20crmn ti steel and rolling method thereof

Abstract

The present application relates to the technical field of metal material deformation heat treatment, and especially relates to a 20CrMnTi steel and a rolling method thereof, the rolling method comprises the following steps in sequence: a heating step, a rough rolling step, a medium rolling step, a finishing rolling step of a reducing and sizing mill set, a water cooling step, and a cold bed air cooling step; wherein, in the heating step, the temperature of the soaking section is 1200-1240 DEG C; in the rough rolling step, the starting rolling temperature is 1130-1170 DEG C; in the finishing rolling step of the reducing and sizing mill set, the final rolling temperature is 880-920 DEG C; and in the cold bed air cooling step, the cooling rate is controlled to be 90-150 DEG C / min. By controlling the final rolling temperature and the cooling rate after rolling, the 20CrMnTi steel with excellent performance and with a banded structure of less than or equal to 1.5 and a grain size of more than or equal to 7.5 is obtained, and the subsequent processing is facilitated.

Description

Technical Field

[0001] This invention relates to the field of deformation heat treatment technology for metallic materials, and in particular to a 20CrMnTi steel and its rolling method. Background Technology

[0002] Gears are one of the important components of mechanical transmission. They are widely used in automobiles, ships, metallurgy, aviation and other fields. In particular, with the booming development of the automobile industry in recent years, the scale of my country's gear industry has continued to expand, driving the continuous demand for gear steel.

[0003] 20CrMnTi is one of the most commonly used gear steels. Its main chemical composition (mass percentage) is: C: 0.17–0.23%, Si: 0.17–0.37%, Mn: 0.8–1.1%, P: ≤0.025%, S: ≤0.02%, Cr: 1–1.3%, Ni: ≤0.30%, Cu ≤0.30%, Ti: 0.04–0.10%, with the remainder being Fe matrix and unavoidable impurities. It has advantages such as fine grain size, mature and stable heat treatment process, and low price, and is widely used in the automotive industry. However, Ti in steel easily forms large, angular TiN particles, which can become fatigue crack initiation sites during use, affecting the service life of gears. At the same time, the mixed grain structure also affects the degree of heat treatment distortion of gears. Generally, the intrinsic grain size of gear steel needs to be ≥6. The banded structure of gear steel will destroy the uniformity of the carburized layer, increase the deformation after quenching, and reduce the gear accuracy and meshing degree. Therefore, the banded structure needs to be strictly controlled. For high-precision automotive gear steel, the banded structure control requirement is ≤2.

[0004] Currently, the industry typically produces 20CrMnTi round steel using high-temperature rolling followed by air cooling, resulting in a banded microstructure generally between grade 2 and 3 (e.g., ...). Figure 1 As shown in a), a small amount of mixed-crystal structure easily forms near the surface (e.g., as shown in a). Figure 1 (As shown in b), this affects the service life of gears. Therefore, researching a new rolling method to control the strip grade and intrinsic grain size of 20CrMnTi rolled round steel is of great significance for achieving the green and sustainable development of the gear steel industry. Summary of the Invention

[0005] In view of the above-mentioned shortcomings in the existing technology, the purpose of this invention is to provide a 20CrMnTi steel and its rolling method. By controlling the final rolling temperature and the post-rolling cooling rate, this invention obtains a 20CrMnTi steel with excellent performance, characterized by banded structure ≤1.5 grade and intrinsic grain size ≥7.5 grade, which is convenient for subsequent processing.

[0006] To achieve the above objectives, the present invention adopts the following technical solution:

[0007] In a first aspect, the present invention provides a rolling method for 20CrMnTi steel, using 20CrMnTi continuously cast billets as raw materials. The rolling method includes the following steps in sequence: heating step, roughing step, intermediate rolling step, finishing rolling step of reducing and sizing mill, water cooling step, and air cooling step of cooling bed, finally obtaining finished bar stock.

[0008] The heating process is divided into four stages: preheating, heating stage one, heating stage two, and heating stage one. The heating stage one is kept at a temperature of 1200-1240℃.

[0009] In the roughing process, the initial rolling temperature is 1130–1170°C;

[0010] In the finishing rolling process of the reducing and sizing mill, the final rolling temperature is 880–920°C;

[0011] In the air-cooling process of the cooling bed, the cooling rate is controlled at 90-150℃ / min.

[0012] This invention obtains high-performance 20CrMnTi steel with banded structure ≤1.5 grade and intrinsic grain size ≥7.5 grade by controlling the final rolling temperature and post-rolling cooling rate, which facilitates subsequent processing.

[0013] Furthermore, in the heating process, the heat soaking time of the heat soaking section is 60 to 90 minutes.

[0014] Furthermore, in the heating process, the temperature of the preheating section is 700-800℃, the temperature of the first heating section is 1140-1200℃, and the temperature of the second heating section is 1200-1240℃.

[0015] Furthermore, in the heating process, the total heating time is 240-360 minutes.

[0016] Furthermore, in the intermediate rolling process, the inlet temperature is 950-1000℃.

[0017] Furthermore, in the finishing rolling process of the reducing and sizing mill, the inlet temperature is 885-925℃.

[0018] Furthermore, in the air-cooling process of the cooling bed, the temperature of the upper cooling bed is 760-800℃.

[0019] Furthermore, in the water cooling process, a water tank is used for water cooling to cool the finished bar to 760-800°C. The water volume of the water tank is 100-320 L / min and the water pressure is 5-8 MPa.

[0020] Furthermore, in the air-cooling process of the cooling bed, there are 1-2 moving teeth between two adjacent bars to control the cooling rate to 90-150℃ / min.

[0021] Furthermore, in the air-cooling process of the cooling bed, the temperature exiting the cooling bed does not exceed 600°C.

[0022] Furthermore, the mass percentage of each element in the continuously cast billet is as follows: C: 0.17-0.23%, Si: 0.17-0.37%, Mn: 0.8-1.1%, P: ≤0.025%, S: ≤0.02%, Cr: 1-1.3%, Ni: ≤0.30%, Cu≤0.30%, Ti: 0.04-0.10%, with the remainder being matrix Fe and unavoidable impurities.

[0023] Furthermore, the finished bar stock has a diameter of 20–60 mm.

[0024] In a second aspect, the present invention provides a 20CrMnTi steel, which is manufactured by the rolling method of the 20CrMnTi steel described in the first aspect.

[0025] Furthermore, the banded structure of the 20CrMnTi steel is ≤1.5 grade, and the intrinsic grain size is ≥7.5 grade.

[0026] Compared with the prior art, the beneficial effects of the present invention include at least the following:

[0027] This invention obtains high-performance 20CrMnTi steel with banded structure ≤1.5 grade and intrinsic grain size ≥7.5 grade by controlling the final rolling temperature and post-rolling cooling rate, which facilitates subsequent processing. Attached Figure Description

[0028] To more clearly illustrate the specific embodiments of the present invention or the technical solutions in the prior art, the drawings used in the description of the specific embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are some embodiments of the present invention. For those skilled in the art, other drawings can be obtained from these drawings without creative effort.

[0029] Figure 1 The diagram shows the banded microstructure and intrinsic grain size of 20CrMnTi steel obtained using existing rolling processes. Figure 1 a is a diagram of the banded microstructure of 20CrMnTi steel obtained using existing rolling processes. Figure 1 b is the intrinsic grain size diagram of 20CrMnTi steel obtained using existing rolling processes;

[0030] Figure 2This is a diagram of the banded microstructure of the 20CrMnTi steel rolled in Example 3 of the present invention, wherein... Figure 2 a is a diagram of the surface banded microstructure of 20CrMnTi steel. Figure 2 b is a diagram of the core banded microstructure of 20CrMnTi steel;

[0031] Figure 3 This is the intrinsic grain size diagram of the 20CrMnTi steel rolled in Example 3 of the present invention, wherein... Figure 3 a is the intrinsic grain size diagram of the surface of 20CrMnTi steel. Figure 3 b is the intrinsic grain size diagram of the core of 20CrMnTi steel. Detailed Implementation

[0032] To make the objectives, technical solutions, and advantages of this invention clearer, the technical solutions in the embodiments of this invention will be clearly and completely described below in conjunction with the embodiments of this invention. Those skilled in the art should understand that the embodiments described are merely illustrative of the invention and should not be considered as specific limitations thereof. All other embodiments obtained by those skilled in the art based on the embodiments of this invention without creative effort are within the scope of protection of this invention. Process parameters not specifically specified in the following embodiments are generally performed under conventional conditions.

[0033] The endpoints and any values ​​of the ranges disclosed in this invention are not limited to the precise ranges or values, and these ranges or values ​​should be understood to include values ​​close to these ranges or values. For numerical ranges, the endpoint values ​​of the various ranges, the endpoint values ​​of the various ranges and individual point values, and individual point values ​​can be combined with each other to obtain one or more new numerical ranges, which should be considered as specifically disclosed in this invention.

[0034] In a first aspect, the present invention provides a rolling method for 20CrMnTi steel, using 20CrMnTi continuously cast billets as raw materials. The rolling method includes the following steps in sequence: heating step, roughing step, intermediate rolling step, finishing rolling step of reducing and sizing mill, water cooling step, and air cooling step of cooling bed, finally obtaining finished bar stock.

[0035] The heating process is divided into four stages: preheating, heating stage one, heating stage two, and homogenization stage. The holding temperature of the homogenization stage is 1200-1240℃ (for example, it can be 1200℃, 1210℃, 1220℃, 1230℃, or 1240℃. If the holding temperature is too low, AlN cannot be fully dissolved, affecting the intrinsic grain size of the rod; if the holding temperature is too high, the surface burn-off is too severe, resulting in poor surface quality of the rod).

[0036] In the roughing process, the initial rolling temperature is 1130-1170℃ (for example, it can be 1130℃, 1150℃ or 1170℃, etc.);

[0037] In the finishing rolling process of the sizing mill, the final rolling temperature is 880-920℃ (for example, it can be 880℃, 900℃ or 920℃, etc.). If the final rolling temperature is too high, the bainite content after rolling will be too high, the cooling deformation will be large and the material hardness will be too high, making it difficult to process during use. If the final rolling temperature is too low, the AlN precipitation effect will be poor, affecting the intrinsic grain size.

[0038] In the air cooling process of the cooling bed, the cooling rate is controlled to be 90-150℃ / min (for example, it can be 90℃ / min, 100℃ / min, 110℃ / min, 130℃ / min or 150℃ / min). If the cooling rate is too high, the bainite content of the bar will be too high, or even martensite structure will be generated. The cooling deformation will be large and the material hardness will be too high, making it difficult to process during use. If the cooling rate is too low, it will aggravate the banded structure.

[0039] This invention controls the banded structure and grain size of the rolled bar by controlling the final rolling temperature and the post-rolling cooling rate. It can obtain high-performance 20CrMnTi steel with a banded structure ≤1.5 grade and an intrinsic grain size ≥7.5 grade without the need for heat treatment such as normalizing. This reduces the production process, saves energy, improves production efficiency, reduces production costs, and facilitates subsequent processing.

[0040] In the above-mentioned rolling method for 20CrMnTi steel, as an optional embodiment, the holding time of the soaking zone in the heating process is 60 to 90 minutes (for example, it can be 60 minutes, 70 minutes, 80 minutes or 90 minutes).

[0041] In the above-mentioned rolling method for 20CrMnTi steel, as an optional embodiment, in the heating process, the temperature of the preheating section is 700-800℃ (for example, it can be 700℃, 720℃, 740℃, 760℃, 780℃ or 800℃), the temperature of the first heating section is 1140-1200℃, and the temperature of the second heating section is 1200-1240℃.

[0042] In the above-mentioned rolling method for 20CrMnTi steel, as an optional embodiment, the total heating time in the heating process is 240-360 min (for example, it can be 240 min, 260 min, 280 min, 300 min, 320 min, 340 min or 360 min).

[0043] In the above-mentioned rolling method for 20CrMnTi steel, as an optional embodiment, the inlet temperature in the intermediate rolling process is 950-1000℃.

[0044] In the above-mentioned rolling method for 20CrMnTi steel, as an optional embodiment, the inlet temperature in the finishing rolling process of the reducing and sizing mill is 885-925℃.

[0045] In the above-mentioned rolling method for 20CrMnTi steel, as an optional implementation, the upper cooling bed temperature in the air cooling process is 760-800℃ (for example, it can be 760℃, 780℃, or 800℃. If the temperature is too high, it will aggravate the banded structure; if the temperature is too low, it will easily lead to large cooling deformation and excessive material hardness, making it difficult to process during use).

[0046] In the above-mentioned rolling method for 20CrMnTi steel, as an optional embodiment, a water tank is used for water cooling in the water cooling process to cool the finished rolled bar to 760-800℃. The water flow rate of the water tank is 100-320L / min (e.g., 100L / min, 200L / min, or 300L / min), and the water pressure is 5-8MPa. In the above-mentioned rolling method for 20CrMnTi steel, as an optional embodiment, in the air cooling process on the cooling bed, 1-2 moving teeth are spaced between adjacent bars to control the cooling rate at 90-150℃ / min.

[0047] In the above-mentioned rolling method for 20CrMnTi steel, as an optional embodiment, the temperature exiting the cooling bed during the air cooling process is no more than 600℃.

[0048] In the above-mentioned rolling method for 20CrMnTi steel, as an optional embodiment, the mass percentage of each element in the continuously cast billet is as follows: C: 0.17-0.23%, Si: 0.17-0.37%, Mn: 0.8-1.1%, P: ≤0.025%, S: ≤0.02%, Cr: 1-1.3%, Ni: ≤0.30%, Cu ≤0.30%, Ti: 0.04-0.10%, with the remainder being matrix Fe and unavoidable impurities.

[0049] In the above-mentioned rolling method for 20CrMnTi steel, as an optional embodiment, the finished bar has a specification of 20-60mm.

[0050] This invention utilizes the controlled rolling and cooling mechanism, combined with the characteristics of 20CrMnTi gear steel, to design a rolling process that controls the banded microstructure and grain size. Compared with existing technologies, it has the following characteristics:

[0051] (1) The 20CrMnTi gear steel rolling process in this invention involves heating at 1220±20℃ and holding for 60 to 90 minutes to ensure that AlN is fully dissolved during the heating process; using water tanks along the rolling line to control the final rolling temperature and the upper cooling bed temperature to promote the dispersion precipitation of AlN; and using 1-2 moving teeth between each bar after rolling to distribute the material, thereby inhibiting the formation of proeutectoid ferrite and preventing the formation of secondary bands. This technology can precisely control the temperature at each key point to obtain the required round bar and has the characteristics of high controllability.

[0052] (2) By controlling the final rolling temperature and the upper cooling bed temperature, the present invention controls the cooling rate after rolling by using the fabric to control the temperature of the final rolling. The resulting gear steel bar has a hot-rolled banded structure of ≤1.5 grade and an intrinsic grain size of ≥7.5 grade, which meets the delivery requirements and does not require normalizing or other heat treatment methods.

[0053] The banded structure includes primary banded structure and secondary banded structure. Primary banded structure is the original banded structure, caused by dendritic segregation during the solidification process of steel ingot casting. Secondary banded structure is a banded structure formed by the stacking of proeutectoid ferrite bands and pearlite bands along the rolling direction after rolling, based on the primary banded structure. In this application, the primary banded structure is improved by high-temperature diffusion, and the holding temperature needs to be no less than 1200℃. The secondary banded structure is improved by controlling the final rolling temperature and the post-rolling cooling rate to suppress the Ar3 temperature difference between the rich and poor solute zones and to suppress the formation of proeutectoid ferrite. The final rolling temperature is selected at 880-920℃, and water cooling is performed after rolling to suppress the formation of proeutectoid ferrite. The temperature of the cooling bed after water cooling is selected at 760-800℃. During cooling bed cooling, each bar is spaced 1-2 moving teeth apart to increase the post-rolling cooling rate and prevent the formation of secondary banded structure.

[0054] The intrinsic grain size affects the strength, toughness, and heat treatment distortion of gears, making it a crucial parameter for gear steel. Austenite grain growth is a thermally activated process related to interfacial energy, primarily consisting of two parts: first, austenite grain boundary migration reduces the grain boundary area, driving grain growth; second, dispersed AlN particles pin the grain boundaries, preventing austenite grain growth. This application controls the intrinsic grain size of gear steel mainly by controlling the solid solution and precipitation of AlN, ensuring that AlN is as uniformly dispersed as possible within the material. Therefore, heating still requires a minimum of 1200℃ to ensure sufficient AlN solid solution during heating, followed by final rolling at 880–920℃, and then AlN disperses and precipitates during cooling.

[0055] In a second aspect, the present invention provides a 20CrMnTi steel, which is manufactured by the rolling method of the 20CrMnTi steel described in the first aspect.

[0056] In the aforementioned 20CrMnTi steel, the banded structure of the 20CrMnTi steel is ≤1.5 grade, and the intrinsic grain size is ≥7.5 grade.

[0057] The present invention will now be described in further detail with reference to specific embodiments and comparative examples.

[0058] The mass percentages of each element in the 20CrMnTi continuous casting billet used in the following examples are shown in Table 1.

[0059] Table 1. Mass percentage of each element in 20CrMnTi continuously cast billet (balance is Fe and unavoidable impurities).

[0060] mass percentage 0.19 0.26 0.88 0.015 0.015 1.05 0.05 0.05 0.055

[0061] Example 1

[0062] A rolling method for 20CrMnTi steel includes the following steps:

[0063] S1. Heating process: Using 20CrMnTi continuous casting billet as raw material, it is heated in a walking beam furnace. The preheating temperature is 755℃, the first heating temperature is 1150℃, the second heating temperature is 1210℃, the soaking temperature is 1225℃, the holding time is 65min, and the total heating time in the heating process is 280min.

[0064] S2. Rough rolling process: The heated steel billet is fed into a 480 fully continuous two-roll mill for rough rolling. After 6 passes of deformation, the rough rolled part is obtained. The initial rolling temperature is 1158℃.

[0065] S3, Intermediate Rolling Process: The rough rolled piece obtained in step S2 is fed into a 464+450+350 fully continuous two-roll mill for intermediate rolling. After 4 passes, 6 passes, and 2 passes of deformation, an intermediate rolled piece with a specification of 27mm is obtained. The intermediate rolling inlet temperature is 975℃.

[0066] S4. Finishing rolling process of the reducing and sizing mill: The 27mm rolled piece obtained after intermediate rolling is fed into the reducing and sizing mill through the conveyor roller table for rolling. After 4 passes of deformation, a 20mm bar is obtained. The finishing rolling inlet temperature is 898℃ and the final rolling temperature is 895℃.

[0067] S5. Water cooling process: After finishing rolling, a combined water tank is used for water cooling. The temperature of the bar on the cooling bed is controlled by controlling the water volume in the water tank. The 20mm bar obtained after finishing rolling is cooled to 770℃. The water volume in the water tank is 215L / min and the water pressure is 6.5Mpa.

[0068] S6. Air-cooling process on a cooling bed: The 20mm bars obtained after precision rolling are air-cooled on a cooling bed (cooled in air). After that, they are sheared, collected, and bundled to finally obtain the finished bars. The temperature of the upper cooling bed is 770℃. During the air-cooling process on the cooling bed, each bar is spaced one moving tooth apart for material distribution (one moving tooth between two adjacent bars) to control the cooling rate at 115-150℃ / min. The temperature of the bars exiting the cooling bed is 400℃. No insulation cover is used on the cooling bed during the cooling process.

[0069] Example 2

[0070] A rolling method for 20CrMnTi steel includes the following steps:

[0071] S1. Heating process: Using 20CrMnTi continuous casting billet as raw material, it is heated in a walking beam furnace. The preheating section temperature is 762℃, the first heating section temperature is 1148℃, the second heating section temperature is 1206℃, the soaking section holding temperature is 1215℃, the holding time is 68min, and the total heating time in the heating process is 290min.

[0072] S2. Rough rolling process: The heated steel billet is fed into a 480 fully continuous two-roll mill for rough rolling. After 6 passes of deformation, the rough rolled part is obtained. The initial rolling temperature is 1155℃.

[0073] S3, Intermediate Rolling Process: The rough rolled piece obtained in step S2 is fed into a 464+450 fully continuous two-roll mill for intermediate rolling. After 4 passes and 6 passes of deformation, an intermediate rolled piece with a specification of 35mm is obtained. The intermediate rolling inlet temperature is 977℃.

[0074] S4. Finishing rolling process of the reducing and sizing mill: The 35mm rolled piece obtained after intermediate rolling is fed into the reducing and sizing mill through the conveyor roller table for rolling. After 4 passes of deformation, a 30mm bar is obtained. The entry temperature of the finishing mill is 903℃ and the final rolling temperature is 900℃.

[0075] S5. Water cooling process: After finishing rolling, a combined water tank is used for water cooling. The temperature of the bar on the cooling bed is controlled by controlling the water volume in the water tank. The 30mm bar obtained after finishing rolling is cooled to 775℃. The water volume in the water tank is 235L / min and the water pressure is 6.5Mpa.

[0076] S6. Air-cooling process on a cooling bed: The 30mm bars obtained after precision rolling are air-cooled on a cooling bed (cooled in air). After that, they are sheared, collected, and bundled to finally obtain the finished bars. The temperature of the upper cooling bed is 775℃. During the air-cooling process on the cooling bed, each bar is spaced one moving tooth apart for material distribution (one moving tooth between two adjacent bars) to control the cooling rate at 110-145℃ / min. No insulation cover is used on the cooling bed during the cooling process. The temperature of the bars exiting the cooling bed is 500℃.

[0077] Example 3

[0078] A rolling method for 20CrMnTi steel includes the following steps:

[0079] S1. Heating process: Using 20CrMnTi continuous casting billet as raw material, it is heated in a walking beam furnace. The preheating temperature is 763℃, the first heating temperature is 1161℃, the second heating temperature is 1212℃, the soaking temperature is 1218℃, the holding time is 72min, and the total heating time in the heating process is 304min.

[0080] S2. Rough rolling process: The heated steel billet is fed into a 480 fully continuous two-roll mill for rough rolling. After 6 passes of deformation, the rough rolled part is obtained. The initial rolling temperature is 1148℃.

[0081] S3, Intermediate Rolling Process: The rough rolled piece obtained in step S2 is fed into a 464+450 fully continuous two-roll mill for intermediate rolling. After 4 passes and 6 passes of deformation, an intermediate rolled piece with a specification of 46mm is obtained. The intermediate rolling inlet temperature is 968℃.

[0082] S4. Finishing rolling process of the reducing and sizing mill: The 46mm rolled piece obtained after intermediate rolling is fed into the reducing and sizing mill through the conveyor roller table for rolling. After 4 passes of deformation, a 40mm bar is obtained. The finishing rolling inlet temperature is 910℃ and the final rolling temperature is 906℃.

[0083] S5. Water cooling process: After finishing rolling, a combined water tank is used for water cooling. The temperature of the bar on the cooling bed is controlled by controlling the water volume in the water tank. The 40mm bar obtained after finishing rolling is cooled to 778℃. The water volume in the water tank is 265L / min and the water pressure is 7Mpa.

[0084] S6. Air-cooling process on a cooling bed: The 40mm bars obtained after precision rolling are air-cooled on a cooling bed (cooled in air). After that, they are sheared, collected, and bundled to finally obtain the finished bars. The temperature of the upper cooling bed is 778℃. During the air-cooling process on the cooling bed, each bar is spaced one moving tooth apart for material distribution (one moving tooth between two adjacent bars) to control the cooling rate at 100-140℃ / min. The temperature of the bars exiting the cooling bed is 450℃. No insulation cover is used on the cooling bed during the cooling process.

[0085] The surface and core banded structures of the finished rod obtained in this embodiment are as follows: Figure 2 a, Figure 2 As shown in b; the intrinsic grain size of the surface and core are respectively as follows: Figure 3 a, Figure 3 As shown in b.

[0086] Example 4

[0087] A rolling method for 20CrMnTi steel includes the following steps:

[0088] S1. Heating process: Using 20CrMnTi continuous casting billet as raw material, it is heated in a walking beam furnace. The preheating temperature is 741℃, the first heating temperature is 1142℃, the second heating temperature is 1201℃, the soaking temperature is 1220℃, the holding time is 75min, and the total heating time in the heating process is 312min.

[0089] S2. Rough rolling process: The heated steel billet is fed into a 480 fully continuous two-roll mill for rough rolling. After 6 passes of deformation, the rough rolled part is obtained. The initial rolling temperature is 1145℃.

[0090] S3, Intermediate Rolling Process: The rough rolled piece obtained in step S2 is fed into a 464+450 fully continuous two-roll mill for intermediate rolling. After four passes of deformation, an intermediate rolled piece with a specification of 60mm is obtained. The entry temperature of the intermediate rolling mill is 965℃.

[0091] S4. Finishing rolling process of the reducing and sizing mill: The 60mm rolled piece obtained after intermediate rolling is fed into the reducing and sizing mill through the conveyor roller table for rolling. After 4 passes of deformation, a 50mm bar is obtained. The finishing rolling inlet temperature is 911℃ and the final rolling temperature is 905℃.

[0092] S5. Water cooling process: After finishing rolling, a combined water tank is used for water cooling. The temperature of the bar on the cooling bed is controlled by controlling the water volume in the water tank. The 50mm bar obtained after finishing rolling is cooled to 785℃. The water volume in the water tank is 280L / min and the water pressure is 7.5Mpa.

[0093] S6. Air-cooling process on a cooling bed: The 50mm bars obtained after precision rolling are air-cooled on a cooling bed (cooled in air). After that, they are sheared, collected, and bundled to obtain the finished bars. The temperature of the upper cooling bed is 785℃. During the air-cooling process on the cooling bed, each bar is spaced 2 moving teeth apart for material distribution (2 moving teeth apart between two adjacent bars) to control the cooling rate at 95-120℃ / min. The temperature of the bars exiting the cooling bed is 300℃. No insulation cover is used on the cooling bed during the cooling process.

[0094] Example 5

[0095] A rolling method for 20CrMnTi steel includes the following steps:

[0096] S1. Heating process: Using 20CrMnTi continuous casting billet as raw material, it is heated in a walking beam furnace. The preheating temperature is 758℃, the first heating temperature is 1157℃, the second heating temperature is 1211℃, the soaking temperature is 1224℃, the holding time is 63min, and the total heating time in the heating process is 278min.

[0097] S2. Rough rolling process: The heated steel billet is fed into a 480 fully continuous two-roll mill for rough rolling. After 6 passes of deformation, the rough rolled part is obtained. The initial rolling temperature is 1140℃.

[0098] S3, Intermediate Rolling Process: The rough rolled piece obtained in step S2 is fed into a 464+450 fully continuous two-roll mill for intermediate rolling. After 4 passes and 2 passes of deformation, an intermediate rolled piece with a specification of 68mm is obtained. The intermediate rolling inlet temperature is 960℃.

[0099] S4. Finishing rolling process of the reducing and sizing mill: The 68mm rolled piece obtained after intermediate rolling is fed into the reducing and sizing mill through the conveyor roller table for rolling. After 4 passes of deformation, a 60mm bar is obtained. The finishing rolling inlet temperature is 913℃ and the final rolling temperature is 908℃.

[0100] S5. Water cooling process: After finishing rolling, a combined water tank is used for water cooling. The temperature of the bar on the cooling bed is controlled by controlling the water volume in the water tank. The 60mm bar obtained after finishing rolling is cooled to 790℃. The water volume in the water tank is 310L / min and the water pressure is 8Mpa.

[0101] S6. Air Cooling Process: The 60mm bars obtained after precision rolling are air-cooled on a cooling bed (cooled in air). After that, they are sheared, collected, and bundled to obtain the finished bars. The temperature of the upper cooling bed is 790℃. During the air cooling process, each bar is spaced 2 moving teeth apart for material distribution (2 moving teeth apart between two adjacent bars) to control the cooling rate at 90-115℃ / min. The temperature of the bar exiting the cooling bed is 320℃. No insulation cover is used on the cooling bed during the cooling process.

[0102] Some specific process parameters of the embodiments are shown in Table 2.

[0103] Table 2

[0104]

[0105] Comparative Example 1

[0106] A rolling method for 20CrMnTi steel includes the following steps:

[0107] S1. Heating process: Using 20CrMnTi continuous casting billet as raw material, it is heated in a walking beam furnace. The preheating section temperature is 763℃, the first heating section temperature is 1161℃, the second heating section temperature is 1212℃, the soaking section holding temperature is 1218℃, the holding time is 72min, and the total heating time in the heating process is 304min.

[0108] S2. Rough rolling process: The heated steel billet is fed into a 480 fully continuous two-roll mill for rough rolling. After 6 passes of deformation, the rough rolled part is obtained. The initial rolling temperature is 1148℃.

[0109] S3, Intermediate Rolling Process: The rough rolled piece obtained in step S2 is fed into a 464+450 fully continuous two-roll mill for intermediate rolling. After 4 passes and 6 passes of deformation, an intermediate rolled piece with a specification of 46mm is obtained. The intermediate rolling inlet temperature is 968℃.

[0110] S4. Finishing rolling process of the reducing and sizing mill: The 46mm rolled piece obtained after intermediate rolling is fed into the reducing and sizing mill through the conveyor roller table for rolling. After 4 passes of deformation, a 40mm bar is obtained. The finishing rolling inlet temperature is 948℃ and the final rolling temperature is 945℃.

[0111] S5. Air-cooling process on a cooling bed: The 40mm bars obtained after precision rolling are air-cooled on a cooling bed (cooled in air). After that, they are sheared, collected, and bundled to finally obtain the finished bars. The temperature of the upper cooling bed is 930℃. During the air-cooling process on the cooling bed, each bar is spaced one moving tooth apart for material distribution (one moving tooth between two adjacent bars) to control the cooling rate at 100-140℃ / min. The temperature of the bars exiting the cooling bed is 450℃. No insulation cover is used on the cooling bed during the cooling process.

[0112] Comparative Example 2

[0113] The rolling method of the 20CrMnTi steel provided in this comparative example is basically the same as that in Example 1, except that in step S4, the finishing rolling inlet temperature is 805°C and the final rolling temperature is 800°C.

[0114] Comparative Example 3

[0115] The rolling method of the 20CrMnTi steel provided in this comparative example is basically the same as that in Example 1, except that the water cooling process is not included, and the temperature of the upper cooling bed in step S6 is 890°C.

[0116] Comparative Example 4

[0117] The rolling method of the 20CrMnTi steel provided in this comparative example is basically the same as that in Example 1. The difference is that in step S6, the 20mm bar obtained after finishing rolling is slowly cooled to 600°C in the cooling bed insulation hood at a cooling rate of 45°C / min. Then, it is cooled in the air on the cooling bed after exiting the insulation hood. After that, it is sheared, collected, and bundled to finally obtain the finished bar. The upper cooling bed temperature is 770°C. During the air cooling on the cooling bed, each bar is spaced one moving tooth for feeding (there is one moving tooth between two adjacent bars). The exit temperature of the cooling bed is 400°C.

[0118] Performance testing

[0119] The 20CrMnTi steels obtained in the embodiments and comparative examples of the present invention were subjected to performance tests. The banded structure test was performed according to GB / T 34474.1, and the grain size test was performed according to ISO 643. The test results are shown in Table 3.

[0120] Table 3

[0121]

[0122] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention, and not to limit them; although the present invention has been described in detail with reference to the foregoing embodiments, those skilled in the art should understand that modifications can still be made to the technical solutions described in the foregoing embodiments, or equivalent substitutions can be made to some or all of the technical features; and these modifications or substitutions do not cause the essence of the corresponding technical solutions to deviate from the scope of the technical solutions of the embodiments of the present invention.

Claims

1. A rolling method for 20CrMnTi steel, characterized in that, Using 20CrMnTi continuously cast billets as raw materials, the rolling method includes the following steps in sequence: heating step, rough rolling step, intermediate rolling step, finishing rolling step of reducing and sizing mill, water cooling step, and air cooling step of cooling bed, finally obtaining finished bar stock; The heating process is divided into four stages: preheating, heating stage one, heating stage two, and heating stage one. The heating stage one is kept at a temperature of 1200-1240℃. In the roughing process, the initial rolling temperature is 1130~1170℃; In the finishing rolling process of the reducing and sizing mill, the final rolling temperature is 880~920℃; In the air-cooling process of the cooling bed, the cooling rate is controlled to be 90-150℃ / min; In the air-cooling process of the cooling bed, the temperature of the upper cooling bed is 760~800℃; In the air-cooling process of the cooling bed, there are 1-2 moving teeth between two adjacent bars to control the cooling rate to 90-150℃ / min; In the water cooling process, a water tank is used for water cooling. The water volume of the water tank is 100~320L / min and the water pressure is 5~8MPa. In the water cooling process, the bar obtained after precision rolling is cooled to 760-800°C.

2. The rolling method for 20CrMnTi steel according to claim 1, characterized in that, In the heating process, the heat soaking time of the heat soaking section is 60-90 minutes; And / or, in the heating process, the temperature of the preheating section is 700-800℃, the temperature of the first heating section is 1140-1200℃, and the temperature of the second heating section is 1200-1240℃; And / or, in the heating process, the total heating time in the heating process is 240-360 min.

3. The rolling method for 20CrMnTi steel according to claim 1, characterized in that, In the intermediate rolling process, the inlet temperature is 950-1000℃; And / or, in the finishing rolling process of the reducing and sizing mill, the inlet temperature is 885-925℃.

4. The rolling method for 20CrMnTi steel according to claim 1, characterized in that, In the air-cooling process of the cooling bed, the temperature exiting the cooling bed shall not exceed 600℃.

5. The rolling method for 20CrMnTi steel according to claim 1, characterized in that, The mass percentages of each element in the continuously cast billet are as follows: C: 0.17–0.23%, Si: 0.17–0.37%, Mn: 0.8–1.1%, P: ≤0.025%, S: ≤0.02%, Cr: 1–1.3%, Ni: ≤0.30%, Cu: ≤0.30%, Ti: 0.04–0.10%, with the remainder being the matrix Fe and unavoidable impurities.

6. The rolling method for 20CrMnTi steel according to claim 1, characterized in that, The finished bar stock has a diameter of 20-60 mm.

7. A 20CrMnTi steel, characterized in that, The 20CrMnTi steel is produced by the rolling method of any one of claims 1-6.

8. The 20CrMnTi steel according to claim 7, characterized in that, The banded structure of the 20CrMnTi steel is ≤1.5 grade, and the intrinsic grain size is ≥7.5 grade.

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