A method for smelting stainless steel using stainless steel scrap

Abstract

The present application belongs to the technical field of stainless steel smelting, and particularly relates to a method for smelting stainless steel by using stainless steel waste, which comprises the following steps: loading raw materials into an AOD furnace, performing primary refining on the raw materials in the AOD furnace to obtain refined molten steel; adding stainless steel waste into a ladle, then tapping the refined molten steel obtained in the AOD refining step into the ladle containing the stainless steel waste, and after the tapping is completed, transferring the ladle to an LF furnace; after the ladle reaches the LF furnace, passing argon gas through the bottom of the ladle, performing power transmission and heating on the lower electrode until the stainless steel waste is completely melted, sampling and analyzing the molten steel, and finely adjusting the alloying components until the components of the molten steel are qualified, and finally adjusting the temperature of the molten steel to obtain the molten steel after LF treatment; performing continuous casting treatment on the molten steel after the LF treatment to obtain stainless steel. The method provided by the present application is efficient, environmentally friendly, low in cost, and high in recovery rate of stainless steel waste.

Description

Technical Field

[0001] This invention belongs to the field of stainless steel smelting technology, and specifically relates to a method for smelting stainless steel using stainless steel scrap. Background Technology

[0002] Stainless steel plants inevitably generate stainless steel waste during production, including slag steel, substandard steel billets, hot-rolled coils, and cold-rolled coils. Simultaneously, with the increasing demand for stainless steel due to societal development, the amount of stainless steel waste generated is also increasing. Recycling stainless steel waste is of great significance for steel plants to improve production efficiency and promote green and environmentally friendly development.

[0003] Currently, stainless steel plants mainly recycle stainless steel scrap through two methods: electric furnace smelting and AOD furnace smelting. However, each method has its corresponding disadvantages: (1) Electric furnace smelting of scrap is noisy, consumes a lot of electricity, and has a low stainless steel scrap recycling rate. At the same time, the investment cost of electric furnaces is high, and some steel plants do not have electric furnaces and cannot use electric furnaces for smelting; (2) AOD furnace smelting of stainless steel scrap has a low recycling rate; the size requirements for stainless steel scrap are strict, and the stainless steel scrap cannot be larger than the furnace opening, otherwise it cannot be added to the furnace for smelting; hot-rolled and cold-rolled stainless steel scrap are all in coils and are relatively large in size. Before being added to the AOD furnace, they need to be cut into small pieces through oxygen pipes. The cutting process will cause three problems: first, a large amount of oxide slag is generated during the oxygen cutting process, and the steel coil is lost. (2) The oxygen cutting process generates a large amount of yellow smoke, resulting in high environmental protection costs. (3) Cutting is difficult and inefficient, leading to the accumulation of some stainless steel waste in steel mills and resulting in asset waste. (4) When the scrap steel billet is added into the AOD furnace, it has a large impact potential energy, which puts a certain burden on the refractory materials and furnace structure of the AOD furnace. (5) In the context of the continuous increase of stainless steel waste, the consumption of cold material in AOD is also increasing day by day. However, the heat source of AOD furnace smelting is limited, and the proportion of cold material has a reasonable range. Further increasing the amount of cold material will lead to insufficient heat source and cause incalculable metal burn-off.

[0004] Therefore, it is of great significance to study a new, efficient, environmentally friendly, and low-cost method for smelting stainless steel using stainless steel scrap. Summary of the Invention

[0005] In view of the above-mentioned shortcomings in the existing technology, the purpose of this invention is to provide a method for smelting stainless steel using stainless steel scrap. The method provided by this invention is efficient, environmentally friendly, low-cost, and has a high recycling rate of stainless steel scrap.

[0006] To achieve the above objectives, the present invention adopts the following technical solution:

[0007] This invention provides a method for smelting stainless steel using stainless steel scrap, comprising the following steps:

[0008] AOD refining steps: The raw materials are loaded into the AOD furnace and the raw materials are initially refined in the AOD furnace to obtain refined molten steel. The tapping temperature is higher than the normal tapping temperature.

[0009] Ladle preparation steps: Add stainless steel scrap into the ladle, then tap the refined molten steel obtained from the AOD refining step into the ladle containing the stainless steel scrap. After tapping, transfer the ladle to the LF furnace.

[0010] LF refining steps: After the ladle arrives at the LF furnace, argon gas is introduced to the bottom of the ladle, and the lower electrode is used to supply electricity to heat the material in the ladle until the stainless steel scrap is melted. The molten steel is sampled and analyzed, and the alloy composition is fine-tuned until the molten steel composition is qualified. Finally, the molten steel temperature is adjusted so that the tapping temperature reaches the continuous casting temperature required to obtain LF-treated molten steel.

[0011] Continuous casting step: The molten steel after LF treatment is continuously cast to obtain stainless steel, wherein the carbon content of the stainless steel is within the upper limit of the qualified range ≥0.07wt%.

[0012] Here, normal tapping temperature refers to the tapping temperature when AOD refining is carried out according to existing technology. The refined molten steel obtained from the AOD refining step will not experience a temperature drop due to the need to mix it with stainless steel solid scrap after tapping. Under normal circumstances, it does not significantly increase steelmaking costs or significantly affect LF smelting time. The molten steel does not cause low-temperature solidification and condensation at the bottom of the ladle during the process from AOD tapping to LF. We call this the normal tapping temperature. Different steel mills will have certain differences in their normal tapping temperature depending on their production and transportation conditions, which may be higher or lower. Normal tapping temperature = steel melting point + production and transportation cooling + casting cooling. It is determined by comprehensively considering factors such as continuous casting temperature (continuous casting requires strict temperature control of the cast steel, with a deviation of ±3℃), temperature drop from AOD tapping to LF furnace, and LF furnace power supply and heating time. For example, 200 series steel grades require 1520~1580℃, and 300 / 400 series steel grades require 1550~1630℃. Under normal circumstances, excessively high tapping temperatures will consume more steelmaking raw materials and require additional time to cool down to the target level before continuous casting, increasing costs. Excessively low tapping temperatures will lead to low-temperature ladle bottom accidents or increase LF furnace heating time, increase power consumption, and affect production rhythm. Therefore, a certain range of tapping temperatures is generally required in production.

[0013] The required temperature for continuous casting is determined based on the melting point of the steel being produced, the casting cooling temperature, and the continuous casting technical specifications. Different steel grades require different temperatures. For a fixed steel grade in production, there will be a fixed required temperature for continuous casting based on the corresponding continuous casting equipment conditions.

[0014] The maximum carbon content of the final steel grade cannot be lower than 0.07%. Stainless steel with a maximum carbon content lower than 0.07% is not suitable for this technology. This is because adding scrap stainless steel to the ladle requires an LF furnace to provide power for melting, during which carbon content increases. If the maximum carbon content requirement is lower than 0.07%, the carbon content of the molten steel may exceed 0.07% after the LF furnace is powered on, resulting in substandard steel composition. If the carbon content requirement for a certain steel grade is ≤0.03%, this technology cannot be implemented because the LF furnace will increase carbon content by 0.01% to 0.07%, depending on the duration of the power supply.

[0015] The method provided by this invention is efficient, environmentally friendly, low-cost, and has a high recycling rate for stainless steel scrap.

[0016] In the above-described method for smelting stainless steel using stainless steel scrap, as a preferred embodiment, the tapping temperature in the AOD refining step is 45-80°C higher than the normal tapping temperature, for example, 45°C, 60°C, 70°C, or 80°C. The refined molten steel obtained from the AOD refining step is tapped into a ladle containing stainless steel scrap, where the scrap begins to melt. The melting rate varies depending on the temperature of the molten steel and the physical state of the stainless steel scrap. The stainless steel scrap in the ladle is at room temperature (25°C), and its melting will cause the temperature of the refined molten steel to drop. If the tapping temperature is not increased, and the stainless steel scrap melts thoroughly during tapping and transfer to the LF furnace, the temperature of the refined molten steel will drop sharply. If the temperature of the refined molten steel drops below its melting point, it will cause the molten steel to form a low-temperature crust at the bottom of the ladle, resulting in a production accident where the molten steel cannot be continuously cast. Therefore, the tapping temperature needs to be increased to prevent excessive cooling.

[0017] In the above-described method for smelting stainless steel using stainless steel scrap, as a preferred embodiment, the raw material does not include the stainless steel scrap.

[0018] In the above-described method for smelting stainless steel using stainless steel scrap, as a preferred embodiment, in the AOD refining step, the carbon content of the tapped steel is 0.01% to 0.05% lower than the lower limit of the acceptable carbon content range for the stainless steel, for example, it can be 0.01%, 0.03%, or 0.05%. Adding stainless steel scrap to the ladle requires an LF furnace for fluxing, during which carbon content increases. This invention, by limiting the tapped steel carbon content to be 0.01% to 0.05% lower than the lower limit of the acceptable carbon content range for the stainless steel, can control the carbon content of the final stainless steel to be within the acceptable range.

[0019] In the above-mentioned method for smelting stainless steel using stainless steel scrap, as a preferred embodiment, the mass ratio of the stainless steel scrap to the refined molten steel is no greater than 35:65. For example, the mass ratio of the stainless steel scrap to the refined molten steel can be 35:65, 25:75, 15:85, 5:95, etc., because the stainless steel scrap is at room temperature, and its melting requires the absorption of a large amount of heat. If the amount of stainless steel scrap added is too large, the total heat of the molten steel (refined molten steel) from the AOD furnace is far from sufficient to provide the heat required to melt the scrap stainless steel. The LF furnace needs to spend a lot of time powering up to supplement the heat. The LF powering electrode is a graphite electrode. During the powering process, carbon will enter the molten steel, causing the molten steel to carbonize. The longer the powering time, the more carbon will be added. After a lot of creative work, the inventors found that in order to prevent the carbon content of the molten steel from exceeding the standard due to excessive powering time, the mass ratio of the stainless steel scrap to the refined molten steel is no greater than 35:65.

[0020] In the above-described method for smelting stainless steel using stainless steel scrap, as a preferred embodiment, in the AOD refining step, when the mass ratio of the stainless steel scrap to the refined molten steel is (25:75) to (35:65) (for example, it can be 25:75, 30:70, or 35:65), the carbon content of the tapped steel is 0.04% to 0.05% lower than the lower limit of the acceptable carbon content range for the stainless steel; when the mass ratio of the stainless steel scrap to the refined molten steel is (15:85) to (25:75) (for example, it can be 15:85, 20:80, or 25:75), the carbon content of the tapped steel is lower than the lower limit of the acceptable carbon content range for the stainless steel. :75), the carbon content of the tapped steel is 0.03% to 0.04% lower than the lower limit of the acceptable carbon content range of the stainless steel; when the mass ratio of the stainless steel scrap to the refined molten steel is (5:95) to (15:85) (for example, it can be 5:95, 10:90 or 15:85), the carbon content of the tapped steel is 0.02% to 0.03% lower than the lower limit of the acceptable carbon content range of the stainless steel; when the mass ratio of the stainless steel scrap to the refined molten steel is less than 5:95, the carbon content of the tapped steel is 0.01% to 0.02% lower than the lower limit of the acceptable carbon content range of the stainless steel.

[0021] In the above-mentioned method for smelting stainless steel using stainless steel scrap, as a preferred embodiment, the pressure of the argon gas passed through the bottom of the ladle in the LF refining step is 0.6-0.8 MPa.

[0022] In the above-mentioned method for smelting stainless steel using stainless steel scrap, as a preferred embodiment, in the LF refining step, a power supply with a current of 8000-32000KVA (for example, 8000KVA, 16000KVA, 24000KVA, 32000KVA), high power level 3-5, and voltage of 234-250V is used for power supply and heating.

[0023] In the above-described method for smelting stainless steel using stainless steel scrap, as a preferred embodiment, in the LF refining step, the lower electrode supplies electricity to heat the material in the ladle until the stainless steel scrap is completely melted, including:

[0024] After the lower electrode supplies electricity to heat the material in the ladle for a preset time, the first temperature is measured to obtain the first temperature.

[0025] When the first temperature is less than 1548-1552℃, the material in the ladle continues to be heated by power supply until the temperature of the material in the ladle is not less than 1548-1552℃, and then the heating is stopped.

[0026] The material inside the ladle is subjected to soft argon blowing and temperature measurement to obtain a second temperature. When the second temperature is 1518-1522℃, the material inside the ladle is heated by power supply until the temperature of the material inside the ladle is not less than 1548-1552℃, and then the heating is stopped.

[0027] The material inside the ladle is subjected to soft argon blowing and temperature measurement. When the cooling rate is consistent with the preset cooling rate, it is determined that the stainless steel scrap has melted completely.

[0028] Here, the preset cooling rate (normal cooling rate) is the cooling rate when all the material in the ladle has melted into a liquid phase, meaning there is no solid matter left in the ladle. This is typically a fixed range. The comparison between the preset cooling rate and the actual cooling rate must be performed under soft blowing conditions in the LF furnace, where the argon flow rate is constant. The argon flow rate in the LF furnace is adjustable; increasing the argon flow rate will accelerate cooling, while decreasing it will slow it down.

[0029] When the second temperature is 1518-1522℃, the material in the ladle is continuously heated by electricity. On the one hand, this can give the scrap a cooling and melting process, improving the heat utilization rate. On the other hand, 1518-1522℃ is 8-10℃ above the continuous casting temperature. If the scrap is melted clean, it will be beneficial for subsequent soft blowing and sedation operations as well as precise control of the continuous casting temperature.

[0030] In the above method for smelting stainless steel using stainless steel scrap, as a preferred embodiment, the preset time (min) = weight of stainless steel scrap in ladle (tons) / A, where A is 2 to 3.

[0031] In the above-described method for smelting stainless steel using stainless steel scrap, as a preferred embodiment, in the LF refining step, the lower electrode supplies electricity to heat the material in the ladle until the stainless steel scrap is completely melted, and the method further includes:

[0032] When the cooling rate is greater than the preset cooling rate, it is determined that the stainless steel scrap has not been completely melted. Power is then supplied to raise the temperature, and the temperature is measured. When the heating rate is consistent with the preset heating rate, it is determined that the stainless steel scrap has been completely melted.

[0033] Here, the preset heating rate (normal heating rate) is the heating rate when all the material in the ladle has melted into a liquid phase, i.e., there is no solid substance in the ladle. It is usually a fixed range. The preset heating rate and the actual heating rate should be compared under the premise that the power supply current is the same. The magnitude of the power supply current will affect the heating rate.

[0034] The normal cooling / heating rate is the unique temperature cooling / heating efficiency of each LF furnace in each steel plant. It varies depending on the LF model. In production, it can be obtained by taking the average value of the temperature cooling / heating degree measured per unit time. This value is generally relatively stable.

[0035] The heating / cooling rates for normal, un-scrap stainless steel furnace runs do not require additional testing. Existing technology provides ample production data to support on-site personnel in collecting the heating / cooling rates for normal runs. Production staff operate the LF furnace based on these rates to adjust the temperature. Therefore, readily available data on the heating / cooling rates for normal, un-scrap stainless steel furnace runs is essential, and every LF furnace process operator should be familiar with this data.

[0036] In the above-described method for smelting stainless steel using stainless steel scrap, as a preferred embodiment, in the LF refining step, the lower electrode supplies electricity to heat the material in the ladle until the stainless steel scrap is completely melted, and the method further includes:

[0037] When the heating rate is less than the preset heating rate, it is determined that the stainless steel scrap has not been completely melted. Power is supplied to continue heating until the temperature of the material in the ladle is not less than 1548-1552℃ (for example, it can be 1548℃, 1550℃, or 1552℃). Heating is then stopped, soft blowing is initiated, and the temperature is measured to determine whether the cooling rate is consistent with the preset cooling rate.

[0038] In the above-mentioned method for smelting stainless steel using stainless steel scrap, as a preferred embodiment, the argon pressure of the soft blowing argon is 0.2-0.3 MPa, and during the soft blowing argon process, the LF electrode is raised and the power supply is stopped.

[0039] In the above-mentioned method for smelting stainless steel using stainless steel scrap, as a preferred embodiment, in the LF refining step, when the composition of the molten steel is unqualified, the corresponding alloy is added to adjust the composition. After adding the corresponding alloy, the lower electrode is energized and heated for no less than 3 minutes. Argon gas is introduced into the bottom of the ladle at a pressure of 0.5-0.7 MPa. The current is 8000-32000 KVA (for example, 8000 KVA, 16000 KVA, 24000 KVA, or 32000 KVA), in 3-5 increments, and the voltage is 234-250 V.

[0040] In the above-mentioned method for smelting stainless steel using stainless steel scrap, as a preferred embodiment, in the LF refining step, the tapping temperature reaches the continuous casting required temperature when the difference between the tapping temperature and the continuous casting required temperature is within ±3℃.

[0041] In the above-described method for smelting stainless steel using stainless steel scrap, as a preferred embodiment, the adjustment of the molten steel temperature in the LF refining step includes:

[0042] After the composition is qualified, power is continued to be supplied to raise the temperature of the molten steel until it is 10-20°C higher than the continuous casting temperature required. Then, heating is stopped, and soft blowing and sintering are performed. After sintering, the temperature of the molten steel is measured. If the temperature is too low, power is supplied to raise the temperature again until it reaches the continuous casting temperature required. If the temperature is too high, sintering and cooling are performed again until the temperature reaches the continuous casting temperature required. This embodiment of the invention, by continuing to supply power to raise the temperature of the molten steel to 10-20°C higher than the continuous casting temperature required, can further homogenize the temperature of the molten steel, preventing localized low or high temperatures from affecting the continuous casting quality.

[0043] In the above-mentioned method for smelting stainless steel using stainless steel scrap, as a preferred embodiment, the stainless steel scrap includes substandard steel billets from steel mills, returned stainless steel of the same grade from hot rolling and cold rolling mills, or first-grade stainless steel scrap with stable composition purchased from external sources.

[0044] Here, the grade 1 scrap stainless steel follows industry standards, and its chromium, manganese, carbon, phosphorus, sulfur and other contents meet the requirements of the steel grade.

[0045] In the above-described method for smelting stainless steel using stainless steel scrap, as a preferred embodiment, in the ladle preparation step, 30-50 minutes (e.g., 30, 40, or 50 minutes) before tapping from the AOD furnace, the stainless steel scrap is added to the ladle and heated with gas. The gas is turned off 5-7 minutes before tapping from the AOD furnace. Once the AOD furnace is ready for tapping, the ladle is moved to the bottom of the AOD furnace for tapping. In this embodiment, heating the ladle with gas further increases the temperature of the stainless steel scrap, accelerating the melting rate of the stainless steel scrap in subsequent processes.

[0046] In the above-described method for smelting stainless steel using stainless steel scrap, as a preferred embodiment, the stainless steel scrap and the stainless steel are of the same series of steel grades.

[0047] In the above-mentioned method for smelting stainless steel using stainless steel scrap, as a preferred embodiment, in the LF refining step, after the stainless steel scrap is melted and cleared, before sampling and analyzing the molten steel, when the temperature of the molten steel is less than 1550°C, the molten steel is heated by electricity for 3-5 minutes, then the heating is stopped, and soft argon blowing is performed for a period of not less than 6 minutes, after which the temperature of the molten steel is not lower than 1514°C; when the temperature of the molten steel is not lower than 1550°C, the heating is stopped, and soft argon blowing is performed for a period of not less than 6 minutes, after which the temperature of the molten steel is not lower than 1514°C.

[0048] After the stainless steel scrap has melted away, the purpose of continuing to supply electricity to raise the temperature is to further homogenize the temperature and composition of the molten steel. This typically takes 3-5 minutes.

[0049] Compared with the prior art, the beneficial effects of the present invention include at least one of the following:

[0050] (1) The method provided by the present invention is efficient, environmentally friendly, low cost and has a high recycling rate of stainless steel waste, which can reach more than 98%.

[0051] (2) Steel coils do not need to be cut, saving labor and environmental costs associated with cutting, and there is no loss of cutting metal; it improves the recycling efficiency of scrap steel coils and reduces the financial pressure on steel mills.

[0052] (3) The impact damage to the refractory material of the ladle caused by the scrap steel billet being hoisted into the ladle is negligible, thus avoiding the impact damage to the AOD furnace caused by the gravitational potential energy of the steel billet when it is added into the AOD furnace.

[0053] (4) Save more heat source and space for AOD furnace to consume other stainless steel return materials, further reducing the unit consumption of molten iron. Detailed Implementation

[0054] To make the objectives, technical solutions, and advantages of this invention clearer, the technical solutions in the embodiments of this invention will be clearly and completely described below in conjunction with the embodiments of this invention. Those skilled in the art should understand that the embodiments described are merely illustrative of the invention and should not be considered as specific limitations thereof. All other embodiments obtained by those skilled in the art based on the embodiments of this invention without creative effort are within the scope of protection of this invention.

[0055] The embodiments of the present invention are implemented under the premise of the technical solution of the present invention, and detailed implementation methods and processes are given. However, the protection scope of the present invention is not limited to the following embodiments. The process parameters in the following embodiments that do not specify specific conditions are generally in accordance with conventional conditions.

[0056] The endpoints and any values ​​of the ranges disclosed in this invention are not limited to the precise ranges or values, and these ranges or values ​​should be understood to include values ​​close to these ranges or values. For numerical ranges, the endpoint values ​​of the various ranges, the endpoint values ​​of the various ranges and individual point values, and individual point values ​​can be combined with each other to obtain one or more new numerical ranges, which should be considered as specifically disclosed in this invention.

[0057] In this invention, unless otherwise specified and / or stated, all values ​​relating to component amounts are in parts by weight. Process parameters in the following examples that do not specify specific conditions are generally performed under conventional conditions. Unless otherwise specified, the experimental reagents used in the following examples are conventional biochemical reagents; and unless otherwise specified, the amounts of experimental reagents used are the amounts used in conventional experimental operations.

[0058] In the following embodiments and comparative examples:

[0059] The composition of high-carbon ferrochrome, by mass percentage, includes: C: 7%, Cr: 52%, Si: 3.5%, P: 0.022%, S: 0.025%, with the remainder being Fe and unavoidable impurities.

[0060] The composition of the silicon-manganese alloy, by mass percentage, includes: Mn: 61%, Si: 28%, C: 0.2%, P: 0.10%, with the balance being Fe and unavoidable impurities.

[0061] The composition of electrolytic manganese, by mass percentage, includes: Mn: 99.7%, with the balance being Fe and unavoidable impurities.

[0062] Example 1

[0063] A steel plant's No. 1 smelting plant produces 80 tons of a certain 201 steel grade. The composition of this steel grade, by mass percentage, includes: C 0.10%–0.13%, Ni 1.0%–1.5%, Cr 13.5%–14.5%, Mn 9.5%–10.5%, Cu 0.55%–0.6%, Si 0.3%–0.8%, P ≤0.045%, S ≤0.005%, N 0.1%–0.14%, with the balance being iron and unavoidable impurities.

[0064] When smelting this 201 steel grade using existing technology (AOD refining, without utilizing stainless steel scrap for smelting), the AOD furnace output is 80 tons (the normal output of the AOD process is 80 tons), and the normal tapping temperature of the AOD furnace is 1550℃.

[0065] The hot rolling mill returned a 22-ton scrap steel coil with the same specifications as the 201 steel grade. The composition of the scrap steel coil by mass percentage includes: C 0.12%, Ni 1.15%, Cr 13.58%, Mn 9.63%, Cu 0.57%, Si 0.45%, P 0.042%, S 0.001%, N 0.13%, with the remainder being iron and unavoidable impurities.

[0066] The method for smelting stainless steel using stainless steel scrap provided in this embodiment includes the following steps:

[0067] S1, AOD refining steps: 46 tons of low-nickel molten iron are added to the AOD furnace, followed by 12 tons of high-carbon ferrochrome with a chromium content of 52%, 0.32 tons of copper, 4 tons of silicon-manganese alloy, and 3 tons of electrolytic manganese. After smelting, 58.3 tons of molten steel (refined molten steel) are tapped at a tapping temperature of 1610℃. The composition of the molten steel at tapping, by mass percentage, includes: C 0.055%, Ni 1.21%, Cr 13.65%, Mn 9.66%, Cu 0.56%, Si 0.36%, P 0.038%, S 0.001%, N 0.12%, with the remainder being iron and unavoidable impurities.

[0068] S2. Ladle preparation steps: 40 minutes before tapping from the AOD furnace, add 22 tons of scrap steel coils to the ladle and heat it with gas for 35 minutes. Then turn off the gas and wait until the AOD furnace is ready for tapping. Open the ladle containing 22 tons of scrap steel coils to the bottom of the AOD furnace. Tap the molten steel from the AOD furnace into the ladle. After tapping, transfer the ladle to the LF furnace.

[0069] S3, LF refining steps: After the ladle arrives at the LF furnace, argon gas is introduced to the bottom of the ladle for smelting. The argon gas flow rate is adjusted by the argon gas ring, and the argon gas pressure is controlled at 0.6 MPa. After the argon gas is turned on, the lower electrode is used to supply electricity to heat the material in the ladle. The supply current is 32000 KVA, 250V at level 3. After heating for 10 minutes, the electrode is raised, and the molten steel is measured for the first time. The temperature is 1486℃. After temperature measurement, the electrode was lowered and power was supplied to raise the temperature, with measurements taken every 10 minutes. The fifth measurement showed a temperature of 1556℃. Power supply was stopped, the electrode was raised, and the argon gas pressure was adjusted to 0.3MPa. Soft blowing was then initiated, with measurements taken every 5 minutes. The fourth measurement showed a temperature of 1519℃. Subsequently, the electrode was lowered and power was supplied to raise the temperature, with measurements taken every 5 minutes. The second measurement showed a temperature of 1551℃. The electrode was raised, power supply was stopped, and soft blowing was initiated. The argon gas pressure was adjusted to 0.3MPa. After 30 minutes of soft blowing, the temperature was measured at 1521℃. This temperature drop (cooling rate) was consistent with the normal temperature drop efficiency (normal cooling rate, 0.8~1.0℃ / min), indicating that the scrap steel coil had been completely melted. After continuing to supply power and heat for 3 minutes, the temperature of the molten steel was measured at 1533℃. Power supply and heating were then stopped, the electrodes were raised, and the argon gas pressure was adjusted to 0.3MPa. Soft blowing was then initiated for 17 minutes, and the temperature of the molten steel was measured at 1516℃. A sample was taken for analysis, and the composition was found to be within acceptable limits. Power supply and heating were then continued for 2 minutes, and the temperature of the molten steel was measured at 1524℃. The electrodes were raised, power supply and heating were stopped, and soft blowing was carried out for 8 minutes. After soft blowing, the argon gas tube was disconnected, and the mixture was allowed to settle for 5 minutes. The temperature of the molten steel was measured again, and it was 1512℃. The continuous casting requirement for the steel plate temperature is 1511℃, and the temperature meets the requirement. Throughout the LF refining process, a power supply current of 32000KVA and a high-power setting of 250V (level 3) were used for power supply and heating. The argon gas pressure was 0.6MPa during the heating process and 0.3MPa during the soft blowing process.

[0070] S4. Continuous casting step: The molten steel after LF treatment is hoisted to the continuous casting platform and cast normally to obtain 80.12 tons of stainless steel billets. The billet quality is normal (the billet is inspected for quality, mainly to observe whether there are transverse / longitudinal cracks / central cracks / scalds on the surface of the billet. If there are no related problems, the billet quality can be judged to be normal).

[0071] The final chemical composition of the stainless steel obtained by smelting in this embodiment, by mass percentage, includes: C 0.106%, Ni 1.18%, Cr 13.61%, Mn 9.68%, Cu 0.567%, Si 0.41%, P 0.041%, S 0.001%, N 0.125%, with the remainder being iron and unavoidable impurities.

[0072] In this embodiment, the AOD furnace output is 58.3 tons of steel, the scrap steel coil is 22 tons, and the continuous casting billet weight is 80.12 tons. Therefore, the scrap steel coil recovery is 21.82 tons. Thus, the scrap steel coil recovery rate in this embodiment is 21.82 / 22 = 99.18%.

[0073] The method for smelting stainless steel using stainless steel scrap provided in this invention has economic benefits. The cost reduction for each ton of stainless steel scrap processed into steel is 348 yuan: Original scrap processing cost (800 yuan) - Additional electricity / gas cost and LF electrode cost (452 ​​yuan) = Cost reduction for scrap processing (348 yuan). This figure varies depending on the equipment and technology level of each steel mill. This value only reflects the cost reduction benefit for a specific steel mill, but overall, cost reduction exists. The magnitude of the benefit varies for each steel mill based on its own conditions. With a metal recovery rate increase exceeding 10%, the cost reduction per ton of stainless steel scrap can be ≥ 10% of the unit price of stainless steel smelting.

[0074] Example 2

[0075] A steel plant's No. 2 smelting plant produced 80 tons of a certain 201 steel grade. The composition of this steel grade, by mass percentage, includes: C 0.07%–0.10%, Ni 1.0%–1.5%, Cr 13.5%–14.5%, Mn 9.9%–11%, Cu 0.75%–1%, Si 0.3%–0.8%, P≤0.045%, S≤0.005%, N 0.1%–0.14%, with the remainder being iron and unavoidable impurities.

[0076] When smelting this 201 steel grade using existing technology (AOD refining, without utilizing stainless steel scrap for smelting), the AOD furnace output is 80 tons (the normal output of the AOD process is 80 tons), and the normal tapping temperature of the AOD furnace is 1550℃.

[0077] Eight tons of two billet heads were returned from the billet yard, with the steel grade marked as consistent with that steel grade.

[0078] The method for smelting stainless steel using stainless steel scrap provided in this embodiment includes the following steps:

[0079] S1, AOD Refining Steps: 56 tons of low-nickel molten iron (molten iron composition by mass percentage includes: C 5.12%, Ni 1.46%, Cr 4.08%, Mn 1.12%, Cu 0.035%, Si 0.92%, P 0.039%, S 0.061%, N 0.009%, with the remainder being iron and unavoidable impurities) are added to the AOD furnace. Subsequently, 15 tons of high-carbon ferrochrome (52% chromium content), 0.58 tons of copper, 5 tons of silicon-manganese alloy, and 3.9 tons of electrolytic manganese are added. After smelting, 72.2 tons of steel are tapped at a tapping temperature of 1595℃. The composition of the tapped steel by mass percentage includes: C 0.045%, Ni 1.06%, Cr 13.71%, Mn 10.05%, Cu 0.81%, Si 0.52%, P 0.039%, S 0.009%, Cu 0.035%, Si 0.92%, P 0.039%, S 0.009%, and the remainder being iron and unavoidable impurities). 0.0015%, N 0.115%, the remainder being iron and unavoidable impurities.

[0080] S2. Ladle preparation steps: 30 minutes before tapping from the AOD furnace, add 8 tons of billet heads (stainless steel scrap) to the ladle and heat it with gas for 25 minutes. Then turn off the gas and wait for the AOD furnace to be ready for tapping. Open the ladle containing 8 tons of billet heads to the bottom of the AOD furnace. The molten steel from the AOD furnace will be tapped into the ladle. After tapping is completed, transfer the ladle to the LF furnace.

[0081] S3, LF refining steps: After the ladle arrives at the LF furnace, argon gas is introduced to the bottom of the ladle for smelting. The argon gas flow rate is adjusted by the argon gas ring, and the argon gas pressure is controlled at 0.65 MPa. After the argon gas is turned on, the lower electrode is used to supply electricity to heat the material in the ladle. The supply current is 32000 KVA, 250V at level 3. After heating for 13 minutes, the electrode is raised to measure the temperature of the molten steel, which is 1506℃. After temperature measurement, the electrode was lowered and power was supplied to increase the temperature, with a temperature measurement taken every 10 minutes. The second temperature measurement showed a temperature of 1564℃. Power supply to increase the temperature was stopped, and the argon gas ring was adjusted to an argon gas pressure of 0.25MPa. Soft blowing was then initiated, with a temperature measurement taken every 5 minutes. The fifth temperature measurement showed a temperature of 1521℃. Power supply to increase the temperature was then supplied again, with a temperature measurement taken every 5 minutes. The second temperature measurement showed a temperature of 1556℃. The electrode was raised, power supply to increase the temperature was stopped, and soft blowing was initiated. The argon gas ring was adjusted to an argon gas pressure of 0.25MPa. After 10 minutes of soft blowing, the temperature measured at 1521℃. This temperature drop rate was faster than the normal temperature drop rate (0.8~1.0℃ / min), indicating that the stainless steel scrap had not been completely melted. The power supply current was 32000KVA, and the temperature was increased by 250V at level 3. Temperature was measured every 5 minutes. The second measurement showed a temperature of 1561℃. Power was then stopped. The heating efficiency (heating rate) was consistent with the normal efficiency (normal heating rate, 4-5℃ / min), indicating that the billet head was basically melted. Soft blowing was then initiated. After 19 minutes of soft blowing, a sample of the molten steel was taken for analysis. The composition was found to be acceptable. Soft blowing continued, with temperature measurements taken every 5 minutes. The fourth measurement after sampling showed a temperature of 1520℃. Power was then supplied for another 3 minutes of heating, and the temperature was measured at 1532℃. Soft blowing continued for 9 minutes. After soft blowing was completed, the argon gas tube was disconnected, and the molten steel was allowed to settle for 6 minutes. The temperature of the molten steel was measured again, showing a temperature of 1516℃. The continuous casting requirement for the steel loading temperature was 1515℃, and this temperature was met. In the LF refining process, a power supply current of 32000KVA and 250V in three stages are used for power supply and heating. The argon pressure during the heating process is 0.65Mpa, and the argon pressure during the soft blowing process is 0.25Mpa.

[0082] S4. Continuous casting step: The molten steel after LF treatment is hoisted to the continuous casting platform and cast normally to obtain 80.11 tons of stainless steel billets. The billet quality is normal (the billet is inspected for quality, mainly to observe whether there are transverse / longitudinal cracks / central cracks / scalds on the surface of the billet. If there are no related problems, the billet quality can be judged to be normal).

[0083] The final chemical composition of the stainless steel obtained by smelting in this embodiment, by mass percentage, includes: C 0.079%, Ni 1.12%, Cr 13.68%, Mn 10.01%, Cu 0.806%, Si 0.48%, P 0.039%, S 0.001%, N 0.12%, with the remainder being iron and unavoidable impurities.

[0084] In this embodiment, the billet (stainless steel scrap) recovery rate is 98.87%.

[0085] Example 3

[0086] A steel plant's No. 3 smelting plant produced 80 tons of a certain 201 steel grade. The composition of this steel grade, by mass percentage, includes: C 0.10%–0.15%, Ni 1.0%–1.5%, Cr 13%–14%, Mn 9.5%–10.5%, Cu 0.2%–0.5%, Si 0.3%–0.8%, P≤0.045%, S≤0.005%, N 0.10%–0.18%, with the balance being iron and unavoidable impurities.

[0087] When smelting this 201 steel grade using existing technology (AOD refining, without utilizing stainless steel scrap for smelting), the AOD furnace output is 80 tons (the normal output of the AOD process is 80 tons), and the normal tapping temperature of the AOD furnace is 1550℃.

[0088] The cold rolling mill returned 10 tons of scrap cut ends, with the steel grade marked as consistent with that steel grade.

[0089] The method for smelting stainless steel using stainless steel scrap provided in this embodiment includes the following steps:

[0090] S1, AOD Refining Steps: 56 tons of low-nickel molten iron (molten iron composition by mass percentage includes: C 5.12%, Ni 1.46%, Cr 4.08%, Mn 1.12%, Cu 0.035%, Si 0.92%, P 0.039%, S 0.061%, N 0.009%, with the remainder being iron and unavoidable impurities) are added to the AOD furnace. Subsequently, 13.2 tons of high-carbon ferrochrome (52% chromium content), 0.14 tons of copper, 5 tons of silicon-manganese alloy, and 3.9 tons of electrolytic manganese are added. After smelting, 70.4 tons of steel are tapped at a temperature of 1606℃. The composition of the molten steel (AOD steel composition) at tapping, by mass percentage, includes: C 0.071%, Ni 1.06%, Cr 13.11%, Mn 9.55%, Cu 0.216%, Si 0.58%, P 0.039%, S 0.009%, Cu 0.035%, Si 0.92%, P 0.039%, S 0.009%, and the remainder being iron and unavoidable impurities) are added. 0.0012%, N 0.135%, the remainder being iron and unavoidable impurities.

[0091] S2. Ladle preparation steps: 45 minutes before tapping from the AOD furnace, add 10 tons of scrap (stainless steel scrap) to the ladle and heat it with gas for 38 minutes. Then turn off the gas and wait for the AOD furnace to be ready for tapping. Once the AOD furnace is ready for tapping, move the ladle containing 10 tons of scrap to the bottom of the AOD furnace. The molten steel from the AOD furnace will be tapped into the ladle. After tapping, transfer the ladle to the LF furnace.

[0092] S3, LF refining steps: After the ladle arrives at the LF furnace, argon gas is introduced to the bottom of the ladle for smelting. The argon gas flow rate is adjusted by the argon gas ring (the knob for adjusting the argon gas pressure), and the argon gas pressure is controlled at 0.6 MPa. After the argon gas is turned on, the lower electrode is used to supply electricity to heat the material in the ladle. The supply current is 32000 KVA, 250V at level 3. After heating for 10 minutes, the electrode is raised to measure the temperature of the molten steel, which is 1478℃. After temperature measurement, the electrode was lowered and power was supplied to increase the temperature, with measurements taken every 10 minutes. The second measurement showed a temperature of 1534℃. The temperature was increased for another 6 minutes, the electrode was raised, and the temperature was measured at 1552℃. Power supply was stopped, and the argon gas pressure was adjusted to 0.2MPa. Soft blowing was then initiated, with measurements taken every 5 minutes. The third measurement showed a temperature of 1518℃. Power supply was then supplied again, with measurements taken every 5 minutes. The second measurement showed a temperature of 1558℃. The electrode was raised, power supply was stopped, and soft blowing was initiated. The argon gas pressure was adjusted to 0.2MPa, and measurements were taken every 5 minutes. After 10 minutes of soft blowing, the temperature was 1529℃. After 15 and 20 minutes of soft blowing, the temperatures were 1524℃ and 1519℃, respectively. During the 10-20 minute soft blowing period, the temperature drop (cooling rate) was consistent with the normal temperature drop (normal cooling rate, 0.8-1.0℃ / min), indicating that the stainless steel scrap had been completely melted. After powering on and heating for another three minutes, the temperature was measured. The argon pressure was 0.6 MPa and the molten steel temperature was 1531℃. Then, soft blowing was performed with an argon pressure of 0.2 MPa for 8 minutes, and the temperature was measured at 1523℃. Sample analysis showed that the composition included C 0.108%, Ni 1.072%, Cr 13.11%, Mn 9.45%, Cu 0.215%, Si 0.56%, P 0.040%, S 0.001%, and N 0.125%. The manganese content was low, so 100 kg of electrolytic manganese was added. The argon flow rate was adjusted using the argon gas ring (the knob for adjusting argon pressure), and the argon pressure was controlled at 0.6 MPa. After powering on and heating for another three minutes, soft blowing was performed for 5 minutes. Sample analysis showed that the composition was within acceptable limits. Afterwards, power was supplied for another 3 minutes to raise the temperature, and the molten steel was measured at 1524℃. Soft blowing was then performed for 7 minutes at an argon pressure of 0.2 MPa. After soft blowing, the argon tube was disconnected, and the mixture was allowed to settle for 6 minutes. The temperature was then measured again, showing 1512℃. The continuous casting requirement for the steel loading temperature was 1512℃, and this temperature was met. In the LF refining process, a power supply current of 32000 KVA was used for heating at 250V in three stages. The argon pressure during heating was consistently 0.6 MPa, and the argon pressure during soft blowing was consistently 0.2 MPa.

[0093] S4. Continuous casting step: The molten steel after LF treatment is hoisted to the continuous casting platform and cast normally to obtain 80.33 tons of stainless steel billets. The billet quality is normal (the billet is inspected for quality, mainly to observe whether there are transverse / longitudinal cracks / central cracks / scalds on the surface of the billet. If there are no related problems, the billet quality can be judged to be normal).

[0094] The final chemical composition of the stainless steel obtained by smelting in this embodiment, by mass percentage, includes: C 0.116%, Ni 1.072%, Cr 13.10%, Mn 9.58%, Cu 0.214%, Si 0.56%, P 0.040%, S 0.001%, N 0.123%, with the remainder being iron and unavoidable impurities.

[0095] In this embodiment, the recovery rate of scrap cuts (stainless steel scrap) is 99.30%, and the overall steel recovery rate is 91.04% (80.33 / (56+13.2+0.14+5+3.9+10)=91.04%).

[0096] Comparative Example 1

[0097] A steel plant's No. 3 smelting plant produced 80 tons of a certain 201 steel grade. The composition of this steel grade, by mass percentage, includes:

[0098] C 0.10%–0.15%, Ni 1.0%–1.5%, Cr 13%–14%, Mn 9.5%–10.5%, Cu 0.2%–0.5%, Si 0.3%–0.8%, P ≤0.045%, S ≤0.005%, N 0.10%–0.18%, with the balance being iron and unavoidable impurities.

[0099] When smelting this 201 steel grade using existing technology (AOD refining, without utilizing stainless steel scrap for smelting), the AOD furnace output is 80 tons (the normal output of the AOD process is 80 tons), and the normal tapping temperature of the AOD furnace is 1550℃.

[0100] The cold rolling mill returned 10 tons of scrap cuts, and the steel grade and specifications marked on the cuts were consistent with those steel grades.

[0101] The method for smelting stainless steel using stainless steel scrap provided in this comparative example includes the following steps:

[0102] S1, AOD Refining Steps: 57 tons of low-nickel molten iron (molten iron composition by mass percentage includes: C 5.17%, Ni 1.43%, Cr 4.11%, Mn 1.10%, Cu 0.035%, Si 1.02%, P 0.041%, S 0.071%, N 0.008%, with the remainder being iron and unavoidable impurities) are added to the AOD furnace. Subsequently, 13.3 tons of high-carbon ferrochrome (52% chromium content), 0.14 tons of copper, 10 tons of scrap metal, 5.5 tons of silicon-manganese alloy, and 3.6 tons of electrolytic manganese are added. After smelting, 80.3 tons of steel are produced and tapped at a temperature of 1552℃. The composition of the molten steel (AOD steel composition) at tapping, by mass percentage, includes: C 0.125%, Ni 1.08%, Cr 13.18%, Mn 9.65%, Cu 0.214%, Si 0.02%, P 0.041%, S 0.071%, N 0.008%, with the remainder being iron and unavoidable impurities) is added. 0.36%, P 0.037%, S 0.0012%, N 0.131%, balance is iron and unavoidable impurities.

[0103] S2. Ladle preparation steps: No stainless steel scrap is added to the ladle. After the AOD is ready for tapping, the ladle is opened to tap the bottom of the furnace. After tapping, the ladle is transferred to the LF furnace.

[0104] S3, LF Refining Steps: After the ladle arrives at the LF furnace, the temperature of the molten steel is measured at 1516℃. Argon gas is introduced into the bottom of the ladle for smelting. The argon gas flow rate is adjusted using the argon gas ring (a knob for adjusting argon gas pressure), and the argon gas pressure is controlled at 0.6 MPa. After connecting the argon gas, the lower electrode is used to supply electricity to heat the material in the ladle. The supply current is 32000 KVA, 250V at level 3. After heating for 6 minutes, the temperature is measured at 1540℃. The power supply is stopped, and the argon gas ring is adjusted to an argon gas pressure of 0.2 MPa. Soft blowing begins, with temperature measured every 5 minutes. The fourth temperature measurement is 1520℃; the temperature drop is normal, and a sample is taken for analysis, showing that the composition is qualified. Power is then supplied again for heating for 2 minutes, and the temperature is measured at 1524℃. Soft blowing continues for 9 minutes. After soft blowing is completed, the argon gas pipe is disconnected, and the ladle is allowed to settle for 6 minutes. The temperature is measured again, showing 1510℃. The continuous casting requirement is a steel loading temperature of 1511℃, which meets the requirement. In the LF refining process, a power supply current of 32000KVA and 250V in three stages are used for power supply and heating. The argon pressure during the heating process is 0.6Mpa, and the argon pressure during the soft blowing process is 0.2Mpa.

[0105] S4. Continuous casting step: The molten steel after LF treatment is hoisted to the continuous casting platform and cast normally to obtain stainless steel billets. The billet quality is normal (the billet is inspected for quality, mainly to observe whether there are transverse / longitudinal cracks / central cracks / scalds on the surface of the billet. If there are no related problems, the billet quality can be judged to be normal).

[0106] In this comparative example, the recovery rate of scrap (stainless steel scrap) was 91.12%. (Because the scrap was added during the AOD smelting process, its individual recovery rate cannot be accurately distinguished; the steel recovery rate for this furnace is 80.3 /

[0107] (57+13.3+0.14+5.5+3.6+10)=89.68%, while the recovery rate of scrap cuts is generally higher than that of normal molten steel (scrap cuts have a low carbon content, generally below 0.2%, while normal molten steel is made from iron, and the carbon content of iron is generally greater than 4.0%, and the carbon is basically oxidized during the steelmaking process). Therefore, based on the normal AOD recovery rate of 89.5% (lower than 89.68%), the recovery rate of scrap cuts is estimated to be 91.12%.

[0108] The final chemical composition of the stainless steel obtained by this comparative smelting, by mass percentage, includes:

[0109] C 0.131%, Ni 1.082%, Cr 13.18%, Mn 9.64%, Cu 0.215%, Si 0.35%, P 0.037%, S 0.001%, N 0.124%, balance being iron and unavoidable impurities.

[0110] Obviously, the above embodiments are merely illustrative examples for clear explanation and are not intended to limit the implementation. Those skilled in the art will recognize that other variations or modifications can be made based on the above description. It is neither necessary nor possible to exhaustively list all possible implementations here. However, obvious variations or modifications derived therefrom are still within the scope of protection of this invention.

Claims

1. A method for smelting stainless steel using stainless steel scrap, characterized in that, Includes the following steps: AOD refining steps: The raw materials are loaded into the AOD furnace and subjected to primary refining in the AOD furnace to obtain refined molten steel. The tapping temperature is 45~80℃ higher than the normal tapping temperature. The raw materials do not include the stainless steel scrap. Ladle preparation steps: Add stainless steel scrap into the ladle, then tap the refined molten steel obtained from the AOD refining step into the ladle containing the stainless steel scrap. After tapping, transfer the ladle to the LF furnace. LF refining steps: After the ladle arrives at the LF furnace, argon gas is introduced to the bottom of the ladle, and the lower electrode is used to supply electricity to heat the material in the ladle until the stainless steel scrap is melted. The molten steel is sampled and analyzed, and the alloy composition is fine-tuned until the composition of the molten steel is qualified. Finally, the temperature of the molten steel is adjusted so that the tapping temperature reaches the continuous casting temperature required to obtain LF-treated molten steel. Continuous casting step: The molten steel after LF treatment is continuously cast to obtain stainless steel, wherein the carbon content of the stainless steel is within the upper limit of the qualified range ≥0.07wt%.

2. The method for smelting stainless steel using stainless steel scrap according to claim 1, characterized in that, In the AOD refining step, the carbon content of the tapped steel is 0.01% to 0.05% lower than the lower limit of the acceptable carbon content range for the stainless steel.

3. The method for smelting stainless steel using stainless steel scrap according to claim 1, characterized in that, The mass ratio of the stainless steel scrap to the refined molten steel is no greater than 35:

65.

4. The method for smelting stainless steel using stainless steel scrap according to claim 3, characterized in that, In the AOD refining step, when the mass ratio of stainless steel scrap to refined molten steel is (25:75) to (35:65), the carbon content of the tapped steel is 0.04% to 0.05% lower than the lower limit of the acceptable carbon content range for stainless steel; when the mass ratio of stainless steel scrap to refined molten steel is (15:85) to (25:75), the carbon content of the tapped steel is 0.03% to 0.04% lower than the lower limit of the acceptable carbon content range for stainless steel; when the mass ratio of stainless steel scrap to refined molten steel is (5:95) to (15:85), the carbon content of the tapped steel is 0.02% to 0.03% lower than the lower limit of the acceptable carbon content range for stainless steel; when the mass ratio of stainless steel scrap to refined molten steel is less than 5:95, the carbon content of the tapped steel is 0.01% to 0.02% lower than the lower limit of the acceptable carbon content range for stainless steel.

5. The method for smelting stainless steel from stainless steel scrap according to claim 1, characterized in that, In the LF refining step, the pressure of the argon gas introduced to the bottom of the ladle is 0.6-0.8 MPa; And / or, in the LF refining step, power supply of 8000-32000KVA, 3-5 levels, and voltage of 234-250V is used for power supply and heating; And / or, in the LF refining step, the lower electrode supplies electricity to heat the material in the ladle until the stainless steel scrap is completely melted, including: After the lower electrode supplies electricity to heat the material in the ladle for a preset time, the first temperature is measured to obtain the first temperature. When the first temperature is less than 1552°C, the material in the ladle continues to be heated by electricity until the temperature of the material in the ladle is not less than 1552°C, and then the heating is stopped. The material inside the ladle is subjected to soft argon blowing and temperature measurement to obtain a second temperature. When the second temperature is 1518~1522℃, the material inside the ladle is heated by power supply until the temperature of the material inside the ladle is not less than 1552℃, at which point the heating is stopped. The material inside the ladle is subjected to soft argon blowing, and the temperature is measured. When the cooling rate is consistent with the preset cooling rate, it is determined that the stainless steel scrap has melted completely.

6. The method for smelting stainless steel from stainless steel scrap according to claim 5, characterized in that, The preset time = weight of stainless steel scrap in the ladle / A, where A is 2~3, the unit of the preset time is min, and the unit of the weight of stainless steel scrap in the ladle is tons; And / or, in the LF refining step, the lower electrode supplies electricity to heat the material in the ladle until the stainless steel scrap is completely melted, further comprising: When the cooling rate is greater than the preset cooling rate, it is determined that the stainless steel scrap has not been completely melted. Power is then supplied to raise the temperature, and the temperature is measured. When the heating rate is consistent with the preset heating rate, it is determined that the stainless steel scrap has been completely melted.

7. The method for smelting stainless steel from stainless steel scrap according to claim 6, characterized in that, In the LF refining step, the lower electrode supplies electricity to heat the material in the ladle until the stainless steel scrap is completely melted, and the process further includes: When the heating rate is less than the preset heating rate, it is determined that the stainless steel scrap has not been completely melted. Power is supplied to continue heating until the temperature of the material in the ladle is not less than 1552°C. Heating is then stopped, and soft blowing is initiated. Temperature is measured to determine whether the cooling rate is consistent with the preset cooling rate.

8. The method for smelting stainless steel from stainless steel scrap according to claim 5, characterized in that, The argon pressure during the soft blowing process is 0.2-0.3 MPa. During the soft blowing process, the LF electrode is raised and the power supply is stopped.

9. The method for smelting stainless steel using stainless steel scrap according to claim 1, characterized in that, In the LF refining step, when the composition of the molten steel is unqualified, the corresponding alloy is added to adjust the composition. After the corresponding alloy is added, the lower electrode is energized and heated. The lower electrode is energized and heated for no less than 3 minutes. Argon gas is introduced into the bottom of the ladle. The pressure of the argon gas is 0.5~0.7MPa, the power supply is 8000-32000KVA, 3-5 levels, and the voltage is 234-250V. And / or, in the LF refining step, the tapping temperature reaches the continuous casting required temperature when the difference between the tapping temperature and the continuous casting required temperature is within ±3℃. And / or, in the LF refining step, adjusting the molten steel temperature includes: After the composition is qualified, continue to supply power to raise the temperature until the molten steel temperature is 10-20°C higher than the continuous casting temperature. Then stop raising the temperature and perform soft blowing and sintering. After sintering, measure the temperature of the molten steel. If the temperature of the molten steel is too low, continue to supply power to raise the temperature until the temperature of the molten steel reaches the continuous casting temperature. If the temperature of the molten steel is too high, continue to sinter and cool down until the temperature of the molten steel reaches the continuous casting temperature. And / or, the stainless steel scrap includes substandard steel billets from steel mills, returned stainless steel of the same grade from hot rolling or cold rolling mills, or grade 1 stainless steel scrap with stable composition purchased from external sources. And / or, in the ladle preparation step, 30 to 50 minutes before the AOD furnace taps steel, the stainless steel scrap is added to the ladle and baked with gas. 5 to 7 minutes before the AOD furnace taps steel, the gas is turned off. After the AOD furnace is ready to tap steel, the ladle is moved to the bottom of the AOD furnace to tap steel. And / or, the stainless steel scrap is of the same series as the stainless steel.

10. The method for smelting stainless steel from stainless steel scrap according to claim 1, characterized in that, In the LF refining step, after the stainless steel scrap is melted and cleaned, before sampling and analyzing the molten steel, when the temperature of the molten steel is less than 1550℃, the molten steel is heated by electricity for 3-5 minutes, then the heating is stopped, and soft argon blowing is performed for no less than 6 minutes. After the soft argon blowing, the temperature of the molten steel is not lower than 1514℃. When the temperature of the molten steel is not lower than 1550℃, the heating is stopped, and soft argon blowing is performed for no less than 6 minutes. After the soft argon blowing, the temperature of the molten steel is not lower than 1514℃.