CN111411208A - Heat treatment method for reducing hypereutectoid steel rail reticular cementite precipitation - Google Patents
Heat treatment method for reducing hypereutectoid steel rail reticular cementite precipitation Download PDFInfo
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- CN111411208A CN111411208A CN202010466343.2A CN202010466343A CN111411208A CN 111411208 A CN111411208 A CN 111411208A CN 202010466343 A CN202010466343 A CN 202010466343A CN 111411208 A CN111411208 A CN 111411208A
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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
- C21D1/78—Combined heat-treatments not provided for above
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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
- C21D9/00—Heat treatment, e.g. annealing, hardening, quenching or tempering, adapted for particular articles; Furnaces therefor
- C21D9/04—Heat treatment, e.g. annealing, hardening, quenching or tempering, adapted for particular articles; Furnaces therefor for rails
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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
- C22C38/18—Ferrous alloys, e.g. steel alloys containing chromium
- C22C38/40—Ferrous alloys, e.g. steel alloys containing chromium with nickel
- C22C38/48—Ferrous alloys, e.g. steel alloys containing chromium with nickel with niobium or tantalum
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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
- C21D2211/003—Cementite
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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 relates to the technical field of steel rail heat treatment, in particular to a heat treatment method for reducing precipitation of hypereutectoid steel rail network cementite. The heat treatment method provided by the invention comprises the following steps: heating the rolled or heat-treated hypereutectoid steel rail to over 900 ℃, and preserving heat to obtain an austenitized steel rail; cooling the austenitized steel rail to an isothermal temperature at a first cooling speed for 30-50 s; then cooling to the final cooling temperature below 400 ℃ at a second cooling speed; naturally cooling to room temperature; the isothermal temperature is 600-630 ℃; the first cooling speed and the second cooling speed are 8-10 ℃/s independently. The embodiment results show that the heat treatment method provided by the invention can effectively reduce the precipitation of the net cementite of the hypereutectoid steel rail and improve the mechanical property of the hypereutectoid steel rail.
Description
Technical Field
The invention relates to the technical field of steel rail heat treatment, in particular to a heat treatment method for reducing precipitation of hypereutectoid steel rail network cementite.
Background
The steel rail is used as an important component of railway traffic, and the use performance of the steel rail is particularly important for guaranteeing the driving safety and the railway operation efficiency. With the economic development, the transportation capacity of heavy haul railways is continuously improved, the contact conditions between wheel rails are worse, the side grinding, stripping, block falling and other damages of the steel rails are increasingly serious, and the traditional pearlite steel rail cannot meet the current use requirements. The hypereutectoid steel rail is firstly developed by Japanese researchers, has higher carbon content and cementite density, the higher carbon content can ensure that the hypereutectoid steel rail obtains higher strength and hardness after heat treatment, and the improvement of the cementite density can improve the rolling contact fatigue resistance and the wear resistance of the hypereutectoid steel rail, and can be used on heavy-duty lines with large carrying capacity and small-radius lines. However, as the content of carbon increases, the network cementite at the grain boundary is precipitated, and microcracks are easily formed at the cementite and continuously expand along the continuous network, which adversely affects the mechanical properties of the steel rail.
Disclosure of Invention
The invention aims to provide a heat treatment method for reducing the precipitation of hypereutectoid steel rail network cementite.
In order to achieve the above object, the present invention provides the following technical solutions:
the invention provides a heat treatment method for reducing hypereutectoid steel rail reticular cementite precipitation, which comprises the following steps:
heating the rolled or heat-treated hypereutectoid steel rail to over 900 ℃, and preserving heat to obtain an austenitized steel rail;
cooling the austenitized steel rail to an isothermal temperature at a first cooling speed for 30-50 s; then cooling to the final cooling temperature below 400 ℃ at a second cooling speed; naturally cooling to room temperature; the isothermal temperature is 600-630 ℃; the first cooling speed and the second cooling speed are 8-10 ℃/s independently.
Preferably, the first cooling rate and the second cooling rate are the same.
Preferably, the carbon content of the rolled or heat-treated hypereutectoid steel rail is 0.94-1.00 wt.%.
Preferably, the chemical composition of the rolled or heat-treated hypereutectoid steel rail comprises the following components in percentage by mass: 0.94-1.00% of C, 0.45-0.80% of Si, 0.75-1.25% of Mn, less than or equal to 0.015% of P, less than or equal to 0.010% of S, 0.625% of Cr + Nb + Nis and the balance of iron.
The invention provides a heat treatment method for reducing hypereutectoid steel rail reticular cementite precipitation, which comprises the following steps: heating the rolled or heat-treated hypereutectoid steel rail to over 900 ℃, and preserving heat to obtain an austenitized steel rail; cooling the austenitized steel rail to an isothermal temperature at a first cooling speed for 30-50 s; then cooling to the final cooling temperature below 400 ℃ at a second cooling speed; naturally cooling to room temperature; the isothermal temperature is 600-630 ℃; the first cooling speed and the second cooling speed are 8-10 ℃/s independently. The method comprises the steps of heating a hypereutectoid steel rail in a rolling state or a heat treatment state to over 900 ℃, so that carbides which are unevenly distributed and have uneven granularity in raw materials are completely dissolved in a solid manner, and are fully austenitized; the pearlite interlayer is cooled to 600-630 ℃ at the speed of 8-10 ℃/s, and the temperature is kept constant for 30-60 s at the temperature, so that the interlayer spacing of the pearlite can be effectively refined, and the occurrence of network cementite is avoided; then cooling the steel plate to a final cooling temperature of 400 ℃ or below at a speed of 8-10 ℃/s. The embodiment result shows that the heat treatment method provided by the invention can effectively reduce the precipitation of the net-shaped cementite of the hypereutectoid steel rail and improve the mechanical property of the hypereutectoid steel rail, and the heat treatment method has the hardness of 396-415 HB, the tensile strength of 1312-1437 MPa, the yield strength of 800-911 MPa, the elongation of 12.24-16.80% and the reduction of area of 20.79-25.70%.
In addition, the heat treatment method provided by the invention is simple and easy to operate, and is suitable for industrial application.
Drawings
FIG. 1 is a schematic view of a heat treatment method according to an embodiment of the present invention;
FIG. 2-a is a metallographic structure diagram of a sample prepared in comparative example 1;
FIG. 2-b is a metallographic structure diagram of a sample prepared in comparative example 2;
FIG. 2-c is a metallographic structure diagram of a sample prepared in comparative example 3;
FIG. 2-d is a metallographic structure of a sample prepared in comparative example 4;
FIG. 2-e is a metallographic structure of a sample prepared in example 1;
FIG. 2-f is a metallographic structure chart of a sample prepared in example 2;
FIG. 2-g is a metallographic structure chart of a sample prepared in example 3;
FIG. 3-a is a microscopic SEM topography of tensile fractures of comparative example 1;
FIG. 3-b is a microscopic SEM topography of tensile fractures of comparative example 2;
FIG. 3-c is a microscopic SEM topography of tensile fractures of comparative example 3;
FIG. 3-d is a microscopic SEM topography of tensile fractures of comparative example 4;
FIG. 3-e is a microscopic SEM topography of tensile fractures of example 1;
FIG. 3-f is a microscopic SEM topography of tensile fractures of example 2;
FIG. 3-g is a microscopic SEM topography of tensile fractures of example 3.
Detailed Description
The invention provides a heat treatment method for reducing hypereutectoid steel rail reticular cementite precipitation, which comprises the following steps:
heating the rolled or heat-treated hypereutectoid steel rail to over 900 ℃, and preserving heat to obtain an austenitized steel rail;
cooling the austenitized steel rail to an isothermal temperature at a first cooling speed for 30-50 s; then cooling to the final cooling temperature below 400 ℃ at a second cooling speed; naturally cooling to room temperature; the isothermal temperature is 600-630 ℃; the first cooling speed and the second cooling speed are 8-10 ℃/s independently.
The invention heats the hypereutectoid steel rail in a rolling state or a heat treatment state to over 900 ℃, and preferably to 900 ℃. And preserving the heat to obtain the austenitized steel rail. In the present invention, the carbon content of the as-rolled or as-heat treated hypereutectoid steel rail is preferably 0.94 to 1.00 wt.%, more preferably 0.95 to 0.96 wt.%. The specific composition of the rolled or heat treated hypereutectoid steel rail is not particularly limited in the present invention, and hypereutectoid steel rails known in the art can be used. In a specific embodiment of the invention, the chemical composition of the hypereutectoid steel rail in a rolled state or a heat treatment state comprises the following components in percentage by weight: 0.94-1.00% of C, 0.45-0.80% of Si, 0.75-1.25% of Mn, less than or equal to 0.015% of P, less than or equal to 0.010% of S, 0.625% of Cr + Nb + Ni and the balance of iron. In the invention, the initial temperature of the rolled or heat-treated hypereutectoid steel rail is preferably room temperature, and the heating rate of raising the temperature from the room temperature of the rolled or heat-treated hypereutectoid steel rail to 900 ℃ is preferably 10 ℃/s. The invention can fully austenitize the hypereutectoid steel rail in a rolled state or a heat treatment state by preserving heat at the temperature of more than 900 ℃. In a specific embodiment of the invention, the incubation time at 900 ℃ or above is preferably 900 s.
After the austenitized steel rail is obtained, the austenitized steel rail is cooled to an isothermal temperature at a first cooling speed for 30-50 s; then cooling to the final cooling temperature below 400 ℃ at a second cooling speed; and naturally cooling to room temperature.
In the invention, the first cooling speed is 8-10 ℃/s, and preferably 8-9 ℃/s. In the invention, the isothermal temperature is 600-630 ℃, preferably 600-610 ℃; the isothermal time is 30-50 s, preferably 30-40 s. The method is firstly cooled to 600-630 ℃ at the speed of 8-10 ℃/s, and the isothermal temperature is kept for 30-50 s at the temperature, so that the pearlite lamellar spacing can be refined, and the occurrence of reticular cementite is avoided.
In the invention, the second cooling speed is 8-10 ℃/s, and preferably 8-9 ℃/s. The method is used for cooling the pearlite to the final cooling temperature of below 400 ℃ at the speed of 8-10 ℃/s, and the cooling below the final cooling temperature has the function of avoiding the growth of the pearlite.
In the present invention, the first cooling rate and the second cooling rate are preferably the same, and have the effect of preventing the precipitation of the network cementite and refining the lamellar spacing of the pearlite, thereby improving the mechanical properties of the hypereutectoid steel. In the present invention, the cooling process is preferably performed in a quenching cooling device, and the cooling medium used is preferably a water mist mixed gas.
In an embodiment of the present invention, a schematic view of the heat treatment method is shown in FIG. 1, and detailed heat treatment processes are shown in examples 1 to 3.
The pearlite inter-layer distance in the hypereutectoid steel rail obtained by the heat treatment method is 110-134.5 nm, the thickness of the cementite piece is 17.6-25.8 nm, the percentage of cementite is 44.22-48.13%, and the precipitation of net-shaped cementite is not obviously found at the grain boundary. The hypereutectoid steel rail obtained by the invention has the tensile strength of 1312-1437 MPa, the yield strength of 800-911 MPa, the elongation of 12.24-16.80%, the reduction of area of 20.79-25.70% and the hardness of 396-415 HB.
The technical solution of the present invention will be clearly and completely described below with reference to the embodiments of the present invention. It is to be understood that the described embodiments are merely exemplary of the invention, and not restrictive of the full scope of the invention. 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 invention.
In the embodiment, the rolled hypereutectoid steel rail or the heat treatment hypereutectoid steel rail comprises the following chemical components in percentage by weight: 0.94-1.00% of C, 0.45-0.80% of Si, 0.75-1.25% of Mn, less than or equal to 0.015% of P, less than or equal to 0.010% of S, 0.625% of Cr + Nb + Ni and the balance of iron.
Example 1
Heating the rolled hypereutectoid steel rail (with the temperature of room temperature) to 900 ℃, and preserving the temperature for 900 +/-30 seconds until the steel rail is fully austenitized to obtain an austenitized steel rail;
cooling the austenitized steel rail to 600 +/-12 ℃ at the speed of 7.8 +/-0.5 ℃/s, and keeping the temperature constant for 30 +/-4 s; then continuously cooling to 400 +/-15 ℃ at the speed of 7.8 +/-0.5 ℃/s, and finally naturally cooling to room temperature to obtain the hypereutectoid steel rail.
Example 2
Heating the rolled hypereutectoid steel rail (with the temperature of room temperature) to 900 ℃, and preserving the heat for 900 +/-25 seconds until the steel rail is fully austenitized to obtain an austenitized steel rail;
cooling the austenitized steel rail to 600 +/-5 ℃ at the speed of 9.6 +/-0.3 ℃/s, and keeping the temperature constant for 30 +/-2 s; then continuously cooling to 400 +/-25 ℃ at the speed of 9.6 +/-0.3 ℃/s, and finally naturally cooling to room temperature to obtain the hypereutectoid steel rail.
Example 3
Heating the rolled hypereutectoid steel rail (with the temperature of room temperature) to 900 ℃, and preserving the temperature for 900 +/-30 seconds until the steel rail is fully austenitized to obtain an austenitized steel rail;
cooling the austenitized steel rail to 630 +/-16 ℃ at the speed of 8.2 +/-0.6 ℃/s, and keeping the temperature constant for 32 +/-2 s; then continuously cooling to 400 +/-6 ℃ at the speed of 8.2 +/-0.6 ℃/s, and finally naturally cooling to room temperature to obtain the hypereutectoid steel rail.
Comparative example 1
The rolled hypereutectoid steel rail is taken as a comparative example 1.
Comparative example 2
The hypereutectoid steel rail in a heat treatment state is taken as a comparative example 2.
Comparative example 3
Heating the rolled hypereutectoid steel rail (with the temperature of room temperature) to 900 ℃, and preserving the temperature for 900 +/-36 s until the steel rail is fully austenitized to obtain an austenitized steel rail;
cooling the austenitized steel rail to 630 +/-18 ℃ at the speed of 4.9 +/-0.3 ℃/s, and keeping the temperature constant for 30 +/-6 s; then continuously cooling to 400 +/-2 ℃ at the speed of 4.9 +/-0.3 ℃/s, and finally naturally cooling to room temperature to obtain the hypereutectoid steel rail.
Comparative example 4
Heating the rolled hypereutectoid steel rail (with the temperature of room temperature) to 900 ℃, and preserving the temperature for 900 +/-27 seconds until the steel rail is fully austenitized to obtain an austenitized steel rail;
cooling the austenitized steel rail to 630 +/-16 ℃ at the speed of 5 +/-0.6 ℃/s, and keeping the temperature constant for 60 +/-2 s; then continuously cooling to 400 +/-18 ℃ at the speed of 5 +/-0.6 ℃/s, and finally naturally cooling to room temperature to obtain the hypereutectoid steel rail.
Test example 1
The samples prepared in examples 1 to 3 and comparative examples 1 to 4 were polished with sandpaper, then corroded with 3% nitric acid alcohol, and then the microstructure was observed with a metallographic microscope, and the results were shown in fig. 2-a to 2-g. Wherein FIG. 2-a is comparative example 1, FIG. 2-b is comparative example 2, FIG. 2-c is comparative example 3, FIG. 2-d is comparative example 4, FIG. 2-e is example 1, FIG. 2-f is example 2, and FIG. 2-g is example 3. As can be seen from FIGS. 2-a to 2-g, the rolled structure of comparative example 1 consists of a pearlite structure with a large lamellar spacing, and a clear lamellar structure can be seen under a microscope, while the distribution of network cementite can be seen at grain boundaries, as indicated by arrows; the pearlite structure of the factory-heat-treated hypereutectoid steel rail of comparative example 2 is still coarse, although being refined compared with the rolled state, the obvious interlayer spacing can still be seen under a microscope, and meanwhile, a small amount of reticular cementite is precipitated at the grain boundary; the pearlite interlamellar spacing of comparative examples 3 and 4 was still coarse and the pearlite interlamellar spacing was still visible in the lower part region under the microscope. Compared with comparative examples 1 to 4, the pearlite interlamellar spacing of examples 1 to 3 is obviously refined, the lamellar structure of pearlite cannot be basically seen under a microscope, and obvious reticular cementite precipitation cannot be observed at grain boundaries.
The distances between the pearlite layers in the SEM photographs of comparative examples 3 to 4 and examples 1 to 3 were counted by a line-cut method, and the average value was obtained, and the content of cementite was measured by software, and the obtained results are shown in table 1.
TABLE 1 pearlite interlamellar spacing and cementite content
As can be seen from table 1, as the isothermal time increases from 30s to 60s, the transformation time becomes longer, the pearlite lamellar spacing increases, and the cementite content decreases. On the premise of constant isothermal temperature and isothermal time, the supercooling degree is increased by increasing the cooling speed, the phase change driving force is increased, and the pearlite inter-lamellar spacing is reduced. However, when the cooling rate reaches a certain value, the inter-lamellar spacing is slightly increased, because the phase change of the pearlite phase into the diffusion-type phase change, the improvement of the cooling rate improves the supercooling degree, but reduces the diffusion rate of carbon atoms, and the combined action of the two finally increases the inter-lamellar spacing of the pearlite phase slightly.
Test example 2
According to GB/T228.1-2010 part 1 of the tensile test of metallic materials: room temperature test method, in which a room temperature tensile test was conducted on a GNT300 electronic universal tester at a tensile rate of 0.6mm/min, and the tensile strength, yield strength, elongation and reduction of area of the samples prepared in examples 1 to 3 and comparative examples 1 to 4 were tested; then, a hardness tester is used according to GB/T231.1-2018 Brinell hardness test part 1 of metal materials: test methods the brinell hardness of each sample was determined. The results are shown in Table 2.
TABLE 2 mechanical Property test results
As can be seen from Table 2, the hardness of the hypereutectoid steel rail after heat treatment is improved compared with that of the rolled steel rail and the heat treatment, the most influence is the isothermal temperature, and when the same isothermal time is 30s, the isothermal hardness at 600 ℃ is greatly improved compared with that at 630 ℃, because the isothermal temperature is low, the refinement degree of the pearlite interlamellar spacing is greater, and meanwhile, the percentage content of hard-phase cementite is also greater; with the increase of the cooling speed, the hardness change uniform process of the hypereutectoid steel rail is in a zigzag shape, the peak value appears at the cooling speed of 8 ℃/s, the hardness at the cooling speed of 10 ℃/s is higher than that at the cooling speed of 5 ℃/s, and the hardness change is consistent with the change of the pearlite lamellar spacing, which shows that the hardness of the refined pearlite lamellar spacing can be effectively improved; by comparing the hardness corresponding to two isothermal times in 600 ℃ isothermal process, the longer the isothermal time is, the lower the hardness of hypereutectoid steel rail is, because the excessively long isothermal time causes the growth of pearlite, so that the interlamellar spacing of the pearlite is increased; example 1 achieved a maximum hardness of 415HB, which was 36.1% higher than the rolled state and 20.3% higher than the hotter treated state.
Test example 3
The microscopic SEM morphologies of tensile fractures of the samples prepared in examples 1-3 and comparative examples 1-4 are shown in FIGS. 3-a-3-g. Wherein, FIG. 3-a is a microscopic SEM topography of a tensile fracture of comparative example 1, FIG. 3-b is a microscopic SEM topography of a tensile fracture of comparative example 2, FIG. 3-c is a microscopic SEM topography of a tensile fracture of comparative example 3, FIG. 3-d is a microscopic SEM topography of a tensile fracture of comparative example 4, FIG. 3-e is a microscopic SEM topography of a tensile fracture of example 1, FIG. 3-f is a microscopic SEM topography of a tensile fracture of example 2, and FIG. 3-g is a microscopic SEM topography of a tensile fracture of example 3. Comparative examples 1 to 4 (FIGS. 3-a, 3-b, 3-c, 3-d) all consisted of cleavage planes, river patterns and tear edges and partial secondary cracks, the type of which is an obvious cleavage fracture, a brittle fracture. Whereas the cleavage plane of example 3 (fig. 3-g) is significantly smaller, the tear edges are shorter and the number is increased, while a certain number of dimples are observed, but the dimples are smaller in size and shallower in depth, so the fracture mode belongs to quasi-cleavage fracture and still to brittle fracture. The micro-sections of example 1 (fig. 3-e) and example 2 (fig. 3-f) exhibited a large number of tearing dimples, the surface was cellular, and the size and depth of the dimples were increased compared to example 3, and the fracture was ductile. As can be seen from FIGS. 3-a to 3-g, the rolled fracture is brittle fracture, while the heat-treated fracture gradually changes from brittle fracture to ductile fracture.
As can be seen from the above examples and comparative examples, the microstructure of the hypereutectoid steel rail after heat treatment is significantly changed from the rolled state. The pearlite lamellar spacing is gradually reduced along with the reduction of isothermal temperature and isothermal time; with the acceleration of the cooling speed, the pearlite lamellar spacing is firstly greatly reduced and then slightly increased; the mechanical property of the hypereutectoid steel rail after heat treatment is improved compared with that of a rolled state and a heat treatment state; the lower the isothermal temperature is, the higher the hardness and the tensile strength are; the shorter the isothermal time, the higher the hardness and tensile strength. The rolled fracture is brittle fracture, and the heat treated fracture is ductile fracture. With the increase of the cooling rate, the decrease of the isothermal temperature and the decrease of the isothermal time, the fracture type is transited from brittle fracture to ductile fracture. The heat treatment method provided by the invention can effectively refine the lamellar spacing of pearlite, simultaneously avoid the occurrence of network cementite in crystal boundary and is beneficial to improving the mechanical property of hypereutectoid steel rails.
The foregoing is only a preferred embodiment of the present invention, and it should be noted that, for those skilled in the art, various modifications and decorations can be made without departing from the principle of the present invention, and these modifications and decorations should also be regarded as the protection scope of the present invention.
Claims (4)
1. A heat treatment method for reducing hypereutectoid steel rail reticular cementite precipitation comprises the following steps:
heating the rolled or heat-treated hypereutectoid steel rail to over 900 ℃, and preserving heat to obtain an austenitized steel rail;
cooling the austenitized steel rail to an isothermal temperature at a first cooling speed for 30-50 s; then cooling to the final cooling temperature below 400 ℃ at a second cooling speed; naturally cooling to room temperature; the isothermal temperature is 600-630 ℃; the first cooling speed and the second cooling speed are 8-10 ℃/s independently.
2. The thermal processing method of claim 1, wherein said first cooling rate and said second cooling rate are the same.
3. The heat treatment method according to claim 1, wherein the carbon content of the as-rolled or as-heat treated hypereutectoid steel rail is 0.94 to 1.00 wt.%.
4. A heat treatment method according to claim 1 or 3, characterized in that the chemical composition of said as-rolled or as-heat treated hypereutectoid steel rail comprises, in mass%: 0.94-1.00% of C, 0.45-0.80% of Si, 0.75-1.25% of Mn, less than or equal to 0.015% of P, less than or equal to 0.010% of S, 0.625% of Cr + Nb + Ni and the balance of iron.
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| CN114058813A (en) * | 2021-11-23 | 2022-02-18 | 包头钢铁（集团）有限责任公司 | Control method of hypereutectoid rare earth steel rail network carbide |
| CN114152617A (en) * | 2021-10-14 | 2022-03-08 | 攀钢集团研究院有限公司 | Method for accurately measuring and reducing proportion and distribution of proeutectoid cementite |
| CN115094338A (en) * | 2022-07-27 | 2022-09-23 | 内蒙古科技大学 | Hypereutectoid steel for steel rail and preparation method thereof |
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| CN112375891A (en) * | 2020-10-20 | 2021-02-19 | 包头钢铁（集团）有限责任公司 | Online tempering process for eliminating bainite steel rail tensile fracture brittleness platform |
| CN114152617A (en) * | 2021-10-14 | 2022-03-08 | 攀钢集团研究院有限公司 | Method for accurately measuring and reducing proportion and distribution of proeutectoid cementite |
| CN114058813A (en) * | 2021-11-23 | 2022-02-18 | 包头钢铁（集团）有限责任公司 | Control method of hypereutectoid rare earth steel rail network carbide |
| CN115094338A (en) * | 2022-07-27 | 2022-09-23 | 内蒙古科技大学 | Hypereutectoid steel for steel rail and preparation method thereof |
| CN115094338B (en) * | 2022-07-27 | 2023-09-22 | 内蒙古科技大学 | Hypereutectoid steel for steel rail and preparation method thereof |
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Application publication date: 20200714 |