Production method of Q500qE high-strength steel plate with thickness of 50-80 mm and excellent low-temperature impact toughness

Abstract

The invention discloses a production method of a Q500qE high-strength steel plate with the thickness of 50-80 mm and excellent low-temperature impact toughness. The production method comprises a smelting-continuous casting production process flow; feeding the plate blank into a furnace, heating and rolling the plate blank; carrying out laminar cooling; straightening the steel plate; steel plate heat treatment; the steel plate comprises the following chemical components in percentage by mass: 0.09%-0.11% of C, 0.20%-0.30% of Si, 1.50%-1.60% 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, 0.040%-0.050% of Nb, 0.010%-0.020% of Ti, 0.030%-0.040% of V, 0.20%-0.30% of Cr and the balance of Fe and impurities. The low-temperature impact energy of the Q500qE steel plate produced by the method disclosed by the invention at the temperature of 40 DEG C below zero is stably controlled to be more than 200J.

Description

Technical Field

[0001] The invention belongs to the technical field of metallurgical plate production, and in particular relates to a method for producing a Q500qE high-strength steel plate with a thickness of 50mm-80mm and excellent low-temperature impact toughness. Background Art

[0002] High-strength bridge structural steel Q500qE is widely used in bridge and other steel structure construction applications due to its high strength and excellent formability. With the advancement of national infrastructure construction and scientific and technological progress, the application of bridge structural steel is expanding to geologically harsh environments such as deserts and Gobi regions, as well as high-altitude cold regions. To ensure both strength and stiffness, the demand for thicker steel plates (50mm to 80mm thick) has increased dramatically, placing higher demands on low-temperature impact toughness. The requirements for Q500qE steel with a thickness of 50mm to 80mm, as specified in GB / T 714-2015, "Structural Steel for Bridges," include yield strength ≥480MPa, tensile strength ≥630MPa, elongation ≥18%, impact energy ≥120J at -40°C, and acceptable bending properties. Steel plates with a thickness greater than 50 mm have very high requirements on the cooling capacity of the rolling mill during the production process, and can hardly be produced by rolling mills without ultra-fast cooling equipment. In view of this situation, the present invention uses tempering heat treatment (quenching + high-temperature tempering) to develop a Q500qE high-strength steel plate with a thickness of 50 mm to 80 mm and excellent low-temperature impact toughness. Summary of the Invention

[0003] The present invention aims to provide a method for producing Q500qE high-strength steel plate with a thickness of 50 mm to 80 mm and excellent low-temperature impact toughness. The method is simple to operate and suitable for industrial production. The Q500qE steel plate produced using the method exhibits high strength, good impact toughness, excellent formability, and weldability. Its low-temperature impact energy at -40°C is consistently controlled at above 200 J, and its mechanical and process properties meet standards and user technical requirements.

[0004] In order to solve the above technical problems, the present invention adopts the following technical solutions:

[0005] The present invention provides a method for producing a Q500qE high-strength steel plate with a thickness of 50mm-80mm and excellent low-temperature impact toughness. The main process parameters include:

[0006] Step 1: Smelting - continuous casting production process, KR desulfurization - converter - LF refining - RH vacuum treatment - slab continuous casting - slow cooling; Among them:

[0007] (1) The sulfur content of molten iron after pretreatment is ≤0.005%. Slag must be removed after desulfurization to ensure that the molten iron contains less slag;

[0008] (2) Use self-produced low-sulfur scrap steel, with the converter end-point hitting the target in one attempt or the number of reblows not exceeding one, and the tapping temperature ≥ 1610 °C;

[0009] (3) During LF refining, slag-making and desulfurization, composition adjustment and heating-up operations are carried out according to the composition and temperature of the converter molten steel, so that the composition and temperature of the molten steel meet the requirements of RH and continuous casting;

[0010] (4) The RH vacuum treatment time ≥ 15 min. After the RH vacuum treatment ends, adjust the argon flow rate to keep the molten steel in a soft blowing state, feed in the calcium wire for calcium treatment, and after wire feeding, the [Ca] content in the molten steel is 0.0008 - 0.0025%, and ensure that the soft blowing time ≥ 10 min after wire feeding;

[0011] (5) For the continuous casting process, the target superheat is 20 - 30 °C, with full protection casting throughout the process. Electromagnetic stirring and soft reduction are adopted, and the casting speed is controlled at 0.7 - 1.0 m / min to ensure the quality of the cast slab. The cast slab is cooled slowly in a heat preservation pit, and the slow cooling time ≥ 48 hours;

[0012] The second step: Slab charging and heating; strictly control the in-furnace time, soaking time and tapping temperature of the slab. The in-furnace time ≥ 220 min, the soaking time is 40 - 60 min, and the tapping temperature is 1230 ± 20 °C;

[0013] The third step: Slab rolling, specifically including rough rolling and finish rolling; among them:

[0014] (1) Rough rolling: After the billet is discharged from the furnace, it is quickly sent to the descaling machine to remove the scale. The rough rolling is completed with as few passes as possible for width spreading. The rough rolling starting temperature ≥ 1170 °C, and the rough rolling final thickness is 1.8 - 2.5 times the finished product;

[0015] (2) Finish rolling: After rough rolling, the slab is kept at a certain temperature, rolled avoiding part of the recrystallization zone to avoid mixed grains. The finish rolling starting temperature ≤ 900 °C, and the finish rolling final temperature is 790 °C - 830 °C;

[0016] The fourth step: Lamellar cooling. The cooling mode of the rolled steel plate adopts the lamellar cooling with the calculation results of the secondary system self-learning; the final cooling temperature is 620 °C ± 25 °C;

[0017] The fifth step: Plate straightening, which is carried out according to the thickness specification of the steel plate and the actual plate shape of the cold-rolled steel plate;

[0018] The sixth step: Plate heat treatment: The quenching temperature is 910 ± 10 °C, and the holding time is 20 ± 5 minutes; the high-temperature tempering temperature is 500 °C - 550 °C, and the holding time is 40 minutes;

[0019] The mass percentage content of the chemical composition of the steel plate is as follows: C: 0.09% - 0.11%, Si: 0.20% - 0.30%, Mn: 1.50% - 1.60%, P: ≤0.010%, S ≤0.005%, Alt: 0.020% - 0.035%, Nb: 0.040% - 0.050%, Ti: 0.010% - 0.020%, V: 0.030% - 0.040%, Cr: 0.20% - 0.30%, and the rest is Fe and inevitable impurities.

[0020] Furthermore, the heat treatment of the steel plate: quenching temperature is 910°C, and the holding time is 20 minutes.

[0021] Furthermore, the mass percentage content of the chemical composition of the steel plate is as follows: C: 0.11%, Si: 0.26%, Mn: 1.57%, P: 0.009%, S: 0.001%, Alt: 0.032%, Nb: 0.045%, Ti: 0.015%, V: 0.031%, Cr: 0.28%, and the rest is Fe and inevitable impurities.

[0022] Furthermore, the mass percentage content of the chemical composition of the steel plate is as follows: C: 0.09%, Si: 0.25%, Mn: 1.55%, P: 0.009%, S: 0.004%, Alt: 0.028%, Nb: 0.047%, Ti: 0.017%, V: 0.032%, Cr: 0.25%, and the rest is Fe and inevitable impurities.

[0023] Furthermore, the mass percentage content of the chemical composition of the steel plate is as follows: C: 0.10%, Si: 0.25%, Mn: 1.59%, P: 0.008%, S: 0.003%, Alt: 0.030%, Nb: 0.045%, Ti: 0.016%, V: 0.033%, Cr: 0.30%, and the rest is Fe and inevitable impurities.

[0024] Furthermore, the mass percentage content of the chemical composition of the steel plate is as follows: C: 0.09%, Si: 0.26%, Mn: 1.55%, P: 0.008%, S: 0.005%, Alt: 0.035%, Nb: 0.046%, Ti: 0.015%, V: 0.035%, Cr: 0.20%, and the rest is Fe and inevitable impurities.

[0025] Furthermore, the Q500qE steel plate produced by the present invention has high strength, good impact toughness, excellent forming performance and welding performance, and the low-temperature impact energy at -40°C can be stably controlled above 200J.

[0026] Compared with the prior art, the beneficial technical effects of the present invention are:

[0027] The Q500qE steel plate produced by the present invention has high strength, good impact toughness, excellent forming performance and welding performance. The low-temperature impact energy at -40°C is stably controlled above 200J, and the mechanical properties and process properties meet the standards and the technical requirements of users. At the same time, the operation method of the present invention is simple and suitable for industrial production. Brief Description of the Drawings

[0028] The present invention will be further described below in conjunction with the drawings.

[0029] Figure 1 It is the microstructural diagram of the steel plate in Example 2 of the present invention. Detailed Embodiments

[0030] The present invention will be described in more detail through specific embodiments below. The embodiments are only descriptions of the best implementation modes of the present invention and do not limit the scope of the present invention in any way.

[0031] Example 1

[0032] The hot metal is subjected to desulfurization pretreatment, and the top-bottom combined blowing converter is used to smelt the hot metal to decarburize and dephosphorize to obtain molten steel. Argon is blown throughout the converter smelting process, and scrap steel is added to the converter. The tapping temperature of the converter is 1630°C. Then, the molten steel after converter smelting is subjected to LF secondary refining, and the refining in-position temperature is ≥1562°C. After LF secondary refining, the molten steel is subjected to RH vacuum treatment, and the vacuum time is maintained for 16 minutes. Slab continuous casting is carried out according to the smelting chemical composition shown in Table 1, with a superheat of 25°C. Then, slab cleaning, slow cooling, and continuous casting billet quality inspection are carried out. The slab heating temperature is 1233°C, the heating time is 245 minutes, and the soaking time is 55 minutes. The heated slab is subjected to high-pressure water descaling. After descaling, rolling is carried out. Both rough rolling and finish rolling use two-high reversing mills. The rough rolling starting temperature is 1179°C, and it is rolled to the intermediate slab thickness for temperature holding. The average finish rolling starting temperature is 888°C, and the average finish rolling temperature is 780°C. The final cooling temperature of the steel plate after laminar cooling is 625°C, and the finished product thickness is 53.0 mm. Then, straightening is carried out. The straightened steel plate is subjected to shot peening and then heat treatment: the quenching temperature is 910°C, and the holding time is 20 minutes; the tempering temperature is 550°C, and the holding time is 40 minutes. Finally, product quality inspection is carried out by sampling according to the standards.

[0033] Example 2

[0034] The hot metal is subjected to desulfurization pretreatment. The top-bottom combined blowing converter is used for smelting to decarburize and dephosphorize the hot metal to obtain molten steel. Argon is blown throughout the converter smelting process. Scrap steel is added to the converter, and the tapping temperature of the converter is 1640 °C. Then, the molten steel after converter smelting is subjected to LF secondary refining, and the refining in-position temperature is ≥1550 °C. After LF secondary refining, the molten steel is subjected to RH vacuum treatment, and the vacuum holding time is 18 min. Slab continuous casting is carried out according to the smelting chemical composition shown in Table 1, with a superheat of 27 °C. Then, slab cleaning, slow cooling, and quality inspection of the continuous casting billet are carried out. The slab heating temperature is 1230 °C, the heating time is 235 min, and the soaking time is 60 min. The heated slab is subjected to high-pressure water descaling. After descaling, rolling is carried out. Both rough rolling and finish rolling use two-high reversing mills. The rough rolling starting temperature is 1185 °C. When rolling to the thickness of the intermediate billet, it is held for temperature. The average finish rolling starting temperature is 890 °C, and the average finish rolling temperature is 790 °C. The final cooling temperature of the steel plate after laminar cooling is 616 °C, and the finished product thickness is 60.0 mm. Then, straightening is carried out. The straightened steel plate is subjected to shot peening and then heat treatment: the quenching temperature is 910 °C, and the holding time is 20 minutes; the tempering temperature is 540 °C, and the holding time is 40 minutes. Finally, samples are taken according to the standard for product quality inspection.

[0035] Example 3

[0036] The hot metal is subjected to desulfurization pretreatment. The top-bottom combined blowing converter is used for smelting to decarburize and dephosphorize the hot metal to obtain molten steel. Argon is blown throughout the converter smelting process. Scrap steel is added to the converter, and the tapping temperature of the converter is 1642 °C. Then, the molten steel after converter smelting is subjected to LF secondary refining, and the refining in-position temperature is ≥1560 °C. After LF secondary refining, the molten steel is subjected to RH vacuum treatment, and the vacuum holding time is 20 min. Slab continuous casting is carried out according to the smelting chemical composition shown in Table 1, with a superheat of 25 °C. Then, slab cleaning, slow cooling, and quality inspection of the continuous casting billet are carried out. The slab heating temperature is 1225 °C, the heating time is 238 min, and the soaking time is 52 min. The heated slab is subjected to high-pressure water descaling. After descaling, rolling is carried out. Both rough rolling and finish rolling use two-high reversing mills. The rough rolling starting temperature is 1195 °C. When rolling to the thickness of the intermediate billet, it is held for temperature. The average finish rolling starting temperature is 900 °C, and the average finish rolling temperature is 815 °C. The final cooling temperature of the steel plate after laminar cooling is 620 °C, and the finished product thickness is 70.0 mm. Then, straightening is carried out. The straightened steel plate is subjected to shot peening and then heat treatment: the quenching temperature is 910 °C, and the holding time is 20 minutes; the tempering temperature is 510 °C, and the holding time is 40 minutes. Finally, samples are taken according to the standard for product quality inspection.

[0037] Example 4

[0038] The hot metal is subjected to desulfurization pretreatment, and the top-bottom combined blowing converter is used for smelting to decarburize and dephosphorize the hot metal to obtain molten steel. Argon is blown throughout the converter smelting process, and scrap steel is added to the converter. The tapping temperature of the converter is 1640 °C. Then, the molten steel after converter smelting is subjected to LF furnace external refining, and the refining in-position temperature is ≥1565 °C. After LF furnace external refining, the molten steel is subjected to RH vacuum treatment, and the vacuum holding time is 17 min. Slab continuous casting is carried out according to the smelting chemical composition shown in Table 1, with a superheat of 26 °C. After that, slab cleaning, slow cooling, and quality inspection of the continuous casting billet are carried out. The slab heating temperature is 1235 °C, the heating time is 235 min, and the soaking time is 55 min. The heated slab is subjected to high-pressure water descaling. After descaling, rolling is carried out. Both rough rolling and finish rolling use 2-high reversible rolling mills. The rough rolling starting temperature is 1190 °C. When rolling to the intermediate slab thickness, it is held for temperature. The average starting temperature of finish rolling is 900 °C, and the average final rolling temperature of finish rolling is 820 °C. The final cooling temperature of the steel plate after laminar flow cooling is 610 °C, and the finished product thickness is 78.0 mm. Then, straightening is carried out. The straightened steel plate is subjected to shot peening and then heat treatment: the quenching temperature is 910 °C, and the holding time is 20 minutes; the tempering temperature is 500 °C, and the holding time is 40 minutes. Finally, samples are taken according to the standard for product quality inspection.

[0039] The chemical compositions of Examples 1 to 4 of the Q500qE steel plate of the present invention are shown in Table 1. The mechanical property test values of the examples are shown in Table 2. It can be seen that the mechanical properties of the examples of the present invention are stable with small fluctuations, and the low-temperature impact toughness value is stably controlled above 200 J. It should be noted that all similar changes directly derived or associated by those skilled in the art from the content disclosed in the present invention shall fall within the protection scope of the present invention.

[0040] Table 1 Chemical compositions (wt%) of Examples 1 to 4 of the present invention

[0041]

[0042] Table 2 Mechanical properties and process properties of Examples 1 to 4 of the present invention

[0043]

[0044] The above-described embodiments are only descriptions of the preferred embodiments of the present invention, and do not limit the scope of the present invention. Without departing from the design spirit of the present invention, various deformations and improvements made by those of ordinary skill in the art to the technical solutions of the present invention shall fall within the protection scope determined by the claims of the present invention.

Claims

1. A production method of Q500qE high-strength steel plate with excellent low-temperature impact toughness and a thickness of 50 mm - 80 mm, characterized in that, The main process parameters include: The first step: the smelting - continuous casting production process flow, KR desulfurization - converter - LF refining - RH vacuum treatment - slab continuous casting - slow cooling; where: (1) After the hot metal pretreatment, the S content ≤ 0.005%, and slag must be skimmed after desulfurization to ensure that the hot metal carries less slag; (2) Use self-produced low-sulfur scrap steel. The converter end point is hit in one go or the number of supplementary blows does not exceed one time, and the tapping temperature ≥ 1610 °C; (3) LF refining makes slag for desulfurization, adjusts the composition and raises the temperature according to the composition and temperature of the converter molten steel, so that the composition and temperature of the molten steel meet the requirements of RH and continuous casting; (4) The RH vacuum treatment time ≥ 15 min. After the RH vacuum treatment is completed, adjust the argon flow rate to make the molten steel in the soft blowing state, feed the calcium wire for calcium treatment, and the [Ca] of the molten steel is 0.0008 - 0.0025% after wire feeding. Ensure that the soft blowing time ≥ 10 min after wire feeding; (5) The target superheat degree of the continuous casting process is 20 - 30 °C, with full protection casting throughout the process. Electromagnetic stirring and soft reduction are used, and the casting speed is controlled at 0.7 - 1.0 m / min to ensure the quality of the cast slab. The cast slab is slowly cooled in a heat preservation pit, and the slow cooling time ≥ 48 hours; The second step: the slab is heated in the furnace; strictly control the time in the furnace, soaking time and tapping temperature of the slab. The time in the furnace ≥ 220 min, the soaking time is 40 - 60 min, and the tapping temperature is 1230 ± 20 °C; The third step: slab rolling, specifically including rough rolling and finish rolling; where: (1) Rough rolling: After the billet is taken out of the furnace, quickly remove the scale at the descaling machine. The rough rolling is completed with as few passes as possible for width spreading. The rough rolling starting temperature ≥ 1170 °C, and the rough rolling final thickness is 1.8 - 2.5 times the finished product; (2) Finish rolling: After rough rolling, the slab is kept warm, rolled avoiding part of the recrystallization zone to avoid mixed grains. The finish rolling starting temperature ≤ 900 °C, and the finish rolling final temperature is 790 °C - 830 °C; The fourth step: laminar cooling. The cooling mode of the rolled steel plate adopts the laminar cooling of the self-learning calculation results of the secondary system; the final cooling temperature is 620 °C ± 25 °C; The fifth step: straightening the steel plate, and straightening according to the thickness specification of the steel plate and the actual shape of the cold-rolled steel plate; The sixth step: heat treatment of the steel plate: the quenching temperature is 910 ± 10 °C, and the holding time is 20 ± 5 minutes; the high-temperature tempering temperature is 500 °C - 550 °C, and the holding time is 40 minutes; The mass percentage content of the chemical composition of the steel plate is C: 0.09% - 0.11%, Si: 0.20% - 0.30%, Mn: 1.50% - 1.60%, P: ≤ 0.010%, S ≤ 0.005%, Alt: 0.020% - 0.035%, Nb: 0.040% - 0.050%, Ti: 0.010% - 0.020%, V: 0.030% - 0.040%, Cr: 0.20% - 0.30%, and the rest is Fe and unavoidable impurities.

2. The production method of the Q500qE high-strength steel plate with a thickness of 50 mm - 80 mm and excellent low-temperature impact toughness according to claim 1, characterized in that, Heat treatment of the steel plate: the quenching temperature is 910 °C, and the holding time is 20 minutes.

3. The production method of the Q500qE high-strength steel plate with a thickness of 50 mm - 80 mm and excellent low-temperature impact toughness according to claim 1, characterized in that, The mass percentage content of the chemical components of the steel plate is: C: 0.11%, Si: 0.26%, Mn: 1.57%, P: 0.009%, S: 0.001%, Alt: 0.032%, Nb: 0.045%, Ti: 0.015%, V: 0.031%, Cr: 0.28%, and the rest is Fe and inevitable impurities.

4. The production method of the Q500qE high-strength steel plate with a thickness of 50 mm - 80 mm and excellent low-temperature impact toughness according to claim 1, characterized in that The mass percentage content of the chemical components of the steel plate is: C: 0.09%, Si: 0.25%, Mn: 1.55%, P: 0.009%, S: 0.004%, Alt: 0.028%, Nb: 0.047%, Ti: 0.017%, V: 0.032%, Cr: 0.25%, and the rest is Fe and inevitable impurities.

5. The production method of the Q500qE high-strength steel plate with a thickness of 50 mm - 80 mm and excellent low-temperature impact toughness according to claim 1, characterized in that, The mass percentage content of the chemical components of the steel plate is: C: 0.10%, Si: 0.25%, Mn: 1.59%, P: 0.008%, S: 0.003%, Alt: 0.030%, Nb: 0.045%, Ti: 0.016%, V: 0.033%, Cr: 0.30%, and the rest is Fe and inevitable impurities.

6. The production method of the Q500qE high-strength steel plate with a thickness of 50 mm - 80 mm and excellent low-temperature impact toughness according to claim 1, characterized in that, The mass percentage content of the chemical components of the steel plate is: C: 0.09%, Si: 0.26%, Mn: 1.55%, P: 0.008%, S: 0.005%, Alt: 0.035%, Nb: 0.046%, Ti: 0.015%, V: 0.035%, Cr: 0.20%, and the rest is Fe and inevitable impurities.

7. The production method of the Q500qE high-strength steel plate with a thickness of 50 mm - 80 mm and excellent low-temperature impact toughness according to claim 1, characterized in that, The Q500qE steel plate produced by the present invention has high strength, good impact toughness, excellent forming performance and welding performance, and the low-temperature impact energy at -40°C can stably meet the requirement of being above 200 J.

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