Method for controlling pickling surface color difference of hot-rolled hot-formed steel

Abstract

The application discloses a pickling surface color difference control method for hot-rolled hot-formed steel, which is realized based on a thin slab short process production and comprises the following steps: S1, reducing the crown of the strip steel in the finishing rolling stage, so as to reduce the scale structure and grain boundary oxidation difference between the edge and the middle of the strip steel; S2, destroying the integrity of the scale structure in the tempering stage, so as to provide an artificial pickling core for the pickling process; and S3, selecting a corresponding pickling scheme according to the equipment conditions of the pickling unit process in the pickling stage. Through the control of the crown of the strip steel in the finishing rolling stage, the destruction of the scale structure in the tempering stage and the control of different pickling unit processes in the pickling stage, the width of the whitening area of the pickling surface of the hot-rolled hot-formed steel can be effectively reduced, the whiteness value difference between the edge and the middle of the strip steel can be reduced, and the whiteness uniformity of the pickling surface is improved.

Description

TECHNICAL FIELD

[0001] The present application relates to a production method of hot-rolled steel plate, in particular to a pickling surface color difference control method for hot-rolled hot-formed steel. BACKGROUND

[0002] With the development of automobile structure steel towards light weight, high strengthening and low cost, thin slab continuous casting and rolling process, i.e. short process, is used to produce thin gauge hot-rolled high-strength pickling steel instead of cold-rolled high-strength products of the same gauge. The short process production process of the hot-rolled high-strength pickling steel in the prior art mainly includes: molten steel smelting, slab continuous casting, soaking furnace heating, finishing rolling, laminar cooling, coiling, storage cooling, leveling, pickling and oiling. After the pickling process, the surface color difference defect of the hot-rolled hot-formed pickling steel produced by the short process has a high occurrence rate. The typical characteristics of the surface color difference defect are: a bright white color in a width of 40-100mm along the width direction of the steel strip from the edge, a dull gray-black color in the middle part, and the whiteness value of the bright white area can reach more than 70%, while the whiteness value of the gray-black area in the middle part is only 50-55%, thereby forming a color difference.

[0003] The bright white area of the edge and the gray-black area of the middle part of the hot-rolled hot-formed pickling steel are analyzed by SEM (scanning electron microscope) for micro-morphology. The bright white area of the edge presents a normal pickling surface, while the gray-black area of the middle part presents a certain preferential corrosion. The corrosion grain boundary groove absorbs part of the light and causes the surface to be dark. Therefore, the grain boundary oxidation is the reason for the preferential corrosion of the grain boundary during pickling, and also the reason for the difference in whiteness between the edge and the middle part.

[0004] Before coiling, the surface of the hot-rolled hot-formed steel forms a three-layer structure of iron oxide skin from the inside to the outside (FeO, Fe3O4, Fe2O3). After coiling of the hot-rolled hot-formed steel, the coil shape is tight. Please refer to the attached Figure 1, the innermost circle, the outermost circle and the two end faces (edge gap 11) of the steel coil 1 are fully oxygenated, and the oxygen supply in the interior of the steel coil is severely limited. In order to control the flatness problem of the thin gauge hot forming steel coil, the coiling temperature is set at a high level (above the Ar3 line, 720-750℃) to prevent the occurrence of flatness. During the cooling process of the high temperature steel coil, the diffusion of Fe ions in the steel substrate in the oxygen-limited area of the steel coil to the outside makes the high-valence oxides (Fe2O3, Fe3O4) transform into low-valence oxides (FeO), and the eutectoid reaction of FeO generates the eutectoid structure of Fe3O4 / Fe. In addition, the "O" in the iron oxide scale layer in the oxygen-limited area of the steel coil can continue to diffuse to the steel substrate, and the grain boundary diffusion coefficient of O is several tens of times that of the bulk diffusion coefficient. In the case where the oxygen partial pressure is not enough to form iron oxide, O combines with elements (Si, Mn, Cr elements) in the hot forming steel whose standard free energy of oxide formation is lower than that of Fe to form grain boundary oxides, resulting in grain boundary oxidation. The steel coil end face position is fully oxygenated, and the three-layer iron oxide scale structure continues to grow and thicken. Therefore, along the width direction of the steel strip, the surface layer of the steel strip will form an iron oxide scale structure as shown in the accompanying drawings: layered Fe2O3+ layered Fe3O4+ mixed structure layer (eutectoid Fe3O4 / Fe+ Fe3O4 precipitation+ residual FeO) at the edge, and mixed structure layer (eutectoid Fe3O4 / Fe+ Fe3O4 precipitation+ residual FeO)+ grain boundary oxidation layer at the middle. Figure 2

[0005] Due to the difference in tensile strength and reaction speed with acid between different iron oxide scale phases, this difference in width direction of the iron oxide scale structure will lead to differences in pickling speed and pickling color difference: iron oxide scale containing more Fe2O3 and Fe3O4 is difficult to pickle, while iron oxide scale containing more FeO is easy to pickle, so that the 40-100mm wide edge of the steel strip appears bright white due to the absence of grain boundary oxidation, while the middle of the steel strip has grain boundary oxidation, and after the removal of the iron oxide scale by pickling, the grain boundary oxides also erode, forming grain boundary gullies, which appear dark in macroscopic vision. The surface darkness is related to the depth and width of the grain boundary gullies. The deeper and narrower the grain boundary gullies, the darker the color. SUMMARY

[0006] The purpose of the present application is to provide a method for controlling the color difference of the pickled surface of hot rolled hot forming steel, which can reduce the width of the whitening area at the edge of the pickled surface of hot rolled hot forming steel, and reduce the whiteness difference between the edge and the middle.

[0007] The present application is implemented as follows:

[0008] ​The application discloses a pickling surface color difference control method for hot-rolled hot-formed steel, which is based on a thin slab short process production and comprises the following steps of: molten iron desulfurization, converter smelting, refining, thin slab continuous casting, soaking, finish rolling, laminar cooling, coiling, cooling, skin passing, pickling and oiling.

[0009] The pickling surface color difference control method for hot-rolled hot-formed steel comprises the following steps of:

[0010] S1: reducing the crown of the strip in the finish rolling stage so as to reduce the structural and grain boundary oxidation difference between the edge and the middle of the strip;

[0011] S2: destroying the integrity of the oxide scale structure in the skin passing stage to provide an artificial pickling core for the pickling process;

[0012] S3: in the pickling stage, corresponding pickling schemes are selected according to the equipment conditions of the pickling unit process section:

[0013] (I) when the pickling section of the pickling unit process section is composed of 2-3 pickling tanks in series, and the total length of the pickling section is 90-100 m, the corresponding pickling scheme is as follows: hydrochloric acid solution is used as the pickling medium, the temperature of the pickling tank is 75-90 DEG C; the strip passes through the pickling medium, and the movement direction of the strip is opposite to that of the pickling medium; along the movement direction of the strip, the concentration of the hydrochloric acid solution in the 2-3 pickling tanks is gradually increased, the concentration of the hydrochloric acid solution in the first pickling tank is greater than or equal to 50 g / l, and the concentration of the pickling medium in the last pickling tank is 180-200 g / l; the pickling speed is 120-150 m / min, and the total pickling time is 36-50 s;

[0014] (II) when the pickling section of the pickling unit process section is composed of 3-4 pickling tanks in series, and the total length of the pickling section is 90-120 m, the corresponding pickling scheme is as follows: hydrochloric acid solution is used as the pickling medium, and a pickling inhibitor is added into the pickling medium, the temperature of the pickling tank is 75-90 DEG C; the strip passes through the pickling medium, and the movement direction of the strip is opposite to that of the pickling medium; along the movement direction of the strip, the concentration of the hydrochloric acid solution in the 3-4 pickling tanks is gradually increased, the concentration of the hydrochloric acid solution in the first pickling tank is greater than or equal to 40 g / l, and the concentration of the pickling medium in the last pickling tank is 160-180 g / l; the pickling speed is 80-120 m / min, and the total pickling time is 45-90 s;

[0015] (III) when the pickling section of the pickling unit process section is composed of 5-7 pickling tanks in series, and the total length of the pickling section is 180-200 m, the corresponding pickling scheme is: using hydrochloric acid solution as the pickling medium, the temperature of the pickling tank is 80-90 DEG C; the strip steel passes through the pickling medium, and the movement direction of the strip steel is opposite to the movement direction of the pickling medium, along the movement direction of the strip steel, the concentration of the hydrochloric acid solution in the 5-7 pickling tanks increases in turn, the concentration of the hydrochloric acid solution in the first pickling tank is >= 40 g / l, the concentration of the hydrochloric acid solution in the middle pickling tank is >= 120 g / l, and the concentration of the pickling medium in the last pickling tank is 180-200 g / l; the pickling speed is 60-90 m / min, and the total pickling time is 120-150 s.

[0016] In the step S1, the crown C of the strip steel in the finishing stage is 40 <= 30 mu m.

[0017] In the step S2, the flattening force of the flattening machine is 180-200 tons, the flattening machine adopts negative bending of the work roll, and the bending force of the work roll is 30-50 tons; the flattening opening tension of the uncoiler is 50-60 KN, and the coiling tension of the coiler is 100-120 KN.

[0018] In the step S3, the mass of the pickling inhibitor accounts for 0.8-1% of the mass of the pickling medium.

[0019] In the step S3, the pickling inhibitor is a mixture of hexamethylene tetramine, propargyl alcohol and water, and the mass ratio of hexamethylene tetramine, propargyl alcohol and water is 25:5:70.

[0020] In the step S3, the strip steel is subjected to tension leveling before pickling, and the tension leveling elongation is 1.0-1.2%.

[0021] The thickness of the hot-rolled hot-formed steel is 1.0-2.5 mm.

[0022] The chemical composition of the hot-rolled hot-formed steel is: according to mass percentage, C: 0.20-0.25%, Si: 0.15-0.35%, Mn: 1.10-1.50%, P <= 0.008%, S <= 0.006%, Cr: 0.15-0.30%, B: 0.002-0.005%, Ti: 0.02-0.05%, Als: 0.02-0.06%, N <= 0.006%, and the rest is Fe and inevitable impurities.

[0023] The hot-rolled hot-formed steel produced by the pickling surface color difference control method for hot-rolled hot-formed steel has a pickling surface whiteness value >= 68%, and the whiteness value of the edge of the strip steel - the whiteness value of the middle of the strip steel <= 6%.

[0024] Compared with the prior art, the present application has the following beneficial effects:

[0025] 1、The present application controls the convexity of the strip steel in the finishing stage 40 ≤30μm, the area of the strip steel edge contacting with air is reduced, the penetration distance of air from the end surface of the steel coil to the inside is shortened, thus the oxide scale structure and the grain boundary oxidation difference between the edge and the middle of the strip steel due to the oxygen supply difference are reduced, and the whitening area of the pickling surface of the edge is narrowed.

[0026] 2、The present application completely destroys the oxide scale structure in the tempering stage, generates a large number of transverse cracks, provides a large number of artificial pickling nuclei for the pickling process, and effectively improves the pickling speed; in addition, by adopting negative bending of the work roll, the damage degree of the oxide scale of the edge is increased, so that the pickling speed of the oxide scale of the strip steel in the width direction can be consistent under the condition of different thickness and structure, and different degrees of erosion to the matrix during pickling are avoided to cause color difference and affect the whiteness uniformity.

[0027] 3、The present application controls the pickling process in the pickling stage, sets the corresponding pickling scheme according to the equipment conditions of different pickling unit process sections, has high adaptability, wide application range, and makes the surface whiteness value after pickling ≥68%, the whiteness value of the edge of the strip steel-the whiteness value of the middle of the strip steel ≤6%, and improves the whiteness uniformity of the pickling surface.

[0028] The present application can effectively reduce the width of the whitening area of the pickling surface of the hot-rolled hot-formed steel and reduce the whiteness difference between the edge and the middle of the strip steel, and improve the whiteness uniformity of the pickling surface by reducing the convexity of the strip steel in the finishing stage, destroying the oxide scale structure in the tempering stage, and controlling different pickling unit processes in the pickling stage. BRIEF DESCRIPTION OF DRAWINGS

[0029] Figure 1 is a cross-sectional view of a hot-rolled hot-formed steel coil after coiling;

[0030] Figure 2 is a cross-sectional surface oxide scale structure diagram of the hot-rolled hot-formed steel;

[0031] Figure 3 is a flowchart of the pickling surface color difference control method for the hot-rolled hot-formed steel according to the present application;

[0032] Figure 4 is a corrosion process schematic diagram of the surface grains and grain boundaries in the post-pickling stage P0 of the hot-rolled hot-formed steel (middle of the strip steel);

[0033] Figure 5 is a corrosion process schematic diagram of the surface grains and grain boundaries in the post-pickling stage P1 of the hot-rolled hot-formed steel (middle of the strip steel);

[0034] Figure 6 is a schematic diagram of the corrosion process of surface grains and grain boundaries in the stage P2 after pickling of hot-rolled hot-formed steel (middle of the strip);

[0035] Figure 7 is a schematic diagram of the corrosion process of surface grains and grain boundaries in the stage P3 after pickling of hot-rolled hot-formed steel (middle of the strip);

[0036] Figure 8 is a schematic diagram of the corrosion process of surface grains and grain boundaries in the stage P3+ after pickling of hot-rolled hot-formed steel (middle of the strip).

[0037] In the figure, 1 is a coil, 11 is an edge gap, 2 is a steel base, 21 is an oxidized grain boundary, 22 is an oxide scale structure, 23 is an eroded grain boundary, and 24 is a steel base grain. DETAILED DESCRIPTION

[0038] The present application will be further described below in conjunction with the accompanying drawings and specific embodiments.

[0039] Please refer to the accompanying drawings Figure 3 A pickling surface color difference control method for hot-rolled hot-formed steel is based on thin slab short process production, and the production process of the short process hot-rolled hot-formed steel comprises: hot metal desulphurization, converter smelting, refining, thin slab continuous casting, soaking, finish rolling, laminar cooling, coiling, cooling, skin passing, pickling and oiling. In the production process, the processes of hot metal desulphurization, converter smelting, refining, thin slab continuous casting, soaking, laminar cooling, coiling, cooling and oiling all adopt conventional processes, which will not be described here, and the present application only improves the finish rolling stage, the skin passing stage and the pickling stage of the short process.

[0040] The pickling surface color difference control method for hot-rolled hot-formed steel comprises:

[0041] S1: reducing the crown of the strip in the finish rolling stage to reduce the difference in the oxidation of the oxide scale structure and the grain boundary between the edge and the middle of the strip. The finish rolling stage can adopt a 7-stand finish rolling mill.

[0042] The crown C of the strip in the finish rolling stage is 40 ≤ 30 μm. By controlling the crown of the strip, the end face gap of the coil is reduced, the layers of the coil are closer, the area of the strip edge in contact with air is reduced, the penetration distance of air from the end face of the coil is shortened, and thus the difference in the oxidation of the oxide scale structure and the grain boundary between the edge and the middle of the strip due to the difference in oxygen supply is reduced, so that the whitish area of the pickling surface at the edge is narrowed.

[0043] S2: destroying the integrity of the oxide scale structure in the skin passing stage to provide artificial pickling nuclei for the pickling process.

[0044] In the flattening stage, the hot formed steel cooled to room temperature after coiling is flattened, the strip steel passes through uncoiler, deep bending roller, straightener, four-roll flattening machine and coiler in turn, in the flattening stage, the flattening force of the flattening machine is 180-200 tons, the flattening machine adopts negative bending of work roller, and the bending force of the work roller is 30-50 tons; the flattening uncoiling tension of the uncoiler is 50-60KN, and the coiling tension of the coiler is 100-120KN.

[0045] The larger flattening force and flattening uncoiling tension and coiling tension can make the structure of the iron oxide scale be damaged under the combined action of tensile stress and compressive stress, form a large number of transverse cracks, and provide a large number of artificial pickling nuclei for the pickling process, so as to improve the pickling speed.

[0046] The pickling of the scale-free crack is a nucleation and growth process, and there is an incubation period of slow pickling reaction, which is called "initial pickling time", that is, the period of pickling nucleus formation. The scale breaking makes the scale crack, and the density and size of the crack increase with the increase of the elongation of the scale, which will play the role of artificial pickling nucleus in pickling. These cracks in the iron oxide scale can make the acid easily reach the steel base without nucleation, so that the incubation period of pickling (initial pickling time) is significantly shortened, and for some cases with larger elongation of the scale, the incubation period can even be completely eliminated.

[0047] Because the edge part of the strip steel is slightly thicker than the middle part, there are more difficult-to-pickling iron oxide scales (i.e. Fe2O3), by negative bending of the work roller, the bending force of the work roller is 30-50 tons, the pressure of the edge part of the strip steel is increased, so that the damage of the structure of the edge part of the scale is increased.

[0048] S3: In the pickling stage, the corresponding pickling scheme is selected according to the equipment conditions of the process section of the pickling unit:

[0049] (I) When the pickling section of the pickling unit process section is composed of 2-3 pickling tanks in series, and the total length of the pickling section is 90-100m, the corresponding pickling scheme is: using hydrochloric acid solution as the pickling medium, the temperature of the pickling tank is 75-90℃; the strip steel passes through the pickling medium, and the movement direction of the strip steel is opposite to that of the pickling medium, along the movement direction of the strip steel, the concentration of the pickling medium in the 2-3 pickling tanks increases in turn, and the concentration of the hydrochloric acid solution in the first pickling tank is ≥50g / l, and the concentration of the pickling medium in the last pickling tank is 180-200g / l; the pickling speed is 120-150m / min, and the total pickling time is 36-50s.

[0050] (II) When the pickling section of the pickling unit process section is composed of 3-4 pickling tanks in series, and the total length of the pickling section is 90-120 m, the corresponding pickling scheme is: using hydrochloric acid solution as the pickling medium, and adding a pickling inhibitor in the pickling medium, the temperature of the pickling tank is 75-90℃, the strip steel passes through the pickling medium, and the movement direction of the strip steel is opposite to that of the pickling medium; along the movement direction of the strip steel, the concentration of the pickling medium in the 3-4 pickling tanks increases in turn, the concentration of the hydrochloric acid solution in the first pickling tank is ≥40 g / l, and the concentration of the hydrochloric acid solution in the last pickling tank is 160-180 g / l; the pickling speed is 80-120 m / min, and the total pickling time is 45-90 s.

[0051] The mass of the pickling inhibitor accounts for 0.8-1% of the mass of the pickling medium.

[0052] The pickling inhibitor is a mixture of hexamethylenetetramine, propargyl alcohol and water, and the ratio of hexamethylenetetramine, propargyl alcohol and water is 25:5:70 by mass percentage. The pickling inhibitor can select other components that can form a film on the surface of the strip steel and prevent the corrosion of the strip steel substrate according to the actual production needs, which will not be described here.

[0053] (III) When the pickling section of the pickling unit process section is composed of 5-7 pickling tanks in series, and the total length of the pickling section is 180-200 m, the corresponding pickling scheme is: using hydrochloric acid solution as the pickling medium, the temperature of the pickling tank is 80-90℃; the strip steel passes through the pickling medium, and the movement direction of the strip steel is opposite to that of the pickling medium, along the movement direction of the strip steel, the concentration of the pickling medium in the 5-7 pickling tanks increases in turn, the concentration of the hydrochloric acid solution in the first pickling tank is ≥40 g / l, the concentration of the hydrochloric acid solution in the middle pickling tank is ≥120 g / l, and the concentration of the hydrochloric acid solution in the last pickling tank is 180-200 g / l; the pickling speed is 60-90 m / min, and the total pickling time is 120-150 s.

[0054] In the pickling stage, the strip steel is tension leveled before pickling, and the tension leveling elongation is 1.0-1.2%, which can further damage the structure of the oxide scale and is beneficial to its peeling in the pickling process.

[0055] The other process flow of hot rolled hot forming steel production adopts a short process conventional production process, which will not be described here.

[0056] The surface whiteness value of the hot rolled hot forming pickling steel is related to the depth and width of the gully formed by the surface layer grain boundary corrosion, and the corrosion process of the surface grain and grain boundary is divided into four stages:

[0057] Stage P0: The structure of the oxide scale is just finished pickling, the oxidized grain boundary 21 has not been eroded, as shown in Figure 1. Figure 4As shown, at this time, the whiteness value of the middle part of the strip is equivalent to that of the edge part of the strip, or the whiteness value of the middle part of the strip is slightly lower than that of the edge part of the strip. Through the pickling scheme (II), the adsorption film is formed on the surface of the strip by using the molecular adsorption characteristics of the pickling inhibitor, which effectively prevents the electrochemical reaction of the acid liquid with the surface of the strip and greatly reduces the corrosion of the acid liquid to the substrate of the strip. The pickling surface of the pickling scheme (II) is in stage P0.

[0058] Stage P1: the acid liquid slightly erodes the oxidized grain boundaries. The eroded grain boundaries 23 are as shown in Fig. 2b. Figure 5 As shown, at this time, the whiteness value of the middle part of the strip is slightly lower than that of the edge part of the strip. Through the pickling scheme (I), the structure of the iron oxide scale on the surface of the strip is quickly dissolved in the pickling section, and after pickling, the strip enters the rinsing section, and the grain boundaries are only slightly eroded. The pickling surface of the pickling scheme (I) is in stage P1.

[0059] Stage P2: the acid liquid continues to erode the oxidized grain boundaries. The eroded grain boundaries 23 are as shown in Fig. 2c. Figure 6 As shown, at this time, the whiteness value of the middle part of the strip is significantly lower than that of the edge part of the strip. The pickling surface of the hot-rolled hot-formed steel produced by the short process of the prior art is in stage P2.

[0060] Stage P3 and P3+: the acid liquid continues to erode the grain boundaries and dissolve the grains. The surface grain of the oxidized steel substrate grain 24 is dissolved into smaller islands (i.e., stage P3), and the eroded grain boundaries 23 are as shown in Fig. 2d. Figure 7 As shown, or the surface grain of the oxidized steel substrate grain 24 is completely dissolved (i.e., stage P3+), as shown in Fig. 2e. Figure 8 As shown, at this time, the whiteness value of the middle part of the strip is equivalent to that of the edge part of the strip. Through the pickling scheme (III), the surface grain that has been oxidized in the grain boundaries is completely dissolved or mostly dissolved, which greatly increases the reflective area of the surface layer. The pickling surface of the pickling scheme (III) is in stage P3 or stage P3+.

[0061] The thickness of the hot-rolled hot-formed steel is 1.0-2.5 mm.

[0062] The chemical composition of the hot-rolled hot-formed steel is as follows: in terms of mass percentage, C: 0.20-0.25%, Si: 0.15-0.35%, Mn: 1.10-1.50%, P≤0.008%, S≤0.006%, Cr: 0.15-0.30%, B: 0.002-0.005%, Ti: 0.02-0.05%, Als: 0.02-0.06%, N≤0.006%, and the balance is Fe and unavoidable impurities.

[0063] The pickling surface whiteness value of the hot-rolled hot-formed steel produced by the pickling surface color difference control method for hot-rolled hot-formed steel is greater than or equal to 68%, and the whiteness value of the strip steel edge is less than or equal to 6% than the whiteness value of the strip steel center.

[0064] Embodiments 1-3:

[0065] Embodiments 1-3 are based on the production of a 1500MPa grade thin-gauge hot-rolled hot-formed steel HF1500 by a short process, and the short process production process includes: hot metal desulphurization, converter smelting, refining, thin slab continuous casting, soaking, 7-stand finish rolling, laminar cooling, coiling, cooling, skin pass, pickling, and oiling. The chemical composition of the hot-rolled hot-formed steel HF1500 is: by mass percent, C: 0.22%, Si: 0.25%, Mn: 1.25%, P≤0.008%, S≤0.006%, Cr: 0.25%, B: 0.0035%, Ti: 0.03%, Als: 0.03%, N≤0.006%, and the balance is Fe and unavoidable impurities.

[0066] The hot metal desulphurization, converter smelting, refining, thin slab continuous casting, soaking, laminar cooling, coiling, cooling, and oiling processes all use conventional processes, which will not be described here, and embodiments 1-3 only improve the finish rolling stage, the skin pass stage, and the pickling stage of the short process.

[0067] In the 7-stand finish rolling stage, the strip steel crown C 40 ≤30μm, so as to reduce the difference in scale structure and grain boundary oxidation between the edge and the center of the strip steel.

[0068] S2: In the skin pass stage, the integrity of the scale structure is destroyed to provide a hot pickling core for the pickling process. The process parameters of the finish rolling stage and the skin pass stage of embodiments 1-3 are shown in Table 1.

[0069] Table 1: Process parameters of the finish rolling stage and the skin pass stage of embodiments 1-3 and comparative example 1

[0070]

[0071] Note: Comparative example 1 is a HF1500 hot-rolled hot-formed steel produced by a traditional short process.

[0072] S3: In the pickling stage, the strip steel is straightened before pickling, and the corresponding pickling scheme is selected according to the equipment conditions of the pickling unit process section. The process parameters of the pickling stage of embodiments 1-3 are shown in Table 2.

[0073] Embodiment 1 uses pickling scheme (I), and the pickling section of the pickling unit process section is composed of three pickling tanks connected in series, which are marked as 1#, 2#, and 3# in turn, and the total length of the pickling section is 100m.

[0074] Example 2 adopts pickling scheme (II), the pickling section of the pickling unit process section is composed of three pickling tanks in series, the three pickling tanks are sequentially marked as 1#, 2# and 3#, and the total length of the pickling section is 100 m.

[0075] Hydrochloric acid solution is used as the pickling medium during pickling, and a pickling inhibitor is added in the pickling medium, the mass of the pickling inhibitor accounts for 0.8-1% of the mass of the pickling medium. The pickling inhibitor is a mixture of hexamethylenetetramine, propargyl alcohol and water, and the mass percentage of the mixture is 25:5:70.

[0076] Example 3 adopts pickling scheme (III), the pickling section of the pickling unit process section is composed of five pickling tanks in series, the three pickling tanks are sequentially marked as 1#, 2#, 3#, 4# and 5#, and the total length of the pickling section is 200 m.

[0077] Table 2 lists the pickling stage process parameters of examples 1-3 and comparative example 1

[0078]

[0079] As shown in Table 2, by controlling the process of the flattening stage and the tension leveling adjustment of the pickling stage, the pickling speed can be obviously improved.

[0080] The pickling surface whiteness values of examples 1-3 and comparative example 1 are measured by using a photoelectric whiteness meter, as shown in Table 3.

[0081] Table 3 lists the whiteness values of examples 1-3 and comparative example 1

[0082]

[0083]

[0084] As shown in Table 3, by controlling the strip crown C 40 of the finishing stage, the width of the whitening area of the strip edge after pickling can be obviously narrowed or even eliminated. By controlling different pickling schemes in the pickling stage, the uniformity of the central whiteness value and the edge whiteness value of the pickling surface of the strip is effectively improved, and the difference between the edge whiteness value and the central whiteness value of the strip is smaller after adopting pickling scheme III and pickling scheme II, which is almost difficult to distinguish by naked eyes.

[0085] The above is only a preferred embodiment of the present application, and is not used to limit the protection scope of the present application, therefore, any modification, equivalent replacement, improvement, etc. made within the spirit and principle of the present application shall be included in the protection scope of the present application.

Claims

1. A method for controlling pickling surface color difference of hot-rolled hot-formed steel, characterized by: The pickling surface color difference control method for hot-rolled hot-formed steel is realized based on a thin slab short process production, and the production process of the hot-rolled hot-formed steel comprises: molten iron desulfurization, converter smelting, refining, thin slab continuous casting, soaking, finish rolling, laminar cooling, coiling, cooling, skin pass, pickling and oiling. The pickling surface color difference control method for hot-rolled hot-formed steel comprises: S1: reducing the crown of the strip at the finish rolling stage, so as to reduce the structure and grain boundary oxidation difference between the edge and the middle of the strip; S2: destroying the integrity of the oxide scale structure at the skin pass stage to provide artificial pickling nuclei for the pickling process; S3: at the pickling stage, a corresponding pickling scheme is selected according to the equipment conditions of the pickling unit process section: (I) when the pickling section of the pickling unit process section is composed of 2-3 pickling tanks in series, and the total length of the pickling section is 90-100 m, the corresponding pickling scheme is: using hydrochloric acid solution as the pickling medium, the temperature of the pickling tank is 75-90 DEG C; the strip passes through the pickling medium, and the movement direction of the strip is opposite to that of the pickling medium; along the movement direction of the strip, the concentration of the hydrochloric acid solution in the 2-3 pickling tanks increases in turn, and the concentration of the hydrochloric acid solution in the first pickling tank is greater than or equal to 50 g / l, and the concentration of the pickling medium in the last pickling tank is 180-200 g / l; the pickling speed is 120-150 m / min, and the total pickling time is 36-50 s; (II) when the pickling section of the pickling unit process section is composed of 3-4 pickling tanks in series, and the total length of the pickling section is 90-120 m, the corresponding pickling scheme is: using hydrochloric acid solution as the pickling medium, and adding a pickling inhibitor in the pickling medium, the temperature of the pickling tank is 75-90 DEG C; the strip passes through the pickling medium, and the movement direction of the strip is opposite to that of the pickling medium; along the movement direction of the strip, the concentration of the hydrochloric acid solution in the 3-4 pickling tanks increases in turn, the concentration of the hydrochloric acid solution in the first pickling tank is greater than or equal to 40 g / l, and the concentration of the pickling medium in the last pickling tank is 160-180 g / l; the pickling speed is 80-120 m / min, and the total pickling time is 45-90 s; (III) when the pickling section of the pickling unit process section is composed of 5-7 pickling tanks in series, and the total length of the pickling section is 180-200 m, the corresponding pickling scheme is: using hydrochloric acid solution as the pickling medium, the temperature of the pickling tank is 80-90 DEG C; the strip passes through the pickling medium, and the movement direction of the strip is opposite to that of the pickling medium; along the movement direction of the strip, the concentration of the hydrochloric acid solution in the 5-7 pickling tanks increases in turn, the concentration of the hydrochloric acid solution in the first pickling tank is greater than or equal to 40 g / l, the concentration of the hydrochloric acid solution in the middle pickling tank is greater than or equal to 120 g / l, the concentration of the pickling medium in the last pickling tank is 180-200 g / l, the pickling speed is 60-90 m / min, and the total pickling time is 120-150 s.

2. The pickling surface color difference control method for hot-rolled hot-formed steel according to claim 1, characterized by: In the step S1, the crown C of the strip in the finishing stage 40 ≤ 30 μm.

3. The pickling surface color difference control method for hot-rolled hot-formed steel according to claim 1, characterized by: The flattening force of the flattening machine is 180-200 tons, the flattening machine adopts negative bending of work rolls, and the bending force of the work rolls is 30-50 tons; the flattening opening tension of the uncoiler is 50-60 KN, and the coiling tension of the coiler is 100-120 KN.

4. The pickling surface color difference control method for hot-rolled hot-formed steel according to claim 1, characterized by: The mass of the pickling inhibitor accounts for 0.8-1% of the mass of the pickling medium.

5. The pickling surface color difference control method for hot-rolled hot-formed steel according to claim 1 or 4, characterized by: The pickling inhibitor is a mixture of hexamethylene tetramine, propargyl alcohol and water, and the mass ratio of the hexamethylene tetramine, the propargyl alcohol and the water is 25:5:

70.

6. The pickling surface color difference control method for hot-rolled hot-formed steel sheet according to claim 1, characterized by: The strip steel is subjected to tension leveling before pickling, and the elongation of the tension leveling is 1.0-1.2%.

7. The pickling surface color difference control method for hot-rolled hot-formed steel sheet according to claim 1, characterized by: The thickness of the hot-rolled hot-formed steel is 1.0-2.5 mm.

8. The pickling surface color difference control method for hot-rolled hot-formed steel according to claim 1 or 7, characterized by: The chemical composition of the hot-rolled hot-formed steel is as follows: the mass percentage of C is 0.20-0.25%, the mass percentage of Si is 0.15-0.35%, the mass percentage of Mn is 1.10-1.50%, the mass percentage of P is less than or equal to 0.008%, the mass percentage of S is less than or equal to 0.006%, the mass percentage of Cr is 0.15-0.30%, the mass percentage of B is 0.002-0.005%, the mass percentage of Ti is 0.02-0.05%, the mass percentage of Als is 0.02-0.06%, the mass percentage of N is less than or equal to 0.006%, and the rest is Fe and inevitable impurities.

9. The pickling surface color difference control method for hot-rolled hot-formed steel sheet according to claim 1, characterized by: The hot-rolled hot-formed steel produced by the pickling surface color difference control method for hot-rolled hot-formed steel has a pickling surface whiteness value of greater than or equal to 68%, and the whiteness value of the edge of the strip steel is less than or equal to 6% of the whiteness value of the middle of the strip steel.

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