WO2023093112A1 - Smelting and continuous casting method for high-cr-si alloyed hot-formed steel - Google Patents

Abstract

A smelting and continuous casting method for a high-Cr-Si alloyed hot-formed steel. During the smelting process, deoxidation and primary alloying are carried out during converter tapping to finish the complete alloying of Al and partial alloying of Si, Mn and Cr; and during the LF refining process, a silicon alloy, a manganese alloy and a chromium alloy are added for secondary alloying to finish the alloying of the remaining Si, Mn and Cr elements; and when continuous casting is carried out after smelting, low-alkalinity protective slag is used. The method aims at the problem of a relatively large addition amount of silicon, manganese and chromium alloys required by a steel, and by rationally matching two modes of adding a steel ladle alloy and adding an LF furnace alloy during converter steelmaking, the alloy components for a coating-free hot-formed steel are accurately controlled; and during the continuous casting process, the low-alkalinity protective slag having uniform heat transfer and a good lubricating property is used, such that the problems of air gaps being easy to form and an uneven blank shell in the steel are solved.

Description

A kind of smelting and continuous casting method of high Cr-Si alloyed hot forming steel technical field

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.

Background technique

As the performance requirements of steel materials are getting higher and higher, such as higher strength, high temperature resistance, low temperature resistance, corrosion resistance and other special physical properties, ordinary carbon steel can no longer meet the requirements. Lightweight technology is one of the key technologies to realize energy saving and emission reduction of automobiles, and high-strength hot stamping technology can greatly reduce weight while ensuring the safety of automobiles. The existing steel types used for hot stamping are mainly boron steel coated with Al-Si coating, and the coating is used to avoid the problem of iron oxide scale formed on the surface of the steel during hot forming.

However, 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. In order to solve this problem, 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. However, 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%. . Usually, 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. However, for the steelmaking converter process, the addition of such a large amount of alloys required for the smelting of the above-mentioned coating-free hot-forming high-strength steel will affect the precise control of the composition, the cooling value is very large, and it is difficult to ensure a high and stable alloy yield. Ratio, alloy addition method is an important factor in the accurate control of hot-formed steel alloy composition.

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.

When using the continuous casting process route to produce slabs, it is usually necessary to add mold slag to the mold. The 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.

Contents of the invention

Aiming at the deficiencies of the prior art, the invention provides a smelting and continuous casting method for high Cr-Si alloyed hot forming steel. During the 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 purpose of coating-free hot-forming steel alloy composition; in the continuous casting process, in view of the problems of easy formation of air gaps and uneven billet shells of this steel type, a special alloy with uniform heat transfer and good lubrication is also proposed for this high Low-alkalinity mold flux for continuous casting of Cr-Si hot forming steel.

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.

Preferably, 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.

Because the total amount of alloys of this steel type can reach 5-10%, after adding a deoxidizer for complete deoxidation, only a certain proportion of Si, Mn, and Cr is alloyed in the expected composition. Specifically, the deoxidation alloying is carried out for about 50- 80% silicon alloying, 85-90% manganese alloying and 25-75% chromium alloying process. For Al, 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. Top slag modification: After tapping the converter, add lime and top slag modifier to the ladle for top slag modification.

Step 4. Secondary alloying: Carry out the refining LF process. In the process of refining LF, add silicon alloys, manganese alloys, and chromium alloys for secondary alloying. 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.

In the above smelting process, the silicon-based alloy used for primary alloying can be ferrosilicon, the manganese-based alloy can be medium-carbon ferromanganese, and 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, and the chromium alloy can be high carbon ferrochromium.

If 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.

In the alloy continuous casting process, 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 physical properties of the continuous casting mold flux are: basicity (R) 0.75±0.2, viscosity at 1300°C (η1300°C)=0.57±0.05Pa·s, hemisphere point temperature (T½)=1151±5°C, transition temperature 1205°C ±5°C, spreading angle, 30°±2°; specific gravity, 0.65±0.1g/cm3, crystallization rate 0.

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. 1～3h) removing volatile matter and uniform slag components to form molten slag; pouring molten slag into water and quenching to obtain a uniform glassy amorphous substance; drying the glassy amorphous substance and pulverizing it into powder to obtain Required mold flux powder.

The steel type targeted by the present invention contains relatively high alloying elements such as carbon, silicon, and chromium, and has unique solidification characteristics. When solidifying in the crystallizer, 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. Usually, in order to reduce 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. Therefore, 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.

Specifically, in the hot forming steel of the present invention, the Cr element improves the hardenability of the steel, and Cr is a carbide forming element, and 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.

At the same time, in order to control the heat transfer uniformity of the slab shell in the mold, it is required that 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. In addition, 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.

According to the above-mentioned problems, 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:

Use a slightly lower basicity to ensure good heat transfer and lubrication between the slab and the crystallizer, and determine the base R of the mold flux to be 0.7-0.95, mainly by adjusting the mass fraction of CaO and SiO ₂ , and at the same time using Na ₂ as a cosolvent O, CaF ₂ , etc. to further adjust the viscosity and melting temperature of the mold flux, adopt a low-fluorine design for environmental protection, and determine the content of Na ₂ O to 5-12%, and the content of CaF ₂ to 0-2%.

In order to improve the heat transfer effect of the mold flux and adjust the melting point and viscosity of the mold flux, 3-7% neutral oxide MnO is added. At the same time, it is also necessary to properly add a suitable content of components with the ability to absorb inclusions into the mold flux. For this purpose, the basic oxide MgO is used, with a mass fraction of 2-3%.

The beneficial effects of the present invention are:

1. For the coating-free high Cr-Si hot-formed steel grades containing silicon, manganese and chromium and other alloys, through the reasonable matching of converter steelmaking during the smelting process, 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. By rationally allocating the alloy addition method and method of a coating-free hot-forming steel with an alloy content of about 5-9%, 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.

2. In view of the unique solidification characteristics of this steel type, 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.

Description of drawings

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.

Detailed ways

A steel factory smelts coating-free hot-formed steel, the grade is HRCF01, the process route is LD-LF-CC, and the ladle is 180 tons. The composition of steel alloy elements in each embodiment of the present invention is shown in the table below:

the	C%	Si%	Mn%	P%	S%	Cr%	Nb%	Als%
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	C%	Si%	Mn%	P%	S%	Cr%	Nb%	Als%
Comparative example 1-1	0.27	1.771	1.931	0.007	0.0018	2.636	0.0336	0.0438
Comparative example 1-2	0.24	1.868	1.828	0.01	0.0026	2.836	0.0366	0.0413

Example 1

Carry out the smelting and casting of steel grade in the above table embodiment 1, concrete method is as follows:

First calculate the amount of alloy added:

Partial alloy composition for alloying %

The calculation method of the alloy addition amount is calculated by taking the alloying of ferrosilicon as an example:

Assuming that 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%, and 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 amount of ferrosilicon added in one alloying = 175 × 1000 × 1% ÷ 76.06% ÷ 91.82% = 2505.789kg

The yield of secondary alloyed ferrosilicon alloy is empirically determined to be 98.8%, and the secondary alloying control silicon content is 0.8%:

The amount of ferrosilicon added for secondary alloying = 175 × 1000 × 0.8% ÷ 76.06% ÷ 98.8% = 1863.008kg.

The specific smelting and casting process is as follows:

1. 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.

2. Primary alloying: start tapping, and carry out deoxidation and alloying in the converter during the process of tapping. The method is to add deoxidizer-aluminum particles-ferrosilicon-medium carbon ferromanganese-high carbon ferrochrome in sequence, and deoxidize and alloy in the converter It starts when 1/5 of the steel is tapped into the ladle, and it is finished when it reaches 2/3. These deoxidized alloyed materials need to 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.

The materials used for primary alloying are: 2009kg medium carbon ferromanganese, 2504kg ferrosilicon, 181kg aluminum particles and 3014kg high carbon ferrochromium.

3. 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.

4. 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.

5. 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.

6. 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.

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.

Example 3

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.

Example 4

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 5

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.

Comparative example 1-1

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.

Comparative example 1-2

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.

It can be seen from the comparative examples that in Examples 1-3 and Comparative Examples 1-1-1-2, the contents of Si, Mn, and Cr are similar, but the amount of alloy used in Examples 1-3 is much smaller than that used in Comparative Examples amount, taking silicon as an example, the comprehensive yield of ferrosilicon using the methods of embodiments 1 to 3 reaches 97.22%, and the comprehensive yield of ferrosilicon in the comparative example is only 90.88%. Therefore, in the process of tapping and refining LF, alloying of Si, Mn, Cr and other elements is carried out twice in the present application, which can greatly increase the yield of these alloying elements.

The effect of using the continuous casting mold flux of the present invention in the continuous casting process will be described below with Examples 6-9. In Examples 6-9, the method used for alloy smelting is also basically the same as the smelting method in Steps 1-5 in Examples 1-5, except that the alloy composition and the specific ratio of the two alloyings are different, and will not be repeated here. .

Example 6

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.

Example 7

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.

Example 8

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.

The composition of the high Cr-Si hot-formed steel applied with mold flux is the same as that of Example 7.

Example 9

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.

Comparative example 2-1

Prepare high basicity mold flux, 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.

Comparative example 2-2

Prepare high basicity mold flux, 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, and 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.

Comparative example 2-3

Prepare high basicity mold flux, 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, and 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, and 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.

According to statistics, 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%. Using the mold flux in Examples 6-9, the quality of the slab is good, and the occurrence rate of surface crack defects is reduced to below 2%.

Claims (10)

1. A method for smelting and continuous casting of high-Cr-Si alloyed hot-formed steel, characterized in that the hot-formed steel comprises the following components: 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%;

   The smelting and casting method comprises the following steps:

   Step 1. Preparation before tapping: Carry out converter steelmaking. No alloying elements are added during the converter steelmaking process. Bottom blowing argon is carried out throughout the steel process, and the bottom blowing argon of the ladle can be completely closed until the steel is tapped to bid or the clearance is judged;

   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 alloy ~ chromium alloy in sequence. The material for deoxidation alloying is added in batches with the steel flow; one alloying completes the complete alloying of Al, and completes the partial alloying of Si, Mn and Cr;

   Step 3. Top slag modification: add lime and top slag modifier to the steel ladle after converter tapping to carry out top slag modification;

   Step 4. Secondary alloying: Carry out the refining LF process. During the refining LF process, silicon alloys, manganese alloys, and chromium alloys are added for secondary alloying, and the remaining parts of Si, Mn, and Cr are completed after secondary alloying Alloying requirements of elements;

   Step 5. Alloy fine-tuning: Alloy fine-tuning is carried out, and carbon alloying is carried out according to the change of carbon in the steel to complete the alloy smelting process.
2. The method for smelting and continuous casting of high Cr-Si alloyed hot-formed steel according to claim 1, further comprising the steps of:

   Step 6. Alloy continuous casting: use the smelted alloy for continuous casting and pouring to make a continuous casting slab of the hot-formed steel;

   In the continuous casting process of step 6, the components of the continuous casting mold flux used are: 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% .
3. The method for smelting and continuous casting of high Cr-Si alloyed hot-formed steel according to claim 2, wherein the continuous casting mold flux is prepared by the following method:

   Weigh the raw materials according to the design target composition mass percentage;

   Mix the weighed raw materials for mechanical stirring, so that the ingredients are evenly mixed;

   Make the mixed raw materials into blocks or balls, pour them into a crucible after drying, put them into a heating furnace to heat, melt and keep warm to form molten slag;

   Pour the molten slag into water for rapid cooling to obtain a uniform glassy amorphous substance;

   The glassy amorphous material is dried and pulverized into powder to obtain the required mold powder powder.
4. The method for smelting and continuous casting of high-Cr-Si alloyed hot-formed steel according to any one of claims 1-3, characterized in that the hot-formed steel also includes microalloy elements Nb, V, Ti, Cu One or more of them, the contents are: Nb: 0.01-0.05%, V: 0.01-0.05%, Ti: 0.01-0.03%, Cu: 0.05-0.15%;

   Nb, V, Ti, and Cu are respectively added in the form of ferro-niobium, ferro-vanadium, ferro-titanium, and metallic copper. According to the composition of the design, ferro-niobium, ferro-vanadium, and ferro-titanium are added in the form of Si, Mn, and Cr in the step 4. After the secondary alloying is completed, it is added to complete the alloying of Nb, V, and Ti. Metal copper is added at any time during the process of tapping and refining LF to complete the alloying of Cu.
5. The method for smelting and continuous casting of high Cr-Si alloyed hot-formed steel according to any one of claims 1 to 3, characterized in that, the alloying of 50 to 80% of silicon is completed in the first alloying, 85 -90% manganese alloying and 25-75% chromium alloying.
6. According to the method for smelting and continuous casting of high Cr-Si alloyed hot-formed steel according to any one of claims 1 to 3, it is characterized in that, in the primary alloying and secondary alloying, the various alloy materials The amount added is calculated according to the following formula:

   Addition amount of alloy material=alloying ratio*component target value/(content ratio of alloy element in added alloy material*alloy yield).
7. The method for smelting and continuous casting of high-Cr-Si alloyed hot-formed steel according to any one of claims 1 to 3, characterized in that the deoxidation and alloying start when the converter taps 1/5 of the steel into the ladle Carry out the addition of materials required for deoxidizer alloying, and the addition is completed when it reaches 2/3.
8. The method for smelting and continuous casting of high Cr-Si alloyed hot-formed steel according to any one of claims 1 to 3, characterized in that, the deoxidized alloyed material is added in batches, and 5 ～18kg/ton of molten steel, the interval between batches is 1～2min.
9. The method for smelting and continuous casting of high-Cr-Si alloyed hot-formed steel according to any one of claims 1 to 3, characterized in that the silicon-based alloys used for the primary alloying are ferrosilicon and manganese-based alloys It is medium carbon ferromanganese, and the chromium alloy is high carbon ferrochrome; the silicon alloy used for secondary alloying is ferrosilicon, the manganese alloy is high carbon ferromanganese, and the chromium alloy is high carbon ferrochrome.
10. The method for smelting and continuous casting of high Cr-Si alloyed hot-formed steel according to claim 4, characterized in that the alloying of each microalloying element is completed once.

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