Scale control method suitable for hot rolling SPHC

Abstract

The invention relates to the technical field of steel and iron, and provides an oxide scale control method suitable for hot rolling SPHC, which comprises the following steps: carrying out continuous casting, casting blank heating, furnace rear descaling, rough rolling, finish rolling, laminar cooling, curling and curling cooling on molten steel to obtain a hot rolling SPHC steel coil; and a gas flow meter is adopted, and when the casting blank is heated, the fuel gas is CO, and the air-fuel ratio is 1.05-1.3. By means of the technical scheme, the problems that in the related technology, the hot-rolled SPHC steel coil oxide scale is thick, and the surface quality is poor after acid pickling are solved.

Description

Technical Field

[0001] The invention relates to the technical field of steel, and in particular to an oxide scale control method suitable for hot-rolled SPHC. Background Art

[0002] SPHC steel is a common hot-rolled carbon structural steel, which is produced by hot rolling process, rolling the steel billet into the required steel coil at high temperature. It can be pickled to remove the oxide scale and then cold rolled. The products produced can be used in the automotive, home appliances, door industry, cabinets, barrel making, office appliances, daily hardware and other industries. When used, it has very high requirements for surface quality.

[0003] The surface defects of cold-rolled steel coils are highly hereditary and are basically caused by the surface defects of hot-rolled steel coils, especially the oxide scale defects. The iron scale pressed into the surface of hot-rolled steel coils can be divided into four categories, namely primary oxide scale, secondary oxide scale, tertiary oxide scale and quaternary oxide scale. Therefore, hot-rolled steel coils will generate oxide scale throughout the production process. We cannot only focus on a certain type of oxide scale, but must globally control the oxide scale generated during the entire production process.

[0004] At present, the existing technologies all control a certain process in the production process of hot-rolled steel coils, resulting in poor control effects. For example, the invention patent with publication number CN118477897A discloses a method for controlling iron scale, which does not consider the effects of roller life and laminar cooling water quality on iron scale; the invention patent with publication number CN118904947A discloses a method for controlling iron scale, which does not consider the effects of heating furnace air-fuel ratio, roller life, and laminar cooling water quality on iron scale. Summary of the invention

[0005] The invention provides a method for controlling iron oxide scale of hot-rolled SPHC, which solves the problem in the related art that the iron oxide scale of hot-rolled SPHC steel coil is thick and the surface quality is poor after pickling.

[0006] The technical solution of the present invention is as follows: The present invention provides a method for controlling iron oxide scale suitable for hot-rolled SPHC, comprising the following steps: obtaining a hot-rolled SPHC steel coil after continuous casting, heating of ingots, descaling after furnace, rough rolling, finishing rolling, laminar cooling, coiling and coil cooling of molten steel; According to the gas flow meter, when the ingot is heated, the fuel gas is CO and the air-fuel ratio is 1.05-1.3.

[0007] As a further technical solution, the fuel gas is a mixture of CO and H2; The volume ratio of CO and H2 is 10:1~3.

[0008] In the present invention, when the fuel gas used for heating the ingot is a mixed atmosphere of CO and H2, the thickness of the iron oxide scale can be further reduced by adjusting the type of fuel gas.

[0009] As a further technical solution, during the continuous casting, the liquid level fluctuation is ≤±3mm.

[0010] In the present invention, during the continuous casting process, the liquid level fluctuation is controlled within the range of ≤±3 mm, which helps to improve the quality of the ingot and reduce the generation of slag inclusions on the surface of the ingot, thereby improving the overall quality of the hot-rolled SPHC steel coil.

[0011] As a further technical solution, when the ingot is heated, the temperature is 1190~1220℃.

[0012] In the present invention, during the heating process of the ingot, the heating temperature is controlled at 1190-1220° C., which can ensure uniform heating of the ingot and effectively avoid the occurrence of local overheating or insufficient heating.

[0013] As a further technical solution, during the rough rolling, the starting rolling temperature is 1100-1150°C, the final rolling temperature is 1060-1080°C, and the cumulative reduction rate of the rough rolling is 60%-85%.

[0014] In the present invention, by optimizing the rough rolling process parameters, it is ensured that the recrystallization in the rolling process is fully and evenly carried out, thus making preparations for the subsequent finishing rolling.

[0015] As a further technical solution, during the finish rolling, the starting rolling temperature is 950-1050°C, the final rolling temperature is 850-950°C, the cumulative reduction rate of the finish rolling is 50%-70%, and the roll life is 600-700km.

[0016] In the present invention, by optimizing the finishing rolling process parameters, the tertiary iron scale generated by the SPHC steel during the finishing rolling process can be reduced, and the influence of the oxide film shedding of the roller on the surface quality of the steel strip can be reduced.

[0017] As a further technical solution, during the laminar cooling, the Cl of the cooling water - Concentration ≤100mg / L, pH value of cooling water is 7~8.

[0018] In the present invention, by controlling the chemical properties of cooling water during laminar cooling, defects such as oxidation spots and pitting on the product surface caused by water quality problems are avoided.

[0019] As a further technical solution, during the curling, the temperature is 520-620°C.

[0020] In the present invention, the fourth oxide scale occurring during the curling process can be reduced by optimizing the curling temperature.

[0021] As a further technical solution, during the curling cooling, the curling cooling rate is ≥7°C / min.

[0022] In the present invention, by optimizing the coiling temperature, the iron oxide scale remaining on the surface of the finished product after cooling can have a more reasonable structure and be more easily pickled.

[0023] As a further technical solution, when 80mg / L≤Cl in cooling water - When the concentration is ≤100 mg / L, the curling cooling rate is ≥10°C / min; When the Cl in cooling water - When the concentration is less than 80 mg / L, 7°C / min≤the curling cooling rate is less than 10°C / min.

[0024] In the present invention, the inventors found that by treating the Cl - The thickness of the oxide scale can be further reduced by synergistically optimizing the concentration and curling cooling rate.

[0025] As a further technical solution, the hot-rolled SPHC steel coil is composed of the following components in weight percentage: C 0.01%~0.1%, Si 0.01%~0.02%, Mn 0.3%~0.5%, Al 0.015%~0.02%, P ≤0.02%, S ≤0.02%, and the rest is Fe and other inevitable impurities.

[0026] The working principle and beneficial effects of the present invention are: In the present invention, by regulating the controlled rolling and controlled cooling process of the entire production line, especially the air-fuel ratio during heating of the ingot, it is ensured that the heating is in a weakly oxidizing atmosphere, so that the amount of iron oxide scale generated is small, the structure is reasonable and it is easy to be removed by pickling, the thickness of the iron oxide scale is reduced, and the surface quality of the hot-rolled SPHC steel coil after pickling is improved. BRIEF DESCRIPTION OF THE DRAWINGS

[0027] The present invention will be further described in detail below in conjunction with the accompanying drawings and specific embodiments.

[0028] Figure 1 This is a surface image of the hot-rolled SPHC steel coil after pickling in Example 1 of the present invention; Figure 2 This is a surface image of the hot-rolled SPHC steel coil after pickling in Example 2 of the present invention; Figure 3 This is a surface image of the hot-rolled SPHC steel coil after pickling in Example 3 of the present invention. DETAILED DESCRIPTION

[0029] The following will be combined with the embodiments of the present invention to clearly and completely describe the technical solutions in the embodiments of the present invention. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of the present invention.

[0030] Example 1 A method for controlling iron oxide scale for hot-rolled SPHC steel comprises the following steps: after continuous casting, heating of ingot casting, descaling after furnace, rough rolling, finishing rolling, laminar cooling, coiling and coil cooling, a hot-rolled SPHC steel coil with a thickness of 3.5 mm is obtained; During continuous casting, control the liquid level fluctuation to ≤±3mm; The heating temperature of the ingot is 1200℃, the air-fuel ratio is 1.05 (the gas flow ratio of air to fuel gas is 1.05, and the fuel gas is CO), and a weak oxidizing atmosphere is ensured. The descaling after the furnace is double-pass, and the descaling pressure is 21MPa. During rough rolling, the starting rolling temperature is 1100°C, the final rolling temperature is 1060°C, and the cumulative reduction rate of rough rolling is 60%; During finishing rolling, the starting rolling temperature is 970℃, the final rolling temperature is 870℃, the cumulative reduction rate of finishing rolling is 60%, and the roller life is controlled to be 620km; During laminar cooling, the Cl of cooling water - The concentration is 10 mg / L and the pH value of cooling water is 7.7; During coiling, the temperature is 540°C, the produced steel coils are stored separately without stacking, and the coiling cooling rate is 13°C / min; The hot rolled SPHC steel coil consists of the following components in weight percentage: C 0.01%, Si 0.01%, Mn 0.3%, Al 0.015%, P 0.02%, S 0.02%, and the rest is Fe and other inevitable impurities.

[0031] Example 2 A method for controlling iron oxide scale for hot-rolled SPHC steel comprises the following steps: after continuous casting, heating of ingot casting, descaling after furnace, rough rolling, finishing rolling, laminar cooling, coiling and coil cooling, a hot-rolled SPHC steel coil with a thickness of 3.5 mm is obtained; During continuous casting, control the liquid level fluctuation to ≤±3mm; The heating temperature of the ingot is 1190℃, the air-fuel ratio is 1.2 (the gas flow ratio of air to fuel gas is 1.2, and the fuel gas is CO), to ensure a weak oxidizing atmosphere, and the descaling after the furnace is double-pass, with a descaling pressure of 21MPa; During rough rolling, the starting rolling temperature is 1130°C, the final rolling temperature is 1070°C, and the cumulative reduction rate of rough rolling is 75%; During finishing rolling, the starting rolling temperature is 950℃, the final rolling temperature is 850℃, the cumulative reduction rate of finishing rolling is 50%, and the roller life is controlled to be 700km; During laminar cooling, the Cl of cooling water - The concentration is 100 mg / L and the pH value of cooling water is 7.7; During coiling, the temperature is 540°C, the produced steel coils are stored separately without stacking, and the coiling cooling rate is 7°C / min; The hot rolled SPHC steel coil consists of the following components in weight percentage: C 0.1%, Si 0.02%, Mn 0.5%, Al 0.02%, P 0.015%, S 0.015%, and the rest is Fe and other inevitable impurities.

[0032] Example 3 A method for controlling iron oxide scale for hot-rolled SPHC steel comprises the following steps: after continuous casting, heating of ingot casting, descaling after furnace, rough rolling, finishing rolling, laminar cooling, coiling and coil cooling, a hot-rolled SPHC steel coil with a thickness of 3.5 mm is obtained; During continuous casting, control the liquid level fluctuation to ≤±3mm; The heating temperature of the ingot is 1220℃, the air-fuel ratio is 1.3 (the gas flow ratio of air to fuel gas is 1.3, and the fuel gas is CO), to ensure a weak oxidizing atmosphere, and the descaling after the furnace is double-pass, with a descaling pressure of 21MPa; During rough rolling, the starting rolling temperature is 1150°C, the final rolling temperature is 1080°C, and the cumulative reduction rate of rough rolling is 85%; During finishing rolling, the starting rolling temperature is 1050℃, the final rolling temperature is 950℃, the cumulative reduction rate of finishing rolling is 70%, and the roller life is controlled to be 600km; During laminar cooling, the Cl of cooling water - The concentration is 80 mg / L and the pH value of cooling water is 7.7; When coiling, the temperature is 540℃, the produced steel coils are stored separately without stacking, and the coiling cooling rate is 9℃ / min; The hot rolled SPHC steel coil consists of the following components in weight percentage: C 0.1%, Si 0.02%, Mn 0.5%, Al 0.02%, P 0.015%, S 0.015%, and the rest is Fe and other inevitable impurities.

[0033] Example 4 The only difference between this embodiment and embodiment 3 is that in this embodiment, the fuel gas is a mixed gas of CO and H2, and the volume ratio of CO to H2 is 10:1.

[0034] Example 5 The only difference between this embodiment and embodiment 4 is that, in this embodiment, the volume ratio of CO to H2 is 10:3.

[0035] Example 6 The only difference between this embodiment and embodiment 3 is that in this embodiment, the coiling cooling rate is 10° C. / min.

[0036] Example 7 The only difference between this embodiment and embodiment 3 is that in this embodiment, the coiling cooling rate is 15° C. / min.

[0037] Example 8 The only difference between this embodiment and embodiment 1 is that in this embodiment, the coiling cooling rate is 10° C. / min.

[0038] Example 9 The only difference between this embodiment and embodiment 1 is that in this embodiment, the coiling cooling rate is 7° C. / min.

[0039] Comparative Example 1 The only difference between this comparative example and Example 1 is that in this comparative example, the air-fuel ratio is 1.

[0040] Comparative Example 2 The only difference between this comparative example and Example 1 is that in this comparative example, the air-fuel ratio is 0.8 to ensure a weak reducing atmosphere.

[0041] Comparative Example 3 The only difference between this comparative example and Example 1 is that in this comparative example, the air-fuel ratio is 0.4 to ensure a weak reducing atmosphere.

[0042] Experimental Example 1 The thickness of the oxide scale of the hot-rolled SPHC steel coil cross section in Examples 1 to 9 and Comparative Examples 1 to 3 was observed using a scanning electron microscope (model JCM-5000), and the test was performed every 2 mm for a total of 5 times, and the arithmetic mean of the 5 times was taken as the thickness of the oxide scale. The test results are shown in Table 1 below.

[0043] Table 1 Iron oxide scale thickness

[0044] Comparison between Example 1 and Comparative Examples 1 to 3 shows that the thickness of the iron oxide scale can be significantly reduced by ensuring that the casting is heated in a weakly oxidizing atmosphere.

[0045] The comparison between Example 3 and Example 4-5 shows that when the fuel gas is a mixed atmosphere of CO and H2 during the heating of the ingot, the thickness of the oxide scale can be further reduced. The comparison between Example 3 and Example 6-7, and Example 1 and Example 8-9 shows that by adjusting the Cl -The thickness of the oxide scale can be further reduced by synergistically optimizing the concentration and curling cooling rate.

[0046] Experimental Example 2 The hot-rolled SPHC steel coils in Examples 1 to 9 and Comparative Examples 1 to 3 were pickled in 20% hydrochloric acid for 20 minutes, and then the surface quality was tested in accordance with GB / T 5213-2019 "Cold-rolled low-carbon steel sheets and strips". The test results are shown in Table 2 below. Figure 1 Example 2: The surface of the hot-rolled SPHC steel coil after pickling is shown in FIG. Figure 2 Example 3: The surface of the hot-rolled SPHC steel coil after pickling is shown in FIG. Figure 3 shown.

[0047] Table 2 Surface quality test results

[0048] Comparison between Examples 1 to 9 and Comparative Examples 1 to 3 shows that the control method of the present invention can significantly improve the surface quality of the hot-rolled SPHC steel coil after pickling.

[0049] The above are only preferred embodiments of the present invention and are not intended to limit the present invention. Any modifications, equivalent substitutions, improvements, etc. made within the spirit and principles of the present invention should be included in the protection scope of the present invention.

Claims

1. A method for controlling scale of hot-rolled SPHC, characterized in that: The following steps are involved: After continuous casting, heating of ingots, descaling after furnace, rough rolling, finishing rolling, laminar cooling, coiling and coil cooling, the molten steel is obtained into hot-rolled SPHC steel coil; According to the gas flow meter, when the ingot is heated, the fuel gas is CO and the air-fuel ratio is 1.05-1.

3.

2. The method for controlling iron oxide scale suitable for hot-rolled SPHC according to claim 1, characterized in that: The fuel gas is a mixture of CO and H2; The volume ratio of CO and H2 is 10:1~3.

3. The method for controlling iron oxide scale suitable for hot-rolled SPHC according to claim 1, characterized in that: During the continuous casting, the liquid level fluctuation is ≤±3mm.

4. The method for controlling iron oxide scale suitable for hot-rolled SPHC according to claim 1, characterized in that: When the ingot is heated, the temperature is 1190-1220°C.

5. The method for controlling iron oxide scale suitable for hot-rolled SPHC according to claim 1, characterized in that: During the rough rolling, the starting rolling temperature is 1100-1150° C., the final rolling temperature is 1060-1080° C., and the cumulative reduction rate of the rough rolling is 60%-85%.

6. The method for controlling iron oxide scale suitable for hot-rolled SPHC according to claim 1, characterized in that: During the finish rolling, the starting rolling temperature is 950-1050° C., the final rolling temperature is 850-950° C., the cumulative reduction rate of the finish rolling is 50%-70%, and the roll life is 600-700 km.

7. The method for controlling iron oxide scale suitable for hot-rolled SPHC according to claim 1, characterized in that: During laminar cooling, the Cl of cooling water - Concentration ≤100mg / L, pH value of cooling water is 7~8.

8. The method for controlling iron oxide scale in hot-rolled SPHC according to claim 1, characterized in that: During the curling, the temperature is 520-620°C.

9. The method for controlling iron oxide scale in hot-rolled SPHC according to claim 1, characterized in that: During the curling cooling, the curling cooling rate is ≥7°C / min.

10. The method for controlling iron oxide scale in hot-rolled SPHC according to claim 9, characterized in that: When 80mg / L≤Cl in cooling water - When the concentration is ≤100 mg / L, the curling cooling rate is ≥10°C / min; When the Cl in cooling water - When the concentration is less than 80 mg / L, 7°C / min≤the curling cooling rate is less than 10°C / min.

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