CN115652211B - Economical 420 MPa-level steel plate cooling uniformity control method for engineering structure - Google Patents
Economical 420 MPa-level steel plate cooling uniformity control method for engineering structure Download PDFInfo
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- Y—GENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; GENERAL TAGGING OF CROSS-SECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
- Y02—TECHNOLOGIES OR APPLICATIONS FOR MITIGATION OR ADAPTATION AGAINST CLIMATE CHANGE
- Y02P—CLIMATE CHANGE MITIGATION TECHNOLOGIES IN THE PRODUCTION OR PROCESSING OF GOODS
- Y02P10/00—Technologies related to metal processing
- Y02P10/20—Recycling
Abstract
The invention discloses a control method for cooling uniformity of a steel plate for an economic 420 MPa-level engineering structure, which comprises the following chemical components in percentage by weight: 0.14 to 0.17 percent of C, 0.25 to 0.35 percent of Si, 1.05 to 1.15 percent of Mn, less than or equal to 0.025 percent of P, less than or equal to 0.02 percent of S, 0.02 to 0.04 percent of Nb, 0.015 to 0.02 percent of Ti, 0.015 to 0.045 percent of Al, 0.003 to 0.006 percent of N, the balance of Fe and unavoidable impurities, less than or equal to 0.0050 percent of O, and the total amount of other impurity elements is less than 0.05 percent. The method comprises the steps of molten steel smelting, external refining, continuous casting, slab reheating, controlled rolling, controlled cooling and air cooling to room temperature. The invention is used for improving the cooling uniformity of the 420MPa grade ultra-long steel plate with the thickness of 6-20mm and the length of 36-55m in the length direction of the rolled steel plate.
Description
Technical Field
The invention belongs to the technical field of low-carbon microalloyed steel production, and particularly relates to a cooling uniformity control method for a 420 MPa-level steel plate for an economic engineering structure, wherein the thickness specification is 6-20mm and the length specification is 36-50m.
Background
The medium plate variety of 420MPa grade is the main variety type of the medium plate, typical varieties are bridge structural steel Q420qC/D/E, pipeline steel X56 and the like, the steel is mainly based on carbon manganese steel, and carbon and nitride forming elements such as microalloy elements Nb, V, ti and the like are added into the steel, so that the toughness of the steel plate is improved through solid solution strengthening, precipitation strengthening and fine crystal strengthening. The medium plates at this intensity level are counted to account for 20-30% of the production per year. Therefore, development of such low-cost steel sheet manufacturing technology research is of great significance. The lower the carbon content of the steel for engineering structure of the higher grade is, the higher the addition amount of the alloy element is. The production cost of the structural steel is correspondingly increased while the quality grade of the structural steel is continuously improved. For 420MPa steel grade structural steel with special requirements on low-temperature toughness, a low-carbon component design with carbon content below 0.10% is traditionally adopted, the manganese content is higher in the range of 1.2% -1.55%, and alloy elements such as niobium, vanadium, titanium and the like are added to ensure the performance, so that the production cost is relatively high. If the medium and high carbon components are adopted to replace the low carbon component design, the addition of alloy elements in steel is reduced, and meanwhile, the process optimization is carried out on the steelmaking, heating, rolling and cooling control production paths, particularly the system optimization is carried out on the cooling control process after rolling, so that the production cost is greatly reduced.
Because the TMCP process (thermo-mechanical control process) produces high-strength and high-toughness steel without adding excessive alloy elements or complex subsequent heat treatment, the TMCP process is considered to be an alloy and energy-saving process which is beneficial to environmental protection, and has become an indispensable technology for producing low-alloy high-strength wide-thickness plates. As the market demands for TMCP steel continue to increase, the TMCP process itself is also continually evolving in application. From the research effort in recent years, emphasis has been placed on controlling cooling, especially in terms of accelerated cooling. By accelerating the cooling rate after rolling, not only the growth of crystal grains can be suppressed, but also the ultra-fine ferrite structure or bainite structure, or even the martensite structure, required for high strength and high toughness can be obtained. However, with the optimization of alloy reduction, steelmaking and heating processes of the 420 MPa-level steel plate, the alloy and the steel plate subjected to process reduction are required to be more strictly designed for the TMCP process production process, and with the reduction of alloy content, rolling and cooling control process windows are narrower and narrower. In addition, with the strong competition of thick plate market, each big steelworks increases the length of thin steel plates to increase the rolling singles, thereby achieving the effect of saving cost. For the TMCP type ultra-long steel plate with the level of 420MPa after the reduction, the performance fluctuation caused by uneven cooling of the steel plate in the length direction is a constraint factor for popularization due to rapid temperature drop of the head and the tail of the steel plate and narrow cooling process window after the alloy reduction.
Therefore, how to solve the problems of the cooling uniformity in the length direction of the 420MPa grade steel grade engineering structural steel with the production thickness of 6-20mm, reduce the production cost, improve the performance qualification rate of the steel plate, and is a key problem to be solved in the mass production process of the 420MPa grade steel grade engineering structural steel with the thickness specification (6-20 mm) and the length specification (36-55 m).
Compared with the prior art:
so far, few research reports on the cooling uniformity control of the ultra-long steel plate for 420MPa engineering structures at home and abroad are provided. Prior to the present invention, application No. CN 103599950B discloses an accelerated cooling device for improving cooling uniformity of a steel plate, wherein an initial speed V of the steel plate is set by adopting accelerated cooling for the steel plate 0 And termination speed V 1 The temperature difference in the length direction is reduced, so that the steel plate is cooled more uniformly, and the structural performance of the steel plate is improved. However, the invention still does not solve the problem that the structure and the performance of the head and the tail of the ultra-long steel plate are inconsistent with those of other positions of the steel plate due to rapid temperature drop, and meanwhile, the cooling length of the steel plate is not clarified. CN 112387789B discloses a method for improving cooling uniformity of TMCP steel plate, which performs constraint cooling on the steel plate in a water cooling area of TMCP production line, and sets the initial speed of roller table to V 0 The final speed of the roller way is set as V, and 0 is less than V-V 0 Less than or equal to 0.5m/s; the length of the steel plate is 45-52 m, the water cooling area is provided with a plurality of water cooling partitions along the length direction of the steel plate, and a plurality of nozzles are arranged on the upper surface and the lower surface of the steel plate along the width direction of the steel plate in the water cooling partitions, but different nozzles and pressures are adopted for different positions of the steel plate; the equipment cost is increased, and meanwhile, the control process is only limited to the length of 45-52 m of the steel plate, so that the limitation is narrow. The patent of CN201811450143.7 discloses a method for producing a thin steel plate for a low yield ratio bridge construction, wherein the steel plate has the components C of 0.10-0.15 and Si of less than or equal to 0.50,mn=1.20-1.50, P is less than or equal to 0.015, S is less than or equal to 0.005, alt=0.02-0.05, ti=0.008-0.025, nb is less than or equal to 0.020, cr=0.25-0.50, in order to make the steel plate possess high strength and excellent low-temperature toughness, the scheme needs to add higher metal elements such as Mn, nb, cr and the like on component design, alloy cost is higher, and tempering at high temperature is needed after rolling, so that production cost is higher. The patent of application No. CN201010243234.0 discloses an X56 pipeline steel and a production method thereof, wherein the X56 pipeline steel comprises the following chemical components of 0.060-0.090% of C, 0.20-0.30% of Si, 1.30-1.50% of Mn, less than or equal to 0.008% of S, less than or equal to 0.020% of P, 0.035-0.055% of Nb, 0.020-0.040% of V, 0.010-0.022% of Ti, less than or equal to 0.008% of N and 0.010-0.040% of Als, in order to ensure that the steel plate has high strength and excellent low-temperature toughness, the scheme needs to be added with metal elements such as higher Mn, nb and the like on the component design, has higher alloy cost, and the production process is not clear for coiled plates and thickness specifications.
The studies disclosed in the above patent documents solve the problem of cooling uniformity of a part of steel plates, but they are high in production and manufacturing cost or narrow in length range of the controlled cooling steel plates, and are not suitable for producing a steel plate for an engineering structure having excellent cooling uniformity and being ultra-long at 420MPa level. By using the technical scheme provided by the invention, the defects can be effectively overcome, the continuous casting billet with the thickness of 150-200mm is used for producing the 420 MPa-level steel plate with the thickness of 6-20mm and the length of 36-55m by means of head-tail shielding model optimization, dynamic adjustment of the micro-tracking position of the steel plate, response time control of a cold flow control regulating valve and the like, the whole plate has good cooling uniformity, and the strength of the same plate difference at any position of the head, middle and tail of the steel plate is within 30MPa.
Disclosure of Invention
The invention aims to overcome the technical problems and defects, and provides a method for improving the cooling uniformity of a 420MPa grade ultra-long steel plate with the thickness of 6-20mm and the length of 36-55m in the length direction of the rolled steel plate, and simultaneously reducing the alloy cost of the steel plate, improving the rolling efficiency, improving the performance uniformity of the same plate difference of the steel plate and the like.
The invention provides a control method for improving cooling uniformity of a steel plate for an economic 420 MPa-level engineering structure, which can effectively solve the problem of uniform cooling of the steel plate for the 420 MPa-level engineering structure in the length direction, simultaneously can reduce the production and manufacturing cost, improve the rolling production efficiency, improve the qualification rate and control performance uniformity, and has the thickness of 6-20mm and the length of 36-55m, wherein a continuous casting blank with the thickness of 150-200mm is used for production on a medium plate reciprocating mill, and the cooling medium is water.
In order to achieve the above purpose, the technical scheme of the invention is as follows:
a steel plate cooling uniformity control method for an economic 420 MPa-level engineering structure comprises the following chemical components in percentage by weight: 0.14 to 0.17 percent of C, 0.25 to 0.35 percent of Si, 1.05 to 1.15 percent of Mn, less than or equal to 0.025 percent of P, less than or equal to 0.02 percent of S, 0.02 to 0.04 percent of Nb, 0.015 to 0.02 percent of Ti, 0.015 to 0.045 percent of Al, 0.003 to 0.006 percent of N, the balance of Fe and unavoidable impurities, less than or equal to 0.0050 percent of O, and the total amount of other impurity elements is less than 0.05 percent.
The thickness of the steel plate for the economic 420MPa level engineering structure is 6-20mm, and the length is 3-55m.
The main elements in the chemical components of the steel plate of the invention have the following functions:
c: the most economical and basic strengthening elements in the steel have obvious effects on improving the strength of the steel through solid solution strengthening and precipitation strengthening, but improving the C content has negative effects on the plasticity, toughness and weldability of the steel. For this reason, the present invention sets the C content to a range of 0.014% to 0.17%.
Mn: the strength of the steel is improved by solid solution strengthening while compensating for the loss of strength of the steel sheet due to the decrease in the C content. In addition, the gamma-alpha transformation temperature can be reduced, ferrite grains are further refined, fine low-temperature transformation products are facilitated to be obtained, and the toughness of the products is improved. However, increasing the Mn content can aggravate the center segregation and the tissue deterioration of the continuous casting billet, is unfavorable for the improvement of the low-temperature toughness of the steel plate, and cannot ensure the uniformity of the cross-section tissue of the steel plate. Therefore, the Mn content range of the present invention is designed to be 1.05% to 1.15%.
Nb: is one of common elements in modern microalloyed pipeline steel, and has good fine grain strengthening and precipitation strengthening effects; austenite recrystallization is also delayed, but excessive Nb increases production costs and difficulty in continuous casting process control. theinventionselectsNbcontentrangeof0.02%-0.04%,andcanobtainuniformcompositephasewithacicularferriteorM-AislandformationstructureasmaincomponentbymatchingwithreasonableTMCPprocess,sothatthecompositephasehasgoodtoughness.
Si: has the functions of deoxidizing steel and improving the strength of the matrix. However, excessive Si can reduce the toughness of a welding heat affected zone of the base material, improve the content of Si, purify ferrite, reduce the content of pearlite and be beneficial to reducing the Bactger effect of the base material. Accordingly, the Si content is set to 0.25% to 0.35% in the present invention.
Al: it is usually used as a deoxidizer in steel and has the effect of refining the structure if AlN is formed. When the Al content exceeds 0.045%, excessive aluminum oxide inclusions may reduce the cleanliness of the steel. If the Al content is too low, deoxidization is insufficient, and oxides are formed from easily oxidized elements such as Ti, so that the lower limit of the Al content is set to 0.015%.
N: the N element in the steel has no obvious effect except forming fine TiN grain refined austenite grains, so that the N element needs to be kept at a lower content level, and the N content range selected by the invention is 0.003-0.006 percent.
Ti: is a strong solid N element, and exists in the form of TiN in the continuous casting billet. The fine TiN particles can effectively inhibit the growth of austenite grains when the continuous casting billet is reheated, and are beneficial to improving the solid solubility of Nb in austenite and improving the impact toughness of a welding heat affected zone. When the Ti addition exceeds a certain value, tiN particles coarsen, and the stress concentration level of the particle interface and the matrix is improved. Therefore, the invention selects the Ti content range of 0.015-0.02%.
P, S: is an unavoidable impurity element in steel, and should be as low as possible. But cannot be infinitely low due to smelting costs and process considerations. Therefore, the upper limit of the P, S content is set to 0.025% and 0.02% in the present invention.
The aim of the invention is realized by the following technical scheme: the invention relates to a method for controlling cooling uniformity of a steel plate for an economic 420 MPa-level engineering structure, which comprises the steps of molten steel smelting, external refining, continuous casting, slab reheating, controlled rolling, controlled cooling, air cooling to room temperature, and specifically comprises the following steps:
1) Steelmaking and continuous casting: smelting according to the following components, wherein the weight percentages of the chemical components are 0.14-0.17% of C, 0.25-0.35% of Si, 1.05-1.15% of Mn, less than or equal to 0.025% of P, less than or equal to 0.02% of S, 0.02-0.04% of Nb, 0.015-0.02% of Ti, 0.015-0.045% of Al, 0.003-0.006% of N, the balance of Fe and unavoidable impurities, less than or equal to 0.0050% of O and the total amount of other impurity elements is less than 0.05%. Raw materials are pretreated by KR molten iron, the content of S is controlled to be lower than 0.02 percent, and the raw materials enter a converter after slag skimming; the double slag method is adopted to remove P in the converter smelting, the content of P is controlled to be less than or equal to 0.025 percent, the content of C is controlled to be 0.14 to 0.17 percent at the end point of the converter smelting, and argon is blown for 20 to 30 minutes during tapping; then LF refining is carried out, then slab continuous casting is carried out, the continuous casting superheat degree is 25-30 ℃, the secondary cooling water cooling strength is 2-3L/Kg, the continuous casting blank drawing speed is 0.6-0.9 m/min, electromagnetic stirring is not added (the superheat degree is improved, the secondary cooling strength is accelerated to promote C, mn diffusion, segregation is reduced, the electromagnetic stirring is not added to reduce the equiaxial crystal proportion, and center segregation is reduced); putting light reduction into a horizontal sector section, namely a solidification tail end, wherein the reduction of a continuous casting billet is 6-10 mm;
2) Heating a casting blank: feeding a casting blank (with the thickness of 150-200 mm) into a step-type heating furnace for heating, and discharging the casting blank after passing through a preheating section, a heating section and a soaking section in sequence; the preheating section temperature interval is 950-1100 ℃ (the carbide and nitride of Nb and Ti are promoted to be quickly and fully dissolved in the matrix and fully diffused), the heating section temperature interval is 1150-1180 ℃, the soaking section temperature interval is 1150-1170 ℃, and the furnace time is 3.5-4.5 hours (the elements such as C, N are further uniformly distributed, and the furnace time and the heating temperature are controlled at the same time) to inhibit the excessive growth of original austenite grains;
3) High-pressure water descaling and controlled rolling: descaling the casting blank after tapping by using high-pressure water for 1-2 min before starting rolling, wherein the pressure of a descaling machine is 20-25 MPa; rolling in two stages: the first stage is that the initial rolling temperature of recrystallization rolling (rough rolling) is more than or equal to 1100 ℃, the final rolling temperature interval of rough rolling is 960-990 ℃, the rough rolling is not more than six times, the pass rolling system is that the first two times ensure the rolling reduction rate to be more than 20%, the last three times have one time not less than 10%, and the thickness of the obtained intermediate blank is 3-4 times of the thickness of the finished product; the second stage is that the temperature range of the non-crystallization rolling (finish rolling) is 870-920 ℃, the temperature range of the finish rolling is 770-840 ℃, the finish rolling is not more than four times, the pass rolling system is that the first two passes ensure the rolling reduction to be more than 15%, the second passes ensure the last pass to have one pass not less than 10%, the deformation of the last pass is controlled below 5mm, the steel is rapidly thrown after rolling, and the steel throwing speed is 5-7 m/s;
4) And (3) controlling cooling: the steel plate cooling temperature range is 710-750 ℃, the final cooling temperature range is 520-540 ℃, the cooling speed is controlled to be 15-20 ℃/s, a sample is divided according to the length of each 1.5-2 m from the head, the initial running speed of each 1/12L part (L is the length of the steel plate) from the head to the tail after the steel plate enters laminar flow is set according to the thickness group distance of the steel plate, the initial running speed of each 1/12L part from the head to the tail is 1.3-1.5 times of the normal roller way running speed, the head and tail shielding value is 600-1200 mm, the roller way running speed is kept for 3-6 s, the normal running speed of the steel plate is recovered to be 1-2 m/s, and the head and tail water yield of the steel plate is controlled to be 75-85 percent of the normal water stable water yield (the normal water yield is 2500-3000 m) 3 /h); the side spraying opening and the air blowing opening after the steel plate is cooled are carried out, and the side spraying pressure and the water quantity are 2-3 MPa and 60-120 m 3 And/h, the wind sweeping pressure is 10-15 MPa, and then the air cooling is carried out to the room temperature. By adopting the components and the controlled rolling and cooling scheme, the defects in the prior art are overcome, the problem of uniformity in cooling of the rolled steel plate in the length direction of 420MPa level is solved, and meanwhile, the problems of reduction of the alloy cost of the steel plate, improvement of the rolling efficiency, reduction of the uniformity of the performance of the same plate difference of the steel plate and the like are solved.
The invention has the beneficial effects that:
(1) The KR molten iron pretreatment is clean in slag skimming after deep desulfurization, the converter adopts a double slag method to remove P, the P, S content of a casting blank is lower, and the argon blowing time is controlled, so that the defects of center segregation, inclusion, H, O content exceeding standard and the like of the casting blank caused by higher Mn content are overcome, and the plastic toughness of the steel plate is improved. The degree of superheat of the continuous casting blank, the cooling strength of secondary cooling water and the blank pulling rate are reasonably controlled, electromagnetic stirring is not input, and under light pressure, the steel blank segregation and the central loosening grade are reduced, austenite grains are refined, internal structure defects are reduced, and the performance uniformity of the finished steel plate is improved.
(2) The invention has reasonable components and low alloy addition, reduces Mn content by increasing C content, greatly reduces alloy cost by adding a small amount of microalloy elements Nb and Ti, reduces high-temperature deformation resistance in rough rolling and finish rolling stages by adopting high-temperature rolling, is beneficial to improving reduction of each pass and is beneficial to ensuring comprehensive performance of the steel plate.
(3) The rolling process is controlled in two stages, the reduction of rough rolling and finish rolling passes is controlled, the thickness of an intermediate blank is reduced, meanwhile, the initial rolling temperature of finish rolling is improved, relaxation waiting is not needed after rolling, and the rolling efficiency of the steel plate is improved.
(4) In order to realize temperature uniformity control in the length direction of the steel plate, a sample is divided into samples according to the length of each 1.5 m from the head, on the basis, each model (temperature, flow, acceleration) and the like performs speed optimization calculation on each sample section, and the control model obtains the optimal running speed trend of each sample according to a steel plate longitudinal temperature measured value, a target final cooling temperature process requirement and a head-tail shielding value calculation formula (head-tail shielding value=HMI interface set shielding distance-shielding time roller speed). For the low-temperature area that steel sheet head and afterbody exist, when steel sheet head gets into laminar flow area or afterbody leaves laminar flow area, according to thickness group distance, suitably increase roll table speed, control head, the tail position water flow of going out in order to reduce the excessive cooling of cooling water to steel sheet head and tail, through side spout and wind blowing input, be favorable to the control of steel sheet shape, improve steel sheet performance uniformity, reduce the probability of buckling head, buckling tail board shape problem, save follow-up cold straightening equipment input cost.
(5) The invention reduces the alloy cost through simple component design, and obtains the control method for the cooling uniformity of the steel plate with the thickness specification of 6-20mm, the length specification of 36-55m and the economic engineering structure of 420MPa level through regulating and controlling the steelmaking, continuous casting and controlled rolling and controlled cooling processes. The specific performance is as follows: the transverse tensile yield strength performance is between 450 and 480MPa, the tensile strength is between 550 and 580MPa, the elongation is more than or equal to 20 percent, and the head-in-tail plate difference strength is less than or equal to 30MPa.
Detailed Description
The following examples are given to illustrate the present invention in detail, but are merely a general description of the present invention and are not intended to limit the present invention.
The economical control method for the cooling uniformity of the steel plate for the 420 MPa-level engineering structure comprises the steps of molten steel smelting, external refining, continuous casting, slab reheating, controlled rolling, controlled cooling and air cooling to room temperature, and specifically comprises the following steps:
1) Steelmaking and continuous casting: smelting according to the following components, wherein the weight percentages of the chemical components are 0.14-0.17% of C, 0.25-0.35% of Si, 1.05-1.15% of Mn, less than or equal to 0.025% of P, less than or equal to 0.02% of S, 0.02-0.04% of Nb, 0.015-0.02% of Ti, 0.015-0.045% of Al, 0.003-0.006% of N, the balance of Fe and unavoidable impurities, less than or equal to 0.0050% of O and the total amount of other impurity elements is less than 0.05%. Raw materials are pretreated by KR molten iron, the content of S is controlled to be lower than 0.02 percent, and the raw materials enter a converter after slag skimming; the double slag method is adopted to remove P in the converter smelting, the content of P is controlled to be less than or equal to 0.025 percent, the content of C is controlled to be 0.14 to 0.17 percent at the end point of the converter smelting, and argon is blown for 20 to 30 minutes during tapping; then LF refining is carried out, then slab continuous casting is carried out, the continuous casting superheat degree is 25-30 ℃, the cooling intensity of secondary cooling water is 2-3L/Kg, the continuous casting blank drawing speed is 0.6-0.9 m/min, and electromagnetic stirring is not carried out; putting light reduction into a horizontal sector section, namely a solidification tail end, wherein the reduction of a continuous casting billet is 6-10 mm;
2) Heating a casting blank: feeding a casting blank (with the thickness of 150-200 mm) into a step-type heating furnace for heating, and discharging the casting blank after passing through a preheating section, a heating section and a soaking section in sequence; the preheating section temperature interval is 950-1100 ℃, the heating section temperature interval is 1150-1180 ℃, the soaking section temperature interval is 1150-1170 ℃, and the furnace time is 3.5-4.5 hours;
3) High-pressure water descaling and controlled rolling: descaling the casting blank after tapping by using high-pressure water for 1-2 min before starting rolling, wherein the pressure of a descaling machine is 20-25 MPa; rolling in two stages: the first stage is that the initial rolling temperature of recrystallization rolling (rough rolling) is more than or equal to 1100 ℃, the final rolling temperature interval of rough rolling is 960-990 ℃, the rough rolling is not more than six times, the pass rolling system is that the first two times ensure the rolling reduction rate to be more than 20%, the last three times have one time not less than 10%, and the thickness of the obtained intermediate blank is 3-4 times of the thickness of the finished product; the second stage is that the temperature range of the non-crystallization rolling (finish rolling) is 870-920 ℃, the temperature range of the finish rolling is 770-840 ℃, the finish rolling is not more than four times, the pass rolling system is that the first two passes ensure the rolling reduction to be more than 15%, the second passes ensure the last pass to have one pass not less than 10%, the deformation of the last pass is controlled below 5mm, the steel is rapidly thrown after rolling, and the steel throwing speed is 5-7 m/s;
4) And (3) controlling cooling: the steel plate cooling temperature range is 710-750 ℃, the final cooling temperature range is 520-540 ℃, the cooling speed is controlled to be 15-20 ℃/s, a sample is divided according to the length of each 1.5-2 m from the head, the initial running speed of each 1/12L part (L is the length of the steel plate) from the head to the tail after the steel plate enters laminar flow is set according to the thickness group distance of the steel plate, the initial running speed of each 1/12L part from the head to the tail is 1.3-1.5 times of the normal roller way running speed, the head and tail shielding value is 600-1200 mm, the roller way running speed is kept for 3-6 s, the normal running speed of the steel plate is recovered to be 1-2 m/s, and the head and tail water yield of the steel plate is controlled to be 75-85 percent of the normal water stable water yield (the normal water yield is 2500-3000 m) 3 /h); the side spraying opening and the air blowing opening after the steel plate is cooled are carried out, and the side spraying pressure and the water quantity are 2-3 MPa and 60-120 m 3 And/h, the wind sweeping pressure is 10-15 MPa, and then the air cooling is carried out to the room temperature.
Examples
As shown in the following table, table 1 is the chemical composition of the example steel, table 2 is the smelting process system of the example steel, and table 3 is the heating system of the casting blank of the example steel and the high-pressure water descaling process before continuous casting blank rolling; table 4 shows heating, rolling and partial cooling control parameters of example steels; table 5 shows the reduction of each pass in different rolling stages of the example steel; table 6 is the main cooling control parameters for the example steels; table 7 shows the dimensions and properties of the steel sheets of examples.
TABLE 1 chemical composition (wt.%)
| Examples | C | Si | Mn | Ti | Nb | Al | N |
| 1 | 0.17 | 0.26 | 1.08 | 0.016 | 0.021 | 0.016 | 0.0042 |
| 2 | 0.15 | 0.28 | 1.05 | 0.019 | 0.033 | 0.025 | 0.0031 |
| 3 | 0.16 | 0.34 | 1.15 | 0.020 | 0.035 | 0.039 | 0.0056 |
| 4 | 0.14 | 0.33 | 1.03 | 0.017 | 0.023 | 0.044 | 0.0043 |
| 5 | 0.15 | 0.29 | 1.08 | 0.015 | 0.029 | 0.043 | 0.0049 |
| 6 | 0.16 | 0.26 | 1.12 | 0.017 | 0.039 | 0.017 | 0.0033 |
Note that: impurity element P in steel is less than or equal to 0.025%; s is less than or equal to 0.02 percent; o is less than or equal to 0.0050 percent, and the total content of other impurity elements is less than 0.05 percent.
Table 2 smelting process system of example steel
TABLE 3 heating system of casting blank of example steel and high-pressure water descaling process before continuous casting blank rolling
TABLE 4 heating, rolling and partial Cold control parameters for example steels
TABLE 5 reduction in various passes for example steels at different Rolling stages
TABLE 6 Primary controlled Cold parameters for example steels
Table 7 example steel sheet sizes and properties
| Examples | Thickness of steel plate/mm | Length/m of steel sheet | R t0.5 /MPa (head-middle-tail) | R m /MPa (head-middle-tail) | A％ |
| 1 | 9 | 50 | 462-472-479 | 565-570-573 | 29 |
| 2 | 16 | 42 | 471-476-462 | 572-561-551 | 25 |
| 3 | 10 | 48 | 480-461-473 | 553-561-577 | 28 |
| 4 | 12 | 49 | 460-478-476 | 551-569-572 | 35 |
| 5 | 6 | 55 | 453-478-480 | 561-575-579 | 31 |
| 6 | 20 | 36 | 472-453-465 | 550-578-563 | 30 |
Compared with the prior art, the method for controlling the cooling uniformity of the steel plate for the economic engineering structure by using the 420MPa level has the advantages that the alloy cost is reduced through simple component design, the thickness specification is 6-20mm, the length specification is 36-55m, and the steel plate for the economic engineering structure is obtained through regulating and controlling the steelmaking, continuous casting and controlled rolling and controlled cooling processes. The specific performance is as follows: the transverse tensile yield strength performance is between 450 and 480MPa, the tensile strength is between 550 and 580MPa, the elongation is more than or equal to 20 percent, and the head-in-tail plate difference strength is less than or equal to 30MPa.
The above embodiments are provided to illustrate the technical concept and features of the present invention and are intended to enable those skilled in the art to understand the content of the present invention and implement the same, and are not intended to limit the scope of the present invention. All equivalent changes or modifications made in accordance with the spirit of the present invention should be construed to be included in the scope of the present invention.
Claims (5)
1. A control method for cooling uniformity of a steel plate for an economic 420 MPa-level engineering structure is characterized by comprising the following steps of: the steel plate comprises the following chemical components in percentage by weight: 0.14 to 0.17 percent of C, 0.25 to 0.35 percent of Si, 1.05 to 1.15 percent of Mn, less than or equal to 0.025 percent of P, less than or equal to 0.02 percent of S, 0.02 to 0.04 percent of Nb, 0.015 to 0.02 percent of Ti, 0.015 to 0.045 percent of Al, 0.003 to 0.006 percent of N, the balance of Fe and unavoidable impurities, less than or equal to 0.0050 percent of O, and the total amount of other impurity elements is less than 0.05 percent;
the method comprises the steps of molten steel smelting, external refining, continuous casting, slab reheating, controlled rolling, controlled cooling and air cooling to room temperature, and specifically comprises the following steps:
1) Steelmaking and continuous casting: raw materials are pretreated by KR molten iron, the content of S is controlled to be lower than 0.02 percent, slag is removed, the raw materials enter a converter, the content of P is controlled to be less than or equal to 0.025 percent, the content of C is controlled to be 0.14 to 0.17 percent at the smelting end point of the converter, and argon is blown for 20 to 30 minutes during tapping; LF refining is carried out, then slab continuous casting is carried out, the continuous casting superheat degree is 25-30 ℃, the cooling intensity of secondary cooling water is 2-3L/Kg, the continuous casting blank drawing speed is 0.6-0.9 m/min, and electromagnetic stirring is not added; putting light reduction into a horizontal sector section, namely a solidification tail end, wherein the reduction of a continuous casting billet is 6-10 mm;
2) Heating a casting blank: heating the casting blank in a heating furnace, and discharging the casting blank after passing through a preheating section, a heating section and a soaking section in sequence; wherein the temperature of the preheating section is 950-1100 ℃, the temperature of the heating section is 1150-1180 ℃, the temperature of the soaking section is 1150-1170 ℃, and the furnace time is 3.5-4.5 hours;
3) High-pressure water descaling and controlled rolling: descaling the casting blank after tapping by using high-pressure water for 1-2 min before starting rolling, wherein the pressure of a descaling machine is 20-25 MPa; rolling in two stages: the initial rolling temperature of rough rolling is more than or equal to 1100 ℃, the final rolling temperature of rough rolling is 960-990 ℃, the rough rolling is not more than six times, and the thickness of the obtained intermediate blank is 3-4 times of the thickness of a finished product; the initial rolling temperature of the finish rolling is 870-920 ℃, the final rolling temperature is 770-840 ℃, the finish rolling is no more than four times, the steel is rapidly thrown after rolling, and the steel throwing speed is 5-7 m/s;
4) And (3) controlling cooling: the steel plate has a temperature range of 710-750 ℃ and a final cooling temperature range of 520-540 ℃ and is controlledThe cooling speed is 15-20 ℃/s, the steel plate is divided into one sample according to the length of each 1.5-2.0 m from the head, the initial running speed of each 1/12 part from the head and the tail after the steel plate enters the laminar flow is set according to the thickness of the steel plate, the initial running speed of each 1/12 part from the head and the tail is 1.3-1.5 times of the normal running speed of the roller way, the shielding value of each head and the tail is 600-1200 mm, the roller way is kept for 3-6 s, then the running speed of the roller way is restored to be normal, the normal running speed of the steel plate is 1-2 m/s, the head and the tail water yield of the steel plate is controlled to be 75-85% of the normal water yield, and the normal water yield is 2500-3000 m 3 /h; the side spraying opening and the air blowing opening of the steel plate after the steel plate is cooled are respectively 2-3 MPa and 60-120 m 3 And/h, the wind sweeping pressure is 10-15 MPa, and then the air cooling is carried out to the room temperature.
2. The method according to claim 1, characterized in that: the thickness of the steel plate is 6-20mm, and the length is 36-50m.
3. The method according to claim 1, characterized in that: the thickness of the casting blank is 150-200mm.
4. The method according to claim 1, characterized in that: the rough rolling pass rolling system is that the rolling reduction rate is ensured to be more than 20% in the first two passes, and one pass is not less than 10% in the last three passes; the rolling reduction system of the finish rolling pass is that the rolling reduction rate of the first two passes is more than 15%, the rolling reduction rate of the second pass is more than 10%, and the deformation of the last pass is controlled below 5 mm.
5. The method according to claim 1, characterized in that: the properties of the produced steel plate are as follows: the yield strength of transverse stretching is 450-480 MPa, the tensile strength is 550-580 MPa, the elongation is more than or equal to 20%, and the strength of the same plate difference between the head and the tail is less than or equal to 30MPa.
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