JPS6144134B2 - - Google Patents

Description

[Detailed description of the invention]

The present invention relates to a precipitation-strengthened 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 (both trade names) for the production of oil country tubular goods. Regarding the corrosion behavior of H ₂ S−CO ₂ −Cl ⁻ in an oil well environment, the details have not yet been fully elucidated, and furthermore, it does not have the high strength required for oil country tubular goods for deep wells. is the current situation. 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 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 (%) ≧70%, 3.5%≦Mo (%) + 1/2W (%) <7.5%, and the Ni content is 25-60
%, and the Cr content is 22.5 to 35%, even if it is a cold-worked material after aging treatment, it can be used in an extremely corrosive H ₂ S−CO ₂ −Cl ⁻ oil well environment, especially below 200°C. It is possible to obtain a surface film that exhibits excellent resistance to stress corrosion cracking in adverse environments. (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 0.25% of N is included as an alloy component, the alloy strength improves. (f) When 0.5 to 4% of one or both of Nb and V are contained as alloying ingredients, the alloy will have even higher strength due to precipitation strengthening. (g) 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. (h) When the P content as an unavoidable impurity is reduced to 0.003% or less, the susceptibility to hydrogen cracking significantly decreases. (i) Cu: 2% or less and Co: 2 as alloy components
% or less, the corrosion resistance is further improved. (j) Rare earth elements: 0.10% or less as alloy components;
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 (j) above were obtained. Therefore, this invention was made based on the above knowledge, and includes C: 1.0% or less, Si:
1.0% or less, Mn: 2.0% or less, P: 0.030% or less,
Preferably, for the purpose of further improving hydrogen cracking resistance, P: 0.003% or less, S: 0.005% or less, desirably S: 0.0007% for the purpose of further improving hot workability.
Below, N: 0.05-0.25%, Ni: 25-60%, Cr:
Contains 22.5 to 35%, one or two of Nb and V: 0.5 to 4%, and one or two of Mo: less than 7.5% and W: less than 15%. , and further one or two of Cu: 2% or less and Co: 2% 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, and the remainder is Fe and unavoidable impurities (all % by weight and % by weight). In addition, it satisfies the following conditional expressions: Cr (%) + 10Mo (%) + 5W≧70%, 3.5%≦Mo + 1/2W (%) <7.5%, and has high strength and excellent stress corrosion cracking resistance. It is a precipitation-strengthened alloy that is particularly suitable for use in the production of oil country tubular goods that 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%, stress corrosion cracking is likely to occur at grain boundaries, so the upper limit value 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 %. It has also been found that as the P content is reduced, hydrogen cracking resistance rapidly improves after reaching 0.003%.
From this point of view, when particularly excellent hydrogen cracking resistance is required, it is desirable that the P content be 0.0030% 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 N has the effect of improving the strength of the alloy through solid solution strengthening, but if its content is less than 0.05%, the desired high strength cannot be obtained;
If the content exceeds 0.25%, nitrides will be formed during aging treatment and the corrosion resistance of the alloy will deteriorate, so the content was set at 0.05 to 0.25%. (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 improved even if its content is less than 22.5%. On the contrary, in order to ensure the desired stress corrosion cracking resistance, the content of Mo and W must be increased by that amount, which is economically disadvantageous. The lower limit was set at 22.5%. On the other hand, if the S content exceeds 35%, deterioration of hot workability cannot be avoided no matter how much the S content is reduced, so the upper limit was set at 35%. (i) Nb and V These components mainly have the uniform effect of forming intermetallic compounds with Ni to strengthen the alloy by precipitation, but if their content is less than 0.5%, the desired high strength cannot be achieved. On the other hand, if the content exceeds 4%, the ductility and toughness will decrease, and the hot workability will also deteriorate. Therefore, the content was set at 0.5 to 4%. Therefore, when manufacturing oil country tubular goods from the alloy of the present invention, it is necessary to perform cold working at a working rate of 10 to 60% or after cold working at a temperature of 450 to 800°C at an appropriate point in the manufacturing process. It is necessary to perform an aging treatment for 20 hours to strengthen the precipitation. (j) 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: 7.5
% or more and W: 15% or more, in a corrosive environment of H ₂ S - CO ₂ - Cl ^- where the environmental temperature is 200°C or less, no further improvement effect will be obtained, and considering economic efficiency. , each content is Mo:
It was set as less than 7.5% and W: less than 15%. Also, Mo
Regarding the content of Therefore, if this value is less than 3.5%, the desired stress corrosion cracking resistance cannot be obtained, especially under the above-mentioned adverse environment of 200℃ or less.On the other hand, even if this value is 7.5% or more, as mentioned above, The content of unnecessary amounts of Mo and W would be uneconomical, and from this point of view, the value of Mo (%) + 1/2 W (%) was set to less than 3.5 to 7.5%. (k) Cu and Co These components have a uniform effect of improving the corrosion resistance of the alloy, and Co has a solid solution strengthening effect, so they can be used as necessary when these properties are especially required. It contains Cu, but Cu is 2
If the Co content exceeds 2%, the hot workability will deteriorate, while if the Co content exceeds 2%, there will be no further improvement effect.
Each content is Cu: 2% or less, Co: 2%
It was determined as follows. (l) Rare earth elements, Y, Mg, and Ca These components have the uniform effect of further improving hot workability, so they may be added as necessary when hot working is performed under severe conditions. However, 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 in fact, deterioration phenomenon appears. Rare earth elements: 0.10% or less, Y: 0.20% or less, Mg: 0.10%
and Ca: 0.10% or less. (m) 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, followed by cold working at a processing rate of 30% for the purpose of improving strength, followed by aging treatment at a temperature of 650°C for 15 hours. A test piece of thickness: 2 mm x width: 10 mm x length: 75 mm was cut out from the steel plate perpendicular to the rolling direction, and the test piece S
_H2S at 10 atm _H2S and 10 atm _CO2 with an applied tensile stress corresponding to 0.2% yield strength.
A stress corrosion cracking test was conducted by immersing the specimen in a 20% NaCl solution (temperature: 200°C) saturated with CO ₂ for 1000 hours, and after the test, the presence or absence of cracking in the test piece was observed. Based on these results, the inventors independently set a conditional expression: Cr
It has become clear that there is a relationship between (%) + 10Mo (%) + 5W (%) and Ni content with respect to stress corrosion cracking resistance, as shown in Figure 1. In FIG. 1, the ◯ mark indicates no cracking, and the x mark indicates cracking. From the results shown in Figure 1, Cr (%) +
It is clear that the desired excellent stress corrosion cracking resistance cannot be obtained when the value of 10Mo (%) + 5W (%) is less than 70% and the Ni content is less than 25%. Furthermore, even if the alloy of the present invention contains Ti, Al, B, Sn, Pb, and Zn as unavoidable impurities within 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 with comparative examples and conventional examples. Example Molten metal having the composition shown in Table 1 is heated in a normal electric furnace, an Ar-oxygen decarburization furnace (AOD furnace) for the purpose of nitrogen inclusion and desulfurization, and, if necessary, for the purpose of dephosphorization. Diameter: 500mm after melting using electroslag melting furnace (ESR furnace)
It is cast into a φ ingot, and then hot forged at a temperature of 1200°C to create a diameter of 150mm.
A billet of φ 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 form a billet with 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 8, and conventional alloy tube materials 1 to 3 were manufactured, respectively, and subsequently, the present invention alloy tube materials 1 to 22 and comparative alloy tube materials 1 to 8 were subjected to aging treatment at a temperature of 650°C for 15 hours. was applied. In addition, Comparative Alloy Tube Materials 1 to 8 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
According to JIS 316, the conventional alloy tube material 2 is Incoloy 800.
Furthermore, the conventional alloy tube material 3 has a composition corresponding to JIS and SUS329J1. Next, the resulting alloy tube materials 1 to 1 of the present invention
22, comparative alloy pipe materials 1 to 8, and conventional alloy pipe material 1
From ~3, cut out a test piece with a length of 20 mm,
A section corresponding to 60° was cut off from this test piece in the length direction, and a bolt was passed through the test piece in this state as shown in the front view in Figure 3, and a nut was inserted into the test piece.

【table】

【table】

【table】

[Table] A tensile stress equivalent to 0.2% proof stress is applied to the outer surface of the tube by tightening it, and to the test piece S in this state,
_H2S partial pressures are 0.1 atm, 1 atm, and 15, respectively.
A stress corrosion cracking test was carried out by immersion in H ₂ S - 10 atm CO ₂ - 20% NaCl solution (liquid temperature: 200°C) for 1000 hours, and the presence or absence of stress corrosion cracking after the test was investigated. The results are shown in Table 2 together with the presence or absence of cracking during hot forging, the tensile test results, and the impact test results. In Table 2, the ○ marks indicate those with no cracks, while the x marks indicate those with cracks. From the results shown in Table 2, comparative alloy tube materials 1 to
No. 8 is inferior in at least one of hot workability, stress corrosion cracking resistance, and strength, whereas alloy tube materials 1 to 22 of the present invention are
Both have excellent hot workability and stress corrosion cracking resistance, and also have high strength and good hot workability, but have relatively low strength and poor stress corrosion cracking resistance. It is clear that this material has even better properties than conventional alloy tube materials 1 to 3, which are inferior. As mentioned above, the alloy of the present invention has particularly high strength and excellent stress corrosion cracking resistance, making it suitable for use in oil and natural gas extraction in harsh environments where these properties are required. It exhibits extremely excellent performance when used as oil country tubular goods (oil country tubular goods), as well as geothermal country tubular goods.

[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 0.25%, Ni: 25 to 60%, Cr: 22.5 to 35%, and one or two of Nb and V:
0.5 to 4%, further containing one or two of Mo: less than 7.5% and W: less than 15%, with the remainder consisting of Fe and unavoidable impurities (wt%), and stress corrosion cracking resistance, which satisfies the following conditions: Cr (%) + 10Mo (%) + 5W (%) ≧70%, 3.5%≦Mo (%) + 1/2W (%) <7.5%. A precipitation-strengthened alloy for high-strength oil country tubular goods with excellent properties. 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 0.25%, Ni: 25 to 60%, Cr: 22.5 to 35%, and one or two of Nb and V:
Contains 0.5-4%, Mo: less than 7.5% and W:
Contains one or two of less than 15%, and further contains one of Cu: 2% or less and Co: 2% or less.
Cr(%)+10Mo(%)+5W(%)≧70%, 3.5%≦Mo+1/2W (%)<7.5%, A precipitation-strengthened alloy for high-strength oil country tubular goods with excellent stress corrosion cracking resistance. 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 0.25%, Ni: 25 to 60%, Cr: 22.5 to 35%, and one or two of Nb and V:
Contains 0.5-4%, Mo: less than 7.5% and W:
Contains one or two of less than 15%, and further includes rare earth elements: 0.10% or less, Y: 0.20% or less,
Contains one or more of Mg: 0.10% or less and Ca: 0.10% or less, with the remainder consisting of Fe and unavoidable impurities (wt%),
And, it is characterized by satisfying the following conditions: Cr (%) + 10Mo (%) + 5W (%) ≧70%, 3.5%≦Mo + 1/2W (%) <7.5%. Precipitation strengthened alloy for strength oil country tubular goods. 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 0.25%, Ni: 25 to 60%, Cr: 22.5 to 35%, and one or two of Nb and V:
Contains 0.5-4%, Mo: less than 7.5% and W:
Contains one or two of less than 15%, and further contains one of Cu: 2% or less and Co: 2% or less.
Species or 2 types, rare earth elements: 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 %), and Cr (%) + 10Mo (%) + 5W (%) ≧70% , 3.5%≦Mo(%)+1/2W(%)<7.5%, A precipitation-strengthened alloy for high-strength oil country tubular goods with excellent stress corrosion cracking resistance.