A method for controlling inclusions of a 60si2mn non-vacuum spring steel

Abstract

The present application belongs to the technical field of steel smelting, and particularly discloses a method for controlling inclusions in non-vacuum spring steel, which comprises the following steps: (1) smelting in a converter according to a normal smelting process, with the content of S in molten steel being less than 0.025% when tapping the converter; (2) the feeding sequence when tapping the converter is ferrosilicon, low-nitrogen carbon additive, alloy, refining slag and lime; no aluminum cake is added when tapping the converter; (3) after tapping the converter, the ladle is transferred to a LF refining station for refining, and Al is not controlled during the whole refining process; (4) rapid slagging is performed during refining, and 100-300 kg of lime is added according to the slag condition when entering the station, with the basicity being controlled to be 3-5; calcium carbide is added for deoxidization before sample one, and silicon carbide is added for deoxidization after sample one; (5) after the LF refining operation is completed, a silicon-calcium wire is fed, and then the molten steel is soft blown for 20-35 min. The present application optimizes the feeding of the converter, controls the amount and adding time of the refining slagging material and deoxidizer, and realizes significant improvement in product quality.

Description

Technical Field

[0001] This invention belongs to the field of iron and steel smelting technology, and relates to the control of steel purity, specifically to a method for controlling inclusions in non-vacuum spring steel. Background Technology

[0002] Spring steel is a key basic material supporting the safe operation of high-end equipment such as automobiles, rail transportation, construction machinery, and energy equipment. It is mainly used to manufacture core spring components such as suspension springs, valve springs, and clutch springs. These components operate under complex conditions such as high-frequency alternating stress, high load, high and low temperatures, and harsh environments for extended periods, requiring materials with high fatigue life, high elastic limit, high toughness, and excellent dimensional stability. With the trend towards lightweight, high-speed, and long-life equipment, increasingly stringent requirements are being placed on the strength grade, fatigue reliability, and service safety of spring steel. Steel purity has become a core indicator determining the quality of spring steel.

[0003] Non-metallic inclusions are the most critical intrinsic defects affecting the performance of spring steel and the primary cause of its early failure. Extensive research and production practice have shown that the fatigue life of spring steel is significantly negatively correlated with total oxygen content, the number, size, morphology, and distribution of inclusions. Controlling inclusion levels and improving the purity of molten steel are the most direct and effective technical approaches to improving spring steel quality. Conducting research on spring steel purity, and systematically optimizing key technologies such as low-oxygen and low-sulfur smelting, efficient inclusion removal, inclusion morphology modification, and maintaining cleanliness throughout the entire process, can fundamentally reduce the harmful effects of inclusions on fatigue life and steadily improve the overall quality and service life of spring steel. Summary of the Invention

[0004] To address the shortcomings of existing technologies, the present invention aims to provide a method for controlling inclusions in 60Si2Mn non-vacuum spring steel. This invention focuses on the converter and refining processes, tackling the purity issues of non-vacuum spring steel. While ensuring that steelmaking costs remain within a controllable range, the invention optimizes converter feeding, controls the amount and timing of refining slag-forming materials and deoxidizers, and achieves a significant improvement in product quality.

[0005] This invention is achieved through the following technical solution: A method for controlling inclusions in 60Si2Mn non-vacuum spring steel includes the following steps: (1) The converter smelting is operated according to the normal smelting process, and the S content of the molten steel is controlled to be <0.025% when the steel is tapped from the converter; (2) The charging sequence for converter tapping is ferrosilicon → low-nitrogen carbon raiser → alloy → refining slag → lime; no aluminum cake is added during converter tapping. (3) After the converter tapping is completed, the ladle is transferred to the LF refining station for refining. The Al is not controlled throughout the refining process. (4) Refining quickly forms slag. When the slag enters the refining station, add 100-300 kg of lime depending on the slag condition and control the alkalinity at 3-5. Add calcium carbide for strong deoxidation before sample 1 and add silicon carbide for deoxidation after sample 1. (5) After the LF refining operation is completed, feed in the silicon-calcium wire and then gently blow the molten steel for 20-35 minutes.

[0006] A further improvement to the present invention is as follows: The amount of refining slag used in step (2) is 300-400 kg / furnace, and the amount of lime used is 300-400 kg / furnace.

[0007] Furthermore, the amount of calcium carbide used in step (4) is 30-50 kg / furnace.

[0008] Furthermore, the amount of silicon carbide used in step (4) is 60-80 kg / furnace.

[0009] Furthermore, in step (4), the argon flow rate is 500-800 NL / min when adjusting the composition and desulfurizing, the argon flow rate is 400-600 NL / min when heating up before sample 3, the argon flow rate is 400-600 NL / min before opening the furnace door for temperature measurement and sampling, and the flow rate of sample 3 is controlled to be <250 NL / min.

[0010] Furthermore, the feed rate of the silicon-calcium wire in step (5) is 70-90m / furnace for the first furnace and 20-40m / furnace for the continuous casting furnace.

[0011] Furthermore, the target composition of the final LF refining slag is: 52-60% CaO, 13-19% SiO2, 18-25% Al2O3, 4-8% MgO, R=3-5.

[0012] Compared with the prior art, the beneficial effects of the present invention are as follows: 1. The method and process of this invention are highly targeted, focusing on mainstream 60Si2Mn non-vacuum spring steel, which is in line with actual production and the experimental results can be quickly implemented.

[0013] 2. This invention strictly controls inclusion formation at the source, precisely controlling the sulfur content in the molten steel to <0.025% in the primary refining furnace, reducing the risk of excessive sulfide inclusions from the raw material end and improving the basic purity of the molten steel. The slag-making and charging processes are standardized, fixing the slag ratio in the primary refining furnace and clarifying the charging sequence at each stage of converter tapping, avoiding slag instability caused by arbitrary operation, and laying a foundation for a uniform slag system in subsequent refining.

[0014] 3. This invention optimizes the refining and deoxidation process in stages. Strong deoxidation is applied in the early stages, while silicon carbide is used in the later stages to maintain a reducing atmosphere. This ensures thorough deoxidation while avoiding the drawbacks of a single deoxidation method, reducing the formation of oxide inclusions. The refining process eliminates the need for subsequent slag additions, requiring slag to be added in one go to prevent secondary oxidation of the molten steel caused by additional slag, reduce the formation of new inclusions, and stabilize the state of the molten steel during refining. The refining stirring parameters are refined, precisely controlling the bottom blowing flow rate at different stages: heating, composition adjustment and desulfurization, temperature measurement and sampling, and after the third sample is taken. This balances inclusion flotation and removal with the uniformity of molten steel composition, avoiding the problems of slag entrapment from strong stirring and incomplete inclusion removal from weak stirring. The wire feeding process is differentiated, with different feed rates for the first furnace and the continuous casting furnace, adapting to the different states of the molten steel in different furnaces. This precisely modifies inclusions, promoting their miniaturization and dispersion, and improving the toughness of the steel.

[0015] 4. The refining slag indicators of this invention are clear and highly adaptable, limiting the content of core components such as CaO and SiO2 and the basicity to 3-5. The high basicity and low oxidizing slag system can effectively adsorb inclusions in molten steel and further improve the purity of molten steel. Attached Figure Description

[0016] Figure 1 The image shows the inclusions exceeding the standard (B coarse 2.5) in Example 3, along with the test results of the inclusion composition. Detailed Implementation

[0017] This invention provides a method for controlling inclusions in 60Si2Mn non-vacuum spring steel. In specific embodiments, unless otherwise specified, the test methods used are conventional methods, and the materials and reagents used are commercially available unless otherwise specified.

[0018] In a specific embodiment of the present invention, the refining slag composition is CaO: 30-40%, Al2O3: 50-60%, MgO: 2-8%, and SiO2 < 5%.

[0019] The present invention will now be described in detail with reference to specific embodiments.

[0020] Example 1 A method for controlling inclusions in 60Si2Mn non-vacuum spring steel, furnace number: 32600483, where the molten iron fed into the converter does not undergo pretreatment, the temperature is 1357℃, and 18 tons of molten iron and 67 tons of scrap steel are added during converter smelting. Key process steps include: (1) The converter smelting is operated according to the normal smelting process, and the S content of the molten steel is controlled to be 0.0166% when the steel is tapped from the converter; (2) The charging sequence for the converter tapping is ferrosilicon → low nitrogen carbon raiser → alloy → refining slag → lime; no aluminum cake is added when tapping the converter, the amount of refining slag added is 403 kg, and the amount of lime added is 405 kg. (3) After the converter tapping is completed, the ladle is transferred to the LF refining station for refining. The Al is not controlled throughout the refining process. (4) Refining is fast slag formation. 224 kg of lime is added at the refining station. To improve the viscosity of the refining slag, 87 kg of cryolite slag is added. 40 kg of calcium carbide is added before sample 1 for strong deoxidation; 40 kg of silicon carbide is added after sample 1; and 30 kg of silicon carbide is added to sample 3 for deoxidation. (5) After the LF refining operation is completed, feed in a 30m silicon-calcium wire and then gently blow the molten steel for 25 minutes.

[0021] The composition of the final refining residue is shown in the table below: content / % 54.44 13.14 19.77 4.34 4.48 Six rolled steel bars were taken from this batch, and a sample was taken from each bar for inclusion testing. The results are shown in the table below: Sample 1 Level 1.0 Level 1.0 Level 0.5 Level 0.5 Level 1.0 Level 0 Level 0.5 Level 1.0 Sample 2 Level 0.5 Level 1.0 Level 0.5 Level 1.0 Level 0.5 Level 1.0 Level 1.0 Level 0.5 Sample 3 Level 0.5 Level 0.5 Level 0.5 Level 1.0 Level 0.5 Level 0.5 Level 0.5 Level 1.0 Sample 4 Level 0.5 Level 1.0 Level 1.0 Level 0.5 Level 0 Level 1.0 Level 0.5 Level 0.5 Sample 5 Level 0.5 Level 1.0 Level 0.5 Level 1.0 Level 0.5 Level 1.0 Level 1.0 Level 0.5 Sample 6 Level 1.0 Level 0.5 Level 1.0 Level 0.5 Level 1.0 Level 1.0 Level 1.0 Level 1.0 As shown in the table above, the inclusion rating of the sample in this embodiment is ≤1.0 (all oxide inclusions are small and fine, with no large inclusions).

[0022] Example 2 A method for controlling inclusions in 60Si2Mn non-vacuum spring steel, furnace number: 32600270. The molten iron fed into the converter undergoes no pretreatment; the iron temperature is 1352℃; 17t of molten iron and 69t of scrap steel are added during converter smelting. Key process steps include: (1) The converter smelting is operated according to the normal smelting process, and the S content of the molten steel is controlled to be 0.0126% when the steel is tapped from the converter; (2) The charging sequence for converter tapping is ferrosilicon → low nitrogen carbon raiser → alloy → refining slag → lime; no aluminum cake is added for converter tapping, the amount of refining slag added is 405 kg, and the amount of lime added is 397 kg. (3) After the converter tapping is completed, the ladle is transferred to the LF refining station for refining. The Al is not controlled throughout the refining process. (4) Refining is fast slag formation. 201 kg of lime is added at the refining station. To improve the viscosity of the refining slag, 88 kg of cryolite slag is added. 40 kg of calcium carbide is added before sample 1 for strong deoxidation; 40 kg of silicon carbide is added after sample 1; and 40 kg of silicon carbide is added to sample 3 for deoxidation. (5) After the LF refining operation is completed, feed in a 30m silicon-calcium wire and then gently blow the molten steel for 25 minutes.

[0023] The composition of the final refining residue is shown in the table below: content / % 52.20 13.33 22.62 4.12 4.07 Six rolled steel bars were taken from this batch, and a sample was taken from each bar for inclusion testing. The results are shown in the table below: Sample 1 Level 0.5 Level 0.5 Level 1.0 Level 0.5 Level 1.0 Level 0.5 Level 0.5 Level 0.5 Sample 2 Level 0.5 Level 1.0 Level 0.5 Level 0.5 Level 0.5 Level 0.5 Level 1.0 Level 1.0 Sample 3 Level 1.0 Level 0.5 Level 0.5 Level 0.5 Level 0.5 Level 0.5 Level 0.5 Level 1.0 Sample 4 Level 0.5 Level 0.5 Level 0.5 Level 1.0 Level 0.5 Level 0.5 Level 0.5 Level 1.0 Sample 5 Level 1.0 Level 1.0 Level 1.0 Level 1.0 Level 0.5 Level 1.0 Level 1.0 Level 0.5 Sample 6 Level 0.5 Level 0.5 Level 1.0 Level 0.5 Level 0.5 Level 1.0 Level 1.0 Level 1.0 As shown in the table above, the inclusion rating of the sample in this embodiment is ≤1.0 (all oxide inclusions are small and fine, with no large inclusions).

[0024] Comparative Example 1 A method for controlling inclusions in 60Si2Mn non-vacuum spring steel, furnace number: 32510719. The molten iron fed into the converter undergoes no pretreatment; the iron temperature is 1348℃; 17t of molten iron and 72t of scrap steel are added during converter smelting. Key process steps include: (1) The converter smelting is operated according to the normal smelting process, and the S content of the molten steel is controlled to be 0.0138% when the steel is tapped from the converter; (2) The charging sequence for the converter tapping is ferrosilicon → low nitrogen carbon raiser → alloy → lime → fluorite; no aluminum cake is added when tapping the converter, the amount of lime added is 508 kg, and the amount of fluorite added is 97 kg. (3) After the converter tapping is completed, the ladle is transferred to the LF refining station for refining. The Al is not controlled throughout the refining process. (4) Rapid slag formation during refining: 199 kg of lime was added upon entering the station. To improve the viscosity of the refining slag, 184 kg of cryolite was added for slag formation. During this process, rapid slag formation was not achieved, and the slag was repeatedly adjusted. 40 kg of calcium carbide was added before sample 1 for strong deoxidation. Excessive cryolite was added, resulting in excessively thin slag. 87 kg of lime was added between sample 1 and sample 2. 30 kg of silicon carbide was added after sample 1, and 50 kg of silicon carbide was added for deoxidation in sample 3. (5) After the LF refining operation is completed, feed in a 30m silicon-calcium wire and then gently blow the molten steel for 25 minutes.

[0025] The composition of the final refining residue is shown in the table below: content / % 52.31 14.93 19.19 3.73 3.50 Four rolls were taken from this batch, and a sample was taken from each roll for inclusion testing. The results are shown in the table below: Sample 1 Level 1.0 Level 0.5 Level 1.0 Level 1.0 Level 0.5 Level 1.0 Level 1.0 Level 0.5 Sample 2 Level 1.0 Level 0.5 Level 0.5 Level 2.5 Level 1.5 Level 0.5 Level 0.5 Level 1.0 Sample 3 Level 1.5 Level 0.5 Level 1.0 Level 1.0 Level 0.5 Level 1.0 Level 1.0 Level 1.5 Sample 4 Level 0.5 Level 1.0 Level 0.5 Level 2.0 Level 0.5 Level 1.0 Level 0.5 Level 1.0 Excessive inclusions of grade B coarse 2.5 were detected.

[0026] The above description of the embodiments is only for illustrating the technical concept and features of the present invention. Its purpose is to enable those skilled in the art to understand the content of the present invention and implement it accordingly. Those skilled in the art can obviously easily make various modifications to these embodiments and apply the general principles described herein to other embodiments without creative effort. Therefore, the above embodiments should not be used to limit the scope of protection of the present invention. All improvements and modifications made by those skilled in the art based on the disclosure of the present invention without departing from the scope of the present invention should be covered within the scope of protection of the present invention.

Claims

1. A method for controlling inclusions in 60Si2Mn non-vacuum spring steel, characterized in that, Includes the following steps: (1) The converter smelting is operated according to the normal smelting process, and the S content of the molten steel is controlled to be <0.025% when the steel is tapped from the converter; (2) The charging sequence for converter tapping is ferrosilicon → low-nitrogen carbon raiser → alloy → refining slag → lime; no aluminum cake is added during converter tapping. (3) After the converter tapping is completed, the ladle is transferred to the LF refining station for refining. The Al is not controlled throughout the refining process. (4) Refining quickly forms slag. When the slag enters the refining station, add 100-300 kg of lime depending on the slag condition and control the alkalinity at 3-5. Add calcium carbide for strong deoxidation before sample 1 and add silicon carbide for deoxidation after sample 1. (5) After the LF refining operation is completed, feed in the silicon-calcium wire and then gently blow the molten steel for 20-35 minutes.

2. The method for controlling inclusions in 60Si2Mn non-vacuum spring steel according to claim 1, characterized in that: The amount of refining slag used in step (2) is 300-400 kg / furnace, and the amount of lime used is 300-400 kg / furnace.

3. The method for controlling inclusions in 60Si2Mn non-vacuum spring steel according to claim 1, characterized in that: The amount of calcium carbide used in step (4) is 30-50 kg / furnace.

4. The method for controlling inclusions in 60Si2Mn non-vacuum spring steel according to claim 1, characterized in that: The amount of silicon carbide used in step (4) is 60-80 kg / furnace.

5. The method for controlling inclusions in 60Si2Mn non-vacuum spring steel according to claim 1, characterized in that: In step (4), the argon flow rate is 500-800 NL / min during component adjustment and desulfurization, the argon flow rate is 400-600 NL / min during the temperature rise before sample 3, the argon flow rate is 400-600 NL / min before opening the furnace door for temperature measurement and sampling, and the flow rate of sample 3 is controlled to be <250 NL / min.

6. The method for controlling inclusions in 60Si2Mn non-vacuum spring steel according to claim 1, characterized in that: The feed rate of the silicon-calcium wire in step (5) is 70-90m / furnace for the first furnace and 20-40m / furnace for the continuous casting furnace.

7. The method for controlling inclusions in 60Si2Mn non-vacuum spring steel according to claim 1, characterized in that: The target composition of the final slag from LF refining is: 52-60% CaO, 13-19% SiO2, 18-25% Al2O3, 4-8% MgO, R=3-5.

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