Smelting method for solving macrosegregation of high-boron steel

Abstract

The invention discloses a smelting method for solving macrosegregation of high-boron steel, and belongs to the technical field of high-end special steel metallurgy. According to the method, titanium diboride (TiB2) powder is sealed in a metal ladle and added into a vacuum induction furnace together with furnace charge, high yield of boron and titanium and liquid phase extreme homogenization are achieved through the synergistic effect of electromagnetic stirring and argon bottom blowing, and a segregation source is eliminated from the source; and deep purification and directional solidification are conducted on the uniform electrode through an electroslag remelting technology, and finally the high-boron steel cast ingot which is free of macrosegregation, fine and dispersed in structure and high in purity is obtained. The technical problems that the high-boron steel is low in yield, serious in segregation and uneven in performance are solved, and the technological process is suitable for industrial large-scale production.

Description

Technical Field

[0001] This invention belongs to the field of high-end special steel metallurgical technology, specifically relating to a smelting method for solving macroscopic segregation in high-boron steel. Background Technology

[0002] High-boron steel plays an irreplaceable role in the nuclear industry, aerospace, and wear-resistant components due to its excellent neutron absorption cross-section, high-temperature strength, and wear resistance. However, the properties of boron pose significant challenges to its smelting. Existing solutions all have obvious shortcomings: The inherent defects of traditional alloying methods are: 1) Extremely low and unstable yield: Currently, industrial production commonly uses ferroborone (Fe-B) or boron carbide (B4C) as the boron source. Due to the extremely reactive nature of boron, it readily reacts with oxygen and nitrogen during high-temperature smelting and is lost through burning and volatilization, resulting in an extremely low boron yield (typically 30%–50%), with significant fluctuations between different heats, making precise composition control extremely difficult. 2) Severe macroscopic segregation: Boron is a very strong negative segregating element. Traditional alloying additives have low melting points and rapid dissolution rates, instantly forming high-concentration zones in localized areas of molten steel. During subsequent solidification, boron is continuously pushed away by the solidification front, eventually drastically accumulating in the core and upper regions of the ingot, forming severe macroscopic segregation bands. This leads to significant differences in microstructure and properties at different locations in the ingot, making it prone to cracking during subsequent hot working (forging, rolling), resulting in unstable finished product performance and an extremely low yield. 3) Deterioration of material properties: Segregation leads to the formation of continuous or semi-continuous brittle boride networks at grain boundaries, which seriously impairs the toughness, plasticity and fatigue properties of steel.

[0003] To address the segregation problem, powder metallurgy can be used, which involves mixing boron powder with iron-based powder and then pressing and sintering the mixture. However, powder metallurgy (PM) suffers from drawbacks such as a long process flow, substantial equipment investment (e.g., powder preparation and hot isostatic pressing equipment), and high raw material costs. Most critically, the density of PM products is typically lower than that of cast parts, exhibiting micropores and original particle boundaries. This results in significant differences in mechanical properties (especially impact toughness and fatigue strength) compared to cast materials, making it difficult to apply to critical structural components with extremely high reliability requirements. Furthermore, the PM method is severely limited in producing large-size, high-tonnage billets.

[0004] Therefore, developing a high-boron steel smelting method that can achieve high yield, extreme uniformity, full densification, and is suitable for large-scale industrial production is the key to overcoming the bottleneck in its engineering application. Summary of the Invention

[0005] The purpose of this invention is to provide a smelting method for solving the problem of macrosegregation in high-boron steel. This method overcomes the shortcomings of both the existing traditional alloy addition method and the powder metallurgy method, and provides a VIM-ESR duplex smelting method with a reasonable process flow, high boron and titanium yield, which can fundamentally eliminate macrosegregation and obtain high-boron steel ingots with ultra-high uniformity and purity.

[0006] A smelting method for solving macrosegregation in high-boron steel includes the following steps: S1. Titanium diboride powder is sealed in a metal bag and loaded into a vacuum induction furnace along with metal furnace charge for melting. After melting, it is refined by electromagnetic stirring and bottom blowing inert gas, and then cast to obtain a consumable electrode. S2. Electroslag remelting of the consumable electrode to obtain a high-boron steel ingot.

[0007] In step S1 of this invention, the particle size of titanium diboride powder is 10-150 μm, and the metal cladding is made of low-carbon steel or pure iron sheet with a shell thickness of 0.5-1.5 mm.

[0008] In step S1 of this invention, the metal cladding is placed in the lower middle part of the furnace charge inside the crucible of the vacuum induction furnace; after evacuating the furnace until the pressure inside the furnace is lower than 10 Pa, it is heated to 1550-1650°C to melt it completely.

[0009] In step S1 of this invention, the bottom-blown inert gas is high-purity argon with a flow rate of 5–15 L / min; the holding time for co-refining is 10–20 minutes.

[0010] In step S1 of this invention, the casting is carried out under the protection of an inert gas.

[0011] In step S2 of this invention, the electroslag remelting uses a pre-melted slag composed of CaO, Al2O3, and MgO, wherein the CaO content is 50%–60%, the Al2O3 content is 20%–30%, and the MgO content is 5%–10% by mass percentage.

[0012] In step S2 of this invention, the electroslag remelting process is carried out under a protective atmosphere using a steady-state remelting regime, with the melting rate controlled at 3.5 to 6.5 kg / min; after remelting, the steel ingot is slowly cooled to below 300°C at a cooling rate of ≤30°C / h before being demolded.

[0013] The high-boron steel ingots prepared by the method of the present invention have a boron (B) and titanium (Ti) yield of ≥95%.

[0014] The high-boron steel ingot prepared by the method of the present invention has a boron element composition range of ≤0.05wt% in different parts.

[0015] The present invention also provides a smelting method for solving the macrosegregation of high boron steel to prepare a high boron steel ingot, wherein the yield of boron (B) and titanium (Ti) elements in the ingot is ≥95%; and the range of boron element composition in different parts of the ingot is ≤0.05wt%.

[0016] The beneficial effects of adopting the above technical solution are as follows: 1. The yield of the present invention is extremely high and stable: the yield of boron and titanium can be stably controlled at over 95%, far exceeding that of the traditional alloy addition method; 2. The present invention fundamentally eliminates macrosegregation: the combination of "pre-encapsulated addition in the furnace" and "cooperative stirring" technology realizes the synchronous dissolution of TiB2 throughout the entire process, completely solving the problem of macrosegregation that the traditional alloy addition method cannot overcome; and avoids the network borides of the traditional smelting method; 3. The present invention is suitable for industrial production: based on the mature VIM-ESR dual-unit equipment, the process is continuous and can produce large-tonnage, high-quality steel ingots, with the dual advantages of traditional methods and PM method in terms of cost and efficiency. Attached Figure Description

[0017] Figure 1 This is a schematic diagram of the sampling location.

[0018] Among them, 2, 1, and 3 are the top axis and the two endpoints, 5, 4, and 6 are the middle axis and the two endpoints, and 8, 7, and 9 are the bottom axis and the two endpoints. Detailed Implementation

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

[0020] A smelting method for solving macrosegregation in high-boron steel includes the following steps: Step 1: Vacuum Induction Furnace (VIM) Melting Process: a. Pretreatment and charging: Titanium diboride (TiB2) powder with a particle size of 10-150 μm is loaded into a sealed metal ladle made of low-carbon steel or pure iron sheet with a shell thickness of 0.5-1.5 mm; the calculated basic furnace charge, including pure iron, low-carbon steel, nickel, and chromium metals, is loaded into the VIM furnace crucible, and the sealed metal ladle is embedded in the lower middle part of the furnace charge; b. Vacuuming and melting: After vacuuming until the pressure inside the furnace is below 10Pa, start electric heating to 1550-1650℃, so that the furnace charge and the sealed metal ladle melt together in a vacuum environment; c. Melting and Co-stirring: After the furnace charge has basically melted, control the melting temperature at 1550-1650℃; turn on the electromagnetic stirrer and at the same time blow high-purity argon gas through the bottom permeable brick of the crucible at a flow rate of 5-15 L / min; under the synergistic effect of electromagnetic stirring and bottom blowing argon gas, refine and hold at the temperature for 10-20 minutes to allow TiB2 to fully dissolve and diffuse evenly. d. Casting: Adjust the temperature of the molten steel to the target casting temperature, and cast it into a consumable electrode for electroslag remelting under inert gas protection.

[0021] Step 2: Electroslag Remelting (ESR) process: e. Preparation: The high-boron steel consumable electrode obtained above is used as the cathode and installed in an electroslag remelting furnace; a pre-melted slag composed of CaO, Al2O3, and MgO is used, wherein, by mass percentage, the CaO content is 50%–60%, the Al2O3 content is 20%–30%, and the MgO content is 5%–10%; f. Remelting: Remelting is carried out under a protective atmosphere using a steady-state remelting process; g. Solidification: After passing through the high-temperature slag pool, the molten metal droplets solidify into steel ingots in a water-cooled crystallizer, with the melting rate controlled at 3.5–6.5 kg / min; h. Cooling and demolding: After remelting, the steel ingots must be slowly cooled to below 300°C in the crystallizer or a special slow cooling pit at a cooling rate of ≤30°C / h before demolding. Example

[0022] A smelting method for resolving macrosegregation in high-boron steel, preparing high-boron steel ingots containing 2wt% B, includes the following steps: A 50kg vacuum induction furnace with a rated power of 100kW and an ultimate vacuum of 6.67×10⁻⁶ is used. -2 Pa.

[0023] Step 1: Vacuum Induction Furnace (VIM) Melting Process: a. Pretreatment and charging: Titanium diboride (TiB2) powder with a particle size of 10-50μm is loaded into a sealed metal ladle made of low-carbon steel or pure iron sheet with a shell thickness of 0.5mm; the calculated basic furnace charge, including pure iron, low-carbon steel, nickel, and chromium metals, is loaded into the VIM furnace crucible, and the sealed metal ladle is embedded in the lower middle part of the furnace charge; b. Vacuuming and melting: After vacuuming until the pressure inside the furnace is below 10Pa, start electric heating to 1550℃, so that the furnace charge and the sealed metal ladle melt together in a vacuum environment; c. Melting and Co-stirring: After the furnace charge has basically melted, control the melting temperature at 1550℃; turn on the electromagnetic stirrer and at the same time blow high-purity argon gas through the bottom permeable brick of the crucible at a flow rate of 5L / min; under the synergistic effect of electromagnetic stirring and bottom blowing argon gas, refine and hold at the temperature for 10 minutes to allow TiB2 to fully dissolve and diffuse evenly. d. Casting: Adjust the molten steel temperature to the target casting temperature, and cast it into a consumable electrode for electroslag remelting under argon protection; take samples for analysis at typical locations on the steel ingot, such as... Figure 1 .

[0024] Step 2: Electroslag Remelting (ESR) process: e. Preparation: The high-boron steel consumable electrode obtained above is used as the cathode and installed in an electroslag remelting furnace; a pre-melted slag composed of CaO, Al2O3, and MgO is used, wherein, by mass percentage, the CaO content is 50%, the Al2O3 content is 25%, and the MgO content is 8%; f. Remelting: Remelting is carried out under a protective atmosphere using a steady-state remelting process; g. Solidification: After passing through the high-temperature slag pool, the molten metal droplets solidify into steel ingots in a water-cooled crystallizer, with the melting rate controlled at 3.5 kg / min; h. Cooling and demolding: After remelting, the steel ingot needs to be slowly cooled to 250°C in the crystallizer or a special slow cooling pit at a cooling rate of 25°C / h before demolding.

[0025] The target composition and detection values ​​of steel ingots smelted in the vacuum induction furnace in this embodiment are shown in Table 1.

[0026] Table 1. Target composition and detection values ​​(wt%) of the VIM electrode in Example 1

[0027] In Table 1, the balance of the components is Fe and unavoidable impurities.

[0028] It can be seen that the yields of B and Ti are 96.5% and 97.8%, respectively; the range of B content is 0.04 wt%. This fundamentally eliminates macroscopic segregation.

[0029] The final ingot performance test results are as follows: Compositional uniformity: Samples were taken from the corresponding locations on the ESR ingot, and the range of B element composition was 0.03 wt%, proving that segregation was perfectly controlled.

[0030] Density: The ultrasonic testing results meet the Class 1 standard of GB / T 6402-2008.

[0031] Metallographic structure: Borides are distributed uniformly in the form of fine, diffuse dots or short rods, without a continuous network structure. Example

[0032] A smelting method for solving the macrosegregation problem in high-boron steel, comprising the following steps: Preparing high-boron steel ingots containing 3 wt% B (target B and Ti contents are both 3.0 wt%, other elements are similar to those in Example 1). A 50kg vacuum induction furnace with a rated power of 100kW and an ultimate vacuum of 6.67×10⁻⁶ is used. -2 Pa.

[0033] Step 1: Vacuum Induction Furnace (VIM) Melting Process: a. Pretreatment and charging: Titanium diboride (TiB2) powder with a particle size of 20-80μm is loaded into a sealed metal ladle made of low-carbon steel or pure iron sheet with a shell thickness of 0.8mm; the calculated basic furnace charge, including pure iron, low-carbon steel, nickel, and chromium metals, is loaded into the VIM furnace crucible, and the sealed metal ladle is buried in the lower middle part of the furnace charge; b. Vacuuming and melting: After vacuuming until the pressure inside the furnace is below 10Pa, start electric heating to 1580℃, so that the furnace charge and the sealed metal ladle melt together in a vacuum environment; c. Melting and Co-stirring: After the furnace charge has basically melted, control the melting temperature at 1580℃; turn on the electromagnetic stirrer and at the same time blow high-purity argon gas through the bottom permeable brick of the crucible at a flow rate of 8L / min; under the synergistic effect of electromagnetic stirring and bottom blowing argon gas, refine and hold at the temperature for 18 minutes to allow TiB2 to fully dissolve and diffuse evenly. d. Casting: Adjust the molten steel temperature to the target casting temperature, and cast it into a consumable electrode for electroslag remelting under argon protection; take samples for analysis at typical locations on the steel ingot, such as... Figure 1 .

[0034] Step 2: Electroslag Remelting (ESR) process: e. Preparation: The high-boron steel consumable electrode obtained above is used as the cathode and installed in an electroslag remelting furnace; a pre-melted slag composed of CaO, Al2O3, and MgO is used, wherein, by mass percentage, the CaO content is 58%, the Al2O3 content is 28%, and the MgO content is 6%; f. Remelting: Remelting is carried out under a protective atmosphere using a steady-state remelting process; g. Solidification: After passing through the high-temperature slag pool, the molten metal droplets solidify into steel ingots in a water-cooled crystallizer, with the melting rate controlled at 5.5 kg / min; h. Cooling and demolding: After remelting, the steel ingot needs to be slowly cooled to 250°C in the crystallizer or a special slow cooling pit at a cooling rate of 20°C / h before demolding.

[0035] Test results: B and Ti yields were 95.8% and 96.2%, respectively; the final ESR ingot B composition range was 0.03 wt%. Example

[0036] A smelting method for solving the macrosegregation problem in high-boron steel, comprising the following steps, for preparing high-boron steel ingots containing 4 wt% B (target B and Ti contents are both 4.0 wt%, and other elements are similar to those in Example 1): A 50kg vacuum induction furnace with a rated power of 100kW and an ultimate vacuum of 6.67×10⁻⁶ is used. -2 Pa.

[0037] Step 1: Vacuum Induction Furnace (VIM) Melting Process: a. Pretreatment and charging: Titanium diboride (TiB2) powder with a particle size of 80-150μm is loaded into a sealed metal ladle made of low-carbon steel or pure iron sheet with a shell thickness of 1.2mm; the calculated basic furnace charge, including pure iron, low-carbon steel, nickel, and chromium metals, is loaded into the VIM furnace crucible, and the sealed metal ladle is buried in the lower middle part of the furnace charge; b. Vacuuming and melting: After vacuuming until the pressure inside the furnace is below 10Pa, start electric heating to 1620℃, so that the furnace charge and the sealed metal ladle melt together in a vacuum environment; c. Melting and Co-stirring: After the furnace charge has basically melted, control the melting temperature at 1620℃; turn on the electromagnetic stirrer and at the same time blow high-purity argon gas through the bottom permeable brick of the crucible at a flow rate of 13L / min; under the synergistic effect of electromagnetic stirring and bottom blowing argon gas, refine and hold at the temperature for 20 minutes to allow TiB2 to fully dissolve and diffuse evenly. d. Casting: Adjust the molten steel temperature to the target casting temperature, and cast it into a consumable electrode for electroslag remelting under argon protection; take samples for analysis at typical locations on the steel ingot, such as... Figure 1 .

[0038] Step 2: Electroslag Remelting (ESR) process: e. Preparation: The high-boron steel consumable electrode obtained above is used as the cathode and installed in an electroslag remelting furnace; a pre-melted slag composed of CaO, Al2O3, and MgO is used, wherein, by mass percentage, the CaO content is 52%, the Al2O3 content is 30%, and the MgO content is 9%; f. Remelting: Remelting is carried out under a protective atmosphere using a steady-state remelting process; g. Solidification: After passing through the high-temperature slag pool, the molten metal droplets solidify into steel ingots in a water-cooled crystallizer, with the melting rate controlled at 6.0 kg / min; h. Cooling and demolding: After remelting, the steel ingot needs to be slowly cooled to 280°C in the crystallizer or a special slow cooling pit at a cooling rate of 28°C / h before demolding.

[0039] Test results: B and Ti yields were 95.8% and 96.2%, respectively; the final ESR ingot B composition range was 0.03 wt%.

[0040] Results: The yields of B and Ti were 96.0% and 95.5%, respectively; the final ESR ingot had a B composition range of 0.04 wt%.

[0041] Comparative example (traditional Fe-B addition method) The same basic furnace charge and target composition as in Example 1 were used, but the boron source was changed to directly added ferroborone (Fe-B). Melting was performed in the same 50kg VIM furnace, with a vacuum of 8 Pa. After melting, only simple mechanical stirring was performed; bottom-blowing argon was not used. Samples were taken from the same location for analysis after casting.

[0042] Results: The boron yield was only 42%, with large compositional fluctuations. The range of boron composition analysis at 9 points on the ingot was as high as 1.35 wt%, with severe boron enrichment in the head and core, and boron depletion at the edges, and macroscopic segregation visible to the naked eye. After remelting the electrode using the same ESR process, the segregation was somewhat improved but not fundamentally eliminated, and the range of boron composition still reached 0.45 wt%. Furthermore, the data dispersion was large. This comparative example fully demonstrates the inherent defects of traditional methods and the significant advantages of this invention.

[0043] The above description is merely a preferred embodiment of the present invention and should not be construed as limiting the scope of the invention. Although the invention has been described in detail with reference to the foregoing embodiments, those skilled in the art can still modify the technical solutions described in the signed embodiments or make equivalent substitutions for some of the technical features. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention are all within the scope of the present invention.

Claims

1. A smelting method for solving macroscopic segregation in high-boron steel, characterized in that: Includes the following steps: S1. Titanium diboride powder is sealed in a metal bag and loaded into a vacuum induction furnace along with metal furnace charge for melting. After melting, it is refined by electromagnetic stirring and bottom blowing inert gas, and then cast to obtain a consumable electrode. S2. Electroslag remelting of the consumable electrode to obtain a high-boron steel ingot.

2. The smelting method for solving macroscopic segregation in high-boron steel according to claim 1, characterized in that: In step S1, the titanium diboride powder has a particle size of 10-150 μm, and the metal cladding is made of low-carbon steel or pure iron sheet with a shell thickness of 0.5-1.5 mm.

3. The smelting method for solving macroscopic segregation in high-boron steel according to claim 1, characterized in that: In step S1, the metal cladding is placed in the lower middle part of the furnace charge inside the crucible of the vacuum induction furnace; after evacuating the furnace until the pressure inside the furnace is below 10 Pa, it is heated to 1550-1650°C to melt it completely.

4. The smelting method for solving macroscopic segregation in high-boron steel according to claim 1, characterized in that: In step S1, the bottom-blown inert gas is high-purity argon with a flow rate of 5–15 L / min; the holding time for co-refining is 10–20 minutes.

5. The smelting method for solving macroscopic segregation in high-boron steel according to claim 1, characterized in that: In step S1, the pouring is carried out under the protection of an inert gas.

6. The smelting method for solving macroscopic segregation in high-boron steel according to claim 1, characterized in that: In step S2, the electroslag remelting uses a pre-melted slag composed of CaO, Al2O3, and MgO, wherein the CaO content is 50%–60%, the Al2O3 content is 20%–30%, and the MgO content is 5%–10% by mass percentage.

7. The smelting method for solving macroscopic segregation in high-boron steel according to claim 1, characterized in that: In step S2, the electroslag remelting process is carried out under a protective atmosphere using a steady-state remelting regime, with the melting rate controlled at 3.5–6.5 kg / min. After remelting, the steel ingot is slowly cooled to below 300°C at a cooling rate of ≤30°C / h before being demolded.

8. A smelting method for solving macrosegregation in high-boron steel according to any one of claims 1-7, characterized in that: The high-boron steel ingots prepared by the method have boron and titanium yields of ≥95%.

9. A smelting method for solving macrosegregation in high-boron steel according to any one of claims 1-7, characterized in that: The high-boron steel ingots prepared by the method have a boron element composition range of ≤0.05wt% in different parts.

10. A high-boron steel ingot prepared by the smelting method for solving macrosegregation in high-boron steel according to any one of claims 1-9, characterized in that: The yield of boron and titanium in the ingot is ≥95%; the range of boron content in different parts of the ingot is ≤0.05wt%.

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