A low-cost steel sheet for a roof panel of a vehicle suitable for a 2c1b coating process and a method for producing the same

Abstract

The application provides a low-cost steel plate suitable for a 2C1B coating process automobile roof outer plate and a production method thereof, and the composition is as follows: C: 0.025-0.030wt%, Si: <=0.030wt%, Mn: 0.08-0.25wt%, Als: 0.025-0.050wt%, P<=0.015wt%, S<=0.015wt%, N<=0.004wt%, and the balance is Fe and inevitable impurity elements. Compared with the prior art, the application realizes that the product deformation after a series of controls such as composition, process and especially the process control in the flattening process is less than or equal to 0.25 mu m. The produced product is suitable for the horizontal piece roof outer plate product with high requirements on the corrugation, and the product does not add noble alloy elements such as Nb and Ti, and has the advantages of low cost.

Description

TECHNICAL FIELD

[0001] The application belongs to the technical field of cold-rolled automobile steel, and particularly relates to a low-cost steel plate suitable for a 2C1B coating process automobile roof outer plate and a production method thereof. BACKGROUND

[0002] At present, domestic automobile manufacturers gradually replace the traditional 3C2B coating process with a 2C1B coating process without a middle coating process for the consideration of low carbon environmental protection and cost. After the 2C1B coating process is used, the paint film thickness is significantly reduced, the ability of the paint film to cover the defects of the steel plate is reduced, and the steel plate needs to have good surface quality and low waviness characteristics. In addition, the automobile horizontal piece has higher indexes of long-wave, short-wave and fresh reflection after coating, and has higher requirements for the control of the waviness of the steel plate after forming.

[0003] A production method of a high-surface-quality high-strength IF cold-rolled steel strip is disclosed in CN112222189A published on January 15, 2021. The method is based on the existing composition and equipment, and adjusts and controls through a consistent process such as steelmaking, hot rolling, pickling and annealing process, without adding equipment and special process, and produces a product that meets the requirements of automobile outer plate in roughness, waviness, surface quality and mechanical properties. The product waviness Wsa(1-5) is less than 0.35 microns. The product design adopts an IF steel composition system, which has a high cost, and the overall waviness of the product after forming has a high waviness.

[0004] A hot-dip galvanized steel plate for automobile side outer plate and a production method thereof are disclosed in CN103774043A published on May 7, 2014. Through the optimization of the composition ratio, and the hot rolling, cold rolling, continuous annealing, hot-dip galvanizing and finishing processes, the continuous annealing hot-dip galvanized steel plate produced has the characteristics of low yield strength, high elongation, and low surface filter center line waviness WCA value, which can be realized on an ordinary production line, reduces the production difficulty, and meets the requirements of automobile outer plate stamping forming and coating. The invention also uses an IF steel composition design, which has a high cost, and the WCA of the original plate produced is low, but the level of the waviness after forming is not controlled. SUMMARY

[0005] The application aims to provide a low-cost steel plate suitable for a 2C1B coating process automobile roof outer plate and a production method thereof. Through the composition, process and parameter control, the steel plate produced has a Wsa of less than or equal to 0.25 microns after 5% deformation, and is suitable for the automobile horizontal piece roof outer plate product with high waviness requirements. The product does not add noble alloy elements such as Nb and Ti, and has a low cost.

[0006] The specific technical scheme of the application is as follows:

[0007] A low-cost steel plate suitable for 2C1B coating process automobile roof outer plate, comprising the following mass percentage components:

[0008] C: 0.025-0.030wt%, Si: ≤0.030wt%, Mn: 0.08-0.25wt%, Als: 0.025-0.050wt%, P ≤0.015wt%, S ≤0.015wt%, N ≤0.004wt%, the balance being Fe and unavoidable impurity elements.

[0009] The average grain size of the low-cost steel plate suitable for 2C1B coating process automobile roof outer plate is 11±2μm;

[0010] The finished product of the low-cost steel plate suitable for 2C1B coating process automobile roof outer plate has a corrugation Wsa ≤0.25μm after 5% deformation, has low corrugation characteristics; meanwhile, the yield strength of the product is between 160-220MPa, the tensile strength is ≥300MPa, the elongation A 80 ≥38%, the n value is ≥0.2, and the r90 is ≥1.8.

[0011] The application provides a production method of a low-cost steel plate suitable for 2C1B coating process automobile roof outer plate, comprising the following process flow:

[0012] Smelting→continuous casting→hot rolling→pickling and cold rolling→cleaning→continuous annealing→overaging treatment→flatting→finished product.

[0013] The smelting is suitable for converter, electric furnace and induction furnace smelting, and target molten steel is obtained;

[0014] The continuous casting is used to produce a casting blank, and the molten steel is shaped and rapidly solidified and crystallized under the action of a crystallizer to form a slab;

[0015] The hot rolling is used to hot roll the continuous casting slab to obtain a hot rolled slab; in the hot rolling process, the heating temperature is controlled to be 1180-1230℃, a higher heating temperature is mainly used to facilitate the dissolution of AlN in the casting blank and make the grain structure uniform, and the final rolling temperature is controlled to be 880±20℃. The hot rolled slab is coiled to obtain a hot rolled steel coil; the coiling temperature is controlled to be 730±15℃, and a higher coiling temperature is favorable for obtaining a steel plate with good deep drawing performance;

[0016] The pickling and cold rolling is used to adopt a conventional pickling process to fully remove the iron oxide scale on the surface of the strip, and then cold rolled to the required thickness specification of the finished product, and the cold rolling reduction rate is controlled to be 65-83%; a higher pickling and cold rolling reduction rate is favorable for the refinement of the finished product structure, thereby ensuring that the product has good low corrugation characteristics after stamping, and the higher pickling and cold rolling reduction rate is favorable for the increase of the proportion of beneficial structure.

[0017] The cleaning: the strip steel cleaning is carried out, and the impurities adhered to the surface of the strip steel during cold rolling, such as rolling oil and iron powder, are removed to improve the cleanliness of the surface of the strip steel.

[0018] The continuous annealing: the steel plate treated in the cleaning step is subjected to continuous annealing, and higher annealing temperature will result in coarse product structure, and higher corrugation after stamping, and lower annealing temperature will result in poor stamping performance of the product, therefore, the annealing temperature is controlled to be 800-820 DEG C, the annealing time is 60-120 S, and the recovery recrystallization structure is obtained.

[0019] The overaging treatment: after the continuous annealing, slow cooling is first carried out at a cooling speed of 2-6 DEG C / s, the slow cooling is carried out to 680±20 DEG C, then fast cooling is carried out at a cooling speed of 20-40 DEG C / s, and after cooling to 350±20 DEG C, overaging treatment is carried out by keeping the temperature for 300-400 seconds; a large amount of supersaturated carbon remains, which is not conducive to stamping performance, and will also result in poor aging performance of the product, and the orange peel defect after stamping is prone to occur, resulting in high corrugation after forming. The overaging treatment is keeping the temperature for 300-400 seconds after cooling to 350±20 DEG C, and since the rapid cooling increases the precipitation power of carbon, keeping heating can promote the precipitation of carbon, so that the product has good stamping and aging resistance.

[0020] The skin passing: the skin passing process involves the replication of the roll corrugation and roughness to the strip steel and the influence on the surface layer structure of the strip steel. The product produced by using the roll with lower roughness has lower corrugation, but the roll with lower roughness is prone to produce color difference defects, and the production cost of the roll with lower roughness is higher, and therefore, the roughness of the skin passing roll is controlled to be 1.8-2.2 mu m for production; the skin passing elongation is controlled to be 1.0-1.2%.

[0021] The design idea of the present application is as follows:

[0022] C: the most effective strengthening element, is the most economical and the strongest strengthening element. When the C content is low, the formability and welding performance are good, but the low C content will result in poor aging resistance of the product, and the orange peel is prone to occur, resulting in high corrugation after forming. In addition, the low C content will result in coarse grains, and the corrugation increment during the forming process of the sample is high, resulting in high corrugation of the formed part. The high C content will result in the obvious decrease of the formability and welding performance, therefore, the C content in the present application is controlled to be 0.025-0.030 wt%.

[0023] Si: has strong strengthening effect in the steel, but Si is easy to form oxide, which is not conducive to pickling and is easy to form oxidation color on the surface after annealing, and also reduces the plating property of the steel plate, therefore, a small amount of Si is added or no Si is added, and the upper limit is controlled to be 0.030 wt%.

[0024] Mn: Mn plays a role of solid solution strengthening in the steel (Mn dissolved in the steel causes lattice distortion, the lattice distortion increases the resistance of dislocation movement, makes it difficult to slip, thus increasing the strength and hardness of the alloy steel), while reducing the yield strength ratio of the steel (toughness and plasticity); in addition, it acts with S in the steel to prevent the generation of hot brittleness of the steel. In the present patent, Mn mainly acts with S to prevent the generation of hot brittleness of the steel, while playing a role of solid solution strengthening, and the upper limit is controlled at 0.25wt%.

[0025] Al: Al mainly plays a role of deoxidation in the steel, while Al can also form AlN precipitates to play a certain role of grain refinement. The presence of a small amount of Al can improve the ductility of the steel under the premise of ensuring the strength performance. However, if the Al content is too high, the crystallizer is easily blocked, the cast blank is easily cracked and other defects, and the cost is also increased. Therefore, the Al content in the present invention is controlled at 0.025wt% to 0.050wt%.

[0026] P: P is an inevitable harmful impurity in the steel, which has adverse effects on the stamping performance, cold brittleness, secondary processing brittleness and the like of the steel, and the P content in the steel should be strictly controlled. In the present invention, P≤0.015wt%.

[0027] N: N mainly causes yield effect and strain aging, and is a harmful impurity, so the upper limit of the N content should be strictly controlled. In the present invention, the upper limit of N is controlled at 0.004wt%.

[0028] S: S is an inevitable harmful impurity in the steel, which has adverse effects on isotropy, hot brittleness, stamping performance, cold bending performance, flanging performance and the like of the steel, and strict control of the S content in the steel will increase the smelting cost of the steel. Therefore, in the present invention, the upper limit of the S content is controlled at 0.015wt%.

[0029] The balance is Fe and inevitable impurity elements, and the fewer impurity elements the better on the basis of not increasing additional cost.

[0030] The leveling process is the core influencing factor of the steel plate's waviness. The roughness of the roll and the leveling elongation during the leveling process have a core impact on the initial waviness of the steel plate and the waviness increment during the 5% deformation process. Table 1 shows the relationship between the initial waviness of the steel plate, the waviness increment during the forming process, and the leveling elongation when using a roll with a specific roughness. The final waviness of the steel plate after 5% deformation is determined by the sum of the initial waviness of the steel plate and the waviness increment during the forming process. Control of the leveling elongation affects the replication of the roll waviness on the steel plate. Too low a leveling elongation will cause the corrugation of the acid-rolled incoming material to dominate, resulting in a higher initial waviness of the steel plate. In addition, too low a leveling elongation will make it impossible to eliminate the yield platform. Therefore, the lower limit of the leveling elongation is 0.6%. When the leveling elongation reaches above 0.6%, the initial waviness of the steel plate is at a low level. The subsequent increase in corrugation of the steel plate during the 5% deformation process will be higher. As the flattening elongation gradually increases, the initial corrugation of the corresponding steel plate becomes larger and larger, but the corrugation increment during the forming process becomes lower. The reason why the corrugation increment decreases with the increase in flattening elongation is that the increase in corrugation of the steel plate during the forming process is mainly due to the uneven and uncoordinated deformation of the surface structure during the deformation process, which leads to an increase in the degree of surface unevenness. The higher flattening elongation is equivalent to a certain pre-deformation of the surface structure in advance, which improves the uneven deformation during the subsequent 5% forming process. Comprehensively considering that the initial corrugation increases with the increase in flattening elongation and the corrugation increment decreases during the forming process, it is finally determined that the appropriate flattening elongation range is between 1.0 and 1.2%.

[0031] Table 1 Relationship between initial corrugation of steel plate, corrugation increment during forming and flattening elongation (2.0 μm roller)

[0032]

[0033] Compared with existing technologies, this invention achieves a post-deformation waviness (Wsa) of 0.25μm or less through a series of controlled processes, particularly during the flattening process. The resulting product is suitable for horizontal roof panels with high waviness requirements. Furthermore, without the addition of precious alloy elements such as Nb and Ti, it offers a low-cost advantage. BRIEF DESCRIPTION OF THE DRAWINGS

[0034] Figure 1 The structure of Example 1 is ferrite with an average grain size of 11.2 μm;

[0035] Figure 2 This is the structure of Comparative Example 5, which is ferrite and has an average grain size of 21.4 μm. DETAILED DESCRIPTION

[0036] In order to make the purposes, technical solutions and advantages of the embodiments of the present application clearer, the technical solutions in the embodiments of the present application will be described clearly and completely below in conjunction with the embodiments of the present application. Obviously, the described embodiments are only some of the embodiments of the present application, rather than all the embodiments of the present application. Based on the embodiments in the present application, all other embodiments obtained by those skilled in the art without creative work fall within the scope of protection of the present application.

[0037] Embodiment 1

[0038] A low-cost steel plate suitable for a 2C1B coating process automobile roof outer plate, comprising the following mass percentage components:

[0039] C: 0.0267wt%, Si: 0.0027wt%, Mn: 0.182wt%, Als: 0.0413wt%, P: 0.0127wt%, S: 0.0077wt%, N: 0.002wt%, and the balance being Fe and unavoidable impurity elements.

[0040] The production method of the low-cost steel plate suitable for a 2C1B coating process automobile roof outer plate in Embodiment 1 comprises the following process flow:

[0041] Smelting → Continuous casting → Hot rolling → Pickling and cold rolling → Cleaning → Continuous annealing → Overaging treatment → Leveling → Finished product.

[0042] The smelting is suitable for converter, electric furnace and induction furnace smelting to obtain target molten steel;

[0043] The continuous casting is used to produce a casting blank, and the molten steel is shaped and rapidly solidified and crystallized under the action of a crystallizer to form a slab;

[0044] The hot rolling is performed on the continuous casting slab to obtain a hot-rolled slab; in the hot rolling process, the heating temperature is controlled at 1205℃, and the finish rolling temperature is controlled at 880℃. The hot-rolled slab is coiled to obtain a hot-rolled steel coil; the coiling temperature is controlled at 730℃;

[0045] The pickling and cold rolling is performed by using a conventional pickling process to fully remove the iron oxide scale on the surface of the strip, and then cold-rolled to the required thickness specification of the finished product, and the cold rolling reduction rate is controlled at 78%;

[0046] The cleaning is performed to remove impurities such as rolling oil and iron powder adhered to the surface of the strip during cold rolling to improve the cleanliness of the surface of the strip.

[0047] The continuous annealing is controlled at an annealing temperature of 810℃ and a holding time of 75S;

[0048] The overaging treatment: first slow cooling, slow cooling speed 4℃ / s, slow cooling to 680℃, then fast cooling, fast cooling speed 30℃ / s, cooling to 350℃, holding for 300 seconds for overaging treatment;

[0049] The skin pass: the skin pass roller roughness is 1.8μm for production; the skin pass elongation target value is 1.2%.

[0050] Example 2

[0051] A low-cost steel plate suitable for 2C1B coating process for automobile roof outer plate, comprising the following mass percentage components:

[0052] C: 0.0275wt%, Si: 0.0037wt%, Mn: 0.190wt%, Als: 0.0421wt%, P: 0.0112wt%, S: 0.0115wt%, N: 0.0022wt%, the balance being Fe and unavoidable impurity elements.

[0053] The production method of the low-cost steel plate suitable for 2C1B coating process for automobile roof outer plate in Example 2 comprises the following process flow:

[0054] Smelting→continuous casting→hot rolling→pickling and cold rolling→cleaning→continuous annealing→overaging treatment→skin pass→finished product.

[0055] The smelting: suitable for converter, electric furnace and induction furnace smelting to obtain target molten steel;

[0056] The continuous casting: using continuous casting to produce billets, the molten steel is shaped and rapidly solidified and crystallized under the action of the crystallizer to form a slab;

[0057] The hot rolling: hot rolling the continuous casting slab to obtain a hot rolled slab; the heating temperature is controlled at 1216℃ and the finishing temperature is controlled at 880℃ during the hot rolling process; the hot rolled slab is coiled to obtain a hot rolled coil; the coiling temperature is controlled at 727℃;

[0058] The pickling and cold rolling: using conventional pickling process to fully remove the iron oxide scale on the surface of the strip, and then cold rolling to the required thickness specification of the finished product, and the cold rolling reduction rate is controlled at 78%;

[0059] The cleaning: cleaning the strip to remove impurities such as rolling oil and iron powder adhered to the surface of the strip during cold rolling to improve the cleanliness of the strip surface.

[0060] The continuous annealing: the annealing temperature is controlled at 812℃ and the holding time is 82S;

[0061] The overaging treatment: first slow cooling, slow cooling rate 5℃ / s, slow cooling to 680℃, then fast cooling, fast cooling rate 25℃ / s, cooling to 350℃, holding for 300 seconds for overaging treatment;

[0062] The skin pass: the skin pass roller roughness is 1.8μm for production; the skin pass elongation target value is 1.2%.

[0063] Example 3

[0064] A low-cost steel plate suitable for 2C1B coating process for automobile roof outer plate, comprising the following mass percentage components:

[0065] C: 0.0256wt%, Si: 0.0035wt%, Mn: 0.194wt%, Als: 0.0429wt%, P: 0.0127wt%, S: 0.0098wt%, N: 0.0016wt%, the balance being Fe and unavoidable impurity elements.

[0066] The production method of the low-cost steel plate suitable for 2C1B coating process for automobile roof outer plate in Example 3 comprises the following process flow:

[0067] Smelting→continuous casting→hot rolling→pickling and cold rolling→cleaning→continuous annealing→overaging treatment→skin pass→finished product.

[0068] The smelting: suitable for converter, electric furnace and induction furnace smelting to obtain target molten steel;

[0069] The continuous casting: using continuous casting to produce billets, the molten steel is shaped and rapidly solidified and crystallized under the action of the crystallizer to form a slab;

[0070] The hot rolling: hot rolling the continuous casting slab to obtain a hot rolled slab; the heating temperature is controlled at 1191℃ and the finishing temperature is controlled at 881℃ during the hot rolling process; the hot rolled slab is coiled to obtain a hot rolled steel coil; the coiling temperature is controlled at 731℃;

[0071] The pickling and cold rolling: using conventional pickling process to fully remove the iron oxide scale on the surface of the strip, and then cold rolling to the required thickness specification of the finished product, and the cold rolling reduction rate is controlled at 78%;

[0072] The cleaning: cleaning the strip to remove impurities such as rolling oil and iron powder adhered to the surface of the strip during cold rolling to improve the cleanliness of the strip surface.

[0073] The continuous annealing: the annealing temperature is controlled at 809℃ and the holding time is 88S;

[0074] The overaging treatment: first slow cooling, slow cooling rate 5℃ / s, slow cooling to 660℃, then fast cooling, fast cooling rate 30℃ / s, cooling to 350℃, holding for 300 seconds for overaging treatment;

[0075] The skin pass: the skin pass roller roughness is 1.8μm for production; the skin pass elongation target value is 1.1%.

[0076] Example 4

[0077] A low-cost steel plate suitable for 2C1B coating process for automobile roof outer plate, comprising the following mass percentage components:

[0078] C: 0.0271wt%, Si: 0.0034wt%, Mn: 0.190wt%, Als: 0.0393wt%, P: 0.0104wt%, S: 0.0088wt%, N: 0.0024wt%, the balance being Fe and unavoidable impurity elements.

[0079] The production method of the low-cost steel plate suitable for 2C1B coating process for automobile roof outer plate of Example 4 comprises the following process flow:

[0080] Smelting→continuous casting→hot rolling→pickling and cold rolling→cleaning→continuous annealing→overaging treatment→skin pass→finished product.

[0081] The smelting: suitable for converter, electric furnace and induction furnace smelting to obtain target molten steel;

[0082] The continuous casting: using continuous casting to produce billets, the molten steel is shaped and rapidly solidified and crystallized under the action of the crystallizer to form a slab;

[0083] The hot rolling: hot rolling the continuous casting slab to obtain a hot rolled slab; the heating temperature is controlled at 1217℃ and the finishing temperature is controlled at 881℃ during the hot rolling process; the hot rolled slab is coiled to obtain a hot rolled coil; the coiling temperature is controlled at 732℃;

[0084] The pickling and cold rolling: using conventional pickling process to fully remove the oxide scale on the surface of the strip, and then cold rolling to the required thickness specification of the finished product, with a cold rolling reduction rate of 78%;

[0085] The cleaning: cleaning the strip to remove impurities such as rolling oil and iron powder adhered to the surface of the strip during cold rolling to improve the cleanliness of the strip surface.

[0086] The continuous annealing: controlling the annealing temperature at 812℃ and the holding time at 112S;

[0087] The overaging treatment: first slow cooling, slow cooling speed 6℃ / s, slow cooling to 660℃, then fast cooling, fast cooling speed 35℃ / s, cooling to 330℃, holding for 300 seconds for overaging treatment;

[0088] The skin pass: the skin pass roller roughness is 1.8μm for production; the skin pass elongation target value is 1.1%.

[0089] Example 5

[0090] A low-cost steel plate suitable for 2C1B coating process for automobile roof outer plate, comprising the following mass percentage components:

[0091] C: 0.0292wt%, Si: 0.0033wt%, Mn: 0.183wt%, Als: 0.0405wt%, P: 0.0111wt%, S: 0.0064wt%, N: 0.0032wt%, the balance being Fe and unavoidable impurity elements.

[0092] The production method of the low-cost steel plate suitable for 2C1B coating process for automobile roof outer plate in Example 5 comprises the following process flow:

[0093] Smelting→continuous casting→hot rolling→pickling and cold rolling→cleaning→continuous annealing→overaging treatment→skin pass→finished product.

[0094] The smelting: suitable for converter, electric furnace and induction furnace smelting to obtain target molten steel;

[0095] The continuous casting: using continuous casting to produce billets, the molten steel is shaped and rapidly solidified and crystallized under the action of the crystallizer to form a slab;

[0096] The hot rolling: hot rolling the continuous casting slab to obtain a hot rolled slab; the heating temperature is controlled at 1193℃ and the finish rolling temperature is controlled at 882℃ during the hot rolling process; the hot rolled slab is coiled to obtain a hot rolled steel coil; the coiling temperature is controlled at 732℃;

[0097] The pickling and cold rolling: using conventional pickling process to fully remove the iron oxide scale on the surface of the strip, and then cold rolling to the required thickness specification of the finished product, with a cold rolling reduction rate of 78%;

[0098] The cleaning: cleaning the strip to remove impurities such as rolling oil and iron powder adhered to the surface of the strip during cold rolling to improve the cleanliness of the strip surface.

[0099] The continuous annealing: controlling the annealing temperature at 810℃ and the holding time at 76S;

[0100] The overaging treatment: first slow cooling, slow cooling rate 3℃ / s, slow cooling to 670℃, then fast cooling, fast cooling rate 35℃ / s, cooling to 350℃, holding for 300 seconds for overaging treatment;

[0101] The skin pass: the skin pass roller roughness is 2.0μm for production; the skin pass elongation target value is 1.0%.

[0102] Example 6

[0103] A low-cost steel plate suitable for 2C1B coating process for automobile roof outer plate, comprising the following mass percentage components:

[0104] C: 0.0265wt%, Si: 0.0037wt%, Mn: 0.190wt%, Als: 0.0421wt%, P: 0.0112wt%, S: 0.0115wt%, N: 0.0026wt%, the balance being Fe and unavoidable impurity elements.

[0105] The production method of the low-cost steel plate suitable for 2C1B coating process for automobile roof outer plate of Example 6 comprises the following process flow:

[0106] Smelting→continuous casting→hot rolling→pickling and cold rolling→cleaning→continuous annealing→overaging treatment→skin pass→finished product.

[0107] The smelting: suitable for converter, electric furnace and induction furnace smelting to obtain target molten steel;

[0108] The continuous casting: using continuous casting to produce billets, the molten steel is shaped and rapidly solidified and crystallized under the action of the crystallizer to form a slab;

[0109] The hot rolling: hot rolling the continuous casting slab to obtain a hot rolled slab; the heating temperature is controlled at 1191℃ and the finishing temperature is controlled at 883℃ during the hot rolling process; the hot rolled slab is coiled to obtain a hot rolled coil; the coiling temperature is controlled at 730℃;

[0110] The pickling and cold rolling: using conventional pickling process to fully remove the iron oxide scale on the surface of the strip, and then cold rolling to the required thickness specification of the finished product, and the cold rolling reduction rate is controlled at 78%;

[0111] The cleaning: cleaning the strip to remove impurities such as rolling oil and iron powder adhered to the surface of the strip during cold rolling to improve the cleanliness of the strip surface.

[0112] The continuous annealing: the annealing temperature is controlled at 808℃ and the holding time is 64S;

[0113] The overaging treatment: first slow cooling, slow cooling rate 4℃ / s, slow cooling to 680℃, then fast cooling, fast cooling rate 35℃ / s, cooling to 350℃ and holding for 300 seconds for overaging treatment;

[0114] The skin pass: the skin pass roller roughness is 2.0μm for production; the skin pass elongation target value is 1.0%.

[0115] Comparative Example 1

[0116] A steel sheet, comprising the following mass percentage components:

[0117] C: 0.0256wt%, Si: 0.0027wt%, Mn: 0.197wt%, Als: 0.0387wt%, P: 0.0139wt%, S: 0.0088wt%, N: 0.0017wt%, the balance being Fe and inevitable impurity elements.

[0118] The production method of the steel sheet of Comparative Example 1, comprising the following process flow:

[0119] Smelting→Continuous casting→Hot rolling→Pickling cold rolling→Cleaning→Continuous annealing→Overaging treatment→Skin pass→Finished product.

[0120] The smelting: suitable for converter, electric furnace and induction furnace smelting, obtaining target molten steel;

[0121] The continuous casting: adopting continuous casting to produce casting blank, the molten steel is shaped and rapidly solidified and crystallized under the action of the crystallizer to form a slab;

[0122] The hot rolling: hot rolling the continuous casting slab to obtain a hot rolled slab; in the hot rolling process, the heating temperature is controlled at 1218℃, the finish rolling temperature is controlled at 921 ℃, and the coiling temperature is controlled at 724℃;

[0123] The pickling cold rolling: adopting conventional pickling process to fully remove the iron oxide scale on the surface of the strip, and then cold rolling to the required thickness specification of the finished product, and the cold rolling reduction rate is controlled at 79%;

[0124] The cleaning: cleaning the strip to remove impurities such as rolling oil and iron powder adhered to the surface of the strip during cold rolling to improve the cleanliness of the strip surface.

[0125] The continuous annealing: the annealing temperature is 820℃, the holding time is 68S, and the recovered recrystallized structure is obtained;

[0126] The overaging treatment: first slow cooling, slow cooling rate 3℃ / s, slow cooling to 690℃, then fast cooling, fast cooling rate 35℃ / s, cooling to 350℃ and holding for 300 seconds for overaging treatment;

[0127] The skin pass: the skin pass roll roughness adopts 2.0 μm, the skin pass elongation target value 0.8％。

[0128] The target value of the skin elongation of the comparative example 1 is low, the increment of the waviness during the forming process is 0.10 μm, the waviness after the forming reaches 0.28 μm, and the waviness is high. 821

[0129] Comparative Example 2

[0130] A steel plate, comprising the following mass percentage components:

[0131] C: 0.0273wt%, Si: 0.0040wt%, Mn: 0.194wt%, Als: 0.0445wt%, P: 0.0123wt%, S: 0.0099wt%, N: 0.0015wt%, the balance being Fe and inevitable impurity elements.

[0132] The production method of the steel plate of Comparative Example 2, comprising the following process flow:

[0133] Smelting→Continuous casting→Hot rolling→Pickling cold rolling→Cleaning→Continuous annealing→Overaging treatment→Skin pass→Finished product.

[0134] The smelting: suitable for converter, electric furnace and induction furnace smelting, obtaining target molten steel;

[0135] The continuous casting: adopting continuous casting to produce a casting blank, the molten steel is shaped and rapidly solidified and crystallized under the action of a crystallizer to form a slab;

[0136] The hot rolling: hot rolling the continuous casting slab to obtain a hot rolled slab, the heating temperature is controlled at 1219℃ in the hot rolling process, and the finish rolling temperature is controlled at 919℃， The coiling temperature is controlled at 722℃;

[0137] The pickling cold rolling: adopting a conventional pickling process to fully remove the iron oxide scale on the surface of the strip, and then cold rolling to the required thickness specification of the finished product, the cold rolling reduction rate is controlled at 79%;

[0138] The cleaning: cleaning the strip to remove impurities such as rolling oil and iron powder adhered to the surface of the strip during cold rolling to improve the cleanliness of the strip surface.

[0139] The continuous annealing: the annealing temperature The roughness of the skin roll is 2.5 μm, and the target value of the skin elongation is 0.80%. ℃, the holding time is 92S, obtaining a recovery recrystallization structure;

[0140] The overaging treatment: first slow cooling, the slow cooling speed is 4℃ / s, slow cooling to 680℃, then fast cooling, the fast cooling speed is 30℃ / s, cooling to 350℃ and holding for 300 seconds for overaging treatment;

[0141] The skin pass: The roughness of the skin roll of the comparative example 2 is high, the initial waviness is 0.23 μm, the waviness after the forming reaches 0.27 μm, and the waviness is high.

[0142] C: 0.0312 wt%, Si: 0.0031 wt% 822 ℃, the holding time is 72 s,

[0143] Comparative Example 3

[0144] A steel sheet comprising the following mass percentage components:

[0145] The skin elongation range is 0.8% Mn: 0.197wt%, Als: 0.0437wt%, P: 0.0108wt%, S: 0.0070wt%, N: 0.0021wt%, the balance being Fe and unavoidable impurity elements.

[0146] The production method of the steel sheet of Comparative Example 3 comprises the following process flow:

[0147] Smelting→Continuous casting→Hot rolling→Pickling cold rolling→Cleaning→Continuous annealing→Overaging treatment→Skin pass→Finished product.

[0148] The smelting: suitable for converter, electric furnace and induction furnace smelting, obtaining target molten steel;

[0149] The continuous casting: adopting continuous casting to produce a casting blank, the molten steel is shaped and rapidly solidified and crystallized under the action of a crystallizer to form a slab;

[0150] The hot rolling: hot rolling the continuous casting slab to obtain a hot rolled slab, the heating temperature is controlled at 1228℃, the finish rolling temperature is controlled at 916℃ , and the coiling temperature is controlled at 722℃;

[0151] The pickling cold rolling: adopting conventional pickling process to fully remove the iron oxide scale on the surface of the strip, and then cold rolling to the required thickness specification of the finished product, the cold rolling reduction rate is controlled at 79%;

[0152] The cleaning: cleaning the strip to remove impurities such as rolling oil and iron powder adhered to the surface of the strip during cold rolling to improve the cleanliness of the strip surface.

[0153] The continuous annealing: the annealing temperature is The C of the comparative example 3 is high, to obtain a recovery recrystallized structure;

[0154] The overaging treatment: first slow cooling, the slow cooling speed is 5℃ / s, slow cooling to 680℃, then fast cooling, the fast cooling speed is 25℃ / s, cooling to 350℃ and holding for 300 seconds for overaging treatment;

[0155] The skin pass: the roughness of the skin pass roll is 2.0μm, but the strength reaches 248 MPa, the r value is 1.7, and the corresponding .

[0156] mechanical properties are poor, and it is difficult to meet the requirements of the mechanical properties. Wavy degree Wsa: 0.23μm,The target value of the skin elongation is 1.50%. The skin elongation of the comparative example 4 is high, the initial waviness is 0.24 μm, the waviness after the forming reaches 0.27 μm, and the waviness is high.

[0157] Comparative Example 4

[0158] A steel sheet comprising the following mass percentage components:

[0159] C: 0.0275wt%, Si: 0.0028wt%, Mn: 0.199wt%, Als: 0.0397wt%, P: 0.0126wt%, S: 0.0064wt%, N: 0.0025wt%, the balance being Fe and inevitable impurity elements.

[0160] The production method of the steel sheet of Comparative Example 4 comprises the following process flow:

[0161] Smelting → Continuous casting → Hot rolling → Pickling cold rolling → Cleaning → Continuous annealing → Overaging treatment → Skin pass → Finished product.

[0162] The smelting: suitable for converter, electric furnace and induction furnace smelting, obtaining target molten steel;

[0163] The continuous casting: adopting continuous casting to produce a casting blank, the molten steel is shaped and rapidly solidified and crystallized under the action of a crystallizer to form a slab;

[0164] The hot rolling: hot rolling the continuous casting slab to obtain a hot rolled slab; in the hot rolling process, the heating temperature is controlled at 1220℃, the finish rolling temperature is controlled at 700-720℃, and the coiling temperature is controlled at 723℃; 921

[0165] The pickling cold rolling: adopting a conventional pickling process to fully remove the iron oxide scale on the surface of the strip, and then cold rolling to the required thickness specification of the finished product, with the cold rolling reduction rate controlled at 79%;

[0166] The cleaning: cleaning the strip to remove impurities such as rolling oil and iron powder adhered to the surface of the strip during cold rolling to improve the cleanliness of the strip surface.

[0167] The continuous annealing: the annealing temperature is 817℃, the holding time is 92S, and a recrystallized structure is obtained;

[0168] The overaging treatment: first slow cooling at a cooling speed of 6℃ / s to 670℃, then fast cooling at a cooling speed of 40℃ / s to 340℃, holding for 30 seconds for overaging treatment;

[0169] The skin pass: the roughness of the skin pass roll is 2.0μm, C: 0.0014 wt%,

[0170] Ti: 0.0578 wt%, The skin elongation range is 0.8%.

[0171] ​Comparative Example 5

[0172] A steel sheet comprising the following mass percentage components:

[0173] The C content of the comparative example 5 is low, and the addition of Ti leads to high cost, and the corresponding Wsa of the product after 5% deformation reaches 0.34 μm, which is high. Si: 0.0041wt%, Mn: 0.117wt%, Als: 0.044wt%, P: 0.0124wt%, S: 0.0057wt%, N: 0.0014wt%, Ti: 0.0389%, Nb: 0.018% the balance being Fe and inevitable impurity elements.

[0174] The production method of the steel sheet of Comparative Example 5 comprises the following process flow:

[0175] Smelting → Continuous casting → Hot rolling → Pickling cold rolling → Cleaning → Continuous annealing → Overaging treatment → Skin pass → Finished product.

[0176] The smelting: suitable for converter, electric furnace and induction furnace smelting, obtaining target molten steel;

[0177] The continuous casting: using continuous casting to produce billets, the molten steel is shaped and rapidly solidified and crystallized under the action of the crystallizer to form a slab;

[0178] The hot rolling: hot rolling the continuous casting slab to obtain a hot rolled slab; in the hot rolling process, the heating temperature is controlled at 1217℃, the finish rolling temperature is controlled at 929℃ , and the coiling temperature is controlled at 663℃；

[0179] The pickling cold rolling: using conventional pickling process to fully remove the iron oxide scale on the surface of the strip, and then cold rolling to the required thickness specification of the finished product, with a cold rolling reduction rate of 79%;

[0180] The cleaning: cleaning the strip to remove impurities such as rolling oil and iron powder adhered to the surface of the strip during cold rolling to improve the cleanliness of the strip surface.

[0181] The continuous annealing: annealing temperature is 816℃, holding time is 84S, obtaining recovery and recrystallization structure;

[0182] The overaging treatment: first slow cooling, slow cooling rate is 5℃ / s, slow cooling to 680℃, then fast cooling, fast cooling rate is 30℃ / s, cooling to 350℃ and holding for 300 seconds for overaging treatment;

[0183] The skin pass: the roughness of the skin pass roll is 2.0μm, The skin elongation range is 0.8%.

[0184] The C of the comparative example 6 is low, and the addition of Ti and Nb leads to high cost, and the corresponding Wsa of the product after 5% deformation reaches 0.28 μm. Case

[0185] Comparative Example 6

[0186] A steel sheet comprising the following mass percentage components:

[0187] C：0.0014％， Si: 0.0050%, Mn: 0.115%, Als: 0.0425%, P: 0.0132%, S: 0.0046%, N: 0.0013%, Si , the balance being Fe and inevitable impurity elements.

[0188] The production method of the steel sheet of Comparative Example 6 comprises the following process flow:

[0189] Smelting → Continuous casting → Hot rolling → Pickling cold rolling → Cleaning → Continuous annealing → Overaging treatment → Skin pass → Finished product.

[0190] The smelting: suitable for converter, electric furnace and induction furnace smelting, obtaining target molten steel;

[0191] The continuous casting: using continuous casting to produce billets, the molten steel is shaped and rapidly solidified and crystallized under the action of the crystallizer to form a slab;

[0192] The hot rolling: hot rolling the continuous casting slab to obtain a hot rolled slab; in the hot rolling process, the heating temperature is controlled at 1221℃, the finish rolling temperature is controlled at 921℃ , and the coiling temperature is controlled at 725℃;

[0193] The pickling cold rolling: using conventional pickling process to fully remove the iron oxide scale on the surface of the strip, and then cold rolling to the required thickness specification of the finished product, and the cold rolling reduction rate is controlled at 79%;

[0194] The cleaning: cleaning the strip to remove impurities such as rolling oil and iron powder adhered to the surface of the strip during cold rolling to improve the cleanliness of the strip surface.

[0195] The continuous annealing: the annealing temperature is 814℃, the holding time is 103S, and the recovered recrystallized structure is obtained;

[0196] The overaging treatment: first slow cooling, the slow cooling speed is 4℃ / s, slow cooling to 680℃, then fast cooling, the fast cooling speed is 25℃ / s, cooling to 370℃ and holding for 300 seconds for overaging treatment;

[0197] The skin pass: the roughness of the skin pass roll is 2.0μm, Mn

[0198] Als Ti

[0199] The component comparison of the above examples and comparative examples is shown in Table 2, and the balance not shown in Table 2 is Fe and inevitable impurities. The production process parameter comparison is shown in Table 3.

[0200] Table 2 Ingredients (wt%) of each example and comparative example

[0201] Nb C Example 1 Example 2 Example 3 P S Example 4 Example 5 N Example 6 0.0267 0.0027 0.182 0.0413 0.0127 0.0077 - - 0.002 Comparative example 1 0.0275 0.0037 0.190 0.0421 0.0112 0.0115 - - 0.0022 Comparative example 2 0.0256 0.0035 0.194 0.0429 0.0127 0.0098 - - 0.0016 Comparative example 3 0.0271 0.0034 0.190 0.0393 0.0104 0.0088 - - 0.0024 Comparative example 4 0.0292 0.0033 0.183 0.0405 0.0111 0.0064 - - 0.0032 Comparative example 5 0.0265 0.0037 0.190 0.0421 0.0112 0.0115 - - 0.0026 Comparative example 6 0.0256 0.0027 0.197 0.0387 0.0139 0.0088 - - 0.0017 ​ 0.0273 0.0040 0.194 0.0445 0.0123 0.0099 - - 0.0015 ​ 0.0312 0.0031 0.197 0.0437 0.0108 0.0070 - - 0.0021 ​ 0.0275 0.0028 0.199 0.0397 0.0126 0.0064 - - 0.0025 ​ 0.0014 0.0041 0.117 0.044 0.0124 0.0057 0.0578 - 0.0014 ​ 0.0014 0.0050 0.115 0.0425 0.0132 0.0046 0.0389 0.018 0.0013

[0202] Table 3 Production process parameters of each example and comparative example

[0203]

[0204] The 5% deformation waviness of the products produced by each example and comparative example is shown in Table 4.

[0205] Table 4 Waviness values after 5% deformation of examples and comparative examples

[0206]

[0207] The above Table 4 is tested according to GB / T 5027 Determination of plastic strain ratio (r value) of metallic materials - sheet and strip, GB / T 5028 Determination of tensile strain hardening exponent (n value) of metallic materials - sheet and strip, GB / T 228 Metallic materials - Tensile testing - Part 1 : Method of test at room temperature, GBT 2523-2022 Metallic materials - Cold rolled flat products - Measurement of surface roughness, peak count and waviness, respectively.

[0208] The above underlined data does not meet the requirements of the present application.

[0209] The above description of the embodiments is to enable those skilled in the art to understand and use the invention. Those skilled in the art can easily make various modifications to these embodiments and apply the general principles described herein to other embodiments without having to go through creative labor. Therefore, the present application is not limited to the above embodiments, and any improvements and modifications made by those skilled in the art within the scope of the present application without departing from the scope of the present application should be within the scope of protection of the present application.

Claims

1. A low-cost steel plate suitable for 2C1B coating process for automobile roof outer panels, characterized in that: The low-cost steel plate suitable for the 2C1B coating process for the outer panel of the automobile roof comprises the following components: C: 0.025~0.030wt%, Si: ≤0.030wt%, Mn: 0.08~0.25wt%, Als: 0.025~0.050 wt%, P≤0.015 wt%, S≤0.015 wt%, N≤0.004wt%, the balance is Fe and unavoidable impurity elements; The average grain size of the low-cost steel plate suitable for the 2C1B coating process for the outer panel of the automobile roof is 11±2 μm; The low-cost finished steel plate suitable for the 2C1B coating process for the outer panel of the automobile roof has a corrugation Wsa ≤ 0.25 μm after 5% deformation, a yield strength between 160 and 220 MPa, a tensile strength ≥ 300 MPa, an elongation A80 ≥ 38%, an n value ≥ 0.2, and an r90 ≥ 1.8; The method for producing a steel plate suitable for a 2C1B coating process for an automobile roof outer panel includes the following process steps: Smelting → continuous casting → hot rolling → pickling and cold rolling → cleaning → continuous annealing → over-aging treatment → flattening → finished product; The leveling: the leveling roller roughness is 1.8~2.2μm, and the leveling elongation is 1.0~1.2%.

2. A method for producing a steel plate suitable for a 2C1B coating process for an automobile roof outer panel according to claim 1, characterized in that: The production method includes the following process: Smelting → continuous casting → hot rolling → pickling and cold rolling → cleaning → continuous annealing → over-aging treatment → flattening → finished product; The leveling: the leveling roller roughness is 1.8~2.2μm, and the leveling elongation is 1.0~1.2%.

3. The production method according to claim 2, characterized in that The hot rolling process includes controlling the heating temperature at 1180-1230° C., the finishing temperature at 880±20° C., and the coiling temperature at 730±15° C.

4. The production method according to claim 2, characterized in that The pickling and cold rolling: the cold rolling reduction rate is controlled at 65-83%.

5. The production method according to claim 2, characterized in that The continuous annealing is performed at a temperature of 800-820°C.

6. The production method according to claim 2, characterized in that The over-aging treatment comprises the following steps: firstly performing slow cooling at a cooling rate of 2-6°C / s to 680±20°C, then performing rapid cooling at a cooling rate of 20-40°C / s to 350±20°C, and then holding the temperature for 300-400 seconds for over-aging treatment.

Images