Smelting method for improving rare earth yield of 4Cr13 steel

Abstract

The invention discloses a smelting method for improving the rare earth yield of 4Cr13 steel, and belongs to the technical field of steel smelting. In order to solve the problems that the rare earth yield is low and difficult to control, the invention provides a smelting method for improving the rare earth yield of 4Cr13 steel, which comprises the following steps: A, smelting by an electric arc furnace oxidation method; b, blowing by an AOD double-slag method; c, LF furnace refining is carried out, wherein the content of Al2O3 in LF slag ranges from 25% to 35%; d, VD vacuum treatment; rE2O3 is added, so that the slag comprises 20-32% of Al2O3, 40-50% of CaO, less than or equal to 6% of MgO, less than or equal to 10% of SiO2 and 10-30% of RE2O3; e, VD soft argon blowing, wherein La / Ce composite rare earth is added; and F, pouring. The rare earth is added in the VD link, and the rare earth yield is remarkably increased by controlling the components in the slag, increasing the content of molten steel solid solution Al, reducing the oxygen content and inhibiting the reaction of the rare earth and the slag.

Description

Technical Field

[0001] The invention belongs to the technical field of steel smelting, and in particular relates to a smelting method for improving the rare earth recovery rate of 4Cr13 steel. Background Art

[0002] Rare earth alloying is an important research field in iron and steel metallurgy. It has a strong chemical affinity with oxygen, sulfur, nitrogen and other elements, which can reduce the content and activity of impurity elements in steel, make the grain boundaries purer, and change the various properties of steel and its alloys. At present, the role of rare earth in steel mainly includes the following three aspects: 1) deep purification of molten steel; 2) metamorphism; 3) microalloying. At present, rare earth treated Cr13 series plastic mold steel has excellent corrosion resistance and polishing performance, and has good application prospects. However, during the rare earth treatment process, the yield control is unstable, resulting in unstable product quality.

[0003] CN111593252A discloses a rare earth steel smelting method, which provides a good condition for the addition of rare earth metals by strictly controlling the operating parameters of each process before the addition of rare earth, the top slag composition and the oxygen and sulfur content in the molten steel. The purity, particle size and packaging container of the rare earth metals used when added are strictly controlled to ensure the recovery rate of rare earths and their uniform distribution in the steel. At the same time, it is ensured that the added rare earth can quickly pass through the slag layer into the molten steel and reach a certain depth in the molten steel; so that the rare earth metal can be quickly melted in the molten steel and evenly distributed in the molten steel through the effect of soft argon blowing. This method improves the recovery rate of rare earths in steel, but the improvement is limited, and the average recovery rate is ≥45%.

[0004] CN114672611A discloses a method for improving the rare earth recovery rate in the process of smelting rare earth steel, comprising: step 1, converter or electric furnace smelting; step 2, LF furnace or LF furnace → RH furnace refining; step 3, continuous casting after refining; the rare earth is Ce and / or La; in step 2, the composition of the LF furnace refined ladle top slag is calculated in mass percentage as CaO: 58-65%, SiO2: 5-8%, MgO%: 11-15, Al2O3: 15-24%, FeO+MnO<0.5%, Ce2O3+La2O3: 0.1-2.9%, CaO / SiO2: 8.0-11; in step 3, the composition of the tundish covering agent is the same as the refined slag composition; the ladle lining, tundish, stopper rod, long nozzle, immersion nozzle and upper nozzle used are all made of magnesia refractory. The rare earth oxide content in the refined slag of this method is only 0.1-2.9%, and the recovery rate from refining to continuous casting is only about 50%.

[0005] It can be seen that the existing technology is to control the rare earth addition link by controlling the content of elements such as O and S in steel before rare earth is added to control the rare earth yield; or, to improve the yield by adjusting the rare earth addition tool; and the amount of rare earth oxide added in the existing technology is also low, and the obtained yield is not representative. Summary of the invention

[0006] The technical problem to be solved by the present invention is that the yield in the rare earth treatment process of the prior art is low and difficult to control.

[0007] In order to solve the above technical problems, the present invention provides a smelting method for improving the rare earth recovery rate of 4Cr13 steel, which comprises the following steps:

[0008] A. Smelting in an electric arc furnace: add lime to the bottom of the ladle, then add smelting raw materials, then turn on the power, blow oxygen to heat up the smelting, and when the temperature reaches 1630℃~1660℃, take samples for analysis. When the molten steel meets the following requirements: P content is less than 0.01% and C content is ≥0.2%, add AOD;

[0009] B. AOD blowing: lime is added before the molten steel is added into AOD, followed by oxygen blowing to reduce carbon. After the oxygen blowing is completed, alloy material is added for alloying, the composition of the molten steel is preliminarily adjusted, and then ferrosilicon is added for the first reduction and deoxidation. After the deoxidation is completed, 1 / 3 to 2 / 3 of the first reduction slag is removed, and then Al ingot is added for the second reduction, and slag auxiliary materials are added to adjust the slag composition, so that the AOD final slag composition meets the following requirements: Al2O3 10 to 20%, CaO 50 to 60%, MgO ≤ 8%, SiO2 ≤ 15%, and the AOD tapping temperature is controlled to be greater than 1580°C;

[0010] C. LF furnace refining: After the ladle enters the LF, feed Al wire to make the Al content of the molten steel meet 0.02%~0.03%, and then add slag auxiliary materials to make the LF slag composition meet: Al2O3 25~35%, CaO 45~55%, MgO≤8%, SiO2≤15%; then send power to increase the temperature for refining, take samples for analysis, and after the molten steel meets the requirements of 4Cr13 steel except RE, feed Al wire to make the Al content of the molten steel meet 0.03%~0.05%, make the [O] content of the molten steel less than 5ppm, and then refine again, control the LF tapping temperature to be greater than 1630℃, and then enter VD vacuum treatment;

[0011] D. VD vacuum treatment: Before VD vacuum treatment, slag is removed to make the ladle slag thickness between 80 and 100 mm, then RE2O3 is added to make the slag composition meet the following requirements: Al2O3 20-32%, CaO 40-50%, MgO≤6%, SiO2≤10%, RE2O310-30%, and then VD vacuum treatment is carried out;

[0012] E. VD soft argon blowing: After the VD vacuum is completed, add 0.1-0.2kg / t La / Ce composite rare earth into the molten steel, and perform soft argon blowing at the same time. Take samples to measure the temperature. When the temperature reaches 1560℃-1580℃, the ladle is ready for pouring.

[0013] F. Pouring: After the ladle is hung, the molten steel is poured into shape to obtain the finished 4Cr13 steel product;

[0014] The chemical composition of the 4Cr13 steel is as follows by weight percentage: C: 0.36%-0.45%, Si: 0.25%-0.5%, Mn: 0.30%-0.50%, Cr: 11.50%-13.50%, S≤0.005%, V≤0.5%, Mo≤0.4%, RE: 0.005-0.015%, and the balance is Fe and unavoidable impurities.

[0015] Wherein, in the above-mentioned smelting method for improving the rare earth recovery rate of 4Cr13 steel, in step A, the amount of lime added is 25-40 kg / t molten steel.

[0016] Wherein, in the above-mentioned smelting method for improving the rare earth recovery rate of 4Cr13 steel, in step B, the amount of lime added is 6-10kg / t molten steel.

[0017] Wherein, in the above-mentioned smelting method for improving the rare earth recovery rate of 4Cr13 steel, in step B, the amount of ferrosilicon added is 1.5-2.5 kg / t molten steel.

[0018] Wherein, in the above-mentioned smelting method for improving the rare earth recovery rate of 4Cr13 steel, in step B, the addition amount of the Al ingot is 2-3 kg / t molten steel.

[0019] Wherein, in the above-mentioned smelting method for improving the rare earth recovery rate of 4Cr13 steel, in step C, the amount of Al wire added for the first time is 0.2-0.3 kg / t molten steel; the amount of Al wire added for the second time is 0.2-0.3 kg / t molten steel.

[0020] Among them, in the above-mentioned smelting method for improving the rare earth recovery rate of 4Cr13 steel, in step C, the conditions for power transmission and heating for refining are: temperature 1600-1640°C, time 30-40 minutes.

[0021] Wherein, in the above-mentioned smelting method for improving the rare earth recovery rate of 4Cr13 steel, in step C, the re-refining time is 5 to 15 minutes.

[0022] Among them, in the above-mentioned smelting method for improving the rare earth recovery rate of 4Cr13 steel, in step D, the conditions of the VD vacuum treatment are: maintaining the ultimate vacuum ≤ 66Pa, maintaining the vacuum for 30 to 40 minutes, and the argon flow rate of 150 to 250 L / min.

[0023] Among them, in the above-mentioned smelting method for improving the rare earth recovery rate of 4Cr13 steel, in step E, the conditions of the soft argon blowing treatment are: argon gas flow rate 30-50L / min, and argon blowing is maintained for 15-30min.

[0024] Among them, in the above-mentioned smelting method for improving the rare earth recovery rate of 4Cr13 steel, in step F, a slit-type argon protection device is used to protect the pouring.

[0025] Wherein, in the above-mentioned smelting method for improving the rare earth recovery rate of 4Cr13 steel, the recovery rate of the La / Ce composite rare earth added in step E is 60% to 80%.

[0026] Beneficial effects of the present invention:

[0027] The present invention controls the components in the slag, adds rare earth in the VD link, and controls the aluminum oxide content in the steel at a relatively high level before the rare earth is added, which is beneficial to increasing the solid-solution Al content, reducing the oxygen content in the molten steel before the rare earth is added, inhibiting the reaction between the rare earth and the slag, and increasing the rare earth recovery rate from about 10% to 60-80%, thereby reducing the waste of rare earth resources; at the same time, the present invention processes the rare earth added to 4Cr13, adjusts the steel grade components, and improves the stability of the steel. DETAILED DESCRIPTION

[0028] Specifically, a smelting method for improving the rare earth recovery rate of 4Cr13 steel comprises the following steps:

[0029] A. Smelting in an electric arc furnace: add lime to the bottom of the ladle, then add smelting raw materials, then turn on the power, blow oxygen to heat up the smelting, and when the temperature reaches 1630℃~1660℃, take samples for analysis. When the molten steel meets the following requirements: P content is less than 0.01% and C content is ≥0.2%, add AOD;

[0030] B. AOD blowing: lime is added before the molten steel is added into AOD, followed by oxygen blowing to reduce carbon. After the oxygen blowing is completed, alloy material is added for alloying, the composition of the molten steel is preliminarily adjusted, and then ferrosilicon is added for the first reduction and deoxidation. After the deoxidation is completed, 1 / 3 to 2 / 3 of the first reduction slag is removed, and then Al ingot is added for the second reduction, and slag auxiliary materials are added to adjust the slag composition, so that the AOD final slag composition meets the following requirements: Al2O3 10 to 20%, CaO 50 to 60%, MgO ≤ 8%, SiO2 ≤ 15%, and the AOD tapping temperature is controlled to be greater than 1580°C;

[0031] C. LF furnace refining: After the ladle enters the LF, feed Al wire to make the Al content of the molten steel meet 0.02%~0.03%, and then add slag auxiliary materials to make the LF slag composition meet: Al2O3 25~35%, CaO 45~55%, MgO≤8%, SiO2≤15%; then send power to increase the temperature for refining, take samples for analysis, and after the molten steel meets the requirements of 4Cr13 steel except RE, feed Al wire to make the Al content of the molten steel meet 0.03%~0.05%, make the [O] content of the molten steel less than 5ppm, and then refine again, control the LF tapping temperature to be greater than 1630℃, and then enter VD vacuum treatment;

[0032] D. VD vacuum treatment: Before VD vacuum treatment, slag is removed to make the ladle slag thickness between 80 and 100 mm, then RE2O3 is added to make the slag composition meet the following requirements: Al2O3 20-32%, CaO 40-50%, MgO≤6%, SiO2≤10%, RE2O310-30%, and then VD vacuum treatment is carried out;

[0033] E. VD soft argon blowing: After the VD vacuum is completed, add 0.1-0.2kg / t La / Ce composite rare earth into the molten steel, and perform soft argon blowing at the same time. Take samples to measure the temperature. When the temperature reaches 1560℃-1580℃, the ladle is ready for pouring.

[0034] F. Pouring: After the ladle is hung, the molten steel is poured into shape to obtain the finished 4Cr13 steel product;

[0035] The chemical composition of the 4Cr13 steel is as follows by weight percentage: C: 0.36%-0.45%, Si: 0.25%-0.5%, Mn: 0.30%-0.50%, Cr: 11.50%-13.50%, S≤0.005%, V≤0.5%, Mo≤0.4%, RE: 0.005-0.015%, and the balance is Fe and unavoidable impurities.

[0036] In the present invention, the smelting raw materials used are conventional raw materials in the art, generally, Benxi Steel return materials of 4Cr13 series steel, alloy return materials similar to 4Cr13 series steel, and industrial pure iron.

[0037] In step A of the present invention, an oxidation method is used for smelting, which is a conventional smelting process in the art, that is, lime is added to the bottom of the ladle before adding smelting raw materials, and then electricity is turned on and oxygen is blown to heat the smelting; in step A, the amount of lime added is 25-40 kg / t of molten steel.

[0038] In step B of the present invention, the double slag method is used for blowing, which is a conventional blowing process in the art. Before the molten steel is added into the AOD, 6-10 kg / t of molten steel lime is added.

[0039] In step B of the present invention, the slag auxiliary material used is the slag auxiliary material commonly used in smelting in the art, for example, it can be a commonly used refined slag (the main components of the refined slag are Al2O3: 45%, CaO: 50%).

[0040] In step B of the present invention, alloying is a conventional operation in the art, and alloy materials such as Cr-Fe, graphite, and Mn-Fe can be used for alloying to preliminarily adjust the molten steel to an appropriate composition.

[0041] In step C of the present invention, the amount of Al wire added for the first time is 0.2-0.3 kg / t molten steel; the amount of Al wire added for the second time is 0.2-0.3 kg / t molten steel.

[0042] In step C of the present invention, the conditions for refining by power transmission and temperature increase are: temperature 1600-1640° C., time 30-40 min.

[0043] In step C of the present invention, the re-refining time is 5 to 15 minutes.

[0044] In step D of the present invention, rare earth is added in the VD stage. Before the rare earth is added, controlling the alumina content in the steel at a higher level is beneficial to increasing the solid solution Al content and reducing the oxygen content in the molten steel before the rare earth is added. In addition, the slag volume will be reduced in the VD stage. At this time, adding RE2O3 to adjust the slag composition can reduce RE2O3 consumption.

[0045] In step D of the present invention, the reason why the rare earth recovery rate is not high is mainly because the rare earth reacts with the slag during the addition process: La+Al2O3=La2O3+Al, and if the oxygen content in the steel is high, the rare earth will also react with oxygen to generate La2O3 and enter the slag. Therefore, in step D of the present invention, RE2O3 is added to the slag before vacuum treatment, and then vacuum stirring treatment is performed, and the steel slag reacts; before rare earth treatment, the oxygen content in the steel is reduced as much as possible, and the rare earth oxide content in the slag is increased to inhibit the reaction.

[0046] In step D of the present invention, the addition of rare earth requires a lower oxygen content in the steel, and thus requires a lower vacuum degree. Therefore, the conditions for controlling the VD vacuum treatment are: maintaining the ultimate vacuum ≤ 66Pa, maintaining the vacuum for 30 to 40 minutes, and an argon flow rate of 150 to 250 L / min.

[0047] In step E of the present invention, La / Ce composite rare earth (purity greater than 98%) is taken out from a sealed can, and after removing its surface oxide layer, it is called pure La / Ce composite rare earth, which is wrapped with pure iron sheets, fixed with iron rods, and inserted under the steel slag. In step E, the conditions of the soft argon blowing treatment are: argon gas flow rate 30-50L / min, argon blowing is maintained for 15-30min.

[0048] In step F of the present invention, a slit-type argon protection device is used to protect the pouring.

[0049] By controlling the composition of the slag, the yield of the La / Ce composite rare earth added in step E can be as high as 60% to 80%. At the same time, the invention adds rare earth to 4Cr13 for processing and adjusts the composition of the steel so that it can be used as large-size plastic mold steel.

[0050] The present invention is further described in detail below by way of examples, but the protection scope of the present invention is not limited to the scope of the examples.

[0051] Example 1

[0052] 1. Smelting in electric arc furnace: The raw materials are mainly returned materials from Benxi Steel and similar alloy returned materials from Benxi Steel, as well as industrial pure iron. Before adding the raw materials, 40kg / t of lime is added to the bottom of the ladle, and then the power is turned on and oxygen is blown to heat up the smelting. When the temperature reaches 1638℃, samples are taken for analysis, and the P content is 0.008%, the C content is 0.25%, and AOD is added.

[0053] 2. AOD blowing: Before the molten steel is added into AOD, 8kg / t lime is added, followed by oxygen blowing to reduce carbon. After the oxygen blowing is completed, alloy materials such as Cr-Fe, graphite, and Mn-Fe are added for alloying, and the composition of the molten steel is preliminarily adjusted. Then, 2.5kg / t ferrosilicon is added for the first reduction and deoxidation. After the deoxidation is completed, 2 / 3 of the first reduction slag is removed, and then 3kg / t Al ingot is added for the second reduction, and slag auxiliary materials (refining slag, main components Al2O3: 45%, CaO: 50%) are added to adjust the slag composition, so that the AOD final slag composition is Al2O3: 16.2%, CaO: 58.5%, MgO: 6.5%, SiO2: 13.4%, and the tapping temperature is 1590℃.

[0054] 3. LF furnace refining: After the ladle enters the LF, feed 0.2kg / t of Al wire into the molten steel to make the Al content of the molten steel between 0.02% and 0.03%, then add slag auxiliary materials (refining slag, main components Al2O3: 45%, CaO: 50%), so that the slag composition is Al2O3: 28.1%, CaO: 51.2%, MgO: 7.3%, SiO2: 11.2%; then send electricity to raise the temperature to 1630℃, and refine for 35m in, take molten steel samples to measure the composition. After the molten steel composition meets the standards (C: 0.37%, Si: 0.31%, Mn: 0.42%, Cr: 13.2%, S: 0.003%, V: 0.42%, Mo: 0.38%), feed 0.25kg / t of Al wire into the molten steel to make the Al content of the molten steel 0.035%, and the [O] content of the molten steel 4ppm. Then refine for 10 minutes, the LF temperature is 1660℃, and then enter VD vacuum treatment.

[0055] 4. VD vacuum treatment: Before VD vacuum treatment, the slag is removed to make the thickness of the ladle slag between 80-100mm, and then RE2O3 is added to make the slag composition Al2O3: 25.3%, CaO: 48.1%, MgO: 5.2%, SiO2: 8.1%, RE2O3: 12.2%, and then VD vacuum treatment is carried out, keeping the ultimate vacuum ≤66pa, the vacuum is maintained for 30min, and the argon flow rate is 150L / min.

[0056] 5. VD soft argon blowing: After the VD vacuum is completed, the La / Ce composite rare earth is taken out from the sealed tank, and after removing the surface oxide layer, 0.15kg / t of La / Ce composite rare earth is weighed / t of molten steel, wrapped with pure iron sheets, fixed with iron rods, and inserted under the steel slag. At the same time, soft argon blowing treatment is carried out, with an argon flow rate of 35L / min. After the argon blowing is maintained for 25 minutes, sampling is performed to measure the temperature. When the temperature reaches 1565℃, the hanging bag is ready for pouring.

[0057] 6. Pouring: Use a narrow argon protection device to protect the pouring, and after the ladle is hung, the molten steel is cast to form a 4Cr14 steel product. The composition of the 4Cr13 steel product is C: 0.37%, Si: 0.31%, Mn: 0.42%, Cr: 13.2%, S: 0.003%, V: 0.42%, Mo: 0.38%, RE: 0.0095%, and the balance is Fe and unavoidable impurities. The yield of La / Ce composite rare earth is maintained at 63%.

[0058] Example 2

[0059] 1. Smelting in electric arc furnace: The raw materials are mainly returned materials from Benxi Steel and similar alloy returned materials from Benxi Steel, as well as industrial pure iron. Before adding the raw materials, 40kg / t of lime is added to the bottom of the ladle, and then the power is turned on and oxygen is blown to heat up the smelting. When the temperature reaches 1640℃, samples are taken for analysis, and the P content is 0.007%, the C content is 0.26%, and AOD is added.

[0060] 2. AOD blowing: Before the molten steel is added into AOD, 8kg / t lime is added, followed by oxygen blowing to reduce carbon. After the oxygen blowing is completed, alloy materials such as Cr-Fe, graphite, and Mn-Fe are added for alloying, and the composition of the molten steel is preliminarily adjusted. Then, 2.5kg / t ferrosilicon is added for the first reduction and deoxidation. After the deoxidation is completed, 2 / 3 of the first reduction slag is removed, and then 3kg / t Al ingot is added for the second reduction, and slag auxiliary materials (refining slag, main components Al2O3: 45%, CaO: 50%) are added to adjust the slag composition, so that the AOD final slag composition is Al2O3: 17.1%, CaO: 56.5%, MgO: 7.1%, SiO2: 12.3%, and the tapping temperature is 1588℃.

[0061] 3. LF furnace refining: After the ladle enters the LF, feed 0.2kg / t of Al wire into the molten steel to make the Al content of the molten steel between 0.02% and 0.03%, then add slag auxiliary materials (refining slag, main components Al2O3: 45%, CaO: 50%), so that the slag composition is Al2O3: 27.5%, CaO: 53.3%, MgO: 6.1%, SiO2: 8.3%; then send electricity to raise the temperature to 1638℃, and refine for 35m in, take molten steel samples to measure the composition. After the molten steel composition meets the standards (C: 0.41%, Si: 0.32%, Mn: 0.45%, Cr: 13.2%, S: 0.002%, V: 0.41%, Mo: 0.38%), feed 0.3kg / t of Al wire into the molten steel to make the Al content of the molten steel 0.045%, and the [O] content of the molten steel 2ppm. Then refine for 15 minutes, the LF temperature is 1670℃, and then enter VD vacuum treatment.

[0062] 4. VD vacuum treatment: Before VD vacuum treatment, slag is removed to make the slag thickness of the ladle into the tank between 80-100mm, and then RE2O3 is added to make the slag composition Al2O3: 24.2%, CaO: 48.1%, MgO: 4.5%, SiO2: 5.1%, RE2O3: 15.2%, and then VD vacuum treatment is carried out, keeping the ultimate vacuum ≤ 66pa, the vacuum is maintained for 30min, and the argon flow rate is 160L / min.

[0063] 5. VD soft argon blowing: After the VD vacuum is completed, the La / Ce composite rare earth is taken out from the sealed tank, and after removing the surface oxide layer, 0.15kg / t of La / Ce composite rare earth is weighed / t of molten steel, wrapped with pure iron sheets, fixed with iron rods, and inserted under the steel slag. At the same time, soft argon blowing treatment is carried out, with an argon flow rate of 37L / min. After the argon blowing is maintained for 28 minutes, sampling is performed to measure the temperature. When the temperature reaches 1560℃, the hanging bag is ready for pouring.

[0064] 6. Pouring: Use a narrow argon protection device to protect the pouring, and after the ladle is hung, the molten steel is cast to form a 4Cr14 steel product. The composition of the 4Cr13 steel product is C: 0.41%, Si: 0.32%, Mn: 0.45%, Cr: 13.2%, S: 0.002%, V: 0.41%, Mo: 0.38%, RE: 0.011%, and the balance is Fe and unavoidable impurities. The yield of La / Ce composite rare earth is maintained at 73%.

[0065] Example 3

[0066] 1. Smelting in electric arc furnace: The raw materials are mainly returned materials from Benxi Steel and similar alloy returned materials from Benxi Steel, as well as industrial pure iron. Before adding the raw materials, 40kg / t of lime is added to the bottom of the ladle, and then the power is turned on and oxygen is blown to heat up the smelting. When the temperature reaches 1630℃, samples are taken for analysis, and the P content is 0.006%, the C content is 0.28%, and AOD is added.

[0067] 2. AOD blowing: Before the molten steel is added into AOD, 8kg / t lime is added, followed by oxygen blowing to reduce carbon. After the oxygen blowing is completed, alloy materials such as Cr-Fe, graphite, and Mn-Fe are added for alloying, and the composition of the molten steel is preliminarily adjusted. Then, 2.5kg / t ferrosilicon is added for the first reduction and deoxidation. After the deoxidation is completed, 2 / 3 of the first reduction slag is removed, and 3kg / t Al ingot is added for the second reduction. Slag auxiliary materials (refined slag, main components Al2O3: 45%, CaO: 50%) are added to adjust the slag composition so that the AOD final slag composition is Al2O3: 13.1%, CaO: 58.5%, MgO: 6.8%, SiO2: 11.3%, and the tapping temperature is 1590℃.

[0068] 3. LF furnace refining: After the ladle enters the LF, feed 0.25kg / t of Al wire into the molten steel to make the Al content of the molten steel between 0.02% and 0.03%, then add slag auxiliary materials (refining slag, main components Al2O3: 45%, CaO: 50%), so that the slag composition is Al2O3: 29.3%, CaO: 49.1%, MgO: 7.2%, SiO2: 10.1%; then send electricity to raise the temperature to 1640℃, and refine for 35 min, take the molten steel sample to measure the composition, after the molten steel composition meets the standard (C: 0.38%, Si: 0.35%, Mn: 0.40%, Cr: 13.1%, S: 0.002%, V: 0.45%, Mo: 0.36%), feed 0.3kg / t of Al wire into the molten steel to make the Al content of the molten steel 0.032%, and the [O] content of the molten steel 4ppm, then refine for 10min, the LF temperature is 1666℃, and then enter the VD vacuum treatment.

[0069] 4. VD vacuum treatment: Before VD vacuum treatment, the slag is removed to make the thickness of the ladle slag between 80-100mm, and then RE2O3 is added to make the slag composition Al2O3: 22.5%, CaO: 43.4%, MgO: 4.7%, SiO2: 4.8%, RE2O3: 25.1%, and then VD vacuum treatment is carried out, keeping the ultimate vacuum ≤66pa, the vacuum is maintained for 30min, and the argon flow rate is 160L / min.

[0070] 5. VD soft argon blowing: After the VD vacuum is completed, the La / Ce composite rare earth is taken out from the sealed tank, and after removing the surface oxide layer, 0.15kg / t of La / Ce composite rare earth is weighed / t of molten steel, wrapped with pure iron sheets, fixed with iron rods, and inserted under the steel slag. At the same time, soft argon blowing treatment is carried out, with an argon flow rate of 36L / min. After the argon blowing is maintained for 30 minutes, sampling is performed to measure the temperature, and the temperature is 1568℃, and the hanging bag is ready for pouring.

[0071] 6. Pouring: Use a slit type argon protection device to protect the pouring, and after the ladle is hung, the molten steel is cast to form a 4Cr14 steel product. The composition of the 4Cr13 steel product is C: 0.38%, Si: 0.35%, Mn: 0.40%, Cr: 13.1%, S: 0.002%, V: 0.45%, Mo: 0.36%, RE: 0.012%, and the balance is Fe and unavoidable impurities. The yield of La / Ce composite rare earth is maintained at 80%.

[0072] Comparative Example

[0073] 1. Smelting in electric arc furnace: The raw materials are mainly returned materials from Benxi Steel and similar alloy returned materials from Benxi Steel, as well as industrial pure iron. Before adding the raw materials, 40kg / t of lime is added to the bottom of the ladle, and then the power is turned on and oxygen is blown to heat up the smelting. When the temperature reaches 1638℃, samples are taken for analysis, and the P content is 0.008%, the C content is 0.25%, and AOD is added.

[0074] 2. AOD blowing: Before the molten steel is added into AOD, 8kg / t lime is added, followed by oxygen blowing to reduce carbon. After the oxygen blowing is completed, alloy materials such as Cr-Fe, graphite, and Mn-Fe are added for alloying, and the composition of the molten steel is preliminarily adjusted. Then, 2.5kg / t ferrosilicon is added for the first reduction and deoxidation. After the deoxidation is completed, 2 / 3 of the first reduction slag is removed, and then 3kg / t Al ingot is added for the second reduction, and slag auxiliary materials (refining slag, main components Al2O3: 45%, CaO: 50%) are added to adjust the slag composition so that the AOD final slag composition is Al2O3: 15.5%, CaO: 57.4%, MgO: 6.8%, SiO2: 14.2%, and the tapping temperature is 1590℃.

[0075] 3. LF furnace refining: After the ladle enters the LF, feed 0.2kg / t of Al wire into the molten steel to make the Al content of the molten steel between 0.02% and 0.03%, then add slag auxiliary materials (refining slag, main components Al2O3: 45%, CaO: 50%), so that the slag composition is Al2O3: 28.5%, CaO: 49.1%, MgO: 7.8%, SiO2: 11.1%; then send electricity to raise the temperature to 1630℃, and refine for 35m in, take molten steel samples to measure the composition. After the molten steel composition meets the standards (C: 0.41%, Si: 0.35%, Mn: 0.40%, Cr: 13.3%, S: 0.003%, V: 0.45%, Mo: 0.37%), feed 0.25kg / t of Al wire into the molten steel to make the Al content of the molten steel 0.035% and the [O] content of the molten steel 4ppm. Then refine for 10 minutes, the LF temperature is 1660℃, and then enter the VD vacuum treatment.

[0076] 4. VD vacuum treatment: Before VD vacuum treatment, remove the slag so that the thickness of the ladle slag entering the tank is between 80-100mm, and then carry out VD vacuum treatment, keeping the ultimate vacuum ≤66pa, the vacuum is maintained for 30min, and the argon flow rate is 150L / min.

[0077] 5. VD soft argon blowing: After the VD vacuum is completed, the La / Ce composite rare earth is taken out from the sealed tank, and after removing the surface oxide layer, 0.15kg / t of La / Ce composite rare earth is weighed / t of molten steel, wrapped with pure iron sheets, fixed with iron rods, and inserted under the steel slag. At the same time, soft argon blowing treatment is carried out, with an argon flow rate of 35L / min. After the argon blowing is maintained for 25 minutes, sampling is performed to measure the temperature. When the temperature reaches 1568℃, the hanging bag is ready for pouring.

[0078] 6. Casting: A narrow argon protection device is used to protect the casting. After the ladle is hung, the molten steel is cast and formed to obtain a 4Cr13 steel product. The composition of the 4Cr13 steel product is C: 0.41%, Si: 0.35%, Mn: 0.40%, Cr: 13.3%, S: 0.003%, V: 0.45%, Mo: 0.37%, RE: 0.003%, and the balance is Fe and unavoidable impurities. The yield of La / Ce composite rare earth is only 20%.

Claims

1. A smelting method for improving the rare earth recovery rate of 4Cr13 steel, characterized in that: The following steps are involved: A. Smelting in an electric arc furnace: add lime to the bottom of the ladle, then add smelting raw materials, then turn on the power, blow oxygen to heat up the smelting, and when the temperature reaches 1630℃~1660℃, take samples for analysis. When the molten steel meets the following requirements: P content is less than 0.01% and C content is ≥0.2%, add AOD; B. AOD blowing: lime is added before the molten steel is added into AOD, followed by oxygen blowing to reduce carbon. After the oxygen blowing is completed, alloy material is added for alloying, the composition of the molten steel is preliminarily adjusted, and then ferrosilicon is added for the first reduction and deoxidation. After the deoxidation is completed, 1 / 3 to 2 / 3 of the first reduction slag is removed, and then Al ingot is added for the second reduction, and slag auxiliary materials are added to adjust the slag composition, so that the AOD final slag composition meets the following requirements: Al2O3 10 to 20%, CaO 50 to 60%, MgO ≤ 8%, SiO2 ≤ 15%, and the AOD tapping temperature is controlled to be greater than 1580°C; C. LF furnace refining: After the ladle enters the LF, feed Al wire to make the Al content of the molten steel meet 0.02%~0.03%, and then add slag auxiliary materials to make the LF slag composition meet: Al2O3 25~35%, CaO 45~55%, MgO≤8%, SiO2≤15%; then send power to increase the temperature for refining, take samples for analysis, and after the molten steel meets the requirements of 4Cr13 steel except RE, feed Al wire to make the Al content of the molten steel meet 0.03%~0.05%, make the [O] content of the molten steel less than 5ppm, and then refine again, control the LF tapping temperature to be greater than 1630℃, and then enter VD vacuum treatment; D. VD vacuum treatment: Before VD vacuum treatment, slag is removed to make the ladle slag thickness between 80 and 100 mm, then RE2O3 is added to make the slag composition meet the following requirements: Al2O3 20-32%, CaO 40-50%, MgO≤6%, SiO2≤10%, RE2O310-30%, and then VD vacuum treatment is carried out; E. VD soft argon blowing: After the VD vacuum is completed, add 0.1-0.2kg / t La / Ce composite rare earth into the molten steel, and perform soft argon blowing at the same time. Take samples to measure the temperature. When the temperature reaches 1560℃-1580℃, the ladle is ready for pouring. F. Pouring: After the ladle is hung, the molten steel is poured into shape to obtain the finished 4Cr13 steel product; The chemical composition of the 4Cr13 steel is as follows by weight percentage: C: 0.36%-0.45%, Si: 0.25%-0.5%, Mn: 0.30%-0.50%, Cr: 11.50%-13.50%, S≤0.005%, V≤0.5%, Mo≤0.4%, RE: 0.005-0.015%, and the balance is Fe and unavoidable impurities.

2. The smelting method for improving the rare earth recovery rate of 4Cr13 steel according to claim 1, characterized in that: In step A, the amount of lime added is 25-40 kg / t molten steel.

3. The smelting method for improving the rare earth yield of 4Cr13 steel according to claim 1, characterized in that: At least one of the following is met: In step B, the amount of lime added is 6-10 kg / t molten steel; In step B, the amount of ferrosilicon added is 1.5-2.5 kg / t molten steel; In step B, the amount of Al ingot added is 2-3 kg / t molten steel.

4. The smelting method for improving the rare earth recovery rate of 4Cr13 steel according to claim 1, characterized in that: In step C, the amount of Al wire added for the first time is 0.2-0.3 kg / t molten steel; the amount of Al wire added for the second time is 0.2-0.3 kg / t molten steel.

5. The smelting method for improving the rare earth recovery rate of 4Cr13 steel according to claim 1, characterized in that: In step C, the conditions for refining by power transmission and temperature increase are: temperature 1600-1640° C., time 30-40 min.

6. The smelting method for improving the rare earth recovery rate of 4Cr13 steel according to claim 1, characterized in that: In step C, the re-refining time is 5 to 15 minutes.

7. The smelting method for improving the rare earth recovery rate of 4Cr13 steel according to claim 1, characterized in that: In step D, the conditions of the VD vacuum treatment are: maintaining the ultimate vacuum ≤ 66 Pa, maintaining the vacuum for 30 to 40 minutes, and the argon gas flow rate of 150 to 250 L / min.

8. The smelting method for improving the rare earth recovery rate of 4Cr13 steel according to claim 1, characterized in that: In step E, the conditions of the soft argon blowing treatment are: argon gas flow rate of 30 to 50 L / min, and argon blowing is maintained for 15 to 30 minutes.

9. The smelting method for improving the rare earth recovery rate of 4Cr13 steel according to claim 1, characterized in that: In step F, a slit-type argon protection device is used to protect the pouring.

10. The smelting method for improving the rare earth recovery rate of 4Cr13 steel according to any one of claims 1 to 9, characterized in that: The yield of the La / Ce composite rare earth added in step E is 60% to 80%.