JPS6144130B2 - - Google Patents

Description

[Detailed description of the invention]

The present invention relates to an alloy that has excellent stress corrosion cracking resistance and hot workability, and is particularly suitable for use in manufacturing oil country tubular goods. In recent years, due to the deterioration of the energy situation, oil and natural gas wells have tended to become deeper and deeper, and they are exposed to harsh corrosive environments containing humid hydrogen sulfide, as well as corrosive components such as carbon dioxide and chloride ions. Extraction of oil and natural gas is becoming more difficult. As oil and natural gas are drilled in such harsh environments, the oil country tubular goods used therein are also required to have excellent corrosion resistance, particularly stress corrosion cracking resistance. On the other hand, as a general anti-corrosion measure for oil country tubular goods, it is known to introduce a corrosion inhibitor called an inhibitor, but this method is often not effective for use in offshore oil wells, for example. 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. At present, the details of the corrosion behavior of H ₂ S−CO ₂ −Cl ⁻ in an oil well environment have not 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 excellent stress corrosion cracking resistance that can withstand oil drilling in a Cl ^- oil well environment, we found that (a) an H ₂ S−CO ₂ −Cl ^- environment; The main type of corrosion in steel 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 (%) ≧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) 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. (f) Cu: 2% or less and Co: 2 as alloy components
% or less, the corrosion resistance is further improved. (g) Rare earth elements: 0.10% or less as alloy components;
Y: 0.20% or less, Mg: 0.10% or less, Ti: 0.5%
When one or more of the following and Ca: 0.10% or less is contained, hot workability is further improved. The findings shown in (a) to (g) above were obtained. Therefore, this invention was made based on the above knowledge, and includes C: 0.1% or less, Si:
1.0% or less, Mn: 2.0% or less, P: 0.030% or less,
S: 0.0007% or less, sol.Al: 0.5% or less, Ni: 25~
60%, Cr: 22.5-35%, Mo: less than 7.5% and W: less than 15%, and further contains Cu: 2% or less, Co:
2% or less, rare earth elements: 0.10% or less, Y: 0.20% or less, Mg: 0.10% or less, Ti: 0.5% or less, and
Contains one or more of Ca: 0.10% or less, with the remainder consisting of Fe and unavoidable impurities (the above weight % and the following % are all weight %), and Cr (%) )+10Mo(%)+5W(%)≧70%, 3.5%≦Mo(%)+1/2W(%)<7.5%, and has excellent stress corrosion cracking resistance and hot workability. The alloy is particularly suitable for use in the production of oil country tubular goods used in oil well environments of extremely corrosive _H2S - _CO2 - ^Cl- at temperatures below 200°C. 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 maintain stress corrosion cracking susceptibility at a low level by determining the following. (e) S If the content of S, which is an unavoidable impurity, is reduced to 0.0007% or less, hot workability will be further improved.
0.0007% so that the alloy has excellent hot workability. This is often used, for example, to evaluate the hot workability of steel ingots (unit weight: 150 kg) of 25% Cr-50% Ni-6% Mo alloys with various S contents. A test piece (parallel part dimensions: diameter 8 mmφ x length 30 mm) was taken for the torsion test, and the number of twists until breakage was measured using this test piece. it is obvious. In other words, Figure 1 shows that with an S content of 0.0007%, the number of twists increases rapidly at lower S contents, and hot workability is significantly improved. has been done. (f) Al Al is effective as a deoxidizing component like Si and Mn, and even if it is contained 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) 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, This results in unnecessary amounts of Mo and W being contained, which is not economical, and from this point of view, the value of Mo (%) + 1/2 W (%) was set at 3.5 to less than 7.5%. (j) Cu and Co These components have a uniform effect of improving the corrosion resistance of the alloy, and Co has the effect of solid solution strengthening, so they are especially necessary when even better corrosion resistance is required. However, if Cu is contained in an amount exceeding 2%, hot workability will deteriorate, while if Co is contained in an amount exceeding 2%, further improvement effects will not appear. Therefore, the upper limit value is Cu: 2%,
Co: set at 2%. (k) Rare earth elements, Y, Mg, Ti, and Ca These components have a uniform effect to further improve hot workability, so they can be used as necessary when hot working is carried out under severe conditions. Rare earth elements: 0.10%, Y:
0.20%, Mg: 0.10%, Ti: 0.5%, and Ca:
Even if the content exceeds 0.10%, there will be no improvement effect on hot workability, and even deterioration will appear.
Rare earth elements: 0.10% or less, Y: 0.20% or less,
Mg: 0.10% or less, Ti: 0.5% or less, and Ca:
It was set at 0.10% or less. (l) Cr (%) + 10Mo (%) + 5W (%) Figure 2 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, 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, 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 3 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: 200
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 2. In addition, in FIG. 2, the mark ◯ indicates no cracking, and the mark x indicates cracking. From the results shown in Figure 2, Cr (%) + 10Mo (%) + 5W
(%) value is less than 70%, 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 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 metals having the respective compositions shown in Table 1 were melted using an ordinary electric furnace and an Ar-oxygen decarburization furnace (AOD furnace) for the purpose of desulfurization, and then made into ingots with a diameter of 500 mmφ. After casting, this ingot is hot-forged at a temperature of 1200°C to form a billet with a diameter of 150 mmφ. In this case, the billet is observed to see if there are any cracks in order to evaluate the hot working. Then, the billet

【table】

[Table] Diameter: 60mmφ x Wall thickness: 4 due to hot extrusion processing
After forming a raw pipe of mm, it is further cold-worked by 22% by drawing process, diameter: 55mmφ x wall thickness:
Inventive alloy tubes 1 to 15, comparative alloy tubes 1 to 4, and conventional alloy tubes 1 to 3 were manufactured by adjusting the size to 3.1 mm. In addition, Comparative Alloy Tube Materials 1 to 4 all have compositions in which the content of any 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
15, comparative alloy pipe materials 1 to 4, and conventional alloy pipe material 1
From ~3, cut out a test piece with a length of 20 mm,
A portion corresponding to 60°C 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 4, and tightened with a nut to 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 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 1 along with the presence or absence of cracking during hot forging. In addition,
In Table 1, the ○ mark indicates that no cracking occurred, while the x mark indicates that cracking occurred. From the results shown in Table 1, comparative alloy pipe materials 1 to
Alloy tube materials 1 to 15 of the present invention have excellent hot workability and poor stress corrosion cracking resistance. Although it has stress corrosion cracking resistance and good hot workability, it is clear that it has even better properties compared to conventional alloy tube materials 1 to 3, which have relatively poor stress corrosion cracking resistance. It is. As mentioned above, the alloy of the present invention has particularly excellent hot workability and stress corrosion cracking resistance, making it suitable for 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 relationship between the S content and the number of twists until rupture in a torsion test for a 25%Cr-50%Ni-6%Mo alloy.
Cr-Ni-Mo system, Cr-Ni-W system, and Cr-Ni-
Figures 3 and 4 are diagrams showing the relationship between Ni content and Cr (%) + 10Mo (%) + 5W (%) regarding the stress corrosion cracking resistance of Mo-W steel. It is a figure which shows the aspect of the stress corrosion cracking test on test piece S.

Claims (1)

[Claims] 1 C: 0.1% or less, Si: 1.0% or less, Mn: 2.0%
Below, P: 0.030% or less, S: 0.0007% or less, sol.
Al: 0.5% or less, Ni: 25-60%, Cr: 22.5-35%
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%. and alloys for oil country tubular goods with excellent hot workability. 2 C: 0.1% or less, Si: 1.0% or less, Mn: 2.0%
Below, P: 0.030% or less, S: 0.0007% or less, sol.
Al: 0.5% or less, Ni: 25-60%, Cr: 22.5-35%
Contains one or two of Mo: less than 7.5% and W: less than 15%, and further contains Cu: 2
% or less and Co: 2% or less, with the remainder consisting of Fe and unavoidable impurities (wt%), and Cr (%) + 10Mo (%) + 5W ( %)≧70%, 3.5%≦Mo%+1/2W(%)<7.5%, an alloy for oil country tubular goods having excellent stress corrosion cracking resistance and hot workability. 3 C: 0.1% or less, Si: 1.0% or less, Mn: 2.0%
Below, P: 0.030% or less, S: 0.0007% or less, sol.
Al: 0.5% or less, Ni: 25-60%, Cr: 22.5-35%
Contains one or two of Mo: less than 7.5% and W: less than 15%, further rare earth elements: 0.10% or less, Y: 0.20% or less, Mg: 0.10% or less, Ti: 0.5 % 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%, for oil country tubular goods with excellent stress corrosion cracking resistance and hot workability. alloy. 4 C: 0.1% or less, Si: 1.0% or less, Mn: 2.0%
Below, P: 0.030% or less, S: 0.0007% or less, sol.
Al: 0.5% or less, Ni: 25-60%, Cr: 22.5-35%
Contains one or two of Mo: less than 7.5% and W: less than 15%, and further contains 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, Ti: 0.5% 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 (%) )≧70%, 3.5%≦Mo(%)+1/2W(%)<7.5%, an alloy for oil country tubular goods having excellent stress corrosion cracking resistance and hot workability.