ES2714371T3 - Method to produce a heavy duty seamless Cr-Ni alloy pipe - Google Patents

Abstract

A method for producing a seamless high-strength Cr-Ni alloy pipe, comprising: preparing an alloy billet having a chemical composition consisting, in mass %, of C: 0.05% or less, Si : 1.0% or less, Mn: less than 3.0%, P: 0.005% or less, S: 0.005% or less, Cu: 0.01 to 4.0%, Ni: 25% or more and less from 35%, Cr: 5 to 30%, Mo: 0.01% or more and less than 4.0%, N: 0.10 to 0.30%, Al: 0.03 to 0.30%, O (oxygen): 0.01% or less, REM (rare earth metal): 0.01 to 0.20%, and optionally at least one element selected from W: less than 8.0%, one or more of Ti, Nb, Zr and V in a total content of 0.5% or less, and either or both of Ca and Mg in a total content of 0.01% or less, and the remainder being Fe and impurities, and that satisfies the following formula (1); hot working to make a seamless material pipe based on a cross-roll mill punching process; subject to solution treatment; and work cold. N x P/REM <= 0.10 ............. formula (1) where P, N and REM in formula (1) represent the contents (% by mass) of P, N and REM, respectively.

Description

DESCRIPTION

Method for producing a heavy duty seamless Cr-Ni alloy tubena

Technical field

The present invention relates to a method for producing a high strength seamless Cr-Ni alloy pipe with excellent hot workability and resistance to stress cracking by corrosion.

Background Technique

Recently, with the rising price of crude oil, oil wells and deep natural gas wells have been developed and in harsh corrosive environments. In parallel with the extraction of oil and natural gas in such harsh environments, it has been required that the oil well pipes for such extractions have high strength, excellent corrosion resistance and excellent resistance to stress cracking under stress.

Due to the recent increased needs of oil and natural gas, oil wells and gas wells for oil and natural gas extraction tend to increase in depth. With the increase in the depth of the wells, it has been required that the materials used for such wells maintain corrosion resistance against carbon dioxide gas, hydrogen sulfide and chloride ion, and at the same time have even greater resistance .

Examples of the material exhibiting corrosion resistance in corrosive environments include the Cr-Ni alloys described in Patent Document 1, Patent Document 2 and Patent Document 3, which describe that it is effective to increase the N content in order of increasing the resistance of the Cr-Ni alloy. However, the alloy reinforced by such a method has a problem that its resistance to deformation is high and its hot workability is poor.

At present, such seamless tubenas that have high strength and poor hot workability that have been described above are generally produced by the hot extrusion tubing manufacturing process, but have low productivity.

On the contrary, as a method capable of efficiently producing seamless tubenas with high productivity, the drilling process with transverse laminator (also called Mannesmann tubing manufacturing process). In this method using a perforating laminator (perforating machine with transverse laminator), the perforation with transverse laminator (hereinafter simply referred to as "perforation-lamination") is applied to a raw billet to produce a tubena of hollow material (hereinafter successively referred to simply as "material tubena"), the resulting material tubena is lengthened by rolling with a laminator such as a punching train or a laminator on a mandrel, and finally ending in the form with a stretch finisher or reducer. However, such seamless tubena that has high strength and poor hot workability tends to cause lamination folds due to the fusion of the edges of the grain, when the drilling process with transverse laminator occurs.

The phenomenon of fusion of the edges of the grain is caused by the fusion of the edges of the grain due to the heat produced by the processing. The appearance of fusion of the edges of the grain rapidly deteriorates the ductility of the material and therefore tends to cause lamination folds due to the fusion of the edges of the grain. The process of drilling with a transverse laminator is better in the working relationship than the manufacturing process of hot extrusion tubenas, and therefore it has a higher heat produced by the processing, thus exhibiting the problem that the formation of Folds tend to be caused due to the fusion of the edges of the grain.

Next, Patent Document 4 describes a technique to prevent melting cracking of the edges of the grain by heating a tubena of material to a temperature equal to or greater than a value determined by a formula that contemplates the circumferential speed of the rolling mill in the perforation. -lamination of a Cr-Ni alloy and the size of the tubena. However, no research has been carried out to improve the resistance to cracking by fusion of the edges of the grain from the point of view of the composition of the alloy and, in addition, the improvement in corrosion resistance that a problem offers More important in high strength materials has not been considered.

Patent Document 5 describes a technique to prevent fissure cracking of the edges of the grain that exhibits a problem in relation to austatic stainless steel, reducing the content of P and the content of S according to the dimensions of the material pipeline. which is going to undergo perforation-lamination. However, the technique described is different from a technique intended for a higher resistance Cr-Ni alloy that is used in an environment that requires high corrosion resistance.

Patent Document 6 describes a seamless Fe-Ni alloy tubena with excellent mechanical properties and corrosion resistance in an acid gas environment where, in the seamless pipeline, the rolling folds and welding failure are they prevent carrying out a perforation-lamination using a tubena of material that has the content of P and the content of S specified so that it is in specific intervals. However, not enough research has been carried out with the purpose of obtaining an alloy pipe of High strength seamless crNi that has excellent hot workability and at the same time has excellent corrosion cracking resistance under stress.

Patent Document 7 describes a super-synthetic stainless steel alloy such that products made of the alloy, in particular tubes and especially seamless tubes and welded tubes, have a combination of high corrosion resistance, especially in inorganic and organic acids and mixtures thereof, good corrosion resistance in general, good structural stability as well as improved mechanical properties in combination with good workability.

Patent Document 8 describes a process for the production of a high-alloy steel pipe that allows the manufacture of hot working pipes and that exhibits satisfactory ductility in the work done after the pipeline manufacturing process. In order to obtain greater strength and is excellent in corrosion resistance.

Appointment List

Patent documents

Patent Document 1 JP57-203735A

Patent Document 2 JP57-207149A

Patent Document 3 JP58-210155A

Patent Document 4 WO 2008/081866

Patent document 5 WO 2004/112977

Patent document 6 WO 2006/003953

Patent document 7 US 2003/143105 A1

Patent document 8 JP 2009-030153 A

Compendium of the invention

Technical problem

An objective of the present invention is to provide a method for producing a seamless Cr-Ni alloy pipe capable of preventing deterioration of hot workability and deterioration of stress cracking resistance under stress caused by the presence of the high strength, and also able to carry out the manufacture of tubenas without causing folds during perforation-lamination.

Solution to the problem

In order to solve the problems described above, the authors of the present invention first tried to prepare a material of greater resistance than conventional materials by increasing the N content. However, a simple increase in the N content impairs hot workability. and resistance to corrosion cracking under stress to hinder the production of seamless tubenas for oil wells. Therefore, as a technique to prevent the deterioration of workability and the deterioration of resistance to corrosion cracking under stress caused by the increase in the N content, the authors of the present invention have focused attention on REM. Earch Metal, rare earth metal). REMs are known to be able to improve hot workability by immobilizing elements such as O, S and P in the alloy. However, no attention has been paid to the effect of REM on corrosion cracking resistance under stress.

The authors of the present invention prepared alloys with high N content that fear various fusion compositions, and evaluated the yields of the resulting alloys. Accordingly, the authors of the present invention have found that the inclusion of REM improves resistance to stress cracking by corrosion. The reason for the improvement of resistance to corrosion cracking under stress by REM is probably attributable to the immobilization, by REM, of P that adversely affects resistance to stress cracking due to corrosion under stress.

However, it has been revealed that the inclusion of Ca, Mg or Si, which until now has been said to be effective for hot workability, in the N-high alloy containing REM, on the other hand deteriorates hot workability . Therefore, the authors of the present invention additionally conducted a thorough study and have found that the inclusion of Al allows satisfactory hot workability to be obtained even in the high N-alloy containing REM. Thus, it has been found that in order to obtain satisfactory hot workability in the high N-alloy containing REM, it is essential to include Al along with the REM.

The Cr-Ni alloy that has a high content of N to increase the resistance has a high resistance to deformation, and therefore tends to cause fusion of the edges of the grain due to the heat produced by the processing in the perforation-lamination that It has a high working relationship. The appearance of fusion of the edges of the grain deteriorates the ductility of the material, leading to a problem that folds in the material are caused during perforation-lamination.

Accordingly, the authors of the present invention prepared, by fusion, high-N Cr-Ni alloys, which have various chemical compositions and examined the workability of the tubena during perforation lamination.

Therefore, it has been found that the reduction of the content of P results in a significant effect to increase the melting temperature of the edges of the grain that makes it difficult to cause the fusion of the edges of the grain, and therefore, the manufacture of the tubena It can be carried out without causing folds during perforation-lamination. It has also been found that the reduction of the Si content and the content of Mn at the same time with the reduction of the P content results in an effect to further increase the melting temperature of the grain edges, which makes it more difficult cause the fusion of the edges of the grain.

The authors of the present invention also prepared a continuous study based on such new findings as described above and, consequently, obtained the following findings (a) through (g).

(a) In the Cr-Ni alloy material, for the purpose of ensuring strength, the content of N is required to be set to 0.10 to 0.30%, and for the purpose of ensuring hot workability , the content of Al is required to be set at 0.03 to 0.30%.

(b) However, when the content of N in the Cr-Ni alloy material is set to 0.10 to 0.30%, hot workability and resistance to stress corrosion cracking deteriorate.

(c) In this sense, when REM is included in the alloy to fix P as compounds of P, not only hot workability but resistance to corrosion cracking under stress can be improved.

(d) Accordingly, the content of REM can be determined from the viewpoint that the content of REM is the content necessary to immobilize P as compounds of P. In other words, the ratio of the content of P to the content of REM P / REM is important.

(e) At lower P / REM, the adverse effect due to P on hot workability is more effectively suppressed. Therefore, even if the N content is quite high, when P / REM is set to be small, deterioration of hot workability can be suppressed.

(f) Accordingly, it has been found that Cr-Ni alloy materials that are satisfactory in stress corrosion cracking resistance are obtained by specifying the relationship between the N content and the P content and the REM content of so that they are within the range that satisfies the following formula (1):

N x P / REM <0, 10 ............... Formula (1)

where P, N and REM in formula (1) represent the contents (mass%) of P, N and REM, respectively.

(g) The reduction of the P content leads to a significant effect to increase the melting temperature of the grain edges. Reducing the content of P to be 0.005% or less, even the perforation lamination using a Cr-Ni alloy that has a high N content and high resistance to deformation can carry out the manufacture of tubena without causing folds during perforation lamination. The further reduction of the Si content and the Mn content result in an effect to further increase the melting temperature of the grain edges, which makes it more difficult to cause the grain edges to melt. The Si content is preferably set at 0.3% or less. The Mn content is preferably set to 0.7% or less and more preferably 0.6% or less. Although the reduction of the Si and Mn content is effective, the reduction of both the Si and Mn content is more preferable.

The present invention has been refined based on the findings described above, and the essence of the present invention is as described in the following points (1) to (3) associated with the method for producing a Cr-Ni alloy tubena without sewing. Reference is made to the following points (1) to (3) as inventions (1) to (3), respectively. Reference may be made to the inventions (1) to (3) together as the present invention.

(1) A method for producing a seamless high-strength Cr-Ni alloy pipe, comprising: preparing an alloy billet having a chemical composition consisting, in mass%, in C: 0.05% or less, If: 1.0% or less, Mn: less than 3.0%, P: 0.005% or less, S: 0.005% or less, Cu: 0.01 to 4.0%, Ni: 25% or more and less than 35%, Cr: 20 to 30%, Mo: 0.01% or more and less than 4.0%, N: 0.10 to 0.30%, Al: 0.03 to 0.30 %, O (oxygen): 0.01% or less, REM (rare earth metal): 0.01 to 0.20%, and optionally at least one element selected from W: less than 8.0%, one or more of Ti, Nb, Zr and V in a total content of 0.5% or less, and either or both of Ca and Mg in a total content 0.01% or less, and the rest being Fe and impurities, and satisfying the following formula (1);

work hot to make a pipe of seamless material based on a drilling process with transverse laminator;

undergo a solution treatment; Y

work in fno.

N x P / REM <0, 10 ............... Formula (1)

where P, N and REM in formula (1) represent the contents (mass%) of P, N and REM, respectively.

(2) The method for producing a seamless high-strength Cr-Ni alloy pipe according to item (1) above, where the billet has a chemical composition containing, in mass%, Si: 0.3% or less and / or Mn: 0.7% or less.

(3) The method for producing a seamless high-strength Cr-Ni alloy pipe according to item (1) or (2) above, where the elastic limit after working in fno is 900 MPa or more in terms of 0.2% plastic deformation.

Advantageous effects of the invention

According to the present invention, it is possible to produce a seamless high strength Cr-Ni alloy pipe, with excellent hot workability and resistance to corrosion cracking under stress, without causing rolling folds during perforation-lamination, although The seamless tubena has a high resistance due to a high content of N in the Cr-Ni alloy.

Description of embodiments

The reasons for limiting the chemical composition of the Cr-Ni alloy according to the present invention are described below. Here, it is appreciated that "%" in each of the contents of the individual elements represents "% by mass".

C: 0.05% or less

C is an impurity contained in the alloy; when the C content exceeds 0.05%, stress corrosion cracking tends to occur accompanied by the fracture of the grain edges due to precipitation of an M23C6 type carbide (M: element such as Cr, Mo or Fe), and therefore, the C content is set at 0.05% or less. The content of C is preferably 0.03% or less.

Yes: 1.0% or less

In the present invention, Si is an element to reduce the melting temperature of the edges of the grain and cause lamination folds during perforation-lamination. Even with a reduced P content, when the Si content exceeds 1.0%, rolling folds occur during drilling-rolling. Therefore, the Si content is set to 1.0% or less. In order to reduce the high resistance to deformation during perforation-lamination, it is preferable to carry out the drilling at even higher temperatures. In this case, with the purpose of preventing rolling folds, it is preferable to increase the melting temperature of the grain edges and the Si content is preferably set to 0.3% or less and more preferably 0.2% or less. . The lower Si content is most preferable, and the lower limit of the Si content is not particularly specified. However, when the Si is contained for deoxidation, Si is preferably contained in a content of 0.01% or more.

Mn: less than 3.0%

In the present invention, Mn is an element for reducing the melting temperature of the edges of the grain and causing folds during perforation-lamination. Even with a reduced P content, when the Mn content is 3.0% or more, they produce folds during perforation-lamination. Accordingly, the content of Mn is adjusted to less than 3.0%, and is preferably less than 1.0%. In order to reduce the high resistance to deformation during perforation-lamination, it is preferable to carry out the drilling at even higher temperatures. In this case, with the purpose of preventing folds, it is preferable to increase the melting temperature of the edges of the grain more and the content of Mn is more preferably adjusted to 0.7% or less and also preferably to 0.6% or less . The content of Mn is even more preferably 0.3% or less. The lowest Mn content is most preferable, where the lower limit of the Mn content is not particularly specified. However, when Mn is contained for deoxidation, the content of Mn is preferably 0.01% or more.

P: 0.005% or less

In the present invention, P is an important element. P is an impurity contained in the alloy; when perforation-lamination is carried out, a high content of P tends to cause lamination folds. Accordingly, the P content is adjusted to 0.005% or less and is preferably 0.003% or less. Additionally, as described above, the P content is required to satisfy the formula (1), in relation to the N content and the REM content.

S: 0.005% or less

Although S does not affect the rolling folds, S is an impurity contained in the alloy, and significantly deteriorates hot workability at low temperatures. Therefore, from the standpoint of preventing deterioration of hot workability, the permitted content of S is required to be 0.005% or less, and the lower content of S is more preferable. The content of S is preferably 0.002% or less and more preferably 0.001% or less.

Cu: 0.01 to 4.0%

Cu is effective in stabilizing the passive film formed on the surface of the alloy, and is necessary to improve pitting resistance and general corrosion resistance. When the Cu content is less than 0.01%, Cu is not effective and when the Cu content exceeds 4.0%, hot workability deteriorates. Therefore, the Cu content is adjusted to 0.01 to 4.0%. The Cu content is preferably 0.1 to 2.0% and more preferably 0.6 to 1.4%.

Ni: 25% or more and less than 35%

Nor is it available for this content as an austenite stabilizing element. From the point of view of corrosion resistance, the Ni content is required to be 25% or more. Ni content of 35% or more leads to increased cost. Therefore, the Ni content is set to 25% or more and less than 35%. The Ni content is preferably 28% or more and less than 33%

Cr: 20 to 30%

Cr is a component that significantly improves resistance to corrosion cracking under stress. When the Cr content is less than 20%, the effect of Cr is not sufficient, and when the Cr content exceeds 30%, nitrides such as CrN and Cr2N and carbides of type M23C6 tend to adversely affect the resistance to corrosion cracking under tension accompanied by fracture of the edge of the grain. Therefore, the Cr content is adjusted to 20 to 30%. The Cr content is preferably 23 to 28%.

Mo: 0.01% or more and less than 4.0%

Mo is effective, like Cu, for stabilizing the passive film formed on the surface of the alloy, and is effective for improving corrosion cracking resistance under stress. When the Mo content is less than 0.01%, Mo is not effective and when the Mo content is 4.0% or more, hot workability and economic efficiency deteriorate. Therefore, the Mo content is adjusted to 0.01% or more and less than 4.0%. The Mo content is preferably 0.1% to 3.5%.

N: 0.10 to 0.30%

N is effective in increasing the strength of the alloy. When the N content is less than 0.10%, the desired high strength cannot be guaranteed, and when the N content exceeds 0.30%, the hot workability and the stress cracking resistance under stress deteriorate. Therefore, the content of N is adjusted to 0.10 to 0.30%. A preferred range of the N content is 0.16 to 0.25%. Additionally, as described below, the N content is required to satisfy the formula (1), in relation to the P content and the REM content.

Al: 0.03 to 0.30%

Al binds to O (oxygen) in the alloy to improve hot workability, and is also effective in preventing REM oxidation. When REM is contained but Al is not contained, inclusions occur in large quantities that significantly deteriorate the hot workability of the alloy. Therefore, when REM is content, it is essential for Him to have this content together. When the content of Al is less than 0.03%, the effect of Al is not sufficient. When the Al content exceeds 0.30%, hot workability deteriorates. Therefore, the Al content is adjusted to 0.03 to 0.30%. The Al content is preferably 0.05 to 0.30% and more preferably more than 0.10% and 0.20% or less.

O (oxygen): 0.01% or less

O (oxygen) is an impurity contained in the alloy, and significantly deteriorates hot workability. By consequently, the content of O (oxygen) is adjusted to 0.01% or less. The content of O (oxygen) is preferably 0.005% or less.

REM: 0.01 to 0.20%

REM (rare earth metal) is effective in improving hot workability and resistance to corrosion cracking under stress, and therefore, this content is required. REM tends to be oxidized, and therefore it is essential that it contains REM together with Al. When the total REM content is less than 0.01%, the effect of REM is not sufficient. When the total REM content exceeds 0.20%, there is no further effect of improvement in hot workability and resistance to stress cracking by corrosion, and even the phenomena of deterioration of these properties are found. Therefore, the REM content is adjusted to 0.01 to 0.20%. The content of REM is preferably 0.02 to 0.10%.

Here, it is appreciated that REM is a generic name for the 17 elements that includes 15 lanthanide elements and Y and Sc, and one or more of these elements may be contained. REM content refers to the sum of the contents of these elements. The method for containing REM may be such that one or more of these elements are added or industrially added in the form of a Misch metal.

Additionally, the REM content is required to satisfy the following formula (1) in relation to the N content and the P content:

N x P / REM <0, 10 ............... Formula (1)

where P, N and REM in formula (1) represent the contents (mass%) of P, N and REM, respectively.

When the content of N is 0.10 to 0.30%, and the relationship between the content of N, the content of P and the content of REM satisfies the formula (1) presented above, the resistance is high and additionally the resistance at corrosion cracking under stress is satisfactory. When better resistance to corrosion cracking is demanded under tension, it is more preferable to satisfy the N * P / REM ratio <0.05.

The Cr-Ni alloy according to the present invention may additionally contain, in addition to the alloy elements described above, one or more elements selected from at least one group of the following First group to Third group.

First group: W: less than 8.0%

Second group: Ti, Nb, V, Zr: 0.5% or less

Third group: Ca, Mg: 0.01% or less

Next, these optional elements are described in detail.

First group: W: less than 8.0%.

W is an optionally contained element. W has an effect of improving corrosion cracking resistance under stress. Therefore, when it is desired to improve the resistance to corrosion cracking under stress, W may be contained if necessary. However, when the content of W is 8.0% or more, hot workability and economic efficiency deteriorate and, therefore, when W is contained, the upper limit of the content of W is adjusted to 8.0% . In order to develop in a certain way the effect of improving the resistance to cracking by corrosion under stress, it is preferred to include W in a content of 0.01% or more. The content of W is more preferably 0.1 to 7.0%.

Second group: one or more selected from Ti: 0.5% or less, Nb: 0.5% or less, V: 0.5% or less and Zr: 0.5% or less, with the total content of one or more elements of 0.5% or less.

Ti, Nb, V and Zr are optionally contained elements. These elements have an effect of making fine grains and improving ductility. Therefore, when even better ductility is demanded, one or more of these elements may be contained, if necessary. However, when the total content of one or more of these elements exceeds 0.5%, inclusions occur in large quantities causing the phenomenon of ductility deterioration and, therefore, when one or more of these elements are contained, the The upper limit of the content of such elements is adjusted to a total content of such elements of 0.5%. With the purpose of developing in a certain way the effect of improving ductility, it is preferred to include such elements in a total content of 0.005% or more. The content of such elements is more preferably 0.01 to 0.5% and more preferably 0.05 to 0.3%.

Third group: any one or both of Ca: 0.01% or less and Mg: 0.01% or less.

Ca and Mg are optionally contained elements. These elements have an effect of improving hot workability and, consequently, any one or both of these elements may be contained if necessary.

However, when any one or both of these elements are contained in a content that exceeds 0.01%, thick inclusions occur causing the phenomenon of deterioration of hot workability. Therefore, when one or both of these elements are contained, the upper limit of the total content is set to 0.01%. With the purpose of developing in a certain way the effect of improving hot workability, it is preferred to include such elements in a total content of 0.0003% or more. The total content of such elements is more preferably 0.0003 to 0.01% and more preferably 0.0005 to 0.005%.

The seamless Cr-Ni alloy pipe according to the present invention contains the essential elements described above or additionally the optional elements described above, and the rest is Fe and impurities.

"Impurities" as referred to herein refers to substances that contaminate materials when Cr-Ni alloys are produced industrially, due to raw materials such as minerals or scrap, and due to other various factors in the production process, and is allowed to contaminate at intervals that do not adversely affect the present invention.

For the fusion of the Cr-Ni alloy of the present invention, an electric oven, an AOD oven, a VOD oven or the like can be used. When the molten alloy obtained by fusion is cast into ingots, the ingots can be converted by forging into flat slabs, billets and billets.

In the present invention, a tubena of seamless material is manufactured by working hot based on a process of manufacturing tubenas by perforation with transverse laminator. The manufacturing process of tubenas by drilling with a transverse laminator is also called the manufacturing process of Mannesmann tuben. This is a process in which the billet as raw material is subjected to a perforation with transverse laminator using a perforating laminator (perforating machine with transverse laminator) to produce a pipe of hollow material, the pipe of resulting material is laminated to lengthen it with a laminator such as a punching train or a laminator on mandrel, and finally the resulting tubena is finished in the form using a finisher or stretch reducer. Perforation with transverse laminator includes perforation with transverse laminator with an edge angle.

The elastic limit of a seamless Cr-Ni alloy pipe suitable for use in deep oil wells and deep gas wells is 900 MPa in terms of 0.2% plastic deformation. The referred elastic limit is more preferably 964 MPa or more. A seamless Cr-Ni alloy pipe is produced that has an elastic limit of 900 MPa or more due to the production process in which the pipe of seamless material for work in fno, manufactured in a pipe by the drilling process With the cross rolling mill described above, it is subjected to a solution treatment and additionally subjected to a work in fno.

In order to obtain a high-strength seamless Cr-Ni alloy pipe having an elastic limit described above, the seamless material pipe for hot work undergoing hot work with the cross-laminating drilling process is after the thermal treatment in solution, it undergoes a work in fno based on the laminate in fno such as stretched in fno or laminated at the pilgrim's pace. The work in fno can be carried out once or a plurality of times, or alternatively, if necessary, after the heat treatment, the work in fno can be carried out once or a plurality of times.

The high-strength Cr-Ni alloy pipe obtained by working at the end after the treatment in solution, which has an elastic limit of 900 MPa or more, is suitable for seamless pipe for oil wells for use in oil wells. Deep oil or deep gas wells. In the case where the final end treatment after the thermal solution treatment is carried out by a final stretch, the working relationship at end is preferably adjusted to 10 to 40% in terms of area reduction. When the working ratio at fno is less than 10%, the desired high resistance cannot be obtained. On the other hand, when the working ratio in fno exceeds 40%, the resistance obtained is high, but the ductility or toughness can deteriorate. The working ratio in fno is more preferably adjusted to 20 to 35%. In the case in which the work in fno is carried out by a laminate in fno such as a laminator at the pilgrim's pace, the work in fno is preferably carried out with the work ratio in fno of 30 to 80% in terms of area reduction. When the working ratio at fno is less than 30%, the desired high resistance cannot be obtained. On the other hand, when the working ratio in fno exceeds 80%, the resistance obtained is high, but the ductility or toughness can deteriorate

Example 1

Table 1 shows the chemical compositions (mass%) of the Examples of the invention (Tests numbers 1 to 23) and the Comparatives (Tests numbers A to J). The alloys according to the Examples of the invention were melted and cast into 30 kg ingots using a vacuum induction melting furnace. The resulting ingots were hot forged to mold into billets of 100 mm external diameter. The billets heated to 1240 ° C and 1260 ° C were subjected to perforation-lamination with a drilling apparatus with a small cross-sectional laminator to produce pipes of 116 mm of external diameter and 20 mm of wall thickness.

Table 1

Tubes of seamless material after perforation-lamination were cut perpendicular to the longitudinal direction, to a position of 50 mm in the longitudinal direction from the rear end of the tubena, and it was observed whether or not creases were caused of lamination in the tubena of material. As a result, the O mark shows that they were not caused, and the * mark shows that rolling folds were caused.

Additionally, the seamless material tubes at 1240 ° C and subjected to perforation-lamination were then subjected to a solution treatment in which the material tubes were heated and maintained at 1050 ° C for 1 hour and then cooled with water . The material tubenas were subjected to a stretch in fno with an area reduction of 30%, which are the seamless tubenas according to the Examples of the invention and Comparatives. It was found that, in the Examples of the invention, omitting the subsequent rolling process with hot elongation and the hot forming rolling process after perforation-rolling does not cause adverse effects to mechanical properties and corrosion resistance . Therefore, in a more simplified manner, the tubenas of seamless material that were subjected to perforation-lamination with a perforation apparatus with a small cross-sectional laminator and were treated directly in solution and worked in fno were used for evaluation.

They were cut in the longitudinal direction of the seamless tuben after work on fno tensile test specimens at room temperature, 6 mm in diameter and 40 mm in length in the parallel portion, and subjected to a temperature tensile test ambient in the air to measure the elastic limit at a plastic deformation of 0.2%. Additionally, with the purpose of evaluating the resistance to corrosion cracking under tension, they were cut in the longitudinal direction of the same tubenas after the work in fno test specimens, of 3.81 mm in diameter and 25.4 mm in length. the parallel portion, and a tensile test with low strain rate was carried out. In the tensile test with low strain rate, in a corrosive environment of 25% NaCl CH3COOH at 0.5% H2S at 709 kPa and 232 ° C, tensile rupture was caused at a strain rate of 4 * 10 '6 sec1, and the area reduction of each of the broken test specimens was measured. At the same time, the same stress test was carried out with low strain rate in an inert environment, the area reduction of each of the broken test specimens was measured. The ratio of the reduction of area in the corrosive environment with respect to the reduction of area in the inert environment was used as an index for resistance to stress cracking under stress; when the ratio was 0.8 or more, the resistance to stress cracking under corrosion was determined to be satisfactory (O), and when the ratio was less than 0.8, it was determined that the stress cracking resistance under stress was bad (*). In Tests numbers B to F, rolling folds were caused and, therefore, measurements of 0.2% plastic deformation and resistance to stress cracking under stress were not carried out.

Table 2 shows the test results and the N * P / REM values.

Table 2

Table 2

As shown in Table 2, in the cases of seamless material tuben of Tests numbers 1 to 19 according to the Examples of the invention, even when the heated billets up to 1240 ° C and 1260 ° C were subjected to drilling with transverse laminator, no rolling fold was caused in any of the billets. The plastic deformation of 0.2% was 900 MPa or more in any of the tubenas. Any of the tubenas satisfied the formula (1) presented above and was satisfactory in resistance to corrosion cracking under stress.

In the cases of the seamless material tuben of Tests numbers 20 to 23 according to the Examples of the present invention, even when the billets heated to 1240 ° C were subjected to perforation with transverse laminator, no folding was caused of lamination in any of the billets. However, in these cases, because the Si content and the Mn content were comparatively large, when the billets heated to 1260 ° C were subjected to perforation with transverse laminator, rolling fold was caused.

In Comparative Example A, neither heating up to 1240 ° C nor heating up to 1260 ° C resulted in rolling fold and resistance to stress cracking under corrosion was satisfactory. In Comparative Example A, however, the content of N was outside the range defined by the present invention, and therefore, the 0.2% plastic deformation was low. In each of Comparative Examples B and C, P was contained in excess, and therefore, both heating to 1240 ° C and heating to 1260 ° C resulted in rolling lamination. In each of Comparative Examples D and E, Mn was contained in excess, and therefore, both heating up to 1240 ° C and heating up to 1260 ° C resulted in rolling lamination. In Comparative Example F, If it was contained in excess, and therefore, both heating to 1240 ° C and heating to 1260 ° C resulted in rolling lamination. In Comparative Example G, REM was not contained, and therefore, the resistance to corrosion cracking under stress was low. In each of Comparative Examples H to J, the chemical composition of the alloy was within the range specified by the present invention, but did not satisfy the formula (1) and, therefore, the resistance to stress cracking by corrosion was low. .

Industrial applicability

In accordance with the present invention, it is possible to produce a seamless high strength Cr-Ni alloy pipe, with excellent hot workability and resistance to corrosion cracking under stress, without causing lamination fold during perforation-lamination, although The seamless tubena has a high strength provided by a high N content. The seamless high strength Cr-Ni alloy pipe obtained by the present invention can be used for extracting oil and natural gas at high depth and corrosive environments. rigorous, which until now have been non-exploitable, and thereby contribute significantly to a stable supply of energy.

Claims (3)

1. A method for producing a seamless high-strength Cr-Ni alloy pipe, comprising: Prepare an alloy billet having a chemical composition consisting, in% by mass, in C: 0.05% or less, If: 1.0% or less, Mn: less than 3.0%, P: 0.005% or less, S: 0.005% or less, Cu: 0.01 to 4.0%, Ni: 25% or more and less than 35%, Cr: 20 to 30%, Mo: 0.01% or more and less 4.0%, N: 0.10 to 0.30%, Al: 0.03 to 0.30%, O (oxygen): 0.01% or less, REM (rare earth metal): 0 , 01 to 0.20%, and optionally at least one element selected from W: less than 8.0%, one or more of Ti, Nb, Zr and V in a total content of 0.5% or less, and any or both of Ca and Mg in a total content of 0.01% or less, and the remainder being Fe and impurities, and satisfying the following formula (1); work hot to make a pipe of seamless material based on a drilling process with transverse laminator; undergo a solution treatment; Y work in fno. N x P / REM <0.10 ............... formula (1) where P, N and REM in formula (1) represent the contents (mass%) of P, N and REM, respectively. 2. The method for producing a seamless high strength Cr-Ni alloy pipe according to claim 1, wherein the billet has a chemical composition containing, in mass%, Si: 0.3% or less and / or Mn: 0.7% or less. 3. The method for producing a seamless high strength Cr-Ni alloy pipe according to claim 1 or 2, wherein the elastic limit after working at fno is 900 MPa or more in terms of the plastic deformation of 0, two%.