High-strength bolt superior in delayed fracture and resistance and relaxation resistance

a high-strength bolt, delayed fracture technology, applied in the direction of screws, heat treatment equipment, furniture, etc., can solve the problems of reducing the use range, difficult to specify the reasons indiscriminately, and common high-strength bolts used in automobiles and various industrial machines have a risk of delayed fracture, etc., to achieve the effect of reducing the content of proeutectoid cementite, preventing precipitation of proeutecto
US20070187003A1Inactive Publication Date: 2007-08-16HONDA MOTOR CO LTD +2
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Patent Information

Authority / Receiving Office
US · United States
Patent Type
Applications(United States)
Current Assignee / Owner
HONDA MOTOR CO LTD
Publication Date
2007-08-16
Estimated Expiration
Not applicable · inactive patent

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Abstract

Disclosed is a high-strength bolt having a tensile strength of 1,200 N / mm2 or more and superior in delayed fracture resistance and relaxation resistance, prepared by wire-drawing a bolt steel containing the following elements: C: 0.5 to 1.0% (mass %, the same shall apply hereinafter), Si: 0.55 to 3%, Mn: 0.2 to 2%, P: 0.03% or less (but not 0%), S: 0.03% or less (but not 0%), and Al: 0.3% or less (but not 0%), and containing proeutectoid ferrite, proeutectoid cementite, bainite and martensite at a total areal rate of less than 20% and pearlite in balance; cold-heading the wire into a bolt shape; and then bluing the bolt in a temperature range of 100 to 500° C.
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Description

TECHNICAL FIELD

[0001] The present invention relates to a high-strength bolt mainly for use in automobiles, and in particular to a high-strength bolt having a tensile strength (strength) of 1,200 N / mm2 or more that is superior in delayed fracture resistance and relaxation resistance. BACKGROUND ART

[0002] Carbon alloy steels (such as SCM435, SCM440, and SCr440) are used for common high-strength bolts, and these bolts are given a desirable strength by quenching and tempering. However, common high-strength bolts used in automobiles and various industrial machines have a risk of generating delayed fracture when they have a tensile strength in the range above approximately 1,200 N / mm2, and thus, have restriction in use.

[0003] The delayed fracture includes both phenomena occurring in corrosive and noncorrosive environments, and the reasons for its occurrence are said to be complicated by various factors, and thus, it is difficult to specify the reasons indiscriminately. The regulatory f...

Claims

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