A method for producing a low-cost cold-rolled steel sheet for a water heater tank

Abstract

The application discloses a production method of a low-cost cold-rolled steel plate for a hot water heater liner, the product chemical composition adopts a low-carbon and low-silicon process technology on the basis of a C-Mn steel, a high-opening rolling temperature and a low-coiling temperature are adopted in the hot rolling and controlled rolling and controlled cooling process principle; the cold rolling reduction is controlled in the range of 60% to 87% so as to ensure the forming performance; a double-ladder curve annealing process is adopted, the holding time and the cooling time are reasonably controlled, the beneficial texture is increased, and the steel plate rigidity and the forming performance are ensured; the elongation is controlled to be not more than 3% by adopting a proper reduction process in the flattening, so as to eliminate the yield platform and improve the plate shape.

Description

Technical Field

[0001] This invention relates to the field of metallurgical steel rolling, and more particularly to a low-cost method for producing cold-rolled steel plates for water heater inner tanks. Background Technology

[0002] With social development and progress, and people's enduring pursuit of beauty, enamel steel, the metal blank used in enamel products, boasts excellent formability. After enamel coating, it exhibits a beautiful appearance, a smooth and delicate surface, rich colors, corrosion resistance, and ease of washing. It is now widely used in everyday kitchenware, home appliances, architectural decorative enamel panels, and important applications such as large pipelines and subway stations. Therefore, the quality of enamel steel directly affects the service life of enamel products. Low-cost production of enamel steel has become one of the production goals of various steel mills. Summary of the Invention

[0003] The purpose of this invention is to provide a low-cost method for producing cold-rolled steel plates for water heater inner tanks. The product utilizes a low-carbon, low-silicon process based on C-Mn steel. Hot rolling employs a controlled rolling and cooling process with high initial rolling temperature and low coiling temperature. Cold rolling reduction is controlled between 60% and 87% to ensure formability. A double-step annealing process is used, with reasonable control of holding and cooling times to increase favorable texture and ensure steel plate rigidity and formability. Leveling employs a suitable reduction process, controlling elongation to no more than 3% to eliminate yield plateaus and improve plate shape.

[0004] To solve the above-mentioned technical problems, the present invention adopts the following technical solution:

[0005] This invention discloses a low-cost method for producing cold-rolled steel plates for water heater inner tanks, comprising:

[0006] (1) Heat the slab with a thickness of 67-72 mm to 1050-1100℃ and hold for 40 minutes;

[0007] (2) Hot rolling control: the initial rolling temperature is greater than 1020℃, and the final rolling temperature is 860~890℃; heating temperature: initial rolling temperature is 1030~1060℃.

[0008] (3) After hot rolling, a dispersed laminar flow cooling mode is used to cool the coiled coils, and the cooling rate and intensity are controlled. The coiling temperature is 550-600℃.

[0009] (4) The cold rolling reduction rate is controlled at 60% to 87%;

[0010] (5) After cold rolling, the annealing process adopts a double-step curve system. The annealing holding temperature is 680~710℃, the annealing holding time is 11~14h, the cooling rate is controlled to be ≤25℃ / h, the cooling is controlled to be 360℃, and the furnace exit temperature is ≤80℃. The annealed microstructure is ferrite with a grain size of 10~11.

[0011] (6) Flattening is done by using a suitable pressing process, and the elongation is controlled to be no more than 3%.

[0012] Furthermore, the chemical composition of the slab by mass percentage is as follows: C: 0.02-0.05%, Si: 0.015-0.28%, Mn: 0.10-0.20%, P≤0.015%, S≤0.015%, Alt≥0.015%, with the remainder being Fe and unavoidable inclusions.

[0013] Furthermore, the total rolling reduction rate is ≥87%.

[0014] Furthermore, the final rolling temperature is 860–890℃.

[0015] Furthermore, the steel plate has a yield strength of less than 207 MPa, a tensile strength of more than 320 MPa, and an elongation of more than 41.0%.

[0016] Compared with the prior art, the beneficial technical effects of the present invention are as follows:

[0017] 1. In today's fiercely competitive market, low cost and high return have become the guiding principle and goal for all businesses. While meeting product requirements, this product adheres to a low-cost production approach, employing low-carbon and low-silicon processing technology on a C-Mn steel base. Optimized production processes improve the overall performance of the steel plate, providing an excellent and environmentally friendly substrate for galvanizing and color coating production.

[0018] 2. This invention employs low-cost clean steelmaking technology, simplifying the process and reducing energy consumption. Single-slag operation is adopted, and subsequent control measures such as rapid slag formation, slag basicity control, and slag-blocking during steel tapping are implemented to reduce the phosphorus (P) content in the molten steel, thereby shortening the production cycle and improving economic efficiency. Sulfur removal mainly occurs during refining, achieved through electrode heating and white slag formation. Sulfur makes steel plates brittle, reducing their ductility and deep-drawing properties. During enameling, sulfur combines with oxygen to form SO2, leading to various defects in the enamel layer such as bubbles and pinholes. High sulfur content easily causes segregation, resulting in a banded structure in the metallographic structure, leading to anisotropy in the physical and mechanical properties of the steel plate. This causes different shrinkage in different directions during cooling, resulting in surface cracking and scaling. The molten steel undergoes Ca treatment, which modifies MnS inclusions and eliminates the harmful effects of sulfur in the steel. Calcium treatment is then performed after refining.

[0019] 3. This invention achieves stable production of 0.8mm thick cold-rolled steel plates for water heater inner tanks at low cost by controlling the rolling and cooling processes. It simplifies the production process and, while meeting user requirements, enables steel with the same chemical composition to serve multiple functions. This reduces costs, simplifies the production process, improves production efficiency, and reduces energy consumption, which aligns with the development direction of developing energy-saving, clean, and green steel. Detailed Implementation

[0020] The production method of low-cost cold-rolled steel plates for water heater inner tanks is further detailed with examples:

[0021] Using steel with the chemical composition listed in Table 1 as raw material, the steel billet was smelted using a process involving low-desulfurization, converter smelting, refining, and calcium treatment. The billet dimensions were 67–72 mm (thickness) × 320 mm (width) × 500 mm (length). The slab was heated in a furnace, homogenized, and hot-rolled with controlled initial and final rolling temperatures. The cooling rate was controlled after rolling. The hot-rolled steel plate underwent cold rolling after pickling. After cold rolling, a double-step annealing process was used, with careful control of holding and cooling times. The annealing holding temperature was 680–710℃, the holding time was 11–14 hours, the cooling rate was controlled to ≤25℃ / h, and the temperature was controlled to 360℃. The furnace exit temperature was ≤80℃. The finished steel plate thickness was 0.8 mm. Mechanical property testing is shown in Table 2.

[0022] Table 1. Chemical composition of the steel of this invention, wt%.

[0023] Serial Number C Si Mn P S Alt 1 0.028 0.025 0.14 0.012 0.006 0.031 2 0.022 0.021 0.13 0.010 0.005 0.035 3 0.034 0.020 0.16 0.015 0.004 0.034 4 0.036 0.026 0.15 0.015 0.004 0.032 5 0.039 0.015 0.13 0.011 0.006 0.030 6 0.047 0.016 0.12 0.010 0.003 0.027

[0024] Controlled rolling and controlled cooling mainly involves strictly controlling the rolling and controlled cooling process parameters according to specifications, including: (1) the initial rolling temperature in the austenite recrystallization zone is 1030~1060℃, (2) the total rolling reduction rate is ≥87%, and the final rolling temperature is 860~890℃. (3) Cooling is carried out in a dispersed laminar flow cooling mode with separate groups to control the cooling rate and intensity, so as to achieve ferrite + a small amount of pearlite.

[0025] The experimental results of the low-cost cold-rolled steel plate for the inner tank of a water heater according to the present invention are listed in Table 2. It can be seen that the yield strength of the steel plate is less than 207 MPa, the tensile strength is greater than 320 MPa, and the elongation is greater than 41.0%. This meets the standards and customer requirements. The fish-scale enamel powder exhibits no scale bursting on one side, while ordinary enamel powder shows no scale bursting on either one or both sides.

[0026] Table 2 Experimental results of the steel of the present invention

[0027]

[0028] The embodiments described above are merely preferred embodiments of the present invention and are not intended to limit the scope of the present invention. Various modifications and improvements made by those skilled in the art to the technical solutions of the present invention without departing from the spirit of the present invention should fall within the protection scope defined by the claims of the present invention.

Claims

1. A method for producing a low-cost cold-rolled steel plate for the inner tank of a water heater, characterized in that: include: (1) Heat the slab with a thickness of 67-72 mm to 1050-1100℃ and hold for 40 minutes; (2) The initial rolling temperature of hot rolling is controlled at 1030-1060℃, and the final rolling temperature is controlled at 860-890℃; (3) After hot rolling, a dispersed laminar flow cooling mode is used to cool the coiled coils, and the cooling rate and intensity are controlled. The coiling temperature is 550-600℃. (4) The hot-rolled steel plate is cold-rolled after pickling; the cold rolling reduction rate is controlled at 60% to 87%; (5) After cold rolling, the annealing process adopts a double-step curve system. The annealing holding temperature is 680~710℃, the annealing holding time is 11~14h, the cooling rate is controlled to be ≤25℃ / h, the cooling is controlled to be 360℃, and the furnace exit temperature is ≤80℃. The annealed microstructure is ferrite with a grain size of 10~11. (6) The flattening process is adopted to control the elongation to be no more than 3%; The chemical composition of the slab is as follows (mass percentage): C: 0.02–0.05%, Si: 0.015–0.28%, Mn: 0.10–0.20%, P ≤ 0.015%, S ≤ 0.015%, Alt ≥ 0.015%, with the remainder being Fe and unavoidable inclusions.

2. The method for producing low-cost cold-rolled steel plate for water heater inner tanks according to claim 1, characterized in that: The steel plate has a yield strength of less than 207 MPa, a tensile strength of more than 320 MPa, and an elongation of more than 41.0%.

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