LOCALIZED MELTING AT SEPARATION OF AISI 4340 STEEL TENSILE SAMPLES

Localized melting due to plastic deformation during the separation of tensile samples has previously been investigated in three commercial titanium alloys. In the present study similar melting accompanied by radial cracking has been observed in AISI 4340 steel tensile samples tested at quasi-static strain rates. However, localized melting and radial cracking are absent in samples strained at high strain rates and samples fractured using an ultrasoft test system in which a large spring is placed in series with the tensile sample. Analysis of the results shows that the suppression of radial cracking and localized melting occurs because high rate plastic deformation prior to separation causes the neck region to be adiabatically heated above the ductile-brittle transition temperature range, causing the material to fail in a fully ductile manner.