High-strength low-temperature-resistant high-corrosion-resistant angle steel for ocean platform and production method thereof

Abstract

The invention discloses high-strength low-temperature-resistant high-corrosion-resistant angle steel for an ocean platform and a production method thereof, and belongs to the technical field of steel and iron material processing. The angle steel comprises the following chemical components in percentage by mass: 0.07 to 0.11 percent of C, 0.80 to 1.10 percent of Mn, 0.26 to 0.34 percent of Si, 0.45 to 0.65 percent of Cr, 0.17 to 0.22 percent of Ni, 0.23 to 0.33 percent of Cu, 0.012 to 0.022 percent of Nb, 0.030 to 0.055 percent of V, 0.008 to 0.018 percent of Als, less than or equal to 0.012 percent of P, less than or equal to 0.01 percent of S and the balance of iron and inevitable impurities. In the continuous casting process, a strong cooling process is matched with a large pulling speed to promote the uniformity of the structure in a casting blank to be improved, the large-deformation rough rolling, water-cooling temperature waiting before finish rolling and controlled cooling processes after rolling are adopted, the structure of the obtained angle steel is P + F + LB + M / A, and the angle steel has high strength and toughness, low temperature resistance and erosion resistance.

Description

Technical Field

[0001] The invention belongs to the technical field of steel material processing, and relates to a high-strength, low-temperature-resistant and high-corrosion-resistant angle steel for an offshore platform and a production method thereof. Background Art

[0002] With the growth of the global economy and the increase in energy demand, the construction of offshore platforms and the research and development of related high-strength steels have received increasing attention. High-strength, low-temperature-resistant and high-corrosion-resistant angle steels used in offshore platform construction are indispensable key materials in marine engineering. Such materials must maintain stable performance in extreme marine environments, including resistance to low temperatures, high corrosion resistance and high strength.

[0003] The use environment of offshore platform steel is harsh, and its underwater structure is corroded by seawater and marine organisms for a long time. In addition, in addition to its own gravity load, it also needs to withstand erosion and damage from natural forces such as wind and waves, ocean currents, submarine earthquakes, and low temperatures. It has a long service life and high stress strength. This type of steel needs to have high strength, high toughness, low temperature resistance, and corrosion resistance. However, there are deficiencies in the research and development of steel for offshore platform construction, such as low strength grade, incomplete specifications, imperfect standards, and poor corrosion resistance.

[0004] As the strength level increases, the content of alloy elements increases, which may lead to a decrease in the corrosion resistance of steel used in offshore platform construction. Therefore, it is necessary to study how to improve the corrosion resistance of materials while maintaining high strength. Angle steel for offshore platforms needs to have good corrosion cracking resistance in complex marine environments and maintain good toughness in low temperature environments to adapt to extreme marine environments. Therefore, it is necessary to increase efforts to develop new high-strength, low-temperature-resistant and high-corrosion-resistant angle steels for offshore platform construction. Summary of the invention

[0005] In order to solve the above technical problems, the present invention provides a high-strength, low-temperature-resistant and high-corrosion-resistant angle steel for offshore platforms and a production method thereof. The microalloying composition design of Nb+V is adopted, the S content is strictly controlled through the smelting KR-BOF-LF process, a high oversteel amount is combined with strong cooling to match a large drawing speed in the continuous casting process to improve the uniformity of the structure in the ingot, the hot rolling process parameters are designed in combination with phase change, and the high-strength, low-temperature-resistant and high-corrosion-resistant angle steel for offshore platforms is produced by adopting a large deformation rough rolling + water cooling before fine rolling + roller air cooling after rolling process. Under the premise of not increasing the load of the rolling mill, the obtained angle steel has a side length of 160-200 mm, a side thickness of 14-24 mm, a yield strength of ≥390 MPa, a tensile strength of ≥540 MPa, an elongation of ≥29%, and an impact energy of >90 J at -40°C.

[0006] In order to achieve the above-mentioned invention object, the technical solution adopted by the present invention is: A high-strength, low-temperature-resistant and high-corrosion-resistant angle steel for an offshore platform, the chemical composition and mass percentage of which are: C: 0.07-0.11%, Mn: 0.80-1.10%, Si: 0.26-0.34%, Cr: 0.45-0.65%, Ni: 0.17-0.22%, Cu: 0.23-0.33%, Nb: 0.012-0.022%, V: 0.030-0.055%, Als: 0.008-0.018%, P≤0.012%, S≤0.010%, and the balance is Fe and unavoidable impurities.

[0007] The functions and controls of the chemical components of the high-strength, low-temperature-resistant and high-corrosion-resistant angle steel of the present invention are as follows: C: 0.07-0.11%. C is a traditional strengthening element, but too high a C content can easily cause segregation and carbide formation, which is not conducive to weldability and corrosion resistance.

[0008] Mn: 0.80-1.10%. Mn improves strength and hardenability, and effectively deoxidizes and desulfurizes, and improves the density of pearlite. Too high a content will reduce welding performance and pitting resistance.

[0009] Si: 0.26-0.34%. Si is an effective element for improving yield strength. Too high a content will reduce the fatigue performance and toughness of steel.

[0010] Cr: 0.45-0.65%. Cr is an important element to improve corrosion resistance and combines with O to form a dense oxide film.

[0011] Ni: 0.17-0.22%. Ni can significantly improve the stability of austenite, while effectively improving the corrosion resistance and plasticity of steel.

[0012] Cu: 0.23-0.33%, Cu is a typical element that improves corrosion resistance. When added together with Cr and Ni, it can effectively form a dense oxide rust layer to prevent further corrosion of the substrate.

[0013] P: ≤0.012%, an impurity element, will have adverse effects on the mechanical properties and weldability of steel, and is strictly controlled in production.

[0014] S: ≤0.010%, is an impurity element, which will have adverse effects on the mechanical properties and impact resistance of steel and is strictly controlled in production.

[0015] Nb: 0.012-0.022%. Nb can effectively refine grains, improve strength and toughness, and improve the welding performance of steel.

[0016] V: 0.030-0.055%. V is a precipitation strengthening element in steel. It forms very stable, dispersed, high-hardness carbonitrides with C and N, thereby improving the strength of steel.

[0017] Als: 0.008-0.018%. Al can improve the oxidation resistance and corrosion resistance of steel, and its oxide is dispersed in the steel, which can prevent the grain growth when the steel is heated.

[0018] Furthermore, the angle steel has a side length of 160 to 200 mm and a side thickness of 14 to 24 mm.

[0019] Furthermore, the metallographic structure of the angle steel is extremely fine lamellar pearlite, uniform equiaxed ferrite, lath bainite and a small amount of M / A islands.

[0020] Furthermore, the angle steel has a yield strength of ≥390 MPa, a tensile strength of ≥540 MPa, an elongation of ≥29%, an impact energy of >90 J at -40°C, and a corrosion rate of ≤0.10 mm·a in a cyclic corrosion test in a 3.5% mass concentration NaCl solution. -1 .

[0021] On the other hand, the present invention also provides a method for producing the above-mentioned high-strength, low-temperature-resistant and high-corrosion-resistant angle steel for offshore platforms, which includes a blank preparation and hot rolling process; Billet preparation process: Billet preparation is carried out through KR molten iron pretreatment - BOF converter smelting - LF refining - CC continuous casting. The CC continuous casting process adopts strong cooling technology, and the casting speed is controlled at 2.6-3.1m / min. Hot rolling process: rough rolling deformation ≥ 80%, water cooling before finishing rolling for 20 to 90 seconds, finishing rolling deformation ≥ 60%; after final rolling, enter the conveyor roller for air cooling, the cooling rate is controlled at 7 to 22 ° C / s, and finally air cooling on the cooling bed.

[0022] Furthermore, in the billet preparation process, the S content of the molten iron is controlled to 0.010-0.020wt% during the KR molten iron pretreatment process, the S content of the molten steel is controlled to 0.030-0.040wt% during the BOF converter smelting process, and the S content of the molten steel is controlled to ≤0.010wt% during the LF refining process.

[0023] Furthermore, in the billet preparation process, during the CC continuous casting process, the water content in the secondary cooling zone is 1.5-2.0 L / kg, and the superheat of the molten steel is controlled at 25-30°C.

[0024] Furthermore, in the hot rolling process, the steel billet is heated in a heating furnace at a heating temperature of 1180-1230°C.

[0025] Furthermore, in the hot rolling process, the starting temperature of rough rolling is 1070-1120°C; and the starting temperature of finishing rolling is 910-960°C.

[0026] Furthermore, in the hot rolling process, the water pressure of the water cooling before finishing rolling is 0.9-1.2 MPa, and the conveying roller speed is 1.2-1.8 m / s.

[0027] The beneficial effects of the above technical solution are: the present invention adopts Nb+V composite microalloy, Cr+Ni+Cu alloy elements to improve strength and corrosion resistance for composition design, and adopts high pulling speed and strong cooling process to make the shell reach a certain thickness, and then the liquid phase solidifies and moves to promote the full diffusion of elements to prevent segregation. The hot rolling process parameters are designed in combination with phase change, and the austenite morphology is controlled by large deformation rough rolling + water cooling before finishing rolling to reduce the recrystallization of deformed austenite, and then the large deformation finishing rolling is used to accumulate sufficient deformation energy storage + roller air cooling process after rolling to promote the precipitation of the second phase of ferrite and ensure the formation of a dense oxide layer, and finally achieve the production of high-strength, low-temperature and high-corrosion-resistant angle steel, which can not only refine the organization, improve the strength and toughness of steel, and improve the comprehensive performance of materials, but also prevent steel from corroding in the marine environment, enhance the safety and reliability of offshore platform structures, and reduce the risk of structural failure.

[0028] The high-strength, low-temperature-resistant and high-corrosion-resistant angle steel for offshore platforms provided by the present invention has excellent comprehensive properties: yield strength ≥390MPa, tensile strength ≥540MPa, elongation ≥29%, -40℃ impact energy >90J, and a cyclic corrosion test in a 3.5% mass concentration NaCl solution, with a corrosion rate ≤0.10mm·a -1 , combining high strength, high toughness, low temperature resistance, corrosion resistance and other properties. BRIEF DESCRIPTION OF THE DRAWINGS

[0029] Figure 1 This is a microstructure diagram of the angle steel obtained in Example 1 of the present invention at room temperature; Figure 2 This is a microstructure diagram of the angle steel obtained in Example 2 of the present invention at room temperature; Figure 3 This is a microstructure diagram of the angle steel obtained in Example 3 of the present invention at room temperature; Figure 4 This is a microstructure diagram of the angle steel obtained in Example 4 of the present invention at room temperature; Figure 5 This is a microstructure diagram of the angle steel obtained in Example 5 of the present invention at room temperature; Figure 6 This is a microstructure diagram of the angle steel obtained in Example 6 of the present invention at room temperature; Figure 7 This is a microstructure diagram of the angle steel obtained in Example 7 of the present invention at room temperature; Figure 8This is the microstructure organization diagram of the angle steel obtained in Example 8 of the present invention at room temperature. DETAILED DESCRIPTION

[0030] The present invention will be further described in detail below in conjunction with specific embodiments.

[0031] Example 1 The chemical composition and mass percentage of the high-strength, low-temperature-resistant and high-corrosion-resistant angle steel for offshore platforms in this embodiment are: C: 0.07%, Mn: 0.80%, Si: 0.26%, Cr: 0.45%, Ni: 0.17%, Cu: 0.23%, Nb: 0.012%, V: 0.033%, Als: 0.008%, P: 0.012%, S: 0.010%, and the balance is Fe and unavoidable impurities; its production method includes billet preparation and hot rolling processes, and the specific steps are as follows: (1) KR-BOF-LF-CC was used to prepare the billet. During the KR hot metal pretreatment process, the sulfur content of the molten iron was removed to 0.013%. During the BOF converter smelting process, the sulfur content of the molten steel was controlled at 0.034%. During the LF refining process, the sulfur content of the molten steel was controlled at 0.010%. The strong cooling process was used for cooling during the continuous casting process. The specific water volume in the secondary cooling zone was 1.7 L / kg, the casting speed was 2.8 m / min, and the superheat was 28 °C.

[0032] (2) The billet size is 200mm×280mm and is heated in a heating furnace. The billet is heated in a heating furnace at a heating temperature of 1180℃; the starting temperature of rough rolling is 1072℃; the deformation of rough rolling is 85%; water cooling is carried out for 35s before finishing rolling, and the water cooling pressure is 1.0MPa; the starting temperature of finishing rolling is 930℃; the deformation of finishing rolling is 62%. After final rolling, the billet enters the conveyor roller for air cooling, with a cooling rate of 12℃ / s and a conveyor roller speed of 1.5m / s, and finally air cooling is carried out on the cooling bed.

[0033] The high-strength, low-temperature-resistant and high-corrosion-resistant angle steel of this embodiment has a size of 160 mm × 14 mm, a yield strength of 403 MPa, a tensile strength of 551 MPa, an elongation of 29%, and an impact energy of 110 J at -40 ° C. A cyclic corrosion test was carried out in a 3.5% NaCl solution, and the corrosion rate was 0.08 mm·a -1 Its metallographic structure is as follows Figure 1 As shown, there are very fine lamellar pearlite + uniform equiaxed ferrite + lath bainite and a small amount of M / A islands.

[0034] Example 2 The chemical composition and mass percentage of the high-strength, low-temperature-resistant and high-corrosion-resistant angle steel for offshore platforms in this embodiment are: C: 0.09%, Mn: 0.90%, Si: 0.26%, Cr: 0.49%, Ni: 0.17%, Cu: 0.28%, Nb: 0.017%, V: 0.041%, Als: 0.009%, P: 0.011%, S: 0.010%, and the balance is Fe and unavoidable impurities; its production method includes billet preparation and hot rolling processes, and the specific steps are as follows: (1) KR-BOF-Lf-CC was used to prepare the billet. During the KR hot metal pretreatment process, the sulfur content of the molten iron was removed to 0.011%. During the BOF converter smelting process, the sulfur content of the molten steel was controlled at 0.033%. During the LF refining process, the sulfur content of the molten steel was controlled at 0.010%. The strong cooling process was used for cooling during the continuous casting process. The specific water volume in the secondary cooling zone was 1.8 L / kg, the casting speed was 2.7 m / min, and the superheat was 27 °C.

[0035] (2) The billet size is 200mm×280mm and is heated in a heating furnace. The billet is heated in a heating furnace at a heating temperature of 1201℃; the starting temperature of rough rolling is 1101℃; the deformation of rough rolling is 83%; water cooling is carried out for 30s before finishing rolling, and the water cooling pressure is 0.9MPa; the starting temperature of finishing rolling is 936℃; the deformation of finishing rolling is 66%. After final rolling, the billet enters the conveyor roller for air cooling, with a cooling rate of 18℃ / s and a conveyor roller speed of 1.4m / s, and finally air cooling is carried out on the cooling bed.

[0036] The high-strength, low-temperature-resistant and high-corrosion-resistant angle steel of this embodiment has a size of 160 mm × 16 mm, a yield strength of 407 MPa, a tensile strength of 558 MPa, an elongation of 30%, and an impact energy of 113 J at -40°C. In a cyclic corrosion test in a 3.5% NaCl solution, the corrosion rate is 0.08 mm·a -1 Its metallographic structure is as follows Figure 2 As shown, there are very fine lamellar pearlite + uniform equiaxed ferrite + lath bainite and a small amount of M / A islands.

[0037] Example 3 The chemical composition and mass percentage of the high-strength, low-temperature-resistant and high-corrosion-resistant angle steel for offshore platforms in this embodiment are: C: 0.10%, Mn: 0.80%, Si: 0.33%, Cr: 0.48%, Ni: 0.19%, Cu: 0.27%, Nb: 0.020%, V: 0.030%, Als: 0.012%, P: 0.012%, S: 0.009%, and the balance is Fe and unavoidable impurities; its production method includes blank preparation and hot rolling processes, and the specific steps are as follows: (1) KR-BOF-Lf-CC was used to prepare the billet. During the KR hot metal pretreatment process, the sulfur content of the molten iron was removed to 0.012%. During the BOF converter smelting process, the sulfur content of the molten steel was controlled at 0.033%. During the LF refining process, the sulfur content of the molten steel was controlled at 0.009%. The strong cooling process was used for cooling during the continuous casting process. The specific water volume in the secondary cooling zone was 1.7 L / kg, the casting speed was 3.0 m / min, and the superheat was 29 °C.

[0038] (2) The billet size is 200mm×280mm and is heated in a heating furnace. The billet is heated in a heating furnace at a heating temperature of 1189℃; the starting temperature of rough rolling is 1103℃; the deformation of rough rolling is 81%; water cooling is carried out for 30s before finishing rolling, and the water cooling pressure is 1.1MPa; the starting temperature of finishing rolling is 947℃; the deformation of finishing rolling is 66%. After final rolling, the billet enters the conveyor roller for air cooling, with a cooling rate of 7℃ / s and a conveyor roller speed of 1.2m / s, and finally air cooling is carried out on the cooling bed.

[0039] The high-strength, low-temperature-resistant and high-corrosion-resistant angle steel of this embodiment has a size of 180 mm × 14 mm, a yield strength of 411 MPa, a tensile strength of 567 MPa, an elongation of 30%, and an impact energy of 118 J at -40°C. A cyclic corrosion test was carried out in a 3.5% NaCl solution, and the corrosion rate was 0.07 mm·a -1 Its metallographic structure is as follows Figure 3 As shown, there are very fine lamellar pearlite + uniform equiaxed ferrite + lath bainite and a small amount of M / A islands.

[0040] Example 4 The chemical composition and mass percentage of the high-strength, low-temperature-resistant and high-corrosion-resistant angle steel for offshore platforms in this embodiment are: C: 0.08%, Mn: 0.80%, Si: 0.34%, Cr: 0.50%, Ni: 0.20%, Cu: 0.33%, Nb: 0.019%, V: 0.037%, Als: 0.015%, P: 0.011%, S: 0.008%, and the balance is Fe and unavoidable impurities; its production method includes blank preparation and hot rolling processes, and the specific steps are as follows: (1) KR-BOF-Lf-CC was used to prepare the billet. During the KR hot metal pretreatment process, the sulfur content of the molten iron was removed to 0.019%. During the BOF converter smelting process, the sulfur content of the molten steel was controlled at 0.037%. During the LF refining process, the sulfur content of the molten steel was controlled at 0.008%. The strong cooling process was used for cooling during the continuous casting process. The specific water volume in the secondary cooling zone was 1.9 L / kg, the casting speed was 3.1 m / min, and the superheat was 30 °C.

[0041] (2) The billet size is 200mm×280mm and is heated in a heating furnace. The billet is heated in a heating furnace at a heating temperature of 1208℃; the starting temperature of rough rolling is 1112℃; the deformation of rough rolling is 82%; water cooling is carried out for 25s before finishing rolling, and the water cooling pressure is 1.0MPa; the starting temperature of finishing rolling is 940℃; the deformation of finishing rolling is 64%. After final rolling, the billet enters the conveyor roller for air cooling, with a cooling rate of 10℃ / s and a conveyor roller speed of 1.3m / s, and finally air cooling is carried out on the cooling bed.

[0042] The high-strength, low-temperature-resistant and high-corrosion-resistant angle steel of this embodiment has a size of 180 mm × 16 mm, a yield strength of 409 MPa, a tensile strength of 562 MPa, an elongation of 31%, and an impact energy of 126 J at -40°C. The cyclic corrosion test was carried out in a 3.5% NaCl solution, and the corrosion rate was 0.07 mm·a -1 Its metallographic structure is as follows Figure 4 As shown, there are very fine lamellar pearlite + uniform equiaxed ferrite + lath bainite and a small amount of M / A islands.

[0043] Example 5 The chemical composition and mass percentage of the high-strength, low-temperature-resistant and high-corrosion-resistant angle steel for offshore platforms in this embodiment are: C: 0.09%, Mn: 1.10%, Si: 0.31%, Cr: 0.58%, Ni: 0.17%, Cu: 0.31%, Nb: 0.018%, V: 0.038%, Als: 0.016%, P: 0.011%, S: 0.008%, and the balance is Fe and unavoidable impurities; its production method includes billet preparation and hot rolling processes, and the specific steps are as follows: (1) KR-BOF-Lf-CC was used to prepare the billet. During the KR hot metal pretreatment process, the sulfur content of the molten iron was removed to 0.020%. During the BOF converter smelting process, the sulfur content of the molten steel was controlled at 0.035%. During the LF refining process, the sulfur content of the molten steel was controlled at 0.008%. The strong cooling process was used for cooling during the continuous casting process. The specific water volume in the secondary cooling zone was 1.5 L / kg, the casting speed was 2.8 m / min, and the superheat was 27 °C.

[0044] (2) The billet size is 200mm×280mm and is heated in a heating furnace. The billet is heated in a heating furnace at a heating temperature of 1210℃; the starting temperature of rough rolling is 1116℃; the deformation of rough rolling is 80%; water cooling is carried out for 25s before finishing rolling, and the water cooling pressure is 1.0MPa; the starting temperature of finishing rolling is 955℃; the deformation of finishing rolling is 68%. After final rolling, the billet enters the conveyor roller for air cooling, with a cooling rate of 22℃ / s and a conveyor roller speed of 1.8m / s, and finally air cooling is carried out on the cooling bed.

[0045] The high-strength, low-temperature-resistant and high-corrosion-resistant angle steel of this embodiment has a size of 180 mm × 18 mm, a yield strength of 404 MPa, a tensile strength of 553 MPa, an elongation of 33%, and an impact energy of 119 J at -40 ° C. A cyclic corrosion test was carried out in a 3.5% NaCl solution, and the corrosion rate was 0.08 mm·a -1 Its metallographic structure is as follows Figure 5 As shown, there are very fine lamellar pearlite + uniform equiaxed ferrite + lath bainite and a small amount of M / A islands.

[0046] Example 6 The chemical composition and mass percentage of the high-strength, low-temperature-resistant and high-corrosion-resistant angle steel for offshore platforms in this embodiment are: C: 0.09%, Mn: 0.80%, Si: 0.29%, Cr: 0.61%, Ni: 0.22%, Cu: 0.30%, Nb: 0.021%, V: 0.049%, Als: 0.016%, P: 0.011%, S: 0.010%, and the balance is Fe and unavoidable impurities; its production method includes billet preparation and hot rolling processes, and the specific steps are as follows: (1) KR-BOF-Lf-CC was used to prepare the billet. During the KR hot metal pretreatment process, the sulfur content of the molten iron was removed to 0.020%. During the BOF converter smelting process, the sulfur content of the molten steel was controlled at 0.040%. During the LF refining process, the sulfur content of the molten steel was controlled at 0.010%. The strong cooling process was used for cooling during the continuous casting process. The specific water volume in the secondary cooling zone was 2.0 L / kg, the casting speed was 2.9 m / min, and the superheat was 28 °C.

[0047] (2) The billet size is 200mm×280mm and is heated in a heating furnace. The billet is heated in a heating furnace at a heating temperature of 1230℃; the starting temperature of rough rolling is 1120℃; the deformation of rough rolling is 82%; water cooling is carried out for 25s before finishing rolling, and the water cooling pressure is 1.2MPa; the starting temperature of finishing rolling is 960℃; the deformation of finishing rolling is 60%, and after final rolling, it enters the conveyor roller for air cooling, with a cooling rate of 20℃ / s and a conveyor roller speed of 1.6m / s, and finally air cooling is carried out on the cooling bed.

[0048] The high-strength, low-temperature-resistant and high-corrosion-resistant angle steel of this embodiment has a size of 200mm×14mm, a yield strength of 391MPa, a tensile strength of 539MPa, an elongation of 30%, and an impact energy of 92J at -40°C. In a cyclic corrosion test in a 3.5% NaCl solution, the corrosion rate is 0.09mm·a -1 Its metallographic structure is as follows Figure 6 As shown, there are very fine lamellar pearlite + uniform equiaxed ferrite + lath bainite and a small amount of M / A islands.

[0049] Example 7 The chemical composition and mass percentage of the high-strength, low-temperature-resistant and high-corrosion-resistant angle steel for offshore platforms in this embodiment are: C: 0.08%, Mn: 1.00%, Si: 0.28%, Cr: 0.65%, Ni: 0.22%, Cu: 0.25%, Nb: 0.022%, V: 0.055%, Als: 0.018%, P: 0.009%, S: 0.007%, and the balance is Fe and unavoidable impurities; its production method includes blank preparation and hot rolling processes, and the specific steps are as follows: (1) KR-BOF-Lf-CC was used to prepare the billet. During the KR hot metal pretreatment process, the sulfur content of the molten iron was removed to 0.010%. During the BOF converter smelting process, the sulfur content of the molten steel was controlled at 0.030%. During the LF refining process, the sulfur content of the molten steel was controlled at 0.007%. The strong cooling process was used for cooling during the continuous casting process. The specific water volume in the secondary cooling zone was 1.9 L / kg, the casting speed was 2.6 m / min, and the superheat was 25 °C.

[0050] (2) The billet size is 200mm×280mm and is heated in a heating furnace. The billet is heated in a heating furnace at a heating temperature of 1188℃; the starting temperature of rough rolling is 1092℃; the deformation of rough rolling is 81%; water cooling is carried out for 20s before finishing rolling, and the water cooling pressure is 1.1MPa; the starting temperature of finishing rolling is 958℃; the deformation of finishing rolling is 63%. After final rolling, the billet enters the conveyor roller for air cooling, with a cooling rate of 15℃ / s and a conveyor roller speed of 1.7m / s, and finally air cooling is carried out on the cooling bed.

[0051] The high-strength, low-temperature-resistant and high-corrosion-resistant angle steel of this embodiment has a size of 200mm×20mm, a yield strength of 407MPa, a tensile strength of 558MPa, an elongation of 30%, and an impact energy of 105J at -40°C. In a cyclic corrosion test in a 3.5% NaCl solution, the corrosion rate is 0.08mm·a -1 Its metallographic structure is as follows Figure 7 As shown, there are very fine lamellar pearlite + uniform equiaxed ferrite + lath bainite and a small amount of M / A islands.

[0052] Example 8 The chemical composition and mass percentage of the high-strength, low-temperature-resistant and high-corrosion-resistant angle steel for offshore platforms in this embodiment are: C: 0.11%, Mn: 0.90%, Si: 0.28%, Cr: 0.63%, Ni: 0.21%, Cu: 0.31%, Nb: 0.022%, V: 0.055%, Als: 0.014%, P: 0.012%, S: 0.009%, and the balance is Fe and unavoidable impurities; its production method includes billet preparation and hot rolling processes, and the specific steps are as follows: (1) KR-BOF-Lf-CC was used to prepare the billet. During the KR hot metal pretreatment process, the sulfur content of the molten iron was removed to 0.017%. During the BOF converter smelting process, the sulfur content of the molten steel was controlled at 0.039%. During the LF refining process, the sulfur content of the molten steel was controlled at 0.009%. The continuous casting process adopted a strong cooling process. The specific water volume in the secondary cooling zone was 1.7 L / kg, the casting speed was 2.6 m / min, and the superheat was 28 °C.

[0053] (2) The size of the billet is 200 mm × 280 mm. The billet is heated in a heating furnace at a heating temperature of 1181 °C and a water cooling pressure of 0.9 MPa. The starting temperature of rough rolling is 1070 °C. The deformation of rough rolling is 80%. The billet is water-cooled for 20 seconds before finishing rolling. The starting temperature of finishing rolling is 951 °C. The deformation of finishing rolling is 64%. After final rolling, the billet enters the conveyor roller for air cooling at a cooling rate of 10 °C / s and a conveyor roller speed of 1.5 m / s. Finally, it is air-cooled on a cooling bed.

[0054] The high-strength, low-temperature-resistant and high-corrosion-resistant angle steel of this embodiment has a size of 200mm×24mm, a yield strength of 407MPa, a tensile strength of 556MPa, an elongation of 30%, and an impact energy of 91J at -40°C. In a cyclic corrosion test in a 3.5% NaCl solution, the corrosion rate is 0.09mm·a -1 Its metallographic structure is as follows Figure 8 As shown, there are very fine lamellar pearlite + uniform equiaxed ferrite + lath bainite and a small amount of M / A islands.

Claims

1. A high-strength, low-temperature-resistant and high-corrosion-resistant angle steel for an offshore platform, characterized in that: Its chemical composition and mass percentage are: C: 0.07~0.11%, Mn: 0.80~1.10%, Si: 0.26~0.34%, Cr: 0.45~0.65%, Ni: 0.17~0.22%, Cu: 0.23~0.33%, Nb: 0.012~0.022%, V: 0.030~0.055%, Als: 0.008~0.018%, P≤0.012%, S≤0.010%, and the balance is Fe and unavoidable impurities.

2. The high-strength, low-temperature-resistant and high-corrosion-resistant angle steel for offshore platforms according to claim 1, characterized in that: The angle steel has a side length of 160 to 200 mm and a side thickness of 14 to 24 mm.

3. The high-strength, low-temperature-resistant and high-corrosion-resistant angle steel for offshore platforms according to claim 2 is characterized in that: The metallographic structure of the angle steel is extremely fine lamellar pearlite, uniform equiaxed ferrite, lath bainite and a small amount of M / A islands.

4. The high-strength, low-temperature-resistant and high-corrosion-resistant angle steel for offshore platforms according to claim 3 is characterized in that: The angle steel has a yield strength of ≥390MPa, a tensile strength of ≥540MPa, an elongation of ≥29%, an impact energy of >90J at -40°C, and a corrosion rate of ≤0.10mm·a in a cyclic corrosion test in a 3.5% mass concentration NaCl solution. -1 .

5. The method for producing high-strength, low-temperature-resistant and high-corrosion-resistant angle steel for offshore platforms according to any one of claims 1 to 4, characterized in that: Including billet preparation and hot rolling process; Billet preparation process: Billet preparation is carried out through KR molten iron pretreatment - BOF converter smelting - LF refining - CC continuous casting. The CC continuous casting process adopts strong cooling technology, and the casting speed is controlled at 1.6-2.0m / min. Hot rolling process: rough rolling deformation ≥ 80%, water cooling before finishing rolling for 20 to 90 seconds, finishing rolling deformation ≥ 60%; after final rolling, enter the conveyor roller for air cooling, the cooling rate is controlled at 7 to 22 ° C / s, and finally air cooling on the cooling bed.

6. The method for producing high-strength, low-temperature-resistant and high-corrosion-resistant angle steel for offshore platforms according to claim 5, characterized in that: In the billet preparation process, the molten iron is desulfurized to 0.010-0.020wt% during KR molten iron pretreatment, the molten steel sulfur content is controlled at 0.030-0.040wt% during BOF converter smelting, and the molten steel sulfur content is controlled at ≤0.010wt% during LF refining.

7. The method for producing high-strength, low-temperature-resistant and high-corrosion-resistant angle steel for offshore platforms according to claim 6, characterized in that: In the billet preparation process, during CC continuous casting, the water content in the secondary cooling zone is 1.5-2.0 L / kg, and the superheat of the molten steel is controlled at 25-30°C.

8. The method for producing high-strength, low-temperature-resistant and high-corrosion-resistant angle steel for offshore platforms according to claim 7, characterized in that: In the hot rolling process, the steel billet is heated in a heating furnace at a heating temperature of 1180-1230°C.

9. The method for producing high-strength, low-temperature-resistant and high-corrosion-resistant angle steel for offshore platforms according to claim 8, characterized in that: In the hot rolling process, the starting temperature of rough rolling is 1070-1120°C; and the starting temperature of finishing rolling is 910-960°C.

10. The method for producing high-strength, low-temperature-resistant and high-corrosion-resistant angle steel for offshore platforms according to claim 9, characterized in that: In the hot rolling process, the water pressure of the water cooling before finishing rolling is 0.9-1.2 MPa, and the conveying roller speed is 1.2-1.8 m / s.

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