JPS625977B2 - - 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 6,000m deep, and some are over 10,000m 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 therein are required to have high strength and excellent corrosion resistance, especially resistance to stress corrosion cracking. . 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 stainless steel and other high-grade corrosion-resistant high-alloy steels such as 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 oil well environments, 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 our research to obtain oil country tubular goods with high strength and excellent stress corrosion cracking resistance that can withstand oil drilling in Cl ^- oil well environments, 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 (%) ≧110%, 7.5%≦Mo (%) + 1/2W (%)≦12%, and the Ni content 30～
60%, and the Cr content is 15 to 35%, H ₂ S—, which is extremely corrosive, even if it is a cold-worked material.
It is possible to obtain a surface film that exhibits excellent resistance to stress corrosion cracking in a CO ₂ - Cl ^- oil well environment, especially in a harsh environment of 200°C or higher. (d) Ni has the effect of increasing stress corrosion cracking resistance not only on the surface film but also on the structure. (e) More than 0.5% to 4% of one or more of Nb, Ti, Ta, Zr, and V (in the case of two or more, the total amount) (however, Nb: 3.1%) as an alloy component
Below, Ta: 3.1% or less, Ti: less than 1%, Zr: 1
% and V: less than 1%),
The alloy becomes even stronger due to precipitation strengthening. (f) When the S content as an unavoidable impurity is reduced to 0.0007% or less, the hot workability of the alloy is 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 when Cu: less than 0.3 to 1.5% is contained as an alloy component. (i) Rare earth elements: 0.1% or less as alloy components;
Y: 0.2% or less, Mg: 0.1% or less, and Ca:
When one or more of the above 0.1% 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 knowledge, and includes C: 0.1% or less, Si:
1% or less, Mn: 2% or less, P: 0.03% or less, preferably to further improve hydrogen cracking resistance, P: 0.003% or less, S: 0.005% or less, preferably to further improve hot workability. Purpose S: 0.0007%
Below, sol.Al: 0.5% or less, Ni: 30-60%, Cr:
Contains 15-35%, Cu: less than 0.3-1.5%, Nb,
One or more of Ti, Ta, Tr, and V (total amount if two or more): more than 0.5 to 4%
(However, Nb: 3.1% or less, Ta: 3.1% or less, Ti: 1
%, Zr: less than 1%, and V: less than 1%), contains one or two of Mo: 12% or less and W: 24% or less, and further contains rare earth elements as necessary. Element: 0.1% or less, Y: 0.2% or less,
Composition containing one or more of Mg: 0.1% or less and Ca: 0.1% or less, with the remainder consisting of Fe and unavoidable impurities (all % by weight and % by weight) It also satisfies the following conditional expressions: Cr (%) + 10Mo (%) + 5W≧110%, 7.5%≦Mo+1/2W (%)≦12%, and has high strength and excellent stress corrosion cracking resistance. However, 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) If the C content exceeds 0.1%, stress corrosion cracking tends to occur at grain boundaries, so the upper limit value should be set.
It was set at 0.1%. (b) Si Si is a necessary component as a deoxidizing component, but if its content exceeds 1%, hot workability deteriorates, so its upper limit was set at 1%. (c) Mn The Mn component has a deoxidizing effect like Si, and since this component has almost no effect on stress corrosion cracking resistance, the upper limit was set at 2%. (d) P The P component as an unavoidable impurity has the effect of increasing stress corrosion cracking susceptibility when its content exceeds 0.03%, so the upper limit is set at 0.03% and the stress corrosion cracking susceptibility is kept in a low state. It is necessary to do so. In addition, as the P content is reduced, 0.003%
It has been found that the hydrogen cracking resistance rapidly improves after the
It is desirable that the content be 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) Al Al is effective as a deoxidizing component like Si and Mn, and even if it is included up to 0.5% in sol.Al content, it will not impair the properties of the alloy. .Al content is set at 0.5% or less. (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 30%, the desired excellent stress corrosion cracking resistance cannot be secured; Even if the content exceeds 30%, no further improvement effect on stress corrosion cracking resistance appears, and the content was set at 30% to 60%, taking economic efficiency into account. (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 15%. On the contrary, in order to secure the desired stress corrosion cracking resistance, Mo
Since the content of W and W must be increased by that amount, which is economically disadvantageous, the lower limit value has been set.
It was set at 15%. 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, Ti, Ta, Zr, and V These components have the uniform effect of forming intermetallic compounds mainly with Ni and strengthening the alloy by precipitation, but their content is 0.5%. It is not possible to obtain the desired high strength if the content is less than
For Nb and Ta, if it exceeds 3.1%,
In the case of Ti, Zr, and V, if it is 1% or more, if two or more are contained, the total amount is 4%.
If the content exceeds 0.5% to 4% (however, Nb: 3.1% or less, Nb: 3.1% or less,
Ta: 3.1% or less, Ti: less than 1%, Zr: less than 1%,
and V: less than 1%). 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 aging treatment for 20 hours to strengthen the precipitation. (J) Mo and W As mentioned above, these components include Ni and
Coexistence with Cr has a uniform effect of improving stress corrosion cracking resistance, but even if the content exceeds 12% Mo and 24% W, the environmental temperature
In the corrosive environment of H ₂ S - CO ₂ - Cl ^- at 200°C or higher, no further improvement effect appeared, and in consideration of economic efficiency, the respective contents were reduced to Mo: 12% or less and W: 24%.
% or less. Furthermore, regarding the content of Mo and W, the conditional expression: Mo (%) + 1/2 W (%) specifies that W has about twice the atomic weight of Mo, and is about 1/2 as effective in terms of effectiveness. If this value is less than 7.5%, the desired stress corrosion cracking resistance cannot be obtained, especially in the adverse environment above 200°C.
Even if the value exceeds %, the content of Mo and W will be substantially unnecessary as described above, which is uneconomical.From this point of view, the value of Mo (%) + 1/2 W (%) is set to 7.5. ~12%. (k) Cu The Cu component has the effect of improving the corrosion resistance of the alloy, but if the content is less than 0.3%, the desired effect of improving corrosion resistance cannot be obtained;
If the content exceeds 0.3%, it will impede the improvement of hot workability and strength during cold working.
It is set at less than 1.5%. (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: 0.1%, Y: 0.2%,
Even if the content exceeds Mg: 0.1% and Ca: 0.1%, there is no improvement effect on hot workability, and even a deterioration phenomenon appears. Therefore, the content of each rare earth element: 0.1% or less, Y:
It was set as 0.2% or less, Mg: 0.1% or less, and Ca: 0.1% or less. (m) Cr (%) + 10Mo (%) + 5W (%) Figure 1 shows the stress corrosion cracking resistance of Cr (%) + 10Mo (%) + 5W (%) and Ni in a severe corrosive environment.
(%). That is,
Cr-Ni-Mo system, Cr-Ni-W system, and Cr-Ni with various contents of Cr, Ni, Mo, and W
- Mo-W steel is melted, cast, forged, and hot rolled to form a plate with a thickness of 7 mm, which is then held at a temperature of 1050°C for 30 minutes and then solution-cooled with water. After the treatment, we added cold working at a processing rate of 22% for the purpose of improving strength, and then performed 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, and a tensile force equivalent to 0.2% proof stress was applied to the test piece S using the three-point support beam jig shown in Figure 2. 10 atm _H2S and 10 atm _CO2 under stress
A stress corrosion cracking test was conducted by immersing the specimen in a 20% NaCl solution (temperature: 300°C) saturated with H ₂ S and 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 (%) + 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 FIG. 1, the ◯ mark indicates no cracking, and the x mark indicates cracking. From the results shown in Figure 2, the values of Cr (%) + 10Mo (%) + 5W (%) are
It is clear that if the Ni content is less than 110% and the Ni content is less than 30%, the desired excellent stress corrosion cracking resistance cannot be obtained. Note that even if the alloy of the present invention contains B, Sn, Pb, and Zn 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 with comparative examples and conventional examples. Example Molten metal having the composition shown in Table 1 was melted in a normal electric furnace and, if necessary, in an Ar-oxygen decarburization furnace (AOD furnace) for the purpose of desulfurization and electroslag melting for the purpose of dephosphorization. After melting using a furnace (ESR furnace), it is cast into an ingot with a diameter of 500mmφ, and then the ingot is heated to a temperature of 1200℃~
Hot forged in a temperature range of 1000℃ 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 by drawing processing to obtain the dimensions of diameter: 55 mmφ x wall thickness: 3.1 mm, thereby producing alloy tube materials 1 to 18 of the present invention. , Comparative alloy tube materials 1 to 10 and conventional alloy tube materials 1 to 4 were manufactured, respectively, and then the present invention alloy tube materials 1 to 18 were manufactured.
Comparative alloy tube materials 1 to 6 were subjected to aging treatment at a temperature of 650°C for 15 hours. In addition, comparative alloy tube materials 1 to 10 all have the content of one of the constituent components (as shown in Table 1).

【table】

【table】

【table】

[Table] is shown with an asterisk) has a composition that is outside the scope of this invention, and the conventional alloy pipe material 1
2 to JIS/SUS 316, 2 to JIS/310 S, 3 to JIS/SUS 316
is Incoloy 800, and conventional alloy tube material 4 is
It has a composition corresponding to JIS and SUS 329 J1. Next, the resulting alloy tube materials 1 to 1 of the present invention
18, comparative alloy pipe materials 1 to 10, and conventional alloy pipe material 1
From ~4, 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 is applied to the specimen S in this state, and H ₂ S
H ₂ S - 10 atm CO ₂ - 20% NaCl solution (liquid temperature:
A stress corrosion cracking test was conducted by immersing the steel in a water temperature (300°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 ○ mark indicates that no cracking occurred, while the x mark indicates that cracking occurred. From the results shown in Table 2, comparative alloy tube materials 1 to
No. 10 is inferior in at least one of hot workability, stress corrosion cracking resistance, and strength, whereas alloy tube materials 1 to 18 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 characteristics than conventional alloy tube materials 1 to 4, which are inferior. As mentioned above, the alloy of the present invention has particularly high strength and excellent resistance to stress corrosion cracking, 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 and 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 test materials, respectively. .

Claims (1)

[Claims] 1 C: 0.1% or less, Si: 1% or less, Mn: 2% or less, P: 0.03% or less, S: 0.005% or less, sol.Al: 0.5% or less, Ni: 30 to 60 %, Cr: 15 to 35%, Cu: less than 0.3 to 1.5%, and contains one or more of Nb, Ta, Ti, Zr, and V (in the case of two or more, the total amount ): 0.5%
Super to 4% (However, Nb: 3.1% or less, Ta: 3.1% or less, Ti: less than 1%, Zr: less than 1%, and V:
(Less than 1%), contains Mo: 12% or less, W: 24% or less, contains one or two of the following, and Cr (%) + 10Mo (%) + 5W (%) ≧ 110 %, 7.5% ≦ Mo (%) + 1/2 W (%) ≦ 12%, and the rest is Fe and other unavoidable impurities (weight %). A precipitation-strengthened alloy for high-strength oil country tubular goods with excellent corrosion cracking resistance. 2 C: 0.1% or less, Si: 1% or less, Mn: 2% or less, P: 0.03% or less, S: 0.005% or less, sol.Al: 0.5% or less, Ni: 30~60%, Cr: 15~ Contains 35%, Cu: 0.3 to less than 1.5%, and one or more of Nb, Ta, Ti, Zr, and V (in the case of two or more, the total amount): 0.5%
Super to 4% (However, Nb: 3.1% or less, Ta: 3.1% or less, Ti: less than 1%, Zr: less than 1%, and V:
1% or less), Mo: 12% or less, W: 24% or less, one or two of the following, furthermore, rare earth elements: 0.1% or less, Y: 0.2% or less, Mg : 0.1% or less, Ca: 0.1% or less, contains one or more of the following, and Cr (%) + 10Mo (%) + 5W (%) ≧ 110%, 7.5% ≦ Mo (%) A high-strength oil well with excellent stress corrosion cracking resistance, characterized by satisfying the following conditions: +1/2W (%) ≦ 12%, with the remainder consisting of Fe and other unavoidable impurities (weight %) Precipitation strengthened alloy for pipes.