CN114000034B - Low-yield-ratio high-strength bainite steel rail and production method thereof - Google Patents

Low-yield-ratio high-strength bainite steel rail and production method thereof Download PDF

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CN114000034B
CN114000034B CN202111286790.0A CN202111286790A CN114000034B CN 114000034 B CN114000034 B CN 114000034B CN 202111286790 A CN202111286790 A CN 202111286790A CN 114000034 B CN114000034 B CN 114000034B
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steel rail
steel
rail
bainite
yield ratio
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CN114000034A (en
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袁俊
韩振宇
邓勇
李若曦
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Pangang Group Panzhihua Iron and Steel Research Institute Co Ltd
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Pangang Group Panzhihua Iron and Steel Research Institute Co Ltd
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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
    • 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
    • C21D1/18—Hardening; Quenching with or without subsequent tempering
    • 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
    • C21D6/004—Heat treatment of ferrous alloys containing Cr and Ni
    • 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
    • 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
    • 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
    • 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
    • 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
    • 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
    • C22C38/008—Ferrous alloys, e.g. steel alloys containing tin
    • 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
    • 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
    • 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
    • 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
    • C22C38/34—Ferrous alloys, e.g. steel alloys containing chromium with more than 1.5% by weight of silicon
    • 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
    • C22C38/42—Ferrous alloys, e.g. steel alloys containing chromium with nickel with copper
    • 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
    • C22C38/44—Ferrous alloys, e.g. steel alloys containing chromium with nickel with molybdenum or tungsten
    • 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
    • C22C38/46—Ferrous alloys, e.g. steel alloys containing chromium with nickel with vanadium
    • 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
    • C22C38/58—Ferrous alloys, e.g. steel alloys containing chromium with nickel with more than 1.5% by weight of manganese
    • C—CHEMISTRY; METALLURGY
    • C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
    • C22C—ALLOYS
    • C22C38/00—Ferrous alloys, e.g. steel alloys
    • C22C38/60—Ferrous alloys, e.g. steel alloys containing lead, selenium, tellurium, or antimony, or more than 0.04% by weight of sulfur
    • E—FIXED CONSTRUCTIONS
    • E01—CONSTRUCTION OF ROADS, RAILWAYS, OR BRIDGES
    • E01B—PERMANENT WAY; PERMANENT-WAY TOOLS; MACHINES FOR MAKING RAILWAYS OF ALL KINDS
    • E01B5/00—Rails; Guard rails; Distance-keeping means for them
    • E01B5/02—Rails
    • E—FIXED CONSTRUCTIONS
    • E01—CONSTRUCTION OF ROADS, RAILWAYS, OR BRIDGES
    • E01B—PERMANENT WAY; PERMANENT-WAY TOOLS; MACHINES FOR MAKING RAILWAYS OF ALL KINDS
    • E01B5/00—Rails; Guard rails; Distance-keeping means for them
    • E01B5/02—Rails
    • E01B5/14—Rails for special parts of the track, e.g. for curves
    • 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
    • C21D2211/001—Austenite
    • 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
    • C21D2211/002—Bainite
    • 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
    • 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
    • C21D2211/008—Martensite

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  • Thermal Sciences (AREA)
  • Crystallography & Structural Chemistry (AREA)
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Abstract

The invention discloses a low yield ratio high strength bainite steel rail and a production method thereof, wherein the method comprises the following steps: smelting a steel billet by a steel smelting process containing 0.1-0.15 wt% of carbon; heating at 1250-1300 deg.C for 200-500 min; in the rolling process of the steel billet, a large reduction rolling technology is adopted, the reduction amount is controlled to be 120-150mm, and the final cooling temperature is between 950-1050 ℃, so that the steel rail is obtained; the steel rail stays for a relaxation time of 150-300s from the finishing mill group to the heat treatment unit; in the heat treatment unit, the heat treatment starting cooling temperature range is 740-820 ℃, the cooling rate is 5-15 ℃/s, and the final cooling temperature is 200-250 ℃. The invention adopts the production method of the low yield ratio high-strength bainite steel rail to obtain the low yield ratio high-strength bainite steel rail with wear resistance and fatigue resistance.

Description

Low-yield-ratio high-strength bainite steel rail and production method thereof
Technical Field
The invention relates to the field of metallurgical environmental protection, in particular to a low-yield-ratio high-strength bainite steel rail and a production method thereof.
Background
The steel rail is used as a key part of the railway, and the performance of the steel rail directly relates to the transportation efficiency and the driving safety of the railway. At present, pearlite steel rails are mainly adopted in China railways. Years of application show that the pearlite high-strength steel rail has excellent wear resistance, and the service life of the steel rail is greatly prolonged. However, in some sections with severe service conditions, the problems of insufficient toughness matching and poor contact fatigue resistance of the pearlite steel rail are reflected, and a steel rail with both excellent wear resistance and excellent fatigue resistance is required. Thus, the development of bainite rails has been paid attention again.
The bainite steel rail is prepared by using low carbon (such as 0.15-0.25 percent of carbon), and adding proper amount of Si, mn, cr, ni, mo and other elements, and obtaining carbide-free bainite or B/M complex phase structure under the air cooling condition. Meanwhile, the steel rail obtains good toughness matching through medium temperature tempering. Research shows that the bainite is produced by adopting an online heat treatment technology, and the following advantages can be obtained: firstly, the bainite steel rail produced by the strong fine-grain strengthening effect of the online heat treatment is more uniformly refined, and the formation of residual austenite can be effectively inhibited. Secondly, by accurately controlling the online heat treatment temperature, the proportion of martensite can be reduced to the maximum, the indexes of strong hardness and toughness and plasticity can be simultaneously and greatly improved, and the wear resistance of the bainite steel rail can reach the level of the existing pearlite heat treatment steel rail while the bainite steel rail fully exerts excellent fatigue performance. And thirdly, the online heat treatment can replace part of precious alloy elements, so that the production cost is further reduced, and a foundation is laid for large-scale popularization and application. However, after the bainite steel rail is subjected to heat treatment, the strength can reach more than 1400MPa, the impact toughness can reach more than 150J, and the yield ratio also reaches more than 0.90.
However, for the steel rail for the railway, the requirement of low yield ratio is also provided by combining service characteristics, the low yield ratio can enable the steel rail to have good cold deformation capacity and higher plastic deformation capacity, more steel rail deformation energy is absorbed, and sudden fracture is not caused even if local overload is unstable, so that the bearing capacity of the steel rail is improved.
Therefore, how to produce the low-yield-ratio high-strength bainite steel rail with wear resistance and fatigue resistance becomes an urgent problem to be solved.
Disclosure of Invention
In order to solve the technical problems in the prior art, the invention provides a production method of a low-yield-ratio high-strength bainite steel rail with wear resistance and fatigue resistance.
The production method of the low-yield-ratio high-strength bainite steel rail is realized by the following technical scheme:
according to the invention, a production method of a low-yield-ratio high-strength bainite steel rail is provided, which comprises the following steps:
smelting a steel billet by a steel smelting process containing 0.1-0.15 wt% of carbon;
heating at 1250-1300 ℃ for 200-500 min;
in the rolling process of the steel billet, a high reduction rolling technology is adopted, the reduction amount is controlled to be 120-150mm, and the final cooling temperature is between 950-1050 ℃, so that a steel rail is obtained;
the steel rail stays for a relaxation time of 150-300s from the finishing mill group to the heat treatment unit;
in the heat treatment unit, the heat treatment starting temperature range is 740-820 ℃, the cooling rate is 5-15 ℃/s, and the final cooling temperature is 200-250 ℃.
According to an embodiment of the present invention, further comprising:
after the steel rail is cooled and straightened, tempering is carried out at the temperature of 300-450 ℃, and the tempering time is 5-12h.
According to one embodiment of the invention, a steel slab is smelted using a steel smelting process containing 0.1-0.15 wt.% carbon, comprising:
during smelting, sulfur content of 0.002-0.010 wt% is used for control.
According to one embodiment of the invention, a steel slab is smelted using a steel smelting process containing 0.1-0.15 wt.% carbon, comprising:
the casting is protected in the whole smelting process.
According to one embodiment of the invention, the composition of the steel slab comprises: 0.001-0.02 wt% Sn.
According to one embodiment of the invention, the composition of the steel slab comprises: 0.05-0.15 wt% Cu.
According to one embodiment of the invention, the composition of the steel slab comprises: 0.01-0.02 wt% of As.
According to one embodiment of the invention, the hydrogen content of the steel slab is less than or equal to 1.5ppm; the oxygen content of the turnout steel rail is less than or equal to 20ppm; the nitrogen content of the turnout steel rail is less than or equal to 60ppm.
According to the invention, the bainite steel rail with low yield ratio and high strength is prepared by adopting the method.
Due to the adoption of the technical scheme, compared with the prior art, the invention has the following advantages:
the production method of the low-yield-ratio high-strength bainite steel rail adopts a steel smelting process containing 0.1-0.15 wt% of carbon to smelt a steel billet; heating at 1250-1300 ℃ for 200-500 min; in the rolling process of the steel billet, a high reduction rolling technology is adopted, the reduction amount is controlled to be 120-150mm, and the final cooling temperature is between 950-1050 ℃, so that a steel rail is obtained; the steel rail stays for a relaxation time of 150-300s from the finishing mill group to the heat treatment unit; in the heat treatment unit, the heat treatment starting temperature range is 740-820 ℃, the cooling rate is 5-15 ℃/s, and the final cooling temperature is 200-250 ℃. Thus, the bainite steel rail obtained by the method has the tensile strength of more than or equal to 1450MPa, the elongation of more than or equal to 12 percent, the yield ratio of less than or equal to 0.90, and the structure contains 5-25 percent of ferrite, 65-75 percent of bainite and a small amount of residual austenite and martensite. It is especially suitable for heavy-duty railway or turnout railway.
Drawings
FIG. 1 illustrates a flow diagram of one embodiment of a method of producing a low yield ratio, high strength bainitic steel rail according to the present disclosure;
FIG. 2 is a drawing of a drawing and metallographic sample location illustrating one embodiment of a method of producing a low yield ratio, high strength bainitic steel rail according to the invention;
FIG. 3 is a metallographic representation of the steel rail metallographic structure illustrating an embodiment of the method of producing a low yield ratio, high strength bainitic steel rail according to the invention;
figure 4 shows a metallographic structure of a rail according to an embodiment of the method of producing a low yield ratio, high strength bainitic steel rail according to the invention.
Detailed Description
In order to make the objects, technical solutions and advantages of the present invention more apparent, the present invention is further described in detail with reference to the following embodiments. It should be understood that the specific embodiments described herein are merely illustrative of the invention and are not intended to limit the invention.
The research on bainitic steels as a rail material began in the 60's of the 20 th century. Since the 20 th century and the 80 th century, research on bainite rails and switches has been conducted in the uk, the usa, japan and other countries, and the bainite rails are known as "rails for the 21 st century". However, bainite rails have not been used in large scale due to their high cost and difficulty in welding.
For railway rails, special requirements are also put forward in combination with service characteristics: 1) Has sufficiently high tensile strength and yield strength. 2) Has smaller fluctuation range of yield strength. When the yield ratio between the steel rails is too large, local fracture is easily caused, and derailment accidents are caused. 3) Has high plasticity and toughness. In order to ensure the safety and reliability of the service of the steel rail, the material is required to have better impact toughness besides a high-strength characteristic value and high yield strength. 4) Low yield ratio: the low yield ratio can enable the steel rail to have good cold deformation capacity and higher plastic deformation capacity, absorb more steel rail deformation energy, and prevent sudden fracture even if the local overload is unstable, thereby improving the bearing capacity of the steel rail. With the continuous increase of the strength, the yield ratio tends to increase, so that the reduction of the yield ratio is a key development index of the bainite steel rail. That is, the yield ratio of the steel is required to be not higher than 0.85, so as to ensure that the bainite steel rail has optimal safety and economy.
Wherein the yield ratio is an ability to resist from yielding to plastically unstable deformation, and the low yield ratio is an important characteristic for representing whether the steel rail bears load or not from the safety point of view. The yield ratio is determined by the microstructure of the steel, and the dual-phase or multi-phase structure is effective in reducing the yield ratio. The adoption of two-phase zone quenching or controlled rolling can obtain a two-phase or multi-phase structure, and the structure of the structure is usually movable dislocation. Soft phase ferrite, hard phase bainite or martensite or acicular ferrite with high density and a complex structure with residual M/A. It has also been shown that increasing the M/a volume fraction in the steel also contributes to a reduction in the yield ratio. The structure composed of soft and hard phases has continuous yield, low yield ratio, high ductility and excellent toughness. The proportion and the hardness of a hard phase and a soft phase in a microstructure are reasonably configured, so that the yield ratio of the steel can be effectively reduced.
Therefore, the type, content and distribution of the microstructure are reasonably controlled, and the high-strength low-yield-ratio dual-function composite material can realize the performance of high strength and low yield ratio. In addition, the impact toughness of the bainite steel rail with high strength and toughness and low yield ratio can reach more than 150J, and obvious plastic deformation occurs before fracture, which belongs to typical ductile fracture. The material has ductile fracture with few catastrophic consequences, however, the fracture micro-mechanism research lags behind the brittle fracture, the ductile fracture process is more complex than the brittle fracture process, the influencing factors are crossed, and at present, no mature theory exists. A large number of studies have shown that the subtle processes of ductile fracture are the initiation of pores, the growth of pores, and the polymerization of pores. However, no specific measures and solutions are provided for controlling crystal defects, inclusion particles, second-phase precipitate particles and a small amount of hard phase structure of the high-toughness steel material so as to effectively control the initiation and polymerization processes of the pores.
The invention provides a production method of a low-yield-ratio high-strength bainite steel rail. As shown in fig. 1, the method for producing a low yield ratio high strength bainite steel rail according to the present invention includes:
s101, smelting a steel billet by adopting a steel smelting process containing 0.1-0.15 wt% of carbon.
For example, the manufacturing process of the steel billet may include: converter smelting, LF refining, RH vacuum treatment, whole-process protective casting, cooling and heating by a heating furnace. Wherein, sulfur with 0.002-0.010 weight percent is adopted for control in the smelting process. Specifically, the content of sulfur may be 0.002 wt%, 0.003 wt%, 0.004 wt%, 0.005 wt%, 0.006 wt%, 0.007 wt%, 0.008 wt%, 0.009 wt%, or 0.010 wt%. Wherein the heating temperature of the heating furnace is 1230-1280 ℃. Specifically, the heating temperature may be 1230 ℃, 1250 ℃, or 1280 ℃. The heating time of the heating furnace can be 150-240min. Specifically, the heating time of the heating furnace may be 150min, 190min or 240min.
S102, heating at 1250-1300 ℃ for 200-500min.
Wherein, the heating temperature of the heating furnace can be 1250-1300 ℃. Specifically, the heating temperature may be 1250 deg.C, 1260 deg.C, 1270 deg.C, 1280 deg.C, 1290 deg.C or 1300 deg.C. The heating time of the heating furnace can be 200-500min. Specifically, the heating time of the heating furnace may be 200min, 350min, or 500min.
S103, in the rolling process of the steel billet, a high reduction rolling technology is adopted, the reduction amount is controlled to be 120-150mm, and the final cooling temperature is 950-1050 ℃, so that the steel rail is obtained.
Wherein the rolling reduction is controlled at 120mm, 130mm, 140mm or 150mm, and the final cooling temperature is 950 ℃, 960 ℃, 970 ℃, 980 ℃, 990 ℃, 1000 ℃, 1100 ℃, 1200 ℃, 1300 ℃, 1400 ℃ or 1050 ℃.
And S104, the steel rail stays for a relaxation time of 150-300S from the final rolling mill group to the heat treatment unit.
Wherein the steel rail stays for 150s relaxation time, 180s relaxation time, 220s relaxation time, 260s relaxation time or 300s relaxation time from the finishing mill group to the heat treatment group.
S105, in the heat treatment unit, the heat treatment starting temperature range is 740-820 ℃, the cooling rate is 5-15 ℃/S, and the final cooling temperature is 200-250 ℃.
Wherein, the first and the second end of the pipe are connected with each other, the temperature of the heat treatment can be 740 ℃, 740 ℃ and 740 DEG C740 ℃, 740 ℃ or 820 ℃. The cooling rate can be 5 ℃/s, 6 ℃/s, 7 ℃/s, 8 ℃/s, 9 ℃/s, 10 ℃/s, 11 ℃/s, 12 ℃/s, 13 ℃/s, 14 ℃/s or 15 ℃/s, and the final cooling temperature can be 200 ℃, 210 ℃, 220 ℃, 230 ℃, 240 ℃ or 250 ℃.
In some implementations, the method for producing a low yield ratio high strength bainitic steel rail may further include:
s106, after cooling and straightening the steel rail, tempering at the temperature of 300-450 ℃ for 5-12 hours.
After the steel rail is cooled and straightened, the tempering temperature can be 300 ℃, 320 ℃, 330 ℃, 350 ℃, 380 ℃, 400 ℃, 420 ℃, 440 ℃ or 450 ℃.
The bainite steel rail prepared by the production method of the low-yield-ratio high-strength bainite steel rail provided by the invention comprises the following components: 0.001-0.02 wt% of Sn, 0.05-0.15 wt% of Cu, 0.01-0.02 wt% of As.
In a particular implementation, the content of Sn in the rail may be 0.001 wt%, 0.003 wt%, 0.005 wt%, 0.008 wt%, 0.009 wt%, 0.011 wt%, 0.014 wt%, 0.016 wt%, 0.018 wt%, or 0.02 wt%.
In a particular implementation, the content of Cu in the rail may be 0.01 wt% or 0.02 wt%.
The hydrogen content of the turnout steel rail is less than or equal to 1.5ppm; the oxygen content of the turnout steel rail is less than or equal to 20ppm; the nitrogen content of the turnout steel rail is less than or equal to 60ppm.
That is, 0.1% of C increases the tensile strength by 190MPa and the yield strength by 230MPa, depending on the relationship between the components and the tensile strength and yield strength; the tensile strength is improved by 13.3MPa and the yield strength is improved by 8.7MPa by 0.1 percent of Si; the tensile strength is improved by 3.4MPa and the yield strength is improved by 2.4MPa by 0.1 percent of Mn. From the above relationship, it can be seen that C significantly improves yield strength, and is also an important strengthening element. By reducing the content of C, the yield strength can be reduced to a certain extent by increasing the contents of Si and Mn. Finally, V (C, N) pinning dislocation is formed by adding V, the strength of the steel rail is improved, and the yield strength is reduced.
The low yield ratio is realized from the technical aspect, coarse grains are firstly provided, and the size of the grains is controlled by the heating temperature of the billet, the heat preservation time and the controlled rolling. Secondly, in order to realize a ferrite/bainite complex phase structure, the volume fraction of proeutectoid ferrite in steel is required to reach 5-60% before rapid cooling, if the volume fraction is lower than 5%, the soft phase ferrite cannot play a role in reducing the yield strength, and the yield ratio of the steel cannot be reduced, and if the volume fraction is higher than 60%, the hard phase bainite or martensite is less, so that the tensile strength of the steel cannot be effectively improved. In order to obtain the high-strength bainite steel rail, accelerated cooling is required, and the accelerated cooling is carried out by utilizing rolling waste heat. In order to obtain ferrite with specified content, the steel rail enters a heat treatment unit at high temperature of 740-820 ℃, the cooling rate is 5-15 ℃/s, and the final cooling temperature is 200-250 ℃. Finally, after the steel rail is tempered at 300-450 ℃ for 5-12h, the tensile strength of the bainite steel rail is more than or equal to 1350MPa, the elongation is more than or equal to 12 percent, the yield ratio is less than or equal to 0.90, and the structure contains 5-25 percent of ferrite, 65-75 percent of bainite and a small amount of residual austenite. It is especially suitable for heavy-duty railway or turnout railway.
Hereinafter, the low yield ratio high strength bainite steel rail and the method for producing the same according to the present invention will be described in detail with reference to examples.
The inventive examples and comparative examples used different chemical compositions.
The embodiment and the comparative example of the invention adopt the same chemical components, and the embodiment and the comparative example adopt 0.002-0.010 percent of S molten iron fed into the furnace, and the whole process is protected for pouring. And (4) slowly cooling the cast blank after pouring in a slow cooling pit. The chemical composition of the steel slab is shown in table 1.
TABLE 1 chemical composition/% of the rails of examples and comparative examples
Figure BDA0003333169830000081
TABLE 2 residual elemental composition/%, of example and comparative example rails
Figure BDA0003333169830000082
Figure BDA0003333169830000091
When the examples and comparative examples used different heating processes, rolling processes, relaxation times and heat treatment processes, as shown in table 3.
TABLE 3 examples and comparative examples heating, rolling and Heat treatment Process
Figure BDA0003333169830000092
After the steel rails of the examples and the comparative examples are cooled and straightened, tempering is carried out at the same temperature of 300-450 ℃ for 5-12h.
Examples and comparative examples tensile specimens were processed and tested according to TB/T2344 requirements of track order Specification of 43kg/m to 75kg/m, at the tensile specimen sampling locations shown in FIG. 3. Meanwhile, according to the attached drawing 3, metallographic structure inspection is carried out on the metallographic specimen inspection position, and a metallographic photograph is shown in the attached drawing 4. Tensile and metallographic statistics are shown in table 4.
TABLE 4 tensile Properties of the example and comparative rails
Figure BDA0003333169830000101
The production method of the bainite steel rail with the low yield ratio is adopted, so that the toughness of the bainite steel rail is improved, the yield strength is reduced, and the operation safety of the steel rail is improved.
In conclusion, the low yield ratio bainite steel rail and the production method thereof provide a production rail head tensile property and a metallographic analysis method, and improve the comprehensive performance requirement of the steel rail.
The production method of the low-yield-ratio high-strength bainite steel rail adopts a steel smelting process containing 0.1-0.15 wt% of carbon to smelt a steel billet; heating at 1250-1300 ℃ for 200-500 min; in the rolling process of the steel billet, a high reduction rolling technology is adopted, the reduction amount is controlled to be 120-150mm, and the final cooling temperature is between 950-1050 ℃, so that a steel rail is obtained; the steel rail stays for a relaxation time of 150-300s from the finishing mill group to the heat treatment unit; in the heat treatment unit, the heat treatment starting temperature range is 740-820 ℃, the cooling rate is 5-15 ℃/s, and the final cooling temperature is 200-250 ℃. Thus, the bainite steel rail obtained by the method has the tensile strength of more than or equal to 1450MPa, the elongation of more than or equal to 12 percent, the yield ratio of less than or equal to 0.90, and the structure contains 5-25 percent of ferrite, 65-75 percent of bainite and a small amount of residual austenite and martensite. It is especially suitable for heavy-duty railway or turnout railway.
The above examples only express embodiments of the present invention, and the description thereof is more specific and detailed, but not construed as limiting the scope of the present invention. It should be noted that various changes and modifications can be made by those skilled in the art without departing from the spirit of the invention, and these changes and modifications are all within the scope of the invention. Therefore, the protection scope of the present patent shall be subject to the appended claims.

Claims (9)

1. A production method of a low-yield-ratio high-strength bainite steel rail is characterized by comprising the following steps:
smelting a steel billet by a steel smelting process containing 0.1-0.15 wt% of carbon;
heating at 1250-1300 ℃ for 200-500 min;
in the rolling process of the steel billet, a high reduction rolling technology is adopted, the reduction amount is controlled to be 120-150mm, and the final cooling temperature is between 950-1050 ℃, so that a steel rail is obtained;
the steel rail stays from the finishing mill group to the heat treatment unit for relaxation time of 150-300 s;
in the heat treatment unit, the heat treatment starting cooling temperature is 740-820 ℃, the cooling rate is 5-15 ℃/s, and the final cooling temperature is 200-250 ℃.
2. The method for producing the low yield ratio high strength bainite steel rail according to claim 1, further comprising:
after the steel rail is cooled and straightened, tempering is carried out at the temperature of 300-450 ℃, and the tempering time is 5-12h.
3. The method of claim 1, wherein the step of smelting the steel slab using a steel smelting process including 0.1-0.15 wt% carbon comprises:
during smelting, sulfur content of 0.002-0.010 wt% is used for control.
4. The method for producing the bainite steel rail with low yield ratio and high strength as claimed in claim 1, wherein the steel billet is smelted by a steel smelting process containing 0.1-0.15 wt% of carbon, and the method comprises the following steps:
the casting is protected in the whole smelting process.
5. The method of claim 1, wherein the bainitic steel rail is produced by a method comprising the steps of,
the steel billet comprises the following components: 0.001-0.02 wt% Sn.
6. The method for producing the bainite steel rail with low yield ratio and high strength according to claim 1,
the steel billet comprises the following components: 0.05-0.15 wt% Cu.
7. The method of claim 1, wherein the bainitic steel rail is produced by a method comprising the steps of,
the steel billet comprises the following components: 0.01-0.02 wt% of As.
8. The method of claim 1, wherein the bainitic steel rail is produced by a method comprising the steps of,
the hydrogen content of the steel billet is less than or equal to 1.5ppm; the oxygen content of the turnout steel rail is less than or equal to 20ppm; the nitrogen content of the turnout steel rail is less than or equal to 60ppm.
9. A low yield ratio high strength bainite steel rail, characterized in that it is manufactured by the method of any one of claims 1 to 8.
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