The influence of prestrain and static strain aging on the cleavage fracture stress σf in a C–Mn steel has been investigated. It is shown that σf increases with increasing amount of prestrain and that the effect of strain aging is to reduce slightly the value of σf. Smith's original theory for cleavage fracture in steel containing grain-boundary carbides is used to determine the effect of prestrain and strain aging on the effective surface energy γeff of crack propagation. It is shown that γeff is approximately prestrain independent and that strain aging makes γeff decrease slightly.
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