An oil and gas steel with excellent performance and a preparation method thereof

Abstract

The application discloses an oil and gas steel with excellent performance and a preparation method thereof. The chemical components of the oil and gas steel are as follows: C: 0.25-0.5%, Si: 0.2-0.4%, Mn: 0.8-1.2%, Cr: 0.3-0.6%, Mo: 0.3-0.5%, Nb: 0.05-0.1%, V: 0.05-0.1%, Al: 0.01-0.03%, Ce: 0.002-0.004%, N: 0.01-0.015%, P: <0.015%, and O+S: <0.003%. The preparation method comprises vacuum smelting and casting, rolling and heat treatment processes. The oil and gas steel provided by the application has the characteristics of uniform structure and excellent mechanical properties, the main structure of which is tempering martensite, the room-temperature yield strength is greater than or equal to 950 MPa, the tensile strength is greater than or equal to 1000 MPa, and the room-temperature full-size V-shaped notch impact energy is greater than or equal to 170 J.

Description

Technical Field

[0001] This invention belongs to the field of steel materials, specifically relating to a high-performance oil and gas steel and its preparation method. Background Technology

[0002] Oil and natural gas, as strategic reserve resources, have always attracted much attention. Most proven oil and natural gas deposits are concentrated in deep subsurface layers and harsh environments such as polar regions and oceans; wells with a completion depth of 4500–6000 meters are generally referred to as deep wells. Statistics show that my country has over 6.2 billion tons of exploitable oil reserves located at depths below 5000 meters. Furthermore, with increasing energy demand and over-exploitation of shallow surface oil resources, countries worldwide are gradually shifting their development focus to deep subsurface layers and oceans—regions rich in reserves but with extremely harsh extraction environments—leading to a continuous increase in demand for deep-well oil casing.

[0003] Conventional oil and gas steels can no longer meet the corrosion resistance requirements of exploration, development, and long-term service, and excessive oxygen content in the steel will seriously affect the material's performance. Ordinary 13Cr materials, when the strength increases to 110 Ksi, have a severely reduced toughness and an impact energy value of <10J, which cannot meet the requirements of high crush resistance and high strength and toughness in the service conditions of shale gas wells.

[0004] Patent application CN202210520840.5 provides a 125ksi grade low alloy oil well pipe steel resistant to sulfide stress cracking. However, its process requires two quenchings and contains nickel and copper. Given the current market prices of both, its production cost remains high and it is not suitable for large-scale production.

[0005] Patent application CN202310447336.1 provides a method for manufacturing 125Ksi high-strength and tough SUP13Cr oil well tubing for shale gas and a hot continuous rolling process. However, it contains high levels of chromium (13%) and nickel (6%), and its alloy cost is more expensive than that of patent CN202210520840.5. In addition, the oxygen control in its composition is relatively lax, which is not conducive to the long-term service of the oil well tubing.

[0006] Therefore, developing a high-strength and high-toughness oil and gas steel with excellent performance that meets or even exceeds 125Ksi, low cost, and suitable for large-scale production is a technical problem that steel companies at home and abroad urgently need to solve. Summary of the Invention

[0007] The purpose of this invention is to provide a high-performance oil and gas steel and its preparation method.

[0008] To achieve the above objectives, the present invention adopts the following technical solution:

[0009] A high-performance oil and gas steel has the following chemical composition: C: 0.25-0.5%, Si: 0.2-0.4%, Mn: 0.8-1.2%, Cr: 0.3-0.6%, Mo: 0.3-0.5%, Nb: 0.05-0.1%, V: 0.05-0.1%, Al: 0.01-0.03%, Ce: 0.002-0.004%, N: 0.01-0.015%, P < 0.015%, O+S < 0.003%, with the balance being iron and unavoidable impurities.

[0010] Furthermore, the main microstructure of the oil and gas steel described in this invention is tempered martensite, with a room temperature yield strength ≥950MPa, a tensile strength ≥1000MPa, and a room temperature full-size V-notch impact energy ≥170J.

[0011] Furthermore, the preparation method of oil and gas steel according to the present invention includes vacuum smelting and casting, rolling, and heat treatment processes.

[0012] Furthermore, the vacuum smelting and casting process of the present invention involves smelting according to the target composition and casting into square ingots with a bottom size of 150*150 to 160*160. During the smelting process, nitrogen is introduced into the gas phase for nitriding before tapping the steel, and the nitriding time is controlled at 10 to 15 minutes.

[0013] Furthermore, the rolling process of the present invention includes rough rolling and finish rolling; in the rough rolling process, the reduction rate of each pass is controlled below 17%, the initial rolling temperature is controlled at 1200±10℃, and the final rolling temperature is controlled at 1130±10℃; in the finish rolling process, the reduction rate of each pass is controlled above 20%, the initial rolling temperature is controlled at 1140±15℃, and the final rolling temperature is controlled at 900±10℃, and the steel plate is slowly cooled to room temperature after rolling, with the final thickness of the finished steel plate controlled at 10-15mm.

[0014] Furthermore, the heat treatment process of the present invention consists of quenching and tempering in sequence; the quenching temperature is 870±20℃, held for 50~70min, and then oil-cooled to room temperature; the tempering temperature is 550±10℃, held for 70~90min, and then slowly cooled to room temperature.

[0015] The beneficial effects of adopting the above technical solution are as follows:

[0016] (1) Nb, V, N and Ce in steel can refine grains and thus improve material properties. Moreover, the components of this invention are all conventional components, containing only trace amounts of rare earth elements. Therefore, the cost of this invention is controllable.

[0017] (2) Using nitrogen for gas phase nitriding can not only ensure the uniformity of nitrogen, but also avoid the increase in the content of inclusions, phosphorus and sulfur and gases caused by the addition of nitriding alloys.

[0018] (3) In this invention, O+S is controlled to within 30ppm, which can not only reduce inclusions in steel from the source, but also improve the rare earth yield in the smelting process.

[0019] (4) By combining roughing and finishing processes, not only can a plate with a suitable thickness be obtained quickly, but also a steel plate with high plate accuracy and excellent surface quality can be obtained.

[0020] (5) Through a simple two-batch heat treatment process, high-performance (superior to general 125Ksi) oil and gas steel can be obtained. Attached Figure Description

[0021] Figure 1 The metallographic structure of the oil and gas steel in Example 1 is shown. Detailed Implementation

[0022] The technical solution of the present invention will be further described in detail below through specific embodiments.

[0023] Example 1

[0024] A type of oil and gas steel, the preparation method of which includes vacuum smelting and casting, rolling, and heat treatment, as detailed below:

[0025] 1) Vacuum smelting and casting

[0026] Based on the relevant target composition, the following components were calculated and weighed: 0.1 kg carbon powder, 0.12 kg metallic silicon, 0.4 kg electrolytic manganese, 0.12 kg metallic chromium, 0.046 kg ferroniobium, 0.0382 kg ferrovanadium, 0.16 kg molybdenum bars, 0.01 kg aluminum granules, 0.008 kg ferrocerium, and 39.01 kg pure iron. The alloy material was baked at 150℃ for 2.5 h. Then, the pure iron was placed in an induction furnace, and after melting, alloying began gradually. After alloying, samples were taken for testing. Before tapping, nitrogen gas at 15000 Pa was introduced for nitriding for 10 min. After the composition was deemed acceptable, the temperature was raised and the steel was cast into 150*150*220 mm square ingots. The steel composition was analyzed, and the results are shown in Table 1.

[0027] Table 1. Measured values ​​(%) of steel composition in Example 1

[0028] element C Si Mn Al Cr Ce Nb V Mo P S O N Measured value 0.251 0.301 0.99 0.02 0.308 0.0020 0.075 0.052 0.4 0.003 0.002 0.0008 0.011

[0029] 2) Rolling

[0030] The surface of the ingot was polished, then heated to 1200℃ and held for 2 hours before rough rolling began. The reduction rate of each pass is shown in Table 2. The final rolling temperature of the rough rolling was 1140℃. After 8 passes, the ingot was rolled into a 46mm thick slab.

[0031] Table 2 Data for each pass of roughing in Example 1

[0032] path 1 2 3 4 5 6 7 8 Thickness (mm) 137 119 101 84 71 59 49 46 Downward pressure rate (%) 8.67％ 13.13％ 15.13％ 16.83％ 15.48％ 16.9％ 16.95％ 6.12％

[0033] The slab obtained from rough rolling was heated to 1155℃ and held for 1.5 hours before finishing rolling. The reduction rate of each pass is shown in Table 3. The finishing rolling temperature was 910℃. After 5 passes of rolling, a slab with a thickness of 12mm was obtained and then slowly cooled to room temperature.

[0034] Table 3 Data for each pass of finishing rolling in Example 1

[0035]

[0036]

[0037] 3) Heat treatment

[0038] Heat the slab to 890℃, hold for 70 minutes, and then oil cool to room temperature; then heat the slab to 560℃, hold for 1.5 hours, and then slowly cool to room temperature to obtain the final product.

[0039] Example 2

[0040] 1) Vacuum smelting and casting

[0041] Based on the relevant target composition, the following components were calculated and weighed: 0.196 kg carbon powder, 0.08 kg silicon metal, 0.48 kg electrolytic manganese, 0.24 kg chromium metal, 0.0522 kg ferroniobium, 0.0612 kg ferrovanadium, 0.2 kg molybdenum bars, 0.006 kg aluminum granules, 0.009 kg ferrocerium, and 38.12 kg pure iron. The alloy material was baked at 150℃ for 2.5 h. Then, the pure iron was placed in an induction furnace, and after melting, alloying began gradually. After alloying, samples were taken for testing. Before tapping, nitrogen gas at 15000 Pa was introduced for nitriding for 15 min. After the composition was deemed acceptable, the temperature was raised and the steel was cast into 160*160*200 mm square ingots. The steel composition was tested, and the results are shown in Table 4.

[0042] Table 4. Measured values ​​(%) of steel composition in Example 2

[0043] element C Si Mn Al Cr Ce Nb V Mo P S O N Measured value 0.49 0.205 1.2 0.011 0.6 0.0035 0.085 0.082 0.5 0.004 0.0018 0.0009 0.0147

[0044] 2) Rough rolling and finish rolling

[0045] The surface of the ingot was polished, then heated to 1210℃ and held for 2.5 hours before rough rolling. The reduction rate of each pass is shown in Table 5. The final rolling temperature of the rough rolling was 1120℃. After 8 passes, the ingot was rolled into a 50mm thick slab.

[0046] Table 5 Data for each pass of roughing in Example 2

[0047] path 1 2 3 4 5 6 7 8 Thickness (mm) 140 118 106 90 77 67 58 50 Downward pressure rate (%) 12.5％ 15.7％ 10.16％ 15.1％ 14.4％ 12.98％ 13.4％ 16％

[0048] The slab obtained from rough rolling is heated to 1125℃ and held for 1.5 hours before finishing rolling. The reduction rate of each pass is shown in Table 6. The finishing rolling temperature is 890℃. After 5 passes of rolling, a slab with a thickness of 15mm is obtained and then slowly cooled to room temperature.

[0049] Table 6 Data for each pass of finishing rolling in Example 2

[0050]

[0051]

[0052] 3) Heat treatment

[0053] Heat the slab to 850℃, hold for 60 minutes, and then oil cool to room temperature; then heat the slab to 540℃, hold for 1.2 hours, and then slowly cool to room temperature to obtain the final product.

[0054] Example 3

[0055] 1) Vacuum smelting and casting

[0056] Based on the relevant target composition, the following components were calculated and weighed: 0.14 kg carbon powder, 0.152 kg metallic silicon, 0.32 kg electrolytic manganese, 0.2 kg metallic chromium, 0.0615 kg ferroniobium, 0.0398 kg ferrovanadium, 0.12 kg molybdenum bars, 0.012 kg aluminum granules, 0.008 kg ferrocerium, and 38.1 kg pure iron. The alloy material was baked at 160℃ for 2 hours. Then, the pure iron was placed in an induction furnace, and after melting, alloying began gradually. After alloying, samples were taken for testing. Before tapping, nitrogen gas at 15000 Pa was introduced for nitriding for 13 minutes. After the composition was deemed acceptable, the temperature was raised and the steel was cast into 150*150*220 mm square ingots. The steel composition was tested, and the results are shown in Table 7.

[0057] Table 7 Measured values ​​(%) of steel composition in Example 3

[0058] element C Si Mn Al Cr Ce Nb V Mo P S O N Measured value 0.35 0.38 0.8 0.03 0.51 0.0025 0.1 0.052 0.3 0.0035 0.0016 0.0007 0.0127

[0059] 2) Rough rolling and finish rolling

[0060] The surface of the ingot was polished, then heated to 1190℃ and held for 2.2 hours before rough rolling. The reduction rate of each pass is shown in Table 8. The final rolling temperature of the rough rolling was 1128℃. After 7 passes, the ingot was rolled into a 50mm thick slab.

[0061] Table 8 Data for each pass of roughing in Example 3

[0062] path 1 2 3 4 5 6 7 Thickness (mm) 135 115 98 83 69 58 50 Downward pressure rate (%) 10％ 14.8％ 14.7％ 15.3％ 16.86％ 16.9％ 13.8％

[0063] The slab obtained from rough rolling is heated to 1135℃ and held for 2 hours before finishing rolling. The reduction rate of each pass is shown in Table 9. The finishing rolling temperature is 905℃. After 6 passes of rolling, a slab with a thickness of 10mm is obtained and then slowly cooled to room temperature.

[0064] Table 9 Data for each pass of finishing rolling in Example 3

[0065] path 1 2 3 4 5 6 Thickness (mm) 39 31 24 18 14 10 Downward pressure rate (%) 22％ 20.5％ 22.5％ 25％ 22.2％ 28.5％

[0066] 3) Heat treatment

[0067] The slab is heated to 870℃ and held for 50 minutes, then oil-cooled to room temperature. The slab is then heated to 548℃ and held for 1.4 hours, followed by slow cooling to room temperature to obtain the final product.

[0068] Example 4

[0069] 1) Vacuum smelting and casting

[0070] Based on the relevant target composition, the following components were calculated and weighed: carbon powder 0.16 kg, metallic silicon 0.144 kg, electrolytic manganese 0.42 kg, metallic chromium 0.18 kg, ferroniobium 0.0338 kg, ferrovanadium 0.0765 kg, molybdenum bars 0.18 kg, aluminum granules 0.01 kg, ferrocerium 0.007 kg, and pure iron 38.79 kg. The alloy material was baked at 150℃ for 2 hours. Then, the pure iron was placed in an induction furnace, and after melting, alloying began gradually. After alloying, samples were taken for testing. Before tapping, nitrogen gas at 15000 Pa was introduced for nitriding for 12 minutes. After the composition was deemed acceptable, the temperature was raised and the steel was cast into 160*160*200 mm square ingots. The steel composition was analyzed, and the results are shown in Table 10.

[0071] Table 10 Measured values ​​(%) of steel composition in Example 4

[0072] element C Si Mn Al Cr Ce Nb V Mo P S O N Measured value 0.4 0.36 1.05 0.025 0.448 0.0040 0.055 0.1 0.45 0.003 0.002 0.0009 0.012

[0073] 2) Rough rolling and finish rolling

[0074] The surface of the ingot was polished, then heated to 1205℃ and held for 2 hours before rough rolling began. The reduction rate of each pass is shown in Table 11. The final rolling temperature of the rough rolling was 1135℃. After 9 passes, the ingot was rolled into a 40mm thick slab.

[0075] Table 11 Data for each pass of roughing in Example 4

[0076] path 1 2 3 4 5 6 7 8 9 Thickness (mm) 142 122 105 90 75 63 53 45 40 Downward pressure rate (%) 11.2％ 14.1％ 13.9％ 14.3％ 16.6％ 16％ 15.8％ 15.1％ 11.1％

[0077] The slab obtained from rough rolling is heated to 1145℃ and held for 1.5 hours before finishing rolling. The reduction ratio of each pass is shown in Table 12. The finishing rolling temperature is 900℃. After 4 passes of rolling, a slab with a thickness of 13mm is obtained and then slowly cooled to room temperature.

[0078] Table 12 Data for each pass of finishing rolling in Example 4

[0079] path 1 2 3 4 Thickness (mm) 32 24 18 13 Downward pressure rate (%) 20％ 25％ 25％ 27.7％

[0080] 3) Heat treatment

[0081] Heat the slab to 875℃, hold for 75 minutes, and then oil cool to room temperature; then heat the slab to 548℃, hold for 1.5 hours, and then slowly cool to room temperature to obtain the final product.

[0082] Example 1: Microstructure of oil and gas steel as follows Figure 1 As shown; by Figure 1 It can be seen that its main structure is tempered martensite. The metallographic structure of the oil and gas steel in the other embodiments is the same as that in Example 1, and will not be listed one by one.

[0083] The mechanical properties of the oil and gas steel in each embodiment were tested, and the results are shown in Table 13.

[0084] Table 13 Mechanical properties of oil and gas steel in various embodiments

[0085] Example Yield strength (MPa) Tensile strength (MPa) Full-size V-notch impact energy at room temperature (J) 1 1178 1323 175 2 1223 1305 181 3 1258 1385 179 4 1198 1361 177 Ordinary 125KSi 870～1000 980～1100 140～150

[0086] As shown in Table 13, the oil and gas steel provided by this invention has excellent mechanical properties, far exceeding those of ordinary 125KSi grade oil and gas casing steel.

Claims

1. A high-performance oil and gas steel, characterized in that, The chemical composition of the oil and gas steel is as follows: C: 0.25-0.5%, Si: 0.2-0.4%, Mn: 0.8-1.2%, Cr: 0.3-0.6%, Mo: 0.3-0.5%, Nb: 0.055-0.1%, V: 0.05-0.1%, Al: 0.01-0.03%, Ce: 0.002-0.004%, N: 0.01-0.015%, P < 0.015%, O+S < 0.003%, with the balance being iron and unavoidable impurities. The main microstructure of the oil and gas steel is tempered martensite, with a room temperature yield strength ≥ 950 MPa, tensile strength ≥ 1000 MPa, and room temperature full-size V-notch impact energy ≥ 170 J.

2. A method for preparing oil and gas steel according to claim 1, characterized in that, This includes vacuum smelting and casting, rolling, and heat treatment processes.

3. The method for preparing oil and gas steel according to claim 2, characterized in that, The vacuum smelting and casting process involves smelting and casting according to the target composition; in the smelting process, nitrogen is introduced into the gas phase for nitriding before tapping the steel, and the nitriding time is controlled at 10-15 minutes.

4. The method for preparing oil and gas steel according to claim 2, characterized in that, The rolling process includes roughing and finishing; in the roughing process, the reduction rate of each pass is controlled below 17%, the initial rolling temperature is controlled at 1200±10℃, and the final rolling temperature is controlled at 1130±10℃; in the finishing process, the reduction rate of each pass is controlled above 20%, the initial rolling temperature is controlled at 1140±15℃, and the final rolling temperature is controlled at 900±10℃; after rolling, the material is slowly cooled to room temperature.

5. The method for preparing oil and gas steel according to claim 2, characterized in that, In the rolling process, the final thickness of the steel plate is controlled at 10-15 mm.

6. The method for preparing oil and gas steel according to claim 2, characterized in that, The heat treatment process includes quenching and tempering; the quenching temperature is 870±20℃, held for 50~70min, and then oil-cooled to room temperature; the tempering temperature is 550±10℃, held for 70~90min, and then slowly cooled to room temperature.

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