A control method for rapid heating and thermal gradient rolling of high-carbon steel

Abstract

The present invention relates to a high carbon steel hot gradient rolling control method, belonging to the technical field of high carbon steel rolling. In order to solve the problems of increased decarburization layer thickness, increased burning loss, large energy consumption and insufficient rolling permeability generated during the heating process of high carbon steel, the present invention provides a high carbon steel rapid heating and hot gradient rolling control method, adopts a hot delivery and temperature charging, rapid heating and low-speed hot gradient rolling process collaborative control method, and the billet is cooled and heat exchanged before entering the rolling roller to obtain a hot gradient layer thickness of 30mm below 40°C at the center, and rolling is performed at a rolling speed of 0.3 to 0.6m / s. The high carbon steel rapid heating and hot gradient rolling control method provided by the present invention can shorten the heating time, increase the rolling penetration, ensure the internal quality of the bar, reduce energy consumption, and improve the rolling production efficiency and the yield rate of the rolled product by using hot delivery and temperature charging to quickly heat the high carbon steel and adopting low-speed hot gradient rolling.

Description

Technical Field

[0001] The present invention belongs to the technical field of high-carbon steel processing, and particularly relates to a control method for rapid heating and thermal gradient rolling of high-carbon steel. Background Art

[0002] Due to the relatively high content of alloying elements in high-carbon steel bloom, dendritic segregation is relatively significant, and the thermal deformation resistance is large. Therefore, it is necessary to fully heat and insulate the continuous casting billet to improve the temperature and composition uniformity. However, due to the relatively high matrix carbon content, problems such as an increase in the decarburized layer thickness, an increase in burning loss, and an increase in energy consumption and emissions will occur when the heating furnace temperature is too high or the holding time is too long.

[0003] Due to the relatively high carbon content in high-carbon steel, during high-temperature diffusion annealing, the carbon in the surface matrix is prone to react with oxygen in the atmosphere, and a decarburized layer of 20 - 500 μm appears on the surface. Decarburization will reduce the surface hardness, wear resistance, and fatigue performance of high-carbon steel, directly affecting the service life. At the same time, due to the relatively high temperature, iron combines with oxygen to form ferrous oxide, and the maximum depth of the oxide layer can reach 200 - 800 μm, and the burning loss caused thereby is about 0.5% - 2% of the total output. Therefore, how to further reduce decarburization and oxidation while improving heat transfer in the heating furnace is an urgent problem to be solved in the hot processing of high-carbon steel.

[0004] The energy conservation and carbon reduction of the heating furnace are mainly reflected in reducing gas consumption, which is directly related to the heating temperature, time, and method, etc. on the one hand, and is also affected by the feeding and charging system of the continuous casting billet on the other hand.

[0005] During the rolling process, if the deformation penetration rate is insufficient, it is still difficult to ensure the quality of the bar center. The stage that has the greatest impact on the center density during the rolling process is the rough rolling stage. The traditional rough rolling process is based on the state of uniform temperature inside and outside for hot processing. Since the deformation gradually decreases from the outside to the inside, its ability to improve center shrinkage and porosity is limited. Summary of the Invention

[0006] To solve the problems of an increase in the decarburized layer thickness, an increase in burning loss, a large energy consumption and emissions, and insufficient rolling penetration rate during the heating process of high-carbon steel, the present invention provides a control method for rapid heating and thermal gradient rolling of high-carbon steel.

[0007] The technical solution of the present invention:

[0008] A control method for rapid heating and thermal gradient rolling of high-carbon steel adopts a cooperative control method of hot charging and warm charging, rapid heating, and low-speed thermal gradient rolling process.

[0009] The hot charging and warm charging means that the high-carbon steel bloom continuous casting billet is charged into the furnace when the temperature drops to 450 - 600 °C during continuous casting and transportation.

[0010] The specific process of rapid heating includes a preheating stage, a heating stage, and a soaking stage. The preheating temperature in the preheating stage is 800°C, the preheating holding time is 30 min, the heating temperature in the heating stage is 1200 - 1240°C, the heating holding time is 80 min, the soaking temperature in the soaking stage is 1180 - 1220°C, and the soaking holding time is 140 min;

[0011] The low-speed thermal gradient rolling process is that the billet is cooled and heat-exchanged before entering the rolling mill, and the thickness of the thermal gradient layer with a temperature difference of more than 40°C below the center is 30 mm;

[0012] The low-speed thermal gradient rolling process includes rough rolling, finish rolling, and final rolling. The rough rolling temperature is not higher than 1200°C, the finish rolling temperature is not lower than 950°C, and the final rolling temperature is not lower than 850°C; the reduction per pass in rough rolling is not higher than 56 mm, and the reduction per pass in finish rolling is not higher than 42 mm; the rolling speed is 0.3 - 0.6 m / s.

[0013] Furthermore, the chemical composition of the high-carbon steel by weight percentage includes: C: 0.8 - 1.1%, Si: 0.15 - 0.75%, Mn: 0.7 - 1.3%, P ≤ 0.030%, S ≤ 0.035%, Cr: 0.8 - 1.2%, Mo ≤ 0.10%, and the rest is Fe and unavoidable impurities.

[0014] Furthermore, the cooling time for the billet to be cooled and heat-exchanged before entering the rolling mill is 150 s, with the ends insulated and the middle part air-cooled.

[0015] Furthermore, the surface temperature of the billet when entering the rolling mill is 1050°C.

[0016] Furthermore, the rough rolling temperature is 975 - 1150°C; the finish rolling temperature is 975 - 1150°C; the final rolling temperature is 850 - 950°C.

[0017] Furthermore, the rolling speed is 0.4 m / s.

[0018] Furthermore, the rough rolling includes 4 passes.

[0019] Furthermore, the finish rolling includes 4 - 6 passes, and the reduction per pass is separately designed according to different specifications.

[0020] Furthermore, the final rolling includes 2 - 6 passes, and the reduction per pass is separately designed according to different specifications.

[0021] The beneficial effects of the present invention:

[0022] The high carbon steel rapid heating and thermal gradient rolling control method provided by the present invention can shorten the heating time, increase the rolling penetration, ensure the internal quality of the bar, reduce energy consumption, and improve the rolling production efficiency and the rolled product yield rate by rapidly heating the high carbon steel through hot delivery and temperature loading while adopting low-speed thermal gradient rolling.

[0023] The present invention can reduce the total heating time of the heating furnace by 60 minutes through hot delivery and warm loading, and the corresponding energy consumption can be reduced by 28.4%. Due to the shortened insulation time in the heating furnace, the burning rate is reduced from 1.7% to 1.5%, and the decarburization layer thickness is reduced from 0.14mm to 0.12mm. For a series of varieties with an annual output of about 200,000 tons, the yield rate is increased by 0.12%, and the efficiency is increased by about 1.2 million yuan / year due to the reduction of burning loss.

[0024] The present invention adopts a low-speed thermal gradient rolling process. Due to the temperature difference between the inside and outside of the ingot during thermal gradient rolling, the average strain in the center area is 23% higher than that in the uniform temperature rolling process. The significant increase in the rolling deformation permeability greatly improves the center quality of the bar, and the flaw detection pass rate is increased from 98.7% to 99.9%. At the same time, the maximum specification of the bar rolling is expanded to We have opened up a technical route for the production of large-size high-carbon steel bars with low compression ratio and high homogenization, and conducted a number of metallurgical and material tests on them, which has greatly reduced production costs. BRIEF DESCRIPTION OF THE DRAWINGS

[0025] Figure 1 This is a low-magnification photograph of the S550A high carbon steel bar produced by the heating process combined with low-speed thermal gradient rolling in Example 1;

[0026] Figure 2 This is a low-magnification photograph of the S550A high carbon steel bar produced by conventional heating process combined with low-speed thermal gradient rolling in Comparative Example 1;

[0027] Figure 3 This is a low-magnification photograph of the HM-4 high carbon steel bar produced by the heating process combined with low-speed thermal gradient rolling in Example 2;

[0028] Figure 4 This is a low-magnification photograph of the HM-4 high carbon steel bar produced by the heating process combined with low-speed uniform temperature rolling in comparative example 1. DETAILED DESCRIPTION

[0029] The technical solution of the present invention will be further described below in conjunction with embodiments, but it is not limited thereto. Any modification or equivalent replacement of the technical solution of the present invention without departing from the spirit and scope of the technical solution of the present invention shall be covered by the protection scope of the present invention. For the process equipment or devices not specifically specified in the following embodiments, conventional equipment or devices in the art are used. Unless otherwise specified, the raw materials used in the embodiments of the present invention can be obtained commercially; unless specifically specified, the technical means used in the embodiments of the present invention are all conventional means well known to those skilled in the art.

[0030] Example 1

[0031] This embodiment provides a control method for rapid heating and thermal gradient rolling of high-carbon steel, specifically adopting a coordinated control method of hot charging and warm charging, rapid heating and low-speed thermal gradient rolling processes. The heating and rolling methods of this embodiment are applicable to 250*280 high-carbon steel continuous casting billets, and the rolling target is High-carbon wear-resistant steel bars.

[0032] The high-carbon steel grade in this embodiment is S550A, and its chemical composition by weight percentage includes: C: 0.75 - 0.85%, Si: 0.15 - 0.40%, Mn: 0.95 - 1.05%, P ≤ 0.025%, S ≤ 0.012%, Cr: 0.95 - 1.05%, Ni ≤ 0.25%, Mo: 0.03 - 0.08%, Cu ≤ 0.40%, N: 0.0045 - 0.0100%, Sn ≤ 0.03%, Ti ≤ 0.010%, Al: 0.015 - 0.030%, V ≤ 0.030%, and the rest is Fe and unavoidable impurities.

[0033] In this embodiment, the continuous casting process of high-carbon steel bloom uses the coordinated control technology of combined light and heavy reduction and electromagnetic stirring. The specific control parameters are as follows: the pouring superheat is 20 - 30°C, the casting speed is 0.65 m / min, the water volume in the mold is 2450 L / min, the specific water volume in secondary cooling is 0.2 L / kg, and the distribution ratio is 38 / 38 / 24%. A five-machine five-strand 250*280 continuous caster is used, with an arc radius of 10 m. The casting speeds of the left and right side strands are both 0.67 m / min. During the pouring process, constant temperature and constant speed are ensured, so as to ensure that the light reduction function is used when the terminal solidification coefficient f is between 0.3 - 0.5, and the heavy reduction function is used when f is between 0.5 - 1. The combined light and heavy reduction parameters are 2 / 3 / 5 / 5 / 5, and the total reduction amount is 20 mm. The electromagnetic stirring parameters are as follows: for M-EMS, the initial stirring parameters are 150 A / 2 Hz, the stirring intensity is 200 GS, and continuous stirring is adopted; for F-EMS, the final stirring parameters are 200 A / 6 Hz, the stirring intensity is 200 Gs, and the forward and reverse alternating stirring mode is adopted, with a cycle of 10 s - 3 s - 10 s. The coordinated control technology of combined light and heavy reduction and electromagnetic stirring enables good control of solute segregation at the center, reducing the requirements for solute homogenization in the heating furnace section.

[0034] Under the conditions of hot charging and warm charging, the temperature of the continuous casting billet is relatively high and the internal and external temperatures are uniform. The temperature of the preheating section and soaking section can be appropriately increased and the corresponding heat preservation time can be reduced. In this embodiment, hot charging and warm charging means that the high-carbon steel bloom continuous casting billet is charged into the heating furnace when the temperature drops to 450 - 600°C during continuous casting and transportation.

[0035] In this embodiment, the gas ratio in the heating furnace is CO:CH4:H2:N2:CO2 = 25:1:2:53:24, the maximum temperature of the heating furnace is 1300°C, and the maximum furnace loading is 400 tons.

[0036] The rapid heating process combined with hot charging and warm charging in this embodiment includes a preheating stage, a heating stage, and a soaking stage. Among them, the preheating temperature in the preheating stage is 800°C, the preheating heat preservation time is 30 min, the heating temperature in the heating stage is 1200 - 1240°C, the heating heat preservation time is 80 min, the soaking temperature in the soaking stage is 1180 - 1220°C, and the soaking heat preservation time is 140 min.

[0037] When the temperature of the casting billet reaches the requirement according to the heating process, the molten steel is tapped and the surface scale is removed by a descaling machine. Before the casting billet enters the rolling mill, it is cooled and heat exchanged. The cooling time is 150 s, with end insulation and air cooling in the middle part. The surface temperature of the casting billet entering the rolling mill is 1050°C, and the thickness of the thermal gradient layer with a temperature difference of more than 40°C below the center is 30 mm. It can be seen that thermal gradient rolling can reduce the area of the deformation zone of the rolled material.

[0038] The rolling production line is equipped with 12 stands of units, including 4 stands of roughing mills with a maximum single-roll reduction of 56 mm; 6 stands of finishing mills and 2 stands of finishing mills with a maximum rolling speed of 1.56 m / s; the KOCKS unit has a controlled cooling function and 5 cooling water tanks.

[0039] The low-speed thermal gradient rolling process in this embodiment includes primary rolling, finishing rolling, and final rolling. In order to enhance the diffusion ability of solute elements, promote the full dissolution of liquid segregation carbides, and improve the matrix homogeneity, the primary rolling temperature is not higher than 1200 °C, the finishing rolling temperature is not lower than 950 °C, and the final rolling temperature is not lower than 850 °C.

[0040] The primary rolling includes 4 passes, and the reduction in each pass is 56, 52, 52, and 56 mm in sequence, and the specific temperature of the primary rolling is 1160 °C.

[0041] The finishing rolling includes 6 passes, and the reduction in each pass is 42, 40, 36, 36, 30, and 28 mm in sequence, and the specific temperature of the finishing rolling is 1050 °C.

[0042] The final rolling includes 2 passes, and the reduction in each pass is 28 and 26 mm in sequence, and the specific temperature of the final rolling is 980 °C.

[0043] The pass areas corresponding to each stand of the primary rolling, finishing rolling, and final rolling are 57982.98, 43466.22, 34738.62, 26880.25, 21187.57, 16512.99, 12471.04, 9852.03, 7207.04, 5541.77, 4230.00, and 3403.00 mm 2 。

[0044] The rolling speed is controlled by adjusting the roll speed. The rolling speed of the thermal gradient rolling in this embodiment is 0.4 m / s. Low-speed rolling can ensure more uniform deformation, that is, the deformation can penetrate better along the thickness direction of the steel billet.

[0045] Example 2

[0046] This embodiment provides a method for rapid heating and thermal gradient rolling control of high-carbon steel, specifically using a coordinated control method of hot charging and temperature holding, rapid heating, and low-speed thermal gradient rolling process. The heating and rolling method in this embodiment is applicable to 250*280 high-carbon steel continuous casting billets, and the rolling target is High-carbon wear-resistant steel bars.

[0047] In this embodiment, the high-carbon steel grade is HM-4, and its chemical composition by weight percentage includes: C: 0.62-0.66%, Si: 1.75-1.90%, Mn: 0.75-0.80%, P≤0.020%, S≤0.020%, Cr: 0.80-0.90%, and the rest is Fe and inevitable impurities.

[0048] In this embodiment, the continuous casting process of the high-carbon steel bloom uses the coordinated control technology of light and heavy combined soft reduction and electromagnetic stirring. The specific control parameters are as follows: the pouring superheat is 20-30°C, the casting speed is 0.65 m / min, the water volume in the mold is 2450 L / min, the secondary cooling specific water volume is 0.2 L / kg, and the distribution ratio is 38 / 38 / 24%. A five-machine five-strand 250*280 continuous caster is used, with an arc radius of 10 m, and the casting speeds of the left and right side strands are both 0.67 m / min. During the pouring process, constant temperature and constant speed are ensured, so as to ensure that the light reduction function is used when the terminal solidification coefficient f is between 0.3 and 0.5, and the heavy reduction function is used when f is between 0.5 and 1. The light and heavy combined soft reduction parameters are 2 / 3 / 5 / 5 / 5, and the total reduction amount is 20 mm. The electromagnetic stirring parameters are: the first stirring parameter of M-EMS is 150 A / 2 Hz, the stirring intensity is 200 GS, and continuous stirring is used; the last stirring parameter of F-EMS is 200 A / 6 Hz, the stirring intensity is 200 Gs, and the forward and reverse alternating stirring method is used, with a cycle of 10 s-3 s-10 s. The coordinated control technology of light and heavy combined soft reduction and electromagnetic stirring has well controlled the solute segregation at the center, reducing the requirement for solute homogenization in the heating furnace section.

[0049] Under the condition of hot charging and warm charging, the temperature of the continuous casting billet is relatively high and the internal and external temperatures are uniform, so the temperatures of the preheating section and the soaking section can be appropriately increased and the corresponding holding time can be reduced. In this embodiment, hot charging and warm charging means that the high-carbon steel bloom is charged into the heating furnace when the temperature drops to 450-600°C during continuous casting and transportation.

[0050] In this embodiment, the gas ratio of the heating furnace is CO:CH4:H2:N2:CO2 = 25:1:2:53:24, the maximum temperature of the heating furnace is 1300°C, and the maximum furnace loading is 400 tons.

[0051] The rapid heating process combined with hot charging and warm charging in this embodiment includes a preheating stage, a heating stage, and a soaking stage. The preheating temperature in the preheating stage is 800 °C, and the preheating holding time is 30 min. The heating temperature in the heating stage is 1200 - 1240 °C, and the heating holding time is 80 min. The soaking temperature in the soaking stage is 1180 - 1220 °C, and the soaking holding time is 140 min. After the casting billet reaches the required temperature according to the heating process, it is discharged from the steelmaking furnace and the surface scale is removed by a descaling machine. Before the casting billet enters the rolling mill, it is cooled and heat-exchanged, and the cooling time is 150 s. The end is insulated and the middle part is air-cooled. The surface temperature of the casting billet when it enters the rolling mill is 1050 °C, and the thickness of the thermal gradient layer with a temperature difference of more than 40 °C below the center is 30 mm. It can be seen that thermal gradient rolling can reduce the area of the deformation zone of the rolled material.

[0052] The rolling production line is equipped with 10 stands of rolling mills, including 4 stands of roughing mills with a maximum single-roll reduction of 56 mm; 4 stands of finishing mills and 2 stands of finishing mills with a maximum rolling speed of 1.05 m / s. The KOCKS mill has a controlled cooling function and 5 cooling water tanks.

[0053] The low-speed thermal gradient rolling process in this embodiment includes primary rolling, finishing rolling, and finishing rolling. In order to enhance the diffusion ability of solute elements, promote the full dissolution of liquid segregation carbides, and improve the matrix homogeneity, the primary rolling temperature is not higher than 1200 °C, the finishing rolling temperature is not lower than 950 °C, and the finishing rolling temperature is not lower than 850 °C. The single-pass reduction in primary rolling is not higher than 56 mm, and the single-pass reduction in finishing rolling is not higher than 42 mm.

[0054] The primary rolling includes 4 passes, and the reduction in each pass is 56, 52, 52, and 56 mm in sequence. The specific temperature of primary rolling is 1050 °C.

[0055] The finishing rolling includes 4 passes, and the reduction in each pass is 42, 40, 36, and 36 mm in sequence. The specific temperature of finishing rolling is 980 °C.

[0056] The finishing rolling includes 2 passes, and the reduction in each pass is 30 and 26 mm in sequence. The specific temperature of finishing rolling is 920 °C.

[0057] The primary rolling is rolling with large reduction and large deformation in the initial stage to ensure the core quality; the finishing rolling is precise sizing in the middle stage to provide qualified incoming material dimensions for the finishing rolling; the finishing rolling meets the ordered dimensions, and the process is supplemented with cooling control to obtain qualified microstructure. The pass areas corresponding to each stand of primary rolling, finishing rolling, and finishing rolling are 57982.98, 43466.22, 34738.62, 26880.25, 21187.57, 16512.99, 12351.36, 9676.89, 6977.30, and 5823.10 mm 2 。

[0058] The rolling speed is controlled by adjusting the roll speed. In this embodiment, the rolling speed of the thermal gradient rolling is 0.4 m / s. Low-speed rolling can ensure more uniform deformation, that is, the deformation can penetrate better along the thickness direction of the steel billet.

[0059] Comparative Example 1

[0060] This comparative example provides a method for rapid heating and thermal gradient rolling control of high-carbon steel. The raw materials for heating and rolling are 250*280 high-carbon steel continuous casting billets, and the rolling target is High-carbon wear-resistant steel bars.

[0061] The high-carbon steel grade in this comparative example is S550A, and its chemical composition is the same as that in Example 1.

[0062] The cold charging heating process in this comparative example is as follows: the preheating temperature in the preheating stage is 700 °C, the preheating holding time is 40 min, the heating temperature in the heating stage is 1180 - 1220 °C, the heating holding time is 100 min, the soaking temperature in the soaking stage is 1170 - 1190 °C, and the soaking holding time is 170 min.

[0063] The thermal gradient rolling control method in this comparative example is the same as that in Example 1.

[0064] Figure 1 is the macrostructure photograph of the S550A high-carbon steel bar with the heating process of Example 1 combined with low-speed thermal gradient rolling; Figure 2 is the macrostructure photograph of the S550A high-carbon steel bar with the traditional heating process of Comparative Example 1 combined with low-speed thermal gradient rolling; As can be seen from the figure, after the heating process is optimized, there are no obvious defects in the macrostructure results of the bars, and its rating is no different from the original heating process; for the carbon element distribution measured by sampling at different positions, there is also no difference between the optimized process and the original process, as shown in Table 1. Under the condition of the same bar quality, due to the reduction of the total time of the optimized process, the heating homogenization efficiency is improved.

[0065] Table 1 Under different heating processes Carbon segregation of high-carbon wear-resistant steel bars

[0066] Carbon segregation Original process of Comparative Example 1 New process of Example 1 Maximum positive segregation ratio 1.05 1.05 Maximum negative segregation ratio 0.96 0.96

[0067] Compared with this comparative example, the total heating time of the hot charging and soaking combined with rapid heating process in Example 1 is reduced by 60 min. After the high-carbon steel continuous casting billets adopt the hot charging and soaking and rapid heating processes, the occupancy rate of the heating furnace is reduced, which provides convenience for the heating scheduling of other steel grades. After promoting the warm charging and rapid heating process, the CO2 emission is reduced by 66.4 kg / t steel compared with the traditional cold charging process, making an important contribution to energy conservation and emission reduction in the iron and steel industry. When the heating time is reduced from 300 min to 240 min, the energy consumption can be reduced by 28.4%, and the corresponding gas consumption can be reduced by about 130 Nm 3 / t, its contribution to reducing energy consumption is very significant.

[0068] Comparative Example 2

[0069] This comparative example provides a rapid heating and uniform temperature rolling control method for high-carbon steel. The raw materials for heating and rolling are 250*280 high-carbon steel continuous casting billets, and the rolling target is High-carbon wear-resistant steel bars.

[0070] The high-carbon steel grade in this comparative example is HM-4, and its chemical composition is the same as that in Example 2.

[0071] The rapid heating process combined with hot charging and warm rolling in this comparative example is the same as that in Example 2.

[0072] When the temperature of the casting billet reaches the requirement according to the heating process, the molten steel is discharged and the surface scale is removed by a descaling machine. The casting billet enters the rolling mill in a uniform temperature state. The surface temperature of the casting billet entering the rolling mill is 1160 °C, and the center temperature is 1180 °C.

[0073] The rolling production line is equipped with 10 stands, including 4 roughing stands with a maximum single-roll reduction of 80 mm; 6 finishing stands with a maximum rolling speed of 10.5 m / s and a maximum bar size of 120 mm; the KOCKS stand has a controlled cooling function and 2 cooling water tanks.

[0074] The low-speed uniform temperature rolling process in this comparative example includes rough rolling, finishing rolling and finishing rolling. The specific process is as follows:

[0075] The rough rolling includes 4 passes, and the reduction in each pass is 56 / 52 / 52 / 56 mm respectively. The specific temperature of the rough rolling is 1160 °C.

[0076] The finishing rolling includes 4 passes, and the reduction in each pass is 42 / 40 / 36 / 36 mm respectively. The specific temperature of the finishing rolling is 1050 °C.

[0077] The finishing rolling includes 2 passes, and the reduction in each pass is 30 / 26 mm respectively. The specific temperature of the finishing rolling is 980 °C.

[0078] The pass areas corresponding to each pass of the rough rolling, finishing rolling and finishing rolling are 57982.98, 43466.22, 34738.62, 26880.25, 21187.57, 16512.99, 12351.36, 9676.89, 6977.30 and 5823.10 mm 2 . The rolling speed is controlled by adjusting the roll speed. The rolling speed of the thermal gradient rolling in this example is 0.4 m / s.

[0079] Due to the temperature difference between the inside and outside of the billet during hot gradient rolling, the hot deformation penetrates more into the internal area, the equivalent strain in the center increases, and the average strain in the center area during hot gradient rolling is 23% higher than that during isothermal rolling, that is, the rolling deformation penetration rate is significantly improved.

[0080] Figure 3 Macro photograph of the HM-4 high carbon steel bar with the heating process of Example 2 combined with low-speed hot gradient rolling; Figure 4 Macro photograph of the HM-4 high carbon steel bar with the heating process of Comparative Example 1 combined with low-speed isothermal rolling; As can be seen from the comparison in the figure, for the continuous casting billet with slightly poor center density under the traditional isothermal rolling process, the center quality of the bar is greatly improved after hot gradient rolling. Sampling the center of the bar and detecting the matrix density under different processes, hot gradient rolling can significantly improve the center density of the bar and has little fluctuation, indicating that the center quality of hot gradient rolling has the best stability.

Claims

1. A control method for rapid heating and thermal gradient rolling of high-carbon steel, characterized in that, Adopt a collaborative control method of hot charging and warm charging, rapid heating and low-speed thermal gradient rolling process. The rapid heating and thermal gradient rolling control method for high-carbon steel is applicable to continuous casting billets of high-carbon steel. The rolling target is high-carbon wear-resistant steel bars with a diameter of φ65mm or φ85mm; The hot charging and warm charging means that the high-carbon steel bloom continuous casting billet is charged into the furnace when the temperature drops to 450-600°C during continuous casting and transportation; The specific process of the rapid heating includes a preheating stage, a heating stage and a soaking stage. The preheating temperature in the preheating stage is 800°C, the preheating holding time is 30 min, the heating temperature in the heating stage is 1200-1240°C, the heating holding time is 80 min, the soaking temperature in the soaking stage is 1180-1220°C, and the soaking holding time is 140 min; The low-speed thermal gradient rolling process means that the billet is cooled and heat exchanged before entering the rolling rolls. The cooling time is 150 s, the end is heat-insulated, and the middle part is air-cooled. The thickness of the thermal gradient layer below the center by more than 40°C is 30 mm; the surface temperature of the billet entering the rolling rolls is 1050°C; The low-speed thermal gradient rolling process includes 4 passes in the rough rolling, 4-6 passes in the finish rolling and 2-6 passes in the finishing rolling. The rough rolling temperature is 975-1150°C, the finish rolling temperature is 975-1150°C, and the finishing rolling temperature is 850-950°C; the reduction per pass in the rough rolling is not higher than 56 mm, and the reduction per pass in the finish rolling is not higher than 42 mm; the rolling speed is 0.3-0.6 m / s. The chemical composition of the high-carbon steel includes by weight percentage: C: 0.8-1.1%, Si: 0.15-0.75%, Mn: 0.7-1.3%, P≤0.030%, S≤0.035%, Cr: 0.8-1.2%, Mo≤0.10%, and the rest is Fe and inevitable impurities.

2. The method for controlling rapid heating and thermal gradient rolling of high-carbon steel according to claim 1, wherein The rolling speed is 0.4 m / s.

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