An ultra-low temperature high manganese steel continuous casting non-reactive protective slag

Abstract

The application discloses a kind of ultra-low temperature high manganese steel continuous casting non-reactive protective slag, belong to the technical field of protective slag.The mass percentage of the protective slag is as follows: CaO: 30%~45%, SiO2: 30%~45%, Al2O3: 6~10%, Na2O:<3%, MnO: 15~20%, F ‑ <5%, Li2O: 3%~5%, MgO≤2%, Fe2O3≤1%, 0.8≤(CaO / SiO2)≤1.3, the rest is impurity.The application aims to provide a kind of non-reactive continuous casting mould protective slag suitable for ultra-low temperature high manganese steel slab.The addition of 15%~20% MnO to the protective slag changes the slag-metal reactivity of high manganese steel, so that (SiO2) in the protective slag does not react with [Mn] in the steel during continuous casting, the composition and performance remain stable, that is, the protective slag has good lubrication and heat control characteristics throughout the continuous casting process, thereby ensuring the smooth continuous casting of ultra-low temperature high manganese steel and good surface quality of the billet.

Description

Technical Field

[0001] This invention relates to the field of protective slag technology, and more specifically, to a non-reactive protective slag for ultra-low temperature high-manganese steel continuous casting. Background Technology

[0002] In recent years, ultra-low temperature high-manganese steel has attracted widespread attention in the industry due to its low-temperature performance comparable to traditional storage tank construction material 9Ni steel, and its significant price advantage. However, the high manganese content of ultra-low temperature high-manganese steel can lead to low thermal conductivity in the billet shell, increased linear expansion coefficient of the cast billet, and significant thermal stress during cooling, greatly increasing the risk of steel leakage. This results in surface quality defects in the billet shell during continuous casting. Factory production surveys indicate that using ordinary carbon steel protective slag for casting in the high-manganese steel production process causes serious slag-metal reactivity problems, affecting the composition and performance of the protective slag, and even making single-furnace casting impossible, resulting in poor billet surface quality. During the casting of ultra-low temperature high-manganese steel, the high manganese content in the molten steel ([Mn] = 22wt%~25wt%) makes it easy to react with (SiO2) in the protective slag. The specific reaction is: 1 / 2(SiO2) + [Mn] = 1 / 2[Si] + (MnO). After the steel slag reacts, the SiO2 content in the protective slag decreases and the MnO content increases, which will lead to an incoordination of the lubrication and heat transfer functions of the protective slag. Changes in properties such as melting point, viscosity and crystallization of the protective slag will prevent the continuous casting process from being completed smoothly, and the billet will produce surface quality defects such as depressions and longitudinal cracks.

[0003] This invention designs a non-reactive protective slag for ultra-low temperature high-manganese steel continuous casting. The purpose is to change the content of MnO and SiO2 in the protective slag so that the Gibbs free energy of the slag-metal reaction is greater than zero, that is, the slag-metal reaction no longer occurs. The composition and properties of the protective slag remain stable during the continuous casting process, and it has good heat transfer control and lubrication performance, thereby ensuring the surface quality of the cast billet.

[0004] Chinese patent CN 113458351 A reports a protective slag containing MnO for high-alumina steel. The principle is to add 12.5% ​​to 14.5% MnO to the protective slag to replace SiO2 and react with Al in the molten steel, thus ensuring the stability of the SiO2 content in the protective slag during the casting process. However, this protective slag is suitable for continuous casting of high-alumina steel with an Al content of less than 0.6% to 1.5%, but not for continuous casting of high-manganese steel for ultra-low temperature applications with a Mn content of 25%.

[0005] Chinese patent CN 107498012A discloses a mold flux for a high-alumina TRIP steel continuous casting mold. This is achieved by adding 5.8–6.9% MnO and 7.2–11.5% BaO to the flux. MnO preferentially reacts with Al in the molten steel, rather than SiO2. 2+The ion compensation effect promotes the networking effect of silicates and aluminates in the melt structure of the protective slag, and controls the crystallization rate of calcium feldspar to 40% to 60%, which meets the performance requirements of continuous casting protective slag. However, the high crystallization rate protective slag cannot meet the lubrication and heat transfer requirements of the protective slag for high manganese steel at ultra-low temperature.

[0006] Chinese patent CN 114054699 A reports a mold flux for high-manganese low-temperature steel continuous casting, with a CaO / Al2O3 ratio of 0.71–2.25. This flux exhibits low viscosity and melting temperature, ensuring a reasonable slag consumption per ton of steel. It also controls the SiO2 content (2–6%) at a low level and adds less than 9% MnO to weaken the steel-slag interface reaction. However, when the Mn content in the steel is too high, slag-metal reaction is still unavoidable, making it unsuitable for ultra-low temperature high-manganese steel continuous casting production.

[0007] Chinese patent CN 116809882 A discloses a protective slag for continuously cast austenitic high-manganese steel slabs, with a CaO / SiO2 ratio of 0.67-1.08. It involves adding 6-8% MnO2 to the slag to inhibit the redox reaction between Mn in the steel and some oxides in the protective slag during continuous casting. However, the presence of 24-30% SiO2 in the slag still results in a reaction with Mn in the steel, failing to completely solve the problem of steel-slag reactivity. As continuous casting progresses, the composition and properties of the protective slag will still exceed the suitable range.

[0008] Chinese patent CN 112828253 A reports a protective slag for continuous casting of high-manganese steel for offshore platforms. It employs a CaO-SiO2 system with a basicity of 1.18–1.54, controlling the melting point of the slag below 1000℃ and reducing the Al2O3 content to decrease the formation of high-melting-point substances. Heat transfer and lubrication are controlled by inhibiting crystal precipitation in the slag. This method is applicable to high-manganese steel with a manganese content of approximately 10%, and is not suitable for ultra-low temperature high-manganese steel continuous casting production with a manganese content exceeding 23%.

[0009] Chinese patent CN 103817302A discloses a mold flux for continuous casting of wear-resistant high-manganese steel for large round billets. The mold flux has a basicity of 0.8 to 1.1. By increasing the viscosity of the mold flux, the liquid slag flows into the gap between the billet shell and the copper plate more evenly, avoiding cracks caused by uneven heat transfer. 2 to 8% MnO is added to the slag to weaken conduction and heat transfer. However, the influence of the amount of MnO added on the reactivity of slag and metal during continuous casting is not considered. Furthermore, the performance requirements of the mold flux are different for slab and large round billet continuous casting. This mold flux is not suitable for the continuous casting production of ultra-low temperature high-manganese steel.

[0010] Chinese patent CN 116020994A reports a low-carbon, high-manganese steel protective slag, the composition of which is CaO: 25-35%, SiO2: 25-35%, Al2O3: 3.5-8%, Na2O: 2-6%, MnO2: 0-2%, F- : 3~8%, MgO: 0.5~2%, Fe2O3: 0~1%, C tot The content of the protective slag is 15-20%, and the moisture content is <1.0%. However, this protective slag is mainly used for continuous casting of large round billets of low carbon high manganese steel ([Mn] = 3.5wt%~8wt%), and is not suitable for continuous casting of ultra-low temperature high manganese steel slabs.

[0011] Chinese patent CN 113523215 B discloses a continuous casting protective slag for high-manganese steel slabs ([Mn] = 20wt%~25wt%), controlling the binary basicity (CaO / SiO2) of the protective slag to be 0.75~0.95, the melting point to be 880~950℃, and the MnO content in the slag to be 4~7%. This protective slag did not consider the reactivity of the slag with metals in its design, and its properties will change during continuous casting, failing to meet the production requirements of high-manganese steel.

[0012] Chinese patent CN 113385647 A reports a protective slag for continuous casting of high-carbon high-manganese steel slabs ([C] = 0.9wt%~1.3wt%, [Mn] = 11wt%~16wt%). The slag uses a CaO-SiO2 system with a binary basicity (CaO / SiO2) of 0.74~0.86, Al2O3 <5%, viscosity of 0.10~0.15 Pa·s, and melting point of 950~1030℃. The lower basicity and melting point ensure the lubrication required for the slab during continuous casting; however, the heat transfer capacity of the protective slag is insufficient for the ultra-low temperature continuous casting production of high-manganese steel, which has even lower thermal conductivity.

[0013] Chinese patent CN 109112418 B discloses a continuous casting method for high manganese steel, in which the protective slag has the characteristics of low melting point and low viscosity. It is used for the production of large square billets with Mn content of 4.5-5.5% in steel, but is not suitable for the continuous casting production of ultra-low temperature high manganese steel. Summary of the Invention

[0014] 1. The technical problem that the invention aims to solve

[0015] To address the shortcomings and deficiencies of existing technologies, this invention provides a non-reactive protective slag for continuous casting of ultra-low temperature high-manganese steel. The invention aims to provide a non-reactive protective slag suitable for continuous casting molds used in ultra-low temperature high-manganese steel slabs. During the continuous casting process, the protective slag does not react with [Mn] in the molten steel, maintaining stable composition and properties. This means that the protective slag possesses excellent lubrication and heat transfer control characteristics throughout the entire continuous casting process, thereby ensuring smooth continuous casting of ultra-low temperature high-manganese steel and good slab surface quality.

[0016] 2. Technical Solution

[0017] To achieve the above objectives, the technical solution provided by this invention is as follows:

[0018] This invention discloses a non-reactive protective slag for ultra-low temperature high-manganese steel continuous casting, wherein the mass percentages of the protective slag are as follows: CaO: 30%–45%, SiO2: 30%–45%, Al2O3: 6–10%, Na2O: <3%, MnO: 15–20%, F - <5%, Li2O: 3%~5%, MgO≤2%, Fe2O3≤1%, 0.8≤(CaO / SiO2)≤1.3, the rest are impurities.

[0019] Furthermore, the chemical composition and mass percentage of the protective slag are as follows: CaO / SiO2 = 0.90, CaO: 32.61%, SiO2: 36.23%, Al2O3: 6.59%, Na2O: 1.09%, MnO: 16.56%, Li2O: 3.38%, F - 2.12%, MgO+Fe2O3=1.42%, the remainder is impurities.

[0020] Further, the chemical composition and mass percentage of the protective slag are as follows: CaO / SiO2 = 1.01, CaO: 35.55%, SiO2: 35.20%, Al2O3: 6.21%, Na2O: 1.42%, MnO: 17.34%, Li2O: 3.04%, F - 0.57%, MgO+Fe2O3=0.67%, the remainder are impurities.

[0021] Furthermore, the chemical composition and mass percentage of the protective slag are as follows: CaO / SiO2 = 1.25, CaO: 37.50%, SiO2: 30.00%, Al2O3: 6.36%, Na2O: 1.34%, MnO: 19.68%, Li2O: 3.47%, F - 0.87%, MgO+Fe2O3=0.78%, the remainder are impurities.

[0022] Furthermore, the metallurgical properties of the non-reactive protective slag are as follows: melting point 920~1180℃, viscosity at 1300℃ 0.05~0.25Pa·s.

[0023] 3. Beneficial effects

[0024] Compared with the prior art, the technical solution provided by this invention has the following advantages:

[0025] The features of this invention are: (1) Compared with traditional slag, the non-reactive protective slag for continuous casting of ultra-low temperature high manganese steel described in this invention is a non-reactive slag. In this invention, the reactive component (only (SiO2)) reacts with [Mn] in ultra-low temperature high manganese steel. By controlling the amount of MnO added to the original slag, the chemical reaction proceeds in reverse, and the Gibbs free energy is greater than 0, thereby effectively inhibiting the slag-metal reaction.

[0026] (2) During continuous casting, the amphoteric oxide Al2O3 will mainly exist in the form of acidic oxide as a network formation, which can stabilize the viscosity of the protective slag within a suitable range (0.05-0.25 Pa·s) to ensure the smooth casting of low-temperature high-manganese steel.

[0027] (3) The protective slag of this invention is a non-reactive protective slag for ultra-low temperature high-manganese steel continuous casting. The basic oxides are CaO, MnO (15%~20%) and Na2O, the acidic oxides are SiO2 and the amphoteric oxide Al2O3 with a low initial content, and the fluxes are Li2O and F. - With a crystallization rate of <10%, it is suitable for ultra-low temperature high manganese steel. Detailed Implementation

[0028] The present invention will be further described below with reference to the embodiments, wherein the impurities in each embodiment are MgO≤2% and Fe2O3≤1%:

[0029] Example 1

[0030] This embodiment describes a non-reactive protective slag for ultra-low temperature high-manganese steel continuous casting. The mass percentage of the protective slag is as follows:

[0031] CaO / SiO2=0.90, CaO: 32.61%, SiO2: 36.23%, Al2O3: 6.59%, Na2O: 1.09%, MnO: 16.56%, Li2O: 3.38%, F - 2.12%, MgO+Fe2O3=1.42%, the remainder is impurities.

[0032] Preparation and testing methods: Weigh the chemically pure reagents for the protective slag according to the designed composition, mechanically stir and mix them, then place the mixed sample into a graphite crucible and place it in a high-temperature silicon-molybdenum furnace, and keep it at 1300℃ for 30 minutes to ensure that the slag composition is uniformly mixed. Use relevant equipment to determine the viscosity and melting temperature of the protective slag for continuous casting crystallizer, and adopt the metallurgical industry standards YB / T 185-2017 and YB / T 186-2014 for the determination.

[0033] The main chemical composition (wt%) and metallurgical performance indicators of the protective slag are shown in Table 1.

[0034] Example 2

[0035] This embodiment describes a non-reactive protective slag for ultra-low temperature high-manganese steel continuous casting. The mass percentage of the protective slag is as follows:

[0036] CaO / SiO2=1.01, CaO: 35.55%, SiO2: 35.20%, Al2O3: 6.21%, Na2O: 1.42%, MnO: 17.34%, Li2O: 3.04%, F - 0.57%, MgO+Fe2O3=0.67%, the remainder are impurities.

[0037] Preparation and testing methods: Same as in Example 1.

[0038] The main chemical composition (wt%) and metallurgical performance indicators of the protective slag are shown in Table 1.

[0039] Example 3

[0040] This embodiment describes a non-reactive protective slag for ultra-low temperature high-manganese steel continuous casting. The mass percentage of the protective slag is as follows:

[0041] CaO / SiO2=1.25, CaO: 37.50%, SiO2: 30.00%, Al2O3: 6.36%, Na2O: 1.34%, MnO: 19.68%, Li2O: 3.47%, F - 0.87%, MgO+Fe2O3=0.78%, the remainder are impurities.

[0042] Preparation and testing methods: Same as in Example 1.

[0043] The main chemical composition (wt%) and metallurgical performance indicators of the protective slag are shown in Table 1.

[0044] Comparative Example 1

[0045] The protective slag in this comparative example consists of the following mass percentages: CaO / SiO2 = 1.20, CaO: 36.74%, SiO2: 30.62%, Al2O3: 10.31%, MgO: 1%, Na2O: 6.9%, Li2O: 2%, F - 7.76%, MnO: 4.67%.

[0046] Preparation and testing methods: Same as in Example 1.

[0047] Comparative Example 2

[0048] The protective slag in this comparative example consists of the following mass percentages: CaO / SiO2 = 0.84, CaO: 27.15%, SiO2: 32.15%, Al2O3: 6.46%, MgO: 1%, Na2O: 10.36%, Li2O: 2%, F - :9.39%, MnO: 4.34%, BaO: 7.15%.

[0049] Preparation and testing methods: Same as in Example 1.

[0050] Comparative Example 3

[0051] The protective slag in this comparative example consists of the following mass percentages: CaO / SiO2 = 0.79, CaO: 27.68%, SiO2: 34.93%, Al2O3: 5.06%, MgO: 3.49%, Na2O: 14.06%, Li2O: 1.50%, F - :8.50%, MnO: 4.58%, BaO: 0.20%.

[0052] Preparation and testing methods: Same as in Example 1.

[0053] The main chemical composition (wt%) and metallurgical performance indicators of the protective slag are shown in Tables 1 and 2.

[0054] Examples 1-3 are non-reactive protective slags for continuous casting of ultra-low temperature high-manganese steel. Laboratory slag-metal reaction experiments and on-site continuous casting production practice results show that the non-reactive protective slags for continuous casting of ultra-low temperature high-manganese steel can meet the casting requirements. During the continuous casting process, the protective slag has suitable lubrication and stable heat transfer characteristics, and the surface quality of the cast billet is significantly improved.

[0055] Table 1. Chemical composition of protective slag and performance indicators of steel slag before and after reaction in Examples 1-3

[0056]

[0057] Table 2. Performance index test results of protective slags in Comparative Examples 1-3

[0058]

[0059] As can be seen from the above indicators, the non-reactive protective slags for continuous casting of ultra-low temperature high manganese steel prepared in Examples 1-3 have better performance indicators and parameters, such as melting point, viscosity and reactivity than those of Comparative Examples 1-3. The performance of the non-reactive protective slags for continuous casting of ultra-low temperature high manganese steel prepared in Examples 1-3 meets the requirements of the process parameters of the actual continuous casting production process, especially in that no slag-metal reaction occurs during the continuous casting process, and the appropriate performance is maintained.

[0060] On-site casting experiments were conducted using the slag from Example 3. Analysis of slag samples showed that the main mineral phases of the slag were gunpowder (Ca4Si2O7F2) and manganese olivine (Mn2[SiO4]), which effectively controlled heat transfer and lubrication. In on-site production, two furnaces were successfully cast consecutively, with no slag streaks or significant liquid level fluctuations in the crystallizer. Problems such as depressions and cracks on the surface of the billet were significantly improved.

[0061] Specifically, the continuous casting mold flux of this invention contains a reactive component (SiO2). By adding a relatively high content of MnO (15-20%), the reaction between (SiO2) in the slag and [Mn] in the steel is effectively suppressed. No more slag-metal reaction will occur during continuous casting, and the mold flux will maintain its initial properties, ensuring smooth continuous casting. The basic metallurgical properties of the non-reactive mold flux for ultra-low temperature high-manganese steel continuous casting are as follows: melting point 920-1180℃, viscosity at 1300℃ 0.05-0.25 Pa·s, suitable for continuous casting production of ultra-low temperature high-manganese steel slabs with [Mn] = 22wt%-25wt%.

[0062] In the protective slag of this invention, CaO and SiO2 are the main components, which are widely available and inexpensive. Increasing the CaO / SiO2 ratio can reduce viscosity. CaO can enhance the steel's ability to absorb oxide inclusions, while O... 2- The release of ions can reduce the viscosity of the slag; SiO2, as a network forger, can increase the degree of polymerization of the slag; Al2O3, as an amphoteric oxide, is acidic in basic slag and basic in acidic slag. CaO and SiO2 are controlled within the range of 30%–45%, and the initial Al2O3 is controlled at 6%–10%.

[0063] F - It is the main fluxing agent in the non-reactive protective slag for ultra-low temperature high-manganese steel continuous casting in this invention. It can effectively adjust viscosity, melting point and crystallization temperature. In order to ensure the performance of the slag after reaction, this invention controls it to be below 5%.

[0064] MnO is the key component for controlling the metal reactivity of the protective slag in this invention. As a transition oxide, MnO can reduce the radiative heat transfer capacity of the protective slag and exert a nonlinear effect on the crystallization activation energy, thereby altering the crystallization properties of the protective slag. Its depolymerization effect on the silicon-oxygen tetrahedral structure in the protective slag can also change its viscosity. Adding 15-20% MnO to the slag ensures that the metal reaction does not occur while simultaneously achieving a balance between lubrication and heat transfer.

[0065] Al2O3 is acidic in the non-reactive continuous casting protective slag of ultra-low temperature high manganese steel and can act as a network forging body to change the viscosity of the protective slag. However, the addition of a large amount of Al2O3 will affect the formation of crystalline mineral phases and have an adverse effect on the heat transfer performance of the protective slag. In this invention, the Al2O3 content is controlled at 6-10%.

[0066] Li₂O is often used as one of the most effective fluxing agents in continuous casting protective slag, which can lower the melting point and viscosity of the slag and inhibit crystallization within a certain range. However, it is expensive and its fluxing effect is significant at low contents (the melting point decreases by 30-48°C for every 1 wt% of Li₂O). Therefore, this invention controls the Li₂O content to be within the range of 3% to 5%.

[0067] Since MgO and Fe2O3 are unavoidable impurities introduced into the protective slag, this invention will control them to be ≤2% for MgO and ≤1% for Fe2O3.

[0068] To address the aforementioned shortcomings of existing technologies, this invention aims to provide a non-reactive mold flux suitable for ultra-low temperature high-manganese steel slab casting. During continuous casting, the flux does not react with [Mn] in the molten steel, maintaining stable composition and properties. This means the flux exhibits excellent lubrication and heat transfer control characteristics throughout the entire continuous casting process, thereby ensuring smooth casting of ultra-low temperature high-manganese steel and good slab surface quality.

[0069] The present invention and its embodiments have been described above illustratively, and this description is not restrictive. Therefore, if those skilled in the art are inspired by this description and design similar structures and embodiments without departing from the spirit of the invention, such designs should fall within the protection scope of the present invention.

Claims

1. A non-reactive protective slag for ultra-low temperature high-manganese steel continuous casting, characterized in that: The mass percentages of the protective slag are as follows: CaO: 30%–45%, SiO2: 30%–45%, Al2O3: 6%–10%, Na2O: <3%, MnO: 15%–20%, F - <5%, Li2O: 3%~5%, MgO≤2%, Fe2O3≤1%, 0.8≤(CaO / SiO2)≤1.3, the rest are impurities.

2. The non-reactive protective slag for ultra-low temperature high-manganese steel continuous casting according to claim 1, characterized in that: The chemical composition and mass percentage of the protective slag are as follows: CaO / SiO2 = 0.90, CaO: 32.61%, SiO2: 36.23%, Al2O3: 6.59%, Na2O: 1.09%, MnO: 16.56%, Li2O: 3.38%, F - 2.12%, MgO+Fe2O3=1.42%, the remainder is impurities.

3. The non-reactive protective slag for ultra-low temperature high-manganese steel continuous casting according to claim 1, characterized in that: The chemical composition and mass percentage of the protective slag are as follows: CaO / SiO2 = 1.01, CaO: 35.55%, SiO2: 35.20%, Al2O3: 6.21%, Na2O: 1.42%, MnO: 17.34%, Li2O: 3.04%, F - 0.57%, MgO+Fe2O3=0.67%, the remainder are impurities.

4. The non-reactive protective slag for ultra-low temperature high-manganese steel continuous casting according to claim 1, characterized in that: The chemical composition and mass percentage of the protective slag are as follows: CaO / SiO2 = 1.25, CaO: 37.50%, SiO2: 30.00%, Al2O3: 6.36%, Na2O: 1.34%, MnO: 19.68%, Li2O: 3.47%, F - 0.87%, MgO+Fe2O3=0.78%, the remainder are impurities.

5. The non-reactive protective slag for ultra-low temperature high-manganese steel continuous casting according to claim 1, characterized in that: The metallurgical properties of the non-reactive protective slag are: melting point 920~1180℃, viscosity at 1300℃ 0.05~0.25Pa·s.

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