A method for preparing φ8mm low-cost, high-quality, high-strength, fine-grained hot-rolled coil

Abstract

The invention discloses a preparation method of a φ8mm low-cost, high-quality, high-strength, fine-grained hot-rolled coil, comprising: a steel tapping temperature of 950-980°C; hot delivery and hot loading of billets, controlling the temperature difference of the billet rolling temperature and the wire rod ≤60°C; controlling the finishing rolling entrance temperature at 910±20°C, and the wire laying temperature at 940-960°C; on the Stelmor air-cooled line, the wire rod is cooled and heat is exchanged naturally, the air-cooled scheme does not start the fan, adopts natural air cooling, adjusts the air-cooled roller speed, reasonably controls the circle spacing of the steel bar on the air-cooled roller, reduces the stacking thickness of the circles, increases the natural heat exchange capacity, and sets the roller speed entrance section to 0.56-0.69m / s. The invention improves and optimizes the rolling process, realizes the guarantee of stable product performance, sufficient margin, good seismic performance and welding performance, reduces the alloy cost in steel, saves resources, effectively reduces production costs, and increases product profitability.

Description

Technical Field

[0001] The invention relates to a method for preparing a φ8mm low-cost, high-quality, high-strength, fine-grain hot-rolled coil. Background Art

[0002] Hot-rolled ribbed steel bars for reinforced concrete are important building materials. my country is in a period of rapid industrialization and urbanization, and the construction industry is developing rapidly. Based on the huge impact of steel bars on building safety, service life, resource conservation, etc., the country attaches great importance to the quality of steel bars and promulgated the national standard 1499.2-2018 (hereinafter referred to as the new national standard).

[0003] As the most important and largest-volume steel product for construction, the improvement of its strength grade and quality level has a direct impact on the sustainable development of my country's economy. Microalloying technology is currently the main process technology solution for producing high-strength steel bars. Alloying elements Si, Mn and microalloy V are considered to be the best alloying elements to improve the strength of HRB400E steel bars. In September 2018, the price of ferrovanadium rose significantly, in order to cope with the survival pressure of the substantial increase in alloy costs. With the implementation of the new national standard, the use of waste heat quenching process to achieve low-cost production cannot meet the requirements of the new national standard for product metallographic structure. Therefore, a low-cost, high-quality, high-strength, fine-grained hot-rolled coil HRB400E preparation method is urgently needed. Comprehensively considering the equipment capabilities of the enterprise and the interests of users, seek the greatest economic and social benefits, and fully reflect the technical advancement and rationality of the standard. Summary of the invention

[0004] The purpose of the present invention is to provide a method for preparing a φ8mm low-cost, high-quality, high-strength, fine-grained hot-rolled coil, using a composition design idea of ​​replacing a high-priced alloy with a low-priced alloy, improving and optimizing the rolling process, and ensuring stable product performance, sufficient margin, good seismic resistance and welding performance, reducing the alloy cost in steel, saving resources, effectively reducing production costs, and increasing product profitability.

[0005] In order to solve the above technical problems, the present invention adopts the following technical solutions:

[0006] The present invention provides a method for preparing a φ8mm low-cost, high-quality, high-strength, fine-grained hot-rolled coil, comprising:

[0007] Steel tapping temperature is 950-980℃; hot delivery and hot loading of billets, and the temperature difference of the billet rolling rod is controlled to be ≤60℃;

[0008] Control the finishing rolling inlet temperature at 910±20℃ and the spinning temperature at 940-960℃;

[0009] On the Stelmor air-cooling line, the cooling of the wire rod is done by natural heat exchange. The air-cooling solution does not start the fan, but adopts natural air cooling. The air-cooling roller speed is adjusted, the circle spacing of the steel bars on the air-cooling roller is reasonably controlled, the stacking thickness of the circles is reduced, the natural heat exchange capacity is increased, and the roller speed entrance section is set at 0.56-0.69m / s.

[0010] Furthermore, the chemical composition of the coiled snail, calculated by mass percentage, includes: C: 0.21%-0.24%, Si: 0.65%-0.75%, Mn: 1.45%-1.55%, P≤0.045%, S≤0.045%, and the rest is Fe and unavoidable impurities.

[0011] Furthermore, the standard deviation of product strength index is <25MPa, and the process capability index is >1.33.

[0012] Furthermore, the product has a grain size of above 9 levels, a metallographic structure of ferrite and pearlite, and a matrix without tempered martensite structure.

[0013] Compared with the prior art, the beneficial technical effects of the present invention are:

[0014] While reducing production costs, the stability of product quality is ensured. After the implementation of the plan, the alloy cost was reduced by 22.6 yuan / ton, and the energy consumption of the process plan was reduced by 0.8 yuan / ton. Based on the annual output of 50,000 tons of this product, the annual profit is: (22.6+0.8) yuan / ton×50,000 tons=1.17 million yuan. For domestic companies using Morgan's fifth-generation high-speed wire production line, we believe that this invention has promotion value and can create considerable economic and social benefits for related companies. BRIEF DESCRIPTION OF THE DRAWINGS

[0015] The present invention will be further described below in conjunction with the accompanying drawings.

[0016] Figure 1 The metallographic structure of the product prepared by the present invention. DETAILED DESCRIPTION

[0017] A method for preparing φ8mm low-cost, high-quality, high-strength, fine-grained hot-rolled coil, the technical scheme adopted is as follows:

[0018] (1) The present invention adds Si and Mn low-cost alloys to replace precious alloys such as V and Ni, balances the amount of alloy, effectively saves resources, and reduces alloy costs; chemical composition scheme: C: 0.21%-0.24%, Si: 0.65%-0.75%, Mn: 1.45%-1.55%, P≤0.045%, S≤0.045%.

[0019] (2) By controlling the process parameters of HRB400E coil rolling temperature, final rolling temperature, rolling deformation rate, rolling speed and optimizing the Stelmor process parameters, the fine grain strengthening effect of fine grain structure can be achieved.

[0020] The key to fine grain steel rolling production lies in low temperature rolling and low temperature rapid cooling, combined with low temperature start rolling and low temperature final rolling of recrystallization, non-recrystallization and deformation induced phase transformation mechanism. Properly controlling the heating temperature of the steel billet makes its original austenite grains uniform and fine, providing good conditions for phase transformation through controlled cooling after rolling to obtain an ideal organizational structure.

[0021] In order to avoid the coarsening of the original austenite grains due to excessively high heating temperature and long heating time, the rough rolling mill load is calculated and the steel-out temperature is designed to be 950-980°C. The billet is hot-delivered and hot-loaded, and the temperature difference of the billet rolling temperature is controlled to be ≤60°C.

[0022] Since high-speed wire rolling has a high deformation rate, the finishing rolling inlet temperature is controlled at 910±20℃. In order to control the grain size after finishing rolling, the wire drawing temperature is controlled at about 950℃ so as to obtain fine ferrite and pearlite grains later.

[0023] (3) By adjusting the parameters of the air-cooling roller on the Stelmore line, such as the speed of the air-cooling roller and the opening of the fan, the cooling speed of the product after rolling can be increased, the growth of grains after rolling can be suppressed, and the strength of the product can be improved. On the Stelmore air-cooling line, the cooling of the wire rod is natural heat exchange. The air-cooling solution does not start the fan, but uses natural air cooling, adjusts the speed of the air-cooling roller, reasonably controls the circle spacing of the steel bar on the air-cooling roller, reduces the stacking thickness of the circles, and increases the natural heat exchange capacity. The roller speed entrance section is set to 0.56-0.69m / s to reasonably control the cooling rate, improve strength, and uniform structure.

[0024] Table 1 Rolling process scheme

[0025]

[0026] Take 12 pieces of materials from the same furnace number and two process schemes respectively. The comparison of mechanical properties after trial production using different process schemes is shown in Table 2 below.

[0027] Table 2 Comparison of mechanical properties of φ8mm coil under different roller speeds

[0028]

[0029] By comparing the data in Table 2, the yield strength Rel and tensile strength Rm of process scheme 2 are improved, while the elongation A and maximum force total elongation Agt remain basically unchanged.

[0030] The coils produced using process solution 2 have small fluctuations in yield strength, tensile strength, and total elongation at maximum force, and have excellent performance stability.

[0031] In summary, both process schemes can achieve the expected goals, and process scheme 2 is the optimal control scheme for the φ8mm coil rolling process.

[0032] The product was tested in industrial trial production using process optimization solution 2. All product properties meet the requirements and have good stability. After the Morgan production line was put into industrial production, the mechanical properties of the product met the standard requirements, and the indicators are shown in Table 3 below:

[0033] Table 3 Statistics of industrial production performance indicators

[0034]

[0035] For the mechanical properties of steel bars, in addition to meeting the basic requirements of the standard for mechanical properties, the smaller the fluctuation of its strength, the better. Therefore, the strength index of this product of Morgan production line in the past 6 months was selected for stability analysis, as shown in Table 4 below:

[0036] Table 4 Stability analysis

[0037]

[0038] Through the stability analysis of the product, the standard deviation of the product strength index is less than 25MPa, and the process capability index is greater than 1.33, reflecting the stability of the process and sufficient process capability. The process limitation of the overlap point and non-overlap point on the air-cooled roller after rolling of the wire rod product has been solved, which makes the performance of the same circle have a large deviation. The average strength deviation of the product in the same circle is small and stable at 25MPa. There is no obvious change in the strength index after aging.

[0039] Figure 1 This is a metallographic structure photo of the industrial trial product. It can be seen from the figure that the actual grain size of the product is above level 9, the metallographic structure is ferrite and pearlite, and the matrix has no tempered martensite structure.

[0040] By replacing high-priced alloys with low-priced alloys, and continuously improving and optimizing the rolling process, we can ultimately achieve stable product performance, good seismic resistance and welding performance, and achieve the goal of reducing production costs, saving resources, and improving product profitability. After the implementation of the plan, the alloy cost was reduced by 22.6 yuan / ton, and the process plan energy consumption cost was reduced by 0.8 yuan / ton. Based on the annual output of 50,000 tons of this product, the annual profit is: (22.6+0.8) yuan / ton×50,000 tons=1.17 million yuan. For domestic companies using Morgan's fifth-generation high-speed wire production line, we believe that this invention has promotion value and can create considerable economic and social benefits for related companies.

[0041] The embodiments described above are only descriptions of the preferred modes of the present invention, and are not intended to limit the scope of the present invention. Without departing from the design spirit of the present invention, various modifications and improvements made to the technical solutions of the present invention by ordinary technicians in this field should all fall within the protection scope determined by the claims of the present invention.

Claims

1. A method for preparing φ8mm low-cost, high-quality, high-strength, fine-grained hot-rolled coil, characterized in that: include: Steel tapping temperature is 950-980℃; hot delivery and hot loading of billets, and the temperature difference of the billet rolling rod is controlled to be ≤60℃; Control the finishing rolling inlet temperature at 910±20℃ and the spinning temperature at 940-960℃; On the Stelmor air-cooling line, the cooling of the wire rod is done by natural heat exchange. The air-cooling solution does not start the fan, the insulation cover is fully opened, natural air cooling is adopted, the air-cooling roller speed is adjusted, the circle distance of the steel bar on the air-cooling roller is reasonably controlled, the stacking thickness of the circles is reduced, the natural heat exchange capacity is increased, and the roller speed entrance section is set to 0.56-0.69m / s; The chemical composition of the coiled snail, calculated by mass percentage, includes: C: 0.21%-0.24%, Si: 0.65%-0.75%, Mn: 1.45%-1.55%, P ≤0.045%, S≤0.045%, and the rest is Fe and unavoidable impurities.

2. The method for preparing φ8mm low-cost, high-quality, high-strength, fine-grained hot-rolled coil according to claim 1, characterized in that: The standard deviation of product strength index is <25MPa, and the process capability index is >1.

33.

3. The method for preparing φ8mm low-cost, high-quality, high-strength, fine-grained hot-rolled coil according to claim 1, characterized in that: The product grain size is above grade 9, the metallographic structure is ferrite and pearlite, and the matrix has no tempered martensite structure.

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