CN111876688A - Smelting method of high-nitrogen sulfur-containing free-cutting steel - Google Patents
Smelting method of high-nitrogen sulfur-containing free-cutting steel Download PDFInfo
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Abstract
The invention discloses a smelting method of high-nitrogen sulfur-containing free-cutting steel, which mainly comprises the following steps: the method comprises the following steps of smelting and tapping in a converter → an LF refining furnace → an RH vacuum furnace → continuous casting, adding an aluminum ingot for pre-deoxidation in the tapping process, manufacturing low-alkalinity slag in the LF refining furnace, adding a small amount of aluminum particles into the slag surface, improving the diffusion deoxidation efficiency and greatly purifying the molten steel; the RH vacuum furnace is driven by nitrogen, the ultimate vacuum is kept for a certain time, the RH vacuum furnace is withdrawn from a first-stage pump to a fourth-stage pump after being broken, the nitrogen-containing alloy is added, and the circulation is carried out for 5min, so that the S content and the N content in the steel can be accurately controlled, the narrow-range accurate control of the molten steel components is ensured, meanwhile, the refining period is stabilized, the operation is simple, and the RH vacuum furnace is suitable for mass production; the method is simple and effective, is easy to operate, can accurately control the refining time and the refining components, improves the quality of molten steel, ensures the production rhythm, and is suitable for wide popularization.
Description
Technical Field
The invention belongs to the technical field of free-cutting steel manufacturing, and particularly relates to a smelting method of high-nitrogen sulfur-containing free-cutting steel.
Background
When many domestic manufacturers produce high-nitrogen sulfur-containing free-cutting steel, the LF refining furnace adopts high-alkalinity slag, the high-alkalinity slag system has great influence on the S content in the steel, particularly the S yield is greatly influenced, and the narrow range control of the S is not easy to stabilize. And N in the steel is at a lower level after RH vacuum treatment, a large amount of nitrogen-containing alloy or cored wires need to be added in the later period, the alloy is melted by opening the bottom blowing stirring, the temperature drop is large, and secondary oxidation of the molten steel is easily caused.
Modern metallurgy has a title of 'narrow component control technology of sulfur in C70S6BY non-quenched and tempered steel', and the article describes a method for performing slag washing desulfurization on a C70S6BY non-quenched and tempered steel converter by using high carbon and top slag technologies, and LF accurately realizes the narrow component control of sulfur in C70S6BY steel by adjusting a slag system and subsequent technological measures for controlling soft blowing time. However, compared with the invention, the premelted refining slag is produced after the converter furnace is adopted, the alkalinity of the refining furnace in the early stage is higher, the slag fluidity is reduced, the slag amount is large, and a large amount of nitrogen and sulfur containing core-spun yarns are fed after RH vacuum treatment, so the operation is complicated, the treatment period is long, and the large-scale production is not facilitated.
In addition, some documents also disclose production methods of low-carbon high-sulfur free-cutting steel, but the problems that vacuum treatment is not performed on molten steel, the purity of the molten steel is low, inclusion control is not facilitated, the yield of N is unstable and the like generally exist, so that the research and development of a smelting method of the high-nitrogen sulfur-containing free-cutting steel realizes the narrow-range accurate control of chemical elements in the molten steel, improves the qualification rate of steel products, and is a problem to be solved urgently at present in the industry.
Disclosure of Invention
The technical problem to be solved by the invention is as follows: aiming at the problems that the control difficulty of the content of nitrogen and sulfur is high, the operation is complicated, the purity of molten steel is low, the inclusion control and mass production are not facilitated and the like in the production process of the high-nitrogen sulfur-containing free-cutting steel in the prior art, the smelting method of the high-nitrogen sulfur-containing free-cutting steel is provided; the method is simple and effective, is easy to operate, can accurately control the refining time and the refining components, improves the quality of the molten steel, ensures the production rhythm, ensures the narrow-range accurate control of the components of the molten steel, and realizes the large-batch stable production of the high-nitrogen sulfur-containing free-cutting steel.
The invention relates to a smelting method of high-nitrogen sulfur-containing free-cutting steel, which comprises the following chemical elements in percentage by mass: c: 0.34-0.38%, Si: 0.60-0.75%, Mn: 0.95-1.05%, P is not more than 0.045%, S: 0.030-0.045%, Cr: 0.10-0.25%, V: 0.25-0.35%, Al is less than or equal to 0.030%, Mo is less than or equal to 0.06%, Ni is less than or equal to 0.20%, and N: 0.0150-0.0200%, and less than or equal to 0.0020% of O;
the smelting method of the free-cutting steel mainly comprises the following steps: converter smelting tapping → LF refining furnace → RH vacuum furnace → continuous casting, in particular:
(1) tapping from converter
Smelting in a converter by using molten iron and scrap steel as raw materials, wherein the molten iron accounts for 80-85% of the mass of the raw materials, the scrap steel accounts for 15-20% of the mass of the raw materials, the temperature of the molten iron is controlled to be not less than 1350 ℃ during smelting, and P is not more than 0.120%; c, controlling at the smelting end: 0.10 to 0.20 percent, P is less than or equal to 0.035 percent, the tapping temperature is 1570-;
adding aluminum ingots into the molten steel in the tapping process, wherein the adding amount of the aluminum ingots is 2.0-2.5kg/t, and then adding ferrosilicon, silicomanganese, ferrochromium and ferrovanadium into the molten steel to adjust the content of Si in the molten steel to be 0.60-0.75%, the content of Mn to be 0.95-1.05%, the content of Cr to be 0.10-0.25% and the content of V to be 0.19-0.20%;
(2) LF refining furnace
Manufacturing low-alkalinity slag by a refining furnace, controlling the alkalinity to be 1.5-2.0, wherein the refining slag contains the following components in percentage by weight: CaO: 40-45% of SiO2：25-30%，Al2O3: 8-13%, MgO: 7-12%, and the rest is inevitable oxide impurities;
secondly, adding aluminum particles to the slag surface for deoxidation in the refining process, wherein the adding amount of the aluminum particles is 0.4-0.5Kg/t, uniformly scattering the aluminum particles on the slag surface, and keeping the white slag for more than or equal to 15 min;
thirdly, according to the content of S in the molten steel, ferrous sulfide is added to adjust the S content to 0.035-0.045%, the molten steel is suspended and wrapped in an RH vacuum furnace, and the refining period is controlled to be 55-60 min;
(3) RH vacuum furnace
Driven by nitrogen and with the flow rate of 90Nm3The treatment ultimate vacuum degree, namely the pressure is less than or equal to 67Pa, and the holding time is more than or equal to 10 min;
secondly, moving back from the first-stage pump to a fourth-stage pump after the steel is broken, namely, increasing the pressure from 67Pa to 8000Pa, adding 1.35kg/t of vanadium-nitrogen alloy, circulating for 5min, adjusting the V content to 0.28-0.30% and the N content to 0.0150-0.0200% in the molten steel, adding a covering agent, and carrying out ladle hanging until continuous casting;
(4) continuous casting
Adopting a continuous casting process of an electromagnetic stirring and weak cooling system, wherein the electromagnetic stirring current is 350A, and the frequency is 3.5 Hz; the cooling water quantity of the crystallizer is 130-140m3The specific water amount of the secondary cooling water is 0.60-0.70L/Kg, and the throwing speed of the 155-square continuous casting billet is 2.2And 2.4m/min, wherein the straightening temperature of the continuous casting billet is 950-.
The covering agent in the step (3) is carbonized chaff and mainly plays a role in keeping the temperature of molten steel.
According to the invention, aluminum ingots are added for pre-deoxidation in the tapping process, low-alkalinity slag (1.5-2.0) is produced in an LF refining furnace, the S content in steel can be effectively controlled in a stable range, a small amount of aluminum particles are added into the slag surface, the diffusion deoxidation efficiency is improved, and the molten steel is greatly purified; the RH vacuum furnace is driven by nitrogen, the ultimate vacuum is kept for a certain time, the vacuum furnace is evacuated after evacuation and retreats from a first-level pump (the vacuum degree is less than or equal to 67 Pa) to a fourth-level pump (the vacuum degree is 8000 Pa), a nitrogenous alloy is added, circulation is carried out for 5min, and N reduction in the vacuum treatment process is avoided. The method is simple and effective, is easy to operate, can accurately control the refining time and the refining components, improves the quality of molten steel, and ensures the production rhythm.
Compared with the prior art, the invention has the following advantages:
(1) the invention manufactures low-alkalinity slag (1.5-2.0) through the LF refining furnace, effectively controls the content of S in steel and ensures the stable production rhythm;
(2) according to the invention, the RH vacuum furnace adopts methods of nitrogen driving, pump withdrawal circulation and the like, so that the N content in steel is accurately controlled, inclusions in the steel are greatly reduced, and the purity of molten steel is improved;
(3) the method is simple, effective, easy to operate and suitable for mass production.
According to the method, the low-alkalinity slag (1.5-2.0) is produced through the LF refining furnace, the S content in the steel can be effectively controlled within a stable range, the RH vacuum furnace is driven by nitrogen, the ultimate vacuum is kept for a certain time, after the vacuum is broken, the RH vacuum furnace moves back from a first-stage pump (the vacuum degree is less than or equal to 67 Pa) to a fourth-stage pump (the vacuum degree is 8000 Pa) after the vacuum is broken, the nitrogen-containing alloy is added, the circulation is carried out for 5min, the N reduction in the vacuum treatment process is avoided, the N content is accurately controlled, the inclusion in the steel is greatly reduced; the method is simple and effective, is easy to operate, can accurately control the refining time and the refining components, improves the quality of the molten steel, ensures the production rhythm, ensures the narrow-range accurate control of the components of the molten steel, and realizes the large-batch stable production of the high-nitrogen sulfur-containing free-cutting steel.
Detailed Description
In order to better explain the technical solution of the present invention, the technical solution of the present invention is further described below with reference to specific examples, which are only exemplary to illustrate the technical solution of the present invention and do not limit the present invention in any way.
Example 1
The smelting method of the free-cutting steel mainly comprises the following steps: converter smelting tapping → LF refining furnace → RH vacuum furnace → continuous casting, in particular:
(1) tapping from converter
Smelting in a converter by using molten iron and scrap steel as raw materials, wherein the molten iron accounts for 81 mass percent of the raw materials, the scrap steel accounts for 19 mass percent of the raw materials, and the molten iron temperature is controlled to be 1377 ℃ and P during smelting: 0.114%; c, controlling at the smelting end: 0.12%, P: 0.023 percent, the tapping temperature is 1595 ℃, and a sliding plate is adopted for slag blocking;
adding an aluminum ingot into the molten steel in the tapping process, wherein the adding amount of the aluminum ingot is 2.2kg/t, and then adding ferrosilicon, silicomanganese, ferrochromium and ferrovanadium into the molten steel to adjust the content of Si, Mn, Cr and V in the molten steel to be 0.65%, 1.00%, 0.17% and 0.19% respectively;
(2) LF refining furnace
Manufacturing low-alkalinity slag by a refining furnace, controlling the alkalinity to be 1.6, wherein the refining slag contains the following components in percentage by weight: CaO: 42.25% of SiO2：26.40%，Al2O3: 10.11%, MgO: 9.23%, the others being inevitable oxide impurities;
secondly, adding aluminum particles to the slag surface for deoxidation in the refining process, wherein the adding amount of the aluminum particles is 0.40Kg/t, uniformly scattering the aluminum particles on the slag surface, and keeping the white slag for 16 min;
thirdly, according to the content of S in the molten steel, ferrous sulfide is added to adjust the S to be 0.040 percent, the molten steel is hung in an RH vacuum furnace, and the refining period is controlled to be 56 min;
(3) RH vacuum furnace
Driven by nitrogen and with the flow rate of 90Nm3The treatment ultimate vacuum degree, namely the pressure is less than or equal to 67Pa, and the holding time is 11 min;
secondly, returning from the first-stage pump to a fourth-stage pump after the steel is broken, namely, increasing the pressure from 67Pa to 8000Pa, adding 1.35kg/t of vanadium-nitrogen alloy, circulating for 5min, adjusting the V content and the N content in the molten steel to be 0.29% and 0.0162%, adding a covering agent, and carrying out ladle lifting until continuous casting;
(4) continuous casting
Adopting a continuous casting process of an electromagnetic stirring and weak cooling system, wherein the electromagnetic stirring current is 350A, and the frequency is 3.5 Hz; the cooling water quantity of the crystallizer is 135m3And h, the specific water amount of secondary cooling water is 0.60L/Kg, the drawing speed of the 155-square continuous casting billet is 2.2-2.2m/min, the straightening temperature of the continuous casting billet is 962 ℃, the continuous casting billet enters a pit for slow cooling for 48h after being cut, a high-temperature embrittlement area is avoided, and the stress is eliminated.
The covering agent in the step (3) is carbonized chaff and plays a role in keeping the temperature of the molten steel.
The high-nitrogen sulfur-containing free-cutting steel smelted by the method of the embodiment contains the following chemical elements in percentage by mass: c: 0.36%, Si: 0.65%, Mn: 0.98%, P: 0.025%, S: 0.038%, Cr: 0.15%, V: 0.29%, Al is less than or equal to 0.010%, Mo: 0.004%, Ni: 0.02%, N: 0.0162 percent and less than or equal to 0.0012 percent of O.
Example 2
The smelting method of the free-cutting steel mainly comprises the following steps: converter smelting tapping → LF refining furnace → RH vacuum furnace → continuous casting, in particular:
(1) tapping from converter
Smelting in a converter by using molten iron and scrap steel as raw materials, wherein the molten iron accounts for 80 mass percent of the raw materials, the scrap steel accounts for 20 mass percent of the raw materials, and the molten iron temperature is controlled to 1380 ℃ and P: 0.110 percent; c, controlling at the smelting end: 0.15%, P: 0.026%, tapping temperature 1590 deg.C, and sliding plate for slag blocking;
adding an aluminum ingot into the molten steel in the tapping process, wherein the adding amount of the aluminum ingot is 2.3kg/t, and then adding ferrosilicon, silicomanganese, ferrochromium and ferrovanadium into the molten steel to adjust the content of Si, Mn, Cr and V in the molten steel to be 0.65%, 0.98%, 0.15% and 0.19%;
(2) LF refining furnace
Manufacturing low-alkalinity slag by a refining furnace, controlling the alkalinity to be 1.5, wherein the refining slag contains the following components in percentage by weight: CaO: 40.62% of SiO2：27.08%，Al2O3: 10.32%, MgO: 9.65%, and the balance inevitable oxide impurities;
secondly, adding aluminum particles to the slag surface for deoxidation in the refining process, wherein the adding amount of the aluminum particles is 0.42Kg/t, uniformly scattering the aluminum particles on the slag surface, and keeping the white slag for 16 min;
thirdly, according to the content of S in the molten steel, ferrous sulfide is added to adjust the S to be 0.038%, the molten steel is suspended and wrapped in an RH vacuum furnace, and the refining period is controlled to be 56 min;
(3) RH vacuum furnace
Driven by nitrogen and with the flow rate of 90Nm3The treatment ultimate vacuum degree, namely the pressure is less than or equal to 67Pa, and the holding time is 12 min;
secondly, returning from the first-stage pump to a fourth-stage pump after the steel is broken, namely, increasing the pressure from 67Pa to 8000Pa, adding 1.35kg/t of vanadium-nitrogen alloy, circulating for 5min, adjusting the V content and the N content in the molten steel to be 0.29% and 0.0155%, adding a covering agent, and carrying out ladle lifting until continuous casting;
(4) continuous casting
Adopting a continuous casting process of an electromagnetic stirring and weak cooling system, wherein the electromagnetic stirring current is 350A, and the frequency is 3.5 Hz; the cooling water quantity of the crystallizer is 138m3And h, the specific water amount of secondary cooling water is 0.62L/Kg, the drawing speed of the 155-square continuous casting billet is 2.2m/min, the straightening temperature of the continuous casting billet is 969 ℃, the continuous casting billet enters a pit for slow cooling for 48h after being cut, a high-temperature embrittlement area is avoided, and the stress is eliminated.
The covering agent in the step (3) is carbonized chaff and plays a role in keeping the temperature of the molten steel.
The high-nitrogen sulfur-containing free-cutting steel smelted by the method of the embodiment contains the following chemical elements in percentage by mass: c: 0.35%, Si: 0.65%, Mn: 0.98%, P: 0.029%, S: 0.037%, Cr: 0.15%, V: 0.29 percent, less than or equal to 0.012 percent of Al, Mo: 0.005%, Ni: 0.02%, N: 0.0155 percent and less than or equal to 0.0010 percent of O.
Example 3
The smelting method of the free-cutting steel mainly comprises the following steps: converter smelting tapping → LF refining furnace → RH vacuum furnace → continuous casting, in particular:
(1) tapping from converter
Smelting in a converter by using molten iron and scrap steel as raw materials, wherein the molten iron accounts for 85 mass percent of the raw materials, the scrap steel accounts for 15 mass percent of the raw materials, and the molten iron temperature is controlled to 1370 ℃ and P during smelting: 0.110 percent; c, controlling at the smelting end: 0.16%, P: 0.026%, tapping temperature 1585 deg.C, sliding plate is used for slag stopping;
adding an aluminum ingot into the molten steel in the tapping process, wherein the adding amount of the aluminum ingot is 2.2kg/t, and then adding ferrosilicon, silicomanganese, ferrochromium and ferrovanadium into the molten steel to adjust the content of Si, Mn, Cr and V in the molten steel to be 0.68%, 1.01%, 0.14% and 0.20%;
(2) LF refining furnace
Manufacturing low-alkalinity slag by a refining furnace, controlling the alkalinity to be 1.5, wherein the refining slag contains the following components in percentage by weight: CaO: 42.36% of SiO2：28.24%，Al2O3: 9.32%, MgO: 10.04%, and the balance inevitable oxide impurities;
secondly, adding aluminum particles to the slag surface for deoxidation in the refining process, wherein the adding amount of the aluminum particles is 0.40Kg/t, uniformly scattering the aluminum particles on the slag surface, and keeping the white slag for 15 min;
thirdly, according to the content of S in the molten steel, ferrous sulfide is added to adjust the S to be 0.040 percent, the molten steel is hung in an RH vacuum furnace, and the refining period is controlled to be 56 min;
(3) RH vacuum furnace
Driven by nitrogen and with the flow rate of 90Nm3The treatment ultimate vacuum degree, namely the pressure is less than or equal to 67Pa, and the holding time is 11 min;
secondly, returning from the first-stage pump to a fourth-stage pump after the steel is broken, namely, increasing the pressure from 67Pa to 8000Pa, adding 1.35kg/t of vanadium-nitrogen alloy, circulating for 5min, adjusting the V content and the N content in the molten steel to be 0.30 percent and 0.016 percent respectively, adding a covering agent, and carrying out continuous casting by a ladle;
(4) continuous casting
Adopting a continuous casting process of an electromagnetic stirring and weak cooling system, wherein the electromagnetic stirring current is 350A, and the frequency is 3.5 Hz; the cooling water quantity of the crystallizer is 135m3And h, the specific water amount of secondary cooling water is 0.65L/Kg, the drawing speed of the 155-square continuous casting billet is 2.3m/min, the straightening temperature of the continuous casting billet is 975 ℃, the continuous casting billet enters a pit for slow cooling for 48h after being cut, a high-temperature embrittlement area is avoided, and the stress is eliminated.
The covering agent in the step (3) is carbonized chaff and plays a role in keeping the temperature of the molten steel.
The high-nitrogen sulfur-containing free-cutting steel smelted by the method of the embodiment contains the following chemical elements in percentage by mass: c: 0.35%, Si: 0.68%, Mn: 1.01%, P: 0.026%, S: 0.040%, Cr: 0.14%, V: 0.30%, Al is less than or equal to 0.015%, Mo: 0.004%, Ni: 0.02%, N: 0.016 percent and less than or equal to 0.0012 percent of O.
Example 4
The smelting method of the free-cutting steel mainly comprises the following steps: converter smelting tapping → LF refining furnace → RH vacuum furnace → continuous casting, in particular:
(1) tapping from converter
Smelting in a converter by using molten iron and scrap steel as raw materials, wherein the molten iron accounts for 83 mass percent of the raw materials, the scrap steel accounts for 17 mass percent of the raw materials, and the molten iron temperature is controlled to be 1375 ℃ and P during smelting: 0.110 percent; c, controlling at the smelting end: 0.18%, P: 0.020%, the tapping temperature is 1582 ℃, and a sliding plate is adopted to block slag;
adding an aluminum ingot into the molten steel in the tapping process, wherein the adding amount of the aluminum ingot is 2.0kg/t, and then adding ferrosilicon, silicomanganese, ferrochromium and ferrovanadium into the molten steel to adjust the content of Si, Mn, Cr and V in the molten steel to be 0.65%, 1.00%, 0.14% and 0.19% respectively;
(2) LF refining furnace
Manufacturing low-alkalinity slag by a refining furnace, controlling the alkalinity to be 1.6, wherein the refining slag contains the following components in percentage by weight: CaO: 41.85% of SiO2：26.17%，Al2O3: 9.85%, MgO: 9.65%, and the balance inevitable oxide impurities;
secondly, adding aluminum particles to the slag surface for deoxidation in the refining process, wherein the adding amount of the aluminum particles is 0.40Kg/t, uniformly scattering the aluminum particles on the slag surface, and keeping the white slag for 15 min;
thirdly, according to the content of S in molten steel, ferrous sulfide is added to adjust the S to be 0.040 percent, and the molten steel is hung in an RH vacuum furnace, and the refining period is controlled to be 55 min;
(3) RH vacuum furnace
Driven by nitrogen and with the flow rate of 90Nm3The treatment ultimate vacuum degree, namely the pressure is less than or equal to 67Pa, and the holding time is 10 min;
secondly, returning from the first-stage pump to a fourth-stage pump after the steel is broken, namely, increasing the pressure from 67Pa to 8000Pa, adding 1.35kg/t of vanadium-nitrogen alloy, circulating for 5min, adjusting the V content and the N content in the molten steel to be 0.29% and 0.0165%, adding a covering agent, and carrying out ladle lifting until continuous casting;
(4) continuous casting
Adopting a continuous casting process of an electromagnetic stirring and weak cooling system, wherein the electromagnetic stirring current is 350A, and the frequency is 3.5 Hz; the cooling water quantity of the crystallizer is 138m3And h, the specific water amount of secondary cooling water is 0.65L/Kg, the drawing speed of the 155-square continuous casting billet is 2.0m/min, the straightening temperature of the continuous casting billet is 966 ℃, the continuous casting billet enters a pit for slow cooling for 48h after being cut, a high-temperature embrittlement area is avoided, and the stress is eliminated.
The covering agent in the step (3) is carbonized chaff and plays a role in keeping the temperature of the molten steel.
The high-nitrogen sulfur-containing free-cutting steel smelted by the method of the embodiment contains the following chemical elements in percentage by mass: c: 0.36%, Si: 0.65%, Mn: 1.00%, P: 0.021%, S: 0.039%, Cr: 0.14%, V: 0.29%, Al is less than or equal to 0.015%, Mo: 0.003%, Ni: 0.02%, N: 0.0165 percent and less than or equal to 0.0014 percent of O.
Example 5
The smelting method of the free-cutting steel mainly comprises the following steps: converter smelting tapping → LF refining furnace → RH vacuum furnace → continuous casting, in particular:
(1) tapping from converter
Smelting in a converter by using molten iron and scrap steel as raw materials, wherein the molten iron accounts for 82 mass percent of the raw materials, the scrap steel accounts for 18 mass percent of the raw materials, and the molten iron temperature is controlled to be 1375 ℃ and P during smelting: 0.105%; c, controlling at the smelting end: 0.16%, P: 0.018 percent, the tapping temperature is 1579 ℃, and a sliding plate is adopted for slag blocking;
adding an aluminum ingot into the molten steel in the tapping process, wherein the adding amount of the aluminum ingot is 2.2kg/t, and then adding ferrosilicon, silicomanganese, ferrochromium and ferrovanadium into the molten steel to adjust the content of Si, Mn, Cr and V in the molten steel to be 0.65%, 1.00%, 0.15% and 0.19% respectively;
(2) LF refining furnace
Manufacturing low-alkalinity slag by a refining furnace, controlling the alkalinity to be 1.6, wherein the refining slag contains the following components in percentage by weight: CaO: 42.34% of SiO2：26.46%，Al2O3: 10.85%, MgO: 10.72%, the others being unavoidable oxide impurities;
secondly, adding aluminum particles to the slag surface for deoxidation in the refining process, wherein the adding amount of the aluminum particles is 0.45Kg/t, uniformly scattering the aluminum particles on the slag surface, and keeping the white slag for 15 min;
thirdly, according to the content of S in the molten steel, ferrous sulfide is added to adjust the S to be 0.039%, the molten steel is suspended and wrapped in an RH vacuum furnace, and the refining period is controlled to be 58 min;
(3) RH vacuum furnace
Driven by nitrogen and with the flow rate of 90Nm3The treatment ultimate vacuum degree, namely the pressure is less than or equal to 67Pa, and the holding time is 10 min;
secondly, returning from the first-stage pump to a fourth-stage pump after the steel is broken, namely, increasing the pressure from 67Pa to 8000Pa, adding 1.35kg/t of vanadium-nitrogen alloy, circulating for 5min, adjusting the V content and the N content in the molten steel to be 0.29% and 0.0160%, adding a covering agent, and carrying out ladle lifting until continuous casting;
(4) continuous casting
Adopting a continuous casting process of an electromagnetic stirring and weak cooling system, wherein the electromagnetic stirring current is 350A, and the frequency is 3.5 Hz; the cooling water quantity of the crystallizer is 135m3And h, the specific water amount of secondary cooling water is 0.68L/Kg, the billet drawing speed of a 155-square continuous casting billet is 2.3m/min, the straightening temperature of the continuous casting billet is 980 ℃, the continuous casting billet enters a pit for slow cooling for 48h after being cut, a high-temperature embrittlement area is avoided, and stress is eliminated.
The covering agent in the step (3) is carbonized chaff and plays a role in keeping the temperature of the molten steel.
The high-nitrogen sulfur-containing free-cutting steel smelted by the method of the embodiment contains the following chemical elements in percentage by mass: c: 0.35%, Si: 0.65%, Mn: 1.00%, P: 0.019%, S: 0.038%, Cr: 0.15%, V: 0.29 percent, less than or equal to 0.014 percent of Al, Mo: 0.004%, Ni: 0.02%, N: 0.0160 percent and less than or equal to 0.0012 percent of O.
After analyzing the results of examples 1 to 5, it was found that: the high-nitrogen sulfur-containing free-cutting steel produced by the method has the advantages of good S, N stability, low O content, high molten steel purity, stable refining period and strong operability. The high-nitrogen sulfur-containing free-cutting steel produced by the method has the advantages of simple process, stable steel quality, suitability for mass production and obvious advantages.
Claims (2)
1. A smelting method of high-nitrogen sulfur-containing free-cutting steel comprises the following chemical elements in percentage by mass: c: 0.34-0.38%, Si: 0.60-0.75%, Mn: 0.95-1.05%, P is not more than 0.045%, S: 0.030-0.045%, Cr: 0.10-0.25%, V: 0.25-0.35%, Al is less than or equal to 0.030%, Mo is less than or equal to 0.06%, Ni is less than or equal to 0.20%, and N: 0.0150-0.0200%, and less than or equal to 0.0020% of O;
the smelting method of the free-cutting steel mainly comprises the following steps: the method comprises the following steps of smelting and tapping in a converter → an LF refining furnace → an RH vacuum furnace → continuous casting, and is characterized in that:
(1) tapping from converter
Smelting in a converter by using molten iron and scrap steel as raw materials, wherein the molten iron accounts for 80-85% of the mass of the raw materials, the scrap steel accounts for 15-20% of the mass of the raw materials, the temperature of the molten iron is controlled to be not less than 1350 ℃ during smelting, and P is not more than 0.120%; c, controlling at the smelting end: 0.10 to 0.20 percent, P is less than or equal to 0.035 percent, the tapping temperature is 1570-;
adding aluminum ingots into the molten steel in the tapping process, wherein the adding amount of the aluminum ingots is 2.0-2.5kg/t, and then adding ferrosilicon, silicomanganese, ferrochromium and ferrovanadium into the molten steel to adjust the content of Si in the molten steel to be 0.60-0.75%, the content of Mn to be 0.95-1.05%, the content of Cr to be 0.10-0.25% and the content of V to be 0.19-0.20%;
(2) LF refining furnace
Making low-alkalinity slag in refining furnace and controlling alkalinityThe refining slag is prepared from 1.5 to 2.0 percent of the following components in percentage by weight: CaO: 40-45% of SiO2：25-30%，Al2O3: 8-13%, MgO: 7-12%, and the rest is inevitable oxide impurities;
secondly, adding aluminum particles to the slag surface for deoxidation in the refining process, wherein the adding amount of the aluminum particles is 0.4-0.5Kg/t, uniformly scattering the aluminum particles on the slag surface, and keeping the white slag for more than or equal to 15 min;
thirdly, according to the content of S in the molten steel, ferrous sulfide is added to adjust the S content to 0.035-0.045%, the molten steel is suspended and wrapped in an RH vacuum furnace, and the refining period is controlled to be 55-60 min;
(3) RH vacuum furnace
Driven by nitrogen and with the flow rate of 90Nm3The treatment ultimate vacuum degree, namely the pressure is less than or equal to 67Pa, and the holding time is more than or equal to 10 min;
secondly, moving back from the first-stage pump to a fourth-stage pump after the steel is broken, namely, increasing the pressure from 67Pa to 8000Pa, adding 1.35kg/t of vanadium-nitrogen alloy, circulating for 5min, adjusting the V content to 0.28-0.30% and the N content to 0.0150-0.0200% in the molten steel, adding a covering agent, and carrying out ladle hanging until continuous casting;
(4) continuous casting
Adopting a continuous casting process of an electromagnetic stirring and weak cooling system, wherein the electromagnetic stirring current is 350A, and the frequency is 3.5 Hz; the cooling water quantity of the crystallizer is 130-140m3And h, the specific water amount of secondary cooling water is 0.60-0.70L/Kg, the billet drawing speed of the 155-square continuous casting billet is 2.2-2.4m/min, the straightening temperature of the continuous casting billet is 950-fold, and the continuous casting billet enters a pit for slow cooling for 48h after being cut, so that a high-temperature embrittlement region is avoided, and the stress is eliminated.
2. The method for smelting a high-nitrogen sulfur-containing free-cutting steel as claimed in claim 1, wherein: the covering agent in the step (3) is carbonized chaff and plays a role in keeping the temperature of the molten steel.
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| CN115505672A (en) * | 2022-09-20 | 2022-12-23 | 中天钢铁集团有限公司 | Low-cost smelting method for low-carbon free-cutting steel |
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