A method for reducing cracks at the connection between the ingot riser and the ingot body

Abstract

The present invention provides a method for reducing cracks at the connection between the ingot riser and the ingot body, which specifically includes the following steps: S1. Wrap a fiber blanket on the upper part of the hot top brick, and install a steel sleeve outside the fiber blanket and the hot top brick for fixation; S2. Bake the ingot mold to above 400 °C; S3. Arrange the ingot mold, the hot top brick and the funnel brick coaxially; S4. After adjusting the pouring temperature of the molten steel, start pouring, and the pouring temperature T satisfies: liquidus of the molten steel + 20 °C ≤ T ≤ liquidus of the molten steel + 60 °C; when the molten steel is poured to 1 / 2 to 3 / 4 of the height of the ingot mold, reduce the pouring speed to 0.8 - 0.9 times of the initial pouring speed, continue pouring until the ingot contacts the hot top brick, then reduce the pouring speed to 0.3 - 0.7 times of the initial pouring speed, heat the molten steel to T1 ≥ T + 30 °C and continue pouring until the pouring is completed. By using the present invention, the cracks at the contact between the ingot riser and the ingot body are significantly reduced.

Description

Technical Field

[0001] The present invention relates to the technical field of iron and steel metallurgy, and in particular to a method for reducing cracks at the connection between an ingot riser and an ingot body. Background Art

[0002] The riser of an ingot is designed to prevent defects such as shrinkage cavities and porosity in the ingot body. The riser is positioned above the ingot body, and insulation cap bricks are placed above the ingot mold to form the riser and ensure that the riser cools slowly, thereby compensating for the shrinkage of the ingot body below the riser. However, for some steels or alloys with high alloy content, when smelting the ingot, the riser contacts the refractory material, while the ingot body contacts the cast iron ingot mold. Due to the different cooling rates of the two, the internal stress is excessive, which easily causes cracks near the connection between the riser and the ingot body. The cracks generally occur within 10 cm of the upper ingot body. To prevent the cracks from affecting the next step of the ingot casting process, the cracked portion must be cut off together with the riser. The occurrence of cracks will affect the yield rate of the ingot product. Ingots with more serious cracks may directly lead to the scrapping of the ingot. Cracks at the ingot riser increase the processing volume of subsequent processing, increasing product production costs.

[0003] To address the generation of cracks at the ingot riser, existing technologies such as patents CN110090927 and CN105598374A both use bottom-pouring sand casting, which has a complex process. Patent CN111014586A reduces the generation of cracks by providing a riser ring combined with a two-step riser cleaning method. However, this method also has problems such as complex process and operation, is not suitable for the smelting environment of a vacuum induction furnace, and has low efficiency, which cannot meet the requirements of cost-saving product development. Chen Xuesong's paper "Analysis and Countermeasures of Crack Defects at the Root of Riser of High-Strength Steel Castings" proposes targeted improvements in riser design and riser cleaning, and uses a heat-insulating riser. After production verification using the improved measures, cracks at the riser root have been completely resolved. However, the method proposed in the paper is targeted at a specific steel grade and provides a heat-insulating riser method. When applied to sand casting, it solves the problem of riser root cracks. However, for some high-alloy steel grades, this method is not as effective. Summary of the Invention

[0004] According to the above-mentioned technical problems of the existing method for reducing cracks at the ingot riser, such as complex process, low efficiency and limited scope of application, a method for reducing cracks at the connection between the ingot riser and the ingot body is provided.

[0005] The technical means adopted in the present invention are as follows:

[0006] A method for reducing cracks at the connection between an ingot riser and an ingot body, comprising the following steps:

[0007] S1. Wrap a fiber blanket around the upper part of the insulating cap brick, and install a steel sleeve outside the fiber blanket and the insulating cap brick for fixation; fill the gap between the insulating cap brick and the steel sleeve with refractory material;

[0008] S2. Bake the ingot mold to a temperature above 400 °C;

[0009] S3. Arrange the ingot mold, the insulating cap brick and the funnel brick coaxially;

[0010] S4. Close the vacuum induction furnace and evacuate it to start steelmaking; after adjusting the pouring temperature of the molten steel, start pouring. The pouring temperature T satisfies: liquidus of the molten steel + 20 °C ≤ T ≤ liquidus of the molten steel + 60 °C. Determine the initial pouring speed according to the steel type and the size of the ingot. The pouring method is top pouring; when the molten steel is poured to 1 / 2 to 3 / 4 of the height of the ingot mold, reduce the pouring speed to 0.8 - 0.9 times of the initial pouring speed; continue pouring until the ingot touches the insulating cap brick, then reduce the pouring speed to 0.3 - 0.7 times of the initial pouring speed, and while pouring, heat the molten steel to T1 and continue pouring until pouring is completed, where T1 ≥ T + 30 °C.

[0011] Furthermore, the inner diameter of the lower part of the insulating cap brick is equal to the diameter of the ingot; the thickness of the fiber blanket is more than 10 mm.

[0012] Furthermore, in step S1, the filled refractory material is magnesite or quartz stone mixed with glass oil.

[0013] Furthermore, step S3 also includes setting a seamless pipe with a side opening between the funnel brick and the insulating cap brick as an observation port.

[0014] Furthermore, the side of the seamless pipe is provided with an opening with a width of 2 / 5 of the circumference of the seamless pipe.

[0015] Compared with the prior art, the present invention has the following advantages:

[0016] By using the method provided by the present invention for reducing cracks at the connection between the ingot riser and the ingot body, the cracks at the contact between the obtained ingot riser and the ingot body are significantly reduced. At the same time, there are no defects inside the ingot, and the weight of the riser is not increased.

[0017] For the above reasons, the present invention can be widely promoted in the field of iron and steel metallurgy. Specific embodiments

[0018] 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 described clearly and completely 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 in no way limits 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 belong to the scope of protection of the present invention.

[0019] The present invention provides a method for reducing cracks at the connection between the ingot riser and the ingot body, specifically including the following steps:

[0020] S1. Wrap a fiber blanket on the upper part of the hot top brick, and install a steel sleeve outside the fiber blanket and the hot top brick for fixation. The steel sleeve is used to fix the hot top brick and the fiber blanket to prevent the brick from cracking during pouring; fill the gap between the hot top brick and the steel sleeve with refractory material, compact it and dry the moisture to prevent the hot top brick from cracking due to heat during pouring; the inner diameter of the lower part of the hot top brick is equal to the diameter of the ingot;

[0021] S2. Bake the ingot mold to above 400°C;

[0022] S3. Arrange the ingot mold, the hot top brick, and the funnel brick coaxially; the commonly used ingot mold assembly in a vacuum induction furnace includes a funnel brick, a hot top brick, and an ingot mold arranged coaxially 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 molten steel level rises to the hot top brick;

[0023] S4. Close the vacuum induction furnace and evacuate it to start steelmaking; after adjusting the pouring temperature of the molten steel, start pouring. The pouring temperature T uses a low superheat of the molten steel and satisfies: liquidus of the molten steel + 20°C ≤ T ≤ liquidus of the molten steel + 60°C. Determine the initial pouring speed according to the steel type and the size of the ingot, and the pouring method is top pouring; when the molten steel is poured to 1 / 2 to 3 / 4 of the height of the ingot mold, reduce the pouring speed to 0.8 - 0.9 times the initial pouring speed, and continue pouring until the ingot contacts the hot top brick, then reduce the pouring speed to 0.3 - 0.7 times the initial pouring speed, and while pouring, heat the molten steel to T1 and continue pouring until pouring is completed, where T1 ≥ T + 30°C.

[0024] Further, in step S1, the fiber blanket is wrapped outside the upper 1 / 3 part of the hot top brick, and the thickness is above 10 mm.

[0025] Further, in step S1, the refractory material filled is refractory materials such as magnesite or quartz stone mixed with glass oil (the main component is sodium silicate).

[0026] Further, step S3 further includes providing a seamless tube with a side opening between the funnel brick and the hot top brick as an observation port for observing the situation of molten steel being poured into the ingot mold, so as to adjust the pouring speed.

[0027] Further, in step S3, the side of the seamless tube is provided with an opening with a width of 2 / 5 of the circumference of the seamless tube.

[0028] The method for reducing cracks at the connection between the ingot riser and the ingot body provided by the present invention reduces the temperature difference at the contact between the ingot body and the hot top brick by increasing the temperature of the ingot mold and performing heat preservation treatment on the upper part of the hot top brick. At the same time, when the molten steel is poured onto the hot top brick, the pouring speed is reduced and the pouring temperature is started to be increased, thereby reducing the solidification speed of the ingot at the riser, reducing the stress generated by solidification, and enhancing the feeding capacity of the hot top brick by extending the riser pouring time to prevent shrinkage cavity and porosity defects; for the ingots smelted by the method provided by the present invention, the crack phenomenon is significantly reduced and alleviated.

[0029] Example 1

[0030] In this embodiment, the method provided by the present invention is applied to smelting a certain Fe-C-Mn-Al steel grade in a 50 kg vacuum induction furnace. The diameter of the ingot mold is 130 mm and the height is 410 mm. The specific steps are as follows:

[0031] S1. Wrap the outer part of the upper 1 / 3 of the hot top brick with a 10 mm thick fiber blanket, and install a steel sleeve outside the fiber blanket and the hot top brick for fixation; fill the gap between the hot top brick and the steel sleeve with refractory material;

[0032] S2. Bake the ingot mold to 600 °C;

[0033] S3. Arrange the ingot mold, the hot top brick, and the funnel brick coaxially; provide a seamless tube with a side opening between the funnel brick and the hot top brick as an observation port. The height of the seamless tube is 80 mm, and the situation of molten steel being poured into the ingot mold can be observed through this observation port;

[0034] S4. Close the vacuum induction furnace and evacuate it to start steelmaking; after adjusting the pouring temperature of the molten steel, start pouring. The pouring temperature T = liquidus of the molten steel + 25°C = 1528°C, the initial pouring speed is 0.8 kg / s, and the pouring method is top pouring; when the molten steel is poured to 3 / 4 of the height of the ingot mold, reduce the pouring speed to 0.9 times the initial pouring speed, and continue pouring until the ingot contacts the hot top brick, then reduce the pouring speed to 0.6 times the initial pouring speed. Meanwhile, during pouring, heat the molten steel to 55°C above the liquidus of the molten steel, that is, 1558°C, and continue pouring until pouring is completed.

[0035] Statistics were made on the ingots smelted in this example, and the crack situation was significantly improved.

[0036] Example 2

[0037] In this example, the method provided by the present invention was applied to smelt a certain tool steel in a 200 kg vacuum induction furnace. The diameter of the ingot mold was about 175 mm and the height was 450 mm. The specific steps were as follows:

[0038] S1. Wrap the outer part of the upper 1 / 3 of the hot top brick with a 20 mm thick fiber blanket, and install a steel sleeve outside the fiber blanket and the hot top brick for fixation; fill the gap between the hot top brick and the steel sleeve with refractory material.

[0039] S2. Bake the ingot mold to 800°C.

[0040] S3. Arrange the ingot mold, the hot top brick, and the funnel brick coaxially; a seamless pipe with a side opening is arranged between the funnel brick and the hot top brick as an observation port. The height of the seamless pipe is 120 mm, and the situation of the molten steel being poured into the ingot mold can be observed through this observation port.

[0041] S4. Close the vacuum induction furnace and evacuate it to start steelmaking; after adjusting the pouring temperature of the molten steel, start pouring. The pouring temperature T = liquidus of the molten steel + 20°C = 1548°C, the initial pouring speed is 1.5 kg / s, and the pouring method is top pouring; when the molten steel is poured to 3 / 4 of the height of the ingot mold, reduce the pouring speed to 0.8 times the initial pouring speed, and continue pouring until the ingot contacts the hot top brick, then reduce the pouring speed to 0.5 times the initial pouring speed. Meanwhile, during pouring, heat the molten steel to 50°C above the liquidus of the molten steel, that is, 1578°C, and continue pouring until pouring is completed.

[0042] Statistics were made on the smelted ingots, and the crack situation was significantly improved.

[0043] 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 them; 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 described in the foregoing embodiments, or perform equivalent replacements on some or all of the technical features; and these modifications or replacements do not cause the essence of the corresponding technical solutions to deviate from the scope of the technical solutions of the embodiments of the present invention.

Claims

1. A method for reducing cracks at the connection between the ingot riser and the ingot body, characterized in that, Specifically, it includes the following steps: S1. Wrap a fiber blanket on the upper part of the hot top brick, and install a steel sleeve outside the fiber blanket and the hot top brick for fixation; fill refractory materials in the gap between the hot top brick and the steel sleeve; S2. Bake the ingot mold to a temperature above 400°C; S3. Arrange the ingot mold, the hot top brick and the funnel brick coaxially; S4. Close the vacuum induction furnace and evacuate it to start steelmaking; start pouring after adjusting the pouring temperature of the molten steel. The pouring temperature T satisfies: liquidus of the molten steel + 20°C ≤ T ≤ liquidus of the molten steel + 60°C. Determine the initial pouring speed according to the steel grade and the size of the ingot. The pouring method is top pouring; when the molten steel is poured to 1 / 2 to 3 / 4 of the height of the ingot mold, reduce the pouring speed to 0.8 - 0.9 times of the initial pouring speed; continue pouring until the ingot contacts the hot top brick, then reduce the pouring speed to 0.3 - 0.7 times of the initial pouring speed, and while pouring, heat the molten steel to T1 and continue pouring until pouring is completed, where T1 ≥ T + 30°C.

2. The method for reducing cracks at the connection between the ingot riser and the ingot body according to claim 1, characterized in that, The inner diameter of the lower part of the hot top brick is equal to the diameter of the ingot; the thickness of the fiber blanket is more than 10 mm.

3. The method for reducing cracks at the connection between the ingot riser and the ingot body according to claim 1, characterized in that, In step S1, the filled refractory material is magnesia or quartzite mixed with glass oil.

4. The method for reducing the crack at the connection between the ingot riser and the ingot body according to claim 1, characterized in that, Step S3 further includes arranging a seamless pipe with a side opening between the funnel brick and the hot top brick as an observation port.

5. The method for reducing cracks at the connection between the ingot riser and the ingot body according to claim 4, characterized in that, The side of the seamless pipe is provided with an opening with a width of 2 / 5 of the circumference of the seamless pipe.