JPS6144128B2 - - 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 10,000m 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 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 stainless steel and other high-grade corrosion-resistant high-alloy steels such as Incoloy and Hasteiro (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%, _H2S − _CO2− , 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 200°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
If one or more of these are contained in an amount of 0.5 to 4%, the alloy will have even higher strength due to the precipitation strengthening effect. (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) Cu: 2% or less and Co: 2 as alloy components
% or less, the corrosion resistance is further improved. (i) 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 (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 35%, one or more of Nb, Ti, Ta, Zr, and V: 0.5 to 4%, Mo: less than 7.5% and W: less than 15% Contains one or two of the following, and if necessary,
One or two of Cu: 2% or less and Co: 2% or less, 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 (all % by weight and % by weight), and Cr (%) + 10Mo ( %)+5W≧70%, 3.5%<Mo+1/2W(%)<7.5%, and has high strength and excellent stress corrosion cracking resistance, and these properties are particularly required. This alloy is characterized by 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) 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%.
has been established. (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 %. 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 0.003% 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 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 the 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 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 an even 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 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 seen. , 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 more than 3.5%, 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 be more than 3.5 and less than 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. Contains Cu:2
If the Co content exceeds 2%, it will prevent improvement in hot workability and strength during cold working, and if Co contains more than 2%
Since there is no further improvement effect even if the content exceeds the above, the respective contents were determined to be Cu: 2% or less and Co: 2% or less. (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 (%)
It shows the relationship between and N: (%). 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, stretched, and hot rolled into a plate with a thickness of 7 mm, and then this plate is heated at a temperature of 1050℃ for 30 minutes.
After holding for 30 minutes, water-cooling solution treatment was applied, cold working was applied at a processing rate of 22% for the purpose of improving strength, and then aging treatment was performed 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 this test piece was attached to the test piece using the three-point support beam jig shown in Figure 2.
A 20% NaCl solution saturated with _{H2S and CO2 (} temperature:
A stress corrosion cracking test was conducted by immersing the test piece in 200°C 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 Figure 1, ○ marks indicate no cracks.
The x marks indicate the occurrence of cracks. From the results shown in Figure 2, Cr (%) + 10Mo
It is clear that the desired excellent stress corrosion cracking resistance cannot be obtained when the value of (%) + 5W (%) is less than 70% and the Ni content is less than 25%. 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 dedensation. 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℃~
Diameter: 150 by hot forging in the temperature range of 1000℃
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 brass tube materials 1 to 4 were manufactured, respectively, and then alloy tube materials 1 to 1 of the present invention were manufactured.
6 and 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
It has a composition corresponding to JIS and SUS329JI. Next, the resulting alloy tube materials 1 to 1 of the present invention
16. Cut out a test piece with a length of 20 mm from Comparative Alloy Tube Materials 1 to 5 and Conventional Alloy Tube Materials 1 to 4, and cut off a portion corresponding to 60°C along the length from this test piece. As shown in the front view in Fig. 3, a bolt is passed through the test piece S and tightened with a nut to apply a tensile stress equivalent to 0.2% proof stress to the outer surface of the tube, and to the test piece S in this state,
_H2S partial pressures are 0.1 atm, 1 atm, and 15, respectively.
H ₂ S − 10 atm CO ₂ − 20% HaCl solution

【table】

【table】

[Table] A stress corrosion cracking test was conducted by immersing the product in a liquid (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 results of the tensile test, and the results of the impact test. In addition,
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. 5 is poor in at least one of hot workability, stress corrosion cracking resistance, and strength, while alloy tube materials No. 1 to 16 of the present invention
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 stress corrosion cracking resistance. Conventional alloy tube materials 1 to 4 with inferior properties
It is clear that it has even better characteristics when compared to 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: 1.0% or less, Mn: 2.0%
Below, P: 0.030% or less, S: 0.005% or less, sol.
Al: 0.5% or less, Ni: 25~~60%, Cr: 22.5~35
%, contains one or more of Mb, Ti, Ta, Zr, and V: 0.5 to 4%, and further contains one of Mo: less than 7.5% and W: less than 15%. Or contains two types, with the remainder consisting of Fe and unavoidable impurities (weight%), and Cr (%) + 10Mo (%) + 5W (%) ≧ 70%, 3.5% < Mo (%) A precipitation-strengthened alloy for high-strength oil country tubular goods with excellent stress corrosion cracking resistance, which satisfies the following conditions: +1/2W (%) < 7.5%. 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, sol.
Al: 0.5% or less, Ni: 25-60%, Cr: 22.5-35%
Contains 0.5 to 4% of one or more of Nb, Ti, Ta, Zr, and V, Mo:
Contains one or two of less than 7.5% and W: less than 15%, and further contains Cu: 2% or less and
Contains one or two of Co: 2% 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 high-strength precipitation-strengthened alloy for 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, sol.
Al: 0.5% or less, Ni: 25-60%, Cr: 22.5-35%
Contains 0.5 to 4% of one or more of Nb, Ti, Ta, Zr, and V, Mo:
Contains one or two of less than 7.5% and W: less than 15%, and further contains rare earth elements: 0.10% or less, Y: 0.20% or less, Mg: 0.10% or less, and
Contains one or more of Ca: 0.10% or less, with the remainder consisting of Fe and unavoidable impurities (weight%), and Cr (%) + 10Mo (%) + 5W (%) A precipitation strength alloy for high-strength oil country tubular goods with excellent stress corrosion cracking resistance, which satisfies the following conditions: ≧70%, 3.5%<Mo+1/2W (%)<7.5%. 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, sol.
Al: 0.5% or less, Ni: 25-60%, Cr: 22.5-35%
Contains 0.5 to 4% of one or more of Nb, Ti, Ta, Zr, and V, Mo:
Contains one or two of 7.5% or less and W: less than 15%, and further contains Cu: 2% or less and
Co: 2% or less, 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 %), and Cr (%) + 10Mo (%) A precipitation-strengthened alloy for high-strength oil country tubular goods with excellent stress corrosion cracking resistance, which satisfies the following conditions: +5W (%)≧70%, 3.5%<Mo+1/2W (%)<7.5%.