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Title:Effect of surface hardening conditions on susceptibility of fasteners to hydrogen embrittlement
Author(s):Medcalf, John Steven
Advisor(s):Thomas, Brian G.
Department / Program:Mechanical Sci & Engineering
Discipline:Mechanical Engineering
Degree Granting Institution:University of Illinois at Urbana-Champaign
Subject(s):hydrogen embrittlement
case hardened
tapping screws
surface hardened
zinc electroplating
Abstract:The goal of this work is to establish the relationship between core hardness, case hardness, and case depth on susceptibility to hydrogen embrittlement of case hardened steel fasteners. While case hardened fasteners have been studied previously, there are currently no processing guidelines supported by quantitative data for fastener standards. Through sustained load and incremental step load embrittlement testing techniques, the susceptibility of case hardened steel tapping screws to internal and environmental hydrogen embrittlement is examined. Further characterization of the fastener samples through microhardness testing, microstructure review, and fracture surface examination allows the determination of susceptibility thresholds. It is shown that core hardness is the primary consideration for susceptibility. However, the fastener surface is prone to failure before the bulk section, up to the case depth, according to the case hardness. The zinc acid electroplating process used to process the fasteners in this study appeared not to induce internal hydrogen embrittlement. Post plating baking operations, however, are shown to lower the threshold strength for embrittlement in high-hardness notched square bars processed on the same plating line.
Issue Date:2016-04-27
Rights Information:Copyright 2016 John Medcalf
Date Available in IDEALS:2016-07-07
Date Deposited:2016-05

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