A melting method for controlling antimony element during the refining process of heat-resistant steel castings

Abstract

The present invention belongs to the technical field of melting of cast steel parts, and particularly relates to a melting method for controlling antimony elements during the refining process of heat-resistant cast steel parts; mainly by adding slag materials such as active lime, aluminum ingots, aluminum-calcium, and lime during the second refining process to improve the reducibility and alkalinity of the molten steel, making it have strong reducibility and strong alkalinity; and by taking measures such as controlling the argon flow rate and increasing the smelting time during the smelting process to reduce the Sb element content from 0.003% to 0.0008%, meeting the requirements of technical specifications.

Description

Technical Field

[0001] The invention belongs to the technical field of smelting steel castings, and in particular relates to a smelting method for controlling antimony elements in the refining process of heat-resistant steel castings. Background Art

[0002] Antimony (Sb) is a residual harmful element that often appears in the smelting process of steel castings. It mainly comes from smelting raw materials. For example, southern iron ore often contains high levels of Sb. This type of element is not easy to be removed during the smelting process and will continue to be enriched and remain in the steel. Since this type of element is present in very small amounts, it will have an adverse effect on the performance of steel parts, resulting in reduced strength and increased brittleness. Therefore, how to control the content of Sb in the smelting process needs to be solved urgently. Summary of the invention

[0003] In order to overcome the shortcomings and deficiencies in the conventional control process, the present application provides a method for controlling the smelting of antimony elements in the refining process of heat-resistant steel castings, so as to effectively control the content of antimony elements, significantly improve the quality of castings, and avoid the scrapping of castings and the increase in costs. The specific technical scheme is as follows:

[0004] A smelting method for controlling antimony elements in the refining process of heat-resistant steel castings, using EAF+LF+VOD+LF smelting process, comprising the following steps:

[0005] EAF furnace smelting control: including rough refining of molten steel, mainly melting molten steel, dephosphorization and decarburization.

[0006] The first LF furnace smelting control: including deoxidation, desulfurization and alloying of molten steel.

[0007] VOD furnace smelting control: including improving CO reaction affinity and reducing Cr oxidation.

[0008] The second LF furnace smelting control includes: after the molten steel reaches the LF furnace, adding a set amount of aluminum ingots for reduction, so that the content of Al element in the molten steel is 0.04% to 0.06%, so that the molten steel has strong reducing properties; adding a set amount of active lime, aluminum calcium, and fluorite to make the basicity of the slag in the molten steel 2.5 to 4, so that the molten steel has strong alkalinity; the total refining time is 60min to 80min, so that Sb in the molten steel has sufficient reaction time with elements such as Ca and F.

[0009] To better implement the present invention, the chemical composition of the heat-resistant steel casting is, by mass percentage: 0.11% ≤ C ≤ 0.14%, 0.20% ≤ Si ≤ 0.30%, 0.80% ≤ Mn ≤ 1.0%, P ≤ 0.015%, S ≤ 0.010%, 9.00% ≤ Cr ≤ 9.60%, 1.40% ≤ Mo ≤ 1.60%, 0.10% ≤ Ni ≤ 0.20%, 0.015% ≤ N ≤ 0.030%, 0.90% ≤ Co ≤ 1.10%, 0.008% ≤ B ≤ 0.013%, Sb ≤ 0.001%, Al ≤ 0.02%, Sn ≤ 0.015%, Cu ≤ 0.1%, As ≤ 0.025%, 0.18% ≤ V ≤ 0.22%, 0.05% ≤ Nb ≤ 0.07%; The contents of these elements need to be strictly controlled during the melting process.

[0010] To better implement the present invention, in the second LF furnace melting control step, the set addition amount of aluminum ingot is 2 - 3 kg / t of steel, which improves the reducibility of the molten steel.

[0011] To better implement the present invention, in the second LF furnace melting control step, the set addition amounts of active lime, aluminum calcium, and fluorite are 10 - 20 kg / t of steel, 5 - 8 kg / t of steel, and 1 - 2 kg / t of steel respectively, which increases the basicity of the steel slag, makes it strongly alkaline, and at the same time increases the Ca and F elements in the steel.

[0012] To better implement the present invention, in the second LF furnace melting control step, after adding the set amounts of active lime, aluminum calcium, and fluorite, the pressure of the argon gas introduced is increased to 0.4 - 0.6 Mpa for stirring.

[0013] To better implement the present invention, the EAF furnace melting control step includes adding scrap steel and pig iron in the EAF, and the weight ratio of scrap steel to pig iron is 7:3; adding a set amount of lime; starting to blow oxygen for decarburization when the temperature of the molten steel ≤ 1620°C; after the oxygen blowing ends, sampling and analyzing the content of P element. If P ≤ 0.005%, then tapping; otherwise, continue to add a set amount of lime for dephosphorization until P ≤ 0.005%.

[0014] To better implement the present invention, in the EAF furnace melting control step, the set addition amount of lime is 40 - 50 kg / t of steel.

[0015] To better implement the present invention, in the EAF furnace melting control step, the decarburization speed is 0.1 - 0.15% / min. After the decarburization amount > 1 / 2, the furnace door is tilted downward by 30° for slag flowing.

[0016] To better implement the present invention, the first LF furnace melting control step includes: after the molten steel reaches the LF furnace, adding a set amount of aluminum and calcium silicate, and then adding a set amount of active lime; when the temperature of the molten steel ≥ 1580 °C and the oxygen activity ≤ 10 ppm, start adding non-oxidizable alloys to meet the standard requirements.

[0017] To better implement the present invention, the VOD furnace melting control step includes: when the temperature of the molten steel is raised to between 1600 - 1620 °C and the vacuum degree is 6000 - 8000 Pa, carry out oxygen blowing; after the oxygen blowing ends, pump to a high vacuum, and when the vacuum degree reaches below 67 Pa, carry out VD (vacuum degassing), and after maintaining for 20 min, the VD (vacuum degassing) ends.

[0018] Compared with the conventional control process, the present invention has the following beneficial effects:

[0019] The melting method for controlling antimony elements in the refining process of heat-resistant steel castings provided by the present invention mainly adds slag materials such as active lime, aluminum ingots, aluminum calcium, and lime during the second refining process to improve the reducibility and alkalinity of the molten steel, making it have strong reducibility and strong alkalinity; and by taking measures such as controlling the argon flow rate and increasing the smelting time during the melting process, the content of Sb element is reduced from 0.003% to 0.0008% to meet the technical specification requirements, and at the same time, it also solves the bottleneck problem of the enterprise's melting technology. Specific embodiments

[0020] To facilitate the understanding of the present invention, the present invention will be described more comprehensively below, and preferred embodiments of the present invention are given. However, the present invention can be implemented in many different forms and is not limited to the embodiments described herein. On the contrary, the purpose of providing these embodiments is to make the disclosure of the present invention more thorough and comprehensive.

[0021] This embodiment provides a melting method for controlling antimony elements in the refining process of heat-resistant steel castings. The chemical composition of the heat-resistant steel castings is calculated by mass percentage as 0.11% ≤ C ≤ 0.14%, 0.20% ≤ Si ≤ 0.30%, 0.80% ≤ Mn ≤ 1.0%, P ≤ 0.015%, S ≤ 0.010%, 9.00% ≤ Cr ≤ 9.60%, 1.40% ≤ Mo ≤ 1.60%, 0.10% ≤ Ni ≤ 0.20%, 0.015% ≤ N ≤ 0.030%, 0.90% ≤ Co ≤ 1.10%, 0.008% ≤ B ≤ 0.013%, Sb ≤ 0.001%, Al ≤ 0.02%, Sn ≤ 0.015%, Cu ≤ 0.1%, As ≤ 0.025%, 0.18% ≤ V ≤ 0.22%, 0.05% ≤ Nb ≤ 0.07%; the contents of these elements need to be mainly controlled during the melting process. Adopt the EAF + LF + VOD + LF smelting process, which specifically includes the following steps:

[0022] Step 01, EAF furnace melting control: In this stage, the molten steel is mainly roughly refined, that is, the molten steel is melted, P is removed, and C is removed. According to the requirements of residual elements, 0.10% ≤ Ni ≤ 0.20%, P ≤ 0.015%, scrap steel and pig iron are added to the EAF, and the weight ratio of the scrap steel to the pig iron is 7:3; at the same time, since the P content requirement of the finished molten steel is very strict, 40 - 50 kg / t of lime is added to the steel (usually 20 - 30 kg / t of lime is added in the conventional control process) to improve the P removal efficiency.

[0023] When the temperature of the molten steel ≤ 1620 °C, oxygen blowing for decarburization starts; the decarburization speed is 0.1 - 0.15% / min. After the decarburization amount > 1 / 2, the furnace door is tilted downward by 30° for slag flowing to prevent P in the steel slag from being reduced again and entering the molten steel during the later reduction process, resulting in an increase in the P content again; at the same time, it is required to observe at any time during the slag flowing process. If the molten steel flows out, the furnace door should be lifted in time.

[0024] After the oxygen blowing ends, the content of P element is sampled and analyzed. If P ≤ 0.005%, then tapping; otherwise, continue to add a set amount of lime for P removal until P ≤ 0.005%.

[0025] Step 02, the first LF furnace melting control: In this stage, the molten steel is mainly deoxidized, desulfurized, and alloyed. After the molten steel arrives at the LF, first 2 - 5 Kg / ton of steel of aluminum and 3 - 5 kg / ton of steel of calcium silicide are added for deoxidation to improve the reducibility of the molten steel; then 10 - 20 Kg / / ton of steel of active lime is added for desulfurization; when the temperature of the molten steel ≥ 1580 °C and the oxygen activity ≤ 10 ppm, alloys that are not easily oxidized such as Co, Mo, Cr, Ni, etc. are added to meet the standard requirements. Note that alloys that are easily oxidized such as Si, Mn, Nb, V, B, N, etc. are not added first to prevent these elements from being oxidized after the molten steel enters the VOD, and C is adjusted to 20 - 30%. If the C content is too high, the oxygen blowing amount increases, wasting costs; if the C content is low, the decarburization amount is insufficient, and inclusions in the steel are not removed sufficiently, and then it enters the VOD furnace.

[0026] Step 03, VOD furnace melting control: In this stage, the affinity of the C - O reaction is mainly improved, and Cr oxidation is reduced; when the temperature of the molten steel is raised to between 1600 - 1620 °C and the vacuum degree is 6000 - 8000 Pa, oxygen blowing is carried out; after the oxygen blowing ends, a high vacuum is pumped, and VD is carried out when the vacuum degree reaches below 67 Pa. After maintaining for 20 min, the VD ends (in the conventional control process, the VD ends after maintaining for 15 min). This is to allow the residual O in the molten steel to further react with C, reduce carbon, remove gas, and remove inclusions; then 1.5 - 3 Kg / ton of steel of Al is added for reduction, and after 5 min, tapping is carried out to the LF furnace for further composition adjustment.

[0027] Step 04, Second LF Furnace Melting Control: This stage is a crucial link in removing the Sb element from the molten steel. The main conditions for removing the Sb element are to control the basicity of the molten steel, strong reducibility, and melting and refining time, etc. It specifically includes the following steps:

[0028] Improve the reducibility of the molten steel: After the molten steel reaches the LF furnace, add 2 - 3% Kg / ton of molten steel aluminum ingots for reduction, so that the content of Al element in the molten steel is 0.04% to 0.06% (in the conventional control process, the content of Al element in the molten steel is 0.02% to 0.03%), making the molten steel have strong reducibility; because as the smelting time continues, the Al in the molten steel will gradually be oxidized, resulting in a decrease in the reducibility of the molten steel, so it is advisable to control the Al content at a high level in the early stage of the second LF furnace melting.

[0029] Improve the basicity of the steel slag: Then add 10 - 20 kg / t of molten steel active lime, 5 - 8 kg / t of molten steel aluminum calcium, and 1 - 2 kg / t of molten steel fluorite to the molten steel, so that the basicity of the steel slag in the molten steel is 2.5 to 4 (in the conventional control process, the basicity of the steel slag in the molten steel is 1.5 to 2.5), making the molten steel have strong alkalinity, and at the same time increasing the Ca and F elements in the steel; under the conditions of strong alkalinity and strong reducibility, CaO, CaAl, and CaF2 decompose into Ca 2+ , Ca 2+ reacts with Sb in the molten steel to form CaSb and SbF and enters the steel slag to achieve the purpose of removal.

[0030] Prolong the refining time: Since the content of Sb in the steel is very weak and the reaction rate between Ca, F and Sb is slow, it is necessary to maintain strong reducibility and strong alkalinity for a period of time before chemical reactions can gradually occur. Therefore, the refining time needs to be increased from the conventional 40 - 60 min to 60 - 80 min to ensure that elements such as Ca and F in the steel slag fully react with Sb in the molten steel, and sample and monitor the Al content during the process to ensure that Al remains between 0.02 - 0.04%.

[0031] Increase argon stirring: After adding active lime, aluminum calcium, and fluorite, the argon flow rate is increased from the conventional 0.2 - 0.3 Mpa to 0.4 - 0.6 Mpa. By increasing argon stirring, the steel slag is fully mixed, the slag-steel reaction rate is increased, and the reaction between Sb and Ca, F is further improved.

[0032] It should be noted that the Sb element in the steel mainly remains as a residue. Although the content is extremely low, it has a great impact on the performance of the casting. Moreover, the metallicity of the Sb element is stronger than that of Fe, so it is very difficult to remove it by oxidation during the electric arc furnace smelting process. Through continuous experiments and summaries, a set of methods for removing Sb in the LF furnace refining process has been obtained, which meets the requirements of technical specifications and solves the technical problems of the enterprise.

[0033] The above embodiments only represent the specific implementation manners of the present invention. The description thereof is relatively specific and detailed, but it should not be construed as a limitation on the scope of the invention patent. It should be noted that for those of ordinary skill in the art, without departing from the concept of the present invention, several modifications and improvements can still be made, and these all belong to the protection scope of the present invention. Therefore, the protection scope of the present invention patent shall be subject to the appended claims.

Claims

1. A melting method for controlling antimony elements during the refining process of heat-resistant steel castings, characterized in that, The chemical composition of the heat-resistant steel casting is as follows in terms of mass percentage: 0.11% ≤ C ≤ 0.14%, 0.20% ≤ Si ≤ 0.30%, 0.80% ≤ Mn ≤ 1.0%, P ≤ 0.015%, S ≤ 0.010%, 9.00% ≤ Cr ≤ 9.60%, 1.40% ≤ Mo ≤ 1.60%, 0.10% ≤ Ni ≤ 0.20%, 0.015% ≤ N ≤ 0.030%, 0.90% ≤ Co ≤ 1.10%, 0.008% ≤ B ≤ 0.013%, Sb ≤ 0.001%, Al ≤ 0.02%, Sn ≤ 0.015%, Cu ≤ 0.1%, As ≤ 0.025%, 0.18% ≤ V ≤ 0.22%, 0.05% ≤ Nb ≤ 0.07%; The melting method includes the following steps: EAF furnace melting control: Add scrap steel and pig iron into the EAF, and the weight ratio of the scrap steel to the pig iron is 7:3; Add 40 - 50 kg / t of lime; Start blowing oxygen for decarburization when the temperature of the molten steel ≤ 1620°C; After the blowing oxygen ends, sample and analyze the content of P element. If P ≤ 0.005%, then tap the steel; Otherwise, continue to add a set amount of lime for P removal until P ≤ 0.005%. First LF furnace melting control: After the molten steel arrives at the LF furnace, add 2 - 5 kg / t of aluminum and 3 - 5 kg / t of calcium silicate, and then 10 - 20 kg / t of active lime; When the temperature of the molten steel ≥ 1580°C and the oxygen activity ≤ 10 ppm, start adding non-oxidizable alloys to meet the standard requirements; VOD furnace melting control; Second LF furnace melting control: After the molten steel arrives at the LF furnace, add 2 - 3 kg / t of aluminum ingots for reduction to make the content of Al element in the molten steel 0.04% to 0.06% in terms of mass percentage; Add 10 - 20 kg / t of active lime, 5 - 8 kg / t of aluminum calcium, and 1 - 2 kg / t of fluorite to make the basicity of the steel slag in the molten steel 2.5 to 4; The total refining time is 60 min to 80 min.

2. The smelting method for controlling antimony elements during the refining process of heat-resistant cast steel parts according to claim 1, characterized in that, In the second LF furnace melting control step, after adding a set amount of active lime, aluminum calcium, and fluorite, increase the pressure of the argon gas introduced to 0.4 - 0.6 MPa for stirring.

3. The smelting method for controlling antimony element during the refining process of the heat-resistant steel casting according to claim 1, characterized in that, In the EAF furnace melting control step, the decarburization speed is 0.1 - 0.15% / min. After the decarburization amount > 1 / 2, tilt the furnace door downward by 30° for slag flowing.

4. The melting method for controlling antimony element during the refining process of the heat-resistant cast steel part according to claim 1, characterized in that, The VOD furnace melting control step includes that when the temperature of the molten steel is increased to between 1600 - 1620°C and the vacuum degree is 6000 - 8000 Pa, blow oxygen; After the blowing oxygen ends, pump to high vacuum, and when the vacuum degree reaches below 67 Pa, carry out vacuum degassing, and keep it for 20 min before the vacuum degassing ends.