A 160-210mm thick marine structure steel s690ql1 and a production method thereof

Abstract

This invention discloses a 160-210mm thick marine structural steel S690QL1 and its production method. The steel has a carbon equivalent (CEV) ≤ 0.65%, is produced using a water-cooled die casting process with a thickness ≥ 800mm. The process involves low-temperature heating, high-temperature controlled rolling, multiple intermittent controlled cooling cycles, and heat treatment. The resulting steel plate has a fine, uniform tempered martensite structure with a small amount of tempered bainite. It undergoes 100% full-coverage flaw detection according to EN10160-1999 requirements and meets S3E4 flaw detection standards. The requirements are as follows: Upon testing, the yield strength at the surface, 1 / 4, and 1 / 2 sections is ≥690MPa; the tensile strength is 770–940MPa; the strength difference across the entire thickness section is within 30MPa; the elongation is ≥18%; the impact performance at -60℃ for sections of different thicknesses is ≥150J; the impact value at -60℃ with 5% transverse strain aging is ≥120J; the steel plate's resistance to lamellar tearing reaches Z45; and the strength and toughness are uniform across the entire thickness section, fully meeting the requirements for marine engineering structural steel.

Description

Technical Field

[0001] This invention relates to the field of extra-thick plate technology, specifically a 160-210mm thick marine structural steel S690QL1 and its production method. Background Technology

[0002] With the rapid development of the global marine engineering field, especially in offshore wind power generation, deep-sea resource development, offshore drilling platforms, and large-scale marine transportation facilities, the demand for Q690 grade marine structural steel, particularly thick steel plates, is showing a continuous upward trend. However, ensuring the uniformity of properties throughout the thickness direction, weld crack sensitivity, corrosion resistance, and resistance to lamellar tearing of thick steel plates, especially those over 150mm, to meet application requirements is an urgent problem to be solved.

[0003] The publication number CN114107805 A discloses "a thick quenched and tempered Q690E / F high-strength steel and its manufacturing method". It produces 328mm billets through continuous casting and 100-120mm thick Q690E / F steel plates through TMCP+QT process. The thickness is small, the compression ratio is insufficient, the flaw detection level is lower than the requirements of EN10160 S3E4 standard, and the performance of the steel plate can only guarantee 1 / 4 of the performance quality requirements of GB / T 16270 standard.

[0004] CN116815074A discloses "A high-strength and tough extra-thick weathering steel plate with excellent thickness uniformity and its preparation method", which uses differential temperature rolling + sub-temperature quenching + tempering process to produce Q690F steel plates with a thickness of 100-140mm; another example is CN106148819A, which discloses "A high-strength structural steel S690QL (QL1) medium-thick plate and its production method", which can produce S690QL1 structural steel plates with a thickness of less than 150mm that maintain performance and flaw detection with high yield strength.

[0005] However, the steel plates obtained by the above methods are relatively thin, have poor flaw detection quality and resistance to lamellar tearing, and cannot guarantee the uniformity of the steel plate thickness and cross-sectional properties, thus failing to meet the current requirements of marine engineering.

[0006] In view of this, this invention is hereby proposed. Summary of the Invention

[0007] To address the aforementioned technical deficiencies, the present invention aims to provide a 160-210mm thick marine structural steel S690QL1. The obtained steel plates exhibit significant advantages in terms of thickness, flaw detection quality, and resistance to lamellar tearing, ensuring uniformity of the steel plate's thickness and cross-sectional properties, thus meeting the current requirements for use in the marine engineering field.

[0008] Another object of the present invention is to provide a method for producing 160-210mm thick marine structural steel S690QL1.

[0009] To achieve the above objectives, the technical solution adopted by this invention is: a 160-210mm thick marine structural steel S690QL1, comprising the following chemical composition by mass percentage: C: 0.06-0.12, Si: 0.08-0.15, Mn: 1.30-1.50, P≤0.006, S≤0.004, Cr: 0.40-0.60, Mo: 0.40-0.55, Ni: 1.50-1.60, Nb: 0.030-0.040, V: 0.060-0.075, Als: 0.030-0.040, B: 0.001-0.003, with the remainder being Fe and residual elements; its carbon equivalent (CEV) is ≤0.65%.

[0010] The production method of the aforementioned 160-210mm thick marine structural steel S690QL1 includes ingot casting, heating, rolling, controlled cooling, and heat treatment, as detailed below:

[0011] 1) Steel ingot casting: Use water-cooled ingot molds with a thickness of 840-1050mm to ensure a compression ratio of 5-6.5 times. Use argon gas protection for casting and control the casting temperature at 1555-1565℃.

[0012] 2) Heating: The cleaning temperature of the steel ingot is ≥430℃. After cleaning, the surface is coated with an anti-high temperature oxidation coating to avoid oxidation and decarburization on the surface of the billet in the high-temperature section and warping during the high-pressure rolling process. The furnace temperature is >400℃, and the steel is soaked for 4-6 hours. The billet is homogenized to allow carbides in the martensite to precipitate, reduce the carbon content, stabilize the structure, and reduce internal stress. When the furnace temperature is <900℃, the heating rate is ≤60℃ / h to reduce the temperature difference between the core and the surface of the billet. Then, the temperature is rapidly increased. The temperature of the soaking section is 1170±10℃, and the holding time in the soaking section is 7.5-9.0min / cm to fully austenitize the billet and ensure that the original austenite structure is uniform and refined.

[0013] 3) Rolling: The initial rolling temperature is ≥1020℃, and the reduction per pass is 50-60mm to ensure that the rolling force fully penetrates to the core of the billet, so that the grains in 1 / 2 part are flattened and elongated, the original austenite that has been coarsened by heating is broken, and the growth of unbroken austenite grains is prevented. High pressure water is applied before each rolling pass and the billet is fully heated before the next rolling pass can be rolled to avoid the billet warping due to low surface temperature during high pressure rolling. The final rolling temperature is 940-950℃.

[0014] 4) Controlled cooling: After rolling, the steel plate is quickly cooled in ACC. After each cooling, it is heated to red for 40-60 seconds before being cooled in water. This cooling process is repeated 6-8 times, with a final cooling temperature of 400-500℃. The rapid cooling of the rolled steel plate in ACC reduces the core temperature to below Ar1, preserving dislocation strengthening. Combined with precipitation strengthening from rapid cooling, this ensures the refinement of the original rolled half-thickness microstructure inside the steel plate, laying a good foundation for the tempering process in the heat treatment of the steel plate.

[0015] 5) Heat treatment: including high-temperature quenching, critical quenching and tempering. High-temperature quenching is carried out at a heating rate of ≥70℃ / h, heating to 910±10℃, holding for 2.0~2.2min / mm, and then rapidly water-cooled to room temperature after holding. Critical quenching is carried out at a heating rate of ≥70℃ / h, heating to 830±10℃, holding for 2.0~2.2min / mm, and then rapidly water-cooled to room temperature after holding. Tempering is carried out at a heating rate of 40~50℃ / h, heating to 600±10℃, holding for 3.0~3.5min / mm. The temperature is raised to 640℃ 30 minutes before the steel plate is taken out of the furnace to increase the surface temperature of the steel plate, soften the hardened layer on the surface of the steel plate, and make the strength uniform in the entire thickness direction. After the steel plate is taken out of the furnace, it is air-cooled to room temperature.

[0016] It should be noted that high-temperature quenching can promote the complete austenitization of the internal structure of the steel plate. Under the interaction of hardenability-enhancing elements such as Ni, Mo, and B, and grain-refining elements such as Nb and V, the overall hardenability of the steel plate is improved, and the austenite is completely martensitized. Critical quenching can austenitize the martensite grain boundaries, retain some undissolved ferrite, and hinder the growth of austenite grains, thereby further refining the grains and improving toughness while ensuring the strength of the steel. The critical quenching process involves heating the steel plate to room temperature and then cooling it at a rate of 0.5-1.0℃ / s, resulting in lath martensite and a small amount of lower bainite. During accelerated cooling, a significant number of dislocations are generated due to the phase transformation volume difference and quenching stress. After tempering at 600℃, the strength and toughness of the steel plate are affected by dislocation recovery, changes in bainite lath width, and precipitation strengthening. After tempering, on the one hand, dislocations slide, recombine, or adjust, reducing the dislocation density and causing a softening process. On the other hand, nanoscale precipitates are dispersed at dislocation lines and other locations. These fine precipitates can effectively hinder dislocation movement, delay matrix recovery, and reduce the softening tendency, thus ensuring the high strength of the tempered steel plate. After tempering, the steel plate exhibits dispersed nanoscale precipitates and maintains a fine lath structure, resulting in good impact toughness.

[0017] Compared with the prior art, the present invention has the following advantages: the solidification principle and process control of water-cooled mold casting result in a larger original billet thickness and better internal feeding effect compared with continuous casting or cast iron mold casting; after rolling, the steel plate undergoes multiple intermittent rapid cooling and heat treatments, resulting in a steel plate with fine and uniform tempered martensite + a small amount of tempered bainite structure. 100% full coverage flaw detection is performed according to the flaw detection requirements of EN10160-1999, which meets the requirements of S3E4 flaw detection.

[0018] The yield strength at the surface, 1 / 4 and 1 / 2 of the steel plate is ≥690MPa, the tensile strength is 770~940MPa, the strength difference of the entire thickness section is within 30MPa, the elongation is ≥18%, the impact performance of different thickness sections at -60℃ is ≥150J, the impact value of the surface at -60℃ with 5% strain aging is ≥120J, the steel plate's resistance to lamellar tearing reaches Z45, and the strength and toughness of the entire thickness section are uniform. It not only fully meets the requirements for the use of marine engineering structural steel, but also the performance is much better than expected, and the reliability and safety are greatly enhanced. Detailed Implementation

[0019] The present invention will be further described in detail below with reference to implementation examples.

[0020] Example 1: S690QL1 steel plate with a rolling thickness of 160mm

[0021] Through hot metal pretreatment, converter smelting, and ladle refining, molten steel with the following chemical composition (unit, wt%) was obtained: C: 0.09, Si: 0.1, Mn: 1.35, P: 0.004, S: ≤0.002, Cr: 0.45, Mo: 0.45, Ni: 1.54, Nb: 0.033, V: 0.065, Als: 0.030, B: 0.0017, CEV: 0.529, with the remainder being Fe and residual elements.

[0022] Casting: The steel ingot adopts an 840 / 800mm taper and a 30-ton ingot design to ensure a 5-fold compression ratio. Argon gas is used for protective casting. After casting, an insulating agent is used to protect the temperature of the cap and ensure that the head of the steel ingot is fully compressed.

[0023] b. Steel ingot heating: The steel ingot is cleaned and charged at a low temperature (cleaning temperature 450℃, furnace temperature 420℃, and simmering for 4.5 hours). After cleaning, the surface is coated with an anti-high temperature oxidation coating to avoid surface oxidation and decarburization in the high-temperature section of the billet and to prevent warping during the high-reduction rolling process. The heating rate in the low-temperature section (<900℃) is 55℃ / h to reduce the temperature difference between the core and the surface of the billet. The heating temperature in the soaking section is 1170℃, and the holding time in the soaking section is controlled at 11 hours to fully austenitize the billet and ensure that the original austenite structure is uniform and refined.

[0024] c. Rolling: After the steel ingot is tapped, it is quickly hoisted into the steel feeding roller table. The initial rolling temperature is controlled at ≥1020℃. During rolling, high-pressure water is applied in each pass and the ingot is fully heated. The reduction per pass is 50-60mm. The rolling force fully penetrates into the core of the billet, flattening and elongating the grains in half of the billet. This breaks up the original austenite that has been coarsened by heating, preventing the growth of unbroken austenite grains. The release temperature is 945℃.

[0025] d. Cooling process: After rolling, the steel plate adopts a multi-intermittent rapid cooling process [TM+NCP] to quickly enter the ACC for cooling. Groups 1-22 of the manifold are fully open, the roller speed is 0.6m / s, and the cooling is carried out 6 times. After each cooling, the steel plate is reddened for 40-60 seconds, and the reddening temperature is 483℃.

[0026] e. Heat treatment process: High-temperature quenching, heating to 900℃ at a heating rate of 78℃ / h, holding for 320min, and then rapidly water-cooled to room temperature after holding; Critical quenching, heating to 820℃ at a heating rate of 76℃ / h, holding for 320min, and then rapidly water-cooled to room temperature after holding; Tempering, heating to 600℃ at a heating rate of 45℃ / h, holding for 480min, raising the temperature to 640℃ 30 minutes before tapping, and air-cooling the steel plate to room temperature after tapping.

[0027] The 160mm thick S690QL1 steel plate produced by the above method was subjected to 100% full coverage flaw detection according to the flaw detection requirements of EN10160-1999 after unstacking. It met the flaw detection requirements of S3E4. The actual properties of the steel plate are shown in Table 1.

[0028] Table 1

[0029]

[0030]

[0031] Example 2: S690QL1 steel plate with a rolling thickness of 190mm

[0032] Through hot metal pretreatment, converter smelting, and ladle refining, molten steel with the following chemical composition (unit, wt%) was obtained: C: 0.08, Si: 0.12, Mn: 1.45, P: 0.003, S: ≤0.002, Cr: 0.50, Mo: 0.50, Ni: 1.53, Nb: 0.035, V: 0.068, Als: 0.030, B: 0.0015, CEV: 0.56, with the remainder being Fe and residual elements.

[0033] a. Casting: The steel ingot adopts a 1050 / 950mm taper and 40-ton ingot design to ensure a 5.5 times compression ratio. Argon gas is used for casting, and after casting, an insulating agent is used to protect the temperature of the cap to ensure that the head of the steel ingot is fully compressed.

[0034] b. Steel ingot heating: The steel ingot is cleaned and charged at a low temperature (cleaning temperature 452℃, furnace temperature 421℃, and simmering for 6 hours). After cleaning, the surface is coated with an anti-high temperature oxidation coating to prevent surface oxidation and decarburization in the high-temperature section of the billet and to prevent warping during the high-reduction rolling process. The heating rate in the low-temperature section (<900℃) is 53℃ / h to reduce the temperature difference between the core and the surface of the billet. The heating temperature in the soaking section is 1180℃, and the holding time in the soaking section is controlled at 15 hours to fully austenitize the billet and ensure that the original austenite structure is uniform and refined.

[0035] c. Rolling: After the steel ingot is tapped, it is quickly hoisted into the steel feeding roller table. The initial rolling temperature is controlled at ≥1020℃. During rolling, high-pressure water is applied in each pass and the ingot is fully heated. The reduction per pass is 50-60mm. The rolling force fully penetrates into the core of the billet, flattening and elongating the grains in half of the billet. This breaks up the original austenite that has been coarsened by heating, preventing the growth of unbroken austenite grains. The release temperature is 938℃.

[0036] d. Cooling process: After rolling, the steel plate adopts a multi-intermittent rapid cooling process [TM+NCP] to quickly enter the ACC for cooling. Groups 1-22 of the manifold are fully open, the roller speed is 0.6m / s, and the cooling is carried out 7 times. After each cooling, the steel plate is reddened for 40-60 seconds, and the reddening temperature is 476℃.

[0037] e. Heat treatment process: High-temperature quenching, heating to 900℃ at a heating rate of 78℃ / h, holding for 380min, and then rapidly water-cooled to room temperature after holding; Critical quenching, heating to 830℃ at a heating rate of 76℃ / h, holding for 320min, and then rapidly water-cooled to room temperature after holding; Tempering, heating to 600℃ at a heating rate of 45℃ / h, holding for 665min, raising the temperature to 640℃ 30 minutes before tapping, and air-cooling the steel plate to room temperature after tapping.

[0038] The 190mm thick S690QL1 steel plate produced by the above method was subjected to 100% full coverage flaw detection according to the flaw detection requirements of EN10160-1999 after unstacking. It met the flaw detection requirements of S3E4. The actual properties of the steel plate are shown in Table 2.

[0039] Table 2

[0040]

[0041] Example 3: S690QL1 steel plate with a rolling thickness of 210mm

[0042] Through hot metal pretreatment, converter smelting, and ladle refining, molten steel with the following chemical composition (in wt%) was obtained: C: 0.078, Si: 0.10, Mn: 1.48, P: 0.003, S: ≤0.002, Cr: 0.55, Mo: 0.53, Ni: 1.60, Nb: 0.034, V: 0.072, Als: 0.030, B: 0.0017, CEV: 0.66, with the remainder being Fe and residual elements.

[0043] a. Casting: The steel ingot adopts a 1050 / 950mm taper and a 40-ton ingot design to ensure a 5-fold compression ratio. Argon gas protection is used for casting. After casting, an insulating agent is used to protect the temperature of the cap to ensure that the head of the steel ingot is fully compressed.

[0044] b. Ingot heating: Ingot cleaning and charging (cleaning temperature 460℃, furnace temperature 428℃, simmering for 6 hours, billet homogenization to precipitate carbides in martensite, reduce carbon content, stabilize microstructure and reduce internal stress), after cleaning, the surface is coated with anti-high temperature oxidation coating to avoid surface oxidation and decarburization in the high temperature section of the billet and warping during the high-reduction rolling process, the low temperature section (<900℃) heating rate is 52℃ / h to reduce the temperature difference between the core and the surface of the billet, the homogenization section heating temperature is 1180℃, the holding time in the homogenization section is controlled at 15 hours (holding time = billet thickness * 7.5~9.0min / cm) to fully austenitize the billet and ensure that the original austenite microstructure is uniform and refined.

[0045] c. Rolling: After the steel ingot is tapped, it is quickly hoisted into the feeding roller table. The initial rolling temperature is controlled at ≥1020℃. During rolling, high-pressure water is applied in each pass and the ingot is fully heated. The reduction per pass is 50-60mm. The rolling force fully penetrates into the core of the billet, causing the grains in half of the billet to be flattened and elongated. This breaks up the original austenite that has been coarsened by heating, preventing the growth of unbroken austenite grains. The release temperature is 943℃.

[0046] d. Cooling process: After rolling, the steel plate adopts a multi-intermittent rapid cooling process [TM+NCP] to quickly enter the ACC for cooling. Groups 1-22 of the manifold are fully open, the roller speed is 0.6m / s, and the cooling is carried out 8 times. After each cooling, the steel plate is reddened for 40-60 seconds, and the reddening temperature is 463℃.

[0047] e. Quenching process: High-temperature quenching: heat to 900℃ at a heating rate of 76℃ / h, hold for 420min, and then rapidly water-cool to room temperature after holding; Critical quenching: heat to 830℃ at a heating rate of 73℃ / h, hold for 420min, and then rapidly water-cool to room temperature after holding; Tempering: heat to 600℃ at a heating rate of 46℃ / h, hold for 735min, raise the temperature to 640℃ 30 minutes before tapping, and air-cool the steel plate to room temperature after tapping.

[0048] The 210mm thick S690QL1 steel plate produced by the above method was subjected to 100% full coverage flaw detection according to the flaw detection requirements of EN10160-1999 after destacking. It met the flaw detection requirements of S3E4. The actual properties of the steel plate are shown in Table 3.

[0049] Table 3

[0050]

[0051] The 160-210mm thick S690QL1 high-strength steel plates obtained using this method meet the quality requirements for various types of offshore platform structures. The internal components undergo 100% full-coverage flaw detection according to EN10160-1999 standards, and comply with S3E4 flaw detection requirements. The plates exhibit uniform and stable performance across their thickness, with good strength and toughness matching. They also demonstrate excellent resistance to lamellar tearing and are suitable for mass production.

Claims

1. A method for producing 160-210mm thick marine structural steel S690QL1, characterized in that, The chemical composition contains the following mass fractions: C: 0.06–0.12, Si: 0.08–0.15, Mn: 1.30–1.50, P ≤ 0.006, S ≤ 0.004, Cr: 0.40–0.60, Mo: The carbon content is 0.40~0.55, Ni: 1.50~1.60, Nb: 0.030~0.040, V: 0.060~0.075, Als: 0.030~0.040, B: 0.001~0.003, with the remainder being Fe and residual elements; its carbon equivalent (CEV) is ≤0.65%; the yield strength at the steel surface, 1 / 4 and 1 / 2 sections is ≥690MPa, the tensile strength is 770~940MPa, the strength difference across the entire thickness section is within 30MPa, the elongation is ≥18%, the impact performance at -60℃ for different thickness sections is ≥150J, the impact value of the surface at -60℃ with 5% transverse strain aging is ≥120J, and the steel plate's resistance to lamellar tearing reaches Z45; The production method of the aforementioned 160-210mm thick marine structural steel S690QL1 includes ingot casting, heating, rolling, controlled cooling, and heat treatment, as detailed below: 1) Steel ingot casting: Use water-cooled ingot molds with a thickness of 840-1050mm to ensure a compression ratio of 5-6.5 times. Use argon gas protection for casting and control the casting temperature at 1555-1565℃. 2) Heating: The cleaning temperature of the steel ingot is ≥430℃, the furnace temperature is >400℃, and the steel is soaked for 4 to 6 hours. When the furnace temperature is <900℃, the heating rate is ≤60℃ / h, followed by rapid heating. The temperature of the soaking zone is 1170±10℃, and the holding time of the soaking zone is 7.5 to 9.0 min / cm. 3) Rolling: The initial rolling temperature is ≥1020℃, the reduction per pass is 50~60mm, high pressure water is sprayed before each rolling pass and the water is fully heated before the next rolling pass can be rolled, and the final rolling temperature is 940~950℃. 4) Controlled cooling: After rolling, the steel plate is quickly put into ACC for cooling. After each cooling, it is heated back to red for 40-60 seconds before being put into water cooling. This cooling process is repeated 6-8 times, with a final cooling temperature of 400-500℃. 5) Heat treatment: including high-temperature quenching, low-temperature quenching and tempering. High-temperature quenching is carried out at a heating rate of ≥70℃ / h, heating to 910±10℃, holding for 2.0~2.2min / mm, and then rapidly water-cooled to room temperature after holding. Low-temperature quenching is carried out at a heating rate of ≥70℃ / h, heating to 830±10℃, holding for 2.0~2.2min / mm, and then rapidly water-cooled to room temperature after holding. Tempering is carried out at a heating rate of 40~50℃ / h, heating to 600±10℃, holding for 3.0~3.5min / mm, raising the temperature to 640℃ 30 minutes before the steel plate is taken out of the furnace, and then air-cooling the steel plate to room temperature after taking it out of the furnace.

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