Smelting method of electromagnetic pure iron for scanning electron microscope electromagnetic lens

Abstract

A smelting method of electromagnetic pure iron for an electromagnetic lens of a scanning electron microscope comprises the steps of KR desulfurization, BOF converter treatment, LF refining, RH vacuum treatment, bloom continuous casting, blank cogging inspection and coping and rolling, and the KR desulfurization adopts a deep desulfurization mode; aluminum particles and lime are sequentially added during converter tapping, and a low-carbon steel slag surface deoxidizing agent is added to the slag surface after tapping is finished; aluminum particles are continuously added in LF refining, and meanwhile calcium carbide and a low-carbon steel slag surface deoxidizing agent are added; a deep decarburization treatment mode is adopted for oxygen blowing forced decarburization in RH vacuum treatment, the addition amount of aluminum particles is controlled according to the oxygen content of molten steel after decarburization is finished, vacuum breaking and steel tapping are conducted after net circulation treatment, a low-carbon steel slag surface deoxidizer is added to the slag surface in the RH vacuum breaking process, and the steel is fed into a continuous casting platform after tapping; and casting is protected in the whole process during bloom continuous casting. According to the method provided by the invention, the inclusion control level of the steel can be ensured under the condition of a relatively high scrap steel ratio, and the situation that the steel wire is not broken due to the inclusion when the steel wire is drawn to be below 0.4 mm is ensured.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of production process in metallurgical industry, and particularly relates to a smelting method of electromagnetic pure iron for scanning electron microscope electromagnetic lens. BACKGROUND

[0002] In the electromagnetic lens system of scanning electron microscope (SEM), electromagnetic pure iron (also known as electrical pure iron or industrial pure iron) is widely used as core magnetic conductive material due to its excellent soft magnetic characteristics and high cost performance. The electromagnetic pure iron belongs to a kind of low carbon steel, the iron content of which is usually 99.50% to 99.90%, the carbon content is strictly controlled below 0.04%, and the content of other impurity elements (such as S, P, O, N, etc.) is as low as possible. Since the purity of the material has not reached the high-purity iron standard of 99.90% to 99.95%, it is still classified as "industrial pure iron" in industry.

[0003] Industrial pure iron has soft texture, high toughness and excellent electromagnetic performance. There are two common uses, one is as deep drawing material, which can be stamped into extremely complex shapes, and the other is as electromagnetic material, i.e. electromagnetic pure iron. The largest amount of industrial pure iron is electromagnetic pure iron, which accounts for about 80%.

[0004] Electromagnetic pure iron has high magnetic susceptibility and low magnetic resistance, and is widely used in electronic and electrical industry, electrical components, magnetic materials, amorphous products, relays, sensors, automobile brakes, textile machines, ammeter electromagnetic valves and other high-precision electromagnetic component products. Its melting point is higher than that of cast iron, it is more difficult to rust than cast iron in humid air, and it can be passivated in cold concentrated sulfuric acid, further widening its industrial applicability.

[0005] From the perspective of electromagnetic performance, the higher the purity of the material, the better the electromagnetic performance. However, the preparation process of high-purity iron (such as more than 99.99%) is complex and the cost is high, which is difficult to be applied on a large scale. Therefore, in industrial production, the smelting mode of molten iron + sponge iron is generally adopted to reduce the influence of residual elements caused by scrap steel. In addition, by adding aluminum, a strong oxidizing element, to deoxidize during smelting, the oxygen content in the molten steel is reduced, and the adverse effects of other impurities on magnetic properties are weakened. However, this method introduces Al2O3 non-metallic inclusions during smelting, which causes the ultra-fine wire to break due to stress concentration during subsequent ultra-fine wire drawing (such as below), seriously affecting the product qualification rate.

[0006] In addition, the electromagnetic lens of scanning electron microscope has very high requirements for material uniformity. If there are micron-level inclusions in the ultra-fine wire, not only the drawing yield will be reduced, but also the magnetic properties of the final device will be affected, which will further lead to the decline of SEM imaging resolution. Therefore, how to effectively reduce the influence of inclusions on ultra-fine wire processing while ensuring the excellent magnetic properties of electromagnetic pure iron has become a technical problem to be solved in the field. SUMMARY

[0007] The technical problem solved by the present application is that the present application provides a smelting method of electromagnetic pure iron for scanning electron microscope electromagnetic lens, which can ensure the control level of inclusions in steel and ensure that the steel wire is not broken due to inclusions when drawn to below 0.4 mm.

[0008] Technical solution: A smelting method of electromagnetic pure iron for scanning electron microscope electromagnetic lens, the method comprises: KR desulfurization-BOF converter-LF refining-RH vacuum treatment-large square billet continuous casting-billet blooming inspection and grinding-rolling, specifically comprising the following steps:

[0009] Step one, KR desulfurization: desulfurizing the molten iron by KR;

[0010] Step two, BOF converter: scrap steel and desulfurized molten iron are charged into the BOF converter, aluminum particles and lime are added in sequence when the converter is tapped, and a low-carbon steel slag surface deoxidizer is added to the slag surface after tapping to pre-deoxidize, the tapping temperature of the molten iron is 1600-1650℃, and the molten steel is transported to the LF refining treatment through the ladle after tapping;

[0011] Step three, LF refining: continue to add aluminum particles to deoxidize the molten steel, and add calcium carbide and low-carbon steel slag surface deoxidizer to deoxidize the molten steel and increase the temperature of the molten steel, the liquidus temperature is 1535℃, the tapping temperature after LF refining is required to be 1670±8℃ for the first furnace, and the continuous casting tapping temperature is 1660±8℃, the temperature is up to standard, and the molten steel is transported to the RH vacuum treatment;

[0012] Step four, RH vacuum treatment: RH inlet temperature ≥1650℃, RH inlet rapid vacuum treatment, the treatment sequence includes oxygen blowing forced decarburization-quantitative deoxidization-net circulation-break, the oxygen blowing forced decarburization adopts deep decarburization treatment mode, the aluminum particle addition amount is controlled according to the oxygen content of the molten steel after decarburization, and the molten steel is broken and tapped after net circulation treatment, the low-carbon steel slag surface deoxidizer is added to the slag surface during the RH breaking process, and the molten steel is sent to the continuous casting platform after tapping, the RH liquidus temperature is 1535℃, the tapping temperature of the first furnace is 1620±8℃, and the continuous casting tapping temperature is 1610±8℃;

[0013] Step five, large square billet continuous casting: during continuous casting, a large ladle long nozzle and argon sealing, an integral submerged entry nozzle, an ultra-low carbon silicon steel tundish covering agent, argon blowing in the tundish for 3-5 minutes before casting, and full-process protection casting are adopted, the liquidus temperature is 1535℃, the tundish molten steel temperature is 1560-1575℃, and the continuous casting speed is controlled at 0.65±0.02 m / min;

[0014] Step six, billet blooming inspection and grinding, control the surface quality;

[0015] Step seven, the blank after grinding is rolled.

[0016] As preferred, in the step two, the total amount of scrap steel and molten iron is 146±4t, wherein the molten iron is 120±2t and the scrap steel is 26±2t, the scrap steel is clean scrap steel, and the content of elements other than iron in the molten iron before desulfurization treatment is as follows in percentage by mass: Si: 0.35-0.75wt%, Mn≤0.25%, P≤0.11%, S≤0.045%, Ti≤0.06%; after desulfurization treatment, the temperature of the molten iron is >1300℃, the content of S is ≤0.002%, and the slag skimming rate is ≥98%.

[0017] As preferred, in the step two, the target slag basicity R of the slag at the end of the tapping of the converter is 3.5, the content of MgO is controlled at 8-10%, the content of C is controlled at below 0.05%, and the contents of P and S are both controlled at below 0.01%; the adding amount of the aluminum grain at the time of tapping is 1-1.5kg / t, the adding amount of the lime is 300kg, and the adding amount of the low-carbon steel slag surface deoxidizer is 50-100kg.

[0018] As preferred, in the step two, at the time of tapping of the converter, the bottom argon blowing of the ladle is started, the pressure is controlled at 0.5-0.7MPa in the early stage before tapping, and the argon blowing pressure is adjusted to 0.4-0.6MPa after 3 / 4 of the tapping.

[0019] As preferred, in the step three, at the time of LF refining, after the ladle is in place, the bottom argon blowing is connected and started, the stirring is strong for 2-3min, the power is on for 4-5min, the oxygen is fixed and the temperature is measured, the aluminum grain is added according to the content of oxygen in the molten iron for deoxidization, the content of Al in the refined molten iron is controlled at 0.015-0.025%, the molten iron is deoxidized to form white slag by using calcium carbide and low-carbon steel slag surface deoxidizer, the lime and fluorite are added for adjustment, and the T.Fe+MnO in the slag at the time of refined tapping is ≤1.5%.

[0020] As preferred, in the step four, the temperature of the vacuum chamber is ≥1200℃; the temperature of the molten iron at the time of starting pouring is ≥1665℃ for the first furnace and ≥1655℃ for the second furnace; at the time of RH vacuum treatment, the C content is ≤20ppm after RH decarburization, the amount of C added after RH deoxidization is less than 5ppm, and the C content is ≤30ppm at the time of RH tapping.

[0021] As preferred, in the step four, at the time of RH vacuum treatment, the vacuum is drawn to a degree of 200mbar, the oxygen blowing is started, the flow rate of the oxygen blowing is 1800Nm 3 / h, after the oxygen blowing is finished, the vacuum degree is reduced to below 2mbar, the cycle is more than 10min, and the forced decarburization amount by RH oxygen blowing is as follows: when the C content at the time of entering the station is 0.02-0.025%, the amount of oxygen blowing is 90-100Nm 3 , for each increase or decrease of 0.005% of the C content of the molten iron at the time of entering the station, the amount of oxygen blowing is increased or decreased by 10Nm3 The basic addition amount of aluminum particles is 10kg. For every 0.01% increase in oxygen content in molten steel, the amount of Al added increases by 14kg. At the end of deoxidation, Al is less than 0.005%. The addition amount of low-carbon steel slag surface deoxidizer is 100-150kg. When adding, spread the low-carbon steel slag surface deoxidizer evenly on the slag surface to ensure that T.Fe in the slag is ≤3%.

[0022] Preferably, the step four further includes calcium treatment, soft stirring and insulation. Calcium treatment is performed after RH is broken, and pure calcium wire is fed. The wire feeding amount of the open pouring furnace is 150-200m, and the wire feeding amount of the continuous pouring furnace is 100-150m. The bottom blowing flow rate during calcium treatment is 300-400NL / min. Soft stirring is performed after the wire feeding is completed. The soft stirring time after calcium treatment is ≥5min, and the slag surface fluctuates slightly, the molten steel is not exposed, and the slag layer is not damaged. After confirming that the soft stirring standard is met, ash-treated rice husks are added for insulation, and the entire slag surface is required to be covered and spread evenly.

[0023] Preferably, in the step five, ultra-low carbon steel protection slag is used during continuous casting, and the slag is added according to the principle of frequent, small and uniform addition to maintain the black slag state; the weight of molten steel in the tundish is not less than 25t when pouring starts, the weight of molten steel is not less than 33t when changing the ladle, and the weight of molten steel is not less than 40t during normal pouring; the crystallizer liquid level is set to 80-90%, the crystallizer liquid level fluctuation is controlled within ±3%, and the crystallization water flow rate is 3000±25L / min; the crystallizer electromagnetic stirring current is 650±5A, and the frequency is 1.5±0.5Hz; soft pressure parameter control: using the MSR soft1-13 mm model; the scrap length of the head billet is not less than 4 meters, the scrap length of the tail billet is not less than 2.5 meters, and the head and tail billets are cut and scrapped.

[0024] Beneficial effects: The present invention strengthens the oxygen blowing operation of the converter to remove the carbon, silicon, manganese, phosphorus and other elements in the converter to the lowest possible level, and then produces white steel through the converter and adds an appropriate amount of aluminum particles for pre-deoxidation. During LF refining, aluminum particles are continued to be added for deoxidation, while calcium carbide and slag surface deoxidizer are added to continue deoxidizing the molten steel and increase the temperature of the molten steel. The RH vacuum treatment process adopts a deep decarburization mode to further reduce the carbon content in the molten steel. When the carbon content is in place, the air is broken and an appropriate amount of aluminum particles and slag surface deoxidizer are continued to be added for deoxidation. The continuous casting adopts full-protection casting, so that the final product can ensure the level of steel inclusion control under the condition of 18% scrap steel ratio, and ensure that the steel wire is not broken due to inclusions when it is drawn to below 0.4mm. DETAILED DESCRIPTION

[0025] The present invention will be further described below with reference to specific embodiments.

[0026] Unless otherwise specified, all percentages in the examples of this specification are by mass.

[0027] The raw materials in the embodiments of the present specification are all from ordinary commercially available products unless otherwise specified, wherein:

[0028] Aluminum particles: Al: ≥99.20%; size requirement: Height: 7-13 mm, single size quantity compliance rate ≥90%.

[0029] Lime: CaO≥92%, MgO<5%, SiO2≤1.5%, S≤0.020%, ignition loss≤2, activity≥360, particle size range 5-35 mm.

[0030] Low-carbon steel slag surface deoxidizer: Al: ≥25%; Al2O3: 12-20%; CaO: (16-24)%; CaF2: 17-23%; SiO2: ≤8%; H2O: ≤1%; particle size: (15-35) mm.

[0031] Calcium carbide: particle size: 2.5-15 mm; gas evolution: ≥280 L / kg.

[0032] Fluorite: CaF2: ≥90%; SiO2: ≤9.3%; S: ≤0.1%; P: ≤0.06%; H2O: ≤0.5%; radiation value: ≤250 nsv / h; particle size: 0.5-2 mm.

[0033] Ashed rice husk: C: TC≤0.5%; H2O: ≤0.5%; self-ignition bulk density: ≤280 g / dm^3; particle size: non-caking, good spreading.

[0034] Ultra-low-carbon special protective slag (ultra-low-carbon steel protective slag): basicity (R): 0.81±0.06; melting point: 1170±30; moisture: ≤0.5%.

[0035] Ladle: carbon-free ladle, MgO≥85%, C≤7%, bulk density≥3.07 g / cm 3 , apparent porosity≤5%, cold compressive strength (110℃×24h)≥45 MPa, 180t carbon-free ladle slag line brick, MgO≥85%, C≤7%, bulk density≥3.07 g / cm 3 , apparent porosity≤5%, cold compressive strength (110℃×24h)≥45 MPa.

[0036] Tundish: MgO≥86%, SiO2content≤7%, Al2O3≤2%, bulk density≥1.8 (110℃×16h), permanent line change-4-0%.

[0037] Example 1 produces SGM6D (Shangang carbon content of 0.006% or less pure iron)

[0038] Component requirements:

[0039] ％ C Si Mn P S Cr Ni Cu Al N Target value ≤0.005 ≤0.05 ≤0.01 - Upper limit value 0.006 0.010 0.08 0.012 0.010 0.05 0.05 0.05 0.005 0.005 Lower limit value

[0040] Note: the rest is Fe.

[0041] The present embodiment is a smelting method of electromagnetic pure iron for scanning electron microscope electromagnetic lens, and the process flow comprises: KR desulfurization-BOF converter-LF refining-RH vacuum treatment-large square billet continuous casting-billet breakdown inspection and grinding-rolling, and the specific preparation method is as follows:

[0042] I. KR desulfurization: the molten iron is subjected to KR desulfurization treatment, and the KR desulfurization adopts a deep desulfurization mode;

[0043] Specifically as follows:

[0044] 1.1 loading amount: the total loading amount of molten iron and scrap steel is stabilized at 146±4t, the molten iron is 120±2t, and the scrap steel is 26±2t, and the high-quality scrap steel (Cr≤0.06%, Ni≤0.06%, Cu≤0.05%, Mo≤0.01%, Ti≤0.05%, Sn≤0.015%, Nb≤0.005%, V≤0.05%, Al≤0.05%, S≤0.006%) produced by Shasteel Group is used.

[0045] 1.2 molten iron condition: according to mass percentage, Si%=0.35-0.75%, Mn%=0.25%, P%=0.11%, S%=0.045%, Ti%=0.06%, and the rest is Fe.

[0046] 1.3 molten iron desulfurization: after desulfurization, the temperature of the molten iron is greater than 1300°C, the S% is less than or equal to 0.002%, and the slag skimming rate is greater than or equal to 98%.

[0047] II. BOF converter: the scrap steel and the molten iron after desulfurization treatment are sent into the BOF converter, after the converter blows oxygen, the aluminum particles and lime are added in sequence when the converter is tapped, and after the tapping is finished, the low-carbon steel slag surface deoxidizer is added to the slag surface for pre-deoxidization, the molten iron is tapped at a temperature of 1600-1650°C, and after the tapping is finished, the molten steel is transported through the ladle to the LF refining treatment.

[0048] Specifically as follows:

[0049] 2.1 slag control: the target basicity R of the converter final slag is 3.5, and the MgO is controlled at 8.0-10.0%.

[0050] 2.2 end point control:

[0051] C％ P％ S％ Tapping temperature (°C) Tapping temperature (°C) 0.02-0.05 ≤0.010 ≤0.010 1600-1650 (LF) ≥ 1650 (RH straight up)

[0052] 2.3 tapping operation: the operation is performed in the order of “aluminum ingot→lime→low-carbon steel slag surface deoxidizer”. The aluminum particle addition amount during the tapping process is

[0053] 1.0-1.5kg / t (1t converter tapping total molten steel quality corresponding to the amount of aluminum particles added 1-1.5kg), lime added 300kg (per furnace), and 50-100kg of low-carbon steel slag surface deoxidizer (per furnace) is added to the slag surface at the end of tapping.

[0054] The composition requirement range after converter tapping using aluminum deoxidation is as follows:

[0055]

[0056] 2.4 Bottom argon control: When the converter starts tapping, open the ladle bottom argon blowing, and the pressure is controlled at 0.5-0.7MPa in the early stage of tapping, and the bottom argon pressure is adjusted to 0.4-0.6MPa after 3 / 4 of the tapping.

[0057] III. LF refining: Continue to add aluminum particles for deoxidation in LF refining, and at the same time, add calcium carbide and low-carbon steel slag surface deoxidizer for deoxidation of molten steel and temperature increase, with liquidus temperature of 1535℃. The tapping temperature requirement at the end of LF refining is 1670±8℃ for the first furnace, and 1660±8℃ for continuous tapping. After the temperature meets the standard, tapping is carried out, and it is transported to RH vacuum treatment.

[0058] Specifically as follows:

[0059] 3.1 Argon control: After the ladle is in place, connect and open the bottom argon blowing, and strong stirring for 2-3 minutes.

[0060] 3.2 Refining treatment: After 4-5 minutes of power-on, oxygen is determined and temperature is measured. According to the oxygen content of the molten steel, appropriate amount of aluminum wire is fed for deoxidation to ensure that the [Al] content of the refining tapping is controlled at 0.015-0.025%. At the same time, calcium carbide and low-carbon steel slag surface deoxidizer (reference addition amount 50-100kg) are used for deoxidation of the slag to form white slag, and the state of the slag is observed. Lime and fluorite are added appropriately to fine-tune the slag. During the middle stage of refining, the slag sample is taken and quickly sent to the laboratory for analysis to ensure that the T.Fe+MnO in the refining tapping slag is ≤1.5%.

[0061] 3.3 Temperature control: The tapping temperature requirement at the end of LF refining (liquidus temperature 1535℃) is:

[0062] Ladle condition Tapping temperature of the first furnace (°C) Tapping temperature of continuous casting (°C) Normal continuous casting ladle 1670±8 1660±8

[0063] Note: New ladles or cold ladles must not be used.

[0064] 3.4 Tapping requirement: After the temperature meets the standard, tapping is carried out, and it is transported to RH vacuum treatment.

[0065] 3.5 Slag sampling: The slag sample is taken at the time of LF tapping and sent to the laboratory for analysis in a timely manner to ensure that the T.Fe+MnO in the refining tapping slag is ≤1.5%.

[0066] Four, RH vacuum treatment: RH inlet temperature ≥1650℃, RH inlet rapid vacuum treatment, the treatment sequence includes oxygen blowing forced decarburization-quantitative deoxidation-clean circulation-emptying, oxygen blowing forced decarburization adopts deep decarburization treatment mode, after decarburization, according to the oxygen content of molten steel, the amount of aluminum particles is controlled, after clean circulation treatment, emptying is carried out, during RH emptying process, low-carbon steel slag surface deoxidizer is added to the slag surface, after tapping, it is sent to the continuous casting platform, RH liquidus temperature is 1535℃, the first furnace tapping temperature is 1620±8℃, and the continuous casting tapping temperature is 1610±8℃. The specific is as follows:

[0067] 4.1 Equipment and medium requirements:

[0068] ① The new vacuum chamber and the front 2 furnaces of the immersion tube cannot smelt the steel grade, and after treating the molten steel containing Cr, Ni, Cu and other elements, the tank must be washed before producing copper clad steel. The vacuum chamber roasting temperature is ≥1200℃;

[0069] ② Ensure that C≤20ppm after RH decarburization, and the amount of C returned after RH deoxidation is less than 5ppm, and C≤30ppm after RH tapping.

[0070] 4.2 Inlet temperature and oxygen content requirements

[0071] ① Molten steel inlet temperature: ≥1665℃ for the first furnace, and ≥1655℃ for the continuous casting furnace.

[0072] 4.3 Vacuum treatment

[0073] ① Treatment mode: deep decarburization treatment mode.

[0074] ② Treatment sequence: oxygen blowing forced decarburization→quantitative deoxidation(14kg[Al] / 100ppm[O])→clean circulation→emptying. The molten steel reaches the treatment position according to the sequence of two-stage water ring pump, four-stage, three-stage steam pump rapid vacuum, the vacuum degree is reduced to about 200mbar, then the lance is started to blow oxygen, the oxygen flow is 1800Nm 3 / h, after the oxygen blowing is finished, the vacuum degree is reduced to below 2mbar, and the circulation is carried out for more than 10min, the reference amount of RH oxygen blowing forced decarburization is:

[0075]

[0076] Note: for every 0.005% increase in C content of molten steel at RH inlet, the oxygen blowing amount increases by 10Nm 3 .

[0077] ③ Molten steel deoxidation: after decarburization, the amount of aluminum is accurately controlled according to the oxygen content of molten steel, the basic amount of aluminum is 10kg, after RH decarburization, for every 0.01% increase in O content of molten steel, the reference amount of aluminum is increased by 14kg, and the residual Al is less than 0.005% after deoxidation.

[0078] (iv) Slag surface deoxidation: 100-150 kg of low carbon steel slag surface deoxidizer is added to the slag surface during the RH breaking process, and is evenly spread on the slag surface to ensure that T.Fe in the slag is ≤3%.

[0079] 4.4 Calcium treatment

[0080] Calcium treatment is performed after the RH breaking process, and pure calcium wire (component index: calcium content ≥98%, Ni ≤0.005%, Mn ≤0.02%, Mg ≤0.5%, Al ≤0.8%, Si ≤0.01%; special requirements: diameter 6.9±0.2 mm, weight 58±2 g / m) is fed. The reference wire feeding amount for the tapping furnace is 150-200 m, the reference wire feeding amount for the continuous casting furnace is 100-150 m, the reference flow rate for the bottom blowing during the calcium treatment is 300-400 NL / min, and soft stirring is performed after the wire feeding is completed.

[0081] 4.5 Soft stirring and holding

[0082] The soft stirring time after the calcium treatment is ≥5 min, with a slight fluctuation of the slag surface and no exposure of the molten steel and no damage to the slag layer. After confirming that the soft stirring standard is met, ashed rice husk is added for holding. The ashed rice husk is required to cover the entire slag surface and be evenly spread.

[0083] 4.6 Temperature control

[0084] Liquidus temperature (1535°C)

[0085] Ladle condition Tapping temperature of the first furnace (°C) Tapping temperature of continuous casting (°C) Normal continuous casting ladle 1620±8 1610±8

[0086] Note: 1) The tapping time is 10 minutes from the continuous casting start time. Each 1 minute of advance or delay can reduce or increase the tapping temperature by 0.4°C. 2) The new ladle or cold ladle can be increased by 5-10°C according to the actual situation.

[0087] Five, Bloom Continuous Casting: During continuous casting, a large ladle long nozzle and argon sealing, integral submerged entry nozzle, ultra-low carbon silicon steel tundish covering agent, argon blowing in the tundish for 3-5 min before starting, full- process protective casting, liquidus temperature is 1535°C, tundish molten steel temperature is 1560-1575°C, continuous casting speed control is 0.65±0.02 m / min.

[0088] Specifically as follows:

[0089] 5.1 Protective casting: large ladle long nozzle and argon sealing, integral submerged entry nozzle, ultra-low carbon silicon steel tundish covering agent, argon blowing in the tundish for 3-5 min before starting, full- process protective casting;

[0090] 5.2 Protective slag: ultra-low carbon steel protective slag is used, and the slag is added by an automatic slag adding device. The slag is added according to the principles of frequent addition, less addition, and uniform addition, and the black slag state is maintained;

[0091] 5.3 Tundish level: The weight of molten steel should be not less than 25 tons at the beginning of casting, not less than 33 tons at the time of tundish change, and not less than 40 tons at the time of normal casting.

[0092] 5.4 Mold level: The height of liquid surface is set to 80-90%, and the fluctuation of mold liquid surface is controlled within ±3%.

[0093] 5.5 Temperature and drawing speed: The liquidus temperature is 1535℃, and constant drawing speed casting is adopted. The tundish temperature and drawing speed are controlled according to the following table:

[0094] Tundish temperature, °C 1560-1575 Continuous casting speed, m / min 0.65±0.02

[0095] 5.6 Cooling water: The water flow of mold is 3000±25L / min, and the specific water flow of secondary cooling is 0.21L / kg.

[0096] 5.7 Electromagnetic stirring parameters: The current of mold electromagnetic stirring is 650±5A, and the frequency is 1.5±0.5Hz.

[0097] 5.8 Light reduction parameters control: The MSR soft 1-13mm model is adopted.

[0098] 5.9 Head and tail billets: The length of head billet cutting waste is not less than 4 meters, and the length of tail billet cutting waste is not less than 2.5 meters. The head and tail billets are cut and wasted.

[0099] Six, the billets are checked and ground after roughing, and the surface quality is controlled.

[0100] The surface and end face of continuous casting square billet should not have visually visible reconnection, peeling, scarring, inclusions, slag inclusion, cracks, pores, shrinkage holes, bumps, pits, scratches, indentations, scratches, depth or height >1mm vibration marks, etc.

[0101] Seven, the billets after grinding are rolled.

[0102] The wire rod rolling specifications are 5.5, 6.5, 12, 14mm, etc. to meet the different product requirements of users. Among them, the 5.5mm specification is mainly used by users to draw ultra-fine wire 0.38mm specification products. The user tested 30t for the first time, and no wire breakage occurred during the drawing process. The main performance test: maximum permeability μ is 0.011-0.013H / m, coercive force Hc≤80A / m, saturation magnetic induction Bs≥2.15T, which meets the user's requirements.

[0103] Through the above measures, the level of inclusion control of steel can be guaranteed under the condition of high scrap steel ratio, and the wire drawing to 0.4mm or below will not be broken due to inclusions.

[0104] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present application, and are not intended to limit the present application; although the present application has been described in detail with reference to the foregoing embodiments, those skilled in the art should understand that the technical solutions recorded in the foregoing embodiments can still be modified, or some or all of the technical features can be replaced by equivalents; and these modifications or replacements do not make the essence of the corresponding technical solutions deviate from the scope of the technical solutions of the embodiments of the present application.

Claims

1. A method for smelting electromagnetic pure iron for electromagnetic lens of scanning electron microscope, characterized in that: The method comprises: KR desulfurization - BOF converter - LF refining - RH vacuum treatment - bloom continuous casting - billet opening, inspection and grinding - rolling, and specifically comprises the following steps: Step 1, KR desulfurization: subject the molten iron to KR desulfurization treatment; Step 2, BOF converter: Scrap steel and molten iron after desulfurization are loaded into the BOF converter. After the converter smelting is completed, aluminum particles and lime are added in sequence when the converter is tapping. After tapping, a low-carbon steel slag surface deoxidizer is added to the slag surface for pre-deoxidation. The tapping temperature of the molten iron is 1600-1650℃. After tapping, the molten steel is transported to the LF refining treatment through a ladle. Step 3, LF refining: During LF refining, aluminum particles are continuously added for deoxidation. Calcium carbide and low-carbon steel slag surface deoxidizers are also added to deoxidize the molten steel and raise the temperature of the molten steel. The liquidus temperature is 1535°C. After LF refining, the tapping temperature of the first furnace is required to be 1670±8°C, and the tapping temperature of the continuous casting is 1660±8°C. After the temperature reaches the standard, the steel is tapped and transported to RH vacuum treatment. Step 4, RH vacuum treatment: RH station temperature ≥ 1650 ° C, RH station rapid vacuum treatment, the treatment sequence includes oxygen blowing forced decarburization - quantitative deoxidation - clean circulation - breaking air, oxygen blowing forced decarburization adopts deep decarburization treatment mode, after decarburization, the amount of aluminum particles added is controlled according to the oxygen content of molten steel, after net circulation treatment, breaking air and tapping, low carbon steel slag surface deoxidizer is added to the slag surface during the RH breaking air process, after tapping, it is sent to the continuous casting platform, the RH liquidus temperature is 1535 ° C, the first furnace tapping temperature is 1620 ± 8 ° C, and the continuous casting tapping temperature is 1610 ± 8 ° C; Step 5, bloom continuous casting: During continuous casting, a long shroud nozzle and argon seal, an integral submerged nozzle, an ultra-low carbon silicon steel tundish covering agent are used, and argon is blown into the tundish for 3-5 minutes before pouring. The casting is protected throughout the entire process. The liquidus temperature is 1535°C, the molten steel temperature in the tundish is 1560-1575°C, and the continuous casting speed is controlled at 0.65±0.02 m / min. Step 6: Open the blank, inspect and grind it to control the surface quality; Step 7: The ground billet is rolled.

2. The method for smelting electromagnetic pure iron for electromagnetic lens of scanning electron microscope according to claim 1, characterized in that: In the step 2, the total loading amount of scrap steel and molten iron is 146±4 t, including 120±2 t of molten iron and 26±2 t of scrap steel. The scrap steel is clean scrap steel. Except for iron, the other contents of the molten iron before desulfurization treatment are as follows in percentage by mass: Si: 0.35-0.75%, Mn≤0.25%, P≤0.11%, S≤0.045%, Ti≤0.06%; after desulfurization treatment, the molten iron temperature is greater than 1300°C, the S content is ≤0.002%, and the slag skimming rate is ≥98%.

3. The method for smelting electromagnetic pure iron for electromagnetic lens of scanning electron microscope according to claim 1, characterized in that: In the step 2, the target basicity of the final slag during converter tapping is R=3.5, the MgO content is controlled at 8-10%, the C content is controlled at below 0.05%, and the P and S contents are both controlled at below 0.01%; the amount of aluminum particles added during tapping is 1-1.5 kg / t, the amount of lime added is 300 kg, and the amount of low-carbon steel slag surface deoxidizer added is 50-100 kg.

4. The method for smelting electromagnetic pure iron for electromagnetic lens of scanning electron microscope according to claim 1, characterized in that: In the step 2, when the converter is tapping, argon blowing is started at the bottom of the ladle, and the pressure is controlled at 0.5-0.7 MPa in the early stage of tapping. After 3 / 4 of the steel is tapped, the bottom blowing argon pressure is adjusted to 0.4-0.6 MPa.

5. The method for smelting electromagnetic pure iron for electromagnetic lens of scanning electron microscope according to claim 1, characterized in that: In the step 3, during LF refining, after the ladle is in place, the bottom blowing of argon is connected and started, strong stirring is carried out for 2-3 minutes, and the power is turned on for 4-5 minutes to determine the oxygen and measure the temperature. Aluminum particles are added for deoxidation according to the oxygen content of the molten steel, and the Al content of the refined steel is controlled to be 0.015-0.025%. At the same time, calcium carbide and low-carbon steel slag surface deoxidizers are used to deoxidize the molten steel to produce white slag, and lime and fluorite are added to adjust the T.Fe+MnO in the refined steel slag to ≤1.5%.

6. The method for smelting electromagnetic pure iron for electromagnetic lens of scanning electron microscope according to claim 1, characterized in that: In step 4, the vacuum chamber baking temperature is ≥1200°C; the molten steel entering RH temperature is: ≥1665°C for the open pouring furnace and ≥1655°C for the continuous pouring furnace; during RH vacuum treatment, the C content at the end of RH decarburization is ≤20 ppm, the returned C content after RH deoxidation is less than 5 ppm, and the C content at RH tapping is ≤30 ppm.

7. The method for smelting electromagnetic pure iron for electromagnetic lens of scanning electron microscope according to claim 1, characterized in that: In the fourth step, during the RH vacuum treatment, the vacuum treatment was carried out until the vacuum degree dropped to 200 mbar and oxygen was blown, with an oxygen flow rate of 1800 Nm 3 / h, after the oxygen blowing is completed, the vacuum degree drops to below 2 mbar, and the cycle lasts for more than 10 minutes. The RH oxygen blowing forced decarburization amount is as follows: When the C content entering the station is 0.02-0.025%, the oxygen blowing amount is 90-100 Nm 3 RH station incoming steel C content increases or decreases by 0.005%, the oxygen blowing amount increases or decreases by 10 Nm 3 The basic amount of aluminum particles added is 10 kg. For every 0.01% increase in oxygen content in molten steel, the amount of Al added increases by 14 kg. The residual Al at the end of deoxidation is <0.005%. The amount of low-carbon steel slag surface deoxidizer added is 100-150 kg. When adding, spread the low-carbon steel slag surface deoxidizer evenly on the slag surface to ensure that T.Fe in the slag is ≤3%.

8. The method for smelting electromagnetic pure iron for electromagnetic lens of scanning electron microscope according to claim 1, characterized in that: The step four also includes calcium treatment, soft stirring and insulation. Calcium treatment is performed after RH is broken, and pure calcium wire is fed. The wire feeding amount of the open pouring furnace is 150-200 m, and the wire feeding amount of the continuous pouring furnace is 100-150 m. The bottom blowing flow rate during calcium treatment is 300-400 NL / min. Soft stirring is performed after the wire feeding is completed. The soft stirring time after calcium treatment is ≥5 min, and the slag surface is slightly fluctuated, the molten steel is not exposed, and the slag layer is not damaged. After confirming that the soft stirring standard is met, ash-treated rice husks are added for insulation, and the entire slag surface is required to be covered and evenly spread.

9. The method for smelting electromagnetic pure iron for electromagnetic lens of scanning electron microscope according to claim 1, characterized in that: In the step 5, ultra-low carbon steel protection slag is used during continuous casting, and the slag is added according to the principles of frequent, small and uniform addition to maintain a black slag state; the weight of molten steel in the tundish is not less than 25 tons when pouring, the weight of molten steel is not less than 33 tons when changing the ladle, and the weight of molten steel is not less than 40 tons during normal pouring; the crystallizer liquid level is set to 80-90%, the crystallizer liquid level fluctuation is controlled within ±3%, and the crystallization water flow rate is 3000±25 L / min; the crystallizer electromagnetic stirring current is 650±5 A, and the frequency is 1.5±0.5 Hz; soft reduction parameter control: using the MSR soft1-13 mm model; the scrap length of the head billet is not less than 4 meters, the scrap length of the tail billet is not less than 2.5 meters, and the head and tail billets are cut and scrapped.

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