SPA-H strip steel for hot-rolled container and preparation method thereof

Abstract

The present invention belongs to the technical field of SPA-H strip preparation, and specifically relates to a SPA-H strip for hot-rolled containers and a preparation method thereof. The preparation method provided by the present invention comprises the following steps: continuously casting molten steel to obtain a continuously cast slab; the continuously cast slab is subjected to a heating treatment in a heating furnace, heated to 1140-1160°C at a first heating rate, then cooled to 1090-1110°C at a first cooling rate, heated to 1280-1290°C at a first heating rate, and finally cooled to 1250-1260°C at a first cooling rate, and the slab is heated and discharged from the furnace; wherein the ratio of the first heating rate to the first cooling rate is (5-8): 1; the heated slab is subjected to rough rolling and finish rolling in sequence, and laminar cooling, coiling, and flattening are performed after the finish rolling to obtain a SPA-H strip for hot-rolled containers. The preparation method of the present invention can effectively reduce the occurrence of copper brittleness defects in the steel strip. After subsequent treatments such as rough rolling and finish rolling, the obtained steel strip not only greatly reduces the occurrence of copper brittleness, but also has excellent strength and elongation.

Description

Technical Field

[0001] The invention belongs to the technical field of SPA-H strip steel preparation, and in particular relates to a SPA-H strip steel for hot-rolled containers and a preparation method thereof. Background Art

[0002] SPA-H strip steel is a high-weather-resistant rolled steel, which is mainly used to manufacture containers, vehicles, towers, etc. With the development of the container industry, hot-rolled container steel is gradually developing towards high strength, light weight, and thinness. High-strength thin strip steel can replace thick traditional low-strength strip steel, achieving thin-for-thickness, while solving the steel consumption and increasing the added value of strip steel. Therefore, the demand for SPA-H strip steel with specifications of 1.6mm and below has increased.

[0003] In order to increase the corrosion resistance of traditional SPA-H strip steel, a certain amount of copper is generally added to the steel. The addition of copper elements is easy to be enriched and liquefied at the grain boundaries, forming grain boundary cracks on the surface of the ingot. In the subsequent hot rolling process, the grain boundary cracks are further enlarged to form copper brittle defects. In order to suppress the copper brittle defects, a certain amount of nickel elements is generally added to the molten steel, but the cost of nickel is relatively high, which will increase the production cost. Summary of the invention

[0004] Therefore, the technical problem to be solved by the present invention is to overcome the defect that the existing SPA-H strip steel is prone to copper brittle defects, and when adding a high content of nickel elements to suppress the copper brittle defects, the production cost will increase. The present invention adds an appropriate amount of B and a small amount of Ce elements to the strip steel components. The B element is easy to segregate at the austenite grain boundary, thereby suppressing the occurrence of copper brittle defects. At the same time, a small amount of Ce element can effectively refine the dendrite structure. At the same time, in combination with a specific heat treatment process, the occurrence of copper brittle defects is well suppressed without using nickel elements.

[0005] In order to solve the above problems, the scheme of the present invention is as follows:

[0006] A method for preparing SPA-H strip steel for hot-rolled containers comprises the following steps:

[0007] 1) Continuously casting molten steel to obtain a continuously cast slab, wherein the components of the continuously cast slab include, by weight percentage, C: 0.06-0.09%, Si: 0.22-0.4%, Mn: 0.4-0.6%, P: 0.075-0.1%, S: ≤0.015%, Cu: 0.25-0.35%, Cr: 0.3-0.5%, B: 0.001-0.002%, Ce: 0.004-0.006%, and the rest are iron and unavoidable impurities;

[0008] 2) The continuous casting slab is heated in a heating furnace, the slab enters the furnace at a temperature of 840-870°C, and is heated to 1140-1160°C at a first heating rate, and is kept at 1140-1160°C for 30-50s, then is cooled to 1090-1110°C at a first cooling rate, and is kept at 1090-1110°C for 40-60min, then is heated to 1280-1290°C at a first heating rate, and is kept at 1280-1290°C for 30-50s, finally is cooled to 1250-1260°C at a first cooling rate, and is kept at 1250-1260°C for 40-60min, and then is heated to 1250-1260°C at a first cooling rate, and is kept at 1250-1260°C for 40-60min, and then the slab is heated and taken out of the furnace; wherein, the ratio of the first heating rate to the first cooling rate is (5-8):1;

[0009] 3) The heated slab is subjected to rough rolling and finish rolling in sequence, and after the finish rolling, laminar cooling, coiling, and flattening are performed to obtain hot-rolled SPA-H strip steel for containers.

[0010] Preferably, the ratio of the first heating rate to the first cooling rate is (6-8):1.

[0011] Preferably, the first heating rate is 35-45°C / s, and the first cooling rate is 4-7°C / s.

[0012] Preferably, the first heating rate is 40-45°C / s, and the first cooling rate is 5-7°C / s.

[0013] Preferably, the molten steel in step 1) is obtained by pre-desulfurization, converter smelting and LF refining of molten iron.

[0014] Preferably, in step 3), descaling is performed in each rough rolling pass, and the rough rolling outlet temperature is 1120-1130°C.

[0015] Preferably, in step 3), the start temperature of the finishing rolling is 1090-1100° C., the final temperature of the finishing rolling is 920-940° C., and the rolling thickness is 1.5-2.0 mm.

[0016] Preferably, the coiling temperature in step 3) is 640-670°C.

[0017] Preferably, the cooling rate during laminar cooling in step 3) is 40-45°C / s.

[0018] The present invention also provides a SPA-H strip steel for hot-rolled containers, which is prepared by the above-mentioned preparation method.

[0019] The technical solution of the present invention has the following advantages:

[0020] The preparation method of SPA-H strip steel for hot-rolled containers provided by the present invention adopts a continuous casting slab with specific components, Cu is the most important and most commonly used alloy element for improving atmospheric corrosion resistance, and when used in combination with P, Cr, etc., the atmospheric corrosion resistance is better, P is the most effective element for improving atmospheric corrosion resistance, and when Cr is used in combination with Cu and P, weather resistance can be improved, and by adding a specific amount of B and a small amount of Ce element to the continuous casting slab component, the B element is easy to segregate at the austenite grain boundary, thereby inhibiting the generation of copper brittle defects, and at the same time, with a small amount of Ce element, the dendrite structure can be effectively refined, and in addition, with a specific heat treatment process, a four-stage heat treatment process is adopted in the heat treatment process, firstly, the temperature is rapidly increased to 1140-1160°C at a high heating rate, and the temperature is rapidly kept at 1140-1160°C, and then the temperature is increased to 1140-1160°C. The temperature is appropriately lowered to 1090-1110°C at a lower cooling rate, and the temperature is kept at 1090-1110°C for a long time, and then the temperature is quickly raised to 1280-1290°C at a high heating rate, and the temperature is quickly kept at 1280-1290°C, and finally the temperature is appropriately lowered to 1250-1260°C at a lower cooling rate, and the temperature is kept at 1250-1260°C for a long time, during which the ratio of the first heating rate and the first cooling rate is controlled to be (5-8):1. Heating the continuous casting slab through this heat treatment procedure is beneficial to inhibiting the segregation of copper elements in the matrix and the oxide layer, reducing the degree of enrichment at the grain boundaries, and thus effectively reducing the occurrence of copper brittleness defects in the strip. After subsequent rough rolling and fine rolling, the obtained strip not only greatly reduces the occurrence of copper brittleness, but also has excellent strength and elongation.

[0021] In addition, the present invention controls the solid solution amount of crack-sensitive element Cu through a specific heating treatment process to avoid its segregation and precipitation at the grain boundary to cause "copper brittleness", and designs a new type of strip steel with low cost and high surface quality that does not contain Ni element. Through chemical composition design and heating process design, it is ensured that P, Cu and Cr elements in hot-rolled steel can play a role in improving the corrosion resistance, yield strength, tensile strength and elongation of SPA-H strip steel for hot-rolled containers; by reasonably controlling the content of harmful elements such as S, the toughness of the steel is improved, and thin steel can be used instead of thick steel, which can save steel and realize lightweight production of containers. DETAILED DESCRIPTION

[0022] The following examples are provided for further understanding of the present invention, but are not intended to limit the best mode of implementation and do not limit the scope of protection of the present invention.

[0023] The experimental steps or conditions not specified in the following embodiments of the present invention can be implemented according to the conventional experimental steps and conditions used in the existing literature in the field. The reagents or instruments used without specifying the manufacturer are all conventional reagents or instruments that can be purchased commercially.

[0024] Example 1

[0025] This embodiment provides a method for preparing SPA-H strip steel for hot-rolled containers, comprising the following steps:

[0026] 1) Pre-desulfurization of molten iron, LF refining after converter smelting, continuous casting of the obtained molten steel to obtain a continuous casting slab, wherein the components of the continuous casting slab are C: 0.07%, Si: 0.34%, Mn: 0.50%, P: 0.08%, S: 0.008%, Cu: 0.30%, Cr: 0.41%, B: 0.0012%, Ce: 0.0042%, and the rest are iron and unavoidable impurities;

[0027] 2) The continuous casting slab is heated in a heating furnace. The slab enters the furnace at a temperature of 850°C and is heated to 1150°C at a heating rate of 40°C / s and kept at 1150°C for 30s. Then, it is cooled to 1100°C at a cooling rate of 5°C / s and kept at 1100°C for 45min. Then, it is heated to 1290°C at a heating rate of 40°C / s and kept at 1290°C for 30s. Finally, it is cooled to 1260°C at a cooling rate of 5°C / s and kept at 1260°C for 45min. The slab is heated and then taken out of the furnace.

[0028] 3) The heated slab is subjected to rough rolling and finish rolling in sequence, descaling is performed in each pass of rough rolling, the outlet temperature of rough rolling is 1120°C, the start rolling temperature of finish rolling is 1095°C, the final rolling temperature of finish rolling is 930°C, the rolling thickness is 1.5 mm, and laminar cooling is performed after finish rolling. The slab is cooled to 660°C at a cooling rate of 40°C / s for coiling, and finally flattened to obtain SPA-H strip for hot-rolled container.

[0029] Example 2

[0030] This embodiment provides a method for preparing SPA-H strip steel for hot-rolled containers, comprising the following steps:

[0031] 1) Pre-desulfurization of molten iron, LF refining after converter smelting, continuous casting of the obtained molten steel to obtain a continuous casting slab, wherein the components of the continuous casting slab are C: 0.07%, Si: 0.34%, Mn: 0.50%, P: 0.08%, S: 0.008%, Cu: 0.30%, Cr: 0.41%, B: 0.0012%, Ce: 0.0042%, and the rest are iron and unavoidable impurities;

[0032] 2) The continuous casting slab is heated in a heating furnace. The slab enters the furnace at a temperature of 850°C and is heated to 1150°C at a heating rate of 42°C / s and kept at 1150°C for 40s. Then, it is cooled to 1100°C at a cooling rate of 7°C / s and kept at 1100°C for 50min. Then, it is heated to 1290°C at a heating rate of 42°C / s and kept at 1290°C for 40s. Finally, it is cooled to 1260°C at a cooling rate of 7°C / s and kept at 1260°C for 50min. The slab is heated and then taken out of the furnace.

[0033] 3) The heated slab is subjected to rough rolling and finish rolling in sequence, descaling is performed in each rough rolling pass, the rough rolling outlet temperature is 1125°C, the finish rolling start temperature is 1090°C, the finish rolling final rolling temperature is 940°C, the rolling thickness is 1.5 mm, and laminar cooling is performed after finish rolling. The slab is cooled to 680°C at a cooling rate of 40°C / s for coiling, and finally flattened to obtain SPA-H strip for hot-rolled containers.

[0034] Example 3

[0035] This embodiment provides a method for preparing SPA-H strip steel for hot-rolled containers, comprising the following steps:

[0036] 1) Pre-desulfurization of molten iron, LF refining after converter smelting, continuous casting of the obtained molten steel to obtain a continuous casting slab, wherein the components of the continuous casting slab are C: 0.07%, Si: 0.34%, Mn: 0.50%, P: 0.08%, S: 0.008%, Cu: 0.30%, Cr: 0.41%, B: 0.0012%, Ce: 0.0042%, and the rest are iron and unavoidable impurities;

[0037] 2) The continuous casting slab is heated in a heating furnace. The slab enters the furnace at a temperature of 850°C and is heated to 1150°C at a heating rate of 35°C / s and kept at 1150°C for 30s. Then, it is cooled to 1100°C at a cooling rate of 7°C / s and kept at 1100°C for 45min. Then, it is heated to 1290°C at a heating rate of 35°C / s and kept at 1290°C for 30s. Finally, it is cooled to 1260°C at a cooling rate of 7°C / s and kept at 1260°C for 45min. The slab is heated and then taken out of the furnace.

[0038] 3) The heated slab is subjected to rough rolling and finish rolling in sequence, descaling is performed in each pass of rough rolling, the outlet temperature of rough rolling is 1140°C, the start rolling temperature of finish rolling is 1085°C, the final rolling temperature of finish rolling is 940°C, the rolling thickness is 1.5 mm, and laminar cooling is performed after finish rolling. The slab is cooled to 640°C at a cooling rate of 35°C / s for coiling, and finally flattened to obtain SPA-H strip for hot-rolled container.

[0039] Comparative Example 1

[0040] The present comparative example provides a preparation method of SPA-H strip steel for hot-rolled containers, which differs from Example 1 in that in step 2), the continuously cast slab is heated in a heating furnace, the slab enters the furnace at a temperature of 850°C, and is heated to 1100°C at a heating rate of 40°C / s, and is kept at 1100°C for 45 minutes, then heated to 1150°C at a heating rate of 5°C / s, and is kept at 1150°C for 30 seconds, then heated to 1260°C at a heating rate of 40°C / s, and is kept at 1260°C for 45 minutes, finally heated to 1290°C at a heating rate of 5°C / s, and is kept at 1290°C for 30 seconds, and the slab is heated and taken out of the furnace.

[0041] Comparative Example 2

[0042] The present comparative example provides a preparation method of SPA-H strip steel for hot-rolled containers, which differs from Example 1 in that in step 2), the continuously cast slab is heated in a heating furnace, the slab enters the furnace at a temperature of 850°C, and is heated to 1150°C at a heating rate of 40°C / s, and is kept at 1150°C for 30s, then cooled to 1100°C at a cooling rate of 15°C / s, and is kept at 1100°C for 45min, then heated to 1290°C at a heating rate of 40°C / s, and is kept at 1290°C for 30s, finally cooled to 1260°C at a cooling rate of 15°C / s, and is kept at 1260°C for 45min, and the slab is taken out of the furnace after being heated.

[0043] Comparative Example 3

[0044] The present comparative example provides a preparation method of SPA-H strip steel for hot-rolled containers, which differs from Example 1 in that in step 2), the continuously cast slab is heated in a heating furnace, the slab enters the furnace at a temperature of 850°C, and is heated to 1150°C at a heating rate of 40°C / s, and is kept at 1150°C for 30s, then cooled to 1100°C at a cooling rate of 5°C / s, and is kept at 1100°C for 45min, then heated to 1290°C at a heating rate of 5°C / s, and is kept at 1290°C for 30s, finally cooled to 1260°C at a cooling rate of 5°C / s, and is kept at 1260°C for 45min, and the slab is taken out of the furnace after being heated.

[0045] Test Example 1

[0046] 100 rolls of SPA-H steel strip were prepared according to the methods of the above-mentioned embodiment and comparative example, and the number of steel strip rolls with copper brittle defects in the 100 steel strip rolls was counted. The copper brittleness occurrence rate (%) = the number of steel strip rolls with copper brittle defects / 100 rolls*100%. The results are shown in Table 1.

[0047] Table 1

[0048]

[0049] Test Example 2

[0050] The mechanical properties of the SPA-H strip steels prepared by the methods of the above embodiments and comparative examples were tested respectively. The test method was carried out in accordance with GB / T228.1-2010 Metallic Material Tensile Test Part I: Room Temperature Test Method. The test results are shown in Table 2.

[0051] Table 2

[0052]

[0053]

[0054] Obviously, for ordinary technicians in the field, other modifications can be made based on the above embodiments, and the obvious modifications brought about by these modifications are still within the protection scope of the present invention.

Claims

1. A method for preparing SPA-H strip steel for hot-rolled container, characterized in that: The steps include: 1) Continuously casting molten steel to obtain a continuous casting slab, wherein the components of the continuous casting slab include, by weight percentage, C: 0.06-0.09%, Si: 0.22-0.4%, Mn: 0.4-0.6%, P: 0.075-0.1%, S: ≤ 0.015%, Cu: 0.25-0.35%, Cr: 0.3-0.5%, B: 0.001-0.002%, Ce: 0.004-0.006%, and the rest are iron and unavoidable impurities; 2) The continuous casting slab is heated in a heating furnace, the slab temperature entering the furnace is 840-870°C, and the temperature is increased to 1140-1160°C at a first heating rate, and kept at 1140-1160°C for 30-50s, then cooled to 1090-1110°C at a first cooling rate, and kept at 1090-1110°C for 40-60min, then heated to 1280-1290°C at a first heating rate, and kept at 1280-1290°C for 30-50s, finally cooled to 1250-1260°C at a first cooling rate, and kept at 1250-1260°C for 40-60min, and then the slab is heated and taken out of the furnace; wherein, the ratio of the first heating rate to the first cooling rate is (5-8):1; 3) The heated slab is subjected to rough rolling and finish rolling in sequence, and after finish rolling, laminar cooling, coiling, and flattening are performed to obtain hot-rolled SPA-H strip steel for containers; The first heating rate is 35-45°C / s, and the first cooling rate is 4-7°C / s.

2. The preparation method according to claim 1, characterized in that: The ratio of the first heating rate to the first cooling rate is (6-8):

1.

3. The preparation method according to claim 1, characterized in that: The first heating rate is 40-45°C / s, and the first cooling rate is 5-7°C / s.

4. The preparation method according to claim 1, characterized in that: The molten steel in step 1) is obtained by pre-desulfurization, converter smelting and LF refining of molten iron.

5. The preparation method according to claim 1, characterized in that: Step 3) Descaling is performed in each rough rolling pass, and the rough rolling outlet temperature is 1120-1130°C.

6. The preparation method according to claim 1, characterized in that: In step 3), the starting temperature of the finishing rolling is 1090-1100°C, the final rolling temperature of the finishing rolling is 920-940°C, and the rolling thickness is 1.5-2.0 mm.

7. The preparation method according to claim 1, characterized in that: In step 3), the coiling temperature is 640-670°C.

8. The preparation method according to claim 1, characterized in that: Step 3) The cooling rate during laminar flow cooling is 40-45°C / s.

9. A SPA-H steel strip for hot-rolled containers, characterized in that: The invention is prepared by the preparation method according to any one of claims 1 to 8.

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