WO2011121887A1 - ばね鋼およびその製造方法 - Google Patents
ばね鋼およびその製造方法 Download PDFInfo
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- WO2011121887A1 WO2011121887A1 PCT/JP2011/001156 JP2011001156W WO2011121887A1 WO 2011121887 A1 WO2011121887 A1 WO 2011121887A1 JP 2011001156 W JP2011001156 W JP 2011001156W WO 2011121887 A1 WO2011121887 A1 WO 2011121887A1
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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
- C21D1/18—Hardening; Quenching with or without subsequent tempering
- C21D1/25—Hardening, combined with annealing between 300 degrees Celsius and 600 degrees Celsius, i.e. heat refining ("Vergüten")
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- F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
- F16—ENGINEERING ELEMENTS AND UNITS; GENERAL MEASURES FOR PRODUCING AND MAINTAINING EFFECTIVE FUNCTIONING OF MACHINES OR INSTALLATIONS; THERMAL INSULATION IN GENERAL
- F16F—SPRINGS; SHOCK-ABSORBERS; MEANS FOR DAMPING VIBRATION
- F16F1/00—Springs
- F16F1/02—Springs made of steel or other material having low internal friction; Wound, torsion, leaf, cup, ring or the like springs, the material of the spring not being relevant
- F16F1/021—Springs made of steel or other material having low internal friction; Wound, torsion, leaf, cup, ring or the like springs, the material of the spring not being relevant characterised by their composition, e.g. comprising materials providing for particular spring properties
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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
- C21D8/00—Modifying the physical properties by deformation combined with, or followed by, heat treatment
- C21D8/06—Modifying the physical properties by deformation combined with, or followed by, heat treatment during manufacturing of rods or wires
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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
- C21D9/00—Heat treatment, e.g. annealing, hardening, quenching or tempering, adapted for particular articles; Furnaces therefor
- C21D9/02—Heat treatment, e.g. annealing, hardening, quenching or tempering, adapted for particular articles; Furnaces therefor for springs
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- C—CHEMISTRY; METALLURGY
- C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
- C22C—ALLOYS
- C22C38/00—Ferrous alloys, e.g. steel alloys
- C22C38/04—Ferrous alloys, e.g. steel alloys containing manganese
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- C—CHEMISTRY; METALLURGY
- C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
- C22C—ALLOYS
- C22C38/00—Ferrous alloys, e.g. steel alloys
- C22C38/18—Ferrous alloys, e.g. steel alloys containing chromium
- C22C38/22—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
- C22C38/34—Ferrous alloys, e.g. steel alloys containing chromium with more than 1.5% by weight of silicon
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- C—CHEMISTRY; METALLURGY
- C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
- C22C—ALLOYS
- C22C38/00—Ferrous alloys, e.g. steel alloys
- C22C38/18—Ferrous alloys, e.g. steel alloys containing chromium
- C22C38/40—Ferrous alloys, e.g. steel alloys containing chromium with nickel
- C22C38/54—Ferrous alloys, e.g. steel alloys containing chromium with nickel with boron
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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
- C21D2211/008—Martensite
Definitions
- the present invention is, for example, a high-strength spring steel used as a material for automobile suspension springs, torsion bars, stabilizers, and the like, particularly high-strength, excellent in pitting corrosion resistance and corrosion fatigue characteristics, and suitable as an undercarriage part for automobiles.
- the present invention relates to a strong spring steel and a manufacturing method thereof.
- General-purpose spring steel is stipulated in JIS G4801, etc.
- the strength after quenching and tempering is about 1600 to 1800MPa.
- Quenching and tempering treatment is performed after heat forming into a spring shape. In the case of a cold formed spring, after drawing, quenching and tempering treatment is performed to form a spring shape.
- SUP7 described in JIS G4801 as a material generally used so far.
- the fatigue properties in the atmosphere are improved when the strength is increased, but the fatigue properties after corrosion are decreased, so that the deterioration of the corrosion fatigue properties due to the increased strength is a problem. Therefore, the upper limit of the usable hardness is the HRC51 level, and the upper limit is 1100 MPa as the design stress, and there is a limit to increase the strength.
- Patent Document 1 by controlling the component composition and the FP value (the following formula 1a) between 2.5 and 4.5, a supercooled structure does not appear in the structure after rolling, and the strength after rolling is cold. It is said that it is suppressed to about 1350 MPa or less, which is easy to process, and uniform and sufficient quenching is performed by subsequent quenching and tempering, and the strength after quenching and tempering can be achieved to a level of 1900 MPa or more.
- it is based on the addition of alloying elements that improve corrosion resistance, and even if the FP value is controlled in the range of 2.5 to 4.5, high strength spring steel with good pitting corrosion resistance and corrosion fatigue properties can be obtained. Is not limited.
- Patent Document 2 in a spring steel in which at least a part of the surface of the spring steel base material is coated with an anticorrosion film functioning as a sacrificial anode, a carbonitride-forming element is added to the spring steel base material, and the spring steel base material is added.
- a spring steel in which carbonitride is finely dispersed in the material is disclosed.
- the anticorrosion film a metal film made of a metal or an alloy that is electrochemically lower than the spring steel base metal, or a metal that is electrochemically lower than the spring steel base metal in a non-metal film or its A composite film in which a large number of alloys are dispersed is used.
- Patent Document 3 describes that C is reduced because C is the cause of a decrease in corrosion fatigue strength, and that the deterioration of sag resistance, which is a concern due to the reduction of C, is prevented by addition of Si, and the ratio of Si / C is It is disclosed that it is important. However, since there is a limit to reducing the amount of C, which is effective in suppressing the decrease in corrosion fatigue strength, high strength spring steel with good pitting corrosion resistance and corrosion fatigue characteristics is not always obtained with the Si / C ratio alone. Absent.
- Patent Document 4 discloses that by reducing the Cr content, the amount of hydrogen generated at the tip of the corrosion pit can be suppressed, the penetration of hydrogen into the steel can be suppressed, the hydrogen embrittlement can be suppressed, and the hydrogen is a steel material. In the case of intrusion, hydrogen brittleness can be suppressed by trapping hydrogen with Ti and V. Therefore, it is disclosed that corrosion fatigue resistance can be improved by appropriately balancing the amount of Cr, Ti and V. Has been. However, even if the hydrogen embrittlement of the spring steel can be suppressed only by optimizing the amounts of Cr, Ti, and V, a high-strength spring steel having good pitting corrosion resistance and corrosion fatigue characteristics is not always obtained.
- Patent Document 5 after heat treatment is performed so that HRC is 50.5 to 55.0, corrosion shot fatigue is performed by performing warm shot peening so as to generate a residual stress of 600 MPa or more at a position 0.2 mm below the surface. It is disclosed that the characteristics can be improved. However, since a process of performing shot peening on the spring steel is required, the manufacturing cost is increased. Moreover, although application of residual stress by shot peening is effective in suppressing the occurrence of surface cracks, high strength spring steel with good pitting corrosion resistance and corrosion fatigue properties is not always obtained.
- Patent Document 6 the amount of C, Si, Mn, Cr, Ni, and Cu from the viewpoint of the hardness of the spring steel, the amount of C, Cr, Ni, and Cu from the viewpoint of the pit shape, and the viewpoint of hydrogen embrittlement resistance.
- a spring steel having an excellent corrosion fatigue property is disclosed by appropriately balancing the amounts of C, Si, Mn, Cr, Ni, Cu, Ti, and Nb.
- An object of the present invention is to provide a high-strength spring steel that suppresses the depth of pitting corrosion that occurs and is high in strength and excellent in pitting corrosion resistance and corrosion fatigue characteristics together with a preferable manufacturing method thereof.
- the gist configuration of the present invention is as follows. 1.
- the component composition further includes: Al: 0.01 mass% or more and 0.50 mass% or less, 3.
- the component composition further includes: W: 0.001% to 2.0% by mass, Nb: 0.001 mass% or more and 0.1 mass% or less,
- the component composition further includes: B: The spring steel as described in any one of 1 to 4 above, containing 0.0002 mass% or more and 0.005 mass% or less.
- the component composition further includes: N: The spring steel as described in any one of 1 to 5 above, containing 0.005 mass% or more and 0.020 mass% or less.
- C more than 0.35% by mass and less than 0.50% by mass
- Si more than 1.75 mass% and 3.00 mass% or less
- Mn 0.2% by mass or more and 1.0% by mass or less
- Cr 0.01% by mass or more and 0.04% by mass or less
- P 0.025 mass% or less
- S 0.025 mass% or less
- the component composition further includes: Al: 0.01 mass% or more and 0.50 mass% or less, The manufacturing method of the spring steel of said 7 or 8 containing 1 type (s) or 2 or more types chosen from Cu: 0.005 mass%-1.0 mass% and Ni: 0.005 mass%-2.0 mass%.
- the component composition further includes: W: 0.001% to 2.0% by mass, Nb: 0.001 mass% or more and 0.1 mass% or less, The manufacturing method of the spring steel as described in any one of 7 to 9 above, containing one or more selected from Ti: 0.001% by mass to 0.2% by mass and V: 0.002% by mass to 0.5% by mass. .
- the component composition further includes: B: The method for producing spring steel as described in any one of 7 to 10 above, containing 0.0002 mass% or more and 0.005 mass% or less.
- the component composition further includes: N: The manufacturing method of the spring steel in any one of said 7 thru
- the spring steel of the present invention is C: more than 0.35% by mass and less than 0.50% by mass, Si: more than 1.75 mass% and 3.00 mass% or less, Mn: 0.2% by mass or more and 1.0% by mass or less, Cr: 0.01% by mass or more and 0.04% by mass or less, P: 0.025 mass% or less, S: 0.025 mass% or less, Mo: 0.1% by mass or more and 1.0% by mass or less and O: 0.0015% by mass or less under the condition that the PC value calculated by the above formula (1) is more than 3.3 to 8.0 or less, Or in addition, Al: 0.01 mass% or more and 0.50 mass% or less, Cu: 0.005% by mass or more and 1.0% by mass or less and Ni: 0.005% by mass or more and 2.0% by mass or less selected from 1 type or 2 types or more, Or in addition, W: 0.001% to 2.0% by mass, Nb: 0.001 mass% or more and 0.1 mass% or less, Ti: 0.001% by mass or more, Si
- C more than 0.35% by mass and less than 0.50% by mass
- C is an essential element for ensuring the necessary strength. If 0.35% by mass or less, it is difficult to ensure a predetermined strength, and in order to ensure a predetermined strength, an alloy The addition of a large amount of element is necessary, leading to an increase in alloy cost. On the other hand, addition of 0.50% by mass or more generates a large amount of carbides in the steel, and the pitting corrosion resistance decreases due to the preferential corrosion at the carbide-matrix interface, leading to deterioration of corrosion fatigue characteristics and toughness. From the above, the C content is more than 0.35 mass% and less than 0.50 mass%.
- Si more than 1.75 mass% but not more than 3.00 mass% Si increases the strength of steel by improving the solid solution strengthening and temper softening resistance as a deoxidizer, and improves the sag resistance of the steel. Furthermore, it is an element added to improve pitting corrosion resistance. In the present invention, it is added in an amount exceeding 1.75% by mass. However, addition exceeding 3.00% by mass reduces ductility and cracks in the raw material during casting, necessitating care of the raw material, leading to increased manufacturing costs. Further, since the strength of the steel is increased, the toughness and coiling properties are significantly reduced. Therefore, the upper limit of Si is 3.00% by mass. For these reasons, the Si content is set to be more than 1.75 mass% and not more than 3.00 mass%.
- Mn 0.2% by mass or more and 1.0% by mass or less Mn improves the hardenability of the steel and is useful for increasing the strength, so 0.2% by mass or more is added. However, addition exceeding 1.0% by mass increases the strength of the steel, leading to a decrease in the base metal toughness. Moreover, since the corrosion rate of steel is increased and the pitting depth is also increased, the corrosion fatigue characteristics are deteriorated. Therefore, the upper limit of Mn is 1.0% by mass. From the above, the amount of Mn is set to 0.2% by mass or more and 1.0% by mass or less.
- P, S 0.025% by mass or less
- P and S segregate at the grain boundaries and cause a reduction in the base metal toughness of the steel.
- the corrosion rate is increased, and accordingly, the pitting depth is also increased.
- S exists in steel as MnS
- the pitting corrosion depth due to dissolution of MnS becomes deep. From the above, it is preferable to reduce these elements as much as possible. Therefore, both P and S are 0.025 mass% or less.
- Cr 0.01% by mass or more and 0.04% by mass or less
- Cr is an element that improves the hardenability of the steel and increases the strength. Therefore, 0.01 mass% or more is added. Moreover, it is an element which suppresses corrosion by densifying the rust produced
- the Cr amount Is controlled to 0.04 mass% or less. From the above, the Cr content is 0.01 mass% or more and 0.04 mass% or less.
- Mo 0.1% by mass or more and 1.0% by mass or less Mo is a particularly important element in the present invention. Mo is an element that improves the corrosion-inhibiting function and pitting corrosion resistance by forming a passive film, and should be added in an amount of 0.1% by mass or more. However, if added in excess of 1.0 mass%, the toughness is lowered due to the increase in strength, and the alloy cost is increased. Based on the above, the Mo content is 0.1 to 1.0 mass%.
- O 0.0015% by mass or less O is bonded to Si or Al to form a hard oxide-based non-metallic inclusion, resulting in a decrease in fatigue life characteristics. Then, up to 0.0015% by mass is allowed.
- PC value (the above formula (1)): more than 3.3 and less than 8.0
- the inventors made spring steel by changing the component composition and the PC value, and investigated the pitting corrosion depth and corrosion fatigue resistance characteristics.
- the pitting depth and the corrosion fatigue characteristic were implemented by the test method mentioned later.
- Table 1 shows the component composition
- Table 2 shows the evaluation results of the pitting depth and corrosion fatigue resistance.
- FIG. 1 and FIG. 2 the evaluation results (vertical axis) of the pitting depth and the corrosion fatigue resistance characteristics are shown with respect to the PC value (horizontal axis).
- the manufacturing conditions of the spring steel were the same except for the standard steel. That is, the manufacturing conditions are as follows. First, the billet melted by vacuum melting was heated to 1100 ° C. and hot-rolled to obtain a round bar having a diameter of 25 mm. Then, after normalizing for 1 hour at 950 ° C., the wire was drawn to a diameter of 15 mm. The obtained wire was subjected to quenching and tempering treatment by high frequency heating. In this heat treatment condition, heating was performed up to 1000 ° C. at a heating rate of 100 ° C./sec. As the tempering conditions, heating was performed up to 300 ° C. at a heating rate of 50 ° C./second, and air cooling was performed after holding for 20 seconds.
- the reference steel (A-1: SUP7 compliant) was subjected to quenching and tempering after wire drawing with a diameter of 15 mm.
- electric furnace heating hereinafter also simply referred to as furnace heating
- quenching was performed with oil at 60 ° C.
- tempering conditions the quenched steel was heated to 510 ° C., held for 1 hour, and then allowed to cool.
- the ratio [Cr] / [Mo] (hereinafter referred to as AR value) is represented by the ratio of the added amount of Cr and Mo.
- Cr is an element that increases the pitting depth as the addition amount increases
- Mo is an element that decreases the pitting depth as the addition amount increases. Therefore, when it is desired to further improve the pitting corrosion depth, it is preferable to manage the addition amount ratio. That is, when the AR value exceeds 0.35, the pitting depth due to Cr becomes deep and the effect of suppressing the pitting depth due to Mo decreases, so the AR value is preferably set to 0.35 or less.
- the spring steel of the present invention can contain the following components in addition to the above components in order to increase the strength and improve the pitting corrosion resistance and corrosion fatigue characteristics of the steel.
- Al 0.01 mass% or more and 0.50 mass% or less
- Cu 0.005 mass% or more and 1.0 mass% or less
- Ni 0.005 mass% or more and 2.0 mass% or less
- Cu or Ni is hardenability or tempering It is an element that increases the later strength and further improves the corrosion resistance of the steel, and can be selected and added.
- Cu and Ni are preferably added at 0.005 mass% or more. However, if Cu is added in an amount of 1.0% by mass and Ni is added in an amount exceeding 2.0% by mass, the alloy cost is increased.
- Al is an element excellent as a deoxidizing agent, and is an element effective for maintaining strength by suppressing austenite grain growth during quenching, so it is preferably added in an amount of 0.01% by mass or more.
- Al is preferably added with an upper limit of 0.50% by mass.
- W 0.001% to 2.0% by mass
- Nb 0.001% to 0.1% by mass
- Ti 0.001% to 0.2% by mass
- V 0.002% to 0.5% by mass
- W, Nb, Ti and V are all elements that increase the hardenability and strength of the steel after tempering, and can be selected and added according to the required strength.
- W is an element that improves the pitting corrosion resistance of steel. In order to obtain such an effect, it is preferable to add 0.001% by mass or more for W, Nb, and Ti and 0.002% by mass or more for V, respectively.
- Nb is added in an amount of more than 0.1% by mass and Ti is added in an amount of more than 0.2% by mass, a large amount of carbides are formed in the steel, and the pitting corrosion resistance is reduced due to the preferential corrosion at the carbide-matrix interface. As a result, the corrosion fatigue resistance is reduced.
- Nb, Ti and V are preferably added with the above values as upper limits.
- W is added in excess of 2.0% by mass, the strength is increased and the toughness is lowered, leading to an increase in alloy cost. Therefore, it is preferable to add W with an upper limit of 2.0% by mass.
- B 0.0002 mass% or more and 0.005 mass% or less B is an element that increases the strength of the steel after tempering by increasing the hardenability, and can be contained if necessary. In order to acquire the said effect, adding at 0.0002 mass% or more is preferable. However, if added over 0.005% by mass, the workability in the cold state deteriorates. Therefore, B is preferably added in the range of 0.0002 to 0.005 mass%.
- N 0.005% by mass or more and 0.020% by mass or less N is an element that improves the corrosion inhibiting function and pitting corrosion resistance of steel materials, and can be added at 0.005% by mass or more in order to exhibit this effect. However, if added over 0.020% by mass, nitrides are likely to be formed at the grain boundaries, causing intergranular corrosion and reducing the corrosion resistance of the steel. In addition, pitting corrosion resistance decreases due to preferential corrosion at the nitride-matrix interface, leading to deterioration in corrosion fatigue characteristics and toughness. From the above, the N amount when N is positively added is 0.005 to 0.020 mass%. As described above, the present invention includes a case where N is not positively added.
- the N content is less than 0.005% by mass and is contained as an inevitable impurity.
- the balance other than the elements described above is Fe and inevitable impurities.
- the steel ingot having the above component composition can be used in both melting by a converter and vacuum melting. And a material such as a steel ingot, slab, bloom or billet is heated and hot-rolled, pickled and scaled, drawn, adjusted to a predetermined thickness, and used for spring steel.
- Martensite fraction 90% or more Martensite is a structure necessary for obtaining strength.
- excellent characteristics can be obtained by forming a martensite structure having a volume ratio of 90% or more. That is, when the volume fraction of martensite is less than 90%, the amount of untransformed phases such as retained austenite phase, which does not contribute to the increase in strength, and precipitates such as carbides increases, resulting in a high strength of over 1900 MPa in tensile strength. It will be difficult to achieve this.
- This martensite fraction may be 100%.
- the Martensite fraction can be increased to 90% or higher by heating to Ac 3 points or higher and quenching, but heating in a temperature range exceeding (Ac 3 points + 200 ° C.) coarsens prior austenite grains. It will be. Therefore, although it depends on the size of the steel material, it is kept in a temperature range of Ac 3 points or more (Ac 3 points + 200 ° C) and cooled to 200 ° C or less at a cooling rate of 10 ° C / s or more and quenched. However, it is most effective in achieving the above-described martensite fraction of 90% or more.
- tempering process it is important to disperse the intra-grain carbide as finely as possible.
- coarse carbides When coarse carbides are formed, a matrix and a local battery are formed, and the carbides are dissolved to form pitting corrosion. Corrosion is promoted at the bottom of the pitting corrosion and the pitting depth is increased. Corrosion fatigue properties decrease as the pitting depth increases.
- tempering conditions are important in order to achieve the above tensile strength. For this purpose, it is effective to perform tempering in the temperature range of 150 to 500 ° C. and then to cool.
- the steel material is made into a wire rod or steel bar by hot rolling and is preferably descaled by pickling and further subjected to a wire drawing treatment.
- the spring is formed by the above-described quenching-before quenching treatment, quenching- It is preferable to carry out after tempering or after quenching.
- the high-strength spring steel thus obtained has high strength, excellent pitting corrosion resistance and corrosion fatigue resistance, although it can be manufactured at low cost, and requires high strength of 1900 MPa or more, for example, an automobile. It can be applied to a suspension spring that is an underbody part.
- the martensite fraction was determined by observing 20 thin-film samples collected from the vicinity of the wire 1 / 4D portion (D is the diameter of the wire) with a transmission electron microscope at a magnification of 20,000 times, and no cementite was precipitated. The area of the region was measured and determined as a martensite fraction based on the ratio of the measured area to the whole.
- Tensile test was performed by taking a tensile test piece with a parallel part diameter of 6mm ⁇ x length of 32mm and a gripping part of 12mm ⁇ centering on 1 / 2D (D is the diameter of the wire), with a distance of 25mm between evaluation points and a tensile speed of 5mm / min. The test was conducted.
- Spray salt water 5% salt water (50 ⁇ 5 g / l), specific gravity 1.029 to 1.036, pH 6.5 to 7.2
- Test chamber temperature 35 °C Spray amount: 1.5 ⁇ 0.5ml / 80cm 2 / 1h ⁇ Constant temperature and humidity test>
- sag resistance which is an important characteristic of spring steel, is preferably evaluated by an actual vehicle test, but this requires a lot of time and cost. Therefore, sag resistance was evaluated by a torsional creep test. That is, a test piece shown in FIG. 4 was collected from a sample that had been drawn to a diameter of 15 mm, and was subjected to a setting test. In the sag test, a 1% pre-strain is applied by simulating the spring setting, then a torsional stress is applied to the test piece with a weight, and the descent amount (sag amount) is measured for 96 hours. The sag resistance was evaluated by the amount of sag afterwards.
- FIG. 5 shows an outline of the sag test.
- Table 5 shows the results of tensile strength, martensite fraction, maximum pitting corrosion depth, corrosion fatigue resistance characteristics, and sag resistance test.
- Steels of B-1 to 4, B-6 to 10, B-14 to 15, B-17 to 18, and B-21 to 25 that satisfy the component composition and PC value of the present invention have a maximum pitting corrosion depth. It can be seen that they are shallow and have good corrosion fatigue resistance.
- the component composition is within the range of the present invention, the B-5 steel whose PC value does not satisfy the range of the present invention has a deep maximum pitting corrosion depth, and the corrosion fatigue resistance property is lowered. I understand that.
- the steels of B-11 to 13, B-19 to 20, and B-27 whose component composition does not satisfy the scope of the present invention have a deep maximum pitting corrosion depth and deteriorate corrosion fatigue characteristics.
- the PC value is smaller than the range of the present invention as in B-16, the allowance for improving pitting corrosion resistance and corrosion fatigue characteristics is small and saturated.
- the amount of C is outside the scope of the present invention, the tensile strength is outside the scope of the present invention.
- the AR value does not satisfy 0.35 or less as in B-23, the maximum pitting corrosion depth is deeper and the corrosion fatigue characteristics are lower than those of the other invention examples.
- the steel having the composition shown in Table 6 was manufactured by melting in a vacuum melting furnace. Billets made from these steels were heated to 1100 ° C. and then hot rolled into round bars with a diameter of 25 mm ⁇ . Then, after normalizing for 1 hour at 950 ° C., the wire was drawn to a diameter of 15 mm ⁇ . The obtained wire was subjected to quenching and tempering treatment by induction heating under the conditions shown in Table 7. The test mentioned above was implemented with respect to the obtained wire, and each evaluated.
- Table 8 shows the tensile strength, martensite fraction, maximum pitting depth, corrosion fatigue characteristics, and sag test results.
- the steels of C-1 to 4, C-6 to 10, C-14 to 15, C-17 to 18, C-21 to 24 and C-27 satisfying the component composition and PC value of the present invention have the largest pores. It can be seen that the depth of corrosion is shallow and has good corrosion fatigue properties. On the other hand, even if the component composition is within the range of the present invention, the C-5 steel whose PC value does not satisfy the range of the present invention has a deep maximum pitting corrosion depth and deteriorated corrosion fatigue characteristics. I understand that.
- the steels of C-11 to 13, C-19 to 20, and C-26 whose component compositions do not satisfy the scope of the present invention, have a deep maximum pitting corrosion depth and deteriorate corrosion fatigue characteristics.
- the PC value is smaller than the range of the present invention as in C-16, the margin for improving pitting corrosion resistance and corrosion fatigue resistance is small and saturated.
- the alloy cost is increased.
- C-25 has a tempering temperature outside the range of the present invention, it can be seen that the tensile strength is low, the maximum pitting depth is deep, and the corrosion fatigue properties are lowered.
- the AR value does not satisfy 0.35 or less, the maximum pitting corrosion depth is deeper and the corrosion fatigue characteristics are lower than those of the other invention examples.
- the steel having the component composition shown in Table 9 was manufactured by melting in a vacuum melting furnace. Billets made from these steels were heated to 1100 ° C. and then hot rolled into round bars with a diameter of 25 mm. Then, after normalizing for 1 hour at 950 ° C., the wire was drawn to a diameter of 15 mm. The obtained wire was subjected to electric furnace heating (hereinafter abbreviated as furnace heating) under the conditions shown in Table 10, and subjected to quenching and tempering treatment. The test mentioned above was implemented with respect to the obtained wire, and each evaluated.
- furnace heating electric furnace heating
- Table 11 shows the tensile strength, the martensite fraction, the maximum pitting corrosion depth, the corrosion fatigue characteristics, and the results of the sag test.
- Steels of D-1 to 4, D-6 to 10, D-14 to 15, D-17 to 18, D-21 to 29, and D-31 that satisfy the component composition and PC value of the present invention have the largest pores. It can be seen that the depth of corrosion is shallow and has good corrosion fatigue properties. On the other hand, even if the component composition is within the range of the present invention, the D-5 steel whose PC value does not satisfy the range of the present invention has a deep maximum pitting corrosion depth and deteriorated corrosion fatigue characteristics. I understand that.
- the steels of D-11 to 13 and D-19 to 20 whose component compositions do not satisfy the scope of the present invention have a deep maximum pitting corrosion depth and deteriorate corrosion fatigue characteristics. It can also be seen that when the PC value is smaller than the range of the present invention as in D-16, the margin for improving pitting corrosion resistance and corrosion fatigue resistance is small and saturated. Moreover, since many alloy elements are added, the alloy cost is increased. It can be seen that the steel of D-30 has a tempering temperature outside the range of the present invention, a low tensile strength, a maximum maximum pitting corrosion depth, and a reduced corrosion fatigue property. Further, when the AR value does not satisfy 0.35 or less as in D-23, the maximum pitting corrosion depth is deeper and the corrosion fatigue characteristics are lower than those of the other invention examples.
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Abstract
Description
記
FP=(0.23[C]+0.1)×(0.7[Si]+1)×(3.5[Mn]+1)×(2.2[Cr]+1)×(0.4[Ni]+1)×(3[Mo]+1)・・・(1a)
但し、[ ]は各元素の含有量(質量%)を表す。
記
PC=4.2×([C]+[Mn])+0.1×(1/[Si]+1/[Mo])+20.3×[Cr]
+0.001×(1/[N]) ・・・(1)
但し、[ ]は該括弧内成分の含有量(質量%)
すなわち、本発明の要旨構成は、以下のとおりである。
1.C:0.35質量%超0.50質量%未満、
Si:1.75質量%超3.00質量%以下、
Mn:0.2質量%以上1.0質量%以下、
Cr:0.01質量%以上0.04質量%以下、
P:0.025質量%以下、
S:0.025質量%以下、
Mo:0.1質量%以上1.0質量%以下および
O:0.0015質量%以下
を、下記(1)式で算出されるPC値が3.3超8.0以下の条件下に含有し、残部不可避的不純物およびFeの成分組成を有し、さらに、マルテンサイト分率が90%以上の組織を有し、かつ引張強さが1900MPa以上であるばね鋼。
記
PC=4.2×([C]+[Mn])+0.1×(1/[Si]+1/[Mo])+20.3×[Cr]
+0.001×(1/[N]) ・・・(1)
但し、[ ]は該括弧内成分の含有量(質量%)
なお、Nは積極的に添加しなくとも、N量:0.005質量%未満の範囲にて不可避的不純物として含有される。従って、上記(1)式におけるN含有量[N]については、不可避的不純物として含有されるNの含有量(質量%)あるいは、後述する積極的に添加した場合にはその含有量(質量%)、の値を用いるものとする。
記
[Cr]/[Mo]≦0.35 ・・・(2)
但し、[ ]は該括弧内成分の含有量(質量%)
Al:0.01質量%以上0.50質量%以下、
Cu:0.005質量%以上1.0質量%以下および
Ni:0.005質量%以上2.0質量%以下
のうちから選ばれる1種または2種以上を含有する前記1または2に記載のばね鋼。
W:0.001質量%以上2.0質量%以下、
Nb:0.001質量%以上0.1質量%以下、
Ti:0.001質量%以上0.2質量%以下および
V:0.002質量%以上0.5質量%以下
のうちから選ばれる1種または2種以上を含有する前記1ないし3のいずれかに記載のばね鋼。
B:0.0002質量%以上0.005質量%以下
を含有する前記1ないし4のいずれかに記載のばね鋼。
N:0.005質量%以上0.020質量%以下
を含有する前記1ないし5のいずれかに記載のばね鋼。
Si:1.75質量%超3.00質量%以下、
Mn:0.2質量%以上1.0質量%以下、
Cr:0.01質量%以上0.04質量%以下、
P:0.025質量%以下、
S:0.025質量%以下、
Mo:0.1質量%以上1.0質量%以下および
O:0.0015質量%以下
を、下記(1)式で算出されるPC値が3.3超8.0以下の条件下に含有する成分組成を有する鋼素材を、Ac3点以上(Ac3点+200℃)以下の温度域に加熱し、10℃/s以上の冷却速度で200℃以下まで冷却し、その後、150℃以上500℃以下の温度域まで加熱し、冷却するばね鋼の製造方法。
記
PC=4.2×([C]+[Mn])+0.1×(1/[Si]+1/[Mo])+20.3×[Cr]
+0.001×(1/[N]) ・・・(1)
但し、[ ]は該括弧内成分の含有量(質量%)
記
[Cr]/[Mo] ≦0.35 ・・・(2)
但し、[ ]は該括弧内成分の含有量(質量%)
Al:0.01質量%以上0.50質量%以下、
Cu:0.005質量%以上1.0質量%以下および
Ni:0.005質量%以上2.0質量%以下
のうちから選ばれる1種または2種以上を含有する前記7または8に記載のばね鋼の製造方法。
W:0.001質量%以上2.0質量%以下、
Nb:0.001質量%以上0.1質量%以下、
Ti:0.001質量%以上0.2質量%以下および
V:0.002質量%以上0.5質量%以下
のうちから選ばれる1種または2種以上を含有する前記7ないし9のいずれかに記載のばね鋼の製造方法。
B:0.0002質量%以上0.005質量%以下
を含有する前記7ないし10のいずれかに記載のばね鋼の製造方法。
N:0.005質量%以上0.020質量%以下
を含有する前記7ないし11のいずれかに記載のばね鋼の製造方法。
C:0.35質量%超0.50質量%未満、
Si:1.75質量%超3.00質量%以下、
Mn:0.2質量%以上1.0質量%以下、
Cr:0.01質量%以上0.04質量%以下、
P:0.025質量%以下、
S:0.025質量%以下、
Mo:0.1質量%以上1.0質量%以下および
O:0.0015質量%以下
を、上記(1)式で算出されるPC値が3.3超8.0以下の条件下に含有し、
あるいはさらに、
Al:0.01質量%以上0.50質量%以下、
Cu:0.005質量%以上1.0質量%以下および
Ni:0.005質量%以上2.0質量%以下
のうちから選ばれる1種または2種以上を含有し、
あるいはさらに、
W:0.001質量%以上2.0質量%以下、
Nb:0.001質量%以上0.1質量%以下、
Ti:0.001質量%以上0.2質量%以下および
V:0.002質量%以上0.5質量%以下
のうちから選ばれる1種または2種以上を含有し、
あるいはさらに、
B:0.0002質量%以上0.005質量%以下
を含有し、
あるいはさらに、
N:0.005質量%以上0.020質量%以下
を含有し、
残部不可避的不純物およびFeの成分組成を有する。
また、本発明のばね鋼の製造方法は、上記組成の鋼素材に上記7に記載の熱処理を施すものである。
C:0.35質量%超0.50質量%未満
Cは、必要な強度を確保するために必須の元素であり、0.35質量%以下では所定の強度確保が難しく、また所定強度を確保するためには、合金元素の多量添加が必要となって、合金コストの上昇を招くことから、0.35質量%超とする。一方、0.50質量%以上の添加は、鋼中に炭化物が多量に生成し、炭化物-母相界面の優先腐食により耐孔食性が低下し、腐食疲労特性の低下や靭性の低下を招く。以上のことから、C量は0.35質量%超0.50質量%未満とする。
Siは、脱酸剤として、また、固溶強化や焼戻し軟化抵抗を向上させることにより鋼の強度を高め、鋼の耐へたり性を向上する。さらに、耐孔食性も向上するため添加される元素であり、本発明では、1.75質量%超で添加する。しかし、3.00質量%を超える添加は、延性が低下し、鋳造時に素材に割れが発生するため、素材の手入れが必要となり製造コストの増加を招く。また、鋼が高強度化するために、靭性およびコイリング性が著しく低下する。よって、Siの上限は3.00質量%とする。以上のことから、Si量は1.75質量%超3.00質量%以下とする。
Mnは、鋼の焼入れ性を向上させ強度増加に有益であるため、0.2質量%以上添加する。しかし、1.0質量%を超える添加は、鋼を高強度化するため、母材靭性の低下を招く。また、鋼の腐食速度を増加させて、孔食深さも深くなるため、腐食疲労特性の低下を招く。よって、Mnの上限は、1.0質量%とする。以上のことから、Mn量は、0.2質量%以上1.0質量%以下とする。
PおよびSは、粒界に偏析して鋼の母材靭性の低下を招く。また、腐食速度を増加させ、それに伴い、孔食深さも深くなる。とくに、SはMnSとして鋼中に存在するため、MnSの溶解による孔食深さが深くなる。以上のことから、これらの元素はできるかぎり低減するのが好ましい。よって、PおよびSはいずれも0.025質量%以下とする。
Crは、鋼の焼入れ性を向上させ強度を増加させる元素である。そのため、0.01質量%以上は添加する。また、表層部に生成する錆を緻密化して腐食を抑制する元素である。一方で、孔食部のpH値を低下させるため、孔食深さを増大させ、耐腐食疲労特性を低下させる元素である、そのため、本発明では、耐孔食性を向上させるために、Cr量は0.04質量%以下に制御する。以上のことから、Cr量は0.01質量%以上0.04質量%以下とする。
Moは、本発明において特に重要な元素である。Moは不動態皮膜の形成により腐食抑制機能ならびに耐孔食性を向上させる元素であり、0.1質量%以上で添加する必要がある。しかし、1.0質量%を超えて添加すると、高強度化による靭性の低下をまねき、また合金コストの上昇をも招く。以上のことから、Mo量は0.1~1.0質量%とする。
Oは、SiやAlと結合し、硬質な酸化物系非金属介在物を形成して、疲労寿命特性の低下を招くため、可能な限り低い方が良いが、本発明では、0.0015質量%までは許容される。
さらに、発明者らは、成分組成並びにPC値を変化させてばね鋼を作製し、その孔食深さおよび耐腐食疲労特性を調査した。なお、孔食深さならびに腐食疲労特性は、後述する試験方法で実施した。表1に成分組成を、表2に孔食深さ並びに耐腐食疲労特性の評価結果を、それぞれ示す。また、図1および図2に、孔食深さ並びに耐腐食疲労特性の評価結果(縦軸)を、PC値(横軸)に関して整理して示した。
まず、真空溶解で溶製したビレットを1100℃に加熱後、熱間圧延を行い、直径25mmの丸棒にした。その後、950℃で1時間のノルマライジング処理を行ってから、直径15mmまで伸線加工を行った。得られた線材に対して、高周波加熱による、焼入れ-焼戻し処理を行った。この熱処理条件は、1000℃まで100℃/秒の加熱速度で加熱を行い、5秒保持後、50℃/秒で50℃まで冷却した。焼戻し条件は、300℃まで50℃/秒の加熱速度で加熱を行い、20秒保持後に空冷した。
但し、[ ]は該括弧内成分の含有量(質量%)
比[Cr]/[Mo](以下、AR値という)は、CrとMoの添加量の比で表される。ここに、Crは添加量の増加に伴い孔食深さを深くする元素であり、Moは添加量の増加に伴い孔食深さを浅くする元素である。そのため、孔食深さをさらに改善したい場合は、その添加量比も管理することが好ましい。すなわち、AR値が0.35超になると、Crによる孔食深さが深くなり、Moによる孔食深さの抑制効果が低下するため、AR値は0.35以下とすることが好ましい。
Al:0.01質量%以上0.50質量%以下、Cu:0.005質量%以上1.0質量%以下およびNi:0.005質量%以上2.0質量%以下のうちの1種または2種以上
CuおよびNiは、焼入れ性や焼戻し後の強度を高め、更には、鋼の耐食性を向上させる元素であり、選択して添加することができる。このような効果を得るためには、CuおよびNiは0.005質量%以上で添加することが好ましい。しかし、Cuは1.0質量%およびNiは2.0質量%を超えて添加すると、却って合金コストが上昇するため、Cuは1.0質量%およびNiは2.0質量%を上限として添加するのが好ましい。
また、Alは脱酸剤として優れた元素であり、さらに、焼入れ時のオーステナイト粒成長を抑制することによって、強度の維持に有効な元素であるため、好ましくは0.01質量%以上で添加する。しかしながら、0.50質量%を超えて添加しても、その効果は飽和してコスト上昇を招く不利が生じる上、冷間でのコイリング性も低下する。よって、Alは0.50質量%を上限として添加することが好ましい。
W、Nb、TiおよびVは、いずれも焼入れ性や焼戻し後の鋼の強度を高める元素であり、必要とする強度に応じて選択して添加することができる。さらに、Wは、鋼の耐孔食性も向上させる元素である。このような効果を得るためには、W、NbおよびTiは、それぞれ0.001質量%以上、Vは0.002質量%以上添加することが好ましい。しかし、Vは0.5質量%、Nbは0.1質量%およびTiは0.2質量%を超えて添加すると、鋼中に炭化物が多量に生成し、炭化物-母相界面の優先腐食により耐孔食性が低下するため、耐腐食疲労特性の低下を招く。Nb、TiおよびVは、それぞれ上記の値を上限として添加するのが好ましい。また、Wは2.0質量%を超えて添加すると、高強度化して靭性が低下し、合金コストの上昇を招く。よって、Wは、2.0質量%を上限として添加するのが好ましい。
Bは、焼入れ性の増大により焼戻し後の鋼の強度を高める元素であり、必要に応じて含有することができる。上記効果を得るためには、0.0002質量%以上で添加するのが好ましい。しかし、0.005質量%を超えて添加すると、冷間での加工性が劣化する。よって、Bは0.0002~0.005質量%の範囲で添加することが好ましい。
Nは、鋼材の腐食抑制機能ならびに耐孔食性を向上させる元素であり、この効果を発現させるために0.005質量%以上で添加することができる。しかし、0.020質量%を超えて添加すると、粒界に窒化物が形成され易くなり、粒界腐食が起こり、鋼の耐食性が低下する。また、窒化物-母相界面の優先腐食により耐孔食性が低下し、腐食疲労特性の低下や、靭性の低下を招く。以上のことからNを積極的に添加する場合のN量は0.005~0.020質量%とする。
なお、上記したように、本発明においては、Nを積極的に添加しない場合を含み、この場合はN量が0.005質量%未満にて不可避的不純物として含有される。上記(1)式におけるN含有量[N]については、不可避的不純物として含有されるNの含有量(質量%)あるいは、積極的に添加した場合にはその含有量(質量%)、の値を用いるものとする。
以上説明した元素以外の残部は、Feおよび不可避的不純物である。
マルテンサイト分率:90%以上
マルテンサイトは、強度を得るために必要な組織である。本発明の場合には、体積率で90%以上のマルテンサイト組織とすることによって、優れた特性が得られる。すなわち、マルテンサイトの体積率が90%未満では、強度の上昇に寄与しない残留オーステナイト相などの未変態相や、炭化物などの析出物の量が多くなりすぎて、引張強さ1900MPa以上という高強度化の達成は困難となる。このマルテンサイト分率は、100%であってもよい。
前述した鋼を得るためには、前述した成分組成の鋼素材に、焼入れ-焼戻し処理を施すことが有効である。すなわち、Ac3点以上に加熱して焼き入れることにより、マルテンサイト分率を90%以上とできるが、(Ac3点+200℃)を超える温度域での加熱は、旧オーステナイト粒を粗大化させることになる。そこで、鋼素材のサイズにもよるが、Ac3点以上(Ac3点+200℃)以下の温度域に保持して10℃/s以上の冷却速度で200℃以下まで冷却して焼き入れする工程が、上述したマルテンサイト分率90%以上を達成する上で最も有効である。
粗大な炭化物が形成されると、母相と局部電池を形成して、炭化物が溶解して孔食が形成され、孔食底部で腐食が促進し孔食深さが深くなる。孔食深さが深くなることで腐食疲労特性が低下する。さらに、上記の引張強さを達成するためにも、焼戻し条件が重要である。このためには、150~500℃の温度域にて、焼戻しを行い、その後冷却することが有効である。
かくして得られた線材を、以下に示す、引張試験、腐食試験、孔食深さ測定、腐食疲労試験およびへたり試験に供した。また、線材のマルテンサイト分率の測定を、次のように行った。
マルテンサイト分率は、線材1/4D部(Dは線材の直径)付近より採取した薄膜状のサンプルを透過型電子顕微鏡により、2万倍の倍率で20視野観察し、セメンタイトの析出していない領域の面積を測定し、その測定面積の全体に対する割合に基づいて、マルテンサイト分率として求めた。
引張試験は、平行部の直径6mmφ×長さ32mm、つかみ部12mmφの引張試験片を1/2D(Dは線材の径)を中心として採取し、評点間距離25mmおよび引張速度5mm/分にて試験を実施した。
耐孔食性並びに耐腐食疲労特性を評価するには、実際にばねを製造し、実車試験を実施するのが好ましいが、それでは多大な時間と費用を要する。そのため、図3に示す試験片を採取し、腐食試験に供した。この腐食試験は、塩水噴霧-恒温恒湿サイクル試験とした。試験片は、前処理として、全試験片について、アセトン中で10分間超音波洗浄し、全試験片について、端部および掴み部をポリエステルテープにてマスキングを行った。マスキング後の試験片を、「塩水噴霧8時間
→ 恒温恒湿(35℃,50%)下で16時間保持」を1サイクルとし、7サイクルにわたり実施した。なお、塩水噴霧試験は、JIS Z2371に準拠して実施した。試験の詳細は下記の通りである。
噴霧塩水:5%塩水(50±5g/l)、比重1.029~1.036、pH6.5~7.2
試験槽内温度:35℃
噴霧量:1.5±0.5ml/80cm2/1h
<恒温恒湿試験>
試験槽内温度:35℃
試験槽内湿度:50%RH
<試験機>
スガ試験機製 塩乾湿複合サイクル試験機 CYP90
上述した腐食試験終了後、JIS Z2371参考表1 化学的腐食生成物除去方法に準拠し、20%クエン酸水素二アンモニウム水溶液-80℃-20分浸漬にて除錆した。その後、平行部を、図6に示すように切り出し、孔食の深さを測定し、一番深い孔食の深さを最大孔食深さと定義した。
上述した腐食試験終了後、JIS Z2371参考表1 化学的腐食生成物除去方法に準拠し、20%クエン酸水素二アンモニウム水溶液-80℃-20分浸漬にて除錆した。その後、島津製作所製 島津小野式回転曲げ疲れ試験機 H7型試験機により、疲労限を導出した。腐食疲労特性は、それぞれの鋼の疲労限の値を基準材の疲労限の値で除して規格化を行い、導出した数値が1.1以上になった場合に腐食疲労特性が向上したと判断した。
ばね鋼の重要特性である耐へたり性は、実車試験で評価するのが好ましいが、それでは多大な時間と費用を要する。そのため、耐へたり性は、ねじりクリープ試験で評価した。すなわち、直径15mmに伸線加工を行ったサンプルから、図4に示す試験片を採取し、へたり試験に供した。へたり試験は、ばねのセッティングを模擬して1%の予歪を負荷した後、試験片にねじり応力を錘で負荷し、錘の降下量(へたり量)を計測して、96時間試験後のへたり量をもって耐へたり性を評価した。図5に、へたり試験の概要を示す。
Claims (12)
- C:0.35質量%超0.50質量%未満、
Si:1.75質量%超3.00質量%以下、
Mn:0.2質量%以上1.0質量%以下、
Cr:0.01質量%以上0.04質量%以下、
P:0.025質量%以下、
S:0.025質量%以下、
Mo:0.1質量%以上1.0質量%以下および
O:0.0015質量%以下
を、下記(1)式で算出されるPC値が3.3超8.0以下の条件下に含有し、残部不可避的不純物およびFeの成分組成を有し、さらに、マルテンサイト分率が90%以上の組織を有し、かつ引張強さが1900MPa以上であるばね鋼。
記
PC=4.2×([C]+[Mn])+0.1×(1/[Si]+1/[Mo])
+20.3×[Cr]+0.001×(1/[N])・・・(1)
但し、[ ]は該括弧内成分の含有量(質量%) - 前記成分組成が、さらに、下記(2)式を満足する請求項1に記載のばね鋼。
記
[Cr]/[Mo]≦0.35 ・・・(2)
但し、[ ]は該括弧内成分の含有量(質量%) - 前記成分組成は、さらに、
Al:0.01質量%以上0.50質量%以下、
Cu:0.005質量%以上1.0質量%以下および
Ni:0.005質量%以上2.0質量%以下
のうちから選ばれる1種または2種以上を含有する請求項1または2に記載のばね鋼。 - 前記成分組成は、さらに、
W:0.001質量%以上2.0質量%以下、
Nb:0.001質量%以上0.1質量%以下、
Ti:0.001質量%以上0.2質量%以下および
V:0.002質量%以上0.5質量%以下
のうちから選ばれる1種または2種以上を含有する請求項1ないし3のいずれかに記載のばね鋼。 - 前記成分組成は、さらに、
B:0.0002質量%以上0.005質量%以下
を含有する請求項1ないし4のいずれかに記載のばね鋼。 - 前記成分組成は、さらに、
N:0.005質量%以上0.020質量%以下
を含有する請求項1ないし5のいずれかに記載のばね鋼。 - C:0.35質量%超0.50質量%未満、
Si:1.75質量%超3.00質量%以下、
Mn:0.2質量%以上1.0質量%以下、
Cr:0.01質量%以上0.04質量%以下、
P:0.025質量%以下、
S:0.025質量%以下、
Mo:0.1質量%以上1.0%以下および
O:0.0015質量%以下
を、下記(1)式で算出されるPC値が3.3超8.0以下の条件下に含有する成分組成を有する鋼素材を、Ac3点以上(Ac3点+200℃)以下の温度域に加熱し、10℃/s以上の冷却速度で200℃以下まで冷却し、その後、150℃以上500℃以下の温度域まで加熱し、冷却するばね鋼の製造方法。
記
PC=4.2×([C]+[Mn])+0.1×(1/[Si]+1/[Mo])
+20.3×[Cr]+0.001×(1/[N])・・・(1)
但し、[ ]は該括弧内成分の含有量(質量%) - 前記成分組成が、さらに、下記(2)式を満足する請求項7に記載のばね鋼の製造方法。
記
[Cr]/[Mo] ≦0.35 ・・・(2)
但し、[ ]は該括弧内成分の含有量(質量%) - 前記成分組成は、さらに、
Al:0.01質量%以上0.50質量%以下、
Cu:0.005質量%以上1.0質量%以下および
Ni:0.005質量%以上2.0質量%以下
のうちから選ばれる1種または2種以上を含有する請求項7または8に記載のばね鋼の製造方法。 - 前記成分組成は、さらに、
W:0.001質量%以上2.0質量%以下、
Nb:0.001質量%以上0.1質量%以下、
Ti:0.001質量%以上0.2質量%以下および
V:0.002質量%以上0.5質量%以下
のうちから選ばれる1種または2種以上を含有する請求項7ないし9のいずれかに記載のばね鋼の製造方法。 - 前記成分組成は、さらに、
B:0.0002質量%以上0.005質量%以下
を含有する請求項7ないし10のいずれかに記載のばね鋼の製造方法。 - 前記成分組成は、さらに、
N:0.005質量%以上0.020質量%以下
を含有する請求項7ないし11のいずれかに記載のばね鋼の製造方法。
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US20140060706A1 (en) | 2014-03-06 |
CN102884216A (zh) | 2013-01-16 |
JP4900516B2 (ja) | 2012-03-21 |
US8608874B2 (en) | 2013-12-17 |
KR20130018808A (ko) | 2013-02-25 |
EP2557195A1 (en) | 2013-02-13 |
CN102884216B (zh) | 2014-08-06 |
JP2011246811A (ja) | 2011-12-08 |
US9618070B2 (en) | 2017-04-11 |
US20130048158A1 (en) | 2013-02-28 |
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