Process method for reducing cluster-shaped warping defect of cold-rolled high-strength steel

Abstract

The invention relates to a process method for reducing cluster-shaped warping defects of cold-rolled high-strength steel, and belongs to the technical field of metallurgy. The method comprises the following steps: carrying out nitrogen content control and micro titanium treatment on molten steel to obtain nitrogen-controlled molten steel; the nitrogen-controlled molten steel is subjected to continuous casting, slow cooling type casting powder is used for the nitrogen-controlled molten steel in the continuous casting process, so that the uniformity of a primary solidified blank shell is improved, the vibration mark depth is reduced, and a casting blank is obtained; the casting blank is heated, the heating temperature parameter is controlled to achieve structure homogenization, and a heated casting blank is obtained; and the heated casting blank is subjected to hot rolling, the finish rolling temperature and the coiling temperature of hot rolling are controlled so that the structure uniformity of the heated casting blank can be improved, and the hot-rolled steel is obtained. By means of the measures of optimizing steelmaking components, controlling nitrogen in the whole process, using slow cooling type casting powder, designing the reasonable continuous casting speed, optimizing heating and hot rolling process parameters and the like, the cluster-shaped warping defect of the cold-rolled high-strength steel is fundamentally reduced.

Description

Technical Field

[0001] This application relates to the field of metallurgical technology, and in particular to a process method for reducing the clustered peeling defect in cold-rolled high-strength steel. Background Technology

[0002] Cold-rolled high-strength steel is widely used in the automotive steel industry due to its excellent mechanical and processing properties. However, during the production process of cold-rolled high-strength steel, especially in the hot-charging reheating stage of the austenitic-ferrite transformation, a serious surface defect—clustered peeling—is prone to occur. This defect not only significantly affects the product quality and performance of cold-rolled high-strength steel, but also leads to a decrease in yield and an increase in production costs, threatening the economic benefits and market competitiveness of enterprises.

[0003] The current production processes and control methods for addressing the clustered peeling defect in cold-rolled high-strength steel have the following problems: Current steelmaking composition design is unfavorable for nitrogen fixation, leading to the preferential precipitation of AlN, NbCN, and other precipitates in grain boundary ferrite at the straightening zone temperature, increasing the risk of clustered peeling defects; in duplex processes, the nitrogen content in molten steel often exceeds 0.005%, and this high nitrogen content further promotes the precipitation of AlN, NbCN, and other precipitates in grain boundary ferrite, exacerbating the formation of clustered peeling defects; unreasonable design of the basicity and viscosity of the continuous casting flux, as well as improper setting of the casting speed for different cross-sections, result in uneven solidification of the initial slab shell, deep oscillation marks on the slab, and a tendency to induce subsurface transverse cracks, thus increasing the probability of clustered peeling defects; improper setting of furnace process parameters and hot rolling process parameters affects the uniformity of the slab's internal structure, leading to coarse grains, reduced mechanical and processing properties of the product, and indirectly promoting the formation of clustered peeling defects. Summary of the Invention

[0004] This application provides a process method for reducing the clustered peeling defect in cold-rolled high-strength steel, in order to solve the following technical problem: how to effectively reduce the incidence of clustered peeling defects in cold-rolled high-strength steel. This application provides a process method for reducing clustered peeling defects in cold-rolled high-strength steel, the method comprising: Nitrogen-controlled molten steel is obtained by controlling the nitrogen content and applying micro-titanium treatment to molten steel. The nitrogen-controlled molten steel is continuously cast, and a slow-cooling protective slag is used on the nitrogen-controlled molten steel during the continuous casting process to improve the uniformity of the initial solidified shell and reduce the depth of the oscillation marks, thereby obtaining a cast billet. The billet is heated, and the heating temperature parameters are controlled to achieve microstructure homogenization, resulting in a heated billet. The heated billet is hot-rolled, and the final rolling temperature and coiling temperature are controlled to improve the microstructure uniformity of the heated billet, thereby obtaining hot-rolled steel.

[0005] Optionally, in the nitrogen-controlled molten steel, the mass fraction of Ti is 0.017% to 0.025%, and the Ti / N ratio is 4 to 5, where Ti / N represents the mass fraction ratio of Ti to N.

[0006] Optionally, in the billet, N < 0.004% by mass fraction.

[0007] Optionally, the basicity R of the slow-cooling protective slag is 1.3 to 1.4, and the viscosity of the slow-cooling protective slag is 0.08 Pa•s to 0.11 Pa•s.

[0008] Optionally, the continuous casting of the nitrogen-controlled molten steel further includes: The casting speed is set according to the cross-sectional width of the billet to avoid cracking of the billet during straightening in the low plasticity zone.

[0009] Optionally, setting the casting speed based on the cross-sectional width of the billet includes: When the cross-sectional width of the cast billet is 900mm to 1550mm, the drawing speed is 1.2m / min to 1.3m / min; When the cross-sectional width of the cast billet is 1600mm to 1650mm, the drawing speed is 1.1m / min to 1.2m / min; When the cross-sectional width of the cast billet is 1700mm to 1850mm, the drawing speed is 1.0m / min to 1.1m / min; When the cross-sectional width of the billet is 1900mm to 2100mm, the drawing speed is 0.9m / min to 1.0m / min.

[0010] Optionally, the furnace entry temperature is 300℃~450℃, and the furnace exit temperature is 1250℃~1300℃.

[0011] Optionally, the heating time is 200 min to 240 min.

[0012] Optionally, the final rolling temperature of the hot rolling is 830℃~910℃.

[0013] Optionally, the hot rolling temperature is 500℃~600℃.

[0014] The technical solutions provided in this application have the following advantages compared with the prior art: This application provides a process for reducing the clustered peeling defect in cold-rolled high-strength steel. The method includes: controlling the nitrogen content and micro-titanium treatment of molten steel to obtain nitrogen-controlled molten steel; continuously casting the nitrogen-controlled molten steel and using a slow-cooling protective slag during the continuous casting process to improve the uniformity of the initial solidified shell and reduce the depth of oscillation marks to obtain a cast billet; heating the cast billet and controlling the heating temperature parameters to achieve microstructure homogenization to obtain a heated cast billet; hot-rolling the heated cast billet and controlling the final rolling temperature and coiling temperature to improve the microstructure uniformity of the heated cast billet to obtain hot-rolled steel.

[0015] By controlling the mass fraction of titanium in the nitrogen-controlled molten steel and controlling nitrogen throughout the entire process, titanium combines with nitrogen to form stable titanium nitride (TiN) or titanium carbonitride (TiCN) compounds. This reduces the amount of harmful nitrides such as AlN and NbCN precipitated at grain boundary ferrite, lowers grain boundary brittleness, and reduces the source of cracks in the billet. The continuous casting process uses a slow-cooling protective slag to reduce the heat transfer rate, ensuring uniform growth of the initial solidified billet shell and reducing stress concentration caused by uneven solidification. This measure, combined with setting the casting speed according to the billet's cross-sectional width, avoids the billet in the straightening zone being in a low plasticity temperature range, reducing the risk of subsurface transverse cracks caused by internal arc tensile stress. By optimizing process parameters such as furnace inlet temperature, furnace outlet temperature, and heating time, the uniformity of the billet's internal structure is improved, making the billet structure more suitable for subsequent hot rolling processes. By optimizing hot rolling process parameters, fine and uniformly dispersed second phases are obtained in hot-rolled steel, refining the grain size and improving its strength and elongation. These measures reduce defects such as grain boundary precipitate segregation and billet cracks at the source. Simultaneously, by refining the grain size and achieving a uniform microstructure, the strength and toughness of the steel are improved, ultimately suppressing the formation of clustered peeling defects. Attached Figure Description The accompanying drawings, which are incorporated in and form part of this specification, illustrate embodiments consistent with this application and, together with the description, serve to explain the principles of this application.

[0016] To more clearly illustrate the technical solutions in the embodiments of this application or the prior art, the drawings used in the description of the embodiments or the prior art will be briefly introduced below. Obviously, for those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0017] Figure 1 This is a schematic flowchart illustrating a process for reducing clustered peeling defects in cold-rolled high-strength steel, as provided in an embodiment of this application. Detailed Implementation

[0018] To make the objectives, technical solutions, and advantages of the embodiments of this application clearer, the technical solutions of the embodiments of this application will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of this application, not all embodiments. Based on the embodiments of this application, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of this application.

[0019] The range descriptions used herein, such as numerical ranges and proportional ranges, include all possible sub-ranges and single numerical values ​​within that range. For example, the range descriptions of "1 to 6" or "1~6" cover all sub-ranges (such as 1 to 3, 2 to 5, etc.) and single numbers (such as 1, 2, 3, 4, 5, 6) between 1 and 6. Unless otherwise specified, the terms "including" and "contains" as used herein mean "including but not limited to"; relational terms such as "first" and "second" are used only to distinguish different entities or operations and do not imply an actual order or relationship; "and / or" indicates that multiple situations can exist individually or simultaneously; expressions such as "at least one," "multiple," and "at least one" refer to any combination of the corresponding objects, including combinations of single or multiple objects. The proportional relationships mentioned herein, such as mass ratios and molar ratios, should be understood as the correspondence between the first and second terms of a proportional formula, according to the order of description. The raw materials, reagents, instruments, and equipment used herein can all be obtained through commercial purchase or prepared using existing methods.

[0020] Figure 1 This is a schematic flowchart illustrating a process for reducing clustered peeling defects in cold-rolled high-strength steel, as provided in an embodiment of this application.

[0021] like Figure 1 As shown in the embodiment of this application, a process method for reducing clustered peeling defects in cold-rolled high-strength steel is provided, the method comprising: S1. Nitrogen content control and micro-titanium treatment are applied to molten steel to obtain nitrogen-controlled molten steel. In some embodiments, the mass fraction of Ti in the nitrogen-controlled molten steel is 0.017% to 0.025%, and the Ti / N ratio is 4 to 5, where Ti / N represents the mass fraction ratio of Ti to N.

[0022] By adding high-titanium ferrophosphate during the RH refining process for micro-titanium treatment, the mass percentage of titanium in the nitrogen-controlled steel melt is controlled at 0.017%–0.025%, and the mass ratio of Ti to N in the nitrogen-controlled steel melt is ensured to be 4–5. Nitrogen content control and micro-titanium treatment allow titanium and nitrogen in the steel melt to combine and form stable titanium nitride (TiN) or titanium carbonitride (TiCN) compounds, thereby reducing the amount of harmful nitrides such as AlN and NbCN precipitated at grain boundary ferrite. By controlling the ratio of titanium to nitrogen in the nitrogen-controlled steel melt, the precipitation of nitrides at grain boundaries is reduced, improving the high-temperature plasticity of the steel and reducing the risk of cracking in the cast billet. For example, the mass fraction of Ti in the nitrogen-controlled steel melt can be 0.017%, 0.019%, 0.021%, 0.023%, 0.025%, etc.

[0023] S2. The nitrogen-controlled steel liquid is continuously cast, and a slow-cooling protective slag is used on the nitrogen-controlled steel liquid during the continuous casting process to improve the uniformity of the initial solidified billet shell and reduce the depth of the oscillation marks, so as to obtain the billet. In some embodiments, N in the billet is less than 0.004% by mass fraction.

[0024] In the production of cold-rolled high-strength steel, nitrogen control is a key step in reducing clustered peeling defects. In this embodiment, the nitrogen control processes in the steelmaking, refining, and continuous casting stages are closely coordinated to form a comprehensive nitrogen control system. This ensures that the mass fraction of nitrogen in the billet is stably controlled below 0.004%, reducing the precipitation of nitrides at grain boundaries and improving the purity and high-temperature plasticity of the steel. For example, the mass fraction of N in the billet can be 0.001%, 0.0015%, 0.002%, 0.0025%, 0.003%, 0.0035%, 0.004%, etc.

[0025] The nitrogen control process in steelmaking specifically includes: The bottom blowing process adopts a full-process argon blowing mode. Through the stirring effect of argon gas, nitrogen in the molten steel is promoted to escape, thereby reducing the nitrogen content of the molten steel.

[0026] Controlling the converter blowing process and avoiding excessive carbon reduction or post-blowing operations at the end of the blowing process reduces the contact time between molten steel and air, thereby reducing the absorption of nitrogen by the molten steel.

[0027] Alloys are selected in the order of "silicon addition to molten steel" and "manganese addition to molten steel," with silicon and manganese added first, and aluminum and iron added last. Alloy materials are added when the steel output exceeds 60 tons to reduce the absorption of nitrogen by the molten steel during alloying.

[0028] During the tapping process, argon is used as the bottom blowing gas in the ladle, with the argon flow rate controlled between 250 NL / min and 300 NL / min. After tapping, a strong stirring operation is performed for 3 minutes. During the strong stirring, the bottom blowing gas in the ladle must meet the following requirements: the argon flow rate is controlled between 300 NL / min and 350 NL / min to reduce the exposed surface of the molten steel and prevent the molten steel from absorbing nitrogen.

[0029] Perform ladle baking and bottom blowing ventilation operations to ensure good bottom blowing effect and promote the escape of gas from molten steel.

[0030] Regularly inspect the nitrogen quick-cut valve in the converter re-blowing chamber and the nitrogen quick-cut valve in the oxygen lance. If any valve is found to be not closing tightly, deal with it promptly to prevent nitrogen leakage from causing nitrogen buildup in the molten steel.

[0031] The refining process further reduces the nitrogen content in molten steel through LF and RH operations. The nitrogen control process specifically includes: During LF operation, a slightly positive pressure is maintained throughout the process to prevent air from entering the furnace and causing nitrogen absorption in the molten steel. Bottom blowing is prohibited during the start-up process from the station to the treatment position. After arriving at the treatment position, bottom blowing is started for 3-5 minutes for pre-blowing argon, and then a station sample is taken. After the pre-blowing argon is completed, slag is added first, followed by the electrode. Before adding the electrode, at least 800 kg of slag must have been added to the ladle. The slag-forming and heating processes are carried out using submerged arc operation, and the number of electrode heatings is controlled to not exceed 3. During electrode heating, the bottom blowing flow rate is controlled at 150-200 NL / min for a single channel (the flow rate can be adjusted according to the actual amount of agitation during the actual stirring time to avoid hearing a "thunder" sound for a long time). Under the premise that bottom blowing meets the desulfurization requirements, bypass is prohibited, and the strong stirring time should be shortened as much as possible to reduce the contact between molten steel and air.

[0032] During RH operation, pre-process the vacuum chamber to cool the steel and rinse the vacuum chamber to avoid nitrogen increase in the molten steel caused by the cold steel; prioritize the processing of the stations with shorter impregnation tube lifespan, and confirm the spraying status of the impregnation tube before smelting to ensure there are no obvious cracks and prevent air leakage and nitrogen increase in the impregnation tube; pre-vacuuming is carried out before RH treatment to ensure that the pre-vacuum degree is ≤300mba in order to further reduce the nitrogen content in the molten steel.

[0033] In the continuous casting process, the initial casting cycle uses a low-position ladle casting. When the tundish weight reaches 20 tons, covering agent is added to the baking holes on both sides of the tundish, using a special grate as a buffer. At least 25 bags of covering agent are added to each baking hole. In the long nozzle casting area of ​​the ladle, covering agent is added immediately after the molten steel has submerged through the long nozzle, ensuring complete coverage of the molten steel to prevent slag agitation and reduce nitrogen absorption. A full protection device for the tundish is used throughout the process to minimize contact between air and molten steel, reducing nitrogen absorption. Argon blowing is performed on the tundish cover during casting, and the plug rod holes and overflow channels are promptly sealed to ensure stable argon flow and back pressure in the three channels, further isolating the molten steel from air. During continuous casting, the long nozzle of the ladle is used for submerged casting to prevent the molten steel from being exposed to air.

[0034] By implementing the above-mentioned nitrogen control measures throughout the entire steelmaking, refining, and continuous casting process, the mass fraction of nitrogen in the molten steel can be effectively controlled below 0.004%. This nitrogen content level helps reduce the precipitation of nitrides such as AlN and NbCN at grain boundaries, improves the high-temperature plasticity of steel, reduces the risk of cracking in the billet, and thus significantly reduces the clustered peeling defects in cold-rolled high-strength steel.

[0035] The continuous casting process also reduces nitrogen absorption and crack formation in the billet during solidification by selecting protective slag and designing the continuous casting speed.

[0036] In some embodiments, the basicity R of the slow-cooling protective slag is 1.3 to 1.4, and the viscosity of the slow-cooling protective slag is 0.08 Pa•s to 0.11 Pa•s.

[0037] Basicity R is an important chemical indicator of mold flux, usually defined as the mass ratio or molar ratio of basic oxides (such as CaO) to acidic oxides (such as SiO2) in the mold flux. It reflects the acid-base properties of the mold flux and has a significant impact on its melting characteristics, glass-forming ability, and interaction with nitrogen-controlled steel liquid. In the embodiments of this application, the basicity R of the slow-cooling mold flux is controlled within the range of 1.3 to 1.4. This range is selected based on the optimization considerations of the mold flux performance, aiming to improve the melting rate and glass content of the mold flux by adjusting the basicity, thereby slowing down heat transfer and improving the uniformity of the initial solidified billet shell. By controlling the basicity within the range of 1.3 to 1.4, the melting rate of the mold flux can be slowed down, allowing the nitrogen-controlled steel liquid to form a more uniform billet shell during solidification. This helps to reduce the depth of oscillation marks on the billet, reduce the risk of cracking in the billet, and thus reduce the clustered peeling defects of cold-rolled high-strength steel. For example, the basicity R of the slow-cooling protective slag can be 1.3, 1.32, 1.34, 1.36, 1.38, 1.4, etc.

[0038] Viscosity is another important physical indicator of mold flux, representing the magnitude of internal friction experienced by the flux during its flow. It directly affects the spreadability, lubricity, and heat retention properties of the mold flux during continuous casting. In this embodiment, the viscosity of the slow-cooling mold flux is controlled within the range of 0.08 Pa•s to 0.11 Pa•s. This range ensures that the mold flux uniformly covers the surface of the nitrogen-controlled molten steel, forming an effective lubricating layer and reducing friction between the billet and the mold. Simultaneously, it slows down the heat transfer rate of the nitrogen-controlled molten steel, contributing to the formation of a more uniform initial solidified shell, thereby reducing the generation of cracks and defects. For example, the viscosity of the slow-cooling mold flux can be 0.08 Pa•s, 0.09 Pa•s, 0.10 Pa•s, 0.11 Pa•s, etc.

[0039] In some embodiments, the continuous casting of the nitrogen-controlled molten steel further includes: The casting speed is set according to the cross-sectional width of the billet to avoid cracking of the billet during straightening in the low plasticity zone.

[0040] In some embodiments, setting the casting speed based on the cross-sectional width of the billet includes: When the cross-sectional width of the cast billet is 900mm to 1550mm, the drawing speed is 1.2m / min to 1.3m / min; When the cross-sectional width of the cast billet is 1600mm to 1650mm, the drawing speed is 1.1m / min to 1.2m / min; When the cross-sectional width of the cast billet is 1700mm to 1850mm, the drawing speed is 1.0m / min to 1.1m / min; When the cross-sectional width of the billet is 1900mm to 2100mm, the drawing speed is 0.9m / min to 1.0m / min.

[0041] The core purpose of setting a scientifically reasonable continuous casting speed for cold-rolled high-strength steel based on the actual width of the billet cross-section is to avoid stress concentration during straightening of the billet in the low-plasticity zone and reduce the risk of cracking by matching the casting speed parameters for different cross-section widths. Specifically, in the straightening zone, the inner arc of the billet is subjected to tensile stress. If the continuous casting speed does not match the cross-sectional width of the billet, it is easy to cause unevenness in the initial solidified shell, thereby causing cracks in the billet during straightening in the low-plasticity zone. The embodiments of this application set differentiated casting speeds based on the actual width of the billet cross-section, which can match the shell growth rate with the crystallizer vibration cycle, reduce the accumulation of molten steel at the bottom of the oscillation mark valley, reduce the risk of subcutaneous transverse cracks in the billet, and at the same time avoid the initial solidified shell being too thin due to excessively fast continuous casting speed, or the production efficiency decreasing due to excessively slow continuous casting speed.

[0042] S3. The billet is heated, and the heating temperature parameters are controlled to achieve uniform microstructure, thereby obtaining a heated billet; In some embodiments, the furnace entry temperature for heating is 300°C to 450°C, and the furnace exit temperature for heating is 1250°C to 1300°C.

[0043] In this embodiment, a furnace inlet temperature of 300℃ to 450℃ allows the billet to heat up slowly and uniformly, reducing damage caused by drastic temperature changes and laying the foundation for subsequent thorough heating and homogenization of the billet's microstructure. If the furnace inlet temperature is below 300℃, the large temperature difference between the inside and outside of the billet can easily generate excessive thermal stress, leading to microcracks inside the billet. If the furnace inlet temperature is above 450℃, the initial heating rate may be too fast, causing an excessive temperature gradient between the surface and core of the billet. For example, the furnace inlet temperature can be 300℃, 330℃, 360℃, 390℃, 420℃, 450℃, etc.

[0044] The furnace exit temperature directly affects the size and uniformity of austenite grains inside the billet. Controlling the furnace exit temperature within the range of 1250℃ to 1300℃ ensures sufficient austenitization within the billet while inhibiting abnormal austenite grain growth, resulting in a fine and uniform austenite grain structure. This provides favorable microstructural conditions for subsequent hot rolling to refine the grains and improve the properties of the hot-rolled steel. If the furnace exit temperature exceeds 1300℃, it can lead to excessive coarsening of the austenite grains inside the billet, reducing grain boundary strength during subsequent rolling and increasing the risk of clustered peeling defects in cold-rolled high-strength steel. If the furnace exit temperature is below 1250℃, the alloying elements in the steel may not dissolve sufficiently, affecting the precipitation strengthening effect of the hot-rolled steel during rolling and thus impacting its mechanical properties. For example, the furnace exit temperature can be 1250℃, 1260℃, 1270℃, 1280℃, 1290℃, 1300℃, etc.

[0045] In some embodiments, the heating time is 200 min to 240 min.

[0046] The heating time must meet the requirements of sufficient heat conduction from the surface to the core of the billet and homogenization of the microstructure. If the heating time is less than 200 min, the core temperature of the billet will be insufficient, easily leading to an incomplete transformation of the core microstructure, resulting in an uneven internal microstructure. If the heating time is longer than 240 min, it will not only increase energy consumption, but may also cause austenite grain coarsening due to the billet being exposed to high temperatures for an extended period. Controlling the heating time within the range of 200 min to 240 min ensures uniform heating across the entire thickness of the billet, allowing for the complete dissolution of precipitates such as carbides and nitrides formed by micro-titanium treatment. Simultaneously, proper heat preservation promotes austenite grain homogenization, significantly improving the uniformity of the internal microstructure of the billet and making the billet microstructure more suitable for the performance requirements of subsequent hot rolling processes. For example, the heating time can be 200 min, 205 min, 210 min, 215 min, 220 min, 225 min, 230 min, 235 min, 240 min, etc.

[0047] S4. The heated billet is hot-rolled, and the final rolling temperature and coiling temperature are controlled to improve the uniformity of the microstructure of the heated billet, thereby obtaining hot-rolled steel.

[0048] In some embodiments, the final rolling temperature of the hot rolling is 830°C to 910°C.

[0049] Controlling the coiling temperature between 500℃ and 600℃ promotes the full precipitation of carbonitrides (such as NbCN and TiN) of microalloying elements like Nb and Ti during the coiling and holding process, forming fine, uniformly dispersed second-phase particles. These particles significantly improve the strength of the steel by pinning grain boundaries and dislocations (precipitation strengthening). If the coiling temperature exceeds 600℃, the precipitated phases will coarsen and become unevenly distributed, weakening the strengthening effect; if the temperature is below 500℃, the precipitation kinetics are insufficient, the number of precipitated phases decreases, and the strengthening effect cannot be fully realized. For example, the final rolling temperature of hot rolling can be 830℃, 850℃, 870℃, 890℃, 910℃, etc.

[0050] In some embodiments, the hot rolling coiling temperature is 500°C to 600°C.

[0051] Controlling the coiling temperature between 500℃ and 600℃ promotes the full precipitation of carbonitrides (such as NbCN and TiN) of microalloying elements like Nb and Ti during the coiling and holding process, forming fine, uniformly dispersed second-phase particles. These particles significantly improve the strength of the steel by pinning grain boundaries and dislocations (precipitation strengthening). If the coiling temperature exceeds 600℃, the precipitated phases will coarsen and become unevenly distributed, weakening the strengthening effect; if the temperature is below 500℃, the precipitation kinetics are insufficient, the number of precipitated phases decreases, and the strengthening effect cannot be fully realized. For example, the coiling temperature for hot rolling can be 500℃, 520℃, 540℃, 560℃, 580℃, 600℃, etc.

[0052] The present application is further illustrated below with reference to specific embodiments. Experimental methods in the following embodiments that do not specify specific conditions are generally determined according to national / industry standards; if there is no corresponding national / industry standard, they are performed according to general international standards, conventional conditions, or conditions recommended by the manufacturer.

[0053] Example 1 In heat 252100179 of the cold-rolled high-strength steel CA613001, the mass percentage of titanium in the nitrogen-controlled molten steel was controlled at 0.0187%. Through a nitrogen-controlled process throughout the steelmaking, refining, and continuous casting processes, the mass fraction of nitrogen in the nitrogen-controlled molten steel was 0.0038%, and the mass fraction ratio of Ti to N was 4.92. A slow-cooling protective slag was used in the continuous casting process, with its basicity R controlled at 1.34 and viscosity at 0.09 Pa•s. The cross-sectional dimensions of the cast billet were 230*1600 mm, and the continuous casting speed was 1.2 m / min. The furnace inlet temperature was 286℃, the outlet temperature was set at 1262℃, and the heating time was 212 min. The hot rolling finishing temperature was 886℃, and the coiling temperature was 545℃. The hot-rolling closure rate of the clustered peeling on the cast billet in this heat was 0.95%, and the spot rate of the clustered peeling on the cast billet in this heat was 0.32%.

[0054] Example 2 In heat 252204060 of the cold-rolled high-strength steel CA613001, the mass percentage of titanium in the nitrogen-controlled molten steel was controlled at 0.0181%. Through a nitrogen-controlled process throughout the steelmaking, refining, and continuous casting processes, the mass fraction of nitrogen in the nitrogen-controlled molten steel was 0.0037%, and the mass fraction ratio of Ti to N was 4.89. A slow-cooling protective slag was used in the continuous casting process, with its basicity R controlled at 1.36 and viscosity at 0.095 Pa•s. The cross-sectional dimensions of the cast billet were 230*1500 mm, and the continuous casting speed was 1.3 m / min. The furnace inlet temperature was 375℃, the outlet temperature was set at 1272℃, and the heating time was 221 min. The hot rolling finishing temperature was 854℃, and the coiling temperature was 556℃. The hot-rolled slab cluster-like peeling rate was 0.88%, and the spot rate of the slab cluster-like peeling was 0.35%.

[0055] Example 3 In heat 252204093 of the cold-rolled high-strength steel CA613001, the mass percentage of titanium in the nitrogen-controlled molten steel was controlled at 0.0174%. Through a nitrogen-controlled process throughout the steelmaking, refining, and continuous casting processes, the mass fraction of nitrogen in the nitrogen-controlled molten steel was 0.0037%, and the mass fraction ratio of Ti to N was 4.7. A slow-cooling protective slag was used in the continuous casting process, with its basicity R controlled at 1.38 and viscosity at 0.10 Pa•s. The cross-sectional dimensions of the cast billet were 230*1400 mm, and the continuous casting speed was 1.3 m / min. The furnace inlet temperature was 364℃, the outlet temperature was set at 1285℃, and the heating time was 218 min. The hot rolling finishing temperature was 866℃, and the coiling temperature was 553℃. The hot-rolled slab cluster-like peeling rate was 0.92%, and the spot rate of slab cluster-like peeling was 0.44%.

[0056] Comparative Example 1 In heat 252204632 of the cold-rolled high-strength steel CA613001, the mass percentage of titanium in the nitrogen-controlled molten steel was controlled at 0.0154%. Through a nitrogen-controlled process throughout the steelmaking, refining, and continuous casting processes, the mass fraction of nitrogen in the nitrogen-controlled molten steel was 0.0048%, and the mass fraction ratio of Ti to N was 3.2. The basicity R of the protective slag used in the continuous casting process was controlled at 1.24, and the viscosity at 0.12 Pa•s. The cross-sectional dimensions of the cast billet were 230*1400 mm, and the continuous casting speed was 1.4 m / min. The furnace inlet temperature was 264℃, the outlet temperature was set at 1223℃, and the heating time was 183 min. The hot rolling finishing temperature was 812℃, and the coiling temperature was 488℃. The hot rolling sealing rate of the clustered peeling on the cast billets in this heat was 2.73%, and the spot rate of the clustered peeling on the cast billets in this heat was 1.44%.

[0057] Furthermore, one or more technical solutions in the embodiments of the present invention have at least the following technical effects or advantages: By implementing the process method of the present invention, the clustered peeling defect of cold-rolled high-strength steel has been significantly reduced.

[0058] The reduction of clustered peeling defects directly improves the yield rate, reduces the scrap rate and rework rate caused by defects, and thus reduces production costs.

[0059] The above description is merely a specific embodiment of this application, enabling those skilled in the art to understand or implement this application. Various modifications to these embodiments will be readily apparent to those skilled in the art, and the general principles defined herein may be implemented in other embodiments without departing from the spirit or scope of this application. Therefore, this application is not to be limited to the embodiments shown herein, but is to be accorded the widest scope consistent with the principles and novel features claimed in this application.

Claims

1. A process for reducing cluster springback defects in cold rolled high strength steel characterized by, The method comprises: controlling nitrogen content and micro-titanium treatment on the molten steel to obtain a controlled nitrogen molten steel; continuously casting the controlled nitrogen molten steel and using a slow cooling type of protecting slag on the controlled nitrogen molten steel during the continuous casting to improve the uniformity of the primary solidification shell and reduce the depth of the oscillation marks, to obtain a casting blank; heating the casting blank and controlling the temperature parameters of the heating to realize the uniformity of the structure, to obtain a heated casting blank; hot rolling the heated casting blank and controlling the finishing temperature and the coiling temperature of the hot rolling to improve the uniformity of the structure of the heated casting blank, to obtain a hot rolled steel material.

2. The method of claim 1, wherein, In the controlled nitrogen molten steel, the mass fraction of Ti is 0.017% to 0.025%, and Ti / N=4 to 5, where Ti / N represents the mass fraction ratio of Ti and N.

3. The method of claim 2, wherein, In the casting blank, the mass fraction of N is less than 0.004%.

4. The method of claim 1, wherein, The basicity R of the slow cooling type of protecting slag is 1.3 to 1.4, and the viscosity of the slow cooling type of protecting slag is 0.08 Pa·s to 0.11 Pa·s.

5. The method of claim 1, wherein, The continuous casting of the controlled nitrogen molten steel further comprises: setting the pulling speed of the continuous casting according to the cross-sectional width of the casting blank to avoid cracks caused by straightening in the low plasticity zone.

6. The method of claim 5, wherein, The setting of the pulling speed of the continuous casting according to the cross-sectional width of the casting blank comprises: when the cross-sectional width of the casting blank is 900 mm to 1550 mm, the pulling speed is 1.2 m / min to 1.3 m / min; when the cross-sectional width of the casting blank is 1600 mm to 1650 mm, the pulling speed is 1.1 m / min to 1.2 m / min; when the cross-sectional width of the casting blank is 1700 mm to 1850 mm, the pulling speed is 1.0 m / min to 1.1 m / min; when the cross-sectional width of the casting blank is 1900 mm to 2100 mm, the pulling speed is 0.9 m / min to 1.0 m / min.

7. The method of claim 1, wherein, The in-furnace temperature of the heating is 300℃ to 450℃, and the out-furnace temperature of the heating is 1250℃ to 1300℃.

8. The method of claim 7, wherein, The heating time is 200 min to 240 min.

9. The method of claim 1, wherein, The finishing temperature of the hot rolling is 830℃ to 910℃.

10. The method of claim 1, wherein, The coiling temperature of the hot rolling is 500℃ to 600℃.

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