JPS6144131B2 - - 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 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 −Cl ^-The main type of corrosion in the environment 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 (%) ≧110%, 7.5%≦Mo (%) + 1/2W (%)≦12%, and the Ni content is 30〜
60%, and the Cr content is 15 to 35%, H ₂ S−, which is extremely corrosive, even in cold-worked materials
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) 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) 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: 30~
60%, Cr: 15 to 35%, contains one or two of Mo: 12% or less and W: 24% or less, and if necessary, 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%≧110%, 7.5%≦Mo%+1/2W(%)<12%, 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 above 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 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 the stress corrosion cracking susceptibility at a low level by setting the (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-10% 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 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 60%, there is no further improvement in stress corrosion cracking resistance, and considering economic efficiency, the content is reduced to 30%.
~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 15%. 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 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) 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: 12
%, and W: Even if the content exceeds 24%, even in a corrosive H ₂ S−CO ₂ −Cl ⁻ environment with an environmental temperature of 200°C or higher, no further improvement effect will be obtained, and economic considerations will be considered. Therefore, the upper limit values of each content were set as 12% for Mo and 24% for W. Also, Mo
Regarding the content of Therefore, if this value is less than 7.5%, the desired stress corrosion cracking resistance cannot be obtained, especially in the above-mentioned adverse environment of 200℃ or higher.On the other hand, even if this value is increased beyond 12%, the above-mentioned As shown in the figure, Mo and W are contained in substantially unnecessary amounts, which is not economical.From this point of view, the value of Mo (%) + 1/2 W (%) was set at 7.5 to 12%. (j) Cu and Co These components have the same effect of improving the corrosion resistance of the alloy, and Co has the effect of solid solution strengthening, so they can be used as necessary especially when even better corrosion resistance is required. Although it contains
If Cu is contained in an amount exceeding 2%, hot workability will deteriorate, while if Co is contained in an amount exceeding 2%, no further improvement effect will be obtained. Cu: 2%, Co:
It was set at 2%. Rare earth elements, Y, Mg, Ti, and Ca These components have the uniform effect of further improving hot workability, so they may be included as necessary when hot working is performed under severe conditions. However, 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 at a processing rate of 30% for the purpose of improving strength, and the resulting steel plate was processed perpendicularly to the rolling direction to a thickness of 2 mm x width of 10 mm. × Length: Cut out a 75mm test piece, and measure the length of the test piece as shown in Figure 3.
Using a point support beam jig, the test piece S was
When added to the tensile stress equivalent to % proof stress,
_H2S and 10 atm _H2S and 10 atm _CO2
20% NaCl solution saturated with _CO2 (temperature: 300
A stress corrosion cracking test was carried out by immersing the test piece in 1,000-hour immersion temperature (°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 (%) + 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 110% and Ni content is 30
%, it is clear that 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 it 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 was hot-forged at a temperature of 1200℃ to form a billet with a diameter of 150mmφ.In this case, for the purpose of evaluating hot workability, whether or not cracks occurred in the billet was determined. The billet was then hot extruded to form a raw tube with a diameter of 60 mmφ and a wall thickness of 4 mm, and then drawn into a 22 mm diameter tube.
% cold working diameter: 55mmφ×

【table】

[Table] Invention alloy tube materials 1 to 15, comparative alloy tube materials 1 to 4, and conventional alloy tube materials 1 to 3 were manufactured by setting the wall thickness to 3.1 mm. In addition, 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 this invention. , and the conventional alloy tube material 1 is
JIS/SUS316, conventional alloy tube material 2 is Incoloy 8
00, and the conventional alloy tube material 3 is JIS/SUS329JI.
The compositions correspond to the respective compositions. Next, the resulting alloy tube materials 1 to 1 of the present invention
15. Cut out a test piece with a length of 20 mm from Comparative Alloy Tube Materials 1 to 4 and Conventional Alloy Tube Materials 1 to 3, and cut off a portion corresponding to 60° along the length direction from this test piece. As shown in the front view in Fig. 4, a bolt is passed through the test piece S and tightened with a nut to apply a tensile force 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.
A stress corrosion cracking test was carried out by immersion in H ₂ S - 10 atm CO ₂ - 20% NaCl solution (liquid 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 1 along with the presence or absence of cracking during hot forging. In Table 1, the marks ◯ indicate those with no cracks, while the marks x indicate those with 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, 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.
Contains Al: 0.5% or less, Ni: 30-60%, Cr: 15-35%, Mo: 12% or less and W: 24% or less, and the rest is Fe. It has a composition (weight%) consisting of unavoidable impurities, and Cr (%) + 10Mo (%) + 5W (%) ≧110%, 7.5%≦Mo (%) + 1/2W (%)≦12%, An alloy for oil country tubular goods with excellent stress corrosion cracking resistance and hot workability, which satisfies the following conditions. 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.
Contains Al: 0.5% or less, Ni: 30 to 60%, Cr: 15 to 35%, one or two of Mo: 12% or less and W: 24% or less, and further Cu: 2 %
One or two of the following and Co: 2% or less
It has a composition (more than % by weight) that contains seeds and the rest is Fe and unavoidable impurities, and Cr (%) + 10Mo (%) + 5W (%) ≧110%, 7.5%≦Mo (%) + 1/ An alloy for oil country tubular goods having excellent stress corrosion cracking resistance and hot workability, which satisfies the following conditions: 2W (%)≦12%. 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.
Contains Al: 0.5% or less, Ni: 30 to 60%, Cr: 15 to 35%, contains one or two of Mo: 12% or less and W: 24% or less, and further contains rare earth elements: A composition containing one or more of the following: 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 inevitable impurities. (or more weight%) and satisfy the following conditions: Cr (%) + 10Mo (%) + 5W (%) ≧110%, 7.5%≦Mo (%) + 1/2W (%)≦12%. An alloy for oil country tubular goods with excellent stress corrosion cracking resistance and hot workability. 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.
Contains Al: 0.5% or less, Ni: 30 to 60%, Cr: 15 to 35%, one or two of Mo: 12% or less and W: 24% or less, and further Cu: 2 %
One or two of the following and Co: 2% or less
Species, 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 (%) )≧110%, 7.5%≦Mo (%) + 1/2W (%)≦12%, an alloy for oil country tubular goods having excellent stress corrosion cracking resistance and hot workability.