CN104174660B - The zerolling method of flexibility - Google Patents

Abstract

The invention discloses a flexible low-temperature rolling method, which comprises the following steps: according to the preset mapping relationship between different grades of steel and critical temperatures, determining the temperature required by the current steel to be rolled in each rolling stage; According to the determined temperature required for each rolling stage, adjust the parameters of the heating furnace, roughing mill and finishing mill; after setting the corresponding rolling schedule according to the yield strength of the steel, the steel is passed through the Rolling takes place in heating furnaces, roughing mills and finishing mills. On the one hand, the flexible low-temperature rolling method can reduce the energy consumption of the rolling process, on the other hand, it can also improve the rolling efficiency and reduce the production cycle.

Description

Flexible Low Temperature Rolling Method

technical field

The invention relates to the technical field of steel rolling control, in particular to a flexible low-temperature rolling method.

Background technique

With the development of modern science and technology and economic construction, it is difficult for large-scale, continuous and intensive steel production to meet users' requirements for diversification, individualization and high-quality steel products. In the hot rolling production process, in order to make the rolling process stable, it is necessary to arrange production according to certain rolling procedures. The existing hot rolling procedures need to consider the heating temperature, composition, strength grade and size requirements of steel grades, and arrange the rolling in an orderly manner in the order of heating temperature from low temperature to high temperature and steel grade strength from low grade to high grade. production. Due to the high heating temperature and strength of some steel types, it is necessary to arrange a large number of transition materials to complete the transition slowly, which greatly limits the flexibility of production, prolongs the rolling cycle of the product, cannot effectively meet the needs of customers, and affects the contract the completion.

With the improvement of hardware equipment in iron and steel enterprises and the development of rolling technology, flexible low-temperature rolling technology can solve the above contradictions. However, the existing hot rolling production technologies all refer to the flexibility of the structure and performance during the rolling process. For steel types with the same chemical composition, different cooling methods after rolling are used to achieve different microstructure and properties. This kind of flexible production is only considered from the perspective of organizational performance, and does not involve the entire rolling production process of hot rolling. At the same time, because the existing rolling temperature is high, it is necessary to install a large number of transition materials, so that The production cycle is long.

Contents of the invention

The main purpose of the present invention is to provide a flexible low-temperature rolling method, aiming at flexible production of the entire rolling production process of hot rolling and improving rolling efficiency at the same time.

In order to achieve the above object, the present invention proposes a flexible low-temperature rolling method, comprising the following steps:

Adjust the parameters of the heating furnace, roughing mill and finishing mill according to the determined temperature required for each rolling stage;

After the corresponding rolling schedule is set according to the yield strength of the steel, the steel is rolled sequentially through the heating furnace, the rough rolling mill and the finishing mill.

Preferably, the preset mapping relationship between different grades of steel grades and critical temperature is:

RH=Max[T (hot embrittlement temperature), T (C solid solution temperature), T (Mn solid solution temperature), T (Nb solid solution temperature), T (Ti solid solution temperature), T (descaler temperature)] ;

RT＝Max[T (capability check of roughing mill), T (bite temperature of roughing mill), T(FT0+ΔT temperature drop during transportation+ΔT descaling temperature drop)];

FT0=Max[T(FT7+ΔT temperature drop during rolling), T(finishing mill capacity check), T(steel recrystallization temperature)];

FT7=Min[T(Ar3), T(NbC precipitation temperature), T(TiC precipitation temperature), T(TiN precipitation temperature)];

CT = T (phase transition temperature);

Wherein, RH is the exit temperature of the heating furnace, RT is the outlet temperature of the rough rolling mill, FT0 is the inlet temperature of the finishing mill, FT7 is the outlet temperature of the finishing mill, and CT is the coiling temperature of the coiler. Temperature, T(Ar3) is the critical temperature at which ferrite begins to precipitate in austenite when the steel is cooled.

Preferably, the step of setting a corresponding rolling schedule according to the yield strength of the steel specifically includes:

When the steel is low-strength grade steel, the rolling schedule is 6-8 pieces of hot-rolled steel, and the rest are low-strength grade steel; when the steel is medium-strength grade steel, the rolling schedule is 6-8 hot-rolled pieces, 2-4 pieces of low-strength steel grades, and the rest are medium-strength grade steel grades; when the steel is high-strength grade steel grades, the rolling procedure is 6-8 pieces of hot-rolled steel grades, 2-4 pieces of low-strength grade steel grades, 4 ～6 medium-strength grade steel grades, and the rest are high-strength grade steel grades, among which, the low-strength grade steel grades are between 180-300Mpa in yield strength; the medium-strength grade steel grades are between 300-500MPa in yield strength; The strength level of steel is above the yield strength of 500MPa.

Preferably, during the rolling process, the rolling process parameters of low-strength steel grades are as follows: the total time in the furnace during the heating process is controlled at 130-155 minutes, the heating furnace maintains a slight positive pressure of 10-12 Pa, the pre-heating furnace The air-fuel ratio of the hot section is controlled at 1.0-1.1, the preheating time is 60-70 minutes, the air-fuel ratio of the heating section of the heating furnace is kept at 0.9-1.0, the heating time is 40-50 minutes, and the temperature of the soaking section of the heating furnace is kept at 1.0 ～1.1, the temperature is controlled at 1140～1160℃, and the soaking time is 30～35min; during the rough rolling process, the descaling passes are greater than or equal to 4, and the rough rolling exit temperature is controlled at 1010～1020℃; The rolling speed is 5-12m/s, the final rolling temperature is 830-840°C; the coiling temperature of the coiler is 610-640°C.

Preferably, during the rolling process, the rolling process parameters of medium-strength grade steel grades are as follows: the total time in the furnace during the heating process is controlled at 135-170 minutes, the heating furnace maintains a slight positive pressure of 10-12 Pa, the pre-heating furnace The air-fuel ratio of the hot section is kept at 1.1-1.2, the preheating time is 60-70 minutes, the air-fuel ratio of the heating section of the heating furnace is kept at 0.9-1.0, the heating time is 50-60 minutes, and the temperature of the soaking section of the heating furnace is kept at 1.0 ～1.1, the temperature is controlled at 1150～1180℃, and the soaking time is 25～40min; in the rough rolling process, the descaling pass is greater than or equal to 4, and the exit temperature of the rough rolling mill is 1020～1030℃; The rolling speed is 5-10m/s, the final rolling temperature is 840-850°C; the coiling temperature of the coiler is 610-640°C.

Preferably, during the rolling process, the rolling process parameters of high-strength grade steel grades are as follows: the total time in the furnace during the heating process is controlled at 160min-200min, the heating furnace maintains a slight positive pressure of 10-12Pa, the preheating furnace The air-fuel ratio of the hot section is kept at 1.0-1.1, the preheating time is 80-90 minutes, the air-fuel ratio of the heating section of the heating furnace is kept at 0.9-1.0, the heating time is 50-60 minutes, and the temperature of the soaking section of the heating furnace is kept at 1.1 ～1.2, the temperature is controlled at 1170～1220℃, and the soaking time is 30～50min; in the rough rolling process, the descaling pass is greater than or equal to 4, and the exit temperature of the rough rolling mill is 1030～1060℃; The rolling speed is 5-10m/s, the final rolling temperature is 850-860°C; the coiling temperature of the coiler is 580-610°C.

Preferably, the flexible low-temperature rolling technology also includes the following steps:

In the laminar flow cooling process of steel, the edge shielding technology is used to reduce the edge temperature drop of the hot-rolled strip during the cooling process.

Preferably, the flexible low-temperature rolling technology also includes the following steps:

The insulation cover is used in the rough rolling process to reduce the temperature drop in the rough rolling process.

The flexible low-temperature rolling method proposed by the present invention determines the temperature required by the steel to be rolled at each rolling stage according to the preset mapping relationship between different grades of steel and the critical temperature, thereby ensuring The temperature required in the stage is above the critical temperature, and the production characteristics of various steel types in hot rolling and the flexible organizational production can make the rolling process more flexible and adaptable, making it more energy-saving. In addition, because the critical temperature required for each rolling stage of the steel is determined first, the temperature does not need to be too high. Therefore, the number of supporting transition materials can be greatly reduced, which improves the production rhythm to a certain extent and shortens the production cycle.

Description of drawings

Fig. 1 is a flow diagram of a preferred embodiment of the flexible low-temperature rolling method of the present invention.

The realization of the purpose of the present invention, functional characteristics and advantages will be further described in conjunction with the embodiments and with reference to the accompanying drawings.

detailed description

It should be understood that the specific embodiments described here are only used to explain the present invention, not to limit the present invention.

Referring to FIG. 1 , FIG. 1 is a schematic flowchart of a preferred embodiment of the flexible low-temperature rolling method of the present invention.

A preferred embodiment of the flexible low-temperature rolling method proposed by the present invention. In this embodiment, the flexible low-temperature rolling method includes the following steps:

Step S10, according to the preset mapping relationship between different grades of steel and the critical temperature, determine the temperature required by the steel to be rolled in each rolling stage, wherein the temperature required by each rolling stage is higher than the required temperature. Corresponding critical temperature;

Step S20, adjusting the parameters of the heating furnace, the rough rolling mill and the finishing mill according to the determined temperature required for each rolling stage;

Step S30, after setting the corresponding rolling schedule according to the yield strength of the steel, rolling the steel in the heating furnace, the rough rolling mill and the finish rolling mill in sequence.

Specifically, for FT7, the constraints should be greater than Ar3 to ensure that the finishing rolling process is rolled in the austenite single-phase region; for FT0, the constraints are to ensure that the temperature of FT7 can be achieved on the one hand, and the other On the one hand, it is also necessary to ensure that the temperature of each pass of the finish rolling is within the allowable range of the rolling mill load. Similarly, other temperature control points, such as RT2/RT4, CT, and RH, also have corresponding constraints.

In this embodiment, the preset mapping relationship between different grades of steel and critical temperature is:

The furnace temperature RH is calculated by the following formula:

RH=Max[T (hot embrittlement temperature), T (C solid solution temperature), T (Mn solid solution temperature), T (Nb solid solution temperature), T (Ti solid solution temperature), T (descaler temperature)] ;

T (hot embrittlement temperature) is the hot embrittlement temperature corresponding to a certain steel grade, T (C solid solution temperature) is the solid solution temperature of C in a certain steel grade, T (Mn solid solution temperature) is the Mn solid solution temperature in a certain steel grade T (Nb solid solution temperature) is the solid solution temperature of Nb in a certain steel grade, T (Ti solid solution temperature) is the solid solution temperature of Ti in a certain steel grade, T (descaler temperature) is Descaling temperature corresponding to a certain steel grade;

The exit temperature RT of the roughing mill is calculated by the following formula:

RT＝Max[T (capability check of roughing mill), T (bite temperature of roughing mill), T(FT0+ΔT temperature drop during transportation+ΔT descaling temperature drop)];

T (capability check of roughing mill) is the lowest temperature that the roughing mill can roll (because the steel temperature is too low, the roughing machine cannot roll the steel), and ΔT descaling temperature drop is the temperature drop value of the steel during the descaling process;

The inlet temperature FT0 of the finishing mill is calculated by the following formula:

FT0=Max[T(FT7+ΔT temperature drop during rolling), T(finishing mill capacity check), T(steel recrystallization temperature)];

T (finishing mill capacity check) is the lowest temperature that the finishing mill can roll (because the steel temperature is too low, the finishing mill will not be able to roll the steel), T (steel recrystallization temperature) is the corresponding temperature of a certain steel type recrystallization temperature;

The exit temperature of the finishing mill is calculated by the following formula:

FT7=Min[T(Ar3), T(NbC precipitation temperature), T(TiC precipitation temperature), T(TiN precipitation temperature)];

T(Ar3) is the critical temperature at which ferrite begins to precipitate in austenite when the steel is cooled, T(NbC precipitation temperature) is the precipitation temperature of NbC in a certain steel, and T(TiC precipitation temperature) is the temperature of a certain steel The precipitation temperature of TiC in the steel of a certain type of steel, T (TiN precipitation temperature) is the precipitation temperature of TiN in the steel of a certain steel type;

The coiling temperature CT of the coiler is calculated by the following formula:

CT = T (phase transition temperature);

T (phase transition temperature) is the phase transition temperature of a certain type of steel.

After the outlet temperature of the roughing mill is determined, the inlet temperature of the roughing mill can be set accordingly according to the outlet temperature. After determining the critical temperature of a certain steel grade at each stage of rolling, it is sufficient to ensure that the rolling temperature is slightly higher than the critical temperature, generally 20-30°C. At this time, it is not only beneficial to energy saving (because the lower the temperature, the lower the power of each equipment), but also ensures the mechanical properties of the steel and the rolling conditions of each equipment (because the temperature is too low, it will not be conducive to equipment rolling).

Specifically, in step S30, the corresponding rolling schedule is set according to the yield strength of the steel. Specifically, the following method is used: when the steel is a low-strength grade steel, the rolling schedule is 6 to 8 pieces of hot-rolled steel, and the rest are low-strength grade steel. When the steel is a medium-strength grade steel, the rolling procedure is 6-8 pieces of hot-rolled steel, 2-4 low-strength grade steel, and the rest are medium-strength grade steel; when the steel is a high-strength grade steel, The rolling procedure is 6-8 pieces of hot roll materials, 2-4 pieces of low-strength steel grades, 4-6 pieces of medium-strength grade steel grades, and the rest are high-strength grade steel grades. Among them, the low-strength grade steel grades are yield strength Between 180 and 300Mpa; medium-strength steel grades have a yield strength of 300-500MPa; high-strength grade steels have a yield strength of 500MPa and above.

Specifically, in this embodiment, three kinds of rolling process parameters for the three kinds of steel materials, namely low-strength grade steel, medium-strength grade steel and high-strength grade steel, are given.

During the rolling process, the rolling process parameters of low-strength steel grades are as follows: the total time in the furnace during the heating process is controlled at 130-155 minutes, the heating furnace maintains a slight positive pressure of 10-12 Pa, and the preheating section of the heating furnace is empty. The fuel ratio is controlled at 1.0-1.1, the preheating time is 60-70 minutes, the air-fuel ratio in the heating section of the heating furnace is kept at 0.9-1.0, the heating time is 40-50 minutes, the temperature and air-fuel ratio of the soaking section of the heating furnace is kept at 1.0-1.1, The temperature is controlled at 1140-1160°C, and the soaking time is 30-35 minutes; during the rough rolling process, the descaling passes are greater than or equal to 4, and the exit temperature of the rough rolling is controlled at 1010-1020°C; the rolling speed of the finishing mill is 5~12m/s, the final rolling temperature is 830~840℃; the coiling temperature of the coiler is 610~640℃.

However, for existing steels of the same low-strength grade, the conventional rolling in the prior art requires 8 to 10 ironing rollers because the temperatures in each rolling stage are high.

During the rolling process, the rolling process parameters of medium-strength steel grades are as follows: the total time in the furnace during the heating process is controlled at 135-170 minutes, the heating furnace maintains a slight positive pressure of 10-12 Pa, and the preheating section of the heating furnace is empty. The fuel ratio is kept at 1.1-1.2, the preheating time is 60-70 minutes, the air-fuel ratio of the heating section of the heating furnace is kept at 0.9-1.0, the heating time is 50-60 minutes, the temperature and air-fuel ratio of the soaking section of the heating furnace is kept at 1.0-1.1, The temperature is controlled at 1150-1180°C, and the soaking time is 25-40 minutes; during the rough rolling process, the descaling pass is greater than or equal to 4, and the exit temperature of the rough rolling mill is 1020-1030°C; the rolling speed of the finishing mill is 5~10m/s, the final rolling temperature is 840~850℃; the coiling temperature of the coiler is 610~640℃.

Under the same conditions, due to the high temperature in each rolling stage, the conventional rolling in the prior art requires 8-10 ironing rolls plus 4-8 low-strength steel grades

During the rolling process, the rolling process parameters of high-strength steel grades are as follows: the total time in the furnace during the heating process is controlled at 160min to 200min, the heating furnace maintains a slight positive pressure of 10 to 12Pa, and the preheating section of the heating furnace is empty. The fuel ratio is kept at 1.0-1.1, the preheating time is 80-90 minutes, the air-fuel ratio of the heating section of the heating furnace is kept at 0.9-1.0, the heating time is 50-60 minutes, the temperature of the soaking section of the heating furnace is kept at 1.1-1.2, The temperature is controlled at 1170-1220°C, and the soaking time is 30-50 minutes; during the rough rolling process, the descaling passes are greater than or equal to 4, and the exit temperature of the rough rolling mill is 1030-1060°C; the rolling speed of the finishing mill is 5~10m/s, the final rolling temperature is 850~860℃; the coiling temperature of the coiler is 580~610℃.

Under the same conditions, due to the high temperature in each rolling stage, conventional rolling of 8-10 hot rolls, 4-8 hot rolls and 6-10 medium-strength steel grades is adopted in the prior art.

Further, the flexible low-temperature rolling method proposed by the present invention also includes the following steps:

In the laminar flow cooling process of steel, the edge shielding technology is used to reduce the edge temperature drop of the hot-rolled strip during the cooling process.

Further, the flexible low-temperature rolling method proposed by the present invention also includes the following steps:

The insulation cover is used in the rough rolling process to reduce the temperature drop in the rough rolling process.

At this time, the low-temperature rolling method that can make this flexible can further reduce the energy consumption of rolling production.

Specifically, in this embodiment, three types of slabs are used for rolling to better illustrate the flexible low-temperature rolling method.

The specific composition of the three slabs is shown in the table below:

Table 1 Smelting composition of three kinds of slabs

Table 2 Rolling process temperature

Rolling process temperature, ℃ RH RT2/RT4 FT0 FT7 CT Slab 1 1160 1020 1010 835 640 Slab 2 1180 1030 1023 840 613 Slab 3 1210 1040 1035 856 580

The slab 1 is a low-strength steel grade, and the rolling procedure is as follows: 8 pieces of hot-rolled rolls are first arranged in the heating furnace, and then the rolling production can be arranged. The corresponding rolling process parameters are adjusted as follows: the total furnace time of the slab 1 during the heating process is controlled at 130 minutes. Keep a slight positive pressure of 12Pa in the furnace to prevent the inhalation of cold wind. The air-fuel ratio in the preheating section is kept at 1.0, the preheating time is 60 minutes, the air-fuel ratio in the heating section is kept at 0.95, and the heating time is 40 minutes. At 1160°C, the soaking time is 30min. In the rough rolling process, the rolling system and the descaling passes are optimized to ensure that the descaling passes are ≥ 4, and the heat preservation cover is used to reduce the temperature drop during the rough rolling process, and the exit temperature of the rough rolling is 1020°C. The entrance of finishing rolling basically remains unchanged or slightly lowered in the original temperature system, and the rolling speed of finishing rolling is increased to ensure that the finishing rolling temperature and coiling temperature remain unchanged in the original conventional hot rolling process, and the rolling speed is 12m/s , The final rolling temperature is 835°C, and the coiling temperature is 640°C. The edge shielding technology is used in the laminar cooling process to reduce the edge temperature drop of the hot-rolled strip during the cooling process.

The slab 2 is a medium-strength steel grade, and the rolling procedure is as follows: first arrange 8 pieces of hot-rolled roll materials in the heating furnace, and then arrange 2 pieces of low-strength grade steel grades, and then arrange its rolling production. The corresponding rolling process parameters are adjusted as follows: the total time in the furnace during the heating process is controlled at 150min. Keep a slight positive pressure of 12Pa in the furnace to prevent the inhalation of cold wind. The air-fuel ratio in the preheating section is kept at 1.1. The preheating time is 60 minutes. The air-fuel ratio in the heating section is kept at 1.0. The heating time is 50 minutes. At 1180°C, the soaking time is 40min. In the rough rolling process, the rolling system and the descaling passes are optimized to ensure that the descaling passes are ≥ 4, and the heat preservation cover is used to reduce the temperature drop during the rough rolling process, and the rough rolling exit temperature is 1030°C. The entrance of finishing rolling basically remains unchanged or slightly lowered in the original temperature system, and the rolling speed of finishing rolling is increased to ensure that the finishing rolling temperature and coiling temperature remain unchanged in the original conventional hot rolling process, and the rolling speed is 10m/s , The final rolling temperature is 840°C, and the coiling temperature is 613°C. The edge shielding technology is used in the laminar cooling process to reduce the edge temperature drop of the hot-rolled strip during the cooling process.

The slab 3 is a high-strength steel grade, and the rolling procedure is as follows: first arrange 8 pieces of hot-rolled roll materials in the heating furnace, arrange 2 pieces of low-strength grade steel grades, and then arrange 4 pieces of medium-strength grade steel grades, and then arrange the rolling. production. The corresponding rolling process parameters are adjusted as follows: the total furnace time of the slab 3 during the heating process is 180 minutes. The furnace maintains a slight positive pressure of 12Pa, the air-fuel ratio of the preheating section is kept at 1.1, the preheating time is 80min, the air-fuel ratio of the heating section is kept at 1.05, and the heating time is 70min. ℃, heating time 30min. In the rough rolling, 3/4 continuous rolling mill is adopted, R1 descaling 1 pass, R2 rolling 5 passes, descaling 2 passes, R3 descaling 1 pass, R4 no descaling, the total descaling pass is 4 passes, heat preservation cover is used to reduce the temperature drop in the rough rolling process, the exit temperature of RT4 rough rolling is 1040°C, the rolling speed is 7.6m/s, the final rolling temperature is 856°C, and the coiling temperature is 580°C. The edge shielding technology reduces the edge temperature drop of the hot-rolled strip during the cooling process.

After the rolling is completed, see Table 3 for the comparison of the mechanical properties of the hot-rolled coils rolled from the three slabs.

Table 3 Comparison of organization and mechanical properties

It can be seen from Table 3 that as long as the rolling temperature at each stage is above the corresponding critical temperature, the microstructure and mechanical properties of the steel coils rolled from the three slabs all meet the standard requirements.

The flexible low-temperature rolling method proposed by the present invention determines the temperature required by the steel to be rolled at each rolling stage according to the preset mapping relationship between different grades of steel and the critical temperature, thereby ensuring The temperature required for the stage is above the critical temperature. On the one hand, the flexible low-temperature rolling method can reduce the energy consumption of the rolling process, and on the other hand, it can also improve the rolling efficiency. The flexible low-temperature rolling method integrates the production characteristics of various hot-rolled steel types, and the flexible tissue production can make the rolling process have greater flexibility and adaptability, and reduce the energy consumption of rolling production. In addition, because the critical temperature required for each rolling stage of the steel is determined first, the temperature does not need to be too high, so the number of supporting transition materials can be greatly reduced, the production rhythm is improved to a certain extent, and the production cycle is shortened. Thereby improving rolling efficiency.

The above are only preferred embodiments of the present invention, and are not intended to limit the patent scope of the present invention. All equivalent structural transformations made by using the description of the present invention and the contents of the accompanying drawings, or directly or indirectly used in other related technical fields, are all the same. included in the scope of patent protection of the present invention.

Claims (7)

1. a flexible low temperature rolling method, is characterized in that, comprises the following steps: According to the preset mapping relationship between different grades of steel and the critical temperature, determine the temperature required by the steel to be rolled in each rolling stage, where the temperature required for each rolling stage is higher than the corresponding critical temperature temperature; Adjust the parameters of the heating furnace, roughing mill and finishing mill according to the determined temperature required for each rolling stage; After setting the corresponding rolling schedule according to the yield strength of the steel, rolling the steel in the heating furnace, the rough rolling mill and the finishing mill in sequence; Wherein, the step of setting a corresponding rolling procedure according to the yield strength of the steel specifically includes: When the steel is low-strength grade steel, the rolling schedule is 6-8 pieces of hot-rolled steel, and the rest are low-strength grade steel; when the steel is medium-strength grade steel, the rolling schedule is 6-8 hot-rolled pieces, 2-4 pieces of low-strength steel grades, and the rest are medium-strength grade steel grades; when the steel is high-strength grade steel grades, the rolling procedure is 6-8 pieces of hot-rolled steel grades, 2-4 pieces of low-strength grade steel grades, 4 ～6 medium-strength grade steel grades, and the rest are high-strength grade steel grades, among which, the low-strength grade steel grades are between 180-300Mpa in yield strength; the medium-strength grade steel grades are between 300-500MPa in yield strength; The strength level of steel is above the yield strength of 500MPa. 2. The low-temperature rolling method according to claim 1, wherein the mapping relationship between the preset different grades of steel and the critical temperature is: RH=Max[T (hot embrittlement temperature), T (C solid solution temperature), T (Mn solid solution temperature), T (Nb solid solution temperature), T (Ti solid solution temperature), T (descaler temperature)] ; RT＝Max[T (capability check of roughing mill), T (bite temperature of roughing mill), T(FT0+ΔT temperature drop during transportation+ΔT descaling temperature drop)]; FT0=Max[T(FT7+ΔT temperature drop during rolling), T(finishing mill capacity check), T(steel recrystallization temperature)]; FT7=Min[T(Ar3), T(NbC precipitation temperature), T(TiC precipitation temperature), T(TiN precipitation temperature)]; CT = T (phase transition temperature); Wherein, RH is the outlet temperature of the heating furnace, RT is the outlet temperature of the rough rolling mill, FT0 is the inlet temperature of the finishing mill, FT7 is the outlet temperature of the finishing mill, and CT is the coiling temperature of the coiler, T(Ar3) is the critical temperature at which ferrite begins to precipitate in austenite when the steel is cooled. 3. The low-temperature rolling method according to claim 1, characterized in that, during the rolling process, the rolling process parameters of the low-strength grade steel are as follows: the total time in the furnace during the heating process is controlled at 130-155min, Maintain a slight positive pressure of 10-12Pa in the heating furnace, control the air-fuel ratio of the preheating section of the heating furnace at 1.0-1.1, and the preheating time is 60-70 minutes. ~50min, the temperature air-fuel ratio in the soaking section of the heating furnace is kept at 1.0~1.1, the temperature is controlled at 1140~1160°C, and the soaking time is 30~35min; The exit temperature of the rough rolling is controlled at 1010-1020°C; the rolling speed of the finishing mill is 5-12m/s, the final rolling temperature is 830-840°C; the coiling temperature of the coiler is 610-640°C. 4. The low-temperature rolling method according to claim 1, characterized in that, during the rolling process, the rolling process parameters of medium-strength grade steel grades are as follows: the total time in the furnace during the heating process is controlled at 135-170min, Keep a slight positive pressure of 10-12Pa in the heating furnace, the air-fuel ratio of the preheating section of the heating furnace is kept at 1.1-1.2, the preheating time is 60-70min, the air-fuel ratio of the heating section of the heating furnace is kept at 0.9-1.0, and the heating time is 50 ~60min, the air-fuel ratio in the soaking section of the heating furnace is kept at 1.0~1.1, the temperature is controlled at 1150~1180°C, and the soaking time is 25~40min; during the rough rolling process, the descaling passes are greater than or equal to 4, The outlet temperature of the roughing mill is 1020-1030°C; the rolling speed of the finishing mill is 5-10m/s, the final rolling temperature is 840-850°C; the coiling temperature of the coiler is 610-640°C. 5. The low-temperature rolling method according to claim 1, characterized in that, during the rolling process, the rolling process parameters of high-strength grade steel grades are as follows: the total time in the furnace during the heating process is controlled at 160min to 200min, The heating furnace maintains a slight positive pressure of 10-12Pa, the air-fuel ratio of the preheating section of the heating furnace is kept at 1.0-1.1, the preheating time is 80-90min, the air-fuel ratio of the heating section of the heating furnace is kept at 0.9-1.0, and the heating time is 50 ~60min, the air-fuel ratio in the soaking section of the heating furnace is kept at 1.1~1.2, the temperature is controlled at 1170~1220°C, and the soaking time is 30~50min; during the rough rolling process, the descaling passes are greater than or equal to 4, The outlet temperature of the roughing mill is 1030-1060°C; the rolling speed of the finishing mill is 5-10m/s, the final rolling temperature is 850-860°C; the coiling temperature of the coiler is 580-610°C. 6. The low temperature rolling method according to any one of claims 3 to 5, further comprising the steps of: In the laminar flow cooling process of steel, the edge shielding technology is used to reduce the edge temperature drop of the hot-rolled strip during the cooling process. 7. The low temperature rolling method according to any one of claims 3 to 5, further comprising the steps of: The insulation cover is used in the rough rolling process to reduce the temperature drop in the rough rolling process.