A hot-rolled bearing steel bar reticulated carbide control model

Abstract

The present application belongs to the technical field of bearing steel hot rolling, and particularly relates to a hot-rolled bearing steel bar reticular carbide control model. The control model sets the roughing temperature range, the finishing temperature range, the temperature range entering the reducing and sizing unit, and the temperature range after the second water cooling in the control model, and combines the preset rolling specification and the performance of the cooling equipment. Since the parameters of the rolling system corresponding to the preset rolling specification are uniquely determined, the rolling speed of the rolling system and the fixed parameter data of the cooling equipment are determined during rolling, forming a fixed combination model of the rolling speed and the rolling cooling data suitable for the preset rolling specification bar. During production, only the respective data based on the rolling specification needs to be input in the computer control module or the corresponding rolling model needs to be directly called, so that the rolling quality is stably controllable.

Description

Technical Field

[0001] This invention relates to the field of hot rolling technology for bearing steel, specifically to a control model for network carbides in hot-rolled bearing steel bars. Background Technology

[0002] Carbides are an important component phase in bearing steel, playing a role in wear resistance, inhibiting grain growth, and absorbing alloying elements to achieve satisfactory performance after heat treatment. However, coarse, polygonal, and segregated carbides are very detrimental to the service life of bearings. Microscopic segregation in bearing steel is mainly manifested as the uneven distribution of alloy carbides. Based on the shape, distribution, and formation cause of carbides in the microstructure of rolled materials, carbides in bearing steel can be divided into banded carbides and network carbides. Among them, network carbides are excess carbides that precipitate along the austenite grain boundaries in hypereutectoid steel during the cooling process and are distributed in a network. Bearing steel belongs to hypereutectoid steel. During the cooling process after rolling, since the diffusion rate of carbide-forming elements along the austenite grain boundaries is much greater than the diffusion rate within the grains, secondary carbides mostly precipitate along the grain boundaries, thus forming a discontinuous or continuous network. Carbide networks increase the brittleness of bearing steel and reduce the fatigue life of bearing components. Therefore, severe carbide network structures are not allowed in the microstructure of bearings under service conditions.

[0003] To reduce the carbide network structure in bearing steel, a well-known control method in the art is to cool the rolled piece to the austenite-carbide two-phase temperature range, approximately 720-900°C, by first-stage water cooling forced cooling. After deformation in the two-phase region, both the proprecipitated carbides and the unrecrystallized austenite undergo plastic deformation simultaneously. The unrecrystallized austenite is deformed, resulting in elongated grains and an increase in deformation bands and dislocation density within the grains. At the same time, the proprecipitated carbides form a large number of dislocations due to plastic deformation, causing the proprecipitated carbides to form fine, dispersed carbide particles, thereby reducing the size of the carbides. The rolled piece is rapidly cooled by a second water cooling process, and the precipitation and growth of carbides are further reduced by passing through the carbide precipitation temperature range of 900℃~700℃. For example, Chinese patent document CN106086353A (201610750155.6) discloses a rolling method for controlling the precipitation of network carbides in large-section GCr15 bearing steel. It limits the temperature range of the rolled piece after the first water cooling and the second water cooling, and limits the range of water cooling pressure and flow rate for the first and second water cooling based on the range of water cooling rate. However, the existing method only gives the range of water cooling pressure and flow rate for the first and second water cooling. In actual production, the water cooling effect is affected by the rolling speed and billet size. When the rolling speed and billet size change, the specific values ​​of water cooling pressure and flow rate for the first and second water cooling need to be adjusted in real time, which increases the workload of on-site workers and causes unstable quality control. Summary of the Invention

[0004] The purpose of this invention is to establish a control model for the network carbide of hot-rolled bearing steel bars, which is used for the rolling control of bars of a certain rolling specification. In actual operation, data can be directly input into the computer control system, making on-site operation convenient and realizing the controllability of the network carbide level of bearing steel.

[0005] The technical problem to be solved by the present invention is achieved by the following technical solution: a control model for network carbides in hot-rolled bearing steel bars, wherein the hot rolling process includes raw material heating, raw material roughing mill rolling, intermediate mill rolling, finishing mill rolling and sizing mill rolling, the billet is subjected to a first water cooling after the finishing mill, and a second water cooling after the sizing mill.

[0006] Set the initial rolling temperature range, final rolling temperature range, temperature range for entering the sizing mill, and temperature range after the second water cooling in the control model;

[0007] A fixed set of rolling mill speeds is determined based on the initial rolling temperature range and the final rolling temperature range to simultaneously apply to the rolling of bars with diameters of specifications a to b. The rolling speed is fixed, and it affects the temperature of the steel after it passes through the water tank. The higher the rolling speed, the higher the temperature after water passage. The goal of the adjustment is to ensure the temperature entering the reducing and sizing mill and the final temperature after water passage. A suitable rolling speed is selected based on meeting the requirements of varying initial and final rolling temperature ranges. Since the rolling system is fixed, the rolling distance is also fixed. Therefore, for different rolling systems, the main adjustment needed is the rolling speed. The technical solution described in this invention determines the establishment of a control model under the rolling system, and no specific rolling distance is limited here.

[0008] Setting parameters for the raw material heating stage: Based on the size of the bar billets with diameters of specifications a to b and the initial rolling temperature range, determine the temperature range and heating time requirements for the preheating section, the temperature range and heating time requirements for heating section I, the temperature range and heating time requirements for heating section II, and the temperature range and heating time requirements for the soaking section, so that the temperature of all billets after heating meets the requirements of the initial rolling temperature range;

[0009] Setting parameters for the first and second water piercing cooling: Based on the dimensions of the billet after finishing rolling, the final rolling temperature range, the temperature range entering the reducing and sizing mill, and the mill speed, a set of fixed cooling parameters for the first water piercing cooling equipment is determined to be applicable to the rolling of bars with diameters of a to b. Based on the dimensions of the finished bar, the temperature range entering the reducing and sizing mill, the temperature range after the second water piercing cooling, and the mill speed, a set of fixed cooling parameters for the second water piercing cooling equipment is determined to be applicable to the rolling of bars with diameters of a to b. Thus, a controlled cooling rolling model for the first and second water piercing cooling is established.

[0010] The rolling process control approach of this invention is twofold: first, to ensure a suitable final rolling temperature, as a lower final rolling temperature facilitates a reduction in the water quenching temperature; and second, to ensure that the rolling temperature of the reducing mill is within the two-phase temperature range. Temperature control is achieved through comprehensive control of raw material heating, the first water quenching cooling, and the second water quenching cooling. This invention utilizes multiple on-site experiments, measuring production process data, and accumulating data on rolling speed, water volume, and water pressure to ultimately determine suitable temperature regimes, rolling speeds, and water tank data. This allows for the establishment of a network carbide control model applicable to hot-rolled bearing steel bars within a specific specification range. Multiple network carbide control models can be developed for various bar specifications; only the appropriate control model needs to be selected based on the microstructure requirements of the dimensional specifications. This significantly reduces the workload of on-site workers and ensures the stability of the rolled bar quality.

[0011] In the preferred embodiment of this invention, when the bearing steel bar specification is Φ50-55mm, the mill speed is 2.97m / s, the initial rolling temperature range is 950~1050℃, the final rolling temperature range is 900~950℃, the temperature range entering the reducing and sizing mill is 800~850℃, and the temperature range after the second water cooling is 610~680℃.

[0012] During the raw material heating stage, the preheating section temperature is 500-850℃, and the preheating time is ≥100 minutes; the heating section I temperature is 900-1170℃, and the heating time is ≥80 minutes; the heating section II temperature is 1170-1240℃, and the heating time is ≥90 minutes; the soaking section temperature is 1180-1220℃, and the soaking time is ≥60 minutes; and the total heating time is ≥330 minutes.

[0013] Preferably, in the first water cooling process of this invention, three water tanks (No. 1 to No. 3) are installed after the finishing mill. The temperature of the water cooling tank is controlled at 800-850℃. After rolling, the bar enters the No. 1 water cooling tank with a water pressure of 2.13MPa and a water flow rate of 190m³. 3 / h, the outlet water cooling box temperature is controlled at 950℃;

[0014] The bar stock enters water cooling tank No. 2 from water cooling tank No. 1, with a water pressure of 1.65 MPa and a water flow rate of 170 m³ / h. 3 / h, the outlet water cooling box temperature is controlled at 750℃;

[0015] The bar stock enters water cooling tank No. 3 from water cooling tank No. 2, with a water pressure of 1.45 MPa and a water flow rate of 150 m³ / h. 3 / h, the outlet water cooling box temperature is controlled at 700℃. For the first water cooling, the water inlets of each water cooling box are connected in parallel, and cooling water of the same temperature is introduced. The approximate temperature of the bar billet is determined based on the outlet water temperature of each water cooling box to ensure that the rolled product quickly passes through the carbide precipitation temperature zone of 900℃~700℃, and to ensure that the rolling temperature entering the reduction mill is within the two-phase temperature range.

[0016] Preferably, in the second water cooling process of this invention, three water tanks (No. 4 to No. 6) are installed after the sizing and reducing mill. The temperature of the inlet water cooling tank is controlled at 500-580℃. The bar stock enters water cooling tank No. 4 with a water pressure of 1.3MPa and a water flow rate of 140m³ / h. 3 / h, the outlet water cooling box temperature is controlled at 660℃;

[0017] The bar stock enters water cooling box No. 5 from water cooling box No. 4, with a water pressure of 0.9 MPa and a water flow rate of 90 m³ / h. 3 / h, the outlet water cooling box temperature is controlled at 600℃;

[0018] The bar stock enters water cooling box No. 6 from water cooling box No. 5, with a water pressure of 0.5 MPa and a water flow rate of 70 m³ / h. 3The outlet temperature of the water cooling box is controlled at 580℃ per hour. The water inlets of each water cooling box in the second water cooling process are also connected in parallel, supplying cooling water at the same temperature. The approximate temperature of the bar billet is determined based on the outlet temperature of each water cooling box to ensure the subsequent cooling temperature before loading onto the bed.

[0019] Preferably, the hot rolling process of this invention further includes air cooling with a walking beam and slow cooling in a pit;

[0020] After being cooled by a water tank, the bar stock enters a long-length cooling bed for further cooling. The temperature of the upper cooling bed is 610-680℃, and the temperature of the lower cooling bed is 290-350℃.

[0021] After the bars are sawn into sections, collected and bundled, they are placed in a slow cooling pit at a temperature of 260–320℃. The bars are allowed to cool slowly in the pit for 24 hours, and the exit temperature is ≤100℃. Controlling the temperatures of the upper and lower cooling beds can control the final entry temperature of the steel into the pit, which has a positive effect on eliminating post-rolling stress. A temperature of 260–320℃ is effective in eliminating post-rolling stress, while an excessively high exit temperature will affect the stress release of the steel.

[0022] Preferably, the roughing mill unit of the present invention consists of 7 mill stands, which are high-rigidity mills with short stress lines, and are arranged alternately in horizontal and vertical configurations.

[0023] The intermediate rolling mill consists of 6 rolling mills, which are high-rigidity rolling mills with short stress lines, and are arranged alternately in horizontal and vertical configurations.

[0024] The finishing mill consists of four mills, which are high-rigidity mills with short stress lines, arranged alternately in horizontal and vertical configurations.

[0025] The sizing and reducing mill unit consists of four rolling mill stands. The number of mills affects the rolling stroke, which in turn affects the temperature change of the billet. The alternating horizontal and vertical arrangement avoids steel turnover and improves rolling efficiency.

[0026] In a preferred embodiment of the present invention, in the controlled cooling rolling model of the first water cooling and the second water cooling, the same mill speed can correspond to multiple sets of fixed values ​​of the cooling parameters of the cooling equipment corresponding to the first water cooling and the cooling parameters of the cooling equipment corresponding to the second water cooling.

[0027] Preferably, the sizing and reducing unit of the present invention is a KOCKS sizing and reducing unit.

[0028] Preferably, the water-cooled boxes of this invention are all Venturi tube type water-cooled boxes.

[0029] Compared with the prior art, the beneficial effects of the present invention are: the present invention establishes a data model for setting rolling specifications, which facilitates on-site operation by directly inputting data into the computer control system.

[0030] This invention determines a fixed set of rolling mill speeds based on the initial rolling temperature range and the final rolling temperature range, so as to be applicable to the rolling of bars with diameters of specifications a to b.

[0031] Based on the dimensions of bar billets with diameters ranging from a to b and the initial rolling temperature range, determine the temperature range and heating time requirements for the preheating section, the temperature range and heating time requirements for heating section I, the temperature range and heating time requirements for heating section II, and the temperature range and heating time requirements for the soaking section, so that the temperature of all billets after heating meets the requirements of the initial rolling temperature range.

[0032] Based on the dimensions of the finished billet, the final rolling temperature range, the temperature range entering the reducing and sizing mill, and the mill speed, a set of fixed cooling parameters for the first water piercing cooling equipment is determined to be applicable to the rolling of bars with diameters of a to b. Based on the dimensions of the finished bar, the temperature range entering the reducing and sizing mill, the temperature range after the second water piercing cooling, and the mill speed, a set of fixed cooling parameters for the second water piercing cooling equipment is determined to be applicable to the rolling of bars with diameters of a to b. Then, a controlled cooling rolling model for the first and second water piercing cooling is established.

[0033] The control model of this invention is based on the initial rolling temperature range, final rolling temperature range, temperature range entering the reducing and sizing mill, and temperature range after the second water cooling in the set control model. It also combines the preset rolling specifications and the performance of the cooling equipment. Since the parameters of the rolling system corresponding to the preset rolling specifications are uniquely determined, the rolling speed of the rolling system and the fixed parameter data of the cooling equipment are determined during rolling. This forms a fixed combination model of rolling speed and rolling cooling data applicable to bars of preset rolling specifications. During production, it is only necessary to input each data into the computer control module based on the rolling specifications or directly retrieve the corresponding rolling model, which ensures the stability and controllability of rolling quality. Attached Figure Description

[0034] Figure 1 This is a chart showing the cooling trend of the water tank.

[0035] Figure 2 This is an inspection diagram of the network carbides in bearing steel. Detailed Implementation

[0036] The technical solutions in the embodiments of the present invention will now be clearly and completely described in conjunction with the accompanying drawings.

[0037] This invention provides a control model for network carbides in hot-rolled bearing steel bars, applicable to the rolling of bars with bearing specifications of Φ50-55mm. The model includes raw material heating, raw material roughing mill rolling, intermediate mill rolling, finishing mill rolling, KOCKS sizing mill rolling, first water cooling, second water cooling, walking beam air cooling, and slow cooling in the pit.

[0038] 1. The raw material heating adopts a three-stage heating furnace. The billet size is 260X300mm. Billet heating is an extremely important process. It is necessary not only to ensure that the billet is heated evenly to the specified temperature to provide good microstructure and plasticity conditions for rolling, but also to reduce the degree of dendritic segregation in the steel during the heating process, so as to eliminate the unevenness of the carbide network.

[0039] The microstructure of bearing steel cooled to room temperature under equilibrium conditions consists of pearlite and secondary carbides. Due to dendritic segregation, a large number of bulk eutectic carbides appear between the dendrites. If the segregation is severe, these bulk eutectic carbides can gradually dissolve during heating, but carbide-forming elements such as carbon and chromium do not diffuse sufficiently and uniformly. In high-concentration zones, they easily precipitate carbide networks along the austenite grain boundaries. The diffusion process of segregated elements accelerates dramatically with increasing temperature, so the heating temperature of bearing steel billets should be as high as possible, with a certain holding time. On the other hand, the final rolling temperature has a significant impact on the carbide network structure of bearing steel. As the final rolling temperature decreases, the grains of the rolled steel become finer, resulting in carbides precipitated along grain boundaries that are distributed on larger grain boundaries, are relatively thin, and have more contact surface with the matrix. This carbide network is easily broken during subsequent spheroidizing annealing, resulting in a lower network level. That is, the final rolling temperature should not be too high. If the final rolling temperature is too high, due to the deformation-induced effect, the deformation will cause the austenite to precipitate secondary cementite at a higher temperature in advance. After slow cooling, the carbides will be coarse and abundant.

[0040] In summary, the specific initial rolling temperature range can be determined according to the heating purpose. Based on the size of the raw material and the specific initial rolling temperature range, the parameters of the heating temperature for each stage can be further determined, as shown in Table 1: Preheating section temperature 500~850℃, heating time of preheating section ≥100 minutes; Heating section I temperature 900~1170℃, heating time of heating section I ≥80 minutes; Heating section II temperature 1170~1240℃, heating time of heating section II ≥100 minutes; Soaking section temperature 1180~1220℃, heating time of soaking section ≥60 minutes; total heating time ≥330 minutes.

[0041] Table 1. Billet Temperature Regulation

[0042]

[0043]

[0044] In Table 1, it is generally believed that the temperature is greater than 1180℃ and enters the high-temperature diffusion stage, meaning that the high-temperature diffusion time includes the homogenization time and the heating time.

[0045] 2. The roughing mill consists of 7 mill stands, which are high-rigidity mills with short stress lines, and are arranged alternately in horizontal and vertical configurations.

[0046] The intermediate rolling mill consists of 6 rolling mills, which are high-rigidity rolling mills with short stress lines, and are arranged alternately in horizontal and vertical configurations.

[0047] The finishing mill consists of four mills, which are high-rigidity mills with short stress lines, arranged alternately in horizontal and vertical configurations.

[0048] The KOCKS reducing and sizing mill unit consists of 4 rolling mill stands.

[0049] 3. For example Figure 1 As shown in Table 2, Figure 1 This is a cooling trend chart for the water tanks, illustrating the cooling process trend of rolled steel in water tanks 1-6. Figure 1 As shown, the surface temperature of the rolled piece drops sharply when passing through the water tank, and the green curve represents the general temperature trend of the rolled piece after reheating. Table 2 shows the controlled rolling and controlled cooling model of bearing steel with Φ50-55mm specifications, displaying the linear identification diagram of data parameters for water tanks 1-6.

[0050] The rolled pieces from the finishing mill are cooled by three sets of water tanks to ensure that the temperature of the rolled pieces entering the reducing and sizing mill is maintained. The rolled pieces are cooled to the temperature range of the austenite and carbide two-phase region by forced cooling, about 720-900℃. After deformation in the two-phase region, the proprecipitated carbides and the unrecrystallized austenite are subjected to plastic deformation at the same time. After deformation, the grains of the unrecrystallized austenite are elongated, and the deformation bands and dislocation density within the grains increase. At the same time, the proprecipitated carbides form a large number of dislocations due to plastic deformation, which causes the proprecipitated carbides to form fine and dispersed carbide particles.

[0051] Three water tanks are installed after the reducing and sizing mill to ensure rapid cooling of the steel after final rolling, allowing the rolled piece to quickly pass through the carbide precipitation temperature zone of 900℃~700℃. The purpose of the water tanks is to cool the steel, with a cooling trend from 900℃ to 700℃.

[0052] Table 2. Controlled rolling and controlled cooling rolling model for bearing steel with Φ50-55mm specifications.

[0053]

[0054] In Table 2, the speed of the last mill stand is the rolling speed, and the mill speed remains consistent throughout the entire rolling process.

[0055] 4. For the first water cooling process, three water tanks are installed after the finishing mill. After rolling, the bars enter the No. 1 water cooling tank with a water pressure of 2.34 MPa and a water flow rate of 184 m³ / h. 3 The water outlet temperature is controlled at 950℃; the bar stock enters water outlet 2 from water outlet 1, with a water pressure of 1.01MPa and a water flow rate of 110m³ / h. 3 The water outlet temperature is controlled at 750℃; the bar stock enters the No. 3 water cooling box from the No. 2 water cooling box, with a water pressure of 0.95MPa and a water flow rate of 110m³ / h. 3 / h, the outlet temperature of the water-cooled box is controlled at 700℃. The water-cooled box is a Venturi tube type water-cooled box.

[0056] 5. For the second water cooling process, three water tanks are installed after the KOCKS reducing and sizing mill. The bars enter water tank No. 4, with a water pressure of 2.34 MPa and a water flow rate of 130 m³ / h. 3 The water outlet temperature is controlled at 660℃; the bar stock enters water tank No. 5 from water tank No. 4, with a water pressure of 2.3MPa and a water flow rate of 120m³ / h. 3 The water outlet temperature is controlled at 600℃; the bar stock enters water outlet 6 from water outlet 5, with a water pressure of 1.73MPa and a water flow rate of 120m³ / h. 3 / h, the outlet temperature of the water-cooled box is controlled at 580℃. The number of nozzles in the water-cooled box for the first and second water-cooling cycles is adjusted according to the water-cooling effect.

[0057] 6. After the bar stock is cooled by the water tank, it enters the long-length cooling bed for further cooling. The temperature of the upper cooling bed is 610-680℃, and the temperature of the lower cooling bed is 290-350℃.

[0058] The bar stock is sawn into sections, collected, and bundled. It is then placed in a slow cooling pit at a temperature of 260–320℃. The bar stock is allowed to cool completely in the slow cooling pit for 24 hours, and the temperature upon exiting the pit is ≤100℃.

[0059] This invention establishes a water tank-controlled cooling model for bearing steel rolling by controlling the final rolling temperature at 900-950℃ (the final rolling temperature of finishing rolling), adjusting the rolling line speed, and coordinating with the research and use of cooling water tanks. This effectively ensures that the network carbide level of bearing steel passes the inspection.

[0060] billet according to Figure 1 The heating process involves high-temperature diffusion before entering the roughing mill, intermediate mill, and finishing mill for rolling. After the first water cooling (in this embodiment, the temperature is 800-850℃) the material enters the KOCKS reducing and sizing mill for rolling. After the second water cooling, the temperature is controlled at 500-580℃. After cooling on the cooling bed, the rolled material is sawn into sections and then slowly cooled in the pit.

[0061] like Figure 2As shown, according to the national standard for bearing steel testing, the illustrated grade is 1.0, and the bearing steel network carbides test results are all qualified.

Claims

1. A control model for network carbides in hot-rolled bearing steel bars, characterized in that: The hot rolling process includes raw material heating, raw material roughing mill rolling, intermediate mill rolling, finishing mill rolling and sizing mill rolling. After the finishing mill, the billet undergoes the first water cooling, and after the sizing mill, it undergoes the second water cooling. Set the initial rolling temperature range, final rolling temperature range, temperature range for entering the sizing and reducing mill, and temperature range after the second water cooling in the control model to ensure that the rolling temperature of the sizing and reducing mill is within the two-phase temperature range. A fixed set of rolling mill speeds is determined based on the initial rolling temperature range and the final rolling temperature range, so as to be applicable to the rolling of bars with diameters of specifications a to b. Setting parameters for the raw material heating stage: Based on the size of the bar billet with diameters of a~b and the initial rolling temperature range, determine the temperature range and heating time requirements for the preheating section, the temperature range and heating time requirements for heating section I, the temperature range and heating time requirements for heating section II, and the temperature range and heating time requirements for the soaking section. Setting parameters for the first and second water piercing cooling: Based on the dimensions of the billet after finishing rolling, the final rolling temperature range, the temperature range entering the reducing and sizing mill, and the mill speed, a set of fixed cooling parameters for the cooling equipment corresponding to the first water piercing cooling is determined to be applicable to the rolling of bars with diameters of a to b. Based on the dimensions of the finished bar, the temperature range entering the reducing and sizing mill, the temperature range after the second water piercing cooling, and the mill speed, a set of fixed cooling parameters for the cooling equipment corresponding to the second water piercing cooling is determined to be applicable to the rolling of bars with diameters of a to b. Thus, a controlled cooling rolling model for the first and second water piercing cooling is established. Based on the organizational requirements of various sizes, control models for the network carbide of bar stock were developed.

2. The network carbide control model for hot-rolled bearing steel bars according to claim 1, characterized in that: When the bearing steel bar specifications are Φ50-55mm, the mill speed is 2.97m / s, the initial rolling temperature range is 950~1050°C, the final rolling temperature range is 900~950°C, the temperature range entering the sizing mill is 800~850°C, and the temperature range after the second water cooling is 610~680°C. During the raw material heating stage, the preheating section temperature is 500~850°C, and the preheating time is ≥100 minutes; the heating section I temperature is 900~1170°C, and the heating time is ≥80 minutes; the heating section II temperature is 1170~1240°C, and the heating time is ≥90 minutes; the soaking section temperature is 1180~1220°C, and the soaking time is ≥60 minutes; the total heating time is ≥330 minutes. The first water cooling process involves three water cooling boxes (No. 1 to No. 3) installed after the finishing mill. The temperature of the water cooling boxes is controlled at 800-850°C. After rolling, the bar enters water cooling box No. 1 with a water pressure of 2.13 MPa and a water flow rate of 190 m³ / h. 3 / h, the outlet water cooling box temperature is controlled at 950°C; The bar stock enters water cooling tank No. 2 from water cooling tank No. 1, with a water pressure of 1.65 MPa and a water flow rate of 170 m³ / h. 3 / h, the outlet water cooling box temperature is controlled at 750°C; The bar stock enters water cooling tank No. 3 from water cooling tank No. 2, with a water pressure of 1.45 MPa and a water flow rate of 150 m³ / h. 3 / h, the outlet water cooling box temperature is controlled at 700°C; The second water cooling process involves three water-cooled boxes (No. 4 to No. 6) installed after the sizing and reducing mill. The inlet temperature of the water-cooled boxes is controlled at 500-580°C. The bars enter water-cooled box No. 4 with a water pressure of 1.3 MPa and a water flow rate of 140 m³ / h. 3 / h, the outlet water cooling box temperature is controlled at 660°C; The bar stock enters water cooling box No. 5 from water cooling box No. 4, with a water pressure of 0.9 MPa and a water flow rate of 90 m³ / h. 3 / h, the outlet water cooling box temperature is controlled at 600°C; The bar stock enters water cooling box No. 6 from water cooling box No. 5, with a water pressure of 0.5 MPa and a water flow rate of 70 m³ / h. 3 / h, the outlet water cooling box temperature is controlled at 580°C.

3. The network carbide control model for hot-rolled bearing steel bars according to claim 2, characterized in that: Hot rolling processes also include walking beam air cooling and pit slow cooling; After being cooled in a water-cooled box, the bar stock is cooled on a long-length cooling bed. The temperature of the upper cooling bed is 610~680°C and the temperature of the lower cooling bed is 290~350°C. The bars are sawn into sections, collected and bundled, and then placed in a slow cooling pit at a temperature of 260~320°C. The bars are allowed to cool slowly in the pit for 24 hours, and the temperature when they come out of the pit is ≤100°C.

4. The network carbide control model for hot-rolled bearing steel bars according to claim 2, characterized in that: The roughing mill consists of 7 mill stands, which are high-rigidity mills with short stress lines, arranged alternately in horizontal and vertical configurations. The intermediate rolling mill consists of 6 rolling mills, which are high-rigidity rolling mills with short stress lines, and are arranged alternately in horizontal and vertical configurations. The finishing mill consists of four mills, which are high-rigidity mills with short stress lines, arranged alternately in horizontal and vertical configurations. The sizing and reducing mill unit includes four rolling mill stands.

5. The network carbide control model for hot-rolled bearing steel bars according to claim 1, characterized in that: In the controlled cooling rolling model of the first and second water cooling, the same mill speed can correspond to multiple sets of fixed values ​​of the cooling parameters of the cooling equipment corresponding to the first water cooling and the cooling parameters of the cooling equipment corresponding to the second water cooling.

6. The network carbide control model for hot-rolled bearing steel bars according to claim 1 or 2, characterized in that: The type of the reducing and sizing unit is KOCKS reducing and sizing unit.

7. The network carbide control model for hot-rolled bearing steel bars according to claim 2, characterized in that: All of the water-cooled boxes mentioned are Venturi tube type water-cooled boxes.

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