CN112239832A - Method for improving surface quality of free-cutting steel - Google Patents
Method for improving surface quality of free-cutting steel Download PDFInfo
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- CN112239832A CN112239832A CN202011135599.1A CN202011135599A CN112239832A CN 112239832 A CN112239832 A CN 112239832A CN 202011135599 A CN202011135599 A CN 202011135599A CN 112239832 A CN112239832 A CN 112239832A
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- C—CHEMISTRY; METALLURGY
- C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
- C22C—ALLOYS
- C22C38/00—Ferrous alloys, e.g. steel alloys
- C22C38/04—Ferrous alloys, e.g. steel alloys containing manganese
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- B—PERFORMING OPERATIONS; TRANSPORTING
- B22—CASTING; POWDER METALLURGY
- B22D—CASTING OF METALS; CASTING OF OTHER SUBSTANCES BY THE SAME PROCESSES OR DEVICES
- B22D11/00—Continuous casting of metals, i.e. casting in indefinite lengths
- B22D11/001—Continuous casting of metals, i.e. casting in indefinite lengths of specific alloys
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- B—PERFORMING OPERATIONS; TRANSPORTING
- B22—CASTING; POWDER METALLURGY
- B22D—CASTING OF METALS; CASTING OF OTHER SUBSTANCES BY THE SAME PROCESSES OR DEVICES
- B22D11/00—Continuous casting of metals, i.e. casting in indefinite lengths
- B22D11/10—Supplying or treating molten metal
- B22D11/103—Distributing the molten metal, e.g. using runners, floats, distributors
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- C—CHEMISTRY; METALLURGY
- C21—METALLURGY OF IRON
- C21C—PROCESSING OF PIG-IRON, e.g. REFINING, MANUFACTURE OF WROUGHT-IRON OR STEEL; TREATMENT IN MOLTEN STATE OF FERROUS ALLOYS
- C21C5/00—Manufacture of carbon-steel, e.g. plain mild steel, medium carbon steel or cast steel or stainless steel
- C21C5/28—Manufacture of steel in the converter
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- C—CHEMISTRY; METALLURGY
- C21—METALLURGY OF IRON
- C21C—PROCESSING OF PIG-IRON, e.g. REFINING, MANUFACTURE OF WROUGHT-IRON OR STEEL; TREATMENT IN MOLTEN STATE OF FERROUS ALLOYS
- C21C7/00—Treating molten ferrous alloys, e.g. steel, not covered by groups C21C1/00 - C21C5/00
- C21C7/0006—Adding metallic additives
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- C—CHEMISTRY; METALLURGY
- C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
- C22C—ALLOYS
- C22C38/00—Ferrous alloys, e.g. steel alloys
- C22C38/002—Ferrous alloys, e.g. steel alloys containing In, Mg, or other elements not provided for in one single group C22C38/001 - C22C38/60
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- C—CHEMISTRY; METALLURGY
- C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
- C22C—ALLOYS
- C22C38/00—Ferrous alloys, e.g. steel alloys
- C22C38/02—Ferrous alloys, e.g. steel alloys containing silicon
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- C—CHEMISTRY; METALLURGY
- C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
- C22C—ALLOYS
- C22C38/00—Ferrous alloys, e.g. steel alloys
- C22C38/60—Ferrous alloys, e.g. steel alloys containing lead, selenium, tellurium, or antimony, or more than 0.04% by weight of sulfur
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- Treatment Of Steel In Its Molten State (AREA)
Abstract
The application relates to the field of steel smelting, and relates to a method for improving the surface quality of free-cutting steel. Molten steel free oxygen: 50ppm to 150ppm, the temperature of the molten steel after tapping is more than or equal to 1544 ℃, the C is less than 0.06 percent, the Mn is 1.00 to 1.25 percent, the ferro-sulphur and ferro-phosphorus are added during tapping, the S in the molten steel after tapping is 0.100 to 0.200 percent, and the P in the molten steel after tapping is 0.050 to 0.070 percent. The insertion depth of the continuous casting water gap is 100-120 mm; temperature of water entering and exiting the crystallizerThe temperature difference is 4-11 ℃, and the water flow is 150-160m3And/h, the current/frequency is (295-305) A/(2.5-3.5) Hz. The method has the advantages that the cutting performance of the steel can be effectively improved by adding a large amount of ferro-sulphur and having higher oxygen content in the steel, and the ferro-sulphur is added in the tapping process of the converter, so that the control of the oxygen content in the steel and the floating removal of subsequent inclusions are facilitated, and the surface quality of the steel can be effectively ensured.
Description
Technical Field
The application relates to the field of steel smelting, in particular to a method for improving the surface quality of free-cutting steel.
Background
Shaft-type steels for OA office appliances such as printers and facsimiles have some special requirements for the properties of the steels.
The method mainly comprises the following steps: (1) free-cutting performance is good because both ends of the shaft need to be turned or drilled into corresponding fitting shapes. (2) The surface of the turned product is smooth and has no defects of cracks, scars and the like. (3) Because the roll paper shaft needs to be encapsulated, the surface of a processed product cannot have pinhole-shaped defects.
In order to meet the above requirements, the conventional technical means in the field is to use high-cost materials, such as copper, stainless steel, etc., instead.
However, this approach is costly.
Disclosure of Invention
The embodiment of the application aims to provide a method for improving the surface quality of free-cutting steel, which guarantees the surface quality of the steel while guaranteeing the cutting performance of the steel.
The application provides a method for improving the surface quality of free-cutting steel, which is regulated in a smelting process, wherein the smelting process comprises the following steps: a molten iron preparation process, a converter smelting process, a converter tapping process, an LF furnace refining process, a continuous casting process and a rolling process;
converter tapping: steel ladle molten steel free oxygen: 50 ppm-150 ppm, and the temperature of molten steel in a steel ladle after tapping is not less than 1544 ℃; in the molten steel after tapping, by mass percent: c is less than 0.06 percent, Mn is 1.00-1.25 percent, ferro-sulphur and ferro-phosphorus are added during tapping, S is 0.100-0.200 percent and P is 0.050-0.070 percent in molten steel after tapping;
and (3) continuous casting process: the insertion depth of the continuous casting water gap is 100-120 mm; the temperature difference between the inlet water and the outlet water of the crystallizer is 4-11 ℃; 150-160m of crystallizer water flow3H; electromagnetic stirring parameters of the crystallizer: the current/frequency is (295-305) A/(2.5-3.5) Hz.
In some embodiments of the present application, the continuous casting process:
the insertion depth of the continuous casting water gap is 100-120 mm.
In some embodiments of the present application, the continuous casting process: the total transfer time of the large ladle is less than or equal to 15min, and the superheat degree of the tundish is less than or equal to 50 ℃;
optionally, when the superheat degree is less than or equal to 20 ℃, the pulling speed is 1.95-2.05 m/min; when the superheat degree is more than 20 ℃ and less than or equal to 45 ℃, the pulling speed is 1.75-1.85 m/min; when the degree of superheat is higher than 45 ℃, the pulling speed is 1.65-1.74 m/min.
In some embodiments of the present application, the continuous casting process:
the temperature difference between the inlet water and the outlet water of the crystallizer is 4-11 ℃; 150-160m of crystallizer water flow3H; electromagnetic stirring parameters of the crystallizer: the current/frequency is (295-305) A/(2.5-3.5) Hz.
In some embodiments of the present application, the continuous casting process:
the fluctuation of the target liquid level is controlled to be less than or equal to +/-10 mm.
In some embodiments of the present application, the rolling process:
temperature of the preheating section: 550 ℃ and 750 ℃, heating section temperature: 1150 ℃ and 1260 ℃, temperature of the soaking section: 1150-1280 ℃ and 1125-1165 ℃ of initial rolling temperature.
In some embodiments of the present application, the rolling process:
inlet temperature of finishing mill group: 1020 to 1060 ℃.
In some embodiments of the present application, the rolling process:
inlet temperature of the double-module rolling mill: 1020 to 1060 ℃.
In some embodiments of the present application, the LF furnace refining process:
and C in the steel water discharged from the station by mass percent: 0.04-0.07%, Si: less than or equal to 0.06 percent, Mn: 1.10-1.35%, P: 0.05-0.09%, S: 0.27-0.38%, free oxygen content of 50-90 ppm, and the temperature of the outbound molten steel is 1581-1591 ℃.
In some embodiments of the present application, the converter smelting process:
stopping blowing phosphorus, wherein the mass percentage of P: 0.03% -0.07%, blowing-out temperature: 1660-1700 ℃;
optionally, the molten iron preparation process: the temperature of the molten iron is more than or equal to 1230 ℃, and the silicon content in the molten iron is as follows by mass percent: 0.10 to 0.80 percent.
The method for improving the surface quality of the free-cutting steel has the advantages that:
according to the embodiment of the application, the method for adding the sulfur iron in the LF furnace in the traditional mode is changed by adding the sulfur iron in the converter tapping process, and the control of the oxygen content in steel and the floating removal of subsequent inclusions are facilitated, so that the surface quality of the steel can be effectively guaranteed, and the defects of cracks, scabs, bubbles and the like on the surface of the steel are avoided. And then the surface quality of the steel can be ensured while the cutting performance of the steel is ensured. Through setting up the continuous casting mouth of a river depth of insertion for 100 ~ 120mm, set up the technological parameter of crystallizer in above-mentioned within range, can effectively reduce the bubble and carry the inclusion, solve in the course of working inclusion and drop, cause the problem of pinhole form defect to improve the surface quality of steel, so that final finished product steel satisfies the axle type spare part steel requirement of OA office appliances such as printer, fax machine.
Drawings
In order to more clearly illustrate the technical solutions of the embodiments of the present application, the drawings that are required to be used in the embodiments will be briefly described below, it should be understood that the following drawings only illustrate some embodiments of the present application and therefore should not be considered as limiting the scope, and for those skilled in the art, other related drawings can be obtained from the drawings without inventive effort.
FIG. 1 is a diagram showing the thermoplasticity of a free-cutting steel provided in example 1 of the present application at 750 ℃ to 1300 ℃.
Detailed Description
In order to make the objects, technical solutions and advantages of the embodiments of the present application clearer, the technical solutions of the embodiments of the present application will be clearly and completely described below, and it is obvious that the described embodiments are some embodiments of the present application, but not all embodiments.
Thus, the following detailed description of the embodiments of the present application is not intended to limit the scope of the claimed application, but is merely representative of selected embodiments of the application. All other embodiments, which can be derived by a person skilled in the art from the embodiments given herein without making any creative effort, shall fall within the protection scope of the present application.
Hereinafter, "%" means mass percent.
The embodiment of the application provides a method for improving the surface quality of free-cutting steel. The steel is a chalcogenide free-cutting steel and is applied to isometric spare parts of printers.
According to the method, the surface quality of the free-cutting steel is improved by regulating and controlling in the smelting process.
The smelting process comprises the following steps: the method comprises a molten iron preparation process, a converter smelting process, a converter tapping process, an LF furnace refining process, a continuous casting process and a rolling process.
And S1, a molten iron preparation process.
Because the Cu, As and Sn elements are not greatly changed in the smelting process, the Cu, As and Sn elements in the molten iron are controlled to meet the component requirements of finished steel, and the molten iron does not need to be subjected to desulfurization treatment.
Further, controlling the temperature of the molten iron to be more than or equal to 1230 ℃, wherein the silicon content in the molten iron is as follows: 0.10 to 0.80 percent.
Further optionally, controlling the content of silicon in the molten iron: 0.11 to 0.79 percent. Further optionally, controlling the content of silicon in the molten iron: 0.12 to 0.78 percent. Illustratively, the silicon content in the molten iron is controlled: 0.12%, 0.15%, 0.20%, 0.25%, 0.30%, 0.35%, 0.40%, 0.50%, 0.65%, 0.70%, or 0.72%.
S2, converter smelting process.
Further, stopping blowing phosphorus, P: 0.03% -0.07%, blowing-out temperature: 1660-1700 ℃;
further optionally, stopping blowing phosphorus, P: 0.035 to 0.065 percent. Illustratively, stop-blowing phosphorus, P: 0.04%, 0.045%, 0.050%, 0.055%, or 0.060%.
Further optionally, the blowing temperature: 1665-1695 ℃; further optionally, the blowing temperature: 1655-1690 deg.C; illustratively, the blowing off temperature: 1660 deg.C, 1665 deg.C, 1670 deg.C, 1675 deg.C, 1680 deg.C or 1685 deg.C.
And S3, converter tapping.
Controlling free oxygen of steel ladle molten steel: 50 ppm-150 ppm, and the temperature of molten steel in a steel ladle after tapping is not less than 1544 ℃; in the molten steel after tapping, by mass percent: less than 0.06 percent of C, 1.00 to 1.25 percent of Mn, adding ferro-sulphur and ferro-phosphorus during tapping, and after tapping, 0.100 to 0.200 percent of S and 0.050 to 0.070 percent of P in molten steel.
The cutting performance of the steel can be effectively improved by adding a large amount of ferro-sulphur and remaining high oxygen content in the steel, but the defects of cracks, scabs, bubbles and the like on the surface of the steel are easily caused. The shaft products used for OA office appliances such as printers and facsimiles have extremely high requirements on the surface quality of steel. How to ensure the surface quality of steel while improving the cutting performance becomes a difficult problem in the field. The conventional method in the field is to add a large amount of ferro-sulphur into an LF furnace to improve the cutting performance of steel, but the method often causes defects in the surface quality of the steel and cannot meet the surface quality requirements of shaft products.
According to the embodiment of the application, the method for adding the sulfur iron in the LF furnace in the traditional mode is changed by adding the sulfur iron in the converter tapping process, and the control of the oxygen content in steel and the floating removal of subsequent inclusions are facilitated, so that the surface quality of the steel can be effectively guaranteed, and the defects of cracks, scabs, bubbles and the like on the surface of the steel are avoided.
Further optionally, controlling the free oxygen of the steel ladle molten steel: 51ppm to 149 ppm; further optionally, controlling the free oxygen of the steel ladle molten steel: 52ppm to 148 ppm; further optionally, controlling the free oxygen of the steel ladle molten steel: 55ppm to 145 ppm. Illustratively, controlling ladle steel free oxygen: 56ppm, 60ppm, 65ppm, 70ppm, 75ppm, 80ppm, 85ppm, 90ppm, 95ppm, 100ppm, 105ppm, 110ppm, 115ppm, 120ppm, 125ppm, 130ppm, 135ppm or 140 ppm.
Further optionally, in the molten steel after tapping, by mass percent: less than 0.06 percent of C, 1.01 to 1.24 percent of Mn, adding ferro-sulphur and ferro-phosphorus during tapping, and after tapping, 0.101 to 0.199 percent of S and 0.051 to 0.069 percent of P in molten steel. Further optionally, in the molten steel after tapping, by mass percent: less than 0.06 percent of C, 1.02 to 1.23 percent of Mn, adding ferro-sulphur and ferro-phosphorus during tapping, and after tapping, 0.102 to 0.198 percent of S and 0.052 to 0.068 percent of P in molten steel. Exemplarily, in the molten steel after tapping: less than 0.06 percent of C, 1.03 percent of Mn, 1.05 percent of Mn, 1.08 percent of Mn, 1.13 percent of Mn, 1.18 percent of Mn, 1.21 percent of Mn or 1.23 percent of Mn. Illustratively, the molten steel after tapping contains 0.103%, 0.105%, 0.108%, 0.115%, 0.120%, 0.125%, 0.130%, 0.135%, 0.140%, 0.145%, 0.150%, 0.155%, 0.160%, 0.165%, 0.170%, 0.175%, 0.180%, 0.185%, or 0.190% of S. Illustratively, the P content in the molten steel after tapping is 0.052%, 0.055%, 0.058%, 0.060%, 0.062% or 0.065%.
And S4, refining in an LF furnace.
Further, the weight percentage of C in the steel liquid discharged from the station is as follows: 0.04-0.07%, Si: less than or equal to 0.06 percent, Mn: 1.10-1.35%, P: 0.05-0.09%, S: 0.27 to 0.38% and a free oxygen content of 50 to 90 ppm.
Further optionally, in percentage by mass, C: 0.045-0.065%, Si: less than or equal to 0.06 percent, Mn: 1.15-1.30%, P: 0.055-0.085%, S: 0.28 to 0.37% and a free oxygen content of 55 to 85 ppm.
Further, the temperature of the molten steel discharged from the station is 1581-1591 ℃. Further optionally, the temperature of the molten steel discharged from the station is 1585-1590 ℃.
And S5, a continuous casting process.
Furthermore, the insertion depth of the continuous casting water gap is 100-120 mm.
The conventional means in the field is to set the insertion depth to 90mm, which easily causes quality defects such as bubbles on the surface of the steel.
The continuous casting nozzle insertion depth is 100-120 mm, so that the problem of bubbles can be effectively reduced, the surface quality of steel is improved, and the final finished steel meets the requirements of shaft type spare parts of OA office appliances such as printers and fax machines.
Further optionally, the continuous casting nozzle has an insertion depth of 101-119 mm. Further optionally, the continuous casting nozzle has an insertion depth of 102-118 mm. Further optionally, the continuous casting nozzle has an insertion depth of 103-117 mm. Illustratively, the continuous casting nozzle insertion depth is 104mm, 105mm, 106mm, 107mm, 108mm, 109mm, 110mm, 111mm, 112mm, 113mm, 114mm, 115mm, 116mm, or 117 mm.
Further, the total transmission time of the big bag is less than or equal to 15 min.
Furthermore, the superheat degree of the tundish is less than or equal to 50 ℃.
Further, when the superheat degree is less than or equal to 20 ℃, the pulling speed is 1.95-2.05 m/min; when the superheat degree is more than 20 ℃ and less than or equal to 45 ℃, the pulling speed is 1.75-1.85 m/min; when the degree of superheat is higher than 45 ℃, the pulling speed is 1.65-1.74 m/min.
Further optionally, when the superheat degree is less than or equal to 20 ℃, the pulling speed is 1.96-2.04 m/min; when the degree of superheat is more than 20 ℃ and less than or equal to 45 ℃, the pulling speed is 1.76-1.84 m/min; when the degree of superheat is higher than 45 ℃, the pulling speed is 1.66-1.73 m/min.
Further optionally, when the superheat degree is less than or equal to 20 ℃, the pulling speed is 1.97-2.03 m/min; when the superheat degree is more than 20 ℃ and less than or equal to 45 ℃, the pulling speed is 1.77-1.83 m/min; when the degree of superheat is higher than 45 ℃, the pulling speed is 1.67-1.72 m/min.
Illustratively, when the degree of superheat is less than or equal to 20 ℃, the pulling speed is 1.98m/min, 1.99m/min, 2.00m/min, 2.01m/min and 2.02 m/min.
Illustratively, when the degree of superheat is more than 20 ℃ and less than or equal to 45 ℃, the pulling speed is 1.78m/min, 1.79m/min, 1.80m/min, 1.81m/min and 1.82 m/min.
Illustratively, when the degree of superheat is > 45 ℃, the pulling rate is 1.68m/min, 1.69m/min, 1.70m/min, 1.71 m/min.
Further, the temperature difference of inlet water and outlet water of the crystallizer is 4-11 ℃; 150-160m of crystallizer water flow3H; electromagnetic stirring parameters of the crystallizer: the current/frequency is (295-305) A/(2.5-3.5) Hz.
The process parameters of the crystallizer are set within the range, bubbles carrying impurities can be effectively reduced, and the problem of pinhole defects caused by falling of the impurities in the machining process is solved.
Further optionally, the temperature difference of inlet and outlet water of the crystallizer is 5-10 ℃; water flow 152-3H; electromagnetic stirring parameters of the crystallizer: the current/frequency is (296-304) A/(2.6-3.4) Hz. Further optionally, the temperature difference of inlet and outlet water of the crystallizer is 6-9 ℃; water flow 153-3H; electromagnetic stirring parameters of the crystallizer: the current/frequency is (298-302) A/(2.8-3.3) Hz.
Illustratively, the temperature difference between the crystallizer inlet and outlet water is 6 ℃, 7 ℃, 8 ℃ and 9 ℃.
Exemplarily, the crystallizer water flow 154m3/h、155m3/h、156m3/h、157m3/h。
Exemplarily, the electromagnetic stirring parameters of the crystallizer: the current/frequency is 299A/2.7Hz, 300A/3.0Hz or 301A/3.1 Hz.
Further, the fluctuation control of the target liquid level is less than or equal to +/-10 mm. Further optionally, the target level fluctuation is controlled to be ≦ 9 mm. Further optionally, the target level fluctuation is controlled to be less than or equal to +/-8 mm.
Further, the secondary cooling water meter is set to be weakly cold.
The weak cooling process is correspondingly set according to different pulling speeds, and the water flow and the specific water flow set at different positions of the second cooling section are specifically shown in table 1:
TABLE 1 Weak Cooling Process
| Pulling speed (m/min) | 1.0 | 1.2 | 1.4 | 1.6 | 1.8 | 2.0 | 2.2 | 2.4 | 2.6 |
| Foot roller (m3/h) | 3.4 | 4.3 | 5.2 | 6.0 | 6.8 | 7.6 | 8.4 | 9.2 | 10.0 |
| Zone 1 (m3/h) | 2.9 | 3.7 | 4.5 | 5.2 | 5.8 | 6.5 | 7.0 | 7.5 | 8.0 |
| Zone 2 (m3/h) | 0.6 | 1.1 | 1.7 | 2.2 | 2.7 | 3.1 | 3.6 | 4.0 | 4.3 |
| Zone 3 (m3/h) | 0.1 | 0.4 | 0.7 | 1.0 | 1.4 | 1.7 | 2.2 | 2.6 | 3.0 |
| Total water volume (m3/h) | 7.0 | 9.5 | 12.1 | 14.4 | 16.7 | 18.9 | 21.2 | 23.3 | 25.3 |
| Specific water volume (L/kg) | 0.52 | 0.59 | 0.65 | 0.68 | 0.71 | 0.72 | 0.73 | 0.74 | 0.74 |
And S6, rolling.
Further, the preheating section temperature: 550 ℃ and 750 ℃, heating section temperature: 1150 ℃ and 1260 ℃, temperature of the soaking section: 1150-1280 ℃ and 1125-1165 ℃ of initial rolling temperature.
The steel grade has high sulfur and oxygen content, the rolling temperature must be in a region with good plasticity in the rolling process, and the rolling deformation has the following rules through research:
firstly, in the deformation process, when the reduction of area is less than 30%, the material belongs to a low-plasticity area, and a large number of cracks are easily generated in the material;
secondly, the reduction of area is between 30 and 40 percent, the plasticity is slightly lower, and the material is easy to generate more cracks;
thirdly, when the reduction of area is 40-50%, the material generates a small amount of cracks in a plastic acceptable area;
fourthly, when the reduction of area is between 50 and 60 percent, the plasticity is good, and the material generates few cracks;
when the reduction of area is 50% -60%, the plasticity is good, and the material generates few cracks;
sixthly, when the reduction of area is more than 70 percent, cracks are rarely generated in a high plasticity area.
Through experimental study, the following curve is obtained from the thermoplasticity condition of 750-1300 ℃ of the steel grade, and is shown in the attached figure 1 of the specification.
According to the description shown in figure 1, when the deformation temperature is higher than 1020 ℃, and the deformation temperature is higher than 1020 ℃, the reduction of area is more than 50%, the plasticity is good, and the material generates few cracks; the requirement that the steel material not have cracks is one of the main characteristics of the product, and is also a requirement for smooth production.
By combining the analysis, the rolling temperature is set to be 1125-1165 ℃, so that the steel can be effectively prevented from cracking, the surface quality of the steel is guaranteed, and the requirements of the steel for OA office appliance shaft products such as printers and fax machines are met.
Further, finishing Block (BGV) inlet temperature: 1020 to 1060 ℃. Further optionally, the finishing train inlet temperature: 1025 to 1055 ℃. Exemplary finishing train inlet temperature: 1025 deg.C, 1030 deg.C, 1035 deg.C, 1040 deg.C, 1050 deg.C.
Further, the inlet temperature of the double module rolling mill (TMB): 1020 to 1060 ℃. Further optionally, the finishing train inlet temperature: 1025 to 1055 ℃. Exemplary, two-module mill inlet temperature: 1025 deg.C, 1030 deg.C, 1035 deg.C, 1040 deg.C, 1050 deg.C.
The features and properties of the present application are described in further detail below with reference to examples:
example 1
Provides free-cutting steel, and the smelting process comprises the following steps: the method comprises a molten iron preparation process, a converter smelting process, a converter tapping process, an LF furnace refining process, a continuous casting process and a rolling process.
S1, molten iron preparation: the temperature of molten iron is more than or equal to 1230 ℃, and the silicon content in the molten iron is as follows: 0.50 percent.
S2, converter smelting process: stopping blowing phosphorus, P: 0.04%, blowing stop temperature: 1692 deg.C.
S3, converter tapping, steel ladle molten steel free oxygen: 140ppm, and the temperature of molten steel in a steel ladle is 1589 ℃ after tapping; in the molten steel after tapping, by mass percent: 0.03 percent of C, 1.21 percent of Mn, and adding ferro-sulphur and ferro-phosphorus during tapping, wherein the S and the P in molten steel are 0.18 percent and 0.06 percent respectively after tapping.
S4, an LF furnace converter tapping process: c, discharging molten steel C: 0.06%, Si: 0.02%, Mn: 1.28%, P: 0.07%, S: 0.32 percent, free oxygen content of 70ppm and the temperature of the outbound molten steel of 1589 ℃.
And S5, a continuous casting process. The specific process parameters are shown in table 1.
And S6, rolling. The specific process parameters are shown in Table 2.
Examples 2 to 7
Provided is free-cutting steel which is substantially the same as the smelting process of example 1 except that the process parameters of the continuous casting process and the rolling process are different, and the specific parameters are shown in tables 1 and 2.
Comparative examples 1 to 6
A free-cutting steel is provided, which is basically the same as the smelting process of example 1, except that the specific process parameters of each process are different, and the specific parameters are shown in Table 2.
Comparative example 7
Provided is free-cutting steel which is basically the same as the smelting process of example 1 except that: and adding ferro-sulphur and ferro-phosphorus in the tapping process of the converter, wherein the ferro-sulphur and the ferro-phosphorus are all added in the LF furnace. The specific process parameters of each process are shown in Table 2.
TABLE 2
The following properties were tested on the steel samples of examples 1 to 7 and comparative examples 1 to 7 under the same experimental conditions, including:
1. casting blank surface indentation ratio/%: the detection method of the surface depression of the casting blank is that the ratio percentage of the number of the surface depression to the total detection number is checked by visual inspection and one by one.
2. Casting blank depression depth is greater than 5mm proportion/%: and measuring the depth of the depression on the surface of the casting blank by adopting a ruler, and checking one by one, wherein the measurement result is the percentage of the ratio of the count larger than 5mm to the total detection count.
3. Casting blank cross section pinhole number/one: according to the macrostructure and defect acid etching inspection method of GB/T226 steel, after the casting blank cross section machine is processed and is subjected to hot acid etching, the number of pinhole-shaped defects is counted.
4. Finished product processing cracking ratio/%: the processed straight rod product is inspected one by one visually, and the percentage ratio of the number of the surface crack-shaped defects to the total number of the inspected number is present.
5. Proportion of pinholes on the surface of the finished product/%: the processed straight rod product is checked by visual inspection, and the percentage ratio of the number of the pinhole-shaped defects on the surface to the total number of the detected parts is present.
6. Cutting performance: the machinability of a metal material is a comprehensive index, and generally refers to a combination of productivity, tool life, cutting force, chip shape, and surface roughness of a part after cutting in material cutting. According to the method, through a turning test, the turning speed, the cutting depth and the feeding amount are given, after turning is finished, the surface roughness and the chip breaking condition of cutting chips are qualitatively observed, the comparison grade of the cutting performance is given, the grade A is the best, and the grade B is the second and the grade C is the worst.
The results are shown in Table 3.
TABLE 3
As can be seen from the detection results in Table 3, the free-cutting steel provided by the embodiment 1-7 greatly improves the surface quality while ensuring the cutting performance. In contrast, in comparative example 1, the process abnormality is that the immersion nozzle insertion depth is insufficient, and as a result, the number of casting blank cross section pinholes is significantly large. Comparative example 2, the process abnormality is that the superheat degree of the tundish is higher, and as a result, the surface of the casting blank has high depression ratio and the number of pinholes on the cross section of the casting blank is large. Comparative example 3, the process abnormality is that the electromagnetic stirring parameter current/frequency of the crystallizer is low, and as a result, the ratio of the depression existing on the surface of the casting blank is high, the number of pinholes on the cross section of the casting blank is large, and the ratio of the opening of the finished product processing is high. Comparative example 4, the process abnormality sets a large water flow setting for the crystallizer, and as a result, the casting blank surface has a high depression ratio, a large number of pinholes on the casting blank cross section, and a high finished product processing opening ratio. Comparative example 5, the process abnormality is that the total transfer time of the large ladle is too long, the superheat degree is low, the pulling speed is accelerated, and as a result, the ratio of the depressions on the surface of the casting blank is high, the number of pinholes on the cross section of the casting blank is large, and the opening ratio of the finished product processing is high. In comparative example 6, the process abnormality was that the rolling temperature was low, with the result that the open ratio of the finished product processing was high. Comparative example 7, the process abnormality is that the ratio of adding ferro-sulphur and ferro-phosphorus is low while tapping, as a result, the number of pinholes on the cross section of the casting blank is large, and the opening ratio of finished product processing is high.
The above description is only a preferred embodiment of the present application and is not intended to limit the present application, and various modifications and changes may be made by those skilled in the art. Any modification, equivalent replacement, improvement and the like made within the spirit and principle of the present application shall be included in the protection scope of the present application.
Claims (10)
1. A method for improving the surface quality of free-cutting steel is characterized in that regulation and control are carried out in a smelting process, and the smelting process comprises the following steps: a molten iron preparation process, a converter smelting process, a converter tapping process, an LF furnace refining process, a continuous casting process and a rolling process;
the converter tapping process comprises the following steps: steel ladle molten steel free oxygen: 50 ppm-150 ppm, and the temperature of molten steel in a steel ladle after tapping is not less than 1544 ℃; in the molten steel after tapping, by mass percent: c is less than 0.06 percent, Mn is 1.00-1.25 percent, ferro-sulphur and ferro-phosphorus are added during tapping, S is 0.100-0.200 percent and P is 0.050-0.070 percent in molten steel after tapping;
the continuous casting process comprises the following steps: the insertion depth of the continuous casting water gap is 100-120 mm; the temperature difference between the inlet water and the outlet water of the crystallizer is 4-11 ℃; the crystallizer water flow is 150-160m3H; the electromagnetic stirring parameters of the crystallizer are as follows: the current/frequency is (295-305) A/(2.5-3.5) Hz.
2. The method for improving the surface quality of free-cutting steel according to claim 1, wherein the continuous casting process comprises: the total transfer time of the large ladle is less than or equal to 15min, and the superheat degree of the tundish is less than or equal to 50 ℃.
3. The method for improving the surface quality of free-cutting steel according to claim 2,
when the superheat degree is less than or equal to 20 ℃, the pulling speed is 1.95-2.05 m/min; when the superheat degree is more than 20 ℃ and less than or equal to 45 ℃, the pulling speed is 1.75-1.85 m/min; when the degree of superheat is higher than 45 ℃, the pulling speed is 1.65-1.74 m/min.
4. The method for improving the surface quality of free-cutting steel according to claim 1, wherein the continuous casting process comprises:
the fluctuation of the target liquid level is controlled to be less than or equal to +/-10 mm.
5. The method for improving the surface quality of free-cutting steel according to any one of claims 1 to 4, wherein the rolling process:
temperature of the preheating section: 550 ℃ and 750 ℃, heating section temperature: 1150 ℃ and 1260 ℃, temperature of the soaking section: 1150-1280 ℃ and 1125-1165 ℃ of initial rolling temperature.
6. The method for improving the surface quality of free-cutting steel according to claim 5, wherein the rolling process comprises:
inlet temperature of finishing mill group: 1020 to 1060 ℃.
7. The method for improving the surface quality of free-cutting steel according to claim 5, wherein the rolling process comprises:
inlet temperature of the double-module rolling mill: 1020 to 1060 ℃.
8. The method for improving the surface quality of free-cutting steel according to claim 1, wherein the LF furnace refining process:
and C in the steel water discharged from the station by mass percent: 0.04-0.07%, Si: less than or equal to 0.06 percent, Mn: 1.10-1.35%, P: 0.05-0.09%, S: 0.27-0.38%, free oxygen content of 50-90 ppm, and the temperature of the outbound molten steel is 1581-1591 ℃.
9. The method for improving the surface quality of free-cutting steel according to claim 1, wherein the converter smelting process comprises:
stopping blowing phosphorus, wherein the mass percentage of P: 0.03% -0.07%, blowing-out temperature: 1660-1700 ℃.
10. The method for improving the surface quality of free-cutting steel according to claim 1,
the molten iron preparation process comprises: the temperature of the molten iron is more than or equal to 1230 ℃, and the silicon content in the molten iron is as follows by mass percent: 0.10 to 0.80 percent.
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Citations (3)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| CN103966531A (en) * | 2014-04-29 | 2014-08-06 | 江苏省沙钢钢铁研究院有限公司 | Production method of low-carbon high-sulfur free-cutting steel with excellent sulfide form |
| CN110722119A (en) * | 2019-10-25 | 2020-01-24 | 广东韶钢松山股份有限公司 | Continuous casting production process for preparing low-carbon high-sulfur high-oxygen free-cutting steel at high drawing speed |
| US20200071783A1 (en) * | 2016-10-18 | 2020-03-05 | Jiangyin Xing Cheng Special Steel Works Co., Ltd | A rack steel plate with a thickness up to 177.8 mm by a continuous casting slab and manufacturing method thereof |
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Patent Citations (3)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| CN103966531A (en) * | 2014-04-29 | 2014-08-06 | 江苏省沙钢钢铁研究院有限公司 | Production method of low-carbon high-sulfur free-cutting steel with excellent sulfide form |
| US20200071783A1 (en) * | 2016-10-18 | 2020-03-05 | Jiangyin Xing Cheng Special Steel Works Co., Ltd | A rack steel plate with a thickness up to 177.8 mm by a continuous casting slab and manufacturing method thereof |
| CN110722119A (en) * | 2019-10-25 | 2020-01-24 | 广东韶钢松山股份有限公司 | Continuous casting production process for preparing low-carbon high-sulfur high-oxygen free-cutting steel at high drawing speed |
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