Continuous casting covering slag suitable for high-Ti wear-resistant steel and application of continuous casting covering slag

Abstract

The invention relates to continuous casting covering slag suitable for high-Ti wear-resistant steel and application of the continuous casting covering slag, and the continuous casting covering slag comprises the following components in percentage by mass: 5-8% of C, 32-36% of CaO, 30-40% of SiO2, 5-10% of Al2O3, 6-8% of B2O3, 5-8% of Li2O, 6-9% of (MnO + TiO2) and inevitable impurities. The casting powder is stable in performance and good in inclusion absorption capacity in the using process, the-20 DEG C impact absorption energy of a steel plate is effectively improved, and the phenomenon that in the high-Ti wear-resistant steel casting process, due to severe slag-metal reaction, the lubricating property and heat conductivity of the casting powder are deteriorated, and consequently surface cracks are generated on a casting blank is avoided. The high-Ti wear-resistant steel continuous casting process can be smoothly carried out, surface cracks of a casting blank are reduced, the impact performance is improved, the product quality is improved, and the service life of the material is prolonged.

Description

Technical Field

[0001] The present invention belongs to the technical field of metallurgy, and particularly relates to a continuous casting mold powder applicable to high-Ti wear-resistant steel and its application. Background Art

[0002] Low-alloy martensitic wear-resistant steel is often used in fields such as engineering machinery and mining due to its good wear resistance, high strength and toughness, and low cost. In recent years, to further improve wear resistance, a new generation of high-Ti wear-resistant steel with TiC as the wear-resistant phase has been developed, with a Ti content of up to 0.4 - 0.8%. Its wear resistance can be increased by more than 50% compared to traditional wear-resistant steel. However, during the continuous casting process of high-Ti wear-resistant steel, Ti in the molten steel easily reacts with SiO2 in the slag, resulting in an increase in the basicity and viscosity of the mold powder. The consumption of SiO2 and the generated TiO2 will also react with CaO in the mold powder to form high-melting-point perovskite, seriously deteriorating the lubrication and heat transfer functions of the mold powder, thereby causing crack defects on the surface of the continuous casting billet. At the same time, Ti elements are also prone to react with N in the air and molten steel, and it is extremely easy to form TiN inclusions in the molten steel under high Ti content, often causing problems such as nozzle nodulation and blockage. Also, because TiN is angular and extremely difficult to deform during the rolling process, it will also seriously affect the impact performance of the steel.

[0003] Therefore, the present invention designs a continuous casting mold powder applicable to high-Ti wear-resistant steel, which has stable performance during use, good ability to absorb inclusions, effectively improves the impact energy absorption at -20°C, and avoids the phenomenon of reduced slag lubricity and thermal conductivity caused by intense slag-metal reactions during the casting of high-Ti wear-resistant steel, thereby preventing surface cracks on the continuous casting billet. The present invention is beneficial to the smooth progress of the continuous casting process of high-Ti wear-resistant steel, reduces surface cracks of the continuous casting billet, improves the impact performance, enhances the product quality, and extends the service life of the material. Summary of the Invention

[0004] The purpose of the present invention is to provide a continuous casting mold powder applicable to high-Ti wear-resistant steel and its application, which has good inclusion dissolution and absorption ability and effectively improves the impact performance of the steel plate at -20°C. After continuous casting, the surface of the continuous casting billet is good, and the crack rate is <1%.

[0005] To solve the above technical problems, the technical solution adopted by the present invention is as follows: A continuous casting mold powder applicable to high-Ti wear-resistant steel, by mass percentage, its components include C: 5 - 8%, CaO: 32 - 36%, SiO2: 30 - 40%, Al2O3: 5 - 10%, B2O3: 6 - 8%, Li2O: 5 - 8%, (MnO + TiO2): 6 - 9%, and inevitable impurities.

[0006] The basicity (CaO / SiO2) of the mold powder described in the present invention is 0.8 to 1.2, and the mass ratio of SiO2 / (MnO+TiO2) ≥ 3.5.

[0007] The basicity of the mold powder described in the present invention is 0.8 to 1.2, and the mass ratio of SiO2 / (MnO+TiO2) ≥ 3.5.

[0008] The viscosity of the mold powder described in the present invention at 1300 °C is 0.1 to 0.25 Pa·s, the hemispherical melting temperature is 920 to 1100 °C, and the mold powder has good ability to dissolve and absorb inclusions.

[0009] Another object of the present invention is to provide the application of the above-mentioned continuous casting mold powder suitable for high-Ti wear-resistant steel in the preparation of high-Ti wear-resistant steel.

[0010] After the high-Ti wear-resistant steel described in the present invention uses this continuous casting mold powder and undergoes quenching + low-temperature tempering heat treatment, the impact performance is effectively improved, and the impact absorption energy at -20 °C ≥ 24 J.

[0011] For the high-Ti wear-resistant steel described in the present invention, the surface of the continuous casting billet is good, and the crack rate < 1%.

[0012] The chemical composition and mass percentage content of the high-Ti wear-resistant steel described in the present invention are: C: 0.19 to 0.21%, Mn: 1.72 to 1.95%, Si: 0.3 to 0.4%, P ≤ 0.015%, S ≤ 0.004%, Cr: 0.28 to 0.5%, Als: 0.4 to 0.6%, Ti: 0.4 to 0.6%, and the balance is Fe and unavoidable impurities.

[0013] The surface hardness of the high-Ti wear-resistant steel described in the present invention ≥ 380 HBW, yield strength ≥ 900 MPa, tensile strength ≥ 1250 MPa.

[0014] The action mechanism and the limitation of the dosage of each component of the continuous casting mold powder suitable for high-Ti wear-resistant steel in the present invention are described as follows: CaO: One of the main components of the mold powder, the main component forming cuspidine, existing in the form of Ca 2+ and O 2- in the molten state. O 2- will break the silicon-oxygen bond in the [SiO4] 4- tetrahedral structure, thus reducing the viscosity of the mold powder. Excessive CaO will overly enhance the initial crystallization ability of the mold powder and affect its lubrication effect. And the mold powder needs to control the heat transfer through crystallization. Therefore, the mass percentage range of CaO in the present invention is determined to be 32 to 36%.

[0015] SiO2: It is also one of the main components of traditional mold fluxes. As a major acidic oxide, it acts as a network former in the molten slag and exists in the form of [SiO4] 4- tetrahedra. When the content of SiO2 increases, the glassiness of the molten slag increases, and the lubrication effect improves. If the content of SiO2 is too low, the basicity of the mold flux will increase, and the crystallization performance of the mold flux will increase, which is not conducive to the lubrication effect. When smelting steel grades with high Ti content, Ti in the molten steel easily reacts with SiO2 in the slag. The consumption of SiO2 and the formed TiO2 react with CaO in the mold flux to form high-melting-point perovskite, seriously deteriorating the lubrication and heat transfer functions of the mold flux. Therefore, by increasing the addition amount of SiO2, the high glassiness of the molten slag is maintained to offset the adverse effects brought by the consumption of SiO2 during the casting process as much as possible. Therefore, the mass percentage range of SiO2 in the present invention is determined to be 30-40%.

[0016] Al2O3: It belongs to amphoteric oxides and is a network former in basic molten slags. The formed [AlO4] 5- tetrahedra and [SiO4] 4- tetrahedra have certain similarities in bond energy and bond angle and can replace SiO2 to a certain extent in the molten slag, weakening the occurrence of slag-metal interface reactions. However, if the content is too high, it will cause too strong crystallization performance, affecting the comprehensive performance of its metallurgical functions such as lubricating the continuous casting billet and controlling heat transfer, and easily leading to problems such as cracks, depressions or deep oscillation marks on the surface of the continuous casting billet. Also, due to its relatively high melting point and the tendency to form high-melting-point compounds in some cases, its content should not be too high. Therefore, the mass percentage range of Al2O3 in the present invention is determined to be 5-10%.

[0017] B2O3: It is an acidic flux and often exists in the form of [BO3] 3- and [BO4] 5- structural units in the molten slag, which can adjust the acidity and basicity of the mold flux. B2O3 can form low-melting-point compounds with other oxides, significantly reducing the melting temperature of the mold flux, increasing the tendency of forming glassy bodies, inhibiting the precipitation of high-temperature phases, improving the ability of the molten slag to absorb inclusions, enhancing the stability of the performance of the mold flux after absorbing inclusions, and also reducing the viscosity of the molten slag and changing the shape and size of the crystallized phases. Therefore, the mass percentage range of B2O3 in the present invention is determined to be 6-8%.

[0018] Li2O: It is a strong flux that will reduce the polymerization degree and viscosity of silicate molten slags. Even if the content is small, it has a great impact on the melting temperature. Due to Li +With a small radius and small steric hindrance, when the Li2O content is too high, high-melting-point precipitates are likely to precipitate, improving the crystallization ability of the mold powder. Therefore, the addition amount of Li2O in the mold powder should not be too high. Adding an appropriate amount of Li2O can obtain a mold powder with a low melting point, low viscosity, and good glassiness. Therefore, the mass percentage range of Li2O in the present invention is determined to be 5-8%.

[0019] MnO + TiO2: MnO belongs to a strongly oxidizing component, which can effectively reduce the viscosity and melting temperature of the mold powder. Appropriate addition can inhibit the reaction between Ti element in the molten steel and SiO2 in the slag, maintaining the glassiness of the molten slag. TiO2 belongs to an amphoteric oxide. Appropriate addition will inhibit the progress of the slag-metal reaction and can play a role in fixing SiO2. Therefore, the mass percentage range of (MnO + TiO2) in the present invention is determined to be 6-9%.

[0020] C: It plays a skeletal role in the mold powder, mainly used to adjust the melting rate of the mold powder. When the carbon content is too low, the heat conduction rate accelerates, which is not conducive to the surface quality of the continuous casting billet. When the carbon content is too high, the melting rate of the mold powder will be reduced. Therefore, the mass percentage range of C in the present invention is determined to be 5-8%.

[0021] The present invention requires that the basicity (CaO / SiO2) range of the mold powder is 0.8-1.1, and the mass ratio of SiO2 / (MnO + TiO2) ≥ 3.5. When the basicity changes in the range of 0.8-1.2, the molten slag has good glassiness. When the basicity is lower than 0.8, the proportion of the vitreous body is too large, which is not conducive to controlling heat transfer and easily affects the surface quality of the continuous casting billet. When the basicity is higher than 1.2, the viscosity of the mold powder will increase, and with the further consumption of SiO2 in the slag, its lubrication and heat transfer performance will be seriously affected. Therefore, the basicity (CaO / SiO2) range of the mold powder is required to be 0.8-1.2; MnO and TiO2, as components that inhibit the reaction between Ti in the molten steel and SiO2 in the slag, have the functions of reducing the slag-metal reaction and fixing SiO2. If the mass ratio of SiO2 / (MnO + TiO2) < 3.5, during the continuous casting process, with the consumption of SiO2, it will be unfavorable to maintain the glassiness of the mold powder, deteriorate the lubricity and thermal conductivity of the mold powder, and affect the smooth progress of the continuous casting process and the surface quality of the continuous casting billet. Therefore, the mass ratio of SiO2 / (MnO + TiO2) ≥ 3.5 is required.

[0022] For high-Ti wear-resistant steel, the main reason for the low impact energy at -20°C is the Ti-containing inclusions with too large sizes. Under the condition that other process conditions remain unchanged in the present invention, improving the inclusion dissolution and absorption ability of the slag system can effectively improve the impact energy at -20°C.

[0023] Compared with the prior art, the present invention has the following beneficial technical effects: The present invention designs a continuous casting mold powder applicable to high-Ti wear-resistant steel, which has stable performance during use, good ability to absorb inclusions, effectively improves the impact energy absorption at -20°C, and avoids the reduction of the slag lubricity and thermal conductivity caused by the violent slag-metal reaction during the casting of high-Ti wear-resistant steel, thereby preventing the occurrence of surface cracks in the cast billet. The present invention is conducive to the smooth progress of the continuous casting process of high-Ti wear-resistant steel, reduces surface cracks of the cast billet, improves the impact performance, enhances the product quality, and extends the service life of the material. Detailed Embodiments

[0024] The present invention will be further described in detail below with reference to specific embodiments.

[0025] Examples 1 - 5 A continuous casting mold powder applicable to high-Ti wear-resistant steel and its application are used to conduct production comparison experiments according to the present invention. The chemical composition range and mass percentage content of high-Ti wear-resistant steel are shown in Table 1.

[0026] Table 1 Chemical Composition of High-Ti Wear-Resistant Steel (wt%)

[0027] The production process adopts the process flow of traditional wear-resistant steel, namely converter → LF refining → RH refining → continuous casting → hot rolling → heat treatment. The mold powder is prepared by a conventional process, and the specific composition components and various parameter indexes are listed in Table 2. Before the continuous casting starts, the special mold powder for high-Ti wear-resistant steel is added. The whole continuous casting process adopts protective casting, and electromagnetic stirring and soft reduction are applied. The cross-section of the cast billet is 230×2050 mm 2 , and the casting speed is 0.8 - 1.0 m / min. Subsequently, the slab is hot rolled to 12 mm, and a conventional heat treatment process of quenching at 860°C + tempering at 180°C for 1 h is adopted.

[0028] The specific composition components and various parameter indexes of the mold powder used in Examples 1 - 5 are listed in Table 2, and the usage of the mold powder and the impact energy absorption of the steel plate at -20°C after tempering treatment are listed in Table 3.

[0029] Comparative Examples 1 - 2 The production process flow is exactly the same as that of the examples. The composition of the mold powder in the comparative examples is used for the production of conventional wear-resistant steel. The specific composition components and various parameter indexes are listed in Table 2. The usage of the mold powder and the impact energy absorption of the steel plate at -20°C after tempering treatment are listed in Table 3.

[0030] Table 2 Specific Chemical Compositions (wt%) and Various Parameter Indexes of the Mold Powder Used in Each Example and Comparative Example

[0031] Table 3 Usage of the Mold Powder and Performance of the Steel Plate

[0032] As can be seen from Table 3, during the casting process, when using the continuous casting mold powder of the high-Ti wear-resistant steel of the present invention, the condition in the mold is good, no slag bars are generated, the consumption rate of the mold powder is normal, the size of the flame is normal, no sticking alarm occurs, the oscillation marks on the surface of the slab are well controlled, the crack rate is <1%, there are no defects such as subcutaneous slag inclusions and pores, and the impact absorption energy at -20 °C has been effectively improved. It shows that compared with the traditional mold powder, the special mold powder for high-Ti wear-resistant steel designed by the present invention helps the continuous casting process to proceed smoothly, the surface of the slab has no cracks, and the impact performance is improved.

[0033] Table 4 Performance of High-Ti Wear-Resistant Steel

[0034] The above embodiments are only used to illustrate rather than limit the technical solutions of the present invention. Although the present invention has been described in detail with reference to the above embodiments, those of ordinary skill in the art should understand that: the present invention can still be modified or equivalently replaced, and any modification or partial replacement without departing from the spirit and scope of the present invention shall be covered by the scope of the claims of the present invention.

Claims

1. A continuous casting mold powder applicable to high-Ti wear-resistant steel, characterized in that, The mold powder, by mass percentage, comprises C: 5-8%, CaO: 32-36%, SiO2: 30-40%, Al2O3: 5-10%, B2O3: 6-8%, Li2O: 5-8%, (MnO + TiO2): 6-9%, and inevitable impurities.

2. The continuous casting powder for high-Ti wear-resistant steel according to claim 1, characterized in that, The basicity of the mold powder is 0.8-1.2, and the mass ratio of SiO2 / (MnO + TiO2) ≥ 3.

5.

3. The continuous casting mold powder for high-Ti wear-resistant steel according to claim 1, characterized in that, The viscosity of the mold powder at 1300 °C is 0.1-0.25 Pa·s, and the hemispherical melting temperature is 920-1100 °C.

4. Application of the continuous casting mold powder for high-Ti wear-resistant steel described in claims 1-3 in the preparation of high-Ti wear-resistant steel.

5. Use of a continuous casting mold powder for high-Ti wear-resistant steel according to claim 4 in the preparation of high-Ti wear-resistant steel, characterized in that, After the high-Ti wear-resistant steel uses this continuous casting mold powder and undergoes quenching + low-temperature tempering heat treatment, the impact energy absorption at -20 °C ≥ 24 J.

6. Use of a continuous casting mold powder for high-Ti wear-resistant steel according to claim 4 in the preparation of high-Ti wear-resistant steel, characterized in that, For the high-Ti wear-resistant steel, the surface of the cast slab is good, and the crack rate < 1%.

7. Use of a continuous casting mold powder for high-Ti wear-resistant steel according to any one of claims 4-6 in the preparation of high-Ti wear-resistant steel, characterized in that The chemical composition and mass percentage content of the high-Ti wear-resistant steel are: C: 0.19-0.21%, Mn: 1.72-1.95%, Si: 0.3-0.4%, P ≤ 0.015%, S ≤ 0.004%, Cr: 0.28-0.5%, Als: 0.4-0.6%, Ti: 0.4-0.6%, and the balance is Fe and inevitable impurities.

8. Use of a continuous casting mold powder for high-Ti wear-resistant steel according to any one of claims 4-6 in the preparation of high-Ti wear-resistant steel, characterized in that, The surface hardness of the high-Ti wear-resistant steel ≥ 380 HBW, the yield strength ≥ 900 MPa, and the tensile strength ≥ 1250 MPa.

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