Tensile Instability in a Hydrogenated Low Alloy Steel

Abstract

Sheet tensile specimens prepared from a cold rolled low alloy steel were annealed at 700°C to get equiaxed ferrite grains of 8, 21.5 and 32.5 μm diameters other than spheroidal carbides and inclusions, charged cathodically in 1 N NaOH and 0.1 N H₂SO₄ solutions with a current density of 50 mA/cm² and tested in a hard beam tensile testing machine at a slow strain rate. Fracture characteristics were studied in SEM. By comparing the values of σ at the point of intersection of computed σ vs. ε and dσ/dε vs. ε curves with the actual values corresponding to UTS a measure of the enhancement of plastic instability by hydrogen was obtained. It has been found that the higher the hydrogen content the lower are the values of stress and strain at which plastic instability was initiated, and the higher the ferrite grain size the greater is the enhancement of this instability. These effects have been discussed in the light of viewed fracture modes.