Q370qE high-strength steel plate with thickness of 60 mm and production method of Q370qE high-strength steel plate

Abstract

The invention discloses a Q370qE high-strength steel plate with the thickness of 60 mm and a production method of the Q370qE high-strength steel plate. The Q370qE high-strength steel plate provided by the invention comprises the following chemical components in percentage by mass: 0.07%-0.08% of C, 0.20%-0.30% of Si, 1.35%-1.45% of Mn, less than or equal to 0.010% of P, less than or equal to 0.005% of S, 0.020%-0.035% of Alt, 0.030%-0.035% of Nb, 0.015%-0.025% of Ti, 0.025%-0.035% of V, 0.10%-0.15% of Cr and the balance of iron and inevitable impurities. The mechanical properties of the Q370qE high-strength steel plate meet the conditions that the yield strength is larger than or equal to 360 MPa, the tensile strength is larger than or equal to 510 MPa, and the impact absorbing energy Kv2 at the temperature of minus 40 DEG C is larger than or equal to 200 J.

Description

Technical Field

[0001] This invention belongs to the field of metallurgical plate production technology, specifically relating to a 60mm thick Q370qE high-strength steel plate and its production method. Background Technology

[0002] High-strength bridge structural steel Q370qE is widely used in bridge and other steel structure construction due to its high strength level and excellent processability. With the advancement of national infrastructure construction and technological progress, the application of bridge structural steel is expanding to environments with harsh geological conditions such as deserts, Gobi, and high-altitude cold regions. To ensure both the strength and rigidity of the steel plates, the demand for thicker steel plates (thickness greater than 50mm) has increased dramatically, while higher requirements are being placed on their low-temperature impact toughness.

[0003] Steel plates thicker than 50mm require high cooling capacity from the rolling mill during production; however, current technology makes it almost impossible to produce such plates on rolling mills without ultra-fast cooling equipment. Summary of the Invention

[0004] The technical problem to be solved by this invention is to provide a 60mm thick Q370qE high-strength steel plate and its production method. This invention is simple to operate and suitable for industrial production. The Q370qE steel plate produced by the method of this invention has high strength, good impact toughness, excellent formability and weldability, and its impact energy at -40℃ is stably controlled above 200J. Its mechanical properties and processability meet the technical requirements of users.

[0005] Specifically, the present invention is mainly achieved through the following technical solutions.

[0006] This invention provides a 60mm thick Q370qE high-strength steel plate, the chemical composition of which, by mass percentage, is: C: 0.07%–0.08%, Si: 0.20%–0.30%, Mn: 1.35%–1.45%, P≤0.010%, S≤0.005%, Alt: 0.020%–0.035%, Nb: 0.030%–0.035%, Ti: 0.015%–0.025%, V: 0.025%–0.035%, Cr: 0.10%–0.15%, with the remainder being iron and unavoidable impurities; and

[0007] The mechanical properties of the Q370qE high-strength steel plate meet the following requirements: yield strength ≥ 360MPa, tensile strength ≥ 510MPa, and impact absorption energy Kv2 ≥ 200J at -40℃.

[0008] In some embodiments, the mechanical properties of the Q370qE high-strength steel plate meet the following requirements: yield strength ≥ 380 MPa, tensile strength ≥ 540 MPa, and impact absorption energy Kv2 ≥ 230 J at -40℃.

[0009] Another aspect of the present invention provides a method for producing Q370qE high-strength steel plate, which includes the following processes: KR desulfurization—converter—LF refining—RH vacuum treatment—slab continuous casting—slow cooling—slab heating—slab rolling—laminar cooling—steel plate straightening—steel plate heat treatment.

[0010] In some implementations, in the KR desulfurization-converter-LF refining-RH vacuum treatment-slab continuous casting process,

[0011] (1) The S content of molten iron after pretreatment is ≤0.005%. After desulfurization, slag must be removed to ensure that the molten iron carries as little slag as possible.

[0012] (2) Use self-produced low-sulfur scrap steel, the converter end point hits once or the number of additional blowing times does not exceed once, and the tapping temperature is ≥1600℃;

[0013] (3) LF refining involves slag formation, desulfurization, composition adjustment, and heating operations based on the composition and temperature of the converter steel so that the steel composition and temperature meet the requirements of RH and continuous casting.

[0014] (4) RH vacuum treatment time ≥ 20 min. After RH vacuum treatment, adjust the argon flow rate to make the molten steel in a soft blowing state, feed in calcium wire for calcium treatment. After wire feeding, the [Ca] of the molten steel is 0.0008~0.0025%. After wire feeding, ensure that the soft blowing time is ≥ 10 min.

[0015] (5) The composition of the molten steel supplied to the casting machine is C: 0.07%~0.08%, Si: 0.20%~0.30%, Mn: 1.35%~1.45%, P≤0.010%, S≤0.005%, Alt: 0.020%~0.035%, Nb: 0.030%~0.035%, Ti: 0.015%~0.025%, V: 0.025%~0.035%, Cr: 0.10%~0.15%, with the remainder being iron and unavoidable impurities; the target superheat of the continuous casting process is 20~30℃, with full-process protective pouring, using electromagnetic stirring and light pressure, and the casting speed is controlled at 0.8~1.1m / min to ensure the quality of the billet. The billet is slowly cooled in the heat preservation pit for ≥48 hours.

[0016] In some implementations, the slab heating process strictly controls the slab's time in the furnace, the soaking time, and the exit temperature, with the furnace time ≥220 min, the soaking time 30–60 min, and the exit temperature 1220 ± 20 °C.

[0017] In some embodiments, the slab rolling process includes roughing and finishing rolling.

[0018] In some embodiments, during the rough rolling, the billet is quickly sent to a descaling machine to remove iron oxide scale after exiting the furnace. The rough rolling is completed with as few passes as possible to achieve the desired width. The initial rolling temperature of the rough rolling is ≥1150℃, and the final rolling thickness of the rough rolling is twice that of the finished product. After rough rolling, the slab is allowed to warm up, avoiding rolling in some recrystallization zones to prevent crystal mixing. The initial rolling temperature of the finish rolling is ≤930℃, and the final rolling temperature of the finish rolling is 790℃±10℃.

[0019] In some embodiments, in the laminar flow cooling process, the post-rolling steel plate cooling mode adopts laminar flow cooling based on the self-learning calculation results of the secondary system, and the final cooling temperature is 600℃±10℃.

[0020] In some embodiments, the steel plate straightening process is carried out according to the steel plate thickness specifications and the actual shape of the steel plate after cooling.

[0021] In some embodiments, in the heat treatment process of the steel plate, the quenching temperature is controlled at 880°C and the holding time is 20 minutes; the tempering temperature is controlled at 510°C and the holding time is 40 minutes.

[0022] The 60mm thick Q370qE steel plate provided by the above technical solution has high strength, good impact toughness, excellent formability and weldability, and its impact energy at -40℃ is stably controlled above 200J. Its mechanical and processing properties meet the user's technical requirements. Furthermore, the operation method of this invention is simple and suitable for industrial production. Attached Figure Description

[0023] Figure 1 This is a microstructure diagram of the steel plate produced in Example 2 of the present invention. Detailed Implementation

[0024] The present invention will be described in more detail below through specific embodiments. These embodiments are merely descriptions of the best mode of implementation and do not limit the scope of the invention in any way.

[0025] Example 1

[0026] Molten iron underwent desulfurization pretreatment, followed by decarburization and descaling in a top-and-bottom blown converter to obtain steel. Argon blowing was performed throughout the converter smelting process, with scrap steel added. The converter tapping temperature was 1633℃. The molten steel was then subjected to LF ladle refining at a refining temperature ≥1560℃. After LF ladle refining, the steel underwent RH vacuum treatment, maintaining the vacuum for 21 minutes. Slabs were continuously cast according to the smelting chemical composition shown in Table 1, with a superheat of 26℃. Slab cleaning, slow cooling, and continuous casting quality inspection followed. The slab heating temperature was 1223℃, heating time 240 minutes, and soaking time 60 minutes. The heated slabs were then descaled using high-pressure water. After descaling, the steel is rolled using a 2-roll reversible mill for both roughing and finishing. The roughing mill starts at 1175℃ and is rolled to the intermediate slab thickness before being allowed to warm. The finishing mill starts at an average temperature of 928℃ and finishes at an average temperature of 790℃. After laminar cooling, the final cooling temperature of the steel plate is 605℃, resulting in a finished thickness of 60.0 mm. The plate is then straightened. Following shot peening, the straightened steel plate undergoes heat treatment: quenching at 880℃ for 20 minutes and tempering at 510℃ for 40 minutes. Finally, samples are taken according to standards for product quality testing.

[0027] Example 2

[0028] Molten iron undergoes desulfurization pretreatment, followed by decarburization and descaling in a top-and-bottom blown converter to obtain steel. Argon blowing is carried out throughout the converter smelting process, with scrap steel added. The converter tapping temperature is 1645℃. The molten steel is then subjected to LF ladle refining at a refining temperature ≥1555℃. After LF ladle refining, the steel undergoes RH vacuum treatment, maintaining the vacuum for 23 minutes. Slabs are continuously cast according to the smelting chemical composition shown in Table 1, with a superheat of 28℃. Slab cleaning, slow cooling, and continuous casting quality inspection are then performed. The slab heating temperature is 1220℃, heating time is 245 minutes, and soaking time is 55 minutes. The heated slabs are then descaled using high-pressure water. After descaling, the steel is rolled using a 2-roll reversible mill for both roughing and finishing. The roughing mill starts at 1175℃ and is rolled to the intermediate slab thickness before being allowed to warm. The finishing mill starts at an average temperature of 910℃ and finishes at an average temperature of 800℃. After laminar flow cooling, the final cooling temperature of the steel plate is 610℃, resulting in a finished thickness of 60.0 mm. The plate is then straightened. After shot peening, the straightened steel plate undergoes heat treatment: quenching at 880℃ for 20 minutes and tempering at 510℃ for 40 minutes. Finally, samples are taken according to standards for product quality inspection. Figure 1 The microstructure of the steel plate produced in Example 2 is shown.

[0029] Example 3

[0030] Molten iron underwent desulfurization pretreatment, followed by decarburization and descaling in a top-and-bottom blown converter to obtain steel. Argon blowing was performed throughout the converter smelting process, with scrap steel added. The converter tapping temperature was 1641℃. The molten steel was then subjected to LF ladle refining at a refining temperature ≥1564℃. After LF ladle refining, the steel underwent RH vacuum treatment, maintaining the vacuum for 20 minutes. Slabs were continuously cast according to the smelting chemical composition shown in Table 1, with a superheat of 25℃. Slab cleaning, slow cooling, and continuous casting quality inspection followed. The slab heating temperature was 1228℃, heating time 241 minutes, and soaking time 60 minutes. The heated slabs were then subjected to high-pressure water descaling. After descaling, the steel is rolled using a 2-roll reversible mill for both roughing and finishing. The roughing mill starts at 1185℃ and is rolled to the intermediate slab thickness before being allowed to warm. The finishing mill starts at an average temperature of 890℃ and finishes at an average temperature of 785℃. After laminar cooling, the final cooling temperature of the steel plate is 605℃, resulting in a finished thickness of 60.0 mm. The plate is then straightened. Following shot peening, the straightened steel plate undergoes heat treatment: quenching at 880℃ for 20 minutes and tempering at 510℃ for 40 minutes. Finally, samples are taken according to standards for product quality testing.

[0031] The chemical composition of the 60mm thick Q370qE steel plates produced in Examples 1-3 of this invention is shown in Table 1. The mechanical property test values ​​of the examples are shown in Table 2. As can be seen from Table 2, the mechanical properties of the steel plates produced in Examples 1-3 of this invention are stable with small fluctuations, and the low-temperature impact toughness value is stably controlled above 200J, preferably above 230J, and also has high yield strength and tensile strength.

[0032] Table 1: Chemical composition (wt%) of Examples 1-3 of the present invention

[0033] chemical composition C Si Mn P S Alt Nb Ti Cr V Example 1 0.08 0.25 1.36 0.009 0.002 0.032 0.035 0.016 0.10 0.028 Example 2 0.07 0.25 1.45 0.009 0.004 0.028 0.032 0.017 0.15 0.031 Example 3 0.07 0.26 1.38 0.008 0.005 0.035 0.031 0.025 0.13 0.035

[0034] Table 2: Mechanical and process properties of Examples 1-3 of the present invention

[0035]

[0036] Finally, it should be noted that the above descriptions are merely preferred embodiments of the present invention and are not intended to limit the present invention. Although the present invention has been described in detail with reference to the foregoing embodiments, those skilled in the art can still modify the technical solutions described in the foregoing embodiments or make equivalent substitutions for some of the technical features. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention should be included within the protection scope of the present invention.

Claims

1. A 60mm thick Q370qE high-strength steel plate, wherein the chemical composition of the Q370qE high-strength steel plate, by mass percentage, is: C: 0.07%–0.08%, Si: 0.20%–0.30%, Mn: 1.35%–1.45%, P≤0.010%, S≤0.005%, Alt: 0.020%–0.035%, Nb: 0.030%–0.035%, Ti: 0.015%–0.025%, V: 0.025%–0.035%, Cr: 0.10%–0.15%, with the remainder being iron and unavoidable impurities; and The mechanical properties of the Q370qE high-strength steel plate meet the following requirements: yield strength ≥ 360MPa, tensile strength ≥ 510MPa, and impact absorption energy Kv2 ≥ 200J at -40℃.

2. The Q370qE high-strength steel plate according to claim 1, wherein the mechanical properties of the Q370qE high-strength steel plate meet the following requirements: yield strength ≥ 380 MPa, tensile strength ≥ 540 MPa, and impact absorption energy Kv2 ≥ 230 J at -40℃.

3. The method for producing Q370qE high-strength steel plate according to claim 1 or 2, comprising the following processes: KR desulfurization—converter—LF refining—RH vacuum treatment—slab continuous casting—slow cooling—slab heating—slab rolling—laminar cooling—steel plate straightening—steel plate heat treatment.

4. The production method according to claim 3, wherein in the KR desulfurization-converter-LF refining-RH vacuum treatment-slab continuous casting process, (1) The S content of molten iron after pretreatment is ≤0.005%. After desulfurization, slag must be removed to ensure that the molten iron carries as little slag as possible. (2) Use self-produced low-sulfur scrap steel, the converter end point hits once or the number of additional blowing times does not exceed once, and the tapping temperature is ≥1600℃; (3) LF refining involves slag formation, desulfurization, composition adjustment, and heating operations based on the composition and temperature of the converter steel so that the steel composition and temperature meet the requirements of RH and continuous casting. (4) RH vacuum treatment time ≥ 20 min. After RH vacuum treatment, adjust the argon flow rate to make the molten steel in a soft blowing state, feed in calcium wire for calcium treatment. After wire feeding, the [Ca] of the molten steel is 0.0008~0.0025%. After wire feeding, ensure that the soft blowing time is ≥ 10 min. (5) The composition of the molten steel supplied to the casting machine is C: 0.07%~0.08%, Si: 0.20%~0.30%, Mn: 1.35%~1.45%, P≤0.010%, S≤0.005%, Alt: 0.020%~0.035%, Nb: 0.030%~0.035%, Ti: 0.015%~0.025%, V: 0.025%~0.035%, Cr: 0.10%~0.15%, with the remainder being iron and unavoidable impurities; the target superheat of the continuous casting process is 20~30℃, with full-process protective pouring, using electromagnetic stirring and light pressure, and the casting speed is controlled at 0.8~1.1m / min to ensure the quality of the billet. The billet is slowly cooled in the heat preservation pit for ≥48 hours.

5. The production method according to claim 3, wherein in the slab heating process, the slab’s time in the furnace, the soaking time, and the exit temperature are strictly controlled, with the time in the furnace ≥ 220 min, the soaking time 30 to 60 min, and the exit temperature 1220 ± 20 °C.

6. The production method according to claim 3, wherein the slab rolling process includes rough rolling and finish rolling.

7. The production method according to claim 6, wherein in the rough rolling, the billet is quickly sent to a descaling machine to remove iron oxide scale after exiting the furnace, the rough rolling is completed in as few passes as possible to achieve the widening, the rough rolling start temperature is ≥1150℃, and the rough rolling finish thickness is twice that of the finished product; after rough rolling, the slab is allowed to heat up, avoiding rolling in part of the recrystallization zone to avoid mixed crystals, the finish rolling start temperature is ≤930℃, and the finish rolling finish temperature is 790℃±10℃.

8. The production method according to claim 3, wherein in the laminar flow cooling process, the cooling mode of the rolled steel plate adopts laminar flow cooling based on the self-learning calculation results of the secondary system, and the final cooling temperature is 600℃±10℃.

9. The production method according to claim 3, wherein in the heat treatment process of the steel plate, the quenching temperature is controlled at 880°C and the holding time is 20 minutes; the tempering temperature is controlled at 510°C and the holding time is 40 minutes.

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