al: 0.1
~1.5%, Ti: 1.5-3.0%, Ca: 0.00
05-0.020%, C≦0.020%, N≦0.01
0%, further Mo≦3.0%, Zr≦0.5%, Nb≦
0.5%, V≦0.5%, one or more kinds, and the balance is Fe and unavoidable impurities.
A method for producing highly corrosion resistant, high strength non-magnetic steel for drill collars, which comprises rolling or forging at ~850°C with a processing rate of 10% or more.