WO2011048971A1 - Steel for high-strength bolts and process for production of high-strength bolts - Google Patents
Steel for high-strength bolts and process for production of high-strength bolts Download PDFInfo
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- WO2011048971A1 WO2011048971A1 PCT/JP2010/067833 JP2010067833W WO2011048971A1 WO 2011048971 A1 WO2011048971 A1 WO 2011048971A1 JP 2010067833 W JP2010067833 W JP 2010067833W WO 2011048971 A1 WO2011048971 A1 WO 2011048971A1
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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
- C21D9/0093—Heat treatment, e.g. annealing, hardening, quenching or tempering, adapted for particular articles; Furnaces therefor for screws; for bolts
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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
- C21D8/02—Modifying the physical properties by deformation combined with, or followed by, heat treatment during manufacturing of plates or strips
- C21D8/0205—Modifying the physical properties by deformation combined with, or followed by, heat treatment during manufacturing of plates or strips of ferrous alloys
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- C—CHEMISTRY; METALLURGY
- C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
- C22C—ALLOYS
- C22C38/00—Ferrous alloys, e.g. steel alloys
- C22C38/02—Ferrous alloys, e.g. steel alloys containing silicon
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- 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
- C22C38/40—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
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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
- C22C38/46—Ferrous alloys, e.g. steel alloys containing chromium with nickel with vanadium
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- C—CHEMISTRY; METALLURGY
- C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
- C22C—ALLOYS
- C22C38/00—Ferrous alloys, e.g. steel alloys
- C22C38/18—Ferrous alloys, e.g. steel alloys containing chromium
- C22C38/40—Ferrous alloys, e.g. steel alloys containing chromium with nickel
- C22C38/48—Ferrous alloys, e.g. steel alloys containing chromium with nickel with niobium or tantalum
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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
- C22C38/50—Ferrous alloys, e.g. steel alloys containing chromium with nickel with titanium or zirconium
Definitions
- the present invention relates to a steel for high-strength bolts excellent in cold workability and delayed fracture resistance, and a method for producing a high-strength bolt using such a steel for bolts.
- Patent Document 3 high strength steel for machine structural use having excellent delayed fracture resistance and a tensile strength of 1800 MPa or more has been proposed (see Patent Document 3). That is, in the structural steel, C is added to improve the strength of the base, and by adding Si and Mo, temper softening resistance is improved, and high strength can be secured even when high temperature tempering is performed. I am doing so.
- the present invention has been made by paying attention to the above-mentioned problems in current high-strength bolts, and has excellent workability, good delayed fracture resistance, and high tensile strength steel exceeding 1500 MPa. And it aims at providing the manufacturing method of the high intensity
- the present inventors have repeatedly conducted intensive studies on the influence of component elements on the cold workability of bolts, such as steel component systems, and as a result, they have excellent manufacturability and delayed fracture resistance.
- a component system that is favorable and exhibits a tensile strength exceeding 1500 MPa was found, and the present invention was completed.
- one or both of 0.20 to 1.50% by mass of Cr and 0.20 to 1.50% by mass of Ni are added as necessary. Can be added. Further, if necessary, at least one selected from the group consisting of 0.002 to 1.50 mass% V, 0.002 to 1.50 mass% Ti, and 0.002 to 1.50 mass% Nb. Can be added.
- the high-strength bolt of the present invention is characterized by using the steel for high-strength bolts of the present invention, and in the method for producing the high-strength bolt, the steel having the above composition is used as a raw material and is cold-formed into a bolt shape. It is characterized by quenching and tempering after molding.
- C, Si, Mn, and Mo and / or W are contained in the above range, the value of ⁇ calculated from the C and Si content is 100 or less, and the tensile strength is 1550 MPa or more. Therefore, a bolt having excellent manufacturability, that is, cold workability and moldability, good delayed fracture resistance, and high tensile strength can be manufactured.
- the value of (Cx ⁇ Si) is 100 or less, the balance is Fe and inevitable impurities, and the tensile strength is 1550 MPa or more.
- C 0.40 to 0.70%
- C (carbon) is an element necessary for ensuring a required strength by heat treatment, and in order to obtain a tensile strength of 1550 MPa or more, it is necessary to have a C content of 0.40% or more.
- the upper limit is made 0.70%.
- the upper limit value of the C amount is suppressed to 0.55%. Is desirable.
- Si 0.40 to 2.50% Si (silicon) has a deoxidizing action during steel melting and prevents softening due to tempering in a low temperature range. In order to obtain such an effect, it is necessary to contain 0.40% or more, but if added in a large amount, the ductility and toughness may be greatly reduced, so the upper limit is made 2.50%.
- Mo 0.25 to 3.00%
- W 0.20 to 3.00%
- Mo (molybdenum) and W (tungsten) are both effective elements for improving the hardenability and are effective elements for suppressing temper softening in a high temperature range.
- the formation of fine carbonitrides during tempering contributes to increasing the strength of the matrix. In order to obtain such an effect, it is necessary to add one or both of these elements.
- Mo 0.25% or more and for W, 0.20% or more are contained.
- the upper limit of these elements is set to 3.00%.
- ⁇ value 100 or less
- the steel for high-strength bolts of the present invention has the above-mentioned C, Si, Mn, Mo and / or W content as an essential component, and the ⁇ value calculated based on the C and Si content is 100 or less. Is an essential requirement, but as other optional components, the following components can be added as necessary.
- V 0.002 to 1.50%
- Ti 0.002 to 1.50%
- Nb 0.002 to 1.50%
- V (vanadium), Ti (titanium) and Nb (niobium) are all elements that contribute to increasing the strength of the matrix by forming fine carbonitrides during tempering.
- One, two or three elements are added. In order to acquire such an effect, it is necessary to contain 0.002% or more, respectively. On the other hand, even if added over 1.50%, there is no further improvement effect and it is not preferable from the viewpoint of economy, so the upper limit values of these elements are set to 1.50%.
- P phosphorus
- S sulfur
- the steel for high-strength bolts of the present invention is made of steel having the above-described component composition, and ensures a tensile strength of 1550 MPa or more.
- the following Such tempering treatment that is, quenching and tempering is performed. That is, by heating the material steel having the above-described component composition to a temperature of Ac 3 or higher, for example, 880 ° C. or higher and quenching rapidly, the material steel becomes a completely quenched structure. Then, the steel for bolts of this invention provided with the target structure
- the tempering temperature at this time is preferably 400 ° C. or higher from the viewpoint of ensuring delayed fracture resistance.
- the high-strength bolt of the present invention is made of bolt steel having the above-described component composition.
- the steel material having the above component composition is cold-worked into a bolt shape, and then the thread portion is rolled into a bolt shape.
- the material molded into the bolt shape is subjected to a tempering treatment, that is, quenching and tempering as follows.
- the temperature bolt material or C3 point A after molding heating for example to 880 ° C. or higher, by quenching, the bolt material will be completely quenched structure. Thereafter, tempering is performed to obtain a high-strength bolt having a desired structure and strength. As the tempering temperature at this time, it is desirable to carry out at a temperature of 400 ° C. or higher from the viewpoint of ensuring delayed fracture resistance.
- Each steel having the component composition shown in Table 1 was melted and then ingot, and each steel was hot-rolled into a wire having a diameter of 14 mm. Thereafter, the wire material was subjected to a film treatment, and then spheroidizing annealing at 600 to 800 ° C. and cold wire drawing were repeated to draw the wire to a diameter of 10.5 mm and subjected to the following tests.
- Tensile strength Tensile test pieces (reduced JIS No. 4 test pieces) were sampled from cold-drawn 10.5 mm diameter wires, quenched at 920 to 950 ° C., and then tempered at 450 ° C. Table 2 shows the results of evaluating the tensile properties of each steel using the test pieces thus prepared.
- each high strength bolt obtained by the above was evaluated by the hydrochloric acid immersion test method. That is, each bolt is placed in a jig, left in an aqueous hydrochloric acid solution diluted to 3% with a constant load (load of 80% of tensile strength) added, and then washed and dried in one cycle. 15 cycles were repeated, and the presence or absence of breakage during this period was confirmed. These results are also shown in Table 2.
- Invented steels (steels 1 to 14) were excellent in bolt moldability and exhibited a tensile strength after quenching and tempering of 1550 MPa or more.
- the steel types (steel 15 to 17) having an ⁇ value exceeding 100 although the tensile strength after the tempering treatment was 1550 MPa or more, cracking and wear of the mold occurred during bolt molding.
- Steels 18 to 22 it was found that the tensile strength after tempering treatment does not satisfy 1550 MPa because C is less than 0.40% or Si is less than 0.40%.
- the steels of the present invention (steels 1 to 14) and comparative steels 15 to 17 are also affected by carbonitrides precipitated by the addition of Mo and W. No delayed fracture was observed in the test.
- the steels 18 to 22 since the amount of carbonitride was small, some bolts were broken during the test. The reason for this is that, as described above, addition of Mo or W forms fine carbonitrides during tempering, thereby realizing high strength of the matrix.
- the steel for high-strength bolts of the present invention has 0.40 to 0.70% C, 0.40 to 2.50% Si, 0.05 to 1.0% Mn, 0% One or both of 25 to 3.00% Mo and 0.20 to 3.00% W, and optionally 0.20 to 1.50% Cr and 0.20 to 1 Selected from the group consisting of one or both of 50% Ni and / or 0.002-1.50% V, 0.002-1.50% Ti and 0.002-1.50% Nb
Abstract
Provided are: a steel for high-strength bolts which has excellent workability and good delayed fracture resistance and which can attain a tensile strength of 1550MPa or more; and a process for the production of high-strength bolts using the steel.
A high-strength bolt that exhibits a tensile strength of 1550MPa or more can be produced by using a specific steel as the raw material and subjecting the specific steel to quenching and tempering. The specific steel contains 0.40 to 0.70 mass% of C, 0.40 to 2.50 mass% of Si, 0.05 to 1.0 mass% of Mn, either 0.25 to 3.00 mass% of Mo and/or 0.20 to 3.00 mass% of W, and, if necessary, either 0.20 to 1.50 mass% of Cr and/or 0.20 to 1.50 mass% of Ni, or at least one selected from the group consisting of 0.002 to 1.50 mass% of V, 0.002 to 1.50 mass% of Ti and 0.002 to 1.50 mass% of Nb. Further, the specific steel has an α value of 100 or less as calculated from the contents of C and Si according to the formula: α = 19.0 + 76.1×C + 30.0×√Si- 4.5×C×√Si.
Description
本発明は冷間加工性、耐遅れ破壊性に優れた高強度ボルト用鋼と、このようなボルト用鋼を用いた高強度ボルトの製造方法に関するものである。
The present invention relates to a steel for high-strength bolts excellent in cold workability and delayed fracture resistance, and a method for producing a high-strength bolt using such a steel for bolts.
近年、自動車の燃費低減等を目的とした各部品の軽量化に伴い、部品の締結用ボルトの分野においても高強度化の要請がますます強くなってきている。
ボルト用鋼として、一般的に使用されている鋼種は、ＪＩＳ Ｇ ４１０１、Ｇ ４１０４、Ｇ ４１０５に規定されているＳＣＭ４３５、ＳＣＭ４４０、ＳＣｒ４４０等の中炭素鋼であり、焼入れ、焼戻しを実施することによって、引張強さ１１００ＭＰａ程度までのボルトとして使用される。 In recent years, with the reduction in weight of parts for the purpose of reducing the fuel consumption of automobiles, there is an increasing demand for higher strength in the field of fastening bolts for parts.
The steel types generally used as bolt steels are medium carbon steels such as SCM435, SCM440, and SCr440 defined in JIS G4101, G4104, and G4105, and they are hardened and tempered. Used as a bolt with a tensile strength of up to about 1100 MPa.
ボルト用鋼として、一般的に使用されている鋼種は、ＪＩＳ Ｇ ４１０１、Ｇ ４１０４、Ｇ ４１０５に規定されているＳＣＭ４３５、ＳＣＭ４４０、ＳＣｒ４４０等の中炭素鋼であり、焼入れ、焼戻しを実施することによって、引張強さ１１００ＭＰａ程度までのボルトとして使用される。 In recent years, with the reduction in weight of parts for the purpose of reducing the fuel consumption of automobiles, there is an increasing demand for higher strength in the field of fastening bolts for parts.
The steel types generally used as bolt steels are medium carbon steels such as SCM435, SCM440, and SCr440 defined in JIS G4101, G4104, and G4105, and they are hardened and tempered. Used as a bolt with a tensile strength of up to about 1100 MPa.
しかし、これらの鋼を引張強さ１２００ＭＰａ以上のボルトに適用すると、耐遅れ破壊性が急激に低下し、ボルトが使用中に破断する危険性が増大するという課題があった。
このような課題を解決するため方策としては、高温で焼戻しを実施することにより、遅れ破壊の起点となる旧オーステナイト粒界の強度を高め、耐遅れ破壊性を向上させることが知られている（例えば、特許文献１参照）。また、ＶやＭｏ等の炭化物を析出させ、水素トラップ効果を付与することが知られている（特許文献２参照）。 However, when these steels are applied to bolts having a tensile strength of 1200 MPa or more, there has been a problem that delayed fracture resistance is drastically reduced and the risk of the bolts breaking during use increases.
As a measure to solve such a problem, it is known that by performing tempering at a high temperature, the strength of the prior austenite grain boundary which is the starting point of delayed fracture is increased, and the delayed fracture resistance is improved ( For example, see Patent Document 1). In addition, it is known that carbides such as V and Mo are deposited to impart a hydrogen trap effect (see Patent Document 2).
このような課題を解決するため方策としては、高温で焼戻しを実施することにより、遅れ破壊の起点となる旧オーステナイト粒界の強度を高め、耐遅れ破壊性を向上させることが知られている（例えば、特許文献１参照）。また、ＶやＭｏ等の炭化物を析出させ、水素トラップ効果を付与することが知られている（特許文献２参照）。 However, when these steels are applied to bolts having a tensile strength of 1200 MPa or more, there has been a problem that delayed fracture resistance is drastically reduced and the risk of the bolts breaking during use increases.
As a measure to solve such a problem, it is known that by performing tempering at a high temperature, the strength of the prior austenite grain boundary which is the starting point of delayed fracture is increased, and the delayed fracture resistance is improved ( For example, see Patent Document 1). In addition, it is known that carbides such as V and Mo are deposited to impart a hydrogen trap effect (see Patent Document 2).
一方、耐遅れ破壊性に優れ、１８００ＭＰａ以上もの引張強度を備えた高強度機械構造用鋼が提案されている（特許文献３参照）。すなわち、当該構造用鋼においては、Ｃを添加して基地の強度を向上させると共に、Ｓｉ、Ｍｏを添加することによって、焼戻し軟化抵抗を向上させ、高温焼戻しを実施した場合でも高い強度を確保できるようにしている。
On the other hand, high strength steel for machine structural use having excellent delayed fracture resistance and a tensile strength of 1800 MPa or more has been proposed (see Patent Document 3). That is, in the structural steel, C is added to improve the strength of the base, and by adding Si and Mo, temper softening resistance is improved, and high strength can be secured even when high temperature tempering is performed. I am doing so.
しかしながら、上記特許文献１及び２により提案されている成分系では、焼戻し時の軟化抵抗が小さく、さらに高強度、例えば１５００ＭＰａを超えるような高強度域で使用可能なボルトは得られない。
また、特許文献３に記載の鋼では、強度を確保するために添加しているＣ、Ｓｉ量が多いため、冷間加工前に素材の球状化焼なまし工程を追加した場合においても、硬度が高く、冷間加工時の加工抵抗が大きくなってしまう。そのため、特許文献３記載の鋼をボルト用鋼として適用する場合は、冷間加工時に型の割れや顕著な磨耗が発生するという問題がある。 However, the component systems proposed in Patent Documents 1 and 2 have a low softening resistance during tempering, and a bolt that can be used in a high strength, for example, a high strength region exceeding 1500 MPa cannot be obtained.
In addition, since the steel described in Patent Document 3 has a large amount of C and Si added to ensure strength, even when a spheroidizing annealing process of the material is added before cold working, the hardness Is high, and the processing resistance during cold processing increases. For this reason, when the steel described in Patent Document 3 is applied as bolt steel, there is a problem in that mold cracks and significant wear occur during cold working.
また、特許文献３に記載の鋼では、強度を確保するために添加しているＣ、Ｓｉ量が多いため、冷間加工前に素材の球状化焼なまし工程を追加した場合においても、硬度が高く、冷間加工時の加工抵抗が大きくなってしまう。そのため、特許文献３記載の鋼をボルト用鋼として適用する場合は、冷間加工時に型の割れや顕著な磨耗が発生するという問題がある。 However, the component systems proposed in Patent Documents 1 and 2 have a low softening resistance during tempering, and a bolt that can be used in a high strength, for example, a high strength region exceeding 1500 MPa cannot be obtained.
In addition, since the steel described in Patent Document 3 has a large amount of C and Si added to ensure strength, even when a spheroidizing annealing process of the material is added before cold working, the hardness Is high, and the processing resistance during cold processing increases. For this reason, when the steel described in Patent Document 3 is applied as bolt steel, there is a problem in that mold cracks and significant wear occur during cold working.
本発明は、現状の高強度ボルトにおける上記課題に着目してなされたものであって、加工性に優れ、耐遅れ破壊特性が良好で、しかも１５００ＭＰａを超える引張強度が得られる高強度ボルト用鋼と、このようなボルト用鋼による高強度ボルトの製造方法を提供することを目的とする。
The present invention has been made by paying attention to the above-mentioned problems in current high-strength bolts, and has excellent workability, good delayed fracture resistance, and high tensile strength steel exceeding 1500 MPa. And it aims at providing the manufacturing method of the high intensity | strength bolt by such steel for bolts.
本発明者らは、上記課題を解決すべく、鋼の成分系など、特にボルトの冷間加工性に対する成分元素の影響について、鋭意検討を繰り返した結果、製造性に優れ、耐遅れ破壊性が良好で、しかも１５００ＭＰａを超える引張強度を示す成分系を見出し、本発明を完成するに至った。
In order to solve the above-mentioned problems, the present inventors have repeatedly conducted intensive studies on the influence of component elements on the cold workability of bolts, such as steel component systems, and as a result, they have excellent manufacturability and delayed fracture resistance. A component system that is favorable and exhibits a tensile strength exceeding 1500 MPa was found, and the present invention was completed.
すなわち、本発明は、上記知見に基づくものであって、本発明の高強度ボルト用鋼は、０．４０～０．７０質量％のＣと、０．４０～２．５０質量％のＳｉと、０．０５～１．０質量％のＭｎと、０．２５～３．００質量％のＭｏ及び／又は０．２０～３．００質量％のＷを含有すると共に、Ｃ及びＳｉ含有量に基づいて、次式により算出されるαの値が１００以下であって、残部がＦｅ及び不可避的不純物から成り、引張強度が１５５０ＭＰａ以上であることを特徴としている。
α＝１９．０＋７６．１×Ｃ＋３０．０×√Ｓｉ－４．５×Ｃ×√Ｓｉ That is, the present invention is based on the above knowledge, and the steel for high-strength bolts of the present invention has a carbon content of 0.40 to 0.70 mass% and Si of 0.40 to 2.50 mass%. 0.05 to 1.0% by mass of Mn, 0.25 to 3.00% by mass of Mo and / or 0.20 to 3.00% by mass of W, and C and Si contents. Based on this, the value of α calculated by the following equation is 100 or less, the balance is made of Fe and inevitable impurities, and the tensile strength is 1550 MPa or more.
α = 19.0 + 76.1 × C + 30.0 × √Si−4.5 × C × √Si
α＝１９．０＋７６．１×Ｃ＋３０．０×√Ｓｉ－４．５×Ｃ×√Ｓｉ That is, the present invention is based on the above knowledge, and the steel for high-strength bolts of the present invention has a carbon content of 0.40 to 0.70 mass% and Si of 0.40 to 2.50 mass%. 0.05 to 1.0% by mass of Mn, 0.25 to 3.00% by mass of Mo and / or 0.20 to 3.00% by mass of W, and C and Si contents. Based on this, the value of α calculated by the following equation is 100 or less, the balance is made of Fe and inevitable impurities, and the tensile strength is 1550 MPa or more.
α = 19.0 + 76.1 × C + 30.0 × √Si−4.5 × C × √Si
本発明の高強度ボルト用鋼においては、上記必須成分に加えて、必要に応じて０．２０～１．５０質量％のＣｒ及び０．２０～１．５０質量％のＮｉの一方又は双方を添加することができる。
さらに必要に応じて、０．００２～１．５０質量％のＶ、０．００２～１．５０質量％のＴｉ及び０．００２～１．５０質量％のＮｂから成る群から選ばれる少なくとも１種の成分を添加することができる。 In the steel for high-strength bolts of the present invention, in addition to the above essential components, one or both of 0.20 to 1.50% by mass of Cr and 0.20 to 1.50% by mass of Ni are added as necessary. Can be added.
Further, if necessary, at least one selected from the group consisting of 0.002 to 1.50 mass% V, 0.002 to 1.50 mass% Ti, and 0.002 to 1.50 mass% Nb. Can be added.
さらに必要に応じて、０．００２～１．５０質量％のＶ、０．００２～１．５０質量％のＴｉ及び０．００２～１．５０質量％のＮｂから成る群から選ばれる少なくとも１種の成分を添加することができる。 In the steel for high-strength bolts of the present invention, in addition to the above essential components, one or both of 0.20 to 1.50% by mass of Cr and 0.20 to 1.50% by mass of Ni are added as necessary. Can be added.
Further, if necessary, at least one selected from the group consisting of 0.002 to 1.50 mass% V, 0.002 to 1.50 mass% Ti, and 0.002 to 1.50 mass% Nb. Can be added.
また、本発明の高強度ボルトは、本発明の上記高強度ボルト用鋼を用いたことを特徴とし、当該高強度ボルトの製造方法においては、上記成分組成の鋼を素材としてボルト形状に冷間成形した後、焼入れ、焼戻しを施すことを特徴としている。
Further, the high-strength bolt of the present invention is characterized by using the steel for high-strength bolts of the present invention, and in the method for producing the high-strength bolt, the steel having the above composition is used as a raw material and is cold-formed into a bolt shape. It is characterized by quenching and tempering after molding.
本発明によれば、Ｃ、Ｓｉ、Ｍｎ、及びＭｏ及び／又はＷを上記の範囲で含有し、Ｃ及びＳｉ含有量から算出されるαの値が１００以下であって、引張強度が１５５０ＭＰａ以上である鋼としたため、製造性、すなわち冷間加工性、成型性に優れ、耐遅れ破壊特性が良好で、高い引張強度を備えたボルトを製造することができる。
According to the present invention, C, Si, Mn, and Mo and / or W are contained in the above range, the value of α calculated from the C and Si content is 100 or less, and the tensile strength is 1550 MPa or more. Therefore, a bolt having excellent manufacturability, that is, cold workability and moldability, good delayed fracture resistance, and high tensile strength can be manufactured.
以下に、本発明の高強度ボルト用鋼について、さらに詳細に説明する。なお、本明細書において、「％」は特記しない限り質量百分率を表すものとする。
Hereinafter, the steel for high-strength bolts of the present invention will be described in more detail. In the present specification, “%” represents mass percentage unless otherwise specified.
本発明の高強度ボルト用鋼は、上記したように、０．４０～０．７０％Ｃ、０．４０～２．５０％Ｓｉ、０．０５～１．０％Ｍｎと、０．２５～３．００％Ｍｏ及び０．２０～３．００％Ｗの少なくとも一方を含有し、Ｃ及びＳｉ含有量から算出されるα（＝１９．０＋７６．１×Ｃ＋３０．０×√Ｓｉ－４．５×Ｃ×√Ｓｉ）の値が１００以下で、残部がＦｅ及び不可避的不純物から成り、引張強度が１５５０ＭＰａ以上である。
まず、本発明における各成分元素について、それらの作用と共に、数値限定理由について説明する。 As described above, the steel for high-strength bolts of the present invention is 0.40 to 0.70% C, 0.40 to 2.50% Si, 0.05 to 1.0% Mn, 0.25 to Α (= 19.0 + 76.1 × C + 30.0 × √Si−4.5) containing at least one of 3.00% Mo and 0.20 to 3.00% W and calculated from the C and Si contents The value of (Cx√Si) is 100 or less, the balance is Fe and inevitable impurities, and the tensile strength is 1550 MPa or more.
First, for each component element in the present invention, the reason for limiting the numerical value will be described together with their effects.
まず、本発明における各成分元素について、それらの作用と共に、数値限定理由について説明する。 As described above, the steel for high-strength bolts of the present invention is 0.40 to 0.70% C, 0.40 to 2.50% Si, 0.05 to 1.0% Mn, 0.25 to Α (= 19.0 + 76.1 × C + 30.0 × √Si−4.5) containing at least one of 3.00% Mo and 0.20 to 3.00% W and calculated from the C and Si contents The value of (Cx√Si) is 100 or less, the balance is Fe and inevitable impurities, and the tensile strength is 1550 MPa or more.
First, for each component element in the present invention, the reason for limiting the numerical value will be described together with their effects.
Ｃ：０．４０～０．７０％
Ｃ（炭素）は、熱処理によって所要の強度を確保するために必要な元素であって、１５５０ＭＰａ以上の引張強度を得るためには、０．４０％以上のＣ含有量とする必要がある。
一方、０．７０％を超えると、焼入れ時の焼割れ感受性が増大すると共に、冷間加工性も悪化するため、その上限を０．７０％とする。 C: 0.40 to 0.70%
C (carbon) is an element necessary for ensuring a required strength by heat treatment, and in order to obtain a tensile strength of 1550 MPa or more, it is necessary to have a C content of 0.40% or more.
On the other hand, if it exceeds 0.70%, the susceptibility to quench cracking at the time of quenching increases and the cold workability deteriorates, so the upper limit is made 0.70%.
Ｃ（炭素）は、熱処理によって所要の強度を確保するために必要な元素であって、１５５０ＭＰａ以上の引張強度を得るためには、０．４０％以上のＣ含有量とする必要がある。
一方、０．７０％を超えると、焼入れ時の焼割れ感受性が増大すると共に、冷間加工性も悪化するため、その上限を０．７０％とする。 C: 0.40 to 0.70%
C (carbon) is an element necessary for ensuring a required strength by heat treatment, and in order to obtain a tensile strength of 1550 MPa or more, it is necessary to have a C content of 0.40% or more.
On the other hand, if it exceeds 0.70%, the susceptibility to quench cracking at the time of quenching increases and the cold workability deteriorates, so the upper limit is made 0.70%.
なお、本発明の高強度ボルト用鋼において、冷間加工時の変形量を大きくして、冷間加工性をさらに向上させるためには、当該Ｃ量の上限値を０．５５％に抑えることが望ましい。
In addition, in the steel for high-strength bolts of the present invention, in order to further increase the cold workability by increasing the amount of deformation during cold work, the upper limit value of the C amount is suppressed to 0.55%. Is desirable.
Ｓｉ：０．４０～２．５０％
Ｓｉ（珪素）は、鋼溶製時における脱酸作用を有していると共に、低温域での焼戻しによる軟化を防ぐ。
このような効果を得るためには、０．４０％以上含有させる必要があるが、多量に添加すると延性、靭性が大きく低下する虞があるため、上限を２．５０％とする。 Si: 0.40 to 2.50%
Si (silicon) has a deoxidizing action during steel melting and prevents softening due to tempering in a low temperature range.
In order to obtain such an effect, it is necessary to contain 0.40% or more, but if added in a large amount, the ductility and toughness may be greatly reduced, so the upper limit is made 2.50%.
Ｓｉ（珪素）は、鋼溶製時における脱酸作用を有していると共に、低温域での焼戻しによる軟化を防ぐ。
このような効果を得るためには、０．４０％以上含有させる必要があるが、多量に添加すると延性、靭性が大きく低下する虞があるため、上限を２．５０％とする。 Si: 0.40 to 2.50%
Si (silicon) has a deoxidizing action during steel melting and prevents softening due to tempering in a low temperature range.
In order to obtain such an effect, it is necessary to contain 0.40% or more, but if added in a large amount, the ductility and toughness may be greatly reduced, so the upper limit is made 2.50%.
Ｍｎ：０．０５～１．０％
Ｍｎ（マンガン）は、鋼溶製時における脱酸作用を有しているとともに、焼入れ性を高める作用を有しており、このような効果を得るためには０．０５％以上含有させる必要がある。一方、１．０％を越えて含有すると、靭性が劣化すると共に、粒界酸化を助長し、耐遅れ破壊性が悪化するためその上限を１．０％とすることが必要である。 Mn: 0.05 to 1.0%
Mn (manganese) has a deoxidizing action at the time of steel melting and has an action of improving hardenability. In order to obtain such an effect, it is necessary to contain 0.05% or more. is there. On the other hand, if the content exceeds 1.0%, toughness deteriorates, grain boundary oxidation is promoted, and delayed fracture resistance deteriorates, so the upper limit must be 1.0%.
Ｍｎ（マンガン）は、鋼溶製時における脱酸作用を有しているとともに、焼入れ性を高める作用を有しており、このような効果を得るためには０．０５％以上含有させる必要がある。一方、１．０％を越えて含有すると、靭性が劣化すると共に、粒界酸化を助長し、耐遅れ破壊性が悪化するためその上限を１．０％とすることが必要である。 Mn: 0.05 to 1.0%
Mn (manganese) has a deoxidizing action at the time of steel melting and has an action of improving hardenability. In order to obtain such an effect, it is necessary to contain 0.05% or more. is there. On the other hand, if the content exceeds 1.0%, toughness deteriorates, grain boundary oxidation is promoted, and delayed fracture resistance deteriorates, so the upper limit must be 1.0%.
Ｍｏ：０．２５～３．００％
Ｗ：０．２０～３．００％
Ｍｏ（モリブデン）及びＷ（タングステン）は、いずれも焼入れ性向上に有効な元素であると共に、高温域での焼戻し軟化を抑制するのに有効な元素である。また、焼戻し時に微細な炭窒化物を形成することでマトリックスの高強度化に寄与する。このような効果を得るためには、これら元素の一方又は両方を添加する必要があり、Ｍｏについては０．２５％以上、Ｗについては０．２０％以上を含有させる。
一方、３．００％以上を添加すると、いずれの効果も飽和し、添加の意味がなくなると共に、過剰な添加は経済性の観点からも好ましくないため、これら元素の上限値をそれぞれ３．００％とする。 Mo: 0.25 to 3.00%
W: 0.20 to 3.00%
Mo (molybdenum) and W (tungsten) are both effective elements for improving the hardenability and are effective elements for suppressing temper softening in a high temperature range. In addition, the formation of fine carbonitrides during tempering contributes to increasing the strength of the matrix. In order to obtain such an effect, it is necessary to add one or both of these elements. For Mo, 0.25% or more and for W, 0.20% or more are contained.
On the other hand, when 3.00% or more is added, all effects are saturated, meaning of addition is lost, and excessive addition is not preferable from the viewpoint of economy, so the upper limit of these elements is set to 3.00%. And
Ｗ：０．２０～３．００％
Ｍｏ（モリブデン）及びＷ（タングステン）は、いずれも焼入れ性向上に有効な元素であると共に、高温域での焼戻し軟化を抑制するのに有効な元素である。また、焼戻し時に微細な炭窒化物を形成することでマトリックスの高強度化に寄与する。このような効果を得るためには、これら元素の一方又は両方を添加する必要があり、Ｍｏについては０．２５％以上、Ｗについては０．２０％以上を含有させる。
一方、３．００％以上を添加すると、いずれの効果も飽和し、添加の意味がなくなると共に、過剰な添加は経済性の観点からも好ましくないため、これら元素の上限値をそれぞれ３．００％とする。 Mo: 0.25 to 3.00%
W: 0.20 to 3.00%
Mo (molybdenum) and W (tungsten) are both effective elements for improving the hardenability and are effective elements for suppressing temper softening in a high temperature range. In addition, the formation of fine carbonitrides during tempering contributes to increasing the strength of the matrix. In order to obtain such an effect, it is necessary to add one or both of these elements. For Mo, 0.25% or more and for W, 0.20% or more are contained.
On the other hand, when 3.00% or more is added, all effects are saturated, meaning of addition is lost, and excessive addition is not preferable from the viewpoint of economy, so the upper limit of these elements is set to 3.00%. And
α値：１００以下
α値（＝１９．０＋７６．１×Ｃ＋３０．０×√Ｓｉ－４．５×Ｃ×√Ｓｉ）は、種々の鋼によるボルト成型実績から導き出された冷間加工性を表すパラメータであって、この値を１００以下に抑えることによって良好な冷間加工性を確保することができる。 α value: 100 or less The α value (= 19.0 + 76.1 × C + 30.0 × √Si−4.5 × C × √Si) represents the cold workability derived from the bolt forming results of various steels. It is a parameter, and good cold workability can be secured by suppressing this value to 100 or less.
α値（＝１９．０＋７６．１×Ｃ＋３０．０×√Ｓｉ－４．５×Ｃ×√Ｓｉ）は、種々の鋼によるボルト成型実績から導き出された冷間加工性を表すパラメータであって、この値を１００以下に抑えることによって良好な冷間加工性を確保することができる。 α value: 100 or less The α value (= 19.0 + 76.1 × C + 30.0 × √Si−4.5 × C × √Si) represents the cold workability derived from the bolt forming results of various steels. It is a parameter, and good cold workability can be secured by suppressing this value to 100 or less.
すなわち、本発明者は、種々の組成のボルト用鋼を用いて、球状化焼鈍ののち、ボルト成型を実施した場合、冷間加工時における型の割れがＣ，Ｓｉ含有量が多い鋼種に発生する傾向に着目した。そして、割れの主因が「炭素（Ｃ）による分散強化」と、「珪素（Ｓｉ）による固溶強化」にあることを見出し、これらによる寄与の大小を考慮した成型性パラメータがある限界値を超えた場合に型割れが発生するとの結論に到った。
そして、上記α値の算出式は、簡略化を目的に、型割れが発生する限界値が「１００」となるように、上記成型性パラメータの各係数を整理することによって得られたものである。 That is, when the present inventor uses bolt steels of various compositions and then performs spheroidizing and then bolt forming, mold cracks during cold working occur in steel types with high C and Si contents. Focused on the tendency to do. And, it was found that the main causes of cracking were “dispersion strengthening by carbon (C)” and “solid solution strengthening by silicon (Si)”, and the formability parameter considering the magnitude of the contribution of these exceeded a certain limit value. The conclusion was reached that mold cracking would occur.
The formula for calculating the α value is obtained by organizing the coefficients of the formability parameter so that the limit value at which mold cracking occurs is “100” for the purpose of simplification. .
そして、上記α値の算出式は、簡略化を目的に、型割れが発生する限界値が「１００」となるように、上記成型性パラメータの各係数を整理することによって得られたものである。 That is, when the present inventor uses bolt steels of various compositions and then performs spheroidizing and then bolt forming, mold cracks during cold working occur in steel types with high C and Si contents. Focused on the tendency to do. And, it was found that the main causes of cracking were “dispersion strengthening by carbon (C)” and “solid solution strengthening by silicon (Si)”, and the formability parameter considering the magnitude of the contribution of these exceeded a certain limit value. The conclusion was reached that mold cracking would occur.
The formula for calculating the α value is obtained by organizing the coefficients of the formability parameter so that the limit value at which mold cracking occurs is “100” for the purpose of simplification. .
本発明の高強度ボルト用鋼は、上記したＣ、Ｓｉ、Ｍｎ、Ｍｏ及び／又はＷの含有量を必須成分とし、Ｃ及びＳｉ含有量に基づいて算出されるα値が１００以下であることを必須の要件とするものであるが、この他の任意成分として、次に示す成分を必要に応じて添加することができる。
The steel for high-strength bolts of the present invention has the above-mentioned C, Si, Mn, Mo and / or W content as an essential component, and the α value calculated based on the C and Si content is 100 or less. Is an essential requirement, but as other optional components, the following components can be added as necessary.
Ｃｒ：０．２０～１．５０％
Ｎｉ：０．２０～１．５０％
Ｃｒ（クロム）及びＮｉ（ニッケル）は、いずれも焼入れ性向上に効果的な元素であるから、必要に応じて、これら元素の一方又は両方を添加する。
これら元素により、焼入れ性をさらに向上させるためには、それぞれ０．２０％以上含有させる必要がある。一方、１．５０％を超えて添加しても、それ以上の効果は得られず、過剰の添加は経済性の観点からも好ましくないため、これらの上限値は１．５０％とする。 Cr: 0.20 to 1.50%
Ni: 0.20 to 1.50%
Since both Cr (chromium) and Ni (nickel) are effective elements for improving the hardenability, one or both of these elements are added as necessary.
In order to further improve the hardenability with these elements, it is necessary to contain 0.20% or more respectively. On the other hand, even if added over 1.50%, no further effect is obtained, and excessive addition is not preferable from the viewpoint of economy, so the upper limit is made 1.50%.
Ｎｉ：０．２０～１．５０％
Ｃｒ（クロム）及びＮｉ（ニッケル）は、いずれも焼入れ性向上に効果的な元素であるから、必要に応じて、これら元素の一方又は両方を添加する。
これら元素により、焼入れ性をさらに向上させるためには、それぞれ０．２０％以上含有させる必要がある。一方、１．５０％を超えて添加しても、それ以上の効果は得られず、過剰の添加は経済性の観点からも好ましくないため、これらの上限値は１．５０％とする。 Cr: 0.20 to 1.50%
Ni: 0.20 to 1.50%
Since both Cr (chromium) and Ni (nickel) are effective elements for improving the hardenability, one or both of these elements are added as necessary.
In order to further improve the hardenability with these elements, it is necessary to contain 0.20% or more respectively. On the other hand, even if added over 1.50%, no further effect is obtained, and excessive addition is not preferable from the viewpoint of economy, so the upper limit is made 1.50%.
Ｖ：０．００２～１．５０％
Ｔｉ：０．００２～１．５０％
Ｎｂ：０．００２～１．５０％
Ｖ（バナジウム）、Ｔｉ（チタン）及びＮｂ（ニオブ）は、いずれも焼戻し時に微細な炭窒化物を形成することによって、マトリクスの高強度化に寄与する元素であって、必要に応じて、これら元素の１種、２種あるいは３種を添加する。
このような効果を得るためには、それぞれ０．００２％以上を含有させる必要がある。一方、１．５０％を超えて添加したとしても、それ以上の向上効果がなく、経済性からも好ましくないため、これら元素の上限値はそれぞれ１．５０％とする。 V: 0.002 to 1.50%
Ti: 0.002 to 1.50%
Nb: 0.002 to 1.50%
V (vanadium), Ti (titanium) and Nb (niobium) are all elements that contribute to increasing the strength of the matrix by forming fine carbonitrides during tempering. One, two or three elements are added.
In order to acquire such an effect, it is necessary to contain 0.002% or more, respectively. On the other hand, even if added over 1.50%, there is no further improvement effect and it is not preferable from the viewpoint of economy, so the upper limit values of these elements are set to 1.50%.
Ｔｉ：０．００２～１．５０％
Ｎｂ：０．００２～１．５０％
Ｖ（バナジウム）、Ｔｉ（チタン）及びＮｂ（ニオブ）は、いずれも焼戻し時に微細な炭窒化物を形成することによって、マトリクスの高強度化に寄与する元素であって、必要に応じて、これら元素の１種、２種あるいは３種を添加する。
このような効果を得るためには、それぞれ０．００２％以上を含有させる必要がある。一方、１．５０％を超えて添加したとしても、それ以上の向上効果がなく、経済性からも好ましくないため、これら元素の上限値はそれぞれ１．５０％とする。 V: 0.002 to 1.50%
Ti: 0.002 to 1.50%
Nb: 0.002 to 1.50%
V (vanadium), Ti (titanium) and Nb (niobium) are all elements that contribute to increasing the strength of the matrix by forming fine carbonitrides during tempering. One, two or three elements are added.
In order to acquire such an effect, it is necessary to contain 0.002% or more, respectively. On the other hand, even if added over 1.50%, there is no further improvement effect and it is not preferable from the viewpoint of economy, so the upper limit values of these elements are set to 1.50%.
この他に、不純物として鋼中に不可避的に含まれる元素として、Ｐ（燐）及びＳ（硫黄）が挙げられる。
これらＰ及びＳは、いずれもオーステナイト温度域において、オーステナイト粒界に偏析し、粒界を脆化させて、耐遅れ破壊性を劣化させる傾向があるため、これらＰ及びＳのの含有量は、それぞれ０．０２％以下に抑えることが望ましい。 In addition, P (phosphorus) and S (sulfur) are mentioned as elements inevitably contained in the steel as impurities.
Since these P and S tend to segregate at the austenite grain boundary in the austenite temperature range, embrittle the grain boundary, and deteriorate the delayed fracture resistance, the content of these P and S is: It is desirable to suppress each to 0.02% or less.
これらＰ及びＳは、いずれもオーステナイト温度域において、オーステナイト粒界に偏析し、粒界を脆化させて、耐遅れ破壊性を劣化させる傾向があるため、これらＰ及びＳのの含有量は、それぞれ０．０２％以下に抑えることが望ましい。 In addition, P (phosphorus) and S (sulfur) are mentioned as elements inevitably contained in the steel as impurities.
Since these P and S tend to segregate at the austenite grain boundary in the austenite temperature range, embrittle the grain boundary, and deteriorate the delayed fracture resistance, the content of these P and S is: It is desirable to suppress each to 0.02% or less.
本発明の高強度ボルト用鋼は、上記した成分組成を有する鋼から成るものであって、１５５０ＭＰａ以上の引張強度を確保するものである、そして、このような引張強度確保のために、次のような調質処理、つまり焼入れ、焼戻しが施される。すなわち、上記した成分組成を有する素材鋼をＡｃ３ 点以上の温度、例えば８８０℃以上の温度まで加熱し、急冷することによって、素材鋼は完全焼入れ組織となる。その後、焼戻しを実施することによって、目的の組織・強度を備えた本発明のボルト用鋼を得ることができる。なお、このときの焼戻し温度としては、耐遅れ破壊性確保の観点から、４００℃以上の温度で実施することが望ましい。
The steel for high-strength bolts of the present invention is made of steel having the above-described component composition, and ensures a tensile strength of 1550 MPa or more. In order to ensure such tensile strength, the following Such tempering treatment, that is, quenching and tempering is performed. That is, by heating the material steel having the above-described component composition to a temperature of Ac 3 or higher, for example, 880 ° C. or higher and quenching rapidly, the material steel becomes a completely quenched structure. Then, the steel for bolts of this invention provided with the target structure | tissue and intensity | strength can be obtained by implementing tempering. The tempering temperature at this time is preferably 400 ° C. or higher from the viewpoint of ensuring delayed fracture resistance.
また、本発明の高強度ボルトは、上記した成分組成を有するボルト用鋼から成るものである。このような高強度ボルトを製造するには、まず、上記成分組成を備えた素材鋼からボルト形状に冷間加工したのち、ねじ部を転造してボルト形状とする。
そして、引張強度確保のために、ボルト形状に成形された素材には、次のように、調質処理、つまり焼入れ、焼戻しが施される。 The high-strength bolt of the present invention is made of bolt steel having the above-described component composition. In order to manufacture such a high-strength bolt, first, the steel material having the above component composition is cold-worked into a bolt shape, and then the thread portion is rolled into a bolt shape.
In order to secure the tensile strength, the material molded into the bolt shape is subjected to a tempering treatment, that is, quenching and tempering as follows.
そして、引張強度確保のために、ボルト形状に成形された素材には、次のように、調質処理、つまり焼入れ、焼戻しが施される。 The high-strength bolt of the present invention is made of bolt steel having the above-described component composition. In order to manufacture such a high-strength bolt, first, the steel material having the above component composition is cold-worked into a bolt shape, and then the thread portion is rolled into a bolt shape.
In order to secure the tensile strength, the material molded into the bolt shape is subjected to a tempering treatment, that is, quenching and tempering as follows.
すなわち、成形後のボルト素材をＡＣ３点以上の温度、例えば８８０℃以上の温度まで加熱し、急冷することによって、ボルト素材は完全焼入れ組織となる。
その後、焼戻しを実施することによって、目的の組織・強度を備えた高強度ボルトを得ることができる。このときの焼戻し温度としては、耐遅れ破壊性確保の観点から、４００℃以上の温度で実施することが望ましい。 That is, the temperature bolt material or C3 point A after molding, heating for example to 880 ° C. or higher, by quenching, the bolt material will be completely quenched structure.
Thereafter, tempering is performed to obtain a high-strength bolt having a desired structure and strength. As the tempering temperature at this time, it is desirable to carry out at a temperature of 400 ° C. or higher from the viewpoint of ensuring delayed fracture resistance.
その後、焼戻しを実施することによって、目的の組織・強度を備えた高強度ボルトを得ることができる。このときの焼戻し温度としては、耐遅れ破壊性確保の観点から、４００℃以上の温度で実施することが望ましい。 That is, the temperature bolt material or C3 point A after molding, heating for example to 880 ° C. or higher, by quenching, the bolt material will be completely quenched structure.
Thereafter, tempering is performed to obtain a high-strength bolt having a desired structure and strength. As the tempering temperature at this time, it is desirable to carry out at a temperature of 400 ° C. or higher from the viewpoint of ensuring delayed fracture resistance.
以下、本発明を実施例に基づいて、具体的に説明するが、本発明はこのような実施例によって何ら限定されないことは言うまでもない。
Hereinafter, although the present invention will be specifically described based on examples, it is needless to say that the present invention is not limited to such examples.
表１に示す成分組成を有する鋼をそれぞれ溶製した後、造塊し、各鋼を直径１４ｍｍの線材に熱間圧延した。
その後、この線材に皮膜処理を施した後、６００～８００℃の球状化焼きなましと、冷間伸線を繰り返し、直径１０．５ｍｍまで伸線し、以下の各試験に供した。 Each steel having the component composition shown in Table 1 was melted and then ingot, and each steel was hot-rolled into a wire having a diameter of 14 mm.
Thereafter, the wire material was subjected to a film treatment, and then spheroidizing annealing at 600 to 800 ° C. and cold wire drawing were repeated to draw the wire to a diameter of 10.5 mm and subjected to the following tests.
その後、この線材に皮膜処理を施した後、６００～８００℃の球状化焼きなましと、冷間伸線を繰り返し、直径１０．５ｍｍまで伸線し、以下の各試験に供した。 Each steel having the component composition shown in Table 1 was melted and then ingot, and each steel was hot-rolled into a wire having a diameter of 14 mm.
Thereafter, the wire material was subjected to a film treatment, and then spheroidizing annealing at 600 to 800 ° C. and cold wire drawing were repeated to draw the wire to a diameter of 10.5 mm and subjected to the following tests.
（１）引張強度
冷間伸線した１０．５ｍｍ径の線材からそれぞれ引張試験片（縮小ＪＩＳ４号試験片）を採取し、９２０～９５０℃で焼入れたのち、４５０℃で焼戻しを実施した。
このように作製した試験片を用いて、各鋼の引張特性を評価した結果を表２に示す。 (1) Tensile strength Tensile test pieces (reduced JIS No. 4 test pieces) were sampled from cold-drawn 10.5 mm diameter wires, quenched at 920 to 950 ° C., and then tempered at 450 ° C.
Table 2 shows the results of evaluating the tensile properties of each steel using the test pieces thus prepared.
冷間伸線した１０．５ｍｍ径の線材からそれぞれ引張試験片（縮小ＪＩＳ４号試験片）を採取し、９２０～９５０℃で焼入れたのち、４５０℃で焼戻しを実施した。
このように作製した試験片を用いて、各鋼の引張特性を評価した結果を表２に示す。 (1) Tensile strength Tensile test pieces (reduced JIS No. 4 test pieces) were sampled from cold-drawn 10.5 mm diameter wires, quenched at 920 to 950 ° C., and then tempered at 450 ° C.
Table 2 shows the results of evaluating the tensile properties of each steel using the test pieces thus prepared.
（２）加工性
冷間伸線した１０．５ｍｍ径の上記線材を６０ｍｍの長さにそれぞれ切断したのち、ボルトヘッド部を備えたボルト形状に冷間加工（型鍛造）した。
そして、冷間加工時における型の状態を観察し、型に割れや顕著な摩耗が発生したものについては「×」、これらの発生が認められないものについては「○」として、各鋼の加工性、成型性を評価した。これらの結果を表２に併せて示す。 (2) Workability After the cold-drawn 10.5 mm diameter wire was cut to a length of 60 mm, it was cold worked (die forged) into a bolt shape having a bolt head portion.
Then, the state of the mold during cold working was observed, and “×” was indicated for those where cracks or significant wear occurred in the mold, and “○” was assigned for those where such occurrence was not observed. Property and moldability were evaluated. These results are also shown in Table 2.
冷間伸線した１０．５ｍｍ径の上記線材を６０ｍｍの長さにそれぞれ切断したのち、ボルトヘッド部を備えたボルト形状に冷間加工（型鍛造）した。
そして、冷間加工時における型の状態を観察し、型に割れや顕著な摩耗が発生したものについては「×」、これらの発生が認められないものについては「○」として、各鋼の加工性、成型性を評価した。これらの結果を表２に併せて示す。 (2) Workability After the cold-drawn 10.5 mm diameter wire was cut to a length of 60 mm, it was cold worked (die forged) into a bolt shape having a bolt head portion.
Then, the state of the mold during cold working was observed, and “×” was indicated for those where cracks or significant wear occurred in the mold, and “○” was assigned for those where such occurrence was not observed. Property and moldability were evaluated. These results are also shown in Table 2.
（３）耐遅れ破壊性
高強度ボルトにおいて懸念される耐遅れ破壊性を確認するために、各鋼から成形したボルトの塩酸浸漬試験を実施した。
まず、１０．５ｍｍ径の上記線材に、それぞれ上記のような冷間加工と、ねじ転造加工を施してボルト素材とし、当該ボルト素材に、９２０～９５０℃の焼入れ、次いで４５０℃での焼戻しを施すことによって高強度ボルト（Ｍ１０×５０）をそれぞれ作製した。 (3) Delayed fracture resistance In order to confirm delayed fracture resistance, which is a concern in high-strength bolts, a hydrochloric acid immersion test was performed on bolts formed from each steel.
First, the above-mentioned wire material having a diameter of 10.5 mm is subjected to the cold working and the thread rolling process as described above to obtain a bolt material. The bolt material is quenched at 920 to 950 ° C. and then tempered at 450 ° C. The high-strength bolt (M10 × 50) was produced by applying
高強度ボルトにおいて懸念される耐遅れ破壊性を確認するために、各鋼から成形したボルトの塩酸浸漬試験を実施した。
まず、１０．５ｍｍ径の上記線材に、それぞれ上記のような冷間加工と、ねじ転造加工を施してボルト素材とし、当該ボルト素材に、９２０～９５０℃の焼入れ、次いで４５０℃での焼戻しを施すことによって高強度ボルト（Ｍ１０×５０）をそれぞれ作製した。 (3) Delayed fracture resistance In order to confirm delayed fracture resistance, which is a concern in high-strength bolts, a hydrochloric acid immersion test was performed on bolts formed from each steel.
First, the above-mentioned wire material having a diameter of 10.5 mm is subjected to the cold working and the thread rolling process as described above to obtain a bolt material. The bolt material is quenched at 920 to 950 ° C. and then tempered at 450 ° C. The high-strength bolt (M10 × 50) was produced by applying
上記により得られた各高強度ボルトについて、その耐遅れ破壊性を塩酸浸漬試験法により評価した。
すなわち、各ボルトを治具に設置し、定荷重（引張強度の８０％の負荷）を付加した状態で３％に希釈した塩酸水溶液中に３０分放置した後、洗浄、乾燥するサイクルを１サイクルとして１５サイクル繰り返し、この間における破断の有無を確認した。これらの結果を表２に併せて示す。 About each high strength bolt obtained by the above, the delayed fracture resistance was evaluated by the hydrochloric acid immersion test method.
That is, each bolt is placed in a jig, left in an aqueous hydrochloric acid solution diluted to 3% with a constant load (load of 80% of tensile strength) added, and then washed and dried in one cycle. 15 cycles were repeated, and the presence or absence of breakage during this period was confirmed. These results are also shown in Table 2.
すなわち、各ボルトを治具に設置し、定荷重（引張強度の８０％の負荷）を付加した状態で３％に希釈した塩酸水溶液中に３０分放置した後、洗浄、乾燥するサイクルを１サイクルとして１５サイクル繰り返し、この間における破断の有無を確認した。これらの結果を表２に併せて示す。 About each high strength bolt obtained by the above, the delayed fracture resistance was evaluated by the hydrochloric acid immersion test method.
That is, each bolt is placed in a jig, left in an aqueous hydrochloric acid solution diluted to 3% with a constant load (load of 80% of tensile strength) added, and then washed and dried in one cycle. 15 cycles were repeated, and the presence or absence of breakage during this period was confirmed. These results are also shown in Table 2.
表１及び表２において、ボルト成型性（加工性）に対して、αの値を比較すると、αが１００を超えた値を持つ鋼においては、型に割れや顕著な磨耗が発生した。このことから、高強度ボルト用の素材鋼として使用するには、αが１００以下となるよう材料設計する必要があることが分かる。
In Tables 1 and 2, when the value of α was compared with the bolt formability (workability), cracks and significant wear occurred in the mold in steels with α exceeding 100. This shows that it is necessary to design the material so that α is 100 or less in order to use it as a material steel for high-strength bolts.
すなわち、所定の化学成分を有し、Ｃ，Ｓｉ含有量から求められるα値（＝１９．０＋７６．１×Ｃ＋３０．０×√Ｓｉ－４．５×Ｃ×√Ｓｉ）が１００以下である本発明鋼（鋼１～１４）は、ボルト成型性に優れ、焼入れ、焼戻し後の引張強度も１５５０ＭＰａ以上の値を示した。
これに対し、α値が１００を超える鋼種（鋼１５～１７）においては、上記調質処理後の引張強度が１５５０ＭＰａ以上を示すものの、ボルト成型時に型の割れや磨耗が発生した。また、鋼１８～２２においては、Ｃが０．４０％未満、あるいはＳｉが０．４０％未満であるため、調質処理後の引張強度が１５５０ＭＰａを満足しないことが判明した。 That is, a book having a predetermined chemical component and an α value (= 19.0 + 76.1 × C + 30.0 × √Si−4.5 × C × √Si) obtained from the C and Si contents is 100 or less. Invented steels (steels 1 to 14) were excellent in bolt moldability and exhibited a tensile strength after quenching and tempering of 1550 MPa or more.
On the other hand, in the steel types (steel 15 to 17) having an α value exceeding 100, although the tensile strength after the tempering treatment was 1550 MPa or more, cracking and wear of the mold occurred during bolt molding. Further, in Steels 18 to 22, it was found that the tensile strength after tempering treatment does not satisfy 1550 MPa because C is less than 0.40% or Si is less than 0.40%.
これに対し、α値が１００を超える鋼種（鋼１５～１７）においては、上記調質処理後の引張強度が１５５０ＭＰａ以上を示すものの、ボルト成型時に型の割れや磨耗が発生した。また、鋼１８～２２においては、Ｃが０．４０％未満、あるいはＳｉが０．４０％未満であるため、調質処理後の引張強度が１５５０ＭＰａを満足しないことが判明した。 That is, a book having a predetermined chemical component and an α value (= 19.0 + 76.1 × C + 30.0 × √Si−4.5 × C × √Si) obtained from the C and Si contents is 100 or less. Invented steels (steels 1 to 14) were excellent in bolt moldability and exhibited a tensile strength after quenching and tempering of 1550 MPa or more.
On the other hand, in the steel types (steel 15 to 17) having an α value exceeding 100, although the tensile strength after the tempering treatment was 1550 MPa or more, cracking and wear of the mold occurred during bolt molding. Further, in Steels 18 to 22, it was found that the tensile strength after tempering treatment does not satisfy 1550 MPa because C is less than 0.40% or Si is less than 0.40%.
一方、耐遅れ破壊性については、本発明鋼（鋼１～１４）と、比較例である鋼１５～１７においては、ＭｏやＷの添加によって析出した炭窒化物の影響もあり、上記塩酸浸漬試験での遅れ破壊は見られなかった。一方、鋼１８～２２においては、炭窒化物量が少ないため、試験中に一部ボルトの破断が認められた。この理由として、上記のようにＭｏ又はＷ添加によって焼戻し時に微細な炭窒化物が形成されてマトリックスの高強度化が実現されるものである。
On the other hand, with regard to delayed fracture resistance, the steels of the present invention (steels 1 to 14) and comparative steels 15 to 17 are also affected by carbonitrides precipitated by the addition of Mo and W. No delayed fracture was observed in the test. On the other hand, in the steels 18 to 22, since the amount of carbonitride was small, some bolts were broken during the test. The reason for this is that, as described above, addition of Mo or W forms fine carbonitrides during tempering, thereby realizing high strength of the matrix.
以上のように、本発明の高強度ボルト用鋼は、０．４０～０．７０％のＣ、０．４０～２．５０％のＳｉ、０．０５～１．０％のＭｎと、０．２５～３．００％のＭｏと０．２０～３．００％のＷの一方又は双方を含有し、さらに必要に応じて、０．２０～１．５０％のＣｒと０．２０～１．５０％のＮｉの一方又は双方、及び／又は０．００２～１．５０％のＶ、０．００２～１．５０％のＴｉ及び０．００２～１．５０％のＮｂから成る群から選ばれる少なくとも１種を含有し、上記Ｃ及びＳｉ含有量から算出されるα（＝１９．０＋７６．１×Ｃ＋３０．０×√Ｓｉ－４．５×Ｃ×√Ｓｉ）の値が１００以下となるようにしたものである。したがって、製造性（冷間加工性、成形性）に優れ、このようなボルト用鋼をボルト形状に冷間加工し、焼入れ、焼戻しの調質処理を施すことによって、１５５０ＭＰａ以上の高強度ボルトとすることができる。
As described above, the steel for high-strength bolts of the present invention has 0.40 to 0.70% C, 0.40 to 2.50% Si, 0.05 to 1.0% Mn, 0% One or both of 25 to 3.00% Mo and 0.20 to 3.00% W, and optionally 0.20 to 1.50% Cr and 0.20 to 1 Selected from the group consisting of one or both of 50% Ni and / or 0.002-1.50% V, 0.002-1.50% Ti and 0.002-1.50% Nb The value of α (= 19.0 + 76.1 × C + 30.0 × √Si−4.5 × C × √Si) calculated from the C and Si contents is 100 or less. It is what I did. Therefore, it is excellent in manufacturability (cold workability, formability), and by cold working such steel for bolts into a bolt shape and applying tempering treatment of quenching and tempering, can do.
Claims (7)
- 質量比で、０．４０～０．７０％のＣと、０．４０～２．５０％のＳｉと、０．０５～１．０％のＭｎと、０．２５～３．００％のＭｏ及び／又は０．２０～３．００％のＷを含有すると共に、次式により算出されるαの値が１００以下であって、残部がＦｅ及び不可避的不純物から成り、引張強度が１５５０ＭＰａ以上であることを特徴とする高強度ボルト用鋼。
α＝１９．０＋７６．１×Ｃ＋３０．０×√Ｓｉ－４．５×Ｃ×√Ｓｉ By mass ratio, 0.40 to 0.70% C, 0.40 to 2.50% Si, 0.05 to 1.0% Mn, and 0.25 to 3.00% Mo. And / or 0.2 to 3.00% W, the value of α calculated by the following formula is 100 or less, the balance is made of Fe and inevitable impurities, and the tensile strength is 1550 MPa or more. A steel for high-strength bolts.
α = 19.0 + 76.1 × C + 30.0 × √Si−4.5 × C × √Si - 質量比で、０．４０～０．７０％のＣと、０．４０～２．５０％のＳｉと、０．０５～１．０％のＭｎと、０．２５～３．００％のＭｏ及び／又は０．２０～３．００％のＷと、０．２０～１．５０％のＣｒ及び／又は０．２０～１．５０％のＮｉを含有すると共に、次式により算出されるαの値が１００以下であって、残部がＦｅ及び不可避的不純物から成り、引張強度が１５５０ＭＰａ以上であることを特徴とする高強度ボルト用鋼。
α＝１９．０＋７６．１×Ｃ＋３０．０×√Ｓｉ－４．５×Ｃ×√Ｓｉ By mass ratio, 0.40 to 0.70% C, 0.40 to 2.50% Si, 0.05 to 1.0% Mn, and 0.25 to 3.00% Mo. And / or 0.20 to 3.00% W, 0.20 to 1.50% Cr and / or 0.20 to 1.50% Ni, and α calculated by the following formula: Is a steel for high-strength bolts, wherein the balance is made of Fe and inevitable impurities, and the tensile strength is 1550 MPa or more.
α = 19.0 + 76.1 × C + 30.0 × √Si−4.5 × C × √Si - 質量比で、０．４０～０．７０％のＣと、０．４０～２．５０％のＳｉと、０．０５～１．０％のＭｎと、０．２５～３．００％のＭｏ及び／又は０．２０～３．００％のＷと、０．００２～１．５０％のＶ、０．００２～１．５０％のＴｉ及び０．００２～１．５０％のＮｂから成る群から選ばれる少なくとも１種を含有すると共に、次式により算出されるαの値が１００以下であって、残部がＦｅ及び不可避的不純物から成り、引張強度が１５５０ＭＰａ以上であることを特徴とする高強度ボルト用鋼。
α＝１９．０＋７６．１×Ｃ＋３０．０×√Ｓｉ－４．５×Ｃ×√Ｓｉ By mass ratio, 0.40 to 0.70% C, 0.40 to 2.50% Si, 0.05 to 1.0% Mn, and 0.25 to 3.00% Mo. And / or the group consisting of 0.20 to 3.00% W, 0.002 to 1.50% V, 0.002 to 1.50% Ti and 0.002 to 1.50% Nb. A value of α calculated by the following formula is 100 or less, the balance is made of Fe and inevitable impurities, and the tensile strength is 1550 MPa or more. Steel for strength bolts.
α = 19.0 + 76.1 × C + 30.0 × √Si−4.5 × C × √Si - 質量比で、０．４０～０．７０％のＣと、０．４０～２．５０％のＳｉと、０．０５～１．０％のＭｎと、０．２５～３．００％のＭｏ及び／又は０．２０～３．００％のＷと、０．２０～１．５０％のＣｒ及び／又は０．２０～１．５０％のＮｉと、０．００２～１．５０％のＶ、０．００２～１．５０％のＴｉ及び０．００２～１．５０％のＮｂから成る群から選ばれる少なくとも１種を含有すると共に、次式により算出されるαの値が１００以下であって、残部がＦｅ及び不可避的不純物から成り、引張強度が１５５０ＭＰａ以上であることを特徴とする高強度ボルト用鋼。
α＝１９．０＋７６．１×Ｃ＋３０．０×√Ｓｉ－４．５×Ｃ×√Ｓｉ By mass ratio, 0.40 to 0.70% C, 0.40 to 2.50% Si, 0.05 to 1.0% Mn, and 0.25 to 3.00% Mo. And / or 0.20 to 3.00% W, 0.20 to 1.50% Cr and / or 0.20 to 1.50% Ni and 0.002 to 1.50% V And at least one selected from the group consisting of 0.002 to 1.50% Ti and 0.002 to 1.50% Nb, and the value of α calculated by the following formula is 100 or less. The balance is made of Fe and inevitable impurities, and has a tensile strength of 1550 MPa or more.
α = 19.0 + 76.1 × C + 30.0 × √Si−4.5 × C × √Si - Ｃ含有量が０．５５％以下であることを特徴とする請求項１～４のいずれか１つの項に記載の高強度ボルト用鋼。 The steel for high-strength bolts according to any one of claims 1 to 4, wherein the C content is 0.55% or less.
- 請求項１～５のいずれか１つの項に記載の高強度ボルト用鋼を用いた高強度ボルト。 A high-strength bolt using the steel for high-strength bolts according to any one of claims 1 to 5.
- 請求項６に記載の高強度ボルトを製造するに際し、請求項１～５のいずれか１つの項に記載の成分組成を有する鋼をボルト形状に冷間成形した後、焼入れ、焼戻しを施すことを特徴とする高強度ボルトの製造方法。 In manufacturing the high-strength bolt according to claim 6, the steel having the component composition according to any one of claims 1 to 5 is cold-formed into a bolt shape, and then quenched and tempered. A method for producing a high-strength bolt characterized by the above.
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| JP2009-243031 | 2009-10-22 | ||
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| JP2013104070A (en) * | 2011-11-10 | 2013-05-30 | Nippon Steel & Sumitomo Metal Corp | High-strength steel excellent in delayed breakage resistance, and high-strength bolt |
| WO2016158361A1 (en) * | 2015-03-27 | 2016-10-06 | 株式会社神戸製鋼所 | Wire material for use in bolts that has excellent acid pickling properties and resistance to delayed fracture after quenching and tempering, and bolt |
| CN106795598A (en) * | 2014-08-29 | 2017-05-31 | 日产自动车株式会社 | High-strength bolt steel and high-strength bolt |
| WO2019150437A1 (en) * | 2018-01-30 | 2019-08-08 | 日産自動車株式会社 | Bolt and fastened structure |
| CN112226588A (en) * | 2020-09-11 | 2021-01-15 | 浙江九隆机械有限公司 | Bolt machining process |
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| CN112226588A (en) * | 2020-09-11 | 2021-01-15 | 浙江九隆机械有限公司 | Bolt machining process |
| CN112226588B (en) * | 2020-09-11 | 2022-02-15 | 浙江九隆机械有限公司 | Bolt machining process |
| CN113584394A (en) * | 2021-08-05 | 2021-11-02 | 安徽安簧机械股份有限公司 | Hot-forging die steel and preparation method thereof, and piston forging forming die and preparation method thereof |
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