CN112795728B - High-purity steel and production process thereof - Google Patents
High-purity steel and production process thereof Download PDFInfo
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Abstract
The application relates to high-purity steel and a production process, which belong to the technical field of steel production, and comprise converter primary smelting, LF refining, VD vacuum treatment and continuous casting processes, wherein the LF refining process comprises the following steps: (21) blowing argon at the bottom on line when the station is entered, wherein the flow rate of the argon is 120-140L/min, and the pressure of the Ar is 0.35-0.4 MPa; (22) then adding a slagging agent and a deoxidizing agent for carrying out first-time electrifying slagging, adopting 6-level voltage, current of 28000-30000A, argon flow of 280-300L/min and argon pressure of 0.35-0.4 MPa, carrying out electric heating on the slag for 8-12min, then sampling, and adding alloy to adjust components; the slag former comprises calcite 4.5-7.2kg/t steel, fluorite 0.7-1.1kg/t steel and bauxite 0.3-0.5kg/t steel; (23) and (3) carrying out second electrifying after adjusting the components, adopting 4-level voltage, the current of 32000-34000A, the argon flow of 70-90L/min and the Ar pressure of 0.3-0.35 MPa, and feeding a calcium silicate wire when the temperature of the molten steel is more than or equal to 1670 ℃. This application has the impurity content that reduces in the molten steel, improves the effect of the purity of molten steel.
Description
Technical Field
The application relates to the technical field of steel smelting, in particular to high-purity steel and a production process thereof.
Background
The chrome-molybdenum steel is widely applied to the manufacture of important components in mechanical parts, such as a large gear for locomotive traction, a crankshaft, a connecting rod, an engine cylinder, a 1200-2000 m petroleum deep well drill rod joint, a fishing tool and the like. In recent years, with the increasing improvement of safety and reliability of petrochemical industry and coal chemical industry equipment by domestic and overseas safety supervision departments, the requirements of chemical components, internal quality and surface quality of medium-high temperature pressure-bearing chromium-molybdenum steel by related design units and manufacturing plants are more and more strict, wherein the purity of steel is a key index for measuring the quality of products.
For chromium molybdenum steel converter smelting, the condition of steel tapping peroxidation is common. If a single manganese alloy and aluminum particle pre-deoxidation mode is adopted in the tapping process, not only can the consumption of aluminum strips be increased due to the early addition of the aluminum strong deoxidizer under the peroxidation condition, but also the problems that a large amount of aluminum oxide inclusions are difficult to remove and the like are faced, and finally the adverse effect is caused on the quality of molten steel. Therefore, it is important to improve the purity of the chromium molybdenum molten steel by improving the steel making process.
Disclosure of Invention
In order to reduce the impurity content in molten steel and improve the purity of the molten steel, the application provides high-purity steel and a production process.
In a first aspect, the present application provides a production process of high purity steel, which adopts the following technical scheme:
a production process of high-purity steel comprises the working procedures of converter primary smelting, LF refining, VD vacuum treatment and continuous casting, wherein the working procedure of LF refining comprises the following steps:
(21) blowing argon at the bottom of the station when the station enters, wherein the flow rate of the argon is 120-140L/min, and the pressure of the argon is 0.35-0.4 MPa;
(22) then adding a slagging agent and a deoxidizing agent for carrying out first-time electrifying slagging, adopting 6-level voltage, current of 28000-30000A, argon flow of 280-300L/min and argon pressure of 0.35-0.4 MPa, carrying out electric heating on the slag for 8-12min, then sampling, and adding alloy to adjust components; the slag former comprises calcite 4.5-7.2kg/t steel, fluorite 0.7-1.1kg/t steel and bauxite 0.3-0.5kg/t steel;
(23) and (3) carrying out second energization after adjusting the components, adopting 4-level voltage, current 32000-34000A, argon flow of 70-90L/min, Ar pressure of 0.3-0.35 MPa, and feeding a calcium silicate wire when the temperature of the molten steel is more than or equal to 1670 ℃.
By adopting the technical scheme, in the refining process of the LF furnace, argon is introduced in the whole process, so that the molten steel can be protected, the reoxidation condition of the molten steel can be reduced while the normal deoxidation of the molten steel is ensured, and the improvement of the purity of the molten steel is facilitated.
The slag former adopts the synergistic effect of three substances, namely calcite, fluorite and bauxite, so that the capacity of the formed slag former for adsorbing impurities is improved, the adding efficiency is high, the slag former is cooperatively matched with a deoxidizer, white slag can be rapidly deoxidized, and the effect of optimizing the quality of molten steel is achieved. Decomposition of calcite at high temperature to CaO and CO 2 Gas, CO 2 The bubbles generated by the gas generate shock waves after being broken, so that the slag former is uniformly dispersed, the caking of the slag former is avoided, the reaction speed of the slag former and the molten steel is increased, the impurities in the slag former are avoided being remained in the molten steel, and the precision of the molten steel is improved; CO produced by calcite, on the other hand 2 The gas can be used as a foaming agent, rapidly cracks in the slag into small dispersed bubbles, plays a foaming role on the slag, and can keep continuous foaming by matching with a deoxidizer, thereby rapidly forming the refining slag with good fluidity and good foaming effect.
The small current heating is adopted in the first electrifying slagging process, the slagging process is prevented from being influenced by overlarge current, the current is increased by the second electrifying, the heating speed is improved, and the refining time is shortened.
Feeding Si-Ca wire to make it and Al in molten steel 2 O 3 Reacting to generate low-melting-point 12CaO 7Al 2 O 3 Is beneficial to the floating of impurities, thereby reducing the content of impurities in the molten steel and improving the cleanliness of the molten steel. In addition, calcium silicon wire and Al 2 O 3 The reaction can reduce the condition of blocking the tundish nozzle in the pouring process, and reduce the production accidents such as nozzle nodulation and the like.
Preferably, the weight ratio of calcite, fluorite and bauxite in the step (22) is (50-60): (8-9): (3-4).
By adopting the technical scheme, the content of calcite powder is low, the lumpiness is uniform, the turbid circulating water of the dust removal and gas recovery system cannot be polluted, and the blockage rate of the dust removal and gas recovery system is greatly reduced. In addition, the content of calcium carbonate in calcite is more than 98%, the content of nonmetal impurities such as P, S, Si and the like is extremely low, the requirement of the existing cleanliness steel is met, and the pollution to molten steel is low.
Fluorite enables the production of CaO from calcite and 2CaO. SiO which hinders the dissolution of CaO 2 The melting point of the outer shell is obviously reduced, and 3CaO. CaF is generated 2 .2SiO 2 Thereby helping to accelerate the dissolution of CaO and rapidly improve slag fluidity. However, excessive use of fluorite can form serious foaming slag, cause splashing, and also aggravate the erosion of the furnace lining and pollute the environment.
Bauxite is used for adjusting slag components to reduce the melting point, and the bauxite can replace part of fluorite to reduce the consumption of the fluorite, so that the pollution of the fluorite to the environment can be reduced under the condition of ensuring the quality of molten steel.
Therefore, tests show that the weight ratio of calcite to fluorite to bauxite is (50-60): (8-9): (3-4), the formed slag has good fluidity and the content of impurities in the molten steel is low.
Preferably, the deoxidizer in the step (22) comprises 0.2-0.21kg/t steel of aluminum particles, 0.3-0.45kg/t steel of silicon carbide and 0.3-0.45kg/t steel of calcium carbide.
By adopting the technical scheme, the deoxidation strength of the aluminum particles, the silicon carbide and the calcium carbide is from strong to weak, the aluminum particles are larger than the silicon carbide and larger than the calcium carbide, the oxidizability of the slag is higher in the initial stage of refining, strong deoxidizers of the aluminum particles are added, the oxidizability of the slag is weak in the later stage of refining, and weak deoxidizers of the silicon carbide and the calcium carbide are added if the reducing atmosphere needs to be kept, so that the aluminum particles, the silicon carbide and the calcium carbide are added in sequence. In addition, Al can form fine and insoluble AlN particles with N in steel while reducing the oxygen content in molten steel, refine crystal grains of the steel, fix nitrogen and oxygen in the steel, lighten the sensitivity of the steel to notches, reduce the steel to aging effect and improve the toughness of the steel.
Preferably, the feeding amount of the calcium silicate wire in the step (23) is 245-255m, and the wire feeding speed is 2.5-4.5 m/s.
Preferably, the converter primary smelting process adopts a composite converting method of stirring top-blown oxygen and bottom-blown argon to smelt, the pressure of the top-blown oxygen is 0.8-1.0MPa, nitrogen is blown 2-4min before bottom blowing, then bottom-blown argon is switched, lime and dolomite are added in the process for whole-process slag melting, and when converting is finished, C in molten steel is more than or equal to 0.08%; p is less than or equal to 0.015 percent; tapping temperature: 1600 ℃ and 1630 ℃.
Preferably, the lime is added to 35kg/t steel and the dolomite is added to 8kg/t steel.
By adopting the technical scheme, the lower carbon content of molten steel in the converter is controlled by adopting composite blowing, and carbon is added during tapping to improve the carbon content of the molten steel, so that the carbon content of the molten steel accords with the subsequent process, S, P in the molten steel can be fully reacted with oxygen at high temperature to be removed from the molten steel, and the cleanliness of the molten steel is improved; the lime and the dolomite are added to facilitate slagging, so that the harmful element S, P in the steel can be removed more effectively, meanwhile, the slag can cover the surface of the molten steel, the molten steel is protected from excessive oxidation, harmful gas is not absorbed, the burning out of beneficial elements is reduced, and the quality of the molten steel is ensured while the inclusion in the molten steel is reduced.
Preferably, in the converter primary smelting process, no slag is discharged in the converter tapping process, and 3.3-3.8kg/t of artificial graphite, 0.7-1.0kg/t of aluminum strips, silicon-manganese alloy, ferrosilicon alloy, high-carbon ferrochrome and ferromolybdenum are sequentially added during the process; wherein, the yield of manganese element is 85%, the yield of silicon element is 75%, the yield of chromium element is 95%, the yield of molybdenum element is 95%, and the molten steel components after the completion are as follows: 0.36 to 0.40 percent of C, 0.15 to 0.20 percent of Si, 0.55 to 0.60 percent of Mn, 0.95 to 1.00 percent of Cr, 0.15 to 0.17 percent of Mo, less than or equal to 0.015 percent of P, and the balance of Fe.
By adopting the technical scheme, slag does not fall in the tapping process, a certain amount of slag is contained in the molten steel, and when the refining is carried out, because the initial temperature is low, the molten steel contains a large amount of phosphorus, and the slag can play a role in dephosphorization at the moment, so that the slag generated in the converter is fully utilized, the consumption of a slagging agent is reduced, and the slag amount is reduced.
Firstly, adding artificial graphite which can react with oxygen in molten steel to generate CO for deoxidation; the addition of the aluminum strips further increases the deoxidation effect in the molten steel; then adding silicon-manganese alloy, and under the environment that enough artificial graphite is doped in the molten steel, the silicon-manganese alloy can rapidly and continuously remove oxygen in FeO in the molten steel, so that the oxygen content in the molten steel is reduced.
Preferably, in the VD vacuum treatment process, the Ar blowing pressure is kept at 0.3-0.4 MPa, the molten steel is ensured not to be exposed, and soft blowing is carried out for 10-20 min.
By adopting the technical scheme, the VD furnace can ensure that Ar can be blown into the furnace from the furnace bottom through vacuum treatment, thereby playing a role in protecting molten steel in the VD furnace and avoiding the metal in the molten steel from being oxidized again.
Preferably, in the continuous casting step, before the continuous casting is started, the tundish is subjected to argon blowing treatment.
By adopting the technical scheme, air in the tundish is removed, the chance of removing air from molten steel is reduced, the situation that metal in the molten steel is oxidized again is further reduced, and the cleanliness of the molten steel is improved.
In a second aspect, the present application provides a high purity steel, which adopts the following technical scheme:
the high-purity steel comprises, by mass, 0.4-0.44% of C, 0.2-0.28% of Si, 0.6-0.68% of Mn, no more than 0.02% of P, no more than 0.02% of S, 1.00-1.10% of Cr, 0.15-0.18% of Mo, 0.005-0.025% of Al, and the balance Fe.
In summary, the present application includes at least one of the following beneficial technical effects:
1, blowing argon in the whole refining process of an LF furnace to protect molten steel and ensure normal deoxidation of the molten steel; meanwhile, the slag former adopts calcite, fluorite and bauxite and is limited in proportion, so that the capacity of the formed slag former for adsorbing inclusions is improved under the combined action of the calcite, the fluorite and the bauxite, the addition efficiency is high, the slag former and a deoxidizer are cooperatively matched, the white slag can be rapidly deoxidized, and the effect of optimizing the quality of molten steel is achieved;
2. feeding Si-Ca wire to make it and Al in molten steel 2 O 3 Reacting to generate low-melting-point 12CaO 7Al 2 O 3 Is beneficial to the floating of impurities, thereby reducing the content of impurities in the molten steel and improving the cleanliness of the molten steel. In addition, calcium silicon wire and Al 2 O 3 The reaction can reduce the condition of blocking a tundish nozzle in the pouring process, and reduce production accidents such as nozzle nodulation and the like;
3. the lower carbon content of molten steel in the converter is controlled by adopting composite blowing, and carbon is added during tapping to improve the carbon content of the molten steel, so that the carbon content of the molten steel accords with the subsequent process, S, P in the molten steel can be fully reacted with oxygen at high temperature to be removed from the molten steel, and the cleanliness of the molten steel is improved.
Detailed Description
The present application will be described in further detail with reference to examples and comparative examples.
Examples
Example 1
A high purity steel prepared by the following process comprises the following steps:
converter primary smelting
(11) Firstly, adding molten iron into a converter, controlling the temperature of the molten iron fed into the converter to be more than or equal to 1250 ℃, wherein the P content in the molten iron is less than or equal to 0.120 percent and the slag content is less than or equal to 0.5 percent according to the mass percentage content; then adding scrap steel into the molten iron, wherein the total adding amount of the molten iron and the scrap steel is 110t, and the total adding amount of the scrap steel is 32 t; then, stirring and composite blowing are carried out for 12-min by adopting top-blown oxygen and bottom-blown argon, the pressure of the top-blown oxygen is 1.0MPa, nitrogen is blown for 2min before bottom blowing, and then bottom-blown argon is switched; 32kg/t steel lime and 9kg/t steel dolomite are added in the blowing process for slagging, the whole process is slagging, and the alkalinity of the slag is controlled to be 3.8; when the converting is finished, C in the molten steel is more than or equal to 0.08 percent; p is less than or equal to 0.015 percent; tapping temperature: 1600 ℃.
(12) Tapping, sampling and analyzing before tapping, wherein slag is not removed in the tapping process, and when the depth of molten steel is 1/4 of the height of a steel ladle in the tapping process, 3.8kg/t of artificial graphite, 0.7kg/t of aluminum strips, silicon-manganese alloy, ferrosilicon, high-carbon ferrochrome and ferromolybdenum are sequentially added according to the analysis result for adjustment, wherein the yield of manganese is 85%, the yield of silicon is 75%, the yield of chromium is 95%, and the yield of molybdenum is 95%; when the depth of the molten steel is 3/4 of the height of a ladle, 400kg of lime is added, and the molten steel comprises the following components: 0.36 percent of C, 0.20 percent of Si, 0.55 percent of Mn, 1.00 percent of Cr, 0.15 percent of Mo, less than or equal to 0.015 percent of P, and the balance of Fe.
(II) refining in LF furnace
(21) Controlling the station entering temperature to 1510 ℃, and blowing argon on line at the bottom in the station entering process, wherein the argon flow is 120L/min, and the Ar pressure is 0.4 MPa; then adding a slagging agent and a deoxidizer, carrying out first electrifying slagging, adopting 6-grade voltage, 28000A, argon flow rate of 300L/min and argon pressure of 0.35MPa, carrying out temperature measurement and sampling after carrying out power transmission heating slagging for 12min, and adding ferrosilicon, silicomanganese, high-carbon ferrosilicon, ferromolybdenum, ferrotitanium, artificial graphite and other alloys according to target components for adjustment; wherein the slag former comprises calcite 4.5kg/t steel, fluorite 1.1kg/t steel and bauxite 0.3kg/t steel; the deoxidizer comprises 0.21kg/t steel of aluminum particles, 0.3kg/t steel of silicon carbide and 0.45kg/t steel of calcium carbide.
(22) Carrying out second electrifying after adjusting the components, adopting 4-level voltage, current 32000A, argon flow 90L/min and Ar pressure 0.3MPa, adding white lime in 2-3 batches in the process, wherein the total amount of the added white lime is more than or equal to 600kg, adding fluorite according to the fluidity of the slag, and adjusting the fluidity of the slag; and adjusting the alkalinity according to the slag amount of the slag to keep the total slag amount at 12 kg/t steel, controlling the alkalinity at 3.0, and keeping the white slag for 10min, wherein FeO is less than 0.5%.
(23) When the temperature of molten steel is more than or equal to 1570 ℃, 100kg of ferrotitanium is added after slag turns white, the ferrotitanium contains 28-30% of Ti by mass percent, the recovery rate is 60-70%, after the components and the temperature before leaving the station meet the process requirements, a calcium-silicon wire is fed at a speed of 255 m/s, and the ladle is taken out.
And (III) VD vacuum treatment:
(31) directly placing the steel ladle into a VD pit, keeping the Ar blowing pressure at 0.3MPa, ensuring that the molten steel is not exposed, and then measuring and sampling the temperature; and then starting vacuum-pumping treatment, wherein after the vacuum-pumping is carried out for 5min, the vacuum degree is below 0.5 torr and is kept for 15min, the argon pressure in the vacuum-pumping process is 0.4MPa, and the argon pressure is 0.3MPa after the vacuum degree is below 0.5 torr.
(32) And (3) breaking the blank:
and (3) closing argon in the vacuum breaking process, blowing argon after the vacuum breaking process is finished, stirring for 10min, hoisting, and adding the carbonized rice hulls to cover the whole slag surface, wherein the temperature of the hoisting is 1555 ℃.
(IV) continuous casting Process
(41) Blowing argon to the baked tundish before casting, discharging air in the tundish, reducing the chance of the molten steel contacting the air, and simultaneously checking the argon sealing condition of key equipment such as a long nozzle, a stopper rod, an invasive nozzle and the like, avoiding secondary oxidation of the molten steel and increasing the content of inclusions;
(42) then, transferring the molten steel to a tundish and casting a blank by a continuous casting machine, casting when the liquid level height of the molten steel of the tundish is more than or equal to 300mm, adding a tundish covering agent when the molten steel of the tundish reaches 2/3, then adding the tundish covering agent twice, adding carbonized rice hulls when the molten steel reaches the maximum to ensure that the molten steel is not exposed to red, simultaneously controlling the temperature of the continuous casting tundish steel to 1510 ℃ in the whole process, protecting high-carbon protective slag by using a crystallizer, and when casting is stopped, the liquid level height of the tundish is more than or equal to 250 mm. The components of the cast strip steel are 0.40 percent of C, 0.28 percent of Si, 0.60 percent of Mn, less than or equal to 0.02 percent of P, less than or equal to 0.02 percent of S, 1.10 percent of Cr, 0.15 percent of Mo, 0.025 percent of Al and the balance of Fe.
Example 2
A high purity steel prepared by the process comprising the steps of:
converter primary smelting
(11) Firstly, adding molten iron into a converter, controlling the temperature of the molten iron in the converter to be more than or equal to 1250 ℃, wherein the P content in the molten iron is less than or equal to 0.120 percent and the slag content is less than or equal to 0.5 percent according to the mass percentage content; then adding scrap steel into the molten iron, wherein the total adding amount of the molten iron and the scrap steel is 112t, and the total adding amount of the scrap steel is 30 t; then, stirring and composite converting for 13min by adopting top-blown oxygen and bottom-blown argon, wherein the pressure of the top-blown oxygen is 0.9MPa, nitrogen is blown for 3min before bottom blowing, and then bottom-blown argon is switched; in the blowing process, lime 35kg/t steel and dolomite 8kg/t steel are added for slagging, the whole process is slagging, and the alkalinity of the slag is controlled to be 3.5; when the converting is finished, C in the molten steel is more than or equal to 0.08 percent; p is less than or equal to 0.015 percent; tapping temperature: 1615 ℃.
(12) Tapping, sampling and analyzing before tapping, wherein no slag is produced in the tapping process, and when the depth of molten steel is 1/4 of the height of a steel ladle in the tapping process, adding 3.5kg/t of artificial graphite, 0.8kg/t of aluminum strips, silicomanganese, ferrosilicon, high-carbon ferrochromium and ferromolybdenum in sequence according to the analysis result for adjustment, wherein the yield of manganese is 85%, the yield of silicon is 75%, the yield of chromium is 95%, and the yield of molybdenum is 95%; when the depth of the molten steel is 3/4 of the height of a ladle, 400kg of lime is added, and the molten steel comprises the following components: 0.38 percent of C, 0.17 percent of Si, 0.58 percent of Mn, 0.98 percent of Cr, 0.16 percent of Mo, less than or equal to 0.015 percent of P, and the balance of Fe.
(II) refining in LF furnace
(21) Controlling the station entering temperature to 1520 ℃, and blowing argon on line at the bottom in the station entering process, wherein the argon flow is 130L/min, and the Ar pressure is 0.38 MPa; then adding a slagging agent and a deoxidizer, then carrying out first-time electrifying slagging, adopting 6-level voltage and current of 29000A, leading argon flow to 290L/min, leading argon pressure to 0.38MPa, carrying out temperature measurement and sampling after carrying out power transmission heating slagging for 10min, and adding ferrosilicon, silicomanganese, high-carbon ferrosilicon, ferromolybdenum, ferrotitanium, artificial graphite and other alloys according to target components for adjustment; wherein the slag former comprises 6kg/t of calcite steel, 0.9kg/t of fluorite steel and 0.4kg/t of bauxite steel; the deoxidizer comprises 0.2kg/t steel of aluminum particles, 0.4kg/t steel of silicon carbide and 0.4kg/t steel of calcium carbide.
(22) After the components are adjusted, the second electrifying is carried out, 4-level voltage, current 33000A, argon flow 80L/min and Ar pressure 0.32MPa are adopted, white lime is added in 2-3 batches in the process, the total adding amount of the white lime is more than or equal to 600kg, fluorite is added according to the fluidity of the slag, and the fluidity of the slag is adjusted; and adjusting the alkalinity according to the slag amount of the slag to keep the total slag amount at 10 kg/t steel, controlling the alkalinity at 3.5, and keeping the white slag for 10min, wherein FeO is less than 0.5%.
(23) When the temperature of molten steel is more than or equal to 1570 ℃, 110kg of ferrotitanium is added after slag turns white, the ferrotitanium contains 28-30% of Ti by mass percent, the recovery rate is 60-70%, after the components and the temperature before leaving the station meet the process requirements, a silico-calcium wire is fed for 250m, the wire feeding speed is 3.5m/s, and the ladle is taken out.
And (III) VD vacuum treatment:
(31) directly placing the steel ladle into a VD pit, keeping the Ar blowing pressure at 0.35MPa, ensuring that the molten steel is not exposed, and then measuring and sampling the temperature; and then starting vacuum pumping treatment, wherein after the vacuum pumping is carried out for 5min, the vacuum degree is kept for 15min under 0.5 torr, the argon pressure in the vacuum pumping process is 0.4MPa, and the argon pressure is 0.25MPa after the vacuum degree is below 0.5 torr.
(32) And (3) breaking the blank:
and (3) closing argon in the vacuum breaking process, blowing argon and stirring for 10min after the vacuum breaking is finished, hoisting, and adding the carbonized rice hulls to cover the whole slag surface, wherein the temperature of the hoisting is 1560 ℃.
(IV) continuous casting Process
(41) Blowing argon to the baked tundish before casting, discharging air in the tundish, reducing the chance of the molten steel contacting the air, and simultaneously checking the argon sealing condition of key equipment such as a long nozzle, a stopper rod, an invasive nozzle and the like, avoiding secondary oxidation of the molten steel and increasing the content of inclusions;
(42) then, transferring the molten steel to a tundish and casting a blank by a continuous casting machine, casting when the liquid level height of the molten steel of the tundish is more than or equal to 300mm, adding a tundish covering agent when the molten steel of the tundish reaches 2/3, then adding the tundish covering agent twice, adding carbonized rice hulls when the molten steel reaches the maximum to ensure that the molten steel is not exposed to red, simultaneously controlling the temperature of the continuous casting tundish steel to 1520 ℃ in the whole process, protecting high-carbon protective slag by using a crystallizer, and stopping casting when the liquid level height of the tundish is more than or equal to 250 mm. The components of the cast strip steel are as follows: 0.42 percent of C, 0.24 percent of Si, 0.64 percent of Mn, 1.05 percent of Cr, 0.16 percent of Mo, less than or equal to 0.015 percent of P, and the balance of Fe.
Example 3
A high purity steel prepared by the process comprising the steps of:
(I) converter primary smelting
(11) Firstly, adding molten iron into a converter, controlling the temperature of the molten iron in the converter to be more than or equal to 1250 ℃, wherein the P content in the molten iron is less than or equal to 0.120 percent and the slag content is less than or equal to 0.5 percent according to the mass percentage content; then adding scrap steel into the molten iron, wherein the total adding amount of the molten iron and the scrap steel is 115t, and the total adding amount of the scrap steel is 25 t; then, stirring and composite blowing are carried out for 15min by adopting top-blown oxygen and bottom-blown argon, the pressure of the top-blown oxygen is 0.8MPa, nitrogen is blown for 4min before bottom blowing, and then bottom-blown argon is switched; adding 37kg/t of lime steel and 7kg/t of dolomite steel in the blowing process for slagging, and carrying out whole-process slagging while controlling the alkalinity of furnace slag to be 3; when the converting is finished, C in the molten steel is more than or equal to 0.08 percent; p is less than or equal to 0.015 percent; tapping temperature: 1630 deg.C.
(12) Tapping, sampling and analyzing before tapping, wherein slag is not removed in the tapping process, and when the depth of molten steel is 1/4 of the height of a steel ladle in the tapping process, 3.3kg/t of artificial graphite, 1.0kg/t of aluminum strips, silicon-manganese alloy, ferrosilicon, high-carbon ferrochrome and ferromolybdenum are sequentially added according to the analysis result for adjustment, wherein the yield of manganese is 85%, the yield of silicon is 75%, the yield of chromium is 95%, and the yield of molybdenum is 95%; when the depth of the molten steel is 3/4 of the height of a ladle, 400kg of lime is added, and the molten steel comprises the following components: 0.40 percent of C, 0.15 percent of Si, 0.60 percent of Mn, 0.95 percent of Cr, 0.17 percent of Mo, less than or equal to 0.015 percent of P, and the balance of Fe.
(II) refining in LF furnace
(21) Controlling the station entering temperature to 1530 ℃, and blowing argon at the bottom of the station in an online manner in the station entering process, wherein the argon flow is 140L/min, and the Ar pressure is 0.35 MPa; then adding a slagging agent and a deoxidizing agent, then carrying out first-time electrifying slagging, adopting 6-grade voltage and current of 30000A, leading argon flow to be 280L/min, leading argon pressure to be 0.4MPa, carrying out temperature measurement and sampling after carrying out power transmission heating slagging for 10min, and adding ferrosilicon, silicomanganese, high-carbon ferrosilicon, ferromolybdenum, ferrotitanium, artificial graphite and other alloys according to target components for adjustment; wherein the slag former comprises calcite 7.2kg/t steel, fluorite 0.7kg/t steel and bauxite 0.5kg/t steel; the deoxidizer comprises 0.21kg/t steel of aluminum particles, 0.45kg/t steel of silicon carbide and 0.3kg/t steel of calcium carbide.
(22) Carrying out second electrifying after adjusting the components, adopting 4-level voltage, current 34000A, argon flow 70L/min and Ar pressure 0.35MPa, adding white lime in 2-3 batches in the process, wherein the total amount of the added white lime is more than or equal to 600kg, adding fluorite according to the fluidity of the slag, and adjusting the fluidity of the slag; and adjusting the alkalinity according to the slag amount of the slag to keep the total slag amount at 8kg/t steel, controlling the alkalinity at 4.5, and keeping the white slag for 10min, wherein FeO is less than 0.5%.
(23) When the temperature of molten steel is more than or equal to 1570 ℃, adding 120kg of ferrotitanium after furnace slag turns white, wherein the ferrotitanium contains 28-30% of Ti by mass percent, the recovery rate is 60-70%, feeding 245m of calcium-silicon wire after the components and the temperature before leaving the station meet the process requirements, feeding the wire at the feeding speed of 4.5m/s, and transferring out the steel ladle.
And (III) VD vacuum treatment:
(31) directly placing the steel ladle into a VD pit, keeping the Ar blowing pressure at 0.4MPa, ensuring that the molten steel is not exposed, and then measuring and sampling the temperature; then, vacuum-pumping treatment is started, after vacuum-pumping is carried out for 3min, the vacuum degree reaches below 0.5 torr and is kept for 15min, the argon pressure in the vacuum-pumping process is 0.5MPa, and the argon pressure after the vacuum degree reaches below 0.5 torr is 0.2 MPa.
(32) And (3) breaking the blank:
and (3) closing argon in the vacuum breaking process, blowing argon after the vacuum breaking process is finished, stirring for 10min, then hoisting, and adding carbonized rice hulls to cover the whole slag surface, wherein the temperature of the hoisting is 1565 ℃.
(IV) continuous casting Process
(41) Blowing argon to the baked tundish before casting, discharging air in the tundish, reducing the chance of the molten steel contacting the air, and simultaneously checking the argon sealing condition of key equipment such as a long nozzle, a stopper rod, an invasive nozzle and the like, avoiding secondary oxidation of the molten steel and increasing the content of inclusions;
(42) then, transferring the molten steel to a tundish and casting a blank by a continuous casting machine, casting when the liquid level height of the molten steel of the tundish is more than or equal to 300mm, adding a tundish covering agent when the molten steel of the tundish reaches 2/3, then adding the tundish covering agent twice, adding carbonized rice hulls when the molten steel reaches the maximum to ensure that the molten steel is not exposed to red, simultaneously controlling the temperature of the continuous casting tundish steel to be 1525 ℃ in the whole process, protecting high-carbon protective slag by using a crystallizer, and when casting is stopped, the liquid level height of the tundish is more than or equal to 250 mm. The components of the strip steel after casting are as follows: 0.44 percent of C, 0.20 percent of Si, 0.68 percent of Mn, 1.00 percent of Cr, 0.18 percent of Mo, less than or equal to 0.015 percent of P, and the balance of Fe.
Example 4
A high purity steel prepared by the following process comprises the following steps: the difference from example 2 is that the slag former comprises calcite 5.0kg/t steel, fluorite 0.9kg/t steel and bauxite 0.3kg/t steel.
Example 5
A high purity steel prepared by the process comprising the steps of: the difference from example 2 is that the slag former comprises 6.0kg/t calcite steel, 0.8kg/t fluorite steel and 0.4kg/t bauxite steel.
Comparative example 1
A high purity steel prepared by the following process, comprising the following steps, which are different from example 2 in that an equal amount of lime is taken in the slag former to replace calcite.
Comparative example 2
A high purity steel was prepared by the following process, which differs from example 2 in that the same amount of calcite was used in the slag former to replace the fluorite.
Comparative example 3
A high purity steel prepared by the following process, comprising the following steps, differing from example 2 in that an equal amount of fluorite was taken in the slag former instead of bauxite.
Comparative example 4
A high purity steel prepared by the following process, comprising the following steps, which are different from example 2, in that an equal amount of silicon carbide is taken in the deoxidizer in place of aluminum particles.
Performance test
(1) The steels obtained in examples 1 to 5 and comparative examples 1 to 4 were subjected to a performance test, and the inclusions were rated as shown in Table 1 with reference to GBT10516-2005, method for measuring the content of nonmetallic inclusions.
TABLE 1 Steel inclusion rating table
As can be seen by combining examples 1 to 5 with Table 1, the steel produced in examples 1 to 5 had A, B, C, D-type fine inclusions, A-type coarse inclusions, and B, C, D-type coarse inclusions, all of which were 1.0 or less, respectively; as can be seen from the combination of comparative examples 1 to 4, the inclusions of examples 1 to 5 are smaller than those of comparative examples 1 to 4; the method proves that the purity of the steel prepared by the production process is higher, and the purity of the steel can be effectively improved.
(2) The yield strengths (R) in examples 1 to 5 and comparative examples 1 to 4 were measured in accordance with GB/T228-2002 Metal Material tensile test method at Room temperature m ) And tensile strength (R) el ) The impact test was carried out according to ASTM A370-2016, and the results are shown in Table 2.
TABLE 2 Steel mechanical Property test results
| Item | Rm/MPa | Rel/MPa | Impact Property/J |
| Example 1 | 1181 | 1085 | 76 |
| Example 2 | 1201 | 1098 | 80 |
| Example 3 | 1192 | 1089 | 77 |
| Example 4 | 1210 | 1105 | 81 |
| Example 5 | 1213 | 1109 | 83 |
| Comparative example 1 | 1085 | 1015 | 63 |
| Comparative example 2 | 1090 | 1020 | 64 |
| Comparative example 3 | 1091 | 1021 | 65 |
| Comparative example 4 | 1089 | 1019 | 64 |
By combining examples 1-5 and comparative examples 1-4, and by combining table 2, it can be seen that the yield strength, tensile strength and impact resistance of the steel in examples 1-5 are better than those of comparative examples 1-4, which indicates that the steel prepared by the preparation process of the present application has better yield strength, tensile strength and impact resistance, and the mechanical properties of the steel are improved.
The above are preferred embodiments of the present application, and the scope of protection of the present application is not limited thereto, so: all equivalent changes made according to the structure, shape and principle of the present application shall be covered by the protection scope of the present application.
Claims (4)
1. A production process of high-purity steel is characterized by comprising the working procedures of converter primary smelting, LF refining, VD vacuum treatment and continuous casting, wherein the working procedure of LF refining comprises the following steps:
(21) blowing argon at the bottom on line when the station is entered, wherein the flow rate of the argon is 120-140L/min, and the pressure of the Ar is 0.35-0.4 MPa;
(22) then adding a slagging agent and a deoxidizing agent for carrying out first-time electrifying slagging, adopting 6-level voltage, current of 28000-30000A, argon flow of 280-300L/min and argon pressure of 0.35-0.4 MPa, carrying out electric heating on the slag for 8-12min, then sampling, and adding alloy to adjust components; the slag former comprises calcite 4.5-7.2kg/t steel, fluorite 0.7-1.1kg/t steel and bauxite 0.3-0.5kg/t steel;
(23) adjusting the components, then carrying out second electrifying, adopting 4-level voltage, current 32000-34000A, argon flow 70-90L/min, Ar pressure 0.3-0.35 MPa, and feeding a calcium silicate wire when the temperature of molten steel is more than or equal to 1670 ℃;
the weight ratio of calcite, fluorite and bauxite in the step (22) is (50-60): 8-9): 3-4;
the deoxidizer in the step (22) comprises 0.2-0.21kg/t of aluminum grain steel, 0.3-0.45kg/t of silicon carbide steel and 0.3-0.45kg/t of calcium carbide steel;
the feeding amount of the calcium silicate wire in the step (23) is 245-255m, and the feeding speed is 2.5-4.5 m/s;
the converter primary smelting process adopts a composite converting method of stirring top-blown oxygen and bottom-blown argon to smelt, the pressure of the top-blown oxygen is 0.8-1.0MPa, nitrogen is blown for 2-4min before bottom blowing, argon is blown at the bottom after the nitrogen is blown, lime and dolomite are added in the process for melting slag in the whole process, and when converting is finished, C in molten steel is more than or equal to 0.08%; p is less than or equal to 0.015 percent; tapping temperature: 1600 ℃ and 1630 ℃;
32-37kg/t steel and 7-9kg/t steel are added with lime;
in the converter primary smelting process, sampling analysis is carried out before tapping, no slag is generated in the converter tapping process, and artificial graphite, aluminum strips, silicomanganese, ferrosilicon, high-carbon ferrochromium and ferromolybdenum are sequentially added according to target components during the converter primary smelting process for adjustment; after the completion, the molten steel comprises the following components: 0.36 to 0.40 percent of C, 0.15 to 0.20 percent of Si, 0.55 to 0.60 percent of Mn, 0.95 to 1.00 percent of Cr, 0.15 to 0.17 percent of Mo, less than or equal to 0.015 percent of P, and the balance of Fe;
the chemical components of the high-purity steel comprise, by mass, 0.4-0.44% of C, 0.2-0.28% of Si, 0.6-0.68% of Mn, less than or equal to 0.02% of P, less than or equal to 0.02% of S, 1.00-1.10% of Cr, 0.15-0.18% of Mo, 0.005-0.025% of Al, and the balance of Fe.
2. The process for producing a high purity steel according to claim 1, wherein: in the VD vacuum treatment process, the Ar blowing pressure is kept at 0.3-0.4 MPa, the molten steel is ensured not to be exposed, and soft blowing is carried out for 10-20 min.
3. A process for the production of a high purity steel as claimed in claim 1, wherein: in the continuous casting process, before continuous casting is started, argon blowing treatment is carried out on the tundish.
4. A high purity steel obtained by the process for producing a high purity steel according to claim 1, wherein: the chemical components of the high-purity steel comprise, by mass, 0.4-0.44% of C, 0.2-0.28% of Si, 0.6-0.68% of Mn, less than or equal to 0.02% of P, less than or equal to 0.02% of S, 1.00-1.10% of Cr, 0.15-0.18% of Mo, 0.005-0.025% of Al, and the balance of Fe.
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