CN113416818A - Heat treatment process of high-strength and high-toughness bainite/martensite multiphase bainite steel rail - Google Patents
Heat treatment process of high-strength and high-toughness bainite/martensite multiphase bainite steel rail Download PDFInfo
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- C21D1/18—Hardening; Quenching with or without subsequent tempering
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- 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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- C22C38/18—Ferrous alloys, e.g. steel alloys containing chromium
- C22C38/40—Ferrous alloys, e.g. steel alloys containing chromium with nickel
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- C22C38/18—Ferrous alloys, e.g. steel alloys containing chromium
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- 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
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- 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
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- 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
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- 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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Abstract
The invention discloses a heat treatment process of a high-strength and high-toughness bainite and martensite multiphase bainite steel rail, which avoids structures with poor performances of upper bainite and granular bainite by controlling the cooling speed of the steel rail in different temperature stages, further forms a lower bainite and low-carbon martensite multiphase structure, can effectively improve structure segregation (martensite segregation zone), can refine original austenite grains, reduce the space between structure sheets and reduce the quantity of residual austenite, and thus, the steel rail has the characteristics of high strength, high plasticity, high toughness, high anti-stripping and anti-chipping property, high wear resistance, high rolling contact fatigue performance and the like.
Description
Technical Field
The invention relates to a heat treatment process of a high-strength and high-toughness bainite/martensite multiphase bainite steel rail.
Background
With the progress of railway heavy-load transportation technology, the railway heavy-load transportation capacity of China is continuously improved, the axle weight of heavy-load trucks is gradually improved, and the heavy-load railway has the characteristics of large axle weight, large transportation capacity, high departure density and the like, for example, the traffic volume of the Taiyuan Daqin line in 2019 reaches 5 hundred million tons per year. The rapid development of the steel rail for the heavy-duty railway puts more rigorous requirements on the strength, toughness, wear resistance and fatigue resistance of steel rail materials in a steel mill. The pearlite steel rail commonly used at present basically exerts the toughness to the utmost limit due to the characteristics of the components and the tissue structure, and has lower impact toughness and fracture toughness, so the pearlite steel rail can not completely meet the service requirement of a heavy haul railway. Under the background, the development of steel rails suitable for heavy-duty transportation railways is promoted, the bainite steel rail has good strength, plasticity, impact toughness, wear resistance and rolling contact fatigue resistance, and the bainite steel rail has better weldability and is very suitable for turnout and main track laying of heavy-duty railways.
The heavy haul railway steel rail has poor service conditions and bears higher external acting force. In order to meet the requirements of high strength and toughness, high wear resistance and excellent fatigue resistance of the steel rail for the heavy haul railway, the bainite steel rail needs to be produced by adopting an online controlled cooling process, so that the grain refinement and the uniform structure of the steel rail are ensured, and various mechanical performance indexes are improved in detail. However, bainite steel rails have different bainite/martensite structure transformation ratios and conventional mechanical properties at different cooling speeds, and can generate higher structural stress in the line controlled cooling process to influence the straightness of the steel rail, and meanwhile, the steel rail can also generate straightening stress in the straightening process, and the structural stress and the straightening stress are superposed to generate higher residual stress on the steel rail, thereby seriously influencing the use and the service of the steel rail. Therefore, the reasonable controlled cooling process and tempering process can effectively improve the comprehensive mechanical property, the wear resistance and the fatigue resistance of the bainite/martensite multiphase steel rail, reduce the residual stress of the steel rail, reduce the sensitivity of bainite/martensite multiphase structure to inclusions, and further effectively improve the service performance of the steel rail.
The development of bainite steel rail is mainly designed by adopting medium and low carbon contents, and is supplemented with proper amount of Si, Mn, Cr, Mo, V, Nb, Ni, Ti and other elements, and the complex phase steel which mainly comprises bainite and martensite and also comprises residual austenite carbide and the like is obtained under the conditions of air cooling and controlled cooling. The bainite steel rail structure should avoid upper bainite, martensite segregation zone, unstable residual austenite, coarse carbide, etc. The ideal structure of the 1380MPa grade on-line controlled cooling bainite steel rail is low-carbon bainite, a martensite complex phase structure and a small amount of residual austenite, and the comprehensive mechanical property of the steel rail is improved through dislocation strengthening, fine crystal strengthening, solid solution strengthening and precipitation strengthening.
Beijing Temetallurgical industry and trade LLC liability company proposes "Bainite steel and Bainite steel rail for curve and heavy-duty steel rail and its production method" (publication number is CN101921971A), but because of adopting air cooling and cooling with cooling rate of 10-20 ℃/min, the strength of the obtained steel rail is low, only 1200-1300 MPa, and can not meet the increasingly developed heavy-duty railway construction. "Bainite structural steel rail having excellent fatigue resistance and method for producing the same" (publication No. CN 1978690A) are proposed by saddle Steel products, but "natural cooling in air after hot rolling" inevitably causes influence of seasonal change on cooling rate, resulting in non-uniform performance and structure. The iron and steel research institute proposes 'an alloy system and a heat treatment method of bainite steel rails thereof' (the publication number is CN105385938A), but because the steel rails need to be subjected to re-austenitizing and normalizing treatment, waste heat treatment is not adopted, and the energy conservation and emission reduction are not facilitated. The Panzhihua steel research institute company Limited of Panzhihua group proposed "a high strength bainite steel rail and its production method" (publication number is CN 104087852A); although a waste heat treatment process is adopted, the rail head part of the steel rail is subjected to accelerated cooling at the cooling speed of 3 ℃/S-6 ℃/S at 450-500 ℃, the temperature interval belongs to an upper bainite transformation interval, so that the structure is coarsened, the performance is poor, the temperature of different temperatures of the steel rail is not accurately controlled, the performance fluctuation is large, a tempering step is omitted, the martensite is brittle, and the improvement of the service performance of the steel rail is not facilitated.
In the heat treatment process of the steel rail, due to different heat capacities at the section positions of the steel rail, the steel rail is easy to have the outstanding problems of uneven structure transformation, overlarge bending deformation degree, higher residual stress, performance difference and the like in the heat treatment process; the internal structure and structure of the material are changed and the performance of the material is also changed due to different heat exchange gradients in the heat treatment process of the steel rail, and the reasonable heat treatment process can ensure that the structure of the steel rail is uniformly changed, reduce the bending deformation, reduce the residual stress and the like.
Disclosure of Invention
The invention aims to provide a heat treatment process of a high-strength and high-toughness bainite steel rail, which can be used for producing bainite/martensite multiphase bainite steel rails and combines the excellent mechanical properties of lower bainite and martensite, so that the conventional mechanical property, wear resistance, contact fatigue wear resistance and service performance of the steel rail are improved.
In order to solve the technical problems, the invention adopts the following technical scheme:
the invention relates to a heat treatment process of a high-strength and high-toughness bainite/martensite multiphase bainite steel rail, which comprises the following steps of:
1) after the steel rail is rolled by CCS (continuous casting) at high precision, cooling the steel rail head to 710-780 ℃ in air at 1.5-3.0 ℃;
2) cooling the rail head of the steel rail to 350-420 ℃ at a cooling speed of 3.0-5.0 ℃ by using high-pressure air of 20-30 KPa;
3) cooling the rail head of the steel rail to 320-370 ℃ by air cooling at a cooling speed of 0-1.0 ℃ by using 10-20MPa weak air pressure;
4) using 5-20m3Cooling the rail head of the steel rail to 120-180 ℃ in an accelerated control mode at a cooling speed of 4.0-6.0 ℃; controlling the cooling speed of the rail web of the steel rail at 3.0-5.0 DEG CCooling to 380-470 ℃;
5) the steel rail head is cooled in air at the speed of 0.5-2 ℃ to return the temperature to 280-330 ℃; cooling the rail web of the steel rail to 310-360 ℃ at a cooling speed of 0-1.0 ℃;
6) naturally cooling the steel rail to room temperature after the steel rail reaches the maximum return temperature;
7) straightening the steel rail by adopting a horizontal and vertical composite straightening machine, wherein the straightening reduction is less than or equal to 18mm, and the straightening speed is more than or equal to 1.5 m/s;
8) and (3) heating the straightened steel rail to 250-330 ℃ in time, and carrying out tempering treatment for 10-30 h.
Further, in the step 7), the straightening of the end or the local unevenness of the steel rail can be supplemented by a press machine.
Further, the steel rail is straightened under light pressure, and the additional residual stress of the steel rail straightening is less than or equal to 150 MPa.
Further, the steel rail comprises the following chemical components in percentage by weight: 0.15-0.30%, Si: 0.60 to 1.40%, Mn: 1.60-2.60%, Cr: 0.45 to 1.30%, 0.20 to 0.70% of Ni, 0.20 to 0.60% of Mo, 0 to 0.20% of V, Nb: 0-0.06%, P is less than or equal to 0.022%, S is less than or equal to 0.015%, Al: less than or equal to 0.010 percent, and the balance of Fe and inevitable impurities.
Further, smelting, continuously casting and slowly cooling a billet; and the smelted steel billet is subjected to continuous casting billet slow cooling treatment in time within the range of 600-900 ℃, the slow cooling time is more than 60 hours, and the hydrogen content in the steel billet is further reduced.
Further, the billet is subjected to BD1, BD2 and CCS reciprocating rolling, and the rolling reduction ratio is not less than 9: 1, ensuring the grain size of the original austenite of the steel rail.
Compared with the prior art, the invention has the beneficial technical effects that:
the tensile strength of the bainite steel rail subjected to online heat treatment is 1380-1450 MPa, the yield strength is 1000-1300 MPa, the elongation is 14-19%, the impact toughness is 110-180J, the tread hardness is 420-460 HBW, the K1C at the temperature of-20 ℃ is 100-120 MPa.m1/2, and the wear resistance (weight loss) of the steel rail is 0.20g/10 ten thousand-0.30 g/10 ten thousand.
The invention avoids the structures with poor performances of upper bainite and granular bainite by controlling the cooling speed of the steel rail at different temperature stages, thereby forming a lower bainite and low-carbon martensite complex phase structure. The cooling speed and the cooling mode in different stages are controlled to ensure that the bainite/martensite multiphase bainite steel rail is subjected to sufficient structure transformation in a lower bainite interval, a certain bainite structure proportion is ensured, then low-carbon martensite structure transformation is carried out, so that a lower bainite/martensite multiphase structure with excellent mechanical property is formed, and the structure segregation (martensite segregation zone) can be effectively improved. The lower bainite/martensite multiphase structure can refine prior austenite crystal grains, reduce the interval between structure sheets and reduce the residual austenite number, so that the steel rail has the characteristics of high strength, high plasticity, high toughness, high stripping and stripping resistance, high wear resistance, high rolling contact fatigue performance and the like.
Drawings
The invention is further illustrated in the following description with reference to the drawings.
FIG. 1 is a microstructure diagram of examples 1 to 4.
Detailed Description
The steel rail of the invention takes C, Mn, Si, Cr, Ni and Mo as main alloy elements, micro-alloying elements such as Nb and V are added, and the steel rail comprises the following chemical components in percentage by weight: 0.15-0.30%, Si: 0.60 to 1.40%, Mn: 1.60-2.60%, Cr: 0.45 to 1.30%, 0.20 to 0.70% of Ni, 0.20 to 0.60% of Mo, 0 to 0.20% of V, Nb: 0-0.06%, P is less than or equal to 0.022%, S is less than or equal to 0.015%, Al: less than or equal to 0.010 percent, and the balance being Fe. The above component blanks are smelted, continuously cast and slowly cooled by steel billets. And (3) carrying out continuous casting billet slow cooling treatment on the smelted steel billet at the temperature of 600-900 ℃ in time, wherein the slow cooling time is more than 60h, and further reducing the hydrogen content in the steel billet.
2) The billet is subjected to BD1, BD2 and CCS reciprocating rolling, and the rolling reduction ratio is not less than 9: 1, ensuring the grain size of original austenite of the steel rail; the steel rail is descaled by adopting multi-stage high-pressure jet in the rolling process so as to effectively remove oxide scale and prevent surface defects caused by pressing-in of the oxide scale and abnormal reflected waves of rail web and rail bottom flaw detection.
3) And controlling the CCS finish rolling temperature of the steel rail at 920-960 ℃, and controlling the finish rolling temperature so as to ensure the grain size of the steel rail.
4) After the steel rail is rolled by CCS (continuous casting) at high precision, cooling the steel rail head to 710-780 ℃ in air at 1.5-3.0 ℃;
5) cooling the rail head of the steel rail to 350-420 ℃ at a cooling speed of 3.0-5.0 ℃ by using high-pressure air of 20-30 KPa;
6) cooling the rail head of the steel rail to 320-370 ℃ by air cooling at a cooling speed of 0-1.0 ℃ by using 10-20MPa weak air pressure;
7) using 5-20m3Cooling the rail head of the steel rail to 120-180 ℃ in an accelerated control mode at a cooling speed of 4.0-6.0 ℃; the rail web of the steel rail is controlled to be cooled to 380-470 ℃ at a cooling speed of 3.0-5.0 ℃;
8) the steel rail head is cooled in air at the speed of 0.5-2 ℃ to return the temperature to 280-330 ℃; and air cooling the rail web of the steel rail to 310-360 ℃ at a cooling speed of 0-1.0 ℃.
9) And naturally cooling the steel rail to room temperature after the steel rail reaches the maximum return temperature.
10) The steel rail is straightened by adopting a vertical and horizontal composite straightener, the straightening reduction is less than or equal to 18mm, the straightening speed is more than or equal to 1.5m/s, the straightening is only allowed once, the straightening can be supplemented by a press machine for straightening the end or local uneven straight part of the steel rail, the steel rail is straightened by adopting a light press, and the additional residual stress of the steel rail straightening is less than or equal to 150 MPa.
11) And (3) heating the straightened steel rail to 250-330 ℃ in time, and carrying out tempering treatment for 10-30 h.
TABLE 1 comparison of different heat treatment processes for the examples
Wherein, the components of the steel rails corresponding to the embodiment 1-4 are the same, and the heat treatment process comparison is carried out under the same components; the components of the steel rail are C: 0.15-0.30%, Si: 0.60 to 1.40%, Mn: 1.60-2.60%, Cr: 0.45 to 1.30%, 0.20 to 0.70% of Ni, 0.20 to 0.60% of Mo, 0 to 0.20% of V, Nb: 0-0.06%, P is less than or equal to 0.022%, S is less than or equal to 0.015%, Al: less than or equal to 0.010 percent, and the balance being Fe.
Research shows that the phase transition temperature of the lower bainite in the bainite/martensite multiphase steel rail is 340-370 ℃, and the steel rail is controlled in the phase transition region of the lower bainite at a higher cooling speed after rolling. At the moment, the surface of the steel rail is influenced by the diffusion of heat of the center part and the web part of the rail head to the surface layer of the rail head and the latent heat of phase change, the surface of the rail head is cooled at a certain speed to offset the transferred heat and the latent heat of phase change, and the long-time and synchronous isothermal transformation is ensured to be carried out at the position of 0-30mm of the steel rail, so that the aims of refining and homogenizing the structure are fulfilled. And certain temperature return temperature and low-temperature tempering treatment can be beneficial to the transformation of low-carbon martensite and the stability of residual austenite. Thereby effectively improving the mechanical property, the mechanical stability and the service performance of the steel rail and realizing the optimal matching of high strength, high toughness and plasticity and high wear resistance.
The steel rail finishes the structure phase change in the control cooling unit, so that the purpose of controlling the structure proportion of the bainite/martensite structure is achieved, the straightness of the steel rail can be effectively guaranteed, the good straightness of the steel rail can be reduced, the straightening stress caused by the straightening of the steel rail can be reduced, and the low-temperature tempering is combined, so that the residual stress of the steel rail can meet the purpose of being less than or equal to 280 MPa.
TABLE 2 mechanical properties corresponding to different heat treatment processes in the examples
As can be seen from Table 2, in the quenching unit, the cooling speed of the steel rail is controlled at different stages, so that different mechanical properties of the steel rail can be obtained. The process of embodiment 4 can ensure that the tensile strength of the steel rail is 1380-1450 MPa, the yield strength is 1000-1300 MPa, the elongation is 14-19%, the impact toughness is 110-180J, the tread hardness is 420-460 HBW, and the temperature is-20 DEG C1CAt 100-120 MPa.m1/2The wear resistance (weight loss) of the steel rail is between 0.20g/10 ten thousand and 0.30g/10 ten thousand. The heat treatment process of the invention can obtain higher strength and hardness, and the toughness and the wear resistance are improved to a certain extent, thereby leading the steel rail to achieve good toughness and wear resistance, and meeting the research and development requirements of high wear resistance and high toughness bainite/martensite multiphase bainite steel rail for heavy haul railwayAnd (6) obtaining. The steel rail produced by the process has good straightness, so that the straightness requirement of the finished steel rail can be met by using smaller straightening pressure for the steel rail, and finally the residual stress of the steel rail can reach less than or equal to 280 MPa.
As can be seen from FIG. 1, bainite steel rails produced by different heat treatment processes have different structures, and the bainite/martensite multiphase structures can be obtained in the examples 1 to 4. However, the heat treatment process of example 4 can obtain a lower bainite + tempered martensite structure, and the process can refine grains of a complex phase structure, make the structure more uniform, make the space between the structure pieces finer, and effectively improve the structure segregation (martensite segregation zone). The uniformly refined shell/martensite multiphase structure can effectively improve the mechanical property of the steel rail, so that the steel rail has high strength, high plasticity, high toughness, high anti-stripping and anti-stripping performance, high wear resistance and excellent service performance.
The above-described embodiments are merely illustrative of the preferred embodiments of the present invention, and do not limit the scope of the present invention, and various modifications and improvements of the technical solutions of the present invention can be made by those skilled in the art without departing from the spirit of the present invention, and the technical solutions of the present invention are within the scope of protection defined by the claims.
Claims (6)
1. A heat treatment process of a high-strength and high-toughness bainite/martensite multiphase bainite steel rail is characterized by comprising the following steps of:
1) after the steel rail is rolled by CCS (continuous casting) at high precision, cooling the steel rail head to 710-780 ℃ in air at 1.5-3.0 ℃;
2) cooling the rail head of the steel rail to 350-420 ℃ at a cooling speed of 3.0-5.0 ℃ by using high-pressure air of 20-30 KPa;
3) cooling the rail head of the steel rail to 320-370 ℃ by air cooling at a cooling speed of 0-1.0 ℃ by using 10-20MPa weak air pressure;
4) using 5-20m3Cooling the rail head of the steel rail to 120-180 ℃ in an accelerated control mode at a cooling speed of 4.0-6.0 ℃; the rail web of the steel rail is controlled to be cooled to 380-470 ℃ at a cooling speed of 3.0-5.0 ℃;
5) the steel rail head is cooled in air at the speed of 0.5-2 ℃ to return the temperature to 280-330 ℃; cooling the rail web of the steel rail to 310-360 ℃ at a cooling speed of 0-1.0 ℃;
6) naturally cooling the steel rail to room temperature after the steel rail reaches the maximum return temperature;
7) straightening the steel rail by adopting a horizontal and vertical composite straightening machine, wherein the straightening reduction is less than or equal to 18mm, and the straightening speed is more than or equal to 1.5 m/s;
8) and (3) heating the straightened steel rail to 250-330 ℃ in time, and carrying out tempering treatment for 10-30 h.
2. The heat treatment process of the high-strength ductile bainite/martensite duplex bainite steel rail in claim 1, wherein in the step 7), the steel rail end or local unevenness can be straightened by a press.
3. The heat treatment process of the high-strength and high-toughness bainite and martensite multiphase bainite steel rail according to claim 2, wherein the steel rail is straightened under a light pressure, and the additional residual stress of the steel rail straightening is less than or equal to 150 MPa.
4. The heat treatment process of the high-strength and high-toughness bainite and martensite multiphase bainite steel rail according to claim 1, wherein the steel rail comprises the following chemical components in percentage by weight: 0.15-0.30%, Si: 0.60 to 1.40%, Mn: 1.60-2.60%, Cr: 0.45 to 1.30%, 0.20 to 0.70% of Ni, 0.20 to 0.60% of Mo, 0 to 0.20% of V, Nb: 0-0.06%, P is less than or equal to 0.022%, S is less than or equal to 0.015%, Al: less than or equal to 0.010 percent, and the balance of Fe and inevitable impurities.
5. The heat treatment process of the high-strength high-toughness bainite/martensite duplex phase bainite steel rail according to claim 4, wherein the billet is subjected to smelting, continuous casting and billet slow cooling; and the smelted steel billet is subjected to continuous casting billet slow cooling treatment in time within the range of 600-900 ℃, the slow cooling time is more than 60 hours, and the hydrogen content in the steel billet is further reduced.
6. The heat treatment process of the high-toughness bainite/martensite duplex phase bainite steel rail according to claim 5, wherein the steel billet is subjected to BD1, BD2 and CCS reciprocating rolling, and the rolling reduction ratio is not less than 9: 1, ensuring the grain size of the original austenite of the steel rail.
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| CN114908297A (en) * | 2022-06-06 | 2022-08-16 | 内蒙古科技大学 | Bainite/martensite complex phase heavy rail steel for reducing fatigue crack propagation rate and method thereof |
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