Low-carbon and low-nitrogen-content steel for welding wires and production method of low-carbon and low-nitrogen-content steel

Abstract

The invention provides steel for a low-carbon and low-nitrogen welding wire and a production method of the steel. The steel comprises the following components: 0.06-0.09% of C, 0.80-0.90% of Si, 1.40-1.60% of Mn, less than 0.015% of P, 0.007-0.015% of S, less than or equal to 0.10% of Cr, less than or equal to 0.10% of Ni, less than or equal to 0.10% of Cu, less than or equal to 0.0015% of Ca, less than or equal to 0.03% of V, less than or equal to 0.02% of Ti, less than or equal to 0.05% of Mo, less than or equal to 0.010% of Al, less than or equal to 0.0020% of O, less than or equal to 0.0035% of N and the balance of Fe and inevitable impurities. Compared with the prior art, various parameters in the smelting and refining processes are accurately controlled, so that carbon and nitrogen elements are effectively removed, and the quality and the performance of the steel for the welding wire are improved. The method is suitable for large-scale industrial production and has high production efficiency and economic benefits.

Description

Technical Field

[0001] The invention belongs to the field of steel production, and in particular relates to a steel for welding wire with low carbon and low nitrogen content and a production method thereof. Background Art

[0002] With the continuous development of welding technology, the performance requirements for welding wire materials are increasing. The traditional steel smelting method for welding wire has deficiencies in controlling the carbon and nitrogen content, which leads to defects such as pores and cracks in the welding wire during use, affecting the welding quality and strength. Therefore, it is of great significance to develop a steel smelting method for welding wire that can efficiently reduce the carbon and nitrogen content.

[0003] The patent with the publication number CN 119082593 A published on December 6, 2024 discloses a method for preparing high-oxygen and low-nitrogen welding wire steel, and the disclosed method includes: S1) mixing steel raw materials and graphite carbon blocks and then smelting in an electric arc furnace; then refining in a ladle refining furnace; and then smelting in an argon oxygen refining furnace; S2) pouring the molten steel obtained in step S1) to obtain high-oxygen pure iron after processing; S3) mixing the high-oxygen pure iron, nickel raw materials, molybdenum raw materials and graphite carbon blocks and then smelting in a vacuum induction furnace; S4) carbon deoxidizing the molten steel obtained in step S3); S5) alloying and pouring the molten steel obtained in step S4) to obtain high-oxygen and low-nitrogen welding wire steel. However, the steel disclosed therein has a high oxygen content, and it is easy to damage the process performance of the welding wire and the reliability of the weld through multiple paths such as pores, inclusions, and arc interference.

[0004] Therefore, it is necessary to provide a steel for welding wire with low oxygen content, low carbon and low nitrogen content. Summary of the invention

[0005] The purpose of the present invention is to provide a low-carbon, low-nitrogen content welding wire steel and a production method thereof, and to achieve effective removal of carbon, nitrogen and oxygen elements by process optimization and precise control of various parameters in the smelting process, thereby obtaining high-quality welding wire steel.

[0006] The specific technical solutions of the present invention are as follows:

[0007] A low carbon, low nitrogen content welding wire steel comprising the following components in percentage by mass:

[0008] C: 0.06-0.09%, Si: 0.80-0.90%, Mn: 1.40-1.60%, P < 0.015%, S: 0.007-0.015%, Cr ≤ 0.10%, Ni: ≤ 0.10%, Cu ≤ 0.10%, Ca ≤ 0.0015%, Ti ≤ 0.02%, Mo ≤ 0.05%, Al ≤ 0.010%, O ≤ 0.0035%, N ≤ 0.0045%, the rest are Fe and unavoidable impurities.

[0009] The low-carbon and low-nitrogen content welding wire steel has a yield strength of 360-380 MPa, a tensile strength of 490-540 MPa, an elongation of ≥42%, and a cross-sectional shrinkage of ≥72%.

[0010] The present invention provides a method for producing low-carbon, low-nitrogen content welding wire steel, comprising the following process flow:

[0011] Converter steelmaking - LF refining - continuous casting of billets;

[0012] The converter steelmaking uses molten iron and scrap steel; the chemical composition of the molten iron is required to be Si≤0.70%, P≤0.12%; the scrap steel used is high-quality scrap steel, the sulfur content of the scrap steel is ≤0.07% and the phosphorus content is ≤0.40%; the scrap steel used can use purchased ship plate steel or self-produced continuous casting scrap steel as the main raw material, ensuring that the impurity content in the raw material is low and meets the above requirements; add appropriate amounts of alloy elements as needed to adjust the chemical composition of the steel. Scrap steel accounts for 10-15%;

[0013] The prepared raw material molten iron and scrap steel are put into the converter for smelting.

[0014] During the steel tapping process of the converter, the steel tapping time is controlled at 4-4.5min; 0.4-0.85kg / ton of steel of calcium carbide, 12kg / ton of steel of ferrosilicon, 17kg / ton of steel of low-carbon ferromanganese and 3.3-4.3kg / ton of steel of slag-forming agent lime are added during the steel tapping process of the converter to remove oxygen and other impurities in the molten steel. The slag-forming agent lime uses new lime;

[0015] Final composition of converter steel: C: 0.04-0.06%, P≤0.015%;

[0016] The LF refining is to pour the molten steel into a refining ladle for LF refining, using a refining ladle with a baking temperature of more than 750°C.

[0017] During the refining process, the argon flow rate is adjusted to 100-120 L / min and the outlet temperature is 1550-1590°C.

[0018] Furthermore, 2.5-4.3 kg / ton of steel lime, 2-3.5 kg / ton of steel fluorite, etc. are added to the refining bag for desulfurization to further remove sulfur from the molten steel and increase the carbon content to the target range.

[0019] During refining, ferrosilicon powder is added for deoxidation, and calcium carbide is added at 0.5-0.85kg / ton of steel; diffusion deoxidation is carried out throughout the refining process; white slag retention time is ≥15min; LF refining cycle is ≥40min; soft blowing time is ≥15min.

[0020] Through precise alloying treatment, the chemical composition of the molten steel is adjusted to meet the requirements of the above-mentioned low-carbon, low-nitrogen and low-oxygen content welding wire steel standards.

[0021] In the present invention, the continuous casting of the billet: the molten steel after LF refining is sent to the continuous casting machine for continuous casting, and the continuous casting is 180mm×180mm billet;

[0022] During the continuous casting process, the continuous casting speed is 1.6-1.7m / min, and the superheat is 25-35℃. The specific water volume is 0.7-0.8L / kg, and the distribution ratio is 32:35:19:14; the protective slag model is welding wire steel protective slag. The crystallizer electromagnetic stirring control current is 300A and the frequency is 4Hz; the end current stirring control current is 100-150A and the frequency is 10Hz. During the casting process, the large package casing time is within 3min, the middle package covering agent is used, and the integral water nozzle is used. The liquid level is stable during the casting process. Ensure that the internal structure and external quality of the ingot are in the best state.

[0023] Finally, the chemical composition of the ingot products is analyzed to ensure that the carbon and nitrogen content indicators of the products meet the requirements of the low-carbon and low-nitrogen welding wire steel standards.

[0024] In the present invention, in the process of producing low-carbon and low-nitrogen content welding wire steel, the goals of low carbon, low nitrogen and low oxygen are achieved through specific chemical composition control, refining process and addition of raw and auxiliary materials. Among them, by strictly controlling the raw materials (molten iron and scrap steel), it is helpful to achieve the characteristics of low-carbon welding wire and ensure good welding performance; in the LF refining process, by heating argon stirring, carbon and other impurities in the steel can be further removed, and controlling the refining time and temperature is helpful for the uniform distribution and further removal of carbon elements in the molten steel. In addition, the stirring effect of argon not only helps to remove oxygen and other impurities in the molten steel, but also reduces the contact between the molten steel and nitrogen in the air, thereby reducing the nitrogen content in the steel. The added ferrosilicon, as a good deoxidizer, can react with oxygen in the molten steel to generate silicon dioxide and remove oxygen, thereby reducing the oxygen content in the steel; lime is added during the steelmaking process of the converter and during LF refining, and the amount added at different times is controlled to first adsorb SiO 2 Oxide inclusions such as FeO and FeO can help remove oxygen and other impurities in the molten steel, and can also improve the fluidity and wettability of the molten steel. By stirring and heating with argon, small inclusions (such as SiO 2 、Al 2 O 3) collide and grow and float to the slag layer to improve the deoxidation effect; then control the amount of lime added in the refining stage to maintain the high basicity of the slag to further adsorb residual oxides; add fluorite to improve the fluidity and mass transfer effect of the slag, and adjust the composition and temperature of the steel to ensure that the inclusions float fully, avoid the retention of inclusions due to insufficient superheat of the molten steel, and ensure the purity and stability of the molten steel. Finally, the carbon, nitrogen and oxygen elements are effectively removed to improve the quality of the welding wire.

[0025] Compared with the prior art, the present invention achieves effective removal of carbon and nitrogen elements by precisely controlling various parameters in the smelting and refining process, thereby improving the quality and performance of welding wire steel. 2 , condensed into large pieces of slag in the welding pool and floated out, thereby achieving a good deoxidation effect. The method of the invention is suitable for large-scale industrial production and has high production efficiency and economic benefits. DETAILED DESCRIPTION

[0026] In order to make the purpose, technical solution and advantages of the embodiments of the present invention clearer, the technical solution in the embodiments of the present invention will be clearly and completely described in combination with the embodiments of the present invention. Obviously, the described embodiments are part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of the present invention.

[0027] The present invention is produced according to 120 tons of steel per furnace.

[0028] Example 1

[0029] A low-carbon, low-nitrogen steel for welding wire comprises the following components in mass percentage: as shown in Table 1, the remainder not shown in Table 1 is Fe and unavoidable impurities.

[0030] Table 1 Composition of steel for welding wire in various embodiments and comparative examples (wt%)

[0031] C Si Mn P S Cu Cr Ni Mo Ti Ca Al O N Example 1 0.070 0.840 1.460 0.011 0.013 0.015 0.035 0.005 0.003 0.004 0.0006 0.006 0.0020 0.0025 Example 2 0.075 0.830 1.450 0.012 0.007 0.017 0.034 0.006 0.001 0.004 0.0007 0.005 0.0034 0.0044 Comparative Example 1 0.080 0.830 1.450 0.011 0.018 0.013 0.038 0.006 0.008 0.003 0.0006 0.006 0.0032 0.0075

[0032] The method for producing low-carbon and low-nitrogen content welding wire steel described in Example 1 includes the following process flow: converter - LF refining - continuous casting of square billets 180 mm × 180 mm; specifically:

[0033] The converter: the converter uses molten iron with Si≤0.70%, P≤0.11% and low Cr scrap steel, and the sulfur content and phosphorus content of the scrap steel are not more than 0.07% and 0.40% respectively, and the scrap steel accounts for 12%; the tapping time is 4 minutes, 100 kg / furnace of calcium carbide is added during the tapping process, and the final composition is: C: 0.04-0.06%, P≤0.015%; 12 kg / ton of deoxidized alloyed ferrosilicon and 17 kg / ton of low-carbon ferromanganese are used to reduce the introduction of C, Ca, and Al elements; tapping slag: use newly produced lime with high activity, few impurities, dryness, and no powdering, with an activity of >85% and a dosage of 400 kg.

[0034] The LF refining: refining process deoxidation and slag adjustment operation: use a refining ladle with a baking temperature greater than 750°C. Add 400kg of lime, and add 400kg / furnace of fluorite depending on the slag condition, and ensure good fluidity of the refined slag; during the refining process, ferrosilicon powder is mainly used for deoxidation, and 70kg / furnace of calcium carbide is added; diffusion deoxidation is carried out throughout the refining process; the white slag is kept for 20 minutes. The argon flow rate is controlled at 100L / min, and argon blowing and stirring are prohibited to be turned over to ensure positive pressure in the furnace and effectively reduce nitrogen and oxygen absorption by molten steel; LF refining cycle (excluding soft blowing outside the furnace) is 45min; soft blowing time is 15min, and calcium treatment is strictly prohibited during the refining process. The outlet temperature is 1550-1590°C.

[0035] Continuous casting process: continuous casting speed is 1.6m / min, superheat is 25-35℃. Specific water volume: 0.7L / kg. Distribution ratio: 32:35:19:14. Protective slag model: welding wire steel protective slag. Crystallizer electromagnetic stirring control current is 300A, frequency is 4Hz; terminal current stirring control current is 100A, frequency is 10Hz. During the casting process, the large package casing time is within 3min, the middle package covering agent, the integral water nozzle is used, and the liquid level is stable during the casting process.

[0036] After the ingot comes off the production line, an online appearance inspection is carried out and the ingot is qualified.

[0037] The method for producing low-carbon and low-nitrogen content welding wire steel described in Example 2 includes the following process flow: converter - LF refining - continuous casting of square billets 180 mm × 180 mm; specifically:

[0038] The converter uses molten iron with Si≤0.70%, P≤0.11% and low Cr scrap steel. The sulfur content of the scrap steel is ≤0.07% and the phosphorus content is ≤0.40%, and the scrap steel accounts for 15%; the tapping time is 4 minutes, and 50kg / furnace of calcium carbide is added during the tapping process. The final composition is: C: 0.04-0.06%, P≤0.015%; deoxidation and alloying use 12kg / ton of ferrosilicon and 17kg / ton of low-carbon ferromanganese to reduce the introduction of C, Ca, and Al elements; tapping slag: use new lime with high activity, few impurities, dryness, and no powdering, with a dosage of 400kg.

[0039] Deoxidation and slag adjustment operation in the refining process: Use a refining ladle with a baking temperature greater than 750℃ and an outlet temperature of 1550~1590℃. Add 300kg of lime, and add 300kg of fluorite / furnace depending on the slag condition, and ensure good fluidity of the refined slag; during the refining process, mainly use ferrosilicon powder for deoxidation, add 60kg of calcium carbide / furnace; diffuse deoxidation is carried out throughout the refining process; the white slag is kept for 15min. The argon flow rate is controlled at 120L / min, and argon blowing and stirring are prohibited to be turned over to ensure positive pressure in the furnace and effectively reduce nitrogen and oxygen absorption by molten steel; LF refining cycle (excluding soft blowing outside the furnace) is 40min; soft blowing time is 15min.

[0040] Continuous casting process: continuous casting speed 1.7m / min, superheat 25-35℃. Specific water volume: 0.8L / kg. Distribution ratio: 32:35:19:14. Protective slag model welding wire steel protective slag. Crystallizer electromagnetic stirring control current 300A, frequency 4Hz; terminal current stirring control current 150A, frequency 10Hz. During the casting process, the large package casing time is within 3min, the middle package covering agent, the integral water nozzle is used, and the liquid level is stable during the casting process.

[0041] After the ingot comes off the production line, an online appearance inspection is carried out and the ingot is qualified.

[0042] Comparative Example 1 A method for producing welding wire steel includes the following process flow: converter - LF refining - continuous casting of square billets 180 mm × 180 mm; specifically:

[0043] The converter uses molten iron with Si≤0.70%, P≤0.11% and low Cr scrap steel. The sulfur content of the scrap steel is ≤0.07% and the phosphorus content is ≤0.40%, and the scrap steel accounts for 12%; the tapping time is 5min, and the end composition is: C: 0.04-0.06%, P≤0.015%; deoxidation and alloying use 12kg / ton of ferrosilicon and 17kg / ton of low-carbon ferromanganese to reduce the introduction of C, Ca, and Al elements; tapping slag: use new lime with high activity, few impurities, dryness, and no powdering, and add 420kg.

[0044] Deoxidation and slag adjustment in the refining process: Use a refining ladle with a baking temperature greater than 750°C. Control the refining temperature Degree 1530℃. Add 500kg of lime, add 250kg of fluorite / furnace depending on the slag condition, and ensure good fluidity of the refined slag; during the refining process, ferrosilicon powder is mainly used for deoxidation, and added Calcium carbide 50kg / furnace ; Diffusion deoxidation is carried out during the whole refining process; White slag retention time is 20 minutes. Argon blowing and stirring are prohibited to overturn, ensure positive pressure in the furnace, and effectively reduce nitrogen and oxygen absorption by molten steel; LF refining cycle (excluding soft blowing outside the furnace) is 35 minutes; soft blowing time is 10 minutes.

[0045] Continuous casting process: continuous casting speed 1.8m / min, Superheat 20℃ Specific water volume: 0.8L / kg. Distribution ratio: 32:35:19:14. Protective slag model welding wire steel protective slag. Crystallizer electromagnetic stirring control current 300A, frequency 4Hz; terminal current stirring control current 100A, frequency 10Hz. During the casting process, the large package casing time is within 3min, the middle package covering agent, the integral water nozzle is used, and the liquid level is stable during the casting process.

[0046] After the ingots came off the line, an online appearance inspection was carried out and the ingots were qualified. However, since the N content of comparative example 1 was significantly higher than that of embodiments 1 and 2 by 30-50 ppm, the final rolled material tensile strength of this solution was 560-575 MPa, 50-60 MPa higher than that of embodiments 1 and 2. The customer had a problem with the material being too hard during the drawing process. Analysis showed that due to the high N content, aging hardening occurred during the drawing deformation process, resulting in material fracture.

[0047] The nitrogen and oxygen contents and performance test results of the products of each embodiment and comparative example are shown in Table 2. According to GB-T228.1-2021 Metal Material Tensile Test Part 1-Room Temperature Test Method.

[0048] Table 2 Nitrogen, oxygen content and performance of each embodiment and comparative example

[0049]

[0050] The underlined data above do not meet the requirements of the present invention.

[0051] The description of the above embodiments is to facilitate the understanding and use of the invention by those skilled in the art. It is obvious that those skilled in the art can easily make various modifications to these embodiments and apply the general principles described herein to other embodiments without creative work. Therefore, the present invention is not limited to the above embodiments, and 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 within the protection scope of the present invention.

Claims

1. A low carbon, low nitrogen content steel for welding wire, characterized in that: The low carbon and low nitrogen content welding wire steel comprises the following components in percentage by mass: C: 0.06-0.09%, Si: 0.80-0.90%, Mn: 1.40-1.60%, P < 0.015%, S: 0.007-0.015%, Cr ≤ 0.10%, Ni: ≤ 0.10%, Cu ≤ 0.10%, Ca ≤ 0.0015%, Ti ≤ 0.02%, Mo ≤ 0.05%, Al ≤ 0.010%, O ≤ 0.0035%, N ≤ 0.0045%, the rest are Fe and unavoidable impurities.

2. A method for producing low-carbon, low-nitrogen content welding wire steel according to claim 1, characterized in that: The production method comprises the following process flow: Converter steelmaking—LF refining—continuous casting of billets.

3. The method for producing low-carbon, low-nitrogen content welding wire steel according to claim 2, characterized in that: The converter steelmaking uses molten iron and scrap steel; the chemical composition of the molten iron is required to be Si≤0.70%, P≤0.12%; the scrap steel used has a sulfur content of ≤0.07% and a phosphorus content of ≤0.40%.

4. The method for producing low-carbon, low-nitrogen content welding wire steel according to claim 2, characterized in that: The steel-tapping time is controlled at 4-4.5min; in the process of steel-tapping from the converter, 0.4-0.85kg / ton of steel of calcium carbide, 12kg / ton of steel of ferrosilicon, 17kg / ton of steel of low-carbon ferromanganese and 3.3-4.3kg / ton of steel of slag-forming agent lime are added; the final composition of steel-tapping from the converter is: C: 0.04-0.06%, P≤0.015%.

5. The method for producing low-carbon, low-nitrogen content welding wire steel according to claim 2, characterized in that: The LF refining: During the refining process, the argon flow rate is adjusted to be controlled at 100-120 L / min, and the outlet temperature is 1550-1590°C.

6. The method for producing low-carbon, low-nitrogen content welding wire steel according to claim 2, characterized in that: Add 2.5-4.3 kg / ton of steel lime and 2-3.5 kg / ton of steel fluorite to the refining bag; add ferrosilicon powder for deoxidation and 0.5-0.85 kg / ton of steel calcium carbide during refining; and carry out diffusion deoxidation throughout the refining process.

7. The method for producing low-carbon, low-nitrogen content welding wire steel according to claim 2, characterized in that: During refining, the white slag retention time is ≥15min, the LF refining cycle is ≥40min; the soft blowing time is ≥15min.

8. The method for producing low carbon and low nitrogen content welding wire steel according to claim 2, characterized in that: During the continuous casting process, the continuous casting speed is 1.6-1.7 m / min, the superheat is 25-35°C, the specific water volume is 0.7-0.8 L / kg, and the distribution ratio is 32:35:19:

14.

9. The method for producing low-carbon, low-nitrogen content welding wire steel according to claim 2, characterized in that: During continuous casting, the crystallizer electromagnetic stirring control current is 300A and the frequency is 4Hz; the terminal current stirring control current is 100-150A and the frequency is 10Hz.

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