A method of smelting a nickel-iron based material

Abstract

The present application belongs to the technical field of casting smelting, and mainly relates to a smelting method of a nickel-iron-based material. The method is mainly controlled through the processes of smelting preparation, EAF furnace smelting, first LF furnace smelting, VOD furnace smelting and second LF furnace smelting, and the specific processes and parameters of each step are reasonably set, so that the purity of the molten steel is significantly improved. Meanwhile, three times of slagging are performed in the VOD furnace smelting process, including before, during and after the VOD furnace smelting, so that the residual SiO2 in the molten steel can be completely removed, and the Si element is prevented from being re-reduced into the molten steel and exceeding the standard, and finally the nickel-iron-based material meeting the standard requirements is smelted.

Description

Technical Field

[0001] This invention belongs to the field of casting smelting technology, and mainly relates to a smelting method for nickel-iron-based materials. Background Technology

[0002] Nickel-iron-based materials are a type of nickel-based high-temperature alloy. The main alloying elements are chromium (15-17%), iron (41-43%), and small amounts of cobalt, iron, molybdenum, tungsten, titanium, and niobium, with a total content of 3-5%. The remainder is all nickel, hence the name nickel-iron-based materials. Chromium ensures the elastic modulus of the casting material at high temperatures and prevents plastic deformation. Titanium and aluminum can form a Ni3(Al,Ti) dispersed phase, which is coherent with the matrix and plays a strengthening role. It is used in applications that withstand high temperatures (up to 1100℃) and high stress during service, such as turbine disks and blades of gas turbines.

[0003] Conventional iron-based materials are mainly produced by smelting scrap steel and then adding alloys, with the alloy proportion accounting for 3-30% of the molten steel. In contrast, nickel-iron-based materials use nickel as the base material. If scrap steel is used as the raw material for smelting, and then elements such as Ni, Cr, Al, and Ti are added, the alloy addition proportion reaches more than 70%, which is 2 to 3 times that of ordinary iron-based high-alloy materials. Secondly, the content of easily oxidized elements such as Al and Ti in nickel-iron-based materials is as high as 1.4% and 2.0% respectively, which is significantly higher than that of conventionally smelted iron-based materials. Finally, the requirements for various residual elements, such as Si, Sn, H, and V, are stringent and difficult to meet. Summary of the Invention

[0004] Based on the aforementioned difficulties in controlling various residual elements when using existing smelting methods to melt nickel-iron-based materials, the purpose of this invention is to provide a novel smelting method for nickel-iron-based materials. According to the chemical composition of the material, the smelting process is formulated as EAF+LF+VOD+LF, followed by casting. The process is mainly controlled through smelting preparation, EAF furnace smelting, first LF furnace smelting, VOD furnace smelting, and second LF furnace smelting. The specific processes and parameters of each step are reasonably set to ultimately smelt nickel-iron-based materials that meet the standard requirements.

[0005] A method for smelting nickel-iron-based materials includes the following steps:

[0006] EAF furnace smelting: The charge is added to the EAF furnace, along with 3% to 5% lime and 1% to 1.5% carburizing agent based on the amount of molten steel. After smelting, oxygen blowing is performed to decarburize the molten steel and remove impurities, as well as phosphorus. When the phosphorus content is ≤0.008%, the steel is tapped to the LF furnace using a slag-avoiding method.

[0007] First LF furnace smelting: Add 3% to 5% lime and 2kg / ton to 3kg / ton of steel Al particles to the molten steel. When the S content is ≤0.01%, add the alloy in batches. When the C content is controlled at 0.3% to 0.4% and the temperature range is adjusted to 1600℃ to 1610℃, tap the steel into the VOD furnace.

[0008] VOD furnace smelting: After vacuuming, oxygen blowing decarburization is carried out. When the oxygen volume is reduced to two-thirds of the total oxygen volume, the vacuum is broken and the ladle is hoisted to the slag removal station for slag removal. The ladle is then put back into the VOD furnace, and vacuuming and oxygen blowing decarburization are carried out again until the total oxygen volume is exhausted. Vacuuming continues until the vacuum degree reaches below 67 Pa, at which point vacuum degassing begins. The steel is then broken and tapped into the LF furnace for smelting.

[0009] Secondary LF furnace smelting: The content of each element is precisely adjusted, and the steel is tapped and cast after the content of each element meets the standard range.

[0010] To better realize the present invention, the alloy needs to be baked before being added to the furnace during the smelting process.

[0011] To better implement this invention, in the initial LF furnace melting step, when adding the alloy in batches, the amount added in each batch is less than or equal to 500 kg. Because the amount of molten steel is small and the temperature drops quickly, the alloy needs to be added slowly in batches. This prevents adding too much alloy at once, causing the molten steel to cool too quickly, and also allows the alloy to melt rapidly, preventing it from sinking to the bottom.

[0012] To better realize this invention, after the initial LF furnace melting is completed, the steel is tapped and slag is removed before it enters the VOD furnace for further melting. This prevents harmful sulfur elements from returning to the molten steel and also prevents SiO2 in the slag from being reduced back, which would increase the Si content. This ensures that the Si content will not exceed the standard during the subsequent refining process.

[0013] To better realize this invention, in the VOD furnace melting step, the vacuum level in the VOD furnace is first evacuated to 6000 Pa to 8000 Pa before oxygen blowing for decarburization. This accelerates the CO reaction under vacuum conditions while reducing Cr oxidation.

[0014] To better realize this invention, in the VOD furnace smelting step, after the oxygen quantity is blown to a set value, a voiding process is performed, where the set value is two-thirds of the total oxygen quantity. The main purpose is to perform a second slag removal to remove the SiO2 generated in the steel, preventing it from being reduced to elemental Si later, which would lead to excessive Si content.

[0015] To better realize this invention, in the VOD furnace smelting step, vacuum degassing is performed when the vacuum degree reaches below 67 Pa. Lime and Al particles are added to reduce the molten steel. After standing for a set time, the steel is broken out of the vacuum and tapped into the LF furnace for smelting. Under high vacuum conditions, the molten steel is degassed and impurities are removed, further purifying the molten steel.

[0016] To better achieve the present invention, the settling time is 5 to 8 minutes, so that the added reducing agent can fully react with the residual oxygen and oxidation in the steel to achieve the purpose of deoxidation.

[0017] To better realize the present invention, in the secondary LF furnace smelting step, aluminum particles are first added to reduce the slag surface, and argon gas is blown in to stir and promote the inclusions to float. When the steel slag no longer solidifies into a shell, the slag is skimmed off again. This can further remove the SiO2 that floats to the slag surface and prevent it from being reduced into the molten steel, which would cause the Si element to exceed the standard.

[0018] To better realize the present invention, in the secondary LF furnace smelting step, after adjusting the content of each element to meet the standard range, the argon flow rate is adjusted to 0.05-0.1MPa for argon soft blowing to promote the floating of inclusions and purify the molten steel.

[0019] To better realize this invention, in the secondary LF furnace melting step, after the content of each element meets the standard range, the steel is tapped and poured. Before pouring, argon gas is blown into the casting cavity to prevent secondary oxidation of the molten steel. Since this material contains elements such as B, Al, and Ti, which are highly oxidizable, it is necessary to reduce the contact between the molten steel and air during the pouring process to prevent the oxidation of B, Al, and Ti elements.

[0020] The method of the present invention has the following beneficial effects:

[0021] The use of an EAF furnace + LF furnace + VOD furnace + LF furnace smelting process, instead of the existing MF furnace (medium frequency furnace) smelting technology, can significantly reduce costs. Furthermore, because the molten steel is refined through the LF furnace and VOD furnace, its purity is significantly improved. Additionally, since scrap steel and recycled materials are used as raw materials, with the addition of necessary alloys, instead of using pure metals directly, the cost is even lower.

[0022] Three slag removal processes are performed during VOD furnace smelting: before, during, and after VOD furnace smelting. This thoroughly removes residual SiO2 from the molten steel, preventing it from being reduced back into the molten steel during later refining, which would lead to excessive Si content and solve the problem of Si content failing to meet standards. Detailed Implementation

[0023] To facilitate understanding of the present invention, a more complete description will be provided below with reference to the invention. Preferred embodiments of the invention are given. However, the invention can be implemented in many different forms and is not limited to the embodiments described herein. Rather, these embodiments are provided so that this disclosure will be thorough and complete.

[0024] This invention provides a method for smelting nickel-iron-based materials. The nickel-iron-based material is mainly HT700Q nickel-iron-based material, with the following specific chemical composition: C≤0.08%, Si≤0.3%, P≤0.028%, S≤0.01%, Cr: 15.5~16.5%, Mo≤0.6%, Cu≤0.2%, Al: 1.3~1.5%, W≤0.6%, Ti: 1.9~2.1%, B: 0.003~0.006%, Fe: 40~45%, Ni: 40~45%, with the remainder being trace impurity elements such as Zr, Pb, Bi, Se, Sn, Ta, N, O, and H. Based on the chemical composition of this material, the smelting process is designed as EAF furnace + LF furnace + VOD furnace + LF furnace, and casting is performed after smelting.

[0025] Step S01, Melting Preparation:

[0026] The ladle usage requirements stipulate that the alloy content of the material reaches 70%. The steel output from the EAF furnace is small, while a large amount of alloy needs to be added in the LF furnace, resulting in a final steel output weight of approximately 50t, requiring a 60t ladle. Due to the small steel output from the EAF furnace, the molten steel is insufficient when using a 60t ladle, causing the electrodes to not make contact with the molten steel during melting and preventing the supply of electricity. Therefore, a 25t ladle is first used to draw molten steel from the EAF furnace, and then nickel-based and ferrochrome alloys are added before the molten steel is poured into the 60t ladle for continued melting. Because of the large amount of alloy added and the long melting time, both ladles used must be new ladles to prevent leakage.

[0027] Alloy preparation: Based on the residual element requirements of Si ≤ 0.1%, Sn ≤ 0.005%, and H ≤ 3ppm, ordinary low-carbon ferrochrome contains a certain amount of Si. Adding it will cause the Si content to exceed the standard. Therefore, a certain amount of metallic chromium needs to be prepared to replace the low-carbon ferrochrome. To prevent Sn content from exceeding the standard, the composition of various alloys needs to be tested before addition. If the Sn content is high, the alloy should not be added. This is especially important for ferrotitanium alloys, as the Sn content will increase significantly after the addition of ferrotitanium alloys. Therefore, metallic titanium needs to be used instead of low-titanium alloys. If high-titanium alloys are selected, the Sn content should be less than or equal to 0.15%. To control the H content, since H mainly comes from the moisture in the alloy, all alloys added to the furnace need to be baked in advance. It is especially important to remove moisture from ferrotitanium alloys and aluminum ingots added after the VOD furnace to prevent the H content from increasing.

[0028] Step S02, EAF furnace smelting:

[0029] High-quality low-manganese scrap steel is added to the EAF furnace, along with 3% to 5% lime and 1% to 1.5% carburizing agent based on the steel volume. After smelting, oxygen blowing is performed to decarburize the steel and remove impurities, including phosphorus (P). When the P content is ≤0.008%, the steel is tapped into the LF furnace using a slag-avoidance method. The tapping amount is less than or equal to the tapping amount specified in the EAF furnace smelting instructions to avoid increasing the amount of alloy added later.

[0030] It should be noted that the main purpose of using an EAF furnace for smelting is to dephosphorize and ensure that residual elements do not exceed the standard. Since the amount of steel tapped from the EAF furnace is small, it is impossible to remove slag from the ladle. Therefore, a slag-avoidance method must be used to tap the steel to prevent slag from entering the ladle.

[0031] Step S03, initial LF furnace smelting:

[0032] Add 3% to 5% lime (based on the steel volume) to the ladle, and add 2 kg / ton to 3 kg / ton of Al particles for slag formation and sulfur removal. After the sulfur content is ≤0.01%, add the alloy in batches. The specific steps are as follows:

[0033] 1) First, electrolytic nickel and ferrochrome are added. Due to the small volume of molten steel and its rapid cooling, the amount of alloy added in each batch is less than or equal to 500 kg, and it is added slowly in batches. Regarding the control of the content of each element, since a large amount of Al and Ti elements need to be added after VOD furnace melting, the Cr and Ni elements in the molten steel will be significantly diluted. Therefore, before entering the VOD furnace, the Cr element content needs to be controlled at 17%, which is 0.5% higher than the standard upper limit, and the Ni element needs to be controlled at the standard upper limit of 38%. In this way, after VOD furnace melting, there is no need to add Ni, Cr, and other alloying elements. To ensure that the Si element content does not exceed the standard, and considering cost factors, half of the metallic chromium is used instead of ferrochrome.

[0034] 2) After adjusting the Cr and Ni content to the standard requirements, pour the molten steel into a 60t ladle and heat it immediately. When the temperature reaches 1600℃, add other non-oxidizing elements, including Mo and W, and adjust the content of Mo and W to the standard upper limit of 0.6%. Since the content of Mo and W is relatively small, the subsequent addition of alloys has no effect on the content of Ni and Cr.

[0035] Because of the high alloy content, there are also many inclusions. Therefore, the C content is controlled at 0.3-0.4%, and the temperature is 1600-1610℃ before entering the VOD for oxygen blowing decarburization.

[0036] Step S04, VOD furnace smelting:

[0037] 1) After the first LF furnace smelting is completed and the steel is tapped, it needs to be slag removed before entering the VOD furnace for smelting. All steel slag must be removed to prevent harmful S elements from returning to the molten steel, and to prevent SiO2 in the steel slag from being reduced back, which would lead to an increase in the Si element content.

[0038] 2) After the vacuum is reduced to 6000-8000 Pa, oxygen blowing for decarburization begins. The amount of oxygen blown is calculated based on the carbon content and the amount of molten steel. After the oxygen amount is blown to 2 / 3 of the total amount of oxygen, the vacuum is broken and the ladle is hoisted to the slag removal station for secondary slag removal. This removes the oxides such as SiO2 and MnO that have formed, preventing them from being reduced back after the VOD furnace smelting is completed.

[0039] 3) The ladle is hoisted back into the VOD furnace, and the vacuum level is raised to 6000-8000 Pa. Oxygen decarburization is continued until all oxygen is exhausted. Vacuuming continues until the vacuum level is <67 Pa, at which point vacuum degassing begins, i.e., VD treatment, to remove non-metallic inclusions and harmful gaseous elements. After 15-20 minutes, 200-400 kg of active lime and 1.5-2 kg / ton of Al particles are added to reduce the molten steel. After standing for 5-8 minutes, the steel is tapped into the LF furnace for further composition adjustment.

[0040] Step S05, Secondary LF furnace smelting:

[0041] 1) The molten steel is placed in the LF furnace again for smelting. The main purpose is to accurately adjust the content of each element. First, 2% to 3% aluminum particles are added to reduce the slag surface, and argon gas is blown in to stir and promote the inclusions to float. When the steel slag no longer solidifies into a shell, the slag is skimmed off again in order to further remove the SiO2 that floats to the slag surface and prevent it from being reduced into the molten steel in the end, which would cause the Si element to exceed the standard.

[0042] 2) Calculate the amount of Al and Ti elements to be added. The calculation formula is: (target value of element - actual value) * steel quantity / alloy content / alloy recovery rate. Al and Ti elements are easily oxidized, and the recovery rate is 0.80% to 0.85%. Add aluminum first. Since aluminum ingots are easily trapped by steel slag, adjust the argon flow rate to 0.3 to 0.4 MPa before adding aluminum ingots, increase the stirring frequency and intensity, and improve its recovery rate. Then add ferrotitanium, with each batch amount <300 kg. After adding, adjust the argon flow rate to 0.1 to 0.2 MPa to prevent excessive argon volume from oxidizing Al and Ti elements.

[0043] 3) Finally, add elements B and Zr. These two elements are not only very easy to oxidize, but also have low content and are very difficult to control. Therefore, adding them last can not only improve the recovery rate, but also allow the steel to be poured shortly after addition, preventing oxidation.

[0044] 4) After all elements have been adjusted to meet the requirements, the argon flow rate is adjusted to 0.05-0.1 MPa for argon soft blowing to promote the floating of inclusions, purify the molten steel, and adjust the temperature. After 20-25 minutes, the steel is poured out.

[0045] Specifically, because the nickel-iron-based material contains many easily oxidized elements, it should be poured immediately after tapping. Before pouring, argon should be blown into the casting cavity, and the pouring cup should be protected with argon to prevent secondary oxidation of the molten steel.

[0046] The method provided in this application, when smelting nickel-iron-based materials, uses an EAF furnace + LF furnace + VOD furnace + LF furnace process to smelt nickel-iron-based materials instead of an MF furnace (medium frequency furnace), which is more cost-effective. At the same time, because the molten steel is refined in the LF furnace and VOD furnace, the purity of the molten steel is higher. Secondly, one of the difficulties in smelting this material is that the Si element content requirement is strict and cannot be met by conventional smelting methods. In the smelting process of this application, a batch slag removal operation is adopted to reduce the SiO2 content in the steel slag, so that the Si content meets the requirements.

[0047] The embodiments described above merely illustrate specific implementations of the present invention, and while the descriptions are detailed, they should not be construed as limiting the scope of the invention patent. It should be noted that those skilled in the art can make various modifications and improvements without departing from the concept of the present invention, and these all fall within the protection scope of the present invention. Therefore, the protection scope of this invention patent should be determined by the appended claims.

Claims

1. A method of smelting a nickel-iron based material, characterized in that, The nickel-iron-based material is mainly HT700Q nickel-iron-based material, and the specific chemical component content meets: C≤0.08%, Si≤0.3%, P≤0.028%, S≤0.01%, Cr: 15.5-16.5%, Mo≤0.6%, Cu≤0.2%, Al: 1.3-1.5%, W≤0.6%, Ti: 1.9-2.1%, B: 0.003-0.006%, Fe: 40-45%, Ni: 40-45%, and the rest is Zr, Pb, Bi, Se, Sn, Ta, N, O, H trace impurity elements; the smelting method comprises the following steps: EAF furnace smelting: the charging material is added into the EAF furnace, and 3% to 5% of lime and 1% to 1.5% of carbon additive are added into the molten steel for smelting, when the P content is less than or equal to 0.008%, the molten steel is discharged into the LF furnace by means of slag avoidance; first LF furnace smelting: 3% to 5% of lime and 2 kg / ton of steel to 3 kg / ton of steel Al particles are added, when the S content is less than or equal to 0.01%, the alloy is added in batches; the adding amount of each batch is less than or equal to 500 kg; when the C content is controlled to be 0.3% to 0.4% and the temperature range is adjusted to be 1600 ℃ to 1610 ℃, the molten steel is discharged into the VOD furnace for smelting; VOD furnace smelting: the vacuum degree in the VOD furnace is extracted to 6000 Pa to 8000 Pa, then oxygen decarburization is carried out, after the oxygen amount reaches the set value, the vacuum is broken, the ladle is hoisted to the slag removal station for slag removal, the ladle is hoisted into the VOD furnace again, vacuum extraction is continued, then oxygen decarburization is carried out until the total oxygen amount is blown out; vacuum degassing is continued until the vacuum degree reaches below 67 Pa; the molten steel is broken and discharged into the LF furnace for smelting; second LF furnace smelting: the content of each element is accurately adjusted, and the molten steel is poured after the content of each element meets the standard range; The alloy added into the furnace in the above steps needs to be roasted in advance.

2. The melting method of a nickel-iron based material according to claim 1, characterized in that, After the first LF furnace smelting is completed, the molten steel is discharged, slag removal is carried out, and then the molten steel is smelted in the VOD furnace.

3. The melting method of a nickel-iron based material according to claim 1, characterized in that, In the VOD furnace smelting step, the vacuum is broken after the oxygen amount reaches the set value, and the set value is two-thirds of the total oxygen amount.

4. The melting method of a nickel-iron based material according to claim 1, characterized in that, In the VOD furnace smelting step, vacuum degassing is carried out when the vacuum degree reaches below 67 Pa, lime and Al particles are added to reduce the molten steel, the molten steel is placed for a set time, then the vacuum is broken, and the molten steel is smelted in the LF furnace.

5. The melting method of a nickel-iron based material according to claim 1, characterized in that, In the second LF furnace smelting step, the slag surface is first reduced by adding aluminum particles, argon is blown in for stirring, and slag removal is carried out.

6. The melting method of a nickel-iron based material according to claim 1, characterized in that, In the second LF furnace smelting step, after the content of each element is adjusted to meet the standard range, the argon flow is adjusted to 0.05-0.1 MPa for argon soft blowing.

7. The melting method of a nickel-iron based material according to claim 1, characterized in that, In the second LF furnace smelting step, after the content of each element meets the standard range, the molten steel is poured, and argon is blown in the mold cavity before pouring.