STP370

    Ultrahigh-Strength Steel Fasteners

    Published: Jan 1965


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    Abstract

    Bolts with tensile strengths as high as 300,000 psi are being produced and reliably used. The manufacturing and application of these bolts are a challenge owing to the basic design of threaded fasteners. There are severe stress concentrations caused by the notches of the threads and the abrupt change in cross section of the head-to-body fillet area. In order to maximize both notch toughness and fatigue strength, large fillet radii are used in both of these critical areas. For additional fatigue strength, the head-to-shank fillet radius is prestressed and the threads are rolled after heat treatment. The material selected for bolting must have a high degree of notch toughness as well as strength. H-11 hot-work die steel has the greatest application for bolts with tensile strengths over 220,000 psi. Corrosion-resisting materials such as A-286 and Inconel 718, which are cold worked prior to aging, are also used. Care must be exercised during the heat treatment of the bolts to prevent carburization or decarburization, both of which reduce fatigue strength. Stresses caused by grinding are removed by retempering prior to fillet stressing and thread rolling. Alloy steel bolts are coated for corrosion protection with electroplating or vacuum-deposited cadmium. Through the use of these methods, hydrogen embrittlement is avoided. Application and environmental conditions greatly affect the life of a bolt in actual usage. Fatigue failures may be caused by corrosion. The performance of the bolt is influenced by the configuration of a nut or tapped hole. The design of the joint and conditions of tightening must also be considered.


    Author Information:

    Hood, A. C.
    Manager, research and development, and director, engineering and development, Standard Pressed Steel Co., Jenkintown, Pa.

    Sproat, R. L.
    Manager, research and development, and director, engineering and development, Standard Pressed Steel Co., Jenkintown, Pa.


    Paper ID: STP47123S

    Committee/Subcommittee: A01.14

    DOI: 10.1520/STP47123S


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