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High-strength bolt

A high-strength bolt, tensile strength technology, applied in the direction of screws, threaded fasteners, furnace types, etc., can solve the problem of increased manufacturing cost, and achieve the effect of high strength and excellent resistance to hydrogen embrittlement

Inactive Publication Date: 2018-07-17
NIPPON STEEL CORP
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  • Abstract
  • Description
  • Claims
  • Application Information

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Problems solved by technology

In this case, sometimes the manufacturing cost increases substantially

Method used

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Embodiment

[0139] Molten steel having the chemical composition of Table 2 was produced.

[0140] [Table 2]

[0141]

[0142] Referring to Table 2, as described above, Steel L has a chemical composition corresponding to SCM435 of JIS G4053 (2008).

[0143] Short bars with a cross-section of 162 mm×162 mm were produced by continuous casting using molten steel. Hot working (hot rolling) was performed on the short bar steel to produce a wire rod with a diameter of 11.5 mm.

[0144] The wire rods of the test numbers shown in Table 3 were subjected to wire drawing to manufacture steel wires. At this time, heat treatment for the purpose of softening is performed. The heat treatment temperature is 750°C, the heat treatment time is 60 minutes, and slow cooling is performed after the heat treatment. Furthermore, after degreasing and pickling, zinc phosphate treatment (75°C, immersion time 600 seconds) and metal soap treatment (80°C, immersion time 180 seconds) are performed to form a zinc p...

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Abstract

Provided is a high-strength bolt having high strength and exceptional hydrogen embrittlement resistance. The bolt according to the present invention has a chemical composition comprising 0.22-0.40% bymass of C, 0.10-1.50% by mass of Si, 0.20% by mass to less than 0.40% by mass of Mn, 0.020% by mass or less of P, 0.020% by mass or less of S, 0.70-1.45% by mass of Cr, 0.005-0.060% by mass of Al, 0.010-0.045% by mass of Ti, 0.0003-0.0040% by mass of B, 0.0015-0.0080% by mass of N, and 0.0020% by mass or less of O, and the remainder comprising Fe and impurities. The chemical composition satisfiesformulae (1) and (2), and the bolt has a tensile strength of 1000-1300 MPa. (1) 0.50 <= C + Si / 10 + Mn / 5 + 5Cr / 22 <= 0.85 (2) Si / Mn > 1.0 Each of the symbols for the elements in formulae (1) and (2)is assigned with the corresponding content content (mass%).

Description

technical field [0001] The present invention relates to a bolt, in particular, to a high-strength bolt. Background technique [0002] In recent years, in order to cope with environmental problems and the like, weight reduction and high strength of members used in automobiles, industrial machines, buildings, and the like have been demanded. In particular, bolts for automobiles represented by engine cylinder head bolts and connecting rod bolts require a tensile strength of 1000 MPa or more. [0003] However, when the tensile strength of the bolt reaches a high strength of 1000 MPa or more, the susceptibility to hydrogen embrittlement increases, and the hydrogen embrittlement resistance (delayed fracture) characteristic decreases. As a raw material for such high-strength bolts, SCM steel (JIS standard) containing a large amount of alloy elements such as Mo, alloy steel containing high-value alloy elements such as V, and the like can be used. These alloy steels are made into w...

Claims

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Application Information

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Patent Type & Authority Applications(China)
IPC IPC(8): C22C38/00C22C38/54F16B35/00C21D9/00
CPCC21D1/18C21D6/004C21D6/005C21D6/008C21D8/005C21D9/0093C22C38/001C22C38/002C22C38/02C22C38/04C22C38/06C22C38/42C22C38/44C22C38/46C22C38/48C22C38/50C22C38/54F16B35/00C22C38/28C22C38/32
Inventor 根石豊佐野直幸松井直树
Owner NIPPON STEEL CORP
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