Method for recycling hot casting slag and method for producing steel

Abstract

The present invention discloses a method for recycling cast waste hot slag and a method for producing steel. The method for recycling cast waste hot slag includes: after molten steel is smelted in a converter, steel is tapped and 1.5t-6t of cast waste hot slag is added to the molten steel, and then the molten steel is refining in an LF furnace. In the present application, it is not necessary to add slag washing lime and synthetic slag during the steel tapping process, and only 1.5t-6t of cast waste hot slag is needed, which can effectively improve the consumption of converter and LF slag material and the effect of rapid slag formation, and can reduce energy and raw material consumption, which is conducive to saving production costs.

Description

Technical Field

[0001] The invention relates to the technical field of steelmaking, and in particular to a method for recycling hot slag from casting and a method for producing steel. Background Art

[0002] At present, the production process of special steel and industrial steel usually includes: molten steel is smelted in a converter, slag washing lime and synthetic slag are added to the steel, and then it enters the LF furnace for refining. After adding a certain amount of lime at the station, lime or fluorite is added to adjust the slag fluidity. After the molten steel is poured in continuous casting, the remaining liquid slag is poured into the slag tank. This process has the following problems:

[0003] 1. The slag is not fully utilized. The residual hot slag in each furnace of steel is poured into the slag pot and treated as waste.

[0004] 2. The hot slag from casting contains unpoured molten steel, which causes waste after the slag is poured out of the slag tank.

[0005] 3. There is a lot of heat and temperature in the casting slag. Recycling and reuse can reduce temperature loss and power loss.

[0006] In view of this, the present invention is proposed. Summary of the invention

[0007] The purpose of the present invention is to provide a method for recycling casting hot slag and a method for producing steel, so as to utilize the casting hot slag and reduce the loss of molten steel and heat in the casting hot slag without reducing the performance of the steel.

[0008] The present invention is achieved in that:

[0009] In a first aspect, the present invention provides a method for recycling hot casting slag, comprising: after molten steel is smelted in a converter, 1.5t-6t of hot casting slag is added to the molten steel after tapping, and then the molten steel is put into an LF furnace for refining.

[0010] In an optional embodiment, during the LF furnace refining process, 340-360 kg of lime is first added, and then lime or fluorite is added.

[0011] In an optional embodiment, all of the following features are met:

[0012] The continuous casting step does not require steel retention operation;

[0013] The converter is tapping or the LF furnace is not feeding back the bottom blowing;

[0014] The clearance of the ladle receiving the hot slag from casting should be ≥400mm;

[0015] The recycling times of the hot casting slag are less than 3 times.

[0016] In an optional embodiment, the hot cast slag is a mixture of slag remaining after continuous casting of molten steel and molten steel, and the molten steel in the hot cast slag added to the molten steel is less than 5 tons;

[0017] And / or, the remaining hot casting slag after continuous casting of molten steel is poured into a furnace receiving the hot casting slag by using an overhead crane to lift the ladle, and then all the hot casting slag in the furnace receiving the hot casting slag is added into the received molten steel at once;

[0018] And / or, during the production process of the cast waste hot slag, no slag is discharged when the converter is tapping steel.

[0019] In an optional embodiment, the method is applied to the production of special steel or industrial steel.

[0020] In a second aspect, the present invention provides a method for producing steel, including the method for recycling hot slag from casting as described in the aforementioned embodiment, wherein the steel is special steel or industrial steel.

[0021] In an optional embodiment, the steel model is at least one of 45 steel, 40Cr, 25, 35, 10, 20CrMo, 40Mn2, 20Mn2 and SAE1020.

[0022] And / or, the steel has no upper or lower limit requirement on sulfur content.

[0023] In an optional embodiment, after being refined in the LF furnace, the molten steel enters the RH refining step. If the slag thickness measured at the RH station exceeds 300 mm, slag pouring is carried out.

[0024] In an optional embodiment, the molten steel enters the RH refining step after being refined in the LF furnace. If the received hot slag from casting needs to be subcontracted due to abnormal composition, and the slag thickness is measured to be more than 300 mm after slag making in the LF furnace refining step, it will be fed back to the RH furnace for slag pouring.

[0025] In an optional embodiment, after the molten steel is refined in the LF furnace, it enters the RH refining step. If there is obvious slag when tapping the converter and the residual hot slag has been received, in the LF furnace refining step, if the slag thickness is measured to be more than 300 mm after slag making is completed, it will be fed back to the RH furnace and the slag will be poured.

[0026] The present invention has the following beneficial effects:

[0027] In the present application, there is no need to add slag washing lime and synthetic slag during the steel tapping process. Only 1.5t-6t of waste hot slag from casting needs to be added, which can effectively improve the slag consumption and rapid slag formation effect of the converter and LF furnace, while reducing energy and raw material consumption, which is beneficial to saving production costs. DETAILED DESCRIPTION

[0028] In order to make the purpose, technical scheme and advantages of the embodiments of the present invention clearer, the technical scheme in the embodiments of the present invention will be described clearly and completely below. If the specific conditions are not specified in the embodiments, they are carried out according to conventional conditions or conditions recommended by the manufacturer. If the manufacturer of the reagents or instruments used is not specified, they are all conventional products that can be purchased commercially.

[0029] In a first aspect, the present invention provides a method for recycling hot casting slag, comprising: after molten steel is smelted in a converter, 1.5t-6t of hot casting slag is added to the molten steel after tapping, and then the molten steel is put into an LF furnace for refining.

[0030] In the present application, there is no need to add slag washing lime and synthetic slag during the steel tapping process. Only 1.5t-6t of waste hot slag from casting needs to be added, which can effectively improve the slag consumption and rapid slag formation effect of the converter and LF furnace, while reducing energy and raw material consumption, which is beneficial to saving production costs.

[0031] In an optional embodiment, during the LF furnace refining process, 340-360 kg of lime is first added, and then lime or fluorite is added.

[0032] Specifically, the furnace that receives hot slag from casting needs to do a good job of slag deoxidation and desulfurization. For the furnace that receives hot slag from casting, the slag must be checked 6-10 minutes before sampling. If the fluidity is too high, lime needs to be added, and if the fluidity is too low, fluorite needs to be added to ensure good deoxidation and desulfurization effects in the early stage to avoid affecting the castability of molten steel.

[0033] In an optional embodiment, all of the following features are met:

[0034] The continuous casting step does not require steel retention, which has strict requirements on inclusions. If the residual hot slag is received, the performance of the product steel may be affected.

[0035] The bottom blowing of the converter is blocked when there is no feedback from the LF furnace. At this time, the steel slag is easy to foam and escape, so it is not suitable to add the residual hot slag;

[0036] The clearance of the ladle receiving the hot slag from casting should be ≥400mm, leaving enough space to accommodate the hot slag from casting and subsequent operations;

[0037] The recycling times of the hot casting slag are less than 3 times. If the recycling times are too many, on the one hand, the adsorption capacity of the hot casting slag will be weakened, which will have a dilution effect on the subsequently added lime and affect the performance of the product steel; on the other hand, the inclusion content in the hot casting slag will increase with the increase in the recycling times, and too many inclusions may affect the performance of the product steel.

[0038] It should be noted that if the LF straight-up process path is adopted, the number of times the casting hot slag is recovered is less than 3 times; if the RH process path is adopted, the number of times the casting hot slag is recovered is less than 2 times.

[0039] It should be noted that in the present application, the first batch of molten steel is smelted in a converter, and slag washing lime and synthetic slag are added to the steel before entering the LF furnace for refining. After a certain amount of lime is added at the station, lime or fluorite is added to adjust the slag fluidity according to the slag fluidity. After the continuous casting of the molten steel, the remaining liquid slag is fresh hot casting slag; the second batch of molten steel is smelted in a converter, and fresh hot casting slag is added to the steel before entering the LF furnace for refining. After a certain amount of lime is added to the steel before entering the LF furnace for refining, after a certain amount of lime is added to the steel before entering the LF furnace for refining, after a certain amount of lime is added to the steel before entering the LF furnace for refining, after a certain amount of lime is added to the steel before entering the LF furnace for refining, after a certain amount of lime is added to the steel before entering the LF furnace for refining, after a certain amount of lime is added to the steel before entering the LF furnace for refining, after a certain amount of lime is added to the steel before entering the LF furnace for refining, after a certain amount of lime is added to the steel before entering the slag fluidity, and after the continuous casting of the molten steel, the remaining liquid slag is twice recovered hot casting slag; and so on.

[0040] In an optional embodiment, the hot cast slag is a mixture of slag remaining after continuous casting of molten steel and molten steel. When the type of steel that produces the hot cast slag is different from the type of steel that receives the hot cast slag, the amount of molten steel in the hot cast slag added to the molten steel is less than 5 tons. If the molten steel content is too much, it may cause the composition to be out of specification.

[0041] And / or, the remaining hot slag after continuous casting of molten steel is poured into a furnace receiving the hot slag by using a crane to lift the ladle, and then all the hot slag in the furnace receiving the hot slag is added into the received molten steel at once, otherwise it may cause drainage;

[0042] And / or, during the production process of the cast hot slag, no slag is discharged when the converter is tapping steel. If obvious slag is discharged when the converter is tapping steel, the phosphorus content in the obtained cast hot slag will be relatively high, which may affect the performance of the steel product receiving the cast hot slag. In this case, synthetic slag must be added immediately according to the process requirements after the steel is tapped, and hot slag recovery shall not be carried out.

[0043] It should be noted that for the furnace that receives the hot slag from casting, the slag samples must be sent to the laboratory to analyze the composition of the hot slag from casting. If the composition of the hot slag from casting is abnormal, the process must be adjusted.

[0044] In an optional embodiment, the method is applied to the production of special steel or industrial steel.

[0045] In a second aspect, the present invention provides a method for producing steel, including the method for recycling hot slag from casting as described in the aforementioned embodiment, wherein the steel is special steel or industrial steel.

[0046] In an optional embodiment, the steel model is at least one of 45 steel, 40Cr, 25, 35, 10, 20CrMo, 40Mn2, 20Mn2 and SAE1020.

[0047] And / or, the steel has no upper or lower limit requirement on sulfur content.

[0048] In an optional embodiment, after the molten steel is refined in the LF furnace, it enters the RH refining step. If the slag thickness measured at the RH station exceeds 300 mm, the slag is poured to avoid slag suction.

[0049] In an optional embodiment, the molten steel enters the RH refining step after being refined in the LF furnace. If the received hot slag from casting needs to be subcontracted due to abnormal composition, and the slag thickness is measured to be more than 300 mm after slag making in the LF furnace refining step, it will be fed back to the RH furnace for slag pouring.

[0050] In an optional embodiment, after the molten steel is refined in the LF furnace, it enters the RH refining step. If there is obvious slag when tapping the converter and the residual hot slag has been received, in the LF furnace refining step, if the slag thickness is measured to be more than 300 mm after slag making is completed, it will be fed back to the RH furnace and the slag will be poured.

[0051] The present invention can effectively reduce the consumption of molten steel slag, ensure the normal smelting of molten steel, save costs, and have great economic and social benefits. Taking 45Cr, 40Cr, 6A and 22A steel as examples:

[0052] 1. The rough estimated benefit of recycling hot slag per ton of steel for 45 and 40Cr is: (200kg lime (530*0.2=106) + 600kg synthetic slag (1739*0.6=1043) + 50kg aluminum iron (9830*0.1=491)) / molten steel quality = 1890 / 135 = 12.14 yuan / ton.

[0053] 2. The rough estimated benefit of 6A recycling hot slag per ton of steel is: (400kg lime (530*0.4=212) + 400kg synthetic slag (1739*0.4=695) + 100kg aluminum iron (9830*0.1=983)) / molten steel quality = 1890 / 135 = 14 yuan / ton.

[0054] 3. The rough estimated benefit of recycling hot slag per ton of steel in 22A is: (300kg lime (530*0.3=106) + 450kg synthetic slag (1739*0.45=782) + 100kg aluminum iron (9830*0.1=983)) / molten steel quality = 1890 / 135 = 13.86 yuan / ton.

[0055] The features and performance of the present invention are further described in detail below in conjunction with the embodiments.

[0056] Example 1

[0057] This embodiment provides a production method of 45 steel LF straight-up process, comprising:

[0058] 1. The first batch of molten steel is smelted in a converter, and 400kg of slag washing lime and 600kg of synthetic slag are added to the steel before it enters the LF furnace for refining. 400kg of lime is added at the station, and then 200kg of lime is added to adjust the slag fluidity according to the slag fluidity. After continuous casting of the molten steel, the remaining hot slag is obtained, which includes 0.5t of molten steel.

[0059] 2. After the second heat of molten steel is smelted in the converter, steel is tapped and 2.1t of all the hot casting slag produced in the first heat is added to the molten steel, and then the steel enters the LF furnace for refining, wherein the ladle is lifted by an overhead crane to pour all the remaining hot casting slag in the ladle into the heat receiving the hot casting slag, and then the hot casting slag in the heat receiving the hot casting slag is added into the received molten steel all at once.

[0060] During the LF furnace refining process, no lime is added at the station, and 100 kg of lime is subsequently added according to the fluidity of the slag. After continuous casting of the molten steel, the remaining hot slag is obtained, and the hot slag includes 0.6 t of molten steel.

[0061] Among them, the continuous casting step does not require steel retention operation;

[0062] The steel tapping from the converter and the bottom blowing of the LF furnace are unobstructed; the clearance of the ladle receiving the residual hot slag from casting is 600mm.

[0063] 3. The production of the third heat is basically the same as that of the second heat. The main difference is that after the molten steel is smelted in the converter, the steel is tapped and 2.2 tons of all the hot slag produced in the second heat is added to the molten steel. Then it enters the LF furnace for refining.

[0064] During the LF furnace refining process, no lime is added at the station, and 150 kg of lime is subsequently added according to the fluidity of the slag. After continuous casting of the molten steel, the remaining hot slag is obtained, and the hot slag includes 0.6 t of molten steel.

[0065] 4. The production of the fourth heat is basically the same as that of the third heat. The main difference is that after the molten steel is smelted in the converter, the steel is tapped and all the hot slag produced in the third heat (2.8t) is added to the molten steel. Then it enters the LF furnace for refining.

[0066] During the LF furnace refining process, 200 kg of lime is first added, and the remaining hot slag is obtained after continuous casting of the molten steel, and the hot slag includes 0.9 t of molten steel.

[0067] 5. The production of the fifth heat is basically the same as that of the fourth heat. The main difference is that after the molten steel is smelted in the converter, the steel is tapped and all the hot slag produced in the fourth heat (2.8 tons) is added to the molten steel. Then it enters the LF furnace for refining.

[0068] During the LF furnace refining process, no lime is added at the station, and 100 kg of lime is subsequently added according to the fluidity of the slag. After continuous casting of the molten steel, the remaining hot slag is obtained, and the hot slag includes 0.9 t of molten steel.

[0069] Example 2

[0070] This embodiment provides a production method of 40Cr steel by RH process, comprising:

[0071] 1. The first batch of molten steel is smelted in a converter, and 400kg of slag washing lime and 600kg of synthetic slag are added to the steel before entering the LF furnace for refining and RH refining. During the LF furnace refining, 400kg of lime is added to the station, and then 300kg of lime is added to adjust the slag fluidity according to the slag fluidity. After continuous casting of the molten steel, the remaining casting hot slag is obtained, which includes 1.1t of molten steel.

[0072] 2. After the second heat of molten steel is smelted in the converter, steel is tapped and 3.2 tons of all the hot casting slag produced in the first heat is added to the molten steel. Then the steel enters the LF furnace for refining and the RH furnace for refining. During the LF furnace refining, the ladle is hoisted by an overhead crane to pour all the remaining hot casting slag in the ladle into the heat receiving the hot casting slag, and then the hot casting slag in the heat receiving the hot casting slag is added into the received molten steel all at once.

[0073] During the LF furnace refining process, no lime is added at the station, and 200 kg of lime is added later according to the fluidity of the slag. After continuous casting of the molten steel, the remaining hot slag is obtained, and the hot slag includes 1.1 t of molten steel.

[0074] Among them, the continuous casting step does not require steel retention operation;

[0075] The converter tapping and LF bottom blowing are smooth;

[0076] The clearance of the ladle receiving the hot slag from casting is 500mm.

[0077] 3. The production of the third heat is basically the same as that of the second heat. The main difference is that after the molten steel is smelted in the converter, the steel is tapped and 3.2 tons of all the hot slag produced in the second heat is added to the molten steel. Then it enters the LF furnace for refining and the RH refining.

[0078] During the LF furnace refining process, no lime is added at the station, and 250 kg of lime is added later according to the fluidity of the slag. After continuous casting of the molten steel, the remaining hot slag is obtained, and the hot slag includes 1.2 t of molten steel.

[0079] 4. The production of the fourth heat is basically the same as that of the third heat. The main difference is that after the molten steel is smelted in the converter, the steel is tapped and all the hot slag produced in the third heat (3.9t) is added to the molten steel. Then it enters the LF furnace for refining and the RH refining.

[0080] During the LF furnace refining process, no lime is added at the station, and 300 kg of lime is subsequently added according to the fluidity of the slag. After continuous casting of the molten steel, the remaining hot slag is obtained, and the hot slag includes 1.4 t of molten steel.

[0081] The properties of the steel produced in the above embodiments were tested, and the results are shown in Table 1.

[0082] Table 1

[0083]

[0084] According to Table 1, for the LF straight-up process, when the number of times the casting waste hot slag is recovered is less than or equal to 3, the performance of the obtained steel is equivalent to that of the steel prepared by the unrecovered casting waste hot slag, but when the number of recovery is greater than 3, the performance of the steel is significantly reduced; similarly, for the over-RH process, when the number of times the casting waste hot slag is recovered is less than or equal to 2, the performance of the obtained steel is equivalent to that of the steel prepared by the unrecovered casting waste hot slag, but when the number of recovery is greater than 2, the performance of the steel is significantly reduced.

[0085] The above description is only a preferred embodiment of the present invention and is not intended to limit the present invention. For those skilled in the art, the present invention may have various modifications and variations. Any modification, equivalent replacement, improvement, etc. made within the spirit and principle of the present invention shall be included in the protection scope of the present invention.

Claims

1. A method for recycling hot slag from casting, characterized in that: include: After the molten steel is smelted in the converter, it is tapped and 1.5t-6t of residual hot slag is added to the molten steel, and then it enters the LF furnace for refining.

2. The method for recycling hot casting slag according to claim 1, characterized in that: During the LF furnace refining process, 340-360 kg of lime is first added, and then additional lime or fluorite is added.

3. The method for recycling hot casting slag according to claim 1, characterized in that: Meet all of the following characteristics: The continuous casting step does not require steel retention operation; The converter is tapping or the LF furnace is not feeding back the bottom blowing; The clearance of the ladle receiving the hot slag from casting should be ≥400mm; The recycling times of the hot casting slag are less than 3 times.

4. The method for recycling hot casting slag according to claim 1, characterized in that: The hot slag is a mixture of slag and molten steel remaining after continuous casting of molten steel, and the molten steel in the hot slag added to the molten steel is less than 5 tons; And / or, the remaining hot casting slag after continuous casting of molten steel is poured into a furnace receiving the hot casting slag by using an overhead crane to lift the ladle, and then all the hot casting slag in the furnace receiving the hot casting slag is added into the received molten steel at once; And / or, during the production process of the cast waste hot slag, no slag is discharged when the converter is tapping steel.

5. The method for recycling hot casting slag according to claim 1, characterized in that: The method is applied to the production of special steel or industrial steel.

6. A method for producing steel, characterized in that: The method comprises the method for recycling hot slag from casting as described in claim 1 or 2, wherein the steel material is special steel or industrial steel.

7. The method for producing steel according to claim 6, characterized in that: The steel type is at least one of 45 steel, 40Cr, 25, 35, 10, 20CrMo, 40Mn2, 20Mn2 and SAE1020; And / or, the steel has no upper or lower limit requirement on sulfur content.

8. The method for producing steel according to claim 6, characterized in that: After being refined in the LF furnace, the molten steel enters the RH refining step. If the slag thickness measured at the RH station exceeds 300mm, slag pouring will be carried out.

9. The method for producing steel according to claim 6, characterized in that: After being refined in the LF furnace, the molten steel enters the RH refining step. If the hot slag from casting has been received and needs to be subcontracted due to abnormal composition, and if the slag thickness exceeds 300mm after slag making in the LF furnace refining step, it will be fed back to the RH furnace for slag pouring.

10. The method for producing steel according to claim 6, characterized in that: After being refined in the LF furnace, the molten steel enters the RH refining step. If there is obvious slag when tapping the converter and the residual hot slag has been received, in the LF furnace refining step, if the slag thickness exceeds 300mm after slag making, it will be fed back to the RH furnace for slag pouring.

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