JPS6144129B2 - - 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 (%) ≧50%, 1.0%≦Mo (%) + 1/2W (%) <3.5%, and the Ni content is 25-60
%, and the Cr content is 22.5 to 40%, _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 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) When the S content as an unavoidable impurity is reduced to 0.0007% or less, the hot workability of the alloy is significantly improved. (f) When Cu: 2% or less is included as an alloy component, 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 to 40%, contains one or two of Mo: less than 3.5% and W: less than 7%, and if necessary, Cu: 2% or less, and a rare earth element. : 0.10% or less, Y: 0.20% or less, Mg:
0.10% or less, Ti: 0.5% or less, and Ca: 0.10%
Contains one or more of the following, with the remainder consisting of Fe and unavoidable impurities (all % by weight and % by weight below), and Cr (%) + 10Mo (%) )+5W(%)≧50%, 1.0%≦Mo(%)+1/2W(%)<3.5%, and has excellent stress corrosion cracking resistance and hot workability. In particular, the alloy is suitable for use in manufacturing oil country tubular goods used in oil well environments of extremely corrosive _H2S - _CO2 - ^Cl- at temperatures below 150°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 its upper limit should be 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 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 adopted, for example, for the purpose of evaluating the hot workability of steel ingots (unit weight: 150 kg) of 25% Cr-50% Ni-3% Mo alloys with various S contents. Test piece for torsion test (dimensions of parallel part: diameter 8 mmφ
This is also clear from Figure 1, which shows the results of measuring the number of twists until breakage using this test piece. That is,
Figure 1 shows that with the S content at 0.0007%,
It has been shown that when the S content is lower than this, the number of twists increases rapidly, and hot workability is significantly improved. (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 its 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 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) 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: 3.5
% or more and W: 7% or more, in a corrosive environment of H ₂ S - CO ₂ - Cl ^- where the environmental temperature is 150°C or less, no further improvement effect appears, and considering economic efficiency, , each content is Mo:
It was set as less than 3.5% and W: less than 7%. Also, Mo
Regarding the content of Therefore, if this value is less than 1.0%, the desired stress corrosion cracking resistance cannot be obtained, especially under the above-mentioned adverse environment of 150℃ or less.On the other hand, even if this value is 3.5% or more, as mentioned above, the desired stress corrosion cracking resistance cannot be obtained. 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 at 1.0 to less than 3.5%. (j) Cu Since the Cu component has the effect of improving the corrosion resistance of the alloy, it is included as necessary especially when even better corrosion resistance is required, but 2%
If the content exceeds 2%, hot workability deteriorates, so the upper limit was 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 needed 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 is applied, and cold working is applied at a processing rate of 30% for the purpose of improving strength.The resulting steel plate is 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: 150
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 50%, 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 it with comparative examples and conventional examples. Example Molten metal having the composition shown in Table 1 was melted using an ordinary electric furnace and an Ar-oxygen decarburization furnace (AOD furnace) for the purpose of desulfurization, and then cast into an ingot with a diameter of 500 mmφ. Then, this ingot was hot-formed at a temperature of 1200℃ to form a billet with a diameter of 150mmφ, and in this case, it was observed whether or not cracks occurred in the billet for the purpose of evaluating hot workability. Then, a raw tube with a diameter of 60 mmφ and a wall thickness of 4 mm was formed from the billet by hot extrusion, and then this was further drawn to form a tube with a diameter of 22 mm.
% cold working diameter: 55mmφ x wall thickness: 3.1
The alloy tube material 1 of the present invention is made with a dimension of mm.
-15, Comparative Alloy Tube Materials 1-4, and Conventional Alloy Tube Materials 1-3 were manufactured, respectively.

【table】

[Table] Comparative alloy tube materials 1 to 4 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 the present invention. The conventional alloy tube material 1 has
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 water temperature (150°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, ○ marks indicate no cracks, while × marks indicate cracks. 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, so it can be used in oil and natural gas applications in harsh environments where these properties are required. It exhibits extremely excellent performance when used as oil country tubular goods used in mining 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-3%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: 22.5~40
%, contains one or two of Mo: less than 3.5% and W: less than 7%, with the remainder consisting of Fe and unavoidable impurities (wt%), and Cr( %)+10Mo(%)+5W(%)≧50%, 1.0%≦Mo(%)+1/2W(%)<3.5%, Stress corrosion cracking resistance and hot working characteristics Alloy for 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: 0.0007% or less, sol.
Al: 0.5% or less, Ni: 25-60%, Cr: 22.5-40%
Contains one or two of Mo: less than 3.5% and W: less than 7%, and further contains Cu: 2
% or less, with the remainder consisting of Fe and unavoidable impurities (weight %), and Cr (%) + 10Mo (%) + 5W (%) ≧50%, 1.0%≦Mo (%) + 1 An alloy for oil country tubular goods having excellent stress corrosion cracking resistance and hot workability, which satisfies the following conditions: /2W(%)<3.5%. 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: 22.5-40%
Contains one or two of Mo: less than 3.5% and W: less than 7%, 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(%)≧50%, 1.0%≦Mo(%)+1/2W(%)<3.5%, 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: 22.5-40%
Contains one or two of Mo: less than 3.5% and W: less than 7%, and further contains Cu: 2
% or less, rare earth elements: 0.10% or less, Y: 0.20%
Below, 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 (%) )≧50%, 1.0%≦Mo(%)+1/2W(%)<3.5%, an alloy for oil country tubular goods having excellent stress corrosion cracking resistance and hot workability.