Q355B steel hot rolling process optimization method based on dynamic temperature control

Abstract

The invention relates to the technical field of steel rolling, and discloses a Q355B steel hot rolling process optimization method based on dynamic temperature control, which comprises the following steps: blank pretreatment, dynamic heating control, high-pressure water descaling, rough rolling process, finish rolling process, laminar cooling and coiling process. According to the method, a collaborative system of multi-section variable-temperature heating and intelligent temperature control is constructed, temperature distribution in a furnace and the heating rate are monitored and dynamically adjusted in real time, it is guaranteed that the core surface temperature of a plate blank is uniform and consistent, thermal stress and the internal crack tendency in the heating process are eliminated, and a high-temperature blank uniform in structure and stable in performance is provided for follow-up rolling; meanwhile, the high-pressure water descaling system optimizes jet flow parameters and introduces chemical additives, so that a protective layer is formed while oxide scales on the surface are removed, the surface cleanliness and quality of the plate blank are improved, and product defects caused by incomplete descaling and surface damage are avoided.

Description

TECHNICAL FIELD

[0001] The application relates to the technical field of steel rolling, in particular to a Q355B steel hot rolling process optimization method based on dynamic temperature control. BACKGROUND

[0002] Q355B is a kind of low-alloy high-strength structural steel, which is widely used in steel structure, bridge, vehicle, ship, building, pressure vessel, special equipment, etc. The hot rolling process can reduce energy consumption cost. The metal has high plasticity and low deformation resistance during hot rolling, thereby reducing the energy consumption of metal deformation, improving the processing performance of the metal and alloy, breaking the coarse grains in the casting state, reducing or eliminating casting defects, and converting the casting structure into a deformation structure to improve the processing performance of the alloy.

[0003] At present, in the hot rolling production process of Q355B steel, due to the uneven temperature field distribution in the heating furnace and the relatively static control mode, the slab core and surface temperature difference and the furnace atmosphere fluctuation cannot be responded in real time, which may cause uneven heating of the slab, internal thermal stress and even cracks, and affect the stability of the subsequent rolling process and the microstructure uniformity of the steel.

[0004] Therefore, the Q355B steel hot rolling process optimization method based on dynamic temperature control is proposed to solve the above problems. SUMMARY

[0005] In view of the deficiencies of the prior art, the application provides a Q355B steel hot rolling process optimization method based on dynamic temperature control, which solves the problems in the background art.

[0006] To achieve the above purpose, the application provides the following technical scheme: a Q355B steel hot rolling process optimization method based on dynamic temperature control, comprising the following steps: Step 1: blank pretreatment, selecting Q355B continuous casting slab, the thickness of the slab is 200-250 mm, and the surface is cleaned, preheated and homogenized; Step 2: dynamic heating control, the pretreated slab is sent into a walking beam furnace, a multi-section variable temperature heating process is adopted, and the temperature distribution and heating rate in the furnace are controlled; Step 3: high-pressure water descaling, high-pressure water jet is used to descale the surface of the heated slab, the water pressure is 18-25 MPa, and the water temperature is controlled at 30-50 DEG C; Step 4: rough rolling process, the descaled slab is sent into a rough rolling mill for multi-pass rolling, the rough rolling temperature is controlled at 1050-1150 DEG C, and the finish rolling temperature is controlled at 950-1000 DEG C; Step five: finish rolling process, the rough rolling after the intermediate blank is sent to the finish rolling mill group for continuous rolling, and the finish rolling roughing temperature is controlled at 880-930℃, and the finish rolling temperature is controlled at 820-880℃; Step six: laminar cooling, a multi-stage laminar cooling system is used to control the cooling of the strip after finish rolling, and the cooling rate is controlled at 5-25℃ / s; Step seven: coiling process, the cooled strip is sent to the coiling machine for coiling, and the coiling temperature is controlled at 550-650℃.

[0007] Preferably, the step one blank pre-treatment includes the following steps: using a shot blasting machine to clean the surface of the slab, removing the iron oxide scale and impurities, sending the cleaned slab to a preheating furnace, preheating at 600-800℃ for 1-2 hours, and then transferring the slab to a soaking furnace, soaking at 1100-1200℃ for 1.5-2.5 hours, so that the core-surface temperature difference of the slab is less than 30℃.

[0008] Preferably, the shot blasting machine uses stainless steel pellets, the pellet diameter is 1.0-1.5mm, the shooting speed is 60-80m / s, the treatment time is 10-20 minutes, the preheating furnace uses natural gas heating, the air-fuel ratio is controlled at 1.05-1.15, the soaking furnace uses resistance heating method, the heating power is 500-800kW, the furnace atmosphere is nitrogen protective atmosphere, and the oxygen content is less than 2%.

[0009] Preferably, the multi-stage temperature heating process in step two uses an intelligent temperature control system, which includes an infrared temperature meter, a furnace temperature sensor and a PLC controller. By real-time monitoring of the slab surface temperature and the temperature distribution in the furnace, the gas flow and air ratio of each heating section are dynamically adjusted, so that the slab heating uniformity is controlled within ±15℃. The multi-stage temperature heating process includes a preheating section, a heating section and a soaking section, wherein the preheating section temperature is 800-950℃, the heating section temperature is 1150-1250℃, and the soaking section temperature is 1200-1250℃. The total heating time is controlled at 2.5-4.5 hours.

[0010] Preferably, the infrared temperature meter uses a dual-color infrared temperature measurement technology, the measurement wavelength range is 1.0-1.6μm, and the temperature measurement accuracy is ±5℃. The furnace temperature sensor uses a K-type thermocouple, the measurement range is 0-1300℃, and the accuracy is ±1.5℃. The PLC controller uses a PID control algorithm, the adjustment period is 0.5-1.0 seconds, and the output signal controls the gas regulating valve and the air blower speed.

[0011] Preferably, the high-pressure water descaling in step three includes a descaling box, a high-pressure water pump, a water filter and a nozzle group, the nozzle adopts a fan-shaped nozzle, the spray angle is 15-30°, the nozzle diameter is 2.0-3.0 mm, the nozzle spacing is 150-250 mm, the descaling water is added with a rust inhibitor and a surfactant, wherein the rust inhibitor is sodium phosphate, the addition amount is 0.1-0.3%, and the surfactant is sodium alkyl benzene sulfonate, the addition amount is 0.05-0.1%.

[0012] Preferably, the rough rolling process in step four adopts a reversible mill, the work roll diameter is 1000-1200 mm, the backup roll diameter is 1400-1600 mm, the rolling speed is controlled to be 2-5 m / s, the lubricating emulsion is used in the rolling process, the emulsion concentration is 3-5%, the flow rate is 500-1000 L / min, the emulsion temperature is controlled to be 40-60℃, and the rough rolling mill adopts a vertical roll and a horizontal roll combined rolling, the rolling pass is 5-7 passes, and the reduction rate of each pass is 15-25%.

[0013] Preferably, the finishing mill process in step five adopts a six-stand four-roll finishing mill, the work roll diameter is 700-800 mm, the backup roll diameter is 1200-1400 mm, the rolling speed is controlled to be 8-15 m / s, the micro-tension control is used in the finishing process, the tension range is 5-15 kN, and the AGC thickness automatic control system is used, and the thickness control precision is ±0.05 mm.

[0014] Preferably, the laminar cooling in step six adopts an upper and lower header arrangement, the upper header cooling water flow rate is 800-1200 m³ / h, the lower header cooling water flow rate is 600-1000 m³ / h, the multi-section laminar cooling system includes a front section fast cooling zone, a middle section slow cooling zone and a rear section adjusting zone, the cooling water flow rate is dynamically adjusted according to the strip thickness and speed, the cooling water is added with a scale inhibitor and a corrosion inhibitor, wherein the scale inhibitor is sodium polyacrylate, the addition amount is 0.05-0.1%, the corrosion inhibitor is sodium molybdate, the addition amount is 0.02-0.05%, and the strip surface temperature uniformity after cooling is controlled to be within ±20℃.

[0015] Preferably, the coiling process in step seven adopts a three-assisted coiling roll type coiler, the coiling tension is controlled to be 50-100 kN, the coiling speed is synchronous with the rolling speed, the steel coil after coiling is subjected to slow cooling treatment, is slowly cooled to room temperature at a cooling rate of 0.5-2℃ / h in an annealing pit, the annealing pit temperature is 300-500℃, and the annealing time is 12-24 hours.

[0016] Beneficial effects Compared with the prior art, the application provides a Q355B steel hot rolling process optimization method based on dynamic temperature control, and has the following beneficial effects: 1. In the present application, by constructing a collaborative system of multi-stage variable temperature heating and intelligent temperature control, the temperature distribution and heating rate in the furnace are monitored and dynamically adjusted in real time, ensuring uniformity of the core and surface temperature of the slab, eliminating thermal stress and internal crack tendency during heating, and providing uniform organization and stable performance of the high-temperature billet for subsequent rolling; at the same time, the high-pressure water descaling system optimizes the jet parameters and introduces chemical additives to form a protective layer while removing the surface iron oxide scale, improving the cleanliness and quality of the slab surface, and avoiding product defects caused by incomplete descaling and surface damage.

[0017] 2. In the present application, by setting temperature window, deformation parameters and integrating micro-tension and thickness automatic control, the rough rolling and finishing rolling processes are carried out under the best thermodynamic conditions, ensuring sufficient deformation penetration and uniform grain refinement, and improving the mechanical properties and dimensional accuracy of the product; at the same time, the laminar cooling system adopts multi-stage partition design and dynamic flow regulation strategy, based on the real-time state of the strip to adaptively adjust the cooling intensity, control the phase change process, eliminate the performance fluctuation and residual stress in the length direction, and ensure the high uniformity and stability of the product organization and performance.

[0018] 3. In the present application, the process parameters from heating, descaling, rolling to cooling and coiling are systematically integrated and cooperatively optimized based on the dynamic temperature control concept, forming a closed-loop feedback and accurate matching between each link, realizing real-time response and dynamic correction of the global process window; finally, through controllable coiling and slow cooling process, internal stress is eliminated and material organization is stabilized, comprehensively improving the consistency of product comprehensive performance, shape accuracy and stability. DETAILED DESCRIPTION

[0019] The technical solutions in the embodiments of the present application will be clearly and completely described below with reference to the embodiments of the present application. Obviously, the described embodiments are only part of the embodiments of the present application, not all the embodiments. Based on the embodiments in the present application, all other embodiments obtained by those skilled in the art without creative labor are within the scope of protection of the present application.

[0020] Embodiment one, a Q355B steel hot rolling process optimization method based on dynamic temperature control, comprising the following steps: Step one: billet pretreatment, selecting Q355B continuous casting slab, the thickness of the slab is 200mm, and the surface is cleaned, preheated and homogenized; Step two: dynamic heating control, the pretreated slab is sent into the walking beam furnace, multi-stage variable temperature heating process is adopted to control the temperature distribution and heating rate in the furnace; Step three: high-pressure water descaling, high-pressure water jet is used to descale the surface of the heated slab, the water pressure is 18MPa, and the water temperature is controlled at 30℃; Step four: rough rolling process, the descaled slab is sent to the rough rolling mill group for multi-pass rolling, the rough rolling temperature is controlled at 1050℃, and the finish rolling temperature is controlled at 950℃; Step five: finish rolling process, the rough rolled intermediate billet is sent to the finish rolling mill group for continuous rolling, the finish rolling rough rolling temperature is controlled at 880℃, and the finish rolling temperature is controlled at 820℃; Step six: laminar flow cooling, a multi-stage laminar flow cooling system is used for controlled cooling of the finished rolled strip, the cooling rate is controlled at 5℃ / s; Step seven: coiling process, the cooled strip is sent to the coiling machine for coiling, and the coiling temperature is controlled at 550℃.

[0021] Step one: billet pretreatment includes the following steps: using a shot blasting machine to clean the surface of the slab, removing iron oxide scale and impurities, sending the cleaned slab to a preheating furnace, preheating at 600℃ for 1 hour, then transferring the slab to a soaking furnace, soaking at 1100℃ for 1.5 hours, so that the core surface temperature difference of the slab is less than 30℃.

[0022] The shot blasting machine uses stainless steel pellets, the pellet diameter is 1.0mm, the ejection speed is 60m / s, the treatment time is 10 minutes, the preheating furnace uses natural gas heating, the air-fuel ratio is controlled at 1.05, the soaking furnace uses resistance heating, the heating power is 500kW, the furnace atmosphere is nitrogen protective atmosphere, and the oxygen content is less than 2%.

[0023] The multi-stage variable temperature heating process in step two uses an intelligent temperature control system, which includes an infrared temperature meter, a furnace temperature sensor and a PLC controller. By real-time monitoring of the slab surface temperature and the temperature distribution in the furnace, the gas flow and air ratio of each heating section are dynamically adjusted, so that the slab heating uniformity is controlled within ±15℃. The multi-stage variable temperature heating process includes a preheating section, a heating section and a soaking section. The preheating section temperature is 800℃, the heating section temperature is 1150℃, and the soaking section temperature is 1200℃. The total heating time is controlled at 2.5 hours.

[0024] The infrared temperature meter uses double-color infrared temperature measurement technology, the measurement wavelength range is 1.0μm, and the temperature measurement accuracy is ±5℃. The furnace temperature sensor uses K-type thermocouple, the measurement range is 0-1300℃, and the accuracy is ±1.5℃. The PLC controller uses PID control algorithm, the adjustment period is 0.5 seconds, and the output signal controls the gas regulating valve and the air blower speed.

[0025] The high-pressure water descaling in step three includes a descaling box, a high-pressure water pump, a water filter and a nozzle group. The nozzle uses a fan-shaped nozzle, the spray angle is 15°, the nozzle diameter is 2.0mm, the nozzle spacing is 150mm, and the descaling water is added with rust inhibitor and surfactant. The rust inhibitor is sodium phosphate, the addition amount is 0.1%, and the surfactant is sodium alkyl benzene sulfonate, the addition amount is 0.05%.

[0026] The rough rolling process in step four adopts a reversible mill, the work roll diameter is 1000 mm, the backup roll diameter is 1400 mm, the rolling speed is controlled at 2 m / s, the lubricating emulsion is used in the rolling process, the emulsion concentration is 3%, the flow rate is 500 L / min, the emulsion temperature is controlled at 40℃, the rough rolling mill adopts vertical roll and horizontal roll combined rolling, the rolling pass is 5, and the reduction rate of each pass is 15%.

[0027] The finishing mill process in step five adopts a six-stand four-roll finishing mill, the work roll diameter is 700 mm, the backup roll diameter is 1200 mm, the rolling speed is controlled at 8 m / s, the micro tension control is used in the finishing rolling process, the tension is 5 kN, and the AGC thickness automatic control system is used, the thickness control precision is ±0.05 mm.

[0028] The laminar cooling in step six adopts upper and lower header arrangement, the cooling water flow rate of the upper header is 800 m³ / h, the cooling water flow rate of the lower header is 600 m³ / h, the multi-section laminar cooling system includes a front section fast cooling zone, a middle section slow cooling zone and a rear section adjusting zone, the cooling water flow rate is dynamically adjusted according to the strip thickness and speed, the cooling water is added with scale inhibitor and corrosion inhibitor, the scale inhibitor is sodium polyacrylate, the addition amount is 0.05%, the corrosion inhibitor is sodium molybdate, the addition amount is 0.02%, and the strip surface temperature uniformity after cooling is controlled within ±20℃.

[0029] The coiling process in step seven adopts a three-assisted coiling roll type coiler, the coiling tension is controlled at 50 kN, the coiling speed is synchronized with the rolling speed, the steel coil after coiling is subjected to slow cooling treatment, the cooling rate in the soaking pit is 0.5℃ / h to room temperature, the soaking pit temperature is 300℃, and the soaking time is 12 hours.

[0030] Example two, a Q355B steel hot rolling process optimization method based on dynamic temperature control, comprising the following steps: Step one: billet pretreatment, selecting a Q355B continuous casting slab, the thickness of the slab is 230 mm, and the slab is subjected to surface cleaning, preheating and soaking treatment; Step two: dynamic heating control, the pretreated slab is sent into a walking beam furnace, a multi-section variable temperature heating process is adopted to control the temperature distribution and heating rate in the furnace; Step three: high-pressure water descaling, high-pressure water jet is used to descale the surface of the heated slab, the water pressure is 23 MPa, and the water temperature is controlled at 40℃; Step four: rough rolling process, the descaled slab is sent into a rough rolling mill for multi-pass rolling, the roughing temperature is controlled at 1100℃, and the finishing temperature is controlled at 970℃; Step five: finish rolling process, the intermediate blank after rough rolling is sent to the finish rolling unit for continuous rolling, the finish rolling starting temperature is controlled at 900℃, and the finish rolling ending temperature is controlled at 850℃; Step six: laminar cooling, a multi-stage laminar cooling system is used to control the cooling of the strip after finish rolling, and the cooling rate is controlled at 15℃ / s; Step seven: coiling process, the cooled strip is sent to the coiling machine for coiling, and the coiling temperature is controlled at 600℃.

[0031] Step one: blank pre-treatment, including the following steps: using a shot blasting machine to clean the surface of the slab, removing the iron oxide scale and impurities, sending the cleaned slab to a preheating furnace, preheating at 700℃ for 1.5 hours, and then transferring the slab to a soaking furnace, soaking at 1150℃ for 2 hours, so that the temperature difference between the core and the surface of the slab is less than 30℃.

[0032] The shot blasting machine uses stainless steel pellets with a diameter of 1.2mm and a projection speed of 70m / s, the treatment time is 15 minutes, the preheating furnace uses natural gas heating, the air-fuel ratio is controlled at 1.1, the soaking furnace uses resistance heating, the heating power is 700kW, and the furnace atmosphere is nitrogen protective atmosphere with an oxygen content of less than 2%.

[0033] The multi-stage variable temperature heating process in step two uses an intelligent temperature control system, which includes an infrared temperature measuring instrument, a furnace temperature sensor and a PLC controller. By real-time monitoring of the slab surface temperature and the temperature distribution in the furnace, the gas flow and air ratio of each heating section are dynamically adjusted to control the slab heating uniformity within ±15℃. The multi-stage variable temperature heating process includes a preheating section, a heating section and a soaking section, with the preheating section temperature being 900℃, the heating section temperature being 1200℃, and the soaking section temperature being 1220℃. The total heating time is controlled at 3.5 hours.

[0034] The infrared temperature measuring instrument uses double-color infrared temperature measurement technology, with a measurement wavelength range of 1.3μm and a temperature measurement accuracy of ±5℃. The furnace temperature sensor uses a K-type thermocouple with a measurement range of 0-1300℃ and an accuracy of ±1.5℃. The PLC controller uses a PID control algorithm with a regulation period of 0.7 seconds, and the output signal controls the gas regulating valve and the air blower speed.

[0035] The high-pressure water descaling in step three includes a descaling box, a high-pressure water pump, a water filter and a nozzle group. The nozzle uses a fan-shaped nozzle with a spray angle of 20°, a nozzle diameter of 2.5mm and a nozzle spacing of 200mm. The descaling water is added with rust inhibitor and surfactant, with the rust inhibitor being sodium phosphate at an addition amount of 0.2% and the surfactant being sodium alkyl benzene sulfonate at an addition amount of 0.07%.

[0036] The rough rolling process in step four adopts a reversible mill, the work roll diameter is 1100 mm, the backup roll diameter is 1500 mm, the rolling speed is controlled at 3 m / s, and lubricating emulsion is used during rolling, the emulsion concentration is 4%, the flow rate is 700 L / min, the emulsion temperature is controlled at 50°C, and the rough rolling mill adopts vertical roll and horizontal roll combined rolling, the rolling passes are 6, and the reduction rate of each pass is 20%.

[0037] The finishing rolling process in step five adopts a six-stand four-roll finishing mill, the work roll diameter is 750 mm, the backup roll diameter is 1300 mm, the rolling speed is controlled at 12 m / s, micro tension control is used during finishing rolling, the tension is 10 kN, and an AGC thickness automatic control system is used, and the thickness control precision is ±0.05 mm.

[0038] The laminar cooling in step six adopts an upper and lower header arrangement, the upper header cooling water flow rate is 1000 m³ / h, the lower header cooling water flow rate is 800 m³ / h, the multi-stage laminar cooling system includes a front fast cooling zone, a middle slow cooling zone and a rear adjustment zone, the cooling water flow rate is dynamically adjusted according to the strip thickness and speed, and the cooling water is added with a scale inhibitor and a corrosion inhibitor, wherein the scale inhibitor is sodium polyacrylate with an addition amount of 0.07%, and the corrosion inhibitor is sodium molybdate with an addition amount of 0.04%, and the strip surface temperature uniformity after cooling is controlled within ±20°C.

[0039] The coiling process in step seven adopts a three-assisted coiling roll type coiler, the coiling tension is controlled at 70 kN, the coiling speed is synchronized with the rolling speed, the coiled steel coil is slowly cooled after coiling, and the cooling rate in the soaking pit is 1°C / h to room temperature, the soaking pit temperature is 400°C, and the soaking time is 18 hours.

[0040] Example three, a Q355B steel hot rolling process optimization method based on dynamic temperature control, including the following steps: Step one: billet pretreatment, selecting a Q355B continuous casting slab, the slab thickness is 250 mm, and the slab is subjected to surface cleaning, preheating and soaking treatment; Step two: dynamic heating control, the pretreated slab is sent into a walking beam furnace, a multi-stage variable temperature heating process is adopted to control the furnace temperature distribution and heating rate; Step three: high-pressure water descaling, high-pressure water jet is used to descale the surface of the heated slab, the water pressure is 25 MPa, and the water temperature is controlled at 50°C; Step four: rough rolling process, the descaled slab is sent to the rough rolling mill for multi-pass rolling, and the rough rolling temperature is controlled at 1150°C, and the finish rolling temperature is controlled at 1000°C; Step five: finishing rolling process, the roughed intermediate billet is sent to the finishing rolling mill for continuous rolling, the finishing rolling roughing temperature is controlled at 930°C, and the finish rolling temperature is controlled at 880°C; Step six: laminar cooling, the multi-stage laminar cooling system is used to control the cooling of the strip after finishing rolling, and the cooling rate is controlled at 25℃ / s; Step seven: coiling process, the cooled strip is sent to the coiler for coiling, and the coiling temperature is controlled at 650℃.

[0041] Step one: blank pre-treatment, including the following steps: using a shot blasting machine to clean the surface of the slab, removing the scale and impurities, sending the cleaned slab to a preheating furnace, preheating at 800℃ for 2 hours, and then transferring the slab to a soaking furnace, soaking at 1200℃ for 2.5 hours, so that the temperature difference between the core and the surface of the slab is less than 30℃.

[0042] The shot blasting machine uses stainless steel pellets with a diameter of 1.5mm, the projection speed is 80m / s, the treatment time is 20 minutes, the preheating furnace uses natural gas heating, the air-fuel ratio is controlled at 1.15, the soaking furnace uses resistance heating, the heating power is 800kW, the furnace atmosphere is nitrogen protective atmosphere, and the oxygen content is less than 2%.

[0043] The multi-stage temperature heating process in step two uses an intelligent temperature control system, which includes an infrared temperature meter, a furnace temperature sensor and a PLC controller. By real-time monitoring of the slab surface temperature and the temperature distribution in the furnace, the gas flow and air ratio of each heating section are dynamically adjusted to control the slab heating uniformity within ±15℃. The multi-stage temperature heating process includes a preheating section, a heating section and a soaking section, with the preheating section temperature being 950℃, the heating section temperature being 1250℃, and the soaking section temperature being 1250℃. The total heating time is controlled at 4.5 hours.

[0044] The infrared temperature meter uses double-color infrared temperature measurement technology, with a measurement wavelength range of 1.6μm and a temperature measurement accuracy of ±5℃. The furnace temperature sensor uses a K-type thermocouple with a measurement range of 0-1300℃ and an accuracy of ±1.5℃. The PLC controller uses a PID control algorithm with a regulation period of 1.0 seconds, and the output signal controls the gas regulating valve and the air blower speed.

[0045] The high-pressure water descaling in step three includes a descaling box, a high-pressure water pump, a water filter and a nozzle group. The nozzle uses a fan-shaped nozzle with a spray angle of 30°, a nozzle diameter of 3.0mm and a nozzle spacing of 250mm. The descaling water is added with rust inhibitor and surfactant, with the rust inhibitor being sodium phosphate at an addition amount of 0.3% and the surfactant being sodium alkyl benzene sulfonate at an addition amount of 0.1%.

[0046] The rough rolling process in step four adopts a reversible rolling mill, the work roll diameter is 1200 mm, the backup roll diameter is 1600 mm, the rolling speed is controlled at 5 m / s, the lubricating emulsion is used in the rolling process, the emulsion concentration is 5%, the flow rate is 1000 L / min, the emulsion temperature is controlled at 60°C, the rough rolling mill adopts vertical roll and horizontal roll combined rolling, the rolling pass is 7, and the reduction rate of each pass is 25%.

[0047] The finishing rolling process in step five adopts six four-roll finishing rolling mills, the work roll diameter is 800 mm, the backup roll diameter is 1400 mm, the rolling speed is controlled at 15 m / s, the micro tension control is used in the finishing rolling process, the tension is 15 kN, and the AGC thickness automatic control system is used, and the thickness control precision is ±0.05 mm.

[0048] The laminar cooling in step six adopts upper and lower header arrangement, the cooling water flow rate of the upper header is 1200 m³ / h, the cooling water flow rate of the lower header is 1000 m³ / h, the multi-section laminar cooling system includes a front section fast cooling zone, a middle section slow cooling zone and a rear section adjusting zone, the cooling water flow rate is dynamically adjusted according to the strip thickness and speed, the cooling water is added with scale inhibitor and corrosion inhibitor, the scale inhibitor is sodium polyacrylate, the addition amount is 0.1%, the corrosion inhibitor is sodium molybdate, the addition amount is 0.05%, and the strip surface temperature uniformity after cooling is controlled within ±20°C.

[0049] The coiling process in step seven adopts a three-assisted coiling roll type coiler, the coiling tension is controlled at 100 kN, the coiling speed is synchronized with the rolling speed, the steel coil after coiling is slowly cooled, the cooling rate in the holding pit is 2°C / h to room temperature, the holding pit temperature is 500°C, and the holding time is 24 hours.

[0050] Comparative Example 1, the difference between the comparative example and Example 1 is that the multi-section variable temperature heating process is not used in the dynamic heating control process of the comparative example.

[0051] Comparative Example 2, the difference between the comparative example and Example 1 is that the antirust agent and the surfactant are not added in the descaling water in the high-pressure water descaling process of the comparative example.

[0052] Comparative Example 3, the difference between the comparative example and Example 1 is that the lubricating emulsion is not used in the rough rolling process of the comparative example.

[0053] Comparative Example 4, the difference between the comparative example and Example 1 is that the scale inhibitor and the corrosion inhibitor are not added in the cooling water in the laminar cooling process of the comparative example.

[0054] The Q355B steel hot-rolled plates prepared in Examples 1-3 and Comparative Examples 1-4 are subjected to performance testing, and the test items and test methods are as follows: Mechanical property testing, using a universal material testing machine, standard tensile specimens were prepared to determine the yield strength, tensile strength and elongation at break; standard V-notch impact specimens were prepared to determine the impact energy absorption at room temperature.

[0055] Surface quality testing, under natural light or equivalent lighting conditions, with an illumination of > 500 lux, 100% visual inspection of the strip steel upper and lower surfaces to evaluate the severity and distribution of residual mill scale, pressed-in mill scale, cracks, and scarring defects.

[0056] Microstructure analysis, metallographic specimens were taken along the rolling direction, after grinding and polishing, using 4% nitric acid alcohol solution etching, observed and recorded the microstructure, grain size and distribution uniformity under the optical microscope, and calculated the average grain size grade.

[0057] Hardness testing, at least 5 test points were selected from the surface to the center of the cross-section of the specimen, applying a test force of 10 kgf, 98.07 N, with a load holding time of 15 seconds, measuring the Vickers hardness value and calculating the average value.

[0058] Cooling rate verification, at the outlet of the laminar cooling section, using a calibrated non-contact infrared temperature measuring instrument to continuously measure the strip steel surface temperature, recording the temperature-time curve of the head, middle and tail of the strip steel within the set cooling interval, calculating the actual cooling rate and comparing it with the process set value.

[0059] The test data of the Q355B steel hot-rolled plates prepared in Examples 1-3 and Comparative Examples 1-4 are recorded in the following table: By comparing and analyzing the data in the table, it can be seen that the Q355B hot-rolled steel plate prepared by the process in Examples 1-3 has more excellent performance compared to the Q355B hot-rolled steel plate prepared by the process in Comparative Examples 1-4. This shows that by constructing a synergistic system of multi-section variable temperature heating and intelligent temperature control, the temperature distribution in the furnace and the heating rate are monitored and dynamically adjusted in real time, ensuring that the core and surface temperatures of the slab are uniform and consistent, eliminating thermal stress and internal crack tendency during heating, and providing a high-temperature billet with uniform structure and stable performance for subsequent rolling; at the same time, the high-pressure water descaling system optimizes the jet parameters and introduces chemical additives to form a protective layer while removing the surface iron oxide scale, improving the cleanliness and quality of the slab surface, and avoiding product defects caused by incomplete descaling and surface damage. By setting the temperature window, deformation parameters and integrating micro-tension and thickness automatic control, the rough rolling and finishing rolling processes are carried out under the best thermodynamic conditions, ensuring sufficient deformation penetration and uniform grain refinement, and improving the mechanical properties and dimensional accuracy of the products; at the same time, the laminar cooling system adopts a multi-section partition design and a dynamic flow control strategy, which adjusts the cooling intensity based on the real-time state of the strip, controls the phase change process, eliminates the performance fluctuations and residual stress in the length direction, and ensures the high uniformity and stability of the product structure and performance. The process parameters from heating, descaling, rolling to cooling and coiling are systematically integrated and synergistically optimized based on the dynamic temperature control concept, forming a closed-loop feedback and accurate matching between each link, realizing real-time response and dynamic correction of the global process window; finally, through controllable coiling and slow cooling process, internal stress is eliminated and material structure is stabilized, comprehensively improving the consistency of product comprehensive performance, shape accuracy and stability.

[0060] By comparing and analyzing the relevant data in the table, it can be seen that the Q355B hot-rolled steel plate prepared by the optimized process has higher strength, better toughness and elongation, and improved surface quality, which shows that the Q355B steel hot-rolling process optimization method based on dynamic temperature control provided by the present application can improve the comprehensive performance of the product, has a wider market prospect, and is more suitable for promotion.

[0061] It should be noted that, in this document, relational terms such as first and second and the like can be used solely to distinguish one entity or action from another entity or action without necessarily requiring or implying any actual such relationship or order between such entities or actions. Moreover, the terms "comprises", "comprising", or any other variations thereof, are intended to cover a non-exclusive inclusion, such that a process, method, article, or apparatus that comprises a list of elements does not include only those elements but can include other elements not expressly listed or inherent to such process, method, article, or apparatus. An element proceeded by "comprises... a" does not, without more constraints, exclude the existence of additional identical elements in the process, method, article, or apparatus that comprises the element.

[0062] While embodiments of the application have been shown and described, it is to be understood that the application is not limited to the details of the embodiments described, since numerous changes, modifications, substitutions and variations can be made thereto without departing from the spirit and scope of the application as defined by the appended claims and their equivalents.

Claims

1. A method for optimizing the hot rolling process of Q355B steel based on dynamic temperature control, characterized in that: Includes the following steps: Step 1: Billet pretreatment. Select Q355B continuous casting slab with a thickness of 200-250mm, and perform surface cleaning, preheating and homogenization treatment on it. Step 2: Dynamic heating control. The pretreated slab is fed into a walking beam furnace, and a multi-stage variable temperature heating process is used to control the temperature distribution and heating rate inside the furnace. Step 3: High-pressure water descaling. High-pressure water jets are used to descale the surface of the heated slab. The water pressure range is 18-25 MPa, and the water temperature is controlled at 30-50℃. Step 4: Rough rolling process. The descaled slab is fed into the rough rolling mill for multiple rolling passes. The initial rolling temperature is controlled at 1050-1150℃ and the final rolling temperature is controlled at 950-1000℃. Step 5: Finishing rolling process. The intermediate billet after rough rolling is sent to the finishing rolling mill for continuous rolling. The starting rolling temperature is controlled at 880-930℃ and the finishing rolling temperature is controlled at 820-880℃. Step 6: Laminar flow cooling. A multi-stage laminar flow cooling system is used to control the cooling of the finished strip, with the cooling rate controlled at 5-25℃ / s. Step 7: Coiling process. The cooled strip is fed into a coiler for coiling, and the coiling temperature is controlled at 550-650℃.

2. The method for optimizing the hot rolling process of Q355B steel based on dynamic temperature control according to claim 1, characterized in that: The aforementioned billet pretreatment process includes the following steps: cleaning the surface of the billet using a shot blasting machine to remove iron oxide scale and impurities; sending the cleaned billet into a preheating furnace and preheating it at 600-800℃ for 1-2 hours; then transferring the billet into a soaking furnace and soaking it at 1100-1200℃ for 1.5-2.5 hours to ensure that the temperature difference between the core and surface of the billet is less than 30℃.

3. The method for optimizing the hot rolling process of Q355B steel based on dynamic temperature control according to claim 2, characterized in that: The shot blasting machine uses stainless steel shot with a diameter of 1.0-1.5mm, a blasting speed of 60-80m / s, and a processing time of 10-20 minutes. The preheating furnace is heated by natural gas with an air-fuel ratio controlled at 1.05-1.

15. The soaking furnace uses resistance heating with a heating power of 500-800kW. The atmosphere inside the furnace is a nitrogen protective atmosphere with an oxygen content of less than 2%.

4. The method for optimizing the hot rolling process of Q355B steel based on dynamic temperature control according to claim 1, characterized in that: The multi-stage variable temperature heating process in step two employs an intelligent temperature control system. This system includes an infrared thermometer, a furnace temperature sensor, and a PLC controller. By monitoring the surface temperature of the slab and the temperature distribution inside the furnace in real time, it dynamically adjusts the gas flow rate and air ratio of each heating section to control the heating uniformity of the slab within ±15℃. The multi-stage variable temperature heating process includes a preheating section, a heating section, and a soaking section. The temperature of the preheating section is 800-950℃, the temperature of the heating section is 1150-1250℃, and the temperature of the soaking section is 1200-1250℃. The total heating time is controlled within 2.5-4.5 hours.

5. The method for optimizing the hot rolling process of Q355B steel based on dynamic temperature control according to claim 4, characterized in that: The infrared thermometer uses dual-color infrared temperature measurement technology, with a measurement wavelength range of 1.0-1.6μm and a temperature measurement accuracy of ±5℃. The furnace temperature sensor uses a K-type thermocouple, with a measurement range of 0-1300℃ and an accuracy of ±1.5℃. The PLC controller uses a PID control algorithm, with an adjustment cycle of 0.5-1.0 seconds, and outputs signals to control the gas regulating valve and the air fan speed.

6. The method for optimizing the hot rolling process of Q355B steel based on dynamic temperature control according to claim 1, characterized in that: Step three, high-pressure water descaling, includes a descaling tank, a high-pressure water pump, a water filter, and a nozzle assembly. The nozzles are fan-shaped with a spray angle of 15-30°, a nozzle diameter of 2.0-3.0 mm, and a nozzle spacing of 150-250 mm. The descaling water contains a rust inhibitor and a surfactant. The rust inhibitor is sodium phosphate, added at a concentration of 0.1-0.3%, and the surfactant is sodium alkylbenzene sulfonate, added at a concentration of 0.05-0.1%.

7. The method for optimizing the hot rolling process of Q355B steel based on dynamic temperature control according to claim 1, characterized in that: In step four, the roughing process uses a reversible mill with a work roll diameter of 1000-1200mm and a support roll diameter of 1400-1600mm. The rolling speed is controlled at 2-5m / s. A lubricating emulsion is used during the rolling process, with an emulsion concentration of 3-5%, a flow rate of 500-1000L / min, and an emulsion temperature controlled at 40-60℃. The roughing mill uses a combination of vertical and horizontal rolls for rolling, with 5-7 rolling passes and a reduction rate of 15-25% per pass.

8. The method for optimizing the hot rolling process of Q355B steel based on dynamic temperature control according to claim 1, characterized in that: In step five, the finishing rolling process uses a six-stand four-high finishing mill with a work roll diameter of 700-800mm and a support roll diameter of 1200-1400mm. The rolling speed is controlled at 8-15m / s. Micro-tension control is used during the finishing rolling process, with a tension range of 5-15kN. An AGC thickness automatic control system is also used, with a thickness control accuracy of ±0.05mm.

9. The method for optimizing the hot rolling process of Q355B steel based on dynamic temperature control according to claim 1, characterized in that: In step six, laminar flow cooling employs an upper and lower manifold arrangement. The cooling water flow rate in the upper manifold is 800-1200 m³ / h, and the cooling water flow rate in the lower manifold is 600-1000 m³ / h. The multi-stage laminar flow cooling system includes a front-stage rapid cooling zone, a middle-stage slow cooling zone, and a rear-stage adjustment zone. The cooling water flow rate is dynamically adjusted according to the strip thickness and speed. Scale inhibitors and corrosion inhibitors are added to the cooling water. The scale inhibitor is sodium polyacrylate, with an addition amount of 0.05-0.1%, and the corrosion inhibitor is sodium molybdate, with an addition amount of 0.02-0.05%. After cooling, the surface temperature uniformity of the strip is controlled within ±20℃.

10. The method for optimizing the hot rolling process of Q355B steel based on dynamic temperature control according to claim 1, characterized in that: In step seven, the coiling process uses a three-aid coiler with coiling tension controlled at 50-100kN. The coiling speed is synchronized with the rolling speed. The coiled steel coil is subjected to slow cooling treatment, which is slow cooling to room temperature in a heat preservation pit at a cooling rate of 0.5-2℃ / h. The temperature of the heat preservation pit is 300-500℃, and the heat preservation time is 12-24 hours.

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