A zirconium and boron containing welding wire steel and vacuum induction melting method thereof

Abstract

The application provides a zirconium-containing and boron-containing welding wire steel and a vacuum induction melting method thereof, and belongs to the technical field of welding wire steel smelting. The method is characterized by multiple alloying elements (containing zirconium and boron), narrow composition window, and strict requirements on gas and impurity content. The method is characterized by the following steps: vacuum induction melting is combined with precise feeding in stages, at least two vacuum refining and inert gas protection atmosphere refining processes are strictly controlled, electromagnetic stirring, online sampling analysis and composition dynamic supplementing are matched in each refining stage, and the deep degassing of molten steel and the precise control of composition are effectively realized. The technical problem that the accurate control of the narrow window composition of the zirconium-containing and boron-containing welding wire steel is cooperated with the realization of ultrahigh purity is solved by the process. The gas content and harmful elements of the obtained product are reduced to an extremely low level, and the comprehensive performance is excellent.

Description

Technical Field

[0001] This invention relates to the field of welding wire steel smelting technology, specifically to a zirconium- and boron-containing welding wire steel and its vacuum induction melting method. Background Technology

[0002] With the rapid development of shipbuilding engineering and offshore platforms towards larger and higher strength, the performance requirements for welding materials are becoming increasingly stringent. Welding wire steel used for welding critical ship structures must simultaneously possess high strength, excellent low-temperature impact toughness, good crack resistance, and fatigue resistance in its deposited metal. To meet these requirements, welding wire steel must simultaneously achieve precise control of both "ultra-high purity" and "extremely narrow composition window."

[0003] Both boron and zirconium are highly chemically reactive elements. Boron is easily oxidized at high temperatures, has extremely low solid solubility, and has a very narrow addition window. Zirconium has a very strong affinity for oxygen, resulting in severe burn-off under conventional smelting conditions. Therefore, precisely controlling the content of these two elements within their respective extremely narrow target ranges and ensuring their stable metallurgical effects places extremely high demands on smelting technology.

[0004] Currently, the industrial production of low-alloy welding wire steel mostly adopts the traditional process route of "electric arc furnace (EAF) or converter primary refining → ladle refining (LF / VD)". However, this process route has inherent limitations in producing the aforementioned high-end welding wire steel with ultra-high purity and extremely narrow compositional window containing zirconium and boron. On the one hand, refining under non-vacuum or low-vacuum conditions has limited control over hydrogen and nitrogen, and the molten steel is repeatedly exposed to air at multiple stages, making it difficult to stabilize the gas content within the target range. On the other hand, reactive elements such as zirconium, boron, and titanium are usually added in the later stages of LF refining. At this time, there is still a high concentration of dissolved oxygen in the molten steel, and the addition process cannot avoid contact with air, resulting in a large amount of alloying elements being oxidized and burned off, leading to large fluctuations in yield and a final composition that deviates significantly from the target value. In addition, this process route lacks means for monitoring and dynamically adjusting the composition during the smelting process, making it impossible to monitor and accurately compensate for the loss of alloying elements in real time. The first-pass yield of the final product is usually less than 80%.

[0005] Existing technology, Chinese patent CN118957395A, entitled "A Melting and Purification Method for High-Strength and Tough Welding Wire Steel," discloses a new process combining traditional techniques with vacuum induction melting. Its core process flow is "converter steelmaking → LF furnace refining → vacuum induction melting furnace degassing → continuous casting." While this method introduces vacuum induction melting to improve purity, it still has significant shortcomings.

[0006] (1) The process is crude, resulting in low alloy element recovery. The comparative document describes a process where oxygen is blown into the converter molten steel to perform a redox reaction and remove some impurities. After oxygen blowing, the residual oxygen concentration in the molten steel is high. Subsequently, metal powders such as chromium, molybdenum, manganese, silicon, nickel, copper, arsenic, niobium, and magnesium are added to the molten steel. Under high-temperature conditions, these metal powders are prone to oxidation reactions with the high concentration of oxygen in the molten steel, generating metal oxides. Among them, active metals with strong reducing properties, such as manganese, silicon, and magnesium, are more easily and severely oxidized, leading to a significant decrease in the recovery rate of alloy elements. This not only wastes raw materials and increases production costs, but also, because the actual recovery of alloy elements deviates from the amount added, the composition of the molten steel is prone to exceeding the control range, increasing the risk of unqualified or even scrapped molten steel.

[0007] (2) The alloying element addition process is unreasonable. The comparative document adds alloying element powders such as chromium, molybdenum, manganese, silicon, nickel, copper, arsenic, niobium and magnesium to the converter for alloying smelting at a temperature of 1600-1800℃. Due to the strong thermal convection and thermal radiation on the surface of the high-temperature molten steel, significant aerodynamic resistance is generated on the powder particles near the molten steel surface. When the metal powder is added, some powder is swept up by the rising hot airflow before it enters the molten steel, forming "dust" and failing to effectively enter the molten steel. This not only causes the loss of alloying elements, but also pollutes the smelting environment.

[0008] (3) Lack of dynamic composition control mechanism. The process route (converter steelmaking → LF furnace refining → vacuum degassing → continuous casting) does not have an intermediate sampling and analysis step, making it impossible to monitor the composition of molten steel in real time during the smelting process. In actual production, when alloy powder is added to molten steel at 1600-1800℃, some powder is lost due to dust generated by the impact of hot airflow; even if the powder enters the molten steel, the alloying elements are easily reacted with the high concentration of oxygen in the steel to form oxides and float into the slag phase. Because the loss of the above elements cannot be grasped in time, it is difficult to accurately control and dynamically compensate for the composition, which can easily lead to the final molten steel composition deviating from the target requirements or even being scrapped.

[0009] (4) There is a risk of secondary contamination of molten steel. In the comparative document, refined molten steel needs to be transferred to a vacuum induction melting furnace for deep deoxidation and degassing treatment, and then transferred to a continuous casting machine via an intermediate ladle to prepare high-strength and high-toughness welding wire steel. In this process, the molten steel after vacuum treatment needs to leave the closed environment of the vacuum furnace and be exposed to the atmosphere again, which destroys the closed conditions of vacuum smelting and significantly increases the risk of secondary oxidation and contamination of the molten steel.

[0010] In summary, the process scheme disclosed in the prior art is insufficient to achieve deep and stepwise removal of gases and inclusions, and the gas content of its welding wire steel products cannot meet the control range required for high-end welding wire steel. Furthermore, this scheme lacks a process monitoring mechanism for steel composition, exhibits poor stability in narrow-window composition control, and fails to establish a dynamic compensation model and closed-loop feedback mechanism for easily burnable and volatile elements. Therefore, this existing technology cannot solve the core technical challenge of synergistic control of ultra-high purity and extremely narrow composition window faced by traditional smelting processes in the production of high-end welding wire steel. Summary of the Invention

[0011] The purpose of this invention is to provide a zirconium- and boron-containing welding wire steel and its vacuum induction melting method. Through a specific melting process, the composition range of the welding wire steel is narrowly controlled and the purity requirement is high. In particular, boron (B) and zirconium (Zr) are added and their contents are precisely controlled. Through the synergistic effect of oxide metallurgy and microalloying, the microstructure of the weld is precisely controlled, thus solving the contradiction that it is difficult to achieve both high strength and excellent toughness.

[0012] To achieve the above objectives, the present invention proposes the following technical solution:

[0013] A zirconium- and boron-containing welding wire steel has the following chemical composition by weight percentage:

[0014] C 0.02%~0.032%, Mn 1.25%~1.40%, Ti 0.07%~0.14%, Cr 0.14%~0.21%, Ni 3.25%~3.35%, Mo 0.14%~0.21%, Al 0.015%~0.045%, Zr 0.025%~0.045%, B 0.0035%~0.0055%, Si≤0.1%, V≤0.01%, Nb≤0.01%, S≤0.005%, P≤0.005%, O≤0.002%, N≤0.003%, H≤0.0003%, balance Fe and unavoidable impurities;

[0015] The method for preparing the welding wire steel includes the following steps:

[0016] At least two vacuum refining processes and at least one inert gas protective atmosphere refining process are carried out, and in-furnace sampling and analysis are performed during the refining process. The composition is dynamically compensated and adjusted based on the sampling and analysis results. The sampling and analysis includes at least the full melt sample analysis after the first vacuum refining and the furnace sample analysis before the first inert gas protective atmosphere refining.

[0017] Nickel, carbon, chromium, molybdenum and iron are added during the initial feeding; titanium, aluminum and zirconium are added after the first vacuum refining; and manganese and boron are added under the inert gas protective atmosphere after the last vacuum refining.

[0018] On the other hand, the present invention also provides a method for preparing zirconium- and boron-containing welding wire steel, comprising the following steps:

[0019] (1) Furnace pretreatment;

[0020] (2) Add the first part of the raw materials into the vacuum induction melting furnace and distribute the materials according to the set method;

[0021] (3) Vacuuming and stepped power supply to heat up the first part of the raw materials to melt and perform the first vacuum refining to obtain the first molten steel. Take a full melt sample from the fully melted first molten steel for composition analysis.

[0022] The first part of the raw materials consists of carbon particles, electrolytic nickel, metallic chromium, industrial pure iron, and molybdenum bars.

[0023] (4) Based on the analysis results of the full melt sample, a second portion of raw materials is added under vacuum conditions to perform a second vacuum melting to obtain a second molten steel;

[0024] The second part of the raw materials consists of sponge zirconium, aluminum granules, and sponge titanium;

[0025] (5) After the second vacuum refining is completed, an inert gas is introduced into the vacuum induction melting furnace, and a third part of raw materials is added to the second molten steel under the protective atmosphere formed by the inert gas to carry out the third inert atmosphere refining to obtain the third molten steel. A sample is taken from the third molten steel for composition analysis.

[0026] The third part of the raw materials consists of electrolytic manganese and ferroboron;

[0027] (6) Determine whether to perform composition fine-tuning based on the analysis results of the pre-furnace sample:

[0028] If fine-tuning is required, the amount of material to be added is calculated based on the analysis results of the furnace front sample and the material addition operation is completed. After material addition, the fourth inert atmosphere refining is carried out, and the fourth molten steel is obtained after the process.

[0029] If no fine-tuning is required, the third molten steel is used as the fourth molten steel, and the process proceeds directly to the next step.

[0030] (7) Take a sample from the fourth molten steel for composition analysis, and perform electric casting at the furnace temperature to obtain the welding wire steel product.

[0031] As a preferred embodiment of the present invention, the furnace washing pretreatment step includes:

[0032] Before melting the welding wire steel, a complete melting and casting process is carried out using high-purity iron material to dissolve and remove impurity elements adsorbed on the inner wall of the crucible in the vacuum induction melting furnace.

[0033] As a preferred embodiment of the present invention, the fabric application method includes:

[0034] First, the electrolytic nickel is laid flat at the bottom of the crucible of the vacuum induction melting furnace, then all the carbon particles are added, followed by all the metallic chromium, all the molybdenum bars and all the industrial pure iron, and the furnace charge height is controlled to the crucible slag line position.

[0035] As a preferred embodiment of the present invention, the vacuuming and stepped power supply heating includes:

[0036] The vacuum induction melting furnace was evacuated to ≤10 Pa;

[0037] The power output gradually increases from 100 kW to 400 kW, and then to 500-800 kW to enter the chemical processing stage.

[0038] As a preferred embodiment of the present invention, the first vacuum refining includes:

[0039] Control the temperature of the molten steel at 1610±20℃, start the three-phase electromagnetic stirring, and stir for 4 to 10 minutes. After stirring, take the full melt sample and send it to a heat preservation power of 250 to 300kW for refining for 40 to 50 minutes.

[0040] As a preferred embodiment of the present invention, the second vacuum refining includes:

[0041] The temperature of the molten steel is controlled at 1600±20℃, and three-phase electromagnetic stirring is carried out for 4 to 10 minutes. After stirring, the steel is sent to a heat preservation power of 250 to 300 kW for refining for 30 to 40 minutes.

[0042] As a preferred embodiment of the present invention, both the third inert atmosphere refining and the fourth inert atmosphere refining include:

[0043] Adjust the temperature of the molten steel to 1590±20℃ and perform three-phase electromagnetic stirring for 4 to 10 minutes. After stirring, send it to a heat preservation power of 250 to 300 kW for refining for 20 to 30 minutes.

[0044] As a preferred embodiment of the present invention, the electrified casting includes:

[0045] The tapping temperature is 1630±15℃, the tapping speed is 300~400kg / min, the power supply is maintained at 360kW during casting, and the casting process is carried out in a protective atmosphere formed by inert gas and in a sealed state of equipment.

[0046] As a preferred embodiment of the present invention, the purity requirements of the raw materials used for smelting are as follows: carbon particles C≥99.5%, electrolytic manganese Mn≥99.8%, electrolytic nickel Ni≥99.95%, metallic chromium Cr≥99.3%, industrial pure iron Fe≥99.9%, molybdenum bars Mo≥99.9%, boron iron with B content of 17.5%, sponge zirconium Zr≥99.5%, aluminum particles Al≥99.5%, and sponge titanium Ti≥99.5%.

[0047] As can be seen from the above technical solutions, the technical solution of the present invention provides a zirconium- and boron-containing welding wire steel and its vacuum induction melting method. The welding wire steel has a narrow composition range and high purity requirements. By controlling the C content in an ultra-low carbon range of 0.02% to 0.032% and combining it with a high Ni (3.25% to 3.35%) alloying design, the welding wire steel obtains excellent low-temperature impact toughness while ensuring the strength of the deposited metal, and can meet the service requirements at -60℃ or even lower temperatures. Meanwhile, by simultaneously introducing Zr (0.025%–0.045%) and B (0.0035%–0.0055%) into the steel and precisely controlling their content window, the two can produce a synergistic effect during the welding process. The Zr-Ti-O composite oxide formed by Zr pins the grain boundaries and inhibits the coarsening of austenite grains, while B segregates at the grain boundaries and inhibits the nucleation of proeutectoid ferrite. Together, they promote the nucleation of a large number of acicular ferrites within the grains, thus achieving both high strength and high toughness in the weld metal. This effectively solves the technical problem of coarsening of the microstructure and decrease in toughness in the heat-affected zone under high heat input welding conditions.

[0048] Compared with existing technologies, this invention employs a vacuum induction melting process, involving multiple refining processes under different conditions (first vacuum refining, temperature 1610±20℃, duration 40-50 min; second vacuum refining, temperature 1600±20℃, duration 30-40 min; third inert gas protective atmosphere refining, temperature 1590±20℃, duration 20-30 min; fourth inert gas protective atmosphere refining, temperature 1590±20℃, duration 20-30 min), four electromagnetic stirrings, and three in-furnace sampling analyses. These operations ensure that the molten steel achieves gas removal, inclusion removal, uniform composition, and effective melting. The key to achieving pure steel smelting (S≤0.005%; P≤0.005%; O≤0.002%; N≤0.003%; H≤0.0003%) and extremely narrow composition control (C±0.006%, Ti±0.035%, Mo±0.035%, Al±0.015%, Zr±0.01%, B±0.01%) is to achieve the same. In addition, the coordinated control of the tapping temperature of 1630±15℃ and the tapping speed of 300~400kg / min is also an important control link that cannot be ignored in the welding wire steel of this invention. Finally, high-quality welding wire steel vacuum ingots are cast, which lays a good foundation for subsequent hot working.

[0049] It should be understood that all combinations of the foregoing concepts and the additional concepts described in more detail below can be considered part of the inventive subject matter of this disclosure, provided that such concepts do not contradict each other.

[0050] The foregoing and other aspects, embodiments, and features of the teachings of the present invention will be more fully understood from the following description in conjunction with the accompanying drawings. Other additional aspects of the invention, such as features and / or beneficial effects of exemplary embodiments, will become apparent from the following description or may be learned through practice of specific embodiments according to the teachings of the present invention. Attached Figure Description

[0051] The accompanying drawings are not drawn to scale. In the drawings, each identical or nearly identical component shown in the various figures may be denoted by the same reference numeral. For clarity, not every component is labeled in each figure. Embodiments of various aspects of the invention will now be described by way of example and with reference to the accompanying drawings, wherein:

[0052] Figure 1 This is a process flow diagram of an embodiment of the present invention. Detailed Implementation

[0053] To make the objectives, technical solutions, and advantages of the embodiments of the present invention clearer, the technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some, not all, of the embodiments of the present invention. All other embodiments obtained by those skilled in the art based on the described embodiments of the present invention without creative effort are within the scope of protection of the present invention. Unless otherwise defined, the technical or scientific terms used herein should have the ordinary meaning understood by those skilled in the art to which this invention pertains.

[0054] The terms "first," "second," and similar words used in the specification and claims of this patent application do not indicate any order, quantity, or importance, but are merely used to distinguish different components. Similarly, unless the context clearly indicates otherwise, the singular forms of "an," "a," or "the," etc., do not indicate a quantity limitation, but rather indicate the presence of at least one. Terms such as "comprising" or "including" mean that the element or object preceding "comprising" encompasses the features, wholes, steps, operations, elements, and / or components listed following "comprising" or "including," and do not exclude the presence or addition of one or more other features, wholes, steps, operations, elements, components, and / or collections thereof. Terms such as "upper," "lower," "left," and "right" are used only to indicate relative positional relationships; when the absolute position of the described object changes, the relative positional relationship may also change accordingly.

[0055] The zirconium- and boron-containing welding wire steel of this invention has the following chemical composition by weight percentage: C 0.02%–0.032%, Mn 1.25%–1.40%, Ti 0.07%–0.14%, Cr 0.14%–0.21%, Ni 3.25%–3.35%, Mo 0.14%–0.21%, Al 0.015%–0.045%, Zr 0.025%–0.045%, B 0.0035%–0.0055%, Si≤0.1%, V≤0.01%, Nb≤0.01%, S≤0.005%, P≤0.005%, O≤0.002%, N≤0.003%, H≤0.0003%, with the balance being Fe and unavoidable impurities.

[0056] In the above composition design, the carbon content is controlled at an extremely low level (0.02%–0.032%) to ensure that the weld metal has good low-temperature toughness and crack resistance, and to avoid increased sensitivity to cold cracking due to excessive carbon content. The Ni content is designed to be 3.25%–3.35%, which is a relatively high level, to ensure that the weld metal can maintain excellent low-temperature impact toughness in extremely cold environments (such as -60℃ or even lower). The addition of Ti is used to form TiN and Ti-O precipitates, providing nucleation sites for acicular ferrite. The addition windows of Zr (0.025%–0.045%) and B (0.0035%–0.0055%) are extremely narrow. Under their synergistic effect, Zr forms Zr-Ti-O composite oxides to pin grain boundaries, and B segregates at grain boundaries to inhibit the formation of proeutectoid ferrite. Together, they promote the nucleation of a large number of acicular ferrites within the grains, thereby achieving a balance between high strength and high toughness in the weld metal. Meanwhile, the extreme requirements for gas content (O, N, H) and harmful impurities (S, P, V, Nb) reflect the pursuit of ultra-high purity in this embodiment.

[0057] To meet the dual requirements of precise component control and ultra-high purity, this invention also provides a complete vacuum induction melting process, the specific steps of which are as follows.

[0058] (1) Raw material selection and control.

[0059] The purity of the raw materials used in smelting directly affects the purity of the final steel grade and the accuracy of composition control. In some specific implementations, the following high-purity raw materials are selected: carbon particles (C≥99.5%), electrolytic manganese (DJMn-A, Mn≥99.8%), electrolytic nickel (Ni≥99.95%), metallic chromium (JCr99A, Cr≥99.3%), industrial pure iron (YT1, Fe≥99.9%), molybdenum bars (Mo-1, Mo≥99.9%), ferroborone (B ≥17.5%), sponge zirconium (Zr≥99.5%), aluminum particles (Al≥99.5%), and sponge titanium (MHTi-100, Ti≥99.5%). Among these raw materials, except for ferroborone which is an intermediate alloy, the purity of the other metal raw materials is expressed as the mass percentage of their main elements.

[0060] Among the selected raw materials, highly pure raw materials were used for reactive metals (such as Ti, Zr, Al, and Mn) to reduce the introduction of foreign inclusions. In addition, boron was added in the form of ferroborone alloy instead of pure boron to avoid the difficulty of rapid melting of pure boron in molten steel due to its high melting point (approximately 2300℃). Ferroborone alloy has a lower melting point, which is beneficial for the rapid homogenization of boron in molten steel.

[0061] (2) Equipment selection.

[0062] This embodiment uses a vacuum induction melting furnace for melting. To ensure the stability of the vacuum atmosphere and the precise control of the molten steel composition during the melting process, the melting equipment meets the following requirements: the leakage rate of the vacuum induction melting furnace melting chamber is less than 1.5 Pa / min, and the ultimate vacuum value of the melting chamber is less than 2 Pa.

[0063] Leakage rate is a key indicator for measuring the sealing performance of a vacuum system. If the leakage rate is too high, outside air will continuously seep into the melting chamber, which will not only damage the vacuum level, but also cause the molten steel to continuously oxidize and absorb nitrogen at high temperatures, making it impossible to meet the limit requirements for gas content in this embodiment.

[0064] In addition, the smelting equipment must have an inert gas (e.g., argon) atmosphere protection function and a three-phase electromagnetic stirring function. Argon atmosphere protection is used to provide a local inert environment when adding easily oxidizable alloying elements to avoid element burn-off; three-phase electromagnetic stirring is used to accelerate the homogenization of the steel composition and temperature, and promote the collision growth and flotation removal of non-metallic inclusions.

[0065] (3) Pure iron furnace washing pretreatment.

[0066] Before smelting the target steel grade, a pretreatment operation of pure iron furnace washing is first carried out. Specifically, a complete smelting and casting process is carried out using high-purity iron (purity ≥ 99.9%). That is, after the high-purity iron is melted, all processes such as refining, stirring, and casting are completed according to conventional operations.

[0067] The crucibles in vacuum induction melting furnaces are mostly made of magnesium aluminum spinel or corundum. Over long-term use, their inner walls absorb or retain impurities such as Nb and V from the molten steel from the previous furnace. These impurities gradually dissolve and release into the molten steel during subsequent melting of the target steel grade, contaminating the steel. Because the embodiments of this invention have extremely strict requirements for the content of Nb and V (both ≤0.01%), conventional furnace cleaning methods are insufficient to completely remove them. This invention uses high-purity iron material for a complete melting process. Utilizing the scouring and dissolving effect of the high-temperature molten iron, the impurities adsorbed on the inner wall of the crucible can be effectively carried out and discharged with the molten iron during pouring. This ensures that trace impurities such as Nb and V in the finished steel meet the minimum requirements from the source, laying the foundation for ultra-high purity.

[0068] (4) Adding and spreading materials.

[0069] The order of charging and the method of material distribution have a significant impact on melting efficiency and the yield of alloying elements. In this embodiment of the invention, the charge is added to the crucible of the vacuum induction melting furnace in the following specific order.

[0070] First, lay all the electrolytic nickel evenly at the bottom of the crucible; then, add all the carbon granules on top of the nickel; next, add all the metallic chromium, all the molybdenum bars, and all the industrial pure iron in sequence. Finally, control the charge height to the slag line of the crucible.

[0071] The above-mentioned feeding sequence is designed with clear process considerations: Electrolytic nickel is placed at the bottom of the crucible because its high melting point (1455℃) and relatively mild scouring and erosion effect on the crucible bottom create a protective "bottoming" layer. This prevents subsequently added carbon particles from directly contacting the crucible bottom during the initial high-temperature melting stage, thus avoiding carburizing and damage to the crucible. Adding carbon particles above the nickel layer ensures sufficient contact between the carbon and molten steel in the early melting stage, promoting the smooth progress of the subsequent carbon-oxygen reaction and facilitating early degassing. Metallic chromium, molybdenum bars, and industrial pure iron, forming the main framework of the molten steel, are placed on top of the carbon particles and gradually dissolve during the melting process.

[0072] If there is any remaining charge that cannot be loaded into the crucible at once (due to volume limitations), it can be added to the crucible from the top charging system via a charging bucket under vacuum during the subsequent melting period.

[0073] However, it should be noted that easily oxidized or volatile alloying elements such as sponge titanium, sponge zirconium, aluminum granules, electrolytic manganese, and boron should not be added at this stage, but rather in stages during the later stages of refining. For example, sponge titanium, sponge zirconium, and aluminum granules are added after the first refining stage, while metallic manganese and ferroboron are added under an inert atmosphere after the second refining stage.

[0074] (5) Vacuuming and stepped heating melting.

[0075] After the material is added, close the furnace door of the melting chamber and start the vacuum system to evacuate the melting chamber, so that the crucible and the material inside the melting chamber are in a vacuum environment. Once the vacuum degree of the melting chamber reaches 10 Pa or below, start powering on to raise the temperature.

[0076] The power supply method adopts a stepped power increase, specifically, it can be gradually increased from 100 kW to 400 kW to enter the formal material preparation stage.

[0077] An initial high vacuum of 10 Pa or less provides a strong thermodynamic driving force for all subsequent degassing reactions. Stepwise heating can gently and thoroughly remove water vapor adsorbed on the furnace charge and crucible surface, preventing direct high temperature from causing rapid decomposition of water vapor and hydrogenation of the molten steel (H2O→H2↑+[O]). At the same time, gentle preheating helps to temporarily heal microcracks in the furnace lining and reduce steel penetration and erosion. This not only improves the safety of equipment and personnel during production but also extends the service life of the furnace lining.

[0078] (6) Chemical processing and first refining.

[0079] Maintaining the vacuum state described above, further increase the power from 400 kW to 500-800 kW to rapidly melt the furnace charge under high vacuum. If there is any remaining charge during the charging process, it can be added to the crucible through the top charging system via a charging bucket during the melting period under vacuum.

[0080] After confirming that the molten steel has completely melted, control the temperature of the molten steel within the range of 1610±20℃, and start the three-phase electromagnetic stirring for 4 to 10 minutes. Electromagnetic stirring not only rapidly homogenizes the temperature and composition of the molten steel, but also promotes the upward movement of bubbles and inclusions inside the melt.

[0081] After stirring, the electromagnetic stirrer is turned off, and a full melt sample is taken for spectral analysis. The analysis results of this first full melt sample represent the true composition of the molten steel in its initial state (i.e., the actual yield of each element in the furnace charge), and are the basic data for subsequent alloy addition calculations. After sampling, the holding power is increased to 250–300 kW to maintain the molten steel temperature and the first refining stage begins, lasting 40–50 minutes.

[0082] During this stage, the high vacuum environment (<10 Pa) and high-temperature molten steel (1610±20℃) provide extremely favorable thermodynamic conditions for the carbon-oxygen reaction. The residual dissolved oxygen in the molten steel reacts with carbon: [C] + [O] = CO↑. The CO bubbles generated continuously rise to the surface and are removed by the vacuum system. This process is called "carbon deoxidation," and its advantage lies in the fact that the deoxidation products are gaseous, unlike silicon or aluminum deoxidation which generate solid oxide inclusions in the molten steel. Simultaneously, the rising bubbles "carry" dissolved hydrogen and nitrogen atoms (i.e., the bubble pump effect) as they pass through the molten steel, promoting the removal of H2 and N2. Furthermore, existing non-metallic inclusions in the molten steel are also adsorbed by the rising bubbles and carried to the slag surface. Therefore, the first refining stage is the core step in achieving deep deoxidation, dehydrogenation, denitrification, and removal of non-metallic inclusions.

[0083] (7) Alloying and two refining processes.

[0084] After the first refining process, based on the analysis results of the full melt sample and the target composition requirements, the weight of the main alloying elements to be added is calculated. These main alloys include sponge titanium, aluminum granules, sponge zirconium, metallic manganese, and ferroborone. These main alloys are added to the molten steel in two stages. Specifically, the first three main alloys are added under vacuum conditions in the first stage; the second stage, to improve the yield of metallic manganese and boron, is added under a protective atmosphere formed by an inert gas (such as argon). The formula for calculating the weight of the alloying elements to be added is as follows:

[0085] The weight of the alloying element to be added = (theoretical furnace charge weight × target value of alloying element composition - real-time molten steel weight × current alloy composition value) / (the yield of the alloying element × the purity of the alloying element).

[0086] The real-time weight of the molten steel is based on the reading from the weighing system. The current alloy composition value is the analytical value of the entire melt sample, and the yield is determined based on previous experience data for similar steel grades. Under vacuum conditions (maintaining a vacuum level of ≤10 Pa in the melting chamber), sponge titanium, aluminum granules, and sponge zirconium are added to the molten steel through the top hopper. After the added alloys have melted completely, a three-phase electromagnetic stirrer is started for 4–10 minutes to ensure that the alloying elements are fully homogenized in the molten steel.

[0087] After the metals such as sponge titanium, aluminum particles and sponge zirconium added under vacuum are melted and cleared, the temperature of the molten steel is controlled within the range of 1600±20℃, and three-phase electromagnetic stirring is carried out for 4 to 10 minutes. After stirring, the heat preservation power of 250 to 300kW is sent to carry out the second refining, which lasts for 30 to 40 minutes.

[0088] After the second refining is completed, high-purity argon gas is introduced into the melting chamber to 25000 Pa. Under this protective atmosphere, the calculated weight of metallic manganese blocks and ferroboron is added through the feeding system. After the melt is clear, the three-phase electromagnetic stirring is started immediately and stirred for 4 to 10 minutes. After stirring is completed, a sample is taken from the furnace. Then the steel temperature is adjusted to 1590±20℃ and 250 to 300 kW of heat preservation power is supplied for the third refining, which lasts for 20 to 30 minutes.

[0089] In this step, the alloying process is carried out in two steps. First, non-volatile metals (such as sponge titanium, aluminum granules, and sponge zirconium) are added in a vacuum environment, followed by volatile metals (such as manganese and boron). This operation not only removes the gas generated when the non-volatile metals are added to the molten steel, but also creates an inert gas protective environment by purging with argon before adding the volatile metals, which can greatly reduce the secondary oxidation of the molten steel caused by adding a large amount of volatile metals. The pressure of 25,000 Pa provides sufficient protection and maintains an appropriate static pressure on the surface of the molten pool, avoiding excessive boiling. During the alloying process, three-phase electromagnetic stirring is carried out twice, which not only accelerates the homogenization of the composition of the molten steel and prepares it for subsequent sampling, but also promotes the escape of gases during the melting of alloying elements, and is also conducive to the flotation and removal of inclusions.

[0090] (8) Fine-tuning of ingredients.

[0091] Based on the spectral analysis results of the furnace sample and the target element values ​​for the final smelting, a decision is made regarding whether to fine-tune the various elements in the molten steel (such as adding a trace amount of easily burnable Ti). If fine-tuning is required, the weight of the element to be added is calculated using the aforementioned formula. After the addition operation is completed, three-phase electromagnetic stirring must be performed immediately for 4–10 minutes. Then, the molten steel temperature is adjusted to 1590±20℃, and a holding power of 250–300 kW is applied for a fourth refining process for 10–20 minutes. This operation ensures that the added metal is promptly melted into the molten steel, preventing additional burn-off caused by a small amount of added metal floating on the surface. The entire material addition process achieves closed-loop correction of the molten steel composition at the ppm level.

[0092] (9) Final temperature adjustment and energized casting.

[0093] The temperature of the molten steel was raised to 1630±15℃, and the final sample after the furnace was taken as the basis for arbitration. Then, under the protection of argon atmosphere, the energized casting was carried out.

[0094] Electric casting maintains the tumbling of molten steel within the furnace lining to a certain extent until it is poured out, effectively reducing macroscopic and microscopic segregation, promoting gas overflow and inclusion flotation, and facilitating steel purification. The high superheat ensures good fluidity of the molten steel during its flow through the long tundish (3.85 m) and during mold filling. After passing through the tundish, the molten steel is finally poured into the mold and solidifies to form an ingot. The entire casting process is carried out under an argon atmosphere, with the equipment in a sealed state, effectively preventing contact between the molten steel and oxygen in the air during casting, laying the foundation for obtaining high-quality ingots.

[0095] Example 1

[0096] 1. [Smelting Process Control]

[0097] 1) Raw material selection: carbon particles (C: 99.5%), electrolytic manganese (DJMn-A, Mn: 99.8%), electrolytic nickel (Ni: 99.96%), metallic chromium (JCr99A, Cr: 99.3%), industrial pure iron (YT1, Fe: 99.93%), molybdenum bars (Mo-1, Mo: 99.9%), ferroboron (B17.5%), aluminum particles (Al: 99.6%), sponge zirconium (Zr 99.7%), sponge titanium (MHTi-100, Ti: 99.5%).

[0098] 2) Requirements for smelting equipment: To ensure that the smelting atmosphere is in a good vacuum state, the leakage rate of the smelting chamber of the vacuum induction smelting furnace is 1.2 Pa / min; the ultimate vacuum value of the smelting chamber is 2 Pa; to ensure effective control of the steel composition, the smelting equipment must have inert gas argon atmosphere protection function and three-phase electromagnetic stirring function.

[0099] 3) Charging and Distribution Principles: When adding furnace charge to the crucible of the vacuum induction melting furnace, the following order must be followed: After laying all the electrolytic nickel flat at the bottom of the crucible, add all the carbon granules, then all the metallic chromium, all the molybdenum bars, and all the industrial pure iron. Finally, control the charge height to the slag line of the crucible. If there is any remaining charge, it can be added to the crucible in a vacuum state through a charging bucket during the later melting stage. Aluminum granules, sponge titanium, and sponge zirconium are added after the first refining stage; electrolytic manganese and ferroboron are added after the second refining stage.

[0100] 4) Smelting process: such as Figure 1 The process flow diagram shown first involves evacuating the melting chamber. Once the vacuum reaches 10 Pa, power is supplied at 200 kW and maintained for 1 hour. Power is then increased to 300 kW and maintained for 1 hour. Finally, power is increased to 500 kW, initiating the material preparation stage. After the molten steel is fully melted, the temperature is adjusted to 1610℃, and electromagnetic stirring is performed for 8 minutes. Following electromagnetic stirring, power is supplied at 280 kW, and a complete melt sample is taken for composition analysis. The molten steel then enters the first refining stage, lasting 50 minutes. Based on the full melt sample analysis results, elemental control parameters, actual molten steel weight, and theoretical furnace feed rate, the required weights of sponge titanium, aluminum granules, sponge zirconium, electrolytic manganese, and ferroborone are calculated.

[0101] Specifically, under vacuum conditions, metals such as sponge titanium, aluminum granules, and sponge zirconium are added. After melting and cleaning, the temperature of the molten steel is controlled within the range of 1600℃, and three-phase electromagnetic stirring is carried out for 6 minutes. After stirring, the heat preservation power of 270 kW is sent to carry out the second refining, which lasts for 35 minutes.

[0102] After the second refining is completed, high-purity argon gas is introduced into the melting chamber to 25000 Pa. Under this protective atmosphere, the calculated weight of manganese and ferroboron blocks is added through the feeding system. After the melt is clear, the three-phase electromagnetic stirring is started immediately and stirred for 4 minutes. After stirring is completed, a sample is taken from the furnace. Then the steel temperature is adjusted to 1590℃ and 270 kW of heat preservation power is supplied for the third refining, which lasts for 25 minutes.

[0103] Once the analysis results of the pre-furnace sample are available, add appropriate amounts of manganese, aluminum, and titanium. After melting and cleaning, stir for 3 minutes, then supply 270kW of heat preservation power. Take out the post-furnace sample and perform the fourth refining for 15 minutes.

[0104] Adjust the steel temperature to the tapping temperature of 1634℃, maintain the power supply at 360 kW, and carry out casting. The casting speed is controlled at 380 kg / min. When the height of the molten steel in the mold reaches three-quarters, adjust the casting speed from 380 kg / min to 200 kg / min. After the mold is completed, turn off the power. Extract the argon gas from the ingot mold chamber. Stop the evacuation when the vacuum degree reaches 100 Pa. Hold the pressure for 12 hours, then break the vacuum in the mold chamber, open it, and finally demold to obtain a vacuum ingot.

[0105] 2. [Analysis and Testing]

[0106] Table 1. Composition Analysis of Welding Wire Steel Products (%)

[0107]

[0108] The reason why the composition analysis of O, N, and H in the full melt sample and the furnace front sample in Table 1 is marked with " / " is because the full melt sample and the furnace front sample are furnace samples, which are obtained under the premise that the furnace charge has not been fully added. The composition of these two samples cannot represent the composition of the ingot, so gas detection is generally not performed. On the other hand, the furnace back sample is taken near the end of steel tapping. At this time, the furnace charge has been fully added. The composition of this furnace sample is generally used as the composition of the ingot. Therefore, composition and gas analysis of this furnace sample is required.

[0109] After the furnace was removed, the sample was subjected to inclusion detection and analysis at a magnification of 400X and a scanning area of ​​90.16 mm². 2 The test results are shown in Table 2.

[0110] Table 2 Analysis of inclusions in samples after furnace operation

[0111]

[0112] As shown in the compositional analysis data in Table 1, the contents of Ti, Zr, and B in the full melt sample are extremely low (Ti only 0.0035%, Zr only 0.0008%, B only 0.0003%), and the C content is 0.010%, all far below the target composition range. This is an expected phenomenon in the process design, because the full melt sample was collected after the first refining and before the first alloying operation. According to the smelting process, Ti, Al, Zr, Mn, and B have not yet been added at this time, and C will be further reduced through the carbon-oxygen reaction in subsequent refining before being fine-tuned and added back to the target range. The purpose of setting this sampling node is to obtain the "initial basic composition of the molten steel" to provide an accurate data benchmark for subsequent alloy addition calculations, rather than to judge the product quality of the intermediate process.

[0113] As the process progressed, the content of key elements in the furnace samples (collected after the second alloying and before the third refining) changed significantly: C increased from 0.010% to 0.024% (after minor adjustments), Ti from 0.0035% to 0.1000%, Zr from 0.0008% to 0.0160%, and B from 0.0003% to 0.0044%, all approaching their respective target ranges. This indicates that the second alloying operation successfully added key elements such as Ti, Zr, and B to the molten steel, and the argon-protected addition method effectively ensured their yield.

[0114] After the third refining and final fine-tuning, all key elements in the post-furnace sample precisely fell within the target window: C 0.028% (target 0.02%–0.032%), Ti 0.11% (target 0.07%–0.14%), Zr 0.040% (target 0.025%–0.045%), and B 0.0045% (target 0.0035%–0.0055%). Taking B as an example, its target window width is only 0.002 percentage points. In this embodiment, the measured value of 0.0045% in the post-furnace sample is precisely located in the middle of the window, with a deviation of no more than ±0.001%. This fully verifies the ability of this process to achieve precise control through a closed-loop control mechanism of "sampling → analysis → calculation → replenishment → stirring → retesting". The Mn content was slightly adjusted from 1.24% in the pre-furnace sample to 1.32% in the post-furnace sample (target 1.25%–1.40%), and the Al content was slightly adjusted from 0.034% in the pre-furnace sample to 0.031% in the post-furnace sample (target 0.015%–0.045%), both falling precisely within the target range.

[0115] Regarding the control of gaseous and impurity elements, the S content in the post-furnace sample was 0.0031% (target ≤ 0.005%), P content was 0.0028% (target ≤ 0.005%), Nb content was 0.0036% (target ≤ 0.01%), and V content was 0.0045% (target ≤ 0.01%), all far exceeding the target requirements. The O content was 0.0007% (target ≤ 0.002%), N content was 0.0028% (target ≤ 0.003%), and H content was 0.0003% (target ≤ 0.0003%), with the gas content reaching the extremely low limit. The H content precisely fell within the upper limit of the target. This was due to the pre-removal of crucible impurities by the pure iron furnace washing, the thorough removal of water vapor by the high-vacuum step heating, and the deep removal of dissolved gases by the carbon-oxygen reaction and bubble pump effect during the first refining process.

[0116] From the fully melted sample to the post-furnace sample, the evolution of molten steel from "coarse" to "refined" is clearly visible: the initial state of high impurities and low alloy content, through multi-stage vacuum refining and degassing, precise control of step-by-step alloying, multiple electromagnetic stirring homogenization processes, and closed-loop composition fine-tuning, is finally transformed into high-quality finished steel where each element precisely hits the narrow window target and gas and impurities reach extremely low values. This process fully demonstrates the effectiveness and reliability of the process system of this invention.

[0117] As can be seen from the inclusion analysis results in Table 2, at 90.16 mm 2 Within the scanned area, a total of 1453 inclusions were detected. In terms of size distribution, 1382 inclusions were in the 1–5 μm range, accounting for approximately 95% of the total; 69 inclusions were in the 5–10 μm range, accounting for approximately 4.7%; only 2 inclusions were in the 10–15 μm range, accounting for approximately 0.14%; and there were no inclusions above the 15 μm range.

[0118] The aforementioned size distribution characteristics directly reflect the process effects of this invention. Firstly, the vast majority of inclusions are smaller than 5 μm, thanks to the effective removal of large inclusions by the bubble pump effect of the carbon-oxygen reaction during vacuum refining, and the promoting effect of electromagnetic stirring on the collisional growth and flotation of inclusions. Secondly, the remaining inclusions are mainly TiS (704), elemental Ti (595), and TiS+MnS composite inclusions (135), all of which are Ti-containing inclusions originating from the sponge titanium added during the first alloying. Fine, dispersed TiS and TiN particles can act as heterogeneous nucleation sites for acicular ferrite in steel, playing a positive role in improving the weld microstructure and should ideally be retained in the steel; however, large TiS and TiN inclusions (>10 μm) are detrimental to toughness and need to be removed during the refining process. In this embodiment, only two inclusions larger than 10 μm were found, and none were larger than 15 μm. This indicates that the second and third refining processes effectively removed harmful inclusions that were too large or aggregated during the alloying process, leaving only beneficial nucleation particles with small sizes (<5 μm).

[0119] The specific distribution of various inclusions also verifies the rationality of the step-by-step alloying process. TiS, TiN, and elemental Ti inclusions account for the vast majority, while only two MnS inclusions were found. This indicates that the electrolytic manganese added under argon protection during the second alloying process did not undergo significant oxidation, and the added Mn effectively entered the molten steel matrix rather than being lost in large quantities as MnS inclusions. This further confirms the role of the argon protective atmosphere in improving the Mn element recovery rate.

[0120] Overall, the inclusion analysis results show that the process of this invention can effectively remove large inclusions that are harmful to toughness, while successfully retaining small (<5μm) Ti-based inclusions that are beneficial to the nucleation of acicular ferrite. This achieves "selective retention" of inclusions, removing the harmful ones and keeping the beneficial ones, thus laying the metallurgical foundation for the optimization of weld structure in the subsequent welding process.

[0121] While the present invention has been disclosed above with reference to preferred embodiments, it is not intended to limit the invention. Those skilled in the art can make various modifications and refinements without departing from the spirit and scope of the invention. Therefore, the scope of protection of the present invention shall be determined by the claims.

Claims

1. A zirconium- and boron-containing welding wire steel, characterized in that, Its chemical composition, by weight percentage, is as follows: C 0.02%~0.032%, Mn 1.25%~1.40%, Ti 0.07%~0.14%, Cr 0.14%~0.21%, Ni 3.25%~3.35%, Mo 0.14%~0.21%, Al 0.015%~0.045%, Zr 0.025%~0.045%, B 0.0035%~0.0055%, Si≤0.1%, V≤0.01%, Nb≤0.01%, S≤0.005%, P≤0.005%, O≤0.002%, N≤0.003%, H≤0.0003%, balance Fe and unavoidable impurities; The method for preparing the welding wire steel includes the following steps: At least two vacuum refining processes and at least one inert gas protective atmosphere refining process are carried out, and in-furnace sampling and analysis are performed during the refining process. The composition is dynamically compensated and adjusted based on the sampling and analysis results. The sampling and analysis includes at least the full melt sample analysis after the first vacuum refining and the furnace sample analysis before the first inert gas protective atmosphere refining. Nickel, carbon, chromium, molybdenum and iron are added during the initial feeding; titanium, aluminum and zirconium are added after the first vacuum refining; and manganese and boron are added under the inert gas protective atmosphere after the last vacuum refining.

2. A method for preparing zirconium- and boron-containing welding wire steel as described in claim 1, characterized in that, Includes the following steps: (1) Furnace pretreatment; (2) Add the first part of the raw materials into the vacuum induction melting furnace and distribute the materials according to the set method; (3) Vacuuming and stepped power supply to heat up the first part of the raw materials to melt and perform the first vacuum refining to obtain the first molten steel. Take a full melt sample from the fully melted first molten steel for composition analysis. The first part of the raw materials consists of carbon particles, electrolytic nickel, metallic chromium, industrial pure iron, and molybdenum bars. (4) Based on the analysis results of the full melt sample, a second portion of raw materials is added under vacuum conditions to perform a second vacuum melting to obtain a second molten steel; The second part of the raw materials consists of sponge zirconium, aluminum granules, and sponge titanium; (5) After the second vacuum refining is completed, an inert gas is introduced into the vacuum induction melting furnace, and a third part of raw materials is added to the second molten steel under the protective atmosphere formed by the inert gas to carry out the third inert atmosphere refining to obtain the third molten steel. A sample is taken from the third molten steel for composition analysis. The third part of the raw materials consists of electrolytic manganese and ferroboron; (6) Determine whether to perform composition fine-tuning based on the analysis results of the pre-furnace sample: If fine-tuning is required, the amount of material to be added is calculated based on the analysis results of the furnace front sample and the material addition operation is completed. After material addition, the fourth inert atmosphere refining is carried out, and the fourth molten steel is obtained after the process. If no fine-tuning is required, the third molten steel is used as the fourth molten steel, and the process proceeds directly to the next step. (7) Take a sample from the fourth molten steel for composition analysis, and perform electric casting at the furnace temperature to obtain the welding wire steel product.

3. The method for preparing zirconium- and boron-containing welding wire steel according to claim 2, characterized in that, The furnace washing pretreatment step includes: Before melting the welding wire steel, a complete melting and casting process is carried out using high-purity iron material to dissolve and remove impurity elements adsorbed on the inner wall of the crucible in the vacuum induction melting furnace.

4. The method for preparing zirconium- and boron-containing welding wire steel according to claim 2, characterized in that, The fabric application method includes: First, the electrolytic nickel is laid flat at the bottom of the crucible of the vacuum induction melting furnace, then all the carbon particles are added, followed by all the metallic chromium, all the molybdenum bars, and all the industrial pure iron. The furnace charge height is controlled to the crucible slag line position.

5. The method for preparing zirconium- and boron-containing welding wire steel according to claim 2, characterized in that, The vacuuming and stepped power supply for heating includes: The vacuum induction melting furnace was evacuated to ≤10 Pa; The power output was gradually increased from 100 kW to 400 kW, and then increased to 500-800 kW to enter the material processing stage.

6. The method for preparing zirconium- and boron-containing welding wire steel according to claim 2, characterized in that, The first vacuum refining includes: Control the temperature of the molten steel at 1610±20℃, start the three-phase electromagnetic stirring, and stir for 4 to 10 minutes. After stirring, take the full melt sample and send it to a heat preservation power of 250 to 300kW for refining for 40 to 50 minutes.

7. The method for preparing zirconium- and boron-containing welding wire steel according to claim 2, characterized in that, The second vacuum refining includes: The temperature of the molten steel is controlled at 1600±20℃, and three-phase electromagnetic stirring is carried out for 4 to 10 minutes. After stirring, the steel is sent to a heat preservation power of 250 to 300 kW for refining for 30 to 40 minutes.

8. The method for preparing zirconium- and boron-containing welding wire steel according to claim 2, characterized in that, Both the third inert atmosphere refining and the fourth inert atmosphere refining include: Adjust the temperature of the molten steel to 1590±20℃ and perform three-phase electromagnetic stirring for 4 to 10 minutes. After stirring, send it to a heat preservation power of 250 to 300 kW for refining for 20 to 30 minutes.

9. The method for preparing zirconium- and boron-containing welding wire steel according to claim 2, characterized in that, The electrified casting includes: The tapping temperature is 1630±15℃, the tapping speed is 300~400kg / min, the power supply is maintained at 360kW during casting, and the casting process is carried out in a protective atmosphere formed by inert gas and in a sealed state of equipment.

10. The method for preparing zirconium- and boron-containing welding wire steel according to claim 2, characterized in that, The purity requirements for the raw materials used in smelting are as follows: carbon particles C≥99.5%, electrolytic manganese Mn≥99.8%, electrolytic nickel Ni≥99.95%, metallic chromium Cr≥99.3%, industrial pure iron Fe≥99.9%, molybdenum bars Mo≥99.9%, boron iron with B content of 17.5%, sponge zirconium Zr≥99.5%, aluminum particles Al≥99.5%, and sponge titanium Ti≥99.5%.

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