Method for controlling titanium element of high-titanium welding wire steel

Abstract

The invention belongs to the technical field of high-titanium welding wire steel, and relates to a method for controlling the titanium element of the high-titanium welding wire steel, which comprises the following steps of: according to the target component of the high-titanium welding wire steel, sequentially carrying out converter or electric furnace smelting, LF (ladle furnace) refining and continuous casting production, when tapping in the smelting process, adding ferrosilicon alloy with the same silicon mass according to the target silicon component mass of 90% of the high-titanium welding wire steel, medium-carbon ferromanganese with the mass equal to that of manganese is added according to the total amount of 90% of the target manganese component of the high-titanium welding wire steel; in the refining process, after deoxidation is completed, the content of (FeO + MnO) in refining slag is controlled to be 1.0% or below, then a low-aluminum low-nitrogen ferrotitanium wire is fed through a wire feeder for fine adjustment of the titanium element, the titanium content in molten steel is controlled within a target range, and meanwhile the content of aluminum and nitrogen in the molten steel is controlled within a steel grade required range; a whole-course protection pouring process is adopted in the continuous casting process, so that titanium content loss caused by secondary oxidation of molten steel is prevented.

Description

Technical Field

[0001] This invention belongs to the technical field of high-titanium welding wire steel, and specifically relates to a method for controlling the titanium element in high-titanium welding wire steel. Background Technology

[0002] The composition design of high-titanium welding wire steel revolves around "ensuring welding performance, inhibiting the precipitation of harmful phases, and improving the cleanliness of molten steel." The content and function of each element are as follows:

[0003] (I) Key alloying elements: Titanium is the core, with precise control over its content and morphology.

[0004] Titanium is a "characteristic element" of high-titanium welding wire steel, and its content and form directly determine the weldability of the wire (such as resistance to porosity and cracking). The titanium content of high-titanium welding wire steel is usually controlled between 0.15% and 0.35%, and the amount needs to be adjusted according to the application of the welding wire. Its main function is to refine the weld grain and reduce the susceptibility to cold cracking. Therefore, deoxidation is required during the steelmaking process to strictly control the oxidation of titanium. Titanium alloying generally uses ferrotitanium (TIA) alloys. However, ferrotitanium alloys contain approximately 10% Al and 0.02% nitrogen. When the titanium content in titanium-containing steel is ≤0.1%, using ferrotitanium alloys (30 ferrotitanium alloy, main components Ti≥25%, Al≤10%; 70 ferrotitanium alloy Ti≥65%, Al≤3.0%) has a limited effect on increasing the Al and N content of the steel and a relatively small impact on the purity of the molten steel. However, high-titanium welding wire steel has a high titanium content. After adjusting the titanium composition using ferrotitanium alloys, the molten steel has a significant increase in Al and N, leading to turbulence and composition deviations during continuous casting. Therefore, precise control of titanium in high-titanium welding wire steel is a technical pain point in the industry.

[0005] (ii) Harmful elements (C, N, S, P): Their content must be controlled at extremely low levels to avoid defects and performance degradation.

[0006] High-titanium welding wire steel has extremely low tolerance for harmful elements, requiring strict control throughout the smelting and refining process. The core objective is to "reduce the reaction with titanium and lower the risk of weld defects." Generally, the requirements are C ≤ 0.10%, N ≤ 0.007% (70ppm), and S ≤ 0.015%. Free N can react with Ti to form coarse TiN inclusions, leading to weld slag inclusions; excessive N increases the weld's susceptibility to cold cracking. S forms low-melting-point compounds with Ti, which easily accumulate at grain boundaries during welding, leading to hot cracking and reducing the weld's low-temperature toughness and corrosion resistance. P tends to segregate at weld grain boundaries, causing "cold brittleness" and increasing the weld's susceptibility to cracking.

[0007] (III) Elements that regulate inclusions (Si, Mn, Al): assist in deoxidation and stabilize performance

[0008] Si, Mn, and Al are "auxiliary elements" in high-titanium welding wire steel. Their main functions are deoxidation, adjusting the fluidity of molten steel, and avoiding interaction with titanium. Their content control is characterized by "low and precise".

[0009] Aluminum: Final deoxidation + control of titanium morphology; the content of ultra-low acid-soluble aluminum (effective aluminum) needs to be strictly controlled. Aluminum content is 0.005%–0.010% (50–100 ppm). Its core role is as a final deoxidizing element, further reducing the oxygen activity of molten steel (Al + O → Al₂O₃) and preventing Ti from being oxidized to TiO₂. Excessive Al content should be avoided; if Al > 0.010%, it will form coarse Al-Ti-O composite inclusions (such as Al₂TiO₅) with Ti, leading to weld porosity or slag inclusions. If Al is too low, the oxygen content of the molten steel will be too high, making titanium prone to oxidation and failure. Summary of the Invention

[0010] The purpose of this invention is to overcome the shortcomings of the prior art and provide a method for controlling the titanium element in high-titanium welding wire steel.

[0011] To achieve the objectives of this invention, the following technical solutions are adopted.

[0012] A method for controlling titanium content in high-titanium welding wire steel, wherein, according to the target composition of high-titanium welding wire steel, the steelmaking process sequentially involves converter or electric furnace smelting, LF refining, and continuous casting, wherein:

[0013] When tapping steel in the converter or electric furnace smelting process, add ferrosilicon alloy of equal silicon mass according to the target silicon content mass of 90% high titanium welding wire steel, and add medium carbon ferromanganese of equal manganese mass according to the total manganese content mass of 90% high titanium welding wire steel.

[0014] After complete deoxidation using silicon carbide and calcium carbide in the LF refining process, the (FeO+MnO) content in the refining slag is controlled below 1.0%. Then, low-aluminum and low-nitrogen titanium iron wire is fed in through a wire feeder to fine-tune the titanium element, thereby controlling the titanium content in the molten steel within the target range. At the same time, the aluminum and nitrogen content in the molten steel are controlled within the range required by the steel grade.

[0015] The continuous casting process employs a full-process protective pouring technique to prevent secondary oxidation of the molten steel from causing a loss of titanium content.

[0016] Furthermore, the titanium element fine-tuning is controlled by the feeding speed and feeding amount of the wire feeder, wherein: the feeding speed is 150-200m / min, the feeding angle is perpendicular to the molten steel surface, and the feeding amount is more than 80% of the titanium recovery rate in the low-nitrogen, low-aluminum titanium-iron wire.

[0017] Furthermore, the low-aluminum, low-nitrogen titanium-iron wire is formed by crushing the low-aluminum, low-nitrogen titanium-iron alloy into low-aluminum, low-nitrogen titanium-iron alloy powder less than 2mm using a jaw crusher and a double roller mill, and then using a cored wire machine to wind the low-aluminum, low-nitrogen titanium-iron alloy powder with steel strip into a cored wire.

[0018] Furthermore, the preparation method of the low-aluminum, low-nitrogen titanium-iron alloy includes the following steps:

[0019] S41. Using sponge titanium, waste pure titanium, and scrap steel as raw materials, the materials are mixed according to the mass ratio of 15%-25% sponge titanium, 48%-54% waste pure titanium, and 25%-33% scrap steel.

[0020] S42. Add the ingredients to the furnace for smelting. During the smelting process, add a refining agent composed of fluorite powder, potassium chloride and calcium oxide. At the same time, argon is blown from the bottom for refining and stirring. The furnace outlet temperature is controlled at 1050-1150℃.

[0021] S43. After being taken out of the furnace, it is rapidly solidified to obtain a low-aluminum, low-nitrogen titanium-iron alloy.

[0022] Furthermore, the main component indicators of the low-aluminum, low-nitrogen titanium-iron alloy are: Ti≥65%, Al≤0.5%, N≤0.05%.

[0023] Furthermore, the continuous casting process uses a calcium aluminate carbon-free intermediate ladle covering agent.

[0024] Furthermore, the components of the calcium aluminate carbon-free intermediate packaging covering agent, by percentage mass, include CaO≥50%, Al2O3≥30%, SiO2≤8%, MgO≤8%, and C≤0.5%.

[0025] Furthermore, in the continuous casting process, an integral submerged nozzle and a stopper rod are used to control the flow, thereby enhancing the protection of the entire continuous casting process.

[0026] Furthermore, the target range is 0.18-0.25%.

[0027] Furthermore, the required range for the steel grade is nitrogen content ≤ 60 ppm and aluminum content ≤ 0.02%.

[0028] Compared with the prior art, the beneficial effects achieved by the present invention are as follows:

[0029] This invention controls the entire process of smelting, refining, and continuous casting, and selects low-aluminum and low-nitrogen titanium iron wire for composition adjustment, optimizing the amount and method of addition. The production process can precisely control the titanium element in high-titanium welding wire steel, which can not only meet the requirement of controlling the titanium content within the target range, but also ensure that the residual nitrogen and aluminum content are within the steel grade requirements, thus guaranteeing the welding performance of high-titanium welding wire steel. Detailed Implementation

[0030] The present invention will now be further described. The following embodiments are only used to more clearly illustrate the technical solution of the present invention, and should not be used to limit the scope of protection of the present invention.

[0031] As an embodiment of the present invention, a method for controlling the titanium element in high-titanium welding wire steel, according to the target composition of high-titanium welding wire steel, the steelmaking process sequentially goes through converter or electric furnace smelting, LF refining, and continuous casting processes, as follows: The control process for each process is as follows:

[0032] (1) Converter smelting control

[0033] Added blowing is prohibited in converters or electric furnaces; the final carbon content must be controlled to ≤0.06%. Based on the target Si and Mn composition of the high-titanium welding wire steel, silicon-manganese alloy and medium-carbon ferromanganese are added at 90% of the target composition during tapping for deoxidation and alloying. After deoxidation and alloying, the oxygen content of the molten steel is determined to be ≤20ppm. If the oxygen content is >20ppm, aluminum wire must be added for deoxidation according to the oxygen content. At tapping, 6-8 kg / t of lime and 2-3 kg / t of fluorite are added to the ladle for top slag formation during LF refining.

[0034] (2) LF refining process control

[0035] In the LF refining process, silicon carbide and calcium carbide are used for deoxidation, with a total deoxidizer dosage of 1-3 kg / t. Medium-carbon ferromanganese and ferrosilicon are used to fine-tune the composition to the target range for the steel grade. After complete deoxidation, when the (FeO+MnO) content in the refining slag is ≤1.0%, (CaO / SiO2) >5, and the aluminum content in the molten steel is 0.005-0.015%, if the Al content is lower than 0.01%, aluminum wire is used to supplement it. After feeding the aluminum wire, soft argon blowing is performed for ≥3 minutes, and finally, titanium alloying is carried out.

[0036] Titanium alloying operation: A low-nitrogen, low-aluminum titanium-iron wire feeding method is used to precisely control the titanium composition to meet the requirements of the steel grade. The low-nitrogen, low-aluminum titanium-iron wire is produced using specialized technology. The wire feeder speed is 150-200 m / min, and the feeding angle is perpendicular to the molten steel surface. The titanium composition is adjusted according to the goal of achieving a titanium recovery rate of over 80% in the low-nitrogen, low-aluminum titanium-iron wire. Compared to using titanium-iron alloys, the flow rate of the cored wire fed into the molten steel using low-nitrogen, low-aluminum titanium-iron wire is controllable (feeding speed, feeding amount), and the addition is uniform, allowing for precise and stable control of the titanium content.

[0037] The low-aluminum, low-nitrogen titanium-iron alloy is produced by crushing titanium-iron powder to less than 2mm using a jaw crusher and a double roller mill, and then using a cored wire machine to wind the titanium-iron powder and steel strip into a cored wire to obtain low-nitrogen, low-aluminum titanium-iron wire.

[0038] The low-nitrogen, low-aluminum titanium-iron alloy uses sponge titanium, waste pure titanium, and scrap steel as main raw materials, with a mass ratio of 15%-25% sponge titanium, 48%-54% waste pure titanium, and 25%-33% scrap steel. The raw materials are added to a furnace for melting, during which a refining agent composed of fluorite powder, potassium chloride, and calcium oxide is added. Simultaneously, refining and stirring are carried out by bottom-blowing argon, and the furnace exit temperature is controlled at 1050-1150℃. After rapid solidification, the low-aluminum, low-nitrogen titanium-iron alloy is obtained. The low-aluminum, low-nitrogen titanium-iron alloy is then made into 0-2mm low-nitrogen, low-aluminum titanium-iron powder, which is then wound with steel strip using a cored wire machine to form low-nitrogen, low-aluminum titanium-iron wire. Main component indicators: Ti≥65%, Al≤0.5%, N≤0.05%, wire diameter 13mm, core powder weight per meter 350-450g / m.

[0039] (3) Continuous casting process control: Calcium aluminate carbon-free tundish covering agent (CaO≥50%, Al2O3≥30%, SiO2≤8%, MgO≤8%, C≤0.5%) is used in continuous casting, with an addition rate of 3-5 kg / t steel. Slag monitoring is implemented in the ladle, and long nozzle argon sealing protection is used. Argon blowing is controlled at 50 L / min to 100 L / min to prevent secondary oxidation from gas absorption. An integral submerged nozzle and stopper rod flow control are adopted to enhance protection throughout the continuous casting process, reduce titanium oxidation and inclusion formation, and ensure stable titanium content.

[0040] Application examples:

[0041] A steel mill produces ER70S-G steel using a continuous casting machine with 10 heats of continuous casting. The composition is precisely controlled within the target range, and the continuous casting process is free of turbulence and surface fluctuations, resulting in stable production quality. The welding wire steel meets all the user's welding requirements. The specific process for producing ER70S-G steel is as follows:

[0042] Production process of high-titanium welding wire steel ER70S-G continuous casting billet: 60t converter → LF refining → continuous casting of square billet. Main process equipment includes: a combined blowing converter with slag-blocking tapping via a sliding plate, smelting cycle of 30 minutes; an LF refining furnace with an average heating rate of 5℃ / min, equipped with a high-precision cored wire feeder; continuous casting using an 8m arc radius 4-machine 4-strand square billet continuous casting, with a cross-section of 160×160mm, the tundish using an internal submerged entry nozzle, automatic stopper rod control, equipped with a crystallizer and electromagnetic stirring at the solidification end, and a multi-point straightening device.

[0043] 1. Converter smelting

[0044] The main measures adopted in converter smelting are as follows: Argon blowing is used for bottom blowing in the converter, and the final tapping is stably controlled throughout the process to ensure that [C] ≤ 0.06%, [P] ≤ 0.010%, temperature ≥ 1620℃, and hit rate is above 95%, thereby reducing the oxygen content of the initial molten steel; slag-blocking tapping is adopted in the converter to achieve slag-free tapping and reduce the amount of phosphorus returned during tapping. High-silicon ferromanganese and high-purity ferrosilicon alloys are used for alloying during the tapping process. Simultaneously, 8 kg / t of lime and 2 kg / t of fluorite are added with the steel stream to form top slag in advance and promote rapid slag formation in the LF furnace. High-quality ferroalloys and slag-forming materials with low residual elements are selected during the smelting process.

[0045] 2. LF Refining Control

[0046] When molten steel enters the LF station, lime or fluorite should be added in appropriate amounts according to the slag condition. Adding 1.5 kg / t of quartz sand can control the basicity and good fluidity of the refining slag, and the binary basicity should be controlled between 1.8 and 2.2. Using a reducing atmosphere, argon blowing and strong stirring are carried out throughout the process to promote the deoxidation and desulfurization chemical reactions at the steel-slag interface and to promote the floating of inclusions.

[0047] The LF refining process uses no less than 1.5 kg / t of composite silicon carbide for slag surface diffusion deoxidation. By producing white slag with suitable alkalinity and good fluidity, the expected deoxidation and desulfurization effects are achieved.

[0048] In the later stages of LF refining, after the slag is deoxidized to form white slag, a special low-nitrogen, low-aluminum ferrotitanium wire is fed in using a wire feeder to adjust Ti to the target value. The low-nitrogen, low-aluminum ferrotitanium wire is made from a low-nitrogen, low-aluminum ferrotitanium alloy, crushed and manufactured into cored wire with a diameter of 13mm and a powder weight of 410g / m. An average of 480 meters of low-nitrogen, low-aluminum ferrotitanium wire is used per heat of steel, and the average Ti recovery rate after wire feeding is 87%.

[0049] After refining and wire feeding in the LF process, the nitrogen content in the steel is ≤0.0006%, and the average nitrogen content of the finished product is 0.0048%, which meets the requirement of ≤0.0060% for steel grades.

[0050] 3. Continuous casting control

[0051] The continuous casting process utilizes a 160×160mm cross-section, integral stopper rod controlled-flow tundish to enhance protective casting control. Constant casting speed (2.4m / min), superheat (35-50℃), and automatic liquid level control (liquid level fluctuation ±2mm) are employed to minimize quality fluctuations caused by unsteady casting during production. A special protective slag for low-carbon steel is used. Inspection of the continuously cast billets revealed no visually visible defects such as scale, porosity, inclusions, depressions, or cracks; the billet surface quality was excellent.

[0052] The above description illustrates preferred embodiments of the present application, but does not limit the scope of the claims of the present application. Any modifications, equivalent substitutions, and improvements made by those skilled in the art without departing from the scope and substance of the present application should be within the scope of the claims of the present application.

Claims

1. A method for controlling the titanium element in high-titanium welding wire steel, characterized in that: Based on the target composition of high-titanium welding wire steel, the steelmaking process sequentially involves converter or electric furnace smelting, LF refining, and continuous casting, among which: When tapping steel in the converter or electric furnace smelting process, add ferrosilicon alloy of equal silicon mass according to the target silicon content mass of 90% high titanium welding wire steel, and add medium carbon ferromanganese of equal manganese mass according to the total manganese content mass of 90% high titanium welding wire steel. After complete deoxidation using silicon carbide and calcium carbide in the LF refining process, the (FeO+MnO) content in the refining slag is controlled below 1.0%. Then, low-aluminum and low-nitrogen titanium iron wire is fed in through a wire feeder to fine-tune the titanium element, thereby controlling the titanium content in the molten steel within the target range. At the same time, the aluminum and nitrogen content in the molten steel are controlled within the range required by the steel grade. The continuous casting process employs a full-process protective pouring technique to prevent secondary oxidation of the molten steel from causing a loss of titanium content.

2. The method for controlling titanium content in high-titanium welding wire steel according to claim 1, characterized in that: The titanium element fine-tuning is controlled by the feeding speed and feeding amount of the wire feeder, wherein: the feeding speed is 150-200m / min, the feeding angle is perpendicular to the molten steel surface, and the feeding amount is more than 80% of the titanium recovery rate in low-nitrogen and low-aluminum titanium-iron wire.

3. The method for controlling titanium content in high-titanium welding wire steel according to claim 2, characterized in that: The low-aluminum, low-nitrogen titanium-iron wire is formed by crushing the low-aluminum, low-nitrogen titanium-iron alloy into low-aluminum, low-nitrogen titanium-iron alloy powder to less than 2mm using a jaw crusher and a double roller mill, and then using a cored wire machine to wind the low-aluminum, low-nitrogen titanium-iron alloy powder with steel strip into a cored wire.

4. The method for controlling titanium content in high-titanium welding wire steel according to claim 3, characterized in that: The preparation method of the low-aluminum, low-nitrogen titanium-iron alloy includes the following steps: S41. Using sponge titanium, waste pure titanium, and scrap steel as raw materials, the materials are mixed according to the mass ratio of 15%-25% sponge titanium, 48%-54% waste pure titanium, and 25%-33% scrap steel. S42. Add the ingredients to the furnace for smelting. During the smelting process, add a refining agent composed of fluorite powder, potassium chloride and calcium oxide. At the same time, argon is blown from the bottom for refining and stirring. The furnace outlet temperature is controlled at 1050-1150℃. S43. After being taken out of the furnace, it is rapidly solidified to obtain a low-aluminum, low-nitrogen titanium-iron alloy.

5. The method for controlling titanium content in high-titanium welding wire steel according to claim 4, characterized in that: The main component indicators of the low-aluminum, low-nitrogen titanium-iron alloy are: Ti≥65%, Al≤0.5%, N≤0.05%.

6. The method for controlling titanium content in high-titanium welding wire steel according to claim 5, characterized in that: The continuous casting process uses a calcium aluminate carbon-free intermediate ladle covering agent.

7. The method for controlling titanium content in high-titanium welding wire steel according to claim 6, characterized in that: The components of the calcium aluminate carbon-free intermediate packaging covering agent, by percentage mass, include CaO≥50%, Al2O3≥30%, SiO2≤8%, MgO≤8%, and C≤0.5%.

8. The method for controlling titanium content in high-titanium welding wire steel according to claim 7, characterized in that: In the continuous casting process, an integral submerged nozzle and a stopper rod are used to control the flow, thereby enhancing the protection of the entire continuous casting process.

9. A method for controlling titanium content in high-titanium welding wire steel according to claim 8, characterized in that: The target range is 0.18-0.25%.

10. A method for controlling titanium content in high-titanium welding wire steel according to claim 9, characterized in that: The required range for the steel grade is: nitrogen content ≤ 60 ppm and aluminum content ≤ 0.02%.