A method for producing a medium alloy steel continuous casting billet

Abstract

The present application relates to alloy smelting technical field, specifically disclose a kind of medium alloy steel continuous casting billet production method.The present application is through alloy preheating and baking, electric arc furnace smelting, molten steel deoxidation and alloying, LF refining, VD refining, continuous casting and billet slow cooling process, using hot steel slag to preheat alloy, then bake, without using alloy baking furnace system can effectively control alloy hydrogen content in molten steel, promote electric arc furnace molten steel alloying after molten steel alloy melting in molten steel;Adopt special slow cooling mode instead of billet annealing, use the carbon knot steel continuous casting hot billet of previous pouring to bottom preheating, while the cover of billet heat preservation, can make billet uniform, slow cooling, effectively release the thermal stress and organizational stress of billet, reduce the possibility of medium alloy steel continuous casting billet center shrinkage or intermediate crack;Through optimizing the casting speed parameter, improve the macroscopic quality of billet.

Description

Technical Field

[0001] This invention relates to the field of alloy smelting technology, and in particular to a method for producing medium alloy steel continuous casting billets. Background Technology

[0002] Medium alloy steel has an alloy element content of 5% to 10% and is often used to manufacture structural components that require high strength and temperature resistance, such as aircraft landing gear, automotive transmission parts, and heavy machinery structural parts. Some medium alloy steels have corrosion resistance, low temperature resistance, or high temperature resistance properties and can be used in chemical equipment (such as pipelines and valves), pressure vessels, and high-temperature industrial components.

[0003] Medium alloy steel, due to its high alloy content and high hydrogen content in the molten steel, exhibits high stress in continuously cast billets, making them prone to shrinkage cavities and central cracks. Current production processes for medium alloy steel continuously cast billets primarily involve: using an alloy baking furnace system to bake the alloy into the billet to 400℃~600℃, followed by vacuum treatment; continuous casting (referred to as continuous casting) at low casting speed with secondary cooling and electromagnetic stirring; and hot charging annealing or slow cooling followed by annealing. This process requires both an alloy baking furnace system and an annealing furnace system, placing high demands on equipment and tooling, resulting in high production costs and complex processes. Furthermore, the unstable hydrogen content in the molten steel leads to central shrinkage cavities and central cracks of grade 2.0 or higher appearing in the billets at low magnification, even resulting in the scrapping of the medium alloy steel continuously cast billets. Therefore, finding a way to produce medium alloy steel continuously cast billets without using alloy baking furnace systems and annealing furnace systems, while reducing production costs and stabilizing billet quality, is of great significance. Summary of the Invention

[0004] To address the aforementioned problems, this invention provides a method for producing medium alloy steel continuous casting billets. Through processes such as alloy preheating and baking, electric arc furnace smelting, steel deoxidation and alloying, LF refining, VD refining, continuous casting, and slow cooling of the billet, this method not only shortens the process flow and refining time, reducing production costs, but also effectively stabilizes the quality of medium alloy steel continuous casting billets, solving the problems of central shrinkage cavities and intermediate cracks that are prone to occur in medium alloy steel continuous casting billets.

[0005] To solve the above-mentioned technical problems, the technical solution provided by the present invention is as follows:

[0006] A method for producing medium alloy steel continuous casting billets includes the following steps:

[0007] S1. Preheating ferrochrome alloy and ferromolybdenum alloy with hot steel slag to obtain preheated alloy;

[0008] S2. The raw materials are smelted in an electric arc furnace to obtain molten steel; a portion of the preheated alloy is added to a ladle and baked; the molten steel is added to the baked ladle for deoxidation and alloying to obtain alloyed molten steel.

[0009] S3. The alloyed steel liquid is subjected to LF refining, VD refining and continuous casting in sequence to obtain a billet; in the LF refining, when the temperature of the steel liquid is ≥1560℃, the remaining preheated alloy is added; in the continuous casting, when the temperature of the steel liquid is 1535℃~1550℃, the casting speed is 2m / min~2.2m / min.

[0010] S4. The slow cooling pit is preheated with a carbon steel continuous casting hot billet, and then the billet and the carbon steel continuous casting hot billet are added in sequence. The slow cooling cover is then placed on top for slow cooling to obtain a medium alloy steel continuous casting billet.

[0011] Compared to existing technologies, the production method of medium alloy steel continuous casting billets provided by this invention uses hot steel slag to preheat ferrochrome alloy and ferromolybdenum alloy (hereinafter referred to as alloys), followed by baking. This effectively controls the hydrogen content introduced into the molten steel by the alloy without the need for an alloy baking furnace system, promoting the melting of the alloy in the molten steel after alloying in the electric arc furnace. By controlling the timing of adding the preheated alloy during LF refining, not only can the composition of the medium alloy steel continuous casting billet be guaranteed to be qualified, but energy consumption is also significantly saved and the LF refining time is shortened. By optimizing the casting speed parameters, the low-magnification quality of the billet is improved, and the overall performance of the subsequent medium alloy steel continuous casting billets is also enhanced. By using a special slow cooling method instead of billet annealing, and using the hot carbon steel continuous casting billet from the previous casting to preheat the bottom of the slow cooling pit while simultaneously insulating the top cover of the billet, the billet can be cooled evenly and slowly, effectively releasing the thermal stress and structural stress of the billet, thereby reducing the possibility of central shrinkage cavities or intermediate cracks in the medium alloy steel continuous casting billet.

[0012] Through extensive testing, this invention has found that if the casting speed is too low during continuous casting, severe cracks are likely to appear in the low magnification center of the billet; if the casting speed is too high, severe shrinkage cavities are likely to appear in the low magnification center of the billet, and even steel leakage may occur.

[0013] Preferably, S1 specifically includes the following steps: uniformly spreading ferrochrome alloy and ferromolybdenum alloy in a hopper, placing the hopper on hot steel slag in a slag pot for preheating, and obtaining a preheated alloy.

[0014] Preferably, in S1, the ferrochrome alloy is a low-carbon ferrochrome alloy or a micro-carbon ferrochrome alloy.

[0015] Preferably, in step S1, the amount of ferrochrome alloy added is 80 kg / t to 83 kg / t, and the amount of ferromolybdenum alloy added is 6.5 kg / t to 7.5 kg / t. More preferably, in step S1, the amount of ferrochrome alloy added is 80.3 kg / t to 82.8 kg / t, and the amount of ferromolybdenum alloy added is 6.8 kg / t to 7.5 kg / t.

[0016] It should be noted that in the unit kg / t of this invention, "t" refers to the mass of molten steel or the mass of medium alloy steel continuously cast billet. The amount of ferrochrome alloy and ferromolybdenum alloy added is based on the mass of molten steel.

[0017] For example, in S1, the hopper is a flat-bottomed, open trapezoidal hopper welded from 8mm~10mm thick steel plates, which can accurately add the alloy in the hopper to the designated area in the slag pot.

[0018] Preferably, in S1, the surface temperature of the hot steel slag is 610℃~790℃, and the amount of hot steel slag added is 25kg / t~35kg / t.

[0019] In this invention, hot slag refers to the residual steel and slag in the ladle after the previous continuous casting. The amount of hot slag added is based on the mass of the medium alloy steel continuous casting billet.

[0020] Preferably, in S1, the preheating time is 60 min to 120 min.

[0021] Preferably, in S1, the surface temperature of the preheated alloy is 180℃~270℃.

[0022] Preferably, in S2, the smelting raw materials include pig iron and scrap steel.

[0023] Preferably, in S2, the power consumption of the electric arc furnace smelting process is 410 kW·h / t to 440 kW·h / t, and the oxygen consumption is 13 m³ / t. 3 / t~18m 3 / t, the smelting cycle is 48min~51min.

[0024] Preferably, in S2, the molten steel has a C content ≤0.07% and a P content ≤0.007%.

[0025] Preferably, in S2, the tapping temperature of the molten steel is 1640℃~1670℃.

[0026] Preferably, in S2, the amount of preheated alloy added during baking is 43 kg / t to 55 kg / t.

[0027] This invention, by limiting the amount of preheating alloy used, can prevent excessive alloy addition from clogging the venting bricks or nozzles of the ladle, thus avoiding adverse effects on subsequent refining and continuous casting. The amount of preheating alloy added is based on the mass of the molten steel.

[0028] For example, in S2, the ladle is a hot-turnover ladle, heated using gas. Before use, the venting bricks and water inlet of the ladle must be cleaned and inspected, and drainage sand must be poured in. The preheating alloy is placed at the bottom of the ladle, avoiding the venting bricks and water inlet.

[0029] Preferably, in step S2, the baking time is 35 min to 50 min.

[0030] Preferably, in step S2, after the baking is completed, the surface temperature of the alloy inside the ladle is 450℃~600℃.

[0031] Preferably, in step S2, the deoxidation and alloying specifically includes the following steps: when the steel is tapped to 9%~12% of its total volume, calcium carbide is added to the ladle for pre-deoxidation; when the steel is tapped to 19%~22% of its total volume, aluminum ingots are added to the ladle for deep deoxidation; when the steel is tapped to 33%~37% of its total volume, pre-melted refining slag, fluorite, ferrosilicon, ferrosilicon, and lime are added to the ladle for slag formation and alloying; all materials are added when the steel is tapped to 60%~65% of its total volume; and after the steel is tapped to 100% of its total volume, alloyed molten steel is obtained.

[0032] More preferably, in S2, the calcium carbide comprises the following components by mass percentage: CaC2 78%~85%, CaO 10%~15%, SiO2 ≤5%, Al2O3 ≤3%, and MgO ≤3%.

[0033] More preferably, in S2, the gas generation capacity of the calcium carbide is ≥260L / kg, and the particle size is 5mm~30mm.

[0034] Through extensive testing, this invention has found that if the gas production of calcium carbide is too low, it will increase the deoxygenation time and have an adverse effect on the deoxygenation effect.

[0035] More preferably, in S2, the amount of calcium carbide added is 0.4 kg / t to 0.6 kg / t (more preferably 0.40 kg / t to 0.52 kg / t).

[0036] More preferably, in S2, the amount of aluminum ingot added is 1.4 kg / t to 1.8 kg / t (more preferably 1.50 kg / t to 1.72 kg / t).

[0037] More preferably, in S2, the pre-melted refining slag comprises the following components by mass percentage: CaO 35%~42%, Al2O3 45%~52%, SiO2 ≤10%, and MgO ≤5%.

[0038] More preferably, in S2, the particle size of the pre-melted refining slag is 5mm to 50mm.

[0039] Through extensive testing, this invention has found that if the particle size of the pre-melted refining slag is too low, it will cause volatilization and lead to waste; if the particle size of the pre-melted refining slag is too high, the melting effect will be poor.

[0040] More preferably, in S2, the fluorite comprises the following components by mass percentage: CaF ≥ 82% and SiO2 ≤ 18%.

[0041] More preferably, in S2, the particle size of the fluorite is 10mm~80mm.

[0042] More preferably, in S2, the amount of pre-melted refining slag added is 3.4 kg / t to 4.2 kg / t, the amount of fluorite added is 1.7 kg / t to 2.4 kg / t, the amount of ferrosilicon alloy added is 6.3 kg / t to 7.2 kg / t, the amount of ferrosilicon alloy added is 0.8 kg / t to 1.2 kg / t, and the amount of lime added is 4.6 kg / t to 5.1 kg / t. More preferably, in S2, the amount of pre-melted refining slag added is 3.45 kg / t to 4.02 kg / t, the amount of fluorite added is 1.72 kg / t to 2.30 kg / t, the amount of ferrosilicon alloy added is 6.32 kg / t to 6.90 kg / t, the amount of ferrosilicon alloy added is 0.80 kg / t to 1.03 kg / t, and the amount of lime added is 4.60 kg / t to 4.83 kg / t.

[0043] In this invention, the amounts of calcium carbide, aluminum ingots, pre-melted refining slag, fluorite, silicon-manganese alloy, silicon-iron alloy, and lime added are based on the mass of molten steel.

[0044] More preferably, in S2, the total tapping time is 90s~120s.

[0045] Through extensive testing, this invention has found that if the tapping time is too short, oxide slag may be incorporated into the molten steel during the tapping process; if the tapping time is too long, the heat loss of the molten steel is large, and energy consumption increases.

[0046] Preferably, in S3, the LF refining specifically includes the following steps: adding the alloyed steel liquid to the LF furnace, slag by electrolysis, and adding lime and fluorite to adjust the basicity and viscosity of the steel slag; when the temperature of the steel liquid is 1560℃~1580℃, adding the remaining preheating alloy to the steel liquid, and deoxidizing it with aluminum particles and calcium carbide, obtaining white slag after 3min~6min; then using ferrosilicon powder to maintain the white slag; when the temperature of the steel liquid is 1570℃~1590℃, finely adjusting the chemical composition of the steel liquid to obtain LF refined steel liquid.

[0047] More preferably, in S3, during the LF refining process, the amount of lime added is 4.5 kg / t to 5.2 kg / t, and the amount of fluorite added is 1.1 kg / t to 1.8 kg / t. More preferably, in S3, during the LF refining process, the amount of lime added is 4.60 kg / t to 5.17 kg / t, and the amount of fluorite added is 1.15 kg / t to 1.72 kg / t.

[0048] More preferably, in S3, during the LF refining process, the amount of aluminum granules added is 0.2 kg / t to 0.4 kg / t, and the amount of calcium carbide added is 0.2 kg / t to 0.4 kg / t. More preferably, in S3, during the LF refining process, the amount of aluminum granules added is 0.23 kg / t to 0.34 kg / t, and the amount of calcium carbide added is 0.23 kg / t to 0.34 kg / t.

[0049] For example, in S3, during the LF refining process, the aluminum granules contain ≥99% Al.

[0050] For example, in S3, during LF refining, the ferrosilicon powder comprises the following components by mass percentage: Si ≥ 50%, C ≤ 0.5%, P ≤ 0.04%, S ≤ 0.02%, with the balance being Fe and unavoidable impurities. The particle size of the ferrosilicon powder is 1 mm to 5 mm.

[0051] More preferably, in S3, the amount of ferrosilicon powder added in the LF refining process is 0.2 kg / t to 0.4 kg / t (more preferably 0.23 kg / t to 0.34 kg / t).

[0052] In the LF refining process of this invention, the amounts of lime, fluorite, aluminum granules, calcium carbide, and calcium silicate powder added are based on the mass of the molten steel.

[0053] More preferably, in S3, during the LF refining process, the time for maintaining the white residue is ≥20 min (more preferably 20 min to 35 min).

[0054] For example, in S3, during LF refining, when fine-tuning the chemical composition of the molten steel, the argon flow rate is 260 NL / min to 300 NL / min.

[0055] Preferably, in S3, the VD refining specifically includes the following steps: adding the obtained LF refined molten steel into a VD furnace for vacuum suction, feeding it into a silicon-calcium wire after breaking the vacuum, and soft blowing to obtain VD refined molten steel.

[0056] More preferably, in S3, during the VD refining process, the vacuum degree of the vacuum suction is ≤67 Pa, and the holding time is ≥18 min. More preferably, in S3, during the VD refining process, the vacuum degree of the vacuum suction is 20 Pa to 67 Pa, and the holding time is 18 min to 23 min.

[0057] More preferably, in S3, during the VD refining process, the feed rate of the silicon-calcium wire is 1 m / t to 1.5 m / t.

[0058] More preferably, in S3, the time for soft blowing during the VD refining process is ≥15 min (more preferably 15 min to 25 min).

[0059] This invention can effectively reduce the gas content in molten steel, remove inclusions, and improve the purity of molten steel by controlling the high vacuum time and soft blowing time in VD refining.

[0060] Preferably, in S3, the pouring temperature of the continuously cast steel is 1535℃~1550℃, and the pouring time is 48min~51min.

[0061] Preferably, in S3, the conditions for drawing steel in the continuous casting process include: when the temperature of the molten steel is 1537℃~1547℃, the drawing speed is 2.05m / min~2.15m / min; and the secondary cooling water volume is 0.25L / kg~0.31L / kg.

[0062] By controlling the casting speed and the amount of water used in the secondary cooling process, this invention can ensure that the surface temperature of the continuously cast billet entering the straightening machine is 1150℃~1270℃ and the surface temperature of the billet exiting the straightening machine is 950℃~1030℃, thus avoiding the brittle zone of 700℃~900℃ for the continuously cast billet and effectively preventing straightening cracks from appearing in the continuously cast billet.

[0063] In a further preferred embodiment, in S3, the conditions for pulling steel in the continuous casting process further include: the rate of electromagnetic stirring in the crystallizer is 380A~400A with a current of 3.6Hz~4.0Hz; and the current of electromagnetic stirring at the end of the crystallizer is 380A~400A with a frequency of 7.5Hz~8.0Hz.

[0064] Because VD-refined molten steel is viscous, both the crystallizer electromagnetic stirring and the end electromagnetic stirring use the maximum rated parameters of the equipment. The crystallizer electromagnetic stirring uses alternating stirring with a stirring cycle of 7s~2s~7s. This stirring mode can promote the nucleation of molten steel crystals and increase the low-magnification equiaxed crystal ratio of the billet. The end electromagnetic stirring uses continuous stirring. This stirring mode can increase the stirring force, break up dendrite bridging during the solidification process of the billet, and increase the conduction of heat from the inside of the billet to the surface of the billet, reducing the thermal stress of the billet. By limiting the secondary cooling water ratio and electromagnetic stirring (referred to as electric stirring) parameters, this invention can be combined with the casting speed to further avoid the occurrence of central cracks and central shrinkage cavities in the billet.

[0065] Preferably, in S3, the cross-sectional diameter of the billet in the continuous casting is 177mm~183mm.

[0066] Preferably, in S3, the billet comprises the following chemical composition by mass percentage: C 0.09%~0.15%, Si 0.15%~0.35%, Mn 0.40%~0.70%, Cr 4.80%~5.50%, Mo 0.45%~0.65%, Al 0.01%~0.045%, P≤0.015%, S≤0.010%, Cu≤0.25%, Ni≤0.25%, and the balance being Fe and unavoidable impurity elements.

[0067] Preferably, in S4, the carbon structural steel continuously cast hot billet comprises the following chemical composition by mass percentage: C 0.32%~0.36%, Si 0.15%~0.35%, Mn 1.30%~1.40%, Al 0.008%~0.04%, P≤0.020%, S≤0.010%, Cr≤0.25%, Ni≤0.25%, Cu≤0.20%, Mo≤0.10%, V≤0.05%, and the balance being Fe and unavoidable impurity elements.

[0068] The carbon structural steel continuous casting hot billet in this invention includes a carbon steel continuous casting billet or a carbon manganese steel continuous casting billet. The carbon structural steel continuous casting hot billet and the medium alloy steel billet are simultaneously subjected to slow cooling, which will not have an adverse effect on the subsequent performance of the carbon structural steel continuous casting hot billet.

[0069] Preferably, in S4, at the start of preheating, the surface temperature of the carbon steel continuous casting hot billet is 540℃~590℃; the preheating time is 90min~120min; and at the end of preheating, the temperature of the pit wall of the slow cooling pit is 270℃~350℃.

[0070] Preferably, in S4, when the slow cooling begins, the surface temperature of the billet is 470℃~530℃; the slow cooling time is ≥120h; and when the slow cooling ends, the surface temperature of the billet is ≤150℃.

[0071] For example, in S4, after slow cooling, the process also includes: removing the billet from the pit and air cooling it to room temperature to obtain a medium alloy steel continuous casting billet.

[0072] Preferably, in S4, the amount of carbon structural steel continuous casting hot billet added during preheating is 90 kg / t to 120 kg / t; the amount of upper carbon structural steel continuous casting hot billet added during slow cooling is 90 kg / t to 120 kg / t.

[0073] In this invention, the amount of carbon structural steel continuously cast hot billet added is based on the mass of the billet or medium alloy steel continuously cast billet.

[0074] The present invention has the following beneficial effects:

[0075] The various processes in this invention are closely linked, which shortens the refining time of molten steel, reduces the gas content and inclusions in the finished molten steel, improves the low-magnification quality of the billet, and effectively releases the thermal stress and structural stress of the billet, thereby obtaining qualified medium alloy steel continuous casting billets. At the same time, it significantly reduces production costs and has high market application value. Attached Figure Description

[0076] Figure 1 This is a low-magnification quality photograph of the medium alloy steel continuous casting billet in Embodiment 2 of the present invention;

[0077] Figure 2 This is a low-magnification quality photograph of the medium alloy steel continuous casting billet of Comparative Example 2 of the present invention. Detailed Implementation

[0078] To make the objectives, technical solutions, and advantages of this invention clearer, the invention will be further described in detail below with reference to embodiments. It should be understood that the specific embodiments described herein are merely illustrative and not intended to limit the invention.

[0079] In the embodiments and comparative examples of this invention, the steel grade used is 12Cr5Mo; unless otherwise specified, all products are commercially available.

[0080] Example 1

[0081] This embodiment provides a method for producing medium alloy steel continuous casting billets, including alloy preheating and baking, electric arc furnace smelting, steel deoxidation and alloying, LF refining, VD refining, continuous steel casting, and billet slow cooling processes, specifically including the following steps:

[0082] S100, Alloy Preheating:

[0083] 7100 kg of low-carbon ferrochrome alloy and 630 kg of ferromolybdenum alloy were evenly spread in the hopper. The hopper was then lifted by a crane and placed on the hot steel slag in the slag pot for preheating. At this time, the surface temperature of the hot steel slag was 700℃~705℃. After 80 minutes, the preheated alloy with a surface temperature of 221℃~249℃ was obtained.

[0084] The addition amount of low-carbon ferrochrome alloy is 81.42 kg / t, the addition amount of ferromolybdenum alloy is 7.22 kg / t, and the addition amount of hot steel slag is 30 kg / t.

[0085] S200, Alloy Baking:

[0086] After cleaning and inspecting the permeable bricks and water inlet of the ladle, and filling it with diversion sand, 4329 kg of preheated alloy is added to the bottom of the ladle (the remaining preheated alloy can be preheated in the hopper using hot steel slag), avoiding the permeable bricks and water inlet of the ladle, and baked with gas for 42 minutes (until the electric arc furnace completes the melting), to obtain a baked alloy with a surface temperature of 512℃~544℃.

[0087] The amount of preheated alloy added is 49.64 kg / t.

[0088] S300, electric arc furnace smelting:

[0089] The smelting raw materials (25% pig iron and 75% scrap steel) are smelted in an electric arc furnace, with an electricity consumption of 425 kW·h / t and an oxygen consumption of 15 m³ / t. 3 The melting cycle is 49 minutes, yielding molten steel with C 0.053%, P 0.0055%, and 1656℃. The steel is then tapped.

[0090] This embodiment does not limit the order of S100~S200 and S300.

[0091] S400, deoxidation and alloying of molten steel:

[0092] Molten steel was added to a ladle containing the baking alloy. When the molten steel reached 8.3t (9.9% of the total), 40kg of calcium carbide was added to the ladle for pre-deoxidation. When the molten steel reached 17.6t (21.1% of the total), 140kg of aluminum ingots were added to the ladle for deep deoxidation. When the molten steel reached 28.9t (34.6% of the total), 330kg of pre-melted refining slag, 170kg of fluorite, 577kg of silicon-manganese alloy, 81kg of silicon-iron alloy, and 408kg of lime were added to the ladle for slag formation and alloying. All materials were added before the molten steel reached 52.2t (62.4% of the total). The total tapping time was 106s, yielding 83.6t of alloyed molten steel.

[0093] Calcium carbide comprises the following components by mass percentage: CaC2 80.5%, CaO 10.6%, SiO2 4.3%, Al2O3 2.1%, and MgO 2.5%. The gas evolution of calcium carbide at 20℃ and 101.3 kPa is 279 L / kg, and the particle size is 9 mm to 21 mm.

[0094] The pre-melted refining slag comprises the following components by mass percentage: CaO 38.4%, Al2O3 49.8%, SiO2 8.2%, and MgO 3.6%. The particle size of the pre-melted refining slag is 20 mm to 35 mm.

[0095] Fluorite comprises the following components by mass percentage: CaF 85.7% and SiO2 14.3%. The grain size of fluorite is 30 mm to 60 mm.

[0096] It should be noted that the impurity components in calcium carbide, pre-melted refining slag, and fluorite were not measured.

[0097] The amount of calcium carbide added is 0.48 kg / t, the amount of aluminum ingot added is 1.67 kg / t, the amount of pre-melted refining slag added is 3.95 kg / t, the amount of fluorite added is 2.03 kg / t, the amount of silicon-manganese alloy added is 6.90 kg / t, the amount of silicon-iron alloy added is 0.97 kg / t, and the amount of lime added is 4.88 kg / t.

[0098] S500, LF Refined:

[0099] The alloyed steel liquid was added to an LF furnace for refining, and slag was formed by electrolysis. 425 kg of lime and 120 kg of fluorite were added to adjust the basicity and viscosity of the steel slag. When the steel liquid temperature reached 1572℃, the remaining 3401 kg of preheating alloy was added to the steel liquid, and 25.5 kg of aluminum granules and 24.8 kg of calcium carbide were used for rapid deoxidation to form white slag for 4.5 min. Then, 25 kg of ferrosilicon powder was used to maintain the white slag for 31 min. When the steel liquid temperature reached 1573℃, a sample was taken, and the chemical composition was analyzed by spectroscopy, including: C 0.122%, Si 0.181%, Mn 0.467%, Cr 4.902%, Mo 0.471%, Al 0.0321%, P 0.0102%, S 0.0066%, Cu 0.032%, and Ni 0.035%.

[0100] When the temperature of the molten steel is 1580℃, the chemical composition of the molten steel is finely adjusted, the argon flow rate is 275NL / min, the stirring is strengthened, and the refining is ended when the temperature of the molten steel is 1663℃ (refining time is 57.6min), yielding 87.2t of LF refined molten steel.

[0101] The amount of lime added is 4.87 kg / t, the amount of fluorite added is 1.38 kg / t, the amount of aluminum granules added is 0.29 kg / t, the amount of calcium carbide added is 0.28 kg / t, and the amount of ferrosilicon powder added is 0.29 kg / t.

[0102] S600, VD Refined:

[0103] The LF-refined molten steel was added to the VD furnace and vacuumed at a vacuum level of 50 Pa for 21 minutes. After the vacuum was broken, the hydrogen concentration was set at 1.5 ppm. A 100 m silicon-calcium wire was then fed in and soft-blown for 20 minutes to obtain the VD-refined molten steel.

[0104] The feed rate of the silicon-calcium wire is 1.15 m / t.

[0105] S700, continuously cast steel:

[0106] The VD refined steel was poured under the following conditions: pouring speed of 2.10 m / min; secondary cooling water ratio of 0.28 L / kg; alternating stirring in the crystallizer with a stirring cycle of 7 s to 2 s to 7 s and a speed of 400 A / 4.0 Hz; and continuous stirring at the end with a speed of 400 A / 8.0 Hz. The pouring temperature was 1538℃ to 1542℃, and the pouring time was 49 min. The surface temperature of the continuously cast billet entering the straightening machine was 1190℃ to 1240℃, and the surface temperature exiting the straightening machine was 975℃ to 1005℃. A sample was taken from the tundish, yielding a billet with a cross-sectional diameter of 180 mm ± 2.5 mm.

[0107] The above-mentioned billet contains the following chemical composition by mass percentage: C 0.133%, Si 0.194%, Mn 0.552%, Cr 5.023%, Mo 0.521%, Al 0.0212%, P 0.0081%, S 0.0055%, Cu 0.031%, and Ni 0.036%, with the balance being Fe and unavoidable impurity elements.

[0108] S800, slow cooling of the cast billet:

[0109] A carbon structural steel continuously cast hot billet with a surface temperature of 551℃~572℃ was used to preheat the slow cooling pit for 110 minutes. When the pit wall temperature was 294℃~321℃, a cast billet with a surface temperature of 490℃~510℃ and a carbon structural steel continuously cast hot billet with a surface temperature of 551℃~572℃ were added in sequence. The slow cooling cover was then placed on the pit for slow cooling. After 134 hours, the billet was removed from the pit, yielding a medium alloy steel continuously cast billet with a surface temperature of 80℃~125℃.

[0110] The continuously cast hot billet of carbon structural steel includes the following chemical composition by mass percentage: C 0.343%, Si 0.176%, Mn 1.312%, Al 0.0166%, P 0.0165%, S 0.0064%, Cr 0.088%, Ni 0.036%, Cu 0.055%, Mo 0.0067%, V 0.0054%, and the balance Fe and unavoidable impurity elements.

[0111] The amount of carbon structural steel continuously cast hot billet added during preheating is 106 kg / t; the amount of upper carbon structural steel continuously cast hot billet added during slow cooling is 106 kg / t.

[0112] Example 2

[0113] This embodiment provides a method for producing medium alloy steel continuous casting billets, including alloy preheating and baking, electric arc furnace smelting, steel deoxidation and alloying, LF refining, VD refining, continuous steel casting, and billet slow cooling processes, specifically including the following steps:

[0114] S100, Alloy Preheating:

[0115] 7000 kg of low-carbon ferrochrome alloy and 600 kg of ferromolybdenum alloy were evenly spread in a hopper. A crane was used to lift the hopper onto the hot steel slag in the slag pot for preheating. At this time, the surface temperature of the hot steel slag was 623℃~640℃. After 65 minutes, a preheated alloy with a surface temperature of 192℃~237℃ was obtained.

[0116] The addition amount of low-carbon ferrochrome alloy is 80.37 kg / t, the addition amount of ferromolybdenum alloy is 6.89 kg / t, and the addition amount of hot steel slag is 25 kg / t.

[0117] S200, Alloy Baking:

[0118] After cleaning and inspecting the permeable bricks and water inlet of the ladle, and filling it with diversion sand, 3866 kg of preheating alloy is added to the bottom of the ladle (the remaining preheating alloy can be preheated in the hopper using hot steel slag), avoiding the permeable bricks and water inlet of the ladle, and baked with gas for 37 minutes (until the electric arc furnace has completed the melting), to obtain a baked alloy with a surface temperature of 461℃~503℃.

[0119] The amount of preheated alloy added is 44.39 kg / t.

[0120] S300, electric arc furnace smelting:

[0121] The smelting raw materials (23% pig iron and 77% scrap steel) are smelted in an electric arc furnace, with an electricity consumption of 410 kW·h / t and an oxygen consumption of 13 m³. 3 / t, the smelting cycle is 51min, and molten steel with C 0.064%, P 0.0047% and 1640℃ is obtained and tapped.

[0122] This embodiment does not limit the order of S100~S200 and S300.

[0123] S400, deoxidation and alloying of molten steel:

[0124] Molten steel was added to a ladle containing the baking alloy. When the molten steel reached 7.9t (9.5% of the total), 35kg of calcium carbide was added to the ladle for pre-deoxidation. When the molten steel reached 16.7t (20.2% of the total), 130kg of aluminum ingots was added to the ladle for deep deoxidation. When the molten steel reached 27.9t (33.7% of the total), 300kg of pre-melted refining slag, 150kg of fluorite, 552kg of silicon-manganese alloy, 70kg of silicon-iron alloy, and 400kg of lime were added to the ladle for slag formation and alloying. All materials were added before the molten steel reached 50.5t (51% of the total). The total tapping time was 90s, yielding 82.8t of alloyed molten steel.

[0125] Calcium carbide comprises the following components by mass percentage: CaC2 82.0%, CaO 10.7%, SiO2 3.5%, Al2O3 2.3%, and MgO 1.5%. Calcium carbide has a gas evolution rate of 268 L / kg at 20℃ and 101.3 kPa, and a particle size of 5 mm to 18 mm.

[0126] The pre-melted refining slag comprises the following components by mass percentage: CaO 36.6%, Al2O3 51.3%, SiO2 8.4%, and MgO 3.7%. The particle size of the pre-melted refining slag is 5 mm to 25 mm.

[0127] Fluorite comprises the following components by mass percentage: CaF 82.1% and SiO2 17.9%. The grain size of fluorite is 10 mm to 40 mm.

[0128] It should be noted that the impurity components in calcium carbide, pre-melted refining slag, and fluorite were not measured.

[0129] The amount of calcium carbide added is 0.42 kg / t, the amount of aluminum ingot added is 1.57 kg / t, the amount of pre-melted refining slag added is 3.62 kg / t, the amount of fluorite added is 1.81 kg / t, the amount of silicon-manganese alloy added is 6.67 kg / t, the amount of silicon-iron alloy added is 0.85 kg / t, and the amount of lime added is 4.83 kg / t.

[0130] S500, LF Refined:

[0131] The alloyed steel liquid was added to an LF furnace for refining, and slag was formed by electrolysis. 400 kg of lime and 100 kg of fluorite were added to adjust the basicity and viscosity of the steel slag. When the steel liquid temperature reached 1560℃, the remaining 3734 kg of preheating alloy was added to the steel liquid, and 20 kg of aluminum granules and 20 kg of calcium carbide were used for rapid deoxidation to create white slag for 6 minutes. Then, 20 kg of ferrosilicon powder was used to maintain the white slag for 22 minutes. When the steel liquid temperature reached 1570℃, a sample was taken, and the chemical composition was analyzed by spectroscopy, including: C 0.134%, Si 0.192%, Mn 0.416%, Cr 4.813%, Mo 0.440%, Al 0.0303%, P 0.0111%, S 0.0055%, Cu 0.029%, and Ni 0.032%.

[0132] When the temperature of the molten steel is 1590℃, the chemical composition of the molten steel is finely adjusted, the argon flow rate is 286NL / min, the stirring is strengthened, and the refining is ended when the temperature of the molten steel is 1669℃ (refining time is 59.1min), yielding 87.1t of LF refined molten steel.

[0133] The amount of lime added is 4.59 kg / t, the amount of fluorite added is 1.15 kg / t, the amount of aluminum granules added is 0.23 kg / t, the amount of calcium carbide added is 0.23 kg / t, and the amount of ferrosilicon powder added is 0.23 kg / t.

[0134] S600, VD Refined:

[0135] The LF-refined molten steel was added to the VD furnace and vacuumed at a vacuum level of 40 Pa for 18 minutes. After the vacuum was broken, the hydrogen concentration was determined to be 1.7 ppm. A 90 m silicon-calcium wire was then fed in and soft-blown for 15 minutes to obtain the VD-refined molten steel.

[0136] The feed rate of the silicon-calcium wire is 1.03 m / t.

[0137] S700, continuously cast steel:

[0138] The VD refined steel was poured under the following conditions: pouring speed of 2.05 m / min; secondary cooling water ratio of 0.28 L / kg; alternating stirring in the crystallizer with a stirring cycle of 7 s to 2 s to 7 s and a speed of 390 A / 4.0 Hz; and continuous stirring at the end with a speed of 390 A / 8.0 Hz. The pouring temperature was 1544℃ to 1547℃, and the pouring time was 51 min. The surface temperature of the continuously cast billet entering the straightening machine was 1150℃ to 1201℃, and the surface temperature exiting the straightening machine was 950℃ to 993℃. A sample was taken from the tundish, yielding a billet with a cross-sectional diameter of 180 mm ± 2.5 mm.

[0139] The above-mentioned billet contains the following chemical composition by mass percentage: C 0.133%, Si 0.205%, Mn 0.556%, Cr 4.991%, Mo 0.514%, Al 0.0193%, P 0.0121%, S 0.0072%, Cu 0.030%, and Ni 0.032%, with the balance being Fe and unavoidable impurity elements.

[0140] S800, slow cooling of the cast billet:

[0141] A carbon structural steel continuously cast hot billet with a surface temperature of 541℃~566℃ was used to preheat the slow cooling pit for 90 minutes. When the pit wall temperature was 271℃~304℃, a cast billet with a surface temperature of 470℃~500℃ and a carbon structural steel continuously cast hot billet with a surface temperature of 541℃~566℃ were added in sequence. The slow cooling pit was covered and slow cooling was carried out. After 120 hours, the billet was removed from the pit, and a medium alloy steel continuously cast billet with a surface temperature of 92℃~145℃ was obtained.

[0142] The continuously cast hot billet of carbon structural steel includes the following chemical composition by mass percentage: C 0.335%, Si 0.189%, Mn 1.324%, Al 0.0187%, P 0.0143%, S 0.0086%, Cr 0.079%, Ni 0.043%, Cu 0.064%, Mo 0.0086%, V 0.0041%, and the balance Fe and unavoidable impurity elements.

[0143] The amount of carbon structural steel continuous casting hot billet added during preheating is 105 kg / t; the amount of upper carbon structural steel continuous casting hot billet added during slow cooling is 115 kg / t.

[0144] Example 3

[0145] This embodiment provides a method for producing medium alloy steel continuous casting billets, including alloy preheating and baking, electric arc furnace smelting, steel deoxidation and alloying, LF refining, VD refining, continuous steel casting, and billet slow cooling processes, specifically including the following steps:

[0146] S100, Alloy Preheating:

[0147] 7200 kg of low-carbon ferrochrome alloy and 650 kg of ferromolybdenum alloy were evenly spread in a hopper. A crane was used to lift the hopper onto the hot steel slag in the slag pot for preheating. At this time, the surface temperature of the hot steel slag was 780℃~790℃. After 90 minutes, a preheated alloy with a surface temperature of 236℃~270℃ was obtained.

[0148] The addition amount of low-carbon ferrochrome alloy is 82.76 kg / t, the addition amount of ferromolybdenum alloy is 7.47 kg / t, and the addition amount of hot steel slag is 35 kg / t.

[0149] S200, Alloy Baking:

[0150] After cleaning and inspecting the permeable bricks and water inlet of the ladle, and filling it with diversion sand, 4710 kg of preheated alloy is added to the bottom of the ladle (the remaining preheated alloy can be preheated in the hopper using hot steel slag), avoiding the permeable bricks and water inlet of the ladle, and baked with gas for 50 minutes (until the electric arc furnace has completed the melting), to obtain a baked alloy with a surface temperature of 534℃~600℃.

[0151] The amount of preheated alloy added is 54.14 kg / t.

[0152] S300, electric arc furnace smelting:

[0153] The smelting raw materials (27% pig iron and 73% scrap steel) are smelted in an electric arc furnace, with an electricity consumption of 440 kW·h / t and an oxygen consumption of 18 m³ / t. 3 / t, the smelting cycle is 48min, and molten steel with C 0.068%, P 0.0065% and 1670℃ is obtained and tapped.

[0154] This embodiment does not limit the order of S100~S200 and S300.

[0155] S400, deoxidation and alloying of molten steel:

[0156] Molten steel was added to a ladle containing the baking alloy. When the molten steel reached 9.5t (11.4% of the total), 45kg of calcium carbide was added to the ladle for pre-deoxidation. When the molten steel reached 18.2t (21.8% of the total), 150kg of aluminum ingot was added to the ladle for deep deoxidation. When the molten steel reached 30.4t (36.4% of the total), 350kg of pre-melted refining slag, 200kg of fluorite, 600kg of silicon-manganese alloy, 100kg of silicon-iron alloy, and 420kg of lime were added to the ladle for slag formation and alloying. All materials were added before the molten steel reached 53.9t (64.5% of the total). The total tapping time was 120s, yielding 83.6t of alloyed molten steel.

[0157] Calcium carbide comprises the following components by mass percentage: CaC2 84.3%, CaO 11.6%, SiO2 1.8%, Al2O3 1.3%, and MgO 1.0%. Calcium carbide has a gas evolution rate ≥272 L / kg at 20℃ and 101.3 kPa, and a particle size of 21 mm to 30 mm.

[0158] The pre-melted refining slag comprises the following components by mass percentage: CaO 41.4%, Al2O3 45.7%, SiO2 8.6%, and MgO 4.3%. The particle size of the pre-melted refining slag is 30 mm to 50 mm.

[0159] Fluorite comprises the following components by mass percentage: CaF 88.4% and SiO2 11.6%. The grain size of fluorite is 50 mm to 80 mm.

[0160] It should be noted that the impurity components in calcium carbide, pre-melted refining slag, and fluorite were not measured.

[0161] The amount of calcium carbide added is 0.54 kg / t, the amount of aluminum ingot added is 1.79 kg / t, the amount of pre-melted refining slag added is 4.19 kg / t, the amount of fluorite added is 2.39 kg / t, the amount of silicon-manganese alloy added is 7.18 kg / t, the amount of silicon-iron alloy added is 1.2 kg / t, and the amount of lime added is 5.02 kg / t.

[0162] S500, LF Refined:

[0163] The alloyed steel liquid was added to an LF furnace for refining, and slag was formed by electrolysis. 450 kg of lime and 150 kg of fluorite were added to adjust the basicity and viscosity of the steel slag. When the steel liquid temperature reached 1570℃, the remaining 3140 kg of preheating alloy was added to the steel liquid, and 30 kg of aluminum granules and 30 kg of calcium carbide were used for rapid deoxidation to create white slag for 3 minutes. Then, 30 kg of ferrosilicon powder was used to maintain the white slag for 35 minutes. When the steel liquid temperature reached 1577℃, a sample was taken, and the chemical composition was analyzed by spectroscopy, including: C 0.129%, Si 0.173%, Mn 0.506%, Cr 4.952%, Mo 0.501%, Al 0.0303%, P 0.0098%, S 0.0032%, Cu 0.027%, and Ni 0.033%.

[0164] When the temperature of the molten steel is 1570℃, the chemical composition of the molten steel is finely adjusted, the argon flow rate is 268NL / min, the stirring is strengthened, and the refining is ended when the temperature of the molten steel is 1659℃ (refining time is 56.0min), yielding 87.0t LF refined molten steel.

[0165] The amount of lime added is 5.17 kg / t, the amount of fluorite added is 1.72 kg / t, the amount of aluminum granules added is 0.34 kg / t, the amount of calcium carbide added is 0.34 kg / t, and the amount of ferrosilicon powder added is 0.34 kg / t.

[0166] S600, VD Refined:

[0167] The LF-refined molten steel was added to the VD furnace and vacuumed at a vacuum level of 30 Pa for 23 minutes. After the vacuum was broken, the hydrogen concentration was set at 1.2 ppm. A 120 m silicon-calcium wire was then fed in and soft-blown for 25 minutes to obtain the VD-refined molten steel.

[0168] The feed rate of the silicon-calcium wire is 1.38 m / t.

[0169] S700, continuously cast steel:

[0170] The VD refined steel was poured under the following conditions: pouring speed of 2.15 m / min; secondary cooling water ratio of 0.28 L / kg; alternating stirring in the crystallizer with a stirring cycle of 7 s to 2 s to 7 s and a speed of 400 A / 3.8 Hz; and continuous stirring at the end with a speed of 400 A / 7.8 Hz. The pouring temperature was 1537℃ to 1545℃, and the pouring time was 48 min. The surface temperature of the continuously cast billet entering the straightening machine was 1193℃ to 1270℃, and the surface temperature exiting the straightening machine was 996℃ to 1030℃. A sample was taken from the tundish, yielding a billet with a cross-sectional diameter of 180 mm ± 2.5 mm.

[0171] The above-mentioned billet contains the following chemical composition by mass percentage: C 0.141%, Si 0.224%, Mn 0.561%, Cr 5.055%, Mo 0.527%, Al 0.0193%, P 0.0103%, S 0.0046%, Cu 0.028%, and Ni 0.031%, with the balance being Fe and unavoidable impurity elements.

[0172] S800, slow cooling of the cast billet:

[0173] A carbon structural steel continuously cast hot billet with a surface temperature of 552℃~590℃ was used to preheat the slow cooling pit for 110 minutes. When the pit wall temperature was 296℃~350℃, a cast billet with a surface temperature of 495℃~530℃ and a carbon structural steel continuously cast hot billet with a surface temperature of 552℃~590℃ were added sequentially. The slow cooling pit was covered and slow cooled. After 146 hours, the billet was removed from the pit, and a medium alloy steel continuously cast billet with a surface temperature of 64℃~103℃ was obtained.

[0174] The continuously cast hot billet of carbon structural steel includes the following chemical composition by weight percentage: C 0.351%, Si 0.206%, Mn 1.353%, Al 0.0201%, P 0.0112%, S 0.0073%, Cr 0.076%, Ni 0.041%, Cu 0.062%, Mo 0.0055%, V 0.0034%, and the balance Fe and unavoidable impurity elements.

[0175] The amount of carbon structural steel continuous casting hot billet added during preheating is 115 kg / t; the amount of upper carbon structural steel continuous casting hot billet added during slow cooling is 105 kg / t.

[0176] Comparative Example 1

[0177] This comparative example provides a method for producing medium alloy steel continuously cast billets, including alloy baking, electric arc furnace smelting, steel deoxidation and alloying, LF refining, VD refining, continuous steel casting, and billet slow cooling processes, specifically including the following steps:

[0178] S100, Alloy Baking (Alloy Preheating Omitted):

[0179] After cleaning and inspecting the venting bricks and water inlet of the ladle, and filling it with diversion sand, add 4329 kg of low-carbon ferrochrome alloy (3976 kg) and ferromolybdenum alloy (353 kg) to the bottom of the ladle, avoiding the venting bricks and water inlet. Bake with gas for 51 minutes (until the electric arc furnace completes the melting) to obtain a baked alloy with a surface temperature of 311℃~355℃.

[0180] S200~S700, the specific operating steps and conditions are similar to S300~S800 in Example 1, the only difference being that in the LF refining, 3401kg of preheated alloy is replaced with 3124kg of low-carbon ferrochrome alloy and 277kg of ferromolybdenum alloy, and the rest will not be repeated. The billet obtained after continuous casting includes the following chemical composition by mass percentage: C 0.135%, Si 0.191%, Mn 0.544%, Cr 5.028%, Mo 0.522%, Al 0.0210%, P 0.0088%, S 0.0057%, Cu 0.029% and Ni 0.037%, and the balance Fe and unavoidable impurity elements.

[0181] Comparative Example 2

[0182] This comparative example provides a method for producing medium alloy steel continuously cast billets, including alloy preheating and baking, electric arc furnace smelting, steel deoxidation and alloying, LF refining, VD refining, continuous steel casting, and billet slow cooling processes, specifically including the following steps:

[0183] S100~S600, the specific operating steps and conditions are the same as S100~S600 in Example 2, and will not be repeated here.

[0184] S700, continuously cast steel:

[0185] The VD refined steel was poured under the following conditions: pouring speed of 1.95 m / min; secondary cooling water ratio of 0.28 L / kg; alternating stirring in the crystallizer with a stirring cycle of 7 s to 2 s to 7 s and a speed of 390 A / 4.0 Hz; and continuous stirring at the end with a speed of 390 A / 8.0 Hz. The pouring temperature was 1540℃ to 1545℃, and the pouring time was 53 min. The surface temperature of the continuously cast billet entering the straightening machine was 1059℃ to 1163℃, and the surface temperature exiting the straightening machine was 902℃ to 954℃. A sample was taken from the tundish, yielding a billet with a cross-sectional diameter of 180 mm ± 2.5 mm.

[0186] The above-mentioned billet contains the following chemical composition by mass percentage: C 0.130%, Si 0.208%, Mn 0.563%, Cr 4.983%, Mo 0.511%, Al 0.0191%, P 0.0126%, S 0.0078%, Cu 0.031%, and Ni 0.042%, with the balance being Fe and unavoidable impurity elements.

[0187] S800, the specific operating steps and conditions are the same as S800 in Example 2, and will not be repeated here.

[0188] Comparative Example 3

[0189] This comparative example provides a method for producing medium alloy steel continuously cast billets, including alloy preheating and baking, electric arc furnace smelting, steel deoxidation and alloying, LF refining, VD refining, continuous steel casting, and billet slow cooling processes, specifically including the following steps:

[0190] S100~S700, the specific operating steps and conditions are the same as those in Example 3, and will not be repeated. The billet obtained after continuous casting of steel includes the following chemical composition by mass percentage: C 0.132%, Si 0.199%, Mn 0.551%, Cr 5.024%, Mo 0.526%, Al 0.0218%, P 0.0095%, S 0.0065%, Cu 0.032% and Ni 0.038%, as well as the balance Fe and unavoidable impurity elements.

[0191] S800, slow cooling of the cast billet:

[0192] The billet with a surface temperature of 495℃~530℃ is added to the slow cooling pit, covered with a slow cooling cover for slow cooling, and removed from the pit after 128 hours to obtain a medium alloy steel continuous casting billet with a surface temperature of 43℃~85℃.

[0193] Verification test

[0194] According to the YB / T 4149-2018 standard, the medium alloy steel continuous casting billets prepared in Examples 1-3 and Comparative Examples 1-3 were subjected to corresponding tests. The test results are shown in Table 1 and Table 2. Figures 1-2 As shown.

[0195] Table 1 shows the test results of various indicators for alloy steel continuously cast billets.

[0196]

[0197] As can be seen from the table and figures, the hot steel slag used in the steel casting of this invention, and the slow cooling of the billet using carbon steel continuous casting hot billet, and the hydrogen content of the medium alloy steel continuous casting billet obtained according to the control parameter range of each step are all below 2.0 ppm, and the lowest level of low magnification center shrinkage cavity and center crack is 0.5 grade. However, when hot steel slag is not used to preheat the alloy, the billet is not slow cooled without the use of carbon steel continuous casting hot billet under and top cover, and the continuous casting speed does not meet the control parameter range (Comparative Examples 1 to 3), the quality of the billet deteriorates significantly, with hydrogen content exceeding 2.0 ppm, high level of low magnification center crack, and billet curvature exceeding 5 mm / m.

[0198] The above description is only a preferred embodiment of the present invention and is not intended to limit the present invention. Any modifications, equivalent substitutions or improvements made within the spirit and principles of the present invention should be included within the protection scope of the present invention.

Claims

1. A method for producing a medium alloy steel continuous casting billet, characterized in that, Includes the following steps: S1. Hot steel slag is used to preheat ferrochrome alloy and ferromolybdenum alloy. The amount of ferrochrome alloy added is 80 kg / t to 83 kg / t, and the amount of ferromolybdenum alloy added is 6.5 kg / t to 7.5 kg / t, to obtain a preheated alloy. The surface temperature of the preheated alloy is 180℃ to 270℃. S2. The raw materials are smelted in an electric arc furnace to obtain molten steel; a portion of the preheating alloy is added to the ladle and baked. The amount of preheating alloy added during baking is 43 kg / t to 55 kg / t. After baking, the surface temperature of the alloy in the ladle is 450°C to 600°C. The molten steel is added to the baked ladle for deoxidation and alloying to obtain alloyed molten steel. S3. The alloyed steel liquid is sequentially subjected to LF refining, VD refining, and continuous casting to obtain a billet; in the LF refining, when the temperature of the steel liquid is ≥1560℃, the remaining preheated alloy is added; in the continuous casting, when the temperature of the steel liquid is 1535℃~1550℃, the casting speed is 2.05m / min~2.15m / min; the billet includes the following chemical composition by mass percentage: C 0.09%~0.15%, Si 0.15%~0.35%, Mn 0.40%~0.70%, Cr 4.80%~5.50%, Mo 0.45%~0.65%, Al 0.01%~0.045%, P≤0.015%, S≤0.010%, Cu≤0.25%, Ni≤0.25%, and the balance Fe and unavoidable impurity elements; S4. The carbon steel continuous casting hot billet is used to preheat the slow cooling pit. At the beginning of the preheating, the surface temperature of the carbon steel continuous casting hot billet is 540℃~590℃, and the preheating time is 90min~120min. Then the billet and the carbon steel continuous casting hot billet are added in sequence, and the slow cooling cover is covered for slow cooling to obtain a medium alloy steel continuous casting billet.

2. The method for producing medium alloy steel continuously cast billets as described in claim 1, characterized in that, In S1, the amount of hot steel slag added is 25 kg / t to 35 kg / t; In S4, the amount of carbon structural steel continuous casting hot billet added during preheating is 90kg / t to 120kg / t, and the amount of upper carbon structural steel continuous casting hot billet added during slow cooling is 90kg / t to 120kg / t.

3. The method for producing medium alloy steel continuously cast billets as described in claim 1 or 2, characterized in that, In S1, the surface temperature of the hot steel slag is 610℃~790℃, and the preheating time is 60min~120min; In S4, when the preheating ends, the temperature of the pit wall of the slow cooling pit is 270℃~350℃; In S4, when the slow cooling begins, the surface temperature of the billet is 470℃~530℃; the slow cooling time is ≥120h; and when the slow cooling ends, the surface temperature of the billet is ≤150℃.

4. The method for producing medium alloy steel continuously cast billets as described in claim 1, characterized in that, In S4, the carbon structural steel continuously cast hot billet comprises the following chemical composition by mass percentage: C 0.32%~0.36%, Si 0.15%~0.35%, Mn 1.30%~1.40%, Al 0.008%~0.04%, P≤0.020%, S≤0.010%, Cr≤0.25%, Ni≤0.25%, Cu≤0.20%, Mo≤0.10%, V≤0.05%, and the balance being Fe and unavoidable impurity elements.

5. The method for producing medium alloy steel continuously cast billets as described in claim 1, characterized in that, In S2, the deoxidation and alloying specifically include the following steps: when the steel is tapped to 9%~12% of the total molten steel, calcium carbide is added to the ladle for pre-deoxidation; when the steel is tapped to 19%~22% of the total molten steel, aluminum ingots are added to the ladle for deep deoxidation; when the steel is tapped to 33%~37% of the total molten steel, pre-melted refining slag, fluorite, ferrosilicon, ferrosilicon, and lime are added to the ladle for slag formation and alloying. All materials are added when the steel is tapped to 60%~65% of the total molten steel. After the steel is tapped to 100% of the total molten steel, alloyed molten steel is obtained. In S3, the LF refining specifically includes the following steps: adding the alloyed steel liquid to the LF furnace, slag formation by electrolysis, and adding lime and fluorite to adjust the basicity and viscosity of the steel slag; when the temperature of the steel liquid is 1560℃~1580℃, adding the remaining preheated alloy to the steel liquid, and deoxidizing it with aluminum particles and calcium carbide, obtaining white slag after 3min~6min; then using ferrosilicon powder to maintain the white slag; when the temperature of the steel liquid is 1570℃~1590℃, fine-tuning the chemical composition of the steel liquid to obtain LF refined steel liquid; In S3, the VD refining specifically includes the following steps: adding the obtained LF refined molten steel into the VD furnace for vacuum suction, feeding it into the silicon-calcium wire after breaking the vacuum, and soft blowing to obtain VD refined molten steel.

6. The method for producing medium alloy steel continuously cast billets as described in claim 1 or 5, characterized in that, In S2, the power consumption of the electric arc furnace smelting process is 410 kW·h / t to 440 kW·h / t, and the oxygen consumption is 13 m³ / t. 3 / t~18m 3 / t, the smelting cycle is 48min~51min; In S2, the molten steel has a carbon content ≤0.07% and a phosphorus content ≤0.007%; the tapping temperature of the molten steel is 1640℃~1670℃, and the total tapping time is 90s~120s; In S2, the baking time is 35 min to 50 min.

7. The method for producing medium alloy steel continuously cast billets as described in claim 5, characterized in that, In S2, the calcium carbide has a gas generation capacity of ≥260L / kg and a particle size of 5mm~30mm; the pre-melted refining slag has a particle size of 5mm~50mm; and the fluorite has a particle size of 10mm~80mm.

8. The method for producing medium alloy steel continuously cast billets as described in claim 5, characterized in that, In S2, the amount of calcium carbide added is 0.4 kg / t to 0.6 kg / t, the amount of aluminum ingot added is 1.4 kg / t to 1.8 kg / t, the amount of pre-melted refining slag added is 3.4 kg / t to 4.2 kg / t, the amount of fluorite added is 1.7 kg / t to 2.4 kg / t, the amount of silicon-manganese alloy added is 6.3 kg / t to 7.2 kg / t, the amount of silicon-iron alloy added is 0.8 kg / t to 1.2 kg / t, and the amount of lime added is 4.6 kg / t to 5.1 kg / t. In S3, during the LF refining process, the amount of lime added is 4.5 kg / t to 5.2 kg / t, the amount of fluorite added is 1.1 kg / t to 1.8 kg / t, the amount of aluminum granules added is 0.2 kg / t to 0.4 kg / t, the amount of calcium carbide added is 0.2 kg / t to 0.4 kg / t, and the amount of ferrosilicon powder added is 0.2 kg / t to 0.4 kg / t. In S3, during the VD refining process, the feed rate of the silicon-calcium wire is 1 m / t to 1.5 m / t.

9. The method for producing medium alloy steel continuously cast billets as described in claim 5, characterized in that, In S3, during the LF refining process, the time for maintaining the white residue is ≥20 min; In S3, during the VD refining process, the vacuum degree of the vacuum suction is ≤67Pa and the holding time is ≥18min; the soft blowing time is ≥15min.

10. The method for producing medium alloy steel continuously cast billets as described in claim 1, characterized in that, In S3, the continuous casting temperature of the steel is 1535℃~1550℃, and the casting time is 48min~51min; In S3, the conditions for drawing steel in the continuous casting process include: when the temperature of the molten steel is 1537℃~1547℃, the drawing speed is 2.05m / min~2.15m / min; The secondary cooling water flow rate is 0.25L / kg~0.31L / kg; the current of the electromagnetic stirring in the crystallizer is 380A~400A, and the frequency is 3.6Hz~4.0Hz; the current of the electromagnetic stirring at the end of the crystallizer is 380A~400A, and the frequency is 7.5Hz~8.0Hz.

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