High-strength hot-rolled steel

Abstract

The present invention relates to the technical field of steel smelting, in particular to high-strength hot-rolled steel. The preparation method of the steel of the present invention includes smelting molten iron, KR desulfurization, converter steelmaking, CAS refining, LF refining, RH refining, continuous casting, hot delivery and rolling; wherein the rolling step includes rough rolling, dephosphorization and finishing rolling; in the dephosphorization step, a group of high-pressure dephosphorization units are configured, and the speed of the dephosphorization roller is configured to be 0.70-0.80 m / s. The high-strength hot-rolled steel of the present invention can reduce head imprinting and has good quality.

Description

Technical Field

[0001] The present invention relates to the technical field of steel smelting, and in particular to high-strength hot-rolled steel. Background Art

[0002] High-strength steel generally also requires good bending resistance and tensile strength; at the same time, defects such as pits, pitting and embossing on the steel surface not only directly affect the appearance of the steel, but also have adverse effects on the products produced by downstream terminals.

[0003] The high-strength hot-rolled steel of related technology is prone to embossing on the head, and the quality of the steel needs to be improved. Summary of the invention

[0004] The object of the present invention is to provide a high-strength hot-rolled steel material which can reduce head stamping and has good quality.

[0005] The present invention is achieved in that:

[0006] The present invention provides a high-strength hot-rolled steel material. The composition of the high-strength hot-rolled steel material includes, by mass percentage, C: 0.2-1.01%, Mn: 0.35-1.8%, Cr: 0.35-1.1%, Mo: 0.1-1%, P≤0.015, S≤0.10, Si: 0.15-0.30%, Ni: 0.40-0.70%, V: 0.10-0.15%, Als: 0.015-0.040%, N≤0.006%, and the balance is Fe and unavoidable impurities;

[0007] The preparation method of high-strength hot-rolled steel includes: smelting molten iron, KR desulfurization, converter steelmaking, CAS refining, LF refining, RH refining, continuous casting, hot delivery and rolling; wherein,

[0008] The rolling steps include rough rolling, dephosphorization and finishing rolling;

[0009] In the dephosphorization step, a group of high-pressure dephosphorization units are configured, and the speed of the dephosphorization roller is configured to be 0.70-0.80m / s.

[0010] In an optional embodiment, the finishing rolling step includes seven rolling passes, wherein the rolling force of the fifth pass is controlled to be ≤1000 tons, the rolling force of the sixth pass is controlled to be ≤900 tons, and the rolling force of the seventh to fifth passes is controlled to be ≤800 tons.

[0011] In an optional embodiment, the rolling force of the fifth pass is controlled to be 850-950 tons, the rolling force of the sixth pass is controlled to be 750-850 tons, and the rolling force of the seventh pass is controlled to be 600-700 tons.

[0012] In an optional embodiment, the distance between the high-pressure dephosphorization unit and the first-pass rolling unit is 8-10m.

[0013] In an optional embodiment, the composition of the high-strength hot-rolled steel includes, by mass percentage: C: 0.66-0.70%, Mn: 0.80-1.0%, Cr: 0.40-0.60%, Mo: 0.15-0.25%.

[0014] In an optional embodiment, the water pressure of the high-pressure dephosphorization unit is ≥20 MPa.

[0015] In an optional embodiment, the step of converter steelmaking includes: adding lime slag for washing when 1 / 4 of the steel is tapped, and sequentially adding at least one of silicon manganese, ferromanganese and ferrosilicon, and aluminum blocks when 1 / 4 of the steel is tapped;

[0016] Add carbon powder after steel is tapped;

[0017] After the molten steel arrives at the station, the temperature is measured, samples are taken, and argon is blown. The pressure of the argon is 0.3-0.5MPa, the flow rate is 200-800L / min, and the diameter of the exposed bright ring of the molten steel is controlled to be less than 500mm.

[0018] In an optional embodiment, the LF refining step includes: connecting argon gas to the molten steel after it reaches the refining station;

[0019] When entering the station to make slag, add 500-1500kg of lime, 300-600kg of refined slag, and 50-200kg of fluorite;

[0020] Power on the slag, take LF1 sample, add 50-150kg aluminum particles to deoxidize and make white slag, FeO+Mn0 in the slag ≤1.0%, and the LF furnace white slag retention time ≥10min;

[0021] The steps of RH refining include:

[0022] Wash the vacuum tank with low-phosphorus steel with a phosphorus content of ≤ 0.025%;

[0023] Measure the temperature upon entering the station, control the vacuum degree of the RH furnace to ≤133Pa and maintain it for 10min or more, and control the pure degassing time to ≥15min.

[0024] In an optional embodiment, the arrival temperature of the pouring furnace in the CAS refining step is 1564-1588°C, the arrival temperature of the pouring furnace in the RH refining step is 1534-1578°C, the exit temperature of the pouring furnace in the RH refining step is 1530-1535°C, the temperature of the ladle of the pouring furnace to the continuous casting platform is 1525-1530°C, and the temperature of the tundish of the pouring furnace is 1485-1510°C;

[0025] The arrival temperature of the continuous casting furnace in the CAS refining step is 1554-1574℃, the arrival temperature of the continuous casting furnace in the RH refining step is 1529-1569℃, the exit temperature of the continuous casting furnace in the RH refining step is 1515-1525℃, the temperature of the ladle of the continuous casting furnace to the continuous casting platform is 1513-1520℃, and the temperature of the middle ladle of the continuous casting furnace is 1485-1505℃.

[0026] In an optional embodiment, the step of continuous casting comprises:

[0027] Control the liquid level in the casting ladle ≥800mm;

[0028] Control Als≤0.0050%, control molten steel N≤8ppm;

[0029] Control the superheat of the tundish to ≤25℃;

[0030] Control the nozzle insertion depth to 120±5mm, and the vibration parameter to satisfy f=170-20V, where V is the vibration frequency;

[0031] The cooling water volume of the mold on the narrow side of the ingot is controlled to be 500±10L / min, and the cooling water volume of the mold on the wide side of the ingot is controlled to be 3800±100L / min;

[0032] When the package temperature ≤T L At +30℃, the pulling speed is controlled to be 1.05-1.15m / min; when the package temperature is greater than T L When the temperature is +30℃, the pulling speed is controlled to be 0.95-1.05m / min; when the package temperature is greater than T L At +40℃, the pulling speed is controlled to be 0.90-1.00m / min; T L is the liquidus temperature of molten steel;

[0033] The step of rolling also includes heating and laminar cooling;

[0034] The heating includes preheating, a first heating section, a second heating section and a soaking section. The temperature of the preheating section is 600-800°C, the temperature of the first heating section is 1100-1200°C, the temperature of the second heating section is 1200-1270°C, the temperature of the soaking section is 1190-1260°C, and in the second heating section and the soaking section, the temperature difference between the upper surface and the lower surface of the ingot is 10°C;

[0035] The water temperature of laminar cooling is ≤35℃;

[0036] In the rough rolling step, the final rolling temperature is 1010-1080°C;

[0037] In the finishing step, when the thickness of the finished product is greater than 1mm and ≤2.75mm, the final rolling temperature is 900±20℃, and the coiling temperature is 700±20℃; when the thickness of the finished product is greater than 2.75mm and ≤4mm, the final rolling temperature is 890±20℃, and the coiling temperature is 620±20℃; when the thickness of the finished product is greater than 4mm and ≤8mm, the final rolling temperature is 860±20℃, and the coiling temperature is 610±20℃; when the thickness of the finished product is greater than 8mm and ≤16mm, the final rolling temperature is 850±20℃, and the coiling temperature is 600±20℃.

[0038] The present invention has the following beneficial effects:

[0039] When producing the steel of the present invention, only one set of high-pressure dephosphorization units is used for high-pressure water dephosphorization before finishing rolling, and a faster dephosphorization roller speed is configured to reduce the temperature drop during the finishing head threading process and reduce the thermal yield strength of the high-strength steel head. At the same time, the rolling force of the last pass (seventh pass) of finishing rolling is reduced to reduce the impact load of the steel, which is beneficial to reducing the head imprint problem and improving the quality of the steel. BRIEF DESCRIPTION OF THE DRAWINGS

[0040] In order to more clearly illustrate the technical solutions of the embodiments of the present invention, the drawings required for use in the embodiments are briefly introduced below. It should be understood that the following drawings only show certain embodiments of the present invention and therefore should not be regarded as limiting the scope. For ordinary technicians in this field, other related drawings can be obtained based on these drawings without creative work.

[0041] Figure 1 This is a schematic diagram of a steel head according to Example 1 of the present invention;

[0042] Figure 2 This is a schematic diagram of the steel head of Comparative Example 1 of the present invention;

[0043] Figure 3 This is a schematic diagram of the steel head of Comparative Example 2 of the present invention. DETAILED DESCRIPTION

[0044] In order to make the purpose, technical scheme and advantages of the embodiments of the present invention clearer, the technical scheme in the embodiments of the present invention will be described clearly and completely below. If the specific conditions are not specified in the embodiments, they are carried out according to conventional conditions or conditions recommended by the manufacturer. If the manufacturer of the reagents or instruments used is not specified, they are all conventional products that can be purchased commercially.

[0045] In the related art, in order to improve the stamping problem of the steel head, the hot rolling final rolling temperature, the thickness and width of the strip after hot rolling are controlled, and the closing or opening of each water cooling device in the finishing mill is controlled separately, and the maximum strip threading speed of the strip in the seventh finishing mill frame is controlled to control the generation of the strip roll mark. However, by closing the water between the head frames and the roller gap spraying water, although the temperature drop of the head temperature can be reduced, limiting the strip threading speed will lead to an increase in the temperature drop, and it is difficult to smoothly reduce the stamping, and the control of the thickness and width of the strip has limited effect on whether the stamping occurs; therefore, it is difficult for the related art to reliably reduce the stamping problem of the head of high-strength steel and improve the quality of steel.

[0046] The inventors have found that reducing the investment in high-pressure dephosphorization units and configuring a faster dephosphorization roller speed can effectively reduce the temperature drop during the finishing head threading process and reduce the thermal yield strength of the high-strength steel head. At the same time, reducing the rolling force of the last pass (seventh pass) of finishing rolling can effectively reduce the impact load of the steel, which is conducive to reliably reducing the head imprinting problem and improving the quality of the steel.

[0047] The composition of the high-strength hot-rolled steel of the present invention includes, by mass percentage: C: 0.2-1.01% (for example: 0.2%, 0.4%, 0.6%, 0.8%, 1%, 1.01%, etc.), Mn: 0.35-1.8% (for example: 0.35%, 0.5%, 0.65%, 0.7%, 0.9%, 1.2%, 1.5%, 1.65%, 1.8%, etc.), Cr: 0.35-1.1% (for example: 0.35%, 0.45%, 0.55%, 0.7%, 0.86%, 1.0%, 1.1%, etc.), Mo: 0.1-1% (for example: 0.1%, 0.3%, 0.5%, 0.7%, 0.9%, 1%, etc.), P≤0.015 (for example: 0.015%, 0.013%, 0.012%, 0.011%, etc.), S≤ 0.10 (for example: 0.1%, 0.08%, 0.07%, 0.06%, etc.), Si: 0.15-0.30% (for example: 0.15%, 0.17%, 0.19%, 0.2%, 0.22%, 0.26%, 0.28%, 0.3%, etc.), Ni: 0.40-0.70% (for example: 0.4%, 0.5%, 0.6%, 0.7%, etc.), V: 0.10-0.15% (for example: 0.1%, 0.12%, 0.13%, 0.14%, 0.15%, etc.), Als: 0.015-0.040% (for example: 0.015%, 0.02%, 0.03%, 0.04%, etc.), N≤0.006% (for example: 0.006%, 0.005%, 0.004%, etc.), the balance is Fe and unavoidable impurities.

[0048] Furthermore, the composition of the high-strength hot-rolled steel includes, by mass percentage: C: 0.66-0.70%, Mn: 0.80-1.0%, Cr: 0.40-0.60%, Mo: 0.15-0.25%.

[0049] It should be noted that the tensile strength of the high-strength hot-rolled steel of the present invention is ≤1400MPa, the elongation is ≥6%, and the Brinell hardness HBW is ≤370.

[0050] The preparation method of the high-strength hot-rolled steel material of the present invention comprises: smelting molten iron, KR desulfurization, converter steelmaking, CAS refining, LF refining, RH refining, continuous casting, hot delivery and rolling.

[0051] In the present invention, S in the molten iron after KR desulfurization is ≤0.005%, and slag is strictly removed. After slag removal, there is no obvious residue on the surface of the molten iron, and the slag is removed to more than 90% of the metal bright surface.

[0052] In the step of converter steelmaking, the charge amount may be 225-255t, of which the charge amount of molten iron may be 185-220t and the charge amount of scrap steel may be 20-50t.

[0053] The end point of converter steelmaking is C ≥ 0.06% (for example: 0.06%, 0.07%, 0.08%, etc.), P ≤ 0.012% (for example: 0.012%, 0.011%, 0.010%, 0.009%, etc.), and S ≤ 0.015% (for example: 0.015%, 0.014%, 0.013%, 0.012%, etc.).

[0054] When tapping steel, use a slide plate + slag stopper to prevent slag from tapping, and the slag layer thickness should be ≤60mm; rephosphorization should be prevented, and the rephosphorization should be ≤20ppm.

[0055] Furthermore, the steel tapping time is ≥4 minutes.

[0056] When 1 / 4 of the steel is tapped, 500 kg of lime is added for slag washing; and when 1 / 4 of the steel is tapped, at least one of silicon manganese, ferromanganese and ferrosilicon, and aluminum blocks are added in sequence; wherein, 1.0-2.0 kg / t of aluminum blocks are deoxidizers.

[0057] Carbon powder is added after steel is tapped; optionally, the carbon powder is low nitrogen carbon powder.

[0058] It should be noted that ferrochrome, nickel plate, ferroniobium and ferromolybdenum can be added in the LF furnace to ensure that the Als of the CAS sample is ≥ 0.030%.

[0059] Furthermore, after the molten steel arrives at the station, the temperature is measured and samples are taken immediately, and the argon pre-sample is taken; argon is blown, and the blowing pressure is 0.3-0.5MPa (for example: 0.3MPa, 0.4 MPa, 0.5 MPa, etc.), the flow rate is 200-800L / min (for example: 200 L / min, 300 L / min, 400L / min, 500 L / min, 600 L / min, 700 L / min, 800 L / min, etc.), and the diameter of the exposed bright circle of the molten steel is controlled to be less than 500mm (for example: 499.1mm, 498.6 mm, etc.).

[0060] In the LF refining step, argon is connected to the molten steel after arriving at the refining station to adjust the gas volume.

[0061] Furthermore, 500-1500kg of lime (for example, 500kg, 700kg, 900kg, 1100kg, 1300kg, 1500kg, etc.), 300-600kg of refined slag (for example, 300kg, 400kg, 500kg, 600kg, etc.), and 50-200kg of fluorite (for example, 50kg, 100kg, 150kg, 200kg, etc.) are added into the slag making station.

[0062] After electrification and slag formation, take LF1 sample, add 50-150kg (e.g. 50kg, 100kg, 150kg, etc.) of aluminum particles according to the slag discharge situation to deoxidize and make white slag, with FeO+Mn0≤1.0% in the slag, perform white slag refining, and the LF furnace white slag retention time ≥10min.

[0063] It should be noted that alloys such as metallic manganese or medium silicon manganese, ferrochrome, nickel plate, ferroniobium and ferromolybdenum, and carbon powder must be added in place during the early stage of LF refining. It is strictly forbidden to add slag such as aluminum particles in the later stage. The adding method is similar to the relevant technology and will not be repeated here.

[0064] In the RH refining step, in order to prevent phosphorus increase caused by residual steel in the RH furnace, the steel is cooled before smelting the high-strength hot-rolled steel of the present invention, and the vacuum tank is washed with low-phosphorus steel with a phosphorus content of ≤0.025%.

[0065] Furthermore, temperature measurement is performed upon entering the station, the vacuum time of the RH furnace is ≥20min, the vacuum degree is ≤133Pa and maintained for more than 10min, and the pure degassing time is ≥15min.

[0066] During the RH treatment, blowing oxygen and adding aluminum particles are prohibited.

[0067] After breaking through the air, adjust the bottom of the ladle to blow argon.

[0068] After the composition temperature reaches the target, the inclusion deformation treatment is carried out, and the pure calcium wire is fed for 350-400m or the seamless calcium wire is fed for 150-230m, and Ca / S is ≥ 0.3. After feeding the wire, the soft argon blowing effect is well controlled, and the slag surface is not blown open, and the creep of the molten steel surface is the best, and the soft blowing time is ≥ 12min.

[0069] In the present invention, the refining arrival and exit temperatures can be controlled according to the following table, where T L is the liquidus temperature of molten steel, which can be 1474℃.

[0070]

[0071] In the continuous casting step, the casting is carried out at a constant liquid level in the tundish, and the liquid level in the casting tundish is controlled to be ≥800mm, for example: 800mm, 810mm, 850mm, 900mm, etc.

[0072] Furthermore, the casting is protected throughout the entire process, Als is controlled to be ≤0.0050% (for example: 0.0050%, 0.0040%, 0.0030%, etc.), and the N increase in molten steel is controlled to be ≤8ppm (for example: 8ppm, 7ppm, etc.).

[0073] During continuous casting, the constant pulling speed is controlled, and dynamic light pressure and electromagnetic stirring are applied. The second and third pairs of electromagnetic stirring are turned on. The overheat of the tundish is controlled to be ≤25℃ to ensure the casting under normal accuracy of the continuous casting rollers.

[0074] During casting, the water inlet insertion depth is controlled to be 120±5mm (for example: 115mm, 120mm, 125mm, etc.), and the vibration parameter satisfies f=170-20V, where V is the vibration frequency; the cooling water volume of the crystallizer on the narrow side of the ingot is controlled to be 500±10L / min (for example: 490L / min, 500 L / min, 510 L / min, etc.), and the cooling water volume of the crystallizer on the wide side of the ingot is controlled to be 3800±100L / min (for example: 3700L / min, 3800 L / min, 3900 L / min, etc.).

[0075] The pulling speed is controlled according to the table below.

[0076]

[0077] It should be noted that about 2 mm of scrap steel can be cut from the head and tail of the ingot obtained by continuous casting.

[0078] The rolling step of the present invention further includes heating and laminar cooling, wherein the heating is performed according to the following table.

[0079]

[0080] That is, the temperature of the preheating section is 600-800℃, the temperature of the first heating section is 1100-1200℃, the temperature of the second heating section is 1200-1270℃, the temperature of the equalizing section is 1190-1260℃, and in the second heating section and the equalizing section, the temperature difference between the upper and lower surfaces of the ingot is 10℃.

[0081] During rolling, the steel tapping temperature is controlled at 1220±20℃, for example: 1200℃, 1210℃, 1220℃, 1230℃, 1240℃, etc.

[0082] The rough rolling and final rolling temperatures are 1010-1080°C, for example: 1010°C, 1020°C, 1030°C, 1040°C, 1050°C, 1060°C, 1070°C, 1080°C, etc.

[0083] It should be noted that the head and tail scrap steel can be cut off after rough rolling.

[0084] In the last pass of rough rolling, high-pressure descaling is carried out and the dephosphorization water pressure should be ≥20 MPa.

[0085] The dephosphorization in the last pass of rough rolling can also be understood as dephosphorization before finishing rolling. In this step, a group of high-pressure dephosphorization units are configured, and the speed of the dephosphorization roller is configured to be 0.70-0.80 m / s, for example: 0.70 m / s, 0.72 m / s, 0.74 m / s, 0.76 m / s, 0.78 m / s, 0.80 m / s, etc., and the water between the frames and the roller gap spraying water in the finishing mill are turned off.

[0086] Further, the finishing rolling step includes seven rolling passes, wherein the rolling force of the fifth pass is controlled to be ≤1000 tons (for example: 1000 tons, 980 tons, 950 tons, 930 tons, 900 tons, 880 tons, 860 tons, 850 tons, 830 tons, etc.), the rolling force of the sixth pass is controlled to be ≤900 tons (for example: 900 tons, 880 tons, 860 tons, 850 tons, 830 tons, 820 tons, 800 tons, 790 tons, 770 tons, 760 tons, 750 tons, 720 tons, etc.), and the rolling force of the seventh to fifth passes is controlled to be ≤800 tons (for example: 800 tons, 790 tons, 770 tons, 760 tons, 750 tons, 720 tons, 700 tons, 680 tons, 660 tons, 640 tons, 620 tons, 600 tons, 580 tons, etc.).

[0087] In a preferred embodiment, the rolling force of the fifth pass is controlled to be 850-950 tons, the rolling force of the sixth pass is controlled to be 750-850 tons, and the rolling force of the seventh pass is controlled to be 600-700 tons.

[0088] Before finishing rolling, only one set of high-pressure dephosphorization units is used for high-pressure water dephosphorization, and a faster dephosphorization roller speed is configured to reduce the temperature drop during the finishing head threading process and reduce the thermal yield strength of the high-strength steel head. At the same time, the rolling force of the last pass (seventh pass) of finishing rolling is reduced to reduce the impact load of the steel, which is beneficial to reduce the head imprint problem and improve the quality of the steel.

[0089] Furthermore, the distance between the high-pressure dephosphorization unit and the first-pass rolling unit is 8-10m, for example, 8m, 9m, 10m, etc. In this way, the distance between the dephosphorization unit and the first-pass rolling mill can be adapted to the speed of the dephosphorization roller. During the dephosphorization process, the temperature drop per second is controlled at about 1.5-2.5°C, and the temperature drop of the rolled piece from the dephosphorization unit to the first-pass rolling unit can be reduced by about 15-30°C.

[0090] In the finishing rolling step, the final rolling temperature and the coiling temperature can be controlled according to the following table.

[0091]

[0092] In the present invention, the water temperature of the laminar cooling is ≤35° C. to ensure the uniformity of cooling.

[0093] It should be noted that in the laminar cooling step, the opened headers can be selected as needed and are similar to related technologies, for example: opening the cooling water of the 2nd to 6th groups of headers and the 20th group of headers to ensure the coiling temperature hit rate, etc., which will not be repeated here.

[0094] The present invention is further described in detail below in conjunction with embodiments.

[0095] Example 1

[0096] The composition of high-strength hot-rolled steel, in terms of mass percentage, includes: C: 0.66%, Mn: 0.80%, Cr: 0.4%, Mo: 0.15%, P: 0.015, S: 0.10, Si: 0.15%, Ni: 0.40%, V: 0.10%, Als: 0.015%, N≤0.006%, and the balance is Fe and unavoidable impurities.

[0097] The preparation method of high-strength hot-rolled steel includes: smelting molten iron, KR desulfurization, converter steelmaking, CAS refining, LF refining, RH refining, continuous casting, hot delivery and rolling.

[0098] When tapping steel from a converter, 500 kg of lime is added to 1 / 4 of the tapped steel for slag washing, and 1.5 tons of silicon manganese, 1.5 tons of ferromanganese, 200 kg of ferrosilicon, and aluminum blocks are added in sequence, with the amount of aluminum blocks added being 1 kg / t. Carbon powder is added after tapping.

[0099] After converter steelmaking, argon is blown. The pressure of argon blowing is 0.3MPa, the flow rate is 200L / min, and the diameter of the exposed bright ring of molten steel is controlled to be 499mm.

[0100] LF refining: add 500kg lime, 300kg refined slag and 50kg fluorite into the slag making station; after electrification of slag, take LF1 sample, add 50kg aluminum particles, deoxidize and make white slag, the (FeO+Mn0) in the slag is 1.0%, carry out white slag refining, and the LF furnace white slag holding time is 10 minutes.

[0101] RH refining: temperature measurement upon entering the station, vacuum degree is 133Pa and maintained for 10 minutes, pure degassing time is 15 minutes; after the composition temperature reaches the target, inclusion deformation treatment is carried out, 350 meters of pure calcium wire is fed, and soft blowing is carried out for 12 minutes.

[0102] Temperature Control:

[0103]

[0104] Continuous casting: pouring tundish liquid level 800mm; tundish superheat 25℃.

[0105] Casting process: the water inlet insertion depth is 120mm, and the vibration parameter satisfies f=170-20V; the cooling water volume of the crystallizer on the narrow side of the ingot is 500L / min, and the cooling water volume of the crystallizer on the wide side of the ingot is 3800L / min.

[0106] Casting speed and temperature:

[0107]

[0108] Rolling:

[0109] Heat as shown in the table below.

[0110]

[0111] The final rolling temperature of the rough rolling is 1010℃.

[0112] For finishing dephosphorization, a high-pressure dephosphorization unit is configured, and the dephosphorization roller speed is configured to be 0.75m / s; the high-pressure descaling water pressure is 20 MPa; the distance between the high-pressure dephosphorization unit and the first rolling unit is 9m. The head temperature of the steel after dephosphorization and before the first rolling is 971℃.

[0113] Rolling process:

[0114]

[0115] The finishing rolling step includes seven rolling passes, wherein the rolling force of the fifth pass is 850 tons, the rolling force of the sixth pass is 750 tons, and the rolling force of the seventh to the last pass is 600 tons.

[0116] like Figure 1 As shown, the head of the steel material of Example 1 has no obvious embossing.

[0117] Example 2

[0118] The composition of high-strength hot-rolled steel, in terms of mass percentage, includes: C: 0.70%, Mn: 1.00%, Cr: 0.6%, Mo: 0.25%, P: 0.012, S: 0.08, Si: 0.30%, Ni: 0.70%, V: 0.15%, Als: 0.040%, N≤0.005%, and the balance is Fe and unavoidable impurities.

[0119] The preparation method of high-strength hot-rolled steel includes: smelting molten iron, KR desulfurization, converter steelmaking, CAS refining, LF refining, RH refining, continuous casting, hot delivery and rolling.

[0120] When tapping steel in the converter, 450 kg of lime is added to 1 / 4 of the tapped steel for slag washing, and 1.5 tons of silicon manganese, 1.5 tons of ferromanganese, and aluminum blocks are added in sequence, with the amount of aluminum blocks added being 2 kg / t. Carbon powder is added after tapping.

[0121] After converter steelmaking, argon is blown. The pressure of argon blowing is 0.5MPa, the flow rate is 800L / min, and the diameter of the exposed bright ring of molten steel is controlled to be 498mm.

[0122] LF refining: add 1500kg of lime, 600kg of refined slag and 100kg of fluorite when entering the station for slag making; after electrification of slag, take LF1 sample, add 150kg of aluminum particles, deoxidize and make white slag, the (FeO+Mn0) in the slag is 0.8%, carry out white slag refining, and the LF furnace white slag holding time is 12 minutes.

[0123] RH refining: temperature measurement upon entering the station, vacuum degree is 130Pa and maintained for 15 minutes, pure degassing time is 20 minutes; after the composition temperature reaches the target, inclusion deformation treatment is carried out, 400 meters of pure calcium wire is fed, and soft blowing is carried out for 15 minutes.

[0124] Temperature Control:

[0125]

[0126] Continuous casting: pouring tundish liquid level 810mm; tundish superheat 23℃.

[0127] Casting process: the water inlet insertion depth is 125mm, and the vibration parameter satisfies f=170-20V; the cooling water volume of the crystallizer on the narrow side of the ingot is 510L / min, and the cooling water volume of the crystallizer on the wide side of the ingot is 3900L / min.

[0128] Casting speed and temperature:

[0129]

[0130] Rolling:

[0131] Heat as shown in the table below.

[0132]

[0133] The final rolling temperature of the rough rolling is 1010℃.

[0134] For finishing dephosphorization, a high-pressure dephosphorization unit is configured, and the dephosphorization roller speed is configured to be 0.8m / s; the high-pressure descaling water pressure is 22 MPa; the distance between the high-pressure dephosphorization unit and the first rolling unit is 8m. The head temperature of the steel after dephosphorization and before the first rolling is 982℃.

[0135] Rolling process:

[0136]

[0137] The finishing rolling step includes seven rolling passes, wherein the rolling force of the fifth pass is 950 tons, the rolling force of the sixth pass is 850 tons, and the rolling force of the seventh to the last pass is 700 tons.

[0138] The head of the steel material of Example 2 has no obvious embossing.

[0139] Comparative Example 1

[0140] Comparative Example 1 is similar to Example 1, except that: in the dephosphorization step, the speed of the dephosphorization roller is configured to be 0.4 m / s, and the head temperature of the steel after dephosphorization and before the first rolling is 947°C s; the remaining process parameters are referred to Example 1.

[0141] like Figure 2 As shown, the head of the steel material of Comparative Example 1 is embossed.

[0142] Comparative Example 2

[0143] Comparative Example 2 is similar to Example 1, except that: in the dephosphorization step, the speed of the dephosphorization roller is configured to be 0.5 m / s, the head temperature of the steel after dephosphorization and before the first rolling pass is 955°C; and the rolling force of the fifth pass, the rolling force of the sixth pass, and the rolling force from the seventh pass to the next are all 1000 tons; the remaining process parameters are referred to Example 1.

[0144] like Figure 3 As shown, the head of the steel material of Comparative Example 2 has obvious embossing.

[0145] In summary, the high-strength hot-rolled steel of the present invention can reduce head stamping and has good quality.

[0146] The above are only preferred embodiments of the present invention and are not intended to limit the present invention. For those skilled in the art, the present invention may have various modifications and variations. Any modification, equivalent replacement, improvement, etc. made within the spirit and principle of the present invention shall be included in the protection scope of the present invention.

Claims

1. A high-strength hot-rolled steel material, characterized in that: The composition of the high-strength hot-rolled steel includes, by mass percentage, C: 0.2-1.01%, Mn: 0.35-1.8%, Cr: 0.35-1.1%, Mo: 0.1-1%, P≤0.015, S≤0.10, Si: 0.15-0.30%, Ni: 0.40-0.70%, V: 0.10-0.15%, Als: 0.015-0.040%, N≤0.006%, and the balance is Fe and unavoidable impurities; The preparation method of the high-strength hot-rolled steel comprises: smelting molten iron, KR desulfurization, converter steelmaking, CAS refining, LF refining, RH refining, continuous casting, hot delivery and rolling; wherein, The rolling steps include rough rolling, dephosphorization and finish rolling; In the dephosphorization step, a group of high-pressure dephosphorization units are configured for the last pass of rough rolling, and the speed of the dephosphorization roller is configured to be 0.70-0.80 m / s.

2. The high-strength hot-rolled steel material according to claim 1, characterized in that: The finishing rolling step includes seven rolling passes, wherein the rolling force of the fifth pass is controlled to be ≤1000 tons, the rolling force of the sixth pass is controlled to be ≤900 tons, and the rolling force of the seventh to fifth passes is controlled to be ≤800 tons.

3. The high-strength hot-rolled steel material according to claim 2, characterized in that: The rolling force of the fifth pass is controlled to be 850-950 tons, the rolling force of the sixth pass is controlled to be 750-850 tons, and the rolling force of the seventh pass is controlled to be 600-700 tons.

4. The high-strength hot-rolled steel material according to claim 2, characterized in that: The distance between the high-pressure dephosphorization unit and the first-pass rolling unit is 8-10m.

5. The high-strength hot-rolled steel material according to claim 1, characterized in that: The components of the high-strength hot-rolled steel include, by mass percentage, C: 0.66-0.70%, Mn: 0.80-1.0%, Cr: 0.40-0.60%, and Mo: 0.15-0.25%.

6. The high-strength hot-rolled steel material according to claim 1, characterized in that: The water pressure of the high-pressure dephosphorization unit is ≥20MPa.

7. The high-strength hot-rolled steel material according to claim 1, characterized in that: The converter steelmaking step includes: adding lime slag for washing when 1 / 4 of the steel is tapped, and sequentially adding at least one of silicon manganese, ferromanganese and ferrosilicon, and aluminum blocks when 1 / 4 of the steel is tapped; Add carbon powder after steel is tapped; After the molten steel arrives at the station, the temperature is measured, samples are taken, and argon is blown. The pressure of the argon is 0.3-0.5MPa, the flow rate is 200-800L / min, and the diameter of the exposed bright ring of the molten steel is controlled to be less than 500mm.

8. The high-strength hot-rolled steel material according to claim 1, characterized in that: The LF refining steps include: connecting argon gas to the molten steel after it reaches the refining station; When entering the station to make slag, add 500-1500kg of lime, 300-600kg of refined slag, and 50-200kg of fluorite; Power on the slag, take LF1 sample, add 50-150kg aluminum particles to deoxidize and make white slag, FeO+Mn0 in the slag ≤1.0%, and the LF furnace white slag retention time ≥10min; The RH refining step comprises: Wash the vacuum tank with low-phosphorus steel with a phosphorus content of ≤ 0.025%; Measure the temperature upon entering the station, control the vacuum degree of the RH furnace to ≤133Pa and maintain it for 10min or more, and control the pure degassing time to ≥15min.

9. The high-strength hot-rolled steel material according to claim 1, characterized in that: The arrival temperature of the pouring furnace in the CAS refining step is 1564-1588°C, the arrival temperature of the pouring furnace in the RH refining step is 1534-1578°C, the exit temperature of the pouring furnace in the RH refining step is 1530-1535°C, the temperature of the ladle of the pouring furnace to the continuous casting platform is 1525-1530°C, and the temperature of the middle ladle of the pouring furnace is 1485-1510°C; The arrival temperature of the continuous casting furnace in the CAS refining step is 1554-1574°C, the arrival temperature of the continuous casting furnace in the RH refining step is 1529-1569°C, the exit temperature of the continuous casting furnace in the RH refining step is 1515-1525°C, the temperature of the ladle of the continuous casting furnace to the continuous casting platform is 1513-1520°C, and the temperature of the middle ladle of the continuous casting furnace is 1485-1505°C.

10. The high-strength hot-rolled steel material according to claim 1, characterized in that: The continuous casting step comprises: Control the liquid level in the casting ladle ≥800mm; Control Als≤0.0050%, control molten steel N≤8ppm; Control the superheat of the tundish to ≤25℃; Control the nozzle insertion depth to 120±5mm, and the vibration parameter to satisfy f=170-20V, where V is the vibration frequency; The cooling water volume of the mold on the narrow side of the ingot is controlled to be 500±10L / min, and the cooling water volume of the mold on the wide side of the ingot is controlled to be 3800±100L / min; When the package temperature ≤T L At +30℃, the pulling speed is controlled to be 1.05-1.15m / min; when the package temperature is greater than T L When the temperature is +30℃, the pulling speed is controlled to be 0.95-1.05m / min; when the package temperature is greater than T L At +40℃, the pulling speed is controlled to be 0.90-1.00m / min; T L is the liquidus temperature of molten steel; The rolling step also includes heating and laminar cooling; The heating step includes a preheating section, a first heating section, a second heating section and a soaking section, the temperature of the preheating section is 600-800°C, the temperature of the first heating section is 1100-1200°C, the temperature of the second heating section is 1200-1270°C, the temperature of the soaking section is 1190-1260°C, and in the second heating section and the soaking section, the temperature difference between the upper surface and the lower surface of the ingot is 10°C; The water temperature of the laminar cooling is ≤35°C; In the step of rough rolling, the final rolling temperature is 1010-1080°C; In the finishing step, when the thickness of the finished product is greater than 1 mm and ≤ 2.75 mm, the final rolling temperature is 900 ± 20 ° C, and the coiling temperature is 700 ± 20 ° C; when the thickness of the finished product is greater than 2.75 mm and ≤ 4 mm, the final rolling temperature is 890 ± 20 ° C, and the coiling temperature is 620 ± 20 ° C; when the thickness of the finished product is greater than 4 mm and ≤ 8 mm, the final rolling temperature is 860 ± 20 ° C, and the coiling temperature is 610 ± 20 ° C; when the thickness of the finished product is greater than 8 mm and ≤ 16 mm, the final rolling temperature is 850 ± 20 ° C, and the coiling temperature is 600 ± 20 ° C.

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