JPS6144125B2 - - Google Patents

Description

[Detailed description of the invention]

The present invention relates to an alloy that has high strength and excellent stress corrosion cracking resistance and is particularly suitable for use in the manufacture of oil country tubular goods. In recent years, due to the deterioration of the energy situation, there has been a marked tendency for oil and natural gas wells to become deeper.
Deep wells have appeared that are over 6,000 meters deep, and some are over 10,000 meters deep. Furthermore, due to similar circumstances, it is becoming increasingly difficult to extract oil and natural gas in a harsh corrosive environment containing humid hydrogen sulfide, as well as corrosive components such as carbon dioxide gas and chloride ions. As oil and natural gas are drilled in such harsh environments, the oil country tubular goods used in this process are now required to have high strength and excellent corrosion resistance, especially stress corrosion cracking resistance. . As a general anti-corrosion measure for oil country tubular goods, it is known to introduce a corrosion suppressant called an inhibitor, but this method is often not effective for use in, for example, offshore oil wells. From this point of view, consideration has recently begun to be given to the use of high-grade corrosion-resistant high-alloy steels such as stainless steel and Incoloy and Hastelloy (all trade names) for the production of oil country tubular goods, but so far,
Regarding these alloys, the details of the corrosion behavior of _H2S - _CO2 - ^Cl- in an oil well environment have not yet been fully elucidated. Therefore, from the above-mentioned point of view, the present inventors investigated deep wells and severe corrosive environments, especially H ₂ S−CO ₂ −
As a result of research aimed at obtaining oil country tubular goods with high strength and excellent stress corrosion cracking resistance that can withstand oil drilling in a Cl ^- oil well environment, we found that (a) H ₂ S−CO ₂ − The main type of corrosion in a Cl ^- environment is stress corrosion cracking, but the behavior of stress corrosion cracking in this case is completely different from that of general austenitic stainless steel. In other words, whereas general stress corrosion cracking is deeply related to the presence of Cl ^- , in the oil well environment mentioned above, the influence of H ₂ S is greater than that of Cl ^- . (b) Steel pipes used for practical use as oil country tubular goods are generally
Cold working is performed to improve strength, but cold working significantly reduces the resistance to stress corrosion cracking. (c) The elution rate (corrosion rate) of steel in an H ₂ S−CO ₂ −Cl ⁻ environment depends on the contents of Cr, Ni, Mo, and W, and is affected by the surface film made of these components. Corrosion resistance is maintained and these components are
It also increases its resistance to stress corrosion cracking, and in particular, Mo is 10 times more effective than Cr and twice as effective as W.
Mo and W satisfy the following conditional expressions: Cr (%) + 10Mo (%) + 5W (%) ≧50%, 1.0%≦Mo (%) + 1/2W (%) <3.5%, and the Ni content is 25-60
%, and the Cr content is 22.5 to 40%, even if it is a cold-worked material, if the environmental temperature is below 150℃, the concentration will be high.
A surface film that exhibits excellent resistance to stress corrosion cracking even under H ₂ S can be obtained. (d) Ni has the effect of increasing stress corrosion cracking resistance not only on the surface film but also on the structure. (e) When 0.05 to 0.30% of N is contained as an alloy component, the alloy strength is further improved. (f) When the S content as an unavoidable impurity is reduced to 0.0007% or less, the hot workability of the alloy will be significantly improved. (g) When the P content as an unavoidable impurity is reduced to 0.003% or less, the susceptibility to hydrogen cracking significantly decreases. (h) Corrosion resistance is further improved by containing 2% or less of Cu as an alloy component. (i) Rare earth elements as alloy components: 0.10% or less,
Y: 0.20% or less, Mg: 0.10% or less, and
Ca: When one or more of 0.10% or less is contained, hot workability is further improved. The findings shown in (a) to (i) above were obtained. Therefore, this invention was made based on the above findings, and includes C: 0.1% or less, Si:
1.0% or less, Mn: 2.0% or less, P: 0.030% or less,
Preferably, P: 0.003% or less, S: 0.005% or less, preferably S: 0.0007% or less, for the purpose of improving hot workability.
N: 0.05-0.30%, Ni: 25-60%, Cr: 22.5-40
%, contains one or two of Mo: less than 3.5% and W: less than 7%, and further contains Cu: 2.0% or less, rare earth elements: 0.10% or less, Y: 0.20. % or less, Mg: 0.10% or less, and
Ca: 0.10% or less of one or more of the following, or both, with the remainder consisting of Fe and unavoidable impurities (more than 0.10% by weight, less than %)
Cr (%) + 10Mo (%) + 5W (%) ≧ 50%, 1.0% ≦ Mo + 1/2W (%) < 3.5%, and satisfies the following conditional expressions: The alloy has high strength and excellent resistance to stress corrosion cracking, making it particularly suitable for use in the production of oil country tubular goods, which require these properties. Next, the reason why the composition range of the alloy of the present invention is limited as described above will be explained. (a) C If its content exceeds 0.10%, intergranular stress corrosion cracking is likely to occur, so the upper limit was set at 0.10%. (b) Si Si is a necessary component as a deoxidizing component, but if its content exceeds 1.0%, hot workability will deteriorate, so the upper limit value should be set at 1.0%.
It was determined that (c) Mn The Mn component has a deoxidizing effect like Si, and since this component has little effect on stress corrosion cracking resistance, the upper limit was set at a rather high value of 2.0%. (d) P The P component as an unavoidable impurity has the effect of increasing stress corrosion cracking susceptibility when its content exceeds 0.030%, so the upper limit should be set at 0.030%.
It is necessary to set the stress corrosion cracking susceptibility to a low state by setting the value as %. Furthermore, it has been found that as the P content is reduced, hydrogen cracking resistance and susceptibility rapidly improves after reaching 0.003%. If required, increase P content to 0.003
% or less. (e) S The S component as an unavoidable impurity has the effect of deteriorating hot workability when its content exceeds 0.005%, so the upper limit is set at 0.005% to reduce the deterioration of hot workability. It is necessary to prevent this. In this way, the S component has the effect of deteriorating hot workability when its content increases, but when its content is lowered to 0.0007%, hot workability is further improved. Therefore, if hot working under severe conditions is required, it is desirable to set the S content to 0.0007% or less. (f) N The N component has the effect of increasing the strength of the alloy, but if the content is less than 0.05%, the desired high strength cannot be achieved, while if the content exceeds 0.30%, the solid solubility limit is reached. Not only is it difficult to solve the problem, but even if solid solution is possible, defects are likely to occur in the alloy, so the content should be reduced to 0.05~
It was set at 0.30%. (g) Ni The Ni component has the effect of improving the stress corrosion cracking resistance of the alloy, but if its content is less than 25%, the desired excellent stress corrosion cracking resistance cannot be secured; Even if the content exceeds 25%, no further improvement in stress corrosion cracking resistance will be obtained, and considering economic efficiency, the content should be reduced to 25%.
~60%. (h) Cr The Cr component is a component that significantly improves stress corrosion cracking resistance when coexisting with Ni, Mo, and W components, but hot workability is not improved even if its content is less than 22.5%. On the contrary, in order to secure the desired stress corrosion cracking resistance, the content of Mo and W must be increased by that amount, which is economically disadvantageous, so the lower limit The value was set at 22.5%. On the other hand, if the S content exceeds 40%, deterioration of hot workability cannot be avoided no matter how much the S content is reduced, so the upper limit was set at 40%. (i) Mo and W As mentioned above, these components have an equal effect on improving stress corrosion cracking resistance when coexisting with Ni and Cr, but each Mo: 3.5
% or more and W: 7% or more, in a corrosive environment of H ₂ S - CO ₂ - Cl ^- where the environmental temperature is 150°C or less, further improvement effects do not appear, and in consideration of economic efficiency, The upper limit values of each content were set as less than 3.5% for Mo and less than 7% for W.
In addition, regarding the content of Mo and W, the conditional expression: Mo
(%) + 1/2 W (%) is specified because the atomic weight of W is about twice that of Mo, and the effect is about 1/2, which is equal, so if this value is less than 1.0%, The desired stress corrosion cracking resistance cannot be obtained, and on the other hand, this value
Even if it is 3.5% or more, as mentioned above, it will contain substantially unnecessary amounts of Mo and W, which is not economical.From this point of view, the value of Mo (%) + 1/2 W (%) is set from 1.0% to 3.5. It was set as less than %. (j) Cu Since the Cu component has the effect of improving the corrosion resistance of the alloy, it is included as necessary especially when even better corrosion resistance is required, but 2%
If the content exceeds 2%, hot workability deteriorates, so the upper limit was set at 2%. (k) Rare earths, Y, Mg, and Ca These components have the uniform effect of further improving hot workability, so they may be included as necessary when hot working is performed under severe conditions. Rare earth elements: 0.10%, Y:
Even if the content exceeds 0.20%, Mg: 0.10%, and Ca: 0.10%, there is no improvement effect on hot workability, and even deterioration phenomenon appears. Rare earth elements: 0.10% or less, Y: 0.20% or less, Mg: 0.10%
and Ca: 0.10% or less. (l) Cr (%) + 10Mo (%) + 5W (%) Figure 1 shows stress corrosion cracking resistance under severe corrosive environments. Cr (%) + 10Mo (%) + 5W (%)
This shows the relationship between Ni (%) and Ni (%). That is, Cr-Ni-Mo system, Cr-Ni-W system with various contents of Cr, Ni, Mo, and W
system, and Cr-Ni-Mo-W system steel,
It is cast, forged and hot rolled into a plate with a thickness of 7mm, and then heated to 1050°C for 30 minutes.
After holding for 30 minutes, water-cooling solution treatment was applied, and cold working was applied to the steel plate at a processing rate of 30% to improve strength.The resulting steel plate was then processed perpendicularly to the rolling direction to a thickness of 2 mm x width: A test piece of 10 mm x length: 75 mm was cut out, and the test piece shown in Figure 2 was
Using a point support beam jig, the test piece S was
With a tensile stress equivalent to % proof stress added,
_H2S and 10 atm _H2S and 10 atm _CO2
20% NaCl solution saturated with _CO2 (temperature: 150
A stress corrosion cracking test was carried out by immersing the test pieces in 1,000 hours of immersion in 1000°C (°C), and after the test, the presence or absence of cracking in the test pieces was observed. Based on these results, the inventors independently set a conditional expression: Cr (%) + 10Mo
It has become clear that there is a relationship between (%) + 5W (%) and Ni content with respect to stress corrosion cracking resistance, as shown in Figure 1. In addition, the first
In the figure, the mark ◯ indicates no cracking, and the mark x indicates cracking. From the results shown in Figure 1, Cr (%) + 10Mo (%) + 5W
(%) value is less than 50%, Ni content is 25%
It is clear that the desired excellent stress corrosion cracking resistance cannot be obtained if it is less than that. Note that even if the alloy of the present invention contains Ti and Al as unavoidable impurities in a range of 0.1% or less, the properties of the alloy of the present invention will not be impaired in any way. Next, the alloy of the present invention will be explained using examples while comparing it with comparative examples and conventional examples. Example Molten metal having the composition shown in Table 1 was heated in a normal electric furnace for the purpose of desulfurization and nitrogen addition.
After melting using an Ar-oxygen decarburization furnace (AOD furnace) and, if necessary, an electroslag melting furnace (ESR furnace) for the purpose of dephosphorization, the diameter: 500.

【table】

【table】

【table】

[Table] Cast into mmφ ingot, then hot forged at 1200℃ to diameter: 150.
A billet of mmφ is formed, and in this case, for the purpose of evaluating hot workability, it is observed whether or not cracks occur in the billet, and then the billet is hot extruded to a diameter of 60 mmφ x wall thickness: After forming a 4 mm raw tube, it was further subjected to 22% cold working through drawing processing to obtain dimensions of diameter: 55 mmφ x wall thickness: 3.1 mm, thereby producing alloy tube materials 1 to 22 of the present invention. , Comparative Alloy Tube Materials 1 to 5, and Conventional Alloy Tube Materials 1 to 3 were manufactured, respectively. In addition, Comparative Alloy Tube Materials 1 to 5 all have compositions in which the content of one of the constituent components (indicated with an asterisk in Table 1) is outside the scope of this invention. And, the conventional alloy tube material 1 is
JIS/SUS316, conventional alloy tube material 2 is Incoloy
800, and the conventional alloy pipe material 3 is JIS/SUS329J1
The compositions correspond to the respective compositions. Next, the resulting alloy tube materials 1 to 1 of the present invention
22, Comparative alloy tube materials 1 to 5, and conventional alloy tube materials 1
From ~3, cut out a test piece with a length of 20 mm,
Cut off a section corresponding to 60° along the length of this test piece, pass a bolt through this test piece as shown in the front view in Figure 3, tighten it with a nut, and attach it to the outside surface of the tube. A tensile stress equivalent to 0.2% proof stress was applied to the specimen in this state, and _{the H2S} partial pressures were set to 0.1 atm, 1 atm, and 15 atm, respectively.H2S - 10 atm CO2 _-20 % MaCl solution (solution temperature:
A stress corrosion cracking test was conducted by immersing the steel in a water temperature (150°C) for 1000 hours, and the presence or absence of stress corrosion cracking after the test was investigated. The results are shown in Table 1 along with the presence or absence of cracking during hot forging and 0.2% proof stress. In Table 1, the marks ◯ indicate those with no cracks, while the marks x indicate those with cracks. From the results shown in Table 1, comparative alloy pipe materials 1 to
Alloy tube materials 1 to 22 of the present invention have high strength and excellent Stress corrosion cracking resistance,
Furthermore, it has good hot workability, and is even better than conventional alloy tube materials 1 to 3, which have good hot workability but relatively low strength and poor stress corrosion cracking resistance. It is clear that it has certain characteristics. As mentioned above, the alloy of the present invention has particularly high strength and excellent stress corrosion cracking resistance.
As oil country tubular goods used in oil and natural gas extraction under harsh environments where these characteristics are required,
Furthermore, it exhibits extremely excellent performance when used as geothermal well pipes.

[Brief explanation of the drawing]

Figure 1 shows the stress corrosion cracking resistance of alloys.
A diagram showing the relationship between content and Cr (%) + 10Mo (%) + 5W (%), Figures 2 and 3 are diagrams showing the mode of stress corrosion cracking tests on plate-shaped and tubular specimens, respectively. .

Claims (1)

[Claims] 1 C: 0.1% or less, Si: 1.0% or less, Mn: 2.0%
Below, P: 0.030% or less, S: 0.005% or less, N:
Contains 0.05 to 0.30%, Ni: 25 to 60%, Cr: 22.5 to 40%, and one or two of Mo: less than 3.5% and W: less than 7%, with the remainder being Fe and unavoidable impurities. It has a composition (weight%) consisting of Cr (%) + 10Mo (%) + 5W (%) ≧ 50%, 1.0% ≦ Mo (%) + 1/2W (%) < 3.5%. A high-strength oil country tubular alloy with excellent stress corrosion cracking resistance. 2 C: 0.1% or less, Si: 1.0% or less, Mn: 2.0%
Below, P: 0.030% or less, S: 0.005% or less, N:
Contains 0.05 to 0.30%, Ni: 25 to 60%, Cr: 22.5 to 40%, contains one or two of Mo: less than 3.5% and W: less than 7%, and further Cu: 2%
Contains the following, with the remainder consisting of Fe and unavoidable impurities (weight%), and Cr (%) + 10Mo (%) + 5W (%) ≧50%, 1.0%≦Mo (%) + 1/ A high-strength oil country tubular alloy with excellent stress corrosion cracking resistance that satisfies the following conditions: 2W (%) < 3.5%. 3 C: 0.1% or less, Si: 1.0% or less, Mn: 2.0%
Below, P: 0.030% or less, S: 0.005% or less, N:
Contains 0.05 to 0.30%, Ni: 25 to 60%, Cr: 22.5 to 40%, one or two of Mo: less than 3.5% and W: less than 7%, and rare earth element: 0.10. % or less, Y: 0.20% or less, Mg: 0.10% or less, and Ca: 0.10% or less, with the remainder consisting of Fe and unavoidable impurities (weight% or more). and satisfies the following conditions: Cr (%) + 10Mo (%) + 5W (%) ≧ 50%, 1.0% ≦ Mo (%) + 1/2W (%) < 3.5%. A high-strength oil country tubular alloy with excellent crack resistance. 4 C: 0.1% or less, Si: 1.0% or less, Mn: 2.0%
Below, P: 0.030% or less, S: 0.005% or less, N:
Contains 0.05 to 0.30%, Ni: 25 to 60%, Cr: 22.5 to 40%, contains one or two of Mo: less than 3.5% and W: less than 7%, and further Cu: 2%
Contains the following and one or more of the following: rare earth elements: 0.10% or less, Y: 0.20% or less, Mg: 0.10% or less, and Ca: 0.10% or less, and the remaining
Composition consisting of Fe and unavoidable impurities (more than % by weight)
and satisfies the following conditions: Cr(%)+10Mo(%)+5W(%)≧50%, 1.0%≦Mo(%)+1/2W(%)<3.5%. A high-strength oil country tubular alloy with excellent stress corrosion cracking resistance.