Patent Application
20080060726
The present invention relates to a heat treatment method of steel rail and a heat treatment apparatus of steel rail using the method.
There have been increasing requirements for steel rails as the railway transportation tends to high speed and heavy load. Years of study and application practice have shown: the heat treatment can produce fine pearlite metallographic structure of steel rails and afford desired mechanical properties to steel rails; it is a powerful means for improving service life of steel rails. In the prior art, there are mainly two ways for heat treatment of steel rails: one way is to reheat the rolled steel rail finished product having normal temperature (also referred to as “off-line heat treatment process”); Another way is to utilize the residual heat of rolling process to heat the steel rails on the steel rolling production line (also referred to as “on-line heat treatment process”). These techniques can be seen from the content disclosed in CN 1083013C and the References cited in the Background Part of CN 1083013C, which are incorporated herein by reference.
The off-line heat treatment process can afford fine pearlitic microstructure and therefore the hardened layer may have higher strength, toughness and hardness because the rolled steel rail experiences two phase transition processes. However, the off-line heat treatment process has the following inherent drawbacks: high energy consumption, shallow hardened layer, existence of a softened belt in the transitional zone between the hardened layer and the non-hardened layer, and low steel rail straightness since the steel rail straightness is ensured by roller straightening which can only be carried out once for the same steel rail; the steel rail has been roller straightened before heat treatment, and therefore it can't be roller straightened again after heat treatment.
The on-line heat treatment process is featured with low energy consumption, deep hardened layer, smooth transition of structure and hardness of the rail head of steel rail, free of hardness caving and softened belt, and high straightness. However, the on-line heat treatment process has the following inherent drawbacks: the rolled steel rail experiences only one phase transition process, and therefore the obtained metallographic structure is not so fine as that of the steel rails treated through off-line heat treatment process.
An object of the present invention is to provide a heat treatment method of steel rail, which can not only make the metallographic structure of the produced steel rails more fine to improve service life of the steel rails, but also reduce energy consumption and steel rail heat treatment cost.
Accordingly, the present invention provides a heat treatment method of steel rail, comprising the following steps: (1) keeping the rolled hot steel rail running continuously, and performing hot straightening process for it; (2) performing the first heat treatment process for the rolled hot steel rail after the hot straightening process, i.e., forced cooling the rail head and the rail base of the steel rail in a jetting air cooling manner; and (3) performing second heat treatment process for the steel rail after the first heat treatment process, i.e., heating the rail head of the steel rail to a temperature of 850˜950° C., and then forced cooling the rail head of the steel rail in a jetting air cooling manner to a temperature that is close to the temperature of the rail base of the steel rail.
The present invention also provides a heat treatment apparatus of steel rail, which is arranged following the steel rail rolling production line, comprising a front supporting unit, a hot straightening unit, a first air cooling unit, a heating unit, and a second air cooling unit that are arranged in the order of the heat treatment processes of the steel rail.
The present invention has the following benefits: since the steel rail experiences the second heat treatment process by reheating just after it is heat treated using the residual heat of rolling, phase transition occurs in the steel rail in the two rapid cooling processes, and finer metallographic structure is obtained in the steel rail, and thereby the wear resistant property, contact fatigue resistant property, and service life of the steel rail are improved and are higher than those of the heat-treated steel rails produced through the prior on-line heat treatment process or off-line heat treatment process. When the steel rail experiences the second heat treatment process, the rail web and the middle part of the rail head have already been at high temperature, therefore the energy consumption in reheating can be reduced by 70% compared with the off-line heat treatment process; therefore, the steel rail production cost can be reduced.
1. steel rail; 2. extended roller track of the rolling production line; 10. front supporting unit; 11. steel rail tilter; 12. front roller track; 13. steel rail lifter; 20. hot straightening unit; 21. active straightening roller; 22. passive straightening roller; 30. first air cooling unit; 31. first jetting air cooler; 32. second jetting air cooler, 33. third jetting air cooler; 34. upper guide mechanism; 35. lower guide mechanism; 40. translating unit; 41. quick steel raising and shifting machine; 50. heating unit; 51. intermediate frequency induction heater; 52. upper guide mechanism; 53. lower guide mechanism; 60. second air cooling unit; 70. collection rack.
Hereunder, the present invention will be described in detail according to the embodiments with reference to the accompanying drawings.
The heat treatment method of steel rail provided in the present invention comprises the following steps:
(1) keeping the rolled hot steel rail running continuously, and performing hot straightening process for it;
(2) performing the first heat treatment process for the rolled hot steel rail after the hot straightening process, i.e., forced cooling the rail head and the rail base of the steel rail in a jetting air cooling manner; and
(3) performing second heat treatment process for the steel rail after the first heat treatment process, i.e., heating the rail head of the steel rail to a temperature of 850˜950° C., and then forced cooling the rail head of the steel rail in a jetting air cooling manner to a temperature that is close to the temperature of the rail base of the steel rail.
Generally speaking, a steel rail comprises the rail head, the rail web and the rail base along the cross section; wherein, the rail head refers to the head part facing upwards when the steel rail is mounted; the rail base refers to the bottom part that is connected to the ground base; the rail web refers to the middle part between the rail head and the rail base.
Generally, the rolled hot steel rail is at 800° C. temperature or above, for example, 860˜1200° C. During hot straightening process, the steel rail temperature can be equal to or slightly lower than the temperature after rolling process, for example, 750˜850° C. In the first heat treatment process at said step (2), the rail head and rail base may be cooled at a rate of 1˜5° C./s for 90˜130 s preferably; and the temperature after cooling is 450˜600° C. preferably. In the second heat treatment process at said step (3), the rail head is cooled at a rate of 1˜5° C./s for 90˜130 s preferably; and the temperature after cooling is 450˜600° C. preferably. In said second heat treatment process, preferably an intermediate frequency induction heater can be used to heat the rail head.
After the second heat treatment process at said step (3), subsequent finishing works can be performed for the steel rail after the steel rail is cooled to the normal temperature.
In the heat treatment method of steel rail provided in the present invention, since the steel rail experiences the second heat treatment process by reheating just after it is heat treated using the residual heat of rolling, phase transition occurs in the steel rail in the two rapid cooling processes, and finer metallographic structure is obtained in the steel rail, and thereby the wear resistant property, contact fatigue resistant property, and service life of the steel rail are improved and are higher than those of the heat-treated steel rails produced through the prior on-line heat treatment process or off-line heat treatment process. When the steel rail experiences the second heat treatment process, the rail web and the middle part of the rail head have already been at high temperature, therefore the energy consumption in reheating can be reduced by 70% compared with the off-line heat treatment process; therefore, the steel rail production cost can be reduced.
Chemical composition of steel rail: C: 0.71˜0.80%; Si: 0.50˜0.80%; Mn: 0.75˜1.05%; P: ≦0.030%; S: ≦0.030%; V: 0.04˜0.12%, the rest: iron and trace impurities. The steel rail heat treatment processes are: when the rolled hot steel rail is cooled to a temperature of 810° C.˜790° C., perform hot straightening on the steel rail; perform first heat treatment process, i.e., forced cooling the rail head and the rail base of the steel rail in a jetting air cooling manner at a rate of about 3° C./s to a temperature of about 550° C.; perform the second heat treatment process, i.e., heat the rail head to a temperature of 870° C., and then forced cooling the rail head in a jetting air cooling manner at a rate of about 3° C./s to the temperature close to the rail base temperature (about 450° C.); after the steel rail is cooled to the normal temperature, perform subsequent finishing works for the steel rail. After the two heat treatment processes, the mechanical properties of the steel rail are: yield strength Rp0.2≧900 MPa, tensile strength Rm≧1300 MPa, and elongation A≧12%.
Chemical composition of steel rail: C: 0.65˜0.77%; Si: 0.15˜0.35%; Mn: 1.10˜1.50%; P: ≦0.035%; S: ≦0.035%; the rest: iron and trace impurities. The steel rail heat treatment processes are: when the rolled hot steel rail is cooled to a temperature of 810° C.˜790° C., perform hot straightening to the steel rail; perform first heat treatment process, i.e., forced cooling the rail head and the rail base in a jetting air cooling manner at a rate of about 3° C./s to a temperature of about 550° C.; perform second heat treatment process, i.e., heat the rail head to a temperature of 870° C., and then forced cooling the rail head in a jetting air cooling manner at a rate of about 3° C./s to the temperature close to the rail base temperature (about 450° C.); after the steel rail is cooled to the normal temperature, perform subsequent finishing works for the steel rail. The mechanical properties of the steel rail are: Rp0.2≧800 MPa, Rm≧1200 MPa, and A≧10%.
Hereunder, the present heat treatment apparatus of steel rail will be described in the embodiments, with reference to the accompanying drawings.
As shown in
The front supporting unit 10, the hot straightening unit 20, the first air cooling unit 30, the heating unit 50, the second air cooling unit 60, and the collection rack 70 can be arranged in different layout schemes, depending on the condition in the production workshop.
As shown in
Alternatively, as shown in
Hereunder, the units of the heat treatment apparatus of steel rail will be described in the embodiments, with reference to the accompanying drawings.
The second air cooling unit 60 can be in the same structure as the first air cooling unit 30; therefore, the drawing and description thereof is omitted here. In addition, the guide mechanisms and the jetting air coolers are known to those skilled in the art, and therefore will not be described further here.
The collection rack 70 is provided to receive the steel rail 1 after heat treatment, so that the steel rail 1 is cooled to the normal temperature on the collection rack 70 and then treated through subsequent straightening, rail end machining, inspection, and finishing works; finally, heat-treated steel rails with long service life will be provided for the railway use.
Hereunder, the application of the heat treatment apparatus of steel rail in the present invention will be further described.
As shown in
When the steel rail 1 is cooled to the temperature of about 810° C.˜790° C., it is conveyed through the front roller track 12 to the hot straightening unit in the direction indicated by the arrow in
As shown in
As shown in
As shown in
As shown in
After the steel rail 1 is cooled to the normal temperature on the collection rack 70, it can be treated through straightening, rail end machining, inspection, and finishing processes; therefore, heat-treated steel rails with long service life can be provided for railway use.
Although the invention has been described with respect to specific embodiments, the details are not to be construed as limitations, for it will become apparent that various embodiments, changes and modifications may be resorted to without departing from the spirit and scope thereof, and it is understood that such equivalent embodiments are intended to be included within the scope of this invention.
| Number | Date | Country | Kind |
|---|---|---|---|
| 200610021821.9 | Sep 2006 | CN | national |
This application claims priority under 35 U.S.C. § 119 from Chinese Patent Application No. 200610021821.9 filed on Sep. 12, 2006, the disclosure of which is incorporated herein by reference in its entirety.
