Method for producing deformed steel bars at high pulling speed by using R8 billet continuous casting machine

Abstract

The invention discloses a method for producing deformed steel bars at a high pulling speed by an R8 billet continuous casting machine, and relates to the technical field of steel production. The element composition of the deformed steel bar does not contain Ti element, so that compared with the molten steel added with Ti element, the molten steel has better flowability, better castability in the continuous casting process and small liquid level fluctuation of a crystallizer, even if the pulling speed is increased and the productivity is improved, the problem of corner cracking of a continuous casting billet is not easily caused, and the performance of the deformed steel bar is not obviously reduced after no Ti element is added; and various properties of the prepared deformed steel bar meet the requirements. Furthermore, in the continuous casting process of the deformed steel bar, the pulling speed of a continuous casting billet is controlled to be 2.5-4 m / min, and the specific water flow is 1.4-1.9 L / kg, so that the quality of the continuous casting billet is guaranteed, and accidents such as bleed-out or central hole shrinkage are prevented. According to the method, the qualified continuous casting billet with stable quality can be obtained at a high pulling speed, and the production capacity of the deformed steel bar is remarkably improved.

Description

Technical Field

[0001] The invention relates to the technical field of steel production, and in particular to a method for producing threaded steel by an R8 square billet continuous casting machine at a high drawing speed. Background Art

[0002] Rebar is the common name for hot-rolled ribbed steel bars. The grade of ordinary hot-rolled ribbed steel bars is composed of HRB and the minimum yield point of the grade. H, R, and B are the first letters of the three words hot-rolled, ribbed, and bars, respectively. According to the new national standard, hot-rolled ribbed steel bars are divided into three grades: HRB400, HRB500, and HRB600. With the development of the economy and the acceleration of the industrialization process, the market demand for steel products continues to increase. The billet continuous casting machine continuously casts molten steel into rectangular billets for subsequent processing to form various specifications of rebar products. Therefore, the release of its production capacity can meet the market demand and provide more opportunities and space for the production and sales of enterprises.

[0003] The release of the capacity of the billet continuous casting machine can be started from many aspects, including the control of the continuous casting process. The capacity of the billet can be significantly released by increasing the casting speed, but increasing the casting speed is also accompanied by changes in the performance of the continuous casting billet, such as the appearance of central shrinkage holes in the continuous casting billet, and frequent steel leakage. Therefore, how to increase the capacity while ensuring the quality of the billet is one of the common goals pursued in this field.

[0004] In view of this, the present invention is proposed. Summary of the invention

[0005] The object of the present invention is to provide a method for producing threaded steel bars by an R8 billet continuous casting machine at a high drawing speed.

[0006] The present invention is achieved in that:

[0007] In a first aspect, the present invention provides a method for producing rebar by an R8 billet continuous casting machine at a high drawing speed, wherein the elemental composition of the rebar does not contain the Ti element, and during the continuous casting process of the rebar, the drawing speed of the continuous casting billet is 2.5 to 4 m / min, and the specific water content is 1.4 to 1.9 L / kg.

[0008] The present invention has the following beneficial effects:

[0009] The present invention provides a method for producing threaded steel by an R8 billet continuous casting machine at a high drawing speed. In the method, no Ti element is added for smelting. Therefore, compared with the molten steel with the addition of Ti element, the molten steel without the addition of Ti element has better fluidity, better castability during the continuous casting process, and small liquid level fluctuation of the crystallizer. Even if the drawing speed is increased and the production capacity is improved, the continuous casting billet is not prone to corner cracking problems, and the performance of the threaded steel is not significantly reduced after the Ti element is not added. All aspects of the performance of the obtained threaded steel meet the requirements. Further, by controlling the specific water amount of the secondary cooling water during the continuous casting process and coordinating the drawing speed of the continuous casting billet, the quality of the continuous casting billet is guaranteed, and accidents such as leakage or center shrinkage cavity are prevented. The method can obtain a continuous casting billet with stable quality and qualified at a high drawing speed, significantly improving the production capacity of the threaded steel. BRIEF DESCRIPTION OF THE DRAWINGS

[0010] In order to more clearly illustrate the technical solutions of the embodiments of the present invention, the drawings required for use in the embodiments are briefly introduced below. It should be understood that the following drawings only show certain embodiments of the present invention and therefore should not be regarded as limiting the scope. For ordinary technicians in this field, other related drawings can be obtained based on these drawings without creative work.

[0011] Figure 1 A morphology diagram of a continuous casting billet during the continuous casting process provided in Example 1 of the present invention;

[0012] Figure 2 This is a morphology diagram of the continuous casting billet during the continuous casting process provided for comparative example 1 of the present invention. DETAILED DESCRIPTION

[0013] In order to make the purpose, technical scheme and advantages of the embodiments of the present invention clearer, the technical scheme in the embodiments of the present invention will be described clearly and completely below. If the specific conditions are not specified in the embodiments, they are carried out according to conventional conditions or conditions recommended by the manufacturer. If the manufacturer of the reagents or instruments used is not specified, they are all conventional products that can be purchased commercially.

[0014] The features and performance of the present invention are further described in detail below in conjunction with the embodiments.

[0015] In a first aspect, the present invention provides a method for producing rebar by an R8 billet continuous casting machine at a high drawing speed, wherein the elemental composition of the rebar does not contain the Ti element, and during the continuous casting process of the rebar, the drawing speed of the continuous casting billet is 2.5 to 4 m / min, and the specific water content is 1.4 to 1.9 L / kg.

[0016] In the preparation process of existing threaded steel, due to the addition of Ti element, TiO in the steel 2The increase of TiS and other compounds makes the fluidity of molten steel poor, the castability also deteriorates, causing the crystallizer liquid level fluctuation to increase, and easy to produce corner cracks and other problems. The present invention solves the above problems by not adding Ti elements, and does not affect the performance of the steel grade, and the obtained steel grade still meets the requirements. Furthermore, the present application increases the continuous casting speed, which can significantly improve the production efficiency of the steel grade, thereby increasing the production capacity.

[0017] In some embodiments, the present invention provides a method for producing rebar by an R8 billet continuous casting machine at a high casting speed as follows:

[0018] S01. Smelting

[0019] In an optional embodiment, the molten iron and scrap steel are subjected to converter smelting, and the steel produced from the converter is sent to an argon station for argon blowing.

[0020] Preferably, the charging system for converter smelting includes: 90-120t of molten iron, 0-33t of scrap steel, and a total amount of 115-130t.

[0021] In an optional implementation, the converter smelting process can be carried out according to the existing smelting method. At the end of the converter smelting, a molten steel sample is taken for testing, and converter tapping can be carried out if the tapping requirements are met.

[0022] The mass percentage of C in the molten steel tapped from the converter is ≥0.04%, the mass percentage of S is ≤0.030%, and the mass percentage of P is ≤0.043%.

[0023] Preferably, the alloy and slag are added 60 seconds after the converter is tapped, and the alloy does not contain Ti. The amount of alloy and slag added is determined according to the smelting requirements of the steel grade.

[0024] In an optional embodiment, argon blowing is started when molten steel begins to tap the converter until the argon blowing at the argon station is completed. The total argon blowing time is ≥6 minutes, and the argon blowing time during the converter tapping process is ≥2 minutes. The argon pressure is 0.5-1.0 MPa.

[0025] Too high oxygen content in molten steel will deteriorate the performance of the mold slag added during continuous casting, thereby affecting the lubrication and heat transfer uniformity of the mold slag and aggravating the incidence of corner cracks. The role of argon is to promote the reaction of oxygen in molten steel with elements such as silicon, manganese, and aluminum that have a stronger affinity with oxygen than iron, to generate deoxidation products that are insoluble in molten steel, and float from the molten steel into the slag, thereby reducing the oxygen content in the molten steel. Therefore, it is necessary to control the argon blowing time within the above range to ensure that the oxygen in the molten steel has sufficient time to float up and reduce the oxygen content in the molten steel.

[0026] Preferably, the molten steel is sampled and the temperature is measured after entering the argon station to detect whether the content of each element in the molten steel meets the requirements of the corresponding steel grade. If some elements do not meet the requirements of the steel grade, it is necessary to add alloys during the argon blowing process at the argon station. When adding alloys during the argon blowing process at the argon station, the argon blowing time is increased to ensure that the added alloys can be dissolved in the molten steel.

[0027] When the mass of the added alloy is less than 200kg, the time of blowing argon at the argon station shall be increased by ≥2min; when the mass of the added alloy is ≥200kg, the time of blowing argon at the argon station shall be increased by ≥4min.

[0028] In the steelmaking process, deoxidation and alloying are often carried out simultaneously, which can not only improve production efficiency, but also ensure that the quality and performance of the steel are in the best state. The molten steel after deoxidation and alloying has a lower oxygen content.

[0029] In an optional embodiment, the element composition of the rebar, by mass percentage, includes C≤0.25%, Si≤0.80%, Mn≤1.60%, S≤0.043%, P≤0.043%, Nb≥0%, and the balance is iron and other inevitable impurities; the carbon equivalent Ceq of the rebar is ≤0.54%.

[0030] Preferably, when the brand name of the rebar is HRB400, the element composition, by mass percentage, includes C: 0.22-0.25%, Si: 0.55-0.65%, Mn: 1.40-1.50%, S≤0.040%, P≤0.040%, Nb: 0.010-0.015%, and the balance is iron and other inevitable impurities; the carbon equivalent Ceq of the rebar is 0.46-0.54%.

[0031] Preferably, when the brand name of the rebar is HRB400E, the element composition, by mass percentage, includes C: 0.22-0.25%, Si: 0.55-0.65%, Mn: 1.40-1.50%, S≤0.043%, P≤0.043%, Nb: 0.010-0.017%, and the balance is iron and other inevitable impurities; the carbon equivalent Ceq of the rebar is 0.46-0.54%.

[0032] Preferably, when the brand name of the rebar is GHRB400 or GHRB400E, the element composition, calculated by mass percentage, includes C≤0.25%, Si≤0.80%, Mn≤1.60%, S≤0.043%, P≤0.043%, Nb≥0%, and the balance is iron and other inevitable impurities; the carbon equivalent Ceq of the rebar is ≤0.54%.

[0033] Preferably, the cross-sectional shape of the threaded steel bars is a square, and the cross-sectional specification of the threaded steel bars is 160×160 mm.

[0034] S02, continuous casting

[0035] The molten steel after argon blowing in the argon station is continuously cast.

[0036] In an optional embodiment, during the continuous casting process, the secondary cooling water distribution ratio includes: 32-34% in the full roll zone, 32.5-33.35% in the first stage, 13-15% in the second stage, 12-13% in the third stage, and 7.5-8.5% in the fourth stage.

[0037] The existing secondary cooling water cooling process has insufficient cooling intensity, and the high superheat of molten steel easily leads to steel leakage when the continuous casting speed increases. The inventors have found through research that by controlling the proportion of each section of secondary cooling water within the above range, the surface properties of the continuous casting billet can be guaranteed while the continuous casting speed is increased, and steel leakage will not occur.

[0038] Reducing the water percentage in the foot roll area can slow down the cooling of the corner cracks of the continuous casting billet and reduce the occurrence of corner cracks; increasing the water percentage in the first stage can shorten the solidification time of the continuous casting billet and increase the shell thickness of the continuous casting billet; increasing the water percentage in the fourth stage can strengthen the cooling of the end and prevent steel leakage accidents caused by the fourth stage temperature recovery at high pulling speed.

[0039] Furthermore, in order to ensure that the above-mentioned secondary cooling water distribution ratio can be more conveniently controlled and at the same time improve the cooling intensity of the secondary cooling water, in an optional embodiment, during the continuous casting process of the rebar, the aperture of the water outlet of the nozzle for spraying secondary cooling water is 1.8~3.8mm, and the inclination angle is 65~70°; when the water pressure is 6kg, the flow rate of the nozzle is 3.7~17.1L / min; when the water pressure is 12kg, the flow rate of the nozzle is 4.9~24.4L / min.

[0040] The incidence of corner cracks can be reduced by increasing the nozzle aperture, increasing the nozzle angle, and improving the cooling intensity and cooling uniformity of the ingot.

[0041] Preferably, the water outlet aperture of the nozzle in the foot roller zone is 3.5-3.8 mm, and the inclination angle is 65-66°; when the water pressure is 6 kg, the flow rate of the nozzle is 17.0-17.1 L / min; when the water pressure is 12 kg, the flow rate of the nozzle is 24.0-24.4 L / min.

[0042] Preferably, the aperture of the water outlet of one section of the nozzle is 2.6-2.8 mm, and the inclination angle is 69-70°; when the water pressure is 6 kg, the flow rate of the nozzle is 9.0-10.0 L / min; when the water pressure is 12 kg, the flow rate of the nozzle is 12-14 L / min.

[0043] Preferably, the aperture of the water outlet of the second-stage nozzle is 2.0-2.5 mm, and the inclination angle is 69-70°; when the water pressure is 6 kg, the flow rate of the nozzle is 6.0-6.5 L / min; when the water pressure is 12 kg, the flow rate of the nozzle is 8.0-9.0 L / min.

[0044] Preferably, the aperture of the water outlet of the three-stage nozzle is 1.9-2.1 mm, and the inclination angle is 69-70°; when the water pressure is 6 kg, the flow rate of the nozzle is 4.5-5.0 L / min; when the water pressure is 12 kg, the flow rate of the nozzle is 6.5-7.0 L / min.

[0045] Preferably, the aperture of the water outlet of the four-stage nozzle is 1.9-2.0 mm, and the inclination angle is 69-70°; when the water pressure is 6 kg, the flow rate of the nozzle is 3.7-4.0 L / min; when the water pressure is 12 kg, the flow rate of the nozzle is 4.9-5.0 L / min.

[0046] By adjusting the angle of the foot roll zone to be inconsistent with the first to fourth sections, overlapping of the corner cooling of the continuous casting billet can be prevented, resulting in double cooling of the corner and causing corner cracks.

[0047] Preferably, the temperature of the molten steel at the argon station of the first furnace of threaded steel is (T L +125)±10℃, the temperature of molten steel after argon blowing is (T L +80)±5℃, the temperature of molten steel when it is delivered to the continuous casting platform is (T L +75)±5℃, molten steel superheat is T L +(10~55)℃, when the temperature of the molten steel in the continuous casting process is ≤T L When the temperature reaches +10℃, replace the molten steel with one with a higher casting temperature than the current one for casting.

[0048] The temperature of the molten steel in the continuous casting furnace to the argon station is (T L +77)±10℃, the temperature of molten steel after argon blowing is (T L +50)±5℃, the temperature of molten steel when it is delivered to the continuous casting platform is (T L +48)±5℃, molten steel superheat is T L +(15~30)℃, when the temperature of the molten steel in the continuous casting process is ≤T L When the temperature reaches +10℃, replace the molten steel with one with a higher casting temperature than the current one for casting.

[0049] Among them, T L It is the liquidus temperature of molten steel, that is, the temperature at which molten steel begins to change from liquid to solid. It is measured in °C and can be calculated based on the different elemental composition of each grade of steel.

[0050] The temperature of the molten steel in each stage of the first furnace is higher than that of the continuous casting furnace. This is because the temperature drop of the molten steel in the first furnace is large during the pouring process. In order to avoid shutdown accidents caused by low temperature in the tundish, the temperature of the molten steel in the first furnace is required to be increased.

[0051] It can be seen from the above temperature changes that the temperature of the molten steel decreases successively during the whole process from the argon station to the continuous casting. The temperature of the molten steel at the argon station is controlled to be relatively high. On the one hand, since the molten steel will be cooled during the argon blowing process at the argon station, controlling the temperature of the molten steel at the argon station within the above range can avoid the molten steel temperature being too low after the argon blowing at the argon station, which will affect the continuous casting effect and the surface properties of the continuous casting billet; on the other hand, the temperature of the molten steel at the argon station is relatively high, and the time for oxygen to float can be fully guaranteed during the argon blowing process at the argon station, which can well reduce the oxygen content in the molten steel, improve the castability of continuous casting, and reduce the occurrence of corner cracks.

[0052] In an optional embodiment, when the molten steel superheat degree>T L At +45℃, the pulling speed of the continuous casting billet is 2.5m / min; when the superheat degree of molten steel is T L +(36~45)℃, the pulling speed of the continuous casting billet is 3.0m / min; when the superheat degree of molten steel is T L +(10~36)℃, excluding molten steel superheat T L +36℃, the pulling speed of continuous casting billet is 3.2m / min; when the superheat of molten steel is less than T L At +10℃, the pulling speed of the continuous casting billet is 3.5m / min.

[0053] By adjusting the casting speed during the continuous casting process according to the superheat of the molten steel, a continuous casting billet with better surface properties and no defects can be obtained.

[0054] In an optional embodiment, during the continuous casting process, the vibration amplitude of the crystallizer is between ±4.5mm and the vibration frequency is 30v+65.

[0055] Where v is the pulling speed of the continuous casting billet, the unit is m / min; the unit of vibration amplitude is mm, and the unit of vibration frequency is Hz.

[0056] By adjusting the vibration parameters of the crystallizer according to the pulling speed of the continuous casting billet, a continuous casting billet with better surface properties and no defects can also be obtained.

[0057] Preferably, the vibration amplitude of the crystallizer is ±4.5 mm, and the vibration frequency is 125-185 Hz.

[0058] In the existing method, the uneven cooling process of the crystallizer will also cause steel leakage. In order to adapt to the higher continuous casting speed and increase the heat dissipation effect of the crystallizer, preferably, the cooling water flow rate of the crystallizer is 120-150m 3 / h, the water inlet pressure is 1.0-1.5MPa, the flow rate of cooling water in the crystallizer is 18-20m / s, and the insertion depth of the immersion nozzle is 120-140mm.

[0059] The protective slag in the crystallizer has a significant impact on the surface quality of the continuous casting billet. The existing protective slag can easily cause cracks on the surface of the continuous casting billet at a higher continuous casting speed. The reason is that as the pulling speed increases, the heat flow through the crystallizer increases, the original thermal balance in the crystallizer is broken, the billet shell at the outlet becomes thinner, and the friction experienced by the crystallizer increases, which can easily cause bulging and steel leakage.

[0060] Therefore, the inventors propose a new protective slag. Preferably, the protective slag is a medium carbon steel high-pulling speed protective slag.

[0061] Preferably, the basicity of the protective slag is 0.9-1.0, the melting point Tm of the crystalline polymer is 1060-1065° C., and the viscosity at 1300° C. is 0.25-0.3P·S.

[0062] Preferably, the mass percentage of each component in the mold slag includes SiO 2 : 29.5~30.0%, MgO: 2.5~3.0%, CaO: 28.0~28.5%, Fe 2 O 3 :0.5~0.8%,Al 2 O 3 :5.2~5.8%,Na 2 O: 10.2 to 10.8%, F: 7.5 to 8.0%, C: 12.0 to 12.5%.

[0063] By controlling the basicity of the protective slag within the above range, compared with the existing protective slag with lower basicity, the protective slag used in the present invention can increase the crystallization rate, slow down the heat transfer, make the heat transfer more uniform, and avoid the generation of longitudinal cracks.

[0064] By controlling the melting point Tm of the crystalline polymer of the protective slag within the above-mentioned range, the protective slag used in the present invention can increase the slag melting rate, meet the stability of the liquid slag layer thickness at high slag consumption, and ensure the thickness of the liquid slag layer, compared with the existing protective slag with a higher crystalline polymer melting point Tm.

[0065] By controlling the viscosity of the protective slag at 1300° C. within the above range, the protective slag used in the present invention can increase the slag consumption compared to the existing protective slag with higher viscosity, so as to ensure sufficient liquid slag lubrication at high pulling speeds.

[0066] In an optional embodiment, the consumption of protective slag in the crystallizer is 0.17-0.31 kg / t.

[0067] Preferably, when the pulling speed of the continuous casting billet is ≥3.5 m / min, the consumption of the protective slag in the crystallizer is 0.17-0.23 kg / t.

[0068] By adopting the above-mentioned protective slag, the slag consumption in the continuous casting process is more appropriate, and has good lubricity, and the slag film thickness between the crystallizer wall and the shell of the continuous casting billet is appropriate and evenly distributed, so as to reduce the friction of the crystallizer and make the heat transfer uniform, thereby preventing the generation of cracks. In addition, the protective slag also has good dissolution, strong inclusion absorption and suitable crystallization ability to meet the heat flow requirements of steel grades, so the basicity is increased to 0.9-1.0.

[0069] In some embodiments provided by the present invention, the average pulling speed of the continuous casting machine can be increased to 3.5 m / min or above, and the surface morphology of the obtained ingot meets the requirements and is defect-free. Therefore, this method can be used in the field of reducing surface corner cracks of rebar ingots produced by R8 continuous casting machines.

[0070] In addition, in some embodiments of the present invention, when the continuous casting speed is ≥3.5 m / min, the leakage rate is significantly reduced compared with before.

[0071] Preferably, the pouring process is protected, the long shroud and quick-change mechanism of the large ladle are properly sealed with argon, and the long shroud is inserted into the liquid surface ≥150mm. The normal pouring liquid level controls the liquid level of the middle ladle at ≥700mm.

[0072] Example 1

[0073] This embodiment provides a method for producing threaded steel bars by an R8 billet continuous casting machine at a high casting speed, comprising the following steps:

[0074] S01. Smelting

[0075] 106 tons of molten iron, 16 tons of scrap steel and 1 ton of pig iron are loaded into the converter for smelting, with a total loading of 123 tons. After the converter smelting is completed, the mass percentage of C in the final molten steel is ≥0.04%, the mass percentage of S is ≤0.030%, and the mass percentage of P is ≤0.043%, and steel tapping begins.

[0076] When the converter starts tapping, argon is turned on for argon blowing, and the argon pressure is 0.5-1.0MPa. After 60s of the converter tapping, alloy (excluding Ti element) and slag are added. The total time for the converter tapping is ≥2min.

[0077] After the converter is finished tapping, the molten steel is immediately measured and sampled at the argon station. The temperature of the molten steel at the argon station is detected to be 1622-1642°C. The composition of the molten steel is: C: 0.23%, Si: 0.6%, Mn: 1.44%, S: 0.019%, P: 0.031%, Nb: 0.001%, and the remainder is iron and other inevitable impurities; the carbon equivalent Ceq is 0.47%, and the liquidus temperature of the molten steel is T L The temperature is 1507℃. Therefore, 20kg of ferroniobium alloy is added to fine-tune the proportion of Nb element to meet the requirements of HRB400E grade. The argon pressure of molten steel is maintained at 0.5-1.0MPa in the argon station, and the argon blowing is ≥4min.

[0078] After the argon blowing was completed, the molten steel temperature was detected to be 1582~1592℃.

[0079] S02, continuous casting

[0080] The molten steel obtained by smelting is continuously cast. The temperature of the molten steel when it is sent to the continuous casting platform is 1577-1587°C, and the temperature of the tundish is 1552-1562°C. Therefore, the pulling speed is controlled to be 2.0-2.5m / min.

[0081] In addition, during the entire continuous casting process, medium carbon steel high-drawing speed protection slag is added to the crystallizer, and the protection slag consumption is 0.22-0.35 kg / t.

[0082] The basicity of the protective slag is 0.95, the melting point Tm of the crystalline polymer is 1062°C, and the viscosity at 1300°C is 0.27P·S.

[0083] The mass percentage of each component in the mold slag includes SiO 2 :29.75%, MgO: 2.87%, CaO: 28.26%, Fe 2 O 3 : 0.7%,Al 2 O 3 : 5.5%, Na 2 O: 10.5%, F: 7.74%, C: 12.1%.

[0084] During the entire continuous casting process, the vibration amplitude of the crystallizer is controlled to be ±4.5mm, and the vibration frequency f is 125-140Hz. The cooling water flow rate of the crystallizer is 150m 3 / h, the water inlet pressure is 1.2MPa, the flow rate of cooling water in the crystallizer is 19m / s, and the insertion depth of the immersion nozzle is 120-140mm.

[0085] In addition, the secondary cooling water specific water volume in the continuous casting process is 1.4-1.7 L / kg, and the nozzle parameters of the secondary cooling water are shown in Table 1.

[0086] Table 1 Parameters of secondary cooling water

[0087]

[0088] The first heat of molten steel is cast by maintaining the above parameters to obtain a 160*160mm continuous casting billet of threaded steel. The continuous casting billet of threaded steel is subjected to rolling and / or drawing to obtain threaded steel.

[0089] Example 2

[0090] This embodiment provides a method for producing rebar at a high drawing speed using an R8 square billet continuous casting machine. As a continuation of the method of Example 1, the preparation is continued in a similar manner to Example 1, including continuously casting molten steel from the continuous casting furnace starting from the second furnace.

[0091] The smelting method of the second furnace of molten steel is similar to that of Example 1, except that after the converter is tapped, the molten steel is immediately temperature-measured and sampled at the argon station. The temperature of the molten steel at the argon station is detected to be 1591°C, and the composition of the molten steel is: C: 0.22%, Si: 0.57%, Mn: 1.42%, S: 0.021%, P: 0.033%, Nb: 0.011%, and the remainder is iron and other unavoidable impurities; the carbon equivalent Ceq is 0.46%. The liquidus temperature T of the molten steel L The temperature is 1507℃. The argon pressure of the molten steel is maintained at 0.5~1.0MPa in the argon station, and the argon blowing time is ≥4min.

[0092] After the argon blowing was completed, the molten steel temperature was detected to be 1562~1572℃.

[0093] Continuous casting was carried out according to the method of Example 1, wherein the temperature of the molten steel provided in this example when it was delivered to the continuous casting platform was 1557-1567°C, and the temperature of the tundish was 1532-1542°C, so the casting speed was controlled to be 3.0-4 m / min. The vibration amplitude f of the crystallizer was further changed to 155-185 Hz, and the vibration frequency was ±4.5 mmHz.

[0094] Example 3

[0095] The present embodiment provides a method for producing rebar at a high drawing speed by an R8 square billet continuous casting machine. As a continuation of the method of Example 1, preparation is continued according to a method similar to Example 1. When continuously casting the molten steel of the continuous casting heat of the 6th furnace, it is detected that the temperature of the molten steel in the tundish is ≤1515°C, and the temperature is too low. At this time, the addition of molten steel of this heat is suspended. After the argon blowing is completed, the temperature of the molten steel of the next heat is detected to be ≥1561°C, so the molten steel of the 7th heat is added to the tundish, and the remaining molten steel of the 6th heat that has not been cast is returned to the furnace for re-smelting.

[0096] Comparative Example 1

[0097] This comparative example provides a method for producing rebar using an R8 billet continuous casting machine, comprising the following steps:

[0098] S01. Smelting

[0099] 104t of molten iron, 18t of scrap steel and 1t of pig iron are loaded into the converter for smelting, with a total loading of 123t. After the converter smelting is completed, the mass percentage of C in the final molten steel is ≥0.04%, the mass percentage of S is ≤0.030%, and the mass percentage of P is ≤0.043%, and steel tapping begins.

[0100] When the converter starts tapping, argon is turned on for argon blowing, and the argon pressure is 0.6MPa. After 60s of tapping, alloy (including Ti element) and slag are added. The total time for tapping the converter is 2min.

[0101] After the converter is finished tapping, the molten steel is immediately measured and sampled at the argon station. The temperature of the molten steel at the argon station is detected to be 1640℃, and the composition of the molten steel is: C: 0.23%, Si: 0.58%, Mn: 1.43%, S: 0.022%, P: 0.031%, Nb: 0.0012%, Ti: 0.007%, and the balance is iron and other inevitable impurities; the carbon equivalent Ceq is 0.47%. Therefore, 20kg of niobium iron alloy needs to be added to fine-tune the Nb element ratio to meet the requirements of HRB400E grade, and the liquidus temperature of the molten steel T L The temperature is 1506℃, the argon pressure of the molten steel is maintained at 0.5-1.0MPa in the argon station, and the argon blowing time is ≥3min.

[0102] After the argon blowing was completed, the molten steel temperature was detected to be 1581~1591℃.

[0103] S02, continuous casting

[0104] The molten steel obtained by smelting is continuously cast. The temperature of the molten steel when it is sent to the continuous casting platform is 1576-1586°C, and the temperature of the tundish is 1551-1561°C, so the pulling speed is controlled to be 2.0-2.5m / min.

[0105] In addition, during the entire continuous casting process, medium carbon steel high-drawing speed protection slag is added to the crystallizer, and the protection slag consumption is 0.13-0.19 kg / t.

[0106] The basicity of the protective slag is 0.79, the melting point Tm of the crystalline polymer is 1096°C, and the viscosity at 1300°C is 0.46P·S.

[0107] The mass percentage of each component in the mold slag includes SiO 2 :29.26%, MgO: 2.39%, CaO: 23.03%, Fe2 O 3 : 1.13%,Al 2 O 3 : 6.51%, Na 2 O: 9.5%, F: 7.06%, C: 12.1%.

[0108] During the entire continuous casting process, the vibration amplitude of the crystallizer is controlled to be ±3.5mm and the vibration frequency is 125-140Hz. The cooling water flow rate of the crystallizer is 150m 3 / h, the water inlet pressure is 1.2MPa, the flow rate of cooling water in the crystallizer is 19m / s, and the insertion depth of the immersion nozzle is 120-140mm.

[0109] In addition, the secondary cooling water specific water volume in the continuous casting process is 1.4-1.7 L / kg, and the nozzle parameters of the secondary cooling water are shown in Table 2.

[0110] Table 2 Parameters of secondary cooling water

[0111]

[0112] The first heat of molten steel is cast by maintaining the above parameters to obtain a continuous casting billet of threaded steel with a side length of 160*160 mm. The continuous casting billet of threaded steel is subjected to rolling and / or drawing to obtain threaded steel.

[0113] Comparative Example 2

[0114] This comparative example provides a method for producing rebar at a high casting speed using an R8 billet continuous casting machine, which is a continuation of the method of comparative example 1, and is prepared in a similar manner to comparative example 1, including continuous casting of molten steel from the continuous casting heat starting from the second furnace. Casting starts from the second furnace and ends at the fifth furnace.

[0115] When the molten steel arrives at the argon station, the temperature is measured and sampled immediately. The temperature of the molten steel at the argon station is 1593℃, C: 0.22%, Si: 0.59%, Mn: 1.44%, S: 0.021%, P: 0.033%, Nb: 0.011%, Ti: 0.0080%, and the remainder is iron and other unavoidable impurities; the carbon equivalent Ceq is 0.46%. The liquidus temperature of the molten steel is T L The temperature is 1506℃, the argon pressure of the molten steel is maintained at 0.5-1.0MPa in the argon station, and the argon blowing time is ≥3min.

[0116] After the argon blowing was completed, the molten steel temperature was detected to be 1561~1571℃.

[0117] Continuous casting was carried out according to the method of comparative example 1. The temperature of the molten steel provided in this embodiment when it was delivered to the continuous casting platform was 1556-1566°C, and the temperature of the tundish was 1531-1541°C, so the casting speed was controlled to be 3.0-4 m / min. The vibration amplitude of the crystallizer was further changed to ±3.5 mm, and the vibration frequency f was 155-185 Hz.

[0118] Test Example 1

[0119] The rebars obtained by rolling the continuous casting billets of the rebars produced by the R8 billet continuous casting machine provided in Example 1 and Comparative Example 1 were subjected to performance testing. The yield strength test method is GB / T28900-2022, the tensile strength test method is GB / T28900-2022, the maximum force total elongation test method is GB / T28900-2022, and the strength-yield ratio is GB / T28900-2022, and the results shown in Table 3 are obtained.

[0120] Table 3 Properties of rebar

[0121]

[0122] It can be seen from Table 3 that although the Ti element is not added in the embodiment of the present invention, the mechanical properties of the obtained rebar are equivalent to those of the rebar with Ti element added in Comparative Example 1, indicating that the Ti element is not added in the embodiment of the present invention, and rebar with better mechanical properties can still be obtained through a reasonable continuous casting process, and without adding the Ti element, the continuous casting capacity can be efficiently improved.

[0123] Test Example 2

[0124] The surface quality of the continuous casting billets obtained in Examples 1 to 3 and Comparative Examples 1 to 2 was tested by naked eye observation, and the results were shown in Table 4 and Figures 1-2 Results shown.

[0125] Table 4 Surface quality of continuous casting billet

[0126] Casting weight Number of angular cracks Angle crack rate per ton of steel (%) Example 1 115t 1 time 0.86％ Example 2 460t 0 times 0％ Example 3 115t 0 times 0％ Comparative Example 1 115t 2 times 1.73％ Comparative Example 2 460t 3 times 0.65％

[0127] From Table 4 and Figures 1-2It can be known that the continuous casting billet obtained by the method provided in the embodiment of the present invention has no defects on the surface and stable quality, and the pulling speed of the embodiment of the present invention is significantly higher. More continuous casting billets can be obtained by continuous casting in the same time, and the production capacity improvement effect is obvious. Comparative Example 1 Due to the long oxygen blowing time and short argon blowing time in smelting, the oxygen content of the molten steel is high. The high oxygen content in the molten steel will cause pores and looseness inside. The high oxygen content increases the iron oxide (FeO) in the molten steel. During the solidification process, FeO will react with other elements in the steel. Some gases will form pores on the surface of the billet shell. When the stress concentration around the pores exceeds the strength limit of the billet shell, cracks will occur, and defects such as corner cracks and steel leakage will occur. Therefore, it is impossible to use a higher pulling speed to obtain a qualified product. Comparative Example 2 On the one hand, due to the addition of Ti element, the Ti content in the molten steel is increased, and TiO is increased. 2 and TiS and other compounds, which affect the fluidity of molten steel, make the liquid level of stable crystallizer unstable during casting, and easily cause defects such as corner cracks and steel leakage in the ingot; on the other hand, the protective slag selected in comparative example 2 has poor performance and low basicity, which reduces the crystallization rate, accelerates heat transfer, causes uneven heat transfer, is prone to longitudinal cracks, and has too high viscosity, which reduces the consumption of protective slag and causes defects such as corner cracks and steel leakage.

[0128] The above are only preferred embodiments of the present invention and are not intended to limit the present invention. For those skilled in the art, the present invention may have various modifications and variations. Any modification, equivalent replacement, improvement, etc. made within the spirit and principle of the present invention shall be included in the protection scope of the present invention.

Claims

1. A method for producing threaded steel bars by using an R8 billet continuous casting machine at a high casting speed, characterized in that: The element composition of the threaded steel does not contain Ti element, and during the continuous casting process of the threaded steel, the drawing speed of the continuous casting billet is 2.5-4 m / min, and the specific water content is 1.4-1.9 L / kg.

2. The method according to claim 1, characterized in that During the continuous casting process, the secondary cooling water distribution ratio includes: 32-34% water distribution in the full roll area, 32.5-33.35% water distribution in the first stage, 13-15% water distribution in the second stage, 12-13% water distribution in the third stage, and 7.5-8.5% water distribution in the fourth stage.

3. The method according to claim 2, characterized in that During the continuous casting process of the threaded steel, the aperture of the nozzle for spraying secondary cooling water is 1.8-3.8 mm, and the inclination angle is 65-70°; when the water pressure is 6 kg, the flow rate of the nozzle is 3.7-17.1 L / min; when the water pressure is 12 kg, the flow rate of the nozzle is 4.9-24.4 L / min; Preferably, the water outlet aperture of the nozzle in the foot roll area is 3.5-3.8 mm, and the inclination angle is 65-66°; when the water pressure is 6 kg, the flow rate of the nozzle is 17.0-17.1 L / min; when the water pressure is 12 kg, the flow rate of the nozzle is 24.0-24.4 L / min; Preferably, the aperture of the water outlet of the nozzle of the first section is 2.6-2.8 mm, and the inclination angle is 69-70°; when the water pressure is 6 kg, the flow rate of the nozzle is 9.0-10.0 L / min; when the water pressure is 12 kg, the flow rate of the nozzle is 12-14 L / min; Preferably, the aperture of the water outlet of the second-stage nozzle is 2.0-2.5 mm, and the inclination angle is 69-70°; when the water pressure is 6 kg, the flow rate of the nozzle is 6.0-6.5 L / min; when the water pressure is 12 kg, the flow rate of the nozzle is 8.0-9.0 L / min; Preferably, the aperture of the water outlet of the three-stage nozzle is 1.9-2.1 mm, and the inclination angle is 69-70°; when the water pressure is 6 kg, the flow rate of the nozzle is 4.5-5.0 L / min; when the water pressure is 12 kg, the flow rate of the nozzle is 6.5-7.0 L / min; Preferably, the aperture of the water outlet of the four-stage nozzle is 1.9-2.0 mm, and the inclination angle is 69-70°; when the water pressure is 6 kg, the flow rate of the nozzle is 3.7-4.0 L / min; when the water pressure is 12 kg, the flow rate of the nozzle is 4.9-5.0 L / min.

4. The method according to claim 1, characterized in that: It includes smelting molten iron and scrap steel in a converter, sending the steel out of the converter to an argon station for argon blowing, and then continuous casting after the argon blowing is completed; Preferably, the temperature of the molten steel of the first furnace of the threaded steel at the argon station is (T L +125)±10℃, the temperature of molten steel after argon blowing is (T L +80)±5℃, the temperature of molten steel when it is delivered to the continuous casting platform is (T L +75)±5℃, molten steel superheat is T L +(10~55)℃, when the temperature of the molten steel in the continuous casting process is ≤T L When the temperature reaches +10℃, replace the molten steel with one with a higher casting temperature for casting; The temperature of the molten steel of the rebar in the continuous casting furnace to the argon station is (T L +77)±10℃, the temperature of molten steel after argon blowing is (T L +50)±5℃, the temperature of molten steel when it is delivered to the continuous casting platform is (T L +48)±5℃, molten steel superheat is T L +(15~30)℃, when the temperature of the molten steel in the continuous casting process is ≤T L When the temperature reaches +10℃, replace the molten steel with one with a higher casting temperature for casting; Among them, T L It is the liquidus temperature of molten steel, in °C.

5. The method according to claim 4, characterized in that When the superheat of molten steel is greater than T L +45℃, the pulling speed of the continuous casting billet is 2.5m / min; when the superheat degree of molten steel is T L +(36~45)℃, the pulling speed of the continuous casting billet is 3.0m / min; when the superheat degree of molten steel is T L +(10~36)℃, excluding molten steel superheat T L +36℃, the pulling speed of the continuous casting billet is 3.2m / min; when the superheat of molten steel is less than T L At +10°C, the pulling speed of the continuous casting billet is 3.5 m / min.

6. The method according to claim 1 or 5, characterized in that: During the continuous casting process, the vibration amplitude of the crystallizer is ±4.5 mm and the vibration frequency is 30v+65; Wherein v is the pulling speed of the continuous casting billet, the unit is m / min; the unit of vibration amplitude is mm, and the unit of vibration frequency is Hz; Preferably, the vibration amplitude of the crystallizer is between ±4.5 mm and the vibration frequency is between 125 and 185 Hz; Preferably, the cooling water flow rate of the crystallizer is 120-150m 3 / h, the water inlet pressure is 0.9-1.2MPa, the flow rate of cooling water in the crystallizer is 18-20m / s, and the insertion depth of the immersion nozzle is 120-140mm.

7. The method according to claim 6, characterized in that The consumption of the protective slag in the crystallizer is 0.17-0.35 kg / t; Preferably, when the casting speed of the continuous casting billet is ≥3.5 m / min, the consumption of the protective slag in the crystallizer is 0.17-0.23 kg / t; Preferably, the basicity of the protective slag is 0.9-1.0, the melting point Tm of the crystalline polymer is 1060-1065°C, and the viscosity at 1300°C is 0.25-0.3P·S; Preferably, the mass percentages of the components in the protective slag include SiO2: 29.5-30.0%, MgO: 2.5-3.0%, CaO: 28.0-28.5%, Fe2O3: 0.5-0.8%, Al2O3: 5.2-5.8%, Na2O: 10.2-10.8%, F: 7.5-8.0%, and C: 12.0-12.5%.

8. The method according to claim 4, characterized in that Argon blowing starts from the moment the molten steel starts tapping from the converter until the argon blowing at the argon station is completed. The total argon blowing time is ≥6 minutes, and the argon blowing time during the converter tapping process is ≥2 minutes. The argon pressure is 0.5-1.0MPa. Preferably, when the alloy is added during the argon blowing process of the argon station, the argon blowing time is increased; When the mass of the added alloy is less than 200kg, the time of blowing argon at the argon station shall be increased by ≥2min; when the mass of the added alloy is ≥200kg, the time of blowing argon at the argon station shall be increased by ≥4min.

9. The method according to claim 4, characterized in that The mass percentage of C in the molten steel tapped from the converter is ≥0.04%, the mass percentage of S is ≤0.030%, and the mass percentage of P is ≤0.043%; Preferably, the charging system of the converter smelting includes: 90-120t of molten iron, 0-33t of scrap steel, and a total amount of 115-130t; Preferably, the alloy and slag are added 60 seconds after the converter taps steel.

10. The method according to claim 1, characterized in that The element composition of the threaded steel, by mass percentage, includes C≤0.25%, Si≤0.80%, Mn≤1.60%, S≤0.043%, P≤0.043%, Nb≥0%, and the balance is iron and other unavoidable impurities; The carbon equivalent Ceq of the threaded steel is ≤0.54%; Preferably, when the brand name of the threaded steel is HRB400, the element composition, by mass percentage, includes C: 0.22-0.25%, Si: 0.55-0.65%, Mn: 1.40-1.50%, S≤0.040%, P≤0.040%, Nb: 0.010-0.015%, and the balance is iron and other inevitable impurities; The carbon equivalent Ceq of the threaded steel is 0.46-0.54%; Preferably, when the brand name of the threaded steel is HRB400E, the element composition, by mass percentage, includes C: 0.22-0.25%, Si: 0.55-0.65%, Mn: 1.40-1.50%, S≤0.043%, P≤0.043%, Nb: 0.010-0.017%, and the balance is iron and other inevitable impurities; The carbon equivalent Ceq of the threaded steel is 0.46-0.54%; Preferably, when the brand name of the threaded steel is GHRB400 or GHRB400E, the element composition, calculated by mass percentage, includes C≤0.25%, Si≤0.80%, Mn≤1.60%, S≤0.043%, P≤0.043%, Nb≥0%, and the balance is iron and other unavoidable impurities; The carbon equivalent Ceq of the threaded steel is ≤0.54%; Preferably, the cross-sectional specification of the threaded steel bar is 160×160 mm.

Images