Method for precisely controlling nitrogen content in smelting process of high-strength iron-nickel-molybdenum alloy

Abstract

The present invention discloses a method for precisely controlling the nitrogen content during the smelting of a high-strength iron-nickel-molybdenum alloy, belonging to the field of metallurgical technology. After the vacuum treatment process in the VD vacuum treatment process is completed, nitrogen is filled into the furnace, and the nitrogen filling pressure is P N2 , and the nitrogen filling pressure P N2 is calculated according to the formula. After the nitrogen filling is completed, vanadium nitride alloy is added, and then the bottom blowing gas is switched to nitrogen, and the nitrogen flow rate is controlled at 50-70 NL / min for 10-15 min, and then the steel is tapped for casting. After the VD vacuum degree treatment in the present invention, under the nitrogen atmosphere condition, nitrogen is increased by adding a nitrogen-containing alloy and bottom blowing nitrogen, and the oxygen and inclusion content in the molten steel are reduced to the greatest extent, and the precise control of the nitrogen content in the high-strength iron-nickel-molybdenum alloy can be realized.

Description

Technical Field

[0001] This invention belongs to the field of metallurgical technology, specifically relating to a method for precisely controlling nitrogen content during the smelting of high-strength iron-nickel-molybdenum alloys. Background Technology

[0002] High-strength iron-nickel-molybdenum alloy reinforced core double-capacity transmission conductors have significant application potential in line capacity expansion and upgrading due to their advantages such as high power transmission capacity, low sag at high temperatures, and long service life. In this material composition system, nitrogen, as an intermediate alloying element, requires precise control to refine the grain size and improve the material's strength and toughness.

[0003] In the smelting of nitrogen-containing materials, the nitrogen content in molten steel is mainly related to the surface-active elements of the molten steel, the partial pressure of nitrogen in the gas phase, alloying elements, and temperature. Under certain pressure, the solubility of nitrogen increases with increasing temperature. Adding alloying elements to molten steel can improve the solubility of nitrogen in steel, but pressure has the greatest impact on nitrogen solubility compared to temperature and alloying elements. In this material composition system, the conventional nitrogen control process involves adding nitrogen after the vacuum is broken following VD smelting. However, under normal pressure, the nitrogen partial pressure is high during the addition process, making it easy for the nitrogen content in the steel to exceed the control limit. This makes the nitrogen control process difficult to achieve precise control of nitrogen content. Furthermore, if the nitrogen content in the steel becomes supersaturated, nitrogen will escape during subsequent refining processes, creating numerous pores in the ingot and causing irreversible damage to subsequent processing. Additionally, adding nitrogen after the vacuum is broken during VD smelting easily leads to oxygenation in the steel, increasing the content of inclusions in the molten steel and affecting the quality of the ingot.

[0004] Therefore, it is necessary to provide a new method for precise control of nitrogen content in the smelting of high-strength iron-nickel-molybdenum alloys, so as to achieve precise control of nitrogen content in ingots. Summary of the Invention

[0005] This invention provides a method for precisely controlling nitrogen content during the smelting of high-strength iron-nickel-molybdenum alloys, so as to ensure precise control of nitrogen content in ingots after the VD smelting process.

[0006] To achieve the above-mentioned objectives, the technical solution adopted by this invention is as follows:

[0007] A method for precisely controlling nitrogen content during the smelting of high-strength iron-nickel-molybdenum alloys includes a VD vacuum treatment process. After vacuum treatment, nitrogen gas is introduced into the furnace at a pressure of P. N2 After nitrogen purging, vanadium nitride alloy is added, and then the bottom blowing gas is switched to nitrogen. The nitrogen flow rate is controlled at 50-70 NL / min for 10-15 min, and then the steel is poured.

[0008] Nitrogen purging pressure P N2 Calculated according to the formula,

[0009] In the formula P N2 The nitrogen purging pressure after vacuum treatment, in Pa;

[0010] N 目标 The target nitrogen content for high-strength iron-nickel-molybdenum alloys is expressed in ppm.

[0011] ρ represents the yield of vanadium nitride alloy, where 50% ≤ ρ ≤ 70%.

[0012] Furthermore, in the VD vacuum treatment process, the vacuuming process time is ≤10min, and bottom blowing gas stirring is prohibited during the vacuuming process; when the vacuum degree is ≤50Pa, bottom blowing argon gas stirring is turned on, the argon gas flow rate is controlled at 40~60NL / min, and the vacuum time is controlled at 8~10min.

[0013] Furthermore, the vacuum time is the time interval from when the vacuum degree is ≤50Pa to when nitrogen is started to be introduced into the furnace.

[0014] Furthermore, the target nitrogen content N of the high-strength iron-nickel-molybdenum alloy 目标 The concentration is 50–150 ppm.

[0015] Furthermore, before the VD vacuum treatment process, the tapping temperature of the LF refining process is controlled at 150-200°C above the liquidus line.

[0016] Furthermore, after the ladle enters the LF station, it is first powered on and heated, then quicklime, fluorite, and calcium carbide are added to create white slag. After stirring with argon, temperature is measured and samples are taken to add alloys according to the target content.

[0017] Furthermore, the chemical composition and mass percentage of the high-strength iron-nickel-molybdenum alloy are as follows: C: 0.2-0.3%, Ni: 34-38%, Mo: 0.30-1.00%, V: 0.60-0.90%, N: 0.005-0.015%, with the balance being Fe and unavoidable impurities.

[0018] Furthermore, the high-strength iron-nickel-molybdenum alloy has a tensile strength ≥1420MPa.

[0019] The beneficial effects of adopting the above technical solution are as follows: This invention controls nitrogen through the LF and VD processes. After VD deep vacuum treatment, nitrogen is increased by adding nitride alloys and bottom-blown nitrogen under nitrogen atmosphere conditions, which minimizes the oxygen and inclusion content in the molten steel. Furthermore, the nitrogen charging pressure of the VD process can be directly calculated using a formula, achieving saturation of nitrogen solubility in the molten steel under this nitrogen partial pressure condition, thus enabling precise control of nitrogen content and significantly reducing the difficulty of nitrogen control in the iron-nickel-molybdenum alloy process. Detailed Implementation

[0020] The present invention will be further described in detail below with reference to specific embodiments. These embodiments are merely descriptions of the best implementation of the present invention and do not limit the scope of the present invention.

[0021] Examples 1-9

[0022] A method for precisely controlling nitrogen content during the smelting of high-strength iron-nickel-molybdenum alloys is disclosed. The smelting process includes an LF refining step and a VD vacuum treatment step. After the ladle enters the LF station, it is first heated by electricity, then quicklime, fluorite, and calcium carbide are added to create white slag. After argon blowing and stirring, temperature sampling is performed, and alloy is replenished according to the target content. The LF refining temperature is controlled at 150–200°C above the liquidus. During the VD high vacuum treatment, the vacuuming time is ≤10 min, and bottom blowing stirring is prohibited. When the vacuum degree is ≤50 Pa, bottom blowing argon stirring is started, with the argon flow rate controlled at 40–60 NL / min and the vacuum time controlled at 8–10 min. After the VD high vacuum treatment, nitrogen is introduced into the furnace at a pressure of P. N2 After nitrogen charging is completed, vanadium nitride alloy is added to the furnace at a nitrogen content of 50-70% and a yield of 50-70%. Then, the bottom blowing gas is switched to nitrogen, and the nitrogen flow rate is controlled at 50-70 NL / min for 10-15 min. Then, the steel is tapped and poured.

[0023] Nitrogen purging pressure P N2 Calculated according to the formula,

[0024] In the formula, P N2 The nitrogen purging pressure after vacuum treatment, in Pa;

[0025] N 目标 The target nitrogen content for high-strength iron-nickel-molybdenum alloys is expressed in ppm.

[0026] ρ represents the yield of vanadium nitride alloy, where 50% ≤ ρ ≤ 70%.

[0027] The chemical composition and mass percentage of the above-mentioned high-strength iron-nickel-molybdenum alloy are as follows: C: 0.2-0.3%, Ni: 34-38%, Mo: 0.30-1.00%, V: 0.60-0.90%, N: 0.005-0.015%, with the balance being Fe and unavoidable impurities.

[0028] The smelting process control parameters for each embodiment are shown in Table 1, with nitrogen charging pressure P. N2 The calculated values ​​and the measured values ​​of nitrogen content in the high-strength iron-nickel-molybdenum alloy billet are shown in Table 2. The chemical composition, mass percentage, and strength of the high-strength iron-nickel-molybdenum alloy are shown in Table 3.

[0029] Table 1. Parameter Control of Smelting Process in Each Embodiment

[0030]

[0031]

[0032] Table 2. Nitrogen charging pressure and endpoint nitrogen content detection for each example.

[0033]

[0034] Table 3. Chemical composition and mass percentage of high-strength iron-nickel-molybdenum alloys in each embodiment, and their strength.

[0035]

[0036]

[0037] As can be seen from the comparison of the target nitrogen content and the endpoint nitrogen content in Tables 1, 2 and 3, the present invention achieves precise control of nitrogen content in high-strength iron-nickel-molybdenum alloys.

Claims

1. A method for precisely controlling nitrogen content during the smelting of high-strength iron-nickel-molybdenum alloys, characterized in that VD After the vacuum treatment process, nitrogen gas is introduced into the furnace at a pressure of P. N2 After nitrogen purging, vanadium nitride alloy is added, and then the bottom blowing gas is switched to nitrogen. The nitrogen flow rate is controlled at 50-70 NL / min for 10-15 min, and then the steel is poured. Nitrogen purging pressure P N2 Calculated according to the formula, In the formula P N2 The nitrogen purging pressure after vacuum treatment, in Pa; N 目标 The target nitrogen content for high-strength iron-nickel-molybdenum alloys is expressed in ppm. ρ represents the yield of vanadium nitride alloy, 50% ≤ ρ ≤ 70%; The target nitrogen content N of the high-strength iron-nickel-molybdenum alloy 目标 The concentration is 50–150 ppm. The chemical composition and mass percentage of the high-strength iron-nickel-molybdenum alloy are as follows: C: 0.2-0.3%, Ni: 34-38%, Mo: 0.30-1.00%, V: 0.60-0.90%, N: 0.005-0.015%, with the balance being Fe and unavoidable impurities; The high-strength iron-nickel-molybdenum alloy has a tensile strength ≥1420MPa.

2. The method for precisely controlling nitrogen content during the smelting of high-strength iron-nickel-molybdenum alloys according to claim 1, characterized in that, The VD vacuum treatment process requires a vacuuming time of ≤10 min, during which bottom blowing gas stirring is prohibited. When the vacuum level is ≤50 Pa, bottom blowing argon gas stirring is started, with the argon gas flow rate controlled at 40-60 NL / min and the vacuum time controlled at 8-10 min.

3. The method for precisely controlling nitrogen content during the smelting of high-strength iron-nickel-molybdenum alloys according to claim 2, characterized in that, The vacuum time is the time interval from when the vacuum level is ≤50Pa to when nitrogen is started to be introduced into the furnace.

4. The method for precisely controlling nitrogen content during the smelting of high-strength iron-nickel-molybdenum alloys according to claim 3, characterized in that, Before the VD vacuum treatment process, the tapping temperature of the LF refining process is controlled at 150-200℃ above the liquidus line.

5. The method for precisely controlling nitrogen content during the smelting of high-strength iron-nickel-molybdenum alloys according to claim 4, characterized in that, After the ladle enters the LF station, it is first powered on and heated. Then, quicklime, fluorite, and calcium carbide are added to make white slag. After stirring with argon, temperature is measured and samples are taken to add alloys according to the target content.

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