Preparation method of low-carbon emission cord steel wire rod

Abstract

The present invention provides a method for preparing a cord steel wire rod with low carbon emissions. In the electric furnace smelting process, all scrap steel is used. After the first batch of scrap steel is added to the electric furnace, power is supplied and coke oven gas and oxygen are introduced. When the power consumption per ton of steel reaches 45 kWh / t, the supply of coke oven gas is stopped and oxygen is introduced into the furnace, and 5 - 6 kg / t of lime is added from the bunker. When the power consumption per ton of steel reaches 100 kWh / t, the second batch of scrap steel is added and coke oven gas and oxygen are introduced into the furnace. When the power consumption per ton of steel reaches 120 kWh / t, 15 - 18 kg / t of carbon powder is injected. When the power consumption per ton of steel reaches 150 kWh / t, the supply of coke oven gas is stopped and oxygen is introduced into the furnace, and lime is added to adjust the basicity of the steel slag to 2.0 - 2.5. When the power consumption per ton of steel reaches 360 kWh / t, the oxygen supply is stopped and lime powder is injected to adjust the basicity of the steel slag to 4.0 - 4.5. When the power consumption per ton of steel reaches 390 - 410 kWh / t, tapping is carried out. This method can improve the quality of the cord steel and is low-carbon and environmentally friendly.

Description

Technical Field

[0001] The present invention belongs to the technical field of steel smelting, and particularly relates to a method for preparing a low-carbon emission cord steel wire rod. Background Art

[0002] Steel cord is a common rubber skeleton material and is widely used in the radial tires of various automobiles, trucks, and airplanes. During the production process of steel cord, it is necessary to draw a cord steel wire rod with a diameter of 5.5 mm into a thin wire with a diameter of 0.15 - 0.38 mm, and its elongation rate is about 1000 times. Therefore, high requirements are put forward for the metallurgical quality of the wire rod, especially for the content of impurity elements, cleanliness, and drawing performance.

[0003] In order to make the cord steel wire rod have excellent cleanliness and drawing performance, blast furnace-converter smelting is commonly used in the current metallurgical field. However, the smelting cycle of the blast furnace-converter is long, and the carbon emission level during the production process is high, which is not environmentally friendly. Nowadays, there are also those using the electric furnace smelting process for steel cord production, but there are also problems of high carbon emission levels and difficult control of steel quality. Summary of the Invention

[0004] The purpose of the present invention is to provide a method for preparing a low-carbon emission cord steel wire rod to reduce carbon dioxide emissions, improve the cleanliness of the finally prepared cord steel, and reduce the wire breakage rate.

[0005] To achieve one of the above purposes, an embodiment of the present invention provides a method for preparing a low-carbon emission cord steel wire rod, including the electric furnace smelting, refining, continuous casting, blooming, high-speed wire rolling, and controlled cooling processes carried out in sequence. All scrap steel is used in the electric furnace smelting process, and the scrap steel is added to the electric furnace in two batches.

[0006] After the first batch of scrap steel is added to the electric furnace, power is turned on, and coke oven gas and oxygen are introduced into the electric furnace through the wall lance. The flow ratio of coke oven gas to oxygen is 2:1, and the gas supply intensity of coke oven gas is 15 - 20 Nm 3 / (h·t);

[0007] When the power consumption per ton of steel reaches 45 kWh / t, stop introducing coke oven gas into the electric furnace, and introduce oxygen into the electric furnace through the wall lance and the door lance. The gas supply intensity of oxygen is 100 - 120 Nm 3 / (h·t), and 5 - 6 kg / t of lime is added from the bunker;

[0008] When the power consumption per ton of steel reaches 100 kWh / t, stop power supply, add the second batch of scrap steel to the molten steel, lower the electrode and start power supply, and introduce coke oven gas and oxygen into the electric furnace through the wall lance. The flow ratio of coke oven gas to oxygen is 2:1, and the gas supply intensity of coke oven gas is 15 - 20 Nm 3 / (h·t);

[0009] When the power consumption per ton of steel reaches 120 kWh / t, 15 - 18 kg / t of carbon powder is blown through the carbon powder lance on the furnace wall, and the blowing flow rate of the carbon powder is 0.7 - 0.8 kg / (t·min);

[0010] When the power consumption per ton of steel reaches 150 kWh / t, the coke oven gas supply to the electric furnace is stopped, and oxygen is supplied to the electric furnace through the lance on the furnace wall and the lance on the furnace door. The oxygen supply intensity is 100 - 120 Nm 3 / (h·t), and lime is added in 3 - 4 batches from the bin and the bottom blowing system of the furnace to adjust the basicity of the steel slag to 2.0 - 2.5. Among them, 15 - 18 kg / t of lime is added from the bin, 6 - 8 kg / t of lime is added from the bottom blowing system of the furnace, and the blowing flow rate of lime powder from the bottom blowing system of the furnace is 1.2 - 1.3 kg / (t·min). The addition interval of lime in different batches is 2 - 3 min;

[0011] When the power consumption per ton of steel reaches 360 kWh / t, the oxygen supply of the lance on the furnace wall and the lance on the furnace door is stopped, and 8 - 12 kg / t of lime powder is blown from the bottom blowing system of the furnace to adjust the basicity of the steel slag to 4.0 - 4.5;

[0012] Tapping is carried out when the power consumption per ton of steel reaches 390 - 410 kWh / t. The tapping temperature ≥ 1650 °C. When tapping, C ≥ 0.03% in the molten steel, P ≤ 0.01%, S ≤ 0.01%, O ≤ 0.002%, N ≤ 0.005%, Sn ≤ 0.015%.

[0013] As a further improvement of an embodiment of the present invention, the thickness of the scrap steel ≥ 2 mm and satisfies: S ≤ 0.025%, Ni ≤ 0.1%, Cr ≤ 0.1%, Cu ≤ 0.1%, Cu + Cr + Ni ≤ 0.25%, Sn ≤ 0.015%, Al ≤ 0.05%, Ti ≤ 0.05%.

[0014] As a further improvement of an embodiment of the present invention, in the electric furnace smelting process, the molten steel remaining in the electric furnace ≥ 10 t, and the total charging amount is 115 - 120 t.

[0015] As a further improvement of an embodiment of the present invention, when the power consumption per ton of steel reaches 150 kWh / t, lime is blown into the molten steel in powder form from the bottom blowing system of the furnace, and the blowing flow rate is 1.5 - 2 kg / (t·min).

[0016] As a further improvement of an embodiment of the present invention, when the power consumption per ton of steel reaches 360 kWh / t, the blowing flow rate of lime powder from the bottom blowing system of the furnace is 1.5 - 2 kg / (t·min).

[0017] As a further improvement of an embodiment of the present invention, eccentric bottom tapping is adopted for tapping molten steel from the electric furnace, and ferrosilicon, ferromanganese, carbon powder, and ferrochrome are sequentially added for deoxidation alloying when 50-60% of the molten steel is tapped, and lime and synthetic slag are added for slag making when 80% of the molten steel is tapped.

[0018] As a further improvement of an embodiment of the present invention, in the refining process, inclusions in the molten steel are regulated by soft stirring, the soft stirring time is ≥30 min, and the argon blowing intensity at the bottom of the ladle during soft stirring is 0.002-0.004 Nm 3 / (t·min).

[0019] As a further improvement of an embodiment of the present invention, in the continuous casting process, the molten steel is heated by electromagnetic induction in the tundish, and the superheat is controlled at 15±5°C, and the heating rate is ≤4°C / min.

[0020] As a further improvement of an embodiment of the present invention, the continuous casting process adopts electromagnetic stirring in the mold and electromagnetic stirring at the solidification end. The current of the electromagnetic stirring in the mold is controlled at 400-500 A, the stirring frequency is 5-8 Hz, the current of the electromagnetic stirring at the solidification end is controlled at 400-500 A, and the stirring frequency is 10-12 Hz.

[0021] As a further improvement of an embodiment of the present invention, the high-speed wire rolling process includes rough rolling and finishing steps carried out in sequence. The outlet temperature of the finishing rolling is 1093-1110°C. After finishing rolling, it enters the water cooling device and the first and third water tanks are turned on. The water flow rates of the first and third water tanks are both 500-600 L / min.

[0022] As a further improvement of an embodiment of the present invention, in the controlled cooling process, the wire rod is temperature-controlled and cooled by a Stelmor cooling line. The air volumes of the 1st and 2nd fans are 100% and 50% respectively, and the other fans are turned off. The laying temperature is controlled at 930-945°C.

[0023] Compared with the prior art, the beneficial effects of the present invention are as follows: By using all scrap steel for electric furnace smelting and optimizing the power supply, gas supply, oxygen supply system and scrap steel charging system, not only can the smelting cycle be shortened, the smelting efficiency be improved, the power consumption be reduced, and the carbon dioxide emissions be reduced. Compared with converter smelting, the carbon dioxide emissions can be reduced by more than 60%, which is green and environmentally friendly; moreover, dephosphorization and enhanced desulfurization can be achieved during the electric furnace smelting stage, and the nitrogen content in the molten steel can be controlled. Especially, the gas supply and oxygen supply system are adjusted according to different levels of power consumption per ton of steel, so that the oxidation reaction can be carried out when the temperature is still at a relatively low level in the early stage of smelting to achieve rapid dephosphorization, and deep desulfurization is carried out in the later stage of smelting, which is beneficial to improving the cleanliness of the finally prepared cord steel and the quality of the cord steel. The inclusion levels of A, B, C, and D types in the cord steel prepared by this method do not exceed 0.5 level, and the number of wire breaks within 100 km during drawing and stranding does not exceed 1 time, which can meet the quality requirements of high-strength cord steel. Specific embodiments

[0024] An embodiment of the present invention provides a method for preparing a low-carbon emission cord steel wire rod, including the following processes carried out in sequence:

[0025] (1) Electric furnace smelting

[0026] All scrap steel is used and the scrap steel is added to the electric furnace in two batches.

[0027] After the first batch of scrap steel is added to the electric furnace, the electrode is lowered and power is supplied. Coke oven gas and oxygen are introduced into the electric furnace through the wall lance. The flow ratio of coke oven gas to oxygen is 2:1, and the gas supply intensity of coke oven gas is 15 - 20 Nm 3 / (h·t).

[0028] When the power consumption per ton of steel reaches 45 kWh / t, the supply of coke oven gas to the electric furnace is stopped, and oxygen is introduced into the electric furnace through the wall lance and the furnace door lance. The gas supply intensity of oxygen is 100 - 120 Nm 3 / (h·t), and 5 - 6 kg / t of lime is added from the bunker. At this time, since the scrap steel has not melted to form a molten pool, adding lime from the bunker is beneficial for the lime to mix into the scrap steel to achieve the dephosphorization effect, avoiding the lime from being difficult to mix into the molten pool through the bottom blowing system of the furnace and accumulating locally. In addition, the slag basicity can be supplemented; wherein, the power consumption per ton of steel refers to the power consumption of each ton of molten steel.

[0029] When the power consumption per ton of steel reaches 100 kWh / t, the power supply is stopped, the second batch of scrap steel is added to the molten steel, the electrode is lowered and power is supplied, and coke oven gas and oxygen are introduced into the electric furnace through the wall lance. The flow ratio of coke oven gas to oxygen is 2:1, and the gas supply intensity of coke oven gas is 15 - 20 Nm 3 / (h·t). The second batch of scrap steel is added when the power consumption per ton of steel reaches 100 kWh / t. The selection of this timing can, on the one hand, ensure that the first batch of scrap steel is completely melted, facilitating the addition of the second batch of scrap steel, and on the other hand, avoid the situation where the first batch of scrap steel becomes a molten pool when added too late, resulting in more heat loss when opening the furnace cover to add the second batch of scrap steel.

[0030] When the power consumption per ton of steel reaches 120 kWh / t, 15 - 18 kg / t of carbon powder is blown through the wall carbon powder lance of the electric furnace to form foamed slag. This can not only bury the electric arc, improve the heat transfer efficiency, facilitate temperature rise and shorten the production time, but also increase the contact area between the slag and the metal, improve the interfacial conditions for dephosphorization, and thus improve the dephosphorization efficiency; among them, the blowing flow rate of the carbon powder is 0.7 - 0.8 kg / (t·min).

[0031] When the power consumption per ton of steel reaches 150 kWh / t, the supply of coke oven gas to the electric furnace is stopped, and oxygen is supplied to the electric furnace through the wall lance and the door lance for dephosphorization. The oxygen supply intensity is 100 - 120 Nm 3 / (h·t), and lime is added in 3 - 4 batches from the bunker and the bottom blowing system of the furnace to adjust the basicity of the steel slag to 2.0 - 2.5. Among them, 15 - 18 kg / t of lime is added from the bunker, 6 - 8 kg / t of lime is added from the bottom blowing system of the furnace, the blowing flow rate of lime powder from the bottom blowing system of the furnace is 1.2 - 1.3 kg / (t·min), and the addition interval of lime in different batches is 2 - 3 min;

[0032] When the power consumption per ton of steel reaches 360 kWh / t, the oxygen supply of the wall lance and the door lance is stopped, and 8 - 12 kg / t of lime powder is blown from the bottom blowing system of the furnace to adjust the basicity of the steel slag to 4.0 - 4.5 for deep desulfurization.

[0033] Tapping is carried out when the power consumption per ton of steel reaches 390 - 410 kWh / t, the tapping temperature ≥ 1650 °C, and when tapping, the C content in the molten steel ≥ 0.03%, P ≤ 0.01%, S ≤ 0.01%, O ≤ 0.002%, N ≤ 0.005%, Sn ≤ 0.015%.

[0034] By using all scrap steel for electric furnace smelting and optimizing the power supply, gas supply, oxygen supply system and scrap steel charging system, not only can the smelting cycle be shortened, the smelting efficiency be improved, the power consumption be reduced, and the carbon dioxide emissions be reduced. Compared with converter smelting, the carbon dioxide emissions can be reduced by more than 60%, which is green and environmentally friendly; moreover, dephosphorization and enhanced desulfurization can be achieved in the electric furnace smelting stage, and the nitrogen content in the molten steel can be controlled. Especially, the gas supply and oxygen supply systems are adjusted according to different levels of power consumption per ton of steel, so that oxidation reactions can be carried out when the temperature is still at a relatively low level in the early stage of smelting to achieve rapid dephosphorization, and deep desulfurization can be carried out in the later stage of smelting, which is beneficial to improving the cleanliness of the finally prepared cord steel and the quality of the cord steel.

[0035] Preferably, the thickness of the scrap steel is ≥2 mm and it satisfies: S≤0.025%, Ni≤0.1%, Cr≤0.1%, Cu≤0.1%, Cu + Cr + Ni≤0.25%, Sn≤0.015%, Al≤0.05%, Ti≤0.05%. By controlling the quality of the scrap steel, not only can carbon emissions and resource consumption be significantly reduced, meeting the requirements of the low-carbon and green era, but also it is beneficial to improve the cleanliness of the finally prepared cord steel and reduce the difficulty of controlling inclusions in electric furnace smelting. Specifically, by controlling the content of Cu, red brittleness can be avoided; by controlling the contents of Cu + Cr + Ni and Sn, segregation of these residual elements at the interface of the steel can be avoided, which may lead to severe segregation of components, and further lead to changes in the crystal grain structure and damage to the continuity of the matrix; by controlling the contents of Al and Ti, the generation of brittle inclusions can be reduced, thereby reducing the wire breakage rate during drawing.

[0036] Preferably, in the electric furnace smelting process, the amount of retained steel in the electric furnace is ≥10 t, and the total charged amount is 115 - 120 t. The so-called amount of retained steel means leaving a part of the molten steel smelted in the previous furnace in the electric furnace. By setting the amount of retained steel, heat sources can be retained for the next furnace, thereby shortening the smelting time and diluting impurity elements to improve the cleanliness of the finally prepared cord steel.

[0037] Preferably, when the power consumption per ton of steel reaches 150 kWh / t, lime is blown into the molten steel through the bottom blowing system in powder form, and the blowing flow rate is 1.5 - 2 kg / (t·min). When the power consumption per ton of steel reaches 150 kWh / t, the scrap steel has melted to form a molten pool. By blowing lime powder into the molten steel through the bottom blowing system, the lime powder can be quickly mixed evenly into the molten steel, avoiding local aggregation of the lime powder, so as to achieve a good dephosphorization effect.

[0038] Preferably, when the power consumption per ton of steel reaches 360 kWh / t, the blowing flow rate of lime powder from the bottom blowing system is 1.5 - 2 kg / (t·min). By controlling the blowing flow rate of the lime powder, the basicity of the steel slag can be controlled to achieve the expected slag basicity.

[0039] Preferably, eccentric bottom tapping is used for tapping, and ferrosilicon, ferromanganese, carbon powder, and ferrochromium are added in sequence for deoxidation alloying when 50 - 60% of the steel is tapped, and lime and synthetic slag are added for slag making when 80% of the steel is tapped. By controlling the addition timing of these alloys such as ferrosilicon, ferromanganese, carbon powder, and ferrochromium, the time of nitrogen absorption can be delayed and the nitrogen increase amount in the molten steel during tapping can be reduced.

[0040] (2) Refining

[0041] The molten steel after electric furnace smelting is fed into the LF refining furnace for chemical composition adjustment, temperature control, and the inclusions in the molten steel are regulated by soft stirring. Then, synthetic slag and lime are added to the molten steel to form slag.

[0042] Preferably, the soft stirring time is ≥30 min, and the argon blowing intensity at the bottom of the ladle during soft stirring is 0.002 - 0.004 Nm 3 / (t·min) to prevent the molten steel from being exposed.

[0043] (3) Continuous casting

[0044] The molten steel is cast into continuous casting billets.

[0045] Preferably, the molten steel is temperature - controlled by electromagnetic induction heating in the tundish, and the superheat of the tundish is controlled at 15 ± 5°C, and the heating rate is ≤4°C / min, that is to say, the heating rate can be as high as 4°C / min.

[0046] Preferably, the continuous casting process adopts mold electromagnetic stirring and electromagnetic stirring at the solidification end. The current of the mold electromagnetic stirring is controlled at 400 - 500 A, the stirring frequency is 5 - 8 Hz, the current of the electromagnetic stirring at the solidification end is controlled at 400 - 500 A, and the stirring frequency is 10 - 12 Hz.

[0047] (4) Blooming

[0048] The continuous casting billets obtained from the continuous casting process are continuously rolled after being heated in a heating furnace, and bloomed into small square billets with a cross - sectional size of 160 mm×160 mm.

[0049] (5) High - speed wire rolling

[0050] The small square billets are rolled into wire rods through the high - speed wire rolling process.

[0051] Preferably, the high - speed wire rolling process includes rough rolling and finish rolling steps carried out in sequence. Among them, the outlet temperature of finish rolling is 1093 - 1110°C. After finish rolling, it enters the water - cooling device and the first and third water tanks in it are turned on. The water flow rates of the first and third water tanks are both 500 - 600 L / min.

[0052] (6) Controlled cooling

[0053] The wire rods are subjected to temperature - controlled cooling using a Stelmor cooling line.

[0054] The Stelmor cooling line is provided with blowers at intervals along the length direction of the roller table. The air volumes of the 1st - 2nd blowers are controlled at 100% and 50% respectively, and the other blowers are turned off. The laying - head temperature is controlled at 930 - 945°C.

[0055] The inclusion grades of types A, B, C, and D in the cord steel prepared by this method do not exceed grade 0.5, and the wire breakage does not exceed once per 100 km during the drawing and stranding processes, meeting the quality requirements of high-strength cord steel.

[0056] This invention is obtained based on a large number of experimental studies. To make the objectives, technical solutions, and advantages of an embodiment of this invention clearer, the following will specifically describe this embodiment in combination with Examples 1 to 3 of an embodiment of this invention. Obviously, the described Examples 1 to 3 are part of the embodiments of this invention, rather than all the embodiments.

[0057] The production methods of each example will be introduced in detail below.

[0058] Example 1

[0059] (1) Electric furnace smelting

[0060] All scrap steel is used and added to the electric furnace in two batches. Among them, the scrap steel uses heavy scrap and shredded material, with a thickness ≥ 3 mm and meeting the requirements: S ≤ 0.025%, Ni ≤ 0.05%, Cr ≤ 0.1%, Cu ≤ 0.1%, Cu + Cr + Ni ≤ 0.25%, Sn ≤ 0.015%, Al ≤ 0.05%, Ti ≤ 0.05%. The electric furnace uses an open-top ultra-high power electric arc furnace, with a retained steel amount of 12 t and a total charging amount of 117 t.

[0061] After adding the first batch of 55 t of scrap steel to the electric furnace, the electrodes are lowered and power is supplied. Coke oven gas and oxygen are introduced into the electric furnace through the wall guns. The flow ratio of coke oven gas to oxygen is 2:1, and the gas supply intensity of coke oven gas is 15 Nm 3 / (h·t).

[0062] When the power consumption per ton of steel reaches 45 kWh / t, stop introducing coke oven gas into the electric furnace, and introduce oxygen into the electric furnace through three wall guns and one door gun. The gas supply intensity of oxygen is 100 Nm 3 / (h·t), and 5 kg / t of lime is added from the bunker.

[0063] When the power consumption per ton of steel reaches 100 kWh / t, stop power supply, add the second batch of 50 t of scrap steel to the molten steel, lower the electrodes and start power supply, and introduce coke oven gas and oxygen into the electric furnace through the wall guns. The flow ratio of coke oven gas to oxygen is 2:1, and the gas supply intensity of coke oven gas is 15 Nm 3 / (h·t).

[0064] When the power consumption per ton of steel reaches 120 kWh / t, blow 15 - 18 kg / t of carbon powder through the wall carbon powder gun to form foamed slag, and the blowing flow rate of carbon powder is 0.7 kg / (t·min).

[0065] When the power consumption per ton of steel reaches 150 kWh / t, stop supplying coke oven gas to the electric furnace, and supply oxygen into the electric furnace through the wall lance and the door lance for dephosphorization. The oxygen supply intensity is 100 Nm 3 / (h·t), and add lime in 3 - 4 batches from the bunker and the bottom blowing system to adjust the basicity of the steel slag to 2.0 - 2.5. Among them, add 15 kg / t of lime from the bunker, add 6 kg / t of lime from the bottom blowing system, and the flow rate of lime powder blown from the bottom blowing system is 1.2 kg / (t·min). The addition interval of lime in different batches is 2 - 3 min;

[0066] When the power consumption per ton of steel reaches 360 kWh / t, stop oxygen supply from the wall lance and the door lance, and blow 10 kg / t of lime powder from the bottom blowing system to adjust the basicity of the steel slag to 4.0 - 4.5. The blowing flow rate of the lime powder is 1.5 kg / (t·min).

[0067] Tapping is carried out when the power consumption per ton of steel reaches 390 kWh / t. At this time, the oxygen consumption reaches 36 Nm 3 / t. Eccentric bottom tapping is adopted for tapping, and ferrosilicon, ferromanganese, carbon powder, and ferrochrome are added in sequence for deoxidation alloying when 50 - 60% of the steel is tapped, and lime and synthetic slag are added for slag making when 80% of the steel is tapped. The tapping temperature is 1650 °C. When tapping, in the molten steel, C ≥ 0.03%, P ≤ 0.01%, S ≤ 0.01%, O ≤ 0.002%, N ≤ 0.005%, Sn ≤ 0.015%.

[0068] (2) Refining

[0069] Send the molten steel after electric furnace smelting into the LF refining furnace for chemical composition adjustment, temperature control, and control inclusions in the molten steel through soft stirring. Then, add synthetic slag and lime to make slag. Among them, the soft stirring time is 30 min, and the argon bottom blowing intensity in the ladle during soft stirring is 0.002 Nm 3 / (t·min).

[0070] (3) Continuous casting

[0071] Cast the molten steel into continuous casting billets. Specifically, the temperature of the molten steel is controlled through electromagnetic induction heating in the tundish, and the superheat of the tundish is controlled at 15 ± 5 °C, and the heating rate can be as high as 4 °C / min; Electromagnetic stirring in the mold and electromagnetic stirring at the solidification end are adopted. The current of electromagnetic stirring in the mold is controlled at 500 A, and the stirring frequency is 8 Hz. The current of electromagnetic stirring at the solidification end is controlled at 400 A, and the stirring frequency is 12 Hz.

[0072] (4) Blooming

[0073] The continuous casting billet obtained from the continuous casting process is continuously rolled after being heated in a heating furnace, and is bloomed into small square billets with a cross-sectional size of 160 mm × 160 mm.

[0074] (5) High-speed wire rolling

[0075] The small square billets are rolled into wire rods through the high-speed wire rolling process, specifically including the rough rolling and finish rolling steps carried out in sequence. Among them, the outlet temperature of the finish rolling is 1095 °C. After finish rolling, it enters the water cooling device and the first and third water tanks therein are turned on. The water flow rates of the first and third water tanks are both 500 L / min.

[0076] (6) Controlled cooling

[0077] The wire rods are subjected to temperature-controlled cooling using a Stelmor cooling line.

[0078] The Stelmor cooling line is provided with blowers at intervals along the length direction of the roller table. The air volumes of the 1st to 2nd blowers are controlled to be 100% and 50% respectively, and the other blowers are turned off. The laying temperature is controlled to be 945 °C.

[0079] The inclusion grades of types A, B, C, and D of the cord steel prepared by this method are all 0.5 level, and the number of wire breaks within 100 km during the drawing and stranding processes does not exceed 1 time, which can meet the quality requirements of high-strength cord steel.

[0080] Example 2

[0081] (1) Electric furnace smelting

[0082] All scrap steel is used and the scrap steel is added to the electric furnace in two batches. Among them, the scrap steel uses heavy scrap and shredded materials, with a thickness ≥ 2 mm and meeting the requirements: S ≤ 0.025%, Ni ≤ 0.05%, Cr ≤ 0.1%, Cu ≤ 0.1%, Cu + Cr + Ni ≤ 0.25%, Sn ≤ 0.015%, Al ≤ 0.05%, Ti ≤ 0.05%. The electric furnace uses an open-top ultra-high power electric arc furnace, with a retained steel amount of 10 t and a total charging amount of 120 t.

[0083] After adding the first batch of 50 t of scrap steel to the electric furnace, the electrodes are lowered and power is turned on, and coke oven gas and oxygen are introduced into the electric furnace through the wall guns. The flow rate ratio of coke oven gas to oxygen is 2:1, and the gas supply intensity of coke oven gas is 16 Nm 3 / (h·t).

[0084] When the power consumption per ton of steel reaches 45 kWh / t, the supply of coke oven gas to the electric furnace is stopped, and oxygen is introduced into the electric furnace through three wall guns and one door gun. The gas supply intensity of oxygen is 100 Nm 3 / (h·t), and 6 kg / t of lime is added from the bunker.

[0085] When the power consumption per ton of steel reaches 100 kWh / t, power supply is stopped, 60 t of scrap steel in the second batch is added to the molten steel, the electrode is lowered and power supply is started, and coke oven gas and oxygen are introduced into the electric furnace through the wall lance. The flow rate ratio of coke oven gas to oxygen is 2:1, and the gas supply intensity of coke oven gas is 16 Nm 3 / (h·t).

[0086] When the power consumption per ton of steel reaches 120 kWh / t, 15 - 18 kg / t of carbon powder is blown through the wall carbon powder lance to form foamy slag, and the blowing flow rate of carbon powder is 0.7 kg / (t·min).

[0087] When the power consumption per ton of steel reaches 150 kWh / t, the supply of coke oven gas to the electric furnace is stopped, and oxygen is introduced into the electric furnace through the wall lance and the door lance for dephosphorization. The gas supply intensity of oxygen is 115 Nm 3 / (h·t), and lime is added in 3 - 4 batches from the bunker and the bottom blowing system of the furnace to adjust the basicity of the steel slag to 2.0 - 2.5. Among them, 18 kg / t of lime is added from the bunker, 6 kg / t of lime is added from the bottom blowing system of the furnace, the blowing flow rate of lime powder from the bottom blowing system of the furnace is 1.3 kg / (t·min), and the addition interval of lime in different batches is 2 - 3 min;

[0088] When the power consumption per ton of steel reaches 360 kWh / t, the oxygen supply of the wall lance and the door lance is stopped, and 10 kg / t of lime powder is blown from the bottom blowing system of the furnace to adjust the basicity of the steel slag to 4.0 - 4.5. The blowing flow rate of lime powder is 1.5 kg / (t·min).

[0089] Tapping is carried out when the power consumption per ton of steel reaches 398 kWh / t. At this time, the oxygen consumption reaches 38 Nm 3 / t. Eccentric bottom tapping is used for tapping, and ferrosilicon, ferromanganese, carbon powder, and ferrochrome are added in sequence for deoxidation alloying when 50 - 60% of the steel is tapped, and lime and synthetic slag are added for slag formation when 80% of the steel is tapped. The tapping temperature is 1650 °C. When tapping, C≥0.03%, P≤0.01%, S≤0.01%, O≤0.002%, N≤0.005%, Sn≤0.015% in the molten steel.

[0090] (2) Refining

[0091] The molten steel after electric furnace smelting is sent into the LF refining furnace for chemical composition adjustment, temperature control, and the inclusions in the molten steel are controlled by soft stirring. Then, synthetic slag and lime are added to the molten steel for slag formation. Among them, the soft stirring time is 32 min, and the argon bottom blowing intensity in the ladle during soft stirring is 0.003 Nm 3 / (t·min).

[0092] (3) Continuous casting

[0093] The molten steel is cast into continuous casting billets. Specifically, the temperature of the molten steel in the tundish is regulated by electromagnetic induction heating, and the superheat of the tundish is controlled at 15 ± 5°C, with a heating rate of up to 4°C / min. Electromagnetic stirring in the mold and electromagnetic stirring at the solidification end are adopted. The current of the electromagnetic stirring in the mold is controlled at 500 A, and the stirring frequency is 8 Hz. The current of the electromagnetic stirring at the solidification end is controlled at 400 A, and the stirring frequency is 12 Hz.

[0094] (4) Blooming

[0095] The continuous casting billets obtained from the continuous casting process are continuously rolled after being heated in a heating furnace to bloom into small square billets with a cross-sectional size of 160 mm × 160 mm.

[0096] (5) High-speed wire rolling

[0097] The small square billets are rolled into wire rods through the high-speed wire rolling process, specifically including rough rolling and finish rolling steps carried out in sequence. The outlet temperature of the finish rolling is 1095°C. After finish rolling, it enters a water cooling device, and the first and third water tanks in it are opened. The water flow rates of the first and third water tanks are both 500 L / min.

[0098] (6) Controlled cooling

[0099] The wire rods are subjected to temperature-controlled cooling using a Stelmor cooling line.

[0100] The Stelmor cooling line is provided with blowers at intervals along the length direction of the roller table. The air volumes of the 1st - 2nd blowers are controlled at 100% and 50% respectively, and the other blowers are turned off. The laying temperature is controlled at 945°C.

[0101] The inclusion grades of types A, B, C, and D in the cord steel prepared by this method are all 0.5 level, and the wire breakage does not exceed 1 time per 100 km during the drawing and stranding processes, which can meet the quality requirements of high-strength cord steel.

[0102] Example 3

[0103] (1) Electric furnace smelting

[0104] All scrap steel is used and added to the electric furnace in two batches. Among them, the scrap steel uses heavy scrap and shredded material, with a thickness ≥ 2 mm and meeting the requirements: S ≤ 0.025%, Ni ≤ 0.05%, Cr ≤ 0.1%, Cu ≤ 0.1%, Cu + Cr + Ni ≤ 0.25%, Sn ≤ 0.015%, Al ≤ 0.05%, Ti ≤ 0.05%. The electric furnace uses an open-top ultra-high power electric arc furnace, with a retained steel amount of 15 t and a total charging amount of 120 t.

[0105] After adding the first batch of 50t of scrap steel into the electric furnace, lower the electrodes and start energizing, and introduce coke oven gas and oxygen into the electric furnace through the wall lance. The flow ratio of coke oven gas to oxygen is 2:1, and the supply intensity of coke oven gas is 20 Nm 3 / (h·t).

[0106] When the power consumption per ton of steel reaches 45 kWh / t, stop introducing coke oven gas into the electric furnace, and introduce oxygen into the electric furnace through the wall lance and the door lance. The supply intensity of oxygen is 120 Nm 3 / (h·t), and add 6 kg / t of lime from the bunker.

[0107] When the power consumption per ton of steel reaches 100 kWh / t, stop energizing, add the second batch of scrap steel into the molten steel, lower the electrodes and start energizing, and introduce coke oven gas and oxygen into the electric furnace through the wall lance. The flow ratio of coke oven gas to oxygen is 2:1, and the supply intensity of coke oven gas is 20 Nm 3 / (h·t).

[0108] When the power consumption per ton of steel reaches 120 kWh / t, inject 15 - 18 kg / t of carbon powder through the wall carbon powder lance to form foamy slag, and the injection flow rate of carbon powder is 0.7 kg / (t·min).

[0109] When the power consumption per ton of steel reaches 150 kWh / t, stop introducing coke oven gas into the electric furnace, and introduce oxygen into the electric furnace through the wall lance and the door lance for dephosphorization. The supply intensity of oxygen is 110 Nm 3 / (h·t), and add lime from the bunker and the bottom blowing system in 3 - 4 batches to adjust the basicity of the steel slag to 2.0 - 2.5. Among them, 18 kg / t of lime is added from the bunker, 8 kg / t of lime is added from the bottom blowing system, and the injection flow rate of lime powder from the bottom blowing system is 1.3 kg / (t·min). The addition interval of lime in different batches is 2 - 3 min;

[0110] When the power consumption per ton of steel reaches 360 kWh / t, stop oxygen supply from the wall lance and the door lance, and inject 10 kg / t of lime powder from the bottom blowing system to adjust the basicity of the steel slag to 4.0 - 4.5. The injection flow rate of lime powder is 1.5 kg / (t·min).

[0111] Tapping is carried out when the power consumption per ton of steel reaches 400 kWh / t. At this time, the oxygen consumption reaches 39 Nm 3 / t. Eccentric bottom tapping is used for tapping, and ferrosilicon, ferromanganese, carbon powder, and ferrochrome are added in sequence for deoxidation alloying when 50 - 60% of the steel is tapped, and lime and synthetic slag are added for slag formation when 80% of the steel is tapped. The tapping temperature is 1655°C. When tapping, C≥0.03%, P≤0.01%, S≤0.01%, O≤0.002%, N≤0.005%, Sn≤0.015% in the molten steel.

[0112] (2) Refining

[0113] The molten steel after electric furnace smelting is sent into the LF refining furnace for chemical composition adjustment, temperature control, and the inclusions in the molten steel are regulated by soft stirring. Then, synthetic slag and lime are added to the molten steel to form slag. Among them, the soft stirring time is 30 min, and the argon blowing intensity at the bottom of the ladle during soft stirring is 0.004 Nm 3 / (t·min).

[0114] (3) Continuous casting

[0115] The molten steel is cast into continuous casting billets. Specifically, the molten steel is temperature-controlled by electromagnetic induction heating in the tundish, and the superheat of the tundish is controlled at 15 ± 5°C, and the heating rate can be as high as 4°C / min; electromagnetic stirring in the mold and electromagnetic stirring at the solidification end are adopted. The current of electromagnetic stirring in the mold is controlled at 500 A, the stirring frequency is 8 Hz, the current of electromagnetic stirring at the solidification end is controlled at 400 A, and the stirring frequency is 12 Hz.

[0116] (4) Blooming

[0117] The continuous casting billets obtained from the continuous casting process are continuously rolled after being heated in a heating furnace and bloomed into small square billets with a cross-sectional size of 160 mm × 160 mm.

[0118] (5) High-speed wire rolling

[0119] The small square billets are rolled into wire rods through the high-speed wire rolling process, which specifically includes rough rolling and finish rolling steps carried out in sequence. Among them, the outlet temperature of finish rolling is 1100°C. After finish rolling, it enters the water cooling device and the first and third water tanks are turned on. The water flow rates of the first and third water tanks are both 600 L / min.

[0120] (6) Controlled cooling

[0121] The wire rods are temperature-controlled and cooled by a Stelmor cooling line.

[0122] The Stelmor cooling line is provided with blowers at intervals along the length direction of the roller table. The air volumes of the 1st - 2nd blowers are controlled at 100% and 50% respectively, and the other blowers are turned off. The spinning temperature is controlled at 940°C.

[0123] The inclusion grades of A, B, C, and D types in the cord steel prepared by this method are all 0.5 level, and the wire breakage does not exceed 1 time per 100 km during drawing and stranding, which can meet the quality requirements of high-strength cord steel.

[0124] As can be seen from the above embodiments, through the production method and process parameter control, the present invention can achieve dephosphorization and enhanced desulfurization in the electric furnace smelting stage, and control the nitrogen content in the molten steel. In particular, the gas supply and oxygen supply system is adjusted according to different levels of power consumption per ton of steel, so as to carry out oxidation reaction when the temperature is still at a relatively low level in the early stage of smelting, achieve rapid dephosphorization, and carry out deep desulfurization in the later stage of smelting, which is beneficial to improving the cleanliness of the finally prepared cord steel and the quality of the cord steel. The inclusion levels of types A, B, C, and D of the cord steel prepared by this method do not exceed grade 0.5, and the wire breakage does not exceed once in 100 km during the drawing and stranding processes, which can meet the quality requirements of high-strength cord steel.

[0125] In addition, the carbon dioxide emissions in the above embodiments can be reduced by more than 60% compared with converter smelting, which is green and environmentally friendly.

Claims

1. A preparation method for a low-carbon emission cord steel wire rod, comprising the steps of electric furnace smelting, refining, continuous casting, blooming, high-speed wire rolling, and controlled cooling, which are carried out in sequence, characterized in that, All the electric furnace smelting processes use scrap steel, and the scrap steel is added to the electric furnace in two batches. After the first batch of scrap steel is added to the electric furnace, power is supplied, and coke oven gas and oxygen are introduced into the electric furnace through the wall lance. The flow ratio of coke oven gas to oxygen is 2:1, and the gas supply intensity of coke oven gas is 15 - 20 Nm 3 / (h·t); When the power consumption per ton of steel reaches 45 kWh / t, stop supplying coke oven gas to the electric furnace, and supply oxygen to the electric furnace through the wall lance and the door lance. The oxygen supply intensity is 100 - 120 Nm 3 / (h·t), and add 5 - 6 kg / t of lime from the bunker; When the power consumption per ton of steel reaches 100 kWh / t, stop power supply, add the second batch of scrap steel into the molten steel, lower the electrode, start power supply, and introduce coke oven gas and oxygen into the electric furnace through the wall lance. The flow ratio of coke oven gas to oxygen is 2:1, and the gas supply intensity of coke oven gas is 15 - 20 Nm 3 / (h·t); When the power consumption per ton of steel reaches 120 kWh / t, 15 - 18 kg / t of carbon powder is injected through the wall carbon powder lance, and the injection flow rate of the carbon powder is 0.7 - 0.8 kg / (t·min). When the power consumption per ton of steel reaches 150 kWh / t, stop supplying coke oven gas to the electric furnace, and supply oxygen to the electric furnace through the wall lance and the door lance. The oxygen supply intensity is 100 - 120 Nm 3 / (h·t), and add lime in 3 - 4 batches from the bunker and the bottom blowing system to adjust the basicity of the steel slag to 2.0 - 2.

5. Among them, 15 - 18 kg / t of lime is added from the bunker, 6 - 8 kg / t of lime is added from the bottom blowing system, and the flow rate of lime powder blown from the bottom blowing system is 1.2 - 1.3 kg / (t·min). The addition interval of lime in different batches is 2 - 3 min; When the power consumption per ton of steel reaches 360 kWh / t, the oxygen supply of the wall lance and the door lance stops, and 8 - 12 kg / t of lime powder is injected from the bottom blowing system of the furnace to adjust the basicity of the steel slag to 4.0 - 4.

5. Tapping is carried out when the power consumption per ton of steel reaches 390 - 410 kWh / t, the tapping temperature ≥ 1650 °C, and when tapping, C ≥ 0.03%, P ≤ 0.01%, S ≤ 0.01%, O ≤ 0.002%, N ≤ 0.005%, Sn ≤ 0.015% in the molten steel.

2. The preparation method of the low-carbon emission cord steel wire rod according to claim 1, characterized in that, The thickness of the scrap steel ≥ 2 mm and meets the requirements: S ≤ 0.025%, Ni ≤ 0.1%, Cr ≤ 0.1%, Cu ≤ 0.1%, Cu + Cr + Ni ≤ 0.25%, Sn ≤ 0.015%, Al ≤ 0.05%, Ti ≤ 0.05%.

3. The preparation method of the low-carbon emission cord steel wire rod according to claim 1, characterized in that, In the electric furnace smelting process, the steel retention amount in the electric furnace ≥ 10 t, and the total charging amount is 115 - 120 t.

4. The preparation method of the low-carbon emission cord steel wire rod according to claim 1, characterized in that, When the power consumption per ton of steel reaches 150 kWh / t, lime is injected into the molten steel from the bottom blowing system of the furnace in powder form, and the injection flow rate is 1.5 - 2 kg / (t·min).

5. The preparation method of the low-carbon emission cord steel wire rod according to claim 1, characterized in that, When the power consumption per ton of steel reaches 360 kWh / t, the injection flow rate of lime powder from the bottom blowing system of the furnace is 1.5 - 2 kg / (t·min).

6. The preparation method of the low-carbon emission cord steel wire rod according to claim 1, characterized in that, The electric furnace tapping adopts eccentric bottom tapping, and ferrosilicon, ferromanganese, carbon powder, and ferrochrome are added in sequence for deoxidation and alloying when 50 - 60% of the tapping is completed, and lime and synthetic slag are added for slag making when 80% of the tapping is completed.

7. The preparation method of the low-carbon emission cord steel wire rod according to claim 1, characterized in that, In the refining process, inclusions in the molten steel are regulated by soft stirring, the soft stirring time is ≥ 30 min, and the argon blowing intensity at the bottom of the ladle during the soft stirring process is 0.002 - 0.004 Nm 3 / (t·min).

8. The preparation method of the low-carbon emission cord steel wire rod according to claim 1, characterized in that, In the continuous casting process, the molten steel is heated by electromagnetic induction in the tundish, and the superheat is controlled at 15 ± 5 °C, and the heating rate ≤ 4 °C / min.

9. The preparation method of the low-carbon emission cord steel wire rod according to claim 1, characterized in that, The continuous casting process adopts electromagnetic stirring in the mold and electromagnetic stirring at the end of solidification. The current of the electromagnetic stirring in the mold is controlled at 400 - 500 A, the stirring frequency is 5 - 8 Hz, the current of the electromagnetic stirring at the end of solidification is controlled at 400 - 500 A, and the stirring frequency is 10 - 12 Hz.

10. The preparation method of the low-carbon emission cord steel wire rod according to claim 1, characterized in that, The high - speed wire rolling process includes rough rolling and finishing rolling steps carried out in sequence. Among them, the outlet temperature of the finishing rolling is 1093 - 1110 °C. After finishing rolling, it enters the water cooling device and the first and third water tanks are opened. The water flow rates of the first and third water tanks are both 500 - 600 L / min.

11. The preparation method of the low-carbon emission cord steel wire rod according to claim 1, characterized in that, In the controlled cooling process, the wire rod is temperature - controlled and cooled by the Stelmor cooling line. The air volumes of the 1 - 2# fans are 100% and 50% respectively, and the other fans are closed. The laying - head temperature is controlled at 930 - 945 °C.