Ocean structural steel S690QL1 with thickness of 160-210 mm and production method thereof

Abstract

The invention discloses 160-210 mm thick ocean structural steel S690QL1 and a production method thereof, the carbon equivalent CEV of the steel is smaller than or equal to 0.65%, a water-cooled mold ingot with the thickness larger than or equal to 800 mm is adopted, and through low-temperature heating, high-temperature controlled rolling, multiple times of intermittent controlled cooling and heat treatment, an obtained steel plate has fine and uniform tempered martensite and a small amount of tempered bainite structures, and the thickness of the steel plate is larger than or equal to 100 mm. 100% complete coverage scanning flaw detection is performed according to EN10160-1999 flaw detection requirements, the S3E4 flaw detection requirements are met, and through detection, the yield strength of the surface, the 1 / 4 position and the 1 / 2 position is larger than or equal to 690 MPa, the tensile strength is 770-940 MPa, the strength difference of the whole thickness section is within 30 MPa, the elongation is larger than or equal to 18%, the impact performance of sections with different thicknesses at the temperature of-60 DEG C is larger than or equal to 150 J, and the tensile strength is larger than or equal to 90 MPa. The transverse 5% strain aging impact value of the surface at-60 DEG C is larger than or equal to 120 J, the lamellar tearing resistance of the steel plate reaches Z45, the obdurability of the whole thickness section is uniform, and the use requirements of ocean engineering structural steel are completely met.

Description

Technical Field

[0001] The invention relates to the technical field of extra-thick plates, and relates to marine structural steel S690QL1 with a thickness of 160 to 210 mm and a production method thereof. Background Art

[0002] With the rapid development of global marine engineering, especially in the fields of offshore wind power generation, deep-sea resource development, offshore drilling platforms, large-scale marine transportation facilities, etc., the demand for Q690 grade marine structural steel, especially thick steel plates, has shown a continuous growth trend. However, how to ensure the uniformity of performance, welding crack sensitivity, corrosion resistance, and lamellar tearing resistance of thick steel plates, especially those with a thickness of more than 150mm, in the full thickness direction to meet the use requirements is an urgent problem to be solved.

[0003] 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 steel plates are small in thickness, have insufficient compression ratio, and have a flaw detection level lower than the EN10160 S3E4 standard requirements. The performance of the steel plates can only guarantee 1 / 4 of the performance quality requirements of the GB / T 16270 standard.

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

[0005] However, relatively speaking, the steel plates obtained by the above schemes are all thinner, with poor flaw detection quality and laminar tearing resistance. The uniformity of the thickness and cross-sectional performance of the steel plates cannot be guaranteed, and they cannot meet the current requirements for use in the marine engineering field.

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

[0007] In order to solve the above-mentioned technical defects, the purpose of the present invention is to provide a 160-210 mm thick marine structural steel S690QL1. The obtained steel plates have obvious advantages in thickness, flaw detection quality, and resistance to laminar tearing performance, and can ensure the uniformity of the thickness and cross-sectional performance of the steel plates, 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 160-210 mm thick marine structural steel S690QL1.

[0009] To achieve the above-mentioned purpose, the technical solution adopted by the present invention is: a 160-210 mm thick marine structural steel S690QL1, comprising the following chemical components in 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, and the rest are Fe and residual elements; its carbon equivalent CEV≤0.65%.

[0010] The production method of the above-mentioned 160-210 mm thick marine structural steel S690QL1 includes ingot casting, heating, rolling, controlled cooling and heat treatment, which is specifically as follows:

[0011] 1) Ingot casting: Use a water-cooled ingot mold with a thickness of 840-1050 mm, ensure a compression ratio of 5-6.5 times, use argon protection for casting, and control the casting temperature at 1555-1565 ° C;

[0012] 2) Heating: The cleaning temperature of the steel ingot is ≥430°C, and the surface is coated with an anti-high temperature oxidation coating after cleaning to avoid oxidation and decarburization of the billet surface in the high temperature section and warping of the steel during high pressure rolling; the furnace temperature is >400°C, and the steel is stewed for 4 to 6 hours. The billet is heated evenly to precipitate carbides in the martensite, reduce the carbon content, stabilize the organization, and reduce internal stress; when the furnace temperature is <900°C, the heating rate is ≤60°C / h to reduce the temperature difference between the core and the surface of the billet, and then the temperature is quickly raised, the temperature of the soaking section is 1170±10°C, and the holding time of the soaking section is 7.5 to 9.0min / cm, so that the billet is fully austenitized and the original austenite organization is ensured to be uniformly refined;

[0013] 3) Rolling: The rolling temperature is ≥1020℃, and the pass reduction is 50-60mm. Ensure that the rolling force fully penetrates into the core of the billet, flattens and elongates the grains in the 1 / 2 part, crushes the heated and coarsened original austenite, and prevents the growth of unbroken austenite grains. High-pressure water is injected before each rolling pass and the next rolling can be carried out only after the water is fully returned to red, so as to avoid the billet from warping due to low surface temperature during rolling under high pressure. The final rolling temperature is 940-950℃;

[0014] 4) Controlled cooling: After rolling, the steel plate quickly enters ACC for cooling. After each cooling, it returns to red for 40-60S and then enters water for cooling. The cooling is repeated 6-8 times, and the final cooling temperature is 400-500°C. The rolled steel plate quickly enters ACC for cooling, so that the core temperature of the steel plate is reduced to below Ar1, dislocation strengthening is retained, and precipitation strengthening is combined with rapid cooling to ensure that the original rolled state 1 / 2 thickness of the steel plate is refined, laying a good foundation for the quenching and tempering process of the steel plate heat treatment process;

[0015] 5) Heat treatment: including high temperature quenching, critical quenching and tempering, wherein the high temperature quenching is heated to 910±10℃ at a heating rate of ≥70℃ / h, the holding time is 2.0~2.2min / mm, and the insulation is completed and the temperature is quickly cooled to room temperature with water; the critical quenching is heated to 830±10℃ at a heating rate of ≥70℃ / h, the holding time is 2.0~2.2min / mm, and the insulation is completed and the temperature is quickly cooled to room temperature with water; the tempering is heated to 600±10℃ at a heating rate of 40~50℃ / h, the holding time is 3.0~3.5min / mm, and 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 full thickness direction. The steel plate is air-cooled to room temperature after it is taken out of the furnace.

[0016] It should be noted that high-temperature quenching can make the internal structure of the steel plate completely austenitized. Under the interaction of elements such as Ni, Mo, B that improve hardenability and elements such as Nb and V that refine grains, the overall hardenability of the steel plate is improved, and the austenite is completely martenized. Intercritical quenching can austenitize the martensite grain boundaries, retain a part of the undissolved ferrite, hinder the growth of austenite grains, and further refine the grains, thereby ensuring the strength of the steel while improving the toughness. The critical quenching heating is quenched to room temperature at a cooling rate of 0.5-1.0℃ / S to produce lath martensite and a small amount of lower bainite structure; in the accelerated cooling process, a considerable number of dislocations will be generated due to the phase transformation volume difference and quenching stress. After the steel plate is tempered at 600℃, the recovery of dislocations, changes in the width of bainite laths, precipitation strengthening and other effects will affect the strength and toughness of the steel plate. After the steel plate is tempered, on the one hand, dislocations slide, recombine or adjust, so that the dislocation density is reduced, resulting in a softening process; on the other hand, nano-scale precipitates are dispersed and precipitated at positions such as dislocation lines. These fine precipitates can effectively hinder dislocation movement, delay the recovery of the matrix, and reduce the softening trend, thereby ensuring the high strength of the steel plate after tempering. After tempering, nano-scale precipitates are dispersed and precipitated, and fine lath structure is maintained, with good impact toughness.

[0017] Compared with the prior art, the present invention has the following advantages: compared with continuous casting or cast iron mold casting, the water-cooled mold pouring and solidification principle and process control are adopted, and the original billet thickness is large and the internal shrinkage compensation effect is good; after the steel plate is rolled, it undergoes multiple intermittent rapid cooling and heat treatment, and the obtained steel plate has a fine and uniform tempered martensite + a small amount of tempered bainite structure, and 100% full coverage scanning flaw detection is carried out according to the EN10160-1999 flaw detection requirements, which meets the S3E4 flaw detection requirements.

[0018] The yield strength of the steel plate surface, 1 / 4 and 1 / 2 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 surface -60℃ transverse 5% strain aging impact value is ≥120J, the steel plate's anti-laminar tearing performance reaches Z45, the strength and toughness of the entire thickness section is uniform, which not only fully meets the use requirements of marine engineering structural steel, but also has performance that is much better than expected, and reliability and safety are greatly enhanced. DETAILED DESCRIPTION

[0019] The present invention is further described in detail below in conjunction with embodiments.

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

[0021] Through molten iron pretreatment, converter smelting and refining outside the furnace, molten steel containing the following mass fractions of chemical composition (unit, wt%) is 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, and the rest are Fe and residual elements.

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

[0023] b. Ingot heating: The ingot is cleaned and loaded warm (the cleaning temperature of the ingot is 450℃, the temperature entering the furnace is 420℃, and the steel is stewed for 4.5 hours). After cleaning, the surface is coated with anti-high temperature oxidation coating to avoid surface oxidation and decarburization of the billet in the high temperature section and warping of the steel during the execution of the large 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 make the billet fully austenitized and ensure the uniform and refined original austenite structure.

[0024] c. Rolling: After the steel ingot is tapped, it is quickly hoisted into the steel feeding roller table, and the rolling temperature is controlled to be ≥1020℃. During rolling, high-pressure water is injected in each pass and the steel is fully reddened. The pass reduction is 50-60mm. The rolling force fully penetrates into the core of the billet, flattens and elongates the grains in 1 / 2 of the billet, crushes the heated and coarsened original austenite, and prevents the unbroken austenite grains from growing. The release temperature is 945℃;

[0025] d. Cooling process: After the steel plate is rolled, it is quickly cooled in ACC by using multiple intermittent rapid cooling processes [TM+NCP]. The 1-22 sets of headers are fully open, the roller speed is 0.6m / s, and it is cooled 6 times. After each cooling, it returns to red for 40-60S, and the red return temperature is 483℃.

[0026] e. Heat treatment process: high temperature quenching, heating to 900℃ at a heating rate of 78℃ / h, keeping warm for 320min, and quickly cooling to room temperature with water after the end of keeping warm; critical quenching, heating to 820℃ at a heating rate of 76℃ / h, keeping warm for 320min, and quickly cooling to room temperature with water after the end of keeping warm; tempering, heating to 600℃ at a heating rate of 45℃ / h, keeping warm for 480min, raising the temperature to 640℃ 30 minutes before steelmaking, and air cooling the steel plate to room temperature after it comes out of the furnace.

[0027] The S690QL1 steel plates with a thickness of 160 mm produced by the above method were subjected to 100% full coverage scanning flaw detection according to the EN10160-1999 flaw detection requirements after being destackered, and met the S3E4 flaw detection requirements. The actual properties of the steel plates are shown in Table 1.

[0028] Table 1

[0029]

[0030]

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

[0032] Through molten iron pretreatment, converter smelting and refining outside the furnace, molten steel containing the following mass fractions of chemical composition (unit, wt%) is 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, and the rest are Fe and residual elements.

[0033] a. Pouring: The steel ingot adopts 1050 / 950mm taper and 40-ton ingot design to ensure a 5.5-fold compression ratio. Argon gas is used for pouring. After pouring, a heat-insulating agent is used to protect the cap temperature to ensure that the head of the steel ingot is fully compensated for shrinkage.

[0034] b. Ingot heating: The ingot is cleaned and loaded warm (the cleaning temperature of the ingot is 452℃, the temperature entering the furnace is 421℃, and the steel is stewed for 6 hours). After cleaning, the surface is coated with anti-high temperature oxidation coating to avoid surface oxidation and decarburization of the billet in the high temperature section and warping of the steel during the execution of the large reduction rolling process. The heating rate in the low temperature section (<900℃) is 53℃ / h to reduce the temperature difference of the core and the remaining 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 make the billet fully austenitized and ensure the uniform and refined original austenite structure.

[0035] c. Rolling: After the steel ingot is tapped, it is quickly hoisted into the steel feeding roller table, and the rolling temperature is controlled to be ≥1020℃. During rolling, high-pressure water is injected in each pass and the steel is fully returned to red. The pass reduction is 50-60mm. The rolling force fully penetrates into the core of the billet, flattens and elongates the grains in 1 / 2 of the billet, crushes the heated and coarsened original austenite, and prevents the unbroken austenite grains from growing. The release temperature is 938℃;

[0036] d. Cooling process: After rolling, the steel plate is rapidly cooled by the intermittent rapid cooling process [TM+NCP]. The 1-22 sets of headers are fully open, the roller speed is 0.6m / s, and the cooling is performed 7 times. After each cooling, the steel plate returns to red for 40 to 60 seconds, and the red return temperature is 476℃.

[0037] e. Heat treatment process: high temperature quenching, heating to 900℃ at a heating rate of 78℃ / h, keeping warm for 380min, and quickly cooling to room temperature with water after the end of keeping warm; critical quenching, heating to 830℃ at a heating rate of 76℃ / h, keeping warm for 320min, and quickly cooling to room temperature with water after the end of keeping warm; tempering, heating to 600℃ at a heating rate of 45℃ / h, keeping warm for 665min, raising the temperature to 640℃ 30 minutes before steelmaking, and air cooling the steel plate to room temperature after it comes out of the furnace.

[0038] The 190mm thick S690QL1 steel plates produced by the above method were destackered and subjected to 100% full coverage scanning flaw detection according to the EN10160-1999 flaw detection requirements. They met the S3E4 flaw detection requirements. The actual properties of the steel plates are shown in Table 2.

[0039] Table 2

[0040]

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

[0042] Through molten iron pretreatment, converter smelting and refining outside the furnace, molten steel containing the following mass fractions of chemical composition (unit, wt%) is 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, and the rest are Fe and residual elements.

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

[0044] b. Ingot heating: Ingot warm cleaning and warm loading (ingot cleaning temperature 460℃, furnace entry temperature 428℃, simmering for 6 hours, billet evenly heated to precipitate carbides in martensite, reduce carbon content, stabilize organization and reduce internal stress). After cleaning, anti-high temperature oxidation coating is applied to the surface to avoid oxidation and decarburization of the billet surface in the high temperature section and warping of the billet during the large reduction rolling process. The heating rate in the low temperature section (<900℃) is 52℃ / h to reduce the temperature difference of the core and the remaining surface of the billet. The heating temperature in the even heating section is 1180℃, and the holding time in the even heating section is controlled at 15 hours (holding time = billet thickness*7.5~9.0min / cm) to fully austenitize the billet and ensure the uniform and refined original austenite organization.

[0045] c. Rolling: After the steel ingot is tapped, it is quickly hoisted into the steel feeding roller table, and the starting rolling temperature is controlled to be ≥1020℃. During rolling, high-pressure water is injected in each pass and the steel is fully returned to red. The reduction per pass is 50-60mm. The rolling force fully penetrates into the core of the billet, so that the grains in 1 / 2 of the part are flattened and elongated, and the original austenite that has been heated and coarsened is broken to prevent the growth of unbroken austenite grains. The release temperature is 943℃.

[0046] d. Cooling process: After the steel plate is rolled, it is quickly cooled in ACC by using multiple intermittent rapid cooling processes [TM+NCP]. The 1-22 sets of headers are fully open, the roller speed is 0.6m / s, and it is cooled 8 times. After each cooling, it returns to red for 40 to 60S, and the red return temperature is 463℃.

[0047] e. Quenching process: high temperature quenching, heating to 900℃ at a heating rate of 76℃ / h, keeping warm for 420min, and quickly cooling to room temperature with water after the end of keeping warm; critical quenching, heating to 830℃ at a heating rate of 73℃ / h, keeping warm for 420min, and quickly cooling to room temperature with water after the end of keeping warm; tempering, heating to 600℃ at a heating rate of 46℃ / h, keeping warm for 735min, raising the temperature to 640℃ 30 minutes before steelmaking, and air cooling the steel plate to room temperature after it comes out of the furnace.

[0048] The S690QL1 steel plates with a thickness of 210 mm produced by the above method were subjected to 100% full coverage scanning flaw detection according to the EN10160-1999 flaw detection requirements after being destackered. They met the S3E4 flaw detection requirements. The actual properties of the steel plates are shown in Table 3.

[0049] Table 3

[0050]

[0051] The 160-210mm thick S690QL1 high-strength steel plates obtained by this scheme meet the requirements of various types of offshore platform structures. The internal EN10160-1999 flaw detection requirements are 100% fully covered and scanned for flaws, which meets the S3E4 flaw detection requirements. The full thickness performance is uniform and stable, and the strength and toughness match is good. The steel plate has excellent anti-laminar tearing performance and can be mass-produced.

Claims

1. A 160-210 mm thick marine structural steel S690QL1, characterized in that: The invention comprises the following chemical components in mass fraction (unit, wt%): 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, and the rest are Fe and residual elements; Its carbon equivalent CEV≤0.65%; the yield strength of the steel plate surface, 1 / 4 and 1 / 2 are ≥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 surface -60℃ transverse 5% strain aging impact value is ≥120J, and the steel plate's anti-laminar tearing performance reaches Z45.

2. The method for producing 160-210 mm thick marine structural steel S690QL1 according to claim 1, characterized in that Including ingot pouring, heating, rolling, controlled cooling and heat treatment, as follows: 1) Ingot casting: Use a water-cooled ingot mold with a thickness of 840-1050 mm, ensure a compression ratio of 5-6.5 times, use argon protection for casting, and control the casting temperature at 1555-1565 ° C; 2) Heating: The cleaning temperature of the steel ingot is ≥430°C, the temperature entering the furnace is >400°C, the steel is stewed for 4 to 6 hours, the heating rate is ≤60°C / h when the furnace temperature is <900°C, and then the temperature is quickly raised, the temperature of the soaking section is 1170±10°C, and the holding time of the soaking section is 7.5 to 9.0 min / cm; 3) Rolling: The starting rolling temperature is ≥1020℃, the pass reduction is 50-60mm, high-pressure water is injected before each rolling pass and the next rolling can only be carried out after the steel is fully reddened, and the final rolling temperature is 940-950℃; 4) Controlled cooling: After rolling, the steel plate quickly enters ACC for cooling. After each cooling, it returns to red for 40 to 60 seconds and then enters water for cooling. The cooling is repeated 6 to 8 times, and the final cooling temperature is 400 to 500 ° C. 5) Heat treatment: including high temperature quenching, low temperature quenching and tempering, wherein the high temperature quenching is heated to 910±10℃ at a heating rate of ≥70℃ / h, the holding time is 2.0~2.2min / mm, and the steel plate is quickly cooled to room temperature with water after the holding period; the low temperature quenching is heated to 830±10℃ at a heating rate of ≥70℃ / h, the holding time is 2.0~2.2min / mm, and the steel plate is quickly cooled to room temperature with water after the holding period; the tempering is heated to 600±10℃ at a heating rate of 40~50℃ / h, the holding time is 3.0~3.5min / mm, the temperature is raised to 640℃ 30 minutes before the steel plate is taken out of the furnace, and the steel plate is air-cooled to room temperature after the steel plate is taken out of the furnace.

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