JPS625976B2 - - 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 over 6000m deep, some over 10000m deep, have appeared. 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. The details of the corrosion behavior of H ₂ S―CO ₂ -Cl― in the oil well environment 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 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 (%) ≧ 50%, 1.0% ≦ Mo (%) + 1/2W (%) < 3.5%, and the Ni content 25-60
%, and the Cr content is 22.5 to 40%, H ₂ S―CO ₂ ―, 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 Cl ^- oil well environment, especially in a harsh environment below 150°C. (d) Ni has the effect of increasing stress corrosion cracking resistance not only on the surface film but also on the structure. (e) Nb, Ti, Ta, Zr, and V as alloying components
When one or more of these are contained in an amount of 0.5 to 4%, the alloy will have even higher strength 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 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) When less than 1.5% of Cu is contained as an alloy component, corrosion resistance is further improved. (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 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, sol.Al: 0.5% or less, Ni: 25-60%, Cr:
Contains 22.5 to 40%, one or more of Nb, Ti, Ta, Zr, and V: 0.5 to 4%, Mo: less than 3.5% and W: less than 7%. Contains one or two types, and further as necessary
Cu: less than 1.5%, 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 (all % by weight and % by weight), and Cr (%) + 10Mo ( %)+5W≧50%, 1.0%≦Mo+1/2W(%)<3.5%, and has high strength and excellent stress corrosion cracking resistance, and these characteristics are particularly required. This is a precipitation-strengthened alloy suitable for use in the production of oil country tubular goods. 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 0.10%, stress corrosion cracking is likely to occur at grain boundaries, so the upper limit value should be set.
It 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 deteriorates, so its upper limit was set at 1.0%. (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 is set at 0.030% and the stress corrosion cracking susceptibility is kept in a low state. It is necessary to do so. Also, as the P content is reduced,
It has been found that hydrogen cracking resistance rapidly improves after reaching 0.003%. From this point of view, when particularly excellent hydrogen cracking resistance is required, the P content should be reduced 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) 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 25%, the desired excellent stress corrosion cracking resistance cannot be secured; Even if the content exceeds 25%, no further improvement effect on stress corrosion cracking resistance appears, and the content was set at 25% to 60%, taking economic efficiency into consideration. (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 ensure the desired stress corrosion cracking resistance,
The lower limit was set at 22.5% because it would be economically disadvantageous to have to increase the content of Mo and W by that much. 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) 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%. If the content is less than 4%, the desired high strength cannot be obtained; on the other hand, if the content exceeds 4%, ductility and toughness will decrease, as well as hot workability. It was set at 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 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 Mo: 3.5% or more and W: 7% or more are contained, H ₂ S—CO at an environmental temperature of 150°C or less _{2 -} In a corrosive environment of Cl ^- ,
Furthermore, since no further improvement effect appeared, the respective contents were changed to Mo: less than 3.5%, considering economic efficiency.
W: Set as less than 7%. 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 1.0%, the desired stress corrosion cracking resistance cannot be obtained, especially under the above adverse environment of 150℃ or less.On the other hand, even if this value is 3.5% or more, as mentioned above, This results in substantially unnecessary amounts of Mo and W being contained, which is uneconomical.From this point of view, the value of Mo (%) + 1/2 W (%) was set to less than 1.0 to 3.5%. (k) Cu The Cu component has the effect of improving the corrosion resistance of the alloy, so it is included as necessary when even better corrosion resistance is required. The content was set at less than 1.5% because it not only deteriorates the carbon content but also impedes the increase in strength through cold working. (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: 0.20%,
Even if the content exceeds Mg: 0.10% and Ca: 0.10%, there is no improvement effect on hot workability, and even deterioration phenomenon appears. Therefore, the content of each rare earth element: 0.10% or less,
Y: 0.20% or less, Mg: 0.10% or less, and Ca:
It was set at 0.10% 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: 150°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 value of Cr (%) + 10Mo (%) + 5W (%) is 50
It is clear that if the Ni content is less than 25%, 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 dimensions of diameter: 55 mmφ x wall thickness: 3.1 mm, thereby producing alloy tube materials 1 to 16 of the present invention. , Comparative alloy tube materials 1 to 5 and conventional alloy tube materials 1 to 4 were manufactured, respectively, and then the present invention alloy tube materials 1 to 16 were manufactured.
Comparative alloy tube materials 1 to 5 were subjected to aging treatment at a temperature of 650°C for 15 hours. 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, same 2 is JIS/310S, same 3 is Incoloy 800, and conventional alloy tube material 4 is JIS/310S.
Each has a composition corresponding to SUS329JI. Next, the resulting alloy tube materials 1 to 1 of the present invention
16, comparative alloy pipe materials 1 to 5, 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 temperature of 150°C for 1000 hours, and the presence or absence of stress corrosion cracking after the test was investigated. This result is compared to the presence or absence of cracking during hot forging, the tensile test results, and the impact

【table】

【table】

[Table] The results are shown in Table 2 along with 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
In contrast, alloy tube materials 1 to 16 of the present invention are inferior in at least one of hot workability, stress corrosion cracking resistance, and strength.
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 4, 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 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: 25 to 60 %, Cr: 22.5 to 40%, and one or more of Nb, Ti, Ta, Zr, and V (in the case of two or more, in total): 0.5 to
4%, furthermore, one of Mo: less than 3.5% and W: less than 7%.
species or two species, and satisfies the following conditions: Cr (%) + 10Mo (%) + 5W (%) ≧ 50%, 1% ≦ Mo (%) + 1/2W (%) < 3.5%, and the remaining A precipitation-strengthened alloy for high-strength oil country tubular goods with excellent stress corrosion cracking resistance, characterized by having a composition (by weight %) consisting of Fe and other unavoidable impurities. 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: 25-60%, Cr: 22.5- 40%, Contains one or more of Nb, Ti, Ta, Zr, and V (total if two or more): 0.5 to
4%, Mo: less than 3.5% and W: less than 7%.
Contains one or two species, Cu: less than 1.5%, and Cr (%) + 10Mo (%) + 5W (%) ≧50%, 1%≦Mo (%) + 1/2W ( %) < 3.5%, and the remainder is Fe and other unavoidable impurities (weight%). A precipitation-strengthened type for high-strength oil country tubular goods with excellent stress corrosion cracking resistance. alloy. 3 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: 25~
60%, Cr: 22.5 to 40%, one or more of Nb, Ti, Ta, Zr, and V (total if two or more): 0.5 to
4%, Mo: less than 3.5% and W: less than 7%.
contains one or more of the following: rare earth elements: 0.1% or less, Y: 0.2% or less, Mg: 0.1% or less, Ca: 0.1% or less, And, the following conditions are satisfied: Cr (%) + 10Mo (%) + 5W (%) ≧ 50%, 1% ≦ Mo (%) + 1/2W (%) < 3.5%, and the rest is free from Fe and other unavoidable impurities. A precipitation-strengthened alloy for high-strength oil country tubular goods with excellent stress corrosion cracking resistance, characterized by having the following composition (the above weight %): 4 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: 25-60%, Cr: 22.5- 40%, Contains one or more of Nb, Ti, Ta, Zr, and V (total if two or more): 0.5 to
4%, Mo: less than 3.5% and W: less than 7%.
Contains one or more of the following: rare earth elements: 0.1% or less, Y: 0.2% or less, Mg: 0.1% or less, Ca: 0.1% or less, Cu: 1.5 %, and satisfies the following conditions: Cr (%) + 10Mo (%) + 5W (%) ≧ 50%, 1% ≦ Mo (%) + 1/2W (%) < 3.5%, and the rest is Fe. A precipitation-strengthened alloy for high-strength oil country tubular goods with excellent stress corrosion cracking resistance, characterized by having a composition (by weight %) consisting of and other unavoidable impurities.