Non-quenched and tempered steel and rolling method thereof

Abstract

The invention relates to the technical field of non-quenched and tempered steel production, in particular to non-quenched and tempered steel and a rolling method thereof.The rolling method of the non-quenched and tempered steel comprises the following steps that a steel billet is sequentially subjected to heating, rolling forming, cooling after rolling, red hot rolling state rapid cooling and slow cooling, and the non-quenched and tempered steel is obtained; wherein in the red hot rolling state rapid cooling step, the following steps are repeatedly executed for multiple times until the surface temperature of the discharged steel is not larger than 100 DEG C, specifically, the steel is completely immersed in water of a water tank to be subjected to water cooling for a first preset time t1, then discharged water returns to the temperature for a second preset time t2, and then the surface temperature of the steel is tested. According to the rolling method provided by the invention, development and production of large-size non-quenched and tempered steel are realized, the surface hardness of a product in a hot rolling state reaches 270-320 HBW, and the mechanical properties meet the standard requirements that the yield strength is greater than or equal to 650 MPa, the tensile strength is greater than or equal to 880 MPa, the ductility is greater than or equal to 15%, the area reduction is greater than or equal to 35%, and the room-temperature longitudinal impact energy is greater than or equal to 38 J.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of non-quenched and tempered steel production, in particular to a non-quenched and tempered steel and a rolling method thereof. BACKGROUND

[0002] The non-quenched and tempered steel generally requires that the surface hardness and mechanical properties in the hot-rolled state meet the requirements of the quenched and tempered state, such as the surface hardness (Brinell hardness) in the hot-rolled state reaching 270-320 HBW, and the mechanical properties meeting the standard requirements of "yield strength ≥ 650 MPa, tensile strength ≥ 880 MPa, elongation ≥ 15%, area reduction ≥ 35%, and room temperature longitudinal impact energy ≥ 38 J". In the rolling line with controlled rolling and controlled cooling facilities, the surface hardness and mechanical properties of the non-quenched and tempered steel in the hot-rolled state can meet the above technical requirements by adopting the controlled rolling and controlled cooling process. However, when developing and producing large-size non-quenched and tempered steel in a large-size rolling line without controlled rolling and controlled cooling devices, how to meet the standard requirements of the surface hardness in the hot-rolled state reaching 270-320 HBW, and the mechanical properties meeting "yield strength ≥ 650 MPa, tensile strength ≥ 880 MPa, elongation ≥ 15%, area reduction ≥ 35%, and room temperature longitudinal impact energy ≥ 38 J" by method innovation is a technical problem to be solved in the field. SUMMARY

[0003] In view of the above deficiencies in the prior art, the present application aims to provide a non-quenched and tempered steel and a rolling method thereof. The rolling method provided by the present application uses the post-rolling residual heat of the large-size non-quenched and tempered steel, and the large-size non-quenched and tempered steel after rolling is completely immersed in a water tank for fast cooling without controlled rolling and controlled cooling devices on the rolling line. In this way, a "new rolling line controlled cooling method" is used to replace the "controlled rolling and controlled cooling process", so as to develop and produce large-size non-quenched and tempered steel and meet the standard requirements of the surface hardness in the hot-rolled state reaching 270-320 HBW, and the mechanical properties meeting "yield strength ≥ 650 MPa, tensile strength ≥ 880 MPa, elongation ≥ 15%, area reduction ≥ 35%, and room temperature longitudinal impact energy ≥ 38 J".

[0004] In order to achieve the above-mentioned purpose, the present application provides the following technical solutions: In a first aspect, the present application provides a rolling method of a non-quenched and tempered steel, which comprises the following steps: sequentially heating a billet, rolling the billet into a finished product, post-rolling cooling, red-hot rolling state fast cooling, and slow cooling, to obtain the non-quenched and tempered steel. In the post-rolling cooling step, the surface temperature of the steel material is cooled to 680-750℃; in the red-hot rolling state fast cooling step, the following steps are repeatedly performed multiple times until the surface temperature of the steel material is not greater than 100℃ after water outlet: the steel material is completely immersed in water in a water tank for water cooling for a first predetermined time t1, then the steel material is taken out of water and warmed up for a second predetermined time t2, and then the surface temperature of the steel material is tested.

[0005] The rolling method provided by the application replaces the controlled rolling and controlled cooling process with a new rolling line cooling method by using the post-rolling residual heat of large-size non-quenched and tempered steel, and by fully immersing the post-rolled large-size non-quenched and tempered steel in a water tank for fast cooling, so as to realize the development and production of large-size non-quenched and tempered steel and meet the standard requirements of the surface hardness of 270-320 HBW in the hot-rolled state, and the mechanical properties of yield strength ≥ 650 MPa, tensile strength ≥ 880 MPa, elongation ≥ 15%, area reduction ≥ 35%, and room temperature longitudinal impact energy ≥ 38 J.

[0006] Further, the billet includes a continuous casting billet; And / or, the cross-sectional size of the billet is (200-400 mm) x (300-500 mm).

[0007] Further, the chemical composition of the billet includes, by weight percentage: C: 0.35-0.45%, Si: 0.30-0.80%, Mn: 1.20-1.60%, P ≤ 0.020%, S ≤ 0.020%, V: 0.05-0.15%, and the rest is Fe and unavoidable impurities.

[0008] Further, in the heating step, the soaking temperature is 1210-1230℃, and the soaking holding time is 100-120 min.

[0009] Further, in the rolling step, the billet treated in the heating step is sent to a rough rolling mill for rough rolling to form an intermediate square billet; the intermediate square billet is transported to a finishing rolling mill group for finishing rolling, and the intermediate square billet is rolled into a round steel by the finishing rolling mill group, wherein the opening rolling temperature of the finishing rolling is 910-950℃, and the final rolling temperature of the finishing rolling is 880-920℃.

[0010] Further, in the rolling step, the rough rolling mill includes a 1350-type rolling mill; And / or, in the rolling step, the cross-sectional size of the intermediate square billet is 220 mm x 220 mm; And / or, in the rolling step, the finishing rolling mill group includes a 750-type rolling mill; And / or, in the rolling step, the finishing rolling mill group includes 3-5 750-type rolling mills.

[0011] Further, in the rolling step, the round steel is rapidly collected offline after rolling is completed, wherein the rapid collection offline includes completing the collection operation before the surface temperature of the round steel drops to 680-750℃ after rolling is completed; And / or, in the step of post-rolling cooling, the cooling mode is air cooling. And / or, in the step of red-hot rolled state fast cooling, the temperature of the steel surface is 680-750℃ when entering water for the first time. And / or, in the step of red-hot rolled state fast cooling, the following steps are repeated for 2-4 times until the temperature of the steel surface is not more than 100℃ when exiting water: the steel is fully immersed in the water tank for water cooling for a first predetermined time t1, then the steel is taken out of water for a second predetermined time t2, and then the temperature of the steel surface is tested. And / or, in the step of red-hot rolled state fast cooling, the temperature of the steel surface is 70-100℃ when exiting water. And / or, in the step of red-hot rolled state fast cooling, the initial temperature of the water in the water tank is 15-40℃. And / or, in the step of red-hot rolled state fast cooling, the following steps are repeated for 3 times until the temperature of the steel surface is 70-100℃ when exiting water: the steel is fully immersed in the water tank for water cooling for a first predetermined time t1, then the steel is taken out of water for a second predetermined time t2, and then the temperature of the steel surface is tested, wherein the temperature of the steel surface is 680-750℃ when entering water for the first time, the time of entering water for the first time is 1-2min, the time of taking out of water for the first time is 50-60s, and then the temperature of the steel surface is tested to be 250-300℃; the temperature of the steel surface is 250-300℃ when entering water for the second time, the time of entering water for the second time is 2-5min, the time of taking out of water for the second time is 40-50s, and then the temperature of the steel surface is tested to be 200-260℃; the temperature of the steel surface is 200-260℃ when entering water for the third time, the time of entering water for the third time is 10-12min, the time of taking out of water for the third time is 30-40s, and then the temperature of the steel surface is tested to be 70-100℃ when exiting water. And / or, in the step of red-hot rolled state fast cooling, the size of the water tank is 11m in length, 1.8m in width and 2m in depth. And / or, the slow cooling includes pit slow cooling, and in the step of slow cooling, the temperature is ≤40℃ when exiting the pit, and the slow cooling time is not less than 24 hours. And / or, the non-quenched and tempered steel includes round steel, and the specification of the round steel is φ(150-180)mm.

[0012] Further, in the step of red-hot rolled state fast cooling, the first predetermined time t1 is 1-12min, and the second predetermined time t2 is 0.5-1min.

[0013] In a second aspect, the present application provides a non-quenched and tempered steel, which is prepared by the rolling method of the non-quenched and tempered steel in the first aspect.

[0014] Further, the surface hardness of the non-quenched and tempered steel is 270-320 HBW, the yield strength is greater than or equal to 650 MPa, the tensile strength is greater than or equal to 880 MPa, the elongation is greater than or equal to 15%, the area reduction is greater than or equal to 35%, and the room temperature longitudinal impact energy is greater than or equal to 38 J.

[0015] Compared with the prior art, the technical scheme of the present application has at least the following technical effects: The rolling method provided by the present application fully immerses the large-specification non-quenched and tempered steel after rolling in a water tank for fast cooling without a controlled rolling and controlled cooling device on the rolling line, so as to replace the controlled rolling and controlled cooling process with "a new rolling line controlled cooling method", realize the development and production of large-specification non-quenched and tempered steel, and meet the standard requirements of the surface hardness of the product in the hot-rolled state reaching 270-320 HBW, and the mechanical properties meeting "yield strength greater than or equal to 650 MPa, tensile strength greater than or equal to 880 MPa, elongation greater than or equal to 15%, area reduction greater than or equal to 35%, and room temperature longitudinal impact energy greater than or equal to 38 J". DETAILED DESCRIPTION

[0016] In order to make the purpose, technical scheme and advantages of the present application clearer, the technical scheme in the embodiments of the present application will be described clearly and completely below in combination with the embodiments of the present application. It should be understood by those skilled in the art that the embodiments are only used to help understand the present application, and should not be regarded as a specific limitation on the present application. Based on the embodiments in the present application, all other embodiments obtained by those skilled in the art without creative labor fall within the scope of protection of the present application. The process parameters not specified in the following embodiments are usually according to the conventional conditions.

[0017] The endpoints of the ranges and any values disclosed in the present application are not limited to the precise values stated. These ranges and values should be construed as having a range of values including the values that are approximately the same as the stated values. For ranges, the endpoints are included within the range unless otherwise indicated. For ranges of values, the endpoints of each range are included within the range, and the ranges of values are inclusive of the individual values.

[0018] In a first aspect, the present application provides a rolling method of non-quenched and tempered steel, the rolling method of non-quenched and tempered steel comprising the following steps: sequentially heating a billet, rolling the billet into a finished product, cooling the finished product after rolling, red-hot rolling state fast cooling, and slow cooling to obtain the non-quenched and tempered steel. In the post-rolling cooling step, the surface temperature of the steel material is cooled to 680-750°C (for example, it can be 680°C, 690°C, 700°C, 710°C, 720°C, 730°C, 740°C or 750°C); in the red-hot rolling state fast cooling step, the following steps are repeatedly performed multiple times until the surface temperature of the steel material after water outlet is not more than 100°C: after water cooling the steel material in the water tank for a first predetermined time t1, the steel material is taken out of the water and is warmed up in the air for a second predetermined time t2, and then the surface temperature of the steel material is tested.

[0019] Specifically, the water outlet warm-up is that the steel material is taken out of the water and is placed in the air to increase the surface temperature of the steel material, so that the surface and core temperatures of the steel material are consistent, that is, the steel material is taken out of the water, and is quickly red-hot in the air to increase the surface temperature of the steel material.

[0020] If the surface temperature of the steel material obtained after post-rolling cooling is too high, the temperature of the steel material entering the water will be too high, so that the elongation and area reduction of the prepared steel material are reduced, which cannot meet the standard requirements, and the steel material is prone to cracking, thereby affecting the qualified rate of the product; if the surface temperature of the steel material obtained after post-rolling cooling is too low, the temperature of the steel material entering the water will be too low, so that the hardness, strength and impact toughness of the prepared steel material are reduced, which cannot meet the standard requirements. If the surface temperature of the steel material after the last water outlet in the red-hot rolling state fast cooling step is too high, the temperature of the steel material entering the pit for slow cooling will be too high, so that the elongation and area reduction of the prepared steel material are reduced, which cannot meet the standard requirements.

[0021] The rolling method provided by the application realizes the development and production of large-size non-quenched and tempered steel and meets the standard requirements of the surface hardness of the product in the hot-rolled state being 270-320HBW and the mechanical properties meeting the standard requirements of the yield strength being greater than or equal to 650MPa, the tensile strength being greater than or equal to 880MPa, the elongation being greater than or equal to 15%, the area reduction being greater than or equal to 35%, and the longitudinal impact energy at room temperature being greater than or equal to 38J by using the post-rolling residual heat of the non-quenched and tempered steel, fully immersing the large-size non-quenched and tempered steel after rolling in a water tank for fast cooling without a controlled rolling and controlled cooling device on the rolling line, and replacing the controlled rolling and controlled cooling process with the online controlled cooling method.

[0022] The application replaces the controlled rolling and controlled cooling process with the online controlled cooling method by using the post-rolling residual heat of the non-quenched and tempered steel, designing and manufacturing a red-hot rolling state quenching fast cooling pool near the cooling bed of the rolling line without the controlled rolling and controlled cooling device, immersing the steel material in the fast cooling pool for cooling when the surface temperature of the steel material after rolling cooling is 680-750°C, and meeting the standard requirements and market orders of the non-quenched and tempered steel product through process innovation.

[0023] In the rolling method of the non-quenched and tempered steel, as an optional implementation manner, the steel billet includes a continuous casting billet.

[0024] In the rolling method of the non-quenched and tempered steel, as an optional implementation, the cross-sectional size of the billet is (200-400 mm) x (300-500 mm), for example, it can be 200 mm x 300 mm, 300 mm x 400 mm or 400 mm x 500 mm.

[0025] The cross-sectional size, also called the cross-sectional size, refers to the size of the cut obtained by cutting the object with a plane (imaginary cutting surface) perpendicular to the length direction of the object. Here, the cross-sectional size of the billet is a rectangle.

[0026] In the rolling method of the non-quenched and tempered steel, as an optional implementation, the chemical composition of the billet includes, in terms of percentage by weight: C: 0.35-0.45% (for example, it can be 0.35%, 0.36%, 0.37%, 0.38%, 0.39%, 0.40%, 0.41%, 0.42%, 0.43%, 0.44% or 0.45%), Si: 0.30-0.80% (for example, it can be 0.30%, 0.40%, 0.50%, 0.60%, 0.70% or 0.80%), Mn: 1.20-1.60% (for example, it can be 1.20%, 1.30%, 1.40%, 1.50% or 1.60%), P≤0.020%, S≤0.020%, V: 0.05-0.15% (for example, it can be 0.05%, 0.06%, 0.07%, 0.08%, 0.10%, 0.12% or 0.15%), and the rest is Fe and unavoidable impurities.

[0027] In the rolling method of the non-quenched and tempered steel, as an optional implementation, in the heating step, the soaking temperature is 1210-1230℃ (for example, it can be 1210℃, 1215℃, 1220℃, 1225℃ or 1230℃), and the soaking time is 100-120 min (for example, it can be 100 min, 105 min, 110 min, 115 min or 120 min).

[0028] In the rolling method of the non-quenched and tempered steel, as an optional implementation, in the rolling step, the billet treated in the heating step is sent to a rough rolling mill for rough rolling to form an intermediate square billet; the intermediate square billet is transported to a finishing rolling mill for finishing rolling, and the intermediate square billet is rolled into a round steel by the finishing rolling mill, wherein the opening rolling temperature of the finishing rolling is 910℃-950℃ (for example, it can be 910℃, 920℃, 930℃, 940℃ or 950℃), and the final rolling temperature of the finishing rolling is 880-920℃ (for example, it can be 880℃, 890℃, 900℃, 910℃ or 920℃).

[0029] In the above-mentioned rolling method for non-quenched and tempered steel, as an optional embodiment, the roughing mill in the rolling forming step includes a 1350 type mill.

[0030] Specifically, in this embodiment, "1350" refers to the diameter of the roughing mill roll being 1350 millimeters.

[0031] In the above-mentioned rolling method for non-quenched and tempered steel, as an optional embodiment, in the rolling forming step, the cross-sectional dimensions of the intermediate square billet are 220mm × 220mm.

[0032] Cross-sectional dimensions, also called cross-sectional dimensions, refer to the size of the cut obtained by cutting an object with a plane (an imaginary cutting surface) perpendicular to its length. After passing through a 1350 type roughing mill, the steel billet is rolled into a square billet with a cross-section of 220mm on each side.

[0033] In the above-mentioned rolling method for non-quenched and tempered steel, as an optional embodiment, the finishing mill unit in the rolling forming step includes a 750 type rolling mill.

[0034] Specifically, in this embodiment, "750" refers to the diameter of the finishing mill roll being 750 millimeters.

[0035] In the above-mentioned rolling method for non-quenched and tempered steel, as an optional embodiment, in the rolling forming step, the finishing mill unit includes 3-5 stands (for example, 3, 4 or 5 stands) of 750 type rolling mill.

[0036] In the above-mentioned rolling method for non-quenched and tempered steel, as an optional embodiment, in the rolling forming step, the round steel is rapidly collected and removed from the rolling line after rolling. The rapid collection and removal includes completing the collection operation after rolling and before the surface temperature of the round steel drops to 680-750℃ (for example, 680℃, 690℃, 700℃, 710℃, 720℃, 730℃, 740℃ or 750℃).

[0037] In the above-mentioned rolling method for non-quenched and tempered steel, as an optional embodiment, the post-rolling cooling... In this process, the cooling method is air cooling.

[0038] In the above-mentioned rolling method for non-quenched and tempered steel, as an optional embodiment, in the rapid cooling step of the red-hot rolled state, the surface temperature of the steel is 680-750℃ (for example, it can be 680℃, 690℃, 700℃, 710℃, 720℃, 730℃, 740℃ or 750℃) when it is first immersed in water.

[0039] In the rolling method of the non-quenched and tempered steel, as an optional embodiment, in the red-hot rolled state rapid cooling step, the following steps are repeated 2-4 times (for example, it can be 2 times, 3 times or 4 times) until the surface temperature of the steel is not more than 100℃ when the water is discharged: after the water cooling of the steel is completely immersed in the water tank for a first predetermined time t1, the water is discharged and the steel is warmed up for a second predetermined time t2, and then the surface temperature of the steel is tested.

[0040] In the rolling method of the non-quenched and tempered steel, as an optional embodiment, in the red-hot rolled state rapid cooling step, the surface temperature of the steel is 70-100℃ (for example, it can be 70℃, 80℃, 90℃ or 100℃) when the water is discharged.

[0041] In the rolling method of the non-quenched and tempered steel, as an optional embodiment, in the red-hot rolled state rapid cooling step, the first predetermined time t1 is 1-12min (for example, it can be 1min, 2min, 4min, 6min, 8min, 10min or 12min), and the second predetermined time t2 is 0.5-1min (for example, it can be 0.5min, 0.6min, 0.7min, 0.8min, 0.9min or 1min).

[0042] In the rolling method of the non-quenched and tempered steel, as an optional embodiment, in the red-hot rolled state rapid cooling step, the initial temperature of the water in the water tank is 15-40℃ (for example, it can be 15℃, 20℃, 25℃, 30℃, 35℃ or 40℃), that is, the water temperature is 15-40℃ before the steel is completely immersed in the water for the first time.

[0043] In the rolling method of the non-quenched and tempered steel, as an optional embodiment, in the red-hot rolled state rapid cooling step, the following step is repeated for 3 times until the surface temperature of the steel is 70-100°C (for example, it can be 70°C, 80°C, 90°C or 100°C) when water is discharged: after water cooling for a first predetermined time t1 by completely immersing the steel in the water tank, the steel is warmed up for a second predetermined time t2 after water discharge, and then the surface temperature of the steel is tested, wherein the surface temperature of the steel is 680-750°C (for example, it can be 680°C, 690°C, 700°C, 710°C, 720°C, 730°C, 740°C or 750°C) when water is first discharged, the first water entry time is 1-2 min (for example, it can be 1 min, 1.2 min, 1.4 min, 1.6 min, 1.8 min or 2 min), the first water discharge is warmed up for 50-60 seconds (for example, it can be 50 seconds, 52 seconds, 54 seconds, 56 seconds, 58 seconds or 60 seconds), and then the surface temperature of the steel is tested to be 250-300°C (for example, it can be 250°C, 260°C, 270°C, 280°C, 290°C or 300°C); the surface temperature of the steel is 250-300°C (for example, it can be 250°C, 260°C, 270°C, 280°C, 290°C or 300°C) when water is secondly discharged, the second water entry time is 2-5 min (for example, it can be 2 min, 2.2 min, 2.4 min, 2.6 min, 2.8 min, 3 min, 3.2 min, 3.4 min, 3.6 min, 3.8 min or 5 min), the second water discharge is warmed up for 40-50 seconds (for example, it can be 40 seconds, 42 seconds, 44 seconds, 46 seconds, 48 seconds or 50 seconds), and then the surface temperature of the steel is tested to be 200-260°C (for example, it can be 200°C, 210°C, 220°C, 230°C, 240°C or 260°C); the surface temperature of the steel is 200-260°C (for example, it can be 200°C, 210°C, 220°C, 230°C, 240°C or 260°C) when water is thirdly discharged, the third water entry time is 10-12 min (for example, it can be 10 min, 10.5 min, 11 min, 11.5 min or 12 min), the third water discharge is warmed up for 30-40 seconds (for example, it can be 30 seconds, 32 seconds, 34 seconds, 36 seconds, 38 seconds or 40 seconds), and then the surface temperature of the steel is tested to be 70-100°C (for example, it can be 70°C, 80°C, 90°C or 100°C).

[0044] In the rolling method of the non-quenched and tempered steel, as an optional embodiment, in the red-hot rolled state rapid cooling step, the size of the water tank is 11 m long*1.8 m wide*2 m deep.

[0045] As an optional embodiment of the rolling method of the non-quenched and tempered steel, the slow cooling includes pit slow cooling, and in the slow cooling step, the slow cooling is performed to a temperature of ≤ 40℃ out of the pit, and the slow cooling time is not less than 24 hours.

[0046] As an optional embodiment of the rolling method of the non-quenched and tempered steel, in the slow cooling step, the slow cooling time is 24-48 hours, for example, can be 24 hours, 26 hours, 28 hours, 30 hours, 35 hours, 40 hours, 42 hours, 44 hours, 46 hours or 48 hours.

[0047] As an optional embodiment of the rolling method of the non-quenched and tempered steel, the non-quenched and tempered steel includes round steel, and the size of the round steel is φ (150-180) mm, for example, the size of the round steel can be φ 150 mm, φ 160 mm, φ 170 mm or φ 180 mm.

[0048] Specifically, the size of φ 150-180 mm refers to that the diameter of the cross section of the round steel (round bar) is 150-180 mm.

[0049] In the second aspect, the application provides a non-quenched and tempered steel prepared by the rolling method of the non-quenched and tempered steel in the first aspect.

[0050] As an optional embodiment of the non-quenched and tempered steel, the surface hardness of the non-quenched and tempered steel is 270-320 HBW, the yield strength is ≥ 650 MPa, the tensile strength is ≥ 880 MPa, the elongation is ≥ 15%, the area reduction is ≥ 35%, and the room temperature longitudinal impact energy is ≥ 38 J.

[0051] The technical requirements of the surface hardness of 270-320 HBW, the yield strength of ≥ 650 MPa, the tensile strength of ≥ 880 MPa, the elongation of ≥ 15%, the area reduction of ≥ 35%, and the room temperature longitudinal impact energy of ≥ 38 J are product performance requirements, and can also be customer requirements, i.e. market demand.

[0052] As an optional embodiment of the non-quenched and tempered steel, the surface hardness of the non-quenched and tempered steel is 310-320 HBW, the yield strength is 780-798 MPa, the tensile strength is 1080-1090 MPa, the elongation is 17-18%, the area reduction is 38-40%, and the room temperature longitudinal impact energy is 40-42 J.

[0053] The application will be further described in detail in combination with specific examples and comparative examples.

[0054] Example 1 The embodiment provides a rolling method of non-quenched and tempered steel, including the following steps: selecting a 300*400mm continuous casting billet (chemical components include, in percentage by weight: C: 0.42%, Si: 0.60%, Mn: 1.40%, P: 0.012%, S: 0.009%, V: 0.13%, and the rest is Fe and inevitable impurities), after heating and keeping for 110min at 1220~1225℃, the billet is sent to a 1350 type rough rolling mill for rough rolling, and a 220mm*220mm intermediate square billet is rolled (i.e. the 1350 type rough rolling mill is opened to 220mm intermediate square billet); then air cooling, after the air cooling is finished, the intermediate square billet is transported to a finishing rolling mill group composed of four 750 type rolling mills for finishing rolling, and a φ160mm round steel is rolled by the finishing rolling mill group, wherein the opening rolling temperature of the finishing rolling is 930℃, and the finish rolling temperature is 890℃ (i.e. the opening rolling temperature of the 750 type finishing rolling mill is controlled to be 930℃, the four 750 type rolling mills are used to form the φ160mm round steel, and the finish rolling temperature is 890℃); after the rolling, the steel is quickly collected and discharged, air cooled, and after the surface temperature of the steel is cooled to 680℃, the steel is completely immersed into a water tank (the water tank has a size of 11m*1.8m*2m) with water at a temperature of 23℃, and after water outlet temperature recovery, the steel is again immersed into water for fast cooling, and the above steps are repeated for three times (the first time, the surface temperature of the steel is 680℃, the water immersion time is 1min, the water outlet temperature recovery time is 60s, and then the surface temperature of the steel is tested; the second time, the surface temperature of the steel is 270℃, the water immersion time is 3min, the water outlet temperature recovery time is 45s, and then the surface temperature of the steel is tested; the third time, the surface temperature of the steel is 250℃, the water immersion time is 780s, the water outlet temperature recovery time is 30s, and then the surface temperature of the steel is 94℃); and then the steel is again immersed into a pit for slow cooling for 36h, and the pit outlet temperature is 35℃. The surface of the non-quenched and tempered steel prepared in the embodiment is free of cracks.

[0055] Embodiment 2 The embodiment provides a rolling method of non-quenched and tempered steel, including the following steps: selecting a 300*400mm continuous casting billet (chemical components include C: 0.39%, Si: 0.40%, Mn: 1.60%, P: 0.009%, S: 0.014%, V: 0.09% by weight percentage, and the rest is Fe and inevitable impurities), after heating and keeping for 120min at 1210-1215℃, the billet is sent to a 1350 type rough rolling mill for rough rolling, and a middle square billet with a section of 220mm*220mm is obtained (i.e. the 1350 type rough rolling mill is opened to 220mm square billet); then air cooling is carried out, after the air cooling is completed, the middle square billet is transported to a finishing rolling mill group composed of four 750 type rolling mills for finishing rolling, and a φ160mm round steel is obtained through the finishing rolling mill group, wherein the opening rolling temperature of the finishing rolling is 940℃, and the finish rolling temperature is 885℃ (i.e. the opening rolling temperature of the 750 type finishing rolling mill is about 940℃, the four 750 type rolling mills are used to obtain a φ160mm round steel, and the finish rolling temperature is about 885℃); after the rolling is completed, the steel is quickly collected and discharged, air cooling is carried out, and when the surface temperature of the steel is cooled to about 710℃, the steel is completely immersed in a water tank (the size of the water tank is 11m*1.8m*2m) with water temperature of 27℃ for cooling, and after the water temperature is recovered, the steel is again immersed in water for fast cooling, and the above steps are repeated for three times (the surface temperature of the steel is 710℃ when the steel is immersed in water for the first time, the water immersion time is 2min, the water recovery time is 60s, and then the surface temperature of the steel is tested; the surface temperature of the steel is 290℃ when the steel is immersed in water for the second time, the water immersion time is 5min, the water recovery time is 45s, and then the surface temperature of the steel is tested; the surface temperature of the steel is 232℃ when the steel is immersed in water for the third time, the water immersion time is 780s, the water recovery time is 30s, and then the surface temperature of the steel is 79℃); then the steel is again immersed in a pit for slow cooling for 24h, and the pit temperature is 32℃. The surface of the non-quenched and tempered steel prepared in the embodiment is free of cracks.

[0056] Comparative example 1 The rolling method of the non-quenched and tempered steel provided in the comparative example is basically the same as that in the embodiment 1, except that the surface temperature of the steel is cooled to 500℃, the steel is completely immersed in a water tank (the size of the water tank is 11m*1.8m*2m) with water temperature of 23℃ for cooling, the water temperature is recovered after the water is discharged, the steel is again immersed in water for fast cooling, the above steps are repeated for three times, the water recovery time is 30s, the surface temperature of the steel is 92℃, the steel is again immersed in a pit for slow cooling for 36h, and the pit temperature is 34℃. The surface of the non-quenched and tempered steel prepared in the comparative example is free of cracks.

[0057] Comparative example 2 The rolling method of the non-quenched and tempered steel provided by the present comparative example is basically the same as that of example 1, except that the steel surface temperature is cooled to 800 DEG C, completely immersed in a water tank (water tank size is 11 m*1.8 m*2 m) with water temperature of 23 DEG C, and then re-immersed in water for fast cooling after water temperature recovery, repeated 3 times, and then the steel surface temperature is measured to be 96 DEG C after water temperature recovery for 30 seconds, and then the steel is re-immersed in the pit for slow cooling for 40 hours, and the out-pit temperature is 36 DEG C. The surface of the non-quenched and tempered steel prepared in the present comparative example has cracks.

[0058] Comparative example 3 The rolling method of the non-quenched and tempered steel provided by the present comparative example is basically the same as that of example 1, except that the steel surface temperature is cooled to 800 DEG C, completely immersed in a water tank (water tank size is 11 m*1.8 m*2 m) with water temperature of 23 DEG C, and then re-immersed in water for fast cooling after water temperature recovery, repeated 3 times, and then the steel surface temperature is measured to be 96 DEG C after water temperature recovery for 30 seconds, and then the steel is re-immersed in the pit for slow cooling for 40 hours, and the out-pit temperature is 36 DEG C. The surface of the non-quenched and tempered steel prepared in the present comparative example has cracks.

[0059] Performance test The non-quenched and tempered steel prepared in examples 1-2 and comparative examples 1-3 is sampled and tested at room temperature, and the yield strength, tensile strength, elongation, and area reduction are tested according to GB / T228.1 metal material tensile test part 1: room temperature tensile test method; The non-quenched and tempered steel prepared in examples 1-2 and comparative examples 1-3 is sampled and tested at room temperature, and the surface Brinell hardness is tested according to GB / T231.1-2018; The non-quenched and tempered steel prepared in examples 1-2 and comparative examples 1-3 is sampled and tested at room temperature, and the room temperature longitudinal impact energy is tested according to GB / T229-2020 metal material charpy pendulum impact test method.

[0060] The test results are shown in table 1.

[0061] Table 1 As can be seen from table 1: Comparing examples 1 and 2 with comparative examples 1-3, it can be seen that when the steel water temperature is too low, the hardness, strength and impact toughness of the steel are correspondingly reduced, which does not meet the standard requirements; on the contrary, when the steel water temperature is too high, the steel is prone to cracking, and the elongation and area reduction of the steel are also correspondingly reduced, which does not meet the standard requirements, in addition, when the steel water temperature is too high, the elongation and area reduction of the steel are reduced, which does not meet the standard requirements.

[0062] The above only describes the preferred embodiments of the present application, and is not intended to limit the present application. For those skilled in the art, the present application can have various modifications and changes. Any modification, equivalent replacement, improvement, etc. made within the spirit and principles of the present application shall be included in the protection scope of the present application.

Claims

1. A rolling method for non-quenched and tempered steel, characterized in that, The rolling method for the non-quenched and tempered steel includes the following steps: heating the steel billet sequentially, rolling it into a finished product, cooling it after rolling, rapidly cooling it in a red-hot rolled state, and slowly cooling it to obtain the non-quenched and tempered steel; In the post-rolling cooling step, the surface temperature of the steel is cooled to 680-750℃; in the hot-rolled rapid cooling step, the following steps are repeated multiple times until the surface temperature of the steel after exiting the water is no greater than 100℃: the steel is completely immersed in the water of the water tank for water cooling for a first predetermined time t1, then exited the water for a second predetermined time t2 to reheat, and then the surface temperature of the steel is tested.

2. The rolling method for non-quenched and tempered steel according to claim 1, characterized in that, The steel billet includes continuously cast billets; And / or, the cross-sectional dimensions of the steel billet are (200-400mm) × (300-500mm).

3. The rolling method for non-quenched and tempered steel according to claim 1, characterized in that, The chemical composition of the steel billet, by weight percentage, includes: C: 0.35-0.45%, Si: 0.30-0.80%, Mn: 1.20-1.60%, P≤0.020%, S≤0.020%, V: 0.05-0.15%, with the remainder being Fe and unavoidable impurities.

4. The rolling method for non-quenched and tempered steel according to claim 1, characterized in that, In the heating step, the heat spread temperature is 1210~1230℃, and the heat spread holding time is 100-120min.

5. The rolling method for non-quenched and tempered steel according to claim 1, characterized in that, In the rolling process, the steel billet after the heating process is fed into a roughing mill for roughing and rolled into an intermediate square billet; the intermediate square billet is then transported to a finishing mill for finishing and rolled into round steel. The initial rolling temperature of the finishing mill is 910℃~950℃, and the final rolling temperature of the finishing mill is 880-920℃.

6. The rolling method for non-quenched and tempered steel according to claim 5, characterized in that, In the rolling process, the roughing mill includes a 1350 type mill; And / or, in the rolling process, the cross-sectional dimensions of the intermediate square billet are 220mm × 220mm; And / or, in the rolling forming step, the finishing mill unit includes a 750 type mill; And / or, in the rolling forming step, the finishing mill unit includes 3-5 stands of 750 type rolling mill.

7. The rolling method for non-quenched and tempered steel according to claim 1, characterized in that, In the rolling forming step, the round steel is quickly collected and removed from the production line after rolling. The quick collection and removal includes collecting the round steel before the surface temperature drops to 680-750°C after rolling. And / or, in the post-rolling cooling step, the cooling method is air cooling; And / or, in the hot-rolled rapid cooling step, the surface temperature of the steel is 680-750°C during the first immersion in water; And / or, in the hot-rolled rapid cooling step, repeat the following steps 2-4 times until the surface temperature of the steel is not greater than 100°C when it comes out of the water: immerse the steel completely in the water of the water tank for water cooling for a first predetermined time t1, then remove it from the water and allow it to return to the temperature for a second predetermined time t2, and then test the surface temperature of the steel. And / or, in the hot-rolled rapid cooling step, the surface temperature of the steel is 70-100°C until it exits the water; And / or, in the hot-rolled rapid cooling step, the initial temperature of the water in the water tank is 15-40°C; And / or, in the hot-rolled rapid cooling step, the following steps are repeated three times until the surface temperature of the steel is 70-100°C upon exiting the water: the steel is completely immersed in the water of the tank for water cooling for a first predetermined time t1, then exited the water for a second predetermined time t2, and then the surface temperature of the steel is tested. The surface temperature of the steel is 680-750°C during the first immersion, the first immersion time is 1-2 minutes, and the first exit from the water for a second time is 50-60 seconds. The surface temperature of the steel is then tested. The surface temperature was 250-300℃ during the second immersion in water; the second immersion time was 2-5 minutes, and the surface temperature recovered after the second immersion was 40-50 seconds, after which the surface temperature of the steel was measured to be 200-260℃; the surface temperature was 200-260℃ during the third immersion in water; the third immersion time was 10-12 minutes, and the surface temperature recovered after the third immersion was 30-40 seconds, after which the surface temperature of the steel was measured to be 70-100℃. And / or, in the hot-rolled rapid cooling step, the dimensions of the water tank are 11m long * 1.8m wide * 2m deep; And / or, the slow cooling includes slow cooling upon entering the pit, wherein in the slow cooling step, the temperature is slow cooled to ≤40℃ before exiting the pit, and the slow cooling time is not less than 24 hours; And / or, the non-quenched and tempered steel includes round steel bars with a specification of φ (150-180) mm.

8. The rolling method for non-quenched and tempered steel according to claim 7, characterized in that, In the hot-rolled rapid cooling step, the first predetermined time t1 is 1-12 min, and the second predetermined time t2 is 0.5-1 min.

9. A non-quenched and tempered steel, characterized in that, The non-quenched and tempered steel is prepared by the rolling method of any one of claims 1-8.

10. The non-quenched and tempered steel according to claim 9, characterized in that, The surface hardness of the non-quenched and tempered steel is 270-320HBW, yield strength ≥650MPa, tensile strength ≥880MPa, elongation ≥15%, reduction of area ≥35%, and longitudinal impact energy at room temperature ≥38J.

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