CN115323255B - Preparation method of 200-square continuous casting blank for high-quality and high-homogeneity bearing steel wire rod - Google Patents
Preparation method of 200-square continuous casting blank for high-quality and high-homogeneity bearing steel wire rod Download PDFInfo
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- C—CHEMISTRY; METALLURGY
- C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
- C22C—ALLOYS
- C22C33/00—Making ferrous alloys
- C22C33/04—Making ferrous alloys by melting
- C22C33/06—Making ferrous alloys by melting using master alloys
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- B—PERFORMING OPERATIONS; TRANSPORTING
- B22—CASTING; POWDER METALLURGY
- B22D—CASTING OF METALS; CASTING OF OTHER SUBSTANCES BY THE SAME PROCESSES OR DEVICES
- B22D11/00—Continuous casting of metals, i.e. casting in indefinite lengths
- B22D11/001—Continuous casting of metals, i.e. casting in indefinite lengths of specific alloys
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- B—PERFORMING OPERATIONS; TRANSPORTING
- B22—CASTING; POWDER METALLURGY
- B22D—CASTING OF METALS; CASTING OF OTHER SUBSTANCES BY THE SAME PROCESSES OR DEVICES
- B22D11/00—Continuous casting of metals, i.e. casting in indefinite lengths
- B22D11/16—Controlling or regulating processes or operations
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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
- C21C7/0006—Adding metallic additives
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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
- C21C7/0025—Adding carbon material
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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
- C21C7/10—Handling in a vacuum
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- C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
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- C22C38/00—Ferrous alloys, e.g. steel alloys
- C22C38/02—Ferrous alloys, e.g. steel alloys containing silicon
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- C—CHEMISTRY; METALLURGY
- C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
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- C22C38/00—Ferrous alloys, e.g. steel alloys
- C22C38/04—Ferrous alloys, e.g. steel alloys containing manganese
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- C—CHEMISTRY; METALLURGY
- C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
- C22C—ALLOYS
- C22C38/00—Ferrous alloys, e.g. steel alloys
- C22C38/06—Ferrous alloys, e.g. steel alloys containing aluminium
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- C—CHEMISTRY; METALLURGY
- C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
- C22C—ALLOYS
- C22C38/00—Ferrous alloys, e.g. steel alloys
- C22C38/18—Ferrous alloys, e.g. steel alloys containing chromium
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- C—CHEMISTRY; METALLURGY
- C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
- C22C—ALLOYS
- C22C38/00—Ferrous alloys, e.g. steel alloys
- C22C38/18—Ferrous alloys, e.g. steel alloys containing chromium
- C22C38/28—Ferrous alloys, e.g. steel alloys containing chromium with titanium or zirconium
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- Y—GENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; GENERAL TAGGING OF CROSS-SECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
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- Y02P—CLIMATE CHANGE MITIGATION TECHNOLOGIES IN THE PRODUCTION OR PROCESSING OF GOODS
- Y02P10/00—Technologies related to metal processing
- Y02P10/20—Recycling
Abstract
The invention relates to a preparation method of a 200-square continuous casting blank for a high-quality and high-homogeneity bearing steel wire rod, and belongs to the technical field of continuous casting blank preparation for bearing steel. The invention provides a preparation method of 200-square continuous casting blank for high-quality and high-homogeneity bearing steel wire rods, which comprises a primary smelting step, a refining step and a continuous casting step. The invention effectively controls inclusions and the like in steel from the initial smelting step tapping, thereby ensuring the purity of molten steel; the LF refining adopts a three-time power transmission method, so that the temperature of molten steel is effectively controlled, and the refining process is more stable; the continuous casting step reduces the segregation index of the casting blank through reasonable control of parameters, improves the internal quality and the component uniformity of the casting blank, provides high-quality base metal for subsequent steel rolling, and finally realizes 1-fire completion rolling, thereby effectively simplifying the production process, improving the production efficiency and reducing the production cost.
Description
Technical Field
The invention belongs to the technical field of continuous casting billet preparation for bearing steel, and particularly relates to a preparation method of a 200-square continuous casting billet for a high-quality and high-homogeneity bearing steel wire rod.
Background
Bearing steel is one of the most famous products in the special steel production field, the production quantity is the largest and the production difficulty is the most important basic mechanical part, and the bearing steel is widely applied in the fields of industry, agriculture, national defense and the like. The bearing steel is mainly used for manufacturing rolling bodies, including balls, rollers, rolling needles, inner and outer ferrules and the like, and is required to have the characteristics of high hardness, wear resistance, fatigue resistance, corrosion resistance and the like. With the continuous casting technology developing continuously, the quality requirements of bearing steel are also becoming strict. Therefore, the quality requirements of continuous casting blanks for bearing steel wire rod production are becoming more and more strict, the production requirements of rolling materials are not only met, and the requirements of uniformity and inclusion of internal tissues and components of casting blanks are higher.
Naturally selecting and crystallizing the casting blank in the solidification process, and collecting molten steel with higher concentration at the central position of the casting blank after solidification, so that the central position segregation is high, shrinkage cavity defects can occur when serious, carbide segregation phenomenon exists in microstructure of the casting blank, the uniformity of the components of the rolled material is finally affected, and breakage can be caused in the subsequent processing. Two fires are often required to control the segregation index of the billet to meet the compositional uniformity of the final wire product, resulting in an increase in process and cost.
Disclosure of Invention
The invention provides a preparation method of a 200-square continuous casting blank for a high-quality and high-homogeneity bearing steel wire rod, which aims to solve the problems of long two-fire rolling process and high cost of the existing bearing steel wire rod for controlling the segregation index of a casting blank.
The technical scheme of the invention is as follows:
the preparation method of the 200-square continuous casting blank for the high-quality and high-homogeneity bearing steel wire rod comprises a primary smelting step, a refining step and a continuous casting step, wherein the content of tapping C in the primary smelting step is not less than 0.25wt%, the tapping temperature is 1620-1640 ℃, the tapping hole heat is not more than 120 times, and calcium-silicon-barium, carbon powder, aluminum ingots, lime and alloy are sequentially added into a steel ladle in the tapping process; the refining step comprises LF refining and RH vacuum circulation degassing refining, wherein the LF refining adopts a three-time power transmission method, the total LF refining time is not less than 50min, and the white slag holding time is not less than 30min; the continuous casting step ensures constant temperature and constant speed blank drawing, and is matched with continuous casting crystallizer stirring, head end electromagnetic stirring, tail end electromagnetic stirring and tail end soft pressing to finally obtain 200 square continuous casting blanks.
Further, the tapping amount in the primary smelting step is calculated according to 100 tons, the proportion of slag and the adjustment of molten steel components are carried out according to requirements, and the concrete method comprises the following steps:
when the adding time of the silicon calcium barium is 20t of tapping, controlling the adding amount to be 60 Kg;
the adding time of the carbon powder is before tapping and 20t of tapping, wherein 200Kg of carbon powder is paved on the ladle bottom according to 20% of carbon content in steel components; the addition amount of carbon powder is controlled to be thrown in one time according to the lower limit of the composition when tapping for 20 t;
the adding time of the aluminum ingot is that after carbon powder is added when tapping is performed for 20t, the adding amount of the aluminum ingot is controlled according to the tapping C content, 90Kg of the aluminum ingot is added when the tapping C content is 0.25-0.30 wt%, and 80Kg of the aluminum ingot is added when the tapping C content is more than 0.30 wt%;
when the adding time of the alloy is 40t of tapping, controlling the adding amount according to the lower limit of the composition;
the lime is added for 40t tapping time, and the adding amount is 600Kg after the alloy is added.
Further, the LF refining transmits power for the first time,
feeding power for 5 minutes, adding 200Kg lime, carrying out diffusion deoxidation by adopting 20Kg aluminum particles, 20Kg silicon carbide and 10Kg carbon powder, feeding 100Kg lime, carrying out diffusion deoxidation by adopting 10Kg aluminum particles, 20Kg silicon carbide and 10Kg carbon powder for 9 minutes, sampling slag white at a temperature of not lower than 1530 ℃, and simultaneously carrying out first sampling.
Further, the LF refining is performed for the second time, when the content of Al is equal to or less than 0.040wt%, 100% of aluminum wires are used for recycling, and the content of Al is adjusted to be 0.040wt%; and (3) maintaining white slag operation after sampling, performing diffusion deoxidation by adopting 20Kg of silicon carbide and 10Kg of carbon powder, adjusting components to internal control requirements, controlling secondary power transmission time to be 10min, and controlling the temperature to be not lower than 1550 ℃.
Further, the LF refining is powered on for the third time, the heating speed is controlled according to the production rhythm, 10-20 Kg of silicon carbide is added to keep the white slag effect, when the temperature of the molten steel reaches the outlet temperature, power is cut off, and the next procedure is carried out to carry out the molten steel vacuum operation.
Further, the ring flow rate of the RH vacuum circulation degassing refining is 1800-2000L/min, the vacuum degree within 5min of the target reaches below 67Pa, and the soft blowing time is not less than 25min.
Further, the continuous casting step adopts an arc six-machine six-strand continuous casting with the radius of 10m to produce 200 x 200 square, the size of a tundish is 40t, and the casting liquid level is controlled to be above 850 mm.
Further, the continuous casting step sets the continuous casting drawing speed to be 1.30m/min according to the superheat degree of 25-30 ℃, the specific water quantity to be 0.53Kg/t and the distribution ratio to be 36/39/25%.
Further, the parameters of the electromagnetic stirring at the head end of the electromagnetic stirring in the continuous casting step are 150A/2Hz, the stirring intensity is controlled at 350.3Gs, and the stirring mode is continuous stirring; the parameters of the electromagnetic stirring at the tail end are 350A/10Hz, the stirring mode is continuous, and the stirring position is at the position of the arc radius of the continuous casting machine of 9.5 m; the parameters of the tip light depression are 2/3/5/5, and the total depression is 15mm.
Further, the bearing steel comprises the following chemical components in percentage by weight: c: 0.96-0.99%, si:0.18 to 0.22 percent of Mn:0.26 to 0.30 percent, less than or equal to 0.015 percent of P, less than or equal to 0.005 percent of S, and Cr:1.43 to 1.47 percent of Al: 0.010-0.015%, ti less than or equal to 0.0015%, and the balance of Fe and unavoidable impurities.
The invention has the beneficial effects that:
according to the preparation method of the 200-square continuous casting billet for the bearing steel wire rod, which is provided by the invention, inclusion and the like in steel are effectively controlled from the initial smelting step of tapping, so that the purity of molten steel is ensured, and the oxygen content in the steel is controlled; the LF refining adopts a three-time power transmission method, so that the temperature of molten steel is effectively controlled, the refining process is more stable, the molten steel is effectively controlled not to be oxidized for the second time to form excessive inclusions, and the influence on the purity of the molten steel is avoided; the segregation index of the casting blank is reduced through reasonable control of parameters in the continuous casting step, the center of the low-power grade of the casting blank is loose, the integral segregation index is controlled to be 0.95-1.08. The invention improves the internal quality and the component uniformity of the casting blank, provides high-quality base metal for subsequent steel rolling, and finally realizes 1-fire rolling, thereby effectively simplifying the production process, improving the production efficiency and reducing the production cost.
Drawings
FIG. 1 is a photograph of the surface quality of a welded blank of 6 blocks obtained by six-strand continuous casting with an arc-shaped six-machine, obtained by cutting a low-power sample, which is subjected to hot pickling and then is spliced;
FIG. 2 is a photograph showing the result of measuring the overall dimensions of 6 continuous casting billets obtained by six-strand casting with an arc-shaped six-machine according to the present invention;
FIGS. 3-8 are photographs of transverse low-power samples of 6 continuous casting billets obtained by six-strand casting using an arc six-machine according to the present invention;
FIG. 9 is a photograph of a longitudinal low-magnification sample of 6 continuous casting billets obtained using six-strand casting with six machines in an arc shape according to the present invention.
Detailed Description
The following embodiments are used for further illustrating the technical scheme of the present invention, but not limited thereto, and all modifications and equivalents of the technical scheme of the present invention are included in the scope of the present invention without departing from the spirit and scope of the technical scheme of the present invention. The process equipment or apparatus not specifically noted in the following examples are all conventional equipment or apparatus in the art, and the raw materials and the like used in the examples of the present invention are commercially available unless otherwise specified; unless specifically indicated, the technical means used in the embodiments of the present invention are conventional means well known to those skilled in the art.
Example 1
The embodiment provides a preparation method of a 200-square continuous casting blank for a high-quality and high-homogeneity bearing steel wire rod.
The bearing steel in the embodiment comprises the following chemical components in percentage by weight: c: 0.96-0.99%, si:0.18 to 0.22 percent of Mn:0.26 to 0.30 percent, less than or equal to 0.015 percent of P, less than or equal to 0.005 percent of S, and Cr:1.43 to 1.47 percent of Al: 0.010-0.015%, ti less than or equal to 0.0015%, and the balance of Fe and unavoidable impurities.
The preparation method of the 200-square continuous casting blank for the bearing steel wire rod comprises a primary smelting step, a refining step and a continuous casting step.
The content of tapping C in the primary smelting step is not less than 0.25wt%, the tapping temperature is 1620-1640 ℃, the tapping hole heat is less than or equal to 120 times, and the tapping time is more than 150 seconds.
A100 ton steel ladle of type A or B is used as a turnover ladle, and the turnover ladle is used for producing steel types containing Ti without smelting, so that Ti in molten steel is prevented from finally affecting the components of the molten steel. The ladle without the ladle bottom is cleaned up, the inclusion in the steel is reduced while the temperature of the ladle is ensured, and the temperature in the ladle reaches more than 1200 ℃.
In the tapping process, the proportion of slag and the components of molten steel are regulated according to the requirements, and silicon-calcium-barium, carbon powder, aluminum ingots, lime and alloy are sequentially added into the steel ladle.
The refining step comprises LF refining and RH vacuum circulation degassing refining, wherein the LF refining adopts a three-time power transmission method, the total LF refining time is not less than 50min, and the white slag holding time is not less than 30min.
The continuous casting step ensures constant temperature and constant speed blank drawing, and is matched with continuous casting crystallizer stirring, head end electromagnetic stirring, tail end electromagnetic stirring and tail end light pressing to finally obtain 200 square continuous casting blanks.
Example 2
The only difference between this example and example 1 is that the initial refining step of this example is:
the content of tapping C in the primary smelting step is not less than 0.25wt%, the tapping temperature is 1620-1640 ℃, the tapping hole heat is less than or equal to 120 times, and the tapping time is more than 150 seconds.
In the primary smelting step, the tapping amount is calculated according to 100 tons, the proportion of slag and the composition of molten steel are regulated according to the requirement, and the silicon-calcium-barium, carbon powder, aluminum ingot, lime and alloy are sequentially added into a steel ladle, and the specific regulation method is as follows:
before tapping, paving carbon powder at the ladle bottom. The addition amount of the carbon powder is that 200Kg of carbon powder is paved at the bottom of the ladle before tapping according to 20 percent of the carbon content in the steel type components.
The carbon powder is paved in advance to enable the molten steel to react with the carbon powder in the steel ladle, so that sufficient precipitation deoxidization is achieved, the oxygen content in the steel is reduced, the carbon powder and the tapped molten steel are contacted to achieve the effect of pre-deoxidization, the alloy yield can be effectively improved, and the smelting production cost is reduced. And when carbon powder is laid in the steel ladle in advance, argon is blown out for purging, so that the ventilation effect of the steel ladle is ensured, and molten steel splashing accidents caused by the condition that the carbon powder is prone to the bottom are prevented.
When tapping for 20t, adding silicon calcium barium into the ladle, wherein the addition amount is controlled to be 60 Kg; adding the residual carbon powder according to the lower limit of the components after adding the silicon-calcium-barium; adding aluminum ingot after adding carbon powder, wherein the adding amount of the aluminum ingot is controlled according to the tapping C content, 90Kg of the aluminum ingot is added when the tapping C content is 0.25-0.30 wt%, and 80Kg of the aluminum ingot is added when the tapping C content is more than 0.30 wt%;
when tapping 40t, adding alloy into the ladle, wherein the addition amount of the alloy is controlled according to the lower limit of the composition; lime is added after the alloy is added, and the addition amount of the lime is 600Kg.
And before tapping 70t, all slag materials are completely added, argon is reduced to ensure micro-motion of the slag surface, and secondary oxidation caused by contact of molten steel with air is prevented.
Example 3
The present embodiment differs from embodiment 1 or embodiment 2 only in that the refining step of this embodiment is:
the refining step comprises LF refining and RH vacuum circulation degassing refining, wherein the total time of LF refining is not less than 50min, and the holding time of white slag is not less than 30min.
LF refining adopts a three-time power transmission method, the first power transmission is performed during refining, the power transmission is performed for 5 minutes, 200Kg lime is added, 20Kg aluminum particles, 20Kg silicon carbide and 10Kg carbon powder are adopted for diffusion deoxidation, 100Kg lime is added during 9 minutes of power transmission, 10Kg aluminum particles, 20Kg silicon carbide and 10Kg carbon powder are adopted for diffusion deoxidation, the slag white sampling temperature is not lower than 1530 ℃, and meanwhile, the first sampling is performed.
The second power transmission, when the Al content is equal to or less than 0.040wt%, recovering the Al by 100% by using an aluminum wire, and adjusting the Al content to 0.040wt%; and (3) maintaining white slag operation after sampling, performing diffusion deoxidation by adopting 20Kg of silicon carbide and 10Kg of carbon powder, adjusting components to internal control requirements, controlling secondary power transmission time to be 10min, and controlling the temperature to be not lower than 1550 ℃.
And thirdly, power is transmitted, the heating speed is controlled according to the production rhythm, 10-20 Kg of silicon carbide is added to keep the white slag effect, when the temperature of molten steel reaches the outlet temperature, power is cut off, and the process enters the next working procedure to carry out RH vacuum circulation degassing refining.
The ring flow rate of RH vacuum circulation degassing refining is 1800-2000L/min, the vacuum degree in the target 5min is below 67Pa, and the soft blowing time is not less than 25min.
In the embodiment, the LF refining adopts a three-time power transmission method, and sampling and verifying components are carried out, so that the temperature of molten steel is effectively controlled, the refining process is more stable, and favorable conditions are provided for the molten steel to enter the next working procedure. And controlling the temperature rise of the molten steel according to the power supply time, effectively controlling the molten steel not to be oxidized secondarily to form excessive inclusions, and avoiding affecting the purity of the molten steel.
The vacuum and soft blowing time can ensure that inclusions in steel float up sufficiently and the purity of molten steel is ensured.
Example 4
The difference between this embodiment and embodiment 1, embodiment 2 or embodiment 3 is only that the continuous casting step of this embodiment is:
the continuous casting step adopts arc six-machine six-stream continuous casting with the radius of 10m to produce 200 x 200 square, the size of a tundish is 40t, and the casting liquid level is controlled to be above 850 mm.
Argon blowing operation is carried out on the tundish before continuous casting production, so that the oxygen content in the tundish is reduced, and the secondary oxidation of molten steel is reduced. During the casting process, the double argon seals are used for protecting the casting long nozzle, so that secondary oxidation of molten steel is prevented, foreign matters formed by contact of the molten steel and air are prevented to the greatest extent, the molten steel is polluted, and the purity of the final molten steel is influenced. The baking time of the tundish is more than or equal to 5 hours, the temperature of the tundish is more than or equal to 1050 ℃, and the temperature drop of molten steel caused by heat absorption in the middle is reduced, so that the success rate of casting is improved.
The continuous casting adopts constant temperature constant pull rate: the drawing speed and the temperature are important factors for controlling the quality of the casting blank, the composition segregation of the casting blank is reduced through the control of the superheat degree and the drawing speed, the terminal solidification position is stabilized, and the quality of the casting blank reaches the expected effect through matching with soft reduction. In this example, the continuous casting drawing speed is set to be 1.30m/min according to the superheat degree of 25-30 ℃.
As the natural separation and crystallization result in the solidification process, the casting blank can cause the segregation of components in the solidification process, so the reasonable control of cooling is an important means for solving the segregation of the casting blank. If the secondary cooling strength is insufficient, the casting blank has large tempering, and the columnar crystals are easy to cause bulging and sinking of the casting blank due to continuous expansion of volume expansion in the growth process, so that the corner crack defect is generated. If the secondary cooling strength is too high, columnar crystals of the casting blank are developed in the solidification process, and the uniformity of internal tissues and components of the casting blank, even the crystal penetration, is affected. So that the cooling strength is enough and the cooling water quantity is reasonably distributed. In the embodiment, the specific water quantity is set to be 0.53Kg/t, the distribution ratio is 36/39/25%, and the defect of subcutaneous cracks caused by casting blank tempering in the casting process is prevented.
Electromagnetic stirring is used as an important technology for improving the segregation index of a casting blank at present, and on one hand, the thermodynamic and kinetic conditions of inhibiting the development of columnar crystals, promoting component uniformity and floating and refining of inclusions are inhibited, so that the solidification structure of the casting blank is controlled, and the quality of the casting blank is improved. On the other hand, the flow of molten steel is increased, the heat transfer between solidification phases is improved, the superheat degree is reduced, the temperature gradient of the solidification front is reduced, and the directional increase of columnar crystals is restrained. The surface temperature of the casting blank is controlled to return to the temperature, so that the casting blank is in a certain temperature return range, and the repeated return of Wen Zaocheng thermal stress of molten steel is prevented from being overlarge. In the embodiment, the parameters of the head-end electromagnetic stirring are 150A/2Hz, the stirring intensity is controlled at 350.3Gs, and the stirring mode is continuous stirring; the parameters of the terminal electromagnetic stirring are 350A/10Hz, the stirring mode is continuous, and the stirring position is at the position of the arc radius of the continuous casting machine of 9.5 m.
The light reduction can play an important role, considering the stability in the continuous casting production process, setting 2 frames to be light reduction while the high pulling speed is 1.30m/min, and setting 2 frames to be heavy reduction, so that the final terminal solidification position influenced by the change of the molten steel temperature can be effectively controlled, the total reduction is properly increased to compact shrinkage cavities, the internal quality of casting blanks is more stable, and the occurrence probability of shrinkage cavities is reduced. The parameters for tip light depression in this example were 2/3/5/5, total depression 15mm.
Example 5
The preparation method of the 200-square continuous casting blank for the bearing steel wire rod provided by the embodiment comprises a primary smelting step, a refining step and a continuous casting step.
The primary smelting step adopts a converter or an electric furnace for smelting, and the specific preparation method comprises the following steps:
82+ -2 tons of molten iron and 25+ -2 tons of scrap are charged into the primary smelting furnace, and the scrap is required to be mainly by weight, and inferior scrap containing Ti, slag iron and the like is forbidden to be used. The molten iron comprises the following components in percentage by mass: c is more than or equal to 4.0 percent, si:0.30 to 0.60 percent, S is less than or equal to 0.040 percent, ti is less than or equal to 0.060 percent, P is less than or equal to 0.080 percent, the balance is Fe and unavoidable impurities, and the temperature of molten iron is controlled to be more than or equal to 1300 ℃.
The batching method of the embodiment can ensure that the tapping amount is 100t, the tapping requirement meets the production requirement, the primary smelting task is finished to the maximum extent, the consumption of steel and iron materials is reduced, and the in-place components are ensured to provide favorable conditions for refining.
The tapping of the final point of the primary smelting furnace is more than or equal to 0.25wt percent and less than or equal to 0.30wt percent, the peroxidation of tapping is prevented, P is less than or equal to 0.010 percent, and the tapping temperature is 1620-1640 ℃. The tapping hole is controlled between 50 and 120 heats, the tapping time is more than 150 seconds, the tapping speed is controlled to be 2 to 5 minutes, and the secondary oxidization of molten steel caused by the contact of the molten steel and air is reduced.
In the embodiment, a 100-ton A-type ladle is adopted as a turnover ladle, and carbon powder is paved at the bottom of the ladle before tapping. The addition amount of the carbon powder is that 200Kg of carbon powder is paved at the bottom of the ladle before tapping according to 20 percent of the carbon content in the steel type components.
When tapping for 20t, adding silicon calcium barium into the ladle, wherein the addition amount is controlled to be 60 Kg; adding the residual carbon powder according to the lower limit of the components after adding the silicon-calcium-barium; adding aluminum ingot to carry out precipitation deoxidation after adding carbon powder, wherein the adding amount of the aluminum ingot is controlled according to the content of tapping C, and the content of tapping C is 0.25-0.30 wt%, so that 90Kg of the aluminum ingot is added;
when tapping 40t, adding alloy into the ladle, wherein the addition amount of the alloy is controlled according to the lower limit of the composition; the alloy is baked in advance by using low-titanium high-chromium, high-carbon ferromanganese, ferrosilicon and low-titanium low-nitrogen carburant, so that the heat loss of molten steel is reduced when the alloy contacts the molten steel, the yield of the alloy is improved to the maximum extent, and the cost is reduced. The alloy is added along with the steel flow, so that slag charge and alloy crust are not prevented, and qualified molten steel is provided for a refining position LF.
Lime is added after the alloy is added, the addition amount of the lime is 600Kg, and the good slag melting and no crust formation are ensured.
And before tapping 70t, all slag materials are completely added, argon is reduced to ensure micro-motion of the slag surface, and secondary oxidation caused by contact of molten steel with air is prevented. And (3) lifting the steel ladle to a refining position within 10 minutes after tapping to heat and slag, so as to prevent secondary oxidation of molten steel caused by overlong waiting time at the tapping position.
The refining step of this example includes LF refining and RH vacuum cycle degassing refining. The LF refining total time of this example was 60min and the white slag holding time was 45min.
The LF refining of the embodiment adopts a three-time power transmission method, and the specific operation method is as follows:
the first power transmission is carried out for 5 minutes, 200Kg lime is added, 20Kg aluminum particles, 20Kg silicon carbide and 10Kg carbon powder are adopted for diffusion deoxidation, 100Kg lime is added for 9 minutes, 10Kg aluminum particles, 20Kg silicon carbide and 10Kg carbon powder are adopted for diffusion deoxidation, the slag white sampling temperature is not lower than 1530 ℃, and meanwhile, the first sampling is carried out.
The second power transmission, when the Al content is equal to or less than 0.040wt%, recovering the Al by 100% by using an aluminum wire, and adjusting the Al content to 0.040wt%; and (3) maintaining white slag operation after sampling, performing diffusion deoxidation by adopting 20Kg of silicon carbide and 10Kg of carbon powder, adjusting components to internal control requirements, controlling secondary power transmission time to be 10min, and controlling the temperature to be not lower than 1550 ℃.
And thirdly, power is transmitted, the heating speed is controlled according to the production rhythm, 15Kg of silicon carbide is added to keep the white slag effect, power is cut when the temperature of molten steel reaches the outlet temperature, the temperature loss caused by vacuum of the molten steel is reserved in advance, and the process enters the next working procedure to carry out RH vacuum circulation degassing refining.
The specific operation method of RH vacuum circulation degassing refining in the embodiment is as follows:
the molten steel reaches a designated station to start vacuum circulation degassing, the number of the converter tubes is not less than 8, the annular flow is 1800-2000L/min, the vacuum degree reaches below 67Pa within 5min, and the soft blowing time is 30min.
According to the embodiment, 1-fire lumber formation is realized through control of the technological parameters of the smelting part, the process flow is shortened, and the cost is reduced.
The operation method of the continuous casting step of the embodiment is as follows:
in the continuous casting step of the embodiment, 200 x 200 square arc six-machine six-strand continuous casting with the radius of 10m is used for production, the size of a tundish is 40t, the casting liquid level is controlled to be above 850mm, and the larger tundish can effectively control and shunt molten steel and can float redundant inclusions in the molten steel.
The casting specification of the embodiment is 200mm by 200mm, the pulling speed is 1.30m/min, the specific water quantity is 0.53kg/t, and the distribution ratio is 36/39/25%; the initial stirring parameter is 150A/2Hz, the final stirring parameter is 350A/8Hz, the final soft reduction parameter is 3/4/5/5, and the total reduction is 15mm.
According to the embodiment, the continuous casting drawing speed is set to be 1.30m/min according to the superheat degree of 25-30 ℃, the constant drawing speed is ensured to finally realize the accuracy of the terminal solidification position, the setting is carried out according to the arc radius of continuous casting and the straightening temperature, the terminal solidification coefficient under light reduction can be ensured to be 0.3-0.9, and therefore the terminal electromagnetic stirring and light reduction technology can be completed to the maximum extent, and the expected effect is exerted.
The pouring temperature is strictly controlled in the pouring process, the constant temperature and the constant speed are ensured, the immersion depth of the water gap of the continuous casting crystallizer is controlled to be 120+/-10 mm, the middle liquid level is controlled to be more than 850mm, the quality of a final product is prevented from being influenced by molten steel slag, and the internal quality and the uniformity of components of a casting blank can be effectively controlled.
The amount of water in the continuous casting mold of this example: crystallizationThe water gap of the tooling is controlled to be 4+/-0.2 mm, the chromium coating on the inner wall of the copper pipe is good, the water inlet pressure of the crystallizer is controlled to be more than 0.90Mpa, and the water flow of the crystallizer is controlled to be 120m 3 The water flow rate of the crystallizer is controlled at 9.0m/s per min, and the water inlet temperature difference of the crystallizer is controlled at 6+/-0.2 ℃. Ensuring that the cooling of the crystallizer is uniform for 1 time, reducing the risk of cracks of casting blanks, weakening the cooling of the crystallizer for 1 time, ensuring that the cooling is more uniform and preventing the occurrence of subcutaneous crack defects.
And (3) secondary cooling, namely, stable pouring pull speed of 1.30m/min by using a dynamic distribution ratio, and distribution by using 7-section spray rings, wherein the proportion is 36/39/25%, so that the uniform tempering of the casting blank in a secondary cooling section is ensured, and the defect of subcutaneous cracks caused by generated thermal stress is prevented.
The electromagnetic stirring at the head end of the embodiment is set at 150A/2Hz, the stirring intensity is controlled at 350.3Gs, the stirring mode is continuous stirring, the proper increase of the stirring intensity can effectively control the decrease of the superheat degree of the molten steel of the crystallizer, and simultaneously promote the growth of a chilled layer, and the smaller stirring intensity controls the segregation index at the 1/2 position of the casting blank between 0.95 and 1.05, so that the component uniformity of the casting blank is completed.
In this embodiment, the terminal electromagnetic stirring is set at 350A/10Hz, the stirring mode is continuous, and the stirring position is at the position of the arc radius of the continuous casting machine of 9.5m, so that the terminal electromagnetic stirring has the expected effect.
In the embodiment, 2 frames are set to be under light pressure while the high pulling speed is 1.30m/min, and 2 frames are set to be under heavy pressure, so that the final terminal solidification position influenced by the change of the molten steel temperature can be effectively controlled, the total reduction is properly increased to compact shrinkage cavities, the internal quality of a casting blank is more stable, and the occurrence probability of shrinkage cavities is reduced. The end soft reduction parameter of this example is 2/3/5/5, total reduction 15mm.
Surface quality verification is carried out on the obtained continuous casting blank, and FIG. 1 is a surface quality photo of a spliced low-power sample obtained by cutting 6 continuous casting billets obtained by arc six-machine six-stream continuous casting according to the invention after hot pickling; as shown, the low-power sample cut from the continuous casting billet was hot pickled without surface crack defects.
Carrying out appearance dimension quality verification on the obtained continuous casting blank, and FIG. 2 is a photograph of the measurement result of the appearance dimension of 6 continuous casting billets obtained by arc six-machine six-stream continuous casting; as shown, the split was measured for low profile dimensions, with 184mm in each vertical plane. Differing by 1mm from the set total depression of 15mm. The cross section is slightly affected by light depression and has slight bulge defect which is not more than 3mm. The difference in diagonal measurements does not exceed 2mm. The outline dimension of the casting blank meets the set target value.
Performing low-power quality verification on the obtained continuous casting blank, sampling and verifying the full-flow coverage of the wheel, checking 30 low-power samples in total, and taking photos of 6 transverse low-power samples of the continuous casting square blank obtained by arc six-machine six-flow continuous casting according to the invention as shown in figures 3-8; the test results show that the water quantity of the crystallizer is reduced to 120m 3 After/h, the angle crack defect of the casting blank is obviously improved, the porosity of the low-power maximum rating center is 1 level, and the rest defects are not found on the low power. Fig. 9 is a photograph of a longitudinal low-power sample of 6 continuous casting billets obtained by arc six-machine six-stream continuous casting, and the improvement effect of the reduction cracks and the central shrinkage holes is obvious after the process parameters are optimized as shown in the figure.
And (3) carrying out overall segregation index quality verification on the obtained continuous casting blank, and respectively selecting low-power samples for S1 flow-S6 flow to carry out full-point segregation test. The overall segregation index was well controlled, but there were still individual points beyond the standard requirements, and the specific test results are shown in table 1.
TABLE 1
| Part(s) | Highest to | Lowest minimum | Average of |
| S1 | 1.041 | 0.918 | 1.004 |
| S2 | 1.081 | 0.938 | 0.999 |
| S3 | 1.051 | 0.938 | 0.998 |
| S4 | 1.041 | 0.939 | 0.989 |
| S5 | 1.020 | 0.918 | 0.992 |
| S6 | 1.061 | 0.950 | 0.994 |
As is clear from the data in Table 1, the overall segregation index of the cast slab obtained in this example was controlled to be 0.95 to 1.08.
Claims (4)
1. The preparation method of the 200-square continuous casting blank for the high-quality and high-homogeneity bearing steel wire rod comprises a primary smelting step, a refining step and a continuous casting step, and is characterized in that the content of tapping C in the primary smelting step is not less than 0.25wt%, the tapping temperature is 1620-1640 ℃, the tapping hole heat is less than or equal to 120 times, and calcium silicate barium, carbon powder, aluminum ingots, alloys and lime are sequentially added into a steel ladle in the tapping process; after carbon powder is added when the adding time of the aluminum ingot is 20-t of tapping, controlling the adding amount of the aluminum ingot according to the content of tapping C, adding 90kg of the aluminum ingot when the content of tapping C is 0.25-0.30wt%, and adding 80kg of the aluminum ingot when the content of tapping C is more than 0.30wt%;
the tapping amount in the primary smelting step is calculated according to 100 tons, the proportion of slag and the adjustment of molten steel components are carried out according to requirements, and the concrete method comprises the following steps:
when the adding time of the silicon calcium barium is 20kg t of tapping, controlling the adding amount to be 60 kg;
the adding time of the carbon powder is 20t before tapping and when tapping, wherein 200kg of carbon powder is paved at the ladle bottom according to the adding amount of the carbon powder before tapping, which is 20% of the carbon content in the steel type components; the addition amount of carbon powder is controlled to be thrown in one time according to the lower limit of the composition when tapping 20 t;
when the adding time of the alloy is 40t of tapping, the adding amount is controlled according to the lower limit of the composition;
the lime is added for 40-t of tapping, and the addition amount is 600kg after the alloy is added;
the refining step comprises LF refining and RH vacuum circulation degassing refining, wherein the LF refining adopts a three-time power transmission method, LF refining is powered for the first time, power transmission is carried out for 5 minutes, 200kg lime is added, 20kg aluminum particles +20kg silicon carbide + kg carbon powder is adopted for diffusion deoxidation, 100kg lime is added, 10kg aluminum particles +20kg silicon carbide + kg carbon powder is adopted for diffusion deoxidation in 9 minutes, the slag white sampling temperature is not lower than 1530 ℃, and meanwhile, the first sampling is carried out;
carrying out LF refining for the second time, when the Al content is equal to or less than 0.040wt%, recovering the Al by 100% by using an aluminum wire, and adjusting the Al content to 0.040wt%; after the first sampling, maintaining white slag operation, performing diffusion deoxidation by adopting 20kg of silicon carbide and 10kg carbon powder, adjusting components to internal control requirements, controlling the secondary power transmission time to be 10min, and controlling the temperature to be not lower than 1550 ℃;
LF refining is carried out for the third time, the heating speed is controlled according to the production rhythm, 10-20 kg of silicon carbide is added to keep the white slag effect, when the temperature of molten steel reaches the outlet temperature, power is cut off, and the next procedure is carried out for vacuum operation of the molten steel;
the total LF refining time is not less than 50min, and the white slag holding time is not less than 30min;
the continuous casting step ensures constant temperature and constant speed blank drawing, the continuous casting drawing speed is set to be 1.30m/min according to the superheat degree of 25-30 ℃, the specific water quantity is set to be 0.53kg/t, the distribution ratio is 36/39/25%, and 200 square continuous casting blanks are finally obtained by matching with continuous casting crystallizer stirring, head end electromagnetic stirring, tail end electromagnetic stirring and tail end light pressing;
the bearing steel comprises the following chemical components in percentage by weight: c: 0.96-0.99%, si:0.18 to 0.22 percent of Mn:0.26 to 0.30 percent, less than or equal to 0.015 percent of P, less than or equal to 0.005 percent of S, and Cr:1.43 to 1.47 percent of Al: 0.010-0.015%, ti less than or equal to 0.0015%, and the balance of Fe and unavoidable impurities.
2. The method for preparing the 200-square continuous casting blank for the high-quality and high-homogeneity bearing steel wire rods, which is disclosed in claim 1, is characterized in that the ring flow rate of RH vacuum circulation degassing refining is 1800-2000L/min, the vacuum degree in a target 5min is less than 67Pa, and the soft blowing time is not less than 25min.
3. The method for preparing 200 square continuous casting billets for high-quality and high-homogeneity bearing steel wire rods, according to claim 2, wherein the continuous casting step is carried out by adopting arc six-machine six-strand continuous casting 200 x 200 square with the radius of 10m, the size of a tundish is 40t, and the casting liquid level is controlled to be above 850 mm.
4. The method for preparing 200 square continuous casting billets for high-quality and high-homogeneity bearing steel wire rods, according to claim 3, wherein the parameters of the electromagnetic stirring at the head end of the electromagnetic stirring in the continuous casting step are 150A/2Hz, the stirring intensity is controlled at 350.3Gs, and the stirring mode is continuous stirring; the parameters of the electromagnetic stirring at the tail end are 350A/10Hz, the stirring mode is continuous, and the stirring position is at the position of the arc radius of the continuous casting machine of 9.5 m; the parameters of the tip light depression are 2/3/5/5, and the total depression is 15mm.
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