A slag system and process for refining carbide size of high speed tool steel by electroslag remelting

Abstract

The application provides an ESR slag system and process for refining the size of carbide of high-speed tool steel, wherein the consumable electrode for ESR is treated by rare earth magnesium, and the slag system comprises the following components in percentage by mass: CaF2: 40-50%; CaO: 10-15%; Al2O3: 10-15%; MgO: 8-12%; RE2O3: 15-20%; SiO2: 0.5-1.0%; and the balance is inevitable impurities, and the impurity content is not more than 1%. By controlling the RE2O3 and MgO content in the slag system, and optimizing the content of key components such as CaF2, Al2O3 and SiO2, the application effectively inhibits the burning loss of rare earth and magnesium in the ESR process, and utilizes the rare earth and magnesium to inhibit the growth of primary carbide in the solidification process of high-speed steel and secondary carbide in the heat treatment process, so as to refine the carbide size of high-speed steel ingot and steel, and significantly improve the hardness, toughness and wear resistance of high-speed steel.

Description

Technical Field

[0001] This invention relates to the field of electrometallurgical technology, specifically to an electroslag remelting slag system and process for refining the carbide size of high-speed tool steel. Background Technology

[0002] High-speed tool steel possesses high hardness, high wear resistance, and high red hardness, making it widely used in the manufacture of cutting tools, molds, and other components. The performance of high-speed steel primarily depends on the size, morphology, and distribution of its carbides. However, in high-speed steel ingots prepared using the traditional electroslag remelting process, the primary carbides are large, and secondary carbides tend to grow during subsequent heat treatment, severely impacting the mechanical properties and service life of the high-speed steel.

[0003] Rare earth elements and magnesium have the functions of purifying molten steel, removing impurities, refining grains, and eliminating carbides, making them effective means of improving the performance of high-speed steel. However, during electroslag remelting, rare earth and magnesium elements are severely burned off due to the high temperature and oxidizing atmosphere, making it difficult for them to play their due role. Existing electroslag remelting slag systems mainly include ANF-6 slag (CaF2: 70%, Al2O3: 30%) and 60 / 20 / 20 slag (CaF2: 60%, Al2O3: 20%, CaO: 20%), but these slag systems are mainly used for ordinary steel grades and do not consider the protection of rare earth and magnesium, making them unsuitable for electroslag remelting of high-speed steel treated with rare earth and magnesium.

[0004] Therefore, how to suppress the burn-off of rare earth and magnesium through slag system design and process optimization, and refine the carbide size of high-speed tool steel, has become a key technical challenge to improve the quality of high-speed steel. Summary of the Invention

[0005] The technical objective of this invention is to address the shortcomings of the prior art by providing an electroslag remelting slag system and process for refining the carbide size of high-speed tool steel. This invention effectively suppresses the burn-off of rare earth and magnesium during electroslag remelting by optimizing the slag system composition and using rare earth magnesium-treated electrodes, thereby refining the carbide size of high-speed steel and improving its mechanical properties.

[0006] The technical solution adopted by this invention to solve its technical problem is: an electroslag remelting slag system for refining the carbide size of high-speed tool steel, wherein the consumable electrode of the electroslag remelting is treated with rare earth magnesium during preparation, and the slag system comprises the following components by mass percentage: CaF2: 40%–50%; CaO: 10%–15%; Al2O3: 10%–15%; MgO: 8%–12%; RE2O3: 15%–20%; SiO2: 0.5%–1.0%; the balance being unavoidable impurities, with an impurity content of no more than 1%.

[0007] Further, by mass percentage, the slag system preferably comprises the following components: CaF2: 42%–48%; CaO: 11%–15%; Al2O3: 11%–15%; MgO: 9%–11%; RE2O3: 16%–20%; SiO2: 0.6%–0.8%; the balance being unavoidable impurities, with an impurity content not exceeding 1%.

[0008] Furthermore, the consumable electrode contains 0.01wt% to 0.015wt% rare earth elements and 0.002wt% to 0.004wt% magnesium elements, and the rare earth elements in the consumable electrode are the same as those in the slag system.

[0009] Furthermore, the RE2O3 is one or a mixture of two of Ce2O3 and La2O3 in any proportion, and the rare earth elements in the slag system are the same as those in the consumable electrode. If the RE2O3 is a mixture of Ce2O3 and La2O3, then the mass ratio of rare earth elements Ce and La in the slag system is the same as the mass ratio of Ce and La in the consumable electrode.

[0010] Furthermore, the high-speed tool steel is tungsten-based high-speed steel, or molybdenum-based high-speed steel, or tungsten-molybdenum-based high-speed steel.

[0011] The present invention also provides an electroslag remelting process based on the above-mentioned electroslag remelting slag system, wherein the consumable electrode of the electroslag remelting is prepared by rare earth magnesium treatment, that is, rare earth and pure magnesium, or rare earth magnesium alloy, are added during the preparation of the consumable electrode to control the content of rare earth and magnesium in the electrode.

[0012] Furthermore, the electroslag remelting process parameters are: voltage 40~50V, current 2000~3500A, and electrode melting rate 1.9~2.5kg / min.

[0013] Furthermore, in the electroslag remelting: the electrode diameter is Φ120~150mm, the crystallizer diameter is Φ260~300mm, the slag amount is 16~26kg, and the corresponding slag pool height in the crystallizer is 110~120mm.

[0014] Furthermore, argon gas protection is used during the electroslag remelting process, with an argon gas flow rate of 5~15L / min.

[0015] Furthermore, the steel ingot obtained after electroslag remelting, after forging and billeting, is rolled into bars, wherein the level of large carbide particles is as follows: for bars with a diameter ≤ 15 mm, the maximum size of large carbide particles is ≤ 10 μm; for bars with a diameter ≤ 30 mm and a diameter < 15 mm, the maximum size of large carbide particles is ≤ 12 μm; and for bars with a diameter ≤ 60 mm and a diameter < 30 mm, the maximum size of large carbide particles is ≤ 14 μm.

[0016] The RE2O3 content in the slag system described in this invention is controlled at 15%–20%. The addition of RE2O3 can form a rare earth enrichment layer at the slag-steel interface, increasing the activity of rare earths in the slag and reducing the mass transfer driving force of rare earths from the molten steel to the slag, thereby inhibiting the oxidation loss of rare earths. The MgO content is controlled at 8%–12%. A higher MgO content can increase the activity of MgO in the slag and reduce the oxidation loss of magnesium. The CaF2 content is controlled at 40%–50%. CaF2 is the main component of electroslag remelting slag, which can lower the melting point and viscosity of the slag and ensure good fluidity. However, excessive CaF2 will reduce the basicity of the slag and increase the loss of magnesium. Therefore, this invention appropriately reduces the CaF2 content. The CaO and Al2O3 contents are controlled at 10%–15% respectively. The two work together to adjust the basicity and viscosity of the slag and ensure the metallurgical performance of the slag. The SiO2 content is strictly controlled below 1.0%. SiO2 is an acidic oxide that will aggravate the loss of magnesium and rare earths. Therefore, this invention controls it at an extremely low level.

[0017] Compared with the prior art, the beneficial effects of the present invention are as follows:

[0018] This invention significantly improves the yield of rare earth and magnesium during electroslag remelting by synergistically combining slag composition with electrode rare earth magnesium treatment. The rare earth and magnesium retained in the steel can effectively inhibit the growth of primary carbides during the solidification process of high-speed steel, and hinder the aggregation and growth of secondary carbides during subsequent forging, rolling and heat treatment, thereby significantly refining the carbide size and improving the hardness, toughness and wear resistance of high-speed steel. Attached Figure Description

[0019] Figure 1 This is a diagram showing the eutectic carbide distribution of five bars rolled from five high-speed steel ingots in five heats in Example 1;

[0020] Figure 2 This is a large particle carbide distribution diagram of the five bars rolled from five high-speed steel ingots in five heats in Example 1;

[0021] Figure 3 The microstructure distribution of carbides in the high-speed steel prepared in Example 1 (2000x magnification).

[0022] Figure 4 The microstructure of VC carbides in the high-speed steel carbide microstructure prepared in Example 1;

[0023] Figure 5 The microstructure of W6C and Mo6C carbides in the high-speed steel carbide microstructure prepared in Example 1;

[0024] Figure 6 Carbide microstructure distribution in the high-speed steel bar prepared for Comparative Example 1 (2000x magnification).

[0025] Figure 7The longitudinal carbide microstructure distribution in the high-speed steel bar prepared for Comparative Example 1 (5000x magnification).

[0026] Figure 8 The distribution of longitudinal banded carbide microstructure in the high-speed steel bar prepared in Comparative Example 1 (5000x magnification).

[0027] Figure 9 The distribution of transverse carbide microstructure in the high-speed steel bar prepared for Comparative Example 1 (5000x magnification). Detailed Implementation

[0028] To make the objectives, technical solutions, and advantages of this invention clearer, the invention will be further described in detail below with reference to embodiments. It should be understood that the specific embodiments described herein are merely illustrative and not intended to limit the invention.

[0029] This invention effectively suppresses the burn-off of rare earth elements and magnesium during electroslag remelting by controlling the content of RE2O3 and MgO in the slag system and optimizing the content of key components such as CaF2, Al2O3 and SiO2. It also utilizes rare earth elements and magnesium to inhibit the growth of primary carbides during the solidification process and secondary carbides during the heat treatment process of high-speed steel, thereby refining the carbide size of high-speed steel ingots and steel products and significantly improving the hardness, toughness and wear resistance of high-speed steel.

[0030] This invention provides an electroslag remelting slag system for refining the carbide size of high-speed tool steel. The consumable electrode for electroslag remelting is treated with rare earth magnesium during preparation. By mass percentage, the slag system comprises the following components: CaF2: 40%–50%; CaO: 10%–15%; Al2O3: 10%–15%; MgO: 8%–12%; RE2O3: 15%–20%; SiO2: 0.5%–1.0%; the balance being unavoidable impurities, with an impurity content not exceeding 1%.

[0031] The RE2O3 is one or a mixture of two of Ce2O3 and La2O3 in any proportion, and the rare earth elements in the consumable electrode are the same as those in the slag system.

[0032] An electroslag remelting method for refining carbide size in high-speed tool steel based on the above-mentioned electroslag remelting slag system includes the following steps:

[0033] (1) Rare earth and pure magnesium, or rare earth magnesium alloy, are added during the preparation of consumable electrode. Usually, they are added in the refining ladle. The rare earth content in the electrode is controlled to be 0.01wt% to 0.015wt%, and the magnesium content is controlled to be 0.002wt% to 0.004wt%.

[0034] (2) The consumable electrode after rare earth magnesium treatment is loaded into the electroslag furnace. The electrode specification is Φ120~150mm, the crystallizer specification is Φ260~300mm, the slag amount is 16~26kg, and the corresponding slag pool height in the crystallizer is 110~120mm. The above slag system is melted in the crystallizer by passing the consumable electrode through electricity. Electroslag remelting is carried out under argon protection. The argon flow rate is 5~15L / min, the voltage is 40~50V, the current is 2000~3500A, and the electrode melting rate is 1.9~2.5kg / min.

[0035] The steel ingots obtained after electroslag remelting were sampled and analyzed to calculate the rare earth and magnesium yields (yield = magnesium / rare earth content in steel ingot ÷ magnesium / rare earth content in electrode × 100%). The steel ingots were forged and then rolled into bars of different diameters, and the microstructure of their carbide structures was observed.

[0036] For details regarding the specific component content of the electroslag remelting slag system, the specific electroslag remelting process parameters, the rare earth and magnesium yields of the prepared high-speed steel, and the microstructure of the carbide structure, please refer to the various embodiments.

[0037] Example 1

[0038] An electroslag remelting slag system for refining carbide size in high-speed tool steel has the following chemical composition by mass percentage: CaF2: 45%; CaO: 12%; Al2O3: 12%; MgO: 10%; Ce2O3: 20%; SiO2: 0.7%; and impurity content: 0.3%.

[0039] The electroslag remelting process based on the above-mentioned electroslag remelting slag system includes:

[0040] (1) W6Mo5Cr4V2 high-speed steel was used as the base material. Cerium-magnesium alloy was added during the preparation of the consumable electrode to control the rare earth cerium content in the electrode to be 0.012wt% and the magnesium content to be 0.003wt%.

[0041] (2) Electrode specifications Φ120mm, crystallizer specifications Φ260mm, argon flow rate 10L / min, melting current 2500A, voltage 45V, slag amount 19kg, electrode melting rate 2.0kg / min.

[0042] After electroslag remelting, the steel ingots were sampled and analyzed. The results showed that the rare earth cerium recovery rate reached 65% and the magnesium recovery rate reached 45%.

[0043] Using the electroslag remelting process of Example 1, an industrial test of electroslag remelting was conducted in 5 heats, and the electroslag ingots obtained from the smelting were rolled into bars with a diameter of 15 mm. Figure 1 Images showing the eutectic carbide distribution of five bars rolled from five high-speed steel ingots from five heats. Figure 2Images show the distribution of large carbide particles in five bars rolled from five high-speed steel ingots in five heats. Table 1 shows the statistical results of the eutectic carbide inhomogeneity and the level of large carbide particles in the five bars.

[0044] Table 1. Statistics on the inhomogeneity and large particle carbide level of eutectic carbides in Example 1

[0045] Furnace 1 2 3 4 5 Eutectic carbide uniformity / grade 2 2 2 2 2 Large particle carbide size / μm 7.5 8.5 7.5 8.5 8.6

[0046] It can be seen that when rolling into 15mm diameter bars using the new electroslag remelting process, the eutectic carbide inhomogeneity is no greater than level 2, and the average eutectic carbide inhomogeneity of the five heats of steel is level 2. The maximum size of large carbide particles is less than 10μm, and the average size of the largest carbide particles in the five heats of steel is 8.12μm, meeting the user's high-quality requirements.

[0047] Figure 3 The image shows the longitudinal carbide microstructure distribution (2000x magnification) of the first batch of M2 high-speed steel bars rolled to a diameter of 15mm. As can be seen from the image, after adopting the new electroslag remelting process, the rolled carbide microstructure is uniform in size and relatively small overall, mainly consisting of VC, W6C, Mo6C, and a small amount of Cr. 23 C6, Figure 4 The microstructure of the high-speed steel prepared in Example 1 shows a typical VC carbide microstructure. Figure 5 The microstructure of the high-speed steel partially prepared in Example 1 shows typical W6C and Mo6C carbide microstructures.

[0048] Example 2

[0049] An electroslag remelting slag system for refining carbide size in high-speed tool steel has the following chemical composition by mass percentage: CaF2: 48%; CaO: 11%; Al2O3: 11%; MgO: 11%; a mixture of Ce2O3 and La2O3: 18% (Ce and La mass ratio is 1:1); SiO2: 0.8%; and impurity content: 0.2%.

[0050] The electroslag remelting process based on the above-mentioned electroslag remelting slag system includes:

[0051] (1) W6Mo5Cr4V2 high-speed steel is used as the base material. The total rare earth content in the consumable electrode is 0.015wt% (Ce and La mass ratio is 1:1), and the magnesium content is 0.004wt%.

[0052] (2) Electrode specifications Φ150mm, crystallizer specifications Φ300mm, melting current 3500A, voltage 45V, slag amount 25kg, electrode melting rate 2.5kg / min, argon flow rate 12L / min;

[0053] After electroslag remelting, the steel ingots were sampled and analyzed. The results showed that the rare earth recovery rate was 68% and the magnesium recovery rate was 48%.

[0054] The electroslag ingots obtained from smelting were rolled into 30mm diameter bars. Multiple samples with a cross-section of 10-12mm in height were obtained by wire cutting for carbide rating. The eutectic carbide inhomogeneity was grade 3, and the largest carbide particle size was 11.7μm.

[0055] Example 3

[0056] An electroslag remelting slag system for refining carbide size in high-speed tool steel has the following chemical composition by mass percentage: CaF2: 42%; CaO: 15%; Al2O3: 15%; MgO: 9%; La2O3: 18%; SiO2: 0.6%; and impurity content: 0.4%.

[0057] The electroslag remelting process based on the above-mentioned electroslag remelting slag system includes:

[0058] (1) W18Cr4V high-speed steel is used as the base material, and the rare earth lanthanum content in the consumable electrode is 0.01wt% and the magnesium content is 0.002wt%;

[0059] (2) Electrode specifications Φ120mm, crystallizer specifications Φ260mm, melting current 2200A, voltage 40V, slag amount 19kg, electrode melting speed 2.0kg / min, argon flow rate 8L / min.

[0060] After electroslag remelting, the steel ingots were sampled and analyzed. The results showed that the rare earth recovery rate was 62% and the magnesium recovery rate was 42%.

[0061] The electroslag ingots obtained from smelting were rolled into bars with a diameter of 60 mm. Multiple samples with a cross-section of 10-12 mm in height were obtained by wire cutting for carbide rating. The eutectic carbide inhomogeneity was grade 3.5, and the average size of the largest carbide particle was 14 μm.

[0062] Comparative Example 1

[0063] The difference from Example 1 is that the conventional ANF-6 slag system (CaF2: 70wt%, Al2O3: 30wt%) was used for electroslag remelting, while the remaining steps and rolled material specifications were the same as in Example 1.

[0064] Test results: Rare earth yield was only 15%, magnesium yield was only 5%; eutectic carbide inhomogeneity was level 3, and the average size of the largest carbide particles was 12μm.

[0065] Figure 6The image shows the carbide microstructure distribution of W6Mo5Cr4V2 high-speed steel after rolling (2000x magnification), where (ab) represents the longitudinal microstructure and (cd) represents the transverse microstructure. It can be observed from the image that the rolled carbides are unevenly distributed, severely aggregated, and of varying sizes. This is because the network of carbides in the ingot is broken up during rolling and cannot disperse in time. Figure 6 In (b), there are still some large-particle banded carbides.

[0066] Figure 7 and Figure 8 The microstructure distribution of longitudinal carbides in rolled W6Mo5Cr4V2 high-speed steel (5000x magnification) is shown. Figure 7 As can be seen, the longitudinal carbide microstructure varies in size after rolling, mainly consisting of VC and a large number of large-sized W6C and Mo6C, along with a small amount of small-sized Cr. 23 C6; From Figure 8 It can be seen that the longitudinal banded carbides are mainly W6C, Mo6C and VC, and the carbides are severely agglomerated and poorly dispersed.

[0067] Figure 9 The microstructure distribution of transverse carbides in rolled W6Mo5Cr4V2 high-speed steel is shown from... Figure 9 As can be seen, some large carbides, mainly W6C and Mo6C, still exist in the transverse carbides after rolling.

[0068] Comparative Example 2

[0069] The difference from Example 1 is that the RE2O3 content in the slag system is 5% (lower than the scope of this invention), while the other components are the same as in Example 1. Electroslag remelting is performed, and the remaining steps and rolled material specifications are the same as in Example 1.

[0070] Test results: Rare earth yield 35%, magnesium yield 25%, eutectic carbide inhomogeneity grade 2.5, and the average size of the largest carbide particles is 13μm.

[0071] Comparative Example 3

[0072] The difference from Example 1 is that the MgO content in the slag system is 3% (lower than the scope of this invention), while the other components are the same as in Example 1. Electroslag remelting is performed, and the remaining steps and rolled material specifications are the same as in Example 1.

[0073] Test results: The magnesium yield was only 18%, the eutectic carbide inhomogeneity was grade 2.5, and the average size of the largest carbide particles was 12 μm.

[0074] The results of the above embodiments and comparative examples show that by optimizing the slag composition, especially by controlling Re2O3 in the range of 15% to 20% and MgO in the range of 8% to 12%, the present invention can significantly improve the yield of rare earth and magnesium and effectively refine the size of high-speed steel carbides.

[0075] The above technical solutions illustrate the technical concept of the present invention, but should not be construed as limiting the scope of protection of the present invention. Any modifications or alterations made to the above technical solutions based on the technical essence of the present invention without departing from the content of the technical solutions of the present invention shall fall within the scope of protection of the technical solutions of the present invention.

Claims

1. An electroslag remelting slag system for refining carbide size in high-speed tool steel, characterized in that: The consumable electrode prepared by electroslag remelting is treated with rare earth magnesium. By mass percentage, the slag system includes the following components: CaF2: 42%–48%; CaO: 11%–15%; Al2O3: 11%–15%; MgO: 9%–11%; RE2O3: 16%–20%; SiO2: 0.6%–0.8%; the balance being unavoidable impurities, with an impurity content not exceeding 1%.

2. The electroslag remelting slag system for refining carbide size in high-speed tool steel according to claim 1, characterized in that: The consumable electrode contains 0.01wt% to 0.015wt% rare earth elements and 0.002wt% to 0.004wt% magnesium elements. The rare earth elements in the consumable electrode are the same as those in the slag system.

3. The electroslag remelting slag system for refining carbide size in high-speed tool steel according to claim 1, characterized in that: The RE2O3 is one or a mixture of two of Ce2O3 and La2O3 in any proportion. The rare earth elements in the slag system are the same as those in the consumable electrode. If the RE2O3 is a mixture of Ce2O3 and La2O3, the mass ratio of Ce and La in the slag system is the same as that in the consumable electrode.

4. The electroslag remelting slag system for refining carbide size in high-speed tool steel according to claim 1, characterized in that: The high-speed tool steel is tungsten-based high-speed steel, or molybdenum-based high-speed steel, or tungsten-molybdenum-based high-speed steel.

5. An electroslag remelting process for refining carbide size in high-speed tool steel based on the slag system described in any one of claims 1 to 4, characterized in that: The consumable electrode prepared by electroslag remelting is treated with rare earth magnesium, that is, rare earth and pure magnesium, or rare earth magnesium alloy, are added during the preparation of the consumable electrode to control the content of rare earth and magnesium in the electrode.

6. The electroslag remelting process for refining carbide size in high-speed tool steel according to claim 5, characterized in that: The electroslag remelting process parameters are: voltage 40~50V, current 2000~3500A, and electrode melting rate 1.9~2.5kg / min.

7. The electroslag remelting process for refining carbide size in high-speed tool steel according to claim 5, characterized in that: In the electroslag remelting process: the electrode diameter is Φ120~150mm, the crystallizer diameter is Φ260~300mm, the slag amount is 16~26kg, and the corresponding slag pool height in the crystallizer is 110~120mm.

8. The electroslag remelting process for refining carbide size in high-speed tool steel according to claim 5, characterized in that: Argon gas protection is used during the electroslag remelting process, with an argon gas flow rate of 5~15L / min.

9. The electroslag remelting process for refining carbide size in high-speed tool steel according to claim 5, characterized in that: The steel ingots obtained after electroslag remelting, after forging and then rolling, produce bars with the following large carbide particle levels: for bars with a diameter ≤ 15 mm, the maximum size of the large carbide particles is ≤ 10 μm; for bars with a diameter ≤ 30 mm and a diameter < 15 mm, the maximum size of the large carbide particles is ≤ 12 μm; and for bars with a diameter ≤ 60 mm and a diameter < 30 mm, the maximum size of the large carbide particles is ≤ 14 μm.

Images