Full-process hydrogen control process method for smelting non-vacuum steel grade

Abstract

The invention relates to a whole-process hydrogen control process method for smelting non-vacuum steel, which comprises the following steps of: adding sludge balls into a converter 4 minutes before blowing oxygen, and only adding the sludge balls with the water content of less than 2 percent; the tapping alloy temperature is controlled to be 500 + / -50 DEG C; and the tapping time is controlled to be longer than 3 min, the water content of the refining slag and the slag material lime is lower than 1%, and the water content of the carburant is lower than 0.1%. During tapping, the steel ladle bottom blowing is kept at 1000 NL / min in the whole process; during wire feeding, the wire feeding speed is controlled to be 2.2 + / -0.3 m / s, the soft blowing argon flow is controlled to be 20-150 NL / min, and the soft blowing time is controlled to be 25 min or above; the continuous casting tundish needs to be controlled to be baked for more than 3 hours, the temperature is more than 1200 DEG C, and the water content of a covering agent and covering slag is controlled to be less than 0.3%. Vacuum treatment hydrogen control is omitted, cost reduction and efficiency improvement are achieved, and equipment investment and operation and maintenance cost are greatly reduced; the production period is remarkably shortened, the productivity is improved, and meanwhile the hydrogen content of finished steel is lower than 3.5 ppm.

Description

Technical Field

[0001] This invention relates to a process for controlling hydrogen throughout the entire process of smelting non-vacuum steel, belonging to the technical field of steelmaking. Background Technology

[0002] The presence of hydrogen in steel can cause defects such as white spots and lamellar fractures, severely damaging the mechanical properties of the steel. In particular, high hydrogen content in steel creates porosity, making cracks more sensitive and significantly reducing the steel's strength, plasticity, fatigue life, and impact toughness.

[0003] In the converter steelmaking process, controlling the hydrogen content of molten steel is a crucial step. This is because hydrogen is one of the harmful elements in steel, and its hazards mainly manifest as serious defects such as hydrogen embrittlement, white spots, point segregation, and static fatigue fracture. It can also lead to the formation of bubbles, cracks, and pinholes in the cast billet. Currently, methods for controlling hydrogen in steelmaking mainly involve source control, process optimization, creating conditions for hydrogen escape or reaction, and hydrogen removal through subsequent treatment. By comprehensively applying the above hydrogen control strategies, relevant steel companies have obtained effective methods and measures for hydrogen control. For example, a refining method for controlling low hydrogen and low nitrogen in ultra-high alloy steel (patent publication number CN117551839A) emphasizes pre-baking the alloy to reduce the hydrogen content in the molten steel. In addition, regarding process optimization, a smelting method for controlling the hydrogen content in molten steel during converter blowing (patent publication number CN118813899A) effectively controls the increase in hydrogen content in molten steel by precisely controlling the oxygen lance position and strictly regulating the timing of raw material addition. For steel grades with strict requirements on hydrogen content, such as heavy rail steel, the key step in deep dehydrogenation during vacuum degassing treatments such as RH and VD is to control the hydrogen content in rails. Patent publication number CN107012298A proposes a method for controlling the hydrogen content in rails. This method uses a combination of measures, including RH vacuum degassing treatment, controlling the moisture content of metallurgical auxiliary materials during continuous casting, and slow cooling of the continuous casting billet to remove hydrogen, to control the hydrogen content in heavy rail steel.

[0004] However, the aforementioned hydrogen control technologies still have certain limitations. For example, they require high standards for raw material drying and processing, only control hydrogen reduction in a specific process, demand high precision in process control, and the use of RH and VD vacuum degassing equipment for hydrogen reduction leads to increased energy consumption and production costs. Therefore, there is still much room for research and exploration in achieving a low-carbon, low-cost, and efficient end-to-end hydrogen control process. Summary of the Invention

[0005] To address the aforementioned problems, this invention discloses a process for controlling hydrogen throughout the entire process of smelting non-vacuum steel grades, the specific technical solution of which is as follows: A process for controlling hydrogen throughout the entire process of smelting non-vacuum steel grades includes the following steps: Step (1) Converter charging: The furnace charge uses scrap steel and molten iron, with scrap steel accounting for 20-25% of the total mass. Step (2) Converter blowing: Cold material sludge balls are added to the converter 4 minutes before the first batch of material is blown with oxygen. The amount of the first batch of sludge balls added is 400~700 kg. The amount of sludge balls added in the middle and later stages of blowing should not exceed 800 kg. Cold material sludge balls are prohibited from being added within 180 seconds before the end of blowing. Only cold material sludge balls are added to the cold material during blowing. Step (3) Converter tapping: Use hot turnover ladle for tapping. The charging sequence during tapping alloying is: deoxidizer → recarburizer → alloy → refining slag → lime; control the tapping time to be greater than 3 min, the moisture content of refining slag and lime to be less than 1%, and the moisture content of recarburizer to be less than 0.1%; during tapping, the bottom blowing of the ladle is maintained at 1000 NL / min throughout the process; Step (4) LF refining: Rapid slag formation during the refining process reduces the amount of lime and refining slag used. The amount of lime is controlled within the range of 200~400kg. Refining slag is added according to the lime:refining slag ratio of 2:1. The refining time is kept above 50 min. The flow rate of bottom blowing argon gas in the ladle during the middle and late stages of refining does not exceed 600 NL / min. When using a bent pipe wire feeder to feed aluminum wire into the ladle to adjust the Al content of the molten steel, or when soft blowing to feed silicon-calcium wire, the wire feeding speed is controlled at 2.2±0.3 m / s, the soft blowing argon flow rate is controlled at 20~150 NL / min, the soft blowing time is controlled at 25 min or more, and the wire feeding and soft blowing stirring are based on the slag surface moving slightly without exposing the molten steel. Step (5) Continuous casting: The tundish used for casting should be kept dry, free of moisture and oil. The tundish should be baked for more than 3 hours at a temperature of more than 1200℃. The moisture content of the covering agent and protective slag should be controlled below 0.3%.

[0006] Furthermore, in step (1), the scrap steel in the furnace charge accounts for 20% by mass, and the scrap steel furnace charge uses dry scrap steel, not oily scrap steel shavings or bottom material.

[0007] Furthermore, before the converter blowing process, the alloy is added to an alloy baking furnace for baking in advance to ensure that the alloy glows red when the steel is tapped, and the alloy temperature is 500±50℃.

[0008] Furthermore, in step (2), a 90-ton top-and-bottom blown converter is used for smelting.

[0009] Furthermore, in step (2), the cold material sludge balls are selected from sludge balls with a moisture content of less than 2%.

[0010] Furthermore, in step (2), the oxygen lance should be positioned at least 1300 mm from the molten steel surface during the blowing process. When drawing carbon, the lance nozzle should be lowered to 700-1100 mm from the molten steel surface. The blowing time should be controlled within the range of 14-16 minutes, and the normal oxygen supply of the oxygen lance should be 14000-18000 Nm³. 3 / h; The bottom blowing gas supply intensity of the converter is adjusted according to the target C content at the end point. The bottom blowing gas supply intensity in the early stage of blowing is 0.05 Nm for steel grades with different carbon contents. 3 / t.min, the subsequent bottom blowing gas supply intensity is divided into 0.09, 0.07, and 0.05 Nm according to the high, medium, and low killed steel grades. 3 / t.min.

[0011] Furthermore, in step (2), during the supplementary blowing period, only sludge balls with a moisture content of less than 2% are added, and the amount added is controlled at ≤600kg.

[0012] Furthermore, in step (2), the final temperature is controlled according to the target steel grade: for steel grades with an internal control limit of phosphorus ≤ 0.015%, the tapping temperature is ≥ 1600℃; for steel grades with 0.015% < internal control limit of phosphorus < 0.020%, the tapping temperature is ≥ 1610℃; for steel grades with an internal control limit of phosphorus ≥ 0.020%, the tapping temperature is ≥ 1620℃.

[0013] Furthermore, in step (4), the refining furnace cover must not leak water, and the auxiliary materials lime, refining slag, and alloy of the LF furnace must be dried and have a moisture content of no more than 2%.

[0014] The beneficial effects of this invention are: This invention provides a process for controlling hydrogen content throughout the entire process of smelting non-vacuum steel. By controlling the selection and dosage of raw materials, process parameters, alloys and slag materials used in the entire smelting process, the hydrogen content of the finished product can be controlled to below 3.5 ppm, thereby improving the quality and performance of the steel.

[0015] The core advantage of this invention is its disruptive breakthrough in cost and efficiency.

[0016] 1. The most direct advantages: Eliminating the need for vacuum hydrogen control reduces costs and increases efficiency, significantly lowering equipment investment and maintenance costs; it significantly shortens the production cycle and increases capacity, as vacuum treatment typically takes 20-40 minutes. By eliminating this step, the entire process from steel smelting to continuous casting is greatly shortened, meaning the same equipment can produce more steel per unit time, directly improving the company's capacity and asset utilization; it reduces process energy and media consumption: the vacuum degassing process consumes a large amount of electricity, argon, etc. Eliminating this step directly reduces the cost of these media and energy.

[0017] 2. Technological advantages: A systematic innovation from "end-of-pipe treatment" to "source and process control". The traditional approach is "smelting first, then vacuum dehydrogenation", while this invention is a "whole-process, systematic" hydrogen control concept.

[0018] (1) Source control, precisely cutting off the hydrogen source: Material drying: By strictly managing the baking and drying of all materials entering the furnace, such as scrap steel, alloys, and slag-forming materials (lime, fluorite), the introduction of moisture, the main source of hydrogen, is fundamentally eliminated.

[0019] Refractory and lining management: Ensure that refractory materials such as ladles and tundishes are fully baked until "red-hot" to completely remove the moisture adsorbed inside.

[0020] (2) Process optimization, combining suppression and removal: Optimize converter operation: reduce hydrogen from the carbon additive in the later stage by controlling the final carbon and avoiding over-oxidation; precisely control the oxygen lance and bottom blowing process parameters, and use the CO bubbles in the later stage of smelting to "carry" hydrogen out.

[0021] Enhanced refining process: In the LF refining furnace, by stabilizing the wire feeding speed, extending the soft blowing argon time and refining time, and optimizing the argon flow rate, a calm molten steel surface is created, promoting the rise of microbubbles and removing residual hydrogen in the molten steel to the maximum extent.

[0022] 3. Advantages in quality and risk control (1) Stable and controllable quality: Through the refined control of the whole process, the hydrogen content of molten steel can be stably controlled within the target range (for example, hydrogen in the ladle during continuous casting ≤ 3.5 ppm), avoiding the risk of excessive hydrogen content due to fluctuations in vacuum treatment effect or operational errors.

[0023] (2) Reduce uncertainty in the production process: Vacuum treatment is a complex physical process with a certain failure rate and operational risks. Eliminating this step simplifies the production process and reduces the risk of scrapping or downgrading of the entire furnace of molten steel due to equipment failure.

[0024] This invention departs from the traditional reactive hydrogen control strategy (treating problems with a vacuum furnace only after they occur) and instead adopts a proactive systems engineering approach. By implementing a comprehensive system across all upstream processes to strictly control hydrogen entry and create dehydrogenation conditions, hydrogen is successfully intercepted from the molten steel. This eliminates the most expensive processing step while producing qualified low-hydrogen steel. This is not only a novel technical solution but also a revolutionary production philosophy, yielding substantial economic (cost reduction, increased production) and operational (process simplification, improved stability) benefits. Detailed Implementation

[0025] The present invention will be further illustrated below with reference to specific embodiments. It should be understood that the following specific embodiments are for illustrative purposes only and are not intended to limit the scope of the invention.

[0026] Currently, the existing technologies most closely related to this invention include: smelting methods for controlling hydrogen content in molten steel during converter blowing, steelmaking methods for controlling hydrogen in non-vacuum processes, methods for reducing hydrogen content in molten steel from top-and-bottom combined blowing converters, methods for effectively controlling abnormally high hydrogen content in molten steel, and methods for controlling hydrogen increase during the steelmaking process. Although each has its own focus, their core hydrogen control methods are all aimed at controlling hydrogen in the converter smelting stage, but they do not control the hydrogen content in molten steel throughout the entire steelmaking process. The main reason is that the hydrogen content in molten steel is unstable, and there are too many factors affecting hydrogen content throughout the entire steelmaking process (converter, refining, continuous casting), making it difficult to control.

[0027] This invention focuses on the entire steelmaking process, implementing full-process hydrogen control for steel grades that do not undergo vacuum treatment. While ensuring steel quality (low hydrogen content), it achieves a significant reduction in production costs and a significant improvement in product quality by systematically optimizing the factors affecting hydrogen content throughout the entire process.

[0028] The present invention provides a process for controlling hydrogen throughout the entire process of smelting non-vacuum steel, the specific steps of which are as follows: (1) Converter charging: The furnace charge is scrap steel + molten iron. The scrap steel content is 20-25% (preferably 20%). The scrap steel materials should not include oily scrap steel such as shavings and briquettes, bottom scrap steel, or other damp scrap steel materials.

[0029] (2) Converter blowing: A 90-ton top-and-bottom blowing converter is used for smelting. Cold material sludge balls are added to the converter 4 minutes before the first batch of material is blown with oxygen, with an addition amount of 400-700 kg. During blowing, only sludge balls are added as cold material, without adding other ores or pellets. For heats where cold material must be added within 180 seconds before the end of oxygen blowing or during supplementary blowing, only sludge balls with a moisture content of less than 2% are added, and the addition amount is controlled at ≤600 kg. The final temperature is controlled according to the target tapping temperature: for steel grades with an internal control limit of ≤0.015% phosphorus, the tapping temperature is ≥1600℃; for steel grades with an internal control limit of <0.020% phosphorus, the tapping temperature is ≥1610℃; for steel grades with an internal control limit of ≥0.020% phosphorus, the tapping temperature is ≥1620℃.

[0030] (3) Converter tapping: Use a reusable ladle; new ladles and intermediate repair ladles are not permitted. The charging sequence during steelmaking alloying is: deoxidizer → recarburizer → alloy → refining slag → lime. Before converter smelting, preheat the alloy in the alloy baking furnace to ensure that the alloy glows red during tapping, with the alloy temperature at 500±50℃. Control the tapping time to be greater than 3 minutes, ensuring that the moisture content of the refining slag and lime is less than 1%, and the moisture content of the recarburizer is less than 0.1%. Maintain the bottom blowing rate of the ladle at 1000 NL / min throughout the tapping process to ensure that the alloy and slag reach maximum melting.

[0031] (4) LF Refining: Steels that cannot be smelted under vacuum are prohibited if the refining furnace cover leaks. Moisture control is crucial for key auxiliary materials (lime, refining slag) and alloys in the LF furnace; the use of damp alloy slag is strictly prohibited. Rapid slag formation during the refining process reduces lime and refining slag usage. Lime usage is controlled within the range of 200-400 kg, and refining slag is added according to a lime:refining slag ratio of 2:1. When feeding aluminum or calcium silicate wire, the feeding speed is controlled at 2.2±0.3 m / s, the soft blowing argon flow rate is controlled at 20-150 NL / min, and the soft blowing time is controlled at over 25 min. Wire feeding and soft blowing stirring should be performed with slight movement of the slag surface without exposing the molten steel.

[0032] (5) Continuous casting: The tundish used for casting shall be kept dry, free of moisture and oil. The tundish shall be baked for more than 3 hours at a temperature of more than 1200℃. The moisture content of the covering agent and protective slag shall be controlled below 0.3%. During the casting process, the covering agent and protective slag shall be used in strict accordance with the process requirements to prevent secondary pollution caused by the exposure of the molten steel.

[0033] By controlling the hydrogen content in each of the above processes, the goal of controlling the hydrogen content from the source can be achieved, and the hydrogen content of the finished product can be controlled below 3.5 ppm.

[0034] Those skilled in the art will understand that, unless otherwise defined, all terms used herein (including technical and scientific terms) have the same meaning as commonly understood by one of ordinary skill in the art to which this application pertains. It should also be understood that terms such as those defined in general dictionaries should be understood to have the same meaning as in the context of the prior art, and should not be interpreted in an idealized or overly formal sense unless defined as herein.

[0035] Based on the above-described preferred embodiments of the present invention, and through the foregoing description, those skilled in the art can make various changes and modifications without departing from the inventive concept. The technical scope of this invention is not limited to the contents of the specification, but must be determined according to the scope of the claims.

Claims

1. A process for controlling hydrogen throughout the entire process of smelting non-vacuum steel, characterized in that, Includes the following steps: Step (1) Converter charging: The furnace charge uses scrap steel and molten iron, with scrap steel accounting for 20-25% of the total mass. Step (2) Converter blowing: Cold material sludge balls are added to the converter 4 minutes before the first batch of material is blown with oxygen. The amount of the first batch of sludge balls added is 400~700 kg. The amount of sludge balls added in the middle and later stages of blowing should not exceed 800 kg. Cold material sludge balls are prohibited from being added within 180 seconds before the end of blowing. Only cold material sludge balls are added to the cold material during blowing. Step (3) Converter tapping: Use hot turnover ladle for tapping. The charging sequence during tapping alloying is: deoxidizer → recarburizer → alloy → refining slag → lime; control the tapping time to be greater than 3 min, the moisture content of refining slag and lime to be less than 1%, and the moisture content of recarburizer to be less than 0.1%; during tapping, the bottom blowing of the ladle is maintained at 1000 NL / min throughout the process; Step (4) LF refining: Rapid slag formation during the refining process reduces the amount of lime and refining slag used. The amount of lime is controlled within the range of 200~400kg. Refining slag is added according to the lime:refining slag ratio of 2:

1. The refining time is kept above 50 min. The flow rate of bottom blowing argon gas in the ladle during the middle and late stages of refining does not exceed 600 NL / min. When using a bent pipe wire feeder to feed aluminum wire into the ladle to adjust the Al content of the molten steel, or when soft blowing to feed silicon-calcium wire, the wire feeding speed is controlled at 2.2±0.3 m / s, the soft blowing argon flow rate is controlled at 20~150 NL / min, the soft blowing time is controlled at 25 min or more, and the wire feeding and soft blowing stirring are based on the slag surface moving slightly without exposing the molten steel. Step (5) Continuous casting: The tundish used for casting should be kept dry, free of moisture and oil. The tundish should be baked for more than 3 hours at a temperature of more than 1200℃. The moisture content of the covering agent and protective slag should be controlled below 0.3%.

2. The process method for controlling hydrogen throughout the entire process of smelting non-vacuum steel according to claim 1, characterized in that, In step (1), the scrap steel in the furnace charge accounts for 20% by mass. Dry scrap steel is used in the scrap steel furnace charge, and oily scrap steel or bottom material containing shavings and briquettes is not used.

3. The process method for controlling hydrogen throughout the entire process of smelting non-vacuum steel according to claim 1, characterized in that, Before the converter blowing process, the alloy is added to the alloy baking furnace for baking to ensure that the alloy is red-hot when the steel is tapped, and the alloy temperature is 500±50℃.

4. The process method for controlling hydrogen throughout the entire process of smelting non-vacuum steel according to claim 1, characterized in that, The step (2) uses a 90-ton top-and-bottom blown converter for smelting.

5. The process method for controlling hydrogen throughout the entire process of smelting non-vacuum steel according to claim 1, characterized in that, In step (2), the cold material sludge balls are selected with a water content of less than 2%.

6. The process method for controlling hydrogen throughout the entire process of smelting non-vacuum steel according to claim 1, characterized in that, In step (2), the oxygen lance should be positioned at least 1300 mm from the molten steel surface during the blowing process. When removing carbon, the nozzle should be lowered to 700-1100 mm from the molten steel surface. The blowing time should be controlled within 14-16 minutes. The normal oxygen supply of the oxygen lance is 14000-18000 Nm³. 3 / h; The bottom blowing gas supply intensity of the converter is adjusted according to the target C content at the end point. The bottom blowing gas supply intensity in the early stage of blowing is 0.05Nm for steel grades with different carbon contents. 3 / t.min, the subsequent bottom blowing gas supply intensity is divided into 0.09, 0.07, and 0.05 Nm according to the high, medium, and low killed steel grades. 3 / t.min.

7. The process method for controlling hydrogen throughout the entire process of smelting non-vacuum steel according to claim 1, characterized in that, In step (2), during the supplementary blowing period, only sludge balls with a moisture content of less than 2% are added, and the amount added is controlled at ≤600kg.

8. The process method for controlling hydrogen throughout the entire process of smelting non-vacuum steel according to claim 1, characterized in that, In step (2), the final temperature is controlled according to the target steel grade: for steel grades with an internal control limit of phosphorus ≤ 0.015%, the tapping temperature is ≥ 1600℃; for steel grades with 0.015% < internal control limit of phosphorus < 0.020%, the tapping temperature is ≥ 1610℃; for steel grades with an internal control limit of phosphorus ≥ 0.020%, the tapping temperature is ≥ 1620℃.

9. The process method for controlling hydrogen throughout the entire process of smelting non-vacuum steel according to claim 1, characterized in that, In step (4), the refining furnace cover must not leak water, and the auxiliary materials of the LF furnace, lime, refining slag and alloy, must be dried and have a moisture content of no more than 2%.