Method for producing cold-rolled electroplated tin steel plates with different hardness grades based on same steel grade
By controlling the high-temperature strain and grain size of solid-solution atoms in carbon and nitrogen gap, combined with hot rolling and cold rolling processes, cold rolling electroplated tin steel plate production with different hardness levels is achieved, and the problem of difficulty in producing different hardness levels is solved in the continuous annealing process. Improves production efficiency and reduces mixed billet losses.
Patent Information
- Application Number
- CN202310726524.8
- Authority / Receiving Office
- CN · China
- Patent Type
- Applications(China)
- Current Assignee / Owner
- Filing Date
- 2023-06-19
- Publication Date
- 2024-12-20
AI Technical Summary
In the prior art, it is difficult to produce cold-rolled electroplated tin steel plates of different hardness grades based on the same steel grade using continuous annealing process, resulting in low production efficiency and multiple component switching required, which increases the losses of the mixed billet and the head and tail billet.
By controlling the high-temperature strain aging of solid-solution atoms in the carbon-nitrogen gap in steel, using the control of grain size and solid-solution carbon-nitrogen C/N content, and using flexible processes of hot rolling and cold rolling to achieve quality conditioning of different hardness levels. Reduce the losses of mixed billets and head-tail billets caused by component switching during steelmaking.
The cold-rolled electroplated tin steel plates with different hardness levels were achieved in the same steel grade, which reduced the losses of mixed billets and head-tail billets in the production process, improved production efficiency, and simplified the difficulty of variety transition.
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Abstract
Description
Technical Field
[0001] The present invention relates to a method for producing cold-rolled tin-plated steel sheets, and in particular to a method for producing cold-rolled tin-plated steel sheets with different hardness grades based on the same steel grade. Specifically, it relates to a method for producing cold-rolled tin-plated steel sheets for the bodies and covers of aerosol cans and food cans that do not require deep drawing, and belongs to the technical field of iron-based alloys. Background Art
[0002] GB / T 2520-2017 Cold-rolled electro-tinned steel sheets and strips specifies that the tempering degree of tinned steel sheets and strips is expressed by the Rockwell hardness (HR30Tm) value, and the hardness range covers 45 to 69. At present, the common technology is to use the hood annealing method to produce tinned steel sheets and strips with a hardness value of 45 to 60, and to use the continuous annealing method to produce tinned steel sheets and strips with a hardness value of 57 to 69. The heat treatment time of hood annealing is usually more than 8 to 10 hours, and the required hardness value is mainly obtained through the annealing holding time and the tempering rolling after annealing, which has flexible adjustment space; the heat treatment time of continuous annealing does not exceed 10 minutes at most, and the space for adjusting the hardness through annealing and tempering rolling is limited. Therefore, when producing tinned sheets by continuous annealing, it is usually necessary to adjust the strengthening elements to achieve the hardness value required by the tempering degree.
[0003] A Chinese patent application with patent publication number CN103556049A discloses a continuously annealed hard tin-plated substrate and a production method thereof, which is strengthened with carbon and manganese, supplemented by a low-nitrogen, high-aluminum, and high-boron component design. The main components include C: 0.07-0.09%, Mn: 0.35-0.45%, N≤0.003%, Als: 0.04-0.06%, and B: 0.001-0.002%. Combined with suitable cold and hot rolling processes, a finished product with a thickness of 0.30-0.35 mm and a tempering degree of T3 or T4 can be produced, and the material hardness HR30Tm is between 59 and 62.5.
[0004] The Chinese patent application with patent publication number CN106319329A discloses a method for producing a hard cold-rolled tin-plated steel sheet, which is strengthened with carbon and manganese, and the main components include C: 0.051-0.079%, Si≤0.1%, Mn: 0.2-0.4%, P≤0.02%, S≤0.02%, Alt: 0.01-0.06%; with suitable cold and hot rolling processes and a large flat elongation of 4.0-7.0% after continuous annealing, a tin-plated sheet with a tempering degree of T5 can be produced, and the material hardness HR30Tm is between 62 and 68.
[0005] Through the strengthening effect of carbon and manganese elements and appropriate hot and cold rolling processes, the requirements of a single tempering degree are achieved, and the hardness changes to 3-6HR30Tm. That is to say, the continuous annealing method to produce steel plates with a hardness value of 57-69HR30Tm requires at least two or more component designs. For modern continuous production steel mills, this means increasing the number of transitions and switches, affecting production efficiency. Summary of the invention
[0006] The purpose of the present invention is to provide a method for producing cold-rolled tin-plated steel sheets with different hardness grades based on the same steel grade, mainly to solve the technical problem that the existing cold-rolled tin-plated steel sheets with different hardness grades cannot be produced by continuous annealing process based on the same steel grade; the method of the present invention realizes that the same steel grade can produce cold-rolled tin-plated steel sheets with different hardness grades under the conditions of continuous annealing process, realizes the common composition of the substrate of cold-rolled tin-plated steel sheets with different hardness grades, reduces the loss of mixed billets and head and tail billets caused by component switching in the steelmaking process, and improves production efficiency.
[0007] The method of the present invention utilizes the unique soft melting production process of tinplate, relies on the high temperature strain aging of carbon and nitrogen interstitial solid solution atoms in steel, and controls the grain size and the solid solution carbon and nitrogen C / N content, so that the slabs with the same composition can obtain different levels of tempering through flexible process control of hot rolling and cold rolling.
[0008] The technical solution adopted by the present invention is a method for producing cold-rolled electro-tinned steel sheets with different hardness grades based on the same steel grade, comprising the following steps:
[0009] 1) molten steel is continuously cast to obtain a continuous casting slab, wherein the molten steel is continuously cast to obtain a continuous casting slab, and the chemical composition of the molten steel is as follows by weight: C: 0.025% to 0.045%, Mn: 0.20% to 0.30%, Alt: 0.035% to 0.065%, N: 0.006% to 0.008%, Si: 0.001 to 0.030%, P≤0.020%, S≤0.020%, and the remainder is Fe and unavoidable impurity elements;
[0010] 2) The continuous casting slab is heated in a heating furnace and then hot rolled. The heating temperature of the continuous casting slab is 1180-1220°C. The hot rolling is a two-stage rolling process. The rough rolling end temperature is 930-960°C. After rough rolling, the thickness of the intermediate slab is controlled to be 39-40 mm. The finishing temperature of the finishing rolling is 850-890°C. After finishing rolling, the thickness of the steel plate is controlled to be 2.0-2.6 mm. The hot rolled steel plate is coiled after laminar cooling to obtain a hot rolled steel coil. The coiling temperature is 520-700°C.
[0011] 3) After the hot-rolled steel coil is unrolled, it is pickled, cold rolled, annealed in a vertical continuous annealing furnace, and flattened on a double-frame flattening machine, and the coil is obtained to obtain a tin-plated substrate with a thickness of 0.20-0.40 mm; the cold rolling reduction rate is 85%-90%, and the annealing temperature of the hardened steel strip after cold rolling in the soaking section of the vertical continuous annealing furnace is 600-700°C, and the annealing time of the steel strip in the soaking section is 60-90s; the steel strip is quenched and cooled to room temperature after leaving the vertical continuous annealing furnace; the steel strip cooled to room temperature after annealing is flattened on a double-frame flattening machine, and the flattening elongation is 1.0%-1.4%;
[0012] 4) The electro-tinned substrate is subjected to alkali washing, pickling, electro-tinning, reflowing, passivation and oiling, and a finished electro-tinned steel sheet with a thickness of 0.20 to 0.40 mm is obtained by coiling; the reflowing temperature is 232 to 240° C., and the reflowing time is 2 to 3 seconds.
[0013] Further, in step 2), when producing a cold-rolled tin-plated steel sheet with a hardness value of 57±3HR30Tm, the preferred coiling temperature of the hot-rolled steel sheet is 660-700°C; when producing a cold-rolled tin-plated steel sheet with a hardness value of 59±3HR30Tm, the preferred coiling temperature of the hot-rolled steel sheet is 600-640°C; when producing a cold-rolled tin-plated steel sheet with a hardness value of 61±3HR30Tm, the preferred coiling temperature of the hot-rolled steel sheet is 600-640°C; when producing a cold-rolled tin-plated steel sheet with a hardness value of 65±3HR30Tm, the preferred coiling temperature of the hot-rolled steel sheet is 520-560°C.
[0014] Further, in step 3), a cold-rolled tin-plated steel sheet with a hardness value of 57±3HR30Tm is produced. Preferably, the annealing temperature of the hardened steel strip after cold rolling in the soaking section of a vertical continuous annealing furnace is 690-700°C, and the annealing time of the steel strip in the soaking section is 60-90s; after soaking, the steel strip is first cooled to 380°C in the annealing furnace at a cooling rate of 20-30°C / s; then, the steel strip is air-cooled to 250°C in the annealing furnace at a cooling rate of 0.4-0.6°C / s; then, the steel strip is air-cooled to 150°C in the annealing furnace at a cooling rate of 5-7°C / s.
[0015] To produce cold-rolled tin-plated steel sheets with a hardness value of 59±3HR30Tm, the annealing temperature of the hardened steel strip after cold rolling in the soaking section of a vertical continuous annealing furnace is preferably 630-640°C, and the annealing time of the steel strip in the soaking section is 60-90s; after soaking, the steel strip is first cooled to 380°C in the annealing furnace at a cooling rate of 20-30°C / s; then the steel strip is naturally cooled to 150°C in the annealing furnace.
[0016] To produce cold-rolled tin-plated steel sheets with a hardness value of 61±3HR30Tm, the annealing temperature of the hardened steel strip after cold rolling in the soaking section of a vertical continuous annealing furnace is preferably 610-620°C, and the annealing time of the steel strip in the soaking section is 60-90s; after soaking, the steel strip is first cooled to 380°C in the annealing furnace at a cooling rate of 20-30°C / s; then the steel strip is naturally cooled to 150°C in the annealing furnace.
[0017] To produce cold-rolled tin-plated steel sheets with a hardness value of 65±3HR30Tm, the preferred annealing temperature of the cold-rolled hardened steel strip in the soaking section of a vertical continuous annealing furnace is 600-610°C, and the annealing time of the steel strip in the soaking section is 60-90s; after soaking, the steel strip is first cooled to 380°C in the annealing furnace at a cooling rate of 20-30°C / s; then the steel strip is naturally cooled to 150°C in the annealing furnace.
[0018] The reasons for the main production process adopted by the present invention are as follows:
[0019] 1. Setting of heating temperature of continuous casting slab
[0020] The slab heating temperature is mainly to ensure the subsequent final rolling temperature, and at the same time to fully dissolve the nitrides in the steel into N atoms to play a role in solid solution strengthening in the subsequent process. Considering the economy and subsequent process guarantee, the slab heating temperature of the present invention is preferably 1180-1220°C.
[0021] 2. Setting of rough rolling end temperature and intermediate billet thickness
[0022] The role of rough rolling is to provide a suitable entry thickness for finishing rolling, that is, the thickness of the intermediate billet, to meet the deformation of finishing rolling. Taking into account the economy and subsequent process guarantee, the rough rolling end temperature of the present invention is set to 930-960°C, and the intermediate billet thickness is set to 39-40mm.
[0023] 3. Setting of finishing temperature
[0024] The purpose of rough rolling is to obtain the appropriate thickness of the hot coil product and ensure good plate shape. In order to avoid two-phase rolling, the finishing temperature needs to be higher than the Ar3 phase transition point temperature. The dynamic phase transition point temperature is measured to be 834°C. Taking into account the material structure and surface quality, the present invention sets the finishing temperature of finishing rolling to 850-890°C.
[0025] 4. Setting of hot rolling coiling temperature
[0026] The coiling temperature affects the precipitation process of nitrides and carbides, especially the precipitation of AlN. A high coiling temperature can promote the precipitation and coarsening of AlN, thereby reducing the content of dissolved N in the steel and weakening the bake hardening effect of dissolved N atoms; a low coiling temperature can inhibit the precipitation of AlN, allowing more N atoms to be dissolved in the grains, and ultimately play a role in bake hardening during the tin plating soft melting stage. In addition, the grain size in the hot-rolled state has a certain heredity in the cold rolling stage, and a large hot-rolled grain size is beneficial to reducing the hardness of the tin-plated steel strip. Taking all factors into consideration, the present invention sets the coiling temperature to 520°C to 700°C according to the hardness value range of the tin-plated steel strip, and further optimizes the coiling temperature range according to the hardness range.
[0027] 5. Setting of annealing temperature, annealing time and cooling speed of steel strip in vertical continuous annealing furnace
[0028] The present invention adopts a vertical continuous annealing furnace to continuously anneal the steel strip after rolling. The temperature and time of the soaking section of the continuous annealing furnace should ensure that the fibrous structure formed in the steel strip during the rolling stage is fully recovered, recrystallized and grained. After soaking, the steel strip is slowly cooled so that the carbon atoms dissolved in the ferrite can be fully precipitated in the form of carbides, and the solid solution carbon content is reduced, thereby reducing the bake hardenability. The variable speed cooling method of first fast cooling, then slow cooling, and then fast cooling is adopted, which is more conducive to the precipitation of carbon in the saturated solid solution as soon as possible. In the present invention, in order to obtain a tin-plated steel strip with a lower hardness value, it is necessary to perform variable speed cooling on the steel strip to minimize the solid solution carbon content; for tin-plated steel strips with high hardness values, more solid solution carbon is required to exist to play a bake hardening role. Comprehensively considered, after repeated tests, the present invention sets the annealing temperature of the steel strip in the soaking section of the vertical continuous annealing furnace to 600-700°C, and the annealing time in the soaking section is set to 60s-90s, and further optimizes the soaking section temperature and cooling method according to the hardness range.
[0029] 6. Setting of soft melting temperature and time
[0030] The purpose of reflowing cold-rolled tinplate is to obtain a bright tin layer and a tin-iron alloy layer. Usually, the reflowing temperature should reach and exceed the melting point of tin, 232°C. However, too high a temperature will cause excessive baking hardening, exceeding the hardness value range. Considering the product performance and the quality of the tin layer, preferably, the reflowing temperature is 232-240°C and the reflowing time is 2-3s.
[0031] The metallographic structure of the cold-rolled tin-plated steel sheet produced by the method of the present invention is ferrite + free cementite, and the grain size of the ferrite in the metallographic structure is I8.0 to I9.5; the lower yield strength R of the cold-rolled tin-plated steel sheet with a thickness of 0.20 to 0.40 mm is eL 240~420MPa, tensile strength R m 350~480MPa, elongation after fracture A50 mm It is 17% to 40%, and the hardness value is 54 to 68HR30Tm.
[0032] Compared with the prior art, the present invention has the following positive effects: 1. The method of the present invention mainly strengthens carbon and manganese, and supplements nitrogen strengthening. The steel billet with the same composition is subjected to the joint regulation of hot rolling and cold rolling processes to obtain electroplated tin-plated substrates with different grain sizes and dissolved carbon and nitrogen atomic contents, and then baked and hardened by soft melting, and finally obtains tin-plated plates with different tempering degrees, which reduces the quality losses such as mixing and casting residue caused by the difference in components during the molten steel smelting process. 2. The key processes for regulating the grain size and dissolved atomic content in the method of the present invention are the hot rolling coiling temperature and the continuous annealing process. Hot rolling and high temperature coiling can promote the nitrogen element to be fully precipitated in the form of AlN, thereby controlling the dissolved nitrogen content; the continuous annealing process mainly provides energy for grain recovery and growth, and further controls the dissolved carbon content and grain size after the recrystallization process is completed; the method of the present invention makes full use of the characteristics of cold-rolled electroplated tin steel sheets, and does not increase the difficulty of variety transition, and is simple and easy. 3. The method of the present invention realizes the common composition of the substrate of cold-rolled tin-plated steel sheets with different hardness values, improves the production efficiency of cold-rolled tin-plated steel sheets with different hardness values, and reduces the loss of mixed billets and head and tail billets caused by component switching during the steelmaking process. DETAILED DESCRIPTION
[0033] The present invention is further described below in conjunction with Examples 1 to 6, as shown in Tables 1 to 5. Table 1 shows the chemical composition (by weight percentage) of the steel of the present invention, with the remainder being Fe and unavoidable impurities.
[0034] Table 1 Chemical composition of the steel of the present invention, unit: weight percentage.
[0035]
[0036] Molten steel with required chemical composition is obtained by converter smelting. The molten steel is treated with argon gas and then continuously cast to obtain a steel billet with a thickness of 210 to 230 mm, a width of 800 to 1100 mm and a length of 6000 to 10000 mm.
[0037] The cut-to-length slabs produced by steelmaking are sent to a heating furnace for reheating, and after being removed from the furnace and dephosphorized, they are sent to a continuous hot rolling mill for rolling; the rolling is controlled by a rough rolling mill and a finishing rolling mill, and the slabs are coiled after laminar cooling to produce qualified hot-rolled steel coils; the thickness of the hot-rolled steel plates is 2.0 to 2.6 mm, and the hot rolling process control is shown in Table 2.
[0038] Table 2 Hot rolling process control parameters of the embodiment of the present invention
[0039]
[0040] After the hot-rolled steel coil is unrolled, it is pickled, cold rolled, annealed in a vertical continuous annealing furnace, and flattened on a double-frame flattening machine, and the coil is obtained to obtain a tin-plated substrate with a thickness of 0.20-0.40 mm; the cold rolling reduction rate is 85%-90%, and the annealing temperature of the hardened steel strip in the vertical continuous annealing furnace soaking section after cold rolling is 600-700°C, and the annealing time of the steel strip in the soaking section is 60-90s; the steel strip cooled to room temperature after annealing is flattened on a double-frame flattening machine, and the flattening elongation is 1.0%-1.4%. The process control parameters of cold rolling, annealing, and flattening are shown in Table 3-4.
[0041] Table 3 Cold rolling, continuous annealing furnace soaking section soaking, flattening elongation parameters of the present invention
[0042]
[0043]
[0044] Table 4 Cooling parameters of steel strip in continuous annealing furnace according to the present invention
[0045]
[0046] The above-mentioned electro-tinned substrate is subjected to alkali washing, acid washing, electro-tinning, soft melting, passivation and oiling, and a finished electro-tinned steel sheet with a thickness of 0.20-0.40 mm is obtained by coiling; the soft melting temperature is 232-240° C., and the soft melting time is 2-3s.
[0047] The cold-rolled tin-plated steel sheet obtained by the above method has a metallographic structure of ferrite + free cementite, a ferrite grain size grade of I8.0 to I9.5, and a lower yield strength R of the cold-rolled tin-plated steel sheet with a thickness of 0.20 to 0.40 mm. eL 240~420MPa, tensile strength R m 350~480MPa, elongation after fracture A 50mm It is 17% to 40%, and the hardness value is 54 to 68HR30Tm.
[0048] The finished tin-plated steel sheet produced by the method of the present invention was subjected to hardness test according to "GB / T230.1-2009 Metallic Materials Rockwell Hardness Test Part 1: Test Method" and tensile test according to "GB / T228.1-2010 Metallic Materials Tensile Test Part 1: Room Temperature Test Method". The performance indicators of the tin-plated steel sheet are shown in Table 5.
[0049] Table 5 Properties of cold-rolled tin-plated steel sheets according to the present invention
[0050]
[0051] In addition to the above embodiments, the present invention may also have other implementation modes. Any technical solution formed by equivalent replacement or equivalent transformation falls within the protection scope required by the present invention.
Claims
1. A method for producing cold-rolled tin-plated steel sheets of different hardness grades based on the same steel grade, characterized in that: The method comprises the following steps: 1) molten steel is continuously cast to obtain a continuous casting slab, wherein the molten steel is continuously cast to obtain a continuous casting slab, and the chemical composition of the molten steel is as follows by weight: C: 0.025% to 0.045%, Mn: 0.20% to 0.30%, Alt: 0.035% to 0.065%, N: 0.006% to 0.008%, Si: 0.001 to 0.030%, P≤0.020%, S≤0.020%, and the remainder is Fe and unavoidable impurity elements; 2) The continuous casting slab is heated in a heating furnace and then hot rolled. The heating temperature of the continuous casting slab is 1180-1220°C. The hot rolling is a two-stage rolling process. The rough rolling end temperature is 930-960°C. After rough rolling, the thickness of the intermediate slab is controlled to be 39-40 mm. The finishing temperature of the finishing rolling is 850-890°C. After finishing rolling, the thickness of the steel plate is controlled to be 2.0-2.6 mm. The hot rolled steel plate is coiled after laminar cooling to obtain a hot rolled steel coil. The coiling temperature is 520-700°C. 3) After the hot-rolled steel coil is unrolled, it is pickled, cold rolled, annealed in a vertical continuous annealing furnace, and flattened on a double-frame flattening machine, and the coil is obtained to obtain a tin-plated substrate with a thickness of 0.20-0.40 mm; the cold rolling reduction rate is 85%-90%, and the annealing temperature of the hardened steel strip after cold rolling in the soaking section of the vertical continuous annealing furnace is 600-700°C, and the annealing time of the steel strip in the soaking section is 60-90s; the steel strip is quenched and cooled to room temperature after leaving the vertical continuous annealing furnace; the steel strip cooled to room temperature after annealing is flattened on a double-frame flattening machine, and the flattening elongation is 1.0%-1.4%; 4) The electro-tinned substrate is subjected to alkali washing, pickling, electro-tinning, reflowing, passivation and oiling, and a finished electro-tinned steel sheet with a thickness of 0.20 to 0.40 mm is obtained by coiling; the reflowing temperature is 232 to 240° C., and the reflowing time is 2 to 3 seconds.
2. The method for producing cold-rolled tin-plated steel sheets with different hardness grades based on the same steel grade as claimed in claim 1, characterized in that: To produce a cold-rolled tin-plated steel sheet with a hardness value of 57±3HR30Tm, the coiling temperature described in step 2) is 660-700°C; the annealing temperature of the hardened steel strip after cold rolling in the soaking section of a vertical continuous annealing furnace is 690-700°C, and the annealing time of the steel strip in the soaking section is 60-90s; after soaking, the steel strip is first cooled to 380°C in the annealing furnace at a cooling rate of 20-30°C / s; then, the steel strip is air-cooled to 250°C in the annealing furnace at a cooling rate of 0.4-0.6°C / s; then, the steel strip is air-cooled to 150°C in the annealing furnace at a cooling rate of 5-7°C / s.
3. The method for producing cold-rolled tin-plated steel sheets of different hardness grades based on the same steel grade as claimed in claim 1, characterized in that: To produce a cold-rolled tin-plated steel sheet with a hardness value of 59±3HR30Tm, the coiling temperature described in step 2) is 600-640°C; the annealing temperature of the hardened steel strip after cold rolling in the soaking section of a vertical continuous annealing furnace is 630-640°C, and the annealing time of the steel strip in the soaking section is 60-90s; after soaking, the steel strip is first cooled to 380°C in the annealing furnace at a cooling rate of 20-30°C / s; then the steel strip is naturally cooled to 150°C in the annealing furnace.
4. The method for producing cold-rolled tin-plated steel sheets of different hardness grades based on the same steel grade as claimed in claim 1, characterized in that: To produce a cold-rolled tin-plated steel sheet with a hardness value of 61±3HR30Tm, the coiling temperature described in step 2) is 600-640°C; the annealing temperature of the hardened steel strip after cold rolling in the soaking section of a vertical continuous annealing furnace is 610-620°C, and the annealing time of the steel strip in the soaking section is 60-90s; after soaking, the steel strip is first cooled to 380°C in the annealing furnace at a cooling rate of 20-30°C / s; then the steel strip is naturally cooled to 150°C in the annealing furnace.
5. The method for producing cold-rolled tin-plated steel sheets of different hardness grades based on the same steel grade as claimed in claim 1, characterized in that: To produce a cold-rolled tin-plated steel sheet with a hardness value of 65±3HR30Tm, the coiling temperature described in step 2) is 520-560°C; the annealing temperature of the hardened steel strip after cold rolling in the soaking section of a vertical continuous annealing furnace is 600-610°C, and the annealing time of the steel strip in the soaking section is 60-90s; after soaking, the steel strip is first cooled to 380°C in the annealing furnace at a cooling rate of 20-30°C / s; then the steel strip is naturally cooled to 150°C in the annealing furnace.
6. The method for producing cold-rolled tin-plated steel sheets of different hardness grades based on the same steel grade as claimed in claim 1, characterized in that: The metallographic structure of the cold-rolled tin-plated steel sheet is ferrite + free cementite, and the grain size of the ferrite in the metallographic structure is I8.0 to I9.5; the lower yield strength R of the cold-rolled tin-plated steel sheet with a thickness of 0.20 to 0.40 mm is eL 240~420MPa, tensile strength R m 350~480MPa, elongation after fracture A 50mm It is 17% to 40%, and the hardness value is 54 to 68HR30Tm.