Abstract
A cantilever type testing apparatus for delayed fracture was developed to investigate the characteristics of delayed fracture in several aqueous environments for two kinds of low alloy high strength steels having a sorbitic and a martensitic structures the tensile strength of which were about 125kg/mm2 and 150kg/mm2 respectively.
These steels were failed even in the air after a long period of time under high sustained stresses, and the fracture strengths were decreased in the sequence of air, water, pH 5-HCl solution, 0.1% NaCl solution, pH 3-HCl solution, 3% NaCl solution, 0.1 N-HCl solution and acetic acid solution saturated with H2S.
The results of the observation of the fracture surfaces, crack initiation behaviour in delayed fracture and the quantitative analysis of hydrogen in steel lead the conclusion that the delayed fracture in these environments occurs by hydrogen induced from the surroundings, and the more active supply of hydrogen promises the lower fracture strength of the steel under sustained load.
