Corrosion-resistant steel suitable for shale oil in-situ conversion heating well environment and preparation method of corrosion-resistant steel

Abstract

The invention discloses corrosion-resistant steel suitable for a shale oil in-situ conversion heating well environment and a preparation method of the corrosion-resistant steel. The corrosion-resistant steel comprises the following chemical components in percentage by weight: less than or equal to 0.01% of C, 1.0-2.0% of Mn, 3.5-5.5% of Si, 13.00-15.00% of Cr, 15.00-17.00% of Ni, 0.75-1.50% of Mo, 0.75-1.50% of Cu and 57.49-66% of Fe. On the basis of increasing the content of Si and reducing the content of high-cost Cr and Ni, alloy elements such as Mo and Cu are added, and the prepared corrosion-resisting steel meets the harsh corrosion environment of a shale oil in-situ conversion heating well on the basis of controlling the cost as much as possible.

Description

Technical Field

[0001] The present invention relates to the technical field of shale oil in-situ conversion and corrosion-resistant materials, and in particular to a corrosion-resistant steel suitable for a shale oil in-situ conversion heating well environment and a preparation method thereof. Background Art

[0002] my country has abundant low-maturity shale oil resources, which require underground in-situ heating and conversion technology for exploitation. In-situ heating and conversion is used to exploit shale oil. The temperature of the heating wellbore can reach up to 600-650℃, and the pressure can reach more than 30MPa. In addition to hydrocarbons, the associated gas formed by in-situ conversion also contains H 2 O、CO 2 , H 2 S.H. 2 Corrosive gases such as carbon monoxide and other gases account for about 20% to 60%. The environmental components are complex, and the service temperature has far exceeded the working conditions of conventional oil and gas wells. The extremely harsh environment has put forward more stringent requirements on the high temperature corrosion resistance of materials.

[0003] The corrosiveness of the in-situ conversion environment of shale oil far exceeds that of the traditional oil and gas field corrosion environment. Commonly used corrosion-resistant oil pipe steels such as 13Cr are difficult to meet the requirements of temperature resistance and corrosion resistance. The cost of materials such as nickel-based alloys remains high. It is imperative to develop a low-cost and highly corrosion-resistant oil well pipe material suitable for the in-situ conversion environment of shale oil. Summary of the invention

[0004] In view of the above problems, the present invention proposes a corrosion-resistant steel suitable for shale oil in-situ conversion heating well environment and a preparation method thereof that overcomes the above problems or at least partially solves the above problems.

[0005] In the first aspect, an embodiment of the present invention provides a corrosion-resistant steel suitable for a shale oil in-situ conversion heating well environment, wherein the corrosion-resistant steel comprises the following chemical components and their weight percentages: C: ≤0.01, Mn: 1.0-2.0, Si: 3.5-5.5, Cr: 13.00-15.00, Ni: 15.00-17.00, Mo: 0.75-1.50, Cu: 0.75-1.50, Fe: 57.49-66.

[0006] Optionally, the structure of the corrosion-resistant steel is austenite and ferrite, with more austenite than ferrite.

[0007] Optionally, if the chemical composition of the corrosion-resistant steel contains S and / or P, the weight percentage of S is ≤0.03, and the weight percentage of P is ≤0.045.

[0008] In a second aspect, an embodiment of the present invention provides a method for preparing corrosion-resistant steel suitable for a shale oil in-situ conversion heating well environment, comprising:

[0009] Corrosion-resistant steel suitable for shale oil in-situ conversion heating well environment is prepared from the following raw materials according to the weight percentage of each raw material:

[0010] Carbon: ≤0.01, manganese: 1.0~2.0, silicon: 3.5~5.5, chromium: 13.00~15.00, nickel: 15.00~17.00, molybdenum: 0.75~1.50, copper: 0.75~1.50, and the rest is iron.

[0011] Optionally, the preparation of corrosion-resistant steel suitable for shale oil in-situ conversion heating well environment comprises the following steps:

[0012] The raw materials are melted into molten steel in a heating furnace, and after refining outside the furnace and vacuum degassing, they are continuously cast into round billets, and cooled to obtain continuously cast billets;

[0013] The continuous casting billet is heated to a first set temperature, kept at a first set time to complete austenitization of the continuous casting billet, and then hot pierced, continuously rolled, sizing, cooled, sawed, straightened, and flaw detected;

[0014] A solution treatment is performed at a second set temperature for a second set time to dissolve the precipitated phase into austenite again.

[0015] Optionally, the first set temperature is 1120-1130°C.

[0016] Optionally, the first set time is 0.5 to 1 hour.

[0017] Optionally, the second set temperature is 1060-1100°C.

[0018] Optionally, the second set time is 0.5h.

[0019] Optionally, heating the continuous casting billet to a first set temperature comprises:

[0020] The continuous casting strand is heated to a first set temperature by a ring heating furnace.

[0021] The beneficial effects of the above technical solution provided by the present invention include at least:

[0022] (1) The corrosion-resistant steel provided by the present invention is suitable for the environment of shale oil in-situ conversion heating wells. By increasing the Si content and auxiliary addition of alloy elements such as Cu and Mo to improve the corrosion resistance, the corrosion-resistant steel obtains corrosion resistance similar to that of alloys with higher Cr and Ni contents. The corrosion-resistant steel is suitable for the harsh environment of shale oil in-situ conversion heating wells; and the reduction of high-cost Cr and Ni contents reduces the preparation cost of the corrosion-resistant steel.

[0023] (2) The corrosion resistance of stainless steel in high temperature corrosive environment is mainly due to the Cr formed on the surface of the material after Cr element oxidation2 O 3 However, blindly pursuing corrosion-resistant materials with high Cr content will not only sharply increase the cost of shale oil in-situ conversion and mining, but also make it difficult for the high-temperature strength of the material to meet the mining needs. The corrosion-resistant steel suitable for shale oil in-situ conversion heating well environment provided by the present invention can not only reduce the Cr content required to achieve the same anti-oxidation level, but also improve the thermal strength of the steel.

[0024] (3) The method for preparing corrosion-resistant steel suitable for shale oil in-situ conversion heating well environment provided by the present invention reduces the intergranular corrosion sensitivity and improves the intergranular corrosion sensitivity resistance of steel compared with similar high-silicon austenitic heat-resistant steel by optimizing the alloy element content, processing and heat treatment process.

[0025] The technical solution of the present invention is further described in detail below through embodiments. BRIEF DESCRIPTION OF THE DRAWINGS

[0026] The accompanying drawings are used to provide a further understanding of the present invention and constitute a part of the specification. Together with the embodiments of the present invention, they are used to explain the present invention and do not constitute a limitation of the present invention. In the accompanying drawings:

[0027] Figure 1 This is a microstructure diagram of the high silicon austenitic corrosion resistant steel in Example 1 of the present invention;

[0028] Figure 2 This is a microstructure diagram of the high silicon austenitic corrosion resistant steel in Example 2 of the present invention;

[0029] Figure 3 This is a microstructure diagram of the high silicon austenitic corrosion resistant steel in Example 3 of the present invention;

[0030] Figure 4 It is a comparison chart of oxidation rates of Examples 1 to 3 and Comparative Examples 1 to 2;

[0031] Figure 5 This is a comparison of the cross-sectional microscopic morphologies of the corrosion films of the high-silicon austenitic corrosion-resistant steel in Example 1 and the nickel-based alloy 028 in Comparative Example 1. DETAILED DESCRIPTION

[0032] The exemplary embodiments of the present invention are described in detail below. Although exemplary embodiments are disclosed, it should be understood that the present invention can be implemented in various forms and should not be limited by the embodiments set forth herein. On the contrary, these embodiments are provided to enable a more thorough understanding of the present invention and to enable the scope of the present invention to be fully communicated to those skilled in the art.

[0033] In order to solve the problems existing in the prior art, the present invention provides a corrosion-resistant steel suitable for a shale oil in-situ conversion heating well environment and a preparation method thereof.

[0034] The invention provides a corrosion-resistant steel suitable for a shale oil in-situ conversion heating well environment. The corrosion-resistant steel comprises the following chemical components and their weight percentages: C: ≤0.01, Mn: 1.0-2.0, Si: 3.5-5.5, Cr: 13.00-15.00, Ni: 15.00-17.00, Mo: 0.75-1.50, Cu: 0.75-1.50, and Fe: 57.49-66.

[0035] The following is a brief description of the mechanism of each component element:

[0036] C: This design uses ultra-low carbon, which can avoid the formation of larger carbides, prevent carbides from forming micro-galvanic couples with the steel matrix, improve corrosion resistance, and reduce the precipitation of carbides at grain boundaries under high temperature conditions, reducing the alloy's intergranular corrosion sensitivity and the risk of intergranular cracking. Therefore, its content is controlled below 0.01%.

[0037] Mn: Mn is the main solid solution strengthening element in steel. It can make up for the decrease in strength caused by reducing the C element in steel. It can also expand the austenite zone and increase the bonding strength between the oxide film and the matrix, thereby improving the alloy's resistance to unstable oxidation and thus improving its antioxidant properties. However, if the Mn content in steel is too high, it will easily lead to Mn segregation or the formation of MnS inclusions, affecting the toughness of the steel. Therefore, its content is controlled at 1.0-2.0%.

[0038] Si: Si can improve the resistivity of steel and enhance its high temperature oxidation resistance. On the other hand, it can improve the thermal strength of steel and increase its strength in high temperature environment. Si element can form SiO 2 Amorphous film or dispersed in Cr 2 O 3 In the film, it improves the oxidation resistance of low Cr content steel, but Si is a strong ferrite forming element. Increasing the silicon content in austenitic stainless steel will promote the precipitation of brittle phases such as δ and χ. These brittle phases will not only reduce the plasticity and toughness of the steel, but also may affect the corrosion resistance and welding performance. Therefore, its content is controlled at 3.5-5.5%.

[0039] Cr: Cr is one of the most commonly used corrosion-resistant elements in corrosion-resistant alloys. It can form a stable and dense layer of Cr on the surface of steel. 2 O 3 Or Cr-rich spinel protective film, which produces a passivation effect and can prevent further corrosion of steel. Properly increasing the Cr content in steel can not only significantly improve the overall corrosion resistance of stainless steel in a specific environment, but also greatly improve the steel's resistance to stress corrosion, pitting corrosion, crevice corrosion, etc. However, the purchase cost of Cr metal is relatively high, so its content is controlled at 13.00-15.00%.

[0040] Ni: Ni has strong thermodynamic stability, and adding Ni can enhance the stability of the steel itself. Increasing the Ni content in steel can promote the transformation of spinel in the corrosion film to a fine and dense structure, refine the grains of the corrosion film, increase the density of the corrosion film, and improve the corrosion resistance of the steel. The addition of a certain amount of Ni can prevent defects caused by Cu during rolling and improve the toughness of the steel, so its content is controlled at 15.00-17.00%.

[0041] Mo: Mo and Cr have the same body-centered cubic structure. Due to the larger atomic size of Mo, adding Mo can improve strength through solid solution hardening. Combined with Cr, it can also improve the strength of Cr by 2 O 3 The stability of the film and the resistance to local corrosion in chlorine-containing water media provide corrosion resistance in environments containing oxidizing and reducing corrosive media. In addition, due to the low diffusion coefficient of Mo, the creep resistance of the alloy is improved. However, too high Mo content will increase the hardenability of steel, which is not conducive to welding, so its content is controlled at 0.75% to 1.50%.

[0042] Cu: Cu is one of the alloying elements that was used earlier in corrosion-resistant alloys and has the best anti-corrosion effect. Adding Cu to corrosion-resistant alloys can enhance the corrosion resistance of steel in acidic media. The enrichment of Cu in the corrosion film can reduce the diffusion rate of anions into the matrix, while increasing the migration resistance of ions in the corrosion film during the corrosion process, increasing the protectiveness of the corrosion film, and improving the corrosion resistance of steel in the shale oil in-situ conversion environment. However, when the Cu content is too high, it will be enriched in the steel, resulting in grain boundary embrittlement, so its content is controlled at 0.75-1.50%.

[0043] The structure of the corrosion-resistant steel provided by the invention is austenite+a small amount of ferrite.

[0044] The corrosion-resistant steel suitable for the shale oil in-situ conversion heating well environment provided by the present invention improves the corrosion resistance by increasing the Si content and auxiliary addition of alloy elements such as Cu and Mo, so that the corrosion-resistant steel obtains corrosion resistance similar to that of alloys with higher Cr and Ni contents. The corrosion-resistant steel is suitable for the harsh environment of shale oil in-situ conversion heating wells; and the reduction of high-cost Cr and Ni contents reduces the preparation cost of the corrosion-resistant steel.

[0045] The corrosion resistance of stainless steel in high temperature corrosive environment is mainly due to the Cr formed on the surface of the material after Cr element oxidation. 2 O 3However, blindly pursuing corrosion-resistant materials with high Cr content will not only sharply increase the cost of shale oil in-situ conversion and mining, but also make it difficult for the high-temperature strength of the material to meet the mining needs. The corrosion-resistant steel suitable for shale oil in-situ conversion heating well environment provided by the present invention can reduce the Cr content required to achieve the same anti-oxidation level by adding Si element, and can also improve the thermal strength of the steel.

[0046] Although the raw materials carbon, manganese, silicon, chromium, nickel, molybdenum, copper and iron are of high purity, they cannot reach 100% purity, so the corrosion-resistant steel produced inevitably contains impurity elements such as S and / or P. The weight percentage of S must be ≤0.03, and the weight percentage of P must be ≤0.045.

[0047] The present invention provides a method for preparing corrosion-resistant steel suitable for the environment of shale oil in-situ conversion heating wells, and the corrosion-resistant steel suitable for the environment of shale oil in-situ conversion heating wells is prepared from the following raw materials according to the weight percentage of each of the following raw materials:

[0048] Carbon: ≤0.01, manganese: 1.0~2.0, silicon: 3.5~5.5, chromium: 13.00~15.00, nickel: 15.00~17.00, molybdenum: 0.75~1.50, copper: 0.75~1.50, and the rest is iron.

[0049] The purity of each raw material reaches 99.9-99.99%.

[0050] Specifically, the preparation of corrosion-resistant steel suitable for shale oil in-situ conversion heating well environment includes the following steps:

[0051] 1. The raw materials are melted into molten steel in a heating furnace, and after refining and vacuum degassing outside the furnace, they are continuously cast into round billets, which are then cooled to obtain continuous casting billets.

[0052] The raw materials can be heated and melted into molten steel using an electric arc furnace.

[0053] 2. The continuous casting billet is heated to a first set temperature, kept warm for a first set time to complete austenitization of the continuous casting billet, and then hot pierced, continuously rolled, sizing, cooled, sawed, straightened, and flaw detected.

[0054] The continuous casting strand may be heated to a first set temperature by means of an annular heating furnace.

[0055] The first set temperature may be 1120-1130° C. The first set time may be 0.5-1 hour.

[0056] 3. Performing solution treatment at a second set temperature for a second set time to dissolve the precipitated phase back into austenite, thereby improving the steel's resistance to intergranular corrosion.

[0057] The second set temperature may be 1060-1100° C., and the second set time may be 0.5 h.

[0058] The method for preparing corrosion-resistant steel suitable for shale oil in-situ conversion heating well environment provided by the present invention reduces the intergranular corrosion sensitivity and improves the intergranular corrosion sensitivity resistance of steel compared with similar high-silicon austenitic heat-resistant steels by optimizing the alloy element content, processing and heat treatment processes.

[0059] To ensure the accuracy of the embodiment, carbon, manganese, silicon, chromium, nickel, molybdenum, copper and iron with a purity of 99.9-99.99% are selected. Before the alloy is prepared, the oxides on the surface of the raw materials are polished clean with 600 mesh SiC sandpaper, and then placed in anhydrous ethanol for ultrasonic cleaning to remove impurities and oil stains remaining on the surface of the raw materials. According to the nominal proportion composition, the mass of each raw material is accurately weighed using an analytical balance with an accuracy of 1 mg (the error is within 5 mg). For elements such as C with a small addition amount, an analytical balance with an accuracy of 0.1 mg is used (the error is within 0.5 mg). Each raw material is added to a crucible for smelting in turn (the total mass of the alloy refined in each embodiment is 80g), and it is placed in a high vacuum arc melting furnace.

[0060] Example 1

[0061] 1. Raw material preparation: carbon: 0.00216g, manganese: 0.8g, silicon: 2.8g, chromium: 11.584g, nickel: 12g, molybdenum: 0.6616g, copper: 0.756g, iron supplemented.

[0062] 2. After passing through an electric arc furnace, refining outside the furnace and vacuum degassing, it is continuously cast into a round billet, and then cooled to obtain a continuously cast billet.

[0063] 3. The cooled continuous casting billet is heated in a ring heating furnace at a heating temperature of 1120°C for a holding time of 1 hour for hot perforation; then it is subjected to continuous rolling, sizing, cooling, sawing, straightening, and flaw detection; finally, a solid solution treatment is performed at 1060°C for 0.5 hours, and the billet is taken out and water-cooled to obtain a high-silicon austenitic corrosion-resistant steel resistant to the corrosive environment of high-temperature and high-pressure shale oil in-situ conversion heating wells.

[0064] Example 2

[0065] 1. Raw material preparation: carbon: 0.0036g, manganese: 1.216g, silicon: 3.512g, chromium: 10.4g, nickel: 12.336g, molybdenum: 1.2g, copper: 0.6g, iron supplemented.

[0066] 2. After passing through an electric arc furnace, refining outside the furnace and vacuum degassing, it is continuously cast into a round billet, and then cooled to obtain a continuously cast billet.

[0067] 3. The cooled continuous casting billet is heated in a ring heating furnace at a heating temperature of 1130°C and a holding time of 0.5h for hot perforation; then it is subjected to continuous rolling, sizing, cooling, sawing, straightening, and flaw detection; finally, it is subjected to a solid solution treatment at 1100°C for 0.5h, and then it is taken out and water-cooled to obtain a high-silicon austenitic corrosion-resistant steel resistant to the corrosive environment of high-temperature and high-pressure shale oil in-situ conversion heating wells.

[0068] Implementation Case 3

[0069] 1. Raw material preparation: carbon: 0.008g, manganese: 1.6g, silicon: 4.4g, chromium: 12g, nickel: 13.6g, molybdenum: 0.6g, copper: 1.2g, iron supplemented.

[0070] 2. After passing through an electric arc furnace, refining outside the furnace and vacuum degassing, it is continuously cast into a round billet, and then cooled to obtain a continuously cast billet.

[0071] 3. The cooled continuous casting billet is heated in a ring heating furnace at a heating temperature of 1125°C and a holding time of 0.7h for hot perforation; then it is subjected to continuous rolling, sizing, cooling, sawing, straightening, and flaw detection; finally, a solid solution treatment is performed at 1080°C for 0.5h, and the billet is taken out and water-cooled to obtain a high-silicon austenitic corrosion-resistant steel resistant to the corrosive environment of high-temperature and high-pressure shale oil in-situ conversion heating wells.

[0072] The corrosion-resistant steels and two 028 nickel-based alloy pipes prepared in the above three embodiments were sampled and subjected to high temperature and high pressure corrosion tests. The test period was 7 days, the total test pressure was 18.82 MPa, the test temperature was 600°C, and the test conditions were shown in Table 1. Table 2 shows the measured chemical composition and weight percentage (wt%) of the corrosion-resistant steels melted in Examples 1 to 3, and Table 3 shows the chemical composition and weight percentage (wt%) of two typical 028 nickel-based alloys in Comparative Examples 1 to 2.

[0073] Table 1 High temperature and high pressure corrosion test conditions

[0074]

[0075] Table 2 Measured chemical composition and weight percentage (wt%) of the corrosion-resistant steel melted in Examples 1 to 3

[0076]

[0077] Table 3 Chemical composition and weight percentage (wt%) of two typical 028 nickel-based alloys

[0078]

[0079] In Tables 1 to 3, bal represents the remainder, that is, the remaining component is Fe.

[0080] Figures 1 to 3The microstructure diagrams of the high silicon austenite heat resistant steels melted in Examples 1 to 3 are respectively, Figure 4 It is a comparison chart of the oxidation rates of Examples 1 to 3 and Comparative Examples 1 to 2, Figure 4 It is shown that after 7 days of corrosion in the simulated shale oil in-situ conversion heating well environment, the oxidation rates of implementation cases 1 to 3 are lower than those of the two comparative examples of 028 nickel-based alloys, indicating that due to the increase of Si elements and the addition of elements such as Mn and Cu, the corrosion resistance of low Cr and Ni austenitic heat-resistant steel in the simulated shale oil in-situ conversion heating well environment reaches or exceeds the level of 028 nickel-based alloy.

[0081] Figure 5 The cross-sectional micromorphology of the samples after corrosion of the material in Example 1 and the material 028 (Comparative Example 1) shows that the thickness of the corrosion film formed by the high-silicon austenitic heat-resistant steel is significantly lower than that of the 028 nickel-based alloy, which verifies that the material in Example 1 has good corrosion resistance, and no intergranular corrosion phenomenon was found in the material in the example.

[0082] It should also be noted that the raw materials used to prepare the corrosion-resistant steel involved in the embodiments of the present invention and the materials involved in the comparative examples are all commercially available general products.

[0083] The above description includes examples of one or more embodiments. Of course, it will be appreciated by those skilled in the art that the various embodiments may be further combined and arranged. Therefore, the embodiments described herein are intended to cover all such changes, modifications and variations that fall within the scope of protection of the appended claims. In addition, with respect to the term "comprising" used in the specification or claims, the word is encompassed in a manner similar to the term "including," as explained by "including," used as a transitional word in the claims. In addition, any term "or" used in the specification of the claims is intended to mean "non-exclusive or."

[0084] Obviously, those skilled in the art can make various changes and modifications to the present invention without departing from the concept and scope of the present invention. Thus, if these modifications and variations of the present invention fall within the scope of the claims of the present invention and their equivalents, the present invention is also intended to include these modifications and variations.

Claims

1. A corrosion-resistant steel suitable for shale oil in-situ conversion heating well environment, characterized in that: The corrosion-resistant steel comprises the following chemical components and their weight percentages: C: ≤0.01, Mn: 1.0-2.0, Si: 3.5-5.5, Cr: 13.00-15.00, Ni: 15.00-17.00, Mo: 0.75-1.50, Cu: 0.75-1.50, Fe: 57.49-66.

2. The corrosion-resistant steel according to claim 1, characterized in that: The corrosion-resistant steel has a microstructure of austenite and ferrite, with more austenite than ferrite.

3. The corrosion-resistant steel according to claim 1, characterized in that: If the chemical composition of the corrosion-resistant steel contains S and / or P, the weight percentage of S is ≤0.03, and the weight percentage of P is ≤0.

045.

4. A method for preparing corrosion-resistant steel suitable for shale oil in-situ conversion heating well environment, characterized in that: include: Corrosion-resistant steel suitable for shale oil in-situ conversion heating well environment is prepared from the following raw materials according to the weight percentage of each raw material: Carbon: ≤0.01, manganese: 1.0~2.0, silicon: 3.5~5.5, chromium: 13.00~15.00, nickel: 15.00~17.00, molybdenum: 0.75~1.50, copper: 0.75~1.50, and the rest is iron.

5. The method according to claim 4, characterized in that The method for preparing corrosion-resistant steel suitable for shale oil in-situ conversion heating well environment comprises the following steps: The raw materials are melted into molten steel in a heating furnace, and after refining outside the furnace and vacuum degassing, they are continuously cast into round billets, and cooled to obtain continuously cast billets; The continuous casting billet is heated to a first set temperature, kept at a first set time to complete austenitization of the continuous casting billet, and then hot pierced, continuously rolled, sizing, cooled, sawed, straightened, and flaw detected; A solution treatment is performed at a second set temperature for a second set time to dissolve the precipitated phase into austenite again.

6. The method according to claim 5, characterized in that The first set temperature is 1120-1130°C.

7. The method according to claim 6, characterized in that The first set time is 0.5 to 1 hour.

8. The method according to claim 5, characterized in that The second set temperature is 1060-1100°C.

9. The method according to claim 8, characterized in that The second set time is 0.5h.

10. The method according to claim 5, characterized in that The step of heating the continuous casting billet to a first set temperature comprises: The continuous casting strand is heated to a first set temperature by a ring heating furnace.

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