CN116695001A - Manufacturing method for improving delayed cracking resistance of heavy rail steel - Google Patents
Manufacturing method for improving delayed cracking resistance of heavy rail steel Download PDFInfo
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- 229910000831 Steel Inorganic materials 0.000 title claims abstract description 240
- 239000010959 steel Substances 0.000 title claims abstract description 240
- 238000005336 cracking Methods 0.000 title claims abstract description 46
- 230000003111 delayed effect Effects 0.000 title claims abstract description 45
- 238000004519 manufacturing process Methods 0.000 title claims abstract description 25
- 238000000034 method Methods 0.000 claims abstract description 53
- XEEYBQQBJWHFJM-UHFFFAOYSA-N iron Substances [Fe] XEEYBQQBJWHFJM-UHFFFAOYSA-N 0.000 claims abstract description 46
- 238000005096 rolling process Methods 0.000 claims abstract description 30
- 238000007670 refining Methods 0.000 claims abstract description 28
- 238000006477 desulfuration reaction Methods 0.000 claims abstract description 24
- 230000023556 desulfurization Effects 0.000 claims abstract description 24
- 229910052742 iron Inorganic materials 0.000 claims abstract description 17
- 238000009749 continuous casting Methods 0.000 claims abstract description 16
- 239000012535 impurity Substances 0.000 claims abstract description 12
- 238000007664 blowing Methods 0.000 claims description 46
- OYPRJOBELJOOCE-UHFFFAOYSA-N Calcium Chemical compound [Ca] OYPRJOBELJOOCE-UHFFFAOYSA-N 0.000 claims description 42
- 239000011575 calcium Substances 0.000 claims description 42
- 229910052791 calcium Inorganic materials 0.000 claims description 42
- 238000009489 vacuum treatment Methods 0.000 claims description 42
- XKRFYHLGVUSROY-UHFFFAOYSA-N Argon Chemical compound [Ar] XKRFYHLGVUSROY-UHFFFAOYSA-N 0.000 claims description 32
- 239000002893 slag Substances 0.000 claims description 29
- 238000005266 casting Methods 0.000 claims description 27
- XAGFODPZIPBFFR-UHFFFAOYSA-N aluminium Chemical compound [Al] XAGFODPZIPBFFR-UHFFFAOYSA-N 0.000 claims description 22
- 229910052782 aluminium Inorganic materials 0.000 claims description 22
- 238000010438 heat treatment Methods 0.000 claims description 22
- 229910052786 argon Inorganic materials 0.000 claims description 16
- 239000005997 Calcium carbide Substances 0.000 claims description 12
- 235000008733 Citrus aurantifolia Nutrition 0.000 claims description 12
- 235000011941 Tilia x europaea Nutrition 0.000 claims description 12
- 239000004571 lime Substances 0.000 claims description 12
- CLZWAWBPWVRRGI-UHFFFAOYSA-N tert-butyl 2-[2-[2-[2-[bis[2-[(2-methylpropan-2-yl)oxy]-2-oxoethyl]amino]-5-bromophenoxy]ethoxy]-4-methyl-n-[2-[(2-methylpropan-2-yl)oxy]-2-oxoethyl]anilino]acetate Chemical compound CC1=CC=C(N(CC(=O)OC(C)(C)C)CC(=O)OC(C)(C)C)C(OCCOC=2C(=CC=C(Br)C=2)N(CC(=O)OC(C)(C)C)CC(=O)OC(C)(C)C)=C1 CLZWAWBPWVRRGI-UHFFFAOYSA-N 0.000 claims description 12
- 239000008188 pellet Substances 0.000 claims description 11
- 238000010583 slow cooling Methods 0.000 claims description 10
- 239000001257 hydrogen Substances 0.000 description 75
- 229910052739 hydrogen Inorganic materials 0.000 description 75
- UFHFLCQGNIYNRP-UHFFFAOYSA-N Hydrogen Chemical compound [H][H] UFHFLCQGNIYNRP-UHFFFAOYSA-N 0.000 description 71
- 238000001816 cooling Methods 0.000 description 40
- 238000003723 Smelting Methods 0.000 description 30
- 230000000052 comparative effect Effects 0.000 description 11
- 238000010079 rubber tapping Methods 0.000 description 11
- 229910052698 phosphorus Inorganic materials 0.000 description 10
- 238000004321 preservation Methods 0.000 description 9
- 230000001681 protective effect Effects 0.000 description 9
- 230000035945 sensitivity Effects 0.000 description 9
- 229910052717 sulfur Inorganic materials 0.000 description 9
- 239000011593 sulfur Substances 0.000 description 9
- 229910052721 tungsten Inorganic materials 0.000 description 9
- NINIDFKCEFEMDL-UHFFFAOYSA-N Sulfur Chemical compound [S] NINIDFKCEFEMDL-UHFFFAOYSA-N 0.000 description 8
- 239000011651 chromium Substances 0.000 description 7
- UCKMPCXJQFINFW-UHFFFAOYSA-N Sulphide Chemical compound [S-2] UCKMPCXJQFINFW-UHFFFAOYSA-N 0.000 description 3
- 238000010521 absorption reaction Methods 0.000 description 3
- 230000008901 benefit Effects 0.000 description 3
- 230000003749 cleanliness Effects 0.000 description 3
- 150000002431 hydrogen Chemical class 0.000 description 3
- 239000000463 material Substances 0.000 description 3
- 239000002245 particle Substances 0.000 description 3
- 238000011160 research Methods 0.000 description 3
- 238000012360 testing method Methods 0.000 description 3
- VYPSYNLAJGMNEJ-UHFFFAOYSA-N Silicium dioxide Chemical compound O=[Si]=O VYPSYNLAJGMNEJ-UHFFFAOYSA-N 0.000 description 2
- 238000009825 accumulation Methods 0.000 description 2
- 238000005275 alloying Methods 0.000 description 2
- WUKWITHWXAAZEY-UHFFFAOYSA-L calcium difluoride Chemical compound [F-].[F-].[Ca+2] WUKWITHWXAAZEY-UHFFFAOYSA-L 0.000 description 2
- 238000013329 compounding Methods 0.000 description 2
- 238000009792 diffusion process Methods 0.000 description 2
- 230000000694 effects Effects 0.000 description 2
- 239000010436 fluorite Substances 0.000 description 2
- 125000004435 hydrogen atom Chemical group [H]* 0.000 description 2
- 230000007774 longterm Effects 0.000 description 2
- 239000000843 powder Substances 0.000 description 2
- 238000002360 preparation method Methods 0.000 description 2
- 238000004886 process control Methods 0.000 description 2
- VYZAMTAEIAYCRO-UHFFFAOYSA-N Chromium Chemical compound [Cr] VYZAMTAEIAYCRO-UHFFFAOYSA-N 0.000 description 1
- QAOWNCQODCNURD-UHFFFAOYSA-N Sulfuric acid Chemical compound OS(O)(=O)=O QAOWNCQODCNURD-UHFFFAOYSA-N 0.000 description 1
- QVGXLLKOCUKJST-UHFFFAOYSA-N atomic oxygen Chemical compound [O] QVGXLLKOCUKJST-UHFFFAOYSA-N 0.000 description 1
- 230000000903 blocking effect Effects 0.000 description 1
- JGIATAMCQXIDNZ-UHFFFAOYSA-N calcium sulfide Chemical compound [Ca]=S JGIATAMCQXIDNZ-UHFFFAOYSA-N 0.000 description 1
- XFWJKVMFIVXPKK-UHFFFAOYSA-N calcium;oxido(oxo)alumane Chemical compound [Ca+2].[O-][Al]=O.[O-][Al]=O XFWJKVMFIVXPKK-UHFFFAOYSA-N 0.000 description 1
- 229910052804 chromium Inorganic materials 0.000 description 1
- 229910052681 coesite Inorganic materials 0.000 description 1
- 229910052906 cristobalite Inorganic materials 0.000 description 1
- 238000000354 decomposition reaction Methods 0.000 description 1
- 230000003009 desulfurizing effect Effects 0.000 description 1
- 238000011161 development Methods 0.000 description 1
- 238000007667 floating Methods 0.000 description 1
- 239000004615 ingredient Substances 0.000 description 1
- 238000012423 maintenance Methods 0.000 description 1
- 239000011572 manganese Substances 0.000 description 1
- 238000013386 optimize process Methods 0.000 description 1
- 229910052760 oxygen Inorganic materials 0.000 description 1
- 239000001301 oxygen Substances 0.000 description 1
- 229910001562 pearlite Inorganic materials 0.000 description 1
- 230000035515 penetration Effects 0.000 description 1
- 238000011056 performance test Methods 0.000 description 1
- 239000011574 phosphorus Substances 0.000 description 1
- 238000010791 quenching Methods 0.000 description 1
- 230000000171 quenching effect Effects 0.000 description 1
- 229910052761 rare earth metal Inorganic materials 0.000 description 1
- 150000002910 rare earth metals Chemical class 0.000 description 1
- 239000002994 raw material Substances 0.000 description 1
- 239000011819 refractory material Substances 0.000 description 1
- 238000007789 sealing Methods 0.000 description 1
- 238000005204 segregation Methods 0.000 description 1
- 239000000377 silicon dioxide Substances 0.000 description 1
- 235000012239 silicon dioxide Nutrition 0.000 description 1
- 238000001179 sorption measurement Methods 0.000 description 1
- 229910052682 stishovite Inorganic materials 0.000 description 1
- CADICXFYUNYKGD-UHFFFAOYSA-N sulfanylidenemanganese Chemical compound [Mn]=S CADICXFYUNYKGD-UHFFFAOYSA-N 0.000 description 1
- 150000004763 sulfides Chemical class 0.000 description 1
- 235000011149 sulphuric acid Nutrition 0.000 description 1
- 230000002195 synergetic effect Effects 0.000 description 1
- 238000005496 tempering Methods 0.000 description 1
- 239000010409 thin film Substances 0.000 description 1
- 229910052905 tridymite Inorganic materials 0.000 description 1
- 238000009849 vacuum degassing Methods 0.000 description 1
- 239000002918 waste heat Substances 0.000 description 1
- XLYOFNOQVPJJNP-UHFFFAOYSA-N water Substances O XLYOFNOQVPJJNP-UHFFFAOYSA-N 0.000 description 1
Classifications
-
- 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
- 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
- C21C7/0006—Adding metallic additives
-
- 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
- C21C7/0056—Treating molten ferrous alloys, e.g. steel, not covered by groups C21C1/00 - C21C5/00 using cored wires
-
- 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
- C21C7/064—Dephosphorising; Desulfurising
-
- 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
-
- 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
- C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
- C22C—ALLOYS
- C22C38/00—Ferrous alloys, e.g. steel alloys
- C22C38/005—Ferrous alloys, e.g. steel alloys containing rare earths, i.e. Sc, Y, Lanthanides
-
- 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
- C22C38/24—Ferrous alloys, e.g. steel alloys containing chromium 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
- C22C38/26—Ferrous alloys, e.g. steel alloys containing chromium with niobium or tantalum
-
- 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
- C22C38/28—Ferrous alloys, e.g. steel alloys containing chromium with titanium or zirconium
-
- 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
- C22C38/38—Ferrous alloys, e.g. steel alloys containing chromium with more than 1.5% by weight of manganese
-
- Y—GENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; GENERAL TAGGING OF CROSS-SECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
- Y02—TECHNOLOGIES OR APPLICATIONS FOR MITIGATION OR ADAPTATION AGAINST CLIMATE CHANGE
- Y02P—CLIMATE CHANGE MITIGATION TECHNOLOGIES IN THE PRODUCTION OR PROCESSING OF GOODS
- Y02P10/00—Technologies related to metal processing
- Y02P10/20—Recycling
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- Metallurgy (AREA)
- Organic Chemistry (AREA)
- Mechanical Engineering (AREA)
- Treatment Of Steel In Its Molten State (AREA)
Abstract
The invention discloses a manufacturing method for improving the delayed cracking resistance of heavy rail steel, which comprises the following steps: the steel comprises, by weight, 0.68% -0.78% of C, 0.43% -0.63% of Si, 1.2% -2.2% of Mn, less than or equal to 0.010% of P, less than or equal to 0.004% of S, and (Nb+V+Ti): 0.020 to 0.050 percent, als less than or equal to 0.003 percent, cr 2.2 to 3.2 percent and Re:0.0010 to 0.0020 percent, H is less than or equal to 0.00005 percent, and the balance is Fe and impurity elements, and the process is completed through molten iron deep desulfurization, LF refining, molten steel continuous casting and rolling. The invention has simple process, easy control, low production cost and excellent performance, and can effectively improve the delayed cracking resistance of heavy rail steel.
Description
Technical Field
The invention belongs to the field of high-strength steel production in the metallurgical industry, and particularly relates to a manufacturing method for improving the delayed cracking resistance of heavy rail steel.
Background
Along with the development of high-speed rails and heavy railways in China, more and more high-strength heavy rails are applied to the infrastructure, and the service life and the safety of the steel rail are directly related to maintenance cost and life and property safety of people. The tensile strength of current rails is 1000MPa, under which there is a risk of hydrogen induced delayed cracking. Numerous studies have demonstrated that delayed cracking of steel, caused by hydrogen in materials and in the environment in which the materials are in service, is unpredictable and abrupt, often resulting in serious safety problems, and therefore is always a problem that heavy rail products must face.
The main reason for causing the hydrogen-induced delayed cracking of the steel rail is the hydrogen content in the steel, wherein the hydrogen in the steel mainly comes from two processes, namely the decomposition of ore and water in raw materials in the smelting process to generate hydrogen in the smelting process and the absorption of hydrogen from the environment in the long-term service process of the steel rail. How to control the hydrogen content in production and how to prevent the absorption of hydrogen and reduce the influence of hydrogen on the material performance in the long-term service process of the steel rail are critical.
The main factors influencing the delayed cracking of heavy rail steel at present are MnS inclusion generated in the smelting process and the control of the hydrogen content in the steel, and the delayed cracking of the steel can be caused by the accumulation of a large amount of hydrogen in the MnS inclusion, so that the delayed cracking source can be realized, and the cracking sensitivity of the steel is very high.
The control method of the hydrogen content of the CN 109082500A steel rail provides a control method of the hydrogen content of the steel rail, which comprises the following steps: selecting low-sulfur and low-phosphorus molten iron and baked and dried scrap steel to carry out converter smelting; after molten steel enters LF refining, heating, slagging and component fine adjustment are carried out; after the molten steel is refined out of the LF, the molten steel enters secondary refining VD for vacuum degassing; before molten steel casting, fully baking the tundish refractory material, and performing argon sealing protection on a ladle nozzle in the casting process; after casting, the casting blank enters a slow cooling pit for stacking and slow cooling; the pit entering temperature is 600-700, and the slow cooling time is 5 days; heating the casting blank in a heating furnace, performing secondary cogging, and slowly cooling in a heat-preserving cover for 5 days; and (5) heating for the second time, and finally warehousing and slow cooling after initial rolling and final rolling. By the technical scheme, the hydrogen content in the steel rail is effectively controlled, the toughness of the high-strength steel rail is obviously improved, particularly the stability and reliability of the performance of the steel rail are improved, and the risk of the high-strength steel rail in the railway service process is reduced.
CN 110923405A is a process control method for reducing hydrogen hazard in steel rail, and relates to a process control method for reducing hydrogen hazard in steel rail, comprising the procedures of molten iron pretreatment, converter smelting, LF refining, RH refining and bloom continuous casting; a molten iron pretreatment procedure, wherein after the molten iron pretreatment is finished, the sulfur content in the molten iron is controlled to be between 0.010 and 0.015 weight percent; and in the converter process, during the alloying of tapping after smelting, synthetic slag with the main components of CaO and SiO2 is added, the argon blowing time is kept to be more than 3 minutes, and the slag is formed rapidly after tapping of the converter, so that the inclusion is ensured to float upwards sufficiently. The invention achieves the purpose of adding hydrogen traps by controlling the content of MnS and inclusions in molten steel in the smelting process, does not cause the content of the inclusions to exceed the standard, and reduces the hydrogen hazard in the steel rail to the minimum.
CN 112280939A discloses a low-hydrogen hypereutectoid steel rail and a preparation method thereof. The method comprises converter smelting or electric furnace smelting, LF refining, RH vacuum treatment, protection casting, cooling, heating by a heating furnace, rolling, heat treatment and post treatment; in the RH vacuum treatment process, fluorite and CaO are sprayed into molten steel, and the mass ratio of the fluorite to the CaO is 1:1-4; the depth of the vacuum pump inserted into the molten steel is 450-700mm; argon flow is 1200-1400NL/min; the vacuum treatment time is more than or equal to 15min, and the vacuum degree is less than or equal to 3mbar and the treatment time is more than or equal to 12min. The method can greatly improve the comprehensive performance of the steel rail while reducing the hydrogen content in the high-strength hypereutectoid steel rail, meets the requirement of the steel rail for the heavy haul railway, and the prepared steel rail steel has the hydrogen content less than or equal to 1.2ppm, the tensile strength more than or equal to 1400MPa and the elongation more than or equal to 10 percent.
CN 112301200A discloses a steel rail with delayed fracture resistance and a preparation method thereof. The method comprises the steps of smelting furnace burden into molten steel through a converter or an electric furnace, aluminum-free deoxidization, LF refining, RH vacuum treatment or VD vacuum treatment, continuous casting of molten steel into steel billets, continuous cooling of the steel billets, heating of the steel billets in a heating furnace, online rolling of the steel billets into steel rails, online heat treatment and post treatment; the online heat treatment comprises the steps of utilizing the final rolling waste heat to cool the rail head and the rail web of the steel rail by compressed air, wherein the cooling rate is controlled to be 2.6-4.2 ℃/s; the initial cooling temperature of the rail head of the steel rail is controlled to be 830-880 ℃, and the steel rail is air-cooled to room temperature when the cooling temperature of the rail head of the steel rail is lower than 500 ℃. The average pearlite lamellar spacing of the rail head of the steel rail prepared by the method is obviously reduced, the hydrogen content of the steel rail is reduced to a certain extent, the crack propagation rate and the rail head impact toughness are optimized, and the delayed fracture resistance of the steel rail is obviously improved. CN 115161435A is blown to remove sulfur and sulfide powder through the bottom of ladle in the refining process of molten steel, the powder reacts at the bottom of ladle to form numerous tiny viscous slag small particles, the slag small particles achieve the purposes of desulfurizing and removing sulfide inclusion by surface adhesion in the floating process of ladle from bottom to top, and even other inclusions can be adhered on the surface of slag small particles. The advantages are that: the method is suitable for the production of high-speed heavy rail steel with very high requirements on A-type inclusions, can realize the deep removal of sulfur in the steel, can realize the removal of sulfides in the steel, and can even achieve the purpose of adhesion removal of other inclusions.
Research shows that the delayed cracking resistance cannot be solved by only a single step or parameter, and the method cannot comprehensively propose a delayed cracking resistance scheme from the whole process of manufacturing and service of the steel rail.
Disclosure of Invention
The invention aims to solve the technical problems and provide the manufacturing method for improving the delayed cracking resistance of the heavy rail steel, which has the advantages of simple process, easiness in control, low production cost and excellent performance.
The method of the invention comprises the following steps: the steel comprises, by weight, 0.68% -0.78% of C, 0.43% -0.63% of Si, 1.2% -2.2% of Mn, less than or equal to 0.010% of P, less than or equal to 0.004% of S, and (Nb+V+Ti): 0.020 to 0.050 percent, als less than or equal to 0.003 percent, cr 2.2 to 3.2 percent and Re:0.0010 to 0.0020 percent, H is less than or equal to 0.00005 percent, and the balance of Fe and impurity elements are finished by molten iron deep desulfurization, LF refining, molten steel continuous casting and rolling,
wherein, in the LF refining step: firstly, soft blowing is carried out for 3-8min, the T [ O ] is controlled to be less than or equal to 0.0020wt%, meanwhile, aluminum pellets or aluminum wires, lime and calcium carbide are added into molten steel to produce slag, desulfurization operation is carried out, and the components of the slag are controlled to be 2.0-2.5 in percentage by mass of W (CaO)/W (Al 2O 3); then calcium treatment is carried out, wherein the concrete treatment process is to feed pure calcium wires into molten steel, soft argon blowing is carried out on the molten steel after the calcium treatment, the soft argon blowing time is 5-10 min, and finally RH vacuum treatment is carried out.
Preferably, the Re: 0.0013-0.0018% of 0.0010-0.0020% of Cr 2.5-3.0%.
Preferably, the addition amount of the pure calcium wire is 0.15-0.40 kg per ton of molten steel during the calcium treatment of the LF refining step.
Preferably, the RH vacuum treatment time of the LF refining step is 30-50 min, the vacuum degree is less than or equal to 50Pa, re is fed into molten steel during RH vacuum treatment, and soft blowing is carried out for 5-10 min after the RH vacuum treatment is finished.
Preferably, during RH vacuum treatment in the LF refining step, the linear Re addition amount is 0.1-0.25 Kg/ton of molten steel.
Preferably, in the molten steel continuous casting step: and controlling the slow cooling time of the cast blank after casting to be 36-72 hours.
Preferably, in the rolling step, the billet is heated, rough rolled, finish rolled into a steel rail, and slowly cooled to room temperature at a slow cooling speed of 0.2 ℃/s-0.5 ℃/s.
Preferably, the billet heating temperature is 1230-1260 ℃.
The inventors have found through many researches that the main factors influencing the delayed cracking of heavy rail steel are MnS inclusions generated in the smelting process and the control of the hydrogen content in the steel, and the delayed cracking of the steel is caused by the accumulation of a large amount of hydrogen in the MnS inclusions, so that the delayed cracking of the steel is a crack source, the cracking sensitivity of the steel is very high, and in order to solve the problems, improvement is needed from various aspects:
1) Adding Cr element: chromium is generally considered to improve hardenability, so that steel has better comprehensive mechanical properties after quenching and tempering, but the inventor further researches that Cr has excellent hydrogen rejection capability, can block hydrogen absorption and inhibit hydrogen diffusion, so that the content of Cr is improved and controlled within a range of 2.20-3.2%, more preferably 2.5-3.0%, the content of Cr within the ranges can effectively form a continuous oxide layer to block penetration of hydrogen atoms from the surface to the steel, and too high content can affect the strength of the steel and the surface quality of the steel, and too low content can affect the continuity of a surface oxide layer and reduce the blocking effect on hydrogen.
2) Re compounding (Nb+V+Ti) is adopted: the rare earth treatment can further modify and refine inclusions, so that the cleanliness of steel is improved, re is an excellent hydrogen trap, and hydrogen atoms can be pinned, so that the delayed cracking sensitivity is greatly reduced; the precipitated phase of (Nb+V+Ti) Nb+V+Ti is a good hydrogen trap, can play a role of pinning hydrogen, and can enlarge the adsorption effect on hydrogen when the two are compounded, so that finer and dispersed hydrogen traps are generated, and an excellent hydrogen-resistant effect is generated. Here, re is defined in consideration of the case of compounding: more preferably 0.0010 to 0.0020%, and still more preferably 0.0013 to 0.0018%, too much will not have obvious synergistic effect, and too little will not act to capture hydrogen. The (Nb+V+Ti) content is preferably in the range of 0.020 to 0.050%.
3) In the LF refining step, the calcium treatment is improved, specifically, soft blowing is carried out for 3-5min, the weight of T [ O ] is controlled to be less than or equal to 0.0020wt%, and the final oxygen content can be … … by strictly controlling; adding aluminum pellets or aluminum wires, lime and calcium carbide into molten steel to produce slag and performing desulfurization operation, wherein the content of the obtained slag is controlled to be 2.0-2.5 in terms of weight percent of W (CaO)/W (Al 2O 3) so as to realize … …; calcium treatment is carried out on molten steel, and pure calcium wires are fed into the molten steel, wherein the adding amount of the pure calcium wires is 0.15-0.40 kg per ton of molten steel.
4) Regarding other element control, P is a harmful element in steel, and is easy to cause center segregation of casting blanks, so that the brittleness of the steel is obviously increased, and the content of P is controlled below 0.008%; s, sulfur is a very harmful element, and the sulfur in the steel is often in the form of manganese sulfide, and the inclusion of the sulfide deteriorates the toughness of the steel, and the lower the sulfur content in the steel is, the better the sulfur content is. The sulfur content in the steel is controlled below 0.003% based on the manufacturing cost.
In summary, aiming at the problems that the existing heavy rail steel has a large amount of MnS inclusions, the inclusions are large in size and strong in ductility, become thin film strips during rolling, are easy to absorb hydrogen to cause high sensitivity of hydrogen-induced delayed cracking, and have cracking risks during use, the inclusions in the steel are modified through calcium treatment, the MnS inclusions are converted into calcium sulfide and calcium aluminate inclusions, and the influence of the inclusions on delayed cracking is reduced; the size and the quantity of the residual inclusions in the steel are reduced through RH treatment, the cleanliness of the molten steel is improved, and the hydrogen content in the smelting process is controlled; the addition of a trace amount of Re continuously modifies the inclusion, so that the cleanliness of molten steel is improved, and meanwhile, the Re serving as a hydrogen trap can better adsorb and pin hydrogen, so that the diffusion rate of hydrogen in the steel is reduced; the Cr is added to improve the hydrogen permeation resistance of the steel, improve the hydrogen permeation in the environment of the steel rail, and the heavy rail steel has higher tensile strength, excellent delayed cracking resistance and excellent application prospect and economic benefit through multiple means.
Detailed Description
Example 1
The manufacturing method for improving the delayed cracking resistance of the heavy rail steel comprises the following components in percentage by weight: 0.68%, si:0.43%, mn:1.4%, P:0.008, S:0.004%, (nb+v+ti): 0.043%, als:0.003%, cr:2.2%, re:0.0010, H:0.00005%, the balance of Fe and impurity element
1) Carrying out deep desulfurization on molten iron, smelting by adopting a converter, adding scrap steel for smelting, and controlling the tapping temperature to 1651; DEG C
2) Soft blowing is carried out in the LF refining process, the soft blowing time is 5min, and the T [ O ] is controlled to be less than or equal to 0.0020 percent; adding aluminum pellets or aluminum wires, lime and calcium carbide into molten steel to produce slag and performing desulfurization operation, wherein the content of the obtained slag is 2.1 in terms of weight percent of W (CaO)/W (Al 2O 3); carrying out calcium treatment on molten steel, wherein the adding amount of pure calcium wires is 0.25Kg per ton of molten steel, and carrying out soft argon blowing on the molten steel after the calcium treatment for 6min; RH vacuum treatment, the time is 35min, the vacuum degree is 45Pa, re is fed into molten steel during RH vacuum treatment, and soft blowing is carried out for 5-10 min after the RH vacuum treatment is finished.
3) Molten steel continuous casting, namely adopting a large tank long nozzle and a crystallizer immersed nozzle to perform protective casting, covering a heat preservation cover on a casting blank, slowly cooling to promote hydrogen in the steel blank to escape and reduce the hydrogen content in the steel blank, and slowly cooling for 38 hours;
4) And heating the steel billet to 1223 ℃, performing rough rolling, finishing rolling to form a steel rail, slowly cooling to room temperature, and slowly cooling at a speed of 0.32 ℃/s.
Example 2
The manufacturing method for improving the delayed cracking resistance of the heavy rail steel comprises the following components in percentage by weight: 0.69%, si:0.45%, mn:1.5%, P:0.007, S:0.003%, (nb+v+ti): 0.043%, als:0.003%, cr:2.5%, re:0.0012, H:0.00005%, the balance of Fe and impurity element
1) Carrying out deep desulfurization on molten iron, smelting by adopting a converter, adding scrap steel for smelting, and controlling the tapping temperature to be 1653 ℃;
2) Soft blowing is carried out in the LF refining process, the soft blowing time is 4min, and the T [ O ] is controlled to be less than or equal to 0.0019%; adding aluminum pellets or aluminum wires, lime and calcium carbide into molten steel to produce slag and performing desulfurization operation, wherein the content of the obtained slag is 2.2 in mass percent of W (CaO)/W (Al 2O 3); carrying out calcium treatment on molten steel, wherein the adding amount of pure calcium wires is 0.26Kg per ton of molten steel, and carrying out soft argon blowing on the molten steel after the calcium treatment for 7min; RH vacuum treatment, the time is 45min, the vacuum degree is 42Pa, re is fed into molten steel during RH vacuum treatment, and soft blowing is carried out for 5-10 min after the RH vacuum treatment is finished.
3) Molten steel continuous casting, namely adopting a large tank long nozzle and a crystallizer immersed nozzle to perform protective casting, covering a heat preservation cover on a casting blank, slowly cooling to promote hydrogen in the steel blank to escape and reduce the hydrogen content in the steel blank, and slowly cooling for 48 hours;
4) Heating the steel billet to 1265 ℃, performing rough rolling, finishing rolling to form a steel rail, slowly cooling to room temperature, and slowly cooling at a speed of 0.31 ℃/s.
Example 3
The manufacturing method for improving the delayed cracking resistance of the heavy rail steel comprises the following components in percentage by weight: 0.71%, si:0.48%, mn:1.5%, P:0.008, S:0.004%, (nb+v+ti): 0.033%, als:0.003%, cr:2.7%, re:0.0013, H:0.00004%, the balance of Fe and impurity elements
1) Carrying out deep desulfurization on molten iron, smelting by adopting a converter, adding scrap steel for smelting, and controlling the tapping temperature to be 1654 ℃;
2) Soft blowing is carried out in the LF refining process, the soft blowing time is 7min, and the T [ O ] is controlled to be less than or equal to 0.0019%; adding aluminum pellets or aluminum wires, lime and calcium carbide into molten steel to produce slag and performing desulfurization operation, wherein the content of the obtained slag is 2.2 in mass percent of W (CaO)/W (Al 2O 3); carrying out calcium treatment on molten steel, wherein the adding amount of pure calcium wires is 0.27Kg per ton of molten steel, and carrying out soft argon blowing on the molten steel after the calcium treatment for 8min; RH vacuum treatment, the time is 50min, the vacuum degree is 40Pa, re wire is fed into molten steel during RH vacuum treatment, and soft blowing is carried out for 8min after the RH vacuum treatment is finished.
3) Molten steel continuous casting, namely adopting a large tank long nozzle and a crystallizer immersed nozzle to perform protective casting, covering a heat preservation cover on a casting blank, slowly cooling to promote hydrogen in the steel blank to escape and reduce the hydrogen content in the steel blank, and slowly cooling for 68 hours;
4) And heating the steel billet to 1230 ℃, performing rough rolling, finishing rolling to form a steel rail, slowly cooling to room temperature, and slowly cooling at a speed of 0.28 ℃/s.
Example 4
The manufacturing method for improving the delayed cracking resistance of the heavy rail steel comprises the following components in percentage by weight: 0.72%, si:0.49%, mn:1.6%, P:0.007, S:0.004%, (nb+v+ti): 0.038%, als:0.003%, cr:2.8%, re:0.0014, H:0.00004%, the balance of Fe and impurity elements
1) Carrying out deep desulfurization on molten iron, smelting by adopting a converter, adding scrap steel for smelting, and controlling the tapping temperature to be 1644 ℃;
2) Soft blowing is carried out in the LF refining process, the soft blowing time is 5min, and the T [ O ] is controlled to be less than or equal to 0.0018%; adding aluminum pellets or aluminum wires, lime and calcium carbide into molten steel to produce slag and performing desulfurization operation, wherein the content of the obtained slag is 2.3 in terms of weight percent of W (CaO)/W (Al 2O 3); carrying out calcium treatment on molten steel, wherein the adding amount of pure calcium wires is 0.25Kg per ton of molten steel, and carrying out soft argon blowing on the molten steel after the calcium treatment for 7min; RH vacuum treatment, the time is 43min, the vacuum degree is 42Pa, re wire is fed into molten steel during RH vacuum treatment, and soft blowing is carried out for 7min after the RH vacuum treatment is finished.
3) Molten steel continuous casting, namely adopting a large tank long nozzle and a crystallizer immersed nozzle to perform protective casting, covering a heat preservation cover on a casting blank, slowly cooling to promote hydrogen in the steel blank to escape and reduce the hydrogen content in the steel blank, and slowly cooling for 64 hours;
4) And heating the steel billet to 1238 ℃, performing rough rolling, finishing rolling, forming a steel rail, slowly cooling to room temperature, and slowly cooling at the speed of 0.29 ℃/s.
Example 5
The manufacturing method for improving the delayed cracking resistance of the heavy rail steel comprises the following components in percentage by weight: 0.73%, si:0.51%, mn:1.7%, P:0.006, S:0.003%, (nb+v+ti): 0.035%, als:0.002%, cr:2.7%, re:0.0015, H:0.00004%, the balance of Fe and impurity elements
1) Carrying out deep desulfurization on molten iron, smelting by adopting a converter, adding scrap steel for smelting, and controlling the tapping temperature to be 1644 ℃;
2) Soft blowing is carried out in the LF refining process, the soft blowing time is 5min, and the T [ O ] is controlled to be less than or equal to 0.0018%; adding aluminum pellets or aluminum wires, lime and calcium carbide into molten steel to produce slag and performing desulfurization operation, wherein the content of the obtained slag is 2.2 in mass percent of W (CaO)/W (Al 2O 3); carrying out calcium treatment on molten steel, wherein the adding amount of pure calcium wires is 0.28Kg per ton of molten steel, and carrying out soft argon blowing on the molten steel after the calcium treatment for 8min; RH vacuum treatment, the time is 45min, the vacuum degree is 42Pa, re is fed into molten steel during RH vacuum treatment, and soft blowing is carried out for 8min after RH vacuum treatment is finished.
3) Molten steel continuous casting, namely adopting a large tank long nozzle and a crystallizer immersed nozzle to perform protective casting, covering a heat preservation cover on a casting blank, slowly cooling to promote hydrogen in the steel blank to escape and reduce the hydrogen content in the steel blank, and slowly cooling for 54 hours;
4) And heating the steel billet to 1248 ℃, performing rough rolling, finishing rolling to form a steel rail, slowly cooling to room temperature, and slowly cooling at a speed of 0.31 ℃/s.
Example 6
The manufacturing method for improving the delayed cracking resistance of the heavy rail steel comprises the following components in percentage by weight: 0.75%, si:0.52%, mn:1.8%, P:0.006, S:0.003%, (nb+v+ti): 0.025%, als:0.002%, cr:2.8%, re:0.0017, H:0.00004%, the balance of Fe and impurity elements
1) Carrying out deep desulfurization on molten iron, smelting by adopting a converter, adding scrap steel for smelting, and controlling the tapping temperature to be 1642 ℃;
2) Soft blowing is carried out in the LF refining process, the soft blowing time is 4min, and the T [ O ] is controlled to be less than or equal to 0.0019%; adding aluminum pellets or aluminum wires, lime and calcium carbide into molten steel to produce slag and performing desulfurization operation, wherein the content of the obtained slag is 2.3 in terms of weight percent of W (CaO)/W (Al 2O 3); carrying out calcium treatment on molten steel, wherein the adding amount of pure calcium wires is 0.24Kg per ton of molten steel, and carrying out soft argon blowing on the molten steel after the calcium treatment for 8min; RH vacuum treatment, the time is 45min, the vacuum degree is 42Pa, re is fed into molten steel during RH vacuum treatment, and soft blowing is carried out for 8min after RH vacuum treatment is finished.
3) Molten steel continuous casting, namely adopting a large tank long nozzle and a crystallizer immersed nozzle to perform protective casting, covering a heat preservation cover on a casting blank, slowly cooling to promote hydrogen in the steel blank to escape and reduce the hydrogen content in the steel blank, and slowly cooling for 54 hours;
4) And heating the steel billet to 1255 ℃, performing rough rolling, finishing rolling to form a steel rail, and slowly cooling to room temperature at a slow cooling speed of 0.26 ℃/s.
Example 7
The manufacturing method for improving the delayed cracking resistance of the heavy rail steel comprises the following components in percentage by weight: 0.77%, si:0.55%, mn:1.9%, P:0.006, S:0.003%, (nb+v+ti): 0.035%, als:0.002%, cr:3.1%, re:0.0019, H:0.00004%, the balance of Fe and impurity elements
1) Carrying out deep desulfurization on molten iron, smelting by adopting a converter, adding scrap steel for smelting, and controlling the tapping temperature to be 1641 ℃;
2) Soft blowing is carried out in the LF refining process, the soft blowing time is 8min, and the T [ O ] is controlled to be less than or equal to 0.0018%; adding aluminum pellets or aluminum wires, lime and calcium carbide into molten steel to produce slag and performing desulfurization operation, wherein the content of the obtained slag is 2.5 in mass percent of W (CaO)/W (Al 2O 3); carrying out calcium treatment on molten steel, wherein the adding amount of pure calcium wires is 0.34Kg per ton of molten steel, and carrying out soft argon blowing on the molten steel after the calcium treatment for 8min; RH vacuum treatment, the time is 45min, the vacuum degree is 41Pa, re wire is fed into molten steel during RH vacuum treatment, and soft blowing is carried out for 8min after the RH vacuum treatment is finished.
3) Molten steel continuous casting, namely adopting a large tank long nozzle and a crystallizer immersed nozzle to perform protective casting, covering a heat preservation cover on a casting blank, slowly cooling to promote hydrogen in the steel blank to escape and reduce the hydrogen content in the steel blank, and slowly cooling for 66 hours;
4) And heating the steel billet to 1268 ℃, performing rough rolling, finishing rolling, forming the steel rail, slowly cooling to room temperature, and slowly cooling at the speed of 0.27 ℃/s.
Example 8
The manufacturing method for improving the delayed cracking resistance of the heavy rail steel comprises the following components in percentage by weight: 0.73%, si:0.51%, mn:2.1%, P:0.006, S:0.003%, (nb+v+ti): 0.042%, als:0.002%, cr:2.9%, re:0.0020, H:0.00004%, the balance of Fe and impurity elements
1) Carrying out deep desulfurization on molten iron, smelting by adopting a converter, adding scrap steel for smelting, and controlling the tapping temperature to be 1643 ℃;
2) Soft blowing is carried out in the LF refining process, the soft blowing time is 5min, and the T [ O ] is controlled to be less than or equal to 0.0019%; adding aluminum pellets or aluminum wires, lime and calcium carbide into molten steel to produce slag and performing desulfurization operation, wherein the content of the obtained slag is 2.4 in terms of weight percent of W (CaO)/W (Al 2O 3); carrying out calcium treatment on molten steel, wherein the adding amount of pure calcium wires is 0.33Kg per ton of molten steel, and carrying out soft argon blowing on the molten steel after the calcium treatment for 8min; RH vacuum treatment, the time is 46min, the vacuum degree is 40Pa, re wire is fed into molten steel during RH vacuum treatment, and soft blowing is carried out for 9min after the RH vacuum treatment is finished.
3) Molten steel continuous casting, namely adopting a large tank long nozzle and a crystallizer immersed nozzle to perform protective casting, covering a heat preservation cover on a casting blank, slowly cooling to promote hydrogen in the steel blank to escape and reduce the hydrogen content in the steel blank, and slowly cooling for 70 hours;
4) And heating the steel billet, performing rough rolling, finishing rolling, forming the steel rail, and slowly cooling to room temperature at a slow cooling speed of 0.24 ℃/s.
Comparative example 1
Example 4 was repeated except that the amount of Cr added was changed to 1.8%.
Comparative example 2
Example 4 was repeated except that Re was not added.
Comparative example 3
Example 4 was repeated except that (Nb+V+Ti) was not added.
Comparative example 4
C:0.72%, si:0.49%, mn:1.6%, P:0.007, S:0.004%, (nb+v+ti): 0.038%, als:0.003%, cr:2.8%, re:0.0014, H:0.00004%, the balance of Fe and impurity elements
1) Carrying out deep desulfurization on molten iron, smelting by adopting a converter, adding scrap steel for smelting, and controlling the tapping temperature to be 1644 ℃;
2) Soft blowing is carried out in the LF refining process, the soft blowing time is 5min, and the T [ O ] is controlled to be less than or equal to 0.0020 percent; lime and calcium carbide are added into molten steel to produce slag and desulfurization operation is carried out, the content of W (CaO)/W (Al 2O 3) of the obtained slag is 1.5 in percentage by mass, and the fine adjustment and alloying of the ingredients ensure the content of molten steel; carrying out calcium treatment on molten steel, wherein the adding amount of pure calcium wires is 0.25Kg per ton of molten steel, and carrying out soft argon blowing on the molten steel after the calcium treatment for 7min; RH vacuum treatment, the time is 43min, the vacuum degree is 42Pa, re wire is fed into molten steel during RH vacuum treatment, and soft blowing is carried out for 7min after the RH vacuum treatment is finished.
3) Molten steel continuous casting, namely adopting a large tank long nozzle and a crystallizer immersed nozzle to perform protective casting, covering a heat preservation cover on a casting blank, slowly cooling to promote hydrogen in the steel blank to escape and reduce the hydrogen content in the steel blank, and slowly cooling for 64 hours;
4) And heating the steel billet to 1238 ℃, performing rough rolling, finishing rolling, forming a steel rail, slowly cooling to room temperature, and slowly cooling at the speed of 0.29 ℃/s.
The test steel and the comparative steel U75V are subjected to conventional mechanical property comparison, and the results are shown in Table 1; meanwhile, the hydrogen induced delayed cracking performance of the test steel and the comparative steel is compared, the hydrogen induced delayed cracking performance is carried out in 0.5mol/L H2SO4, the charging current is dynamically applied, and the charging current density is 0.5mA/cm 2 Tensile strain rate 1.0X10 -5 /s, by calculating the surface shrinkage loss (hydrogen embrittlement index I HE )To evaluate the hydrogen induced delayed cracking resistance, I ε Smaller values represent better hydrogen induced delayed cracking resistance. The comparative steels and the hydrogen embrittlement resistant hot forming steels produced by the method have hydrogen induced delayed cracking resistance comparative shown in Table 1.
Table 1 shows the results of performance tests for each example and comparative example of the present invention
As can be seen from the test results in Table 1, the tensile strength of each of the examples 1 to 8 is 1028-1064MPa, the elongation is 12.4-13.8%, and the two properties are higher than those of the comparative examples 1 to 4 and higher than that of the conventional steel U75V. The hydrogen embrittlement law is characterized by higher strength of steel, higher hydrogen embrittlement sensitivity index, while in the embodiments 1-8, although higher in strength, the lowest hydrogen embrittlement sensitivity is provided, the hydrogen embrittlement sensitivity index is not more than 40%, which is lower than 41-43% of the comparative examples 1-4, and the hydrogen embrittlement sensitivity index of the conventional U75V product is as high as 52%. Wherein, the embodiment cases 3-6 are the preferable process products, the hydrogen embrittlement sensitivity index is only 31-33%, and the performance is more excellent, which indicates that the performance of the steel after the preferable steel is further improved. In conclusion, the novel heavy rail steel generation method, particularly the optimized process method, can effectively improve the delayed cracking resistance of the steel.
The above-described embodiments are only preferred examples and are not intended to limit the practice of the present invention.
Claims (9)
1. A manufacturing method for improving the delayed cracking resistance of heavy rail steel is characterized in that the steel comprises, by weight, 0.68% -0.78% of C, 0.43% -0.63% of Si, 1.2% -2.2% of Mn, less than or equal to 0.010% of P, less than or equal to 0.004% of S and (Nb+V+Ti): 0.020 to 0.050 percent, als less than or equal to 0.003 percent, cr 2.2 to 3.2 percent and Re:0.0010 to 0.0020 percent, H is less than or equal to 0.00005 percent, and the balance of Fe and impurity elements are finished by molten iron deep desulfurization, LF refining, molten steel continuous casting and rolling,
wherein, in the LF refining step: firstly, soft blowing is carried out for 3-8min, the T [ O ] is controlled to be less than or equal to 0.0020wt%, meanwhile, aluminum pellets or aluminum wires, lime and calcium carbide are added into molten steel to produce slag, desulfurization operation is carried out, and the components of the slag are controlled to be 2.0-2.5 in percentage by mass of W (CaO)/W (Al 2O 3); then calcium treatment is carried out, wherein the concrete treatment process is to feed pure calcium wires into molten steel, soft argon blowing is carried out on the molten steel after the calcium treatment, the soft argon blowing time is 5-10 min, and finally RH vacuum treatment is carried out.
2. The method for manufacturing heavy rail steel with improved delayed cracking resistance according to claim 1, wherein the Re:0.0013 to 0.0018 percent.
3. The method of manufacturing heavy rail steel according to claim 1, wherein the weight ratio is 2.5 to 3.0%.
4. The method for improving the delayed cracking resistance of heavy rail steel according to claim 1, wherein the amount of pure calcium wire added in the calcium treatment in the LF refining step is 0.15 to 0.40kg per ton of molten steel.
5. The method for improving delayed cracking resistance of heavy rail steel according to any one of claims 1 to 4, wherein the RH vacuum treatment time in the LF refining step is 30 to 50 minutes, the vacuum degree is 50Pa or less, re is fed into the molten steel during RH vacuum treatment, and soft blowing is performed for 5 to 10 minutes after the RH vacuum treatment is completed.
6. The method for manufacturing heavy rail steel with improved delayed cracking resistance according to claim 5, wherein the Re linear addition amount is 0.1-0.25 Kg/ton of molten steel during the RH vacuum treatment in the LF refining step.
7. The method for improving the delayed cracking resistance of a heavy rail steel according to any one of claims 1 to 4, wherein in the molten steel continuous casting step: and controlling the slow cooling time of the cast blank after casting to be 36-72 hours.
8. The method for improving the delayed cracking resistance of a heavy rail steel according to any one of claims 1 to 4, wherein in the rolling step, the slab is heated, rough rolled, finish rolled into a rail, and slowly cooled to room temperature at a slow cooling rate of 0.2 ℃/s to 0.5 ℃/s.
9. The method for manufacturing heavy rail steel having improved delayed cracking resistance according to claim 8, wherein in said rolling step, the billet heating temperature is 1230-1280 ℃.
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