CN109530646B - Control method for reducing temperature difference between head and tail of continuous casting billet in direct rolling process - Google Patents
Control method for reducing temperature difference between head and tail of continuous casting billet in direct rolling process Download PDFInfo
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- CN109530646B CN109530646B CN201811614600.1A CN201811614600A CN109530646B CN 109530646 B CN109530646 B CN 109530646B CN 201811614600 A CN201811614600 A CN 201811614600A CN 109530646 B CN109530646 B CN 109530646B
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Abstract
A control method for reducing the temperature difference between the head and the tail of a continuous casting billet in a direct rolling process belongs to the technical field of direct rolling. The process comprises the following steps: adding two sections of heat preservation covers on a conveying roller way of each flow of a continuous casting machine, wherein one section of heat preservation cover is added between a cutting position and a fixed length position of a casting blank, the length of the heat preservation cover is half of the fixed length of the casting blank, and the starting point of the heat preservation cover is 0.25m of a fixed length head monitoring point; and the other section is that a heat preservation cover is added on the conveying roller way before the continuous casting blank enters the steel moving area, the length of the heat preservation cover is half of the fixed length of the casting blank, and the starting point of the heat preservation cover is the front edge of the steel moving area. Before each continuous casting billet enters a steel moving area to be subjected to parallel flow, the temperature of each continuous casting billet needs to be kept on a continuous casting conveying roller way for 0.5-1.5 min, and the temperature keeping time is adjusted according to the drawing speed of a continuous casting machine. Has the advantages that: the effect of reducing the head-tail temperature difference of the continuous casting billet is realized, the investment is low, and the effect is quick. The requirement on strength is met, the weight is light, and field workers can conveniently lift off the steel tube at any time for overhauling and maintaining.
Description
Technical Field
The invention belongs to the technical field of direct rolling and provides a control method for reducing the temperature difference between the head and the tail of a continuous casting billet in a direct rolling process.
Background
The direct rolling technology of the continuous casting billet refers to a process technology that the continuous casting billet is directly sent to a rolling mill for rolling after being cut off by a continuous casting machine without being heated by a heating furnace. The technology not only reduces the production cost and the energy consumption, but also reduces the emission of greenhouse gases. Although the direct rolling technology has many advantages, because the continuous casting machine is not subjected to temperature equalization treatment by a heating furnace after being cut off, the head-tail temperature difference of the continuous casting billet before rolling is large, generally 150-square continuous casting billets with the length of 10 meters are 80-100 ℃ at the head and the tail before rolling. Taking the production of the twisted steel as an example, when the head-tail temperature difference of the continuous casting billet is greater than 80 ℃, the fluctuation range of the mechanical property of the twisted steel is 100MPa, and the fluctuation range of the mechanical property of the twisted steel produced by a traditional heating furnace is less than 30MPa, so that the head-tail temperature difference before the rolling of the straight-rolling continuous casting billet seriously influences the stability of the structure and the performance of a steel product, and the product quality is reduced.
Other methods for controlling the head-to-tail temperature difference of the casting blank are as follows: the invention discloses a control method for the head-tail temperature difference of a 201010237764.4 semi-endless rolling super-long casting blank, which belongs to the field of semi-endless rolling technology and mainly realizes the control of the head-tail temperature difference of the casting blank by adjusting the conveying speed of the continuous casting blank in different time periods after the continuous casting blank enters a soaking furnace. At present, no effective method for remarkably reducing the head-tail temperature difference before rolling of the direct rolling continuous casting billet exists.
Disclosure of Invention
The invention aims to provide a control method for reducing the head-to-tail temperature difference before rolling of a continuous casting blank in a direct rolling process, which is mainly used for carrying out heat preservation and temperature waiting process treatment on a steel blank in a continuous casting high-temperature section so as to improve the temperature uniformity before rolling of the continuous casting blank, reduce the mechanical property fluctuation of the yield and improve the product quality.
The head-tail temperature difference of the continuous casting billet is caused by the fact that billet shells are solidified successively in the continuous casting process, the drawing speed V produced by a continuous casting machine in the direct rolling process is 2.0-2.8 m/min, and therefore, for the continuous casting billet with the length L, the head-tail air cooling time difference is 3-5 min at the moment of tail cutting, and therefore, the head-tail temperature difference of the continuous casting billet cannot be avoided in the production process of the direct rolling process and can only be reduced through other process methods. The specific process and the controlled technical parameters are as follows:
(1) adding two sections of heat preservation covers on a conveying roller way of each flow of a continuous casting machine, wherein one section of heat preservation cover is added between a cutting position and a fixed length position of a casting blank, the length of the heat preservation cover is half of the fixed length of the casting blank, and the starting point of the heat preservation cover is 0.25m of a fixed length head monitoring point; the other section is that a heat preservation cover is added on the roller conveyor before the continuous casting blank enters the steel moving area, the length of the heat preservation cover is half of the fixed length of the casting blank, and the starting point of the heat preservation cover is the front edge of the steel moving area (see figure 1)
(2) Before each continuous casting billet enters a steel moving area to be subjected to parallel flow, the temperature of each continuous casting billet needs to be kept on a continuous casting conveying roller way for 0.5-1.5 min, and the temperature keeping time is adjusted according to the drawing speed of a continuous casting machine;
taking a continuous casting billet with the length of 150mm multiplied by 150mm as an example, under the process of dynamically adjusting secondary cooling distribution water of a continuous casting machine, the selection range of the temperature waiting time of the casting billet at the head and the tail of the casting billet is reduced by the direct rolling process as follows:
when the drawing speed is 2.0-2.2 m/min, the temperature waiting time of the continuous casting billet is 0-0.5 min;
when the drawing speed is 2.2-2.5 m/min, the temperature waiting time of the continuous casting billet is 0.5-1.0 min;
when the drawing speed is 2.5-2.8 m/min, the temperature waiting time of the continuous casting billet is 1.0-1.5 min.
Further description of the Process arrangement
The invention needs to add two sections of heat preservation covers on a conveying roller way of each flow of a continuous casting machine, and has the principle that the continuous casting blank drawing production process is slow, after the head of the casting blank goes out of a hydraulic shearing position, the head of the casting blank is directionally preserved, the back half part of the continuous casting blank is continuously cooled in air, and finally the head-tail temperature difference of the continuous casting blank is reduced, so that the temperature of the continuous casting blank in the length direction is as uniform as possible, as shown in figure 1.
The heat preservation cover in position 1 mainly has utilized the continuous casting billet when not cutting off, and its speed equals conticaster casting speed V, carries out the head heat preservation that time length is L/V to the continuous casting billet head, and this time is longer than subsequent roll table transfer time, the head heat loss of reduction continuous casting billet that can be abundant. The initial position of the heat preservation cover at this position should avoid the position that conticaster scale detected to influence the normal scale of continuous casting billet and cut off production, through the on-the-spot repeated experiment, need vacate the distance that is greater than 0.25 m. But the distance is not easy to be too large so as not to influence the temperature equalizing effect of the section 1 of the heat-insulating cover.
The heat preservation cover at the position 2 mainly utilizes the characteristic that the continuous casting billet needs to wait in the parallel flow process, and according to the difference of the casting machine pulling speed, the waiting time before the continuous casting machine is adjusted in real time to carry out directional heat preservation on the head of the continuous casting billet, thereby reducing the heat loss of the head of the continuous casting billet. The invention carries out directional heat preservation process operation on the head of the continuous casting billet through the two sections of heat preservation covers, and achieves the purpose of reducing the head-tail temperature difference of the continuous casting billet in the direct rolling process.
Further description of the Process parameters
The general continuous casting billet direct rolling process requires the initial rolling temperature of a casting billet to be at least above 900 ℃, so the casting billet temperature of a conveying section of a continuous casting machine is required. In order to better set the temperature waiting process of the continuous casting billet, the surface temperatures of the continuous casting billets with different drawing speeds need to be calculated.
When a continuous casting billet with 150mm multiplied by 150mm is produced by a continuous casting machine with the most common arc radius of 8m and is in a standard state, when the drawing speed is calculated to be 2m/min, the temperature field change of the billet in the whole continuous casting process is shown as 3, the time interval between the cutting position and the lowest temperature position of rolled steel is 1.5min, and the necessary conveying time between the common casting billet and the rolled steel is about 1.5min, so that when the drawing speed is 2m/min, the billet cannot wait at the position 2 and must be timely conveyed to a rolling mill for rolling. Similarly, it can also be calculated that under the previous standard state condition, when the pulling speed is 2.8m/min, the time interval between the cutting position and the lowest temperature position of the rolled steel is 3min, the necessary conveying time for removing the casting blank is 1.5min, the maximum waiting time of the casting blank at the position 2 is 1.5min, and the temperature field change of the steel blank in the whole continuous casting process is shown as 4.
The temperature waiting time of the continuous casting billet of the section 2 of the heat-insulating cover is determined according to the temperature state of the continuous casting billet and the minimum temperature required by steel rolling. The calculation shows that when the drawing speed of the continuous casting machine is 2.0-2.8 m/min, the maximum allowable waiting time of the continuous casting slab is 0-1.5 min, so that in the field of on-site production, the drawing speed range of the continuous casting machine is divided into three sections, and different waiting time is adopted for each section of the continuous casting slab.
Design of the heat preservation cover:
traditional heat preservation cover adopts the mode of steel sheet welding rib, and steel sheet itself need provide certain intensity and support, therefore its thickness ratio is bigger, selects more than 3mm mostly. In addition, the design length of traditional heat preservation cover is longer, does not conform to the production condition of conticaster conveying section, has brought the trouble for maintenance and has influenced production.
The heat-insulating cover adopts angle steel as a structural frame, and the outer surface of the heat-insulating cover is welded with a steel plate with the thickness of 1 mm. The length of the heat-insulating cover is 1m, the upper surface of the heat-insulating cover adopts a single person and double handles, so that the heat-insulating cover is convenient for field personnel to splice and replace randomly in the production process, and the production and maintenance are convenient. The specific design sketch of the heat-insulating cover is shown in figure 2.
The invention has the following advantages:
1. the original roller way and production mode are not changed, the effect of reducing the head-tail temperature difference of the continuous casting billet can be realized only by adding two sections of heat preservation covers and matching with a temperature waiting process, the investment is low, and the effect is quick.
2. Aiming at the continuous casting process under different pulling speed states, different casting blank waiting times are adopted, the loss of the head temperature of the casting blank can be reduced to the maximum extent, and the head-tail temperature difference of the continuous casting blank is reduced.
3. The heat preservation cover adopts the upper buckle formula, and single heat preservation cover length is 1m, and two sections heat preservation positions can splice the use according to continuous casting billet length at will, adopt the frame construction of angle steel, satisfy the strength requirement and the quality is comparatively light, make things convenient for the on-the-spot workman to lift off at any time and overhaul and maintain.
Drawings
FIG. 1 is a layout diagram of the on-site process of the present invention, which defines the application location of the two-stage insulation cover.
Fig. 2 is a design diagram of the heat-preservation cover, which comprises information of specific sizes, materials and the like.
FIG. 3 is a graph showing the temperature change of the surface and the core of a cast slab in the whole continuous casting process with time at a drawing speed of 2m/s in a conventional 150-square continuous casting machine.
FIG. 4 is a graph showing the temperature change of the surface and the core of a cast slab in the whole continuous casting process with time at a drawing speed of 2.8m/s in a conventional 150-square continuous casting machine.
FIG. 5 is a statistical data plot of the yield strength and tensile strength of HRB400 without the application of this method.
FIG. 6 is a data statistical plot of the yield strength and tensile strength of HRB400 after application of the present method.
Detailed Description
An electric furnace short-flow direct rolling process is adopted by a certain long section bar production enterprise to produce HRB400 steel bars, and the specification of continuous casting billets is150mm × 150mm, length 6m, pulling speed 2.4m/min, crystallizer water amount 170m3At a casting temperature of 1530 ℃ and the product has the dimensional specification of
The chemical composition is shown in table 1.
TABLE 1 chemical composition of HRB400 steel bar of a certain plant (balance Fe)
| Composition (I) | C | Si | Mn | P | S | Nb | V |
| Content (wt.) | 0.23 | 0.45 | 0.85 | ≤0.04 | ≤0.03 | ≤0.01 | 0.04 |
When the temperature equalization process control is not performed by adopting the discovery, the temperature of the upper surface of the head part is 955 ℃ and the temperature of the upper surface of the tail part is 1035 ℃ when the casting blank is cut off, and the temperature difference between the head and the tail is 80 ℃. After parallel flow, the continuous casting blank enters a quick conveying roller way and is conveyed to a roughing mill, the temperature of the upper surface of the head of the continuous casting blank is 905 ℃, the temperature of the upper surface of the tail of the continuous casting blank is 975 ℃, and the temperature difference between the head and the tail of the continuous casting blank is 70 ℃.
When the 2-section type heat preservation cover is used for temperature equalization control, the temperature waiting time of the casting blank at the 2-section heat preservation position is 0.8 min. The temperature of the upper surface of the head part when the cast slab is cut off is 965 ℃, the upper surface of the tail part is 1035 ℃, and the temperature difference between the head part and the tail part is 70 ℃. Subsequently, the continuous casting billet is waited for 0.8min before the parallel flow, and the directional heat preservation of the head is carried out. And then the continuous casting billet enters a quick conveying roller way after parallel flow, and is conveyed to a roughing mill, wherein the temperature of the upper surface of the head part of the continuous casting billet is 910 ℃, the temperature of the upper surface of the tail part of the continuous casting billet is 950 ℃, and the temperature difference between the head part and the tail part of the continuous casting billet is 40 ℃. Obviously, the heat loss of the head of the continuous casting billet is obviously reduced by the temperature equalization of the 2-section heat preservation cover.
Therefore, the temperature equalizing effect of the continuous casting billet in the steel mill is obvious, the head-tail temperature difference of the continuous casting billet before rough rolling is reduced to 40 ℃ from 70 ℃, and is reduced by 57%. The change of the mechanical properties of the product is shown in fig. 5 and 6, the fluctuation range of the yield strength and the tensile strength is reduced from 100MPa to 50MPa, and the effect of stabilizing the product performance by the method is obvious.
Claims (2)
1. A control method for reducing the temperature difference between the head and the tail of a continuous casting billet in a direct rolling process is characterized by comprising the following steps:
(1) adding two sections of heat preservation covers on a conveying roller way of each flow of a continuous casting machine, wherein one section is formed by adding one section of heat preservation cover between a casting blank cutting position and a fixed length position, the length of the heat preservation cover is half of the fixed length of the casting blank, and the starting point of the heat preservation cover is 0.25m away from a fixed length head monitoring point; the other section is that a heat preservation cover is added on the conveying roller way before the continuous casting blank enters the steel moving area, the length of the heat preservation cover is half of the fixed length of the casting blank, and the starting point of the heat preservation cover is the front edge of the steel moving area;
(2) before each continuous casting billet enters a steel moving area to carry out parallel flow, the temperature of each continuous casting billet needs to be kept for 0-1.5 min on a continuous casting conveying roller way, and the temperature keeping time is adjusted according to the drawing speed of a continuous casting machine.
2. The control method for reducing the temperature difference between the head and the tail of the continuous casting slab in the direct rolling process according to claim 1, wherein the control method comprises the following steps: for a continuous casting blank with the length of 150mm multiplied by 150mm, under the process of dynamically adjusting secondary cooling distribution water of a continuous casting machine, the selection range of the casting blank temperature waiting time for reducing the head-tail temperature difference of the casting blank by the direct rolling process is as follows:
when the drawing speed is 2.0-2.2 m/min, the temperature waiting time of the continuous casting billet is 0-0.5 min;
when the drawing speed is more than 2.2m/mi and less than 2.5m/min, the temperature waiting time of the continuous casting billet is 0.5-1.0 min;
when the drawing speed is 2.5-2.8 m/min, the temperature waiting time of the continuous casting billet is 1.0-1.5 min.
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| CN110125359A (en) * | 2019-06-10 | 2019-08-16 | 中冶赛迪技术研究中心有限公司 | A kind of control method and system of the continuous casting secondary cooling water reducing continuous casting billet head and tail temperature difference |
| CN110711785B (en) * | 2019-10-10 | 2021-03-12 | 中冶南方连铸技术工程有限责任公司 | Method and system for controlling temperature of fixed-length casting blank before rolling |
| CN111167855B (en) * | 2019-12-26 | 2022-03-15 | 河钢股份有限公司承德分公司 | Rod and wire rod concurrent heating rolling process |
| CN114589376B (en) * | 2022-03-15 | 2022-10-04 | 山东钢铁集团永锋临港有限公司 | Uncut alarm method for cutting casting blank by flame cutting machine |
| CN114799095B (en) * | 2022-04-28 | 2023-12-29 | 广西柳州钢铁集团有限公司 | Reinforcement bar heating-free direct rolling method and reinforcement bar rolled by heating-free direct rolling method |
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