CN114749619A - Short-flow production process of high-purity, high-precision and low-residual-stress steel rail - Google Patents
Short-flow production process of high-purity, high-precision and low-residual-stress steel rail Download PDFInfo
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- CN114749619A CN114749619A CN202210464907.8A CN202210464907A CN114749619A CN 114749619 A CN114749619 A CN 114749619A CN 202210464907 A CN202210464907 A CN 202210464907A CN 114749619 A CN114749619 A CN 114749619A
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- B—PERFORMING OPERATIONS; TRANSPORTING
- B22—CASTING; POWDER METALLURGY
- B22D—CASTING OF METALS; CASTING OF OTHER SUBSTANCES BY THE SAME PROCESSES OR DEVICES
- B22D11/00—Continuous casting of metals, i.e. casting in indefinite lengths
- B22D11/009—Continuous casting of metals, i.e. casting in indefinite lengths of work of special cross-section, e.g. I-beams, U-profiles
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- B—PERFORMING OPERATIONS; TRANSPORTING
- B21—MECHANICAL METAL-WORKING WITHOUT ESSENTIALLY REMOVING MATERIAL; PUNCHING METAL
- B21B—ROLLING OF METAL
- B21B1/00—Metal-rolling methods or mills for making semi-finished products of solid or profiled cross-section; Sequence of operations in milling trains; Layout of rolling-mill plant, e.g. grouping of stands; Succession of passes or of sectional pass alternations
- B21B1/08—Metal-rolling methods or mills for making semi-finished products of solid or profiled cross-section; Sequence of operations in milling trains; Layout of rolling-mill plant, e.g. grouping of stands; Succession of passes or of sectional pass alternations for rolling structural sections, i.e. work of special cross-section, e.g. angle steel
- B21B1/085—Rail sections
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- B—PERFORMING OPERATIONS; TRANSPORTING
- B22—CASTING; POWDER METALLURGY
- B22D—CASTING OF METALS; CASTING OF OTHER SUBSTANCES BY THE SAME PROCESSES OR DEVICES
- B22D11/00—Continuous casting of metals, i.e. casting in indefinite lengths
- B22D11/001—Continuous casting of metals, i.e. casting in indefinite lengths of specific alloys
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- B—PERFORMING OPERATIONS; TRANSPORTING
- B22—CASTING; POWDER METALLURGY
- B22D—CASTING OF METALS; CASTING OF OTHER SUBSTANCES BY THE SAME PROCESSES OR DEVICES
- B22D11/00—Continuous casting of metals, i.e. casting in indefinite lengths
- B22D11/04—Continuous casting of metals, i.e. casting in indefinite lengths into open-ended moulds
- B22D11/045—Continuous casting of metals, i.e. casting in indefinite lengths into open-ended moulds for horizontal casting
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- B—PERFORMING OPERATIONS; TRANSPORTING
- B22—CASTING; POWDER METALLURGY
- B22D—CASTING OF METALS; CASTING OF OTHER SUBSTANCES BY THE SAME PROCESSES OR DEVICES
- B22D11/00—Continuous casting of metals, i.e. casting in indefinite lengths
- B22D11/16—Controlling or regulating processes or operations
- B22D11/18—Controlling or regulating processes or operations for pouring
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- C—CHEMISTRY; METALLURGY
- C21—METALLURGY OF IRON
- C21C—PROCESSING OF PIG-IRON, e.g. REFINING, MANUFACTURE OF WROUGHT-IRON OR STEEL; TREATMENT IN MOLTEN STATE OF FERROUS ALLOYS
- C21C5/00—Manufacture of carbon-steel, e.g. plain mild steel, medium carbon steel or cast steel or stainless steel
- C21C5/52—Manufacture of steel in electric furnaces
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- C—CHEMISTRY; METALLURGY
- C21—METALLURGY OF IRON
- C21C—PROCESSING OF PIG-IRON, e.g. REFINING, MANUFACTURE OF WROUGHT-IRON OR STEEL; TREATMENT IN MOLTEN STATE OF FERROUS ALLOYS
- C21C7/00—Treating molten ferrous alloys, e.g. steel, not covered by groups C21C1/00 - C21C5/00
- C21C7/0075—Treating in a ladle furnace, e.g. up-/reheating of molten steel within the ladle
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- C—CHEMISTRY; METALLURGY
- C21—METALLURGY OF IRON
- C21C—PROCESSING OF PIG-IRON, e.g. REFINING, MANUFACTURE OF WROUGHT-IRON OR STEEL; TREATMENT IN MOLTEN STATE OF FERROUS ALLOYS
- C21C7/00—Treating molten ferrous alloys, e.g. steel, not covered by groups C21C1/00 - C21C5/00
- C21C7/04—Removing impurities by adding a treating agent
- C21C7/072—Treatment with gases
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- C—CHEMISTRY; METALLURGY
- C21—METALLURGY OF IRON
- C21C—PROCESSING OF PIG-IRON, e.g. REFINING, MANUFACTURE OF WROUGHT-IRON OR STEEL; TREATMENT IN MOLTEN STATE OF FERROUS ALLOYS
- C21C7/00—Treating molten ferrous alloys, e.g. steel, not covered by groups C21C1/00 - C21C5/00
- C21C7/10—Handling in a vacuum
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- C—CHEMISTRY; METALLURGY
- C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
- C22C—ALLOYS
- C22C33/00—Making ferrous alloys
- C22C33/04—Making ferrous alloys by melting
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- C—CHEMISTRY; METALLURGY
- C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
- C22C—ALLOYS
- C22C38/00—Ferrous alloys, e.g. steel alloys
- C22C38/02—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
- C22C38/24—Ferrous alloys, e.g. steel alloys containing chromium with vanadium
Abstract
The invention discloses a short-flow production process of a high-purity high-precision low-residual stress steel rail, which sequentially comprises the following steps: an electric furnace + LF + VD smelting + vacuum horizontal continuous casting + near-net shape continuous casting special-shaped blank process is adopted to replace the prior long-flow blast furnace + converter + LF + VD (RH) + continuous casting + bloom process; the steel rolling adopts a multi-frame universal mill rolling, full universal finish rolling, online heat treatment and stretching straightening process. The prior cogging rolling, universal rough rolling, universal middle rolling, semi-universal finish rolling and roller straightening process is replaced. The steel rail produced by the process improves the purity and the dimensional precision of the steel rail, reduces the residual stress and prolongs the fatigue life of the steel rail.
Description
Technical Field
The invention relates to a production process of a steel rail, in particular to a production process of a steel rail with high purity, high precision and low residual stress.
Background
The steel rail is an important basic material required by the railway, the quality and the performance of the steel rail are directly related to the safety of railway transportation, particularly, the requirements on the quality and the performance of the steel rail are further improved along with the development of high-speed heavy-duty railways, the purity and the size precision of the steel rail are key problems on the safety of railway traffic, and the fatigue life of the steel rail is influenced due to the fact that the steel rail is damaged by stripping, block falling and the like because of large inclusions and residual stress, so that the problem is worldwide difficult.
At present, the production process of steel rails in various countries in the world adopts a long-flow process, namely, a blast furnace, a converter, refining, vacuum degassing, continuous casting of a large square billet, cogging of a cogging mill, rolling in a universal mill, semi-universal finish rolling, straightening of a horizontal and vertical combined straightening machine, ultrasonic flaw detection and mechanical processing. The main problems with this process are:
(1) long process, high energy consumption and serious environmental pollution.
(2) In the smelting and pouring process, molten steel is easy to be polluted and secondarily oxidized, so that impurities in the steel are caused, the fatigue life of the steel rail is shortened, and the steel rail is damaged.
(3) As shown in fig. 2, a common continuous casting billet has a rectangular cross section 1, but the pass design of a cogging mill adopts asymmetric and uneven deformation, and even if the rear part adopts a universal pass design, the asymmetry of the billet coming out of the cogging mill can be corrected, but the symmetry of the rail cross section and the integrity of the profile are still difficult to ensure, and the geometric dimensional precision of the rail is influenced.
(4) The steel rail is straightened by adopting the horizontal and vertical combined straightening process, and the repeated bending is adopted to straighten the steel rail, so that the process has large straightening pressure, causes large residual stress of the steel rail, reduces the fatigue resistance of the steel rail and influences the service life of the steel rail.
The other process is to produce steel by an electric furnace plus LF plus VD (RH), produce a special-shaped blank by vacuum horizontal continuous casting, adopt full universal rolling and adopt stretching and straightening. The vacuum horizontal continuous casting near-net-shape blank, all-universal rolling and stretching straightening process can raise the purity and size precision of steel rail, reduce residual stress and prolong the fatigue resisting life of steel rail
In view of the above, the present invention is particularly proposed.
Disclosure of Invention
The invention aims to provide a novel production process of a fatigue-resistant steel rail with high purity, high dimensional accuracy and low residual stress for a steel rail for a high-speed heavy haul railway.
The invention discloses a short-process steel rail production process, which aims at solving the problems existing in the existing long-process, provides a brand-new steel rail production process, and comprises technical innovations in smelting, rolling and processing, so that the performance of a steel rail is comprehensively improved.
In order to realize the purpose, the production process of the steel rail with high purity, high dimensional precision and low residual stress sequentially comprises the steps of smelting, continuous casting, heating, primary rolling, intermediate rolling, finish rolling, cooling, straightening and online heat treatment;
the smelting adopts an electric furnace + LF + VD (RH), the continuous casting adopts vacuum horizontal continuous casting of a special-shaped blank, the rolling adopts full-universal rolling, and the straightening adopts stretching and straightening.
The vacuum horizontal continuous casting is to continuously cast the molten steel under the condition of ensuring the vacuum degree to be 1Pa, prevent the molten steel from being secondarily oxidized to generate inclusions in the casting process, and simultaneously can reduce the content of various harmful gases, wherein A, B, C, D inclusions in the steel rail are required to be controlled to be less than 1 grade, so that the contents of H, 0 and N elements in the steel rail respectively reach below 1ppm, 5ppm and 12ppm, and the purity of the steel rail reaches the pure steel level. The vacuum horizontal continuous casting is that the tundish and the crystallizer work under the vacuum condition, so that the molten steel is prevented from being oxidized.
Meanwhile, because the near-net-shape special-shaped blank is directly cast continuously, the rolling passes are reduced, and the dimensional precision of the steel rail is improved.
The invention adopts a new rolling process of a universal rolling mill, which comprises the following steps: the universal hole type system and the rolling mill are composed of a universal rough rolling unit, a universal middle rolling unit and a universal finishing rolling unit, and particularly, the universal finishing rolling unit adopts a universal design; because the whole universal hole type system adopts a symmetrical design, the deformation of the steel billet is uniform and symmetrical, the symmetry of the section of the steel rail is improved, and the dimensional precision is improved.
The invention adopts a new technology of straightening the steel rail by stretching, the straightening principle of the invention is fundamentally different from the prior horizontal and vertical combined straightening, and the invention is a brand new steel rail straightening technology. It applies pulling force to two ends of the rail, and when the pulling force exceeds the yield strength of the rail, the original fibers with different lengths along the length direction of the rail can be changed into fibers with the same length, thereby straightening the rail. The residual stress of the stretching straightening process is extremely low and is similar to that of a hot-rolled steel rail. The roller type straightening process is to straighten the steel rail by repeatedly bending the steel rail, the straightened steel rail has great tensile stress at the rail head and the rail bottom, and the tensile stress is superposed with the contact stress of the wheel rail when a train passes through, so that the fatigue damage of the steel rail is often caused. The tensile straightening can not cause large tensile stress of the steel rail, but also can improve the yield strength of the steel rail, is beneficial to overcoming the abrasion and stripping of the steel rail and falling of blocks, and prolongs the service life of the steel rail.
Compared with the prior art, the process has the beneficial effects that: the steel rail has less impurities, high purity, high rail shape precision and small residual stress.
Drawings
FIG. 1 is a process flow diagram of the present invention;
FIG. 2 is a cross section of a near-net-shape continuous casting special-shaped blank, a cross section of a continuous rectangular blank and a cross section of a finished product;
FIG. 3 is a schematic view of a rolling process of a universal unit;
FIG. 4 is a schematic view of a stretch straightener;
FIG. 5 is a schematic view of a vacuum horizontal continuous casting apparatus.
Detailed Description
The present invention will be further described with reference to the following specific embodiments and accompanying drawings to assist in understanding the contents of the invention.
The embodiment is a high-purity, high-dimensional precision and low-residual stress steel rail
As shown in fig. 1, the production method comprises the following steps in sequence:
(1) smelting: the smelting alloy comprises the following components in percentage by weight: 0.70-0.80 percent of C, 80-0.90 percent of Mn, 0.6-0.75 percent of Si, 0.80-1.0 percent of Cr, 0.12-0.15 percent of V and the balance of Fe. After molten steel is smelted by an electric arc furnace, LF refining and VD vacuum degassing are carried out, and then a near-net-shape special-shaped continuous casting billet is cast by a vacuum horizontal continuous casting machine with the vacuum degree of 1Pa, so that the contents of [ o ], [ H ], [ N ] in the steel are effectively controlled to be respectively less than 5ppm, 1ppm and 12 ppm.
The steel making adopts high-quality scrap steel as raw materials, in order to ensure the stable quality of molten steel and improve the steel making efficiency, the scrap steel is sorted and preheated, the preheating uses high-temperature furnace gas of an electric furnace, and the preheated scrap steel is sent to the electric furnace for charging.
The (ultra) high power electric furnace is selected to have a furnace capacity of over 100 tons according to the design productivity and economic efficiency of the steel rail, and the annual output is about 60 ten thousand tons. The electric furnace is provided with a nozzle specially used for blowing lime or carbon powder and an oxygen supply burner nozzle, and is used for blowing oxygen to melt scrap steel and reducing carbon. The tilting device for tapping and deslagging of the electric furnace has the steel retaining operation function. The ladle transport vehicle is provided with a ladle preheater and a ladle transport vehicle with a weighing sensor.
(2) LF refining: the refining furnace LF has the functions of heating molten steel, blowing argon, fine adjusting components and the like, a top cover of the refining furnace LF is provided with a wire feeding hole, and a furnace bottom of the refining furnace LF is provided with a gas permeable brick for blowing argon and stirring the molten steel.
(3) VD refining: a vacuum degassing VD pot was used. After the cover of the tank is closed, the vacuum degree in the tank reaches vacuum less than 30Pa through a multi-stage steam jet pump, and molten steel is degassed. The temperature of the molten steel can be adjusted and the components can be adjusted by wire feeding while degassing. The content of hydrogen in the molten steel after vacuum treatment is less than 1.5ppm, the content of nitrogen is less than 50ppm, the content of oxygen is less than 15ppm, and the number of inclusions in the molten steel is reduced by more than 90%.
(4) Vacuum horizontal near-net shape continuous casting: as shown in FIG. 5, in a vacuum horizontal continuous casting apparatus having a tundish 11 containing molten steel 20 in a vacuum vessel 10, a vacuum pump 12 at the top for vacuum pumping of the vacuum vessel, the vacuum degree of the apparatus is 1Pa during operation, and an argon blowing device 13 at the bottom of the tundish 11 having a large capacity in the vacuum vessel for blowing Ar is provided. A sealing connection is provided between the tundish 11 and the mould 15, and a separating ring 14 is provided between the two to control the flow of molten steel. The crystallizer 15 is composed of an integral copper sleeve section and water mist cooling, the crystallizer 15 is of a near-net-shape casting blank section long-type multi-stage design, and a surface shot blasting device is installed at an outlet of the crystallizer 15. An electromagnetic stirring device is arranged at the second cooling section, a blank drawing device 17 is controlled by a hydraulic servo system to control the drawing speed of the steel blank 16, and the casting blank is cut into fixed length by adopting flame.
As shown in figure 2, the section 2 of the billet formed after the vacuum horizontal continuous casting is a near-final continuous casting section, namely, the section is close to the section 3 of a final finished product steel rail, and the billet always adopts a symmetrical billet shape, so that the rolling passes are few, and the precision is high.
And conveying the cut casting blank to a cooling bed through a roller way, and conveying the casting blank to a heating furnace for heating after the cooling bed is checked. The heating capacity of the heating furnace is matched with the capacity of the rolling mill. The heating furnace adopts a non-oxidation atmosphere design, so that the surface quality of the casting blank is ensured.
(5) Rolling by a full universal machine set: the casting blank needs to be subjected to high-pressure water dephosphorization for many times before and during rolling. As shown in fig. 3, the required rail model blank is first rough rolled in the universal rough rolling mill train 4. After the head and the tail are cut, the steel is sent to a universal middle rolling mill unit 5 to be rolled into a shape which is more approximate to the shape of a finished product; and finally, sending the blank to a universal finishing mill unit 6 for finishing. The universal hole type system is symmetrically designed, so that the size and the appearance of the steel rail can meet the standard requirements. The whole all-purpose rolling is realized by the online control of a computer.
(6) Head and tail cutting printing: and cutting off the rail type nonstandard parts of the head and the tail of the rail, and printing the rail.
(7) Online heat treatment: and directly conveying the printed steel rail needing heat treatment to a heat treatment line for on-line quenching or tempering treatment. The heat treatment production line carries out on-line treatment on the microstructure required by the steel rails made of different materials. The production line has the functions of controllable heating and cooling speed.
(8) And (3) cooling: and naturally cooling the steel rail subjected to heat treatment or the steel rail not required to be subjected to heat treatment to room temperature.
(9) Stretching and straightening: after cooling, the stretching straightener applies pulling force to the two ends of the steel rail, as shown in fig. 4, the hydraulic cylinders 7 of the stretching straightener fix the two ends of the steel rail 8 through the chucks 9, and the two hydraulic cylinders 7 apply pulling force to the two ends of the steel rail. The tensile force exceeds the yield strength of the steel rail, so that the original fibers with different lengths of the steel rail along the length direction are changed into the same length, the steel rail is straightened, and the straightness of the steel rail reaches the standard requirement.
The straightening force of the stretching straightener is 1000 tons, and the steel rails with various sections can be straightened.
(10) Shot peening: and performing shot peening strengthening on the steel rail.
(11) Quality inspection: the straightened steel rail enters a detection center, and the steel rail is detected in the detection center as follows:
-using laser ruler to measure flatness of full length of rail in horizontal and vertical directions
-inspection of rail surface quality using eddy current inspection apparatus
-inspection of rail internal defects using ultrasonic waves
(12) Drilling by using a milling head: and finally processing the steel rail qualified by inspection, and milling and drilling by using a hard alloy sawing and drilling machine tool.
(13) Finished product inspection, warehousing and tracking: and finally inspecting the machined steel rail before delivery, and issuing a quality guarantee certificate for qualified persons. Warehousing qualified persons, delivering according to a contract, and tracking the use condition after delivery.
The management, operation and various detections of the whole production line are under the control of artificial intelligence and big data, and the on-line computer management and regulation are realized. The system has the functions of self-learning, self-adaption and self-control. The coordination and unification of the whole production and operation system from raw material storage, fuel storage, steel making, steel rolling and finished product delivery are achieved, and all automatic intelligent precise management is achieved.
(14) The result of the detection
After vacuum horizontal continuous casting is carried out, the high vacuum degree of a vacuum tank is controlled, and the hydrostatic pressure of molten steel is reduced by adopting horizontal continuous casting, so that the probability of oxidizing the molten steel in a tundish is reduced, the amplitude of non-metallic inclusions in the steel rail is greatly reduced, and the detection result is as follows:
TABLE 1 grade of nonmetallic inclusions in rails
Through adopting the pneumatic cylinder to give the chuck with pulling force, rethread chuck is stretched the rail, makes the rail reach straight back from crooked state, through tensile aligning back, and rail residual stress reduces than the roller-type aligning, and the testing result is as follows 2:
TABLE 2 residual stress values of different technological rail parts
| Straightening method | Rail head (MPa) | Rail waist (MPa) | Rail bottom (MPa) |
| Hot rolling | +39 | -20～+30 | +70 |
| Roller type straightening process | +290 | -110～-140 | +210 |
| Stretching and straightening process | +10 | -18～-21 | 0 |
The gas content of the steel rail is reduced compared with the gas content of the steel rail by degassing and vacuum continuous casting the molten steel so that the gas originally melted in the molten steel escapes from the molten steel, and the measurement results of the gas content of the steel rail are shown in the following table 3:
TABLE 3 content value of H, O, N in steel rail by different continuous casting processes
| [H]ppm | [O]ppm | [N]ppm | |
| Target | 1.5 | 10 | 20 |
| Ordinary continuous casting process | 1.5 | 18 | 30 |
| Vacuum horizontal continuous casting process | 0.8 | 5 | 12 |
The yield strength of the steel rail is improved after the steel rail is stretched and straightened, and the performance of the steel rail is measured as shown in the following table 4:
TABLE 4 mechanical Properties of rails for different straightening processes
| Yield strength (MPa) | Tensile Strength (MPa) | |
| Hot-rolled rail | 512 | 960 |
| Roller type straightening process | 483 | 945 |
| Tension straightening process | 596 | 957 |
The near-net-shape beam blank and the full universal process are adopted, the dimensional accuracy of the steel rail is improved, and the measurement of the steel rail dimension is shown in the table 5:
TABLE 5 specification and size of steel rail for different rolling process
Claims (6)
1. A short-flow production process for high-purity, high-precision and low-residual-stress steel rails, which comprises the following steps:
smelting, continuous casting, heating, primary rolling, intermediate rolling, finish rolling, cooling, straightening and online heat treatment;
the smelting adopts an electric furnace + LF + VD (RH), the continuous casting adopts vacuum horizontal continuous casting of a special-shaped blank, the rolling adopts full-universal rolling, and the straightening adopts stretching and straightening.
2. The production process according to claim 1, wherein: the vacuum horizontal continuous casting is adopted to continuously cast molten steel under the condition of ensuring the vacuum degree of 1Pa, the level of impurities in steel is reduced, A, B, C, D impurities in the steel rail are required to be controlled to be less than 1 grade, the contents of H, 0 and N elements in the steel rail respectively reach below 1ppm, 5ppm and 12ppm, and the purity of the steel rail reaches the level of pure steel.
3. The production process according to claim 1, wherein: the universal hole type system and the rolling mill are composed of a universal rough rolling unit, a universal middle rolling unit and a universal finishing rolling unit, and the whole universal hole type system is symmetrically designed.
4. The production process according to claim 1, wherein: the stretching and straightening is to apply pulling force to two ends of the steel rail, and the pulling force exceeds the yield strength of the steel rail, so that the original fibers with different lengths of the steel rail along the length direction are changed into the same length, and the steel rail is straightened.
5. The production process according to claim 1, wherein: the vacuum horizontal continuous casting realizes purity control through a vacuum horizontal continuous casting device, a tundish containing molten steel is arranged in a vacuum tank, a vacuum pump is arranged at the top of the vacuum tank for vacuumizing, the vacuum degree of the equipment during working reaches 1Pa, an argon blowing device is arranged at the bottom of the high-capacity tundish in the vacuum tank for blowing Ar, the tundish and the crystallizer are connected in a sealing way, and a separating ring is arranged between the tundish and the crystallizer for controlling the flow of the molten steel.
6. The production process according to claim 5, wherein: the crystallizer is formed by an integral copper sleeve section and water mist cooling, the crystallizer adopts a near-net casting blank section long multi-stage design, and a surface shot blasting device is arranged at the outlet of the crystallizer.
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| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| CN202210464907.8A CN114749619A (en) | 2022-04-29 | 2022-04-29 | Short-flow production process of high-purity, high-precision and low-residual-stress steel rail |
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|---|---|---|---|
| CN202210464907.8A CN114749619A (en) | 2022-04-29 | 2022-04-29 | Short-flow production process of high-purity, high-precision and low-residual-stress steel rail |
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