WO2015045951A1 - 耐遅れ破壊性およびボルト成形性に優れた高強度ボルト用鋼およびボルト - Google Patents
耐遅れ破壊性およびボルト成形性に優れた高強度ボルト用鋼およびボルト Download PDFInfo
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- WO2015045951A1 WO2015045951A1 PCT/JP2014/074393 JP2014074393W WO2015045951A1 WO 2015045951 A1 WO2015045951 A1 WO 2015045951A1 JP 2014074393 W JP2014074393 W JP 2014074393W WO 2015045951 A1 WO2015045951 A1 WO 2015045951A1
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- bolt
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- 230000003111 delayed effect Effects 0.000 title claims abstract description 96
- 229910000831 Steel Inorganic materials 0.000 title claims abstract description 68
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- 229910052804 chromium Inorganic materials 0.000 claims description 7
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- 239000012535 impurity Substances 0.000 claims description 5
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Images
Classifications
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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
-
- 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
-
- 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")
-
- 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
- C21D6/00—Heat treatment of ferrous alloys
- C21D6/004—Heat treatment of ferrous alloys containing Cr and Ni
-
- 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
- C21D6/00—Heat treatment of ferrous alloys
- C21D6/005—Heat treatment of ferrous alloys containing Mn
-
- 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
- C21D6/00—Heat treatment of ferrous alloys
- C21D6/008—Heat treatment of ferrous alloys containing Si
-
- 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
- C21D9/0093—Heat treatment, e.g. annealing, hardening, quenching or tempering, adapted for particular articles; Furnaces therefor for screws; for bolts
-
- 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
-
- 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
- C22C38/001—Ferrous alloys, e.g. steel alloys containing N
-
- 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
- C22C38/02—Ferrous alloys, e.g. steel alloys containing silicon
-
- C—CHEMISTRY; METALLURGY
- C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
- C22C—ALLOYS
- C22C38/00—Ferrous alloys, e.g. steel alloys
- C22C38/04—Ferrous alloys, e.g. steel alloys containing manganese
-
- C—CHEMISTRY; METALLURGY
- C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
- C22C—ALLOYS
- C22C38/00—Ferrous alloys, e.g. steel alloys
- C22C38/06—Ferrous alloys, e.g. steel alloys containing aluminium
-
- C—CHEMISTRY; METALLURGY
- C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
- C22C—ALLOYS
- C22C38/00—Ferrous alloys, e.g. steel alloys
- C22C38/18—Ferrous alloys, e.g. steel alloys containing chromium
- C22C38/40—Ferrous alloys, e.g. steel alloys containing chromium with nickel
- C22C38/42—Ferrous alloys, e.g. steel alloys containing chromium with nickel with copper
-
- 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
- C22C38/44—Ferrous alloys, e.g. steel alloys containing chromium with nickel with molybdenum or tungsten
-
- 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
- C22C38/46—Ferrous alloys, e.g. steel alloys containing chromium with nickel with vanadium
-
- C—CHEMISTRY; METALLURGY
- C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
- C22C—ALLOYS
- C22C38/00—Ferrous alloys, e.g. steel alloys
- C22C38/18—Ferrous alloys, e.g. steel alloys containing chromium
- C22C38/40—Ferrous alloys, e.g. steel alloys containing chromium with nickel
- C22C38/50—Ferrous alloys, e.g. steel alloys containing chromium with nickel with titanium or zirconium
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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
- F16B—DEVICES FOR FASTENING OR SECURING CONSTRUCTIONAL ELEMENTS OR MACHINE PARTS TOGETHER, e.g. NAILS, BOLTS, CIRCLIPS, CLAMPS, CLIPS OR WEDGES; JOINTS OR JOINTING
- F16B31/00—Screwed connections specially modified in view of tensile load; Break-bolts
- F16B31/06—Screwed connections specially modified in view of tensile load; Break-bolts having regard to possibility of fatigue rupture
Definitions
- the present invention relates to a steel for bolts used in automobiles and various industrial machines, and a bolt obtained using this steel for bolts.
- the present invention relates to a bolt steel useful as a material for a high-strength bolt that exhibits excellent delayed fracture resistance and bolt formability even when the tensile strength is 1100 MPa or more, and a high-strength bolt.
- JIS standard steels such as SCM435 and SCM440 are generally used as general bolt steels.
- these general-purpose steels when the tensile strength is 1100 MPa or more, there is a problem that so-called delayed fracture that suddenly brittle fractures after using for a certain period is likely to occur. Accordingly, steel for high-strength bolts with improved temper softening resistance has been proposed as an object of improving delayed fracture characteristics, that is, delayed fracture resistance.
- Patent Document 1 discloses a composite compound such as a Mo compound, a Ti compound, a V compound, and a carbide or nitride containing two or more elements selected from Mo, Ti, and V.
- a technique for improving the resistance to hydrogen embrittlement and improving delayed fracture resistance by dispersing an appropriate amount of a composite compound of 50 nm or less in steel has been proposed.
- Patent Documents 2 and 3 propose techniques for improving delayed fracture resistance by adjusting the chemical composition of steel and appropriately adjusting the quenching and tempering conditions during bolt production.
- delayed fracture resistance is increased to some extent by generating a large amount of composite compounds such as carbides and nitrides to generate hydrogen trap sites, and increasing the temper softening resistance by devising the bolt manufacturing process. It can be improved.
- the amount of invading hydrogen that penetrates into the bolt from the usage environment exceeds the limit amount of hydrogen that can be neutralized by hydrogen traps with carbides and nitrides, causing delayed fracture.
- the diffusible hydrogen that increases may lead to breakage.
- Patent Document 3 relates to a high-strength bolt having a tensile strength of 1400 MPa or more and excellent delayed fracture resistance.
- the tensile strength is 1400 MPa or more
- the delayed fracture resistance may be deteriorated in a severe environment where the corrosion of the steel material and the hydrogen ingress proceed in parallel.
- the said patent document 3 since it is necessary to provide a compressive residual stress to a screw bottom part, there exists a possibility of causing the increase in manufacturing cost.
- the present invention has been made by paying attention to the above-described circumstances, and its purpose is to maintain the high strength required for the bolt, and to increase the amount of hydrogen entering the bolt and the amount of corrosion.
- Cr 0.8 to 1.2%
- Mo 0.8 to 1.5%
- V 0.05 to 0.13%
- Ti 0.02 to 0.08%
- Al 0.
- the content is 01 to 0.1%, N: 0.001 to 0.01%, the balance being iron and inevitable impurities, and satisfying the following formulas (1) and (2) Have 0.85 ⁇ [C] + [Si] / 7 + [Mn] / 5 + [Ni] / 20 + [Cr] / 9 + [Mo] /2 ⁇ 1.3 (1) [C] ⁇ (0.07 ⁇ [Mo] + 0.20 ⁇ [V]) ⁇ 0.20 (2) However, [C], [Si], [Mn], [Ni], [Cr], [Mo], and [V] are mass%, respectively, of C, Si, Mn, Ni, Cr, Mo, and V. Indicates the content.
- the steel for high-strength bolts of the present invention further contains Cu: more than 0% and not more than 0.70% if necessary. Addition of Cu further improves delayed fracture resistance.
- the high-strength bolt excellent in delayed fracture resistance according to the present invention that has solved the above problems is a bolt obtained by using the steel for high-strength bolts described above, and the grain size number of the prior austenite grain size Is 10.0 or more.
- the high strength bolt excellent in delayed fracture resistance according to the present invention that can solve the above-mentioned problems is quenched at 880 to 960 ° C. and tempered at 550 to 650 ° C. using the above steel for high strength bolts.
- the tensile strength satisfies 1100 to 1400 MPa.
- a high-strength bolt steel excellent in delayed fracture resistance and bolt formability can be obtained by strictly defining the chemical composition in the steel while satisfying a predetermined relational expression.
- a high-strength bolt can be obtained, which exhibits excellent bolt formability. Therefore, the steel for high-strength bolts of the present invention is extremely useful as a material for high-strength bolts excellent in delayed fracture resistance and bolt formability.
- FIG. 1 is a schematic view showing the shape of a tensile test specimen.
- FIG. 2 is a schematic diagram showing the shape of a corrosion test specimen.
- FIG. 3 is a schematic diagram showing the shape of a delayed fracture test specimen.
- FIG. 4 is a schematic diagram showing the shape of a test piece for compression test.
- the present inventors examined from various angles in order to improve the delayed fracture resistance of the steel for bolts. It is known that delayed fracture is more likely to occur mainly as the strength of the bolt increases, and that it becomes significantly worse particularly when the tensile strength is 1100 MPa or more. For these reasons, conventionally, a technique has been proposed in which a large amount of composite compounds such as carbides and nitrides are precipitated to generate hydrogen trap sites and improve delayed fracture resistance. However, in severe environments, even if the amount of critical hydrogen is increased by precipitation of complex compounds as described above, the amount of hydrogen penetrating into the steel is very large, so it is difficult to exhibit excellent delayed fracture resistance. is there.
- the present inventors have earnestly researched bolt steels and bolts that can exhibit sufficient delayed fracture resistance even under harsh environments. As a result, while suppressing the C content to 0.30% or less and controlling each element to satisfy a predetermined relational expression, the ductility is dramatically improved while maintaining the high strength required for the bolt. It has been found that the delayed fracture resistance can be improved. Moreover, while suppressing the C content to 0.30% or less and adding a predetermined amount of Ni, it has also been found that the corrosion resistance of the bolt can be dramatically improved and the delayed fracture resistance can be further improved. completed.
- the C content is suppressed to 0.30% or less, and the strength is maintained by satisfying the relationship of the above formulas (1) and (2). It becomes possible to greatly improve the ductility. Further, by suppressing the C content to 0.30% or less and adding Ni, the corrosion resistance can be greatly improved as compared with the case of adding Ni in a state where the C content is high. As a result, if the bolt steel of the present invention was used, delayed fracture resistance in harsh environments could be dramatically improved.
- the steel whose C content is suppressed to 0.30% or less as described above is subjected to predetermined quenching and tempering, and particularly by tempering at a temperature of 550 ° C. or higher, Cr,
- the precipitation hardening elements such as Mo, V, and Ti can be precipitated as alloy carbides. Therefore, the amount of solute C contained in the parent phase of the bolt steel can be further reduced from 0.30%. Since the fine carbide containing the precipitation hardening type element can improve not only the strength but also the critical hydrogen amount in the steel, the improvement in ductility by reducing the C content and the effect of suppressing the intrusion hydrogen amount can be achieved. By combining them, the delayed fracture resistance can be dramatically improved.
- the steel for bolts of the present invention has a C content of 0.30% or less and contains Ni and other precipitation hardening elements in a certain range, thereby improving the corrosion resistance and ductility of the bolts and being harsh. It is characterized by enhanced delayed fracture resistance in a difficult environment. In order to ensure other characteristics necessary for the bolt, it is necessary to satisfy the chemical composition as follows.
- C (C: 0.10 to 0.30%) C is an element necessary for ensuring hardenability and strength, but as its content increases, ductility and corrosion resistance decrease.
- the lower the C content the better the ductility.
- the C content is less than 0.10%, in the mass production process, it becomes difficult to cause martensitic transformation during quenching, and subsequent precipitation strengthening It becomes insufficient. Therefore, it becomes difficult to highly stabilize the strength of the bolt after quenching and tempering.
- the C content exceeds 0.30%, delayed fracture resistance deteriorates due to deterioration of ductility.
- the preferable lower limit of the C content is 0.15% or more, more preferably 0.20% or more, and the preferable upper limit is 0.27% or less, more preferably 0.25% or less.
- Ni is an element effective in improving corrosion resistance, suppressing hydrogen intrusion, and improving delayed fracture resistance. In order to exhibit such effects sufficiently, it is necessary to contain 0.4% or more of Ni after suppressing the C content to 0.30% or less as described above. On the other hand, when Ni is contained excessively, the effect is saturated and the cost is increased. Therefore, the upper limit of the Ni content is set to 0.7% or less.
- the preferable lower limit of the Ni content is 0.45% or more, more preferably 0.50% or more, and the preferable upper limit is 0.65% or less, more preferably 0.60% or less.
- Si 0% to 0.2%)
- Si is an element effective for ensuring the strength, but if its content is excessive, the bolt formability deteriorates. Therefore, the Si content needs to be 0.2% or less. Preferably it is 0.15% or less, More preferably, it is 0.1% or less.
- the lower limit of the Si content may be 0%, but since there is a mixture from raw materials, refractories, etc., Si is, for example, about 0.005% or more, particularly about 0.01% or more. preferable.
- Mn is a hardenability improving element and is an element useful for achieving high strength. In order to exhibit such an effect, it is necessary to contain 0.3% or more of Mn. On the other hand, when the Mn content is excessive, segregation to the grain boundary is promoted and the grain boundary strength is lowered, so that delayed fracture is likely to occur. From such a viewpoint, the upper limit of the Mn content is suppressed to 0.8% or less.
- the minimum with preferable Mn content is 0.40% or more, More preferably, it is 0.45% or more, and a preferable upper limit is 0.70% or less, More preferably, it is 0.60% or less.
- P is an element that promotes grain boundary fracture due to grain boundary segregation and degrades delayed fracture resistance, so a lower value is desirable, and its upper limit is 0.03% or less. It is difficult to reduce the P content to 0%, and it is generally preferable that the P content is 0.001% or more.
- the upper limit with preferable P content is 0.02% or less, More preferably, it is 0.01% or less.
- S (S: more than 0% and 0.03% or less) S forms MnS in the steel, and this MnS becomes a stress concentration point when stress is applied, and can be a starting point of delayed fracture. Therefore, in order to improve delayed fracture resistance, it is necessary to reduce the S content as much as possible, and in the present invention, it is suppressed to 0.03% or less. It is difficult to make the S content 0%, and it is generally preferable that the S content is 0.001% or more.
- the upper limit with preferable S content is 0.02% or less, More preferably, it is 0.01% or less.
- Cr 0.8-1.2%) Cr has the effect of enhancing the hardenability and corrosion resistance of the steel and, as described above, precipitates as carbides during tempering, and thus effectively acts to improve strength and delayed fracture resistance. In order to fully exhibit such an effect, it is necessary to contain 0.8% or more of Cr. On the other hand, if the Cr content is excessive, the cold workability deteriorates and the bolt formability decreases, so it is necessary to make it 1.2% or less.
- the preferable lower limit of the Cr content is 0.90% or more, more preferably 0.95% or more, and the preferable upper limit is 1.10% or less, more preferably 1.05% or less.
- Mo is an element effective for improving the strength after tempering because it is a hardenability improving element and is also a precipitation hardening type element.
- the C content is suppressed to 0.30% or less. Therefore, in order to ensure the high strength required for the bolts, it is necessary to contain 0.8% or more of Mo. There is.
- the Mo content is excessive, the cold workability is deteriorated and the bolt formability is lowered. Therefore, the upper limit of the Mo content is set to 1.5% or less.
- the minimum with preferable Mo content is 0.85% or more, More preferably, it is 0.90% or more, A preferable upper limit is 1.20% or less, More preferably, it is 1.10% or less.
- V (V: 0.05-0.13%) V can refine the crystal grains of steel and improve strength and delayed fracture resistance by carbides precipitated during tempering. In order to exert these effects, the V content needs to be 0.05% or more. However, if the V content is excessive, it precipitates as coarse carbides during rolling, resulting in deterioration of cold workability and an increase in cost. Therefore, the upper limit of the V content needs to be 0.13% or less. There is.
- the minimum with preferable V content is 0.06% or more, More preferably, it is 0.08% or more, and a preferable upper limit is 0.10% or less, More preferably, it is 0.09% or less.
- Ti 0.02-0.08%
- Ti becomes TiN or TiC in the rolling stage and can be used as a hydrogen trap site.
- the Ti content needs to be 0.02% or more.
- the upper limit is made 0.08% or less.
- the preferable lower limit of the Ti content is 0.03% or more, more preferably 0.04% or more, and the preferable upper limit is 0.07% or less, more preferably 0.06% or less.
- Al is an element effective as a deoxidizing agent, and also has an effect of forming AlN to refine crystal grains. Considering the use as a deoxidizer, it actually exceeds 0%, and from the viewpoint of exhibiting the effect of refining crystal grains, it is present at 0.01% or more. Preferably it is 0.02% or more, More preferably, it is 0.03% or more. On the other hand, as the Al content increases, the amount of coarse carbonitride inclusions increases and the delayed fracture resistance tends to decrease. Therefore, the Al content is suppressed to 0.1% or less. Preferably it is 0.08% or less, More preferably, it is 0.06% or less.
- N combines with Ti in the solidification stage after steel melting to form TiN. Since TiN does not dissolve even when heated at a high temperature, the amount of TiC generated at the time of tempering is reduced, resulting in a decrease in delayed fracture resistance. Therefore, N needs to be 0.01% or less. It is difficult to make N 0%, and it is usually 0.001% or more.
- the preferable lower limit of the N content is 0.005% or more, more preferably 0.006% or more, and the preferable upper limit is 0.009% or less, more preferably 0.008% or less.
- the basic components in the steel for high-strength bolts of the present invention are as described above, and the balance is iron and inevitable impurities. Specifically, impurities other than the above P and S are allowed, but as the unavoidable impurities, mixing of elements brought in depending on the situation of raw materials, materials, manufacturing facilities, etc. can be allowed.
- the steel for high-strength bolts of the present invention further contains Cu: more than 0% and not more than 0.70% if necessary.
- Cu more than 0% and 0.70% or less
- Cu is an element effective for enhancing corrosion resistance, suppressing hydrogen intrusion, and further improving delayed fracture resistance.
- the upper limit of the Cu content is preferably 0.70% or less.
- the upper limit with more preferable Cu content is 0.65% or less, More preferably, it is 0.60% or less.
- the minimum with preferable Cu content for exhibiting said effect effectively is 0.40% or more, More preferably, it is 0.45% or more, More preferably, it is 0.50% or more.
- the bolt steel of the present invention cannot achieve the object of the present invention only by appropriately adjusting the range of each component as described above, and the following relational expressions (1) and (2) Need to be satisfied.
- These functions and effects are as follows. 0.85 ⁇ [C] + [Si] / 7 + [Mn] / 5 + [Ni] / 20 + [Cr] / 9 + [Mo] /2 ⁇ 1.3 (1) [C] ⁇ (0.07 ⁇ [Mo] + 0.20 ⁇ [V]) ⁇ 0.20 (2)
- [C], [Si], [Mn], [Ni], [Cr], [Mo], and [V] are mass%, respectively, of C, Si, Mn, Ni, Cr, Mo, and V. Indicates the content.
- the value calculated by ([C] + [Si] / 7 + [Mn] / 5 + [Ni] / 20 + [Cr] / 9 + [Mo] / 2) is referred to as the A value.
- a value calculated by [[C] ⁇ (0.07 ⁇ [Mo] + 0.20 ⁇ [V])] may be referred to as a B value.
- the above formula (1) is a formula corresponding to the carbon equivalent of steel.
- the amount of invading hydrogen is reduced by suppressing the C content to 0.30% or less.
- the carbon equivalent represented by the A value needs to be 0.85 or more.
- the A value is smaller than 0.85, it becomes difficult to secure a strength of 1100 MPa or more at a tempering temperature of 550 ° C. or more.
- the upper limit was made 1.3 or less.
- the preferable lower limit of the A value is 0.93 or more, more preferably 0.95 or more, and the preferable upper limit is 1.10 or less, more preferably 1.05 or less.
- the above equation (2) is a relational expression that conveniently indicates how much carbon in the steel is consumed by Mo and V precipitated as carbides in the tempering treatment.
- the coefficient of Mo of 0.07 is the atomic weight ratio of Mo and C in the carbide Mo 2 C
- the coefficient of V of 0.20 is the atomic weight ratio of V and C in the carbide V 4 C 3. is there.
- the B value does not mean the amount of solute C in steel, but can be used as a numerical value for relatively comparing how much solute C remains after tempering. . Therefore, the B value serves as an index indicating whether the ductility is good. In order to exhibit good ductility, the B value needs to be 0.20 or less.
- the upper limit with preferable B value is 0.17 or less, More preferably, it is 0.15 or less, A preferable minimum is 0.02 or more, More preferably, it is 0.03 or more.
- the present invention also includes bolts obtained using the above steel for bolts.
- the bolt of the present invention is obtained by quenching at 880 to 960 ° C. and tempering at 550 to 650 ° C. using the above steel for bolts, and has excellent delayed fracture resistance and tensile strength. Satisfies high strength of 1100 to 1400 MPa.
- the bolt steel of the present invention having the above chemical composition has potentially excellent strength characteristics and delayed fracture resistance, but the steel has sufficient strength characteristics and delayed fracture resistance.
- the heating temperature during quenching is 880 ° C. or higher.
- precipitation hardening type elements such as Cr, Mo, V, and Ti do not dissolve in the steel, and sufficient precipitates cannot be secured even after tempering.
- spheroidizing annealing may be performed before quenching, but if the heating temperature during quenching is low, spheroidized carbides may be present in the structure before quenching, and the spheroidized carbides remain undissolved and have a predetermined tensile strength. It becomes difficult to obtain strength.
- the heating temperature during quenching is preferably 900 ° C. or higher.
- the heating temperature at the time of quenching is too high, defects such as uneven burning and coarsening of the crystal grains at the time of quenching occur, and cost increases such as facility improvement occur.
- the heating temperature during quenching is 960 ° C. or lower. More preferably, it is 930 degrees C or less.
- the tempering temperature is set to 550 ° C. or higher in order to precipitate precipitation hardening type elements such as Cr, Mo, V, Ti, etc., which are solid-dissolved during quenching heating, as fine precipitates. Even if tempering is performed at a temperature lower than 550 ° C., fine carbides are hardly precipitated, and temper softening resistance and a hydrogen trap effect cannot be obtained. Therefore, delayed fracture resistance cannot be sufficiently improved. Further, when the tempering temperature is lowered, the precipitation of cementite becomes insufficient and the ductility is lowered. More preferably, the heating temperature during tempering is 570 ° C. or higher.
- the tempering temperature is too high, the effect of the temper softening resistance is diminished and sufficient softening resistance cannot be obtained, and a predetermined strength cannot be obtained. More preferably, it is 600 degrees C or less. Both the quenching temperature and the tempering temperature are obtained by measuring the surface temperature of steel formed into a bolt shape.
- the bolt of the present invention is characterized in that it is quenched and tempered at the above temperature using the bolt steel of the present invention.
- Conditions other than the heating temperature in quenching and tempering can be appropriately set in consideration of the respective heating temperatures and the characteristics of the precipitation hardening type elements. For example, the following conditions can be employed. [Hardening conditions] Holding time of heating: preferably 10 minutes or more, more preferably 20 minutes or more, preferably 1 hour or less, more preferably 50 minutes or less Cooling conditions: preferably oil cooling or water cooling
- the heating holding time at the time of quenching is set in order to sufficiently dissolve the precipitation hardening type element present in the steel central portion, and is preferably 10 minutes or more. Moreover, since the coarsening of a crystal grain will be anxious if the holding time of the heating at the time of hardening becomes long, a preferable upper limit was made into 1 hour or less.
- Holding time of heating preferably 30 minutes or more, preferably 70 minutes or more, preferably 3 hours or less, preferably 2 hours or less
- Cooling conditions preferably oil cooling, water cooling or air cooling
- the heating holding time during tempering is preferably 30 minutes or more in order to precipitate the alloy carbide. Moreover, even if the heating holding time during tempering exceeds 3 hours, the effect is saturated, so the preferable upper limit is set to 3 hours or less.
- manufacturing conditions other than those described above are not limited, and bolts can be manufactured using a commonly used method. Specifically, for example, after hot rolling using a bolt that satisfies the above chemical component composition, the wire is drawn after spheroidizing annealing as necessary. Then, after performing cold working such as cold forging to form a bolt shape, it is possible to manufacture the bolt by performing threading by rolling and then performing quenching and tempering as described above.
- the above-described spheroidizing annealing is a process generally performed when a high-strength bolt having a tensile strength of 1100 MPa or more is manufactured, and then bolt forming is performed.
- the steel for bolts in which the C content is suppressed to 0.30% or less is used, it is possible to form the bolt shape without performing spheroidizing annealing.
- the bolt of the present invention obtained as described above exhibits a high strength with a tensile strength of 1100 MPa or more. Moreover, although the bolt of the present invention has a high tensile strength of 1100 MPa or more, good delayed fracture resistance is exhibited. Specifically, in the bolt described above, grain coarsening at the time of quenching is prevented, and the grain size number of the prior austenite grain size is as fine as 10.0 or more, so that the ductility is improved and under high load stress. Excellent delayed fracture resistance at high temperatures. More preferably, the prior austenite grain size number is 10.5 or more, more preferably 11.0 or more. As a result, the delayed fracture strength ratio described later is 0.80 or more, preferably 0.90 or more.
- the upper limit of the prior austenite grain size number is not particularly limited, but is preferably controlled to 13.0 or less in consideration of the balance with productivity and cost.
- the prior austenite grain size can be adjusted to the above range by appropriately controlling, for example, the amount of Ti in the steel and the quenching temperature.
- the upper limit of the tensile strength in the bolt of the present invention is 1400 MPa or less.
- the high-strength bolt of the present invention can be applied to, for example, high tension bolts, torcia-type bolts, hot-dip galvanized high-strength bolts, rust-proof high-strength bolts, refractory steel high-strength bolts and the like.
- the bolt is optimal as a bolt having high strength, corrosion resistance, and delayed fracture resistance used in fields such as the automobile field, the architectural field, and the industrial machine field.
- a test piece for corrosion test shown in FIG. 2 was prepared by cutting, and a corrosion test by acid immersion was performed. The unit in the figure is mm.
- the corrosion test was performed by immersing the above test piece for corrosion test in an acidic aqueous solution of 15% by mass HCl for 30 minutes. After the mass change amount of the test piece before and after immersion was divided by the initial mass of the test piece, a value converted to a percentage was obtained as “corrosion weight loss”. In this example, corrosion weight loss of 0.02% or less was evaluated as being excellent in corrosion resistance.
- the corrosion test was not performed about the test piece whose tensile strength is less than 1100 MPa, it described as "-" in the table
- a delayed fracture strength ratio of 0.80 or more was evaluated as being excellent in delayed fracture resistance. It is known that when the delayed fracture strength ratio satisfies the above numerical value, the probability that delayed fracture actually occurs is extremely small. In addition, since the delayed fracture test was not performed about the test piece whose tensile strength is less than 1100 MPa, it described as "-" in the table
- the Ac 1 transformation point of each steel is obtained by the following equation (3), held at a temperature of (Ac 1 transformation point + 10 ° C.) for 5 hours, and at a cooling rate of 10 ° C./Hr at 680 ° C. The reaction was carried out after cooling.
- Ac 1 transformation point 723-10.7 ⁇ [Mn] ⁇ 16.9 ⁇ [Ni] + 29.1 ⁇ [Si] + 16.9 ⁇ [Cr] (3)
- [Mn], [Ni], [Si] and [Cr] are each in mass% and indicate the contents of Mn, Ni, Si and Cr.
- Test No. Nos. 1 to 12 satisfy the requirements defined in the present invention, and show high strength of 1100 MPa or more and excellent delayed fracture resistance in harsh environments. In addition, the crack limit compression rate is high, and the bolt formability is excellent.
- test no. Nos. 13 to 34 do not satisfy any of the requirements defined in the present invention, and any of the characteristics is deteriorated.
- Test No. Nos. 13 and 14 satisfy the requirements defined in the present invention with respect to the chemical composition. However, since the tempering temperature is low, the tensile strength exceeds 1400 MPa, and the delayed fracture strength ratio decreases. Test No. No. 13 is a test no. Since the tempering temperature was lower than that of No. 14, cementite was not sufficiently precipitated, the squeezing was lowered, and the ductility was also lowered.
- Test No. 15 is an example using the steel type A1 of Table 1 with a low C content. Therefore, even if predetermined heat treatment conditions are performed, martensitic transformation does not occur at the time of quenching, and a desired strength cannot be ensured.
- Test No. 16 is an example using the steel type B1 of Table 1 with a large C content. Therefore, the amount of invading hydrogen increased due to the deterioration of corrosion resistance, the delayed fracture strength ratio was lowered, and the delayed fracture resistance deteriorated.
- Test No. 17 is an example using the steel type C1 in Table 1 having a high Si content. Therefore, although the delayed fracture resistance showed an excellent value, the crack limit compression rate was lowered and bolt forming was difficult.
- Test No. 18 is an example using the steel type D1 of Table 1 with a low Mn content. Therefore, the hardenability of steel is low, quenching becomes insufficient, and a predetermined tensile strength cannot be secured.
- Test No. 19 is an example using steel type E1 of Table 1 with excessive Mn content. As a result, the grain boundary strength decreased, the delayed fracture strength ratio decreased, and the delayed fracture resistance deteriorated.
- Test No. No. 20 is an example using the steel type F1 of Table 1 with a high P and S content. As a result, the grain boundaries became brittle and the delayed fracture resistance deteriorated.
- Test No. 21 is an example using the steel type G1 of Table 1 with a low Ni content. As a result, the corrosion resistance deteriorated, the amount of invading hydrogen increased, the delayed fracture strength ratio decreased, and the delayed fracture resistance deteriorated.
- Test No. 22 is an example using the steel type H1 of Table 1 with a low Cr content. Therefore, the hardenability is low and the precipitation strengthening at the time of tempering is insufficient, so that a predetermined tensile strength cannot be secured.
- Test No. 23 is also an example using the steel type I1 of Table 1 with a low Cr content. Therefore, although the tensile strength could be ensured, the corrosion resistance deteriorated. Moreover, since the amount of invading hydrogen increased, the delayed fracture strength ratio was lowered, and the delayed fracture resistance deteriorated.
- Test No. 24 is an example using the steel type J1 of Table 1 with excessive Cr content. Therefore, although tensile strength and delayed fracture resistance are excellent, bolt forming is difficult because the crack limit compression rate has decreased.
- Test No. 25 is an example using the steel type K1 of Table 1 with a low Mo content and a low A value. Therefore, the hardenability is low and the precipitation strengthening at the time of tempering is insufficient, so that a predetermined tensile strength cannot be secured.
- Test No. 26 is an example using the steel type L1 of Table 1 with a large Mo content. Therefore, the delayed fracture resistance is excellent, but the crack forming limit compression rate is lowered, so that bolt forming is difficult.
- Test No. 27 is an example using the steel type M1 of Table 1 to which V content is not added. Therefore, as shown in Table 2, even when tempering at 580 ° C., no precipitated carbide crystals were formed, and the hydrogen trap effect was not sufficient, so the delayed fracture strength ratio was lowered and the delayed fracture resistance deteriorated.
- Test No. 28 is an example using the steel type N1 of Table 1 with a large V content. For this reason, coarse carbides precipitate, the crack limit compression ratio decreases, and bolt forming is difficult.
- Test No. 29 is an example using the steel type O1 of Table 1 which does not add Ti content. Therefore, the prior austenite crystal grains became coarse and the ductility decreased. Further, since there was no hydrogen trap effect by TiC, the delayed fracture strength ratio was lowered, and the delayed fracture resistance was deteriorated.
- Test No. 30 is an example using the steel type P1 of Table 1 with a large Ti content. Therefore, coarse carbides precipitate, the crack limit compression ratio decreases, and bolt forming is difficult.
- Test No. Nos. 31 and 32 are examples using the steel types Q1 and R1 of Table 1 which satisfy the requirements of the present invention for each additive element but have a small A value. Therefore, high tensile strength could not be ensured.
- Test No. No. 33 is an example using the steel type S1 of Table 1 having a large B value, although the individual additive elements satisfy the requirements of the present invention. Therefore, the amount of dissolved C was large, the delayed fracture strength ratio was lowered due to the deterioration of ductility, and the delayed fracture resistance was degraded.
- Test No. 34 is an example using the steel type T1 of Table 1 which simulated SCM435 of conventional steel. Specifically, the amount of C is large, Ni, V, and Ti are not contained, the A value is small, and the B value is large. Therefore, the prior austenite crystal grains became coarse and ductility decreased. Moreover, since Ni was not added, corrosion resistance fell. Further, since there was no hydrogen trap effect by TiC, the delayed fracture strength ratio was lowered, and the delayed fracture resistance was lowered.
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Abstract
Description
0.85≦[C]+[Si]/7+[Mn]/5+[Ni]/20+[Cr]/9+[Mo]/2≦1.3 ・・・(1)
[C]-(0.07×[Mo]+0.20×[V])≦0.20 ・・・(2)
但し、[C],[Si],[Mn],[Ni],[Cr],[Mo]および[V]は夫々、質量%で、C,Si,Mn,Ni,Cr,MoおよびVの含有量を示す。
Cは、焼入れ性と強度確保のために必要な元素であるが、その含有量が増大するにつれて延性と耐食性が低下する。本発明のボルト用鋼では、C含有量が低くなるほど延性が向上するが、C含有量が0.10%未満になると、量産工程では焼入れ時にマルテンサイト変態を起こしにくくなり、その後の析出強化も不十分となる。そのため、焼入れ・焼戻し後のボルトの強度を高度に安定させることが難しくなる。一方、C含有量が0.30%を超えると、延性の悪化により耐遅れ破壊性が劣化する。C含有量の好ましい下限は0.15%以上、より好ましくは0.20%以上であり、好ましい上限は0.27%以下、より好ましくは0.25%以下である。
Niは、耐食性を向上させて水素侵入を抑制し、耐遅れ破壊性を改善する上で有効な元素である。こうした効果を十分に発揮させるには、上記のとおりC含有量を0.30%以下に抑制した上で、Niを0.4%以上含有させる必要がある。一方、Niを過剰に含有させると、その効果が飽和すると共にコストアップを招く。そのため、Ni含有量の上限を0.7%以下とした。Ni含有量の好ましい下限は0.45%以上、より好ましくは0.50%以上であり、好ましい上限は0.65%以下、より好ましくは0.60%以下である。
Siは、強度確保に有効な元素であるが、その含有量が過剰になるとボルト成形性が低下する。従って、Si含有量は0.2%以下とする必要がある。好ましくは0.15%以下、より好ましくは0.1%以下である。尚、Si含有量の下限は、0%であってもよいが、原料や耐火物等からの混入があるため、Siは例えば0.005%以上、特に0.01%以上程度であることが好ましい。
Mnは焼入れ性向上元素であり、高強度を達成するために有用な元素である。このような効果を発現させるには、Mnを0.3%以上含有させる必要がある。一方、Mn含有量が過剰になると、粒界への偏析が助長されて粒界強度が低下するため、遅れ破壊が生じ易くなる。こうした観点から、Mn含有量の上限は0.8%以下に抑える。Mn含有量の好ましい下限は0.40%以上、より好ましくは0.45%以上であり、好ましい上限は0.70%以下、より好ましくは0.60%以下である。
Pは、粒界偏析による粒界破壊を助長して耐遅れ破壊性を劣化させる元素であるため、低いほうが望ましく、その上限を0.03%以下とする。P含有量を0%にすることは困難であり、おおむね、0.001%以上であることが好ましい。P含有量の好ましい上限は0.02%以下、より好ましくは0.01%以下である。
Sは、鋼中にMnSを形成し、該MnSが応力負荷時に応力集中箇所となり、遅れ破壊の起点となり得る。従って、耐遅れ破壊性の改善には、S含有量をできるだけ減少させる必要があり、本発明では0.03%以下に抑える。S含有量を0%にすることは困難であり、おおむね、0.001%以上であることが好ましい。S含有量の好ましい上限は0.02%以下、より好ましくは0.01%以下である。
Crは、鋼の焼入れ性および耐食性を高める作用があると共に、前述した通り、焼戻し時に炭化物として析出するため、強度と耐遅れ破壊性を向上させるのに有効に作用する。こうした効果を十分に発揮させるには、Crを0.8%以上含有させる必要がある。一方、Cr含有量が過剰になると、冷間加工性が劣化してボルト成形性が低下するため、1.2%以下にする必要がある。Cr含有量の好ましい下限は0.90%以上、より好ましくは0.95%以上であり、好ましい上限は1.10%以下、より好ましくは1.05%以下である。
Moは、焼入れ性向上元素であり、且つ析出硬化型元素でもあるため、焼戻し後の強度を向上させるのに有効な元素である。前述したとおり本発明のボルト用鋼では、C含有量を0.30%以下に抑制しているため、ボルトに要求される高い強度を確保するには、Moを0.8%以上含有させる必要がある。一方、Mo含有量が過剰になると、冷間加工性が悪化してボルト成形性が低下するため、Mo含有量の上限を1.5%以下とした。Mo含有量の好ましい下限は0.85%以上、より好ましくは0.90%以上であり、好ましい上限は1.20%以下、より好ましくは1.10%以下である。
Vは、鋼の結晶粒を微細化すると共に、焼戻し時に析出する炭化物により、強度と耐遅れ破壊性を向上させることができる。これらの作用を発揮させるには、V含有量を0.05%以上とする必要がある。しかしながら、V含有量が過剰になると、圧延時に粗大な炭化物として析出し、冷間加工性が悪化したり、コストアップの要因となるため、V含有量の上限は0.13%以下とする必要がある。V含有量の好ましい下限は0.06%以上、より好ましくは0.08%以上であり、好ましい上限は0.10%以下、より好ましくは0.09%以下である。
Tiは、圧延段階でTiNやTiCとなり、水素トラップサイトとして活用することができる。この様な効果を発揮させるには、Ti含有量を0.02%以上とする必要がある。しかしながら、Ti含有量が過剰になると、粗大な炭化物が析出して冷間加工性が劣化したり、コストアップの要因となるため、上限を0.08%以下とする。Ti含有量の好ましい下限は0.03%以上、より好ましくは0.04%以上であり、好ましい上限は0.07%以下、より好ましくは0.06%以下である。
Alは、脱酸剤として有効な元素であり、またAlNを形成して結晶粒を微細化する効果もある。脱酸剤としての利用を考慮すると、現実的には0%を超えており、結晶粒微細化効果を発揮させる観点からは0.01%以上存在させる。好ましくは0.02%以上、より好ましくは0.03%以上である。一方、Al含有量の増加に伴い、粗大な炭窒化物系介在物量が増大して、耐遅れ破壊性が低下し易くなる。よってAl含有量は0.1%以下に抑える。好ましくは0.08%以下、より好ましくは0.06%以下である。
Nは、鋼の溶製後の凝固段階でTiと結合してTiNを形成する。TiNは高温で加熱しても溶解しないため、焼戻し時に生成するTiC量を低下させて、耐遅れ破壊性の低下を招く。従って、Nは0.01%以下とする必要がある。Nを0%にすることは困難であり、通常0.001%以上である。N含有量の好ましい下限は0.005%以上、より好ましくは0.006%以上であり、好ましい上限は0.009%以下、より好ましくは0.008%以下である。
Cuは前述したNiと同様に、耐食性を高めて水素侵入を抑制し、耐遅れ破壊性を更に向上させるのに有効な元素である。しかしながら、Cuを過剰に含有させると、効果が飽和すると共にコストアップの原因となる。こうした観点から、Cu含有量の上限は0.70%以下とすることが好ましい。Cu含有量のより好ましい上限は0.65%以下、更に好ましくは0.60%以下である。また、上記の効果を有効に発揮させるためのCu含有量の好ましい下限は0.40%以上であり、より好ましくは0.45%以上、更に好ましくは0.50%以上である。
0.85≦[C]+[Si]/7+[Mn]/5+[Ni]/20+[Cr]/9+[Mo]/2≦1.3 ・・・(1)
[C]-(0.07×[Mo]+0.20×[V])≦0.20 ・・・(2)
但し、[C],[Si],[Mn],[Ni],[Cr],[Mo]および[V]は夫々、質量%で、C,Si,Mn,Ni,Cr,MoおよびVの含有量を示す。
[焼入れ条件]
加熱の保持時間:好ましくは10分以上、より好ましくは20分以上
好ましくは1時間以下、より好ましくは50分以下
冷却条件:好ましくは油冷または水冷
加熱の保持時間:好ましくは30分以上、好ましくは70分以上
好ましくは3時間以下、好ましくは2時間以下
冷却条件:好ましくは油冷,水冷または空冷
ビレットの再加熱温度:1000~1200℃、仕上げ圧延温度:900~1100℃、その後、0.05~10℃/秒の平均冷却速度で300℃まで冷却。
焼入れ・焼戻しを行った試料の横断面のD/4部(D:直径)を観察し、JIS G 0551に規定の「鋼-結晶粒度の顕微鏡試験方法」に従って、旧オーステナイト結晶粒度番号を測定した。
上記旧オーステナイト結晶粒度番号を測定した後、図1に示す引張試験用試験片を切削加工により作製して、JIS Z2241に基づいて引張試験を行った。図中の単位はmmである。本実施例では、引張強度が1100MPa以上のものを十分な引張強度を示すと評価した。また、JIS Z2241に基づき、引張試験での絞りを測定し、絞りが65.0%よりも大きいものを延性に優れていると評価した。
上記旧オーステナイト結晶粒度番号を測定した後、図2に示す腐食試験用試験片を切削加工により作製して酸浸漬による腐食試験を行った。図中の単位はmmである。腐食試験は、上記腐食試験用試験片を15質量%HClの酸性水溶液に30分浸漬して行った。浸漬前・後の試験片の質量変化量を試験片の初期質量で除した後、百分率に換算した値を「腐食減量」として求めた。本実施例では、腐食減量が0.02%以下のものを、耐食性に優れると評価した。なお、引張強度が1100MPa未満の試験片については腐食試験を行わなかったため、表中に「―」と記載した。
上記旧オーステナイト結晶粒度番号の測定および引張試験を行った後、引張強度が1100MPa以上の試験片について、図3に示すボルトのねじ部を模擬した遅れ破壊試験用試験片を切削加工により作製して遅れ破壊試験を行った。図中の単位はmmである。上記試験片での遅れ破壊試験結果は、実ボルトでの遅れ破壊試験結果と良い相関が得られることが知られている。遅れ破壊試験は、上記遅れ破壊試験用試験片を15質量%HClの酸性水溶液中に30分浸漬し、種々のレベルの応力を100時間に亘って負荷し続けても破断しない最大負荷応力を、試験片の引張強度で除した値を「遅れ破壊強度比」として求めた。本実施例では、遅れ破壊強度比:0.80以上のものを、耐遅れ破壊性に優れると評価した。遅れ破壊強度比が上記数値を満足するものは、遅れ破壊の実際に生じる確率が極めて小さいことが知られている。なお、引張強度が1100MPa未満の試験片については遅れ破壊試験を行わなかったため、表中に「―」と記載した。
熱間圧延後の供試鋼を球状化焼鈍した球状化材を用い、図4に示す円柱状の圧縮試験用試験片に加工した後、プレス機を用いて圧縮試験を実施した。図中の単位はmmである。圧縮試験時における圧縮率を70~80%の範囲で変化させ、下記(a)~(c)の手順によって圧縮試験片に割れが発生しない限界の圧縮率を求め、これを割れ発生限界圧縮率と表記とした。本実施例では、割れ限界圧縮率が、ボルトのフランジ加工が可能となる75.0%以上のものを、冷間加工性に優れる、すなわち、ボルト成形性に優れると評価した。尚、球状化焼鈍については、各鋼のAc1変態点を下記(3)式によって求め、(Ac1変態点+10℃)の温度で5時間保持し、10℃/Hrの冷却速度で680℃まで冷却して実施した。
Ac1変態点=723-10.7×[Mn]-16.9×[Ni]+29.1×[Si]+16.9×[Cr] ・・・(3)
但し、[Mn],[Ni],[Si]および[Cr]は夫々、質量%で、Mn,Ni,SiおよびCrの含有量を示す。
(a)下記(4)式で示される圧縮率が50%となる圧縮試験を、各試験片の夫々について3回行ない、3回とも割れが発生しなかった場合に、圧縮率を52.5%として新しい試験片を用いて圧縮試験を実施した。
圧縮率=[(h0-h)/h0]×100(%) ・・・(4)
但し、h0:試験片の初期高さを意味し、15mmである
h:試験片の試験後の高さ
(b)圧縮率を52.5%となる圧縮試験を、各試験片の夫々について3回行ない、3回とも割れが発生しなかった場合に、圧縮率を55.0%として新しい試験片を用いて圧縮試験を実施した。
(c)n=3回の圧縮試験で1つも割れが発生しない圧縮率の最大値を「割れ限界圧縮率」とした。
Claims (4)
- 質量%で、
C :0.10~0.30%
Ni:0.4~0.7%、
Si:0%以上0.2%以下
Mn:0.3~0.8%、
P :0%超0.03%以下
S :0%超0.03%以下
Cr:0.8~1.2%、
Mo:0.8~1.5%、
V :0.05~0.13%、
Ti:0.02~0.08%、
Al:0.01~0.1%、
N :0.001~0.01%、
を夫々含有し、残部が鉄および不可避不純物からなり、
且つ、下記(1)式および(2)式を満足することを特徴とする耐遅れ破壊性およびボルト成形性に優れた高強度ボルト用鋼。
0.85≦[C]+[Si]/7+[Mn]/5+[Ni]/20+[Cr]/9+[Mo]/2≦1.3 ・・・(1)
[C]-(0.07×[Mo]+0.20×[V])≦0.20 ・・・(2)
但し、[C],[Si],[Mn],[Ni],[Cr],[Mo]および[V]は夫々、質量%で、C,Si,Mn,Ni,Cr,MoおよびVの含有量を示す。 - 更に、Cu:0%超0.70%以下を含むものである請求項1に記載の高強度ボルト用鋼。
- 請求項1または2に記載の高強度ボルト用鋼を用いて得られるボルトであって、旧オーステナイト結晶粒度の結晶粒度番号が10.0以上である耐遅れ破壊性に優れた高強度ボルト。
- 請求項1または2に記載の高強度ボルト用鋼を用い、880~960℃で焼入れ、550~650℃で焼戻しをすることにより得られる、引張強度が1100~1400MPaの耐遅れ破壊性に優れた高強度ボルト。
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US15/022,857 US10060015B2 (en) | 2013-09-25 | 2014-09-16 | Steel for high-strength bolts which has excellent delayed fracture resistance and bolt formability, and bolt |
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Citations (9)
Publication number | Priority date | Publication date | Assignee | Title |
---|---|---|---|---|
JPH06271975A (ja) * | 1993-03-19 | 1994-09-27 | Kobe Steel Ltd | 耐水素脆化特性に優れた高強度鋼およびその製法 |
JPH09263876A (ja) * | 1996-03-29 | 1997-10-07 | Nippon Steel Corp | 遅れ破壊特性の優れた高強度機械構造用鋼およびその製造方法 |
JPH1017985A (ja) | 1996-06-27 | 1998-01-20 | Kobe Steel Ltd | 耐水素脆化特性に優れた高強度鋼およびその製法 |
JP2004076086A (ja) * | 2002-08-15 | 2004-03-11 | Kobe Steel Ltd | 耐遅れ破壊特性に優れた高強度鋼部品及びその製造方法 |
JP2004084010A (ja) | 2002-08-27 | 2004-03-18 | Kobe Steel Ltd | 冷間加工性及び耐遅れ破壊特性に優れた高強度鋼及び高強度鋼部品 |
JP2006045670A (ja) * | 2004-07-05 | 2006-02-16 | Nippon Steel Corp | 耐遅れ破壊特性に優れた高強度調質鋼およびその製造方法 |
JP2006291295A (ja) * | 2005-04-11 | 2006-10-26 | Nippon Steel Corp | 耐遅れ破壊特性に優れた高強度ボルトおよびその製造方法 |
JP2007031734A (ja) | 2005-07-22 | 2007-02-08 | Nippon Steel Corp | 耐遅れ破壊特性に優れた高強度ボルトおよびその製造方法 |
JP2011047010A (ja) * | 2009-08-27 | 2011-03-10 | Kobe Steel Ltd | 耐遅れ破壊性の改善された高強度ボルト及びその製造方法 |
Family Cites Families (7)
Publication number | Priority date | Publication date | Assignee | Title |
---|---|---|---|---|
JPH0860236A (ja) | 1994-08-17 | 1996-03-05 | Kobe Steel Ltd | 高精度部品の製造方法 |
JP3494798B2 (ja) * | 1996-03-29 | 2004-02-09 | 新日本製鐵株式会社 | 遅れ破壊特性の優れた高強度ボルトおよびその製造方法 |
CN1131334C (zh) | 2000-04-17 | 2003-12-17 | 冶金工业部钢铁研究总院 | 耐延迟断裂性能优良的高强度螺栓钢 |
JP5034308B2 (ja) | 2006-05-15 | 2012-09-26 | Jfeスチール株式会社 | 耐遅れ破壊特性に優れた高強度厚鋼板およびその製造方法 |
JP2008280583A (ja) | 2007-05-10 | 2008-11-20 | Daido Steel Co Ltd | 水素脆性型の面疲労強度に優れた肌焼鋼 |
KR101322534B1 (ko) | 2010-03-11 | 2013-10-28 | 신닛테츠스미킨 카부시키카이샤 | 내지연파괴 특성이 우수한 고강도 강재와 고강도 볼트 및 그 제조 방법 |
CN102260831B (zh) | 2011-07-08 | 2013-01-30 | 宁波市胜源技术转移有限公司 | 一种高强钢制备的螺栓、螺母等紧固件 |
-
2013
- 2013-09-25 JP JP2013198742A patent/JP6159209B2/ja active Active
-
2014
- 2014-09-16 US US15/022,857 patent/US10060015B2/en active Active
- 2014-09-16 EP EP14847973.6A patent/EP3050987B1/en active Active
- 2014-09-16 KR KR1020167007717A patent/KR101817451B1/ko active IP Right Grant
- 2014-09-16 MX MX2016003563A patent/MX2016003563A/es unknown
- 2014-09-16 WO PCT/JP2014/074393 patent/WO2015045951A1/ja active Application Filing
- 2014-09-16 CN CN201480052313.XA patent/CN105579603B/zh active Active
- 2014-09-24 TW TW103133010A patent/TWI535864B/zh active
Patent Citations (9)
Publication number | Priority date | Publication date | Assignee | Title |
---|---|---|---|---|
JPH06271975A (ja) * | 1993-03-19 | 1994-09-27 | Kobe Steel Ltd | 耐水素脆化特性に優れた高強度鋼およびその製法 |
JPH09263876A (ja) * | 1996-03-29 | 1997-10-07 | Nippon Steel Corp | 遅れ破壊特性の優れた高強度機械構造用鋼およびその製造方法 |
JPH1017985A (ja) | 1996-06-27 | 1998-01-20 | Kobe Steel Ltd | 耐水素脆化特性に優れた高強度鋼およびその製法 |
JP2004076086A (ja) * | 2002-08-15 | 2004-03-11 | Kobe Steel Ltd | 耐遅れ破壊特性に優れた高強度鋼部品及びその製造方法 |
JP2004084010A (ja) | 2002-08-27 | 2004-03-18 | Kobe Steel Ltd | 冷間加工性及び耐遅れ破壊特性に優れた高強度鋼及び高強度鋼部品 |
JP2006045670A (ja) * | 2004-07-05 | 2006-02-16 | Nippon Steel Corp | 耐遅れ破壊特性に優れた高強度調質鋼およびその製造方法 |
JP2006291295A (ja) * | 2005-04-11 | 2006-10-26 | Nippon Steel Corp | 耐遅れ破壊特性に優れた高強度ボルトおよびその製造方法 |
JP2007031734A (ja) | 2005-07-22 | 2007-02-08 | Nippon Steel Corp | 耐遅れ破壊特性に優れた高強度ボルトおよびその製造方法 |
JP2011047010A (ja) * | 2009-08-27 | 2011-03-10 | Kobe Steel Ltd | 耐遅れ破壊性の改善された高強度ボルト及びその製造方法 |
Non-Patent Citations (1)
Title |
---|
See also references of EP3050987A4 * |
Cited By (4)
Publication number | Priority date | Publication date | Assignee | Title |
---|---|---|---|---|
WO2017094487A1 (ja) * | 2015-12-04 | 2017-06-08 | 新日鐵住金株式会社 | 高強度ボルト |
CN108291284A (zh) * | 2015-12-04 | 2018-07-17 | 新日铁住金株式会社 | 高强度螺栓 |
JPWO2017094487A1 (ja) * | 2015-12-04 | 2018-08-16 | 新日鐵住金株式会社 | 高強度ボルト |
US10487372B2 (en) | 2015-12-04 | 2019-11-26 | Nippon Steel Corporation | High-strength bolt |
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