Production method of hot-rolled structural steel with excellent ultralow-temperature impact toughness and thickness of 40-50 mm

Abstract

The invention discloses a production method of hot-rolled structural steel with excellent ultralow-temperature impact toughness and the thickness of 40-50 mm. The production method comprises the following steps: (1) smelting and continuous casting: molten steel for a casting machine comprises the following components in percentage by mass: 0.07-0.09% of C, 0.30-0.50% of Si, 1.0-1.3% of Mn, less than or equal to 0.020% of P, less than or equal to 0.010% of S, 0.010-0.020% of Als, 0.35-0.45% of Cr, 0.06-0.10% of Ni, 0.030-0.050% of Ti, 0.030-0.040% of Nb, 0.01-0.02% of V, 0.001-0.003% of B and 20-50 ppm of Ce; (2) a hot rolling production process; and (3) a heat treatment process. On the premise of meeting high strength, the low-temperature impact performance at-60 DEG C also needs to be ensured.

Description

TECHNICAL FIELD

[0001] The present application belongs to the technical field of metallurgical plate production, and particularly relates to a production method of 40-50mm thick hot-rolled structural steel with excellent super-low-temperature impact toughness. BACKGROUND

[0002] High-strength structural steel is widely used in the manufacture of engineering machinery, coal mine machinery, and pressure steel pipes of hydropower stations, and the like, and the steel plate is in large quantity and has high profitability, and belongs to typical "high-technology content and high-added value" products. In order to improve the strength and reduce the production cost, a medium-carbon component design is generally adopted, so that the welding performance is reduced or the steel plate is not easy to weld. With the continuous improvement of the conditions and requirements of the steel plate, the production enterprises need to not only produce high-strength steel plates to meet the requirements of normal temperature use, but also produce steel plates with good low-temperature performance. The low-temperature mechanical performance of the steel is greatly related to its crystal structure, and the strength, hardness and elastic modulus of almost all steel grades are improved with the decrease of temperature. However, the plasticity and toughness of most steels are reduced to different degrees with the decrease of temperature. In order to meet the requirements of sufficient strength, good process performance, processing performance and corrosion resistance of the steel at low temperature, it is imperative to produce high-strength and high-toughness steel plates. SUMMARY

[0003] In order to solve the above technical problems, the purpose of the present application is to provide a production method of 40-50mm thick hot-rolled structural steel with excellent super-low-temperature impact toughness. The 40-50mm thick 550MPa grade structural steel of the present application meets the requirements of high strength and guarantees the low-temperature impact performance at-60℃, and the product has good market prospects.

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

[0005] The production method of 40-50mm thick hot-rolled structural steel with excellent super-low-temperature impact toughness of the present application mainly includes the following process and parameters:

[0006] (1) Smelting-continuous casting process flow: hot metal pretreatment-top and bottom combined blowing of converter-smelting in LF furnace-outer refining in RH vacuum degassing-continuous casting of slab-pile slow cooling;

[0007] The composition of the molten steel for the casting machine is C: 0.07-0.09%, Si: 0.30-0.50%, Mn: 1.0-1.3%, P: ≤0.020%, S: ≤0.010%, Als: 0.010-0.020%, Cr: 0.35-0.45%, Ni: 0.06-0.10%, Ti: 0.030-0.050%, Nb: 0.030-0.040%, V: 0.01-0.02%, B: 0.001-0.003%, Ce: 20-50ppm, and the rest is Fe and inevitable impurities;

[0008] (2) Hot rolling production process: slab heating - descaling - rough rolling - finishing rolling - cooling - straightening - quality inspection;

[0009] The casting blank is discharged at a temperature of 1250-1260℃, the rough rolling is performed by using a 3+3 mode 2-rack rolling mill, the finishing rolling is performed by using a 7-rack continuous variable crown rolling mill, the finishing rolling is performed at a finish rolling temperature of 850±10℃, and the hot-rolled steel plate has a thickness of 50mm; the cooling is performed by using a laminar flow cooling device, a front dispersion cooling mode is used, and the final cooling temperature is 550±15℃;

[0010] (3) Heat treatment process: steel plate surface quality inspection - surface shot blasting - quenching - tempering - cold straightening - sampling - inspection;

[0011] The shot blasting is performed before quenching, the steel plate is quenched at a temperature of 900±10℃, the holding time is 30min, and the steel plate is water-cooled after quenching; the steel plate is tempered at a temperature of 580±10℃, and the holding time is 30min.

[0012] Further, the composition of the structural steel is C: 0.07%, Si: 0.37%, Mn: 1.23%, P: 0.010%, S: 0.002%, Als: 0.012%, Cr: 0.40%, Ni: 0.07%, Ti: 0.037%, V: 0.01%, Nb: 0.012%, B: 0.001%, Ce: 43ppm, and the rest is Fe and inevitable inclusions.

[0013] Further, the composition of the structural steel is C: 0.07%, Si: 0.40%, Mn: 1.18%, P: 0.012%, S: 0.001%, Als: 0.013%, Cr: 0.40%, Ni: 0.07%, Ti: 0.043%, V: 0.01%, Nb: 0.013%, B: 0.001%, Ce: 35ppm, and the rest is Fe and inevitable inclusions.

[0014] Further, the structural steel has the following components in percentage of mass: C: 0.07%, Si: 0.41%, Mn: 1.18%, P: 0.009%, S: 0.002%, Als: 0.012%, Cr: 0.42%, Ni: 0.07%, Ti: 0.040%, V: 0.02%, Nb: 0.012%, B: 0.002%, Ce: 28ppm, and the rest is Fe and inevitable inclusions.

[0015] Further, the molten iron is pretreated by desulfurization, and is smelted by top and bottom combined blowing converter to make the molten iron decarburization and dephosphorization to obtain the molten steel, argon is blown in the whole process of converter smelting, scrap steel is added into the converter, and the tapping temperature of the converter is 1620℃. Then, the molten steel after the converter smelting is refined by LF external refining, the in-place temperature is greater than or equal to 1560℃, the temperature and component are adjusted by the LF external refining; the slab continuous casting superheat is 22℃, then the slab cleaning, slow cooling and continuous casting slab quality inspection are carried out; the slab heating temperature is 1255℃, the heating time is 210min, the high-pressure water is used to remove phosphorus after the slab is heated; the width is fixed by the fixed-width press, 2-stand rough rolling and 7-stand CVC finishing rolling are adopted; the finishing rolling temperature is 860℃, the finished product thickness is 50mm; the laminar cooling is carried out by front dispersion cooling, the steel plate final cooling temperature is 563℃; the steel plate heat treatment quenching temperature is 900℃, the holding time is 30min, the tempering temperature is 585℃, and the holding time is 30min; finally, the performance detection is carried out.

[0016] Further, the molten iron is pretreated by desulfurization, and is smelted by top and bottom combined blowing converter to make the molten iron decarburization and dephosphorization to obtain the molten steel, argon is blown in the whole process of converter smelting, scrap steel is added into the converter, and the tapping temperature of the converter is 1620℃. Then, the molten steel after the converter smelting is refined by LF external refining, the in-place temperature is greater than or equal to 1560℃, the temperature and component are adjusted by the LF external refining; the slab continuous casting superheat is 22℃, then the slab cleaning, slow cooling and continuous casting slab quality inspection are carried out; the slab heating temperature is 1255℃, the heating time is 210min, the high-pressure water is used to remove phosphorus after the slab is heated; the width is fixed by the fixed-width press, 2-stand rough rolling and 7-stand CVC finishing rolling are adopted; the finishing rolling temperature is 860℃, the finished product thickness is 50mm; the laminar cooling is carried out by front dispersion cooling, the steel plate final cooling temperature is 563℃; the steel plate heat treatment quenching temperature is 900℃, the holding time is 30min, the tempering temperature is 585℃, and the holding time is 30min; finally, the performance detection is carried out.

[0017] Furthermore, the molten iron undergoes desulfurization pretreatment, and top-and-bottom blowing converter is used for smelting to decarburize and dephosphorize the molten iron to obtain molten steel. Argon is blown throughout the converter smelting process, scrap steel is added to the converter, and the converter tapping temperature is 1625℃. The molten steel from the converter is then subjected to LF ladle refining at a refining temperature ≥1560℃. Temperature measurement and composition fine-tuning are performed during LF ladle refining. The slab superheating is 20℃, followed by slab cleaning, slow cooling, and continuous casting slab quality inspection. The slab heating temperature is 1260℃ for 210 minutes, and the heated slab is then subjected to high-pressure water descaling. The width is fixed using a fixed-width press, followed by rough rolling on a 2-stand mill and finish rolling on a 7-stand CVC mill. The final finishing temperature is 858℃, and the finished thickness is 50mm. Laminar flow cooling uses pre-dispersion cooling, and the final cooling temperature of the steel plate is 540℃. The steel plate undergoes heat treatment with a quenching temperature of 900℃ for 30 minutes and a tempering temperature of 580℃ for 30 minutes. Finally, performance testing is performed.

[0018] Compared with the prior art, the beneficial technical effects of the present invention are as follows:

[0019] The 40-50mm thick high-strength hot-rolled structural steel produced by the method provided in this invention is mainly used in the structures of engineering machinery and heavy-duty vehicles. Its surface quality and performance indicators all meet the requirements of relevant technical standards. Its mechanical and technological properties meet the requirements of GB / T16270 standard. Furthermore, the preparation method of this invention is simple and suitable for industrial production. Attached Figure Description

[0020] The present invention will be further described below with reference to the accompanying drawings.

[0021] Figure 1 This is a microstructure diagram of Embodiment 1 of the present invention. Detailed Implementation

[0022] 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.

[0023] Example 1

[0024] Molten iron undergoes desulfurization pretreatment, followed by decarburization and dephosphorization in a top-and-bottom blown converter to obtain steel. Argon blowing is performed throughout the converter smelting process, with scrap steel added. The converter tapping temperature is 1620℃. The molten steel is then subjected to LF ladle refining at a refining temperature ≥1560℃. Temperature measurement and composition fine-tuning are performed during LF ladle refining. The chemical composition supplied to the casting machine after LF ladle refining is shown in Table 1. The slab superheating is 20℃, followed by slab cleaning, slow cooling, and continuous casting slab quality inspection. The slab heating temperature is 1255℃ for 210 minutes, and the heated slab is then subjected to high-pressure water dephosphorization. Width is determined using a width-fixing press, followed by a 2-stand roughing mill and a 7-stand CVC finishing mill. The finishing rolling temperature is 860℃, and the finished product thickness is 50mm. Laminar flow cooling uses pre-dispersion cooling, with a final cooling temperature of 563℃. The steel plate was heat-treated by quenching at 900℃ for 30 minutes, followed by tempering at 585℃ for 30 minutes. Finally, performance testing was performed.

[0025] Example 2

[0026] Molten iron undergoes desulfurization pretreatment, followed by decarburization and dephosphorization in a top-and-bottom blown converter to obtain steel. Argon blowing is performed throughout the converter smelting process, with scrap steel added. The converter tapping temperature is 1620℃. The molten steel is then subjected to LF ladle refining at a refining temperature ≥1560℃. Temperature measurement and composition fine-tuning are performed during LF ladle refining. The chemical composition supplied to the casting machine after LF ladle refining is shown in Table 1. The slab superheating is 20℃, followed by slab cleaning, slow cooling, and continuous casting slab quality inspection. The slab heating temperature is 1250℃ for 210 minutes, and the heated slab is then subjected to high-pressure water dephosphorization. Width is determined using a width-fixing press, followed by a 2-stand roughing mill and a 7-stand CVC finishing mill. The finishing rolling temperature is 848℃, and the finished product thickness is 50mm. Laminar flow cooling uses pre-dispersion cooling, with a final cooling temperature of 550℃. The steel plate was heat-treated by quenching at 895℃ for 20 minutes, followed by tempering at 590℃ for 30 minutes. Finally, performance testing was performed.

[0027] Example 3

[0028] Molten iron undergoes desulfurization pretreatment, followed by decarburization and dephosphorization in a top-and-bottom blown converter to obtain steel. Argon blowing is performed throughout the converter smelting process, with scrap steel added. The converter tapping temperature is 1620℃. The molten steel is then subjected to LF ladle refining at a refining temperature ≥1560℃. Temperature measurement and composition fine-tuning are performed during LF ladle refining. The chemical composition supplied to the casting machine after LF ladle refining is shown in Table 1. The slab superheating is 20℃, followed by slab cleaning, slow cooling, and continuous casting slab quality inspection. The slab heating temperature is 1260℃ for 210 minutes, and the heated slab is then subjected to high-pressure water dephosphorization. Width is determined using a width-fixing press, followed by a 2-stand roughing mill and a 7-stand CVC finishing mill. The finishing rolling temperature is 858℃, and the finished product thickness is 50mm. Laminar flow cooling uses pre-dispersion cooling, with a final cooling temperature of 540℃. The steel plate was heat-treated by quenching at 900℃ for 30 minutes, followed by tempering at 580℃ for 30 minutes. Finally, performance testing was performed.

[0029] Comparative Example 1

[0030] Molten iron undergoes desulfurization pretreatment, followed by decarburization and dephosphorization in a top-and-bottom blown converter to obtain steel. Argon blowing is performed throughout the converter smelting process, with scrap steel added. The converter tapping temperature is 1620℃. The molten steel is then subjected to LF ladle refining at a refining temperature ≥1560℃. Temperature measurement and composition fine-tuning are performed during LF ladle refining. The chemical composition supplied to the casting machine after LF ladle refining is shown in Table 1. The slab superheating is 20℃, followed by slab cleaning, slow cooling, and continuous casting slab quality inspection. The slab heating temperature is 1220℃ for 250 minutes, and the heated slab is then subjected to high-pressure water dephosphorization. Width is determined using a width-fixing press, followed by a 2-stand roughing mill and a 7-stand CVC finishing mill. The finishing rolling temperature is 806℃, and the finished product thickness is 80mm. Laminar flow cooling uses pre-dispersion cooling, with a final cooling temperature of 580℃. The steel plate was heat-treated by quenching at 907℃ for 21 minutes and then tempering at 603℃ for 30 minutes. Finally, performance testing was performed.

[0031] Comparative Example 2

[0032] Molten iron undergoes desulfurization pretreatment, followed by decarburization and dephosphorization in a top-and-bottom blown converter to obtain steel. Argon blowing is performed throughout the converter smelting process, with scrap steel added. The converter tapping temperature is 1620℃. The molten steel is then subjected to LF ladle refining at a refining temperature ≥1560℃. Temperature measurement and composition fine-tuning are performed during LF ladle refining. The chemical composition supplied to the casting machine after LF ladle refining is shown in Table 1. The slab superheating is 20℃, followed by slab cleaning, slow cooling, and continuous casting slab quality inspection. The slab heating temperature is 1230℃ for 210 minutes, and the heated slab is then subjected to high-pressure water dephosphorization. Width is determined using a width-fixing press, followed by a 2-stand roughing mill and a 7-stand CVC finishing mill. The finishing rolling temperature is 806℃, and the finished thickness is 50mm. Laminar flow cooling uses pre-dispersion cooling, with a final cooling temperature of 580℃. The steel plate was heat-treated by quenching at 900℃ for 20 minutes, followed by tempering at 600℃ for 20 minutes. Finally, performance testing was performed.

[0033] Table 1. Chemical composition (wt%) of Examples 1-3 of the present invention

[0034]

[0035]

[0036] The mechanical properties of the steel coils in Examples 1 to 3 of the present invention were tested, and the test results are shown in Table 2.

[0037] Table 2 Mechanical properties of steel coils from Examples 1-3 of the present invention

[0038]

[0039] As shown in Table 2, the mechanical and technological properties of a 40-50mm thick hot-rolled structural steel with excellent low-temperature impact toughness produced according to the method provided in this invention meet the requirements of GB / T16270.

[0040] The embodiments described above are merely preferred embodiments of the present invention and are not intended to limit the scope of the present invention. Various modifications and improvements made by those skilled in the art to the technical solutions of the present invention without departing from the spirit of the present invention should fall within the protection scope defined by the claims of the present invention.

Claims

1. A method for producing 40-50mm thick hot-rolled structural steel with excellent ultra-low temperature impact toughness, characterized in that: The main processes and parameters are as follows: (1) Smelting-continuous casting production process: hot metal pretreatment—converter top and bottom blowing smelting—LF ladle refining—RH vacuum degassing—slab continuous casting—stacking slow cooling; The composition of the molten steel supplied to the casting machine by mass percentage is as follows: C: 0.07-0.09%, Si: 0.30-0.50%, Mn: 1.0-1.3%, P: ≤0.020%, S: ≤0.010%, Als: 0.010-0.020%, Cr: 0.35-0.45%, Ni: 0.06-0.10%, Ti: 0.030-0.050%, Nb: 0.030-0.040%, V: 0.01-0.02%, B: 0.001-0.003%, Ce: 20-50ppm, with the remainder being Fe and unavoidable impurities. (2) Hot rolling production process: slab heating—descaling—rough rolling—finish rolling—cooling—straightening—quality inspection; The billet exit temperature is 1250-1260℃. The roughing rolling adopts a 3+3 mode 2-stand rolling mill, and the finishing rolling adopts a 7-stand continuous variable crown rolling mill. The final rolling temperature of the finishing rolling is 850±10℃, and the thickness of the hot-rolled steel plate is 50mm. The cooling adopts laminar flow cooling equipment, with a front-dispersed cooling mode, and the final cooling temperature is 550±15℃. (3) Heat treatment process: steel plate surface quality inspection—surface shot blasting—quenching—tempering—cold straightening—sampling—inspection; Shot blasting was performed before quenching. The quenching temperature of the steel plate was 900±10℃, and the holding time was 30min. After quenching, the steel plate was water-cooled. The tempering temperature of the steel plate was 580±10℃, and the holding time was 30min.

2. The method for producing 40-50mm thick hot-rolled structural steel with excellent ultra-low temperature impact toughness according to claim 1, characterized in that: The structural steel composition by mass percentage is C: 0.07%, Si: 0.37%, Mn: 1.23%, P: 0.010%, S: 0.002%, Als: 0.012%, Cr: 0.40%, Ni: 0.07%, Ti: 0.037%, V: 0.01%, Nb: 0.012%, B: 0.001%, Ce: 43ppm, with the remainder being Fe and unavoidable inclusions.

3. The method for producing 40-50mm thick hot-rolled structural steel with excellent ultra-low temperature impact toughness according to claim 1, characterized in that: The structural steel composition by mass percentage is C: 0.07%, Si: 0.40%, Mn: 1.18%, P: 0.012%, S: 0.001%, Als: 0.013%, Cr: 0.40%, Ni: 0.07%, Ti: 0.043%, V: 0.01%, Nb: 0.013%, B: 0.001%, Ce: 35ppm, with the remainder being Fe and unavoidable inclusions.

4. The method for producing 40-50mm thick hot-rolled structural steel with excellent ultra-low temperature impact toughness according to claim 1, characterized in that: The structural steel composition by mass percentage is C: 0.07%, Si: 0.41%, Mn: 1.18%, P: 0.009%, S: 0.002%, Als: 0.012%, Cr: 0.42%, Ni: 0.07%, Ti: 0.040%, V: 0.02%, Nb: 0.012%, B: 0.002%, Ce: 28ppm, with the remainder being Fe and unavoidable inclusions.

5. The method for producing 40-50mm thick hot-rolled structural steel with excellent ultra-low temperature impact toughness according to claim 2, characterized in that: The molten iron is pre-treated for desulfurization, and then smelted in a top-and-bottom blown converter to remove carbon and phosphorus to obtain molten steel. Argon is blown throughout the converter smelting process, and scrap steel is added to the converter. The converter tapping temperature is 1620℃. The molten steel from the converter is then subjected to LF ladle refining at a refining temperature ≥1560℃. Temperature measurement and composition fine-tuning are performed during LF ladle refining. The superheat of the slab continuous casting is 22℃, followed by slab cleaning, slow cooling, and continuous casting slab quality inspection. The slab heating temperature is 1255℃ for 210 minutes, and the heated slab is then subjected to high-pressure water descaling. The width is fixed using a fixed-width press, followed by rough rolling on a 2-stand mill and finish rolling on a 7-stand CVC mill. The final rolling temperature is 860℃, and the finished thickness is 50mm. Laminar flow cooling uses pre-dispersion cooling, and the final cooling temperature of the steel plate is 563℃. The steel plate undergoes heat treatment with a quenching temperature of 900℃ for 30 minutes and a tempering temperature of 585℃ for 30 minutes. Finally, performance testing is performed.

6. The method for producing 40-50mm thick hot-rolled structural steel with excellent ultra-low temperature impact toughness according to claim 3, characterized in that: The molten iron is pre-treated for desulfurization, and then smelted in a top-and-bottom blown converter to remove carbon and phosphorus to obtain molten steel. Argon is blown throughout the converter smelting process, and scrap steel is added to the converter. The converter tapping temperature is 1620℃. The molten steel from the converter is then subjected to LF ladle refining at a refining temperature ≥1560℃. Temperature measurement and composition fine-tuning are performed during LF ladle refining. The slab is continuously cast with a superheat of 20℃, followed by slab cleaning, slow cooling, and continuous casting slab quality inspection. The slab is heated to 1250℃ for 210 minutes, and then subjected to high-pressure water descaling. The width is fixed using a fixed-width press, followed by rough rolling on a 2-stand mill and finish rolling on a 7-stand CVC mill. The final rolling temperature is 848℃, and the finished thickness is 50mm. Laminar flow cooling uses pre-dispersion cooling, with a final cooling temperature of 550℃. The steel plate undergoes heat treatment with a quenching temperature of 895℃ for 20 minutes and a tempering temperature of 590℃ for 30 minutes. Finally, performance testing is performed.

7. The method for producing 40-50mm thick hot-rolled structural steel with excellent ultra-low temperature impact toughness according to claim 4, characterized in that: The molten iron is pre-treated for desulfurization, and then smelted in a top-and-bottom combined blowing converter to remove carbon and phosphorus and obtain molten steel. Argon is blown throughout the converter smelting process, scrap steel is added to the converter, and the converter tapping temperature is 1625℃. The molten steel from the converter is then subjected to LF ladle refining at a refining temperature ≥1560℃. Temperature measurement and composition fine-tuning are performed during LF ladle refining. The slab superheating is 20℃, followed by slab cleaning, slow cooling, and continuous casting slab quality inspection. The slab heating temperature is 1260℃ for 210 minutes, and the heated slab is then subjected to high-pressure water descaling. The width is fixed using a fixed-width press, followed by rough rolling on a 2-stand mill and finish rolling on a 7-stand CVC mill. The final finishing temperature is 858℃, and the finished thickness is 50mm. Laminar flow cooling uses pre-dispersion cooling, and the final cooling temperature of the steel plate is 540℃. The steel plate undergoes heat treatment with a quenching temperature of 900℃ for 30 minutes and a tempering temperature of 580℃ for 30 minutes. Finally, performance testing is performed.

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