WO2011111872A1 - 耐遅れ破壊特性に優れた高強度鋼材と高強度ボルト、及び、その製造方法 - Google Patents

耐遅れ破壊特性に優れた高強度鋼材と高強度ボルト、及び、その製造方法 Download PDF

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WO2011111872A1
WO2011111872A1 PCT/JP2011/056481 JP2011056481W WO2011111872A1 WO 2011111872 A1 WO2011111872 A1 WO 2011111872A1 JP 2011056481 W JP2011056481 W JP 2011056481W WO 2011111872 A1 WO2011111872 A1 WO 2011111872A1
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steel material
delayed fracture
bolt
less
strength
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PCT/JP2011/056481
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English (en)
French (fr)
Japanese (ja)
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大輔 平上
徹志 千田
敏三 樽井
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新日本製鐵株式会社
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Priority to JP2012502334A priority Critical patent/JP5177323B2/ja
Priority to US13/515,444 priority patent/US20120247618A1/en
Priority to EP20110753527 priority patent/EP2546379B1/en
Priority to IN5089DEN2012 priority patent/IN2012DN05089A/en
Priority to CN201180013427XA priority patent/CN102812145A/zh
Priority to KR1020127010100A priority patent/KR101366375B1/ko
Publication of WO2011111872A1 publication Critical patent/WO2011111872A1/ja

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    • 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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    • C21D8/00—Modifying the physical properties by deformation combined with, or followed by, heat treatment
    • C21D8/06—Modifying the physical properties by deformation combined with, or followed by, heat treatment during manufacturing of rods or wires
    • C21D8/065—Modifying the physical properties by deformation combined with, or followed by, heat treatment during manufacturing of rods or wires of ferrous alloys
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    • C21D9/00—Heat treatment, e.g. annealing, hardening, quenching or tempering, adapted for particular articles; Furnaces therefor
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    • C21D9/00—Heat treatment, e.g. annealing, hardening, quenching or tempering, adapted for particular articles; Furnaces therefor
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    • 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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    • C22C38/00—Ferrous alloys, e.g. steel alloys
    • C22C38/18—Ferrous alloys, e.g. steel alloys containing chromium
    • C22C38/40—Ferrous alloys, e.g. steel alloys containing chromium with nickel
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    • C22C38/00—Ferrous alloys, e.g. steel alloys
    • C22C38/18—Ferrous alloys, e.g. steel alloys containing chromium
    • C22C38/40—Ferrous alloys, e.g. steel alloys containing chromium with nickel
    • C22C38/54—Ferrous alloys, e.g. steel alloys containing chromium with nickel with boron
    • 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
    • C22C38/58—Ferrous alloys, e.g. steel alloys containing chromium with nickel with more than 1.5% by weight of manganese
    • C—CHEMISTRY; METALLURGY
    • C23—COATING METALLIC MATERIAL; COATING MATERIAL WITH METALLIC MATERIAL; CHEMICAL SURFACE TREATMENT; DIFFUSION TREATMENT OF METALLIC MATERIAL; COATING BY VACUUM EVAPORATION, BY SPUTTERING, BY ION IMPLANTATION OR BY CHEMICAL VAPOUR DEPOSITION, IN GENERAL; INHIBITING CORROSION OF METALLIC MATERIAL OR INCRUSTATION IN GENERAL
    • C23C—COATING METALLIC MATERIAL; COATING MATERIAL WITH METALLIC MATERIAL; SURFACE TREATMENT OF METALLIC MATERIAL BY DIFFUSION INTO THE SURFACE, BY CHEMICAL CONVERSION OR SUBSTITUTION; COATING BY VACUUM EVAPORATION, BY SPUTTERING, BY ION IMPLANTATION OR BY CHEMICAL VAPOUR DEPOSITION, IN GENERAL
    • C23C8/00—Solid state diffusion of only non-metal elements into metallic material surfaces; Chemical surface treatment of metallic material by reaction of the surface with a reactive gas, leaving reaction products of surface material in the coating, e.g. conversion coatings, passivation of metals
    • C23C8/06—Solid state diffusion of only non-metal elements into metallic material surfaces; Chemical surface treatment of metallic material by reaction of the surface with a reactive gas, leaving reaction products of surface material in the coating, e.g. conversion coatings, passivation of metals using gases
    • C23C8/08—Solid state diffusion of only non-metal elements into metallic material surfaces; Chemical surface treatment of metallic material by reaction of the surface with a reactive gas, leaving reaction products of surface material in the coating, e.g. conversion coatings, passivation of metals using gases only one element being applied
    • C23C8/24—Nitriding
    • C23C8/26—Nitriding of ferrous surfaces
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    • C21D2211/00—Microstructure comprising significant phases
    • C21D2211/008—Martensite
    • C—CHEMISTRY; METALLURGY
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    • 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
    • C21D2221/00—Treating localised areas of an article
    • C21D2221/10—Differential treatment of inner with respect to outer regions, e.g. core and periphery, respectively

Definitions

  • the present invention relates to a high-strength steel material used for wire rods, PC steel rods (prestressed concrete steel rods) and the like, in particular, a high-strength steel material having excellent delayed fracture resistance and a tensile strength of 1300 MPa or more, a high-strength bolt, and production thereof It is about the method.
  • High-strength steels used in many machines, automobiles, bridges, and building structures are medium carbon steels with a C content of 0.20 to 0.35%, such as SCr specified in JIS G 4104 and JIS G 4105. , SCM and the like are subjected to a tempering process. However, in any steel type, if the tensile strength exceeds 1300 MPa, the risk of delayed fracture increases.
  • a method for improving the delayed fracture resistance of high-strength steel a method in which the steel structure is a bainite structure or a method in which prior austenite grains are refined is effective.
  • Patent Document 1 discloses a steel in which old austenite grains are refined to increase delayed fracture resistance, and Patent Documents 2 and 3 increase delayed fracture resistance by suppressing segregation of steel components. Steel is disclosed. However, it is difficult to significantly improve the delayed fracture resistance by refinement of prior austenite grains and suppression of component segregation.
  • the bainite structure contributes to the improvement of the delayed fracture resistance, but the formation of the bainite structure requires appropriate additive elements and heat treatment, which increases the cost of steel.
  • Patent Documents 4 to 6 a pearlite structure having an area ratio of 80% or more is subjected to strong wire drawing to give a strength of 1200 N / mm 2 or more and excellent delayed fracture resistance. % Of high-strength bolts are disclosed.
  • Patent Document 7 discloses a coil spring in which the occurrence of delayed fracture after cold coiling is suppressed by using an oil tempered wire having an internal hardness of Hv550 or more.
  • the product surface hardness after nitriding is Hv 900 or more, and the delayed fracture characteristics are low under high load stress such as bolts and PC steel bars, and there is a problem that delayed fracture occurs when the corrosive environment becomes more severe.
  • Patent Document 8 discloses a high-strength steel material excellent in delayed fracture resistance mainly composed of a tempered martensite structure obtained by nitriding a steel having a required component composition.
  • the high-strength steel material disclosed in Patent Document 8 exhibits delayed fracture resistance even in a corrosive environment containing hydrogen.
  • the corrosive environment has become more severe, and there is a demand for a high-strength steel material that exhibits excellent delayed fracture resistance even under severe corrosive environments.
  • the present invention provides a high-strength steel material (wire rod, PC steel bar) and high-strength bolt that exhibit excellent delayed fracture resistance even in a severe corrosive environment, and a manufacturing method for manufacturing them at low cost. The purpose is to provide.
  • the inventors of the present invention have intensively studied a method for solving the above-described problems.
  • the steel material contains a predetermined amount of V and / or Mo that forms precipitates that trap hydrogen, and
  • This invention was made
  • the balance consists of Fe and unavoidable impurities
  • the structure is a steel material whose structure is mainly tempered martensite, and in the surface layer of the steel material, (A) a nitride layer having a thickness from the surface of the steel material of 200 ⁇ m or more and a nitrogen concentration of 12.0% by mass or less, which is 0.02% by mass or more higher than the nitrogen concentration of the steel material; and (B) A low carbon region having a depth from the surface of the steel material of 100 ⁇ m or more and 1000 ⁇ m or less and a carbon concentration of 0.05% by mass or more and 0.9 times or less of the carbon concentration of the steel material is formed. High strength steel with excellent delayed fracture resistance.
  • the amount of hydrogen entering the steel material is 0.5 ppm or less due to the presence of the nitride layer and the low carbon region, and the limit diffusible hydrogen content of the steel material is 2.00 ppm or more.
  • the steel material is, by mass%, Al: 0.003-0.1%, Ti: 0.003-0.05%, Mg: 0.0003-0.01%, Ca: 0.00. It has excellent delayed fracture resistance according to the above (1) or (2), characterized by containing one or more of 0003 to 0.01%, Zr: 0.0003 to 0.01% High strength steel.
  • the steel material is, in mass%, Al: 0.003-0.1%, Ti: 0.003-0.05%, Mg: 0.0003-0.01%, Ca: 0.00. It has excellent delayed fracture resistance as described in (8) or (9) above, comprising one or more of 0003 to 0.01%, Zr: 0.0003 to 0.01% High strength bolt.
  • a method for producing a high-strength steel material having excellent delayed fracture resistance according to any one of (1) to (7), (1)
  • the steel material having the composition described in (1) or (3) is heated, and the carbon concentration is 0.05% by mass or more from the surface of the steel material to a depth of 100 ⁇ m or more and 1000 ⁇ m or less.
  • Form a low carbon region of 0.9 times or less of the carbon concentration then cooled as it is to make the steel structure a martensite-based structure
  • the steel material is subjected to nitriding treatment at a temperature exceeding 500 ° C. and not more than 650 ° C., and the nitrogen concentration of the steel material is 12.0% by mass or less and 0.02% by mass than the nitrogen concentration of the steel material.
  • a method for producing a bolt having excellent delayed fracture resistance according to any one of (8) to (14), (1) The bolt which processed the steel material of the component composition as described in said (8) or (10) is heated, and carbon concentration is 0.05 mass% or more from the surface of a bolt to the depth of 100 micrometers or more and 1000 micrometers or less. , Forming a low carbon region of 0.9 times or less of the carbon concentration of the steel material, then cooled as it is, the steel material structure is a martensite-based structure, (2) The bolt is subjected to nitriding treatment at over 500 ° C.
  • a method for producing a high-strength bolt excellent in delayed fracture resistance characterized in that a nitride layer having a thickness of 200 ⁇ m or more from the surface of the bolt is formed, and the steel is made of a tempered martensite-based structure. .
  • a high-strength steel material (wire rod, PC steel bar) and high-strength bolt that exhibit excellent delayed fracture resistance even in a severe corrosive environment, and a manufacturing method capable of manufacturing them at low cost. I can.
  • FIG.1 (a) is a figure which shows typically the hydrogen release rate curve obtained by the hydrogen analysis by a temperature rising method.
  • FIG.1 (b) is a figure which shows typically the relationship between the fracture
  • FIG. 2 is a diagram showing a method for obtaining the depth (thickness) of a low carbon region from a carbon concentration curve obtained by an energy dispersive X-ray fluorescence spectrometer (EDX).
  • FIG. 3 is a diagram showing a method for obtaining the thickness (depth) of a nitride layer from a nitrogen concentration curve obtained with an energy dispersive X-ray fluorescence spectrometer (EDX).
  • FIG. 4 is a view showing a test piece used for a delayed fracture test of a steel material.
  • FIG. 5 is a diagram showing an embodiment of the delayed fracture tester.
  • FIG. 6 is a diagram showing the relationship between temperature, humidity and time in
  • FIG. 1 (a) schematically shows a hydrogen release rate curve obtained by hydrogen analysis by a temperature raising method. As shown in FIG. 1A, the amount of diffusible hydrogen released reaches a peak around 100 ° C. In the present invention, the sample is heated at 100 ° C./h, and the integrated value of the amount of hydrogen released between room temperature and 400 ° C. is defined as the amount of diffusible hydrogen. The amount of hydrogen released can be measured with a gas chromatograph.
  • the minimum amount of diffusible hydrogen that causes delayed fracture is referred to as the limit diffusible hydrogen amount.
  • the amount of critical diffusible hydrogen varies depending on the type of steel.
  • FIG. 1B schematically shows the relationship between the rupture time and the amount of diffusible hydrogen obtained in the constant load delayed fracture test of steel. As shown in FIG. 1B, the break time is short when the amount of diffusible hydrogen is large, and the break time is long when the amount of diffusible hydrogen is small. That is, if the amount of diffusible hydrogen is small, delayed fracture does not occur, and if the amount of diffusible hydrogen is large, delayed fracture occurs.
  • the maximum diffusible hydrogen amount that did not break for 100 hours or more was defined as the limit diffusible hydrogen amount, as shown in FIG. Comparing the amount of intrusive hydrogen and the amount of limit diffusible hydrogen, if the amount of limit diffusible hydrogen is greater than the amount of intrusion hydrogen, delayed fracture does not occur. Conversely, if the amount of limit diffusible hydrogen is less than the amount of intrusion hydrogen , Delayed fracture occurs. Therefore, the greater the amount of critical diffusible hydrogen, the more delayed the occurrence of delayed fracture. However, when the amount of hydrogen entering the steel material from the corrosive environment exceeds the limit diffusible hydrogen amount, delayed fracture occurs.
  • the present inventors examined the component composition of the steel material on the premise that the hydrogen that has entered the steel material is trapped by the fine precipitates and made harmless in order to increase the critical diffusible hydrogen content.
  • the present inventors contain an appropriate amount of one or two of V and Mo, and fine precipitates composed of carbides, nitrides, and / or carbonitrides of V and Mo in the steel material. It was confirmed that the amount of critical diffusible hydrogen can be increased by precipitation. However, on the other hand, it has also been confirmed that even if one or both of V and Mo are contained in the steel material, the delayed fracture resistance cannot be sufficiently improved. Therefore, the present inventors have made extensive studies by paying attention to the relationship between the crystal form of fine precipitates, the amount of critical diffusible hydrogen and the amount of invading hydrogen, and as a result, the following has been found.
  • Hexagonal Mo carbides, nitrides, and carbonitrides have a greater effect on increasing the amount of limit diffusible hydrogen than on increasing the amount of invading hydrogen, and thus greatly contribute to the improvement of delayed fracture resistance.
  • the strength improvement effect by fine precipitation is small compared with V carbide, nitride, and carbonitride of NaCl type crystal.
  • V-type carbides, nitrides, and carbonitrides of NaCl-type crystals are excellent in strength improvement effect by fine precipitation.
  • the NaCl-type crystal V carbide, nitride, and carbonitride increase the critical diffusible hydrogen amount while increasing the intrusion hydrogen amount.
  • the inventors have studied to improve the delayed fracture resistance by reducing the hardness of the nitrided layer, subjecting the surface to decarburization treatment, and further accelerating corrosion test and exposure of the steel material subjected to nitriding treatment Tests were conducted to investigate the hydrogen penetration characteristics and delayed fracture resistance of steel materials.
  • a nitride layer having a predetermined nitrogen concentration and thickness is formed on the surface of a steel material having a predetermined component composition and structure, and further, a low carbon region having a predetermined carbon concentration and depth is formed on the steel surface. It was found that the delayed fracture resistance is remarkably improved as compared with the case where only the nitride layer is formed on the steel surface.
  • a thickness of 200 ⁇ m or more from the surface of the steel material, a nitrogen concentration of 12.0% by mass or less, and 0.02% by mass or more higher than the steel material A nitride layer is formed, and (b) a low carbon region having a carbon concentration of 0.05% by mass or more and a carbon concentration of 0.9 times or less of the steel material at a depth of 100 ⁇ m or more and 1000 ⁇ m from the steel surface.
  • the high-strength steel material and high-strength bolt of the present invention have a predetermined composition, and have a nitride layer and a low carbon region simultaneously on the surface thereof.
  • the nitrogen concentration is 12.0 mass% or less, 0.02 mass% or more higher than the nitrogen concentration of the steel material, and the carbon concentration is 0.05 mass%.
  • the carbon concentration is 0.05 mass%.
  • the carbon concentration is 0.05% by mass or more and 0.9% or less of the carbon concentration of the steel material below the nitride layer.
  • the element content will have a low carbon region equivalent to steel.
  • the low carbon region will be described.
  • the low carbon region is a region having a carbon concentration of 0.05% by mass or more and 0.9 times or less the carbon concentration of the high-strength steel material or high-strength bolt.
  • a low carbon region is formed from the steel material surface to a depth of 100 ⁇ m or more and 1000 ⁇ m.
  • the depth and carbon concentration of the low carbon region are adjusted by the heating atmosphere, the heating temperature, and the holding time in the heat treatment for forming the low carbon region. For example, when the carbon potential of the heating atmosphere is low, the heating temperature is high, and the holding time is long, the low carbon region becomes deep and the carbon concentration in the low carbon region decreases. If the carbon concentration in the low carbon region is less than 0.05% by mass, the lower limit of 0.10% by mass of the carbon concentration of the steel material is not more than half, and the predetermined strength and hardness cannot be ensured in the low carbon region.
  • the low carbon region is defined as a region having a carbon concentration of 0.05% by mass or more and 0.9 times or less the carbon concentration of the steel material.
  • the carbon concentration in the low carbon region is 0.05% by mass or more and 0.9 times or less the carbon concentration of the steel material, the increase in the surface hardness due to the formation of the nitride layer can be reduced.
  • the hardness of the surface layer of the steel material is equal to the hardness of the steel material or lower than the hardness of the steel material, and the reduction of the critical diffusible hydrogen amount can be prevented.
  • the depth (thickness) of the low carbon region was set to a depth (thickness) of 100 ⁇ m or more from the surface of the steel material or bolt so as to obtain the above effect.
  • the depth (thickness) of the low carbon region is preferably as deep (thick) as possible, but if it exceeds 1000 ⁇ m, the strength of the entire steel material or the entire bolt decreases, so the depth (thickness) of the low carbon region is 1000 ⁇ m. Is the upper limit.
  • the nitride layer will be described.
  • the nitride layer is a region having a nitrogen concentration of 12.0% by mass or less and 0.02% by mass or more higher than the nitrogen concentration of the steel material or bolt.
  • the nitride layer is formed with a thickness of 200 ⁇ m or more from the surface of the steel material or bolt.
  • the thickness and nitrogen concentration of the nitride layer can be adjusted by the heating atmosphere, heating temperature, and holding time during the nitriding treatment. For example, when the concentration of ammonia or nitrogen in the heating atmosphere is high, the heating temperature is high, and the holding time is long, the nitride layer becomes thick and the nitrogen concentration of the nitride layer becomes high.
  • the nitrogen concentration in the nitride layer is higher than the nitrogen concentration in the steel material, the amount of hydrogen entering the steel material from the corrosive environment can be reduced, but the difference between the nitrogen concentration in the nitride layer and the nitrogen concentration in the steel material is less than 0.02% by mass. And the effect of reducing the amount of intrusion hydrogen cannot be sufficiently obtained. Therefore, the nitrogen concentration of the nitrided layer is set to a concentration higher than the nitrogen concentration of the steel material by 0.02% by mass or more. On the other hand, if the nitrogen concentration exceeds 12.0% by mass, the hardness of the nitrided layer increases excessively and becomes brittle, so 12.0% by mass was made the upper limit.
  • Corrosion occurs when a nitride layer is formed on the steel surface with a nitrogen concentration of 12.0 mass% or less, 0.02 mass% or more higher than the nitrogen concentration of the steel material, and a depth of 200 ⁇ m or more from the surface.
  • the amount of hydrogen entering the steel from the environment is greatly reduced.
  • the nitrided layer was limited to a thickness (depth) of 200 ⁇ m or more from the surface of the steel material or bolt so that the above effect was obtained.
  • the upper limit of the thickness of the nitrided layer is not particularly specified, but if it exceeds 1000 ⁇ m, the productivity is lowered and the cost is increased, so 1000 ⁇ m or less is preferable.
  • the depth (thickness) of the low carbon region formed in the high-strength steel material or high-strength bolt of the present invention can be determined from the carbon concentration curve from the surface of the steel material or bolt. Polishing the cross section of a steel material or bolt having a low carbon region and a nitride layer on the surface layer, an energy dispersive X-ray fluorescence analyzer (hereinafter sometimes referred to as “EDX”), or a wavelength dispersive X-ray fluorescence analyzer ( Hereinafter, the carbon concentration in the depth direction from the surface is measured by performing a line analysis.
  • FIG. 2 shows a method for obtaining the depth (thickness) of the low carbon region from the carbon concentration curve obtained by EDX. That is, FIG.
  • FIG. 2 is a diagram showing the relationship between the distance from the steel material surface and the carbon concentration obtained by measuring the carbon concentration in the depth direction from the surface using EDX.
  • the carbon concentration increases as the distance (depth) from the steel surface increases. This is because a low carbon region is formed on the steel surface by decarburization.
  • the carbon concentration is substantially constant (average carbon concentration a).
  • the average carbon concentration a is a carbon concentration in a region not affected by the decarburization process, and is equivalent to the carbon amount of the steel material before the decarburization process. Therefore, in the present invention, the chemical analysis value of the carbon concentration of the steel material is used as a reference value for determining the depth of the low carbon region. As shown in FIG.
  • the depth (thickness) of the low carbon region can be evaluated by determining the distance (depth) from the steel material surface at the boundary in the depth direction of the range.
  • the thickness (depth) of the nitride layer can be determined from the change in the nitrogen concentration from the surface of the steel material or bolt as in the low carbon region. Specifically, the cross section of a steel material or bolt having a low carbon region and a nitride layer on the surface layer is polished, and line analysis is performed by EDX or WDS to measure the nitrogen concentration in the depth direction from the surface.
  • FIG. 3 shows a method for determining the thickness (depth) of the nitride layer from the nitrogen concentration curve obtained with an energy dispersive X-ray fluorescence spectrometer (EDX). That is, FIG. 3 is a diagram showing the relationship between the distance from the steel material surface and the nitrogen concentration obtained by measuring the nitrogen concentration in the depth direction from the surface using EDX. As the distance (depth) from the steel material surface increases, the nitrogen concentration decreases, but the carbon concentration is substantially constant (average nitrogen concentration) in a region not affected by nitriding treatment. The average nitrogen concentration is a nitrogen concentration in a range not affected by the nitriding treatment, and is equivalent to the nitrogen amount of the steel material before the nitriding treatment.
  • EDX energy dispersive X-ray fluorescence spectrometer
  • the chemical analysis value of the nitrogen concentration of the steel material is used as a reference value for determining the thickness of the nitride layer.
  • a range in which the nitrogen concentration from the steel surface to the required depth is 0.02% by mass or more of the average nitrogen concentration is determined, and from the steel surface at the boundary in the depth direction of the range.
  • the thickness (depth) of the nitride layer can be evaluated.
  • the depth of the low carbon region and the thickness of the nitrided layer are obtained by simply averaging the values measured at any five points in the cross section of the steel material or bolt.
  • the carbon concentration and the nitrogen concentration of the steel material may be obtained by measuring the carbon concentration and the nitrogen concentration at a position sufficiently deeper than the depth of the low carbon region and the nitrided layer, for example, at a depth of 2000 ⁇ m or more from the surface. Good.
  • an analytical sample may be collected from a position at a depth of 2000 ⁇ m or more from the surface of the steel material or bolt, and obtained by chemical analysis.
  • the formation of a nitride layer in the low carbon region formed on the steel material surface suppresses the amount of intruded hydrogen
  • the steel material surface By forming the low carbon region, the delayed fracture resistance is remarkably improved by a synergistic effect with the increase in the amount of critical diffusible hydrogen.
  • the presence of a nitride layer and a low carbon region on the surface layer of the steel material suppresses the amount of hydrogen entering the steel material to 0.5 ppm or less, and the limit diffusible hydrogen content of the steel material Can be increased to 2.00 ppm or more.
  • C is an essential element for securing the strength of the steel material. If it is less than 0.10%, the required strength cannot be obtained, and if it exceeds 0.55%, ductility and toughness are lowered and delayed fracture resistance is also lowered, so C is 0.10 to 0.00. 55%.
  • Si Si is an element that increases strength by solid solution strengthening. If it is less than 0.01%, the effect of addition is insufficient, and if it exceeds 3%, the effect is saturated, so Si was made 0.01 to 3%.
  • Mn is an element not only for deoxidation and desulfurization but also for increasing the hardenability by lowering the transformation temperature of the pearlite structure or the bainite structure in order to obtain a martensite structure. If it is less than 0.1%, the effect of addition is insufficient. If it exceeds 2%, it segregates at the grain boundary during austenite heating, embrittles the grain boundary, and deteriorates the delayed fracture resistance.
  • the high-strength steel material or high-strength bolt of the present invention contains one or two of V and Mo in order to improve delayed fracture resistance.
  • V is an element for precipitating carbides, nitrides, and / or carbonitride fine precipitates in the steel material.
  • V is an element that contributes to improving the strength by lowering the transformation temperature of the pearlite structure or bainite structure to enhance the hardenability and the softening resistance during the tempering treatment. If V exceeds 1.5%, the solution temperature for precipitation strengthening becomes high, and the force for trapping hydrogen is saturated, so it was made 1.5% or less. If V is less than 0.05%, the effect of improving the strength due to the precipitation of fine precipitates cannot be obtained sufficiently, so 0.05% or more is preferable.
  • Mo is an element that precipitates carbides, nitrides, and / or carbonitride fine precipitates in the steel material. This fine precipitate captures the hydrogen that has entered the steel material, renders it harmless, and acts to increase the amount of critical diffusible hydrogen. Moreover, the fine precipitate contributes to the improvement of the delayed fracture resistance by increasing the critical diffusible hydrogen amount while contributing to the strength improvement of the steel material. Mo is an element that contributes to the improvement of strength by lowering the transformation temperature of the pearlite structure and bainite structure to increase the hardenability and the softening resistance during the tempering treatment. If Mo exceeds 3.0%, the solution temperature for precipitation strengthening becomes high, and the force for capturing hydrogen is saturated, so it was made 3.0% or less.
  • V + 1 / 2Mo In the present invention, Mo and V need to satisfy V + 1 / 2Mo> 0.4%. If V and Mo satisfy the above formula, the amount of V that increases not only the amount of limit diffusible hydrogen but also the amount of invading hydrogen is relatively small with respect to the amount of Mo. Delayed fracture resistance can be obtained.
  • the high-strength steel material or high-strength bolt of the present invention is one or two kinds of Cr, Nb, Cu, Ni, and B as long as the excellent delayed fracture resistance is not excluded for the purpose of improving the strength. You may contain the above.
  • Cr Cr is an element that lowers the transformation temperature of the pearlite structure or bainite structure to increase the hardenability, and increases the softening resistance during the tempering process, thereby contributing to the improvement of the strength. If it is less than 0.05%, the effect of addition cannot be sufficiently obtained, and if it exceeds 1.5%, the toughness is deteriorated, so Cr is made 0.05 to 1.5%.
  • Nb Nb, like Cr, is an element that contributes to improving strength by increasing hardenability and temper softening resistance. If it is less than 0.001%, the effect of addition is not sufficiently obtained, and if it exceeds 0.05%, the effect of addition is saturated, so Nb was made 0.001 to 0.05%.
  • Cu is an element that contributes to improving the hardenability, increasing the temper softening resistance, and improving the strength due to the precipitation effect. If it is less than 0.01%, the effect of addition cannot be sufficiently obtained. If it exceeds 4%, grain boundary embrittlement occurs and the delayed fracture resistance deteriorates, so Cu was made 0.01 to 4%.
  • Ni Ni is an element that increases the hardenability and is effective in improving ductility and toughness that decrease with increasing strength. If it is less than 0.01%, the effect of addition is not sufficiently obtained, and if it exceeds 4%, the effect of addition is saturated, so Ni was made 0.01 to 4%.
  • B is an element that suppresses grain boundary fracture and is effective in improving delayed fracture resistance.
  • B is an element that segregates at the austenite grain boundary and remarkably increases the hardenability.
  • the content is less than 0.0001%, the effect of addition cannot be sufficiently obtained.
  • the content exceeds 0.005%, B carbide or Fe carbon boride is generated at the grain boundary, and grain boundary embrittlement occurs, resulting in delay resistance. Since the fracture characteristics deteriorate, B is set to 0.0001 to 0.005%.
  • the high-strength steel material and high-strength bolt of the present invention are one or two of Al, Ti, Mg, Ca, and Zr as long as the excellent delayed fracture resistance is not excluded for the purpose of refining the structure. It may contain seeds or more.
  • Al is an element that forms oxides and nitrides, prevents coarsening of austenite grains, and suppresses deterioration of delayed fracture resistance. If it is less than 0.003%, the effect of addition is insufficient, and if it exceeds 0.1%, the effect of addition is saturated. Therefore, Al is preferably 0.003 to 0.1%.
  • Ti Ti, like Al, is an element that forms oxides and nitrides to prevent coarsening of austenite grains and suppress deterioration of delayed fracture resistance. If it is less than 0.003%, the effect of addition is insufficient, and if it exceeds 0.05%, Ti carbonitride is coarsened during rolling or processing, or during heat treatment, and the toughness is reduced.
  • Mg has deoxidation and desulfurization effects, and forms Mg oxide, Mg sulfide, Mg-Al, Mg-Ti, Mg-Al-Ti complex oxides and sulfides, etc.
  • Ca has a deoxidizing and desulfurizing effect, and also forms Ca oxide, Ca sulfide, Al, Ti, Mg composite oxide and composite sulfide to prevent austenite grain coarsening. It is an element that suppresses the deterioration of delayed fracture resistance. If it is less than 0.0003%, the effect of addition is insufficient, and if it exceeds 0.01%, the effect of addition is saturated. Therefore, Ca is preferably 0.0003 to 0.01%.
  • Zr forms Zr oxide, Zr sulfide, composite oxide or composite sulfide of Al, Ti, Mg, Zr, etc., prevents austenite grains from coarsening, and deteriorates delayed fracture resistance. It is an element to suppress.
  • the steel structure of the present invention is mainly tempered martensite, it has a good ductility and toughness even when the tensile strength is 1300 MPa or more.
  • the area ratio of tempered martensite in the low carbon region and the region excluding the nitrided layer is 85% or more, and the balance is a structure composed of one or more of retained austenite, bainite, pearlite, and ferrite.
  • the area ratio of tempered martensite is the deeper of the depth at which the carbon concentration is constant in the carbon concentration curve shown in FIG. 2 and the depth at which the nitrogen concentration is constant in the nitrogen concentration curve shown in FIG. Measure with For example, the area ratio of tempered martensite may be measured at a depth of 2000 ⁇ m or more from the surface of the steel material or bolt, or at a site that is 1/4 of the thickness or diameter of the steel material.
  • the area ratio of martensite can be obtained by observing the C cross section of a steel material using an optical microscope and measuring the area of martensite per unit area. Specifically, the C cross section of the steel material is polished and etched with a nital etchant, the area of martensite in five fields in the range of 0.04 mm 2 is measured, and the average value is calculated. Further, in the steel material of the present invention, the compressive residual stress on the steel material surface is generated by heating and rapid cooling during the nitriding treatment, thereby improving delayed fracture resistance. When the compressive residual stress is 200 MPa or more, the delayed fracture resistance is improved. Therefore, the compressive residual stress on the surface of the steel of the present invention is preferably 200 MPa or more.
  • the compressive residual stress can be measured using an X-ray residual stress measuring device. Specifically, the residual stress on the steel material surface is measured, and then the steel material surface is etched by 25 ⁇ m by electropolishing to measure the residual stress in the depth direction. It is preferable to measure three arbitrary points and use the average value.
  • the tensile strength is 1300 MPa or more
  • the occurrence frequency of delayed fracture is remarkably increased. Therefore, when the tensile strength is 1300 MPa or more, the delayed fracture resistance of the steel material of the present invention in which the low carbon region and the nitride layer are formed on the surface layer is remarkably excellent.
  • the manufacturing method of the steel material of the present invention includes a decarburization process in which a decarburization process is performed by heating a steel material (wire material, PC steel rod, steel material processed into a predetermined shape) having a required component composition, and a decarburized steel material.
  • the structure of the steel material of the present invention becomes a structure mainly composed of tempered martensite by the nitriding step.
  • the steel material of the present invention is decarburized, and the carbon concentration is 0.05% or more and 0.9 times or less of the carbon concentration of the steel material from the surface of the steel material to a depth of 100 ⁇ m or more and 1000 ⁇ m or less. To do.
  • the atmosphere of the heating furnace can be weakly decarburized by adjusting the concentration of methane gas to form a low carbon region.
  • the heating temperature in the decarburization treatment is preferably Ac 3 to 950 ° C. By heating to Ac 3 or higher, the steel structure becomes austenite, decarburization from the surface layer is promoted, and a low carbon region can be easily formed.
  • the upper limit of the heating temperature is preferably 950 ° C. from the viewpoint of suppressing coarsening of crystal grains and improving delayed fracture resistance.
  • the holding time at the heating temperature is preferably 30 to 90 minutes. By maintaining at the above heating temperature for 30 minutes or more, the depth of the low carbon region can be sufficiently secured and the steel structure can be made homogeneous.
  • the holding time at the heating temperature is preferably 90 minutes or less.
  • the heated steel material is cooled to a martensite-based structure.
  • the heated steel material may be quenched with oil as it is.
  • the area ratio of tempered martensite is preferably 85% or more in the steel structure of the present invention
  • the area ratio of martensite after quenching is preferably 85% or more.
  • nitriding treatment is performed on a steel material whose steel structure is mainly martensite and a low carbon region is formed on the surface layer.
  • a nitride layer having a thickness from the steel surface of 200 ⁇ m or more and a nitrogen concentration of 12.0% or less and 0.02% or more higher than the nitrogen concentration of the steel material is formed.
  • Tempering is performed to make the steel structure a structure mainly composed of tempered martensite and to precipitate fine precipitates that capture hydrogen.
  • the steel material contains one or both of V and Mo, fine carbides, nitrides, and / or carbonitrides (fine particles) that act to trap hydrogen in the nitriding step. Precipitate).
  • the nitriding treatment is performed, for example, by heating a steel material in an atmosphere containing ammonia or nitrogen.
  • the nitriding treatment is preferably held at 500 ° C. or higher and 650 ° C. or lower for 30 to 90 minutes. If the nitriding temperature exceeds 650 ° C., the strength of the steel material decreases, so the nitriding temperature is set to 650 ° C. or lower. If the nitriding temperature is 500 ° C.
  • the nitriding temperature is set to be over 500 ° C. Further, if the temperature of the nitriding treatment exceeds 500 ° C., the time required for diffusion of nitrogen from the steel material surface is shortened, the treatment time is shortened, and the productivity is increased. If the nitriding time is less than 30 minutes, the depth of the nitrided layer may not reach 200 ⁇ m or more from the surface, so the nitriding time is preferably 30 minutes or longer. Although the upper limit of the nitriding time is not specified, since the nitriding temperature is high in the present invention, a sufficiently thick nitride layer can be formed even in 90 minutes or less.
  • nitriding step a general nitriding method such as a gas nitriding method, a gas soft nitriding method, a plasma nitriding method, or a salt bath nitriding method can be used.
  • a method for producing the high-strength bolt of the present invention hereinafter sometimes referred to as “the bolt of the present invention”.
  • the manufacturing method of the bolt according to the present invention includes a processing step for processing the steel material according to the present invention into a bolt, a decarburizing step for heating and decarburizing the bolt, cooling the heated bolt, and It consists of a quenching process with a site-based structure and a nitriding process in which the quenched bolt is nitrided at a temperature of more than 500 ° C. and 650 ° C. or less.
  • the steel structure of the bolt becomes a structure mainly composed of tempered martensite.
  • a wire material that is a steel material may be cold-forged and rolled into a bolt shape.
  • the manufacturing method of the bolt of the present invention differs from the manufacturing method of the steel material of the present invention only in the processing step of processing the steel material into a bolt shape, the description of the other steps is omitted.
  • the compressive residual stress on the surface of the steel material or bolt can be set to 200 MPa or more. Due to the presence of this compressive residual stress, the delayed fracture resistance is further improved.
  • the atmosphere in the heating furnace was controlled to be weakly decarburized, and quenching was oil-cooled so that the cooling rate in the range of 700 to 300 ° C. was 5 ° C./s or more.
  • the depth of the low carbon region was adjusted by the carbon potential of the furnace atmosphere, the heating temperature and the holding time.
  • the steel material was subjected to nitriding treatment to form a nitrided layer by gas soft nitriding. After nitriding, the range of 500 to 200 ° C. was quenched at the cooling rate shown in Table 2 (cooling rate after tempering). 1 to 25 high strength steel materials were obtained.
  • the nitriding treatment was performed at a temperature shown in Table 2 with an ammonia volume ratio in the treatment gas atmosphere of 30 to 50% and a treatment time of 30 to 90 minutes.
  • the thickness of the nitride layer was adjusted by changing the heating temperature and holding time.
  • the nitrogen concentration of the nitride layer was adjusted by changing the ammonia volume ratio in the processing gas atmosphere.
  • Steel materials (wires) shown in Table 1 were processed into bolts and manufactured No. In the same process as the high-strength steel materials (wires) 1 to 25, the production No. 26 to 40 high-strength bolts were obtained.
  • the nitriding treatment was performed in the temperature range shown in Table 3, and after the nitriding treatment, the range of 500 to 200 ° C.
  • the C section of 26 to 40 high-strength bolts was polished and etched with a nital etchant, and using an optical microscope, the area of martensite with 5 visual fields in the range of 0.04 mm 2 was measured. did.
  • the remaining structure of the tempered martensite was one or more of retained austenite, bainite, pearlite, and ferrite.
  • Tensile strength The tensile strength was measured according to JIS Z 2241. Low carbon region depth and nitride layer thickness No. 1 to 25 high strength steel and production No.
  • the cross-sections of 26 to 40 high-strength bolts were polished, and the carbon concentration and the nitrogen concentration in the depth direction from the surface were measured at any five locations in the longitudinal direction using EDX.
  • the depth (thickness) of the region where the carbon concentration is 0.9 times or less the carbon concentration of the steel material ((carbon concentration in the low carbon region / carbon concentration in the steel material) ⁇ 0.9) is expressed as “low carbon region depth.
  • the depth (thickness) of the region where the nitrogen concentration is 0.02% or more higher than the nitrogen concentration of the steel material is referred to as “nitride layer thickness”. did.
  • the depth of the low carbon region and the thickness of the nitride layer were average values of values measured at arbitrary five locations in the longitudinal direction.
  • Compressive residual stress The compressive residual stress of the surface was measured using an X-ray residual stress measuring apparatus. Production No. 1 to 25 high-strength steel materials and production no. After measuring the residual stress on the surface of 26 to 40 high-strength bolts, the surface was etched by 25 ⁇ m by electrolytic polishing, and the residual stress in the depth direction was measured. The compressive residual stress was an average value of values measured at three arbitrary locations. Limiting diffusible hydrogen content and delayed fracture resistance No. 1 to 25 high strength steel and production No. A delayed fracture specimen having the shape shown in FIG.
  • the balance weight 2 is arranged at one end of the lever having the fulcrum 3 as a fulcrum, and the test piece 1 is arranged at the other end.
  • the test was conducted. And as shown in FIG.1 (b), the maximum value of the diffusible hydrogen amount of the test piece 1 which did the constant load delayed fracture test for 100 hours or more and did not fracture
  • the amount of diffusible hydrogen in test piece 1 the delayed fracture test piece was heated at 100 ° C./h, and the integrated value of the amount of hydrogen released between room temperature and 400 ° C. was measured with a gas chromatograph.
  • the delayed fracture resistance indicates “no delayed fracture” when the intrusion hydrogen amount shown in Table 2 and Table 3 is less than the limit diffusible hydrogen amount, and when the intrusion hydrogen amount is equal to or greater than the limit diffusible hydrogen amount. It was evaluated that there was delayed fracture.
  • Intrusion hydrogen amount The intrusion hydrogen amount is determined according to the production no. No. 1 to 25 high strength steel and production No.
  • Test pieces of 26 to 40 high-strength bolts were prepared, and 30 cycles of the corrosion acceleration test using the temperature / humidity / time pattern shown in FIG. 6 were performed. After removing the corrosion layer on the surface of the test piece by sand blasting, hydrogen analysis was performed by a temperature rising method, and the amount of hydrogen released from room temperature to 400 ° C. was measured to determine the amount of invading hydrogen. As shown in Table 2, the production No. of the invention example.
  • high-strength steel materials have a low carbon region depth of 100 ⁇ m or more and a nitrided layer thickness of 200 ⁇ m or more, all of which have a tensile strength of 1300 MPa or more and an intrusion hydrogen amount of 0.5 ppm or less.
  • the amount of ionic hydrogen was 2.00 ppm or more and the amount of invading hydrogen was less than the limit diffusible hydrogen amount, indicating “no delayed fracture”.
  • Each of the high strength steel materials 1 to 15 had a tempered martensite ratio of 50% or more, and was a tempered martensite-based structure.
  • production No. All the high strength steel materials 1 to 15 had a compressive residual stress of 200 MPa or more.
  • the production No. No. 16 high-strength steel material is an example in which the amount of C, the amount of Si and the amount of Mn are small and the strength is low.
  • Production No. No. 17 has a large amount of C.
  • No. 18 has a large amount of Mn.
  • No. 19 has a large amount of Cr.
  • No. 21 has a large amount of Cu.
  • No. 22 has a large amount of B.
  • No. 20 is an example in which the amount of critical diffusible hydrogen is low because “V + 1 / 2Mo” is low, resulting in “with delayed fracture”.
  • Production No. 23 is an example in which the heating time for quenching is short, the depth of the low carbon region is less than 100 ⁇ m, the amount of critical diffusible hydrogen is low, and “delayed fracture occurs”.
  • Production No. No. 24 is an example in which the time for the nitriding treatment is short, the nitrided layer thickness is less than 200 ⁇ m, the amount of invading hydrogen is large, and “delayed fracture occurs”.
  • Production No. In No. 25 since the concentration of ammonia in the nitriding gas was lowered, the difference in nitrogen concentration with the steel material was 0.01% by mass in the region from the surface to a depth of 200 ⁇ m, and the amount of invading hydrogen was large. This is an example.
  • High strength bolts of 26 to 40 have a low carbon region depth of 100 ⁇ m or more, a nitrided layer thickness of 200 ⁇ m or more, all of which have a tensile strength of 1300 MPa or more, an intrusion hydrogen amount of 0.5 ppm or less, and limit diffusion.
  • the amount of ionic hydrogen was 2.00 ppm or more and the amount of invading hydrogen was less than the limit diffusible hydrogen amount, indicating “no delayed fracture”.
  • Each of the high-strength bolts of 26 to 40 had a tempered martensite ratio of 50% or more, a tempered martensite-based structure, and a compressive residual stress of 200 MPa or more.
  • high-strength steel materials wire rods, PC steel rods
  • high-strength bolts that exhibit excellent delayed fracture resistance even in severe corrosive environments, and these can be manufactured at low cost.
  • a manufacturing method can be provided. Therefore, the present invention has extremely high applicability in the steel material manufacturing and use industries.
  • test piece 2 balance weight 3 fulcrum

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PCT/JP2011/056481 2010-03-11 2011-03-11 耐遅れ破壊特性に優れた高強度鋼材と高強度ボルト、及び、その製造方法 WO2011111872A1 (ja)

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Cited By (9)

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WO2014014540A3 (en) * 2012-04-27 2014-03-27 Crs Holdings, Inc. High strength, high toughness steel alloy
CN104395489A (zh) * 2012-06-20 2015-03-04 新日铁住金株式会社 油井管用钢及其制造方法
WO2018230717A1 (ja) * 2017-06-15 2018-12-20 新日鐵住金株式会社 ばね鋼用圧延線材
JP2020176286A (ja) * 2019-04-16 2020-10-29 高周波熱錬株式会社 耐遅れ破壊特性に優れたｐｃ鋼材及びその製造方法
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Families Citing this family (29)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US9598760B2 (en) * 2011-02-23 2017-03-21 Dowa Thermotech Co., Ltd. Nitrided steel member and manufacturing method thereof
CN104781440B (zh) * 2012-11-05 2018-04-17 新日铁住金株式会社 抗硫化物应力裂纹性优异的低合金油井管用钢及低合金油井管用钢的制造方法
CN102943210B (zh) * 2012-11-09 2015-02-04 谢亚平 一种高强度螺栓及其加工方法
KR20140121229A (ko) * 2013-04-05 2014-10-15 태양금속공업주식회사 인장강도가 우수한 고강도 볼트의 제조방법
TWI551697B (zh) 2013-06-07 2016-10-01 Nippon Steel & Sumitomo Metal Corp Heat treatment steel and its manufacturing method
NL2011269C2 (en) * 2013-08-05 2015-02-09 Onderzoekscentrum Voor Aanwending Van Staal N V Structure for use in a corrosive environment.
JP6422176B2 (ja) * 2014-08-29 2018-11-14 日産自動車株式会社 高強度ボルト用鋼及び高強度ボルト
CN104313492B (zh) * 2014-11-07 2017-04-12 广东鼎耀工程技术有限公司 一种具有高强度韧性的pc钢棒及其热处理方法
DE102014017275A1 (de) * 2014-11-18 2016-05-19 Salzgitter Flachstahl Gmbh Hochfester lufthärtender Mehrphasenstahl mit hervorragenden Verarbeitungseigenschaften und Verfahren zur Herstellung eines Bandes aus diesem Stahl
EP3315626B1 (en) * 2015-06-29 2020-12-23 Nippon Steel Corporation Bolt
CN105861919A (zh) * 2016-06-14 2016-08-17 江苏永昊高强度螺栓有限公司 高强度螺栓的生产工艺
EP3483293B1 (en) * 2016-07-05 2024-08-28 Nippon Steel Corporation Rolled wire rod
CN106521316B (zh) * 2016-11-15 2018-08-07 江阴兴澄特种钢铁有限公司 一种紧固件用高淬透性中碳低合金圆钢及其制造方法
CN106756516B (zh) * 2017-02-07 2018-06-08 和县隆盛精密机械有限公司 一种适用于机械臂锁紧螺栓的合金铸件及其铸造工艺
CN107058705A (zh) * 2017-02-17 2017-08-18 江苏佳杰特种螺钉有限公司 一种应用在高铁上的紧固件的生产工艺
RU2635641C1 (ru) * 2017-03-28 2017-11-14 Юлия Алексеевна Щепочкина Литейная сталь
CN107513664A (zh) * 2017-07-10 2017-12-26 安徽长江紧固件有限责任公司 一种扭剪型高强度螺栓及其加工工艺
CN107604243B (zh) * 2017-08-09 2019-10-08 宁波市镇海甬鼎紧固件制造有限公司 一种高强度螺栓材料及其制备方法
JP2019124481A (ja) * 2018-01-12 2019-07-25 株式会社神戸製鋼所 残留応力測定方法
US11708622B2 (en) * 2018-01-30 2023-07-25 Nissan Motor Co., Ltd. Bolt and fastened structure
JP7134411B2 (ja) 2018-01-30 2022-09-12 日産自動車株式会社 ボルト
CN109266964B (zh) * 2018-10-25 2021-03-05 青岛天赢智能工业股份有限公司 一种钢锻件生产加工工艺
CN113322410B (zh) * 2020-02-28 2022-06-28 宝山钢铁股份有限公司 一种耐延迟断裂性能优异的高强度螺栓用钢及其制备方法
CN111931309B (zh) * 2020-08-24 2022-09-09 长江水利委员会长江科学院 一种锚杆/锚索结构拉伸硬化软化断裂模拟的方法
CN112795854A (zh) * 2020-12-23 2021-05-14 石家庄钢铁有限责任公司 高强度紧固件螺栓用钢及其生产方法
CN115433871B (zh) * 2021-06-02 2023-07-07 宝山钢铁股份有限公司 一种耐氢脆延迟断裂的高强度钢及其制造方法
CN114058974B (zh) * 2021-11-30 2022-09-13 马鞍山钢铁股份有限公司 一种15.9级耐腐蚀高强度螺栓用钢及其生产方法和热处理方法
CN117230363A (zh) * 2022-06-07 2023-12-15 宝山钢铁股份有限公司 一种高淬透性结构钢及其制造方法
CN115386803B (zh) * 2022-08-31 2023-07-25 马鞍山钢铁股份有限公司 一种高强韧性风电螺栓用非调质钢及其生产方法

Citations (3)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
JPH10141341A (ja) * 1996-11-13 1998-05-26 Nkk Corp 遅れ破壊特性に優れた高強度ボルト
JPH10226817A (ja) * 1996-12-11 1998-08-25 Sumitomo Metal Ind Ltd 軟窒化用鋼材の製造方法及びその鋼材を用いた軟窒化部品
JP2009299180A (ja) * 2008-05-13 2009-12-24 Nippon Steel Corp 耐遅れ破壊特性に優れた高強度鋼材、高強度ボルト及びその製造方法

Family Cites Families (6)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
JPH08165557A (ja) * 1994-12-13 1996-06-25 Sumitomo Metal Ind Ltd 耐ピッチング性軟窒化歯車の製造方法
JP3754788B2 (ja) * 1997-03-12 2006-03-15 中央発條株式会社 耐遅れ破壊性に優れたコイルばね及びその製造方法
JP2000337332A (ja) * 2000-01-01 2000-12-05 Kobe Steel Ltd 耐遅れ破壊性に優れた高強度ボルト
JP2000337334A (ja) * 2000-01-01 2000-12-05 Kobe Steel Ltd 耐遅れ破壊性に優れた高強度ボルト
JP3851533B2 (ja) * 2001-10-05 2006-11-29 株式会社神戸製鋼所 高強度非調質アプセットボルト用線材およびその製造方法並びに高強度非調質アプセットボルトの製造方法
JP5251633B2 (ja) * 2008-05-13 2013-07-31 新日鐵住金株式会社 耐遅れ破壊特性に優れた高強度鋼材、高強度ボルト及びその製造方法

Patent Citations (3)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
JPH10141341A (ja) * 1996-11-13 1998-05-26 Nkk Corp 遅れ破壊特性に優れた高強度ボルト
JPH10226817A (ja) * 1996-12-11 1998-08-25 Sumitomo Metal Ind Ltd 軟窒化用鋼材の製造方法及びその鋼材を用いた軟窒化部品
JP2009299180A (ja) * 2008-05-13 2009-12-24 Nippon Steel Corp 耐遅れ破壊特性に優れた高強度鋼材、高強度ボルト及びその製造方法

Cited By (20)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
WO2014014540A3 (en) * 2012-04-27 2014-03-27 Crs Holdings, Inc. High strength, high toughness steel alloy
CN104395489A (zh) * 2012-06-20 2015-03-04 新日铁住金株式会社 油井管用钢及其制造方法
EP2865775A4 (en) * 2012-06-20 2015-08-19 Nippon Steel & Sumitomo Metal Corp STEEL FOR AN OIL CORE TUBE AND METHOD FOR THE MANUFACTURE THEREOF
US10407758B2 (en) 2012-06-20 2019-09-10 Nippon Steel Corporation Steel for oil country tubular goods and method of producing the same
WO2018230717A1 (ja) * 2017-06-15 2018-12-20 新日鐵住金株式会社 ばね鋼用圧延線材
JP6447799B1 (ja) * 2017-06-15 2019-01-09 新日鐵住金株式会社 ばね鋼用圧延線材
US11118251B2 (en) 2017-06-15 2021-09-14 Nippon Steel Corporation Rolled wire rod for spring steel
JP2020176286A (ja) * 2019-04-16 2020-10-29 高周波熱錬株式会社 耐遅れ破壊特性に優れたｐｃ鋼材及びその製造方法
JP7479794B2 (ja) 2019-04-16 2024-05-09 高周波熱錬株式会社 耐遅れ破壊特性に優れたｐｃ鋼材及びその製造方法
WO2020230872A1 (ja) * 2019-05-14 2020-11-19 日本製鉄株式会社 ボルト、及びボルト用鋼材
JP2020190027A (ja) * 2019-05-14 2020-11-26 日本製鉄株式会社 ボルト、及びボルト用鋼材
JPWO2020230872A1 (enrdf_load_stackoverflow) * 2019-05-14 2020-11-19
JP7464832B2 (ja) 2019-05-14 2024-04-10 日本製鉄株式会社 ボルト、及びボルト用鋼材
JP7164032B2 (ja) 2019-05-14 2022-11-01 日本製鉄株式会社 ボルト、及びボルト用鋼材
JPWO2021106086A1 (enrdf_load_stackoverflow) * 2019-11-26 2021-06-03
JP7360060B2 (ja) 2019-11-26 2023-10-12 日本製鉄株式会社 鋼及び軸受
WO2021106086A1 (ja) * 2019-11-26 2021-06-03 日本製鉄株式会社 鋼及び軸受
CN116445829B (zh) * 2023-06-16 2023-09-08 中国矿业大学(北京) 一种抗腐蚀锚杆及其生产工艺
CN116445829A (zh) * 2023-06-16 2023-07-18 中国矿业大学(北京) 一种抗腐蚀锚杆及其生产工艺
CN118516613A (zh) * 2024-06-19 2024-08-20 邯郸市睿智紧固件制造有限公司 一种高强度螺栓

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