CN115044827A - Production method of isothermal annealing-free low-carbon gear steel - Google Patents
Production method of isothermal annealing-free low-carbon gear steel Download PDFInfo
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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
- C22C38/18—Ferrous alloys, e.g. steel alloys containing chromium
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- C—CHEMISTRY; METALLURGY
- C21—METALLURGY OF IRON
- C21D—MODIFYING THE PHYSICAL STRUCTURE OF FERROUS METALS; GENERAL DEVICES FOR HEAT TREATMENT OF FERROUS OR NON-FERROUS METALS OR ALLOYS; MAKING METAL MALLEABLE, e.g. BY DECARBURISATION OR TEMPERING
- C21D1/00—General methods or devices for heat treatment, e.g. annealing, hardening, quenching or tempering
- C21D1/26—Methods of annealing
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- C—CHEMISTRY; METALLURGY
- C21—METALLURGY OF IRON
- C21D—MODIFYING THE PHYSICAL STRUCTURE OF FERROUS METALS; GENERAL DEVICES FOR HEAT TREATMENT OF FERROUS OR NON-FERROUS METALS OR ALLOYS; MAKING METAL MALLEABLE, e.g. BY DECARBURISATION OR TEMPERING
- C21D6/00—Heat treatment of ferrous alloys
- C21D6/002—Heat treatment of ferrous alloys containing Cr
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- C—CHEMISTRY; METALLURGY
- C21—METALLURGY OF IRON
- C21D—MODIFYING THE PHYSICAL STRUCTURE OF FERROUS METALS; GENERAL DEVICES FOR HEAT TREATMENT OF FERROUS OR NON-FERROUS METALS OR ALLOYS; MAKING METAL MALLEABLE, e.g. BY DECARBURISATION OR TEMPERING
- C21D6/00—Heat treatment of ferrous alloys
- C21D6/005—Heat treatment of ferrous alloys containing Mn
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- C—CHEMISTRY; METALLURGY
- C21—METALLURGY OF IRON
- C21D—MODIFYING THE PHYSICAL STRUCTURE OF FERROUS METALS; GENERAL DEVICES FOR HEAT TREATMENT OF FERROUS OR NON-FERROUS METALS OR ALLOYS; MAKING METAL MALLEABLE, e.g. BY DECARBURISATION OR TEMPERING
- C21D6/00—Heat treatment of ferrous alloys
- C21D6/008—Heat treatment of ferrous alloys containing Si
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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
- C22C38/001—Ferrous alloys, e.g. steel alloys containing N
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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
- C22C38/04—Ferrous alloys, e.g. steel alloys containing manganese
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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
- C22C38/06—Ferrous alloys, e.g. steel alloys containing aluminium
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- Y—GENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; GENERAL TAGGING OF CROSS-SECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
- Y02—TECHNOLOGIES OR APPLICATIONS FOR MITIGATION OR ADAPTATION AGAINST CLIMATE CHANGE
- Y02P—CLIMATE CHANGE MITIGATION TECHNOLOGIES IN THE PRODUCTION OR PROCESSING OF GOODS
- Y02P10/00—Technologies related to metal processing
- Y02P10/20—Recycling
Abstract
The invention relates to a production method of isothermal annealing-free low-carbon gear steel, which comprises the following process flows of converter primary smelting → refining furnace refining → RH furnace vacuum degassing → continuous casting square billet → high-temperature heating → rough rolling → medium rolling → finish rolling → high-temperature round steel water penetrating → steel entering a slow cooling pit for slow cooling. The metallographic structure of the gear steel is ferrite and pearlite, the width of a ferrite strip is less than or equal to 20 mu m, the austenite grain size is 7-9 grade, the hardness of the product is less than or equal to 170HBW, the hardness range of the whole section of the product is less than or equal to 10HBW, and the longitudinal banded structure of the product is less than or equal to 2.0 grade. The chemical components by weight percentage are 0.17-0.20% of C, Si: less than or equal to 0.07 percent, Mn: 0.70-0.90%, Cr: 1.15-1.25%, P: less than or equal to 0.010 percent, S: 0.023-0.040%, Al: 0.025-0.040%, N: 0.008-0.0190% of Ca, 0.0020-0.0050% of Ca, (Mn + Ca)/S is not less than 25, and the balance of Fe and inevitable impurity elements.
Description
Technical Field
The invention relates to the technical field of special steel smelting and rolling, in particular to a production method of isothermal annealing-free low-carbon gear steel.
Background
The isothermal annealing low-carbon gear steel is mainly used for manufacturing automobile shaft parts after cold forging, and has strict requirements on the banded structure grade of round steel, the strip width of ferrite, the actual grain size and austenite grain size of the round steel and the hardness of the cross section of the round steel. The main production process of the traditional isothermal annealing low-carbon gear steel at present comprises primary smelting, refining, vacuum degassing, continuous casting, heating by a heating furnace, rolling, air cooling and isothermal annealing in an isothermal annealing furnace. The specific mode of annealing in the traditional isothermal annealing furnace is as follows: feeding the steel into an isothermal annealing furnace and heating to AC 3 And (3) after the temperature is kept for a period of time at the temperature of 30-50 ℃, cooling the steel to a certain proper temperature in a pearlite transformation area in an air cooling mode, keeping the temperature for a period of time at the temperature to homogenize the temperature of different parts of the steel, uniformly finishing the transformation of ferrite and pearlite at the temperature, and then finishing the heat treatment process of final cooling in air. After the steel is subjected to the traditional isothermal annealing treatment in the furnace, the microstructure of the steel is ferrite and pearlite which are uniformly distributed; the longitudinal banded structure of the round steel is less than or equal to 2.0 grade; the austenite grain size should be 5-8 grades; the requirement of the cold forging steel on the hardness of the material is strict, the hardness of the steel after isothermal furnace annealing is less than or equal to 170HBW, and the hardness difference of the same section of the steel is less than or equal to 10 HBW.
Patent publication No. CN106086374A discloses a heat treatment process for a railway vehicle axle by using forging waste heat to perform isothermal annealing in advance, which uses hot forming preheating to perform isothermal annealing, so that the axle obtains a microstructure close to an equilibrium state, and the axle is prepared for subsequent heat treatment: the microstructure of the axle after the conventional heat treatment of 'two positive and one negative' is obviously uniform and fine, and after the axle is finally heat treated, a sample is taken at the 1/2 radius of the axle, and the grain size difference can be controlled to be less than or equal to 1.5 grade according to GB/T6394 or ASTM E112 standard detection. The waste heat of thermal forming is utilized, so that the energy is saved, and the production cost is reduced. The phenomena of unqualified axle grain size and poor ultrasonic flaw detection sound transmission caused by the occurrence of coarse-grain structures can be reduced, and the fatigue fracture of the axle caused by mixed crystal can be prevented. The patent controls the finish forging temperature to be more than or equal to 750 ℃, puts the forged axle into a heat treatment furnace for isothermal annealing, then carries out one or two times of normalizing on the axle and finally carries out tempering.
The method disclosed in patent publication No. CN106086374A still requires annealing in an isothermal annealing furnace, and only utilizes the residual temperature after forging, thereby reducing energy consumption to a limited extent.
The development of round steel without isothermal annealing obviously can obviously reduce the production energy consumption of products, reduce carbon emission and improve market competitiveness.
Disclosure of Invention
The application aims to provide a production method of isothermal annealing-free low-carbon gear steel, steel after steel rolling is finished does not need to enter an isothermal annealing furnace for isothermal annealing treatment, round steel does not need to reduce the depth of a decarburized layer on the surface of the steel through a turning procedure, and the same effect of isothermal annealing in the furnace can be achieved only by implementing an effective cooling control means after rolling, so that the purpose of isothermal annealing is achieved, the production process flow is effectively shortened, and the production energy consumption is reduced.
The low carbon gear steel obtained according to the method comprises the following steps: the longitudinal banded structure of the round steel is less than or equal to 2.0 grade, and the width of a ferrite band is less than or equal to 20 mu m; the actual grain size of the round steel is 4-6 grade, and the austenite grain size is 7-9 grade; the hardness of the round steel is less than or equal to 170HBW, and the hardness range of the whole section is less than or equal to 10 HBW.
The technical scheme adopted by the invention is as follows: the isothermal annealing-free low-carbon gear steel comprises the following chemical components in percentage by weight of 0.17-0.20% of C, Si: less than or equal to 0.07 percent, Mn: 0.70-0.90%, Cr: 1.15-1.25%, P: less than or equal to 0.010%, S: 0.023-0.040%, Al: 0.025-0.040%, N: 0.008-0.0190% of Ca, 0.0020-0.0050% of Ca, (Mn + Ca)/S is not less than 25, and the balance of Fe and inevitable impurity elements.
The main action and the content that the chemical element of this application gear steel corresponds set up the basis:
carbon is a core element forming cementite in the steel, and the proper increase of the carbon content can reduce the content of pure ferrite in the steel, and is beneficial to reducing ferrite strips in a rolled material, thereby reducing the grade of a banded structure of the steel. However, too high a carbon content results in a hot rolled steel having a high hardness, which is disadvantageous in cold forging properties of the steel. Therefore, the carbon content in the steel is selected within the range of 0.17-0.20%.
Si-Si content is too high to cause a cold hardening phenomenon in the steel during cold forging. Therefore, the invention needs to strictly control the silicon content, and the selection range of the silicon content is that Si is less than or equal to 0.10 percent.
Mn is an important element influencing the strength and the hardenability of steel, and a proper amount of manganese element is added into the steel, so that the hardness of the core part of the gear part after quenching can be ensured. Manganese is also a good deoxidizer and desulfurizer. Proper amount of manganese can effectively improve the hot brittleness of steel caused by sulfur. Therefore, the content of manganese in the steel is selected within the range of 0.70-0.90%.
Cr is added into steel, mainly used for improving the hardenability of the steel, simultaneously solid-solution strengthening of a matrix and improving the strength of the steel, but the excessively high content of the chromium can improve the hardness of the steel and reduce the cold extrusion performance of the steel. Therefore, the selection range of the chromium content in the steel is 1.15-1.25%.
S, combining sulfur and manganese elements in the steel to form MnS, wherein the MnS can be stretched and extended along the rolling direction during rolling to form more strip-shaped manganese sulfide, thereby improving the cutting processability of the steel. Some of the sulfur elements are bonded to Ca elements to form CaS inclusions in the steel.In steel (Mn)+The heat brittleness phenomenon of the steel can be effectively controlled only when the Ca/S is more than or equal to 25, so that the continuous casting billet is solidified Fixed time withoutIs easy to crack。
According to experience, (Mn + Ca)/S in the sulfur-containing steel is more than or equal to 25, and the hot brittleness phenomenon of the steel can be effectively controlled. When the (Mn + Ca)/S is higher, cracks are not easy to generate in the continuous casting solidification process. The Mn and Ca elements can control the form of the S element in the steel, the S has the defects that eutectic with a low melting point is easily formed and is accumulated in a large amount in a grain boundary, the melting point of FeS is only 988 ℃, the sulfide in a molten state can seriously reduce the strength of the grain boundary, and the hot brittleness phenomenon of the steel is caused, the Mn and Ca are added to form MnS and CaS, the melting point of the MnS reaches 1620 ℃, and the melting point of the CaS reaches 2400 ℃, so that the low-melting-point FeS (the eutectic melting temperature of Fe and FeS is 988 ℃, the probability of FeS precipitation in the grain boundary is reduced) is replaced, and the sufficient Mn and Ca elements can effectively avoid the hot brittleness phenomenon in the continuous casting process. Therefore, the content of sulfur in the steel is selected within the range of 0.023-0.040%.
Al is added into the steel as a deoxidizer and an element for refining austenite grain size. The selection range of the Al content is 0.025-0.040%.
N is added into the steel as an element for refining the austenite grain size and is combined with Al element in the steel to form AlN particles. The N content selection range of the invention is 0.008-0.0190%.
Ca, a proper amount of calcium silicate wire is fed into the molten steel in the steelmaking process, the form of aluminum oxide inclusion with a high melting point in the steel can be changed, a calcium-aluminum compound with a low melting point is formed, and the formed calcium-aluminum compound can quickly float up to a steel slag interface and is absorbed by slag at the top of the molten steel, so that the cleanliness of the molten steel is improved, the casting performance of the molten steel is improved, the problem of nozzle blockage of a tundish is reduced, and smooth casting in the continuous casting process is ensured. The residual calcium element and the sulfur element in the steel are combined and exist in the molten steel in the form of CaS, and a proper amount of Ca can effectively improve the hot brittleness of the steel caused by sulfur. The content of Ca in the invention is selected from 0.0020-0.0050%.
The production method of the isothermal annealing-free low-carbon gear steel comprises the following steps:
step one, smelting molten steel: primary smelting, refining and vacuum degassing are involved;
step two, casting: casting the molten steel in the step one into a steel billet;
step three, heating before rolling: the heating temperature is 1180-1220 ℃;
step four, rolling: carrying out rough rolling, intermediate rolling and finish rolling in sequence to roll the billet into round steel, wherein the rough rolling compression ratio is 2.2-2.8, the intermediate rolling compression ratio is 2.1-2.7, the finish rolling compression ratio is 1.9-2.5, the requirements on the rough rolling compression ratio, the intermediate rolling compression ratio, the finish rolling compression ratio and the total compression ratio are 9-18;
step five, cooling: the temperature of the rolled round steel is not less than 920 ℃, firstly, a water penetrating process is adopted, and the round steel is quickly cooled to Ar after penetrating water 1 And immediately putting the round steel into a slow cooling pit for slow cooling at the temperature of 20-30 ℃, and taking the round steel out of the pit after the round steel is slowly cooled to room temperature.
Preferably, in the step one, aluminum deoxidation (silicon deoxidation is not adopted) is adopted in the refining process, silicon-free alloy blocks are added to adjust the components of the molten steel, and the silicon content of the molten steel in the refining process is strictly controlled to avoid introducing silicon.
Preferably, in the first step, the RH furnace is adopted for vacuum degassing, the molten steel after vacuum degassing is fed into a calcium-silicon wire, and the molten steel after wire feeding adopts bottom blowing nitrogen, so that the nitrogen content in the molten steel is improved, simultaneously, the form of high-melting-point aluminum oxide inclusions is accelerated to change, a low-melting-point calcium-aluminum compound is formed, the aim of removing the aluminide trioxide is achieved, and the cleanliness and the castability of the molten steel are improved.
Preferably, the Si-Ca wire diameter is 10mm, the Ca content is 60 wt% and the Si content is 40 wt%.
Preferably, the second step is to adopt a continuous casting process to cast the molten steel into a square billet, and the continuous casting crystallizer adopts a section of more than 200mm x 200mm to realize large-compression-ratio rolling so as to reduce the micro and macro segregation of the continuous casting billet. And step four, the specification of the hot-rolled round steel is phi 26.6 mm-phi 37.6 mm.
Preferably, in the third step, the heating time is 220min-240 min.
The isothermal annealing-free low-carbon gear steel adopts low-carbon and low-silicon design in composition, and controls the contents of Mn, S and Ca in the steel and the relationship among the Mn, S and Ca; in the production process, a converter is adopted for primary smelting, and a refining furnace adopts silico-ferromanganese and ferrochrome smelting; feeding the molten steel subjected to vacuum degassing into a high-quality calcium-silicon wire, and performing bottom nitrogen blowing treatment after wire feeding to achieve the purpose of improving the purity of the molten steel and the nitrogen content of the molten steel; the continuous casting crystallizer adopts a section of more than 200 mm. The heating time and temperature of the continuous casting billet are controlled by steel rolling, and the compression ratios of rough rolling, medium rolling and finish rolling of steel are controlled in the rolling process; the hot rolled round steel manufactured by the water cooling and pit lowering slow cooling process after rolling can be used for manufacturing automobile shaft parts after cold forging.
Compared with the prior art, the invention has the advantages that:
(1) in the component design, the invention adopts a low-carbon and low-silicon design (C: 0.17-0.20% and Si:nomore than 0.07%) suitable for a cold forging process, and controls the contents of Mn, S and Ca in steel and the relation of Mn, S and Ca to meet (Mn + Ca)/S is no less than 25 so as to ensure the surface quality of continuous casting billets. The continuous casting crystallizer adopts a section of 200mm by 200mm to reduce the micro segregation and the macro segregation of steel.
(2) The hot-rolled round steel produced by the method has excellent banded structures (the banded structures are less than or equal to 2.0 grade, and the width of ferrite strips is less than or equal to 20 mu m), has the characteristic of small macrosegregation and microsegregation of a continuous casting billet by adopting a small section of a crystallizer for continuous casting billets, and then narrows the width of the ferrite strips of the steel along with the continuous increase of the rolling compression ratio by controlling the rolling compression ratio and the rolling total compression ratio in the processes of rough rolling, intermediate rolling and finish rolling, and obviously increases the number of the ferrite strips; the high-temperature round steel after rolling can further improve the banded structure of the steel by controlling the water penetration and pit entering slow cooling process after rolling, and the width of fewer ferrite strips and narrower ferrite strips is beneficial to reducing the anisotropy of the steel, so that the fatigue life of the steel is prolonged.
The utility model provides a gear steel possesses suitable actual grain size, through control roughing, well rolling, the compression ratio of finish rolling, the big grain of continuous casting billet is progressively broken into tiny crystalline grain, the actual grain size stable control of final round steel is at 4-6 grades, if actual grain size is greater than 6 grades, be unfavorable for the cutting process of steel, and actual grain size is less than 4 grades, the ability and the trend that the crystalline grain grows up among the steel carburization process can be bigger, the mixed crystal phenomenon appears easily in the steel after the carburization. Has fine austenite grain size, and the austenite grain size of the steel can be controlled in 7-9 grades by controlling the actual grain size in the steel and adding aluminum and nitrogen elements into the steel to refine the austenite grain size of the steel.
The gear steel has low and uniform hardness, and water penetrates through the rolled high-temperature round steel (more than or equal to 920 ℃) to promote the steel to be rapidly cooled to Ar 1 The temperature of (695 ℃) is lower than 20 ℃ to 30 ℃, steel materials immediately enter a slow cooling pit for slow cooling, and supercooled austenite is completely converted into ferrite and pearlite structures which are distributed uniformly. The steel is rapidly cooled to 20-30 ℃ below Ar1(695 ℃), the spacing between pearlite plates formed by conversion in the temperature range is larger, the spacing between the pearlite plates is 350-400 nm, the hardness value of the steel at the spacing between the pearlite plates is less than or equal to 170HBW, and the hardness range of the whole section is less than or equal to 10 HBW.
According to the production method, the obtained round steel does not need to enter an isothermal annealing furnace for isothermal annealing treatment, the depth of a decarburized layer on the surface of the steel is not needed to be reduced by the round steel through a skin turning process, the same effect of isothermal annealing in the furnace can be achieved only by implementing an effective cooling control section after rolling, the production process flow is effectively shortened, and the production cost is reduced.
Detailed Description
The present invention is described in further detail below with reference to specific embodiments, it should be understood that the contents of the embodiments are exemplary, are intended to explain or assist in understanding the inventive concepts of the present application, and should not be construed as limiting the present application.
Example 1 and example 2:
the two embodiments relate to a production method of isothermal annealing-free low-carbon gear steel: converter primary smelting → refining furnace refining → RH furnace vacuum degassing → continuous casting small square billet (200mm x 200mm) → heating furnace high-temperature heating → rough rolling → medium rolling → finish rolling → high-temperature round steel water penetration → steel material entering a slow cooling pit for slow cooling → inspection and warehousing. Two batches of isothermal annealing-free low-carbon gear steel with the diameter of 26.6mm and the diameter of 37.6mm are respectively manufactured, and the method is suitable for manufacturing hot-rolled round steel with the diameter of 26.6 mm-37.6 mm.
The specific processes of heating, rolling, water penetration and slow cooling of the heating furnace in the embodiment 1 are as follows: the heating time of the continuous casting billet is 230min, the heating temperature is 1200 ℃, the rough rolling compression ratio is 2.20, the medium rolling compression ratio is 2.10, the finish rolling compression ratio is 1.95, and the diameter of the hot rolled round steel is phi 37.6 mm. And (3) performing water penetration treatment on the high-temperature round steel at 930 ℃ after rolling, controlling the water temperature at 23 ℃, quickly cooling the round steel to 670 ℃ by penetrating water, immediately putting the round steel into a slow cooling pit for slow cooling, and taking the round steel out of the pit after the round steel is slowly cooled to the room temperature of 25 ℃.
The specific processes of heating, rolling, water penetration and slow cooling of the heating furnace in the embodiment 2 are as follows: the heating time of the continuous casting billet is 235min, the heating temperature is 1190 ℃, the rough rolling reduction ratio is 2.80, the medium rolling reduction ratio is 2.66, the finish rolling reduction ratio is 2.42, and the diameter of the hot rolled round steel is phi 26.6 mm. And (3) carrying out water penetration treatment on the high-temperature round steel after rolling at 935 ℃, controlling the water temperature at 21 ℃, rapidly cooling the high-temperature round steel to 675 ℃ by penetrating water, immediately entering a slow cooling pit for slow cooling, slowly cooling to room temperature, and taking the round steel out of the pit at 22 ℃.
The chemical composition of the hot rolled round steel obtained in examples 1 and 2 is shown in Table 1.
TABLE 1 (wt%)
The band structure grades and the maximum widths of the ferrite bands of the hot rolled round steels obtained in examples 1 and 2 are shown in Table 2.
TABLE 2
| Nominal diameter | Strip tissue | Maximum width of ferrite strip | |
| Example 1 | φ37.6mm | 1.0 stage | 19um |
| Example 2 | φ26.6mm | 1.5 grade | 12um |
The actual grain size grades and austenite grain size grades of the hot rolled round steels obtained in examples 1 and 2 are shown in Table 3.
TABLE 3
| Nominal diameter | Actual grain size | Austenite grain size | |
| Example 1 | φ37.6mm | Grade 4.0 | Stage 8.0 |
| Example 2 | φ26.6mm | Grade 6.0 | Stage 8.5 |
The hardness, hardness range and pearlite block spacing of the hot rolled round steels obtained in examples 1 and 2 are shown in Table 4.
TABLE 4
The invention adopts low-carbon and low-silicon design (C: 0.17-0.20% and Si:nomore than 0.07%) suitable for cold forging process in component design, and controls the contents of Mn, S and Ca in steel and the relation of Mn, S and Ca to meet (Mn + Ca)/S no less than 25 so as to ensure the surface quality of continuous casting billets. In the production process, a converter, refining, vacuum degassing and small square billet (200mm x 200mm) continuous casting are adopted in the steelmaking process; the steel rolling process adopts high-temperature heating, water penetration after rolling and immediate pit-discharging and slow cooling treatment after water penetration. The isothermal annealing-free low-carbon gear steel is manufactured by a reasonable steel-making and steel-rolling controlled cooling process, and fills the domestic blank.
The process flow of the application is different from the production flow of the traditional isothermal annealing gear steel:
the process flow of the application is converter primary smelting → refining furnace refining → RH furnace vacuum degassing → continuous casting small square billet (200mm x 200mm) → heating furnace high-temperature heating → rough rolling → medium rolling → finish rolling → high-temperature round steel water penetrating → steel entering a slow cooling pit for slow cooling → inspection and warehousing. And the traditional process is converter primary smelting → refining furnace refining → RH furnace vacuum degassing → continuous casting small square billet (200mm x 200mm) → heating furnace high temperature heating → rough rolling → medium rolling → finish rolling → round steel air cooling → isothermal annealing in furnace → wagon → inspection and warehousing.
Although preferred embodiments of the present invention have been described in detail hereinabove, it should be clearly understood that modifications and variations of the present invention are possible to those skilled in the art. Any modification, equivalent replacement, or improvement made within the spirit and principle of the present invention should be included in the protection scope of the present invention.
Claims (9)
1. The isothermal annealing-free low-carbon gear steel is characterized by comprising the following components in parts by weight: the metallographic structure is ferrite and pearlite, the width of a ferrite strip is less than or equal to 20 mu m, the grain size of austenite is 7-9 grades, the hardness of the product is less than or equal to 170HBW, the hardness range of the whole section of the product is less than or equal to 10HBW, and the longitudinal banded structure of the product is less than or equal to 2.0 grades.
2. The steel according to claim 1, characterized in that: the chemical components by weight percentage are 0.17-0.20% of C, Si: less than or equal to 0.07 percent, Mn: 0.70-0.90%, Cr: 1.15-1.25%, P: less than or equal to 0.010%, S: 0.023-0.040%, Al: 0.025-0.040%, N: 0.008-0.0190% of Ca, 0.0020-0.0050% of Ca, (Mn + Ca)/S is not less than 25, and the balance of Fe and inevitable impurity elements.
3. A production method of isothermal annealing-free low-carbon gear steel is characterized by comprising the following steps: comprises the steps of (a) preparing a mixture of a plurality of raw materials,
step one, smelting molten steel: primary smelting, refining and vacuum degassing are involved;
step two, casting: casting the molten steel in the first step into a steel billet;
step three, heating before rolling: the heating temperature is 1180-1220 ℃;
step four, rolling: carrying out rough rolling, intermediate rolling and finish rolling in sequence to roll the billet into round steel, wherein the rough rolling compression ratio is 2.2-2.8, the intermediate rolling compression ratio is 2.1-2.7, the finish rolling compression ratio is 1.9-2.5, the requirements on the rough rolling compression ratio, the intermediate rolling compression ratio, the finish rolling compression ratio and the total compression ratio are 9-18;
step five, cooling: the temperature of the rolled round steel is not less than 920 ℃, firstly, a water penetrating process is adopted, and the round steel is quickly cooled to Ar after penetrating water 1 And immediately putting the round steel into a slow cooling pit for slow cooling at the temperature of 20-30 ℃, and taking the round steel out of the pit after the round steel is slowly cooled to room temperature.
4. The method of claim 3, wherein: step one, aluminum deoxidation is adopted in the refining process, silicon-free alloy blocks are added to adjust the components of molten steel, the silicon content of the molten steel in the refining process is strictly controlled, and silicon is prevented from being introduced.
5. The method as claimed in claim 3, wherein in the first step, the RH furnace is used for vacuum degassing, the calcium silicate wire is fed into the molten steel after vacuum degassing, and nitrogen is blown from the bottom into the molten steel after wire feeding, so that the nitrogen content in the molten steel is increased, and simultaneously the form of high-melting-point aluminum oxide inclusion is accelerated to change, a low-melting-point calcium-aluminum compound is formed, and the aim of removing the aluminum sesquioxide is fulfilled.
6. The method of claim 5, wherein: the diameter of the calcium silicate wire is phi 10mm, the calcium content is 60 wt%, and the silicon content is 40 wt%.
7. The method of claim 3, wherein: and step two, casting the molten steel into a square billet by adopting a continuous casting process, wherein the continuous casting crystallizer adopts a section of more than 200 mm.
8. The method of claim 7, wherein: step four, the specification of the hot-rolled round steel is phi 26.6 mm-phi 37.6 mm.
9. The method of claim 3, wherein: and step three, the heating time is 220min-240 min.
Priority Applications (1)
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