Steel billet smelting method capable of realizing nondestructive recovery of waste billet

Abstract

The invention belongs to the technical field of steel billet smelting, and particularly relates to a steel billet smelting method for waste billet nondestructive recovery. The smelting method comprises the following steps of: slagging molten steel and then deoxidizing and slagging; raising the temperature to be greater than or equal to 1600 DEG C under the condition of bottom blowing of inert gas, then adding the waste blank, and continuing bottom blowing of inert gas and raising the temperature to melt the waste blank; and carrying out alloying adjustment and temperature adjustment on the obtained molten steel, carrying out vacuum degassing, calcium treatment and soft blowing impurity removal, and carrying out continuous casting pouring to obtain a finished product steel billet. The waste blank is cut into a fixed size, hoisted and added into a refined LF steel ladle, the waste blank is melted through electrode heating, lossless recycling and reusing of the waste blank are achieved, the waste blank recycling rate reaches 100%, meanwhile, the quality of molten steel is not affected, and the product quality control requirement is completely met. After the method is applied, the waste blank recovery rate can be greatly improved, and meanwhile the secondary machining cost of the waste blank is reduced.

Description

Technical Field

[0001] The invention belongs to the technical field of steel billet smelting, and in particular relates to a steel billet smelting method for lossless recovery of waste billets. Background Art

[0002] During the steelmaking process, the quality of the first and last billets varies significantly due to factors such as the cleanliness of the tundish, protective pouring, and the final billet finish. If used as normal billets, the impact is significant. Generally, steel mills consider the first and last billets scrap and recycle them. The conventional method is to cut the first and last billets, along with other scrap billets, into blocks and then melt them in a converter to produce molten steel for secondary processing. This method results in 5-10% blowdown, and some easily oxidized elements, such as manganese and silicon, are almost completely lost, resulting in significant alloy cost waste. Summary of the Invention

[0003] In view of the above problems existing in the prior art, the present invention provides a steel billet smelting method for lossless recovery of waste billets, which can achieve lossless utilization of steel billets.

[0004] To achieve the above-mentioned purpose, the technical solution provided by the present invention is as follows:

[0005] In a first aspect, the present application provides a steel billet smelting method for lossless recycling of scrap billets, comprising the following steps:

[0006] 1) Molten steel is slag-formed and then deoxidized to form slag;

[0007] 2) heating the molten steel obtained in 1) to ≥1600°C under bottom blowing of inert gas, adding scrap, and continuing to blow inert gas from the bottom and heating to melt the scrap;

[0008] 3) The molten steel obtained in 2) is alloyed and temperature-adjusted as required, and then vacuum degassed, calcium treated, and soft-blown to remove impurities, and then continuously cast to obtain the finished steel billet.

[0009] Optionally, the amount of scrap added to every 150 tons of molten steel is 1-2 tons.

[0010] Optionally, the slagging conditions are 200-220V and 50-60KA current.

[0011] Optionally, the flow rate of the bottom blowing inert gas before adding the waste billets is 200-300 NL / min; the flow rate of the bottom blowing inert gas after adding the waste billets is 600-800 NL / min.

[0012] Optionally, bottom blowing of inert gas is also performed while adding the waste blanks, and the flow rate of the bottom blowing inert gas is 50-100NL / min.

[0013] Optionally, the deoxidation and slag making includes: adding lime and fluorite to adjust fluidity, and adding aluminum wire + aluminum wire to deoxidize the molten steel.

[0014] Optionally, the mass ratio of the aluminum wire to the aluminum filament is 1:(1-2).

[0015] Optionally, after adding the waste blank, the temperature rising conditions are: voltage 240-250V, current 50-60KA, and temperature rising for 3-5 minutes.

[0016] Optionally, the temperature of the molten steel is ≥1600°C when the scrap is added.

[0017] Optionally, the scrap blank has a size of: length ≤ 2000 mm, width ≤ 600 mm, and thickness ≤ 500 mm.

[0018] Compared with the prior art, this application has at least the following beneficial effects:

[0019] This method cuts scrap into fixed sizes, hoists it into a refining LF ladle, and melts it using electrodes to heat it, achieving non-destructive recycling and reuse of the scrap. This method achieves a 100% scrap recovery rate without affecting the quality of the molten steel, fully meeting product quality control requirements. This method significantly improves scrap recovery rates while reducing the cost of secondary processing. DETAILED DESCRIPTION

[0020] The present invention is described in further detail below:

[0021] Unless otherwise specified, the experimental methods used in the embodiments of the present invention are conventional methods.

[0022] The reagents and materials used in this example can be purchased conventionally. The quantitative experiments involved in the examples were repeated at least three times, and the results were averaged.

[0023] Example

[0024] 1) The initial conditions for LF smelting molten steel are shown in Table 1. After slagging the molten steel and adding lime and fluorite to adjust fluidity, aluminum wire and aluminum wire are added for deoxidation and slagging. The slagging conditions and the mass of the materials added for deoxidation and slagging are shown in Table 2.

[0025] Table 1 Initial conditions of molten steel in two LF furnaces

[0026] Furnace number Temperature Molten steel volume T Slag amount T C Mn Si P S AL Ni 01 1519 168 1 0.030 0.55 0.14 0.0043 0.0053 0.022 8.29 02 1522 167 0.997 0.028 0.52 0.13 0.0043 0.0050 0.017 8.38

[0027] Table 2 Additives for slagging and deoxidation slagging

[0028] Furnace number Slag conditions Slag time Lime (kg) Fluorite (kg) Aluminum wire (kg) Aluminum wire (kg) 01 220V, 60KA 128 882 62 66 90 02 200V, 50KA 133 869 30 66 100

[0029] 2) Raise the temperature for 3 minutes at a voltage of 240-250V and a current of 50-60kA. Simultaneously, blow argon from the bottom at a flow rate of 200-300 nL / min to prevent large temperature drop losses during stirring and poor stirring and temperature stratification. After heating to 1608°C, add scrap (150 mm * 580 mm * 1700 mm, weighing 1.15 tons) to Furnace 01. After heating to 1605°C, add scrap (150 mm * 580 mm * 1680 mm, weighing 1.14 tons) to Furnace 02. When adding scrap, adjust the bottom blowing opening to 50-100 nL / min and park the ladle. Observe the molten steel clearance. Add the scrap when the clearance is ≥500mm. After adding the scrap, perform strong bottom blowing and stirring (adjust the bottom blowing opening to 600-800 nL / min) for 2-3 minutes. Then continue heating and melting. The voltage for heating is 240V and the current is 50kA. The heating and melting time was adjusted according to the weight of the scrap added (2 minutes / ton). The scrap composition and the molten steel composition before and after the scrap addition are shown in Table 3.

[0030] Table 3 Scrap composition, molten steel composition before and after scrap addition (%)

[0031] Furnace number Ingredient comparison% C Mn Si P S AL Ni 01 Scrap composition 0.042 0.68 0.21 0.0046 0.0011 0.028 8.68 01 Before joining 0.033 0.56 0.18 0.0044 0.0033 0.038 8.29 01 After joining 0.035 0.56 0.18 0.0044 0.0029 0.02 8.29 02 Scrap composition 0.044 0.66 0.20 0.0046 0.0010 0.030 8.62 02 Before joining 0.031 0.52 0.17 0.0046 0.0028 0.041 8.42 02 After joining 0.033 0.53 0.17 0.0047 0.0022 0.025 8.43

[0032] 3) Alloying adjustment of molten steel: According to the sampling results and the composition requirements of the smelting steel grade, the composition alloying adjustment is carried out (according to the composition requirements of X7NI9 steel grade, 180 kg of metallic manganese, 86 kg of ferrosilicon, 15 kg of carbon powder, and 720 kg of nickel plate are added to furnace No. 01 for alloying; 250 kg of metallic manganese, 110 kg of ferrosilicon, 15 kg of carbon powder, and 300 kg of nickel plate are added to furnace No. 02 for alloying; both meet the composition requirements of the steel grade quality plan).

[0033] Temperature adjustment: After alloying is completed, the temperature is adjusted according to the temperature requirements of the steel quality plan (according to the temperature requirements of X7NI9 steel: the temperature of furnace No. 01 is 1656℃ after continuing to heat up for 17 minutes; the temperature of furnace No. 01 is 1653℃ after continuing to heat up for 15 minutes).

[0034] Carry out vacuum degassing treatment according to the vacuum requirements of the steel grade.

[0035] After the composition and temperature are qualified, calcium treatment is carried out to denature the inclusions.

[0036] After calcium treatment, static stirring is required for ≥15 minutes. The soft stirring bottom blowing rate is precisely controlled at 30-50 NL / min to maintain slag peristalsis and prevent the molten steel from being exposed. This allows inclusions to fully aggregate, float, and be absorbed by the slag after denaturation. The final molten steel composition at the end of treatment is shown in Table 4.

[0037] Table 4 Final molten steel composition%

[0038] Furnace number C Mn P S Si Alt Ni 01 0.046 0.65 0.0046 0.0009 0.22 0.031 8.69 02 0.044 0.65 0.0047 0.0010 0.22 0.029 8.67

[0039] Continuous casting then proceeded. Argon was blown through a protective casing, a covering agent (200 kg added to the first furnace (the first one) at the start of pouring, and 40 kg added after the second furnace) and carbonized rice husks were added to the tundish (75 kg added after the first furnace and 20 kg added after the second furnace). Protective slag was also added to the mold to ensure full protection during the casting process. The continuous casting protective pouring control was stable, with an endpoint T[O] of 9 ppm and [N] of 28 ppm. The low-magnification quality was excellent, and 314 tons of steel plates were tested and all passed the inspection.

[0040] This method achieves lossless scrap recovery, achieving a 100% scrap recovery rate. It also maintains a stable production rhythm and molten steel quality, meeting the requirements of large-scale on-site production. This method reduces alloy costs. Conventional converter scrap recovery of manganese and silicon is essentially completely lost through blowout, while this method eliminates this loss and reduces scrap processing costs.

[0041] The above description is merely a specific embodiment of the present invention, but the scope of protection of the present invention is not limited thereto. Any modifications or substitutions that can be easily conceived by a person skilled in the art within the technical scope disclosed in the present invention should be included within the scope of protection of the present invention. Therefore, the scope of protection of the present invention should be based on the scope of protection of the claims.

[0042] Obviously, the above embodiments are merely examples for clarity of explanation and are not intended to limit the implementation methods. Those skilled in the art will readily appreciate that other variations or modifications based on the above descriptions are possible. It is not necessary and impossible to enumerate all implementation methods here. Obvious variations or modifications arising therefrom remain within the scope of protection of the present invention.

Claims

1. A steel billet smelting method for non-destructive recycling of waste billets, characterized in that: The steps include: 1) Molten steel is slag-formed and then deoxidized to form slag; 2) heating the molten steel obtained in 1) to ≥1600°C under bottom blowing of inert gas, adding scrap, and continuing to blow inert gas from the bottom and heating to melt the scrap; 3) The molten steel obtained in 2) is alloyed and temperature-adjusted as required, and then vacuum degassed, calcium treated, and soft-blown to remove impurities, and then continuously cast to obtain the finished steel billet.

2. The steel billet smelting method for non-destructive recycling of scrap billets according to claim 1, characterized in that: The amount of scrap added to every 150 tons of molten steel is 1-2 tons.

3. The steel billet smelting method for non-destructive recycling of scrap billets according to claim 1, characterized in that: The slag-forming conditions are 200-220V and 50-60KA current.

4. The steel billet smelting method for non-destructive recycling of scrap billets according to claim 1, characterized in that: The flow rate of the bottom blowing inert gas before adding the waste billets is 200-300NL / min; the flow rate of the bottom blowing inert gas after adding the waste billets is 600-800NL / min.

5. The steel billet smelting method for non-destructive recycling of scrap billets according to claim 1, characterized in that: While adding the waste billets, bottom blowing of inert gas is also carried out, and the flow rate of the bottom blowing inert gas is 50-100NL / min.

6. The steel billet smelting method for non-destructive recycling of scrap billets according to claim 1, characterized in that: The deoxidation slag making includes: adding lime and fluorite to adjust the fluidity, and adding aluminum wire + aluminum wire to deoxidize the molten steel.

7. The steel billet smelting method for non-destructive recycling of scrap billets according to claim 6, characterized in that: The mass usage ratio of aluminum wire and aluminum filament is 1:(1-2).

8. The steel billet smelting method for non-destructive recycling of scrap billets according to claim 1, characterized in that: After adding the waste billet, the heating conditions are: voltage 240-250V, current 50-60KA, and heating for 3-5 minutes.

9. The steel billet smelting method for non-destructive recycling of scrap billets according to claim 1, characterized in that: When adding the scrap, the temperature of the molten steel is ≥1600°C.

10. The steel billet smelting method for non-destructive recycling of scrap billets according to claim 1, characterized in that: The scrap blank has the following dimensions: length ≤ 2000 mm, width ≤ 600 mm, and thickness ≤ 500 mm.