Environmental Assisted Cracking in High Hardness Armor Steel
ARMY MATERIALS AND MECHANICS RESEARCH CENTER WATERTOWN MA
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At the request of several program managers, AMMRC investigated cracking of high hardness armor steel MIL-A-46100. Cracks were first reported on detail parts that were stored after being cut from large plates. In addition the cracking was reported during subsequent fabrication steps, as well as in fielded vehicles. AMMRC found an environmental assisted cracking EAC mechanism to be responsible for the cracking phenomenon. AMMRC further identified two significant factors which could be controlled and thereby reduce the likelihood of EAC occurring the residual stress level in the parts, and microcrack formation at cut edges. The residual stress level in the detail parts was related to the heat treatment of the high hardness steel. The AMMRC investigation identified a minimum tempering temperature and time 350 deg. F30 min to minimize the residual stress level in the heat treated plates. These tempering parameters were incorporated into the latest revision of MIL-A-46100 in April 1983. AMMRC further recommended the best cutting procedure in order to minimize the number of microcracks on plate edges, which acted as EAC initiation sites.
- Metallurgy and Metallography