Smelting process for improving cleanliness of Cr13 series steel by using rare earth refining slag

Abstract

The invention discloses a smelting process for improving the cleanliness of Cr13 series steel by using rare earth refining slag, and belongs to the technical field of steel smelting. In order to improve the cleanliness of Cr13 series steel, the invention provides a smelting process for improving the cleanliness of the Cr13 series steel by using rare earth refining slag, 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, wherein slag auxiliary materials and RE2O3 are added, and LF slag comprises 32%-32% of Al2O3, 35%-45% of CaO, less than or equal to 6% of MgO, 8%-15% of SiO2 and 5%-20% of RE2O3; d, VD vacuum treatment; e, VD soft argon blowing; and F, pouring. By adding the rare earth oxide, the aluminum oxide inclusion activity in the slag is reduced, the inclusion control level of Cr13 series plastic die steel is improved, and the steel purity is improved.

Description

Technical Field

[0001] The invention belongs to the technical field of steel smelting, and in particular relates to a smelting process for improving the cleanliness of Cr13 series steel by utilizing rare earth refined slag. Background Art

[0002] Cr13 series steel belongs to martensitic stainless steel with good mechanical processing performance. After quenching and tempering treatment, it has excellent corrosion resistance, polishing performance, high strength and wear resistance. The level of inclusion control in steel has a significant impact on the corrosion resistance and polishing performance of steel. Improving the level of inclusion control in steel has a significant improvement in the polishing performance of steel. However, the current refined slag adopts the CaO-MgO-Al2O3-SiO2 quaternary slag system, in which Al2O3: 25-35%, CaO: 45-55%, SiO2: 10%-20%, MgO≤8%, but due to the high Al2O3 content in the slag, its activity is large and its ability to absorb alumina inclusions is weak, resulting in Class B exceeding the standard. After adding rare earth to steel, the activity of Al2O3 is significantly reduced, and the slag's ability to absorb inclusions increases.

[0003] At present, the method of Ca treatment is generally used to control the inclusions in steel. CN116516235A discloses a method for controlling Class B inclusions in pipeline steel, including: converter smelting, LF refining, calcium treatment, RH vacuum refining, magnesium treatment, soft blowing, continuous casting, rolling, LF refining process adjusts the composition of molten steel and slag basicity, after LF refining, Si-Ca alloy cored wire is fed into the molten steel for calcium treatment, and after RH refining, Mg-Al alloy cored wire is fed into the molten steel for magnesium treatment. In this method, there are no large-sized CaO-Al2O3 inclusions in the molten steel, and the inclusions are mainly CaO-Al2O3-MgO-CaS with high MgO content. After hot rolling, the inclusions are dispersed small-particle magnesium-aluminum spinel, and most of the Class B inclusions are grade 0.

[0004] CN116516235A discloses a method for improving the inclusion level of wind power steel, comprising: steelmaking raw materials are sequentially subjected to KR molten iron pretreatment, converter smelting, LF refining, VD vacuum treatment, and continuous casting processes to obtain continuous casting billets; during the steel tapping process of the converter smelting process, aluminum blocks, high carbon ferromanganese, cleaning agent, lime and fluorite are sequentially added into the ladle to ensure the thickness of the slag layer, the slag basicity and the slag viscosity; lime and bauxite are added to adjust the slag in the early stage of LF refining; diffusion deoxidizer composed of aluminum beans, carbon powder and silicon carbide is used for diffusion deoxidation in the middle and late stages of LF refining to control the basicity of the final slag of the refined slag; silicon calcium wire is added to the furnace before leaving the station to perform weak calcium treatment on the molten steel; lanthanum wire is fed after breaking the air in the VD vacuum treatment process to limit the generation and amount of inclusions in the steel, improve and stabilize the inclusion grade, and the inclusions of A, B, C, D, and DS in the continuous casting billet are within grade 1.0 or less.

[0005] In summary, most of the existing technologies use Ca treatment to control inclusions in steel. Ca treatment controls alumina inclusions in steel. On the one hand, it mainly modifies alumina inclusions into calcium aluminate, and liquid inclusions are difficult to float up and remove, resulting in excessive D-type inclusions; on the other hand, the Ca yield is unstable and does not utilize inclusions for stable control. Therefore, it is necessary to develop a new smelting process to improve the cleanliness of Cr13 series steel. At present, there is no report on the use of rare earth refined slag to control inclusions in steel. Summary of the invention

[0006] The technical problem to be solved by the present invention is that the alumina activity in the traditional refined slag is high, and the ability to absorb alumina inclusions is weak, which leads to the problem that the Class B inclusions easily exceed the standard, which is not conducive to improving the cleanliness of Cr13 series steel.

[0007] The present invention provides a smelting process for improving the cleanliness of Cr13 series steel by using rare earth refined slag, wherein the Cr13 series steel includes 1Cr13, 2Cr13, 3Cr13 or 4Cr13, and the process 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. If the molten steel meets the following requirements: P content is less than 0.01%, C content is ≥0.1% when smelting 1Cr13 and 2Cr13, and C content is ≥0.2% when smelting 3Cr13 and 4Cr13, then 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 is used for furnace refining: after the ladle enters the LF, the Al wire is fed to make the Al content of the molten steel meet 0.02% to 0.03%, and then slag auxiliary materials and RE2O3 are added to make the LF slag composition meet: Al2O3 22 to 32%, CaO 35 to 45%, MgO ≤ 6%, SiO2 8 to 15%, RE2O3 5 to 20%; then the power is sent to increase the temperature for refining, and sampling and analysis are performed. After the molten steel meets the requirements of the Cr13 series steel composition, the Al wire is fed to make the Al content of the molten steel meet 0.03% to 0.05%, and the LF tapping temperature is controlled to be greater than 1630℃, and then it enters the VD vacuum treatment;

[0011] D. VD vacuum treatment: Before VD vacuum treatment, slag should be removed to make the thickness of ladle slag between 80 and 100 mm, and then VD vacuum treatment should be carried out;

[0012] E. VD soft argon blowing: After the VD vacuum is completed, soft argon blowing treatment is carried out, sampling and temperature measurement are carried out, and when the temperature reaches 1560℃~1580℃, the hanging bag is ready for pouring;

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

[0014] Among them, in the above-mentioned smelting process for improving the cleanliness of Cr13 series steel using rare earth refined slag, the components of the Cr13 series steel are as follows by mass percentage: C content is 1Cr13, C: 0.08%~0.15%; 2Cr13, C: 0.16%~0.25%; 3Cr13, C: 0.30%~0.35%; 4Cr13, C: 0.36%~0.45%, and the remaining components are Si: 0.25%~0.5%, Mn: 0.30%~0.50%, Cr: 11.50%~13.50%, S≤0.01%, and the remainder is iron and unavoidable impurities.

[0015] Wherein, in the above-mentioned smelting process for improving the cleanliness of Cr13 series steel by using rare earth refined slag, in step A, the amount of lime added is 25-40 kg / t molten steel.

[0016] Wherein, in the above-mentioned smelting process for improving the cleanliness of Cr13 series steel by using rare earth refined slag, in step B, the amount of lime added is 6-10 kg / t molten steel.

[0017] Among them, in the above-mentioned smelting process for improving the cleanliness of Cr13 series steel by using rare earth refined slag, in step B, the amount of ferrosilicon added is 1.5-2.5kg / t molten steel.

[0018] Wherein, in the above-mentioned smelting process for improving the cleanliness of Cr13 series steel by using rare earth refined slag, in step B, the amount of Al ingot added is 2-3 kg / t molten steel.

[0019] Among them, in the above-mentioned smelting process for improving the cleanliness of Cr13 series steel using rare earth refined slag, 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 process for improving the cleanliness of Cr13 series steel by using rare earth refined slag, in step C, the refining conditions are: temperature 1600-1640°C, time 30-40 minutes.

[0021] Among them, in the above-mentioned smelting process for improving the cleanliness of Cr13 series steel by using rare earth refined slag, in step D, the conditions of the VD vacuum treatment are: maintaining the ultimate vacuum ≤100pa, maintaining the vacuum for 30 to 40 minutes, and the argon flow rate of 150 to 250L / min.

[0022] Among them, in the above-mentioned smelting process for improving the cleanliness of Cr13 series steel by using rare earth refined slag, 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.

[0023] Among them, in the above-mentioned smelting process for improving the cleanliness of Cr13 series steel by using rare earth refined slag, in step F, a slit-type argon protection device is used to protect the pouring.

[0024] Beneficial effects of the present invention:

[0025] The invention studies the relationship between the ability of steel slag to absorb aluminum oxide inclusions and the activity of aluminum oxide in the slag, reduces the activity of aluminum oxide inclusions in the slag by adding rare earth oxides, promotes the slag to absorb aluminum oxide inclusions in steel, converts Al2O3 inclusions in the steel into Ca-Al-O, reduces the content of solid-dissolved Al in the steel, avoids oxidation during the steel tapping process to cause waste, and does not generate new inclusions. The composition of the steel slag is easy to stably control, thereby effectively improving the inclusion control level of Cr13 series plastic mold steel, significantly improving the purity of the steel, and improving its polishing, wear resistance, corrosion resistance and other properties. BRIEF DESCRIPTION OF THE DRAWINGS

[0026] Figure 1 This is a diagram showing the influence of rare earth oxide content in slag on the activity of other slag components.

[0027] Figure 2 This is a typical inclusion morphology and composition diagram in Example 1.

[0028] Figure 3 This is the typical inclusion morphology and composition diagram in Example 2.

[0029] Figure 4 This is the typical inclusion morphology and composition diagram in Example 3.

[0030] Figure 5 This is the typical inclusion morphology and composition diagram in Comparative Example 1. DETAILED DESCRIPTION

[0031] Specifically, a smelting process for improving the cleanliness of Cr13 series steel using rare earth refined slag, wherein the Cr13 series steel includes 1Cr13, 2Cr13, 3Cr13 or 4Cr13, comprises the following steps:

[0032] 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. If the molten steel meets the following requirements: P content is less than 0.01%, C content is ≥0.1% when smelting 1Cr13 and 2Cr13, and C content is ≥0.2% when smelting 3Cr13 and 4Cr13, then add AOD;

[0033] 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;

[0034] C. LF is used for furnace refining: after the ladle enters the LF, the Al wire is fed to make the Al content of the molten steel meet 0.02% to 0.03%, and then slag auxiliary materials and RE2O3 are added to make the LF slag composition meet: Al2O3 22 to 32%, CaO 35 to 45%, MgO ≤ 6%, SiO2 8 to 15%, RE2O3 5 to 20%; then the power is sent to increase the temperature for refining, and sampling and analysis are performed. After the molten steel meets the requirements of the Cr13 series steel composition, the Al wire is fed to make the Al content of the molten steel meet 0.03% to 0.05%, and the LF tapping temperature is controlled to be greater than 1630℃, and then it enters the VD vacuum treatment;

[0035] D. VD vacuum treatment: Before VD vacuum treatment, slag should be removed to make the thickness of ladle slag between 80 and 100 mm, and then VD vacuum treatment should be carried out;

[0036] E. VD soft argon blowing: After the VD vacuum is completed, soft argon blowing treatment is carried out, sampling and temperature measurement are carried out, and when the temperature reaches 1560℃~1580℃, the hanging bag is ready for pouring;

[0037] F. Pouring: After the ladle is hoisted, the molten steel is poured into shape to obtain the Cr13 series steel finished product.

[0038] Among them, in the above-mentioned smelting process for improving the cleanliness of Cr13 series steel using rare earth refined slag, the components of the Cr13 series steel are as follows by mass percentage: C content is 1Cr13, C: 0.08%~0.15%; 2Cr13, C: 0.16%~0.25%; 3Cr13, C: 0.30%~0.35%; 4Cr13, C: 0.36%~0.45%, and the remaining components are Si: 0.25%~0.5%, Mn: 0.30%~0.50%, Cr: 11.50%~13.50%, S≤0.01%, and the remainder is iron and unavoidable impurities.

[0039] In the present invention, the smelting raw materials used are conventional raw materials in the art, generally Benxi Steel return materials of Cr13 series steel, alloy return materials similar to Cr13 series steel, and industrial pure iron.

[0040] 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.

[0041] 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.

[0042] 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%).

[0043] 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.

[0044] In step B of the present invention, since the AOD tapping performs the slag mixing operation, the AOD tapping slag is generally consistent with the LF furnace refined slag in composition, but it will also absorb air and oxidize during the slag mixing process. If the AOD tapping slag composition is controlled according to the Al2O3 22-32% in the LF refining process, the solid-dissolved Al content in the steel will increase, and oxidation will occur during the tapping process, causing waste. Therefore, the present invention reduces the Al2O3 content in the slag. At the same time, Figure 1 It can be seen that the ability of steel slag to absorb alumina inclusions is closely related to the activity of alumina in the slag. After adding rare earth oxides, the activity of alumina inclusions in the slag is significantly reduced, which promotes the slag to absorb alumina inclusions in steel. Figure 1It can be seen that when the RE2O3 content is greater than 20%, the activity of alumina does not further decrease. Therefore, in step B of the present invention, RE2O3 is added to make the RE2O3 content in the LF slag 5-20% to reduce the Al2O3 content in the slag.

[0045] In step B of the present invention, the amount of ferrosilicon added is 1.5-2.5 kg / t molten steel.

[0046] In step B of the present invention, the amount of Al ingot added is 2-3 kg / t molten steel.

[0047] 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.

[0048] In step C of the present invention, the refining conditions are: temperature 1600-1640° C., time 30-40 min.

[0049] In step D of the present invention, VD vacuum treatment is performed to further improve the inclusion rating. The conditions of the VD vacuum treatment are: maintaining the ultimate vacuum ≤ 100 Pa, maintaining the vacuum for 30 to 40 minutes, and the argon flow rate of 150 to 250 L / min.

[0050] In step E of the present invention, the conditions for the soft argon blowing treatment are: an argon gas flow rate of 30 to 50 L / min, and the argon blowing is maintained for 15 to 30 minutes.

[0051] In step F of the present invention, a slit-type argon protection device is used to protect the pouring.

[0052] 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.

[0053] Example 1

[0054] The Cr13 series steel smelted in this embodiment is 4Cr13.

[0055] 1. Smelting in electric arc furnace: The raw materials are mainly 4Cr13 Benxi steel return and 4Cr13 Benxi steel similar alloy return and 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 1642℃, the sample is taken for analysis, and the P content is 0.008%, and the C content of the steel is 0.36%. Then AOD is added to the molten steel.

[0056] 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, 1.8kg / 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 2.5kg / 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: 18%, CaO: 52%, MgO: 7%, SiO2: 11.2%, and the tapping temperature is 1590℃.

[0057] 3. LF is used for furnace refining: after the ladle enters the LF, 0.3kg / t Al wire of molten steel is fed to make the Al content of the molten steel between 0.02% and 0.03%, and then slag auxiliary materials (refining slag, main components Al2O3: 45%, CaO: 50%) and RE2O3 are added to make the LF slag composition Al2O3: 31.22%, CaO: 40.7%, MgO: 5.2%, SiO2: 8.4%, RE2O3: 5.6%; then power is supplied to raise the temperature to 1610℃, and the refining is carried out for 30min. The molten steel is taken to detect the composition. After the composition is appropriate (C: 0.38%, Si: 0.37%, Mn: 0.42%, Cr: 13.2%, S: 0.002%), 0.25kg / t Al wire of molten steel is fed to make the Al content of the molten steel 0.04%, the LF outlet temperature is 1638℃, and then it enters the VD vacuum treatment.

[0058] 4. VD vacuum treatment: Before vacuum treatment, remove the slag first, 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 ≤100pa, the vacuum is maintained for 30min, and the argon flow rate is 235L / min.

[0059] 5. VD soft argon blowing: After the VD vacuum is completed, soft argon blowing treatment is carried out with an argon flow rate of 41L / min. After the argon blowing is maintained for 20 minutes, sampling and temperature measurement are performed. When the temperature is 1566℃, the bag is ready for pouring.

[0060] 6. Pouring: The slit type argon protection device is used for protection pouring. After the ladle is hung, the molten steel is poured and formed to obtain 4Cr13 finished steel. Its chemical composition by weight percentage is: C: 0.38%, Si: 0.37%, Mn: 0.42%, Cr: 13.2%, S: 0.002%, and the balance is Fe and unavoidable impurities. Its typical inclusions are shown in Figure 2 , and its inclusion rating is shown in Table 1.

[0061] Depend on Figure 2As can be seen from Table 1, the inclusions of the 4Cr13 finished steel of this embodiment are spherical, mainly composed of Ca-Al-O, and have a high purity.

[0062] Table 1 Inclusion rating of finished steel of Example 1

[0063] A thick A thin B thick B thin C thick C Thin D thick D Thin 0 0 0 0.5 0 0 0 1

[0064] Example 2

[0065] The Cr13 series steel smelted in this embodiment is 1Cr13.

[0066] 1. Smelting in electric arc furnace: The raw materials are mainly 1Cr13 Benxi steel return and 1Cr13 Benxi steel similar alloy return and 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 1658℃, the sample is taken for analysis, and the P content is 0.004%, and the C content of the steel is 0.15%. Then AOD is added to the molten steel.

[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, 2kg / 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 (refined slag, main components Al2O3: 45%, CaO: 50%) are added to adjust the slag composition so that the AOD final slag composition is Al2O3: 16.1%, CaO: 51.2%, MgO: 7.8%, SiO2: 8.9%, and the tapping temperature is 1588℃.

[0068] 3. LF is used for furnace refining: after the ladle enters the LF, 0.3kg / t Al wire of molten steel is fed to make the Al content of the molten steel between 0.02% and 0.03%, and then slag auxiliary materials (refining slag, main components Al2O3: 45%, CaO: 50%) and RE2O3 are added to make the LF slag composition Al2O3: 27.3%, CaO: 42.18%, MgO: 5.7%, SiO2: 9.4%, RE2O3: 9.2%; then power is supplied to raise the temperature to 1630℃, and the refining is carried out for 40min. The molten steel is taken to detect the composition. After the composition is appropriate (C: 0.11%, Si: 0.46%, Mn: 0.45%, Cr: 13.4%, S: 0.002%), 0.2kg / t Al wire of molten steel is fed to make the Al content of the molten steel 0.04%, the LF outlet temperature is 1642℃, and then it enters the VD vacuum treatment.

[0069] 4. VD vacuum treatment: Before vacuum treatment, slag should be removed to make the thickness of the ladle slag between 80-100mm, and then VD vacuum treatment should be carried out to maintain the ultimate vacuum ≤100pa, the vacuum should be maintained for 30min, and the argon flow rate should be 200L / min.

[0070] 5. VD soft argon blowing: After the VD vacuum is completed, soft argon blowing treatment is carried out with an argon flow rate of 40L / min. After the argon blowing is maintained for 20 minutes, sampling and temperature measurement are performed. When the temperature is 1576℃, the bag is ready for pouring.

[0071] 6. Pouring: The slit type argon protection device is used for protection pouring. After the ladle is hung, the molten steel is poured and formed to obtain 1Cr13 finished steel. Its chemical composition by weight percentage is: C: 0.11%, Si: 0.46%, Mn: 0.45%, Cr: 13.4%, S: 0.002%, and the balance is Fe and unavoidable impurities. Its typical inclusions are shown in Figure 3 , and its inclusion rating is shown in Table 2.

[0072] Depend on Figure 3 As can be seen from Table 2, the inclusions of the 1Cr13 finished steel of this embodiment are spherical, mainly composed of Ca-Al-O, and have a high purity.

[0073] Table 2 Inclusion rating of finished steel of Example 2

[0074] A thick A thin B thick B thin C thick C Thin D thick D Thin 0 0 0 1 0 0 0 1

[0075] Example 3

[0076] The Cr13 series steel smelted in this embodiment is 4Cr13.

[0077] 1. Smelting in electric arc furnace: The raw materials are mainly 4Cr13 Benxi steel return and 4Cr13 Benxi steel similar alloy return and 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℃, the sample is taken for analysis, and the P content is 0.006%, and the C content of the steel is 0.38%. Then AOD is added to the molten steel.

[0078] 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, 2kg / 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 2.5kg / 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: 13.4%, CaO: 52.3%, MgO: 4.5%, SiO2: 7.3%, and the tapping temperature is 1586℃.

[0079] 3. LF is used for furnace refining: after the ladle enters the LF, 0.3kg / t Al wire of molten steel is fed to make the Al content of the molten steel between 0.02% and 0.03%, and then slag auxiliary materials (refining slag, main components Al2O3: 45%, CaO: 50%) and RE2O3 are added to make the LF slag composition Al2O3: 22.8%, CaO: 38.2%, MgO: 5.2%, SiO2: 8.4%, RE2O3: 19.3%; then power is supplied to raise the temperature to 1610°C, and the refining is carried out for 30 minutes. The molten steel sample is taken to measure the composition. After the composition is appropriate (C: 0.41%, Si: 0.38%, Mn: 0.42%, Cr: 13.1%, S: 0.003%), 0.25kg / t Al wire of molten steel is fed to make the Al content of the molten steel 0.03%, the tapping temperature is 1632°C, and then it enters the VD vacuum treatment.

[0080] 4. VD vacuum treatment: Before vacuum treatment, slag should be removed to make the thickness of the ladle slag between 80-100mm, and then VD vacuum treatment should be carried out to maintain the ultimate vacuum ≤100pa, the vacuum should be maintained for 30min, and the argon flow rate should be 200L / min.

[0081] 5. VD soft argon blowing: After the VD vacuum is completed, soft argon blowing treatment is carried out with an argon flow rate of 40L / min. After the argon blowing is maintained for 20 minutes, sampling and temperature measurement are performed. When the temperature is 1566℃, the bag is ready for pouring.

[0082] 6. Pouring: The slit type argon protection device is used to protect the pouring. After the ladle is hung, the molten steel is poured and formed to obtain 4Cr13 finished steel. Its chemical composition by weight percentage is: C: 0.41%, Si: 0.38%, Mn: 0.42%, Cr: 13.1%, S: 0.003%, and the balance is Fe and unavoidable impurities. Its typical inclusions are shown in Figure 4 , and its inclusion rating is shown in Table 3.

[0083] Depend on Figure 4As can be seen from Table 3, the inclusions of the 4Cr13 finished steel of this embodiment are spherical, mainly composed of Ca-Al-O, and have a high purity.

[0084] Table 3 Inclusion rating of finished steel of Example 3

[0085] A thick A thin B thick B thin C thick C Thin D thick D Thin 0 0 0 0.5 0 0 0 0.5

[0086] Comparative Example 1

[0087] The Cr13 series steel smelted in this comparative example is 4Cr13.

[0088] 1. Smelting in electric arc furnace: The raw materials are mainly 4Cr13 Benxi steel return and 4Cr13 Benxi steel similar alloy return and 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℃, the sample is taken for analysis, and the P content is 0.006%, and the C content of the steel is 0.39%. Then AOD is added to the molten steel.

[0089] 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, 2kg / 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 2.5kg / 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: 14.1%, CaO: 51.2%, MgO: 7.7%, SiO2: 12.6%, and the tapping temperature is 1588℃.

[0090] 3. LF is used for furnace refining: after the ladle enters the LF, 0.3kg / t Al wire of molten steel is fed to make the Al content of the molten steel between 0.02% and 0.03%, and then slag auxiliary materials (refining slag, main components Al2O3: 45%, CaO: 50%) are added to make the LF slag composition Al2O3 25.8%, CaO 46.1%, MgO 7.2%, SiO2 10.1%; then power is supplied to raise the temperature to 1620℃, and the refining is carried out for 30min. The molten steel sample is taken to measure the composition. After the composition is appropriate (C: 0.39%, Si: 0.34%, Mn: 0.38%, Cr: 13.2%, S: 0.002%), 0.25kg / t Al wire of molten steel is fed to make the Al content of the molten steel 0.03%, and the tapping temperature is 1632℃, and then it enters the VD vacuum treatment.

[0091] 4. VD vacuum treatment: Before vacuum treatment, slag should be removed to make the thickness of the ladle slag between 80-100mm, and then VD vacuum treatment should be carried out to maintain the ultimate vacuum ≤100pa, the vacuum should be maintained for 30min, and the argon flow rate should be 200L / min.

[0092] 5. VD soft argon blowing: After the VD vacuum is completed, soft argon blowing treatment is carried out with an argon flow rate of 40L / min. After the argon blowing is maintained for 25 minutes, sampling and temperature measurement are performed. When the temperature is 1568℃, the bag is ready for pouring.

[0093] 6. Pouring: The slit type argon protection device is used for protection pouring. After the ladle is hung, the molten steel is poured and formed to obtain 4Cr13 finished steel. Its chemical composition by weight percentage is: C: 0.39%, Si: 0.34%, Mn: 0.38%, Cr: 13.2%, S: 0.002%, and the balance is Fe and unavoidable impurities. Its typical inclusions are shown in Figure 5 , and its inclusion rating is shown in Table 4.

[0094] Depend on Figure 5 As can be seen from Table 4, the inclusions of the 4Cr13 finished steel of this comparative example are in the shape of strings, mainly composed of Al2O3, the B-type inclusions exceed the standard seriously, and the purity of the steel is low.

[0095] Table 4 Inclusion rating of finished steel of comparative example 1

[0096] A thick A thin B thick B thin C thick C Thin D thick D Thin 0 0 1 2.5 0 0 0 0.5

Claims

1. A smelting process for improving the cleanliness of Cr13 series steel by using rare earth refined slag, wherein the Cr13 series steel includes 1Cr13, 2Cr13, 3Cr13 or 4Cr13, 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. If the molten steel meets the following requirements: P content is less than 0.01%, C content is ≥0.1% when smelting 1Cr13 and 2Cr13, and C content is ≥0.2% when smelting 3Cr13 and 4Cr13, then 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 is used for furnace refining: after the ladle enters the LF, the Al wire is fed to make the Al content of the molten steel meet 0.02% to 0.03%, and then slag auxiliary materials and RE2O3 are added to make the LF slag composition meet: Al2O3 22 to 32%, CaO 35 to 45%, MgO ≤ 6%, SiO2 8 to 15%, RE2O3 5 to 20%; then the power is sent to increase the temperature for refining, and sampling and analysis are performed. After the molten steel meets the requirements of the Cr13 series steel composition, the Al wire is fed to make the Al content of the molten steel meet 0.03% to 0.05%, and the LF tapping temperature is controlled to be greater than 1630℃, and then it enters the VD vacuum treatment; D. VD vacuum treatment: Before VD vacuum treatment, slag should be removed to make the thickness of ladle slag between 80 and 100 mm, and then VD vacuum treatment should be carried out; E. VD soft argon blowing: After the VD vacuum is completed, soft argon blowing treatment is carried out, sampling and temperature measurement are carried out, and when the temperature reaches 1560℃~1580℃, the hanging bag is ready for pouring; F. Pouring: After the ladle is hoisted, the molten steel is poured into shape to obtain the Cr13 series steel finished product.

2. The smelting process for improving the cleanliness of Cr13 series steel by using rare earth refined slag according to claim 1, characterized in that: The components of the Cr13 series steel are as follows by mass percentage: C content of 1Cr13 is 0.08% to 0.15%; 2Cr13 is 0.16% to 0.25%; 3Cr13 is 0.30% to 0.35%; 4Cr13 is 0.36% to 0.45%, and the remaining components are Si: 0.25% to 0.5%, Mn: 0.30% to 0.50%, Cr: 11.50% to 13.50%, S≤0.01%, and the balance is iron and unavoidable impurities.

3. The smelting process for improving the cleanliness of Cr13 series steel by using rare earth refined slag according to claim 1, characterized in that: In step A, the amount of lime added is 25-40 kg / t molten steel.

4. The smelting process for improving the cleanliness of Cr13 series steel by using rare earth refined slag 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.

5. The smelting process for improving the cleanliness of Cr13 series steel by using rare earth refined slag 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.

6. The smelting process for improving the cleanliness of Cr13 series steel by using rare earth refined slag according to claim 1, characterized in that: In step C, the refining conditions are: temperature 1600-1640° C., time 30-40 min.

7. The smelting process for improving the cleanliness of Cr13 series steel by using rare earth refined slag according to claim 1, characterized in that: In step D, the conditions of the VD vacuum treatment are: maintaining the ultimate vacuum ≤ 100 Pa, maintaining the vacuum for 30 to 40 minutes, and the argon gas flow rate of 150 to 250 L / min.

8. The smelting process for improving the cleanliness of Cr13 series steel by using rare earth refined slag 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 process for improving the cleanliness of Cr13 series steel by using rare earth refined slag according to any one of claims 1 to 8, characterized in that: In step F, a slit-type argon protection device is used to protect the pouring.

Images