WO2023093112A1 - 一种高Cr-Si合金化热成形钢的冶炼和连铸方法 - Google Patents

一种高Cr-Si合金化热成形钢的冶炼和连铸方法 Download PDF

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WO2023093112A1
WO2023093112A1 PCT/CN2022/109343 CN2022109343W WO2023093112A1 WO 2023093112 A1 WO2023093112 A1 WO 2023093112A1 CN 2022109343 W CN2022109343 W CN 2022109343W WO 2023093112 A1 WO2023093112 A1 WO 2023093112A1
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alloying
alloy
continuous casting
smelting
steel
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PCT/CN2022/109343
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English (en)
French (fr)
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徐伟
王鲁宁
王飞
胡军
杨得草
王灵禺
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东北大学
本钢板材股份有限公司
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Priority claimed from CN202111438770.0A external-priority patent/CN113857448B/zh
Priority claimed from CN202111438757.5A external-priority patent/CN114032473B/zh
Application filed by 东北大学, 本钢板材股份有限公司 filed Critical 东北大学
Publication of WO2023093112A1 publication Critical patent/WO2023093112A1/zh

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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
    • B22D11/10—Supplying or treating molten metal
    • B22D11/11—Treating the molten metal
    • B22D11/111—Treating the molten metal by using protecting powders
    • 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
    • C22C38/20—Ferrous alloys, e.g. steel alloys containing chromium with copper
    • 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
    • C22C38/24—Ferrous alloys, e.g. steel alloys containing chromium with vanadium
    • 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
    • C22C38/26—Ferrous alloys, e.g. steel alloys containing chromium with niobium or tantalum

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  • the invention belongs to the technical field of iron and steel smelting and casting, and in particular relates to a method for smelting and continuous casting of high-Cr-Si alloyed hot-formed steel.
  • the coated hot-formed steel also has the problems of cold rolling in the rolling process, and the coating has problems such as sticking to the roll during the rolling process.
  • a coating-free hot-forming high-strength steel is proposed, with carbon content ⁇ 0.3%, silicon ⁇ 0.8%, manganese content ⁇ 0.8%, chromium content ⁇ 1.5%, and a certain amount of Ni, Nb, Ti and other microalloying elements.
  • the high Cr-Si alloying enables this hot-formed steel to reduce the scale formed by surface oxidation, thereby eliminating the aluminum-silicon coating commonly used in existing hot-formed steels.
  • the composition of this coating-free high Cr-Si hot forming steel contains relatively large amounts of silicon, manganese and chromium alloys, the total amount of alloys is about 9-18 tons (per 180 tons of molten steel), and the proportion of alloys can reach 5-10%. .
  • the alloy is added during the smelting process during the tapping process of the converter, and is added along with the tapping flow. In order to ensure the uniformity of alloying, alloy addition usually requires deoxidation alloying to start when 1/5 of the steel is tapped from the converter, and the addition is completed when 2/3 of the steel is tapped.
  • Chinese patent CN10540440A provides a method for adding alloys to medium and high manganese alloy steels for converter smelting, the method is aimed at medium and high manganese steels, medium manganese steel with Mn content of 3.0%-6.0% and high manganese with Mn ⁇ 6.0% Steel, this method adds alloys before tapping or in the converter to solve the problem of adding a large amount of alloys, but adding alloys to large tanks (ladles) before tapping will affect the ventilation effect of the ladle vent bricks, resulting in the ladle not being able to blow argon at the bottom gas; adding the alloy in the converter affects the yield of the alloy and the cost is high.
  • mold slag added to the mold should evenly transfer heat to the slab and reduce the friction between the mold and the slab. Improve the surface quality of continuous casting slabs, and at the same time absorb inclusions to prevent secondary oxidation and heat preservation of molten steel. If the mold slag has poor performance, it will flow into the air gap unevenly, resulting in uneven heat transfer. Under the action of internal stress and friction in the mold, more microcracks and longitudinal cracks will appear on the surface of the continuous casting slab.
  • the high Cr-Si alloying of the above-mentioned coating-free hot-forming steel will increase the strength of the steel, increase the hardenability, and cause a large shrinkage during the solidification process.
  • the slab shell is not uniform, and the performance of the existing continuous casting mold flux can hardly fully meet the use requirements of this steel type.
  • the invention provides a smelting and continuous casting method for high Cr-Si alloyed hot forming steel.
  • smelting process in view of the large amount of alloys containing silicon, manganese and chromium required for this type of steel, by reasonably matching the two methods of adding alloys in the ladle and adding alloys in the refining LF furnace for steelmaking, accurate control is achieved.
  • the high Cr-Si hot forming steel of the present invention has the following specific components (by mass fraction): C: 0.15-0.35%, Mn: 0.8-3.2%, Si: 0.8-2.8%, S: ⁇ 0.01%, P: ⁇ 0.015%, Al: 0.01-0.05%, Cr: 1.5-3.9%, and one or several microalloying elements such as Nb, V, Ti, Cu, etc., if the composition contains these microalloying elements, The contents are: Nb: 0.01-0.05%, V: 0.01-0.05%, Ti: 0.01-0.03%, Cu: 0.05-0.15%, and the balance is Fe and other unavoidable impurities.
  • the production process of steel grades is converter smelting-converter tapping-ladle refining furnace LF-continuous casting (LD-LF-CC).
  • the smelting and continuous casting methods of the high Cr-Si hot-formed steel are as follows:
  • Step 1 Preparation before tapping: Carry out converter steelmaking. No alloy elements are added during the converter steelmaking process. Open the ladle under the furnace within 5-8 minutes before tapping the converter, open the ladle, and blow argon to the bottom of the ladle. The bottom argon blowing operation must be carried out throughout the tapping process, and the bottom blowing argon can not be completely closed until the steel is tapped to throw the slag dart or judge the clearance. When tapping, it is necessary to add refining slag and lime to the converter under the condition of bottom blowing argon.
  • Step 2 Primary alloying: start tapping, and carry out deoxidation alloying in the converter during the tapping process.
  • the method is to add deoxidizer-aluminum balls or aluminum particles-silicon alloy-manganese in sequence in the order of first strong and then weak Alloys - Chromium-based alloys.
  • the deoxidation alloying starts when the converter taps 1/5 of the steel into the ladle, and finishes adding 2/3 of the time.
  • These materials for deoxidation alloying can be added in batches with the steel flow, and the material added in each batch is 5-18kg/ton of molten steel, and the interval between batches is 1-2min until the planned alloy addition amount is completed.
  • the deoxidation alloying is carried out for about 50- 80% silicon alloying, 85-90% manganese alloying and 25-75% chromium alloying process.
  • the entire alloying process is completed in the deoxidation alloying stage.
  • the formula for calculating the amount of alloy added is: alloying ratio * target value of composition / (proportion of alloy element content in the added alloy * alloy yield). Alloying in the deoxidation alloying stage is called primary alloying process.
  • Step 3 After tapping the converter, add lime and top slag modifier to the ladle for top slag modification.
  • Step 4 Carry out the refining LF process.
  • refining LF In the process of refining LF, add silicon alloys, manganese alloys, and chromium alloys for secondary alloying.
  • silicon alloys, manganese alloys In the secondary alloying, silicon alloys, manganese alloys, There is no fixed order for the addition of chromium alloys. Secondary alloying requires Si, Mn, and Cr elements to complete the alloying requirements of the remaining parts.
  • the calculation formula for alloy addition can also refer to the above "alloying ratio * target value of components / (in the alloy Alloy element content ratio * alloy yield)", except that the alloying ratio used here is 1 minus the alloying ratio of the first alloying.
  • the conventional refining LF process will carry out slagging and desulfurization, which also helps to improve the yield of each alloy.
  • Step 5 Alloy fine-tuning: Carry out alloy fine-tuning, carry out alloying of carbon according to the change of carbon, and complete the smelting process of the alloy to be prepared. Carbon alloying can be carried out with carburizers.
  • the silicon-based alloy used for primary alloying can be ferrosilicon
  • the manganese-based alloy can be medium-carbon ferromanganese
  • the chromium-based alloy can be high-carbon ferrochromium
  • the silicon-based alloy used for secondary alloying can be ferrosilicon
  • the manganese alloy can be high carbon ferromanganese
  • the chromium alloy can be high carbon ferrochromium
  • the composition also includes micro-alloying elements Nb, V, Ti, Cu, etc., Nb, V, and Ti are more expensive, and they need to be added after the addition of silicon-based alloys, manganese-based alloys, and chromium-based alloys during the secondary alloying process, respectively. It is added in the form of ferro-niobium, ferro-vanadium and ferro-titanium. Cu can be added through metal copper, because it is not easy to be oxidized, it can be added at any time, such as adding during primary alloying or secondary alloying, or directly into the converter when tapping. These microalloys need to be added in a low amount, and can complete 100% alloying at one time.
  • Step 6 Alloy continuous casting: the smelted alloy is used for continuous casting to produce a continuous casting slab of the hot-formed steel.
  • the following low-alkalinity continuous casting mold flux can be used: CaO, 30-40%; SiO 2 , 40%-50%; MgO, 2-3%; Al 2 O 3 , 0.1- 1.0%; Fe 2 O 3 ⁇ 2.0%; MnO, 3 ⁇ 7%; Na 2 O, 5 ⁇ 12%; K 2 O, 0.1 ⁇ 1.0%; CaF 2 , 0 ⁇ 2%; C, 0 ⁇ 3% .
  • the continuous casting mold flux can be prepared by the following method:
  • the mold powder is produced by the pre-melting method, and the industrial materials such as wollastonite, quartz sand, soda, fluorite and other industrial materials used to make the mold powder are weighed according to the mass percentage of the design target composition; the weighed raw materials are mixed and mechanically stirred , so that the ingredients are mixed evenly; the mixed samples are made into blocks or balls and dried, then poured into a crucible and placed in a heating furnace such as an intermediate frequency induction furnace to heat and melt.
  • the industrial materials such as wollastonite, quartz sand, soda, fluorite and other industrial materials used to make the mold powder are weighed according to the mass percentage of the design target composition
  • the weighed raw materials are mixed and mechanically stirred , so that the ingredients are mixed evenly
  • the mixed samples are made into blocks or balls and dried, then poured into a crucible and placed in a heating furnace such as an intermediate frequency induction furnace to heat and melt.
  • the steel type targeted by the present invention contains relatively high alloying elements such as carbon, silicon, and chromium, and has unique solidification characteristics.
  • the initial billet shell solidifies and shrinks greatly, and the solidification shrinkage is uneven, so that the billet shell surface There are many microcracks or longitudinal cracks.
  • the method is to use high-basic mold flux, but the slag film formed by high-basic mold flux cannot be effectively in close contact with the billet shell, and the heat transfer rate is low, and the silicon content of the steel grades targeted by the present invention High, rapid heat transfer is required in the crystallizer to form an effective shell thickness, and the heat transfer rate of mold flux with high alkalinity (CaO/SiO 2 >1.1) cannot meet the heat transfer requirements.
  • the continuous casting mold flux in order to solve the quality problems such as micro-cracks or longitudinal cracks on the surface of the slab of this steel type, it is necessary for the continuous casting mold flux to have multiple properties such as uniform heat transfer, fast and good lubrication, so as to strictly control the transfer of the slab shell in the mold.
  • Thermal uniformity in the production of high Cr-Si alloyed coating-free hot forming steel, solves the problem of surface defects in cast billets.
  • the Cr element improves the hardenability of the steel
  • Cr is a carbide forming element
  • the precipitation at the grain boundary increases the stress concentration and increases the brittle area of the steel, which requires protection
  • Slag has good lubricity, and needs to have low alkalinity, low viscosity, and the melting temperature and transition temperature should not be too high to form a sufficient liquid slag film to ensure good heat transfer and lubrication between the billet and the mold.
  • the basicity, transition temperature and melting temperature of the mold slag should not be too low, so as to form a sufficient solid slag film, so that the mold slag can inhibit heat transfer and be uniform.
  • the ability to transfer heat there are oxides such as Al 2 O 3 and Cr 2 O 3 floating in the molten steel of the steel type targeted by the present invention, which will easily cause assimilation and absorption of mold slag when they enter the slag, so the alkalinity should not be too low.
  • the heat transfer performance (including heat transfer capability and heat transfer uniformity) of the mold flux for continuous casting of the present invention should be considered, and secondly, the lubrication of the mold flux should be considered. Therefore, the basicity R of the mold flux should be strictly controlled. , melting temperature, transition temperature, viscosity and other properties are within the appropriate range:
  • the alloy is added and refined in the LF furnace when the converter is tapped
  • the alloy is added to achieve the purpose of accurately controlling the alloy composition of the coating-free hot forming steel.
  • the two processes of converter and refining LF ladle furnace are used to complete the alloying process of this steel type and optimize its alloy. Add the proportioning relationship to achieve accurate control of the ingredients of the brand. At the same time, the yield of the alloy can be improved, and the cost can be saved.
  • the present invention uses low-basicity mold flux, by adjusting the basicity and adding a certain amount of MnO and other components, to ensure good heat transfer and lubrication between the billet and the crystallizer, and at the same time It has good uniformity of heat transfer and reduces the occurrence of microcracks and longitudinal cracks on the surface of the slab. The occurrence rate of surface crack defects can be reduced from 20% before use to 2% after use.
  • the low-alkalinity mold flux proposed by the present invention has a lower fluorine content, which can meet the heat transfer and lubrication performance of crack-sensitive steel continuous casting mold flux, reduce the fluorine content in air and water, reduce pollution and reduce the impact of fluorine-containing water on equipment Corrosion, and does not use Li 2 O, B 2 O 3 and other components with high prices, the cost is low, and the cost of use is saved.
  • Fig. 1 is a photograph of the surface of a cast slab produced during continuous casting using mold flux in Comparative Example 2-1.
  • Fig. 2 is a photograph of the surface of a cast slab produced during continuous casting using mold flux in Example 6.
  • the composition of steel alloy elements in each embodiment of the present invention is shown in the table below:
  • Example 1 0.26 1.871 1.931 0.006 0.0008 2.836 0.0373 0.0421
  • Example 2 0.23 1.868 1.928 0.009 0.0006 2.818 0.0364 0.0413
  • Example 3 0.24 1.87 1.929 0.009 0.0009 2.828 0.0371 0.0416
  • the calculation method of the alloy addition amount is calculated by taking the alloying of ferrosilicon as an example:
  • the target proportion of steel silicon is 1.8%
  • the tapping amount is 175t
  • the target component value is 175 ⁇ 1000 ⁇ 1.8% kg
  • the silicon content of ferrosilicon is 76.06%
  • the alloy yield is determined to be 91.82% based on experience.
  • the composition of primary alloyed silicon is controlled to 1%, that is, the primary alloying ratio is 1/1.8:
  • the yield of secondary alloyed ferrosilicon alloy is empirically determined to be 98.8%, and the secondary alloying control silicon content is 0.8%:
  • Preparation before tapping Open the ladle under the furnace within 5-8 minutes before tapping, open the ladle, and blow the bottom argon on the ladle. Only when the bottom blowing argon can be completely closed. After tapping, add refining slag and lime to the converter under the condition of bottom blowing argon.
  • the materials used for primary alloying are: 2009kg medium carbon ferromanganese, 2504kg ferrosilicon, 181kg aluminum particles and 3014kg high carbon ferrochromium.
  • Top slag modification Lime and top slag modifier are added to the ladle after converter tapping for top slag modification. Add 500kg of lime and 400kg of top slag modifier.
  • Secondary alloying carry out the refining LF process. During the refining LF process, add 1853kg of ferrosilicon, 6523kg of high-carbon ferrochrome, 800kg of high-carbon ferromanganese, and 90kg of ferro-niobium for secondary alloying. , high-carbon ferrochromium and high-carbon ferromanganese are all added before adding, and the secondary alloying completes the alloying requirements of the remaining parts of Si, Mn, and Cr elements, and completes all the alloying requirements of Nb.
  • Alloy fine-tuning carry out alloy fine-tuning, carry out alloying of carbon according to the change of carbon, and use refined recarburizing agent, the addition amount is 138kg.
  • Alloy continuous casting the smelted alloy is used for continuous casting to make the continuous casting slab of the hot-formed steel.
  • the chemical composition of low-alkalinity coating-free mold flux used in the continuous casting process is CaO, 33.66%; SiO 2 , 44.98%; MgO, 2.56%; Al 2 O 3 , 0.68%; Fe 2 O 3 ⁇ 2.0%; MnO, 5.38%; Na2O , 9.71%; K2O , 0.38%; CaF2 , 0.96%; C, 1.26%.
  • the basicity (CaO/SiO 2 ) of the mold flux is 0.75, the hemispherical point temperature is 1148°C, and the viscosity at 1300°C is 0.59Pa ⁇ s.
  • Pre-melting method is used for the production and preparation of mold slag, and industrial materials such as wollastonite, quartz sand, soda, fluorite and other industrial materials used for making mold slag are weighed according to the mass percentage of the design target composition; the weighed raw materials are mixed and mechanically stirred , so that the ingredients are mixed evenly; the mixed samples are made into blocks or balls and dried, then poured into a crucible and placed in an intermediate frequency induction furnace, heated and melted at 1000-1500 ° C, and kept for 1-3 hours to remove volatiles and uniform slag components ; Pour molten slag into water to rapidly cool to obtain a uniform glass-like amorphous substance; dry the glass-like amorphous substance and pulverize it into powder to obtain the required mold slag powder.
  • industrial materials such as wollastonite, quartz sand, soda, fluorite and other industrial materials used for making mold slag are weighed according to the mass percentage of the design target composition; the weighed raw materials are
  • Example 2 Basically the same as Example 1, the difference is that the materials used for primary alloying are medium carbon ferromanganese 2008kg, ferrosilicon 2500kg, aluminum particles 186kg and high carbon ferrochrome 3008kg; secondary alloying (refining LF process) used The materials are 92kg of ferro-niobium, 1851kg of ferrosilicon, 6520kg of high-carbon ferrochrome, and 802kg of high-carbon ferromanganese; the refining recarburizer used for alloy fine-tuning is 136kg.
  • the materials used for primary alloying are medium carbon ferromanganese 2008kg, ferrosilicon 2500kg, aluminum particles 186kg and high carbon ferrochrome 3008kg; secondary alloying (refining LF process) used The materials are 92kg of ferro-niobium, 1851kg of ferrosilicon, 6520kg of high-carbon ferrochrome, and 802kg of high-carbon ferromanganese
  • Example 2 Substantially the same as Example 1, the difference is that the materials used for primary alloying are medium carbon ferromanganese 2006kg, ferrosilicon 2508kg, aluminum particles 182kg and high carbon ferrochrome 3012kg; secondary alloying (refining LF process) used The materials are 88kg of ferro-niobium, 1853kg of ferrosilicon, 6523kg of high-carbon ferrochrome, and 800kg of high-carbon ferromanganese; the refining recarburizer used for alloy fine-tuning is 133kg.
  • the materials used for primary alloying are medium carbon ferromanganese 2006kg, ferrosilicon 2508kg, aluminum particles 182kg and high carbon ferrochrome 3012kg; secondary alloying (refining LF process) used The materials are 88kg of ferro-niobium, 1853kg of ferrosilicon, 6523kg of high-carbon ferrochrome, and 800kg of high-carbon ferromanganes
  • Example 2 It is basically the same as Example 1, except that the alloy composition also contains 0.03% vanadium, and 103kg of ferrovanadium is added after ferroniobium.
  • Example 2 It is basically the same as Example 1, except that the content of niobium in the steel target composition is different from Example 1, and also contains other microalloying elements: Nb: 0.03%, V: 0.03%, Ti: 0.02%, Cu: 0.08 %.
  • the alloy composition used is ferroniobium containing 65.5% of niobium, ferrovanadium containing 53.29% of vanadium, ferrotitanium containing 33.6% of titanium, and copper is added in the form of copper metal containing 99.8% of copper.
  • the yield of the alloy is empirically determined to be 98.9% of ferroniobium, 95.75% of ferro-vanadium, 85.56% of ferro-titanium and 98% of copper.
  • All microalloying elements are added after the alloying of silicon, chromium, and manganese is completed in the secondary alloying process.
  • the tapping amount is 175t, and the alloying amounts are 82kg ferroniobium, 103kg ferrovanadium, 122kg ferrotitanium, and 145kg copper.
  • Example 1 The difference from Example 1 is that the alloying of all Si, Cr, and Mn elements is completed in the converter tapping process, and only the alloying of niobium and the final alloy fine-tuning are performed in the refining LF process.
  • the materials used for alloying in the converter tapping process are 3038kg of medium-carbon ferromanganese, 4668kg of ferrosilicon, 191kg of aluminum particles and 9828kg of high-carbon ferrochrome; 89kg of ferroniobium and 116kg of refined recarburizer in the refining LF process.
  • Example 1 The difference from Example 1 is that the alloying of all Si, Cr, and Mn elements is completed in the converter tapping process, and only the alloying of niobium and the final alloy fine-tuning are performed in the refining LF process.
  • the materials used for alloying in the converter tapping process are 2969kg of medium-carbon ferromanganese, 4703kg of ferrosilicon, 176kg of aluminum particles and 9719kg of high-carbon ferrochrome; 87kg of ferroniobium and 128kg of refining recarburizer in the refining LF process.
  • the method for preparing mold flux is similar to that of Example 1.
  • the chemical composition of the prepared low-alkalinity mold flux is CaO, 34.13%; SiO 2 , 47.46%; MgO, 2.12%; Al 2 O 3 , 0.58%; Fe 2 O 3 ⁇ 2.0%; MnO, 4.02%; Na2O , 9.79%; K2O , 0.45%; CaF2 , 0.83%; C, 0.61%.
  • the basicity (CaO/SiO 2 ) of the prepared mold flux is 0.72, the hemispherical point temperature is 1151°C, and the viscosity at 1300°C is 0.57Pa ⁇ s.
  • the mold slag is used for the continuous casting of high Cr-Si hot-formed steel with the following components smelted according to steps 1 to 5 of the present invention.
  • the components of the steel are: C: 0.20%, Mn: 1.5%, Si: 2.0%, S: ⁇ 0.01%, P: ⁇ 0.015%, Al: 0.03%, Cr: 2.0%, Nb: 0.01%, V: 0.05%, Ti: 0.03%, Cu: 0.15%, the balance is Fe and other unavoidable of impurities.
  • the method for preparing mold flux is similar to that of Example 1.
  • the chemical composition of the prepared low-alkalinity mold flux is CaO, 36.68%; SiO 2 , 46.85%; MgO, 2.69%; Al 2 O 3 , 0.76%; Fe 2 O 3 ⁇ 2.0%; MnO, 4.19%; Na2O , 6.9%; K2O , 0.62%; CaF2 , 0.37%; C, 0.8%.
  • the basicity (CaO/SiO 2 ) of the prepared mold flux is 0.78, the hemispherical point temperature is 1147°C, and the viscosity at 1300°C is 0.6Pa ⁇ s.
  • the mold slag is used for the continuous casting of high Cr-Si hot-formed steel with the following components smelted according to steps 1 to 5 of the present invention.
  • the components of the steel are: C: 0.15%, Mn: 3.0%, Si: 1.0%, S: ⁇ 0.01%, P: ⁇ 0.015%, Al: 0.05%, Cr: 3.5%, Nb: 0.03%, V: 0.03%, Ti: 0.02%, Cu: 0.10%, the balance is Fe and other unavoidable of impurities.
  • the method of preparing mold flux is similar to that of Example 1.
  • the chemical composition of the prepared low-alkalinity mold flux is CaO, 35.28%; SiO 2 , 44.35%; MgO, 2.64%; Al 2 O 3 , 0.69%; Fe 2 O 3 ⁇ 2.0%; MnO, 5.28%; Na2O , 9.9%; K2O , 0.53%; CaF2 , 0.63%; C, 0.7%.
  • the basicity (CaO/SiO 2 ) of the prepared mold flux is 0.80, the hemispherical point temperature is 1150°C, and the viscosity at 1300°C is 0.56Pa ⁇ s.
  • composition of the high Cr-Si hot-formed steel applied with mold flux is the same as that of Example 7.
  • the method of preparing mold flux is similar to that of Example 1.
  • the chemical composition of the prepared low-alkalinity mold flux is CaO, 33.26%; SiO 2 , 44.37%; MgO, 2.85%; Al 2 O 3 , 0.59%; Fe 2 O 3 ⁇ 2.0%; MnO, 6.36%; Na2O , 9.83%; K2O , 0.69%; CaF2 , 0.75%; C, 0.87%.
  • the basicity (CaO/SiO 2 ) of the prepared mold flux is 0.75, the hemispherical point temperature is 1149°C, and the viscosity at 1300°C is 0.58Pa ⁇ s.
  • the mold slag is used for the continuous casting of high Cr-Si hot-formed steel with the following components smelted according to steps 1 to 5 of the present invention.
  • the components of the steel are: C: 0.30%, Mn: 1.0%, Si: 2.5%, S: ⁇ 0.01%, P: ⁇ 0.015%, Al: 0.02%, Cr: 1.5%, Nb: 0.05%, V: 0.01%, Ti: 0.03%, Cu: 0.05%, the balance is Fe and other unavoidable of impurities.
  • the chemical composition is CaO, 34.17%; SiO 2 , 26.99%; MgO, 2.79%; Al 2 O 3 , 3.79%; Fe 2 O 3 ⁇ 2.0%; MnO, 5.14 %; O, 7.94%; K2O , 0.14%; CaF2 , 7.45%; C, 7.74%.
  • the basicity (CaO/SiO 2 ) of the mold flux is 1.27, the hemispherical point temperature is 1101°C, and the viscosity at 1300°C is 1.06Pa ⁇ s.
  • the high Cr-Si hot-formed steel applied with mold flux is the same as that in Example 6.
  • the chemical composition is CaO, 34.17%; SiO 2 , 26.8%; MgO, 2.63%; Al 2 O 3 , 3.89%; Fe 2 O 3 ⁇ 2.0%; MnO, 5.17 %; O, 8.06%; K2O , 0.34%; CaF2 , 7.5%; C, 7.85%.
  • the basicity (CaO/SiO 2 ) of the mold flux is 1.28
  • the hemispherical point temperature is 1103°C
  • the viscosity at 1300°C is 1.04Pa ⁇ s.
  • the high Cr-Si hot-formed steel applied with mold flux is the same as that in Example 7.
  • the chemical composition is CaO, 34.15%; SiO 2 , 26.89%; MgO, 2.69%; Al 2 O 3 , 3.86%; Fe 2 O 3 ⁇ 2.0%; MnO, 5.16%; Na 2 O, 7.98%; K2O , 0.29%; CaF2 , 7.46%; C, 7.76%.
  • the basicity (CaO/SiO 2 ) of the mold flux is 1.27
  • the hemispherical point temperature is 1102°C
  • the viscosity at 1300°C is 1.05Pa ⁇ s.
  • the high Cr-Si hot-formed steel applied with mold flux is the same as that in Example 9.
  • Comparative Examples 2-1 to 2-3 are high-alkalinity mold fluxes commonly known to reduce cracks.
  • Fig. 1 is a slab produced when using the mold flux in Comparative Example 2-1 for continuous casting
  • Fig. 2 is a slab produced when using the mold flux in Example 6 for continuous casting. It can be clearly seen that when the high-basicity mold flux that is generally known to reduce cracks in Comparative Example 2-1 is used, there are still many cracks on the surface of the slab, while the mold flux made by using the mold flux in Example 1 of the present invention The billet surface quality is better and no cracks appear.
  • the mold slags in Comparative Examples 2-1 to 2-3 are used for the coating-free hot-forming steel, and the quality of the slabs produced is poor, and the occurrence rate of surface crack defects is nearly 20%.
  • the quality of the slab is good, and the occurrence rate of surface crack defects is reduced to below 2%.

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Abstract

一种高Cr-Si合金化热成形钢的冶炼和连铸方法，冶炼过程中，在转炉出钢时进行脱氧和第一次合金化，完成Al的全部合金化和Si、Mn、Cr的部分合金化；在进行LF精炼过程中，加入硅类合金、锰类合金、铬类合金进行二次合金化，完成剩余部分的Si、Mn、Cr元素的合金化；在冶炼后进行连铸时，采用低碱度保护渣。该方法针对钢种要求的硅、锰和铬合金加入量较大的问题，通过合理匹配转炉炼钢时钢包合金加入和精炼LF炉合金加入两种方式，准确控制用于免涂层热成形钢的合金成分；在连铸过程中，使用具有均匀传热和良好润滑的低碱度保护渣，解决了该钢种易形成气隙和坯壳不均匀的问题。

Description

一种高Cr-Si合金化热成形钢的冶炼和连铸方法 技术领域
本发明属于钢铁冶炼铸造技术领域，具体涉及一种高Cr-Si合金化热成形钢的冶炼和连铸方法。
背景技术
随着对钢铁材料性能要求的越来越高，如更高的强度、抗高温、低温、耐腐蚀等特殊物理性能，普通碳钢已经不能满足要求。轻量化技术是实现汽车节能减排的关键技术之一，而高强度热冲压成形技术在保证汽车安全性的同时能较大幅度实现轻量化。现有的用于热冲压成型的钢种主要是镀铝硅涂层的硼钢，采用镀层以避免钢材在热成形时表面形成氧化铁皮的问题。
然而有涂层的热成形钢同样也具有轧制过程需要冷轧、镀层在轧制过程中存在沾辊等问题。为解决这一问题，提出一种免涂层热成形高强钢，碳含量≤0.3％，硅≥0.8％，锰含量≥0.8％，铬含量≥1.5％，还含有一定含量的Ni、Nb、Ti等微合金元素。高Cr-Si合金化使这种热成形钢可以减少因表面氧化而形成的氧化铁皮，进而免去现有的热成形钢通常采用的铝硅涂层。但这种免涂层高Cr-Si热成形钢的成分中硅、锰和铬合金含量较大，合金总量约9-18吨(每180吨钢水)，合金占比可达5-10％。通常情况下，冶炼过程中的合金加入是在转炉出钢过程中，随着出钢钢流加入。为了保证合金化的均匀性，合金加入通常要求在转炉出钢1/5时开始进行脱氧合金化，出至2/3时加完。但对于炼钢转炉工序，进行上述免涂层热成形高强钢冶炼时所需的这种大量合金的加入，会影响成分的精确控制，降温值非常大，难以保证较高且稳定的合金收得率，合金加入方法是准确热成形钢合金成分控制的重要影响因素。
中国专利CN10540440A提供了一种转炉冶炼中、高锰合金钢的合金加入方法，该方法针对的是中高锰钢种，Mn含量在3.0％-6.0％的中锰钢和Mn≥6.0％的高锰钢，该方法在出钢前或在转炉内加入合金来解决大量合金加入的问题，但出钢前在大罐(钢包)中加入合金将影响钢包透气砖的透气效果，造成钢包不能底吹氩气；在转炉内加入合金影响合金的收得率且成本较高。
在采用连铸工艺路线生产铸坯时，通常需要向结晶器中加入保护渣，加入到结晶器中的保护渣要起到均匀铸坯传热，减少结晶器与铸坯之间的摩擦力，提高连铸坯的表面质量，同时要吸附夹杂防止钢液二次氧化和保温的作用。若保护渣性能不良，则流入气隙不均匀，造成传热不均匀，结晶器内在内应力和摩擦力的作用下使连铸坯表面产生较多的微裂纹和纵裂。 上述免涂层热成形钢的高Cr-Si合金化会使钢强度增加，淬透性增大，在凝固过程中产生较大的收缩，局部坯壳和结晶器壁易形成气隙，使产生的坯壳不均匀，现有的连铸保护渣的性能很难完全满足该钢种的使用需求。
发明内容
针对现有技术的不足，本发明提供了一种针对高Cr-Si合金化热成形钢的冶炼和连铸方法。在冶炼过程中，针对该钢种要求的含硅、锰和铬合金加入量较大的问题，通过合理匹配转炉炼钢在钢包合金加入和精炼LF炉合金加入两种方式，达到准确控制用于免涂层热成形钢合金成分的目的；在连铸过程中，针对该钢种易形成气隙和坯壳不均匀的问题，还提出了一种具有均匀传热和良好润滑的专用于该高Cr-Si热成形钢连铸过程的低碱度保护渣。
本发明所述的高Cr-Si热成形钢，具体成分如下(按质量分数计)：C：0.15～0.35％，Mn：0.8～3.2％，Si：0.8～2.8％，S：＜0.01％，P：＜0.015％，Al：0.01～0.05％，Cr：1.5～3.9％，还可以包括Nb、V、Ti、Cu等微合金元素的一种或几种，如果成分包含这些微合金元素的话，含量分别为：Nb：0.01～0.05％，V：0.01～0.05％，Ti：0.01～0.03％，Cu：0.05～0.15％，余量为Fe和其他不可避免的杂质。钢种的生产流程为转炉冶炼-转炉出钢-钢包精炼炉LF-连铸浇注(LD-LF-CC)。
所述高Cr-Si热成形钢的冶炼和连铸方法具体如下：
步骤1.出钢前准备：进行转炉炼钢，转炉炼钢过程中不加入任何合金元素，在转炉出钢前5-8min内将钢包开至炉下，打开钢包，对钢包进行底吹氩，出钢过程必须全程进行底吹氩操作，直至出钢至投挡渣镖或判断净空时方可完全关闭底吹氩。出钢时需要在底吹氩的条件下向转炉中加入精炼渣、石灰。
步骤2.一次合金化：开始出钢，在出钢的过程中进行转炉脱氧合金化，方法为按照先强后弱的顺序，依次加入脱氧剂-铝球或铝粒-硅类合金-锰类合金-铬类合金。
优选地，脱氧合金化在转炉向钢包中出钢1/5时开始进行，出至2/3时加完。脱氧合金化的这些材料可以需随钢流分批次加入，每批次加入的材料为5-18kg/吨钢水，批次间间隔时间1-2min，直至完成计划的合金加入量。
因该钢种合金总量可达5～10％，因此在加入脱氧剂完全脱氧后，只对Si、Mn、Cr进行预期成分中一定比例的合金化，具体地，脱氧合金化进行约50～80％的硅的合金化、85～90％的锰的合金化和25～75％的铬的合金化过程。对于Al，在脱氧合金化阶段完成其全部的合金化过程。
可参考的合金加入量计算公式为：合金化比例*成分目标值/(加入的合金中合金元素含量比例*合金收得率)。脱氧合金化阶段的合金化，称为一次合金化过程。
步骤3.顶渣改质：转炉出钢后钢包中加入石灰和顶渣改质剂进行顶渣改质。
步骤4.二次合金化：进行精炼LF工序，在精炼LF过程中，加入硅类合金、锰类合金、铬类合金进行二次合金化，二次合金化中硅类合金、锰类合金、铬类合金的加入没有固定顺序，二次合金化对于Si、Mn、Cr元素完成剩余部分的合金化要求，合金加入量计算公式也可参考上面的“合金化比例*成分目标值/(合金中合金元素含量比例*合金收得率)”，只不过这里用的合金化比例是1减去一次合金化的合金化比例。常规精炼LF过程会进行造渣脱硫，也有助于提高各合金收得率。
步骤5.合金微调：进行合金微调，根据碳的变化情况，进行碳的合金化，完成要制备的合金的冶炼过程。碳合金化可以采用增碳剂进行。
上述冶炼过程中，一次合金化所用的硅类合金可以为硅铁，锰类合金可以为中碳锰铁，铬类合金为高碳铬铁；二次合金化所用的硅类合金可以为硅铁，锰类合金可以为高碳锰铁，铬类合金为高碳铬铁。
如果成分还包括微合金元素Nb、V、Ti、Cu等，Nb、V、Ti较贵重，需要在二次合金化过程中硅类合金、锰类合金、铬类合金加完后再加入，分别以铌铁、钒铁、钛铁形式加入。Cu可通过金属铜方式加入，因为不易氧化，可在任意时候加入，比如一次合金化或二次合金化过程中加入，或出钢时直接加入转炉内。这些微合金需要加入的含量低，可一次完成100％的合金化。
步骤6.合金连铸：采用冶炼后的合金进行连铸浇注，制成所述热成形钢的连铸坯。
在合金连铸过程中，可采用以下成分的低碱度连铸保护渣：CaO，30～40％；SiO 2，40％～50％；MgO，2～3％；Al 2O 3，0.1～1.0％；Fe 2O 3≤2.0％；MnO，3～7％；Na 2O，5～12％；K 2O，0.1～1.0％；CaF 2，0～2％；C，0～3％。该连铸保护渣的物理性能为：碱度(R)0.75±0.2，1300℃粘度(η1300℃)＝0.57±0.05Pa·s，半球点温度(T半)＝1151±5℃，转折温度1205±5℃，铺展角，30°±2°；比重，0.65±0.1g/cm3，结晶率0。
所述连铸保护渣可采用以下方法制备：
采用预熔法进行保护渣的生产制作，将制作保护渣用的硅灰石、石英砂、苏打、萤石等工业原料按设计目标成分质量百分比称重；将称重好的原料混合进行机械搅拌，使得各成分混合均匀；将混合好的样品制作成块或球烘干后倒入坩埚中放入中频感应炉等加热炉中加热熔化，加热温度可以为1000～1500℃，保温一段时间(约1～3h)除去挥发分和均匀熔渣成分，形成熔融态渣；将熔融态渣倒入水中急冷得到均匀的玻璃状非晶体物质；将玻璃状非晶体物质烘干后粉碎处理成粉末，得到所需的保护渣粉末。
本发明针对的钢种中含有较高的碳、硅、铬等合金元素，具有独特的凝固特性，在结晶 器内凝固时初始坯壳凝固收缩较大，凝固收缩不均匀，从而使坯壳表面产生较多微裂纹或纵裂。通常为了减少裂纹，方法是采用高碱度保护渣，但是高碱度保护渣形成的渣膜不能有效的与坯壳紧密接触，且传热速率较低，而本发明针对的钢种的硅含量高，结晶器内需要快速传热形成有效坯壳厚度，高碱度(CaO/SiO 2＞1.1)的保护渣的传热速率不能满足传热需求。因此为了解决该钢种铸坯表面产生微裂纹或纵裂等质量问题，需要连铸保护渣同时具有传热均匀、快速和良好润滑等多种性质，以严格控制结晶器中铸坯坯壳传热的均匀性，在高Cr-Si合金化的免涂层热成形钢的生产中解决铸坯产生表面缺陷的问题。
具体来说，本发明的热成形钢中，Cr元素提高钢的淬透性，且Cr是碳化物形成元素，在晶界的析出增加了应力集中，使钢的脆性区域增大，这要求保护渣具有较好的润滑性，需要有低碱度、低粘度并且熔化温度和转折温度不能太高，以形成足够的液渣膜保证铸坯和结晶器间良好的传热和润滑。
而同时，为了控制结晶器中铸坯坯壳传热的均匀性，要求保护渣碱度、转折温度和熔化温度不能太低，以形成足够的固渣膜，使保护渣具有抑制传热而均匀传热的能力。并且本发明针对的钢种的钢液中存在Al 2O 3、Cr 2O 3等氧化物上浮，进入渣中易引起保护渣同化和吸收，因此决定了碱度也不能太低。
根据上述问题，本发明的连铸用保护渣重点考虑传热性能(包括传热能力以及传热的均匀性)，其次还需考虑保护渣的润滑，为此要严格控制保护渣的碱度R、熔化温度、转折温度、粘度等性能在合适的范围内：
采用稍低的碱度，保证铸坯和结晶器间良好的传热和润滑，确定保护渣的碱R＝0.7-0.95，主要通过调控CaO和SiO 2的质量分数实现，同时采用助溶剂Na 2O、CaF 2等进一步调整保护渣粘度和熔化温度，出于环保考虑采用低氟设计，确定Na 2O含量5-12％，CaF 2含量0-2％。
为了改善保护渣的传热效果，同时也调整保护渣的熔点和粘度，添加3-7％的中性氧化物MnO。同时保护渣中还需要适当加入合适含量的具有吸收夹杂能力的成分，为此采用的是碱性氧化物MgO，质量分数2-3％。
本发明的有益效果在于：
1.针对含硅、锰和铬等合金量较大的免涂层高Cr-Si热成形钢钢种，通过在冶炼过程中，合理匹配转炉炼钢在转炉出钢时合金加入和精炼LF炉合金加入，达到了准确控制用于免涂层热成形钢合金成分的目的。通过合理的分配一种合金含量达到5-9％左右的免涂层热成形钢的合金加入方式和方法，采用转炉和精炼LF钢包炉两工序完成该钢种合金化的过程，优化其合金的加入配比关系，达到准确控制该牌号的成分。同时也能提高合金收得率，节约了成本。
2.针对该钢种的独特凝固特性，本发明采用低碱度保护渣，通过调整碱度并配加一定量的MnO等成分，保证铸坯和结晶器间良好的传热和润滑，同时也具有良好的传热均匀性，减少了铸坯表面微裂纹和纵裂的发生。表面裂纹缺陷发生率可由使用前的20％降为使用后的2％。
本发明提出的低碱度保护渣具有较低的氟含量，能够满足裂纹敏感性钢种连铸保护渣传热和润滑性能，减少空气和水中的氟含量，减少污染降低含氟水对设备的腐蚀，并且不采用价格较高的Li 2O，B 2O 3等成分，造价较低，节约使用成本。
附图说明
图1为使用比较例2-1中的保护渣进行连铸时制成的铸坯表面照片。
图2为使用实施例6中的保护渣进行连铸时制成的铸坯表面照片。
具体实施方式
某钢厂冶炼免涂层热成形钢，牌号为HRCF01，工艺路线为LD-LF-CC，采用钢包为180吨钢包。本发明中各个实施例中钢种合金元素成分如下表所示：
  C％ Si％ Mn％ P％ S％ Cr％ Nb％ Als％
实施例1 0.26 1.871 1.931 0.006 0.0008 2.836 0.0373 0.0421
实施例2 0.23 1.868 1.928 0.009 0.0006 2.818 0.0364 0.0413
实施例3 0.24 1.87 1.929 0.009 0.0009 2.828 0.0371 0.0416
  C％ Si％ Mn％ P％ S％ Cr％ Nb％ Als％
比较例1-1 0.27 1.771 1.931 0.007 0.0018 2.636 0.0336 0.0438
比较例1-2 0.24 1.868 1.828 0.01 0.0026 2.836 0.0366 0.0413
实施例1
进行上表实施例1中钢种的冶炼和铸造，具体方法如下：
首先进行合金加入量计算：
用于合金化的部分合金成分 ％
Figure PCTCN2022109343-appb-000001
合金加入量的计算方法，以硅铁的合金化为例计算：
假设钢种硅的成分目标比例为1.8％，出钢量为175t，成分目标值即为175×1000×1.8％kg，硅铁含硅量为76.06％，合金收得率经经验测定为91.82％，一次合金化硅的成分控制到1％，即一次合金化比例为1/1.8：
一次合金化加入的硅铁量＝175×1000×1％÷76.06％÷91.82％＝2505.789kg
二次合金化硅铁合金收得率经验测定为98.8％，二次合金化控制硅的成分量为0.8％：
二次合金化加入的硅铁量＝175×1000×0.8％÷76.06％÷98.8％＝1863.008kg。
具体冶炼和铸造过程如下：
1.出钢前准备：出钢前5-8min内将钢包开至炉下，打开钢包，对钢包进行底吹氩，出钢过程必须全程进行底吹氩操作，直至出钢至投标或判断净空时方可完全关闭底吹氩。出钢后，在底吹氩的条件下向转炉中加入精炼渣、石灰。
2.一次合金化：开始出钢，在出钢的过程中进行转炉脱氧合金化，方法为依次加入脱氧剂-铝粒-硅铁-中碳锰铁-高碳铬铁，脱氧合金化在转炉向钢包中出钢1/5时开始进行，出至2/3时加完。这些脱氧合金化的材料需随钢流分批次加入，每批次加入的材料为5-18kg/吨钢水，批次间间隔时间1-2min。
一次合金化采用的材料为：中碳锰铁2009kg、硅铁2504kg、铝粒181kg和高碳铬铁3014kg。
3.顶渣改质：转炉出钢后钢包中加入石灰和顶渣改质剂进行顶渣改质。加入石灰500kg、顶渣改质剂400kg。
4.二次合金化：进行精炼LF工序，在精炼LF过程中，加入硅铁1853kg、高碳铬铁6523kg、高碳锰铁800kg、铌铁90kg，进行二次合金化，铌铁在硅铁、高碳铬铁和高碳锰铁都加完后再加入，二次合金化对于Si、Mn、Cr元素完成剩余部分的合金化要求，并完成Nb的全部合金化要求。
5.合金微调：进行合金微调，根据碳的变化情况，进行碳的合金化，采用精炼增碳剂，添加量为138kg。
6.合金连铸：采用冶炼后的合金进行连铸，制成所述热成形钢的连铸坯。
连铸过程中所采用的低碱度免涂层保护渣化学成分为CaO，33.66％；SiO 2，44.98％；MgO，2.56％；Al 2O 3，0.68％；Fe 2O 3≤2.0％；MnO，5.38％；Na 2O，9.71％；K 2O，0.38％；CaF 2，0.96％；C，1.26％。
保护渣的碱度(CaO/SiO 2)为0.75，半球点温度1148℃，1300℃粘度0.59Pa·s。
采用预熔法进行保护渣的生产制备，将制作保护渣用的硅灰石、石英砂、苏打、萤石等工业原料按设计目标成分质量百分比称重；将称重好的原料混合进行机械搅拌，使得各成分混合均匀；将混合好的样品制作成块或球烘干后倒入坩埚中放入中频感应炉中，1000～1500℃ 加热熔化，保温1～3h除去挥发分和均匀熔渣成分；将熔融态渣倒入水中急冷得到均匀的玻璃状非晶体物质；将玻璃状非晶体物质烘干后粉碎处理成粉末，得到所需的保护渣粉末。
实施例2
与实施例1基本相同，不同之处在于，一次合金化所用的材料为中碳锰铁2008kg、硅铁2500kg、铝粒186kg和高碳铬铁3008kg；二次合金化(精炼LF过程)所用的材料为铌铁92kg、硅铁1851kg、高碳铬铁6520kg、和高碳锰铁802kg；合金微调所用的精炼增碳剂为136kg。
实施例3
与实施例1基本相同，不同之处在于，一次合金化所用的材料为中碳锰铁2006kg、硅铁2508kg、铝粒182kg和高碳铬铁3012kg；二次合金化(精炼LF过程)所用的材料为铌铁88kg、硅铁1853kg、高碳铬铁6523kg、和高碳锰铁800kg；合金微调所用的精炼增碳剂为133kg。
实施例4
与实施例1基本相同，不同之处在于，合金成分还含有0.03％的钒，103kg钒铁在铌铁之后加入。
实施例5
与实施例1基本相同，不同之处在于，钢种目标成分中铌含量与实施例1不同，还含有其他微合金元素：Nb：0.03％，V：0.03％，Ti：0.02％，Cu：0.08％。
采用的合金成分为铌铁含铌65.5％，钒铁含钒53.29％，钛铁含钛33.6％，铜以含铜99.8％的铜金属形式加入。
合金收得率经经验测定铌铁98.9％，钒铁95.75％，钛铁85.56％，铜98％。
所有微合金元素在二次合金化过程中完成硅、铬、锰的合金化之后加入，出钢量175t，合金加入量分别为铌铁82kg，钒铁103kg，钛铁122kg，铜145kg。
比较例1-1
与实施例1不同之处在于，在转炉出钢过程中完成所有Si、Cr、Mn元素的合金化，在精炼LF过程中只进行铌的合金化和最后的合金微调。转炉出钢过程中合金化所用的材料为中碳锰铁3038kg、硅铁4668kg、铝粒191kg和高碳铬铁9828kg；精炼LF过程铌铁89kg、精炼增碳剂116kg。
比较例1-2
与实施例1不同之处在于，在转炉出钢过程中完成所有Si、Cr、Mn元素的合金化，在精炼LF过程中只进行铌的合金化和最后的合金微调。转炉出钢过程中合金化所用的材料为中碳锰铁2969kg、硅铁4703kg、铝粒176kg和高碳铬铁9719kg；精炼LF过程铌铁87kg、精炼增碳剂128kg。
从比较例可以看出，实施例1～3和比较例1-1～1-2中，Si、Mn、Cr含量相近，但实施例1～3使用的合金量远小于比较例中使用的合金量，以硅为例，采用实施例1～3方法硅铁的综合收得率达到97.22％，比较例中硅铁的综合收得率仅为90.88％。因此，本申请在出钢和精炼LF过程中，分两次进行Si、Mn、Cr等元素的合金化，能够大大提高这些合金元素的收得率。
下面以实施例6～9说明连铸过程中采用本发明的连铸保护渣的效果。实施例6～9中，合金冶炼采用的方法也与实施例1～5中步骤1～5的冶炼方法基本相同，只是合金成分以及两次合金化的具体比例有所区别，此处不再赘述。
实施例6
制备保护渣的方法与实施例1相似，所制备的低碱度保护渣化学成分为CaO，34.13％；SiO 2，47.46％；MgO，2.12％；Al 2O 3，0.58％；Fe 2O 3≤2.0％；MnO，4.02％；Na 2O，9.79％；K 2O，0.45％；CaF 2，0.83％；C，0.61％。
所制备的保护渣的碱度(CaO/SiO 2)为0.72，半球点温度1151℃，1300℃粘度0.57Pa·s。
将保护渣用于按照本发明的步骤1～5完成冶炼的以下成分的高Cr-Si热成形钢的连铸，钢的成分为：C：0.20％，Mn：1.5％，Si：2.0％，S：＜0.01％，P：＜0.015％，Al：0.03％，Cr：2.0％，Nb：0.01％，V：0.05％，Ti：0.03％，Cu：0.15％，余量为Fe和其他不可避免的杂质。
实施例7
制备保护渣的方法与实施例1相似，所制备的低碱度保护渣化学成分为CaO，36.68％；SiO 2，46.85％；MgO，2.69％；Al 2O 3，0.76％；Fe 2O 3≤2.0％；MnO，4.19％；Na 2O，6.9％；K 2O，0.62％；CaF 2，0.37％；C，0.8％。
所制备的保护渣的碱度(CaO/SiO 2)为0.78，半球点温度1147℃，1300℃粘度0.6Pa·s。
将保护渣用于按照本发明的步骤1～5完成冶炼的以下成分的高Cr-Si热成形钢的连铸，钢的成分为：C：0.15％，Mn：3.0％，Si：1.0％，S：＜0.01％，P：＜0.015％，Al：0.05％，Cr：3.5％，Nb：0.03％，V：0.03％，Ti：0.02％，Cu：0.10％，余量为Fe和其他不可避免的杂质。
实施例8
制备保护渣的方法与实施例1相似，所制备的低碱度保护渣化学成分为CaO，35.28％；SiO 2，44.35％；MgO，2.64％；Al 2O 3，0.69％；Fe 2O 3≤2.0％；MnO，5.28％；Na 2O，9.9％；K 2O，0.53％；CaF 2，0.63％；C，0.7％。
所制备的保护渣的碱度(CaO/SiO 2)为0.80，半球点温度1150℃，1300℃粘度0.56Pa·s。
保护渣应用的高Cr-Si热成形钢的成分与实施例7相同。
实施例9
制备保护渣的方法与实施例1相似，所制备的低碱度保护渣化学成分为CaO，33.26％；SiO 2，44.37％；MgO，2.85％；Al 2O 3，0.59％；Fe 2O 3≤2.0％；MnO，6.36％；Na 2O，9.83％；K 2O，0.69％；CaF 2，0.75％；C，0.87％。
所制备的保护渣的碱度(CaO/SiO 2)为0.75，半球点温度1149℃，1300℃粘度0.58Pa·s。
将保护渣用于按照本发明的步骤1～5完成冶炼的以下成分的高Cr-Si热成形钢的连铸，钢的成分为：C：0.30％，Mn：1.0％，Si：2.5％，S：＜0.01％，P：＜0.015％，Al：0.02％，Cr：1.5％，Nb：0.05％，V：0.01％，Ti：0.03％，Cu：0.05％，余量为Fe和其他不可避免的杂质。
比较例2-1
制备高碱度的保护渣，化学成分为CaO，34.17％；SiO 2，26.99％；MgO，2.79％；Al 2O 3，3.79％；Fe 2O 3≤2.0％；MnO，5.14％；Na 2O，7.94％；K 2O，0.14％；CaF 2，7.45％；C，7.74％。
保护渣的碱度(CaO/SiO 2)为1.27，半球点温度1101℃，1300℃粘度1.06Pa·s。
保护渣应用的高Cr-Si热成形钢与实施例6相同。
比较例2-2
制备高碱度的保护渣，化学成分为CaO，34.17％；SiO 2，26.8％；MgO，2.63％；Al 2O 3，3.89％；Fe 2O 3≤2.0％；MnO，5.17％；Na 2O，8.06％；K 2O，0.34％；CaF 2，7.5％；C，7.85％。
保护渣的碱度(CaO/SiO 2)为1.28，半球点温度1103℃，1300℃粘度1.04Pa·s。
保护渣应用的高Cr-Si热成形钢与实施例7相同。
比较例2-3
制备高碱度的保护渣，化学成分为CaO，34.15％；SiO 2，26.89％；MgO，2.69％；Al 2O 3，3.86％；Fe 2O 3≤2.0％；MnO，5.16％；Na 2O，7.98％；K 2O，0.29％；CaF 2，7.46％；C，7.76％。
保护渣的碱度(CaO/SiO 2)为1.27，半球点温度1102℃，1300℃粘度1.05Pa·s。
保护渣应用的高Cr-Si热成形钢与实施例9相同。
比较例2-1～2-3为通常认知下用于减少裂纹的高碱度保护渣。图1为使用比较例2-1中的保护渣进行连铸时制成的铸坯，图2为使用实施例6中的保护渣进行连铸时制成的铸坯。可以明显看出使用比较例2-1中通常认知中可以减少裂纹的高碱度保护渣时，铸坯表面出现裂纹依然较多，而使用本发明实施例1中的保护渣制成的铸坯表面质量更好，未出现裂纹。
根据统计，免镀层热成形钢采用比较例2-1～2-3中的保护渣，制成的铸坯质量较差，表面裂纹缺陷发生率将近20％。采用实施例6～9中的保护渣，铸坯质量良好，表面裂纹缺陷发生 率降为2％以下。

Claims (10)

  1. 一种高Cr-Si合金化热成形钢的冶炼和连铸方法，其特征在于，所述热成形钢包括以下成分：C：0.15～0.35％，Mn：0.8～3.2％，Si：0.8～2.8％，S：＜0.01％，P：＜0.015％，Al：0.01～0.05％，Cr：1.5～3.9％；
    所述冶炼和铸造方法包括以下步骤：
    步骤1.出钢前准备：进行转炉炼钢，转炉炼钢过程中不加入合金元素，在完成转炉炼钢后，将钢包开至转炉下，打开钢包，对钢包进行底吹氩，并且在出钢过程全程进行底吹氩，直至出钢至投标或判断净空时方可完全关闭钢包的底吹氩；
    步骤2.一次合金化：开始出钢，在出钢的过程中进行转炉脱氧合金化，方法为依次加入脱氧剂～铝球或铝粒～硅类合金～锰类合金～铬类合金，这些用于脱氧合金化的材料随钢流分批次加入；一次合金化完成Al的全部合金化，完成Si、Mn、Cr的部分合金化；
    步骤3.顶渣改质：转炉出钢后钢包中加入石灰和顶渣改质剂进行顶渣改质；
    步骤4.二次合金化：进行精炼LF工序，在精炼LF过程中，加入硅类合金、锰类合金、铬类合金进行二次合金化，二次合金化完成剩余部分的Si、Mn、Cr元素的合金化要求；
    步骤5.合金微调：进行合金微调，根据钢中碳的变化情况，进行碳的合金化，完成合金的冶炼过程。
  2. 根据权利要求1所述的高Cr-Si合金化热成形钢的冶炼和连铸方法，其特征在于，还包括以下步骤：
    步骤6.合金连铸：采用冶炼后的合金进行连铸浇注，制成所述热成形钢的连铸坯；
    所述步骤6的连铸过程中，采用的连铸保护渣的成分为：CaO，30～40％；SiO 2，40％～50％；MgO，2～3％；Al 2O 3，0.1～1.0％；Fe 2O 3≤2.0％；MnO，3～7％；Na 2O，5～12％；K 2O，0.1～1.0％；CaF 2，0～2％；C，0～3％。
  3. 根据权利要求2所述的高Cr-Si合金化热成形钢的冶炼和连铸方法，其特征在于，所述连铸保护渣采用以下方法制备：
    将原料按设计目标成分质量百分比称重；
    将称重好的原料混合进行机械搅拌，使得各成分混合均匀；
    将混合好的原料制作成块或球，烘干后倒入坩埚中，放入加热炉中加热熔化并保温，形成熔融态渣；
    将熔融态渣倒入水中急冷得到均匀的玻璃状非晶体物质；
    将玻璃状非晶体物质烘干后粉碎处理成粉末，得到所需的保护渣粉末。
  4. 根据权利要求1～3中任一项所述的高Cr-Si合金化热成形钢的冶炼和连铸方法，其特征在于，所述热成形钢还包括微合金元素Nb、V、Ti、Cu中的一种或几种，含量为：Nb：0.01～0.05％， V：0.01～0.05％，Ti：0.01～0.03％，Cu：0.05～0.15％；
    Nb、V、Ti、Cu分别以铌铁、钒铁、钛铁、金属铜的形式加入，按照设计的成分，铌铁、钒铁、钛铁在所述步骤4中Si、Mn、Cr元素二次合金化完成后加入以完成Nb、V、Ti的合金化，金属铜在出钢和精炼LF过程中任意时间加入以完成Cu的合金化。
  5. 根据权利要求1～3中任一项所述的高Cr-Si合金化热成形钢的冶炼和连铸方法，其特征在于，所述一次合金化完成50～80％的硅的合金化、85～90％的锰的合金化和25～75％的铬的合金化。
  6. 根据权利要求1～3中任一项所述的高Cr-Si合金化热成形钢的冶炼和连铸方法，其特征在于，所述一次合金化和二次合金化中，各种合金材料的加入量按以下公式计算：
    合金材料加入量＝合金化比例*成分目标值/(加入的合金材料中合金元素含量比例*合金收得率)。
  7. 根据权利要求1～3中任一项所述的高Cr-Si合金化热成形钢的冶炼和连铸方法，其特征在于，所述脱氧合金化在转炉向钢包中出钢1/5时开始进行脱氧剂合金化所需材料的加入，出至2/3时加完。
  8. 根据权利要求1～3中任一项所述的高Cr-Si合金化热成形钢的冶炼和连铸方法，其特征在于，所述分批次加入脱氧合金化的材料，每批次加入5～18kg/吨钢水，批次间隔时间为1～2min。
  9. 根据权利要求1～3中任一项所述的高Cr-Si合金化热成形钢的冶炼和连铸方法，其特征在于，所述一次合金化所用的硅类合金为硅铁，锰类合金为中碳锰铁，铬类合金为高碳铬铁；二次合金化所用的硅类合金为硅铁，锰类合金为高碳锰铁，铬类合金为高碳铬铁。
  10. 根据权利要求4所述的高Cr-Si合金化热成形钢的冶炼和连铸方法，其特征在于，每种微合金元素的合金化均是一次完成。
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