WO2021070452A1 - レール及びその製造方法 - Google Patents
レール及びその製造方法 Download PDFInfo
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- WO2021070452A1 WO2021070452A1 PCT/JP2020/028616 JP2020028616W WO2021070452A1 WO 2021070452 A1 WO2021070452 A1 WO 2021070452A1 JP 2020028616 W JP2020028616 W JP 2020028616W WO 2021070452 A1 WO2021070452 A1 WO 2021070452A1
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- rail
- abdomen
- pearlite
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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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- 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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- C—CHEMISTRY; METALLURGY
- C21—METALLURGY OF IRON
- C21D—MODIFYING THE PHYSICAL STRUCTURE OF FERROUS METALS; GENERAL DEVICES FOR HEAT TREATMENT OF FERROUS OR NON-FERROUS METALS OR ALLOYS; MAKING METAL MALLEABLE, e.g. BY DECARBURISATION OR TEMPERING
- C21D1/00—General methods or devices for heat treatment, e.g. annealing, hardening, quenching or tempering
- C21D1/02—Hardening articles or materials formed by forging or rolling, with no further heating beyond that required for the formation
-
- C—CHEMISTRY; METALLURGY
- C21—METALLURGY OF IRON
- C21D—MODIFYING THE PHYSICAL STRUCTURE OF FERROUS METALS; GENERAL DEVICES FOR HEAT TREATMENT OF FERROUS OR NON-FERROUS METALS OR ALLOYS; MAKING METAL MALLEABLE, e.g. BY DECARBURISATION OR TEMPERING
- C21D1/00—General methods or devices for heat treatment, e.g. annealing, hardening, quenching or tempering
- C21D1/84—Controlled slow cooling
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- C—CHEMISTRY; METALLURGY
- C21—METALLURGY OF IRON
- C21D—MODIFYING THE PHYSICAL STRUCTURE OF FERROUS METALS; GENERAL DEVICES FOR HEAT TREATMENT OF FERROUS OR NON-FERROUS METALS OR ALLOYS; MAKING METAL MALLEABLE, e.g. BY DECARBURISATION OR TEMPERING
- C21D7/00—Modifying the physical properties of iron or steel by deformation
- C21D7/13—Modifying the physical properties of iron or steel by deformation by hot working
-
- C—CHEMISTRY; METALLURGY
- C21—METALLURGY OF IRON
- C21D—MODIFYING THE PHYSICAL STRUCTURE OF FERROUS METALS; GENERAL DEVICES FOR HEAT TREATMENT OF FERROUS OR NON-FERROUS METALS OR ALLOYS; MAKING METAL MALLEABLE, e.g. BY DECARBURISATION OR TEMPERING
- C21D9/00—Heat treatment, e.g. annealing, hardening, quenching or tempering, adapted for particular articles; Furnaces therefor
- C21D9/04—Heat treatment, e.g. annealing, hardening, quenching or tempering, adapted for particular articles; Furnaces therefor for rails
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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
- C22C38/002—Ferrous alloys, e.g. steel alloys containing In, Mg, or other elements not provided for in one single group C22C38/001 - C22C38/60
-
- C—CHEMISTRY; METALLURGY
- C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
- C22C—ALLOYS
- C22C38/00—Ferrous alloys, e.g. steel alloys
- C22C38/04—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
- C22C38/18—Ferrous alloys, e.g. steel alloys containing chromium
-
- 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
- C22C38/20—Ferrous alloys, e.g. steel alloys containing chromium with copper
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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
- C22C38/22—Ferrous alloys, e.g. steel alloys containing chromium with molybdenum or tungsten
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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
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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
- C22C38/26—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
- C22C38/32—Ferrous alloys, e.g. steel alloys containing chromium with boron
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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
- C22C38/38—Ferrous alloys, e.g. steel alloys containing chromium with more than 1.5% by weight of 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
- C22C38/40—Ferrous alloys, e.g. steel alloys containing chromium with nickel
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- E—FIXED CONSTRUCTIONS
- E01—CONSTRUCTION OF ROADS, RAILWAYS, OR BRIDGES
- E01B—PERMANENT WAY; PERMANENT-WAY TOOLS; MACHINES FOR MAKING RAILWAYS OF ALL KINDS
- E01B5/00—Rails; Guard rails; Distance-keeping means for them
- E01B5/02—Rails
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- C—CHEMISTRY; METALLURGY
- C21—METALLURGY OF IRON
- C21D—MODIFYING THE PHYSICAL STRUCTURE OF FERROUS METALS; GENERAL DEVICES FOR HEAT TREATMENT OF FERROUS OR NON-FERROUS METALS OR ALLOYS; MAKING METAL MALLEABLE, e.g. BY DECARBURISATION OR TEMPERING
- C21D2211/00—Microstructure comprising significant phases
- C21D2211/009—Pearlite
Definitions
- the present invention relates to a rail for a railway having a foot, an abdomen, and a head, and a method for manufacturing the rail.
- High-axle heavy railroads with a large load capacity such as those mainly for transporting ore, have a much higher load on the axles of freight cars than passenger cars, and the rail usage environment is harsh. Further, in order to improve the efficiency of transportation by rail, the weight loaded on freight cars is being further increased, and it is required to improve wear resistance, fatigue damage resistance and delayed fracture resistance.
- Patent Documents 1 to 8 disclose rails in which the amount of C is increased from more than 0.85% by mass to 1.20% by mass or less to improve wear resistance. Further, in Patent Documents 3 and 4, the amount of C is set to more than 0.85% by mass and 1.20% by mass or less, and the head of the rail is heat-treated to increase the cementite fraction and thereby wear resistance.
- the improved rail is disclosed.
- Patent Document 5 proposes a rail in which the formation of proeutectoid cementite is suppressed by adding Al and Si, and the fatigue damage resistance is improved.
- Patent Document 6 discloses a rail in which the service life of the rail is improved by setting the Vickers hardness in a range of at least 20 mm from the corner portion of the head portion and the surface of the crown portion of the rail to Hv370 or more. ..
- Patent Document 7 the abdomen is rapidly cooled at a cooling rate of 15 ° C./sec or more, then cooled to a temperature of 250 to 450 ° C., and when the bainite transformation reaches 30% or more, the abdomen is cooled to the Ms point or less.
- a method for making the abdomen into a tough tempered martensite tissue by obtaining the martensite tissue is disclosed.
- Patent Document 8 imparts the residual stress of compression by cooling from the crown to the upper neck or the abdomen with a high-pressure gas or a hydrous gas, and imparts the ability to suppress crack growth in the abdomen.
- Patent Document 7 it is necessary to maintain the temperature until the bainite transformation starts, which lowers the manufacturing efficiency. Further, in the technique disclosed in Patent Document 8, since it is most important to obtain wear resistance / fatigue damage resistance of the head, it is not always possible to obtain a desired ability to suppress crack growth in the abdomen, and manufacturing conditions. Some may produce martensite tissue that is sensitive to cracking.
- the present invention has been made in view of the above circumstances, and provides a rail and a method for manufacturing the rail, which can suppress the growth of cracks in the abdomen and suppress the occurrence of breakage while improving the manufacturing efficiency. With the goal.
- a rail provided with a foot, an abdomen, and a head.
- the composition of the abdominal component C 0.70 to 1.20% by mass, Si: 0.20 to 1.20% by mass, Mn: 0.20 to 1.50% by mass, P: 0.035% by mass or less, S: 0.0005 to 0.012% by mass, Cr: 0.20 to 2.50% by mass, the balance consisting of Fe and unavoidable impurities.
- the area ratio of pearlite in the abdomen is 95% or more. Rails with an average pearlite block size of 60 ⁇ m or less.
- the crack growth rate of the abdomen can be reduced, and the crack growth and breakage of the abdomen can be suppressed.
- FIG. 1 It is a perspective view which shows the preferable embodiment of the rail of this invention. It is a top view which shows the preferable embodiment of the rail of this invention. It is a schematic diagram which shows an example of the rail manufacturing apparatus used in the rail manufacturing method of this invention. It is a schematic diagram which shows an example of the test piece used for the abdominal crack growth test.
- FIG. 1 is a schematic view showing a preferred embodiment of the rail of the present invention.
- the rail 1 in FIG. 1 supports a load for a passenger railroad or a freight railroad, and guides a railroad vehicle in the traveling direction (arrow Y direction), and has a foot (bottom) 2, an abdomen 3, and a head.
- a part 4 is provided.
- the foot portion 2 is placed on a sleeper and has a cross-sectional shape extending in the width direction (arrow X direction).
- the abdomen 3 has a shape extending from the foot 2 in the vertical direction (arrow Z direction), and has a function of ensuring bending rigidity of the rail 1 itself as a beam.
- the head 4 is provided on the upper part of the abdomen 3 and comes into contact with the wheels of the train to directly support the load of the train. When the train travels on the rail 1, the load from the wheels of the train is transmitted from the head 4 to the abdomen 3 and from the abdomen 3 to the foot 2.
- the abdomen 3 Since the abdomen 3 is not a part where the wheels come into direct contact like the head 4, the wear resistance characteristics equivalent to those of the head 4 are not required.
- the abdomen 3 since the abdomen 3 transmits the wheel load applied to the head 4 to the foot 2, when the wheel load is eccentrically applied in the width direction from the center of the head 4, bending stress is applied to the abdomen 3. It may occur and cause horizontal cracks. Therefore, the abdomen 3 is required to have excellent crack growth characteristics. Therefore, the abdomen 3 of the rail 1 has the following composition and steel structure.
- Rail 1 has C: 0.70 to 1.20% by mass, Si: 0.20 to 1.20% by mass, Mn: 0.20 to 1.50% by mass, P: 0.035% by mass or less, S. : 0.0005 to 0.012% by mass, Cr: 0.20 to 2.50% by mass.
- each composition component will be described separately.
- C 0.70 to 1.20% by mass
- C is an essential element for ensuring the strength of the pearlite structure, that is, the fatigue damage resistance, and the fatigue damage resistance improves as the content increases.
- it is less than 0.70% by mass, it is difficult to obtain excellent fatigue damage resistance as compared with the conventional heat-treated pearlite steel rail.
- it exceeds 1.20% by mass a large amount of proeutectoid cementite is generated at the austenite grain boundaries during the pearlite transformation after hot rolling, and the fatigue damage resistance is remarkably lowered.
- proeutectoid cementite is present even when it is 1.20% by mass or less, the effect on fatigue damage resistance is minor because the amount produced is very small. Therefore, the amount of C is set to 0.70 to 1.20% by mass. It is preferably 0.75 to 1.00% by mass. More preferably, it is 0.75 to 0.85%.
- Si 0.20 to 1.20% by mass Si is required as an oxygen scavenger and a strengthening element of the pearlite structure in an amount of 0.20% by mass or more, but if it exceeds 1.20% by mass, the formation of surface defects on the rail is promoted. Therefore, the amount of Si is 0.20 to 1.20% by mass. It is preferably 0.50 to 1.00% by mass.
- Mn 0.20 to 1.50% by mass Since Mn has the effect of lowering the pearlite transformation temperature and making the lamellar spacing denser, it is an effective element for maintaining high hardness up to the inside of the rail 1. If it is less than 0.20% by mass, a sufficient effect cannot be obtained. If it exceeds 1.50% by mass, a martensite structure is likely to be formed, and hardening or embrittlement is likely to occur during heat treatment and welding, and the material is likely to deteriorate. Further, due to the high hardenability of Mn, a large amount of bainite structure is generated on the surface layer of the internal high hardness type rail, and the wear resistance is lowered.
- the amount of Mn is set to 0.20 to 1.50% by mass. It is preferably 0.40 to 1.20% by mass.
- the amount of P is set to 0.035% by mass or less. It is preferably 0.020% by mass or less.
- the steelmaking cost in order to make it less than 0.001%, the steelmaking cost must be increased, so that the content of 0.001% or more is permissible.
- S 0.0005 to 0.012% by mass
- S is mainly present in the steel material in the form of A-based inclusions, but when it exceeds 0.012% by mass, the amount of these inclusions increases remarkably, and at the same time, coarse inclusions are generated, so that the cleanliness of the steel material deteriorates. To do. Further, if it is less than 0.0005% by mass, the steelmaking cost increases. Therefore, the amount of S is set to 0.0005 to 0.012% by mass. It is preferably 0.0005 to 0.010% by mass. More preferably, it is 0.0005 to 0.008% by mass.
- Cr 0.20 to 2.50% by mass Cr is an element that raises the pearlite equilibrium transformation temperature, contributes to the miniaturization of the lamellar interval, and at the same time brings about further increase in strength by strengthening the solid solution. However, if it is less than 0.20% by mass, sufficient internal hardness cannot be obtained. On the other hand, if it is added in an amount of more than 2.50% by mass, the hardenability becomes high and the martensite structure is easily formed. Further, when manufactured under the condition that the martensite structure is not formed, pro-eutectoid cementite is formed at the former austenite grain boundaries. Therefore, wear resistance and fatigue damage resistance are reduced. Therefore, the amount of Cr is set to 0.20 to 2.50% by mass. It is preferably 0.60 to 1.30% by mass.
- the composition of the rail of the present invention is Cu: 1.0% by mass or less, Ni: 1.0% by mass or less, Nb: 0.05% by mass or less, Mo: 1.0% by mass. % Or less, V: 0.005 to 0.10% by mass, W: 1.0% by mass or less, B: 0.005% by mass or less, whichever one or more may be contained.
- each composition component will be described separately.
- Cu 1.0% by mass or less
- Cu is an element that can further increase the strength of steel by solid solution strengthening like Cr. However, if the content exceeds 1.0% by mass, Cu cracking is likely to occur. Therefore, when the component composition contains Cu, the amount of Cu is preferably 1.0% by mass or less. More preferably, it is 0.005 to 0.5% by mass.
- Ni 1.0% by mass or less
- Ni is an element that can increase the strength of steel without deteriorating ductility.
- the rail 1 contains Cu, it is desirable to add Ni together with Cu because it is possible to suppress Cu cracking by adding Ni.
- the Ni content exceeds 1.0% by mass, the hardenability of the steel is further increased and martensite is generated, and the fatigue damage resistance and the fatigue damage resistance tend to be lowered. Therefore, when Ni is contained, the Ni content is preferably 1.0% by mass or less. More preferably, it is 0.005 to 0.5% by mass.
- Nb 0.05% by mass or less Nb is precipitated as carbide during and after hot rolling for forming a rail by combining with C in steel, and effectively acts on the miniaturization of the old austenite particle size. ..
- Nb may be contained with the upper limit of its content being 0.05% by mass. If the amount of Nb is less than 0.001% by mass, it is difficult to obtain a sufficient effect on extending the life of the rail. The effect of extending the service life can be obtained at 0.001% by mass or more. Therefore, when Nb is contained, the Nb content is preferably 0.001% by mass or more. More preferably, it is 0.001 to 0.03% by mass.
- Mo 1.0% by mass or less Mo is an element that can improve hardenability and further increase the strength of steel by solid solution strengthening. However, when the amount of Mo exceeds 1.0% by mass, martensite is formed in the steel, and the wear resistance and the fatigue damage resistance tend to decrease. Therefore, when the component composition of the rail contains Mo, the amount of Mo is preferably 1.0% by mass or less. More preferably, it is 0.005 to 0.5% by mass.
- V 0.005 to 0.10% by mass
- V is an element that forms a carbonitride and is dispersed and precipitated in the matrix to improve fatigue damage resistance and delayed fracture resistance. If the amount of V is less than 0.005% by mass, the effect is small. On the other hand, if the amount of V exceeds 0.10% by mass, the workability deteriorates and the alloy cost also increases, so that the manufacturing cost of the rail material increases. Therefore, the amount of V is set to 0.005 to 0.10% by mass or less. It is preferably 0.01 to 0.08% by mass.
- W 1.0% by mass or less
- W is an element that precipitates as carbide during and after hot rolling for forming into a rail shape, and improves the strength and ductility of the rail by strengthening the precipitation.
- the amount of W exceeds 1.0% by mass, martensite is formed in the steel, and as a result, the ductility is lowered. Therefore, when W is added, the amount of W is preferably 1.0% by mass or less.
- the lower limit of the amount of W is not particularly limited, but it is preferably 0.001% by mass or more in order to exhibit the above-mentioned action of improving strength and ductility. More preferably, it is 0.005 to 0.5% by mass.
- B 0.005% by mass or less
- B is an element that improves hardenability and rail strength by segregating at the old austenite grain boundaries. However, if the B content exceeds 0.005% by mass, a martensite structure is formed, and as a result, wear resistance and fatigue damage resistance are lowered. Therefore, when B is contained, the B content is preferably 0.005% by mass or less.
- the lower limit of the amount of B is not particularly limited, but it is preferably 0.001% by mass or more in order to exhibit the above-mentioned action of improving strength and ductility. More preferably, it is 0.001 to 0.003% by mass.
- Fe and unavoidable impurities are contained in the balance of the above composition components.
- Inevitable impurities are those that are present in the raw material or are inevitably mixed in the manufacturing process, and are originally unnecessary, but they are allowed to be contained because they are in trace amounts and do not affect the characteristics.
- unavoidable impurities include N, O and the like, where N can be tolerated up to 0.0080% by mass and O can be tolerated up to 0.004% by mass.
- Ti forms an oxide and causes a decrease in fatigue damage resistance, which is a basic characteristic of the rail. Therefore, it is preferable to control it to 0.0010% by mass or less.
- the abdomen 3 of the rail 1 is composed of pearlite tissue having an area ratio of 95% or more.
- the abdomen 3 of the rail 1 may contain a trace amount of bainite structure, martensite structure, proeutectoid cementite structure, and proeutectoid ferrite structure in total of 5% or less.
- the pearlite structure (pearlite block) is a lamellar structure in which ferrite and cementite are arranged in layers, and the pearlite block is composed of a group of pearlite grains having the same orientation. There is a relationship between the pearlite structure and crack growth, and the pearlite grain boundaries serve as a barrier to crack growth. When the area ratio of the pearlite tissue in the abdomen 3 is less than 95%, the pearlite grain boundaries that hinder crack growth are insufficient. Therefore, the abdomen 3 of the rail 1 contains a pearlite tissue having an area ratio of 95% or more.
- the pearlite block has an average size of 60 ⁇ m or less.
- the pearlite grain boundaries have a function of acting as a barrier when cracks grow and hindering cracks from growing. Therefore, when the size of the pearlite block is miniaturized, the probability of passing through the grain boundaries having the effect of suppressing crack growth increases, and as a result, crack growth is suppressed. If the average size of the pearlite block is larger than 60 ⁇ m, the effect of suppressing crack growth cannot be sufficiently obtained. Therefore, the average size of the pearlite block is 60 ⁇ m or less, preferably 40 ⁇ m or less.
- FIG. 3 is a schematic view showing an example of a rail manufacturing apparatus.
- the rail manufacturing apparatus 10 of FIG. 3 includes a BD (breakdown) rolling mill 11, rough rolling mills 12 and 13, a finishing rolling mill 14, and a cooling facility 15.
- the BD rolling mill 11, the rough rolling mills 12, 13 and the finishing rolling mill 14 hot-roll the steel pieces, and the cooling facility 15 cools the hot-rolled steel pieces.
- the finish rolling mill 14 is used for rolling by, for example, a hole rolling method, in which holes are arranged on two upper and lower rolls according to a desired cross-sectional shape, and the holes are directly placed on the abdomen 3, the head 4, and the foot 2. Add rolling. By adjusting the shape of the hole provided in the upper and lower rolls, the amount of reduction of the abdomen 3, the head 4, and the foot 2 is controlled.
- the steel piece SS (material billet) reheated in the heating furnace is rolled in the BD (breakdown) rolling mill 11 so as to have an approximate shape of the rail 1.
- the steel piece SS rolled by the BD rolling mill 11 is hot-rolled by the rough rolling mills 12 and 13.
- the austenite grains coarsened by heating are refined by repeating rolling and recrystallization in the recrystallization temperature range in the BD rolling mill 11 and the rough rolling mills 12 and 13.
- the finishing temperature means the surface temperature of the abdomen 3 at the time of finish rolling, but the surface temperature of the head 4 may be regarded as the finishing temperature of the abdomen 3.
- the austenite grains are elongated without being recrystallized, and a deformation zone is formed in the grains. Then, at the time of transformation from austenite to pearlite, the deformation zone in the grain acts as a nucleation site of pearlite transformation together with the austenite grain boundary. Then, the pearlite grains become finer. If the finishing temperature is higher than the recrystallization temperature range, recovery by recrystallization occurs, so that the pearlite block cannot be miniaturized to an average size of 60 ⁇ m or less.
- an unrecrystallized temperature range low temperature range
- the finish temperature at the time of finish rolling is set to 1000 ° C. or lower, which is the unrecrystallized temperature range (low temperature range). If the finishing temperature is less than 800 ° C., the load on the roll during rolling becomes extremely large. Further, since rolling is performed in a low temperature region of austenite, a remarkable processing strain is introduced into the austenite crystal grains, and as a result, a desired effect of suppressing crack growth cannot be obtained. Therefore, the finish rolling is preferably performed at a finishing temperature of 800 to 900 ° C.
- finish rolling is performed so that the surface reduction rate of the abdomen 3 is 10% or more.
- the surface reduction rate is smaller than 10%, the pearlite block cannot be miniaturized to an average size of 60 ⁇ m or less, and the effect of suppressing crack growth cannot be obtained. More preferably, the reduction rate is 30% or more.
- the abdomen 3 of the rail is accelerated and cooled at a cooling rate of 1 to 5 ° C./s from a temperature above the pearlite transformation start temperature to a temperature range of 400 to 600 ° C. in the cooling facility 15.
- the cooling stop temperature means, for example, the surface temperature when the central portion of the rail abdomen 4 is measured with a radiation thermometer when cooling is stopped.
- the cooling rate means the cooling rate (° C./sec) by converting the temperature change from the start of cooling to the stop of cooling per unit time (seconds).
- the cooling rate is faster than 5 ° C./s, the area ratio of the pearlite structure decreases and the area ratio of the martensite structure or the like increases, and the pearlite structure cannot have an area ratio of 95% or more.
- the abdomen 3 made of pearlite containing pearlite tissue in an area ratio of 95% or more can be formed. Further, unlike the conventional case, it is not necessary to maintain the temperature until the bainite transformation starts, so that the production efficiency can be improved.
- FIG. 4 is a schematic view showing an example of a test piece.
- Table 2 shows the rail manufacturing conditions and test results.
- the finishing temperature is a value obtained by measuring the surface temperature of the abdomen 3 on the entrance side of the finishing rolling mill 14 with a radiation thermometer
- the cooling stop temperature is the surface temperature of the abdomen 3 when cooling is stopped. Is the value measured with a radiation thermometer.
- a test piece for microscopic L cross-section observation is collected from the center position of the abdomen of the rail, embedded, mirror-polished, and then orientation analysis is performed using EBSD (Electron backscatter diffraction pattern), and each orientation. It is a value obtained by measuring the particle size of pearlite grains in the equivalent of a circle and averaging them. A grain boundary having an orientation difference of 5 ° or more between adjacent crystal orientations was determined to be another pearlite block.
- the measurement area was 300 ⁇ m square, the measurement steps were 0.3 ⁇ m intervals, and measurement points with a confidex index of 0.1 or less, which indicates the reliability of the measurement orientation, were excluded from the measurement. Furthermore, the crystal grains on the edge of the measurement region were also excluded from the measurement targets.
- P in Table 2 refers to the case where the area ratio of the pearlite structure is 95% or more and a total of 5% or less contains a trace amount of bainite structure, martensite structure, proeutectoid cementite structure, and proeutectoid ferrite structure. means.
- a known technique can be used to measure the area ratio of the pearlite structure. For example, the collected test piece is polished and then corroded with nital, and the type of the structure is identified by 400 times cross-sectional observation using an optical microscope. Then, the area ratio of the pearlite structure is calculated by image analysis.
- the structure of the abdomen 3 of the rail 1 is controlled by controlling the steel composition, the finish rolling conditions and the cooling conditions, and the crack growth rate of the abdomen 3 of the rail 1 is reduced. It is possible to suppress crack growth and breakage of the abdomen 3.
- the embodiment of the present invention is not limited to the above embodiment, and various modifications can be made.
- the manufacturing conditions of the abdomen 3 are illustrated, but when the abdomen 3 is hot-rolled, the foot portion 2 and the head portion 4 are also hot-rolled at the same time. Therefore, for example, using a steel piece containing a composition component that satisfies the performance requirements of both the abdomen 3 and the head 4, hot rolling and cooling under different conditions are performed on the abdomen 3 and the head 4, and the abdomen 3 is subjected to hot rolling and cooling.
- a rail 1 that satisfies both the crack growth suppressing property and the wear resistance of the head 4 may be manufactured.
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Abstract
Description
[1] 足部と、腹部と、頭部とを備えたレールであって、
前記腹部の成分組成が、
C:0.70~1.20質量%、
Si:0.20~1.20質量%、
Mn:0.20~1.50質量%、
P:0.035質量%以下、
S:0.0005~0.012質量%、
Cr:0.20~2.50質量%を含有し、残部がFeおよび不可避的不純物からなり、
前記腹部におけるパーライトの面積率は、95%以上であり、
パーライトブロックの平均サイズは、60μm以下であるレール。
[2] さらに、Cu:1.0質量%以下、Ni:1.0質量%以下、Nb:0.05質量%以下、Mo:1.0質量%以下およびV:0.005~0.10質量%、W:1.0質量%以下、B:0.005質量%以下のいずれか1種または2種以上を含有する[1]に記載のレール。
[3] 応力拡大係数ΔK=20MPa・m1/2における前記腹部のき裂進展速度da/dN(m/cycle)は、8.0×10-8以下である[1]または[2]に記載のレール。
[4] [1]から[3]のいずれかに記載の成分組成を有する鋼片からレールを製造するレールの製造方法であって、
仕上温度が1000℃以下であって、前記腹部の減面率が10%以上になるように仕上げ圧延し、
仕上げ圧延後の前記腹部をパーライト変態開始温度以上の温度から400~600℃の温度域までを1~5℃/sの冷却速度で冷却するレールの製造方法。
[5] 前記仕上温度が800~900℃の範囲内で前記腹部の仕上げ圧延を行う[4]に記載のレールの製造方法。
Cはパーライト組織の強度すなわち耐疲労損傷性を確保するための必須元素であり、含有量の増加に伴い耐疲労損傷性が向上する。しかし、0.70質量%未満では従来の熱処理型パーライト鋼レールと比較して優れた耐疲労損傷性を得ることが難しい。また、1.20質量%を超えると熱間圧延後のパーライト変態時に多量の初析セメンタイトがオーステナイト粒界に生成し、耐疲労損傷性が著しく低下する。なお、初析セメンタイトは1.20質量%以下の場合にも存在するが、生成する量が微量であるため、耐疲労損傷性への影響は軽微である。したがって、C量は0.70~1.20質量%とする。好ましくは0.75~1.00質量%である。さらに好ましくは0.75~0.85%である。
Siは脱酸素剤及びパーライト組織の強化元素として0.20質量%以上必要であるが、1.20質量%を超えるとレールの表面疵の生成を促進させる。したがってSi量は0.20~1.20質量%とする。好ましくは0.50~1.00質量%である。
Mnはパーライト変態温度を低下させてラメラー間隔を緻密にする効果があるため、レール1の内部まで高硬度を維持するために有効な元素である。0.20質量%未満では十分な効果が得られない。1.50質量%を超えるとマルテンサイト組織が生じ易く、熱処理時及び溶接時に硬化や脆化を生じ材質が劣化し易い。また、Mnの高い焼入れ性のため、内部高硬度型レールの表層に多量のベイナイト組織が生成され、耐摩耗性が低下する。さらに、過剰な添加はパーライトの平衡変態温度を低下させ、過冷度が小さくなりラメラー間隔が粗大化する。したがって、Mn量は0.20~1.50質量%とする。好ましくは0.40~1.20質量%である。
0.035%を超えるPの含有は延性を劣化する。したがって、P量は0.035質量%以下とする。好ましくは0.020質量%以下である。なお、0.001%未満とするためには、製鋼コストの増加が余儀なくされることから、0.001%以上の含有は許容される。
Sは主にA系介在物の形態で鋼材中に存在するが、0.012質量%を超えるとこの介在物量が著しく増加し、同時に粗大な介在物を生成するため、鋼材の清浄性が悪化する。また、0.0005質量%未満にすると、製鋼コストが増加する。したがって、S量は0.0005~0.012質量%とする。好ましくは0.0005~0.010質量%である。より好ましくは0.0005~0.008質量%である。
Crはパーライト平衡変態温度を上昇させ、ラメラー間隔の微細化に寄与すると同時に、固溶強化によりさらなる高強度化をもたらす元素である。しかし、0.20質量%未満では十分な内部硬度が得られない。一方、2.50質量%を超えて添加すると焼入れ性が高くなり、マルテンサイト組織が生成し易くなる。また、マルテンサイト組織が生成しない条件で製造した場合、旧オーステナイト粒界に初析セメンタイトが生成する。そのため、耐摩耗性および耐疲労損傷性が低下する。したがって、Cr量は0.20~2.50質量%とする。好ましくは0.60~1.30質量%である。
Cuは、Crと同様に固溶強化により鋼の更なる高強度化を図ることができる元素である。ただし、その含有量が1.0質量%を超えるとCu割れが生じ易くなる。したがって、成分組成がCuを含有する場合は、Cu量は1.0質量%以下とすることが好ましい。より好ましくは0.005~0.5質量%である。
Niは、延性を劣化することなく鋼の高強度化を図ることができる元素である。また、レール1がCuを含有する場合、Niを添加するとCu割れを抑制することができるため、NiをCuとともに複合添加することが望ましい。ただし、Ni含有量が1.0質量%を超えると、鋼の焼入れ性がより上昇し、マルテンサイトが生成するようになり、耐疲労損傷性と耐疲労損傷性が低下する傾向がある。したがって、Niが含有される場合は、Ni含有量は1.0質量%以下とすることが好ましい。より好ましくは0.005~0.5質量%である。
Nbは、鋼中のCと結び付いてレールを成形するための熱間圧延中および熱間圧延後に炭化物として析出し、旧オーステナイト粒径の微細化に有効に作用する。その結果、耐疲労損傷性、耐疲労損傷性及び延性が大きく向上し、レールの長寿命化に大きく寄与する。ただし、Nb量が0.05質量%超えても、耐摩耗性、耐疲労損傷性の向上効果が飽和し、含有量上昇に見合う効果が得られない。したがって、Nbは、その含有量の上限を0.05質量%として含有してもよい。なお、Nb量は0.001質量%未満では、上記のレールの長寿命化に対して十分な効果が得られにくい。0.001質量%以上で長寿命化の効果が得られる。したがって、Nbを含有させる場合は、Nb含有量は0.001質量%以上であることが好ましい。より好ましくは0.001~0.03質量%である。
Moは焼入れ性を向上させ、固溶強化によってさらなる鋼の高強度化を図ることができる元素である。ただし、Mo量が1.0質量%を超えると、鋼中にマルテンサイトが生成するようになり、耐摩耗性と耐疲労損傷性とが低下する傾向がある。したがって、レールの成分組成がMoを含有する場合は、Mo量は1.0質量%以下とすることが好ましい。より好ましくは0.005~0.5質量%である。
Vは炭窒化物を形成し、基地中へ分散析出し、耐疲労損傷性および耐遅れ破壊特性を向上させる元素である。V量が0.005質量%未満ではその効果が少ない。一方、V量が0.10質量%を超えると、加工性が劣化し、合金コストも増加するため、レール材の製造コストが増加する。したがって、V量は0.005~0.10質量%以下とする。好ましくは0.01~0.08質量%である。
Wは、レール形状への成形を行う熱間圧延中及び熱間圧延後に炭化物として析出し、析出強化によりレールの強度や延性を向上させる元素である。しかし、W量が1.0質量%を超えると鋼中にマルテンサイトが生成し、その結果、延性が低下する。そのため、Wを添加する場合、W量を1.0質量%以下とすることが好ましい。一方、W量の下限は特に限定されないが、上記の強度や延性を向上させる作用を発現させるためには0.001質量%以上とすることが好ましい。より好ましくは0.005~0.5質量%である。
Bは、旧オーステナイト粒界に偏析することで、焼入れ性を向上させレールの強度を向上させる元素である。しかし、B含有量が0.005質量%を超えるとマルテンサイト組織が生成され、その結果、耐摩耗性と耐疲労損傷性が低下する。そのため、Bを含有する場合、B含有量を0.005質量%以下とすることが好ましい。一方、B量の下限は特に限定されないが、上記の強度や延性を向上させる作用を発現させるためには0.001質量%以上とすることが好ましい。より好ましくは0.001~0.003質量%である。
レール1の腹部3は、95%以上の面積率のパーライト組織からなっている。なお、レール1の腹部3には、合計5%以下の微量なベイナイト組織、マルテンサイト組織、初析セメンタイト組織、初析フェライト組織が含まれていてもよい。パーライト組織(パーライトブロック)はフェライトとセメンタイトとが層状に配列されたラメラー組織であって、パーライトブロックは同一方位を有するパーライト粒の集団からなるものである。パーライト組織とき裂進展との間には関連性があり、パーライト粒界はき裂進展の障壁となる機能を有する。腹部3のパーライト組織の面積率が95%未満である場合、き裂進展の障害になるパーライト粒界が不足する。このため、レール1の腹部3は、95%以上の面積率のパーライト組織を含有したものになっている。
図3は、レール製造装置の一例を示す模式図である。図3のレール製造装置10は、BD(ブレークダウン)圧延機11、粗圧延機12、13、仕上げ圧延機14及び冷却設備15を有する。このBD圧延機11、粗圧延機12、13及び仕上げ圧延機14が鋼片に熱間圧延を行い、冷却設備15が熱間圧延された鋼片を冷却する。仕上げ圧延機14は、例えば孔型圧延法により圧延を行うものであって、上下2つのロールに所望の断面形状に応じた孔型を配置し、腹部3、頭部4ならびに足部2に直接圧下を加える。この上下ロールに設ける孔型の形状を調整することで、腹部3、頭部4ならびに足部2の圧下量が制御される。
はじめに、組成成分の異なる鋼A1~A15、B1~B6が作製される。下記表1に鋼A1~A15、B1~B6の成分を示す。なお、表1において空白の部分は含有されてない、もしくは含有量が不可避不純物の範疇であって無視できることを意味する。
図4の試験片を用いて応力比R=0.1の条件で疲労き裂伝播試験を行い、応力拡大係数ΔK=20MPa・m1/2における、疲労き裂伝播速度da/dN(m/cycle)を測定し、腹部の耐表面損傷性を評価した。この数値が8.0×10-8以下であればき裂伝播抑止性能があると評価した。
2 足部(底部)
3 腹部
4 頭部
10 レール製造装置
11 BD圧延機
12、13 粗圧延機
14 仕上げ圧延機
15 冷却設備
SS 鋼片
Claims (5)
- 足部と、腹部と、頭部とを備えたレールであって、
前記腹部の成分組成が、
C:0.70~1.20質量%、
Si:0.20~1.20質量%、
Mn:0.20~1.50質量%、
P:0.035質量%以下、
S:0.0005~0.012質量%、
Cr:0.20~2.50質量%を含有し、残部がFeおよび不可避的不純物からなり、
前記腹部におけるパーライトの面積率は、95%以上であり、
パーライトブロックの平均サイズは、60μm以下であるレール。 - さらに、Cu:1.0質量%以下、Ni:1.0質量%以下、Nb:0.05質量%以下、Mo:1.0質量%以下およびV:0.005~0.10質量%、W:1.0質量%以下、B:0.005質量%以下のいずれか1種または2種以上を含有する請求項1に記載のレール。
- 応力拡大係数ΔK=20MPa・m1/2における前記腹部のき裂進展速度da/dN(m/cycle)は、8.0×10-8以下である請求項1または2に記載のレール。
- 請求項1から3のいずれか1項に記載の成分組成を有する鋼片からレールを製造するレールの製造方法であって、
仕上温度が1000℃以下であって、前記腹部の減面率が10%以上になるように仕上げ圧延し、
仕上げ圧延後の前記腹部をパーライト変態開始温度以上の温度から400~600℃の温度域までを1~5℃/sの冷却速度で冷却するレールの製造方法。 - 前記仕上温度が800~900℃の範囲内で前記腹部の仕上げ圧延を行う請求項4に記載のレールの製造方法。
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- 2020-07-27 WO PCT/JP2020/028616 patent/WO2021070452A1/ja unknown
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Also Published As
Publication number | Publication date |
---|---|
JPWO2021070452A1 (ja) | 2021-10-21 |
CA3157401C (en) | 2024-04-09 |
CA3157401A1 (en) | 2021-04-15 |
CN114502761B (zh) | 2024-01-09 |
JP7063400B2 (ja) | 2022-05-09 |
AU2020364505B2 (en) | 2023-08-03 |
US20230250505A1 (en) | 2023-08-10 |
EP4023777A1 (en) | 2022-07-06 |
AU2020364505A1 (en) | 2022-04-28 |
CN114502761A (zh) | 2022-05-13 |
EP4023777A4 (en) | 2023-03-01 |
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