CN113789480A - Cold-forged gear steel and preparation method thereof - Google Patents
Cold-forged gear steel and preparation method thereof Download PDFInfo
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- CN113789480A CN113789480A CN202110964634.9A CN202110964634A CN113789480A CN 113789480 A CN113789480 A CN 113789480A CN 202110964634 A CN202110964634 A CN 202110964634A CN 113789480 A CN113789480 A CN 113789480A
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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
- C22C38/28—Ferrous alloys, e.g. steel alloys containing chromium with titanium or zirconium
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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
- C21C7/04—Removing impurities by adding a treating agent
- C21C7/06—Deoxidising, e.g. killing
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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
- C21D8/00—Modifying the physical properties by deformation combined with, or followed by, heat treatment
- C21D8/005—Modifying the physical properties by deformation combined with, or followed by, heat treatment of ferrous alloys
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- C—CHEMISTRY; METALLURGY
- C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
- C22C—ALLOYS
- C22C33/00—Making ferrous alloys
- C22C33/04—Making ferrous alloys by melting
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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
- C22C38/02—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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- 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
- C22C38/20—Ferrous alloys, e.g. steel alloys containing chromium with copper
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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
- C21D2211/00—Microstructure comprising significant phases
- C21D2211/005—Ferrite
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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
- C21D2211/00—Microstructure comprising significant phases
- C21D2211/009—Pearlite
Abstract
The invention belongs to the technical field of steel, and particularly relates to cold-forged gear steel and a preparation method thereof. The gear steel comprises the following chemical components in percentage by mass: c: 0.15% -0.25%, Si: 0.05-0.40%, Mn: 0.30% -1.40%, P: 0-0.03%, S: s: 0-0.035%, Cr: 0.80-1.50%, Ti: 0-0.05%, Al: 0-0.045%, Cu: 0-0.15%, N: 0-0.0150%, the balance being Fe and unavoidable impurities; the metallographic structure of the gear steel comprises austenite, and the grain size of the austenite is 6-7. The gear steel meets the performance of the gear, has lower hardness in a hot rolling state, and solves the problem of large cold deformation resistance of the conventional gear steel; by reducing the contents of Si and Mn elements, the cold deformation resistance of the gear steel blank is reduced, and the problem of local coarse grains is solved.
Description
Technical Field
The invention belongs to the technical field of steel, and particularly relates to cold-forged gear steel and a preparation method thereof.
Background
In recent years, with the rapid development of the machining industry, the cold forging technology is widely applied to the industrial fields of automobiles, machine tools, instruments and the like as a low-material/non-cutting machining process with low material consumption, high efficiency and excellent performance. The great technical superiority and good economic benefit exhibited by the cold forging technology become the development direction of precision production of medium and small forged pieces such as gears and the like gradually.
The conventional preparation process of the gear comprises the following steps: gear steel raw material → blanking → hot forging → heat treatment after forging → gear processing (hobbing, gear shaping, gear milling, gear planing) → carburizing → quenching, tempering → surface cleaning → inspection → warehousing. At present, the gear product is quite mature in production process and widely applied to the gear manufacturing industry, but the forging flow line of a blank is cut off by the tooth profile processing after hot forging in the process, so that the mechanical property of the gear is reduced. In addition, the process has long cutting working time, low utilization rate of the gear blank and high production cost, and greatly influences the development of the gear industry.
The cold forging technology is introduced into the gear processing industry, so that the problems can be fully solved and solved, and the gear processing method has the following specific advantages: the cold precision forging gear has the advantages that the strength, the wear resistance of the tooth surface, the heat treatment performance and the meshing noise of the gear are superior to those of a gear machined by cutting because metal streamline is distributed along the tooth profile and the structure is compact. Compared with the gear machined by cutting, the strength of the cold precision forging gear can be improved by 20 percent, the bending fatigue life can be improved by 20 percent, the heat treatment deformation is reduced by 30 percent, and the production cost is reduced by more than 20 percent. Rapid production of high quality gears by cold precision forging has become a global trend.
However, although the cold precision forging technology is good, it puts higher demands on the gear steel raw material, and in order to reduce the abrasion of the blank to the die, the blank is required to have higher cold plasticity and smaller deformation resistance so as to improve the service life of the die. The traditional solution is to reduce the hardness of the raw material by spheroidizing annealing, thus seriously reducing the production efficiency and greatly increasing the production cost. Therefore, the conventional gear steel raw material is difficult to meet the requirements of the cold precision forging technology, and a novel gear steel is urgently needed, has lower hardness and good cold plasticity on the basis of meeting the gear performance, and is suitable for the cold forging technology.
Disclosure of Invention
In view of the above problems, the present invention provides a cold-forged gear steel and a method for manufacturing the same to overcome or at least partially solve the above problems.
The embodiment of the invention provides cold forging gear steel, which comprises the following chemical components in percentage by mass: c: 0.15% -0.25%, Si: 0.05-0.40%, Mn: 0.30% -1.40%, P: 0-0.03%, S: 0-0.035%, Cr: 0.80-1.50%, Ti: 0-0.05%, Al: 0-0.045%, Cu: 0-0.15%, N: 0-0.0150%, the balance being Fe and unavoidable impurities; the metallographic structure of the gear steel comprises austenite, and the grain size of the austenite is 6-7.
Optionally, the properties of the gear steel are as follows: the tensile strength is more than or equal to 1080MPa, the impact toughness is more than or equal to 60J, and the hardness of a hardenability J9 point is 30-40 HRC.
Optionally, the metallographic structure further comprises ferrite and pearlite, and the ferrite ratio is greater than 50%.
A method of producing a cold-forged gear steel, the method comprising:
pouring and continuously casting the smelted molten steel in sequence to obtain a casting blank;
heating the casting blank, and then descaling to obtain a descaled casting blank;
sequentially rolling and cooling the descaled casting blank to obtain the gear steel;
the rolling comprises rough rolling and finish rolling, wherein the initial rolling temperature of the rough rolling is 1050-1100 ℃, the finish rolling temperature is 850-950 ℃, and the total deformation of a finish rolling unit is 40-60%.
Optionally, the casting temperature is 1500-1580 ℃; the heating temperature is 1150-1200 ℃, and the heating time is 2.5-3.5 h.
Optionally, the method for pouring and continuously casting the smelted molten steel to obtain a casting blank further comprises the following steps: smelting the molten steel containing the chemical components, and performing vacuum degassing in the smelting process to obtain smelted molten steel; the vacuum degassing time is 4-7 min.
Optionally, the smelting comprises external vacuum refining, and the external vacuum refining specifically comprises: and maintaining the pressure for 10-12 min in a vacuum pressure environment with the pressure less than 67 Pa.
Optionally, the external vacuum refining comprises deoxidizing and adjusting aluminum content of the molten steel, so that the molten steel refined to a station contains 0.045-0.070% of aluminum by mass fraction, and the deoxidizer for deoxidation is aluminum alloy.
Optionally, the cooling comprises in sequence entering a cooling bed and covering a heat preservation cover, exiting the cooling bed, entering a slow cooling pit and exiting the slow cooling pit.
Optionally, the temperature of the entering slow cooling pit is 550-650 ℃, and the temperature of the exiting slow cooling pit is less than or equal to 300 ℃; the structure of the gear steel out of the slow cooling pit is ferrite and pearlite.
One or more technical solutions in the embodiments of the present invention have at least the following technical effects or advantages:
the cold forging gear steel provided by the invention comprises the following chemical components in percentage by mass: c: 0.15% -0.25%, Si: 0.05-0.40%, Mn: 0.30% -1.40%, P: 0-0.03%, S: 0-0.035%, Cr: 0.80-1.50%, Ti: 0-0.05%, Al: 0-0.045%, Cu: 0-0.15%, N: 0-0.0150%, the balance being Fe and unavoidable impurities; the metallographic structure of the gear steel comprises austenite, the grain size of the austenite is 6-7 grades, the gear steel has lower hardness in a hot rolling state on the basis of meeting the performance of a gear, and can be directly used for cold forging, so that the problem of large cold deformation resistance of the conventional gear steel 20CrMnTi is solved; the cold deformation resistance of the gear steel blank is reduced by reducing the contents of Si and Mn elements; by a low-temperature large-deformation finish rolling mode, the number of deformation zones inside austenite grains is greatly increased, a large number of nucleation positions are provided for ferrite phase transformation, and the ferrite phase transformation is promoted; the delivery state hardness of the cold forging gear steel can reach below 220HBW, is equivalent to the hardness of the spheroidizing annealing state conventional gear steel 20CrMnTi, has lower cold deformation resistance, and can be used for cold forging; by adopting a proper heat treatment process, the tensile strength is more than or equal to 1080MPa, the impact toughness is more than or equal to 60J, the hardness of a hardenability J9 point reaches 30-40 HRC, the grain size of carburized austenite at the temperature of not more than 980 ℃ is not less than 6 grade and is less than 7.0 grade, and the occurrence of local coarse grains is avoided.
The foregoing description is only an overview of the technical solutions of the present invention, and the embodiments of the present invention are described below in order to make the technical means of the present invention more clearly understood and to make the above and other objects, features, and advantages of the present invention more clearly understandable.
Drawings
In order to more clearly illustrate the technical solutions in the embodiments of the present invention, the drawings needed to be used in the description of the embodiments are briefly introduced below, and it is obvious that the drawings in the following description are some embodiments of the present invention, and it is obvious for those skilled in the art to obtain other drawings based on the drawings without creative efforts.
FIG. 1 is a graph comparing hardenability curves of steel of examples of the present invention and comparative example 1;
FIG. 2 is a graph comparing the cold stress-strain curves of example of the present invention and comparative steel 1;
FIG. 3 shows the prior austenite grain morphology of the gear steel of example 1 after carburization at 980 ℃ for 1 h;
FIG. 4 shows the prior austenite grain morphology of comparative example 1 steel of the present invention after carburization at 980 ℃ for 1 h;
FIG. 5 shows the prior austenite grain morphology of comparative example 2 steel of the present invention after carburization at 980 ℃ for 1 h;
FIG. 6 shows the prior austenite grain morphology of the gear steel of example 1 after carburization at 980 ℃ for 6 hours;
FIG. 7 shows the prior austenite grain morphology of comparative example 1 steel of the present invention after carburization at 980 ℃ for 6 h;
FIG. 8 shows the prior austenite grain morphology of comparative example 2 steel of the present invention after carburization at 980 ℃ for 6 h.
Detailed Description
The present invention will be described in detail below with reference to specific embodiments and examples, and the advantages and various effects of the present invention will be more clearly apparent therefrom. It will be understood by those skilled in the art that these specific embodiments and examples are for the purpose of illustrating the invention and are not to be construed as limiting the invention.
Throughout the specification, unless otherwise specifically noted, terms used herein should be understood as having meanings as commonly used in the art. Accordingly, unless defined otherwise, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this invention belongs. If there is a conflict, the present specification will control.
Unless otherwise specifically stated, various raw materials, reagents, instruments, equipment and the like used in the present invention are commercially available or can be prepared by existing methods.
In order to solve the technical problems, the general idea of the embodiment of the application is as follows:
according to an exemplary embodiment of the present invention, a cold-forged gear steel comprises the following chemical components by mass fraction: c: 0.15% -0.25%, Si: 0.05-0.40%, Mn: 0.30% -1.40%, P: 0-0.03%, S: 0-0.035%, Cr: 0.80-1.50%, Ti: 0-0.05%, Al: 0-0.045%, Cu: 0-0.15%, N: 0-0.0150%, the balance being Fe and unavoidable impurities; the metallographic structure of the gear steel comprises austenite, and the grain size of the austenite is 6-7.
The cold deformation resistance of the gear steel blank is reduced by reducing the contents of Si and Mn elements; the method has the advantages that the number of deformation zones in austenite grains is greatly increased by a low-temperature large-deformation finish rolling mode, a large number of nucleation positions are provided for ferrite phase transformation, ferrite phase transformation is promoted, the retention time of a ferrite phase region is increased by a slow cooling mode after rolling, the proportion of ferrite in a rolled material tissue can be increased, and the cold deformation resistance is reduced.
In austenite, the grain size after carburization at the temperature of not more than 980 ℃ is 6-7 grades, so that the occurrence of local coarse grains is avoided.
As an alternative embodiment, the metallographic structure further comprises ferrite and pearlite, and the ferrite ratio is > 50%.
The number of deformation zones in the austenite grains is greatly increased, a large number of nucleation positions are provided for ferrite phase transformation, and the ferrite phase transformation is promoted.
As an alternative embodiment, the properties of the gear steel are as follows: the tensile strength is more than or equal to 1080MPa, the impact toughness is more than or equal to 60J, and the hardness of a hardenability J9 point is 30-40 HRC.
The hardness of the gear steel can reach below 220HBW, is determined by the metallographic structure of the gear steel, is equivalent to the hardness of the spheroidized annealed conventional gear steel 20CrMnTi, has low cold deformation resistance, and can be used for cold forging.
As an optional implementation mode, the finished specification range of the cold-forging gear steel is phi 8 mm-phi 250 mm.
A method of producing a cold-forged gear steel, the method comprising:
pouring and continuously casting the smelted molten steel in sequence to obtain a casting blank;
heating the casting blank, and then descaling to obtain a descaled casting blank;
sequentially rolling and cooling the descaled casting blank to obtain the gear steel;
the rolling comprises rough rolling and finish rolling, wherein the initial rolling temperature of the rough rolling is 1050-1100 ℃, the finish rolling temperature is 850-950 ℃, and the total deformation of a finish rolling unit is 40-60%.
The method has the advantages that the number of deformation zones in austenite grains is greatly increased by a low-temperature large-deformation finish rolling mode, a large number of nucleation positions are provided for ferrite phase transformation, ferrite phase transformation is promoted, the retention time of a ferrite phase region is increased by a slow cooling mode after rolling, the proportion of ferrite in a rolled material tissue can be increased, and the cold deformation resistance is reduced.
After the refining is finished, the steel billet can be directly obtained by continuous casting, and the molten steel can be subjected to vacuum degassing (by selecting one or more of VD, RH or VOD).
As an optional embodiment, the casting temperature is 1500-1580 ℃; the heating temperature is 1150-1200 ℃, and the heating time is 2.5-3.5 h.
As an optional embodiment, the pouring and continuous casting of the smelted molten steel to obtain a casting blank further comprises: smelting the molten steel containing the chemical components, and performing vacuum degassing in the smelting process to obtain smelted molten steel; the vacuum degassing time is 4-7 min.
As an optional embodiment, the smelting comprises an external vacuum refining, and the external vacuum refining specifically comprises: and maintaining the pressure for 10-12 min in a vacuum pressure environment with the pressure less than 67 Pa.
As an optional embodiment, the out-of-furnace vacuum refining comprises deoxidizing and adjusting aluminum of the molten steel, so that the molten steel refined to a station has an aluminum content of 0.0450-0.070% in mass fraction, and the deoxidizer for deoxidizing is an aluminum alloy.
On the basis of ensuring the low oxygen content in the steel, the cold deformation capability is improved.
As an alternative embodiment, the molten steel is smelted by an electric furnace or a converter, and the aluminum content of the primary component J1 refined to the station is controlled to be 0.0450-0.070%.
Controlling the carbon content (mass fraction) at the tapping end point to be 0.08-0.12%; then the steel is fed into an LF furnace for secondary refining, an aluminum wire is fed for 4-5 m/t after the steel is placed in a ladle, the target aluminum content of a refining arrival primary component J1 is controlled to reach 0.050% -0.070%, the amount of lime and fluorite is added according to the slag condition and the sulfur content condition during steel tapping, good slag fluidity is ensured, and in order to obtain good cold forging performance,
the aluminum wire can be effectively added into molten steel, high and stable aluminum yield is obtained, and the cold deformation capacity is improved by fixing nitrogen by adopting aluminum on the basis of ensuring low oxygen content in the steel by controlling the aluminum content in the steelmaking process; the quality of the molten steel is improved, the deoxidation alloying cost can be greatly reduced, and the economic benefit is obvious. The reason for controlling the aluminum content is: on the basis of ensuring the low oxygen content in steel, aluminum is adopted to fix nitrogen, and the cold deformation capability is improved.
As an optional embodiment, the cooling speed on the cooling bed is 0-2 ℃/s. Preferably, the cooling speed range is 0-0.5 ℃/s.
As an optional implementation mode, the cooling sequentially comprises an inlet cooling bed, a cover heat preservation cover, an outlet cooling bed, an inlet slow cooling pit and an outlet slow cooling pit.
As an optional embodiment, the temperature of the entering slow cooling pit is 550-650 ℃, and the temperature of the exiting slow cooling pit is less than or equal to 300 ℃; the structure of the gear steel out of the slow cooling pit is ferrite and pearlite.
The reason for entering the cooling bed and covering the heat-insulating cover is to reduce the air convection near the cooling bed to slow down the cooling speed of the rolled stock as much as possible; the slow cooling mode after rolling is adopted, the retention time of a ferrite phase region is increased, the proportion of ferrite in a rolled material structure can be improved, and the cold deformation resistance is reduced.
The temperature of the water entering the slow cooling pit is 550-650 ℃, the temperature of the water leaving the slow cooling pit is less than or equal to 300 ℃, and the structure of the water leaving the slow cooling pit is ferrite and pearlite. The temperature of the entering slow cooling pit and the temperature of the exiting slow cooling pit are controlled to avoid the appearance of abnormal structures
As an optional embodiment, the casting blank is a rectangular blank with the size range of (120-350) mmX (120-350) mm or a round blank with the diameter of phi 100 mm-phi 350 mm.
A cold-forged gear steel and a method for manufacturing the same according to the present application will be described in detail with reference to examples, comparative examples, and experimental data.
Example 1
In the embodiment, the gear steel comprises the following components in percentage by mass: 0.17% of C, 0.08% of Si, 0.60% of Mn, 0.010% of P, 0.025% of S, 1.30% of Cr, 0.04% of Ti, 0.033% of Al, 0.13% of Cu, 0.0065% of N, and the balance of Fe and inevitable impurities. The metallographic structure of the gear steel comprises austenite, and the grain size of the austenite is 6-7.
The specific control parameters of the novel cold-forging gear steel with the production specification of phi 80mm are as follows:
(1) smelting by adopting an electric furnace, and controlling the carbon content (mass fraction) at the tapping end point to be 0.10%; then the steel is put into an LF furnace for external refining, an aluminum wire is fed for 4.5m/t after the steel is placed in a ladle, the J1 target aluminum content is controlled to reach 0.060 percent, and the amount of lime and fluorite is supplemented according to the slag condition and the sulfur content condition during tapping, so that the good slag fluidity is ensured; and then carrying out VD vacuum degassing on the molten steel, wherein the pump feeding time is 5min, and the vacuum pressure maintaining time is less than 67Pa and reaches 12 min.
(2) And carrying out protective pouring on the molten steel in the whole process, wherein the pouring temperature is 1550 ℃, the superheat degree is 25 ℃, and a two-stage electromagnetic stirring and reasonable cooling system is adopted to solidify to obtain a casting blank.
(3) Putting the casting blank into a heating furnace at the normal temperature, wherein the heating temperature is 1180 ℃, and the heating time is 3 hours; taking the mixture out of the heating furnace for high-pressure water descaling; after descaling, the steel plate is hot rolled by a continuous rolling unit, the initial rolling temperature is 1080 ℃, the finish rolling temperature is 900 ℃, and the total deformation of the finish rolling unit is controlled at 40%; after finish rolling, cooling at a cooling rate of 0.3 ℃/s; and (3) after finish rolling, covering a heat preservation cover on a cooling bed, discharging the cooling bed into a slow cooling pit, wherein the temperature of the discharged cooling bed into the slow cooling pit is 520 ℃, and the temperature of the discharged slow cooling pit is 260 ℃.
Example 2
In the embodiment, the gear steel comprises the following components in percentage by mass: c: 0.15%, Si: 0.05%, Mn: 0.30%, Cr: 0.80%, Ti: 0 to 0.05% and the balance Fe and unavoidable impurities. The metallographic structure of the gear steel comprises austenite, and the grain size of the austenite is 6-7.
The cold forging gear steel and the preparation method thereof sequentially comprise continuous casting and rolling, and the specific technological parameters are as follows:
pouring the molten steel at 1500 ℃ to obtain a casting blank;
heating the casting blank at 1150 ℃ for 2.5h, and then descaling;
the open rolling temperature in the rolling is 1050 ℃, and the finish rolling temperature in the rolling is 850 ℃.
Example 3
In the embodiment, the gear steel comprises the following components in percentage by mass: c: 0.25%, Si: 0.40%, Mn: 1.40%, P: 0.03%, S: 0.01%, Cr: 1.50%, Ti: 0.05%, Al: 0.045%, Cu: 0.15%, N: 0.0150 percent, and the balance of Fe and inevitable impurities. The metallographic structure of the gear steel comprises austenite, and the grain size of the austenite is 6-7.
The cold forging gear steel and the preparation method thereof sequentially comprise continuous casting and rolling, and the specific technological parameters are as follows:
pouring the molten steel at 1580 ℃ to obtain a casting blank;
heating the casting blank at 1200 ℃ for 3.5h, and then descaling;
the open rolling temperature in the rolling is 1080 ℃, and the finish rolling temperature in the rolling is 900 ℃.
Example 4
In the embodiment, the gear steel comprises the following components in percentage by mass: c: 0.21%, Si: 0.35%, Mn: 0.36%, P: 0.01%, S: 0.008%, Cr: 1.10%, Ti: 0.03%, Al: 0-0.045%, Cu: 0-0.15%, N: 0 to 0.0150%. The metallographic structure of the gear steel comprises austenite, and the grain size of the austenite is 6-7.
Comparative example 1
The conventional hot-rolled gear steel 20CrMnTi is used as a comparative example, and comprises the following components in percentage by mass: 0.20% of C, 0.29% of Si, 0.96% of Mn, 0.015% of P, 0.013% of S, 1.21% of Cr, 0.07% of Ti, 0.0075% of N, and the balance of Fe and inevitable impurities.
Comparative example 2
The conventional annealed gear steel 20CrMnTi is used as a comparative example, and comprises the following components in percentage by mass: 0.20% of C, 0.25% of Si, 0.70% of Mn, 0.015% of P, 0.013% of S, 0.91% of Cr, 0.0065% of N, and the balance of Fe and inevitable impurities. Spheroidizing annealing process: maintaining at 780 ℃ for 1.5h, cooling to 680 ℃ along with the furnace, maintaining for 3h, cooling to 500 ℃ along with the furnace, and discharging and slowly cooling.
Related experiments:
the steels obtained in example 1 and comparative examples 1 to 2 were subjected to performance tests, and the test results are as follows.
The steel blanks of the gear steels of the examples and the comparative examples are subjected to hardness, hardenability, cold deformation resistance, grain size after carburization and mechanical property comparison after heat treatment, and the results are as follows:
(1) hardness: example 1: 148 HBW: comparative example 1: 184 HBW: comparative example 2: 143 HBW. The hardness of the examples and the comparative examples meets the requirement of the gear steel blank; the comparative example hardness is superior to the examples, while the low hardness of the examples can be used directly for cold forging.
(2) Hardenability: the hardenability test was carried out in accordance with GB/T5216-. The hardenability of the examples is good and better than that of the comparative examples.
(3) Cold deformation resistance: a cold upset test was conducted according to YB/T5293-2014 "metallic Material upset test method", the steel blanks of the gears of the examples and comparative examples were compressed to a position of 1/3, and the cold deformation resistance of the test specimens was observed to obtain a stress-strain curve, and the results are shown in FIG. 2.
(4) Grain size after carburization: carburizing is carried out according to GB/T28694-.
(5) Mechanical properties of heat treatment: after carburization, oil cooling quenching at 850 ℃ and tempering at 190 ℃ for 2h, wherein the tensile strength of example 1 reaches 1096MPa, and the impact energy reaches 63J; comparative example 1 tensile strength reached 1086MPa, impact energy reached 66J; comparative example 2 has tensile strength of 1090MPa and impact power of 65J. The tensile strength and the impact energy of the examples and the comparative examples meet the requirements of the gear steel blank, and the heat treatment mechanical property of the comparative example is superior to that of the examples.
Therefore, the hardness and cold deformation resistance of the gear steel are obviously lower than those of the conventional gear steel 20CrMnTi in a hot rolling state, and the gear steel is close to the annealing state and can be used for cold forging; meanwhile, the hardenability of the steel meets the national standard and is superior to the conventional 20 CrMnTi; in the embodiment of the invention, after heat preservation for 1h and 6h, the fine austenite grain size can be kept, the grain size level is less than 7.0 level, and the phenomenon of coarse local grains is not generated; the mechanical property after heat treatment is similar to that of the conventional 20CrMnTi gear steel.
Detailed description of the drawings 1-8:
as shown in FIG. 1, the hardness at the hardenability J9 point of example 1 was 34HRC, and the hardness at the hardenability J9 point of comparative example 1 was 31 HRC. The hardenability of example 1 is good and better than that of comparative example 1, the hardenability of comparative example 1 is low, and local coarse grains are likely to appear after carburizing and quenching after cold forging.
As shown in fig. 2, when the strain is 0.55 or more, the real stress of the comparative example is respectively greater than that of the example, and the real stress is too large, which easily causes deformation in the subsequent processing of the steel.
3-8, are prior austenite grain morphologies after carburization at 980 ℃ for 1H and 6H for the examples and comparative examples; according to the embodiment of the invention, after the heat preservation carburization is carried out for 1h and 6h, the fine austenite grain size can be kept, the grain size level is not less than 6 and is less than 7.0, the local mixed crystal phenomenon is not generated, and the local coarse crystal problem is solved; and the local mixed crystal phenomenon and the local coarse crystal problem occur after the comparative examples 1 and 2 are subjected to heat preservation and carburization for 1h and 6 h.
Finally, it should also be noted that the terms "comprises," "comprising," or any other variation thereof, are intended to cover a non-exclusive inclusion, such that a process, method, article, or apparatus that comprises a list of elements does not include only those elements but may include other elements not expressly listed or inherent to such process, method, article, or apparatus.
While preferred embodiments of the present invention have been described, additional variations and modifications in those embodiments may occur to those skilled in the art once they learn of the basic inventive concepts. Therefore, it is intended that the appended claims be interpreted as including preferred embodiments and all such alterations and modifications as fall within the scope of the invention.
It will be apparent to those skilled in the art that various changes and modifications may be made in the present invention without departing from the spirit and scope of the invention. Thus, if such modifications and variations of the present invention fall within the scope of the claims of the present invention and their equivalents, the present invention is also intended to include such modifications and variations.
Claims (10)
1. The cold-forging gear steel is characterized by comprising the following chemical components in percentage by mass: c: 0.15% -0.25%, Si: 0.05-0.40%, Mn: 0.30% -1.40%, P: 0-0.03%, S: 0-0.035%, Cr: 0.80-1.50%, Ti: 0-0.05%, Al: 0-0.045%, Cu: 0-0.15%, N: 0-0.0150%, the balance being Fe and unavoidable impurities; the metallographic structure of the gear steel comprises austenite, and the grain size of the austenite is 6-7.
2. The cold-forged gear steel according to claim 1, wherein said gear steel has the following properties: the tensile strength is more than or equal to 1080MPa, the impact toughness is more than or equal to 60J, and the hardness of a hardenability J9 point is 30-40 HRC.
3. The cold-forged gear steel as claimed in claim 1, wherein said metallographic structure further comprises ferrite and pearlite, and said ferrite ratio is > 50%.
4. A method for producing a cold-forged gear steel according to any one of claims 1 to 3, comprising:
pouring and continuously casting the smelted molten steel in sequence to obtain a casting blank;
heating the casting blank, and then descaling to obtain a descaled casting blank;
sequentially rolling and cooling the descaled casting blank to obtain the gear steel;
the rolling comprises rough rolling and finish rolling, wherein the initial rolling temperature of the rough rolling is 1050-1100 ℃, the finish rolling temperature is 850-950 ℃, and the total deformation of a finish rolling unit is 40-60%.
5. The preparation method according to claim 4, wherein the casting temperature is 1500-1580 ℃; the heating temperature is 1150-1200 ℃, and the heating time is 2.5-3.5 h.
6. The preparation method according to claim 4, wherein the step of pouring and continuously casting the smelted molten steel to obtain a casting blank further comprises the following steps: smelting the molten steel containing the chemical components, and performing vacuum degassing in the smelting process to obtain smelted molten steel; the vacuum degassing time is 4-7 min.
7. The method according to claim 4, wherein the smelting comprises an external vacuum refining, the external vacuum refining comprising: and maintaining the pressure for 10-12 min in a vacuum pressure environment with the pressure less than 67 Pa.
8. The method for preparing the alloy steel of claim 7, wherein the vacuum refining outside the furnace comprises deoxidizing and adjusting aluminum content of the molten steel, so that the molten steel refined to a station has the aluminum content of 0.0450-0.070% in mass fraction, and the deoxidizer for deoxidizing is aluminum alloy.
9. The method of claim 4, wherein the cooling comprises, in order, entering a cooling bed and covering a heat-insulating cover, exiting the cooling bed, entering a buffer cooling pit and exiting the buffer cooling pit.
10. The preparation method of claim 4, wherein the temperature of the entering slow cooling pit is 550-650 ℃, and the temperature of the exiting slow cooling pit is less than or equal to 300 ℃; the structure of the gear steel out of the slow cooling pit is ferrite and pearlite.
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| CN115449703A (en) * | 2022-07-29 | 2022-12-09 | 江阴兴澄特种钢铁有限公司 | Isothermal annealing gear steel bar suitable for cold forging processing and manufacturing method thereof |
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| CN115449703A (en) * | 2022-07-29 | 2022-12-09 | 江阴兴澄特种钢铁有限公司 | Isothermal annealing gear steel bar suitable for cold forging processing and manufacturing method thereof |
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