A method for reducing the specific gravity of the ingot riser of a vacuum induction furnace

Abstract

The present invention provides a method for reducing the proportion of the ingot riser in a vacuum induction furnace, which specifically includes the following contents: (1) A circular pipe with a side opening is arranged between the hot top brick and the funnel brick; (2) The ingot mold, the hot top brick and the funnel brick are heated to above 200 °C; (3) The initial pouring temperature T1 ≥ the liquidus of the molten steel + 20 °C, and the initial pouring speed is 0.4 kg / s - 0.8 kg / s; (4) When the molten steel level rises to 1 / 3 of the total height of the ingot mold, the pouring temperature is increased to T2 ≥ the liquidus of the molten steel + 30 °C, and the pouring speed is reduced to 0.3 kg / s - 0.5 kg / s; (5) When the molten steel rises into the hot top brick, the pouring speed is reduced to 0.1 kg / s - 0.3 kg / s, and the pouring temperature is increased to T3 ≥ the liquidus of the molten steel + 40 °C. The present invention can significantly reduce the proportion of the ingot riser, which is reduced from about 20% originally to below 12.5%.

Description

Technical Field

[0001] The present invention relates to the field of vacuum induction melting, and in particular to a method for reducing the specific gravity of a riser of an ingot in a vacuum induction furnace. Background Art

[0002] During the solidification process, the steel ingot will shrink in volume, and shrinkage cavities and shrinkage porosity will occur in the area where the molten steel solidifies last. In order to improve the quality of the steel ingot and ensure that the ingot body is free of defects, a riser needs to be set on the top of the ingot to replenish the molten steel lost due to the shrinkage of the steel ingot. To ensure that the riser can fully complete the shrinkage compensation task, it is necessary to use insulation bricks at the riser position to extend the solidification time of the molten steel. Alternatively, a heat-generating riser can be used or an insulation or heat-generating agent can be added to the top of the riser after pouring to ensure that the molten steel at the riser solidifies last, achieving the purpose of normal shrinkage compensation. The specific gravity of the riser varies according to the shape of the steel ingot. Generally, the weight of the riser accounts for about 20%-25% of the entire steel ingot. For some steel grades with large shrinkage, the riser weight can even reach more than 40% of the total ingot mass. An excessively large riser weight requires subsequent cutting and remelting of the riser, resulting in a waste of manpower and resources, reduced yield, and increased costs. When using a vacuum induction furnace to smelt ingots, since the entire metallurgical process is carried out in a negative pressure vacuum furnace body, the heating riser or the method of adding a heat preservation agent after pouring provided in the prior art is not applicable and has a poor effect in reducing the riser weight. Therefore, it is necessary to provide a method for reducing the riser weight that can be applied to vacuum induction furnace smelting. Summary of the Invention

[0003] Based on the above technical problems that the existing methods of reducing the riser proportion are poorly effective and not suitable for the vacuum induction furnace smelting environment, a method for reducing the riser proportion of vacuum induction furnace ingots is provided. By preheating the ingot mold and insulating riser bricks in combination with a suitable casting process, the proportion of the riser in the steel ingot can be reduced to below 12.5%, thereby improving the product yield, saving resources and reducing costs.

[0004] The technical means adopted in the present invention are as follows:

[0005] A method for reducing the specific gravity of a vacuum induction furnace ingot riser specifically comprises the following contents:

[0006] (1) The ingot mold assembly includes a funnel brick, an insulation cap brick, and an ingot mold coaxially arranged from top to bottom; a circular ring tube with a side opening is provided between the insulation cap brick and the funnel brick, which is used as an observation port for observing the pouring of molten steel into the ingot mold;

[0007] (2) Before pouring, the ingot mold, the insulation cap brick and the funnel brick are heated to above 200°C;

[0008] (3) Start pouring. The pouring method is top pouring. The initial pouring temperature T1 ≥ liquidus of the molten steel + 20°C, and the initial pouring speed is 0.4 kg / s - 0.8 kg / s;

[0009] (4) During the pouring process, when the molten steel level rises to 1 / 3 - 1 / 2 of the total height of the ingot mold, raise the pouring temperature to T2 ≥ liquidus of the molten steel + 30°C, and reduce the pouring speed to 0.3 kg / s - 0.5 kg / s;

[0010] (5) When the molten steel fills the ingot mold and starts to rise into the internal part of the hot top brick, reduce the pouring speed to 0.1 kg / s - 0.3 kg / s, raise the pouring temperature to T3 ≥ liquidus of the molten steel + 40°C, and continue pouring until the pouring is completed; The pouring temperatures T1, T2, and T3 satisfy: T3 > T2 > T1.

[0011] Furthermore, the hot top brick and the funnel brick are made of refractory materials.

[0012] Furthermore, when the molten steel starts to rise into the internal part of the hot top brick, after reducing the pouring speed, use the intermittent pouring method to pour until the pouring is completed. The intermittent pouring method refers to the process of repeating pouring for a period of time and then stopping pouring.

[0013] Furthermore, when the molten steel starts to rise into the internal part of the hot top brick, observe the molten steel level situation in real time through the opening on the circular tube. If the phenomenon of the ingot edge solidifying towards the center occurs due to too fast temperature drop of the molten steel, it is necessary to raise the pouring temperature.

[0014] Furthermore, it also includes installing an angle measuring scale for measuring the tilting angle of the induction coil spindle on the part of the induction coil spindle of the vacuum induction furnace located outside the furnace body, or on the cable connected to the induction coil spindle outside the furnace body.

[0015] Furthermore, the central aperture of the adopted funnel brick is 10 - 30 mm.

[0016] Compared with the prior art, the present invention has the following advantages:

[0017] The method for reducing the proportion of the ingot riser of the vacuum induction furnace provided by the present invention can significantly reduce the proportion of the ingot riser, from about 20% originally to less than 12.5%. While the riser is reduced, there are no defects inside the ingot, and the composition segregation situation is improved.

[0018] Based on the above reasons, the present invention can be widely promoted in the field of vacuum induction melting. Specific Embodiments

[0019] To make the objectives, technical solutions and advantages of the embodiments of the present invention clearer, the technical solutions in the embodiments of the present invention will be clearly and completely described below. Apparently, the described embodiments are only a part rather than all of the embodiments of the present invention. The description of at least one exemplary embodiment is actually only illustrative and shall in no way be construed as any limitation to the present invention and its application or use. All other embodiments obtained by those of ordinary skill in the art based on the embodiments of the present invention without creative efforts shall fall within the scope of protection of the present invention.

[0020] The present invention provides a method for reducing the specific gravity of the ingot riser of a vacuum induction furnace, which specifically includes the following contents:

[0021] (1) The commonly used ingot mold assembly of a vacuum induction furnace includes a funnel brick, a hot top brick and an ingot mold coaxially arranged from top to bottom. When pouring molten steel, it first enters the funnel brick and flows into the ingot mold through the small hole in the center of the funnel brick until the liquid level of the molten steel rises to the inside of the hot top brick.

[0022] In this application, a circular tube with a side opening is arranged between the hot top brick and the funnel brick, which is used as an observation port for observing the situation of pouring molten steel into the ingot mold, so as to adjust the pouring speed.

[0023] (2) Before pouring, heat the ingot mold, the hot top brick and the funnel brick to above 200 °C.

[0024] (3) Start pouring. The pouring method is top pouring. The initial pouring temperature T1 ≥ the liquidus of the molten steel + 20 °C, and the initial pouring speed is 0.4 kg / s - 0.8 kg / s.

[0025] (4) During the pouring process, when the liquid level of the molten steel rises to 1 / 3 - 1 / 2 of the total height of the ingot mold, increase the heating power to raise the pouring temperature to T2 ≥ the liquidus of the molten steel + 30 °C, and reduce the pouring speed to 0.3 kg / s - 0.5 kg / s.

[0026] (5) When the molten steel fills the ingot mold and starts to rise into the hot top brick, reduce the pouring speed to 0.1 kg / s - 0.3 kg / s, raise the pouring temperature to T3 ≥ the liquidus of the molten steel + 40 °C, and continue pouring until the pouring is completed. The pouring temperatures T1, T2, and T3 satisfy: T3 > T2 > T1.

[0027] Furthermore, the hot top brick and the funnel brick are made of refractory materials.

[0028] Further, when the molten steel starts to rise into the internal part of the hot top brick, after reducing the casting speed, intermittent casting is adopted until the casting is completed. The intermittent casting method refers to the process of repeating casting for a period of time and then stopping casting. During the intermittent casting process, both the casting time and the stopping casting time can be adjusted according to actual needs.

[0029] Further, when the molten steel starts to rise into the internal part of the hot top brick, the liquid level of the molten steel is observed in real time through the opening on the circular pipe. If the phenomenon of the ingot edge solidifying towards the center occurs due to too rapid temperature drop of the molten steel, the casting temperature needs to be increased.

[0030] Further, the method for reducing the proportion of the ingot riser of the vacuum induction furnace further includes setting an angle measuring scale for measuring the tilting angle of the main shaft of the induction coil on the part of the main shaft of the induction coil of the vacuum induction furnace located outside the furnace body, or on the cable connected to the main shaft of the induction coil outside the furnace body; the weight of the remaining molten steel in the crucible of the vacuum induction furnace can be determined according to the tilting angle of the main shaft of the induction coil. When the staff controls the casting speed of the molten steel by observing the situation of the molten steel being cast into the ingot mold through the observation window, the weight of the remaining molten steel in the crucible can also provide certain reference; when the main shaft of the induction coil tilts due to the change in the weight of the crucible in the vacuum induction furnace, the cable connected to the main shaft of the induction coil will also tilt synchronously with the main shaft of the induction coil, so its tilting angle can also represent the tilting angle of the main shaft of the induction coil; for different vacuum induction furnaces, the specific corresponding relationship between the tilting angle of the main shaft of the induction coil and the weight of the remaining molten steel in the furnace can be calibrated by the staff through multiple tests.

[0031] Further, the central aperture of the funnel brick adopted is 10 - 30 mm, and it can be specifically selected according to the weight of the ingot.

[0032] Further, during the casting process, the rising situation of the molten steel can be observed through the opening on the circular pipe to ensure that the molten steel rises slowly in the ingot mold.

[0033] The method for reducing the proportion of the ingot riser of the vacuum induction furnace provided by the present invention observes the position of the molten steel in the ingot mold group during the casting process through the circular pipe provided, and then adjusts parameters such as the casting speed. It can also observe the liquid level situation of the molten steel and timely adjust the casting temperature. By using the method provided by the present invention, the proportion of the ingot riser can be significantly reduced, from about 20% originally to below 12.5%. While the riser is reduced, it can ensure that there are no defects inside the ingot, and the component segregation situation is improved.

[0034] Example 1

[0035] In this embodiment, the method provided by the present invention is applied to the smelting of a certain steel grade in a 500 kg vacuum induction furnace. The diameter of the ingot mold is about 380 mm and the height is 600 mm. According to theoretical calculations, the weight of the riser should account for 19.8% of the total weight. The normal pouring speed is generally 0.8 kg / s - 1.2 kg / s. The specific contents are as follows:

[0036] (1) A circular pipe with a side opening is provided between the hot top brick and the funnel brick, which is used as an observation port for observing the situation of molten steel pouring into the ingot mold;

[0037] (2) Before pouring, the ingot mold, the hot top brick and the funnel brick are heated to 800 °C; the central aperture of the funnel brick used is 20 mm;

[0038] (3) Use a vacuum induction furnace to smelt the steel grade. After the molten steel is melted, start pouring. The pouring method is top pouring. The initial pouring temperature T1 is 1550 °C and the initial pouring speed is 0.75 kg / s;

[0039] (4) During the pouring process, when the molten steel level rises to 1 / 3 of the total height of the ingot mold, raise the pouring temperature to T2 = 1570 °C and lower the pouring speed to 0.45 kg / s;

[0040] (5) When the molten steel fills the ingot mold and starts to rise into the hot top brick, lower the pouring speed to 0.25 kg / s and continue pouring. Raise the pouring temperature to T3 ≥ 1600 °C and continue pouring until the pouring is completed; the pouring temperatures T1, T2, and T3 satisfy: T3 > T2 > T1; because the pouring speed is slow, it is necessary to use an intermittent pouring method until the pouring is completed, that is, pour for 5 s and stop for 10 or 15 s; during pouring, observe the molten steel level situation in real time through the opening on the circular pipe. If the phenomenon of the ingot edge solidifying towards the center appears due to too fast temperature drop of the molten steel, it is necessary to raise the pouring temperature.

[0041] By cutting and weighing the ingots smelted in this embodiment, the results show that the surface quality of the ingot body is intact and uniform, there are no defects such as shrinkage cavities and porosity at the cut of the riser, and the proportion of the riser is 10.6%.

[0042] Embodiment 2

[0043] In this embodiment, the method provided by the present invention is applied to the smelting of a certain steel grade in a 200 kg vacuum induction furnace. The diameter of the ingot mold is about 175 mm and the height is 450 mm. According to theoretical calculations, the weight of the riser should account for 20% of the total weight. The normal pouring speed is generally 0.7 kg / s - 0.9 kg / s. The specific contents are as follows:

[0044] (1) A circular tube with a side opening is arranged between the insulating cap brick and the funnel brick, which is used as an observation port for observing the situation of molten steel being poured into the ingot mold.

[0045] (2) Before pouring, heat the ingot mold, the insulating cap brick and the funnel brick to 600 °C; the central aperture of the used funnel brick is 15 mm.

[0046] (3) Use a vacuum induction furnace to smelt the steel grade. After the molten steel is melted, start pouring. The pouring method is top pouring. The initial pouring temperature T1 is 1536 °C, and the initial pouring speed is 0.6 kg / s.

[0047] (4) During the pouring process, when the molten steel level rises to 1 / 3 of the total height of the ingot mold, raise the pouring temperature to T2 = 1556 °C and lower the pouring speed to 0.4 kg / s.

[0048] (5) When the molten steel fills the ingot mold and starts to rise into the insulating cap brick, lower the pouring speed to 0.25 kg / s and continue pouring. Raise the pouring temperature to T3 ≥ 1576 °C and continue pouring until the pouring is completed; the pouring temperatures T1, T2, and T3 satisfy: T3 > T2 > T1; because the pouring speed is slow, it is necessary to use the intermittent pouring method until the pouring is completed, that is, pour for 3 - 5 s and stop for 5 - 8 s or longer; during pouring, observe the molten steel level situation in real time through the opening on the circular tube. If the phenomenon of the ingot edge solidifying towards the center occurs due to too rapid temperature drop of the molten steel, it is necessary to raise the pouring temperature.

[0049] By cutting and weighing the steel ingots smelted in this embodiment, the results show that the surface quality of the ingot body is intact and uniform, there are no defects such as shrinkage cavities and porosity at the cut of the riser, and the proportion of the riser is 12.2%.

[0050] Finally, it should be noted that: the above embodiments are only used to illustrate the technical solutions of the present invention, rather than to limit it; although the present invention has been described in detail with reference to the foregoing embodiments, those of ordinary skill in the art should understand that: they can still modify the technical solutions recorded in the foregoing embodiments, or perform equivalent replacements on some or all of the technical features; and these modifications or replacements do not make the essence of the corresponding technical solutions deviate from the scope of the technical solutions of the embodiments of the present invention.

Claims

1. A method for reducing the specific gravity of the ingot riser of a vacuum induction furnace, characterized in that, Specifically, it includes the following contents: (1) The ingot mold assembly includes a funnel brick, a hot top brick, and an ingot mold that are coaxially arranged from top to bottom; a circular tube with a side opening is provided between the hot top brick and the funnel brick, which is used as an observation port for observing the situation of molten steel pouring into the inside of the ingot mold; (2) Before pouring, heat the ingot mold, the hot top brick, and the funnel brick to above 200 °C; (3) Start pouring. The pouring method is top pouring. The initial pouring temperature T1 ≥ liquidus of molten steel + 20 °C, and the initial pouring speed is 0.4 kg / s - 0.8 kg / s; (4) During the pouring process, when the molten steel level rises to 1 / 3 - 1 / 2 of the total height of the ingot mold, raise the pouring temperature to T2 ≥ liquidus of molten steel + 30 °C, and lower the pouring speed to 0.3 kg / s - 0.5 kg / s; (5) When the molten steel fills the ingot mold and starts to rise into the hot top brick, lower the pouring speed to 0.1 kg / s - 0.3 kg / s, raise the pouring temperature to T3 ≥ liquidus of molten steel + 40 °C, and continue pouring until pouring is completed; the pouring temperatures T1, T2, and T3 satisfy: T3 > T2 > T1; When the molten steel starts to rise into the hot top brick, observe the molten steel level situation in real time through the opening on the circular tube. If the phenomenon of the ingot edge solidifying towards the center occurs due to too rapid temperature drop of the molten steel, it is necessary to raise the pouring temperature; It also includes an angle measuring scale for measuring the tilting angle of the induction coil spindle, which is arranged on the part of the induction coil spindle of the vacuum induction furnace located outside the furnace body, or on the cable connected to the induction coil spindle outside the furnace body.

2. The method for reducing the specific gravity of the ingot riser of a vacuum induction furnace according to claim 1, characterized in that, The hot top brick and the funnel brick are made of refractory materials.

3. The method for reducing the specific gravity of the ingot riser of a vacuum induction furnace according to claim 1, characterized in that, When the molten steel starts to rise into the hot top brick, after lowering the pouring speed, use an intermittent pouring method to pour until pouring is completed. The intermittent pouring method refers to the process of repeating pouring for a period of time and then stopping pouring.

4. The method for reducing the specific gravity of the ingot riser of a vacuum induction furnace according to claim 1, characterized in that, The central aperture of the adopted funnel brick is 10 - 30 mm.