A method for controlling the quality of a hem portion of a CSP thin slab continuous casting and rolling high-strength steel

Abstract

This invention discloses a method for controlling the edge quality of CSP thin slab continuously cast and rolled high-strength steel, including steelmaking, continuous casting, slab heating, continuous rolling, laminar flow cooling, and coiling steps. Specifically, it includes the following control steps: 1) In the steelmaking step, control 0.015≤Als≤0.045% and N≤0.006%; in the thin slab continuous casting step, use tundish protection casting and secondary cooling water weak cooling control process; 2) Use a 7-stand finishing rolling process, employing a slow entry speed into the finishing F1 stand and a fast final rolling strip-threading speed, shutting off the cooling water on the finishing side guide plate, and controlling the cooling water flow rate of the work rolls, the final rolling temperature, and the edge temperature; adjust the reduction rates of the F1 stand + F2 stand, the F6 stand, and the F7 stand. This invention can effectively improve the edge microstructure and toughness of thin slabs and finished microalloyed high-strength steel coils, solving problems such as edge cracking and edge burrs in microalloyed high-strength steel; and the control method involved is simple and easy to promote for large-scale industrial production.

Description

Technical Field

[0001] This invention belongs to the field of thin slab continuous casting and rolling technology, specifically relating to a method for quality control of the rolled edge of CSP thin slab continuous casting and rolling high-strength steel. Background Technology

[0002] Thin slab continuous casting and rolling, as a new short-process strip steel production technology, is significantly different from the current traditional strip steel production process. It has advantages such as significant energy saving, high product yield, simplified production process, and short product production cycle, and has become very mature in recent years. However, in the process of producing high-strength steel containing microalloyed elements such as Nb and Ti, severe cracks frequently occur at the edges and corners of the hot-rolled coils, and quality defects such as edge damage, chipping, burrs, and edge breakage occur on the edges of the coils. This leads to the re-judgment and downgrading of finished products, seriously affecting the profitability and competitiveness of the products.

[0003] To effectively eliminate edge and corner crack defects in the continuous casting process of low-alloy steel thin slabs, researchers at home and abroad have carried out a lot of work. For example, patents CN201644727 U and CN202052915 U both passivate the corner structure of the crystallizer in the continuous casting of thin slabs or bevel the narrow face of the crystallizer. Patent CN107400827A discloses a method for controlling edge cracks in CSP containing Nb, which mainly controls the steel composition, precise protection casting in the tundish, and adds T-shaped drainage grooves to the inner arc of the bending roller in the second cooling of continuous casting, thereby increasing the corner temperature of the slab and reducing the precipitation of Nb(C,N), thereby improving the plasticity of the slab corner structure and reducing the occurrence of edge cracks in alloy steel. Patent CN108405818A discloses an equipment and process for improving the plasticity of the corner structure of microalloy steel thin slabs, which can stably realize the dispersion precipitation of microalloy carbonitrides in the corner structure of the slab, and comprehensively and stably improve the plasticity of the corner structure of the slab. However, the above solutions are all based on the principle of the third brittle temperature zone of steel. They aim to improve the plasticity of the billet corners by designing a passivated crystallizer corner structure or developing a weak cooling water distribution technology for secondary cooling in the casting flow, thereby increasing the temperature of the corners and edges of the billet. Alternatively, they aim to improve the plasticity of the corners and edges of the billet by controlling the steel composition and continuous casting protective casting, thereby reducing the precipitation of microalloyed carbonitrides at the grain boundaries of the billet. In actual thin slab continuous casting production, due to the high casting speed and overall high cooling intensity, the corners of the billet are affected by two-dimensional heat transfer. It is difficult for the corner temperatures in the straightening and other zones to completely avoid the corresponding third brittle temperature zone of the steel, resulting in unstable control of the plasticity of the billet corners. Furthermore, controlling the steel composition within a narrow range or reducing residual elements such as nitrogen in the steel is difficult to implement in actual steelmaking processes and is hard to maintain stably.

[0004] Furthermore, in practice, it was found that the edges of microalloyed high-strength steel thin slabs are relatively brittle. Simultaneously, excessively low edge temperatures during rolling cause the edges to prematurely enter the ferrite region during rolling, precipitating second-phase particles and increasing edge brittleness. In subsequent rolling, the deformation resistance of ferrite and austenite is inconsistent, leading to edge cracking, resulting in edge burrs or roughness. Further development of a process and method to fundamentally and stably improve the edge quality of continuously cast and rolled high-strength steel coils from thin slabs is of practical significance for achieving high-quality, efficient, and green production of microalloyed steel through continuous casting and rolling of thin slabs. Summary of the Invention

[0005] The purpose of this invention is to address the problems and shortcomings of existing edge crack control technologies by providing a method for controlling the edge quality of high-strength steel coils produced by continuous casting and rolling of thin slabs. This method comprehensively and stably improves the plasticity and toughness of the edge structure of high-strength steel coils without excessively narrowing the composition control.

[0006] To achieve the above objectives, the technical solution adopted by the present invention is as follows:

[0007] A method for quality control of the rolled edge of CSP thin slab continuously cast and rolled high-strength steel includes steelmaking, continuous casting, slab heating, continuous rolling, laminar flow cooling, and coiling steps, specifically including the following control steps:

[0008] 1) Steelmaking and thin slab continuous casting control:

[0009] The steelmaking process controls Als to be 0.015 ≤ Als ≤ 0.045% and N to be 0.006%, reducing the precipitation of AlN and other carbonitrides at grain boundaries without increasing the difficulty of steelmaking.

[0010] The thin slab continuous casting process adopts tundish protection casting and secondary cooling water weak cooling control process;

[0011] 2) Finishing process control: The 7-stand finishing process is adopted, with a slow entry speed into the finishing F1 stand and a fast final rolling strip threading speed. The cooling water of the finishing side guide plate is turned off, and the cooling water flow rate of the work roll, the final rolling temperature and the edge temperature are controlled. The reduction rate of the F1 stand + F2 stand, the reduction rate of the F6 stand and the reduction rate of the F7 stand are adjusted.

[0012] In the above scheme, the main chemical components and their mass ratios in the thin slab continuous casting and rolling high-strength steel include: C 0.04-0.07%, Mn 1.0-1.55%, Ti 0.11-0.145%, Nb 0-0.02%, Cr 0-0.2%, Als 0.015-0.045%, and N≤0.06%.

[0013] In the above scheme, the thickness of the slab in the thin slab continuous casting is 60-70mm.

[0014] In the above scheme, in the intermediate ladle protective casting + secondary cooling water weak cooling control process, the secondary cooling water volume is 1.93-2.15L / kg, which increases the temperature of the thin slab passing through the straightening zone, controls the surface temperature of the slab entering the furnace to above 920℃, and the surface temperature of the thin slab at the edges and corners to above 850℃, reduces the γ→α phase transformation, and prevents the precipitation of α ferrite film at the austenite grain boundaries and embrittlement of the grain boundaries when the phase transformation temperature zone (ferrite precipitation temperature 834℃) is reached.

[0015] In the above scheme, during the slab heating step, the slab enters the heating furnace at a speed of 4.0-4.2 m / min, is heated to 1210-1240℃ in the heating zone at a speed of 15-25℃ / min, and then accelerated by rollers No. 50 and above at a speed of 0.18-0.3 m / s. 2 The acceleration begins, reaching a speed of 48-54 m / min as it passes through the soaking zone, and finally exits the furnace at 1200-1230℃ (soaking zone temperature). This invention employs a slow heating and high-temperature heating process, which can effectively promote the full dissolution of AlN and other carbonitride second-phase particles precipitated at low edge temperatures, as well as the previously precipitated α-chromium film, reducing their adverse effects on the grain boundaries.

[0016] Furthermore, after the slab exits the furnace, it undergoes high-pressure descaling followed by precision rolling.

[0017] In the above scheme, the speed of entering the finishing mill F1 stand is 0.4-0.7m / s, and the final rolling speed is above 9.2m / s.

[0018] In the above scheme, the flow rate of the cooling water for the work roll is 500-580 m³ / h. 3 / h; final rolling temperature is 880-910℃.

[0019] In the above scheme, in the finishing rolling process, the reduction rate of F1 stand + F2 stand is ≥100%, the reduction rate of F6 stand is ≤18%, and the reduction rate of F7 stand is ≤10%; the reduction rates of other stands are adjusted according to the model settings. This invention reduces the deformation unevenness when the edge and middle temperatures are uneven at low temperatures by increasing the reduction amount of the front stand at high temperatures and reducing the reduction amount of the rear stand at low temperatures, thereby effectively reducing the probability of cracking.

[0020] In the above scheme, the laminar flow cooling step adopts front-end cooling.

[0021] In the above scheme, the winding temperature is 610-640℃.

[0022] In the above scheme, the thickness of the thin slab continuously cast and rolled high-strength steel is 1.5 to 3.0 mm.

[0023] The principle of this invention is as follows:

[0024] 1) Als and N control range: Considering the difficulty of on-site equipment and process control, for the existing thin slab continuous casting and rolling process, the control method of Als≤0.045% and N≤0.006% is adopted. Without increasing the difficulty of on-site smelting, it is conducive to the full dissolution of AlN during heating and ensures the quality of the edge.

[0025] 2) Slab heating process: The slab is heated slowly and at high temperature to ensure that the AlN and other carbonitride second-phase particles precipitated at the low edge temperature, as well as the α-chromium film precipitated earlier, are fully dissolved, thereby reducing their adverse effects on the grain boundaries at the edge.

[0026] 3) By combining high-speed finishing rolling, large reduction in the front stand and small reduction in the rear stand, shutting off the cooling water for the finishing side guide plates, reducing the cooling water for the work rolls, and high-temperature final rolling, the temperature drop at the edge is slowed down, the precipitation of brittle phases at the edge is reduced, and the deformation uniformity is improved. On the one hand, this can improve the plasticity and toughness of the edge structure. On the other hand, it can prevent the edge from entering the ferrite region in advance during the rolling process due to excessively low edge temperature, and avoid the inconsistency between the deformation resistance of ferrite and austenite in subsequent processes, which can lead to cracking at the edge during the rolling process, resulting in edge burrs or roughness.

[0027] Compared with the prior art, the beneficial effects of the present invention are as follows:

[0028] 1) This invention uses steelmaking Als and N control, combined with improved continuous casting, slab heating, and continuous rolling processes, which can effectively improve the plasticity and toughness of the edge structure of thin slabs and finished microalloyed high-strength steel coils, and solve the long-standing problems of edge cracking and edge burrs in microalloyed high-strength steel that have plagued the CSP thin slab continuous casting and rolling process.

[0029] 2) It does not pursue extremely narrow window of composition and process, and the production process is stable, which can provide a new idea for the preparation of high-quality continuous casting and rolling high-strength steel;

[0030] 3) The invention involves low cost and easy operation, making it suitable for large-scale industrial production. Attached Figure Description

[0031] Figure 1 The edge morphology of high-strength steel BST700X produced by the prior art as described in Comparative Example 2 is shown in the figure.

[0032] Figure 2 This is a side morphology diagram of the high-strength steel BST700X obtained in Example 2 of the present invention. Detailed Implementation

[0033] The present invention will be further described in detail below with reference to embodiments, so as to facilitate a clearer understanding of the present invention, but these embodiments do not constitute a limitation on the present invention.

[0034] Example 1

[0035] The high-strength hot-rolled steel coil with no edge cracks produced in this embodiment is made from the following components by weight percentage: C 0.052%, Mn 1.3%, Ti 0.128%, Nb 0.02%, Als 0.032%, N 0.0052%, with the remainder being Fe and unavoidable impurities. It has a thickness of 3.0 mm and a tensile strength of 700 MPa. The quality control method for the edge portion of the continuously cast and rolled high-strength steel coil includes the following steps:

[0036] 1) Steelmaking process control: Al 0.035wt%, N 0.0050wt%;

[0037] The continuous casting adopts tundish protection casting and conventional secondary cooling slow cooling process. The secondary cooling water volume is 2.15L / kg, the slab thickness is 70mm, the surface temperature of the slab entering the furnace is controlled at 956℃, and the surface temperature of the thin slab at the edge and corner is controlled at 912℃.

[0038] 2) The resulting continuously cast thin slab enters the heating furnace at a speed of 4.1 m / min, and is heated to 1216℃ in the heating zone at a speed of 18℃ / min. Then, it is accelerated by roller No. 52 at a speed of 0.2 m / s. 2 The acceleration begins to increase, reaching a speed of 54 m / min as it passes through the soaking zone and exits the furnace at 1212℃;

[0039] 3) A 7-stand finishing rolling process is adopted. After the slab exits the furnace, it undergoes high-pressure descaling, with a descaling pressure of ≥200 bar at the inlet and ≥240 bar at the outlet. Then, it is finished rolled to a finished thickness of 2 mm. The slab enters the finishing mill F1 stand at a speed of 0.64 m / s, and the final rolling threading speed is controlled at 9.2 m / s. The cooling water on the side guide plates of each finishing mill stand is turned off, and the cooling water for the work rolls is set at 580 m. 3 / h flow rate control, final rolling temperature controlled at 880℃;

[0040] Stand reduction control: The reduction rate of F1+F2 is 100%, and the reduction rates of F6 and F7 are 14.3% and 9.15% respectively; the final reduction rate is determined by tracking the slab thickness and the finished product thickness, and the reduction rates of other stands are the same below;

[0041] 4) Perform laminar flow cooling and winding. Laminar flow cooling is front-end cooling, and the winding temperature is 610℃.

[0042] Example 2

[0043] The high-strength hot-rolled steel coil with no edge cracks produced in this embodiment is composed of the following components by weight percentage: C 0.067%, Mn 1.24%, Ti 0.145%, Nb 0.018%, Als 0.037%, N 0.0060%, with the remainder being Fe and unavoidable impurities. It has a thickness of 2.0 mm and a tensile strength of 750 MPa. The quality control method for the edge portion of the continuously cast and rolled high-strength steel coil includes the following steps:

[0044] 1) Steelmaking process control: Al 0.038wt%, N 0.006wt%;

[0045] The continuous casting adopts tundish protection casting and secondary cooling slow cooling process. The secondary cooling water volume is 2.05L / kg, the slab thickness is 65mm, the surface temperature of the slab entering the furnace is controlled at 967℃, and the surface temperature of the thin slab at the edge and corner is controlled at 905℃.

[0046] 2) The obtained continuously cast thin slab enters the heating furnace at a speed of 4.0 m / min, and is heated to 1232°C in the heating zone at a speed of 17°C / min. Then, it is accelerated at 0.18 m / s by roller No. 55. 2 The acceleration begins to increase, reaching a speed of 48 m / min as it passes through the soaking zone, and exits the furnace at 1224℃;

[0047] 3) A 7-stand finishing rolling process is adopted. After the slab exits the furnace, it undergoes high-pressure descaling with a descaling pressure of ≥200 bar at the inlet and ≥240 bar at the outlet. Then, it is finished rolled to a finished thickness of 2.0 mm. The slab enters the finishing mill F1 stand at a speed of 0.6 m / s, and the final rolling threading speed is controlled at 9.7 m / s. The cooling water on the side guide plates of each finishing mill stand is turned off, and the cooling water for the work rolls is set at 540 m / s. 3 / h flow rate control, final rolling temperature controlled at 890℃;

[0048] Rack reduction control: The reduction rate of F1+F2 is 102%, and the reduction rates of F6 and F7 are 17.6% and 9.72%, respectively;

[0049] 4) Perform laminar flow cooling and winding, where laminar flow cooling is front-end cooling and winding temperature is 630℃.

[0050] Example 3

[0051] The high-strength hot-rolled steel coil with no edge cracks produced in this embodiment is made from the following components by weight percentage: C 0.059%, Mn 1.55%, Ti 0.14%, Cr 0.2%, Als 0.045%, N 0.0042%, with the remainder being Fe and unavoidable impurities. It has a thickness of 1.8 mm and a tensile strength of 750 MPa. The quality control method for the edge portion of the continuously cast and rolled high-strength steel coil includes the following steps:

[0052] 1) Steelmaking process control: Al 0.045wt%, N 0.0042wt%;

[0053] The continuous casting adopts tundish protection casting and secondary cooling slow cooling process. The secondary cooling water volume is 1.98L / kg, the slab thickness is 60mm, the surface temperature of the slab entering the furnace is controlled at 937℃, and the surface temperature of the thin slab at the edge and corner is controlled at 875℃.

[0054] 2) The resulting continuously cast thin slab enters the heating furnace at a speed of 4.0 m / min, and is heated to 1228°C in the heating zone at a speed of 20°C / min. Then, it is accelerated at 0.25 m / s starting from the No. 55 acceleration roller. 2 The acceleration begins to increase, reaching a speed of 52 m / min as it passes through the soaking zone and exits the furnace at 1220°C.

[0055] 3) A 7-stand finishing rolling process is adopted. After the slab exits the furnace, it undergoes high-pressure descaling, with a descaling pressure of ≥200 bar at the inlet and ≥240 bar at the outlet. Then, it is finished rolled to a finished thickness of 1.8 mm. The slab enters the finishing mill F1 stand at a speed of 0.5 m / s, and the final strip threading speed is controlled at 9.82 m / s. The cooling water on the side guide plates of each finishing mill stand is turned off, and the cooling water for the work rolls is set at 560 m. 3 The flow rate is controlled at / h, and the final rolling temperature is controlled at 900℃.

[0056] Rack reduction control: The reduction rate of F1+F2 is 104%, and the reduction rates of F6 and F7 are 14.7% and 7.9%, respectively;

[0057] 4) Perform laminar flow cooling and winding, where laminar flow cooling is front-end cooling and winding temperature is 640℃.

[0058] Example 4

[0059] The high-strength hot-rolled steel coil with no edge cracks produced in this embodiment is made from the following components by weight percentage: C 0.048%, Mn 1.15%, Ti 0.13%, Als 0.031%, N 0.0058%, with the remainder being Fe and unavoidable impurities. It has a thickness of 1.5 mm and a tensile strength of 700 MPa. The quality control method for the edge portion of the continuously cast and rolled high-strength steel coil includes the following steps:

[0060] 1) Steelmaking process control: Al 0.031wt%, N 0.0058wt%;

[0061] The continuous casting adopts tundish protection casting and secondary cooling slow cooling process. The secondary cooling water volume is 1.93L / kg. The surface temperature of the slab with a thickness of 60mm entering the furnace is controlled at 965℃, and the surface temperature of the thin slab at the edge and corner is controlled at 905℃.

[0062] 2) The obtained continuously cast thin slab enters the heating furnace at a speed of 4.2 m / min, and is heated to 1237°C in the heating zone at a speed of 25°C / min. Then, it is accelerated at 0.3 m / s starting from the No. 55 acceleration roller. 2 The acceleration begins to increase, reaching a speed of 54 m / min as it passes through the soaking zone and exits the furnace at 1230°C.

[0063] 3) A 7-stand finishing rolling process is adopted. After the slab exits the furnace, it undergoes high-pressure descaling, with a descaling pressure of ≥200 bar at the inlet and ≥240 bar at the outlet. Then, it is finished rolled to a finished thickness of 1.5 mm. The slab enters the finishing mill F1 stand at a speed of 0.38 m / s, and the final rolling threading speed is controlled at 10.2 m / s. The cooling water on the side guide plates of each finishing mill stand is turned off, and the cooling water for the work rolls is set at 530 m. 3 / h flow rate control, final rolling temperature controlled at 890℃;

[0064] Rack reduction control: The reduction rate of F1+F2 is 104%, and the reduction rates of F6 and F7 are 16.6% and 8.6%, respectively;

[0065] 4) Perform laminar flow cooling and winding, where laminar flow cooling is front-end cooling and winding temperature is 620℃.

[0066] Comparative Example 1

[0067] A conventional production method for high-strength steel BST700X, wherein the main chemical composition and content of the high-strength steel include: C 0.057%, Mn 1.3%, Ti 0.128%, Nb 0.02%, Als 0.052%, N 0.0063%, with the remainder being Fe and unavoidable impurities; the thickness is 3.0 mm, and the tensile strength level is 700 MPa; the specific preparation steps include:

[0068] 1) The continuous casting adopts the tundish protection casting and secondary cooling slow cooling process. The secondary cooling water ratio is set by the reference system. The furnace temperature is 865℃, the slab edge temperature is 820℃, and the slab thickness is 70mm.

[0069] 2) The obtained continuously cast thin slab enters the heating furnace at a speed of 4.0 m / min, and is heated to 1230℃ in the heating zone at a speed of 30℃ / min. Then, it starts to accelerate at 0.35 m / s using the No. 42 acceleration roller. 2 The acceleration begins to increase, reaching a speed of 64 m / min as it passes through the soaking zone and exits the furnace at 1220°C.

[0070] 3) A 7-stand finishing rolling process is adopted. After the slab exits the furnace, it undergoes high-pressure descaling with a descaling pressure of ≥200 bar at the inlet and ≥240 bar at the outlet. Then, it is finished rolled to a thickness of 3.0 mm. It enters the finishing rolling F1 stand at a speed of 0.5 m / s. The final rolling threading speed is controlled at 8.96 m / s. The cooling water of the side guide plates of each finishing rolling stand is normally used, the cooling water of the work roll is controlled at 100% flow rate, and the final rolling temperature is controlled at 870℃.

[0071] The rack reduction is controlled according to the model settings: the reduction rate of F1+F2 is 92%, and the reduction rates of each rack of F6 and F7 are 18% and 12%, respectively;

[0072] 4) Perform laminar flow cooling and winding, where laminar flow cooling is front-end cooling and winding temperature is 620℃.

[0073] Comparative Example 2

[0074] A method for producing high-strength steel BST750X, wherein the main chemical composition and content of the high-strength steel include: C 0.062%, Mn 1.3%, Ti 0.145%, Nb 0.02%, Als 0.032%, N 0.0057%, with the remainder being Fe and unavoidable impurities; the thickness is 2.0 mm, and the tensile strength level is 750 MPa; the specific preparation steps include:

[0075] 1) Steelmaking process control: Al 0.032wt%, N 0.0057wt%;

[0076] The continuous casting adopts tundish protection casting and secondary cooling slow cooling process. The secondary cooling water ratio is set by the reference system. The slab thickness is 65mm, the furnace temperature is 895℃, and the slab edge temperature is 843℃.

[0077] 2) The obtained continuously cast thin slab enters the heating furnace at a speed of 4.0 m / min, and is heated to 1210℃ in the heating zone at a speed of 25℃ / min. Then, it starts to accelerate at 0.32 m / s using the No. 42 acceleration roller. 2 The acceleration begins to increase, reaching a speed of 58 m / min as it passes through the soaking zone and exits the furnace at 1210°C.

[0078] 3) A 7-stand finishing rolling process is adopted. After the slab exits the furnace, it undergoes high-pressure descaling with a descaling pressure of ≥200 bar at the inlet and ≥240 bar at the outlet. It is then finished rolling with a finished thickness of 2.0 mm. The slab enters the finishing rolling F1 stand at a speed of 0.5 m / s. The final rolling threading speed is controlled at 9.15 m / s. The cooling water of the side guide plates of each finishing rolling stand is normally used, the cooling water of the work rolls is controlled at 100%, and the final rolling temperature is controlled at 880℃.

[0079] The rack reduction is controlled according to the model settings: the reduction rate of F1+F2 is 94%, and the reduction rates of each rack of F6 and F7 are 20% and 14%, respectively;

[0080] 4) Perform laminar flow cooling and winding, with laminar flow cooling being front-end cooling, and the winding temperature at 640℃.

[0081] Comparative Example 3

[0082] A method for producing high-strength steel BST750X, wherein the main chemical composition and content of the high-strength steel include: C 0.069%, Mn 1.52%, Ti 0.138%, Cr 0.22%, Al 0.048%, N 0.0058%, with the remainder being Fe and unavoidable impurities; the thickness is 1.8 mm, and the tensile strength level is 750 MPa; the specific preparation steps include:

[0083] 1) The continuous casting adopts the tundish protection casting and secondary cooling slow cooling process. The secondary cooling water ratio is set by the reference system. The slab thickness is 60mm, the furnace temperature is 865℃, and the slab edge temperature is 812℃.

[0084] 2) The resulting continuously cast thin slab enters the heating furnace at a speed of 4.0 m / min, and is heated to 1220°C in the heating zone at a speed of 28°C / min. Then, it is accelerated at 0.32 m / s starting from the No. 48 acceleration roller. 2 The acceleration begins to increase, reaching a speed of 60 m / min as it passes through the soaking zone and exits the furnace at 1210°C.

[0085] 3) A 7-stand finishing rolling process is adopted. After the slab exits the furnace, it undergoes high-pressure descaling with a descaling pressure of ≥200 bar at the inlet and ≥240 bar at the outlet. Then, it is finished rolled to a thickness of 1.8 mm. The slab enters the finishing rolling F1 stand at a speed of 0.5 m / s. The final rolling threading speed is controlled at 9.73 m / s. The cooling water of the side guide plates of each finishing rolling stand is normally used, the cooling water of the work roll is controlled at 100% flow rate, and the final rolling temperature is controlled at 880℃.

[0086] The rack reduction is controlled according to the model settings: the reduction rate of F1+F2 is 98%, and the reduction rates of each rack of F6 and F7 are 21% and 13.9%, respectively;

[0087] 4) Subsequent laminar flow cooling and winding were performed according to the standard process settings, with laminar flow cooling being the front-end cooling and the winding temperature at 630℃ (Comparative Example 4).

[0088] A method for producing high-strength steel BST750X, wherein the main chemical composition and content of the high-strength steel include: C 0.07%, Mn 1.15%, Ti 0.13%, Als 0.031%, N 0.0072%, with the remainder being Fe and unavoidable impurities; the thickness is 1.5 mm, and the tensile strength level is 700 MPa; the specific preparation steps include:

[0089] 1) The continuous casting adopts tundish protection casting and secondary cooling slow cooling process. The secondary cooling water ratio is set by the reference system. The slab thickness is 60mm, the furnace temperature is 864℃, and the slab edge temperature is 820℃.

[0090] 2) The obtained continuously cast thin slab enters the heating furnace at a speed of 4.0 m / min, and is heated to 1230℃ in the heating zone at a speed of 30℃ / min. Then, it starts to accelerate at 0.34 m / s using the No. 48 acceleration roller. 2 The acceleration begins to increase, reaching a speed of 57 m / min as it passes through the soaking zone and exits the furnace at 1220°C.

[0091] 3) A 7-stand finishing rolling process is adopted. After the slab exits the furnace, it undergoes high-pressure descaling with a descaling pressure of ≥200 bar at the inlet and ≥240 bar at the outlet. It is then finished rolling with a finished thickness of 1.5 mm. The slab enters the finishing rolling F1 stand at a speed of 0.5 m / s. The final rolling threading speed is controlled at 9.96 m / s. The cooling water of the side guide plates of each finishing rolling stand is normally used, the cooling water of the work rolls is controlled at 100% flow rate, and the final rolling temperature is controlled at 880℃.

[0092] The rack reduction is controlled according to the model settings: the reduction rate of F1+F2 is 99%, and the reduction rates of each rack of F6 and F7 are 21% and 14.7%, respectively;

[0093] 4) The subsequent laminar flow cooling and winding are carried out according to the conventional process settings, with laminar flow cooling being the front-end cooling and the winding temperature being 620℃.

[0094] Table 1. Performance test results of continuously cast and rolled high-strength steel obtained from the embodiments of the present invention and comparative examples.

[0095]

[0096] Figure 1 and Figure 2 The images show the edge morphology of the high-strength steel BST750X obtained in Comparative Example 2 and the high-strength steel BST750X obtained in Example 2 of this invention, respectively. The results show that by controlling the Al and N contents, coordinating with the weak cooling of the secondary cooling in continuous casting, setting the position of the accelerating roller in the heating zone, closing the cooling water of the finishing rolling side guide plate, and matching the rolling reduction rate, it is beneficial to control edge cracks in high-strength steel and reduce problems such as edge burrs or edge roughness.

[0097] This invention is not limited to the embodiments described above. Those skilled in the art can make various improvements and modifications without departing from the principles of this invention, and these improvements and modifications are also considered within the scope of protection of this invention. Contents not described in detail in this specification are prior art known to those skilled in the art.

Claims

1. A method for quality control of the rolled edge of CSP thin slab continuously cast and rolled high-strength steel, comprising the steps of steelmaking, continuous casting, slab heating, continuous rolling, laminar flow cooling, and coiling, characterized in that, Specifically, the control steps include the following: 1) Steelmaking and thin slab continuous casting control: The steelmaking process should be controlled with 0.015 ≤ Als ≤ 0.045% and N ≤ 0.006%. The thin slab continuous casting process adopts tundish protection casting and secondary cooling water weak cooling control process, with a secondary cooling water volume of 1.93-2.15 L / kg; 2) Finishing process control: The 7-stand finishing process is adopted, with a slow entry speed into the finishing F1 stand and a fast finishing strip threading speed. The cooling water of the finishing side guide plate is turned off, and the cooling water flow rate, finishing temperature and edge temperature of the work roll are controlled. Adjust the reduction ratio of F1 rack + F2 rack, F6 rack, and F7 rack; The main chemical components and their mass percentages in the thin slab continuously cast and rolled high-strength steel are as follows: C 0.04-0.07%, Mn 1.0-1.55%, Ti 0.11-0.145%, Nb 0-0.02%, Cr 0-0.2%, Als 0.015-0.045%, N≤0.006%; In the slab heating step, the slab enters the heating furnace at a speed of 4.0-4.2 m / min, is heated to 1210-1240℃ at a speed of 15-25℃ / min in the heating zone, and after that, the speed of the 50# and later accelerating rollers is accelerated to 0.18-0.3 m / s 2 The acceleration starts to accelerate, passes through the soaking zone at a speed of 48-54 m / min, and finally leaves the furnace at a temperature of 1200-1230℃. After the slab exits the furnace, it undergoes high-pressure descaling followed by precision rolling. In the finishing rolling process, the reduction rate of F1 stand + F2 stand is ≥100%, the reduction rate of F6 stand is ≤18%, and the reduction rate of F7 stand is ≤10%.

2. The method for quality control of the rolled edge according to claim 1, characterized in that, The surface temperature of the slab entering the furnace is controlled at above 920℃, and the surface temperature of the slab at the edges and corners is above 850℃.

3. The method for quality control of the rolled edge according to claim 1, characterized in that, The speed at which the strip enters the finishing F1 stand is 0.4-0.7 m / s, and the final strip-passing speed is above 9.2 m / s.

4. The method for quality control of the rolled edge according to claim 1, characterized in that, The flow rate of the cooling water for the work roll is 500-580 m³ / h. 3 / h; final rolling temperature is 880-910℃.

5. The method for quality control of the rolled edge according to claim 1, characterized in that, The laminar flow cooling step uses front-end cooling.

6. The method for quality control of the rolled edge according to claim 1, characterized in that, The winding temperature is 610-640℃.

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