CN112626302B - Smelting method of high-cleanliness microalloyed high-strength steel - Google Patents
Smelting method of high-cleanliness microalloyed high-strength steel Download PDFInfo
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- C—CHEMISTRY; METALLURGY
- C21—METALLURGY OF IRON
- C21C—PROCESSING OF PIG-IRON, e.g. REFINING, MANUFACTURE OF WROUGHT-IRON OR STEEL; TREATMENT IN MOLTEN STATE OF FERROUS ALLOYS
- C21C1/00—Refining of pig-iron; Cast iron
- C21C1/02—Dephosphorising or desulfurising
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- C—CHEMISTRY; METALLURGY
- C21—METALLURGY OF IRON
- C21C—PROCESSING OF PIG-IRON, e.g. REFINING, MANUFACTURE OF WROUGHT-IRON OR STEEL; TREATMENT IN MOLTEN STATE OF FERROUS ALLOYS
- C21C5/00—Manufacture of carbon-steel, e.g. plain mild steel, medium carbon steel or cast steel or stainless steel
- C21C5/28—Manufacture of steel in the converter
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- C—CHEMISTRY; METALLURGY
- C21—METALLURGY OF IRON
- C21C—PROCESSING OF PIG-IRON, e.g. REFINING, MANUFACTURE OF WROUGHT-IRON OR STEEL; TREATMENT IN MOLTEN STATE OF FERROUS ALLOYS
- C21C7/00—Treating molten ferrous alloys, e.g. steel, not covered by groups C21C1/00 - C21C5/00
- C21C7/04—Removing impurities by adding a treating agent
- C21C7/06—Deoxidising, e.g. killing
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- C—CHEMISTRY; METALLURGY
- C21—METALLURGY OF IRON
- C21C—PROCESSING OF PIG-IRON, e.g. REFINING, MANUFACTURE OF WROUGHT-IRON OR STEEL; TREATMENT IN MOLTEN STATE OF FERROUS ALLOYS
- C21C7/00—Treating molten ferrous alloys, e.g. steel, not covered by groups C21C1/00 - C21C5/00
- C21C7/04—Removing impurities by adding a treating agent
- C21C7/064—Dephosphorising; Desulfurising
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- C—CHEMISTRY; METALLURGY
- C21—METALLURGY OF IRON
- C21C—PROCESSING OF PIG-IRON, e.g. REFINING, MANUFACTURE OF WROUGHT-IRON OR STEEL; TREATMENT IN MOLTEN STATE OF FERROUS ALLOYS
- C21C7/00—Treating molten ferrous alloys, e.g. steel, not covered by groups C21C1/00 - C21C5/00
- C21C7/04—Removing impurities by adding a treating agent
- C21C7/072—Treatment with gases
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- C—CHEMISTRY; METALLURGY
- C21—METALLURGY OF IRON
- C21C—PROCESSING OF PIG-IRON, e.g. REFINING, MANUFACTURE OF WROUGHT-IRON OR STEEL; TREATMENT IN MOLTEN STATE OF FERROUS ALLOYS
- C21C7/00—Treating molten ferrous alloys, e.g. steel, not covered by groups C21C1/00 - C21C5/00
- C21C7/10—Handling in a vacuum
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Abstract
The smelting method of the high-cleanliness microalloyed high-strength steel comprises the working procedures of molten iron pre-desulfurization, converter smelting, LF refining and RH refining, wherein the refining functions of the LF furnace and the RH furnace are simplified and efficient by redistributing the smelting key points of the working procedures, and the influence of secondary oxidation of molten steel and corrosion of steel ladle refractory on the cleanliness of the molten steel is reduced while harmful components such as the molten steel P, S are removed; the invention reduces the dosage of aluminum deoxidizer, secondarily removes slag by top slag before RH vacuum circulation, does not feed calcium wire after RH vacuum circulation and does not stir, thereby reducing Al in molten steel2O3The content of the inclusions is reduced, the contact reaction of the molten steel with a slag layer and the atmosphere in the middle and later stages is relieved, and the inclusions O, N, H in the molten steel are controlled to be extremely low. The invention can lead the smelting molten steel to have high cleanliness and provide a high-quality casting blank for the subsequent rolling of high-quality microalloyed high-strength steel products.
Description
Technical Field
The invention belongs to the technical field of ferrous metallurgy, and particularly relates to a smelting method of high-cleanliness microalloyed high-strength steel.
Background
The microalloyed high-strength steel is formed by adding a small amount of alloying elements (such as niobium, vanadium, titanium and the like) into common low-alloy steel, and the obdurability of the steel is improved and good formability and weldability are obtained through the organic combination of the controlled rolling and cooling technology of the microalloyed elements and steel and the behaviors of fine grain strengthening, precipitation strengthening and the like of the microalloyed elements. Microalloyed steel belongs to the category of low-alloy high-strength steel, is also called microalloyed low-alloy high-strength steel, is a novel low-alloy high-strength steel developed recently, is applied to various industries such as automobile manufacturing, energy network construction, bridge construction and the like at present, and gradually plays an important role as a raw material.
According to different applications of microalloyed high-strength steel products, the requirements on the mechanical properties of the products are different, but with the popularization and application of microalloyed steel in various fields, steel practitioners increasingly recognize that the influence of molten steel cleanliness on the performance of final products, particularly the processing and using performance is very important, and the production technology of clean steel and ultra-clean steel becomes a research hotspot of the industry.
The conventional clean steel production technology at present relates to a plurality of process links, and generally comprises molten iron desulfurization treatment, pre-dephosphorization, top-bottom combined blown converter blowing, tapping slag stopping, deoxidation, slag modification in a steel ladle, argon stirring, LF external refining treatment, RH or VD and other vacuum treatment, calcium treatment, protective casting, tundish metallurgy, crystallizer protective slag, molten steel flow control in a crystallizer and the like.
Disclosure of Invention
The invention aims to solve the technical problem of providing a method for smelting high-cleanliness microalloyed high-strength steel, which can effectively reduce the content of harmful components P, S, O, N, H in molten steel and the level of inclusions, and improve the cleanliness of the molten steel and the quality of casting blanks.
In order to solve the technical problems, the technical scheme adopted by the invention is as follows: a smelting method of high-cleanliness microalloyed high-strength steel comprises the working procedures of molten iron pre-desulfurization, converter smelting, LF refining and RH refining and is characterized in that,
(1) Pre-desulfurization of molten iron: controlling the S content of the molten iron to be 0.003-0.008 wt% after the working procedure is finished;
(2) smelting in a converter: controlling the content of C at the smelting end point to be 0.04-0.12 wt%, controlling the content of O at the smelting end point to be less than or equal to 350ppm, selecting one or more of silicomanganese, ferromanganese, calcium carbide, silicon carbide and carburant for deoxidation alloying in the tapping process, determining the addition type and the addition amount according to the lower limit of the content range of the target components C, Si and Mn of the steel, and then selecting an aluminum block to ensure that molten steel is completely deoxidized;
(3) LF refining: adjusting the temperature of the molten steel to be 80-100 ℃ above the liquidus temperature of the steel grade, and then adding calcium carbide for diffusion deoxidation;
(4) RH refining: and (3) slagging off after jacking the ladle, reducing the thickness of a slag layer to 70-150mm, and adding 0.4-1.4 kg/ton of steel top slag modifier after circulation begins.
Preferably, in the converter smelting process, 5-10 kg of synthetic slag former is added per ton of steel in the tapping process, bottom blowing stirring is carried out on a steel ladle after tapping is finished, and 2.4-4.8 kg of low-carbon submerged arc slag former is added per ton of steel after bottom blowing is finished.
Preferably, the bottom blowing stirring time in the converter smelting process is 5-15 minutes.
Preferably, in the LF refining process, calcium carbide is added, stirred for 3-5 minutes and then added with alloy for alloying.
Preferably, in the LF refining process, alloying is carried out, the components of C, Si, Mn and Als in the steel are finely adjusted according to the test result after the converter is used, and microalloy components such as Nb and Ti are added in the LF.
Preferably, after the addition of the alloy in the LF refining process is finished, stirring for 2-4 minutes, and then closing bottom blowing.
Preferably, in the LF refining process, the LF treatment period is less than or equal to 25 minutes.
Preferably, the RH refining process, the recycling process does not add any alloy.
Preferably, the RH refining step does not perform the calcium treatment after the cycle is completed.
Preferably, in the RH refining process, the steel ladle is not bottom-blown after the circulation is finished, and the molten steel is kept stand for 20-40 minutes.
Although P, S, O, N, H in steel of a casting blank produced by a traditional process is controlled to be at a low level in the industrial production of a large amount of clean steel, the situation that various types of inclusions exceed requirements can continuously occur in the metallographic examination process of a product, the types of the inclusions comprise magnesium aluminate spinel inclusions, calcium oxide alumina composite inclusions, alumina inclusions and the like, and the analysis mainly has the following reasons by combining the actual control situation of a field process: 1) excessive aluminum deoxidizer and Al in steel2O3And Al2O3The complex inclusions with CaO or MgO are difficult to completely remove; 2) LF deep desulfurization requires long-time refining, resulting in liquid CaO-Al generated by molten steel-slag-lining reaction 2O3(-MgO) inclusions contaminate molten steel; 3) the calcium treatment process has poor application effect in actual production, firstly, the oxygen and nitrogen increase of the exposed molten steel is easily caused, secondly, the calcium element is extremely active, the modification degree of inclusions in the steel is different after the calcium wire yield is unstably driven into the calcium wire with a certain meter number, and the generated low-melting-point CaO-Al2O3The composite inclusions are not easy to remove. And a large amount of CaS inclusions are easily generated due to excessive feeding of the calcium wire, so that the molten steel inclusions are increased; 4) the various alloys contain oxygen, nitrogen and other impurities to different degrees, and are not easy to completely remove after being brought into molten steel after being alloyed too late.
Compared with the prior art, the invention has the following distinguishing technical characteristics:
1) through the combination of pre-desulfurization and argon stirring desulfurization by blowing argon from the bottom after tapping of the converter, S is controlled within the range required by steel grade, the link of LF slagging and desulfurization is eliminated, the LF treatment period is greatly shortened, the refining slagging amount is reduced, on one hand, the reaction of molten steel-slag-ladle lining is reduced, so that the quantity of impurities such as magnesium aluminate spinel, magnesium oxide and the like is reduced, and on the other hand, the opportunity of nitrogen increase and secondary oxidation of the molten steel refined for a long time is reduced;
2) different deoxidizers are selected for the converter end point high carbon drawing low end point oxygen matching with the tapping deoxidation alloying of different steel grades to reduce The consumption of the deoxidized aluminum products in the molten steel is reduced, so that Al in the molten steel2O3The generation amount is obviously reduced, and the floating is removed in the subsequent bottom blowing and stirring process;
3) after an LF slagging and desulfurizing link is omitted, adding calcium carbide into LF for deoxidation to maintain the reducibility of slag, closing bottom blowing after LF treatment, adding a certain amount of top slag modifier into slag before RH vacuum circulation, and not opening bottom blowing and calcium-free treatment after RH treatment, so as to reduce the influence of slag on the O content and cleanliness of molten steel;
4) alloying is carried out by adding the traditional easily-oxidized alloy RH such as coarse converter adjustment, fine LF adjustment, ferrotitanium and the like into the converter adjustment, adding the rest alloy of LF, and carrying out pure vacuum circulation on RH without adding any alloy, so that oxygen, nitrogen and other impurities contained in the alloy can enter molten steel as early as possible, and although the overall yield of partial alloys such as ferrotitanium and the like is slightly reduced, the O, N, H and solid inclusions in the molten steel can be obviously removed by the long-time pure degassing circulation of RH;
5) before RH treatment, the thickness of a slag layer of the slag is reduced, and a reducing slag modifier is added, so that the diffusion rate and quantity of oxygen and inclusions in the slag to the molten steel surface in the vacuum circulation process can be effectively reduced, and the cleanliness of the molten steel is improved;
6) After the RH treatment is finished, the calcium treatment in the conventional process is removed, so that on one hand, the secondary oxidation of molten steel in the calcium treatment process can be avoided, and on the other hand, the generation of low-melting-point calcium-aluminum composite inclusion and CaS inclusion can be avoided.
Adopt the produced beneficial effect of above-mentioned technical scheme to lie in:
by redistributing smelting key points of all working procedures, refining functions of an LF furnace and an RH furnace are simplified and efficient, harmful ingredients such as molten steel P, S are removed, and meanwhile, the influence of secondary oxidation of the molten steel and corrosion of steel ladle refractory on the cleanliness of the molten steel is reduced; the invention reduces the dosage of aluminum deoxidizer, secondarily removes slag by top slag before RH vacuum circulation, does not feed calcium wire after RH vacuum circulation and does not stir, thereby reducing Al in molten steel2O3The content of the inclusions is reduced, the contact reaction of the molten steel with a slag layer and the atmosphere in the middle and later stages is relieved, and the inclusions, O and N, H in the molten steel are controlled to be extremely low. The invention can makeThe smelted molten steel has high cleanliness, and a high-quality casting blank is provided for subsequently rolling a high-quality microalloyed high-strength steel product.
Detailed Description
The invention relates to a smelting method of high-cleanliness microalloyed high-strength steel, wherein microalloyed elements in the microalloyed high-strength steel comprise Nb, V, Ti, Mo, Cr and the like, wherein Nb + V + Ti is less than or equal to 0.22%, Mo + Cr is less than or equal to 0.30%, and a small amount of Cu, Ni, B and other elements can be added to meet special application of products; the microalloyed high-strength steel contains one or more of Nb, V, Ti, Mo, Cr, Cu, Ni, B and other elements, wherein Nb + V + Ti is less than or equal to 0.22 percent, and Mo + Cr is less than or equal to 0.30 percent.
The smelting process comprises molten iron pre-desulfurization, converter smelting, LF refining and RH refining;
the molten iron pre-desulfurization step, namely controlling the S content of the molten iron to be 0.003-0.008 wt% according to different steel requirements when the step is finished, and stirring and desulfurizing the molten iron after converter tapping is matched to finish, so that an LF slagging and desulfurizing link is omitted;
a converter smelting process, namely, slag retention and slag splashing protection, wherein the waste steel is self-produced low-sulfur waste steel, the ratio of the waste steel is 5-10%, the top and the bottom of the converter are blown compositely, the end point P is controlled to be less than or equal to 0.008wt%, a carbon pulling process is adopted, and the end point carbon is not controlled to be 0.04-0.12% according to the steel type; steel tapping is carried out to deoxidize molten steel, one or more of silicomanganese, ferromanganese, calcium carbide, silicon carbide and carburant are selected and added according to the content requirements of components C, Si and Mn of steel grades, then an aluminum block is added, composite deoxidation is carried out to the molten steel, the carburant and alloy are added according to the lower limit of the content range of target components C, Si, Mn and Als of the steel grades, meanwhile, 5-10 kg of synthetic slag former is added per ton of steel, bottom blowing stirring is carried out on the steel ladle for 5-15 minutes after the steel tapping is finished, a component test sample is taken after the bottom blowing is closed, and 2.4-4.8 kg of low-carbon submerged arc slag former is added per ton of steel;
an LF refining process, wherein the molten steel is subjected to station entry submerged arc power transmission, the temperature of the molten steel is adjusted to be 80-100 ℃ higher than the liquidus temperature of a steel grade, then calcium carbide is added for diffusion deoxidation, after stirring is carried out for 3-5 minutes, one or more of ferroniobium, ferromolybdenum, ferrotitanium and other alloys are added according to the target components of the steel grade, the other components such as C, Si, Mn, Als and the like are finely adjusted according to the post-converter test result, the components such as C, Mn, Nb, Mo and the like are controlled according to the target component content of the steel grade, the components such as Ti and Als are controlled according to the upper limit of the target component range of the steel grade, bottom blowing is closed after stirring is carried out for 2-4 minutes, and the LF treatment period is less than or equal to 25 minutes;
RH refining process, lifting to a certain height, then carrying out slag skimming operation, reducing the thickness of a slag layer to 70-150mm, circularly adding 0.4-1.4 kg/ton of steel top slag modifier into the slag layer, not carrying out alloy feeding in the process, ensuring that the vacuum degree is less than or equal to 1.0mbar, circulating gas flow is 2000-2800L/min, deep vacuum circulating time is 15-25 minutes, not starting ladle bottom blowing after the circulation is finished, not carrying out calcium treatment, and standing the molten steel for 20-40 minutes.
In order to make the objects, technical solutions and advantages of the present invention more apparent, the present invention is further described in detail with reference to the following embodiments. It should be understood that the specific embodiments described herein are merely illustrative of the invention and are not intended to limit the invention.
In order to better illustrate the invention, the following examples are given by way of further illustration.
Example 1
A250-ton top-bottom combined blown converter is adopted for smelting, the steel grade is high-strength automobile compartment steel 700XT, and the chemical component range (wt%) of the steel grade is as follows: c: 0.05-0.15, Si: 0.5-0.35, Mn: 1.00-2.50, P: less than or equal to 0.020, S: 0.005 or less, Als: 0.020 to 0.040, Nb: 0.010-0.050, Ti: 0.070-0.150.
The specific smelting steps are as follows:
a molten iron pre-desulfurization step, wherein the initial sulfur content in the molten iron is 0.035wt%, 350 kg of magnesium powder and 850 kg of lime powder are sprayed through the pre-desulfurization step, and the sulfur content is reduced to 0.07wt% after slagging-off operation;
A converter working procedure, namely adding 35 tons of self-produced low-sulfur waste steel into a converter, converting for 18 minutes, wherein the converting end point temperature is 1662 ℃, the end point C is 0.04wt%, the end point P is 0.008wt%, the end point O is 350ppm, and the weight of molten steel is 250 tons; tapping, slag stopping and deoxidation alloying, wherein 1200 kg of calcium carbide and 1400 kg of silicon carbide are added firstly, 2200 kg of ferro-silico-manganese, 1800 kg of high-carbon ferro-manganese and 88 kg and 1850 kg of aluminum blocks are added to synthesize a slagging agent, the using amount of the aluminum blocks is reduced by 50 percent compared with that of a full-aluminum product deoxidation mode, bottom blowing is closed after strong stirring is carried out for 10 minutes after tapping, and 814 kg of low-carbon submerged arc slagging agent is added;
an LF refining process: adjusting the temperature of molten steel to 1615 ℃ by station entering submerged arc power transmission, wherein the temperature is 94 ℃ higher than the liquidus temperature of steel, adding 280 kg of calcium carbide on the slag surface of the molten steel after power transmission is stopped for diffusion deoxidation, adding ferroniobium and ferrotitanium after stirring for 3 minutes, adjusting C, Si, Mn and Als according to a test sample of the molten steel after the furnace, controlling components C, Si, Mn and Nb according to target components, controlling components Ti and Als according to the upper limit of the range of the target components, closing bottom blowing after stirring for 3 minutes, and refining for 23 minutes;
RH refining procedure: after the steel ladle is jacked to a proper height, slagging-off treatment is carried out, the thickness of a treated slag layer is 70mm, 240 kg of top slag modifier is added into the slag layer after circulation begins, alloy feeding is not carried out in the circulation process, the process vacuum degree is 0.8mbar, the circulation gas flow rate is 2300L/min, the circulation time is 24 minutes, bottom blowing is not carried out on the steel ladle after circulation is finished, calcium treatment is not carried out, and molten steel is kept stand for 26 minutes;
After refining, the molten steel has smelting components in weight percent of P0.006, S0.002, O0.0008, N0.0025 and H0.0001.
Example 2
Smelting by adopting a 250-ton top-bottom combined blown converter, wherein the steel grade is high-strength automobile wheel steel 590CL, and the chemical component range (wt%) of the steel grade is as follows: c: 0.08-0.10, Si: 0.15-0.40, Mn: 0.80-1.60, P: less than or equal to 0.020, S: 0.005 or less, Als: 0.020 to 0.040, Nb: 0.020-0.050, Ti: 0.010-0.025, Cr: 0.10-0.25.
The specific smelting steps are as follows:
a molten iron pre-desulfurization process, wherein the initial sulfur content in the molten iron is 0.037wt%, 450 kg of magnesium powder and 880 kg of lime powder are sprayed through the pre-desulfurization process, and the sulfur content is reduced to 0.006wt% after slagging-off operation;
a converter working procedure, namely adding 40 tons of self-produced low-sulfur scrap steel into a converter, converting for 17 minutes, wherein the converting end point temperature is 1674 ℃, the end point C is 0.06wt%, the end point P is 0.006wt%, the end point O is 334ppm, and the weight of molten steel is 250 tons; tapping and slag stopping operation, performing deoxidation alloying, adding 1700 kg of calcium carbide, 1600 kg of silicon carbide, 2400 kg of ferro-silico-manganese, 1900 kg of high-carbon ferro-manganese, 100 kg of aluminum blocks and 2350 kg of synthetic slag former, wherein the using amount of the aluminum blocks is reduced by 40 percent compared with that of a full-aluminum product deoxidation mode, closing bottom blowing after the steel tapping is finished and is stirred for 12 minutes, and adding 850 kg of low-carbon submerged arc slag former;
An LF refining process: adjusting the temperature of molten steel to 1615 ℃ by station-entering submerged arc power transmission, wherein the temperature is 87 ℃ higher than the liquidus temperature of steel, adding 450 kg of calcium carbide on the slag surface of the molten steel after the power transmission is stopped for diffusion deoxidation, adding ferrocolumbium, ferrotitanium and ferrochromium after stirring for 4 minutes, adjusting C, Si, Mn and Als according to a post-furnace molten steel test sample, controlling the components C, Si, Mn, Nb and Cr according to target components, controlling the components Ti and Als according to the upper limit of the target component range, closing bottom blowing after stirring for 2 minutes, and refining for 21 minutes;
RH refining process: carrying out slag skimming treatment after the steel ladle is jacked to a proper height, wherein the thickness of a processed slag layer is 142mm, adding 350 kg of top slag modifier into the processed slag layer after circulation starts, carrying out no alloy feeding in the circulation process, wherein the vacuum degree in the process is 0.7mbar, the circulation gas flow is 2400L/min, the circulation time is 25 minutes, carrying out no bottom blowing on the steel ladle after the circulation is finished, carrying out no calcium treatment, and standing the molten steel for 20 minutes;
after the refining is finished, the molten steel smelting components (wt%) include P0.006, S0.002, O0.0008, N0.0027 and H0.0001.
Example 3
Smelting by adopting a 250-ton top-bottom combined blown converter, wherein the steel grade is hot-rolled dual-phase high-strength wheel steel DP590, and the chemical component range (wt%) of the steel grade is as follows: c: 0.07-0.12, Si: 0.15-0.25, Mn: 1.00-2.00, P: less than or equal to 0.020, S: less than or equal to 0.010, Als: 0.015-0.035, Nb: 0.010-0.030, Ti: 0.025-0.040.
The specific smelting steps are as follows:
a molten iron pre-desulfurization process, namely, the initial sulfur content in the molten iron is 0.024wt%, 200 kg of magnesium powder and 600 kg of lime powder are sprayed through the pre-desulfurization process, and the sulfur content is reduced to 0.003wt% after slagging-off operation;
a converter working procedure, namely adding 20 tons of self-produced low-sulfur scrap steel into a converter, converting for 15 minutes, wherein the converting end point temperature is 1645 ℃, the end point C is 0.05wt%, the end point P is 0.005wt%, the end point O is 346ppm, and the weight of molten steel is 250 tons; tapping, slag stopping operation and deoxidation alloying, wherein 700 kg of calcium carbide and 1600 kg of silicon carbide are added, 1000 kg of ferro-silico-manganese, 1500 kg of high-carbon ferro-manganese and 60 kg and 1600 kg of aluminum blocks are added to synthesize a slag former, the using amount of the aluminum blocks is reduced by 60 percent compared with that of a full-aluminum product deoxidation mode, bottom blowing is closed after strong stirring is carried out for 5 minutes after tapping, and 600 kg of low-carbon submerged arc slag former is added;
an LF refining process: adjusting the temperature of molten steel to 1620 ℃ by submerged arc power transmission when the molten steel is in a station, wherein the temperature is 80 ℃ higher than the liquidus temperature of a steel grade, adding 450 kg of calcium carbide on the slag surface of the molten steel after power transmission is stopped for diffusion deoxidation, stirring for 5 minutes, then adding ferrocolumbium and ferrotitanium, adjusting C, Si, Mn and Als according to a test sample of the molten steel after the furnace, controlling components C, Si, Mn and Nb according to target components, controlling components Ti and Als according to the upper limit of the range of the target components, stirring for 4 minutes, then closing bottom blowing, and refining for 20 minutes;
RH refining procedure: lifting a steel ladle to a proper height, then carrying out slag skimming treatment, wherein the thickness of a treated slag layer is 87mm, adding 340 kg of top slag modifier into the slag layer after circulation starts, carrying out no alloy feeding in the circulation process, ensuring the process vacuum degree to be 0.4mbar, circulating gas flow to be 2500L/min, circulating time to be 15 minutes, carrying out no bottom blowing on the steel ladle after circulation ends, carrying out no calcium treatment, and standing molten steel for 30 minutes;
after the refining, the molten steel has the smelting components (wt%) that P is 0.006, S is 0.001, O is 0.0009, N is 0.0027 and H is 0.0001.
Example 4
Smelting by using a 250-ton top-bottom combined blown converter, wherein the steel is hot-rolled quality-free wear-resistant steel NM400TP, and the chemical component ranges (wt%) of the steel are as follows: c: 0.16-0.22, Si: 0.60-0.80, Mn: 1.20-2.50, P: 0.015 or less, S: 0.005 or less, Als: 0.010-0.030, Nb: 0.010-0.030, Mo: 0.010-0.030.
The specific smelting steps are as follows:
a molten iron pre-desulfurization process, wherein the initial sulfur content in the molten iron is 0.036wt%, 470 kg of magnesium powder and 1100 kg of lime powder are sprayed through the pre-desulfurization process, and the sulfur content is reduced to 0.004wt% after slagging-off operation;
converter working procedure, adding 35 tons of self-produced low-sulfur scrap steel into a converter, converting for 16 minutes, wherein the converting end point temperature is 1620 ℃, the end point C is 0.12wt%, the end point P is 0.005wt%, the end point O is 240ppm, and the weight of molten steel is 250 tons; carrying out steel tapping and slag stopping operation, carrying out deoxidation alloying, adding 1800 kg of calcium carbide, 1600 kg of silicon carbide, 2500 kg of ferro-silico-manganese, 2500 kg of high-carbon ferro-manganese, 120 kg of carburant, 62 kg of aluminum blocks and 1350 kg of synthetic slag former, reducing the consumption of the aluminum blocks by 53 percent compared with the deoxidation mode of an all-aluminum product, closing bottom blowing after strong stirring for 14 minutes after steel tapping is finished, and adding 1000 kg of low-carbon submerged arc slag former;
An LF refining procedure: adjusting the temperature of molten steel to 1600 ℃ by station-entering submerged arc power transmission, wherein the temperature is 100 ℃ higher than the liquidus temperature of steel, adding 350 kg of calcium carbide on the slag surface of the molten steel after the power transmission is stopped for diffusion deoxidation, stirring for 3.4 minutes, then adding ferrocolumbium and ferromolybdenum, adjusting C, Si, Mn and Als according to a post-furnace molten steel test sample, controlling the components C, Si, Mn, Nb and Mo according to target components, controlling the components Als according to the upper limit of the target component range, stirring for 2.6 minutes, then closing bottom blowing, and refining for 19 minutes;
RH refining process: carrying out slag skimming treatment after the steel ladle is jacked to a proper height, wherein the thickness of a treated slag layer is 150mm, adding 100 kg of top slag modifier into the slag layer after circulation starts, carrying out no alloy feeding in the circulation process, wherein the vacuum degree in the process is 0.2mbar, the circulation gas flow is 2000L/min, the circulation time is 15 minutes, carrying out no bottom blowing on the steel ladle after the circulation is finished, carrying out no calcium treatment, and standing the molten steel for 34 minutes;
after the refining is finished, the molten steel smelting components (wt%) include P0.007, S0.002, O0.0012, N0.0029 and H0.0001.
Example 5
A250-ton top-bottom combined blown converter is adopted for smelting, the steel grade is high-strength automobile stirring tank steel 620JJ, and the chemical component range (wt%) of the steel grade is as follows: c: 0.10-0.16, Si: less than or equal to 0.15, Mn: 0.60-1.20, P: 0.025 or less, S: less than or equal to 0.010, Als: 0.020 to 0.040, Ti: 0.040-0.060, Cu: 0.20-0.40.
The specific smelting steps are as follows:
a molten iron pre-desulfurization process, namely, the initial sulfur content in the molten iron is 0.039wt%, 490 kg of magnesium powder and 1100 kg of lime powder are sprayed through the pre-desulfurization process, and the sulfur content is reduced to 0.008wt% after slagging-off operation;
a converter working procedure, namely adding 20 tons of self-produced low-sulfur waste steel into a converter, converting for 17 minutes, wherein the converting end point temperature is 1639 ℃, the end point C is 0.08wt%, the end point P is 0.008wt%, the end point O is 302ppm, and the weight of molten steel is 250 tons; carrying out steel tapping and slag stopping operation, carrying out deoxidation alloying, adding 950 kg of calcium carbide, 3500 kg of high-carbon ferromanganese, 75 kg of carburant, 80 kg of aluminum blocks and 1250 kg of synthetic slag former, wherein the use amount of the aluminum blocks is reduced by 47 percent compared with that of the full-aluminum product deoxidation mode, closing bottom blowing after strong stirring for 8 minutes after steel tapping is finished, and adding 1200 kg of low-carbon submerged arc slag former;
an LF refining process: adjusting the temperature of molten steel to 1610 ℃ by submerged arc power transmission when the molten steel enters a station, raising the temperature to 90 ℃ higher than the liquidus temperature of steel, adding 450 kg of calcium carbide on the slag surface of the molten steel after the power transmission is stopped for diffusion deoxidation, stirring for 3.8 minutes, then adding a copper plate and ferrotitanium, adjusting C, Mn and Als according to a test sample of the molten steel after the furnace, controlling the components C, Mn and Cu according to target components, controlling the components Ti and Als according to the upper limit of the range of the target components, stirring for 2.9 minutes, then closing bottom blowing, and refining for 17 minutes;
RH refining procedure: lifting the steel ladle to a proper height, then carrying out slag skimming treatment, wherein the thickness of a treated slag layer is 130mm, adding 100 kg of top slag modifier into the slag layer after circulation starts, carrying out no alloy feeding in the circulation process, ensuring the process vacuum degree to be 0.6mbar, circulating gas flow to be 2000L/min, circulating time to be 15 minutes, carrying out no bottom blowing on the steel ladle after circulation ends, carrying out no calcium treatment, and standing the molten steel for 40 minutes;
and finishing refining, wherein the molten steel smelting composition (wt%) comprises 0.009P, 0.006S, 0.0012O, 0.0025N and 0.0001H.
Example 6
A250-ton top-bottom combined blown converter is adopted for smelting, the steel grade is 700L of high-strength automobile girder steel, and the chemical composition range (wt%) of the steel grade is as follows: c: 0.06-0.08, Si: 0.20-0.35, Mn: 1.00-2.50, P: less than or equal to 0.020, S: 0.005 or less, Als: 0.015-0.035, Nb: 0.020-0.060, Ti: 0.080-0.120, Cr: 0.10-0.30.
The specific smelting steps are as follows:
a molten iron pre-desulfurization process, wherein the initial sulfur content in the molten iron is 0.034wt%, 500 kg of magnesium powder and 1200 kg of lime powder are sprayed through the pre-desulfurization process, and the sulfur content is reduced to 0.003wt% after slagging-off operation;
a converter working procedure, namely adding 20 tons of self-produced low-sulfur steel scrap into the converter, converting for 19 minutes, wherein the converting end point temperature is 1668 ℃, the end point C is 0.04wt%, the end point P is 0.006wt%, the end point O is 310ppm, and the weight of molten steel is 250 tons; carrying out tapping slag stopping operation and carrying out deoxidation alloying, firstly adding 1600 kg of calcium carbide and 1400 kg of silicon carbide, then adding 2300 kg of ferro-silico-manganese, 1700 kg of high-carbon ferro-manganese and 95 kg and 2500 kg of aluminum blocks to synthesize a slag former, wherein the using amount of the aluminum blocks is reduced by 49 percent compared with that of a full-aluminum product deoxidation mode, closing bottom blowing after strong stirring is carried out for 15 minutes after tapping is finished, and adding 630 kg of low-carbon submerged arc slag former;
An LF refining process: the molten steel temperature is adjusted to 1615 ℃ by station-entering submerged arc power transmission, the temperature is 93 ℃ higher than the liquidus temperature of steel, after the power transmission is stopped, 450 kg of calcium carbide is added to the slag surface of the molten steel for diffusion deoxidation, after the molten steel is stirred for 4.2 minutes, ferroniobium, ferrotitanium and ferrochromium are added, C, Si, Mn and Als are adjusted according to a post-furnace molten steel assay sample, the components C, Si, Mn, Nb and Cr are controlled according to target components, the components Ti and Als are controlled according to the upper limit of the target component range, bottom blowing is closed after the molten steel is stirred for 3.2 minutes, and the refining period is 25 minutes;
RH refining procedure: carrying out slag skimming treatment after the steel ladle is jacked to a proper height, wherein the thickness of a treated slag layer is 80mm, adding 190 kg of top slag modifier into the slag layer after circulation starts, carrying out no alloy feeding in the circulation process, wherein the vacuum degree in the process is 0.6mbar, the circulation gas flow is 2200L/min, the circulation time is 18 minutes, carrying out no bottom blowing on the steel ladle after the circulation is finished, carrying out no calcium treatment, and standing the molten steel for 32 minutes;
after refining, the molten steel has smelting components in weight percent of P0.007, S0.002, O0.0008, N0.0024 and H0.0001.
Example 7
Smelting by adopting a 250-ton top-bottom combined blown converter, wherein the steel grade is steel ZDG400 for a wheel brake drum, and the steel grade comprises the following chemical components in percentage by weight: c: 0.12-0.16, Si: less than or equal to 0.15, Mn: 1.00-1.80, P: less than or equal to 0.025, S: 0.005 or less, Als: 0.020 to 0.40, Nb: 0.030-0.050, Cr: 0.10-0.50.
The specific smelting steps are as follows:
a molten iron pre-desulfurization process, namely, the initial sulfur content in the molten iron is 0.046wt%, 240 kg of magnesium powder and 700 kg of lime powder are sprayed through the pre-desulfurization process, and the sulfur content is reduced to 0.005wt% after slagging-off operation;
converter working procedure, namely adding 36 tons of self-produced low-sulfur scrap steel into a converter, converting for 17 minutes, wherein the converting end point temperature is 1620 ℃, the end point C is 0.09wt%, the end point P is 0.008wt%, the end point O is 320ppm, and the weight of molten steel is 250 tons; the method comprises the following steps of carrying out steel tapping and slag stopping operation, carrying out deoxidation alloying, adding 1400 kg of calcium carbide, 2500 kg of high-carbon ferromanganese, 80 kg of carburant and 70 kg and 2125 kg of aluminum blocks to synthesize a slag former, wherein the using amount of the aluminum blocks is reduced by 57 percent compared with that of a full-aluminum product deoxidation mode, closing bottom blowing after strong stirring is carried out for 6 minutes after steel tapping is finished, and adding 700 kg of low-carbon submerged arc slag former;
an LF refining procedure: adjusting the temperature of molten steel to 1622 ℃ by station-entering submerged arc power transmission, wherein the temperature is 89 ℃ higher than the liquidus temperature of steel, 200 kg of calcium carbide is added to the slag surface of the molten steel after the power transmission is stopped for diffusion deoxidation, the ferrocolumbium and ferrochrome are added after the stirring is carried out for 4.7 minutes, C, Mn and Als are adjusted according to a post-furnace molten steel test sample, the components C, Mn, Nb and Cr are controlled according to target components, the component Als is controlled according to the upper limit of the target component range, bottom blowing is closed after the stirring is carried out for 3.6 minutes, and the refining period is 18 minutes;
RH refining process: lifting the steel ladle to a proper height, slagging off, wherein the thickness of a processed slag layer is 110mm, adding 290 kg of top slag modifier into the processed slag layer after circulation starts, alloy feeding is not carried out in the circulation process, the vacuum degree in the process is 0.4mbar, the circulation gas flow is 2300L/min, the circulation time is 15 minutes, bottom blowing is not carried out on the steel ladle after circulation is finished, calcium treatment is not carried out, and the molten steel is kept stand for 31 minutes;
after the refining is finished, the molten steel smelting components (wt%) include 0.008P, 0.004S, 0.012O, 0.0021N and 0.0001H.
The finished steel sheets 700XT, 590CL, 590DP, NM400TP, 620JJ and 700L, ZDG400 produced in examples 1 to 7 were subjected to inclusion test rating in accordance with GB/T10561-2005/ISO 4967:1998(E) microscopic examination method for determination of the content of nonmetallic inclusions in steel, and the rating results for A-type sulfide inclusions, B-type oxide inclusions, C-type silicate inclusions, D-type spherical oxide inclusions and DS-type single-particle spherical inclusions were all 0 grade.
Although the present invention has been described in detail with reference to the above embodiments, it should be understood by those skilled in the art that: modifications and equivalents may be made thereto without departing from the spirit and scope of the invention and it is intended to cover in the claims the invention as defined in the appended claims.
Claims (5)
1. A smelting method of high-cleanliness microalloyed high-strength steel comprises the working procedures of molten iron pre-desulfurization, converter smelting, LF refining and RH refining and is characterized in that,
(1) pre-desulfurization of molten iron: controlling the S content of the molten iron to be 0.003-0.008 wt% after the working procedure is finished;
(2) smelting in a converter: controlling the content of C at the smelting end point to be 0.04-0.12 wt%, controlling the content of O at the smelting end point to be less than or equal to 350ppm, selecting one or more of silicomanganese, ferromanganese, calcium carbide, silicon carbide and carburant for deoxidation alloying in the tapping process, determining the addition type and the addition amount according to the lower limit of the content range of the target components C, Si and Mn of the steel, and then selecting an aluminum block to ensure that molten steel is completely deoxidized; adding 5-10 kg of synthetic slag former per ton of steel in the tapping process, and carrying out bottom blowing stirring on a steel ladle after tapping is finished;
(3) LF refining: adjusting the temperature of the molten steel to be 80-100 ℃ above the liquidus temperature of the steel grade, and then adding calcium carbide for diffusion deoxidation; the LF treatment period is less than or equal to 25 minutes; adding calcium carbide, stirring for 3-5 minutes, and then adding alloy for alloying; during the alloying, the components of C, Si, Mn and Als in the steel are finely adjusted according to the test result after the converter is used for LF refining, and other alloy components in the steel are added in the LF;
(4) RH refining: and (3) slagging off is carried out after the steel ladle is jacked, the thickness of a slag layer is reduced to 70-150mm, 0.4-1.4 kg/ton of steel top slag modifier is added after circulation begins, no alloy is added in the circulation process, and calcium treatment is not carried out after circulation is finished.
2. The method for smelting high-cleanliness microalloyed high-strength steel as claimed in claim 1, wherein in the converter smelting process, 2.4-4.8 kg of low-carbon submerged arc slagging agent is added per ton of steel after bottom blowing is finished.
3. A method of producing a high-cleanliness microalloyed high-strength steel as claimed in claim 2, wherein the bottom-blowing stirring time is 5 to 15 minutes.
4. The method for smelting high-cleanliness microalloyed high-strength steel as claimed in claim 1, wherein in the LF refining process, after the addition of the alloy in the LF furnace is finished, the bottom blowing is closed after stirring for 2-4 minutes.
5. The method for smelting high-cleanliness microalloyed high-strength steel according to any one of claims 1 to 4, wherein the RH refining process is performed, the ladle is not bottom-blown after the circulation is finished, and the molten steel is left for 20 to 40 minutes.
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