A production method of 80-120mm thick seawater corrosion resistant steel 10CrMoAl

Abstract

The application discloses a production method of 80-120mm-thick seawater corrosion-resistant steel 10CrMoAl, adopts a water-cooled mold casting steel ingot with a thickness of greater than or equal to 600mm to ensure a compression ratio, combines non-recrystallization zone rolling, controlled cooling and high-temperature tempering, has a short technological process, and obtains the special-thick corrosion-resistant steel with refined microstructure grains, a strong and tough matching of a surface layer, a thickness of 1 / 4 and a thickness of 1 / 2, and internal flaw detection quality meeting the Ⅰ-grade flaw detection requirement of NB / T47013.2015, and the performance is as follows: yield strength is greater than or equal to 320MPa, tensile strength is 570-620MPa, elongation is greater than or equal to 23%, 0℃ impact value is greater than or equal to 100J, and the steel plate anti-laminated tearing reaches the Z35 performance requirement. The steel plate is superior to the use requirement of a customer in a subsequent rolling and processing forming process.

Description

Technical Field

[0001] This invention belongs to the field of extra-thick plate production technology, specifically relating to a production method of 80-120mm thick seawater corrosion resistant steel 10CrMoAl. Background Technology

[0002] 10CrMoAl steel is a commonly used low-alloy corrosion-resistant steel in marine environments. It has good strength and toughness matching, weldability, and corrosion resistance coefficient. It is mainly used in coastal oil fields, natural gas, media pipelines, steel structures, and flanges. In recent years, with the country's heavy investment in the construction of offshore oil platforms, 10CrMoAl has been used extensively as a low-cost corrosion-resistant seawater steel.

[0003] Chinese patent CN103937946 A discloses a "low-temperature tempering method for seawater corrosion resistant steel 10CrMoAl". This patent emphasizes a heat treatment process that alternately stacks rolled steel plates with freshly rolled hot-rolled thick steel plates, replacing the low-temperature tempering of thin plates. However, this method has significant limitations, requiring proper furnace setup of billets before steel plate production. Furthermore, the slow cooling temperature after rolling cannot be precisely controlled, thus it is only suitable for steel plates with a thickness ≤20mm. For extra-thick plates, uneven microstructure may occur on the surface and at half the thickness, leading to uneven deformation or stress cracking during the later tube rolling process.

[0004] Chinese patent CN 116590619 A discloses "a production method for 10CrMoAl steel resistant to seawater corrosion". This patent uses a 260mm cross-section continuous casting billet to produce steel plates with a thickness of 10-40mm, and the heat treatment adopts a normalizing + tempering process. However, this method still has limitations and cannot produce steel plates with a thickness of more than 80mm. Summary of the Invention

[0005] To address the aforementioned technical deficiencies, the present invention aims to provide a production method for 80-120mm thick seawater corrosion resistant steel 10CrMoAl, which not only enables the production of steel plates thicker than 80mm, but also ensures uniform microstructure on the surface and at half the thickness of the steel plate, thus preventing uneven deformation or stress cracking during the pipe rolling process.

[0006] To achieve the above objectives, the technical solution adopted in this invention is: a production method for 80-120mm thick seawater corrosion resistant steel 10CrMoAl, comprising the following chemical composition by mass percentage (unit, wt%): C: 0.09-0.11, Si: 0.35-0.45, Mn: 0.50-0.60, P: ≤0.010, S≤0.002, Cr: 1.0-1.1, Mo: 0.28-0.32, Alt: 0.65-0.75, Cu: 0.15-0.25, with the remainder being Fe and residual elements; yield strength ≥320MPa, tensile strength 570-620MPa, elongation ≥23%, 0℃ impact value ≥100J, and the steel plate's resistance to lamellar tearing meets the Z35 performance requirements;

[0007] The steel production method includes ingot heating, controlled rolling and cooling, and tempering, as detailed below:

[0008] a. Steel ingot heating: Water-cooled molded steel ingots with a thickness ≥600mm are heated in a heating furnace. The furnace temperature is ≤450℃. After loading into the furnace, the steel is kept in the furnace for 4-5 hours to ensure uniform temperature of the billet. Then, the temperature is increased to 970℃ at a heating rate of ≤60℃ / h, and then increased to 1240±20℃ at a rate of ≥90℃ / h. In the soaking zone at 1240±20℃, the holding time is 5~10min / cm.

[0009] The low-temperature section uses slow heating and simmering to bring the temperature of the steel ingot core and the surface layer close, effectively avoiding excessive temperature difference between the steel ingot core and the surface layer, which could cause large thermal stress and steel ingot cracking. The high-temperature section heats up rapidly to prevent the growth of the original austenite grains.

[0010] b. Controlled rolling and cooling: Two-stage rolling is adopted, namely recrystallization zone and non-recrystallization zone; Rough rolling stage: the initial rolling temperature is 1060-1100℃, the final rolling temperature is greater than 1040℃, and the reduction per pass is ≥50mm, so that the reduction force can fully penetrate into the core of the billet and fully weld the loose defects inside the billet. The steel is dried after rolling to the finished thickness +50mm.

[0011] In the finishing rolling stage, the initial rolling temperature is 840-860℃ and the final rolling temperature is 800-840℃. The purpose is to elongate the austenite grains and form a large number of deformation bands within the grains, thereby increasing the nucleation energy during the transformation of austenite to ferrite and obtaining extremely fine ferrite grains to improve the strength and toughness of the steel.

[0012] After rolling, the steel plate is quickly put into ACC water cooling, and the cooling rate is controlled at 8-12℃ / s to increase the phase transformation undercooling, increase the nucleation rate, refine the grains, and transform the deformed austenite into ferrite and pearlite. The red temperature is controlled at 510-550℃ to reduce the proportion of transformed bainite on the surface of the steel plate.

[0013] c. Tempering: The tempering method is a rapid high-temperature heating method. First, the temperature is raised to 630±10℃ at a rate of 50~60℃ / h and held for 2.0~2.5min / mm. Then, the temperature is raised to 650℃ within 10 minutes and held for 0.5 hours. After being taken out of the furnace, it is air-cooled to room temperature.

[0014] The beneficial effects of this invention are: the invention selects billets with a diameter of ≥600mm, adopts rolling with a large reduction, has a total compression ratio of ≥5, and achieves the internal flaw detection quality of the steel plate to meet the requirements of forgings, thus having a greater cost advantage.

[0015] The entire rolling process of this invention is completed within the crystallization zone and the non-recrystallization zone, thereby obtaining finer and more uniform austenite grains, optimizing the material properties of the rolled piece, and significantly improving its strength and toughness.

[0016] In particular, this invention rapidly increases the temperature to 650°C in the later stage of tempering and holds it at that temperature for 0.5 hours. This fully releases the surface stress of the rolled and hardened steel plate, which is conducive to making the surface and core structures of the steel plate more consistent and reducing internal stress.

[0017] The 80-120mm thick 10CrMoAl steel plates for seawater corrosion resistance obtained according to this scheme have internal flaw detection quality that meets the requirements of NB / T 47013.-2015 Class I flaw detection. In terms of performance: yield strength ≥320MPa, tensile strength 570-620MPa, elongation ≥23%, 0℃ impact value ≥100J, and the steel plate's resistance to lamellar tearing meets the Z35 performance requirements. Detailed Implementation

[0018] The present invention will be further described in detail below with reference to implementation examples.

[0019] Example 1: 10CrMoAl seawater corrosion resistant steel with a rolled plate thickness of 80mm

[0020] a. Smelting composition: C: 0.09, Si: 0.40, Mn: 0.52, P: 0.008, S≤0.002, Cr: 1.0, Mo: 0.29, Alt: 0.67, Cu: 0.20, the rest being Fe and residual elements.

[0021] b. The converter uses high-alloy steel scrap as waste steel, and the carbon content of the steel tapped from the converter is 0.05%. The process route is VD decarbonization + LF refining + VD vacuum degassing. After VD decarbonization, the carbon content is 0.04%. During the LF refining process, white slag is generated to adsorb inclusions, and Ca is added to modify the inclusions. After VD vacuum degassing, the hydrogen content in the molten steel is 0.85 ppm, oxygen content is 19 ppm, and nitrogen content is 25 ppm.

[0022] c. Use a 600mm thick water-cooled ingot mold to cast the steel ingot. The temperature of the molten steel during casting is 1563℃. The casting time is 22 minutes. Demolding is done 10 hours after casting.

[0023] d. Demold the steel ingot and allow it to cool slowly for 24 hours. Clean the ingot at a temperature of 380℃ and charge it into the furnace at a temperature of 350℃.

[0024] e. Steel ingot heating: The furnace temperature for loading steel ingots is 380℃. After loading, the steel is kept in the furnace for 4.5 hours. First, the temperature is increased to 970℃ at a rate of 52℃ / h, and then increased to the temperature of the soaking zone of 1243-1258℃ at a rate of 95℃ / h. The holding time is 9 hours.

[0025] f. Controlled rolling and cooling: After the steel ingots exit the furnace, they are grouped and rolled. In the roughing stage, the reduction is 60mm / pass, allowing the reduction force to fully penetrate into the core of the billet and fully weld the internal porosity defects. The first stage rolling temperature is 1081℃, rolling to a thickness of 130mm, and the final rolling temperature is 1052℃, after which the steel is dried on the roller table. The finishing rolling temperature is 850℃, with a rolling reduction of 10mm / pass, rolling to the target size, and the final rolling temperature is 827℃. The purpose is to elongate the austenite grains and simultaneously... Numerous deformation bands are formed, increasing the nucleation energy during the transformation of austenite to ferrite, resulting in extremely fine ferrite grains to improve the strength and toughness of the steel. After rolling, the steel plate is rapidly cooled in an ACC system with a roll speed of 0.6 m / s, 1-22 sets of manifolds are opened, the water ratio is 2.2, and the cooling rate is controlled at 5-8℃ / s to facilitate the transformation of deformed austenite to ferrite and pearlite. The reddening temperature is 523℃, reducing the proportion of transformed bainite on the surface of the steel plate. After rolling, the steel plate is stacked and slowly cooled at a stacking temperature of 435℃.

[0026] Table 1. Rolling parameters for rough rolling of steel plates

[0027]

[0028] g. Tempering Process: The steel plate is tempered using a rapid high-temperature heating method, with the temperature increased to 630℃ at a rate of 55℃ / h and held for 160 minutes. Then, the temperature is increased to 650℃ within 10 minutes and held for 0.5 hours. After being removed from the furnace, it is air-cooled to room temperature. The lath bainite on the surface of the steel plate caused by rapid cooling gradually disappears through the rapid high-temperature tempering process, resulting in a significant softening effect on strength. Furthermore, the ferrite at the 1 / 4 position is refined. Especially in the later stage of the tempering process, the temperature is rapidly increased to 650℃ and held for 0.5 hours, which fully releases the surface stress of the rolled and hardened steel plate. This promotes a more consistent microstructure between the surface and core of the steel plate, reducing internal stress and improving core strength and toughness.

[0029] The 80mm thick 10CrMoAl seawater corrosion-resistant steel plate produced by the above method meets the internal flaw detection requirements of NB / T 47013.-2015 Class I flaw detection. In terms of performance: yield strength 320-345MPa, tensile strength 605~640MPa, elongation 23-27%, 0℃ impact resistance 145-186J, and resistance to lamellar tearing ≥40%. Specific performance data are shown in Table 2.

[0030] Table 2 Performance Tests of 80mm 10CrMoA1 Seawater Corrosion-Resistant Steel Plate

[0031]

[0032] Example 2: 10CrMoAl seawater corrosion resistant steel with a rolled plate thickness of 100mm

[0033] a. Smelting composition: C: 0.10, Si: 0.42, Mn: 0.55, P: 0.010, S≤0.002, Cr: 1.05, Mo: 0.30, Alt: 0.70, Cu: 0.20, the rest being Fe and residual elements.

[0034] b. The converter uses high-alloy steel scrap as waste steel, and the carbon content of the steel tapped from the converter is 0.04%. The process route adopted is VD decarbonization + LF refining + VD vacuum degassing. After VD decarbonization, the carbon content is 0.03%. During the LF refining process, white slag is generated to adsorb inclusions, and Ca is added to modify the inclusions. After VD vacuum degassing, the hydrogen content in the molten steel is 0.85 ppm, oxygen content is 19 ppm, and nitrogen content is 25 ppm.

[0035] c. Use a water-cooled ingot mold with a thickness of 630mm to cast the steel ingot. The target compression ratio is 6.3. The temperature of the molten steel during casting is 1562℃. The casting time of the main body is 24min. Demolding is performed 11h after casting.

[0036] d. Demolding and slow cooling of steel ingots for 24 hours, cleaning temperature 367℃, and steel ingot charging temperature 328℃;

[0037] e. Steel ingot heating: The furnace temperature for loading steel ingots is 393℃. After loading, the steel is kept in the furnace for 5 hours. First, the temperature is increased to 970℃ at a rate of 48℃ / h, and then increased to the temperature of the soaking zone of 1251-1260℃ at a rate of 90℃ / h. The holding time is 9 hours.

[0038] f. Controlled rolling and cooling: After the steel ingots are taken out of the furnace, they are grouped and rolled. The reduction amount in the rough rolling stage is 55mm / pass, so that the reduction force can fully penetrate into the core of the billet and fully weld the loose defects inside the billet. The first stage involves initial rolling at 1086℃, rolling to a thickness of 150mm, and a final rolling temperature of 1058℃, followed by drying on the roller table. The finishing rolling begins at 845℃, with a rolling reduction of 10mm per pass, rolling to a thickness of 100mm, and a final rolling temperature of 820℃. The purpose is to elongate the austenite grains and simultaneously form numerous deformation bands within the grains, increasing the nucleation energy during the austenite-ferrite transformation, resulting in extremely fine ferrite grains to improve the steel's strength and toughness. After rolling, the steel plate quickly enters the ACC cooling system, with a roll speed set at 0.6m / s. Groups 1-22 of the manifold are opened, and water is cooled once at a ratio of 2.2. Groups 1-8 of the manifold are then opened again, and water is cooled once more at a ratio of 2.3, controlling the cooling rate at 5-7℃ / s. The reheating temperature is 510℃, reducing the proportion of bainite transformation on the steel plate surface. After rolling, the steel plate is stacked for slow cooling at a temperature of 420℃.

[0039] Table 3 Rolling parameters for the roughing stage of steel plates

[0040]

[0041] g. Tempering Process: The steel plate is tempered using a rapid high-temperature heating method, with the temperature increased to 620℃ at a rate of 50℃ / h, held for 220 minutes, then increased to 650℃ in 9 minutes and held for 0.5 hours. After being removed from the furnace, it is air-cooled to room temperature. The lath bainite on the surface of the steel plate caused by rapid cooling gradually disappears through the rapid high-temperature tempering process, resulting in a significant softening effect on strength. Furthermore, the ferrite at the 1 / 4 position is refined. Especially in the later stage of the tempering process, the temperature is rapidly increased to 650℃ and held for 0.5 hours, which fully releases the surface stress of the rolled and hardened steel plate, increasing its toughness and making the surface and core structures of the steel plate more consistent, thus reducing internal stress.

[0042] The 100mm thick 10CrMoAl seawater corrosion-resistant steel plate produced by the above method meets the Class I flaw detection requirements of NB / T 47013.-2015. Its performance characteristics are: yield strength 323-352MPa, tensile strength 618-652MPa, elongation 24-26%, 0℃ impact resistance 143-174J, and resistance to lamellar tearing ≥43%. Specific performance data are shown in Table 4.

[0043] Table 4 Performance Tests of 100mm 10CrMoAl Seawater Corrosion-Resistant Steel Plate

[0044]

[0045] Example 3: 10CrMoAl seawater corrosion resistant steel with a rolled plate thickness of 120mm

[0046] a. Smelting composition: C: 0.10, Si: 0.38, Mn: 0.56, P: 0.009, S≤0.002, Cr: 1.06, Mo: 0.31, Alt: 0.72, Cu: 0.20, the rest being Fe and residual elements.

[0047] b. The converter uses high-alloy steel scrap as waste steel, and the carbon content of the steel tapped from the converter is 0.04%. The process route is VD decarbonization + LF refining + VD vacuum degassing. After VD decarbonization, the carbon content is 0.03%. During the LF refining process, white slag is generated to adsorb inclusions, and Ca is added to modify the inclusions. After VD vacuum degassing, the hydrogen content in the molten steel is 0.88 ppm, oxygen content is 20 ppm, and nitrogen content is 21 ppm.

[0048] c. Use a water-cooled ingot mold with a thickness of 630mm to cast the steel ingot. The compression ratio is 5.2. The temperature of the molten steel during casting is 1562℃. The casting time of the main body is 21min. Demolding is performed 12h after casting.

[0049] d. Demold the steel ingot and allow it to cool slowly for 24 hours. Clean the ingot at a temperature of 363℃ and charge it into the furnace at a temperature of 320℃.

[0050] e. Steel ingot heating: The furnace temperature for loading steel ingots is 392℃. After loading, the steel is kept in the furnace for 4.5 hours. First, the temperature is increased to 970℃ at a rate of 55℃ / h, and then increased to the temperature of the soaking zone of 1250-1260℃ at a rate of 92℃ / h. The holding time is 8 hours.

[0051] f. Controlled rolling and cooling: After the steel ingots are taken out of the furnace, they are grouped and rolled. The reduction in the rough rolling stage is 60mm / pass, the reduction rate is 11-34%, and the deformation coefficient is 0.32-0.96, so that the reduction force can fully penetrate into the core of the billet and fully weld the loose defects inside the billet. The first stage of rolling begins at 1090℃, rolling to a thickness of 170mm, with a final rolling temperature of 1059℃, followed by drying on the roller table. The finishing rolling begins at 840℃, with a rolling reduction of 10mm per pass, and a final rolling temperature of 815℃. The purpose is to elongate the austenite grains and simultaneously form a large number of deformation bands within the grains, increasing the nucleation energy during the transformation of austenite to ferrite, resulting in extremely fine ferrite grains to improve the strength and toughness of the steel. After rolling, the steel plate quickly enters the ACC cooling system, with the roller speed set at 0.6m / s. Groups 1-22 of the manifold are opened, and the water ratio is 2.2 for one water cooling cycle. Then, groups 1-15 of the manifold are opened, and the water ratio is 2.2 for another water cooling cycle, controlling the cooling rate to 9-12℃ / s. The reheating temperature is ≤523℃, reducing the proportion of bainite transformation on the surface of the steel plate.

[0052] After rolling, the steel plates are stacked and cooled slowly at a temperature of 450℃.

[0053] Table 5 Rolling parameters for the roughing stage of steel plates

[0054]

[0055] g. Tempering Process: The steel plate is tempered using a rapid high-temperature heating method, with the temperature increased to 625℃ at a rate of 55℃ / h, held for 245 minutes, then increased to 650℃ in 10 minutes and held for 0.5 hours. After being removed from the furnace, it is air-cooled to room temperature. The lath bainite on the surface of the steel plate caused by rapid cooling gradually disappears through the rapid high-temperature tempering process, resulting in a significant softening effect on strength. Furthermore, the ferrite at the 1 / 4 position is refined. Especially in the later stage of the tempering process, the temperature is rapidly increased to 650℃ and held for 0.5 hours, which fully releases the surface stress of the rolled and hardened steel plate, promoting a more consistent microstructure between the surface and core of the steel plate and reducing internal stress.

[0056] The 120mm thick 10CrMoAl seawater corrosion-resistant steel plate produced by the above method meets the Class I flaw detection requirements of NB / T 47013.-2015. Its performance characteristics are: yield strength 327-348MPa, tensile strength 597-621MPa, elongation 25-30%, 0℃ impact resistance 135-192J, and resistance to lamellar tearing ≥46%. Specific performance data are shown in Table 6.

[0057] Table 6. Performance Tests of 120mm 10CrMoA1 Seawater Corrosion-Resistant Steel Plate

[0058]

[0059] Based on the above examples, the 80-120mm thick seawater corrosion resistant steel 10CrMoAl obtained by the present invention was used to conduct 100% coverage flaw detection scanning with an HS610e digital ultrasonic flaw detector in accordance with the NB / T47013.-2015 standard, which meets the Class I flaw detection requirements.

[0060] The steel plates obtained in Examples 1-3 were sampled from both ends according to GB / T 2975, and tensile tests were conducted according to GB / T 228.1. The yield strength margin of the steel plates was 62-107 MPa, the tensile strength was 207-262 MPa, and the elongation margin was 3%-10%. Impact tests were conducted using a ZBC2302N-3 pendulum impact testing machine according to the Charpy impact test method in GB / T 229, with an average impact energy of 132-185 J at 0℃. Tests were conducted on the steel plates according to the thickness direction properties in GB / T 5313 using a SHT5305 electro-hydraulic servo universal testing machine, with a lamellar tear resistance of 41-57%. These products fully meet the requirements for use in water, oil, and gas pipelines, steel structures, flanges, and other components in coastal oil fields, natural gas, and petrochemical plants, and are suitable for mass production.

Claims

1. A method for producing 80-120mm thick seawater corrosion-resistant steel 10CrMoAl, characterized in that, The steel contains the following chemical composition by mass percentage: C: 0.09–0.11, Si: 0.35–0.45, Mn: 0.50–0.60, P: ≤0.010, S ≤0.002, Cr: 1.0–1.1, Mo: 0.28–0.32, Alt: 0.65–0.75, Cu: 0.15–0.25, with the remainder being Fe and residual elements; yield strength ≥320 MPa, tensile strength 570–620 MPa, elongation ≥23%, 0℃ impact value ≥100 J, and the steel plate's resistance to lamellar tearing meets the Z35 performance requirements; the steel production method includes ingot heating, controlled rolling and cooling, and tempering, as detailed below: a. The process route of VD decarbonization + LF refining + VD vacuum degassing is adopted. During the LF refining process, white slag is generated to adsorb inclusions, and Ca is added to modify the inclusions. After VD vacuum degassing, the H in the molten steel is controlled to be 0.85 ppm, O to be 19 ppm, and N to be 25 ppm. b. Steel ingot heating: Water-cooled molded steel ingots with a thickness ≥600mm are heated in a heating furnace. The furnace temperature is ≤450℃. After loading into the furnace, the steel is kept in the furnace for 4-5 hours to ensure uniform temperature of the billet. Then, the temperature is increased to 970℃ at a heating rate of ≤60℃ / h, and then increased to 1240±20℃ at a heating rate of ≥90℃ / h. The holding time in the soaking zone at 1240±20℃ is 5~10min / cm. c. Controlled rolling and cooling: Two-stage rolling is adopted, namely recrystallization zone and non-recrystallization zone; Rough rolling stage: initial rolling temperature 1060-1100℃, final rolling temperature greater than 1040℃, reduction per pass ≥50mm, and steel drying begins when the finished thickness is +50mm; Finish rolling stage: initial rolling temperature 840-860℃, final rolling temperature 800-840℃; After rolling, the steel plate is quickly put into ACC water cooling, the cooling rate is controlled at 8~12℃ / S, and the reddening temperature is 510-550℃; d. Tempering: The tempering method is to use rapid high-temperature heating. First, the temperature is raised to 630±10℃ at a rate of 50~60℃ / h and held for 2.0~2.5min / mm. Then, the temperature is raised to 650℃ within 10 minutes and held for 0.5 hours. After being taken out of the furnace, it is air-cooled to room temperature.

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