Method for slow cooling of hot-rolled medium bar

Abstract

The present application relates to a kind of bar production technical field, especially a kind of hot-rolled medium bar slow cooling method, including 1) construction slow cooling box;2) after the hot-rolled medium bar of final rolling temperature 950~1020 ℃ is cut to size saw cutting is completed, cooling to slow cooling start temperature + (30~50) ℃, then collection packing;3) bar stack is hoisted to slow cooling box, slow cooling start temperature is 350~450 ℃, average cooling speed is 10~20 ℃ / h;4) when bar stack center temperature drops to 100~200 ℃, air cooling to room temperature.The present application uses special slow cooling box, utilizes low-cost material and unpowered heat preservation principle, realizes the uniform, slow cooling of hot-rolled medium bar, effectively prevents the generation of white spot and crack defect, saves production cost, improves production efficiency.

Description

Technical Field

[0001] This invention relates to the field of bar production technology, and in particular to a method for slow cooling of hot-rolled bars. Background Technology

[0002] Hot-rolled bars (typically referring to bars with a diameter of ø50mm to ø150mm) are prone to generating significant thermal and structural stresses after rolling due to their large cross-sectional dimensions and inconsistent cooling rates between the interior and surface. For certain alloy steels, high-carbon steels, or special steels sensitive to white spots, excessively rapid cooling can easily lead to internal hydrogen embrittlement, white spot defects, or cracking due to excessive stress, severely impacting product yield and performance.

[0003] Currently, the commonly used slow cooling methods in the industry mainly include the following: (1) Slow cooling in a slow cooling pit: The hot-rolled bar is placed in a slow cooling pit and cooled slowly by relying on the heat preservation performance of the slow cooling pit and the residual temperature of the bar itself. This method requires a large investment and a special slow cooling pit needs to be built; and if the temperature of the bar is high when it enters the pit, it is easy to bend after it leaves the pit, and it needs to be straightened later, resulting in low production efficiency and high cost.

[0004] (2) Slow cooling with insulation cover: Cover the stack of bars with a large insulation cover. This method is not flexible, the insulation effect is greatly affected by the ambient wind speed and temperature, and the insulation cover itself is expensive and easily damaged.

[0005] (3) Heat treatment in a slow cooling furnace: The bars are sent into a slow cooling furnace and cooled at a controlled temperature according to a program. This method has the best effect, but the equipment investment and operating costs (gas and electricity) are extremely high, which is difficult for many enterprises that pursue low-cost production to bear.

[0006] In summary, existing slow cooling technologies for hot-rolled bars generally suffer from problems such as large equipment investment, high costs, low production efficiency, and poor flexibility. There is an urgent need for a new slow cooling method that can ensure the slow cooling effect, significantly reduce costs and operational difficulties, and improve production efficiency. Summary of the Invention

[0007] This invention provides a method for slow cooling of hot-rolled bars. It uses a specially designed slow cooling box and low-cost materials and non-powered heat preservation principle to achieve uniform and slow cooling of hot-rolled bars, effectively preventing the generation of white spots and cracks, saving production costs and improving production efficiency.

[0008] To achieve the above objectives, the present invention employs the following technical solution: A method for slow cooling of hot-rolled bars includes the following steps: 1) Construction of slow cooling box: The slow cooling box is constructed on the open ground where the hot rolled bars are stacked. The slow cooling box consists of a box body and a box cover. The box body is made of steel profiles as the frame and steel plates as the wall panels. The top of the box body is open and can be closed by the matching box cover. The four walls and bottom of the box body and the bottom of the box cover are all equipped with insulation material layers. 2) After the hot-rolled bar stock with a final rolling temperature of 950-1020℃ is cut to length by the fixed-length saw, it is cooled to the slow cooling start temperature + (30-50)℃, and then collected and packaged. 3) Collect the bundled bar stacks and hoist them into the slow cooling box. Then immediately close the box lid, leaving gaps between the bar stacks and the four walls of the slow cooling box. The initial slow cooling temperature is 350-450℃. The bar stacks are slowly cooled in the slow cooling box using their own residual heat through natural convection and radiation. The average cooling rate is 10-20℃ / h. 4) When the center temperature of the bar stack drops to 100-200℃, remove the box cover and allow it to air cool to room temperature.

[0009] The thickness of the steel plate is ≥5mm.

[0010] The steel section is an I-beam with a cross-sectional height of not less than 200mm.

[0011] The insulation material layer is formed by cast-in-place insulation material; the cast-in-place insulation material is aluminum silicate fiber castable, lightweight perlite insulation castable, or high-temperature foamed cement.

[0012] The distance between the stack of bar stock and the corresponding side slow cooling box wall panel is 100-500 mm.

[0013] In step 2), the hot-rolled bar stock after being cut to length is cooled by a walking rack and pinion cooling bed.

[0014] In step 2), the cooled bars are collected and packaged using a chain-type steel transfer machine.

[0015] Compared with the prior art, the beneficial effects of the present invention are: (1) Low cost: The bar stock can be delivered immediately after slow cooling in the slow cooling box without straightening; compared with the slow cooling pit method, it can save the subsequent straightening process and transportation costs.

[0016] (2) High efficiency: The operation process is simple and does not require complicated furnace loading, ignition and temperature control procedures. The bar can be quickly put into the box after being cooled to a suitable temperature on the cooling bed, and can be delivered immediately after being taken out of the box. Compared with the slow cooling furnace slow cooling method, it significantly saves production costs, shortens the production cycle and improves the site turnover rate.

[0017] (3) Energy saving and environmental protection: The entire slow cooling process fully utilizes the residual heat of the hot-rolled bar itself, without the need for any external energy (gas, electricity) input, realizing "zero energy consumption" slow cooling, which is in line with the concept of green manufacturing.

[0018] (4) Reliable slow cooling effect: The slow cooling box adopts a multi-layer insulation structure of "steel plate body + insulation material + box cover", which can effectively block heat loss in the form of convection, radiation and conduction, creating a uniform slow cooling environment. Compared with the slow cooling method of insulation cover, it can effectively ensure the slow cooling quality and prevent white spots and crack defects. Detailed Implementation

[0019] The present invention discloses a method for slow cooling of hot-rolled bars, comprising the following steps: 1) Construction of slow cooling box: The slow cooling box is constructed on the open ground where the hot rolled bars are stacked. The slow cooling box consists of a box body and a box cover. The box body is made of steel profiles as the frame and steel plates as the wall panels. The top of the box body is open and can be closed by the matching box cover. The four walls and bottom of the box body and the bottom of the box cover are all equipped with insulation material layers. 2) After the hot-rolled bar stock with a final rolling temperature of 950-1020℃ is cut to length by the fixed-length saw, it is cooled to the slow cooling start temperature + (30-50)℃, and then collected and packaged. 3) Collect the bundled bar stacks and hoist them into the slow cooling box. Then immediately close the box lid, leaving gaps between the bar stacks and the four walls of the slow cooling box. The initial slow cooling temperature is 350-450℃. The bar stacks are slowly cooled in the slow cooling box using their own residual heat through natural convection and radiation. The average cooling rate is 10-20℃ / h. 4) When the center temperature of the bar stack drops to 100-200℃, remove the box cover and allow it to air cool to room temperature.

[0020] Furthermore, the thickness of the steel plate is ≥5mm.

[0021] Furthermore, the steel section is an I-beam with a cross-sectional height of not less than 200mm.

[0022] Furthermore, the insulation material layer is formed by cast-in-place insulation material; the cast-in-place insulation material is aluminum silicate fiber castable, lightweight perlite insulation castable, or high-temperature foamed cement.

[0023] Furthermore, the distance between the stack of bars and the corresponding side slow cooling box wall panel is 100-500mm.

[0024] In step 2), the hot-rolled bar stock after being cut to length is cooled by a walking rack and pinion cooling bed.

[0025] In step 2), the cooled bars are collected and packaged using a chain-type steel transfer machine.

[0026] The slow cooling method for hot-rolled bars described in this invention can meet the slow cooling requirements of bars of different steel grades, effectively eliminate or reduce thermal stress and structural stress after hot rolling. The slow cooling box has the functions of stress relief, hydrogen removal, and prevention of white spots and crack defects, and is conducive to improving the appearance quality of products and reducing finishing work; thereby reducing production costs and shortening the delivery cycle.

[0027] To more intuitively illustrate the present invention, the embodiments of the present invention will be further described in conjunction with the examples. The following examples are merely preferred embodiments of the present invention, but the scope of protection of the present invention is not limited thereto. Any technical solutions that can be obviously obtained by those skilled in the art within the scope of the technology disclosed in the present invention, including simple variations or equivalent substitutions, are all within the scope of protection of the present invention.

[0028]

Example

[0029] Examples 1 and 2 both involve slow cooling in a slow cooling chamber. The initial slow cooling temperatures were 369°C and 387°C, respectively, with average cooling rates of 12°C / h and 18°C / h. The chamber lid was removed when the center temperature of the bar stack dropped to 130°C and 160°C, respectively, and the bars were air-cooled to room temperature.

[0030] Comparative Examples 3 and 4 were both subjected to slow cooling in a slow cooling pit, with the initial temperature of slow cooling ranging from 441℃ to 474℃.

[0031] In Examples 1 and 2, the wall panels of the slow cooling box are made of 5mm thick steel plates, the frame is made of I-beams with a cross-sectional height of 200mm, and the insulation material layer is formed by pouring high-temperature foamed cement.

[0032] Table 1 shows the Brinell hardness comparison of the bars in each embodiment and each comparative example. Table 2 shows the metallographic structure test results of the bars in each embodiment and each comparative example. Table 3 shows the gas content test results of the bars in each embodiment and each comparative example. Table 4 shows the residual stress analysis results of the bars in each embodiment and each comparative example.

[0033] Table 1 - Brinell Hardness (HBW) Comparison Table for Bars Table 2 - Metallographic Structure Test Results of Bars Table 3 - Detection results of gas content in bars Table 4 - Residual stress (MPa) analysis results of bars The above description is only a preferred embodiment of the present invention, but the scope of protection of the present invention is not limited thereto. Any equivalent substitutions or modifications made by those skilled in the art within the scope of the technology disclosed in the present invention, based on the technical solution and inventive concept of the present invention, should be covered within the scope of protection of the present invention.

Claims

1. A method for slow cooling of hot-rolled bars, characterized in that, Includes the following steps: 1) Construction of slow cooling box: The slow cooling box is constructed on the open ground where the hot rolled bars are stacked. The slow cooling box consists of a box body and a box cover. The box body is made of steel profiles as the frame and steel plates as the wall panels. The top of the box body is open and can be closed by the matching box cover. The four walls and bottom of the box body and the bottom of the box cover are all equipped with insulation material layers. 2) After the hot-rolled bar stock with a final rolling temperature of 950-1020℃ is cut to length by the fixed-length saw, it is cooled to the slow cooling start temperature + (30-50)℃, and then a chain-type steel transfer machine is used to collect and pack it. 3) Collect the bundled bar stacks and hoist them into the slow cooling box. Then immediately close the box lid, leaving gaps between the bar stacks and the four walls of the slow cooling box. The initial slow cooling temperature is 350-450℃. The bar stacks are slowly cooled in the slow cooling box using their own residual heat through natural convection and radiation. The average cooling rate is 10-20℃ / h. 4) When the center temperature of the bar stack drops to 100-200℃, remove the box cover and allow it to air cool to room temperature.

2. The method for slow cooling of hot-rolled bars according to claim 1, characterized in that, The thickness of the steel plate is ≥5mm.

3. The method for slow cooling of hot-rolled bars according to claim 1, characterized in that, The steel section is an I-beam with a cross-sectional height of not less than 200mm.

4. The method for slow cooling of hot-rolled bars according to claim 1, characterized in that, The insulation material layer is formed by cast-in-place insulation material; the cast-in-place insulation material is aluminum silicate fiber castable, lightweight perlite insulation castable, or high-temperature foamed cement.

5. The method for slow cooling of hot-rolled bars according to claim 1, characterized in that, The distance between the stack of bar stock and the corresponding side slow cooling box wall panel is 100-500 mm.

6. The method for slow cooling of hot-rolled bars according to claim 1, characterized in that, In step 2), the hot-rolled bar stock after being cut to length is cooled by a walking rack and pinion cooling bed.

7. The method for slow cooling of hot-rolled bars according to claim 1, characterized in that, In step 2), the cooled bars are collected and packaged using a chain-type steel transfer machine.

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