Crack prevention and control method in steel bar calendering processing

Abstract

The invention relates to the technical field of wire rod smelting, and particularly discloses a crack prevention and control method in steel bar calendering processing, which comprises the following steps: selecting a high-quality steel billet: selecting a steel billet with low sulfur and low phosphorus in percentage by mass of chemical components, controlling the content of sulfur and phosphorus in a finished steel bar product, and controlling the mechanical property of the finished steel bar product; an electric furnace production route is set, heating smelting is conducted through an electric arc furnace, a low-frequency furnace and a vacuum refining furnace, then a continuous casting procedure is conducted, and desulfurization, dephosphorization and deoxidation operation is conducted in electric furnace production; controlling the heating temperature of the electric furnace; the rolling temperature and the rolling speed of a rolling mill are controlled, and the initial rolling temperature ranges from 1135 DEG C to 1155 DEG C; a screw-down device of the rolling mill is adjusted, and the screw-down rate is controlled; according to the method, the purity of the steel is improved, the produced steel meets the mechanical properties such as tensile strength, yield point and elongation, cracks generated in the machining process are reduced, the heating temperature and the rolling temperature are reasonably adjusted, technological parameters such as the reduction rate and the rolling speed are optimized, the deformation rate is reduced, and formation and extension of cracks are reduced.

Description

Technical Field

[0001] The present invention relates to the technical field of wire rod smelting, and in particular to a method for preventing and controlling cracks in steel bar rolling processing. Background Art

[0002] Among the types of wire rod, rebar is the most commonly used and is widely used in foundation engineering soil in construction. Rebar is generally made into coils when leaving the factory, or thicker steel bars are made into bundles. Bundled steel bars also bend during transportation and need to be straightened by rolling on a calender. Coils require straightening on a calender. Cracks are often found on the surface of the steel bars during the straightening operation. There are many reasons for this cracking phenomenon. One is due to the reduction of strength and plasticity of steel at high temperatures and excessive local thermal stress; the second is due to structural transformation and stress during the cooling process, as well as the diffusion and accumulation of hydrogen; the third is cracks caused by the steel undergoing a certain number of cycles under alternating stress.

[0003] like Figure 2 As shown in the metallographic structure diagram of steel bars produced in the prior art, the presence of cracks on the steel bars reduces the strength and toughness of the steel, reduces the effective bearing area of ​​the steel, and causes stress concentration, resulting in reduced strength and toughness of the steel. The expansion of cracks will increase the brittleness of the steel, making it more prone to fracture. Cracks are the starting point of fatigue damage, and their presence will significantly reduce the fatigue life of the steel. Under the combined action of stress and environmental factors, the cracks will continue to expand until they reach a critical size, causing the steel to fracture. The presence of cracks significantly increases the risk of steel fracture, especially under high stress and harsh environments. The fracture of steel caused by crack expansion may lead to serious safety accidents and affect the quality of the project. Therefore, it is necessary to design a crack prevention and control method in steel bar rolling processing to solve the problem of large influence of human factors in concrete sampling in the prior art. Summary of the Invention

[0004] In view of the problems existing in the prior art, the purpose of the present invention is to provide a method for preventing and controlling cracks in steel bar rolling processing.

[0005] The technical solution adopted by the present invention to solve the technical problem is: a method for preventing and controlling cracks in steel bar rolling processing, comprising the following steps:

[0006] S1. Select high-quality steel billets: Select steel billets with low sulfur and low phosphorus content in the chemical composition by mass percentage to control the sulfur and phosphorus content of the finished steel bars and control the mechanical properties of the finished steel bars;

[0007] S2. Set the electric furnace production route: After heating and smelting in an electric arc furnace, a low-frequency furnace, and a vacuum refining furnace, it enters the continuous casting process, and desulfurization, dephosphorization, and deoxidation operations are performed in the electric furnace production;

[0008] S3. Control the heating temperature of the electric furnace, furnace temperature control: upper heating temperature is 1120-1200℃, lower heating temperature is 1200-1270℃, soaking zone temperature is 1200-1250℃;

[0009] S4, control the rolling temperature and rolling speed of the rolling mill, and the starting rolling temperature is 1135-1155℃;

[0010] S5. Adjust the rolling mill's reduction device to control the reduction rate.

[0011] Specifically, the chemical composition of the steel billet in step S1 is as follows by mass: C: 0.24-0.27%, Si: 0.15-0.35%, Mn: 0.50-0.80%, P≤0.030%, S≤0.030%, Cr: 0.90-1.20%, Ni: 1.00-1.30%, Mo: 0.15-0.25%, B: 0.0005-0.003%, and the remainder is Fe and unavoidable impurities.

[0012] Specifically, the mechanical properties in step S1 meet the following requirements: yield strength Rp0.2≥930MPa, tensile strength Rm≥1080MPa, impact resistance KV / Ku≥34J, elongation A%≥12%, and cross-sectional shrinkage Z%≥45%.

[0013] Specifically, the electric arc furnace raw materials in step S2 are molten iron and scrap steel in a mass ratio of 40%, and the scrap steel is added in two batches. Iron-phosphorus balls made of 3 tons of lime and 1 ton of iron oxide scale are added to the bottom of the hanging basket of the first feeding for low-temperature dephosphorization in the early stage of smelting; the carbon mass percentage at the end of the electric arc furnace is controlled between 0.03% and 0.05%, the carbon mass percentage of the finished product is controlled between 0.24% and 0.27%, the oxygen content at the end of the electric arc furnace is basically between 600-800ppm, and the tapping amount is controlled between 130-150 tons. Before tapping, 1 ton of desulfurizer is added to the bottom of the ladle, 200kg of aluminum blocks and other alloys, lime, and scouring slag are added during the tapping process, and 200 meters of aluminum wire is fed after tapping to deeply deoxidize the molten steel; and the vacuum refining furnace uses a silicon-calcium-aluminum synthetic deoxidizer to diffusely deoxidize the top slag.

[0014] Specifically, the desulfurizer is silicon-calcium alloy.

[0015] Specifically, the rolling temperature in step S4 is 1135-1145°C, the rolling speed of the hot-rolled ribbed steel bars with a diameter of ф20 mm and ф28 mm is controlled at 10.5 m / s, and under uncontrolled cooling conditions, for large-size hot-rolled ribbed steel bars with a diameter of ф32 mm, the rolling speed is controlled at 7 m / s.

[0016] Specifically, the rolling mill in step S5 adopts built-in screw-down devices in the roughing mill group, the intermediate rolling mill group and the finishing mill group, which are controlled by hydraulic motor linkage.

[0017] Specifically, the reduction rate of the roughing mill group is controlled at 15%-20% to ensure smooth biting into the rolling mill;

[0018] The reduction rate of the intermediate rolling mill is controlled at 25%-30% to fully utilize the equipment capacity;

[0019] The reduction rate of the finishing mill is controlled at 5%-10% to ensure the dimensional accuracy of the steel bars leaving the rolling mill.

[0020] The present invention has the following beneficial effects:

[0021] The crack prevention and control method during steel bar rolling processing designed by the present invention selects steel billets with low sulfur and phosphorus content to reduce hot brittleness and cold brittleness, performs dephosphorization, desulfurization and deoxidation treatments, controls the content and form of non-metallic inclusions in the steel, and improves the purity of the steel. The produced steel has sufficient mechanical properties such as tensile strength, yield point, and elongation to reduce the occurrence of cracks during the processing process.

[0022] The crack prevention and control method designed in the steel bar rolling processing of the present invention reasonably adjusts the heating temperature and rolling temperature to avoid excessively high or low temperatures that lead to internal stress concentration and crack generation in the material, optimizes process parameters such as the reduction rate and rolling speed, reduces the deformation rate, and reduces the formation and expansion of cracks. BRIEF DESCRIPTION OF THE DRAWINGS

[0023] Figure 1 It is the metallographic structure diagram of steel bars produced by crack prevention and control methods in steel bar rolling processing.

[0024] Figure 2 It is the metallographic organization diagram of steel bars produced in the prior art. DETAILED DESCRIPTION

[0025] The following will be combined with the accompanying drawings in the embodiments of the present invention to clearly and completely further describe the technical solutions in the embodiments of the present invention. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without making creative work are within the scope of protection of the present invention.

[0026] A method for crack prevention and control in steel bar rolling processing. The mechanical properties of the produced steel bars meet the following requirements: yield strength Rp0.2≥930MPa, tensile strength Rm≥1080MPa, impact resistance KV / Ku≥34J, elongation A%≥12%, and section shrinkage Z%≥45%.

[0027] The metallographic structure of steel bars produced Figure 1shown.

[0028] Example 1.

[0029] A method for preventing and controlling cracks in steel bar rolling processing comprises the following steps:

[0030] 1. Select high-quality steel billets: Select steel billets with low sulfur and low phosphorus content in terms of chemical composition by mass percentage to control the sulfur and phosphorus content of the finished steel bars and the mechanical properties of the finished steel bars; the chemical composition by mass percentage of the steel billets is: C: 0.24%, Si: 0.15%, Mn: 0.50%, P≤0.030%, S≤0.030%, Cr: 0.90%, Ni: 1.00%, Mo: 0.15%, B: 0.0005%, and the balance is Fe and unavoidable impurities.

[0031] 2. Set the electric furnace production route: After heating and smelting in an electric arc furnace, a low-frequency furnace, and a vacuum refining furnace, the continuous casting process begins. Desulfurization, dephosphorization, and deoxidation operations are performed during electric furnace production. Before tapping, one ton of high-efficiency desulfurizer is added to the bottom of the ladle. During the tapping process, 800 kg of lime and 300 kg of refined slag are added. Pre-desulfurization is achieved by mixing molten steel and slag. After tapping, 200 meters of aluminum wire is fed to further reduce the content of aluminum in the steel. In the later stages of the electric arc furnace tapping port, the amount of steel retained in the furnace is increased to avoid slag discharge or to minimize the production of low-phosphorus and ultra-low-sulfur steel. During refining, a silicon-calcium-aluminum synthetic deoxidizer is added to strengthen the deoxidation of the top slag. Ensure good argon stirring in the ladle to promote rapid desulfurization reactions at the steel-slag interface.

[0032] The raw materials of the electric arc furnace are molten iron and scrap steel in a mass ratio of 40%. The scrap steel is added in two times. Iron-phosphorus balls made of 3 tons of lime and 1 ton of iron oxide scale are added to the bottom of the hanging basket of the first feeding, which are used for low-temperature dephosphorization in the early stage of smelting. The carbon mass percentage of the electric arc furnace end point is controlled between 0.03%, and the carbon mass percentage of the finished product is controlled between 0.24%. The oxygen content of the electric arc furnace end point is basically between 600ppm, and the steel tapping volume is controlled at 130 tons. Before tapping, 1 ton of desulfurizer is added to the bottom of the ladle. During the tapping process, 200kg of aluminum blocks and other alloys, lime, and refined slag are added. After tapping, 200 meters of aluminum wire is fed to deeply deoxidize the molten steel. The vacuum refining furnace uses a silicon-calcium-aluminum synthetic deoxidizer to diffusely deoxidize the top slag.

[0033] The impact of slag volume on dephosphorization. To improve dephosphorization efficiency, the FeO and CaO contents in the slag must be increased. In the industrial production of low-phosphorus steel, iron-phosphorus pellets, made from 3 tons of lime and 1 ton of iron oxide scale, are added to the bottom of the scrap container to enhance low-temperature dephosphorization in the early stages of smelting. The total amount of lime added to the electric arc furnace is 8 tons. The composition of the slag sample before tapping from the electric arc furnace is: CaO: 47%, TFe: 25%, SiO: 13%, and the basicity is controlled at 2.5.

[0034] The impact of molten steel oxygen activity on desulfurization. Reducing the oxygen activity of molten steel will cause the sulfur in the molten steel to transfer to the slag. In the industrial production of ultra-low sulfur steel, an oxygen analyzer is used to measure the oxygen content of molten steel after refining, and the oxygen activity in the molten steel is controlled to within 2.5ppm.

[0035] The influence of slag volume and aluminum consumption on desulfurization. From the thermodynamic mechanism of desulfurization reaction, large slag volume increases the sulfur distribution ratio between slag and steel. In addition, large aluminum consumption is conducive to deep deoxidation of molten steel. However, excessive slag volume and aluminum consumption will lead to excessively high production costs for the enterprise. When the slag volume is controlled at 22kg / t steel and the aluminum consumption reaches 1.85Kg / t steel, the effect of deep desulfurization can be achieved.

[0036] Argon stirring can greatly promote the sulfur exchange between slag and molten steel. Good gas stirring is mainly based on not exposing the steel liquid surface. Otherwise, air will continuously enter the molten steel, which will not only increase the oxygen activity of the molten steel, causing desulfurization difficulties, but also deteriorate the purity of the molten steel.

[0037] 3. Control the heating temperature of the electric furnace and the furnace temperature control: the upper heating temperature is 1120℃, the lower heating temperature is 1200℃, and the soaking section temperature is 1200℃.

[0038] 4. Control the rolling temperature and rolling speed of the rolling mill. The starting rolling temperature is 1135℃. When the rolling temperature is 1135℃, the rolling speed of hot-rolled ribbed steel bars with a diameter of ф20mm and ф28mm is controlled at 10.5m / s. Under uncontrolled cooling conditions, for large-size hot-rolled ribbed steel bars with a diameter of ф32mm, the rolling speed is controlled at 7m / s.

[0039] The rolling mill's roughing mill, intermediate rolling mill and finishing mill all use built-in screw-down devices, which are controlled by hydraulic motor linkage.

[0040] 5. Adjust the rolling mill's reduction device to control the reduction rate. The roughing mill's reduction rate is controlled at 15% to ensure smooth mill entry; the intermediate mill's reduction rate is controlled at 25% to fully utilize the equipment's capacity; and the finishing mill's reduction rate is controlled at 5% to ensure dimensional accuracy of the rebar exiting the mill.

[0041] By utilizing the characteristics of reflection and refraction of ultrasonic waves when they propagate in materials and encounter defects such as cracks, the internal cracks of the steel bars are detected. The internal cracks of the steel bars are greatly reduced, and no obvious external cracks are found after the calender operation.

[0042] Example 2.

[0043] A method for preventing and controlling cracks in steel bar rolling processing comprises the following steps:

[0044] 1. Select high-quality steel billets: Select steel billets with low sulfur and low phosphorus content in terms of chemical composition by mass percentage to control the sulfur and phosphorus content of the finished steel bars and the mechanical properties of the finished steel bars; the chemical composition by mass percentage of the steel billets is: C: 0.27%, Si: 0.35%, Mn: 0.80%, P≤0.030%, S≤0.030%, Cr: 1.20%, Ni: 1.30%, Mo: 0.25%, B: 0.003%, and the balance is Fe and unavoidable impurities.

[0045] 2. Set the electric furnace production route: After heating and smelting in an electric arc furnace, a low-frequency furnace, and a vacuum refining furnace, the continuous casting process begins. Desulfurization, dephosphorization, and deoxidation operations are performed during electric furnace production. Before tapping, one ton of high-efficiency desulfurizer is added to the bottom of the ladle. During the tapping process, 800 kg of lime and 300 kg of refined slag are added. Pre-desulfurization is achieved by mixing molten steel and slag. After tapping, 200 meters of aluminum wire is fed to further reduce the content of aluminum in the steel. In the later stages of the electric arc furnace tapping port, the amount of steel retained in the furnace is increased to avoid slag discharge or to minimize the production of low-phosphorus and ultra-low-sulfur steel. During refining, a silicon-calcium-aluminum synthetic deoxidizer is added to strengthen the deoxidation of the top slag. Ensure good argon stirring in the ladle to promote rapid desulfurization reactions at the steel-slag interface.

[0046] The raw materials of the electric arc furnace are molten iron and scrap steel in a mass ratio of 40%. The scrap steel is added in two times. Iron-phosphorus balls made of 3 tons of lime and 1 ton of iron oxide scale are added to the bottom of the hanging basket of the first feeding, which are used for low-temperature dephosphorization in the early stage of smelting. The carbon mass percentage of the electric arc furnace end point is controlled between 0.05%, and the carbon mass percentage of the finished product is controlled between 0.27%. The oxygen content of the electric arc furnace end point is basically between 800ppm, and the steel tapping volume is controlled at 150 tons. Before tapping, 1 ton of desulfurizer is added to the bottom of the ladle. During the tapping process, 200kg of aluminum blocks and other alloys, lime, and refined slag are added. After tapping, 200 meters of aluminum wire is fed to deeply deoxidize the molten steel. The vacuum refining furnace uses a silicon-calcium-aluminum synthetic deoxidizer to diffusely deoxidize the top slag.

[0047] The impact of slag volume on dephosphorization: To improve dephosphorization efficiency, the FeO and CaO contents in the slag must be increased. In the industrial production of low-phosphorus steel, iron-phosphorus pellets, made from 3 tons of lime and 1 ton of iron oxide scale, are added to the bottom of the scrap container to enhance low-temperature dephosphorization in the early stages of smelting. The total amount of lime added to the electric arc furnace is 8-9 tons. The composition of the slag sample before tapping from the electric arc furnace is: CaO: 52%, TFe: 41%, SiO: 18%, and the basicity is controlled at 3.1.

[0048] The impact of molten steel oxygen activity on desulfurization. Reducing the oxygen activity of molten steel will cause the sulfur in the molten steel to transfer to the slag. In the industrial production of ultra-low sulfur steel, an oxygen analyzer is used to measure the oxygen content of molten steel after refining, and the oxygen activity in the molten steel is controlled to within 2.5ppm.

[0049] The influence of slag volume and aluminum consumption on desulfurization. From the thermodynamic mechanism of desulfurization reaction, large slag volume increases the sulfur distribution ratio between slag and steel. In addition, large aluminum consumption is conducive to deep deoxidation of molten steel. However, excessive slag volume and aluminum consumption will lead to excessively high production costs for the enterprise. When the slag volume is controlled at 22kg / t steel and the aluminum consumption reaches 1.85Kg / t steel, the effect of deep desulfurization can be achieved.

[0050] Argon stirring can greatly promote the sulfur exchange between slag and molten steel. Good gas stirring is mainly based on not exposing the steel liquid surface. Otherwise, air will continuously enter the molten steel, which will not only increase the oxygen activity of the molten steel, causing desulfurization difficulties, but also deteriorate the purity of the molten steel.

[0051] 3. Control the heating temperature of the electric furnace and the furnace temperature control: the upper heating temperature is 1200℃, the lower heating temperature is 1270℃, and the soaking section temperature is 1250℃.

[0052] 4. Control the rolling temperature and rolling speed of the rolling mill. The starting rolling temperature is 1155℃; the rolling temperature is 1145℃, and the rolling speed of hot-rolled ribbed steel bars with a diameter of ф20mm and ф28mm is controlled at 10.5m / s. Under uncontrolled cooling conditions, for large-size hot-rolled ribbed steel bars with a diameter of ф32mm, the rolling speed is controlled at 7m / s.

[0053] The rolling mill's roughing mill, intermediate rolling mill and finishing mill all use built-in screw-down devices, which are controlled by hydraulic motor linkage.

[0054] 5. Adjust the rolling mill's reduction device to control the reduction rate. The roughing mill's reduction rate is controlled at 20% to ensure smooth entry into the mill; the intermediate mill's reduction rate is controlled at 30% to fully utilize the equipment's capacity; and the finishing mill's reduction rate is controlled at 10% to ensure dimensional accuracy of the rebar exiting the mill.

[0055] By utilizing the characteristics of reflection and refraction of ultrasonic waves when they propagate in materials and encounter defects such as cracks, the internal cracks of the steel bars are detected. The internal cracks of the steel bars are greatly reduced, and no obvious external cracks are found after the calender operation.

[0056] The present invention is not limited to the above-mentioned embodiments. Anyone should be aware that any structural changes made under the guidance of the present invention, and any technical solutions that are the same or similar to those of the present invention, fall within the scope of protection of the present invention.

[0057] The technology, shape, and structure not described in detail in the present invention are all well-known technologies.

Claims

1. A method for preventing and controlling cracks in steel bar rolling processing, characterized in that: The following steps are involved: S1. Select high-quality steel billets: Select steel billets with low sulfur and low phosphorus content in the chemical composition by mass percentage to control the sulfur and phosphorus content of the finished steel bars and control the mechanical properties of the finished steel bars; S2. Set the electric furnace production route: After heating and smelting in an electric arc furnace, a low-frequency furnace, and a vacuum refining furnace, it enters the continuous casting process, and desulfurization, dephosphorization, and deoxidation operations are performed in the electric furnace production; S3. Control the heating temperature of the electric furnace, furnace temperature control: upper heating temperature is 1120-1200℃, lower heating temperature is 1200-1270℃, soaking zone temperature is 1200-1250℃; S4, control the rolling temperature and rolling speed of the rolling mill, and the starting rolling temperature is 1135-1155℃; S5. Adjust the rolling mill's reduction device to control the reduction rate.

2. The method for preventing and controlling cracks in steel bar rolling processing according to claim 1, wherein: The chemical composition of the steel billet in step S1 is as follows by mass: C: 0.24-0.27%, Si: 0.15-0.35%, Mn: 0.50-0.80%, P≤0.030%, S≤0.030%, Cr: 0.90-1.20%, Ni: 1.00-1.30%, Mo: 0.15-0.25%, B: 0.0005-0.003%, and the remainder is Fe and unavoidable impurities.

3. The method for preventing and controlling cracks in steel bar rolling processing according to claim 1, wherein: The mechanical properties in step S1 meet the following requirements: yield strength Rp0.2≥930MPa, tensile strength Rm≥1080MPa, impact resistance KV / Ku≥34J, elongation A%≥12%, and cross-sectional shrinkage Z%≥45%.

4. The method for preventing and controlling cracks in steel bar rolling processing according to claim 1, wherein: The electric arc furnace raw materials in step S2 are molten iron and scrap steel in a mass ratio of 40%, and the scrap steel is added in two batches. Iron-phosphorus balls made of 3 tons of lime and 1 ton of iron oxide scale are added to the bottom of the hanging basket of the first feeding for low-temperature dephosphorization in the early stage of smelting. The carbon mass percentage at the end of the electric arc furnace is controlled between 0.03% and 0.05%, the carbon mass percentage of the finished product is controlled between 0.24% and 0.27%, the oxygen content at the end of the electric arc furnace is basically between 600-800ppm, and the tapping amount is controlled between 130-150 tons. Before tapping, 1 ton of desulfurizer is added to the bottom of the ladle. During the tapping process, 200 kg of aluminum blocks and other slag materials such as alloys, lime, and refined slag are added. After tapping, 200 meters of aluminum wire is fed to deeply deoxidize the molten steel. The vacuum refining furnace uses a silicon-calcium-aluminum synthetic deoxidizer to diffusely deoxidize the top slag.

5. The method for preventing and controlling cracks in steel bar rolling processing according to claim 4, wherein: The desulfurizer is a silicon-calcium alloy.

6. The method for preventing and controlling cracks in steel bar rolling processing according to claim 1, characterized in that: The rolling temperature in step S4 is 1135-1145°C, and the rolling speed of the hot-rolled ribbed steel bars with a diameter of ф20 mm and ф28 mm is controlled at 10.5 m / s. Under uncontrolled cooling conditions, for large-size hot-rolled ribbed steel bars with a diameter of ф32 mm, the rolling speed is controlled at 7 m / s.

7. The method for preventing and controlling cracks in steel bar rolling processing according to claim 1, characterized in that: In the step S5, the rolling mill adopts built-in screw-down devices in the roughing mill group, the intermediate rolling mill group and the finishing mill group, and is controlled by hydraulic motor linkage.

8. The method for preventing and controlling cracks in steel bar rolling processing according to claim 7, wherein: The reduction rate of the roughing mill group is controlled at 15%-20% to ensure smooth biting into the rolling mill; The reduction rate of the intermediate rolling mill is controlled at 25%-30% to fully utilize the equipment capacity; The reduction rate of the finishing mill is controlled at 5%-10% to ensure the dimensional accuracy of the steel bars leaving the rolling mill.

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