JPS5974221A - Production of high strength seamless steel pipe - Google Patents

Abstract

PURPOSE:To produce a titled steel pipe which has excellent resistance to sulfide stress corrosion cracking and excellent toughness at low temp. and permits production of a blank material by continuous casting also by hot working and hardening a steel having a limited compsn. then holding the same under specific conditions and subjecting the steel to a tempering treatment. CONSTITUTION:A blank material for a seamless steel pipe having the compsn. contg., by weight %, 0.1-0.5% C, 0.1-0.3% Si, 0.2-0.8% Mn, 1.0-4.0% Cr, 0.005-0.1% Al, <=0.005% P, <=0.005% S, <=0.004% N, 0.2-1.0% Mo, 0.01-0.1% Nb, and 0.005-0.1% (Zr+Ti), and further contg. >=1 kinds of <=0.1 V and <=0.005% B if necessary, is subjected to the following treatment: The above- mentioned blank material is hot worked and is held for the time tau shown by the equation tau>=t/25.4 (tau; holding time at the tempering temp. in hr, t; the wall thickness of the pipe in mm.) according to the wall thickness (t) of the pipe in a temp. range of >=620 deg.C-<=AC1 during the tempering treatment in succession to hardening. The excellent resistance to sulfide stress corrosion cracking is provided at 70-120kgf/mm.<2> yield strength or 0.6% yield strength is thus obtd. tau=(1/25.4)t

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a method for manufacturing high-strength seamless steel pipes, and in particular, to a method for manufacturing high-strength seamless steel pipes, the trend is particularly toward deep wells due to the tendency toward souring.

We would like to propose a new development result that effectively avoids the risk of sulfide stress corrosion cracking in oil country tubular goods or similar applications at a yield strength as high as at least 'IOm/m-. That is.

In response to the above-mentioned tendency of deep wells and sour wells, the sulfide stress corrosion cracking resistance generally deteriorates as the strength increases, so the current yield strength is 64 to 74 kgf due to the 1 tf balance between the two. / mm2 class (3r -M.

The system QjA is considered to be excellent.

Recently, according to Japanese Patent Application Laid-Open No. 58-78917, the conventional 6
Compared to Ikyf/m-grade Or-Mo steel, 75~nokgf/At-grade steel has been developed with increased amounts of Or and Mo and the addition of a large amount of V to improve sulfide stress corrosion cracking resistance. However, since it contains a large amount of expensive elements such as MO and V, it is expensive, and since it contains a large amount of V, cracks are likely to occur during hot working of the material by continuous casting.

In addition, La-added steel with excellent resistance to sulfide stress corrosion cracking was proposed in both Japanese Patent Application Laid-Open No. 57-19822 and F17-19828, but the yield strength of this steel was at most +11
0 kgf/2 fins, and there is virtually no improvement in strength compared to conventional steel.

Further, in Japanese Patent Application Laid-Open No. 57-15622, P.

A high-strength oil well steel with reduced S content has been disclosed.

Although its strength value has not been clarified, from the examples it can be said that the strength is quite high, reaching a yield strength of 91 to 98 9f/ff1-, but this steel is produced in an alkaline environment. Stress corrosion cracking resistance is guaranteed only when only a trace amount of H2S is contained.

In addition, none of the above-mentioned masterpieces takes into account low-temperature toughness. Of course, oil country tubular goods in operating oil wells are
Since the temperature inside the well is generally high, low-temperature toughness is not directly required, but new oil fields in the vicinity are often located in cold regions, and in this case, accidents may occur during transportation or docking. This point should not be overlooked, as it also has a sexual nature.

The present invention solves the above-mentioned problems of the prior art by providing an inexpensive composition system that does not contain large amounts of expensive elements and is suitable for continuous eruption, as well as sulfide stress IK corrosion resistance and low temperature corrosion resistance. This is the result of development aimed at providing high-strength seamless steel pipes with excellent toughness.

For this purpose, the inventors.

(1) Intergranular cracking is the starting point for sulfide stress corrosion cracking in steels with a yield strength of 7 Q kgf' 7fa- or more. (2) Reduction of P, S, and N can cause intergranular cracking, especially sulfide stress corrosion cracking. The suitability of this invention was derived based on the following experimental findings that (3) the longer the tempering retention time, the better the resistance to sulfide stress corrosion cracking. It is.

In general, the fracture surface morphology of sulfide stress corrosion cracking in the periphery is not constant, showing a variety of morphology such as intergranular cracking, coagulation cleavage, and dimples, but the inventors have examined the fracture surfaces of steels of various strengths in detail. As a result, we found that intergranular cracking becomes particularly important as the strength increases, and that intergranular cracking is the starting point for most fractures in Or@-containing steels with a yield strength of 701ayf/2 or higher. Ta.

Furthermore, the sulfide stress corrosion cracking resistance and low-temperature toughness of such steels are closely related to tempering embrittlement, and can be significantly improved by reducing PS and N as well as adding MO, Zr, and/or T1 appropriately. Also, if Nt) is added, Nt)
found that the formation of P oxides further prevents the segregation of P at grain boundaries, which is also effective, and that this effect is particularly better exhibited as the tempering retention time is longer.

Based on the above knowledge, the inventors have established a method for manufacturing seamless steel pipes that has high strength, excellent sulfide corrosion cracking resistance, and low-temperature toughness and can also be manufactured by continuous casting as follows. .

This invention has a weight ratio of On 0.1 to 0.5 (hereinafter simply referred to as ratio), Si: 0.1 to 0.84, and Ins 0.
．． 2 to 0.81, Or: 1.0 to 4.04, A/: 0.005 to 0.1 m, and both P and S are 0.005 inches or less.

and Nb: 0.0041 or less, respectively. Mcij O,1~1.01 and Nb: 0.0
1NO, 11, Zr and /mat= HaTi: o
, On5~o, 1% (!: Tomo ni,.

If necessary, V: 0.11 or less and B:
0.0054 or less, during the tempering treatment subsequent to quenching, after hot working and tempering treatment of a seamless steel pipe material having a composition containing at least one of the following:
In the temperature range from 10°C to AC1 point, at least τ (holding time at tempering temperature, hr) = -↓- depending on the wall thickness t of the tube.
x (tube thickness, fin) over a holding time τ given by 25.4 yield strength or 0.
The present invention proposes a method for producing a high-strength seamless steel pipe that has both excellent sulfide stress corrosion cracking resistance and low-temperature toughness at 20 kgf/-.

First, the reason why the proportions of each additive element are limited in this invention will be explained.

0: 0.1-0. r) Excellent When C is less than 0.1, hardenability is impaired.

If it exceeds 0.5, quench cracking will occur, so 0.1
The range was 0.5 to 0.5.

Si: 0. I NO, 84 Si is used to deoxidize steel and increase its strength. ] or more is required, but if it exceeds 0.8, the toughness will deteriorate, so 0.
The range was 1 to 0.8.

Mn: 0.2 to 0.8 '4 In improves strength and toughness by adding a modulus of 0.2 or more, and is also effective in deoxidizing, but if it exceeds a modulus of 0.8, segregation of P, S, etc. Since this causes deterioration of sulfide stress corrosion cracking resistance, the ratio is set to be in the range of 0.2 to 0.8.

Or: 1.0 to 4.0 Or is 1 strength for corrosion resistance, 1.0 for increasing tempering resistance
Although it is more necessary than rumored, if it exceeds 4.01, the toughness deteriorates, so it was set in the range of 1.0 to 4.0.

A/: 0.0015 to 0.11 A not only contributes to deoxidation but also combines with N to prevent N from segregating into grain boundaries and improves sulfide stress corrosion cracking resistance. 0LIFi 1 or more is required, but 0.11
If it exceeds 0.0, the effect will be saturated and the toughness will deteriorate.
The range was 0.005 to 0.1'1.

P, S ≦ 0.005 and N ≦ 0.0 (14 Since it has an adverse effect on interfacial cracking type sulfide corrosion cracking, it is desirable to reduce it as much as possible in order to prevent this.According to the present invention, MO and Nb, and Zr and/or T1 are added to reduce the impurity content. Even when fixing the elements, in order to obtain the desired strength, sulfide stress corrosion cracking resistance, and low-temperature toughness, the upper limits should be 0.005 for both P and S and 0.004 for N. There is a need to.

No: MO of 0.2 to 1.0 increases corrosion resistance, strength, and tempering resistance, prevents grain boundary segregation of P, and improves sulfide stress corrosion cracking resistance.
．． 21 or more is necessary, but if the content exceeds 1.0, the toughness deteriorates and it becomes expensive, so it is 0.2 to 1.
．． The range was 01.

Nb: 0.01-0.1 When Nb is added to the steel containing Or and Mo, it makes the carbides fine in the structure of the steel after tempering and disperses them uniformly within the grains. Fixing and preventing segregation to the grain boundaries helps improve sulfide stress corrosion cracking resistance, and for this purpose, 0.1 or more is required; if it exceeds 0.11, the toughness deteriorates. , and cause cracks to occur during material production by continuous casting.
．． The range is O2N2.1.

zr and/or Ti: 0.005 to 0.14 These elements have a strong affinity for N, and have the effect of fixing it, preventing segregation to grain boundaries, and improving sulfide stress corrosion cracking resistance. Since the effect is the same, Ti * Z
Each of r may be added singly or simultaneously, and in order to bring about the above effect, the total amount of r should be 0. No. 5 (+ or more is required; on the other hand, if it exceeds 0.1, the toughness deteriorates, so it should be in the range of 0.0051 to 0.1.

Steel having a limited composition as described above is hot worked into a seamless steel tube, and then quenched and tempered. Although the quenching conditions are not limited, it is preferable that 90 or more pieces have a martensitic structure.

Then, at a temperature of 620° or more and A01 or less, the tube wall thickness is maintained for 7 hours according to the following formula depending on the time, and a tempering treatment is performed. The holding time according to the formula is to prevent the segregation of impurities to the austenite grain boundaries and to uniformly and finely precipitate the spherical carbides to achieve the necessary strength.

Necessary to obtain toughness and resistance to sulfide stress corrosion cracking. When the AC point exceeds 3, austenite is formed, which becomes martensite which does not undergo tempering when cooled to room temperature, and the resistance to sulfide stress corrosion cracking is significantly deteriorated.

As described above, a high-strength seamless steel pipe with excellent low-temperature toughness and sulfide stress corrosion cracking resistance can be obtained. Depending on the situation, one or two of V and H may be added in an amount of 0, ol or more for V and 0.011051 or more for B.

The effects of this invention can be further improved.

However, when added in excess, both deteriorate the toughness of the steel.
Also, when manufacturing materials by continuous casting, the upper limit is 0.14 for V and 0.00 for B, as this can cause cracks.
54.

In this invention, the yield strength or 0.6 yield strength of the steel pipe is limited to the range from 70 kgf/- to 1!90 fl/Gt- because if it is less than 70 to 9 f/IIl+12, sulfide stress corrosion will occur. mainly exhibits a fracture surface in the form of coagulation cleavage or dimples, and rarely has a single grain boundary value surface. Because the cracking mechanisms are different, it is necessary to limit the amounts of P, S, and N and to Mo, N that prevents segregation into the field
This is because there is no particular meaning in adding Zr and/or T1 and specifying the tempering temperature and holding time; However, it deteriorates significantly.

Next, the implementation side of this invention is described in Table 0. Composition of seamless steel pipe, pipe wall thickness, tempering conditions, yield strength after tempering YS, tensile strength TS% sulfide stress JA corrosion cracking resistance, Charpy yTrs determined in the test is shown in comparison with a comparative example.

Sulfide stress corrosion cracking resistance was tested using a round rod tensile test piece in NAOE solution (saturated hydrogen sulfide water with 0.54 acetic acid and 5 tbsp of sodium chloride added) by applying a stress of 75 times the yield strength. did.

In Table 1, the ○ marks indicate those that did not break in the above test for 30 days, and the X marks indicate those that did. Symbols 1 to 4 in Table 1 are steel pipes according to the present invention, and all of them exhibit good sulfide stress corrosion cracking resistance and good low-temperature toughness. symbol 5,
Although the composition of the steel pipe No. 6 is within the scope of this invention, it is designated as No. 5.
Since the tempering temperature for the sample No. 6 and the holding time for the No. 6 sample are outside the range of the present invention, both the sulfide stress corrosion cracking resistance and the low temperature toughness are poor. Symbol 7 is P2 Symbol 8 is S, Symbol 9 is HaN, Symbol 10 is T1, Zr, Symbol ]1 is M
O and symbol 12 indicate that Nb is outside the component range of this invention, so even if the tempering treatment is performed within the range of this invention, excellent sulfide stress corrosion cracking resistance and low temperature toughness cannot be obtained. As described above, the present invention improves sulfide stress corrosion cracking resistance in steel pipes for oil wells or similar uses, such as line pipes, steel pipes for chemical plants, steel plates, etc. that require high strength and low-temperature toughness. When applied, it can bring about remarkable effects that are unparalleled heretofore.

Patent applicant: Kawasaki Steel Corporation

Claims (1)

[Claims] 1, e: o, 1 to 0.5 vehicle volume ratio, Si: 0
．． 1 to 0.3 river, Mn: 0.2 to (1,8 vehicle volume, Or: 1.0 to 41.0, including kl
: 0.005 to 0.1 weight in: 4, both P and S are below 0.005 weight, and N: (1
,004 respectively, and Mo:
(1゜2~1.0 vehicle volume and Nb: 0. old ~ 0.1
The weight coefficient is calculated by setting the total amount of Zr and/or Ti to 0.0 (1
Along with 5-0.1 Shigeharu, if necessary, Zaraani V
: 0.1 weight or less and B: 0.005 weight!
After hot working a seamless m' material that has a component composition that also contains at least one of the following: In the following temperature range, over at least the holding time τ given by the following formula according to the wall thickness t of the tube, the yield strength or 0.6 coefficient cuff resistance 0~] 2 Q kgf /
tnynE A method for manufacturing a high-strength seamless steel pipe characterized by having both sulfide stress corrosion cracking resistance and low-temperature toughness. τ = −1 25,4 In the formula, τ: Holding time at tempering temperature (hr) t = Tube wall thickness
(mm)