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JP-7856897-B2 - bolt

JP7856897B2JP 7856897 B2JP7856897 B2JP 7856897B2JP-7856897-B2

Inventors

  • 梅原 美百合
  • 小林 由起子
  • 谷口 俊介
  • 山▲崎▼ 真吾
  • 松井 直樹
  • 崎山 裕嗣

Assignees

  • 日本製鉄株式会社

Dates

Publication Date
20260512
Application Date
20220913

Claims (5)

  1. In mass percent, C: 0.30-0.50%, Si: more than 0.30 to 1.50%, Mn: 0.10 to 1.50%, P: 0.030% or less, S: 0.030% or less, Cr: 0.01-0.80%, Mo: 0.70-1.50% V: 0.01-0.50%, Al: 0.005–0.100%, and, N: Contains 0.0010 to 0.0300%, The remainder consists of Fe and impurities. The tensile strength TS is 1300 MPa or more. The number density ND of the MC-type carbide is 2.0 × 10²² particles/ m³ or more. When the atomic percentage of C in the MC-type carbide is defined as [C], the atomic percentage of Mo is defined as [Mo], and the atomic percentage of V is defined as [V], the C ratio Rc defined by formula (1) is 0.30 to 0.42. bolt. Rc=[C]/([C]+[Mo]+[V]) (1)
  2. In mass percent, C: 0.30-0.50%, Si: more than 0.30 to 1.50%, Mn: 0.10 to 1.50%, P: 0.030% or less, S: 0.030% or less, Cr: 0.01-0.80%, Mo: 0.70-1.50% V: 0.01-0.50%, Al: 0.005–0.100%, and, N: Contains 0.0010 to 0.0300%, Furthermore, it contains one or more elements selected from the groups consisting of Group 1 to Group 3, with the remainder being Fe and impurities. The tensile strength TS is 1300 MPa or more. The number density ND of the MC-type carbide is 2.0 × 10²² particles/ m³ or more. When the atomic percentage of C in the MC-type carbide is defined as [C], the atomic percentage of Mo is defined as [Mo], and the atomic percentage of V is defined as [V], the C ratio Rc defined by formula (1) is 0.30 to 0.42. bolt. Rc=[C]/([C]+[Mo]+[V]) (1) [Group 1] Cu: 0.40% or less, Ni: 0.40% or less, B: 0.0100% or less, Zr: 0.300% or less, Hf: 0.100% or less, Ta: 0.100% or less, One or more selected from the group consisting of W: 0.20% or less [Group 2] Ti: 0.100% or less, One or more selected from the group consisting of Nb: 0.100% or less [Group 3] Ca: 0.0050% or less, Bi: 0.020% or less, One or more selected from the group consisting of Te: 0.010% or less.
  3. A bolt according to claim 2, The first group contains, bolt.
  4. A bolt according to claim 2, The following include the second group: bolt.
  5. A bolt according to claim 2, The following contain the third group: bolt.

Description

This disclosure relates to bolts. Bolts are used in industrial machinery, automobiles, and buildings such as bridges. In recent years, with the increasing performance of industrial machinery and automobiles, and the growing size of buildings, there has been a demand for higher-strength bolts. Specifically, bolts with a tensile strength of 1300 MPa or more are required. Bolts with such high strength exhibit increased susceptibility to hydrogen embrittlement. Therefore, excellent resistance to hydrogen embrittlement is required for high-strength bolts. Japanese Patent Publication No. 2019-218584 (Patent Document 1), International Publication No. 2017/094487 (Patent Document 2), and Japanese Patent Publication No. 2013-163865 (Patent Document 3) propose bolts having high strength and excellent resistance to hydrogen embrittlement. The bolt disclosed in Patent Document 1 has the following composition by mass%, C: 0.22-0.40%, Si: 0.10-1.50%, Mn: less than 0.20-0.40%, Cr: less than 0.70-1.60%, Al: 0.005-0.060%, Ti: 0.010-0.050%, B: 0.0003-0.0040%, N: 0.0015-0.0080%, Cu: 0.50% or less, Ni: 0.30% or less, M The material contains o: 0.05% or less, V: 0.050% or less, Nb: 0.050% or less, and further contains one or more selected from the group consisting of Sb: 0.001 to 0.100%, Sn: 0.001 to 0.100%, and Bi: 0.001 to 0.100%, and further contains O: 0.0020% or less, P: 0.020% or less, S: 0.020% or less, with the remainder being Fe and impurities. This bolt further satisfies formula (1) (0.50 ≤ C + (1/10) × Si + (1/5) × Mn + (5/22) × Cr ≤ 0.85) and formula (2) (0.003 ≤ Sb + Sn + Bi ≤ 0.100). Patent Document 1 states that in this bolt, by adjusting the content of Sb, Sn, and Bi in the chemical composition to satisfy formula (2), excellent hydrogen embrittlement resistance can be obtained even if the tensile strength of the shaft portion is 1000 to 1300 MPa. The bolt disclosed in Patent Document 2 contains, by mass%, C: 0.22 to 0.40%, Si: 0.10 to 1.50%, Mn: less than 0.20 to 0.40%, P: 0.020% or less, S: 0.020% or less, Cr: 0.70 to 1.45%, Al: 0.005 to 0.060%, Ti: 0.010 to 0.045%, B: 0.0003 to 0.0040%, N: 0.0015 to 0.0080%, O: 0.0020% or less, Cu: 0 to 0.50%, Ni: 0 to 0.30%, Mo: 0 to 0.04%, V: 0 to 0.05%, and Nb: 0 to 0.050%, with the remainder being Fe and impurities. This bolt also satisfies equation (1) (0.50 ≤ C + Si/10 + Mn/5 + 5Cr/22 ≤ 0.85) and equation (2) (Si/Mn > 1.0). Patent Document 2 states that this bolt increases the strength of the bolt to 1000 to 1300 MPa by satisfying formula (1), and improves the hydrogen embrittlement resistance of the bolt by satisfying formula (2). The bolt disclosed in Patent Document 3 contains, by mass%, C: 0.30 to 0.50%, Si: 1.0 to 2.5%, Mn: 0.1 to 1.5%, P: 0.015% or less (excluding 0%), S: 0.015% or less (excluding 0%), Cr: 0.15 to 2.4%, Al: 0.10% or less (excluding 0%), and N: 0.015% or less (excluding 0%), and further contains Cu: 0.10 to 0.50% and Ni: 0.1 to 1.0% such that [Ni]/[Cu] ≥ 0.5, and further contains Ti: 0.05 to 0.20% and V: 0.20% or less (including 0%) such that [Ti] + [V] : 0.085 to 0.30%, with the remainder being Fe and impurities. Furthermore, this bolt has an austenite grain size number of 9.0 or higher in the bolt shaft, and the G value (%), which indicates the proportion of carbides precipitated at the austenite grain boundaries in the bolt shaft, satisfies formula (1) (G value: (L/L0) × 100 ≤ 60, where L is the total length of carbides with a thickness of 50 nm or more precipitated at the austenite grain boundaries, and L0 is the length of the austenite grain boundary). Patent Document 3 states that this bolt achieves excellent hydrogen embrittlement resistance even at high strength by suppressing the precipitation of carbides at the grain boundaries. Japanese Patent Publication No. 2019-218584International Publication No. 2017/094487Japanese Patent Publication No. 2013-163865 Figure 1 is a side view showing an example of a bolt according to this embodiment.Figure 2 shows the relationship between the carbon ratio Rc in the MC-type carbide and the critical hydrogen content in a bolt in which the content of each element in the chemical composition is within the range of this embodiment, the tensile strength TS is 1300 MPa or more, and the number density ND of the MC-type carbide is 2.0 × 10²² particles/ m³ or more. The inventors investigated bolts possessing a tensile strength (TS) of 1300 MPa or higher and excellent hydrogen embrittlement resistance. As a result, the inventors obtained the following findings. First, the inventors investigated bolts with high strength and excellent hydrogen embrittlement resistance from the viewpoint of chemical composition. As a result, the inventors found that the following composition (in mass%) is desirable: C: 0.30-0.50%, Si: greater than 0.30-1.50%, Mn: 0.10-1.50%, P: 0.030% or less, S: 0.030% or less, Cr: 0.01-0.80%, Mo: less than 0.70-1.50%, V: 0.01-0.50%, Al: 0.005-0.100%, N: 0.0010-0.0300%, Cu: 0-0.40%, Ni: 0-0.40%, B: 0