CN114799095A

CN114799095A - Heating-free direct rolling method for steel bars and steel bars rolled by heating-free direct rolling method

Info

Publication number: CN114799095A
Application number: CN202210471382.0A
Authority: CN
Inventors: 钱学海; 周博文; 李显; 李西德; 陈学良; 周从锐; 李宗强
Original assignee: Guangxi Liuzhou Iron and Steel Group Co Ltd
Current assignee: Guangxi Liuzhou Iron and Steel Group Co Ltd
Priority date: 2022-04-28
Filing date: 2022-04-28
Publication date: 2022-07-29
Anticipated expiration: 2042-04-28
Also published as: CN114799095B

Abstract

The embodiment of the invention provides a heating-free direct rolling method for a steel bar and the steel bar rolled by the heating-free direct rolling method, which comprises the following steps: sequentially carrying out blast furnace molten iron smelting, molten iron desulphurization pretreatment, converter molten steel smelting, square billet continuous casting, hot continuous rolling and fixed-length shearing; in the square billet continuous casting process, the difference between the head temperature and the tail temperature of a casting blank is controlled to be 20-40 ℃; in the hot continuous rolling procedure, the difference between the head temperature and the tail temperature of the rolled piece is controlled to be 20-30 ℃. By adopting the technical scheme of the invention, the head-tail temperature difference of the steel bar obtained by adopting the heating-free direct rolling process can be controlled within a reasonable range, and the problem of poor consistency of head-tail strength caused by overlarge head-tail temperature difference is solved. The steel bar rolled by the heating-free direct rolling method comprises the following chemical components in percentage by weight: c: 0.23 Wt%, Si: 0.50 Wt%, Mn: 1.19 Wt%, P: 0.030 Wt%, S: 0.026 Wt%, Nb: 0.002 Wt%, Ti: 0.002 Wt%, Alt: 0.0019 Wt%, V: 0.026 Wt%, N: 0.0075 Wt%.

Description

Heating-free direct rolling method for steel bars and steel bars rolled by heating-free direct rolling method

Technical Field

The invention relates to the technical field of steel production, in particular to a heating-free direct rolling method for a steel bar and the steel bar rolled by the heating-free direct rolling method.

Background

The heating-free direct rolling of the square billet becomes the development direction of the current bar and wire production, and in the process, the casting billet can directly enter a rolling mill for rolling without being reheated by a heating furnace, so that the efficiency is improved, and the production cost is reduced.

In the process of implementing the invention, the inventor finds that at least the following problems exist in the prior art:

because the directly rolled casting blank is not reheated by a heating furnace, the head part of the casting blank is produced in a continuous casting machine firstly, and the tail part of the casting blank is produced later, so that the head part temperature and the tail part temperature of the casting blank are high, the head part mechanical strength and the tail part strength of rolled steel are high, and the quality stability of the product is influenced. Therefore, how to control the temperature difference between the head and the tail of the steel bar within a reasonable range in the square billet direct rolling without heating is the problem to be solved, so that the mechanical properties of the head and the tail of the final finished product are stable.

Disclosure of Invention

The embodiment of the invention provides a heating-free direct rolling method for a steel bar, which aims to solve the problem that the mechanical strength difference of the head and the tail of a finished steel bar product obtained by the existing heating-free direct rolling mode is large.

In order to achieve the above object, an embodiment of the present invention provides a method for directly rolling a steel bar without heating, including:

sequentially carrying out blast furnace molten iron smelting, molten iron desulphurization pretreatment, converter molten steel smelting, square billet continuous casting, hot continuous rolling and fixed-length shearing;

wherein, the blank heating procedure between the square billet continuous casting and the hot continuous rolling is eliminated;

in the square billet continuous casting process, the difference value of the head temperature and the tail temperature of a casting blank is controlled to be 20-40 ℃;

in the hot continuous rolling procedure, the difference value of the head temperature and the tail temperature of the rolled piece is controlled to be 20-30 ℃.

Further, before the blast furnace molten iron smelting process, the method also comprises the following steps:

determining the chemical components and weight percentage of the steel bar as follows: c: 0.20-0.25 Wt%, Si: 0.40-0.55 Wt%, Mn: 1.10-1.25 Wt%, P: less than or equal to 0.045 Wt%, S: less than or equal to 0.045 Wt%, Nb: less than or equal to 0.004 Wt%, Ti: less than or equal to 0.007 Wt%, Alt: less than or equal to 0.006 Wt%, V: 0.02-0.03 Wt%, N: 0.005-0.011 Wt%.

Further, the steel bar comprises the following chemical components in percentage by weight: c: 0.23 Wt%, Si: 0.50 Wt%, Mn: 1.19 Wt%, P: 0.030 Wt%, S: 0.026 Wt%, Nb: 0.002 Wt%, Ti: 0.002 Wt%, Alt: 0.0019 Wt%, V: 0.026 Wt%, N: 0.0075 Wt%.

Further, the difference between the head temperature and the tail temperature of the casting blank is controlled to be 20-40 ℃, and the method specifically comprises the following steps:

a casting blank sizing and shearing process is arranged in the square billet continuous casting process;

the casting blank sizing and shearing process is completed by adopting hydraulic shearing; the casting blank sizing and shearing process specifically comprises the following steps:

a contact type sizing device is arranged on the blank conveying roller way at a preset distance from the hydraulic shear;

when the head of the casting blank contacts the contact type sizing device, the contact type sizing device outputs a shearing action signal to the control system;

the control system sends an action instruction to the hydraulic shears;

and the hydraulic shear cuts off the casting blank according to the action instruction.

Further, the difference between the head temperature and the tail temperature of the casting blank is controlled to be 20-40 ℃, and the method further comprises the following steps:

setting a scale removing process, a measuring process and a casting blank cooling control process after the casting blank sizing and shearing process; wherein the content of the first and second substances,

in the scale removing procedure, removing the scale on the side surface of the casting blank by a steel wire brush;

in the measuring procedure, the temperature of the surface of the casting blank, on which scale is removed, on the side is recorded and measured at preset time intervals through a pyrometer, and a casting blank temperature curve is generated according to the measurement result, wherein the casting blank temperature curve is used for reflecting the temperature difference of different positions of the casting blank from the head part to the tail part;

and finishing the casting blank cooling control procedure according to the casting blank temperature curve.

Further, the casting blank cooling control procedure is completed according to the casting blank temperature curve, and the method specifically comprises the following steps:

determining an initial position on the casting blank, wherein the initial position is 20 ℃ higher than the temperature of the head of the casting blank according to the temperature curve of the casting blank;

spraying water to the part behind the initial position on the casting blank through casting blank cooling control spray heads respectively arranged at four positions of the outer side of the casting blank, namely the upper left position, the lower right position and the upper right position;

and adjusting the water spray intensity of each casting blank cooling control spray head in real time according to the temperature curve of the casting blank and the moving speed of the casting blank.

Further, the difference value of the head temperature and the tail temperature of the rolled piece is controlled to be 20-30 ℃, and the method specifically comprises the following steps:

the hot continuous rolling process is sequentially provided with the processes of rough rolling, rough rolling controlled cooling, intermediate rolling controlled cooling, finish rolling and finish rolling controlled cooling;

wherein, temperature measurement is carried out in the rough rolling procedure, and a first temperature curve is generated according to the measurement result;

the rough rolling cooling control procedure specifically comprises the following steps:

arranging a water spray head at the outer side of the rolled piece;

selecting a water spraying starting position on a rolled piece;

spraying water to the part behind the initial water spraying position on the rolled piece through the water spray header;

and adjusting the water spraying intensity of each water spraying head in real time according to the first temperature curve.

Further, the difference value of the head temperature and the tail temperature of the rolled piece is controlled to be 20-30 ℃, and the method further comprises the following steps:

measuring the temperature in the middle rolling procedure, and generating a second temperature curve according to the measurement result;

the temperature of the rolled piece is adjusted by adopting a water penetrating device in the middle rolling and cooling control procedure, and the cooling control strength of the middle rolling and cooling control procedure is adjusted in real time according to a second temperature curve;

measuring the temperature in the finish rolling procedure, and generating a third temperature curve according to the measurement result;

and in the finish rolling and cooling control procedure, the temperature of the rolled piece is adjusted by adopting a multi-stage cooling control device, and the cooling control strength of the finish rolling and cooling control procedure is adjusted in real time according to a third temperature curve.

Further, after the finish rolling and controlled cooling process, the method further comprises the following steps:

temperature measurement after finish rolling and controlled cooling after finish rolling;

wherein, temperature measurement is carried out in the temperature measurement procedure after finish rolling, and a fourth temperature curve is generated according to the measurement result;

and in the post-finishing-rolling controlled cooling process, the temperature of the rolled piece is adjusted by adopting a multi-stage controlled cooler, and the controlled cooling strength of the post-finishing-rolling controlled cooling process is adjusted in real time according to a fourth temperature curve.

Further, the method also comprises the working procedures of pre-finish rolling and pre-finish rolling controlled cooling before the finish rolling working procedure;

wherein, temperature measurement is carried out in the pre-finish rolling procedure, and a fifth temperature curve is generated according to the measurement result;

and in the pre-finish rolling and cooling control procedure, the temperature of a rolled piece is adjusted by adopting a multi-stage nozzle, and the cooling control strength of the pre-finish rolling and cooling control procedure is adjusted in real time according to a fifth temperature curve.

The invention also provides a steel bar rolled by the heating-free direct rolling method, which comprises the following chemical components in percentage by weight: c: 0.20-0.25 Wt%, Si: 0.40-0.55 Wt%, Mn: 1.10-1.25 Wt%, P: less than or equal to 0.045 Wt%, S: less than or equal to 0.045 Wt%, Nb: less than or equal to 0.004 Wt%, Ti: less than or equal to 0.007 Wt%, Alt: less than or equal to 0.006 Wt%, V: 0.02-0.03 Wt%, N: 0.005-0.011 Wt%, and the heating-free direct rolling method of the steel bar is adopted.

Further, the reinforcing steel bars are HRB400E anti-seismic reinforcing steel bars.

Furthermore, the specification of the steel bar is phi 12-40 mm.

Further, the specification of the steel bar is phi 28 mm.

Further, the steel bar is formed by rolling a casting blank with the section of 165mm multiplied by 165mm and the length of 11 m.

The technical scheme has the following beneficial effects:

in the technical scheme of the invention, the temperature difference at the tail part of the reinforcing steel bar head is adjusted by a multi-level temperature control means: 1. the contact type mechanical sizing device with a simple and reliable structure is matched with hydraulic shearing operation, so that a casting blank can be cut off quickly, and the waiting time and the temperature drop are reduced; 2. The surface temperature of the casting blank is measured to form a temperature trend line, the water spray intensity of each casting blank cooling control spray head is adjusted in real time according to the temperature trend line, and the rear section of the casting blank is cooled in such a way, so that the head-tail temperature difference of the casting blank before entering a rolling mill is controlled within a reasonable range; 3. a multi-level cooling control device is arranged in the rolling process, a water spray head in a unique form is designed in a rough rolling section, all cooling control processes take the measured temperature trend line as reference, real-time adjustment of temperature control of different positions on a rolled piece is realized, and the head-tail temperature difference of the rolled piece is effectively reduced. By adopting the technical means, the strength difference of the head and the tail of the final finished product is controlled within a reasonable range, and the quality stability of the product is greatly improved.

Drawings

In order to more clearly illustrate the embodiments of the present invention or the technical solutions in the prior art, the drawings needed in the embodiments will be briefly described below, and it is obvious that the drawings in the following description are only some embodiments of the present invention, and it is obvious for those skilled in the art to obtain other drawings without creative efforts.

FIG. 1 is a flow chart of a heating-free direct rolling method for reinforcing steel bars according to an embodiment of the present invention;

FIG. 2 is a schematic structural diagram of an apparatus for descaling, temperature measurement of a cast slab, and controlled cooling of a cast slab in a continuous casting process of a billet in an embodiment of the present invention;

FIG. 3 is a schematic layout diagram of a casting blank controlled cooling spray head in the embodiment of the invention;

FIG. 4 is a schematic view of the spray protection range of the casting blank controlled cooling spray head in the embodiment of the invention (view in the direction A in FIG. 2);

FIG. 5 is a schematic view of a nozzle hole structure of a casting blank controlled cooling nozzle in the embodiment of the invention;

FIG. 6 is a schematic structural view of a contact type sizing apparatus in a billet continuous casting process according to an embodiment of the present invention;

reference numerals: 1. casting blanks; 11. a corner portion; 2. a special heat preservation cover; 3. a blank conveying roller way; 31. a side plate of a blank conveying roller way; 4. A casting blank cooling control spray head; 41. spraying a hole; 42. a rectangular water spray coverage area; 5. a pyrometer; 6. a control system; 7. a wire brush; 8. a contact sizing device; 81. a long connecting rod; 82. a movable contact; 83. a sizing device support; 84. a stationary contact; 85. A protective cover; 87. a return spring.

Detailed Description

The technical solutions in the embodiments of the present invention will be clearly and completely described below with reference to the drawings in the embodiments of the present invention, and it is obvious that the described embodiments are only a part of the embodiments of the present invention, and not all of the embodiments. All other embodiments, which can be derived by a person skilled in the art from the embodiments given herein without making any creative effort, shall fall within the protection scope of the present invention.

As shown in fig. 1, an embodiment of the present invention provides a method for directly rolling a steel bar without heating, including: sequentially carrying out blast furnace molten iron smelting, molten iron desulphurization pretreatment, converter molten steel smelting, square billet continuous casting, hot continuous rolling and fixed-length shearing; wherein, the blank heating procedure between the square billet continuous casting and the hot continuous rolling is eliminated; in the square billet continuous casting procedure, the difference value of the head temperature and the tail temperature of the casting blank is controlled to be 20-40 ℃; in the hot continuous rolling procedure, the difference between the head temperature and the tail temperature of the rolled piece is controlled to be 20-30 ℃.

In the heating-free direct rolling process, because the casting blank does not need to be reheated by a heating furnace, the tail temperature of the casting blank is obviously higher than the head temperature, and the temperature of the tail part is higher as the casting blank is closer to the tail part, correspondingly, in the subsequent process, the tail temperature of the rolled piece is also obviously higher than the head temperature, so that the head and tail strength of the finished piece is inconsistent, and further the quality problem is generated. Analysis and actual measurement prove that the difference between the head temperature and the tail temperature of the casting blank is controlled to be 20-40 ℃, and the difference between the head temperature and the tail temperature of the rolled piece is controlled to be 20-30 ℃, so that the quality of a final reinforcing steel bar finished product can be effectively ensured, and the head and tail strength of the finished product tends to be consistent.

The rolling method omits a heating furnace; the casting blank is directly sent into the rolling mill through the blank sending roller way, and the casting blank does not need to be sent into the heating furnace through the blank sending roller way. In addition, in order to reduce the temperature drop of the casting blank, a fully-closed multi-layer heat-insulating cover is adopted to cover the whole process from the continuous casting machine to the inlet of the rolling mill. The outer layer of the heat-insulating cover is a steel shell, the middle layer of the heat-insulating cover is high-temperature-resistant heat-insulating cotton, and the inner layer of the heat-insulating cover is high-temperature-resistant reflecting material, so that the heat loss is reduced to the greatest extent

In order to obtain better effect, the application carries out special component design:

1) and the addition of alloy elements with low solubility, such as Nb, Ti and Al, after the austenitizing of the steel at the direct rolling temperature is reduced. The alloy elements have high solubility point of nitrides and carbides formed in the steel at the direct rolling temperature and are difficult to dissolve, and the elements increase the austenite recrystallization temperature of the steel, can inhibit recrystallization and grain growth after recrystallization in the rolling process, and has remarkable fine grain strengthening effect in the direct rolling state. If the elements are added, the influence of the temperature change of the rolled piece on the performance of the steel is larger, the temperature difference between the head and the tail of the steel after casting blank rolling is increased, and the quality stability of the product is influenced.

2) And adding a proper amount of V element. At the direct rolling temperature, nitrides and carbides of vanadium are almost completely dissolved in the austenite region, and mainly play a role in precipitation strengthening in steel.

3) And controlling the N element. N can strengthen the strengthening effect of V and reduce the cost, and can be added in the form of silicon iron nitride. As in table 1.

4) And controlling the contents of Si and Mn. Si and Mn play a role in solid solution strengthening, and the strengthening effect is slightly influenced by the temperature of a casting blank. Si has larger contribution to tensile strength, Mn has equivalent contribution to tensile strength and yield strength, and a certain amount of Si is needed to ensure that the yield ratio is qualified due to low rolling temperature and stronger fine grain strengthening effect in a direct rolling state

Tests prove that better implementation effect can be obtained by selecting the chemical components of the material according to the values.

Further, the difference between the head temperature and the tail temperature of the casting blank is controlled to be 20-40 ℃, and the method specifically comprises the following steps: setting a casting blank fixed-length shearing process in the square billet continuous casting process; the casting blank sizing and shearing process is completed by adopting hydraulic shearing; the casting blank sizing and shearing process specifically comprises the following steps: a contact type sizing device is arranged on the blank conveying roller way at a preset distance from the hydraulic shear; when the head of the casting blank contacts the contact type sizing device, the contact type sizing device outputs a shearing action signal to a control system; the control system sends an action command to the hydraulic shears; and the hydraulic shear cuts off the casting blank according to the action instruction.

The casting blank sizing is controlled by two modes, namely contact type mechanical device control sizing and infrared imaging control sizing. Before the stepped ejection is formed, the stepped ejection is formed by adopting a stopper flow control and infrared imaging mode, then all the heat-insulating covers are covered, the flow pulling speeds are controlled to be equal, and the stepped ejection is switched to a contact type mechanical device (namely a contact type sizing device) to control the cutting according to the sizing. By using a stepped billet discharging mode, the casting blank can enter a high-speed billet conveying roller way as soon as being sheared, and enters a rolling mill at the highest speed, so that the temperature drop in the waiting time is reduced.

The continuous casting machine uses the hydraulic shear to shear the casting blank, the casting blank shearing speed of the hydraulic shear is high, and the waiting time and the temperature drop of the casting blank can be reduced. The contact type sizing device 8 is configured as shown in fig. 6, and a mechanical contact type sizing device 8 is provided at a casting blank sizing position (for example, a position 10m or 11m from a hydraulic shear). The contact type sizing device 8 is provided with a horizontally arranged long connecting rod 81, the middle part of the long connecting rod is hinged with a sizing device support 83 and can rotate by taking a hinged point as a circle center, one end of the long connecting rod 81 extends into the inner side of the blank conveying roller way 3 through an opening on the blank conveying roller way side plate 31 and is positioned on the running track of the casting blank 1, the other end of the long connecting rod is provided with a movable contact 82, a fixed contact 84 is fixedly arranged above the movable contact 82, and the fixed contact 84 is electrically connected with a signal receiving end of an external control system 6 through a lead. When the casting blank 1 runs to the position of the contact type sizing device 8 on the blank conveying roller way 3, one end of the long connecting rod 81 extending to the inner side of the blank conveying roller way 3 is pressed down, and the other end of the long connecting rod is lifted up in the reverse direction (meanwhile, the reset spring 87 is elongated), so that the movable contact 82 is contacted with the fixed contact 84, an electric signal is sent to the control system 6 (a computer or a PLC and the like), the control system 6 immediately sends a shearing signal to the hydraulic shear, and the hydraulic shear cuts off the casting blank 1; the casting blank 1 is sent away by the blank sending roller way 3 after being sheared, the contact type sizing device 8 is reset (namely, the long connecting rod 81 is restored to the initial horizontal state) under the action of the pulling force of the reset spring 87, when the next casting blank 1 passes through again, the long connecting rod 81 of the contact type sizing device 8 is pressed down again, and the control system 6 gives a casting blank shearing signal for 1 time again. And repeating the steps to realize continuous casting blank shearing operation. In the device, in order to avoid scraping the casting blank 1, a plurality of cylindrical guide wheels can be arranged at one end part of the long connecting rod 81 extending to the inner side of the blank conveying roller way 3, and when the guide wheels contact with the casting blank 1, the guide wheels can rotate along with the movement of the casting blank 1. Meanwhile, in order to avoid the influence of the falling of foreign matters on the use, a protective cover 85 can be arranged on the outer side of the device, and when the adjustment or the maintenance is needed, the protective cover 85 can be lifted from the upper side to be removed. In order to ensure contact reliability and avoid contact failure, the stationary contact 84 may be made of a long sheet-like elastic metal material.

In order to reduce heat loss as much as possible, a heat preservation cover between a withdrawal and straightening machine and a hydraulic shear of the continuous casting machine is not provided with a hole, and a small hole with the diameter of 10mm is formed in the position, at the fixed length, of a casting blank at the upper part of the heat preservation cover after the hydraulic shear, so that the position of the casting blank can be observed conveniently.

Further, the difference between the head temperature and the tail temperature of the casting blank is controlled to be 20-40 ℃, and the method further comprises the following steps: a scale removing process, a casting blank measuring process and a casting blank cooling control process are arranged after a fixed-length shearing process in a square blank continuous casting process; wherein in the descaling step, scale on the side surface of the casting blank is removed by a wire brush; in the casting blank measuring procedure, the temperature of the surface of the casting blank, on which the scale is removed, on the surface is recorded and measured at preset time intervals through a pyrometer, and a casting blank temperature curve is generated according to the measurement result, wherein the casting blank temperature curve is used for reflecting the temperature difference of different positions of the casting blank from the head part to the tail part; and finishing the casting blank cooling control procedure according to the casting blank temperature curve.

In order to control the head-tail temperature difference of the casting blank, the casting blank cooling control spray head with special design is adopted in the method, and the part with higher temperature at the rear end in the casting blank is cooled, so that the temperature of the part is consistent with the temperature of the head. In order to reasonably control the temperature change, the water yield of the spray head needs to be quantized and reasonably controlled, so that before the casting blank cooling control spray head is adopted for cooling, the temperature of the surface of the casting blank is measured to obtain the actual temperature of each recording point, a temperature curve reflecting the temperature change trend of different positions of the casting blank is drawn according to the actual temperature of each recording point, and then the temperature curve is input into a control system, so that the control system can distinguish and treat each point on the casting blank according to the temperature curve, the higher the temperature is, the larger the water spray quantity of the corresponding casting blank cooling control spray head is, the largest cooling amplitude is, and the lower temperature is, the smaller the water spray quantity is. By the method, the difference between the head temperature and the tail temperature of the casting blank can be controlled between 20 ℃ and 40 ℃.

In order to avoid the influence of the iron scale on the accuracy of subsequent temperature measurement, the oxide scale on the surface of the casting blank is removed before the temperature is measured. The iron scale removing device is a cylindrical steel wire brush 7 driven by a motor to rotate, and the rotation direction of the iron scale removing device is opposite to the movement direction of the casting blank 1; the cylindrical wire brush 7 is vertical to the ground and is arranged on the side surface of the blank conveying roller table 3 in front of the rolling mill, and when the casting blank 1 passes through, the motor drives the wire brush 7 to rotate to remove the iron oxide on the surface of the casting blank 1.

After the oxide scale removing device, a plurality of temperature measuring points are further arranged along the direction of the blank conveying roller way 3, each casting blank temperature measuring point is provided with a pyrometer 5 for measuring the temperature of the casting blank, the casting blank temperature measuring points and the cylindrical steel wire brushes 7 are positioned on the same horizontal line, the pyrometers 5 measure the temperature of the casting blank 1 after the oxide scales are removed, measuring values are recorded at preset time intervals (for example, 1 number of the measuring values is recorded every 0.1S), and after the measuring values are transmitted into a control system 6 (for example, a computer and the like), the measuring values can be drawn into a trend line according to data of the plurality of measuring values, and the trend line represents the temperature condition from the head to the tail of the casting blank 1.

As shown in fig. 2, in order to meet the special requirements of the processes of removing oxide scale, measuring temperature of a casting blank and controlling cooling of the casting blank, the heat-insulating cover comprises a special heat-insulating cover 2 for measuring and controlling cooling (the structure of the heat-insulating layer of the heat-insulating cover is not different from that of the heat-insulating cover or the conventional common heat-insulating cover, but equipment such as an oxide scale removing device, a temperature measuring point, a temperature adjusting device and the like are arranged in the heat-insulating cover, so that the special heat-insulating cover 2 is positioned in front of the rolling mill. Along the conveying direction of the casting blank 1, the special heat-insulating cover 2 comprises equipment applied by three processes, namely an iron scale removing device, a casting blank temperature measuring point and a casting blank temperature adjusting device, wherein the iron scale removing device is located in the special heat-insulating cover 2.

Further, the step of performing controlled cooling on the casting blank according to the casting blank temperature curve specifically includes: determining an initial position on the casting blank, which is 20 ℃ higher than the temperature of the head of the casting blank, according to the casting blank temperature curve; spraying water to the part behind the initial position on the casting blank through casting blank cooling control spray heads respectively arranged at four positions of the outer side of the casting blank, namely the upper left position, the lower right position and the upper right position; and adjusting the water spray intensity of each spray head in real time according to the casting blank temperature curve and the moving speed of the casting blank.

The special heat-insulating cover 2 is also provided with a temperature adjusting device for completing the cold control process. The length of the temperature adjusting device is equivalent to that of the casting blank 1, as shown in fig. 3, the temperature adjusting device mainly comprises a plurality of casting blank spray heads 4, and the casting blank spray heads 4 are arranged at the positions of four corners of the special heat preservation cover 2 outside the blank conveying roller way 3. And, should guarantee to have 1 casting blank shower nozzle 4 respectively arranged on 4 angles of the same cross-section of casting blank 1, namely 4 casting blank shower nozzles 4 are total in the same cross-section upper left, upper right, lower left, lower right, and should not arrange casting blank shower nozzle 4 under casting blank 1 to avoid casting blank shower nozzle 4 to drop and block up and then lead to unable the use because of the iron scale on casting blank 1. In the length direction of the special heat preservation cover 2, the casting blank spray heads 4 are uniformly arranged, namely 4 rows of casting blank spray heads are formed, and the space between the casting blank spray heads in the same row takes the configuration principle that the sprayed water can completely cover the surface of the casting blank 1. Since there is a gap between the lower rollers of the slab conveying table 3 and between the lower rollers and between the side surfaces thereof, the casting nozzles 4 located at the lower left and lower right are capable of spraying cooling water onto the side surfaces and lower sides of the cast slab 1.

In addition, the spray holes 41 of the casting nozzle 4 should not be designed as normal circular holes, but the spray holes 41 are designed as hollow rectangles (as shown in fig. 5), so that the protection range of the sprayed water can be formed as a rectangular water spray coverage area 42 (also called as an annular water spray coverage area with a rectangular periphery, and the protection range of the water discharged from normal circular holes is circular or annular) as shown in fig. 4. In this way, the casting blank 1 is a square blank, and the casting blank spray heads 4 are arranged at four corner points on the inner side of the special heat-preservation cover 2, so that the casting blank spray heads 4 are positioned on a diagonal line of the square section of the casting blank 1; because the corner 11 of the casting blank 1 is in two-dimensional heat transfer and the temperature drop speed is high, the water quantity of the middle part of the water spray coverage area 42 sprayed by the casting blank spray head 4 is small, the water quantity of the two side parts is large, the excessive temperature drop of the corner 11 of the casting blank 1 can be avoided, and the integral temperature uniformity of the casting blank 1 is kept.

When the head of the casting blank 1 enters the rolling mill, water is sprayed to control the surface temperature, and the head area of the casting blank 1 is low in temperature and does not spray water; the surface temperature trend curve of the casting blank 1 is used as a standard, the water quantity of the casting blank spray nozzle 4 is controlled by a computer (a control system 6), water spray cooling is started when the temperature is increased by 20 ℃ than the head from the head of the casting blank 1, the more the temperature is increased, the higher the water spray strength is, and the water outlet area moves along with the movement of the casting blank 1.

Further, the difference between the head temperature and the tail temperature of the rolled piece is controlled to be 20-30 ℃, and the method specifically comprises the following steps: the hot continuous rolling process is sequentially provided with the processes of rough rolling, rough rolling controlled cooling, intermediate rolling controlled cooling, finish rolling and finish rolling controlled cooling; wherein, temperature measurement is carried out in the rough rolling procedure, and a first temperature curve is generated according to the measurement result; the rough rolling controlled cooling process specifically comprises the following steps: arranging a water spray head at the outer side of the rolled piece; selecting a water spraying starting position on a rolled piece; spraying water through the water spray heads to a portion of the rolled piece after the water spray start position; and adjusting the water spraying intensity of each water spray head in real time according to the first temperature curve.

Before cooling control, the temperature of the surface of a rolled piece is measured to obtain the actual temperature of each recording point, a temperature curve reflecting the temperature change trend of the rolled piece at different positions is drawn according to the actual temperature of each recording point, and then the temperature curve is input into a control system, so that the control system can distinguish and treat each point on the rolled piece according to the temperature curve, the higher the temperature is, the higher the corresponding cooling control intensity is, the larger the cooling control intensity is, the maximum cooling amplitude is, and the lower the temperature is, the lower the cooling control intensity is.

For this purpose, a plurality of temperature measuring points can be arranged along the direction of the blank conveying roller way, and the temperature measuring points are distributed at corresponding positions in the processes of rough rolling, medium rolling, pre-finish rolling, finish rolling and the like. Each temperature measuring point is provided with a pyrometer for temperature measurement, measured values are recorded at preset time intervals (for example, 1 number of the measured values are recorded every 0.1S), and after the measured values are transmitted into a control system (for example, a computer and the like), a temperature curve can be drawn according to a plurality of measured value data, wherein the temperature curve represents the current head-tail temperature difference condition of a rolled piece.

In the rough rolling temperature control procedure, a special water spray head is adopted as a cooling control device, a plurality of water spray heads are arranged at proper distance positions outside a rolled piece, the water spray heads are arranged at four corner positions around the outer side of a billet conveying roller way, and a support can be arranged for fixing the water spray heads. And, should guarantee to have 1 water shower respectively at 4 angles of the same cross-section of rolled piece 1, namely the total 4 water shower in the same cross-section upper left, upper right, lower left, lower right, and should not arrange water shower 4 under casting blank 1 to avoid being blockked up by impurity that drops on rolled piece 1, etc.. In the length direction of the blank conveying roller way, water nozzles are uniformly arranged, namely 4 rows of nozzles are formed, and the nozzle spacing on the same row adopts the configuration principle that sprayed water can completely cover the surface of the rolled piece 1. In order to control the temperature difference between 20 ℃ and 30 ℃, before the water spraying temperature reduction, a position which is 20 ℃ higher than the head temperature of the rolled piece is found on the rolled piece according to a temperature curve generated in advance and is used as a water spraying initial position, and the part behind the water spraying initial position is cooled.

Further, the difference between the head temperature and the tail temperature of the rolled piece is controlled to be 20-30 ℃, and the method further comprises the following steps: measuring the temperature in the middle rolling procedure, and generating a second temperature curve according to the measurement result; the temperature of the rolled piece is adjusted by adopting a water penetrating device in the middle rolling and cooling control procedure, and the cooling control intensity of the middle rolling and cooling control procedure is adjusted in real time according to the second temperature curve; measuring the temperature in the finish rolling procedure, and generating a third temperature curve according to the measurement result; and in the finish rolling and cooling control procedure, the temperature of the rolled piece is adjusted by adopting a multi-stage cooling control device, and the cooling control strength of the finish rolling and cooling control procedure is adjusted in real time according to the third temperature curve.

In the remaining cooling control processes, the amount of cooling control is adjusted according to the corresponding temperature profile, although other cooling control devices than the aforementioned water spray heads are used. Temperature measuring points are respectively arranged in the middle rolling stand and the finish rolling stand, so that corresponding temperature curves are generated in the middle rolling process and the finish rolling process according to temperature measuring results, and the corresponding temperature curves are respectively used for controlled cooling adjustment in the middle rolling controlled cooling process and the finish rolling controlled cooling process.

Further, the finish rolling and controlled cooling process further comprises the following steps: temperature measurement after finish rolling and controlled cooling after finish rolling; measuring the temperature in the temperature measuring process after the finish rolling, and generating a fourth temperature curve according to the measurement result; and in the post-finishing-rolling controlled cooling process, the temperature of the rolled piece is adjusted by adopting a multi-stage controlled cooler, and the controlled cooling strength of the post-finishing-rolling controlled cooling process is adjusted in real time according to the fourth temperature curve.

In some rolled piece production lines, besides rough rolling, intermediate rolling and finish rolling, after the finish rolling and cooling control process, the controlled cooling treatment needs to be carried out again (namely controlled cooling after finish rolling), at the moment, temperature measurement needs to be carried out, a temperature curve is generated, and then the controlled cooling process after finish rolling is carried out according to the temperature curve.

Further, the method also comprises a pre-finish rolling process and a pre-finish rolling and controlled cooling process before the finish rolling process; wherein, temperature measurement is carried out in the pre-finish rolling procedure, and a fifth temperature curve is generated according to the measurement result; and the pre-finish rolling and cooling control procedure adopts a multi-stage nozzle to adjust the temperature of the rolled piece, and adjusts the cooling control strength of the pre-finish rolling and cooling control procedure in real time according to the fifth temperature curve.

In some rolled piece production lines, pre-finish rolling is required between intermediate rolling and finish rolling, temperature is measured in the pre-finish rolling process to generate a corresponding temperature curve, and then a pre-finish rolling controlled cooling process is carried out according to the temperature curve.

The control method of the head-tail temperature difference of the rolled piece in the application is specifically explained as follows:

1. designing a rolling line: the rolling line is provided with a multi-level controlled cooling device in the rolling process.

Ordinary rod production line: 6 roughing mills + roughing controlled cooling device +6 middle rolling mills + middle rolling controlled cooling device +4 finishing mills + finishing controlled cooling device + recovery section + temperature measuring device after finishing rolling +2 finishing mills + cooling controlled device after finishing rolling + recovery section + cooling bed (temperature measurement is respectively carried out after the 4 th frame of roughing mills, middle rolling and finishing mills, the time for returning can be supplied for the rolled piece before temperature measurement, surface temperature is uniform, and the influence on surface temperature measurement precision due to uneven surface temperature and surface supercooling of the rolled piece brought by the cooling controlled device is avoided).

High-speed rod production line: 6 roughing mills + roughing rolling control cold device +6 middle rolling mills + middle rolling control cold device +6 pre-finishing mills + pre-finishing rolling control cold device +4 finishing mills + finishing rolling control cold device + recovery section + post-finishing temperature measuring device +2 finishing mills + post-finishing rolling control cold device + recovery + cold bed (respectively, temperature measurement after 4 th frame of roughing mills, middle rolling, pre-finishing rolling, time for returning rolled pieces before temperature measurement, surface temperature uniformity, and uneven surface temperature and surface overcooling of rolled pieces brought by the cold control devices are avoided).

High-speed wire rod production line: 6 roughing mills + roughing controlled cooling device +6 middle rolling mills + middle rolling controlled cooling device +6 pre-finishing mills + pre-finishing controlled cooling device + recovery section +8 finishing mills + finishing controlled cooling device + recovery section + post-finishing temperature measuring device +2 shearing units + post-finishing controlled cooling device (temperature measurement is carried out respectively after 4 th frame of roughing mills, middle rolling, pre-finishing and 8 th frame of finishing mills, time for returning can be provided for rolled pieces before temperature measurement, surface temperature is uniform, and uneven surface temperature and surface supercooling of rolled pieces brought by controlled cooling devices are avoided).

2. And drawing a temperature trend line at each temperature measuring point according to the temperature of the rolled piece at each measuring point, and adjusting the temperature of the rolled piece according to the temperature trend line in a cooling control procedure after each temperature measuring point of the rolling line so as to control the head-tail temperature difference of the rolled piece. And starting water spraying cooling from the head part of the rolled piece to the back part of the rolled piece, wherein the temperature is increased by 20 ℃ compared with the head part, and the more the temperature is increased, the higher the water spraying strength is.

3. Different cold control devices are adopted at different positions: the rough rolling cold control procedure adopts a water nozzle, the middle rolling cold control procedure adopts a water penetrating device, the pre-finish rolling cold control procedure adopts a multi-stage nozzle, the finish rolling cold control procedure adopts a multi-stage cold control device, and the finish rolling post-cold control procedure adopts a multi-stage cold control device.

Wherein, the rough rolling controlled cooling adopts a water spray head: because the rolled piece at the rough rolling outlet is large, and the head part of the rolled piece can have the problems of bending and the like, a cooling device (namely a cooling control device) is arranged behind the No. 1 flying shear, and the cooling device at the position consists of a plurality of groups of water spray heads. 4 angles of the same section of the rolled piece are respectively provided with 1 water nozzle, and 4 water nozzles are arranged in the same section, so that the condition that the nozzles positioned right below are blocked due to falling of casting blank iron scales can be avoided, and the use is influenced. The water outlet of the water spray head is rectangular, and the coverage area of the water spray head is based on that 4 spray heads completely cover the surface of a rolled piece.

The middle rolling cooling control is a water penetrating device: because the size of a rolled piece at a medium rolling outlet is also large, the head part of the rolled piece can be bent and the like, a cooling device (a cooling control device) is arranged behind a No. 2 flying shear and is cooled by a water penetrating device commonly used for bar rolling lines.

The pre-finish rolling, the finish rolling machine and the post-finish rolling controlled cooling all adopt multi-stage controlled coolers (grading controlled cooling devices), and each position is composed of a plurality of small-sized controlled cooling devices which can independently control water quantity.

The steel bar heating-free direct rolling method of the application is described as a specific example below:

in one embodiment of the production of the HRB400E rebar, the chemical composition of the material is as follows:

HRB400E ingredient (wt%)

TABLE 1 HRB400E materials ingredient Table

The steelmaking process of the embodiment comprises the following steps:

the process route is as follows: blast furnace molten iron smelting → molten iron desulphurization pretreatment → converter molten steel smelting → square billet continuous casting → hot continuous rolling → fixed-length shearing → inspection, packaging and warehousing; wherein, the process characteristics of each stage are as follows:

smelting molten steel in a converter: the molten iron S fed into the furnace is 0.040 Wt%; no alloy with high Nb, Ti and Al contents is added after the furnace.

The process of slag elution S is adopted after the converter is started: before and during tapping, slagging materials such as lime, synthetic slag and the like are added into the steel ladle respectively, reasonable slag components and fluidity are controlled, and a deoxidation process, a temperature control process and a chlorine blowing process are standardized, so that the aim of slag washing and desulfurization is fulfilled. (1) The basicity of the ladle top slag (CaO/SiO2) is 2.8. (2) And in the tapping process, a deoxidizing material is additionally added to perform reinforced deoxidization on the molten steel and the top slag, the deoxidizing material is put into the ladle slag surface after tapping, and the ladle top slag (FeO) is 1.7% after tapping. (3) The tapping temperature is improved by 15 ℃ compared with the conventional low-S heat. (4) The stirring strength in the tapping process and the desulphurization process is improved, and the strong argon blowing time is 6 minutes after tapping.

And (3) square billet continuous casting: the ladle slag discharge detection control is adopted, the pouring temperature of the tundish is 1530 ℃, the tundish uses a common covering agent and common square billet covering slag, and the casting blank single flow pulling speed is 3.6 m/min. The casting blank is sheared by hydraulic shear, the step-shaped blank ejection mode is adopted, and the casting blank temperature at the shearing position is 1000-1100 ℃, such as 1020 ℃, 1050 ℃ and 1080 ℃. The specific water amount of the cast strand was 1.1L/min using a full water-cooled nozzle.

As shown in fig. 2, this rolling method, the heating furnace is eliminated; the casting blank is directly sent into the rolling mill through the blank sending roller way 3, and the casting blank does not need to be sent into the heating furnace through the blank sending roller way 3. Hot continuous rolling of bars: the blank is sent into a rolling mill by a direct-feeding roller way, a high-speed motor is used for feeding the blank, and the length of the blank-feeding roller way 3 is within 200m, such as 180 m or 200 m. The time from cutting to entry into the mill was 60 seconds.

The cross section of the casting blank is 165mm multiplied by 165mm, the length of the casting blank is 11m, the temperature curve generated after mapping shows that the temperature of the casting blank at 5m is increased by 20 ℃ compared with the temperature of the head and the temperature of the casting blank at 10m is increased by 55 ℃ compared with the temperature of the head, water spraying cooling is started from the casting blank at 5m, the more the temperature is increased, the higher the water spraying strength is, and finally the temperature difference between the head and the tail of the casting blank is controlled to be 28 ℃.

Before the casting blank enters the rolling mill, the temperature of the head of the casting blank is 890-910 ℃, the temperature of the tail of the casting blank is 870-875 ℃, for example, the temperature of the head of the casting blank is 900 ℃, and the temperature of the tail of the casting blank is 873 ℃.

The production line is according to the aforesaid ordinary rod production line arrangement, promptly, 6 roughing mills + roughing controlled cooling device +6 rolling mills in + rolling controlled cooling device +4 finishing mills + finishing controlled cooling device + return section + post-finishing temperature measuring device +2 finishing mills + post-finishing controlled cooling device + return section + cooling bed (respectively in roughing, intermediate rolling, temperature measurement behind the 4 th frame of finishing mill, can be for the time that the rolled piece supplied the answer before the temperature measurement, even surface temperature). The specification of the produced steel bar is 28mm, the length of the rolled piece finished product after being put on a cooling bed is 486m, and finally the temperature difference between the head and the tail of the rolled piece is controlled to be 25 ℃.

The results obtained are shown in the following table:

TABLE 2 summary of head and tail temperature and head and tail performance

When in hot continuous rolling, the head temperature of the rolled piece is controlled to be 890-:

the temperature of the head of the first rolled piece is 900 ℃, the yield strength of the head of the rolled piece is 440Mpa, and the elongation after fracture is 21%; the tail temperature is 880 ℃, the yield strength of the tail of the rolled piece is 455MPa, and the elongation after fracture is 22%;

the temperature of the head of the second rolled piece is 905 ℃, the yield strength of the head of the rolled piece is 430Mpa, and the elongation after fracture is 20%; the tail temperature is 880 ℃, the yield strength of the tail of the rolled piece is 450MPa, and the elongation after fracture is 21%;

the temperature of the head of the third rolled piece is 892 ℃, the yield strength of the head of the rolled piece is 425Mpa, and the elongation after fracture is 23%; the tail temperature is 863 ℃, the yield strength of the tail of the rolled piece is 455MPa, and the elongation after fracture is 22%; (ii) a

The temperature of the head of the fourth rolled piece is 910 ℃, the yield strength of the head of the rolled piece is 435MPa, and the elongation after fracture is 22 percent; the tail temperature is 890 ℃, the yield strength of the rolled piece tail is 460Mpa, and the elongation after fracture is 20%. Compared with the traditional cold billet reheating method, the method can save 140m of gas for each ton of steel ³ The loss of the cast blank iron scale is reduced, and the yield of the rolled steel metal is improved by 0.5-1.0%.

In the foregoing detailed description, various features are grouped together in a single embodiment for the purpose of streamlining the disclosure. This method of disclosure is not to be interpreted as reflecting an intention that the claimed embodiments of the subject matter require more features than are expressly recited in each claim. Rather, as the following claims reflect, invention lies in less than all features of a single disclosed embodiment. Thus, the following claims are hereby expressly incorporated into the detailed description, with each claim standing on its own as a separate preferred embodiment of the invention.

The previous description of the disclosed embodiments is provided to enable any person skilled in the art to make or use the present invention. To those skilled in the art; various modifications to these embodiments will be readily apparent, and the generic principles defined herein may be applied to other embodiments without departing from the spirit or scope of the disclosure. Thus, the present disclosure is not intended to be limited to the embodiments shown herein but is to be accorded the widest scope consistent with the principles and novel features disclosed herein.

The above-mentioned embodiments are intended to illustrate the objects, technical solutions and advantages of the present invention in further detail, and it should be understood that the above-mentioned embodiments are merely exemplary embodiments of the present invention, and are not intended to limit the scope of the present invention, and any modifications, equivalent substitutions, improvements and the like made within the spirit and principle of the present invention should be included in the scope of the present invention.

Claims

1. A heating-free direct rolling method for steel bars is characterized by comprising the following steps:

wherein, the blank heating procedure between the billet continuous casting and the hot continuous rolling is eliminated;

in the square billet continuous casting procedure, the difference value of the head temperature and the tail temperature of the casting blank is controlled to be 20-40 ℃;

in the hot continuous rolling procedure, the difference between the head temperature and the tail temperature of the rolled piece is controlled to be 20-30 ℃.

2. The heating-free direct rolling method of steel bars according to claim 1, further comprising, before the blast furnace molten iron smelting process:

3. The heating-free direct rolling method for reinforcing steel bars according to claim 1, wherein the difference between the head temperature and the tail temperature of the casting blank is controlled to be 20-40 ℃, and the method specifically comprises the following steps:

setting a casting blank fixed-length shearing process in the square billet continuous casting process;

when the head of the casting blank contacts the contact type sizing device, the contact type sizing device outputs a shearing action signal to a control system;

the control system sends an action command to the hydraulic shears;

4. The heating-free direct rolling method of a reinforcing steel bar according to claim 4, wherein the difference between the head temperature and the tail temperature of the cast slab is controlled to be 20 ℃ to 40 ℃, and further comprising:

in the scale removing procedure, removing scale on the side surface of the casting blank by a steel wire brush;

in the measuring procedure, measuring the temperature of the scale-removed side surface of the casting blank by a pyrometer at preset time intervals, and generating a casting blank temperature curve according to the measurement result, wherein the casting blank temperature curve is used for reflecting the temperature difference of different positions of the casting blank from the head part to the tail part;

5. The heating-free direct rolling method of steel bars according to claim 4, wherein the casting blank controlled cooling process is completed according to the casting blank temperature curve, and specifically comprises the following steps:

determining an initial position on the casting blank, which is 20 ℃ higher than the temperature of the head of the casting blank, according to the casting blank temperature curve;

and adjusting the water spray intensity of each casting blank cooling control spray head in real time according to the casting blank temperature curve and the moving speed of the casting blank.

6. The heating-free direct rolling method for the steel bars as claimed in claim 1, wherein the difference between the head temperature and the tail temperature of the rolled pieces is controlled to be 20-30 ℃, and the method specifically comprises the following steps:

the rough rolling controlled cooling process specifically comprises the following steps:

arranging a water spray head at the outer side of the rolled piece;

selecting a water spraying starting position on a rolled piece;

spraying water through the water spray heads to a portion of the rolled piece after the water spray start position;

and adjusting the water spraying intensity of each water spray head in real time according to the first temperature curve.

7. The heating-free direct rolling method for reinforcing steel bars according to claim 7, wherein the difference between the head temperature and the tail temperature of the rolled piece is controlled to be 20-30 ℃, and the method further comprises the following steps:

the temperature of the rolled piece is adjusted by adopting a water penetrating device in the middle rolling and cooling control procedure, and the cooling control intensity of the middle rolling and cooling control procedure is adjusted in real time according to the second temperature curve;

and in the finish rolling and controlled cooling process, the temperature of a rolled piece is adjusted by adopting a multi-stage controlled cooler, and the controlled cooling strength of the finish rolling and controlled cooling process is adjusted in real time according to the third temperature curve.

8. The method for directly rolling reinforcing bar without heating as claimed in claim 8, further comprising, after the finish rolling and cooling step:

measuring the temperature in the temperature measuring process after the finish rolling, and generating a fourth temperature curve according to the measurement result;

and in the post-finishing-rolling cooling control procedure, a multi-stage cooling controller is adopted to adjust the temperature of the rolled piece, and the cooling control strength of the post-finishing-rolling cooling control procedure is adjusted in real time according to the fourth temperature curve.

9. The heating-free direct rolling method of reinforcing steel bars according to claim 9, further comprising a pre-finish rolling step, a pre-finish rolling step and a controlled cooling step before the finish rolling step;

and the pre-finish rolling and cooling control procedure adopts a multi-stage nozzle to adjust the temperature of the rolled piece, and adjusts the cooling control strength of the pre-finish rolling and cooling control procedure in real time according to the fifth temperature curve.

10. A steel bar rolled by a heating-free direct rolling method is characterized by comprising the following chemical components in percentage by weight: c: 0.20-0.25 Wt%, Si: 0.40-0.55 Wt%, Mn: 1.10-1.25 Wt%, P: less than or equal to 0.045 Wt%, S: less than or equal to 0.045 Wt%, Nb: less than or equal to 0.004 Wt%, Ti: less than or equal to 0.007 Wt%, Alt: less than or equal to 0.006 Wt%, V: 0.02-0.03 Wt%, N: 0.005-0.011 Wt%, using the heating-free direct rolling method of the steel bar according to any one of claims 1-9.