Steel for wheel

Abstract

A steel for wheel contains, in mass %, C: 0.65 to 0.84%, Si: 0.4 to 1.0%, Mn: 0.50 to 1.40%, Cr: 0.02 to 0.13%, S: 0.04% or less and V: 0.02 to 0.12%, wherein Fn1 expressed by formula (1) is 32 to 43, and Fn2 expressed by formula (2) is 25 or less, the balance being Fe and impurities. P, Cu and Ni as impurities are P: 0.05% or less, Cu: 0.20% or less and Ni: 0.20% or less:
Fn1=2.7+29.5'C+2.9'Si+6.9'Mn+10.8'Cr+30.3'Mo+44.3'V   (1)
Fn2=exp(0.76)'exp(0.05'C)'exp(1.35'Si)'exp(0.38'Mn)'exp(0.77'Cr)'exp(3.0'Mo)'exp(4.6'V)  (2).
The steel has excellent properties for use as a wheel.

Claims

1. A steel for wheel comprising: in mass %, C: 0.65 to 0.84%; Si: 0.65 to 1.0%; Mn: 0.50 to 1.40%; Cr: 0.02 to 0.13%; S: 0.04% or less and V: 0.02 to 0.12%, wherein Fn1 expressed by the following formula (1) is 32 to 43, and Fn2 expressed by the following formula (2) is 25 or less, the balance being Fe and impurities, and P, Cu and Ni in the impurities are P: 0.05% or less, Cu: 0.20% or less, and NI: 0.20% or less:
Fn1=2.7+29.5×C+2.9×Si+6.9×Mn+10.8×Cr+30.3×Mo+44.3×V  (1)
Fn2=exp(0.76)×exp(0.05×C)×exp(1.35×Si)×exp(0.38×Mn)×exp(0.77×Cr)×exp(3.0×Mo)×exp(4.6×V)  (2) where each symbol of element in the formulas (1) and (2) means content (mass %) of each element.

2. The steel for wheel according to claim 1, comprising, in mass %, Mo: 0.07% or less in place of a part of Fe, and a total content of V and Mo is 0.02 to 0.12%.

3. The steel for wheel according to claim 1, comprising, in mass %, Al: 0.20% or less in place of a part of Fe.

4. The steel for wheel according to claim 2, comprising, in mass %, AI: 0.20% or less in place of a part of Fe.

Description

BRIEF DESCRIPTION OF DRAWINGS

(1) FIG. 1 is a view schematically explaining “monoblock wheel” as an example of a wheel.

(2) FIG. 2 is a diagram organizing and showing a relationship of “40 mm hardness” that is Rockwell C hardness at a position 40 mm from a water cooled end and “Fn1” expressed by the formula (1), with respect to steels 1 to 24. “Bainite” in the drawing indicates that a bainitic microstructure is formed in part.

(3) FIG. 3 is a diagram organizing and showing a relationship of “M50%” that is a distance from a water-cooled end in a unit of millimeter where a martensitic microstructure fraction becomes 50% and “Fn2” expressed by the formula (2), with respect to steels 1 to 24.

(4) FIG. 4 is a view showing configurations of “wheel test specimen” and “rail test specimen” used in a rolling contact fatigue test. (a) in the drawing shows “wheel test specimen”, and (b) shows “rail test specimen”. Note that the unit of the dimensions in the drawing is “mm”.

(5) FIG. 5 is a view showing configurations of “wheel test specimen” and “rail test specimen” used in wear test. (a) in the drawing shows “wheel test specimen”, and (b) shows “rail test specimen”. Note that the unit of the dimensions in the drawing is “mm”.

(6) FIG. 6 is a view schematically explaining a method for a rolling contact fatigue test using the wheel test specimen shown in FIG. 4(a), and the rail test specimen shown in FIG. 4(b).

(7) FIG. 7 is a diagram organizing and showing a relationship of rolling contact fatigue life and “Fn1” expressed by the formula (1). “Bainite” in the drawing indicates that a bainitic microstructure is formed in part.

(8) FIG. 8 is a view schematically explaining a method for wear test using the wheel test specimen shown in FIG. 5(a) and the rail test specimen shown in FIG. 5(b).

(9) FIG. 9 is a diagram organizing and showing a relationship of amount of wear and “Fn1” expressed by the formula (1). “Bainite” in the drawing indicates that a bainitic microstructure is formed in part.

(10) FIG. 10 is a diagram organizing and showing a relationship of a thickness of a white layer and “Fn2” expressed by the formula (2), with respect to each of steel 1, steel 2, steel 5, steel 11, steel 12 and steel 14.

(11) FIG. 11 is a diagram organizing and showing a relationship of crack initiation life and “Fn2” expressed by the formula (2), with respect to each of steel 1, steel 2, steel 5, steel 11, steel 12 and steel 14.

(12) FIG. 12 is a diagram organizing a result of high temperature yield strength with V content.

(13) FIG. 13 is a diagram organizing a result of normal temperature elongation with the V content.

(14) FIG. 14 is a view explaining equipment used in an example for performing so-called “tread quench” for a wheel.

(15) FIG. 15 is a view explaining a measurement position of Brinell hardness of the wheel produced in the example.

(16) FIG. 16 is a view explaining a position where a microstructure of a rim portion of the wheel produced in the example was examined.

(17) FIG. 17 is a view explaining a position where a microstructure of a hub portion of the wheel produced in the example was examined.

(18) FIG. 18 is a view explaining a position where wear test specimen, a rolling contact fatigue test specimen and a Jominy test specimen were taken from the wheel produced in the example. With the positions shown by “a”, “b” and “c” in the drawing as the references, the wear test specimen, the rolling contact fatigue test specimen and the Jominy test specimen were taken respectively.

MODE FOR CARRYING OUT THE INVENTION

(19) Hereinafter, respective requirements of the present invention will be described in detail. Note that “%” of a content of each element means “mass %”.

(20) C: 0.65 to 0.84%

(21) C increases hardness, and improves wear resistance and rolling contact fatigue resistance. Further, C in this range has a small influence on hardenability, and can increase hardness without reducing spalling resistance so much. When the content of C is below 0.65%, sufficient hardness cannot be obtained, an area fraction of ferrite further increases, and wear resistance is reduced. When the content of C exceeds 0.84%, coarse hyper-eutectoid cementite is formed in a wheel hub portion, and sometimes extremely reduced toughness and fatigue life, which is not favorable in safety. Therefore, the content of C is set at 0.65 to 0.84%. The content of C is preferably set at 0.68% or more, and is preferably set at 0.82% or less.

(22) Si: 0.4 to 1.0%

(23) Si is an element that increases hardness by decreasing the lamellar spacing of pearlite, and solid-solution strengthening ferrite in a pearlitic microstructure, and further increases high temperature strength and ductility. When the content of Si is below 0.4%, the aforementioned effects are insufficient, and it is difficult to obtain high temperature strength and ductility. When the content of Si exceeds 1.0%, toughness is reduced, hardenability is further increased and spalling resistance is also reduced. Therefore, the content of Si is set at 0.4 to 1.0%. However, in order to increase hardness, high temperature strength and ductility by Si, the content thereof is preferably set at 0.5% or more in particular, and is more preferably set at 0.65% or more. Meanwhile, Si increases hardenability, and therefore, the content thereof is preferably set at 0.90% or less.

(24) Mn: 0.50 to 1.40%

(25) Mn is an element that increases hardness by decreasing lamellar spacing of pearlite, and solid-solution strengthening ferrite in a pearlitic microstructure. Mn also has an effect of forming MnS to trap S in the steel, and suppressing grain boundary embrittlement. When the content of Mn is less than 0.50%, the aforementioned effects, above all, the trapping effect of S becomes insufficient. When the content of Mn exceeds 1.40%, a bainitic microstructure is formed to reduce wear resistance, hardenability is further increased, and spalling resistance is also reduced. Therefore, the content of Mn is set at 0.50 to 1.40%. The content of Mn is preferably set at 1.20% or less.

(26) Cr: 0.02 to 0.13%

(27) Cr has the effect of significantly increasing the hardness of pearlite by decreasing lamellar spacing of the pearlite. When the content of Cr is less than 0.02%, these effects are not sufficient. When the content of Cr exceeds 0.13%, carbides are difficult to dissolve into austenite at the time of heating, and depending on the heating conditions, there arise the possibility of undissolved carbides being formed to reduced hardness, toughness, fatigue strength and the like. Further, when a heat-treated wheel is produced, a bainitic microstructure with low wear resistance is easily formed directly under a tread. Further, hardenability is increased, and spalling resistance is reduced. Therefore, the content of Cr is set at 0.02 to 0.13%. The content of Cr is preferably set at 0.05% or more, and is preferably set at 0.12% or less.

(28) S: 0.04% or less

(29) S is an impurity normally contained in steel, and has a small influence on hardness and hardenability, but has the effect of improving machinability. Therefore, S may be positively contained, but excessive S reduced toughness of steel. Therefore, the content of S is set at 0.04% or less. The content of S is preferably set at 0.03% or less. Note that the effect of improving machinability is remarkable when the content of S is 0.005% or more.

(30) V: 0.02 to 0.12%

(31) V precipitates on ferrite in pearlite as a V carbide, and has the effect of significantly increasing the hardness of the pearlite. Further, V has the effect of increasing yield strength at a high temperature. When the content of V is less than 0.02%, these effects are not sufficient. When V exceeding 0.12% is contained, normal temperature elongation is reduced, in addition to which, hardenability is increased, and spalling resistance is reduced. Therefore, when V is contained, the content thereof is set at 0.02 to 0.12%. The content of V is preferably set at 0.07% or less, and is more preferably set at 0.05% or less.

(32) Fn1 (refer to formula (1)): 32 to 43

(33) When Fn1 is less than 32, wear resistance and rolling contact fatigue resistance are hardly improved as compared with the case of using the steel for railway wheel of “Class C” of AAR, and depending on the case, wear resistance and rolling contact fatigue resistance become lower than “Class C”. Therefore, steel with Fn1 being less than 32 is difficult to use as the steel of a railway wheel used under extremely harsh environments in which the traveling distances increase and loading capacities increase. When Fn1 exceeds 43, it becomes difficult to obtain a microstructure consisting principally of pearlite, and wear resistance is reduced. Further, hardness increases too much, and therefore, ductility and toughness are reduced. Therefore, Fn1 is set to be in a range of 32 to 43. Fn1 is preferably 37 or less, and is more preferably 36 or less.

(34) Fn2 (refer to formula (2)): 25 or less

(35) When Fn2 exceeds 25, hardenability becomes high, which leads to reduced in spalling resistance. Fn2 is preferably 20 or less, and is more preferably 15 or less.

(36) Note that when Fn2 is less than 3, it becomes difficult to make Fn1 expressed by the formula (1) 32 or more. Therefore, Fn2 is preferably 3 or more.

(37) One of steels for wheel of the present invention contains the above described elements, the balance consists of Fe and impurities, and the contents of P, Cu and Ni as the impurities should be limited to a certain range. The range of the contents of the respective elements and the reason of limitation are as follows.

(38) P: 0.05% or less

(39) P is an impurity contained in steel. When the content of P exceeds 0.05%, toughness is reduced. Accordingly, the content of P in the impurities is set at 0.05% or less. The content of P, which is more preferable, is 0.025% or less.

(40) Cu: 0.20% or less

(41) Cu is an impurity contained in steel. When the content of Cu exceeds 0.20%, the occurrence of a surface defect at the production time increases, hardenability is further increased, and spalling resistance is reduced. Accordingly, the content of Cu in the impurities is set at 0.20% or less. The content of Cu which is more preferable is 0.10% or less.

(42) Ni: 0.20% or less

(43) Ni is an impurity contained in steel. When the content of Ni exceeds 0.20%, hardenability is increased and spalling resistance is reduced. Accordingly, the content of Ni in the impurities is set at 0.20% or less. The content of Ni which is more preferable is 0.10% or less.

(44) The steel for wheel of the present invention may contain Mo in place of part of Fe, in accordance with necessity. The range of the content of Mo and the reason of limitation are as follows.

(45) Mo: 0.07% or less

(46) Mo has an effect of increasing the hardness of pearlite, and has the effect of increasing yield strength at a high temperature, similarly to V. When the content of Mo exceeds 0.07%, it become easy to form a bainitic microstructure directly under a tread to reduced wear resistance when a heat-treated wheel is produced, hardenability is further increased, and spalling resistance is reduced. Therefore, when Mo is contained, the content thereof is set at 0.07% or less. The content of Mo is preferably set at 0.02% or more.

(47) Especially when both V and Mo are contained, the total content (V+Mo) is set at 0.02 to 0.12%. The upper limit that is more preferable is 0.07%, and the upper limit that is far more preferable is 0.05%.

(48) The steel for wheel of the present invention may contain Al in accordance with necessity. A range of the content of Al and the reason of limitation are as follows.

(49) Al: 0.20% or less

(50) Al may be contained, because Al has the effect of refining grains to improve toughness. However, if the content of Al exceeds 0.20%, coarse inclusions increase, and reduced toughness and fatigue strength. Accordingly, when Al is contained, the content thereof is set at 0.20% or less. The Al content is preferably set at 0.08% or less. The effect of improving toughness is remarkable when the Al content is 0.002% or more. In particular, the Al content is preferably set at 0.011% or more.

(51) The microstructure of the wheel with the steel for wheel of the present invention desirably has 90% or more of the area fraction of the pearlitic microstructure with respect to the rim portion, and the most desirably has 100% of pearlitic microstructure. The reason is that the microstructures other than the microstructure of pearlite, such as the microstructures of ferrite and bainite have low wear resistance, and therefore, the total area fraction of the microstructures other than the microstructure of pearlite is desirably 10% or less. Further, the microstructure in which hyper-eutectoid cementite does not precipitate is desired. The reason thereof is that precipitation of hyper-eutecticoid cementite reduce toughness.

(52) With respect to the hub portion, the microstructure is desirably similar to that of the rim portion, and it does not especially become a problem if the area fraction of the microstructures other than pearlite exceeds 10%. However, the microstructure in which hyper-eutectoid cementite does not precipitate is desirable. The reason thereof is that there is the case in which precipitation of the hyper-eutecticoid cementite causes extreme reduced of toughness and fatigue life, and at least formation of the hyper-eutecticoid cementite that can be observed by an optical microscope has to be avoided.

(53) The wheel which adopts the steel for wheel of the present invention as can be produced by sequentially performing treatments described in the following <1> to <3>, for example. After the treatment of <3>, temper treatment may be performed.

(54) <1> Melt and Casting of Steel:

(55) After steel is melted by an electric furnace, a converter or the like, the steel is cast into an ingot. Note that the ingot may be any one of a cast piece by continuous casting, and an ingot molded in a mold.

(56) <2> Forming into Wheel:

(57) In order to form the steel into a predetermined wheel configuration, the steel is formed by a proper method such as hot forging and machining directly from the ingot, or after the ingot is formed into end steel pieces. Note that the steel may be directly formed into a wheel configuration by casting, but hot forging is desirably performed.

(58) <3> Quench:

(59) A quench method give a compression residual stress to the rim portion, such as “tread quench method” is adopted. Note that the heating temperature on the occasion of quench is preferably set at Ac.sub.3 point to (Ac.sub.3 point+250° C.). When the heating temperature is less than Ac.sub.3 point, the steel is not transformed into austenite, and pearlite with high hardness cannot be obtained by cooling after heating in some cases, whereas when the heating temperature exceeds (Ac.sub.3 point+250° C.), the grains coarsen and toughness is reduced in some cases, which is not preferable in performance of a wheel.

(60) Cooling after heating is preferably performed by a proper method such as water cooling, oil cooling, mist cooling, and air cooling so as to obtain the desirable microstructure described above for the wheel, with the size of the wheel, the facility and the like taken into consideration.

(61) Hereinafter, the present invention will be described more specifically according to examples, but the present invention is not limited to these examples.

Examples

(62) After steels 37 to 63 of Table 4 were melted in an electric furnace, the steels were cast into molds 513 mm in diameter to produce ingots, the respective ingots were each cut into a length of 300 mm, and were heated to 1200° C., after which, the respective ingots were subjected to hot forging by a normal method to produce wheels 965 mm in diameter. The wheels each has the configuration of “AAR TYPE: B-38” described in the M-107/M-207 standard of AAR.

(63) TABLE-US-00004 TABLE 4 Steel Chemical Composition (mass %, the balance Fe and impurities) No. C Si Mn P S Cu Ni Cr Mo V Al Fn1 Fn2 37 0.69 0.29* 0.78 0.014 0.011 0.02 0.02 0.09 — —* 0.024 30.3* 4.7 38 0.57* 0.46 0.82 0.017 0.008 0.03 0.03 0.07 — 0.16* 0.042 34.3 12.2 39 0.88* 0.47 0.81 0.014 0.011 0.02 0.02 0.07 — —* 0.043 36.4 6.1 40 0.72 0.89 0.83 0.016 0.012 0.03 0.02 0.11 — 0.06 0.045 36.1 14.6 41 0.73 0.48 1.18 0.014 0.009 0.03 0.03 0.11 — 0.08 0.034 38.5 10.4 42 0.79 0.83 1.15 0.013 0.008 0.02 0.02 0.13 — 0.12 0.041 43.1* 20.3 43 0.75 0.49 0.83 0.013 0.012 0.03 0.02 0.13 — 0.04 0.04 35.1 7.8 44 0.71 0.49 0.81 0.015 0.012 0.02 0.03 0.09 — 0.11 0.039 36.5 10.4 45 0.66 0.45 0.68 0.016 0.009 0.03 0.02 0.05 — 0.03 0.035 30.0* 6.3 46 0.79 0.48 0.80 0.014 0.011 0.03 0.02 0.11  0.10* 0.18* 0.041 45.1* 19.4 47 0.71 1.02* 0.82 0.016 0.008 0.02 0.02 0.07  0.10* 0.10* 0.035 40.5 27.1* 48 0.76 0.81 0.79 0.014 0.009 0.03 0.03 0.12 — 0.11 0.043 39.1 16.3 49 0.72 0.48 0.83 0.014 0.034 0.02 0.02 0.10 — 0.08 0.041 35.7 9.1 50 0.73 0.48 0.80 0.015 0.008 0.09 0.02 0.09 — 0.09 — 36.1 9.3 51 0.71 0.47 0.83 0.016 0.012 0.02 0.08 0.09 — 0.09 — 35.7 9.3 52 0.73 0.47 0.80 0.014 0.009 0.02 0.03 0.10 — 0.09 0.091 36.2 9.3 53 0.73 0.67 0.81 0.016 0.008 0.02 0.02 0.11 — 0.02 — 33.8 8.9 54 0.72 0.68 0.82 0.014 0.009 0.02 0.02 0.10 — 0.04 — 34.4 9.8 55 0.72 0.68 0.83 0.016 0.011 0.02 0.03 0.10 — 0.11 — 37.6 13.6 56 0.72 0.25* 0.81 0.015 0.010 0.02 0.02 0.10 — 0.02 — 32.2 5.0 57 0.72 0.24* 0.81 0.014 0.010 0.03 0.02 0.09 — 0.11 — 36.1 7.4 58 0.74 0.85 0.84 0.014 0.008 0.03 0.02 0.13 0.01 0.04 0.025 36.3 13.2 59 0.70 0.76 0.78 0.016 0.011 0.02 0.03 0.07 — 0.02 0.054 32.6 9.6 60 0.66 0.43 0.62 0.015 0.009 0.03 0.02 0.02 — 0.04 — 29.7* 6.1 61 0.72 0.72 0.81 0.013 0.011 0.02 0.03 0.09 0.03 0.03 — 34.8 10.7 62 0.73 0.73 0.79 0.014 0.008 0.03 0.02 0.11 0.03 0.07 — 37.0 13.2 63 0.73 0.70 0.79 0.016 0.011 0.02 0.02 0.11  0.06* 0.09* — 38.7 15.2 *means it does not satisfy the claimed range. Fn1 = 2.7 + 29.5 × C + 2.9 × Si + 6.9 × Mn + 10.8 × Cr + 30.3 × Mo + 44.3 × V Fn2 = exp(0.76) × exp(0.05 × C) × exp(1.35 × Si) × exp(0.38 × Mn) × exp(0.77 × Cr) × exp(3.0 × Mo) × exp(4.6 × V)

(64) Next, after the respective wheels were heated at 900° C. for two hours, the respective wheels were heat-treated by the method which cools the wheels by injecting water from nozzles while rotating the wheels (so-called “tread quench”) with use of the equipment shown in FIG. 14. After the heat treatment, temper treatment (treatment of cooling the wheels in air atmosphere after keeping the wheels at 500° C. for two hours) was carried out.

(65) With respect to the wheels produced like this, a hardness test of the rim portions, microstructure examination of the rim portions and the hub portions, wear test, a rolling contact fatigue test and a Jominy test were carried out. The results are shown in Table 5. For the respective tests, the test result of steel 37, which corresponds to the steel for railway wheel of “Class C” of AAR was used as the reference.

(66) [1] Hardness Test of the Rim Portions:

(67) For each of the steels, the Brinell hardness (hereinafter, called “HBW”) in the position 40 mm from the tread of the tread central portion of the rim portion was measured, as shown in FIG. 15.

(68) [2] Microstructure Examination of the Rim Portions

(69) For each of the steels, the microstructure in the position 40 mm from the tread of the tread central portion of the rim portion was examined, as shown in FIG. 16. Note that the tread central portion was etched with nital, and the microstructure was observed with an optical microscope under magnification of 400 times, and was identified.

(70) Note that when the microstructure contains ferrite or bainitic microstructure, the area fraction thereof was measured, and when the microstructure contains 5% or more of ferrite or bainitic microstructure, it is recognized as a microstructure that contains ferrite and bainite. When the microstructure contains ferrite or bainite, “P+F” or “P+B” was described in Table 5 which will be described later.

(71) [3] Microstructure Examination of the Hub Portion:

(72) For each of the steels, the microstructure in the central position of the hub portion was examined, as shown in FIG. 17. Note that the hub portion was etched with nital, and the microstructure is observed similarly to the rim portion.

(73) [4] Wear Test:

(74) For each of the steels, “wheel test specimen” for use in wear test specimen (the configuration shown in FIG. 5(a)) was taken, with the position 40 mm from the tread of the tread central portion of the rim portion (position shown by “a” in the drawing) as the reference as shown in FIG. 18. With use of these “wheel test specimens” and “rail test specimen” of steel 1, the wear test was performed under the conditions of the Hertzian stress: 2200 MPa, the slip ratio: 0.8%, and the revolutions: 776 rpm at the wheel side, and 800 rpm at the rail side by the Nishihara-type wear testing machine, and the test was carried out under dry condition. After the test was performed up to the number of cycles of 5×10.sup.5 times, the amount of wear was obtained from the mass difference of the test specimen before and after the test.

(75) [5] Rolling Contact Fatigue Test:

(76) For each of the steels, “wheel test specimen” for use in the rolling contact fatigue test specimen (the configuration shown in FIG. 4(a)) was taken with the position 40 mm from the tread of the tread central portion of the rim portion (position shown by “b” in the drawing) as the reference as shown in FIG. 18. With use of these “wheel test specimens” and “rail test specimen” of steel 1, the rolling contact fatigue test was performed under the conditions of the Hertzian stress: 1100 MPa, the slip ratio: 0.28%, the revolutions: 1000 rpm at the wheel side and 602 rpm at the rail side, and under water lubrication, and the number of cycles of detection of 0.5 G with an accelerometer was set as the rolling contact fatigue life, and evaluated.

(77) [6] Jominy Test:

(78) For each of the steels, a Jominy test specimen was taken with the position 40 mm from the tread of the tread central portion of the rim portion (position shown by “c” in the drawing) as the reference as shown in FIG. 18, and was austenitized at 900° C. for 30 minutes under air atmosphere, after which, end quench was performed, parallel cutting of 1.0 mm was performed next, the hardness distribution up to the position 50 mm from the water-cooled end was measured, and “M50%” was obtained.

(79) [7] High Temperature Tensile Test

(80) For each of the steels, in accordance with the ASTM E21 standard, the tensile test at 538° C. (1000° F.) was carried out, and the high temperature yield strength was measured.

(81) [8] Normal Temperature Tensile Test

(82) For each of the steels, the normal temperature tensile test was carried out in accordance with the ASTM E370 standard, and the normal temperature elongation was measured.

(83) TABLE-US-00005 TABLE 5 Microstructure Microstructure High Hardness of rim portion of hub portion Rolling temperature Normal of rim Hyper- Hyper- Amount fatigue yield temperature Steel portion eutectic eutectic of wear life M50% strength elongation No. (HBW) Phase θ Phase θ (g) (cycle) (mm) (MPa) (%) 37 318 P- None P None 0.318 1,865,869 5.2 297 15.2 38 342 P + F None P + F None 0.338 2,785,401 10.9 424 15.8 39 366 P None P Present 0.253 3,328,765 6.2 381 9.8 40 358 P None P None 0.264 3,194,736 14.8 365 14.7 41 382 P None P None 0.247 3,917,628 10.2 392 12.8 42 404 P + B None P None 0.325 5,857,203 20.5 394 10.3 43 354 P None P None 0.281 2,998,457 8.5 351 15.0 44 363 P None P None 0.270 3,328,475 11.2 394 12.2 45 305 P None P None 0.331 1,643,892 7.4 346 16.3 46 412 P + B None P + B None 0.319 5,893,821 18.7 477 9.5 47 389 P None P None 0.271 4,875,209 29.3 481 10.3 48 391 P None P None 0.234 5,013,493 16.8 403 12.7 49 352 P None P None 0.275 3,137,515 10.2 385 13.2 50 353 P None P None 0.268 3,174,892 9.3 384 12.9 51 351 P None P None 0.279 3,084,952 9.8 385 12.5 52 359 P None P None 0.279 3,074,662 9.4 376 12.7 53 346 P None P None 0.292 2,543,938 9.5 346 15.8 54 348 P None P None 0.284 2,647,392 10.1 366 15.3 55 377 P None P None 0.249 3,758,295 14.2 389 12.2 56 322 P None P None 0.308 2,093,584 5.4 334 15.4 57 360 P None P None 0.269 3,147,213 7.5 375 10.4 58 357 P None P None 0.266 3,218,493 12.8 359 15.4 59 332 P None P None 0.301 2,184,572 9.5 352 15.8 60 301 P None P None 0.335 1,548,329 6.9 346 16.2 61 349 P None P None 0.281 2,794,738 10.8 388 14.1 62 369 P None P None 0.260 3,514,847 12.9 401 12.8 63 387 P None P None 0.243 4,095,948 14.9 433 10.2

(84) As shown in Table 5, steels 37 to 39, 42, 45 to 47, 56, 57, 60 and 63 which do not satisfy the conditions defined by the present invention were inferior as compared with steels 40, 41, 43, 44, 48 to 55, 58, 59, 61 and 62 which satisfy the conditions defined by the present invention, in any one or more tests of the wear test, the rolling contact fatigue test, the Jominy test, the high temperature tensile test and the normal temperature tensile test.

INDUSTRIAL APPLICABILITY

(85) The steel for wheel of the present invention is excellent in balance of wear resistance, rolling contact fatigue resistance and spalling resistance, and can give a long life to the wheel. The wheel adopting the steel for wheel of the present invention has the amount of wear decreased by 30% at the largest, and the rolling contact fatigue life becomes as long as 3.2 times at the largest, and a low risk of spalling occurrence, as compared with the wheel adopting the steel for railway wheel of “Class C” of AAR. Further, the wheel adopting the steel for wheel of the present invention includes both high temperature strength and ductility, and therefore, has a low risk of occurrence of TMS and a crack on the tread. Accordingly, the steel for wheel of the present invention is extremely preferable for use as the railway wheels that are used under extremely harsh environments in which the traveling distances increase, and the loading capacities increase.