A method for smelting high-cleanliness steel using lf refining slag

Abstract

The present application relates to the metallurgical technology field, specifically discloses a kind of method for smelting high clean steel using LF refining slag.The method provided by the present application carries out primary slagging in the process of electric furnace tapping, after tapping, LF refining slag recovered in continuous casting process is added to carry out secondary slagging, and the ladle after secondary slagging is hoisted to refining process to adjust the composition of furnace slag, to carry out third slagging, after refining, it is hoisted to continuous casting station and poured, and LF refining slag is recycled, so the process is carried out in a cycle, effectively realizes the recycling of LF refining slag, and also through three-step slagging process, the slag system of LF refining slag is stabilized for multiple uses, the purity of molten steel in the process is improved, which lays a foundation for steelmaking enterprises to continuously develop low-cost high-clean steel grades, and has significant economic and social benefits.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of metallurgy, and in particular to a method for smelting high-cleanliness steel by using LF refining slag. BACKGROUND

[0002] The LF ladle refining furnace has good metallurgical effects on improving the purity of molten steel, homogenizing the composition and temperature of molten steel, and removing non-metallic inclusions in molten steel, and is therefore widely used in the steel smelting industry. After the initial molten steel is sent to the LF furnace, the slag is sent, adjusted, controlled, fed, stirred, and alloyed, and the molten steel is deoxidized and desulfurized, the inclusions are removed, the composition is adjusted, and the temperature is controlled, and when the LF furnace refining and tapping conditions are met, the molten steel is tapped. The LF refining slag has high CaO and Al2O3 contents, high basicity, and strong reducing properties, which ensure the refining effect of low sulfur and low oxygen content of the molten steel, and the LF refining slag remaining in the ladle after refining and casting has strong reducing and desulfurizing capacity, as well as a large amount of heat, and direct discharge is a great waste of resources and pollutes the environment.

[0003] The most efficient way to use the LF refining slag is metallurgical recycling, and the LF refining slag has low melting point, fast melting speed, high basicity, and low oxidizing property, which can be recycled in hot state for the refining process. However, due to the high sulfur content in the LF refining slag, the phenomenon of "resulfurization" of the molten steel occurs during metallurgical recycling, thereby limiting the recycling and reuse of the LF refining slag. Moreover, the LF refining slag recycling technology is not mature, and cannot guarantee the stability of the refining slag system composition between each furnace of steel. During the smelting of high-cleanliness steel, the instability of the refining slag system composition not only reduces the utilization rate of electric energy, but also is not conducive to the deoxidation, desulfurization and inclusion removal of the molten steel. Therefore, how to recycle and utilize the LF refining slag has become the most concerned topic for enterprises to produce high-cleanliness steel. SUMMARY

[0004] In view of the above problems existing in the recycling of the LF refining slag, the present application provides a method for smelting high-cleanliness steel by using LF refining slag.

[0005] To achieve the above-mentioned application purposes, the embodiments of the present application adopt the following technical solutions:

[0006] A method for smelting high-cleanliness steel by using LF refining slag, comprising the following steps:

[0007] S1: all of the LF refining slag after the first furnace continuous casting is completed is used;

[0008] S2: When the electric furnace tapping reaches 9%–10% of the steel volume, silicon carbide is added to the ladle for pre-deoxidation; when the tapping reaches 24%–26% of the steel volume, aluminum ingots are added for precipitation deoxidation; when the tapping reaches 32%–34% of the steel volume, carburizing agent, alloy and slag-forming auxiliary materials are added; when the tapping reaches 49%–51% of the steel volume, calcium carbide is added; at the end of tapping, the aforementioned LF refining slag is added;

[0009] S3: After 1 to 2 minutes of LF refining and power supply, lime is added, along with calcium carbide, silicon carbide, and aluminum particles for diffusion deoxidation;

[0010] S4: The refined molten steel is sent to the continuous casting process. After casting is completed, the LF refining slag is recovered.

[0011] S5: Repeat the operations from S2 to S4 to carry out the cyclic smelting of high-purity steel.

[0012] Compared to existing technologies, the method for smelting high-purity steel using LF refining slag provided by this invention significantly improves the stability of the refining slag system and extends the retention time of refined white slag through a unique electric arc furnace deoxidation and primary slag-forming process during steel tapping, a secondary slag-forming process for recycling LF refining slag after steel tapping, and a three-step slag-forming process for adjusting slag composition during LF refining. This also effectively reduces refining slag-forming costs by 13-16 yuan / ton of steel. More importantly, the high purity of molten steel is maintained during the recycling of LF refining slag, reducing the inclusions after conventional rolling from grade 1.5-2.0 to grade 0-0.5. This lays the foundation for smelting high-purity steel using LF refining slag and achieves resource utilization of waste, resulting in significant economic, social, and environmental benefits and extremely high practical value.

[0013] Further, in step S1, the first batch of LF refining slag is prepared through the following process:

[0014] For S101, when the electric furnace tapping reaches 9%–10%, silicon carbide is added to the ladle for pre-deoxidation; when the tapping reaches 24%–26%, aluminum ingots are added for precipitation deoxidation; when the tapping reaches 32%–34%, carburizing agent, alloy and slag-forming auxiliary materials are added; when the tapping reaches 49%–51%, calcium carbide is added.

[0015] S102: After 1 to 2 minutes of LF refining and power supply, lime is added, followed by silicon carbide for diffusion deoxidation;

[0016] S103: The refined molten steel is sent to the continuous casting process. After casting is completed, all LF refining slag is recovered.

[0017] The optimized smelting process for the first furnace of molten steel is beneficial to improving the stability of the recycled LF refining slag system, thereby increasing the number of times the LF refining slag can be recycled and reused, ensuring the stability of the LF refining slag system in each recycling cycle, and improving the cleanliness of the molten steel.

[0018] It should be noted that, using the process provided by the present invention, the LF refining slag can be recycled 4 times. After 4 times, it will no longer be recycled. New LF refining slag needs to be obtained again according to step S1, and then the LF refining slag recycling process will be executed.

[0019] In conjunction with the above, further, in S101, the amount of silicon carbide added is 0.25 kg / t to 0.45 kg / t; the amount of aluminum ingot added is 1 kg / t to 1.3 kg / t; and the amount of calcium carbide added is 0.37 kg / t to 0.57 kg / t.

[0020] In conjunction with the above, further, in S101, the slag-forming auxiliary materials include lime, fluorite, and synthetic slag; wherein, for steel grades with C ≤ 0.25%: the amount of lime added is 5 kg / t to 6 kg / t, the amount of fluorite added is 0.5 kg / t to 1.2 kg / t, and the amount of synthetic slag added is 2.7-3.2 kg / t; for steel grades with C > 0.25%: the amount of lime added is 4 kg / t to 5 kg / t, the amount of fluorite added is 0.4 kg / t to 1.0 kg / t, and the amount of synthetic slag added is 3.0-3.5 kg / t.

[0021] In conjunction with the above, further, in S102, the amount of lime added is 2.8 kg / t to 3.1 kg / t, and the amount of silicon carbide added is 0.6 kg / t to 0.8 kg / t.

[0022] Furthermore, the composition and content of the synthetic slag include: 45%–50% Al2O3, 32%–40% CaO, 4%–10% SiO2, <3% MgO, and the remainder being impurities.

[0023] For example, the carburizing agent is artificial graphite with a carbon content greater than 90%, the remainder being impurities. The amount of carburizing agent, alloy, and slag-forming auxiliary materials added is determined according to the steel grade being produced.

[0024] Furthermore, in step S2, the amount of silicon carbide added is 0.25 kg / t to 0.45 kg / t.

[0025] Furthermore, in step S2, the amount of aluminum ingot added is 1 kg / t to 1.3 kg / t.

[0026] Furthermore, in step S2, the amount of calcium carbide added is 0.37 kg / t to 0.57 kg / t.

[0027] Furthermore, in step S2, the carbon raiser is artificial graphite with a carbon content greater than 90%, and the remainder is impurities.

[0028] Furthermore, in step S2, the slag-forming auxiliary material is lime.

[0029] Before using aluminum ingots for precipitation deoxidation, silicon carbide, a diffusion deoxidizer, is used to pre-deoxidize the molten steel. At the same time, the molten steel dynamics during the tapping process are fully utilized to ensure that the steel slag and deoxidizer are thoroughly mixed, which effectively improves the deoxidation effect. In addition, after adding slag-forming auxiliary materials, calcium carbide, a diffusion deoxidizer, is added to the slag surface to improve the modification effect on the top slag of the ladle.

[0030] Further, in step S2, the slag-forming auxiliary material is lime, and its specific addition amount is:

[0031] (1) If the steel grade has C ≤ 0.25%:

[0032] In step S1, the amount of slag-forming auxiliary material added is (0.3n+1.7~0.3n+2.2) kg / t, where n is the number of recycling times, 1≤n≤4;

[0033] (2) If the steel grade has C > 0.25%:

[0034] In step S1, the amount of slag-forming auxiliary material added is (0.2n+1.6~0.2n+2.1) kg / t, where n is the number of recycling times, 1≤n≤4.

[0035] Precisely controlling the amount of slag-forming auxiliary materials added based on the number of times the LF refining slag is recycled is beneficial to improving the slag formation effect and the stability of the recycled refining slag system, thus ensuring the improvement of the cleanliness of molten steel.

[0036] Further, in step S3, the amount of lime added is 1.1 kg / t to 1.3 kg / t, the amount of calcium carbide added is 0.23 kg / t to 0.25 kg / t, the amount of silicon carbide added is 0.44 kg / t to 0.46 kg / t, and the amount of aluminum granules added is 0.08 kg / t to 0.10 kg / t.

[0037] Furthermore, in step S4, the specific operation for recovering the LF refining slag is as follows: first discard (1+2) n-2 ) / 6~(2+2 n-2 The slag is 1 / 6, and then the remaining slag in the continuous casting ladle is recovered; where n is the number of recovery times, 1≤n≤3.

[0038] Based on the number of times the LF refining slag is recycled, the amount of LF refining slag recycled each time (that is, the amount of LF refining slag added in the secondary slag making) can be precisely controlled. This can ensure the minimum amount of refining submerged arc slag and avoid the occurrence of smelting difficulties caused by excessive amount of refining slag.

[0039] Furthermore, when the refining slag is recycled repeatedly in step S5, the amount of LF refining slag recovered at the end of the ladle casting in S4 needs to be determined based on the number of times the LF refining slag is recycled.

[0040] Specifically, in step S4, if S2 involves the recycling of LF refining slag 1 to 3 times, then the amount of LF refining slag recovered from the continuous casting ladle after continuous casting is: first, discard the total slag amount (1+2). n-2 ) / 6~(2+2 n-2 The slag is 1 / 6 of the slag, and then the remaining slag in the continuous casting ladle is recycled; where n is the number of recycling times, 1≤n≤3; if the LF refining slag is recycled 4 times, then all the slag in the continuous casting ladle is poured out after the continuous casting is completed, and no further recycling is carried out.

[0041] Furthermore, in step S4, the amount of slag dumped is controlled by controlling the tilting angle of the continuous casting ladle. The tilting angle of the ladle opening along the horizontal direction is (n×15°-15°)~(n×15°), where n is the number of times it is recycled, and 1≤n≤3.

[0042] For example, using the auxiliary hook of the overhead crane, the bottom of the ladle is suspended, and the horizontal tilt angle of the ladle opening is adjusted by raising and lowering the auxiliary hook.

[0043] The preferred method for controlling the amount of refining slag recovered is simple to operate, easy to use, and facilitates improving the accuracy of LF refining slag recovery.

[0044] Furthermore, in step S5:

[0045] If the LF refining slag added in S2 is recycled 2 to 3 times, then in step S3, the amount of lime added is 0.6(n+1)±0.1kg / t, the amount of calcium carbide added is (0.1n+0.13~0.1n+0.15)kg / t, the amount of silicon carbide added is (0.54-0.1n~0.56-0.1n)kg / t, and the amount of aluminum granules added is (0.03n+0.05~0.03n+0.07)kg / t, where n is the number of recycling times, 2≤n≤3;

[0046] If the LF refining slag added in S2 is recycled four times, then in step S3, the amount of lime added is 2.8 kg / t to 3.1 kg / t, the amount of calcium carbide added is 0.46 kg / t to 0.48 kg / t, the amount of silicon carbide added is 0.23 kg / t to 0.25 kg / t, and the amount of aluminum granules added is 0.15 kg / t to 0.17 kg / t.

[0047] By precisely controlling and adjusting the amount of each raw material added in the slag composition process (i.e., the three-stage slag-making process) based on the number of times the LF refining slag is recycled, it is beneficial to fully deoxidize, desulfurize, and adsorb inclusions in the refining process, thereby further improving the cleanliness of the molten steel and also improving the stability of the LF refining slag system.

[0048] The method provided by this invention involves primary slag formation during the electric arc furnace tapping process, secondary slag formation using LF refining slag recovered from the continuous casting process after tapping, and a tertiary slag formation process using the ladle after the secondary slag formation, where the slag composition is adjusted. After refining, the ladle is then hoisted to the continuous casting station for casting, recovering the LF refining slag. This cyclical process effectively achieves the recycling and reuse of LF refining slag and improves the purity of molten steel during multiple reuses of LF refining slag. This lays the foundation for steelmaking enterprises to continuously develop low-cost, high-cleanliness steel grades, resulting in significant economic and social benefits. Attached Figure Description

[0049] Figure 1 This is a schematic diagram of the process flow for smelting high-purity steel using LF refining slag in an embodiment of the present invention.

[0050] Figure 2 This is a metallographic image of the seamless tube prepared in an embodiment of the present invention;

[0051] Figure 3 This is a metallographic diagram of the seamless tube prepared in the comparative example of this invention. Detailed Implementation

[0052] To make the objectives, technical solutions, and advantages of this invention clearer, the invention will be further described in detail below with reference to embodiments. It should be understood that the specific embodiments described herein are merely illustrative and not intended to limit the invention.

[0053] To better illustrate the present invention, further examples are provided below.

[0054] Example 1

[0055] The steel produced in this embodiment is 34Mn6 steel, with the following main components: C: 0.32-0.36%; Si: 0.15-0.35%; Mn: 1.20-1.60%; Cr: 0.10-0.30%.

[0056] Preparation of the first batch of LF refining slag:

[0057] After the electric arc furnace smelting is completed, when the steel reaches 10% of its capacity, 0.30 kg / t silicon carbide is added to the ladle for pre-deoxidation; when the steel reaches 25% of its capacity, 1 kg / t aluminum ingot is added for precipitation deoxidation; when the steel reaches 33% of its capacity, 1.6 kg / t carbon raiser, 20 kg / t alloy (9.6 kg / t silicon-manganese alloy, 10.4 kg / t high-manganese alloy), 4 kg / t lime, 0.42 kg / t fluorite, and 3.0 kg / t synthetic slag are added; when the steel reaches 50% of its capacity, 0.45 kg / t calcium carbide is added, and tapping is completed.

[0058] The steel is hoisted to the refining station. 1.5 minutes after the refining power supply is turned on, 2.9 kg / t of lime and 0.7 kg / t of silicon carbide are added for diffusion deoxidation. The temperature and composition of the molten steel are adjusted during the refining process. Slag samples are taken after the refining is completed.

[0059] After refining, the slag is hoisted to the continuous casting station for casting. After casting, all LF refining slag is recycled and retained.

[0060] Recycled once:

[0061] When the electric arc furnace smelting is completed and the steel reaches 10% of its capacity, 0.30 kg / t silicon carbide is added to the ladle for pre-deoxidation; when the steel reaches 25% of its capacity, 1 kg / t aluminum ingot is added for precipitation deoxidation; when the steel reaches 33% of its capacity, 1.65 kg / t carbon raiser, 20 kg / t alloy (9.6 kg / t silicon-manganese alloy and 10.4 kg / t high-manganese alloy) and 1.9 kg / t lime are added; when the steel reaches 50% of its capacity, 0.45 kg / t calcium carbide is added; and after the steel is tapped, all the LF refining slag from the first furnace is added.

[0062] The steel is hoisted to the refining station. After the refining power supply is turned on for 1.5 minutes, 1.1 kg / t of lime, 0.23 kg / t of calcium carbide, 0.46 kg / t of silicon carbide and 0.08 kg / t of aluminum granules are added for diffusion deoxidation. The temperature and composition of the molten steel are adjusted during the refining process. Slag samples are taken after the refining is completed.

[0063] After refining, the ladle is hoisted to the continuous casting station for pouring. After pouring, the ladle is positioned at an angle of approximately 0° to 15° to the horizontal. One-quarter of the slag is then poured out, and the remaining slag in the ladle is recovered.

[0064] Recycled twice:

[0065] After the electric arc furnace smelting is completed, when the steel reaches 10% of its capacity, 0.30 kg / t silicon carbide is added to the ladle for pre-deoxidation; when the steel reaches 25% of its capacity, 1 kg / t aluminum ingot is added for precipitation deoxidation; when the steel reaches 33% of its capacity, 1.65 kg / t carbon raiser, 20 kg / t alloy (9.6 kg / t silicon-manganese alloy and 10.4 kg / t high-manganese alloy) and 2.2 kg / t lime are added; when the steel reaches 50% of its capacity, 0.45 kg / t calcium carbide is added; after the steel is tapped, the remaining LF refining slag recovered from the above-mentioned recycling process is added.

[0066] The steel is hoisted to the refining station. After the refining power supply is turned on for 1.5 minutes, 1.7 kg / t of lime, 0.34 kg / t of calcium carbide, 0.34 kg / t of silicon carbide and 0.11 kg / t of aluminum granules are added for diffusion deoxidation. The temperature and composition of the molten steel are adjusted during the refining process. Slag samples are taken after the refining is completed.

[0067] After refining, the ladle is hoisted to the continuous casting station for pouring. After pouring, the ladle is positioned at an angle of approximately 15° to 30° to the horizontal. One-third of the slag is then poured out, and the remaining slag in the continuous casting ladle is recovered.

[0068] Recycled 3 times:

[0069] After the electric arc furnace smelting is completed, when the steel reaches 10% tapping, 0.30 kg / t silicon carbide is added to the ladle for pre-deoxidation; when the steel reaches 25% tapping, 1 kg / t aluminum ingot is added for precipitation deoxidation; when the steel reaches 33% tapping, 1.65 kg / t carbon raiser, 20 kg / t alloy (9.6 kg / t silicon-manganese alloy and 10.4 kg / t high-manganese alloy) and 2.5 kg / t lime are added; when the steel reaches 50% tapping, 0.45 kg / t calcium carbide is added; after tapping, the remaining LF refining slag recovered from the above two processes is added.

[0070] The steel is hoisted to the refining station. After the refining power supply is turned on for 1.5 minutes, 2.3 kg / t of lime, 0.45 kg / t of calcium carbide, 0.24 kg / t of silicon carbide and 0.15 kg / t of aluminum granules are added for diffusion deoxidation. The temperature and composition of the molten steel are adjusted during the refining process. Slag samples are taken after the refining is completed.

[0071] After refining, the ladle is hoisted to the continuous casting station for pouring. After pouring, the ladle is positioned at an angle of approximately 30° to 45° to the horizontal. Half of the slag is then poured out, and the remaining slag in the continuous casting ladle is recovered.

[0072] Recycled 4 times:

[0073] After the electric arc furnace smelting is completed, when the steel reaches 10% of its capacity, 0.30 kg / t silicon carbide is added to the ladle for pre-deoxidation; when the steel reaches 25% of its capacity, 1 kg / t aluminum ingot is added for precipitation deoxidation; when the steel reaches 33% of its capacity, 1.65 kg / t carbon raiser, 20 kg / t alloy (9.6 kg / t silicon-manganese alloy and 10.4 kg / t high-manganese alloy) and 2.6 kg / t lime are added; when the steel reaches 50% of its capacity, 0.45 kg / t calcium carbide is added; after the steel is tapped, the remaining LF refining slag recovered from the above three processes is added.

[0074] The steel is hoisted to the refining station. After the refining power supply is turned on for 1.5 minutes, 2.8 kg / t of lime, 0.46 kg / t of calcium carbide, 0.23 kg / t of silicon carbide and 0.15 kg / t of aluminum granules are added for diffusion deoxidation. The temperature and composition of the molten steel are adjusted during the refining process. Slag samples are taken after the refining is completed.

[0075] After refining, the ladle is hoisted to the continuous casting station for pouring. After pouring, all the slag in the ladle is dumped out.

[0076] The results of the slag sample test after refining in this embodiment are shown in Table 1.

[0077] Table 1. Composition and content (%) of slag samples

[0078]

[0079]

[0080] Compared to the smelting cost in the preparation of the first batch of LF refining slag, the cost of recycling LF refining slag for 1 to 4 steel smelting processes is reduced by 13 to 16 yuan per ton of steel, and the amount of slag-forming auxiliary materials such as lime, fluorite and synthetic slag is reduced.

[0081] Example 2

[0082] The steel produced in this embodiment is 34Mn6 steel, with the following main components: C: 0.32-0.36%; Si: 0.15-0.35%; Mn: 1.20-1.60%; Cr: 0.10-0.30%.

[0083] Preparation of the first batch of LF refining slag:

[0084] After the electric arc furnace smelting is completed, when the steel reaches 9% of its final content, 0.25 kg / t silicon carbide is added to the ladle for pre-deoxidation; when the steel reaches 24% of its final content, 1.3 kg / t aluminum ingot is added for precipitation deoxidation; when the steel reaches 32% of its final content, 1.7 kg / t carbon raiser, 20 kg / t alloy (9.6 kg / t silicon-manganese alloy and 10.4 kg / t high-manganese alloy), 5 kg / t lime, 0.6 kg / t fluorite, and 3.5 kg / t synthetic slag are added; when the steel reaches 49% of its final content, 0.57 kg / t calcium carbide is added, and tapping is completed.

[0085] The steel is hoisted to the refining station. One minute after the refining power is supplied, 2.8 kg / t of lime and 0.8 kg / t of silicon carbide are added for diffusion deoxidation. The temperature and composition of the molten steel are adjusted during the refining process. Slag samples are taken after the refining is completed.

[0086] After refining, the slag is hoisted to the continuous casting station for casting. After casting, all LF refining slag is recycled and retained.

[0087] Recycled once:

[0088] After the electric arc furnace smelting is completed, when the steel reaches 9% of its final volume, 0.25 kg / t silicon carbide is added to the ladle for pre-deoxidation; when the steel reaches 24% of its final volume, 1.3 kg / t aluminum ingot is added for precipitation deoxidation; when the steel reaches 32% of its final volume, 1.65 kg / t carbon raiser, 20 kg / t alloy (9.6 kg / t silicon-manganese alloy and 10.4 kg / t high-manganese alloy) and 1.8 kg / t lime are added; when the steel reaches 49% of its final volume, 0.57 kg / t calcium carbide is added; after tapping, all the LF refining slag from the first furnace is added.

[0089] The steel is hoisted to the refining station. One minute after the refining power is supplied, 1.3 kg / t of lime, 0.24 kg / t of calcium carbide, 0.44 kg / t of silicon carbide and 0.09 kg / t of aluminum granules are added for diffusion deoxidation. The temperature and composition of the molten steel are adjusted during the refining process. Slag samples are taken after the refining is completed.

[0090] After refining, the ladle is hoisted to the continuous casting station for pouring. After pouring, the ladle is positioned at an angle of approximately 0° to -15° to the horizontal. One-third of the slag is then poured out, and the remaining slag in the ladle is recovered.

[0091] Recycled twice:

[0092] After the electric arc furnace smelting is completed, when the steel reaches 9%, 0.25 kg / t silicon carbide is added to the ladle for pre-deoxidation; when the steel reaches 24%, 1.3 kg / t aluminum ingot is added for precipitation deoxidation; when the steel reaches 32%, 1.65 kg / t carbon raiser, 20 kg / t alloy (9.6 kg / t silicon-manganese alloy and 10.4 kg / t high-manganese alloy) and 2.0 kg / t lime are added; when the steel reaches 49%, 0.57 kg / t calcium carbide is added; after the steel tapping is completed, the remaining LF refining slag recovered from the above-mentioned recycling process is added.

[0093] The steel is hoisted to the refining station. One minute after the refining power is supplied, 1.8 kg / t of lime is added, along with 0.33 kg / t of calcium carbide, 0.35 kg / t of silicon carbide, and 0.12 kg / t of aluminum granules for diffusion deoxidation. The temperature and composition of the molten steel are adjusted during the refining process. Slag samples are taken after the refining is completed.

[0094] After refining, the ladle is hoisted to the continuous casting station for pouring. After pouring, the ladle is positioned at an angle of approximately 15° to 30° to the horizontal. Half of the slag is then poured out, and the remaining slag in the ladle is recovered.

[0095] Recycled 3 times:

[0096] After the electric arc furnace smelting is completed, when the steel reaches 9%, 0.25 kg / t silicon carbide is added to the ladle for pre-deoxidation; when the steel reaches 24%, 1.3 kg / t aluminum ingot is added for precipitation deoxidation; when the steel reaches 32%, 1.65 kg / t carbon raiser, 20 kg / t alloy (9.6 kg / t silicon-manganese alloy and 10.4 kg / t high-manganese alloy) and 2.7 kg / t lime are added; when the steel reaches 49%, 0.57 kg / t calcium carbide is added; after the steel is tapped, the remaining LF refining slag recovered from the above two processes is added.

[0097] The steel is hoisted to the refining station. One minute after the refining power is supplied, 2.5 kg / t of lime, 0.43 kg / t of calcium carbide, 0.25 kg / t of silicon carbide and 0.14 kg / t of aluminum granules are added for diffusion deoxidation. The temperature and composition of the molten steel are adjusted during the refining process. Slag samples are taken after the refining is completed.

[0098] After refining, the ladle is hoisted to the continuous casting station for pouring. After pouring, the ladle is positioned at an angle of approximately 30° to 45° to the horizontal. Two-thirds of the slag is then poured out, and the remaining slag in the ladle is recovered.

[0099] Recycled 4 times:

[0100] After the electric arc furnace smelting is completed, when the steel reaches 9%, 0.25 kg / t silicon carbide is added to the ladle for pre-deoxidation; when the steel reaches 24%, 1.3 kg / t aluminum ingot is added for precipitation deoxidation; when the steel reaches 32%, 1.65 kg / t carbon raiser, 20 kg / t alloy (9.6 kg / t silicon-manganese alloy and 10.4 kg / t high-manganese alloy) and 2.4 kg / t lime are added; when the steel reaches 49%, 0.57 kg / t calcium carbide is added; after the steel is tapped, the remaining LF refining slag recovered from the above three processes is added.

[0101] The steel is hoisted to the refining station. One minute after the refining power is supplied, 2.9 kg / t of lime, 0.48 kg / t of calcium carbide, 0.25 kg / t of silicon carbide and 0.17 kg / t of aluminum granules are added for diffusion deoxidation. The temperature and composition of the molten steel are adjusted during the refining process. Slag samples are taken after the refining is completed.

[0102] After refining, the ladle is hoisted to the continuous casting station for pouring. After pouring, all the slag in the ladle is dumped out.

[0103] Example 3

[0104] The steel produced in this embodiment is 34Mn6 steel, with the following main components: C: 0.32-0.36%; Si: 0.15-0.35%; Mn: 1.20-1.60%; Cr: 0.10-0.30%.

[0105] Preparation of the first batch of LF refining slag:

[0106] After the electric arc furnace smelting is completed, when the steel reaches 10% of its final volume, 0.45 kg / t silicon carbide is added to the ladle for pre-deoxidation; when the steel reaches 26% of its final volume, 1.2 kg / t aluminum ingot is added for precipitation deoxidation; when the steel reaches 34% of its final volume, 1.65 kg / t carbon raiser, 20 kg / t alloy (9.6 kg / t silicon-manganese alloy and 10.4 kg / t high-manganese alloy), 4.5 kg / t lime, 1.0 kg / t fluorite, and 3.0 kg / t synthetic slag are added; when the steel reaches 51% of its final volume, 0.37 kg / t calcium carbide is added, and tapping is completed.

[0107] The steel is hoisted to the refining station. Two minutes after the refining power is supplied, 3.1 kg / t of lime and 0.6 kg / t of silicon carbide are added for diffusion deoxidation. The temperature and composition of the molten steel are adjusted during the refining process. Slag samples are taken after the refining is completed.

[0108] After refining, the slag is hoisted to the continuous casting station for casting. After casting, all LF refining slag is recycled and retained.

[0109] Recycled once:

[0110] After the electric arc furnace smelting is completed, when the steel reaches 10% of its capacity, 0.45 kg / t silicon carbide is added to the ladle for pre-deoxidation; when the steel reaches 26% of its capacity, 1.2 kg / t aluminum ingot is added for precipitation deoxidation; when the steel reaches 34% of its capacity, 1.65 kg / t carbon raiser, 20 kg / t alloy (9.6 kg / t silicon-manganese alloy and 10.4 kg / t high-manganese alloy) and 2.3 kg / t lime are added; when the steel reaches 51% of its capacity, 0.37 kg / t calcium carbide is added, and after the steel is tapped, all the LF refining slag from the first furnace is added.

[0111] The steel is hoisted to the refining station. Two minutes after the refining power is supplied, 1.2 kg / t of lime, 0.25 kg / t of calcium carbide, 0.45 kg / t of silicon carbide and 0.10 kg / t of aluminum granules are added for diffusion deoxidation. The temperature and composition of the molten steel are adjusted during the refining process. Slag samples are taken after the refining is completed.

[0112] After refining, the ladle is hoisted to the continuous casting station for pouring. After pouring, the ladle is positioned at an angle of approximately 0° to 15° to the horizontal. 5 / 12 of the slag is then poured out, and the remaining slag in the ladle is recovered.

[0113] Recycled twice:

[0114] After the electric arc furnace smelting is completed, when the steel reaches 10% of its capacity, 0.45 kg / t silicon carbide is added to the ladle for pre-deoxidation; when the steel reaches 26% of its capacity, 1.2 kg / t aluminum ingot is added for precipitation deoxidation; when the steel reaches 34% of its capacity, 1.65 kg / t carbon raiser, 20 kg / t alloy (9.6 kg / t silicon-manganese alloy and 10.4 kg / t high-manganese alloy) and 2.5 kg / t lime are added; when the steel reaches 51% of its capacity, 0.37 kg / t calcium carbide is added; after the steel is tapped, the remaining LF refining slag recovered from the above-mentioned recycling process is added.

[0115] The steel is hoisted to the refining station. Two minutes after the refining power is supplied, 1.9 kg / t of lime, 0.35 kg / t of calcium carbide, 0.36 kg / t of silicon carbide and 0.13 kg / t of aluminum granules are added for diffusion deoxidation. The temperature and composition of the molten steel are adjusted during the refining process. Slag samples are taken after the refining is completed.

[0116] After refining, the ladle is hoisted to the continuous casting station for pouring. After pouring, the ladle is positioned at an angle of approximately 15° to 30° to the horizontal. One-third of the slag is then poured out, and the remaining slag in the ladle is recovered.

[0117] Recycled 3 times:

[0118] After the electric arc furnace smelting is completed, when the steel reaches 10% of its capacity, 0.45 kg / t silicon carbide is added to the ladle for pre-deoxidation; when the steel reaches 26% of its capacity, 1.2 kg / t aluminum ingot is added for precipitation deoxidation; when the steel reaches 34% of its capacity, 1.65 kg / t carbon raiser, 20 kg / t alloy (9.6 kg / t silicon-manganese alloy and 10.4 kg / t high-manganese alloy) and 2.2 kg / t lime are added; when the steel reaches 51% of its capacity, 0.37 kg / t calcium carbide is added; after the steel is tapped, the remaining LF refining slag recovered from the above two processes is added.

[0119] The steel is hoisted to the refining station. Two minutes after the refining power is supplied, 2.4 kg / t of lime, 0.44 kg / t of calcium carbide, 0.26 kg / t of silicon carbide and 0.16 kg / t of aluminum granules are added for diffusion deoxidation. The temperature and composition of the molten steel are adjusted during the refining process. Slag samples are taken after the refining is completed.

[0120] After refining, the ladle is hoisted to the continuous casting station for pouring. After pouring, the ladle is positioned at an angle of approximately 30° to 45° to the horizontal. Half of the slag is then poured out, and the remaining slag in the ladle is recovered.

[0121] Recycled 4 times:

[0122] After the electric arc furnace smelting is completed, when the steel reaches 10% of its capacity, 0.45 kg / t silicon carbide is added to the ladle for pre-deoxidation; when the steel reaches 26% of its capacity, 1.2 kg / t aluminum ingot is added for precipitation deoxidation; when the steel reaches 34% of its capacity, 1.65 kg / t carbon raiser, 20 kg / t alloy (9.6 kg / t silicon-manganese alloy and 10.4 kg / t high-manganese alloy) and 2.9 kg / t lime are added; when the steel reaches 51% of its capacity, 0.37 kg / t calcium carbide is added; after the steel is tapped, the remaining LF refining slag recovered from the above three processes is added.

[0123] The steel is hoisted to the refining station. Two minutes after the refining power is supplied, 3.1 kg / t of lime, 0.47 kg / t of calcium carbide, 0.24 kg / t of silicon carbide and 0.16 kg / t of aluminum granules are added for diffusion deoxidation. The temperature and composition of the molten steel are adjusted during the refining process. Slag samples are taken after the refining is completed.

[0124] After refining, the ladle is hoisted to the continuous casting station for pouring. After pouring, all the slag in the ladle is dumped out.

[0125] The composition and content of the synthetic slag in Examples 1-3 above include: Al2O3 45%-50%, CaO 32%-40%, SiO2 4%-10%, MgO <3%, and the balance being impurities.

[0126] Comparative Example 1

[0127] The steel used in this comparative example is 34Mn6 steel, with the following main components: C: 0.32-0.36%; Si: 0.15-0.35%; Mn: 1.20-1.60%; Cr: 0.10-0.30%.

[0128] The process for smelting the above-mentioned steel grade in this comparative example is the same as that in Example 1, except that when the LF refining slag is recycled 1 to 4 times, half of the LF refining slag is recycled after each continuous casting process, and the three slag-forming processes are not performed in the refining process. The other steps are exactly the same, and the specific steps are as follows:

[0129] Preparation of the first batch of LF refining slag:

[0130] After the electric arc furnace smelting is completed, when the steel reaches 10% of its capacity, 0.30 kg / t silicon carbide is added to the ladle for pre-deoxidation; when the steel reaches 25% of its capacity, 1 kg / t aluminum ingot is added for precipitation deoxidation; when the steel reaches 33% of its capacity, 1.6 kg / t carbon raiser, 20 kg / t alloy (9.6 kg / t silicon-manganese alloy, 10.4 kg / t high-manganese alloy), 4 kg / t lime, 0.42 kg / t fluorite, and 3.0 kg / t synthetic slag are added; when the steel reaches 50% of its capacity, 0.45 kg / t calcium carbide is added, and tapping is completed.

[0131] The steel is hoisted to the refining station. 1.5 minutes after the refining power supply is turned on, 2.9 kg / t of lime and 0.7 kg / t of silicon carbide are added for diffusion deoxidation. The temperature and composition of the molten steel are adjusted during the refining process. Slag samples are taken after the refining is completed.

[0132] After refining, the slag is hoisted to the continuous casting station for casting. After casting, all LF refining slag is recycled and retained.

[0133] Recycled once:

[0134] When the electric arc furnace smelting is completed and the steel reaches 10% of its capacity, 0.30 kg / t silicon carbide is added to the ladle for pre-deoxidation; when the steel reaches 25% of its capacity, 1 kg / t aluminum ingot is added for precipitation deoxidation; when the steel reaches 33% of its capacity, 1.65 kg / t carbon raiser, 20 kg / t alloy (9.6 kg / t silicon-manganese alloy and 10.4 kg / t high-manganese alloy) and 1.9 kg / t lime are added; when the steel reaches 50% of its capacity, 0.45 kg / t calcium carbide is added; and after the steel is tapped, all the LF refining slag from the first furnace is added.

[0135] Adjust the temperature and composition of molten steel during the refining process, and take slag samples after refining is completed;

[0136] After refining, the ladle is hoisted to the continuous casting station for pouring. After pouring, the ladle is positioned at an angle of approximately 30° to 45° to the horizontal, and half of the slag is discarded.

[0137] Recycled twice:

[0138] After the electric arc furnace smelting is completed, when the steel reaches 10% of its capacity, 0.30 kg / t silicon carbide is added to the ladle for pre-deoxidation; when the steel reaches 25% of its capacity, 1 kg / t aluminum ingot is added for precipitation deoxidation; when the steel reaches 33% of its capacity, 1.65 kg / t carbon raiser, 20 kg / t alloy (9.6 kg / t silicon-manganese alloy and 10.4 kg / t high-manganese alloy) and 2.2 kg / t lime are added; when the steel reaches 50% of its capacity, 0.45 kg / t calcium carbide is added; after the steel is tapped, all the LF refining slag recovered in the above-mentioned recycling process is added.

[0139] Adjust the temperature and composition of molten steel during the refining process, and take slag samples after refining is completed;

[0140] After refining, the ladle is hoisted to the continuous casting station for pouring. After pouring, the ladle is positioned at an angle of approximately 30° to 45° to the horizontal. Half of the slag is then poured out, and the remaining slag in the ladle is recovered.

[0141] Recycled 3 times:

[0142] After the electric arc furnace smelting is completed, when the steel reaches 10% of its capacity, 0.30 kg / t silicon carbide is added to the ladle for pre-deoxidation; when the steel reaches 25% of its capacity, 1 kg / t aluminum ingot is added for precipitation deoxidation; when the steel reaches 33% of its capacity, 1.65 kg / t carbon raiser, 20 kg / t alloy (9.6 kg / t silicon-manganese alloy and 10.4 kg / t high-manganese alloy) and 2.5 kg / t lime are added; when the steel reaches 50% of its capacity, 0.45 kg / t calcium carbide is added; after the steel is tapped, all the LF refining slag recovered from the above two processes is added.

[0143] Adjust the temperature and composition of molten steel during the refining process, and take slag samples after refining is completed;

[0144] After refining, the ladle is hoisted to the continuous casting station for pouring. After pouring, the ladle is positioned at an angle of approximately 30° to 45° to the horizontal. Half of the slag is then poured out, and the remaining slag in the ladle is recovered.

[0145] Recycled 4 times:

[0146] After the electric arc furnace smelting is completed, when the steel reaches 10% of its capacity, 0.30 kg / t silicon carbide is added to the ladle for pre-deoxidation; when the steel reaches 25% of its capacity, 1 kg / t aluminum ingot is added for precipitation deoxidation; when the steel reaches 33% of its capacity, 1.65 kg / t carbon raiser, 20 kg / t alloy (9.6 kg / t silicon-manganese alloy and 10.4 kg / t high-manganese alloy) and 2.6 kg / t lime are added; when the steel reaches 50% of its capacity, 0.45 kg / t calcium carbide is added; after the steel is tapped, all the LF refining slag recovered from the above three processes is added.

[0147] Adjust the temperature and composition of molten steel during the refining process, and take slag samples after refining is completed;

[0148] After refining, the ladle is hoisted to the continuous casting station for pouring. After pouring, all the slag in the ladle is dumped out.

[0149] The results of the slag sample test after refining in this embodiment are shown in Table 2.

[0150] Table 2. Composition and content (%) of slag samples

[0151]

[0152]

[0153] The molten steel refined in Example 1 was processed into steel pipes using the following conventional process:

[0154] The refined molten steel is hoisted to the continuous casting process via a ladle for pouring. After continuous casting, the amount of steel left in the tundish is 4-4.5t / heat, and the tail billet is more than 4 meters / strand. Then the billet is heated in a ring furnace and enters the piercing process. The diameter is expanded using a diameter expansion guide plate. After piercing, the tube is rotated and naturally cooled at the front of the rolling mill. Before entering the rolling mill, the oxide scale on the surface of the tube is removed by water descaling. Then it is rolled to obtain a seamless tube.

[0155] The rolled seamless tubes were characterized by metallographic microscopy, and the inclusion content was determined according to GB / T 10561-2005. The results are shown in Table 3 and... Figure 2 As shown.

[0156] Table 3

[0157]

[0158] Seamless tubes were prepared from the refined steel of Comparative Example 1 using the same process as in Example 1. The rolled seamless tubes were characterized using a metallographic microscope, and the inclusion content was determined according to GB / T 10561-2005. The results are shown in Table 4. Figure 3 As shown.

[0159] Table 4

[0160]

[0161]

[0162] As can be seen from the table above, the non-metallic inclusions in the 34Mn6 steel prepared in Comparative Example 1 fluctuate greatly, proving that if the composition of the refining slag system is not considered during the recycling of LF refining slag, it is not conducive to the control of the cleanliness of molten steel.

[0163] In summary, the content of non-metallic inclusions in the 34Mn6 steel prepared by the embodiments of the present invention meets the standard requirements, proving that the slag-making process provided by the present invention can effectively reduce the content of inclusions, improve the purity of molten steel, and at the same time, effectively reduce the discharge of LF refining slag, promote green, ecological metallurgy and clean production in iron and steel smelting, and has high practical value.

[0164] The above description is only a preferred embodiment of the present invention and is not intended to limit the present invention. Any modifications, equivalent substitutions or improvements made within the spirit and principles of the present invention should be included within the protection scope of the present invention.

Claims

1. A method for smelting high-purity steel using LF refining slag, characterized in that, Includes the following steps: S1: All the LF refining slag after the first continuous casting is completed will be retained; S2: When the electric furnace tapping reaches 9%~10%, silicon carbide is added to the ladle for pre-deoxidation; when the tapping reaches 24%~26%, aluminum ingots are added for precipitation deoxidation; when the tapping reaches 32%~34%, carburizing agent, alloy and slag-forming auxiliary materials are added; when the tapping reaches 49%~51%, calcium carbide is added; at the end of tapping, the aforementioned LF refining slag is added; S3: After 1 to 2 minutes of LF refining and power supply, lime is added, along with calcium carbide, silicon carbide, and aluminum particles for diffusion deoxidation; S4: The refined molten steel is sent to the continuous casting process. After casting is completed, the LF refining slag is recovered. S5: Repeat the operations of S2 to S4 to carry out the cyclic smelting of high-purity steel; In step S2, the slag-forming auxiliary material is lime, and its specific addition amount is as follows: (1) For steel grades with C ≤ 0.25%: In step S2, the amount of slag-forming auxiliary material added is (0.3n+1.7~0.3n+2.2) kg / t, where n is the number of recycling times, 1≤n≤4; (2) If the steel grade has C > 0.25%: In step S2, the amount of slag-forming auxiliary material added is (0.2n+1.6~0.2n+2.1) kg / t, where n is the number of recycling times, 1≤n≤4.

2. The method for smelting high-purity steel using LF refining slag as described in claim 1, characterized in that: In step S2, the amount of silicon carbide added is 0.25 kg / t to 0.45 kg / t; and / or In step S2, the amount of aluminum ingot added is 1 kg / t to 1.3 kg / t; and / or In step S2, the amount of calcium carbide added is 0.37 kg / t to 0.57 kg / t.

3. The method for smelting high-purity steel using LF refining slag as described in claim 1, characterized in that: In step S3, the amount of lime added is 1.1 kg / t to 1.3 kg / t, the amount of calcium carbide added is 0.23 kg / t to 0.25 kg / t, the amount of silicon carbide added is 0.44 kg / t to 0.46 kg / t, and the amount of aluminum granules added is 0.08 kg / t to 0.10 kg / t.

4. The method for smelting high-purity steel using LF refining slag as described in claim 1, characterized in that: In step S4, 1 / 4 to 5 / 12 of the total slag in the LF refining slag in the continuous casting ladle is first poured off, and then the remaining slag in the continuous casting ladle is recovered.

5. The method for smelting high-purity steel using LF refining slag as described in claim 1, characterized in that: In step S5, the amount of LF refining slag recovered from the continuous casting ladle in S4 is determined based on the number of times the LF refining slag is recycled. Specifically, the operation is as follows: first, discard (1+2) of the total slag amount. n-2 ) / 6~(2+2 n-2 The slag is 1 / 6 of the total slag, and then the remaining slag in the continuous casting ladle is recycled; where n is the number of times the slag is recycled, and 2≤n≤3. When n=4, all the slag in the continuous casting ladle is discarded and no longer recycled.

6. The method for smelting high-purity steel using LF refining slag as described in claim 5, characterized in that: The amount of slag discarded is controlled by adjusting the tilting angle of the continuous casting ladle. The tilting angle of the ladle opening along the horizontal direction is (n×15°-15°)~(n×15°), where n is the number of times the slag is recycled, and 1≤n≤3.

7. The method for smelting high-purity steel using LF refining slag as described in claim 1, characterized in that: In step S5: If the LF refining slag added in S2 is recycled 2-3 times, then in step S3, the amount of lime added is 0.6(n+1)±0.1kg / t, the amount of calcium carbide added is (0.1n+0.13~0.1n+0.15)kg / t, the amount of silicon carbide added is (0.54-0.1n~0.56-0.1n)kg / t, and the amount of aluminum granules added is (0.03n+0.05~0.03n+0.07)kg / t, where n is the number of recycling times, 2≤n≤3; If the LF refining slag added in S2 is recycled four times, then in step S3, the amount of lime added is 2.8 kg / t to 3.1 kg / t, the amount of calcium carbide added is 0.46 kg / t to 0.48 kg / t, the amount of silicon carbide added is 0.23 kg / t to 0.25 kg / t, and the amount of aluminum granules added is 0.15 kg / t to 0.17 kg / t.

8. The method for smelting high-purity steel using LF refining slag as described in claim 1, characterized in that: In step S1, the first batch of LF refining slag is prepared through the following process: S101, when the electric furnace tapping reaches 9%~10%, silicon carbide is added to the ladle for pre-deoxidation; when the tapping reaches 24%~26%, aluminum ingots are added for precipitation deoxidation; when the tapping reaches 32%~34%, carburizing agent, alloy and slag-forming auxiliary materials are added; when the tapping reaches 49%~51%, calcium carbide is added. S102: After 1 to 2 minutes of LF refining and power supply, lime is added, followed by silicon carbide for diffusion deoxidation; S103: The refined molten steel is sent to the continuous casting process. After casting is completed, all LF refining slag is recovered.

9. The method for smelting high-purity steel using LF refining slag as described in claim 8, characterized in that: In S101, the amount of silicon carbide added is 0.25 kg / t to 0.45 kg / t; the amount of aluminum ingot added is 1 kg / t to 1.3 kg / t; the amount of calcium carbide added is 0.37 kg / t to 0.57 kg / t; and / or In S101, the slag-forming auxiliary materials include lime, fluorite, and synthetic slag; wherein, for steel grades with C ≤ 0.25%: the amount of lime added is 5 kg / t ~ 6 kg / t, the amount of fluorite added is 0.5 kg / t ~ 1.2 kg / t, and the amount of synthetic slag added is 2.7-3.2 kg / t; for steel grades with C > 0.25%: the amount of lime added is 4 kg / t ~ 5 kg / t, the amount of fluorite added is 0.4 kg / t ~ 1.0 kg / t, and the amount of synthetic slag added is 3.0-3.5 kg / t; and / or In S102, the amount of lime added is 2.8 kg / t to 3.1 kg / t, and the amount of silicon carbide added is 0.6 kg / t to 0.8 kg / t.

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