A low-carbon tungsten-containing steel and its production method

Abstract

The present invention relates to the technical field of tungsten steel smelting, and specifically discloses a low-carbon tungsten-containing steel and a production method thereof. The production method of the low-carbon tungsten-containing steel provided by the present invention includes processes such as electric arc furnace smelting, pre-deoxidation and alloying of molten steel, LF refining and continuous steel casting. During the pre-deoxidation process of the molten steel of the present invention, the composite deoxidizer reacts with the oxygen in the molten steel to generate carbon monoxide, so that a protective atmosphere is formed in the ladle, which reduces the amount of inclusions generated by oxygen and nitrogen increase during the steel tapping process; by controlling the timing of adding ferrotungsten, the use of different deoxidizers, the timing of fine-tuning the chemical composition, and full-process protective casting, the melting of ferrotungsten is accelerated, the homogenization of the chemical composition in the molten steel is promoted, and at the same time, inclusions are effectively removed, thereby improving the purity of the molten steel. The various process steps of the present invention are closely linked, which shortens the refining time of the molten steel, reduces the number of inclusions in the finished molten steel, and thus improves the purity of the low-carbon tungsten-containing steel.

Description

Technical Field

[0001] The invention relates to the technical field of tungsten steel smelting, and specifically discloses a low-carbon tungsten-containing steel and a production method thereof. Background Art

[0002] Tungsten is the alloying element with the highest melting point and is also a strong carbide-forming element. Its carbides are very hard and have high strength, hardness and wear resistance. It is widely used in the production of various steels. Common tungsten-containing steels include high-speed steel and tool steel. When there are special needs, tungsten can also be used in case-hardening steel and quenched and tempered steel.

[0003] Tungsten has a high melting point (3410±20℃) and a high specific gravity, making its alloy difficult to melt during the molten steel smelting process. Currently, there are two smelting processes for tungsten-containing steel: one is to add ferrotungsten in the middle or late stages of tapping in an electric furnace or converter. This process requires the tapping temperature to be raised by 20-30℃, which causes significant erosion of the furnace refractory materials and incomplete melting of the ferrotungsten. To prevent the tungsten element from exceeding the target range, fine-tuning of the tungsten element is required in the late stages of refining, which increases the refining time. The other is to add ferrotungsten in batches after the molten steel is heated to a certain temperature in the early stages of LF refining, stirring under argon. This process takes a long time to refine, causes significant erosion of the ladle refractory materials, and makes the molten steel susceptible to secondary oxidation. Therefore, controlling or shortening the refining time and improving the purity of the molten steel are of great significance. Summary of the Invention

[0004] In view of the problems of existing tungsten-containing steel smelting process such as severe erosion of refractory materials, long refining time, and easy secondary oxidation of molten steel, the present invention provides a low-carbon tungsten-containing steel and a production method thereof.

[0005] In order to solve the above technical problems, the technical solution provided by the present invention is:

[0006] A method for producing low-carbon tungsten-containing steel includes an electric arc furnace melting process, a molten steel pre-deoxidation and alloying process, an LF refining process, and a continuous steel casting process, specifically comprising the following steps:

[0007] S1 Electric Arc Furnace Melting: The raw materials are melted in an electric arc furnace to obtain electric arc furnace endpoint molten steel with C 0.05% to 0.08% and P ≤ 0.009%, and then the steel is tapped;

[0008] S2 Pre-deoxidation and alloying of molten steel: when the steel is tapped to 9% to 11% of the total amount of molten steel, a composite deoxidizer is added to the ladle for pre-deoxidation; when the steel is tapped to 19% to 21% of the total amount of molten steel, aluminum ingots are added to the ladle for deep deoxidation; when the steel is tapped to 24% to 26% of the total amount of molten steel, tungsten-ferroalloy is added to the ladle; when the steel is tapped to 32% to 35% of the total amount of molten steel, pre-melted refined slag, silicon-manganese alloy, high manganese alloy, high chromium alloy, low chromium alloy, ferromolybdenum alloy, ferrovanadium alloy and lime are added to the ladle. All materials are added before the steel is tapped to 58% to 62% of the total amount of molten steel to obtain a metallurgical solution;

[0009] S3 LF refining: adding lime and fluorite to the metallurgical solution to form slag, first using a strong deoxidizer to quickly deoxidize to form white slag, then using a weak deoxidizer to maintain the white slag, and then when the molten steel temperature is ≥1600°C, fine-tuning the alloy chemical composition to obtain refined molten steel;

[0010] S4 continuous steel casting: The refined steel liquid is cast with full protection, and the aluminum loss during the continuous casting process is controlled to be ≤0.002%, thereby obtaining the low-carbon tungsten-containing steel.

[0011] Compared with the prior art, the production method of low-carbon tungsten-containing steel provided by the present invention, during the pre-deoxidation process of molten steel, the composite deoxidizer reacts with the oxygen in the molten steel to generate carbon monoxide, so that a protective atmosphere is formed in the ladle, thereby reducing the amount of inclusions generated by oxygen and nitrogen increase during the tapping process of the molten steel. In the alloying process, the specific timing of adding ferrotungsten alloy is conducive to the melting of ferrotungsten: if the ferrotungsten alloy is added too early, there is less molten steel in the ladle and the temperature is low, the ferrotungsten alloy is difficult to melt, and it is easy to sink to the bottom of the ladle, increasing the refining time; if the ferrotungsten alloy is added too late, there is more alloy in the molten steel at this time, and the time for the molten steel to impact the molten alloy is short, the ferrotungsten alloy is easy to clump on the surface of the molten steel, making it difficult to lower the electrode in the refining process, thereby prolonging the refining time. By controlling the use of different deoxidizers in the LF refining process and fine-tuning the timing of chemical composition, and protecting the pouring throughout the continuous casting process, the melting of ferrotungsten is accelerated, the chemical composition in the molten steel is promoted to be homogenized, and at the same time, inclusions are effectively removed and the purity of the molten steel is improved. The close integration of each process step shortens the refining time of the molten steel, effectively preventing erosion of the ladle refractory by the molten steel, and simultaneously reduces the probability of large inclusions in the finished molten steel, thereby improving the purity of the low-carbon, tungsten-containing steel. The results of the embodiment show that the refining time of the low-carbon, tungsten-containing steel obtained using the above production method is shortened by 7.7 to 9.5 minutes; the oxygen content in the tube billet is reduced by 1.9 to 4.4 ppm; and the maximum inclusion level of Class B in the steel pipe rolled from the tube billet is 1.0, and the maximum total inclusion level is 2.5, showing high practical value and promotional value.

[0012] Preferably, the weight percentages of the low-carbon tungsten-containing steel components are: C 0.13% to 0.17%, W 0.2% to 0.4%, Si 0.15% to 0.3%, Mn 1.6% to 1.75%, Cr 0.8% to 1.0%, Mo 0.3% to 0.4%, V 0.07% to 0.12%, Al 0.010% to 0.045%, P ≤ 0.015%, S ≤ 0.005%, Ni ≤ 0.10%, Cu ≤ 0.20%, Ti ≤ 0.05%, N ≤ 0.0070%, O ≤ 0.0020%, and the remainder of Fe and impurity elements.

[0013] Preferably, in step S1, the power consumption of the electric arc furnace smelting process is 420-450kW·h / t, and the oxygen consumption is 15-20m 3 / t, the smelting cycle is 46 to 50 minutes.

[0014] Preferably, in step S1, the tapping temperature is ≥1630°C, preferably 1630-1650°C.

[0015] The present invention controls the tapping temperature of the molten steel at the end of the electric arc furnace to be 10-30° C. higher than the normal tapping temperature, which is beneficial to the melting of ferrotungsten and does not corrode the refractory material of the ladle.

[0016] Preferably, in step S2, the composite deoxidizer includes the following components in percentage by mass: CaC2 76% to 85%, CaO 8% to 12%, SiO2 1% to 5%, Al2O3 1% to 5%, and MgO 1% to 5%; the composite deoxidizer has a gas generation capacity of ≥280 L / kg at normal temperature and pressure, and a particle size of 5 to 30 mm.

[0017] Preferably, in step S2, the amount of the composite deoxidizer added is 0.34-0.58 kg / t, and the amount of the aluminum ingot added is 1.38-1.84 kg / t.

[0018] For example, in step S2, the aluminum ingot has an Al content of ≥99.5% and a total impurity content of <0.5%.

[0019] Preferably, in step S2, the pre-melted refined slag comprises the following components in percentage by mass: CaO 32% to 40%, Al2O3 46% to 54%, SiO2 5% to 15%, and MgO 1 to 3%; and the particle size of the pre-melted refined slag is 5 to 50 mm.

[0020] Preferably, in step S2, the amount of tungsten-ferroalloy added is 2.75-3.22 kg / t, the amount of pre-melted refined slag added is 2.64-3.1 kg / t, the amount of silicon-manganese alloy added is 9.43-16.1 kg / t, the amount of high-manganese alloy added is 10.34-16.1 kg / t, the amount of high-chromium alloy added is 2.64-3.1 kg / t, the amount of low-chromium alloy added is 10.34-13.79 kg / t, the amount of molybdenum-ferroalloy added is 4.71-5.4 kg / t, the amount of vanadium-ferroalloy added is 1.37-2.3 kg / t, and the amount of lime added is 4.02-5.18 kg / t.

[0021] For example, in step S2, the temperature of the molten steel pre-deoxidation and alloying process is 1610-1650° C., and the time is 120-150 seconds.

[0022] By means of the above-mentioned molten steel pre-deoxidation and alloying process, a metallurgical melt can be obtained in which, when LF refining is reached, the ladle top slag has good melting point, good fluidity, appropriate basicity, and turns yellowish-white or grayish-white, the Als content in the molten steel is between 0.030% and 0.070%, the oxygen content and inclusion content are low, and the alloy composition is lower than but close to the lower limit of the internal control composition.

[0023] For example, in step S3, the fluorite includes the following components in percentage by mass: CaF2 ≥ 80%, SiO2 ≤ 18%.

[0024] Preferably, in step S3, the amount of lime added is 4.02-5.18 kg / t; the amount of fluorite added is 0.45-0.58 kg / t; and the particle size of the fluorite is 20-80 mm.

[0025] Preferably, in step S3, the strong deoxidizer is aluminum particles and a composite deoxidizer, and the usage ratio of the two is 1:(2-3); the weak deoxidizer is silicon carbide; the composite deoxidizer has a gas evolution capacity of ≥280 L / kg at room temperature and pressure, and a particle size of 5-30 mm.

[0026] Preferably, in step S3, the amount of the strong deoxidizer added is 0.45-0.81 kg / t; the amount of the weak deoxidizer added is 0.22-0.46 kg / t.

[0027] By controlling the use of different deoxidizers, the present invention can rapidly deoxidize and produce white slag, fully float inclusions in molten steel, accelerate the melting of ferrotungsten, and promote chemical composition homogenization. The aluminum particles and composite deoxidizer can float in the slag layer of the ladle top slag, rapidly removing oxygen from the ladle top slag to form white slag. The silicon carbide has weaker deoxidizing properties, further maintaining the white slag.

[0028] Preferably, in step S3, the temperature of making white slag is 1540-1570° C., and the time is 3-8 min; and the time of keeping the white slag is ≥20 min, preferably 25-35 min.

[0029] For example, in step S3, before fine-tuning the chemical composition of the alloy, the method further includes: taking samples when the LF refining slag is white and the molten steel temperature is ≥1570°C, and performing chemical composition spectrum analysis.

[0030] For example, in step S3, the specific operation of fine-tuning the chemical composition of the alloy is: according to the results of chemical composition spectrum analysis, tungsten iron, low chromium and / or molybdenum iron alloy are added at one time, the argon flow rate is controlled at 250-310NL / min, and stirring is strengthened.

[0031] In the present invention, fine-tuning the alloy's chemical composition shortens the alloy's melting time and homogenizes the composition of the molten steel. Since some oxygen and other impurities are introduced into the molten steel along with the alloy during chemical composition fine-tuning, subsequent refining time is shortened. Adding the alloy components all at once avoids the situation where oxygen and other impurities fail to float up in time when added multiple times, thereby facilitating the removal of inclusions.

[0032] Preferably, in step S4, the specific operation of the full-process protection pouring is: the joint between the ladle water inlet and the long nozzle is sealed with a vermiculite sealing gasket, and argon is blown into the long nozzle bowl through the argon pipeline above the long nozzle manipulator; the flow rate of the argon is 115~145NL / min, and the pressure is 2~2.5MPa; the pouring temperature is 1530~1550℃, and the pouring time is 46~49min.

[0033] In the continuous casting process of the present invention, the sealing gasket is made of vermiculite, which is not easily damaged under high-temperature heating conditions. Compared with the existing technology (such as asbestos fibers are easily pulverized under long-term high-temperature heating conditions), the service life of the sealing gasket can be extended; the entire casting process is protected by double sealing measures of vermiculite sealing gasket and argon protection. The full-process protection casting can control the aluminum loss in the continuous casting process to ≤0.002%, and the aluminum loss of the first furnace of the casting is ≤0.003%.

[0034] For example, the specification of the billet cast in the continuous steel casting process is a Φ200mm tube billet.

[0035] The present invention provides a low-carbon tungsten-containing steel obtained by the above production method.

[0036] The low-carbon, tungsten-containing steel provided by the present invention achieves fully melted ferrotungsten and uniform distribution of its components. Experimental results show that the oxygen content in the low-carbon, tungsten-containing steel tube billet is reduced by 1.9 to 4.4 ppm. In the steel pipe rolled from the tube billet, the maximum B-type inclusion level is 1.0, and the maximum total inclusion level is 2.5, representing reductions of 0.5 and 1.0 levels, respectively, compared to the prior art. This demonstrates high practical and promotional value. DETAILED DESCRIPTION

[0037] In order to make the purpose, technical solutions and advantages of the present invention more clearly understood, the present invention is further described in detail below in conjunction with the embodiments. It should be understood that the specific embodiments described herein are only used to explain the present invention and are not intended to limit the present invention.

[0038] Example 1

[0039] This embodiment provides a method for producing low-carbon tungsten-containing steel, comprising the following steps:

[0040] S1 Electric Arc Furnace Melting: The raw materials are melted in an electric arc furnace (power consumption is 435kW·h / t, oxygen consumption is 18m 3 / t, melting period of 48min), obtaining 87t of EAF endpoint molten steel with C 0.063%, P 0.0065%, and tapping temperature of 1636℃;

[0041] S2 steel liquid pre-deoxidation and alloying: During the tapping process of the electric arc furnace, when the steel liquid reaches 8.7t, 35kg of composite deoxidizer (components are CaC2 80%, CaO 10%, SiO2+Al2O 3+ MgO10%; gas evolution 289L / kg at 20℃, 101.3kPa, particle size 10-20mm) for pre-deoxidation; when the steel liquid reaches 17.4t, 140kg aluminum ingot is added to the ladle for deep deoxidation; when the steel liquid reaches 21.8t, 250kg tungsten-iron alloy is added; when the steel liquid reaches 29t, 253kg pre-melted refined slag (CaO 36%, Al2O3 50%, SiO2 12%, MgO 2%), 860kg silicon manganese alloy, 1350kg high manganese alloy, 250kg high chromium alloy, 1000kg low chromium alloy, 460kg ferromolybdenum alloy, 150kg ferrovanadium alloy and 402kg lime. All materials are added before the steel reaches 52.2t of molten steel to obtain a metallurgical solution; the temperature of the entire molten steel pre-deoxidation and alloying process is 1613-1636°C and the time is 130s;

[0042] S3 LF refining: 405 kg of lime and 50 kg of fluorite (particle size of 40-50 mm) were added to the metallurgical solution to form slag. 14.5 kg of aluminum particles and 35.8 kg of a composite deoxidizer (gas evolution of 285 L / kg at 20°C and 101.3 kPa, particle size of 10-20 mm) were first used at 1555°C to rapidly deoxidize the slag to form white slag for 5 minutes. 30 kg of silicon carbide was then used to maintain the white slag for 25 minutes.

[0043] Sample 1 was taken when the LF refining slag was white and the molten steel temperature was 1577°C. The chemical composition of the sample by spectroscopic analysis included: C 0.142%, W 0.233%, Si 0.181%, Mn 1.687%, Cr 0.872%, Mo 0.321%, V 0.088%, Al 0.0321%, P 0.0082% and S 0.0146%;

[0044] Then, when the temperature of the molten steel is 1607°C, a corresponding amount of low-chromium alloy is added at one time according to the chemical content of each corresponding element to fine-tune the chemical composition. The argon flow rate is controlled at 282NL / min, and stirring is strengthened. Refining is completed when the temperature of the molten steel is 1672°C (refining time is 51.6 minutes) to obtain refined molten steel.

[0045] S4 continuous steel casting: The refined steel liquid is cast under full protection. The junction between the ladle water inlet and the shroud is sealed with a vermiculite gasket. Argon is blown into the shroud bowl through the argon pipeline above the shroud manipulator. The argon flow rate is 126NL / min and the pressure is 2.3MPa. The pouring temperature is 1540℃ and the pouring time is 48min. The finished product sample is taken from the tundish, and the O content is 18.1ppm. The aluminum loss during the continuous casting process is 0.0014%, and a Φ200mm low-carbon tungsten-containing steel tube blank is obtained.

[0046] The chemical composition of the low-carbon tungsten-containing steel is: C 0.153%, W 0.236%, Si 0.194%, Mn 1.692%, Cr 0.901%, Mo 0.321%, V 0.088%, Al 0.0212%, P 0.0081% and S 0.0025%, and the balance is Fe and impurity elements.

[0047] Example 2

[0048] This embodiment provides a method for producing low-carbon tungsten-containing steel, comprising the following steps:

[0049] S1 Electric Arc Furnace Melting: The raw materials are melted in an electric arc furnace (power consumption is 420kW·h / t, oxygen consumption is 15m 3 / t, melting period of 50min), obtaining 87t of EAF endpoint steel liquid with C 0.051%, P 0.0088%, and tapping temperature of 1643℃;

[0050] S2 steel liquid pre-deoxidation and alloying: During the tapping process of the electric arc furnace, when the steel liquid reaches 7.9t, 30kg of composite deoxidizer (components are CaC2 85%, CaO 8%, SiO2+Al2O 3+ MgO7%; gas evolution 285L / kg at 20℃, 101.3kPa, particle size 5-15mm) for pre-deoxidation; when the steel liquid reaches 16.6t, 160kg aluminum ingot is added to the ladle for deep deoxidation; when the steel liquid reaches 20.9t, 240kg tungsten-iron alloy is added; when the steel liquid reaches 27.9t, 230kg pre-melted refined slag (CaO 32%, Al2O3 54%, SiO2 12%, MgO 2%), 1350kg silicon manganese alloy, 910kg high manganese alloy, 250kg high chromium alloy, 1000kg low chromium alloy, 420kg ferromolybdenum alloy, 120kg ferrovanadium alloy and 350kg lime. All materials are added before the steel reaches 50.5t of molten steel to obtain a metallurgical solution; the temperature of the entire molten steel pre-deoxidation and alloying process is 1620-1643℃ and the time is 120s;

[0051] S3 LF refining: 350 kg of lime and 50 kg of fluorite (particle size of 20-30 mm) were added to the metallurgical solution to form slag. 13.3 kg of aluminum particles and 26.7 kg of a composite deoxidizer (gas evolution of 285 L / kg at 20°C and 101.3 kPa, particle size of 5-15 mm) were first used at 1545°C to rapidly deoxidize the slag to form white slag for 8 minutes. 40 kg of silicon carbide was then used to maintain the white slag for 30 minutes.

[0052] Sample 1 was taken when the LF refining slag was white and the molten steel temperature was 1570°C. The chemical composition of the sample 1 by spectroscopic analysis was as follows: C 0.137%, W 0.221%, Si 0.272%, Mn 1.720%, Cr 0.852%, Mo 0.304%, V 0.072%, Al 0.0433%, P 0.0091% and S 0.0165%;

[0053] Then, when the temperature of the molten steel is 1601°C, the corresponding mass of tungsten-iron, low chromium, molybdenum-iron and other alloys are added at one time according to the chemical content of each corresponding element to fine-tune the chemical composition, the argon flow rate is controlled at 252NL / min, stirring is strengthened, and refining is completed when the temperature of the molten steel is 1668°C (refining time is 52.2 minutes) to obtain refined molten steel;

[0054] S4 continuous steel casting: The refined steel liquid is cast under full protection. The junction between the ladle water inlet and the shroud is sealed with a vermiculite gasket. Argon is blown into the shroud bowl through the argon pipeline above the shroud manipulator. The argon flow rate is 116NL / min and the pressure is 2.0MPa. The pouring temperature is 1530℃ and the pouring time is 49min. The finished product sample is taken from the tundish, and the O content is 17.4ppm. The aluminum loss during the continuous casting process is 0.0012%, and a Φ200mm low-carbon tungsten-containing steel tube blank is obtained.

[0055] The chemical composition of the low-carbon tungsten-containing steel is: C 0.146%, W 0.239%, Si 0.283%, Mn 1.723%, Cr 0.873%, Mo 0.317%, V 0.071%, Al 0.0306%, P 0.009% and S 0.0029%, and the balance is Fe and impurity elements.

[0056] Example 3

[0057] This embodiment provides a method for producing low-carbon tungsten-containing steel, comprising the following steps:

[0058] S1 Electric Arc Furnace Melting: The raw materials are melted in an electric arc furnace (power consumption is 450kW·h / t, oxygen consumption is 20m 3 / t, melting period of 46min), obtaining 87t of EAF endpoint steel liquid with C 0.079%, P 0.0058%, and tapping temperature of 1630℃;

[0059] S2 steel liquid pre-deoxidation and alloying: During the tapping process of the electric arc furnace, when the steel liquid reaches 9.5t, 50kg of composite deoxidizer (components are CaC2 76%, CaO 12%, SiO2+Al2O 3+ MgO12%; gas evolution 282L / kg at 20℃, 101.3kPa, particle size 20-30mm) for pre-deoxidation; when the steel liquid reaches 18.2t, 125kg aluminum ingot is added to the ladle for deep deoxidation; when the steel liquid reaches 22.6t, 280kg tungsten-iron alloy is added; when the steel liquid reaches 30.4t, 270kg pre-melted refined slag (CaO 40%, Al2O3 46%, SiO2 12%, MgO 2%), 910kg silicon manganese alloy, 1200kg high manganese alloy, 250kg high chromium alloy, 1100kg low chromium alloy, 450kg ferromolybdenum alloy, 190kg ferrovanadium alloy and 450kg lime. All materials are added before the steel reaches 53.9t of molten steel to obtain a metallurgical solution; the temperature of the entire molten steel pre-deoxidation and alloying process is 1610-1630℃ and the time is 140s;

[0060] S3 LF refining: 405 kg of lime and 40 kg of fluorite (particle size of 70-80 mm) were added to the metallurgical solution to form slag. 17.5 kg of aluminum particles and 52.5 kg of a composite deoxidizer (gas evolution of 285 L / kg at 20°C and 101.3 kPa, particle size of 20-30 mm) were first used at 1552°C to rapidly deoxidize the slag to form white slag for 3 minutes. 20 kg of silicon carbide was then used to maintain the white slag for 27 minutes.

[0061] Sample 1 was taken when the LF refining slag was white and the molten steel temperature was 1575°C. The chemical composition of the sample by spectroscopic analysis included: C 0.151%, W 0.265%, Si 0.192%, Mn 1.607%, Cr 0.984%, Mo 0.308%, V 0.110%, Al 0.0332%, P 0.0081% and S 0.0141%;

[0062] Then, when the temperature of the molten steel is 1610°C, a corresponding mass of high manganese alloy, molybdenum iron and other alloys are added at once according to the chemical content of each corresponding element to fine-tune the chemical composition, the argon flow rate is controlled at 282NL / min, stirring is strengthened, and refining is completed when the temperature of the molten steel is 1670°C (refining time is 51.9 minutes) to obtain refined molten steel;

[0063] S4 continuous steel casting: The refined steel liquid is cast with full protection. The junction between the ladle water inlet and the shroud is sealed with a vermiculite gasket. Argon is blown into the shroud bowl through the argon pipeline above the shroud manipulator. The argon flow rate is 145NL / min and the pressure is 2.5MPa. The pouring temperature is 1550℃ and the pouring time is 46min. The finished product sample is taken from the tundish, and the O content is 17.9ppm. The aluminum loss during the continuous casting process is 0.0013%, and a Φ200mm low-carbon tungsten-containing steel tube blank is obtained.

[0064] The chemical composition of the low-carbon tungsten-containing steel is: C 0.162%, W 0.266%, Si 0.195%, Mn 1.626%, Cr 0.985%, Mo 0.315%, V 0.110%, Al 0.0224%, P 0.008% and S 0.0019%, and the balance is Fe and impurity elements.

[0065] Comparative Example 1

[0066] This comparative example provides a method for producing low-carbon tungsten-containing steel, which is similar to Example 1, except that no pre-deoxidation is performed, the timing of adding the ferro-tungsten alloy is different (it is added after the other alloys are added in the alloying process), the corresponding tapping temperature is different, and the number and timing of chemical composition analysis sampling are different. Specifically, the following steps are included:

[0067] S1 Electric Arc Furnace Melting: The raw materials are melted in an electric arc furnace (power consumption is 435kW·h / t, oxygen consumption is 18m 3 / t, melting period of 48min), obtaining 87t of EAF endpoint molten steel with C 0.071%, P 0.0073%, and tapping temperature of 1647℃;

[0068] S2 steel pre-deoxidation and alloying: During the electric arc furnace tapping process, when the total amount of molten steel reaches 17.4 tons, 140kg of aluminum ingots are added to the ladle for deep deoxidation; when the total amount of molten steel reaches 29 tons, 253kg of pre-melted refined slag (CaO36%, Al2O3 50%, SiO2 12%, MgO 2%), 850kg of silicon manganese alloy, 1350kg of high manganese alloy, 250kg of high chromium alloy, 1150kg of low chromium alloy, 470kg of molybdenum iron alloy, 140kg of vanadium iron alloy, 250kg of tungsten iron alloy and 402kg of lime are added to the ladle. All materials are added before the total amount of steel reaches 52.2 tons to obtain a metallurgical solution; the temperature of the entire steel pre-deoxidation and alloying process is 1625-1647℃, and the time is 135s;

[0069] S3 LF refining: 405 kg of lime and 50 kg of fluorite (particle size of 40-50 mm) were added to the metallurgical solution to form slag. 14.5 kg of aluminum particles and 35.8 kg of a composite deoxidizer (gas evolution of 285 L / kg at 20°C and 101.3 kPa, particle size of 10-20 mm) were first used at 1555°C to rapidly deoxidize the slag to form white slag for 5 minutes. 30 kg of silicon carbide was then used to maintain the white slag for 31 minutes.

[0070] When the LF refining slag was white and the molten steel temperature was 1584℃, sample 1 was taken. The chemical composition of the spectral analysis was as follows: C 0.141%, W 0.198%, Si 0.183%, Mn 1.688%, Cr 0.872%, Mo 0.323%, V 0.082%, Al 0.0424%, P 0.0078%, S 0.0144%; the electric refining was continued, the argon flow rate was adjusted to 282NL / min, and the stirring was carried out for 3 minutes. When the LF refining slag was white and the molten steel temperature was 1616℃, sample 2 was taken. The chemical composition of the spectral analysis was as follows: C 0.145%, W 0.236%, Si 0.190%, Mn 1.690%, Cr 0.874%, Mo 0.323%, V 0.082%, Al 0.0335%, P 0.0081%, S 0.0032%; according to the chemical content of W, the corresponding mass of tungsten-iron alloy is added to fine-tune the chemical composition, and the refining is completed when the molten steel temperature is 1672°C (refining time is 59.3min) to obtain refined molten steel;

[0071] S4 continuous steel casting: The refined steel liquid is cast with full protection. The junction between the ladle water inlet and the shroud is sealed with a vermiculite gasket. Argon is blown into the shroud bowl through the argon pipeline above the shroud manipulator. The argon flow rate is 126NL / min and the pressure is 2.3MPa. The pouring temperature is 1540℃ and the pouring time is 48min. The finished product sample is taken from the tundish, the O content is 20.0ppm, the aluminum loss during the continuous casting process is 0.0023%, and a Φ200mm low-carbon tungsten-containing steel tube blank is obtained.

[0072] The chemical composition of the above-mentioned low-carbon tungsten-containing steel is: C 0.154%, W 0.283%, Si 0.191%, Mn 1.690%, Cr 0.874%, Mo 0.323%, V 0.082%, Al 0.0221%, P 0.008%, S 0.0035%, and the balance Fe and impurity elements.

[0073] Comparative Example 2

[0074] This comparative example provides a method for producing low-carbon tungsten-containing steel, which is similar to Example 1, except that no pre-deoxidation is performed, the timing of adding tungsten-ferroalloy is different (adding it during the LF refining process), the corresponding tapping temperature is different, and the sampling frequency and timing are different. Specifically, the following steps are included:

[0075] S1 Electric Arc Furnace Melting: The raw materials are melted in an electric arc furnace (power consumption is 435kW·h / t, oxygen consumption is 18m 3 / t, melting period of 48min), obtaining 87t of EAF endpoint molten steel with C 0.076%, P 0.0065%, and tapping temperature of 1626℃;

[0076] S2 steel pre-deoxidation and alloying: During the electric arc furnace tapping process, when the total amount of molten steel reaches 17.4 tons, 140 kg of aluminum ingots are added to the ladle for deep deoxidation; when the total amount of molten steel reaches 29 tons, 253 kg of pre-melted refined slag (CaO36%, Al2O3 50%, SiO2 12%, MgO 2%), 820 kg of silicon manganese alloy, 1380 kg of high manganese alloy, 250 kg of high chromium alloy, 950 kg of low chromium alloy, 460 kg of ferromolybdenum alloy, 130 kg of ferrovanadium alloy and 402 kg of lime are added to the ladle. All materials are added before the total amount of steel reaches 52.2 tons to obtain a metallurgical solution; the temperature of the entire molten steel pre-deoxidation and alloying process is 1608-1626 ° C, and the time is 130 seconds;

[0077] S3 LF refining: 405 kg of lime and 50 kg of fluorite (particle size of 40-50 mm) were added to the metallurgical solution to form slag. 14.5 kg of aluminum particles and 35.8 kg of a composite deoxidizer (gas evolution of 285 L / kg at 20°C and 101.3 kPa, particle size of 10-20 mm) were first used at 1554°C to rapidly deoxidize the slag to form white slag for 5 minutes. 30 kg of silicon carbide was then used to maintain the white slag for 33 minutes.

[0078] Sample 1 was taken when the LF refining slag was white and the molten steel temperature was 1577°C. Spectral analysis showed that the chemical composition was: C 0.139%, W 0.023%, Si 0.174%, Mn 1.678%, Cr 0.842%, Mo 0.317%, V 0.076%, Al 0.0431%, P 0.0068%, S 0.0154%. Electric refining was continued, and when the molten steel temperature was 1613°C, corresponding amounts of ferrotungsten, low chromium, ferromolybdenum and other alloys were added at one time to adjust the chemical composition.

[0079] The argon flow rate was adjusted to 282 NL / min, and the mixture was stirred for 6 minutes. Sample 2 was taken when the molten steel temperature was 1634° C., and the chemical composition of the sample 2 was analyzed by spectral analysis, which showed that the sample had the following chemical compositions: C 0.140%, W 0.236%, Si 0.195%, Mn 1.684%, Cr 0.851%, Mo 0.329%, V 0.082%, Al 0.0332%, P 0.0088%, and S 0.0036%. Refining was completed when the molten steel temperature was 1672° C. (refining time was 61.1 minutes), thereby obtaining refined molten steel.

[0080] S4 continuous steel casting: The refined steel liquid is cast with full protection. The junction between the ladle water inlet and the shroud is sealed with a vermiculite gasket. Argon is blown into the shroud bowl through the argon pipeline above the shroud manipulator. The argon flow rate is 126NL / min and the pressure is 2.3MPa. The pouring temperature is 1540℃ and the pouring time is 48min. The finished product sample is taken from the tundish, and the O content is 22.5ppm. The aluminum loss during the continuous casting process is 0.0024%, and a Φ200mm low-carbon tungsten-containing steel tube blank is obtained.

[0081] The chemical composition of the above-mentioned low-carbon tungsten-containing steel is: C 0.151%, W 0.236%, Si 0.196%, Mn 1.684%, Cr 0.851%, Mo 0.329%, V 0.082%, Al 0.0216%, P 0.0089%, S 0.0033%, and the balance Fe and impurity elements.

[0082] Comparative Example 3

[0083] This comparative example provides a production method for low-carbon tungsten-containing steel, which is similar to Example 1, except that: in the S2 molten steel pre-deoxidation and alloying process, the timing of adding aluminum ingots and tungsten-iron alloy is different (when the steel is tapped to 17% of the total amount of molten steel, the aluminum ingot is added to the ladle, and when the steel is tapped to 20% of the total amount of molten steel, the tungsten-iron alloy is added to the ladle), the corresponding tapping temperature is different, and the sampling times and timing are different. Specifically, the following steps are included:

[0084] S1 electric arc furnace smelting: same as in Example 1;

[0085] S2 Pre-deoxidation and alloying of molten steel: During the tapping process of the electric arc furnace, when the molten steel reaches 8.7 tons, 35 kg of composite deoxidizer (gas emission of 285 L / kg at 20°C and 101.3 kPa, particle size of 10-20 mm) is added to the ladle for pre-deoxidation; when the molten steel reaches 14.8 tons, 140 kg of aluminum ingots are added to the ladle for deep deoxidation; when the molten steel reaches 17.4 tons, 250 kg of tungsten-iron alloy is added; when the molten steel reaches 29 tons, 253 kg of pre-melted refined slag (CaO 36%, Al2O3 50%, SiO212%, MgO2%), 910kg silicon manganese alloy, 1250kg high manganese alloy, 250kg high chromium alloy, 1000kg low chromium alloy, 450kg ferromolybdenum alloy, 150kg ferrovanadium alloy and 402kg lime. All materials are added before 52.2t of molten steel is tapped to obtain a metallurgical solution. The temperature of the entire molten steel pre-deoxidation and alloying process is 1612-1636°C and the time is 135s.

[0086] S3 LF refining: 402kg lime and 50kg fluorite slag (particle size of 40-50mm) were added to the metallurgical solution, and 14kg aluminum particles and 35.1kg composite deoxidizer (components of CaC280%, CaO 10%, SiO2+Al2O 3+ MgO 10%; gas evolution 289L / kg at 20°C, 101.3kPa, particle size 10-20mm), rapid deoxidation to produce white slag for 8 minutes, then 31kg of silicon carbide is used to maintain the white slag for 28 minutes;

[0087] Sample 1 was taken when the LF refining slag was white and the molten steel temperature was 1577°C. The chemical composition of the sample 1 by spectrum analysis was as follows: C 0.151%, W 0.193%, Si 0.191%, Mn 1.677%, Cr 0.881%, Mo 0.310%, V 0.085%, Al 0.0421%, P 0.0078% and S 0.0148%. The refining was continued at elevated temperature. Sample 2 was taken when the molten steel temperature was 1592°C. The chemical composition of the sample 2 by spectrum analysis was as follows: C 0.157%, W 0.233%, Si 0.196%, Mn 1.681%, Cr 0.882%, Mo 0.311%, V 0.086%, Al 0.0355%, P 0.0082% and S 0.005%.

[0088] Then, when the temperature of the molten steel is 1610°C, the corresponding mass of tungsten iron, low chromium and other alloys are added at one time according to the chemical content of each corresponding element to fine-tune the chemical composition, the argon flow rate is controlled at 283NL / min, stirring is strengthened, and refining is completed when the temperature of the molten steel is 1674°C (refining time is 59.6 minutes) to obtain refined molten steel;

[0089] S4 continuous steel casting: The refined steel liquid is cast with full protection. The junction between the ladle water inlet and the shroud is sealed with a vermiculite gasket. Argon is blown into the shroud bowl through the argon pipeline above the shroud manipulator. The argon flow rate is 122NL / min, the pressure is 2.4MPa, the pouring temperature is 1542℃, and the pouring time is 48min. The finished product sample is taken from the tundish, the O content is 22.1ppm, the aluminum loss during the continuous casting process is 0.0023%, and a Φ200mm low-carbon tungsten-containing steel tube blank is obtained.

[0090] The chemical composition of the low-carbon tungsten-containing steel is: C 0.163%, W 0.246%, Si 0.201%, Mn 1.683%, Cr 0.911%, Mo 0.311%, V 0.086%, Al 0.0203%, P 0.0081% and S 0.003%, and the balance is Fe and impurity elements.

[0091] Table 1 Indicators of low carbon tungsten steel tubes prepared in Examples 1 to 3 and Comparative Examples 1 to 3

[0092]

[0093] As can be seen from the above table, compared with Comparative Examples 1 to 3, the endpoint molten steel temperature and the temperature at which the sample is basically qualified in Example 1 of the low-carbon tungsten-containing steel prepared in Example 1 of the present invention are significantly lower than those in Comparative Examples 1 to 3, the refining time is shortened by 7.7 to 9.5 minutes, the oxygen content is reduced by 1.9 to 4.4 ppm, and the continuous casting aluminum loss is reduced by 0.0009% to 0.001%. In Comparative Example 1, the ferrotungsten alloy is added too late, there is more alloy in the molten steel, and the time for the molten steel to impact the molten alloy is short, the ferrotungsten alloy is easy to clump on the surface of the molten steel, making it difficult to lower the electrode in the refining process, increasing the difficulty of operation, and even posing the risk of electrode breakage, thereby prolonging the refining time; in Comparative Example 3, the ferrotungsten alloy is added too early, there is less molten steel in the ladle, the temperature is low, the ferrotungsten alloy is difficult to melt, and it is easy to sink to the bottom of the ladle, which increases the refining time. This further shows that in the preparation process of low-carbon tungsten-containing steel, the present invention controls the timing of adding each material, thereby reducing the refining temperature (the duration of the period with higher refining temperature is shorter), shortening the refining time, and effectively avoiding the corrosion of the furnace refractory material by the molten steel. The molten steel is not easy to be secondary oxidized, and the oxygen content of the low-carbon tungsten-containing steel finished tube blank is low.

[0094] The low carbon tungsten steel tubes prepared in Examples 1 to 3 and Comparative Examples 1 to 3 were heated in a ring furnace and pierced and rolled to obtain The steel pipes were tested for inclusions using the GB / T 10561-2005 standard. The test results are shown in Table 2.

[0095] Table 2 Inclusion test of steel pipes prepared in Examples 1 to 3 and Comparative Examples 1 to 2

[0096]

[0097] As can be seen from the above table, compared with comparative examples 1 to 3, the steel pipes prepared by examples 1 to 3 of the present invention have less inclusion content, which shows that the production method of low-carbon tungsten-containing steel provided by the present invention can significantly improve the purity of molten steel.

[0098] 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 in the scope of protection of the present invention.

Claims

1. A method for producing low-carbon tungsten-containing steel, characterized in that: The process includes electric arc furnace melting process, molten steel pre-deoxidation and alloying process, LF refining process and continuous steel casting process, specifically including the following steps: S1 Electric Arc Furnace Melting: The raw materials are melted in an electric arc furnace to obtain electric arc furnace endpoint molten steel with C 0.05%~0.08% and P≤0.009%, and then the steel is tapped; S2 Pre-deoxidation and alloying of molten steel: when the steel is tapped to 9%~11% of the total amount of molten steel, a composite deoxidizer is added to the ladle for pre-deoxidation; when the steel is tapped to 19%~21% of the total amount of molten steel, aluminum ingots are added to the ladle for deep deoxidation; when the steel is tapped to 24%~26% of the total amount of molten steel, tungsten-ferroalloy is added to the ladle; when the steel is tapped to 32%~35% of the total amount of molten steel, pre-melted refined slag, silicon-manganese alloy, high manganese alloy, high chromium alloy, low chromium alloy, ferromolybdenum alloy, ferrovanadium alloy and lime are added to the ladle. All materials are added when the steel is tapped to 58%~62% of the total amount of molten steel to obtain a metallurgical solution; S3 LF refining: adding lime and fluorite to the metallurgical solution to form slag, first using a strong deoxidizer to quickly deoxidize to form white slag, then using a weak deoxidizer to maintain the white slag, and then when the molten steel temperature is ≥1600°C, fine-tuning the alloy chemical composition to obtain refined molten steel; S4 continuous steel casting: the refined steel liquid is cast in a fully protected manner, and the aluminum loss during the continuous casting process is controlled to be ≤0.002%, thereby obtaining the low-carbon tungsten-containing steel; The weight percentages of the low-carbon tungsten-containing steel components are: C 0.13%~0.17%, W 0.2%~0.4%, Si 0.15%~0.3%, Mn 1.6%~1.75%, Cr 0.8%~1.0%, Mo 0.3%~0.4%, V 0.07%~0.12%, Al 0.010%~0.045%, P≤0.015%, S≤0.005%, and the remainder of Fe and impurity elements.

2. The method for producing low-carbon tungsten-containing steel according to claim 1, wherein: In step S1, the tapping temperature is ≥1630°C; and / or The power consumption of the arc furnace smelting process is 420~450kW·h / t, and the oxygen consumption is 15~20m 3 / t, the smelting cycle is 46~50min.

3. The method for producing low-carbon tungsten-containing steel according to claim 1, wherein: In step S2, the composite deoxidizer comprises the following components in percentage by mass: CaC2 76% to 85%, CaO 8% to 12%, SiO2 1% to 5%, Al2O3 1% to 5%, MgO 1% to 5%; and / or In step S2, the pre-melted refined slag includes the following components in percentage by weight: CaO 32%-40%, Al2O3 46%-54%, SiO2 5%-15%, and MgO 1-3%; the particle size of the pre-melted refined slag is 5-50 mm.

4. The method for producing low-carbon tungsten-containing steel according to claim 3, wherein: In step S2, the composite deoxidizer has a gas emission of ≥280 L / kg and a particle size of 5-30 mm; and / or In step S2, the amount of the composite deoxidizer added is 0.34-0.58 kg / t, and the amount of the aluminum ingot added is 1.38-1.84 kg / t.

5. The method for producing low-carbon tungsten-containing steel according to claim 1, wherein: In step S2, the amount of tungsten-ferroalloy added is 2.75-3.22 kg / t, the amount of pre-melted refined slag added is 2.64-3.1 kg / t, the amount of silicon-manganese alloy added is 9.43-16.1 kg / t, the amount of high-manganese alloy added is 10.34-16.1 kg / t, the amount of high-chromium alloy added is 2.64-3.1 kg / t, the amount of low-chromium alloy added is 10.34-13.79 kg / t, the amount of ferromolybdenum alloy added is 4.71-5.4 kg / t, the amount of ferrovanadium alloy added is 1.37-2.3 kg / t, and the amount of lime added is 4.02-5.18 kg / t.

6. The method for producing low-carbon tungsten-containing steel according to claim 1, wherein: In step S3, the amount of lime added is 4.02-5.18 kg / t; the amount of fluorite added is 0.45-0.58 kg / t, and the particle size of the fluorite is 20-80 mm; and / or In step S3, the strong deoxidizer is aluminum particles and a composite deoxidizer, and the mass ratio of the two is 1:(2-3); the weak deoxidizer is silicon carbide; and / or In step S3, the amount of the strong deoxidizer added is 0.45-0.81 kg / t; the amount of the weak deoxidizer added is 0.22-0.46 kg / t.

7. The method for producing low-carbon tungsten-containing steel according to claim 1, wherein: In step S3, the temperature of making white slag is 1540-1570° C., and the time is 3-8 minutes; and the time of keeping the white slag is ≥20 minutes.

8. The method for producing low-carbon tungsten-containing steel according to claim 1, wherein: In step S4, the specific operation of the full-process protection pouring is as follows: the joint between the ladle outlet and the shroud is sealed with a vermiculite gasket, and argon is blown into the shroud bowl through the argon pipeline on the shroud manipulator; the flow rate of the argon is 115~145NL / min, and the pressure is 2~2.5MPa; the pouring temperature is 1530~1550℃, and the pouring time is 46~49min.

9. A low carbon tungsten-containing steel, characterized in that: The low-carbon tungsten-containing steel is prepared by the production method of any one of claims 1 to 8.

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