Effect of Flame Cutting on Notch Sensitivity of Structural Steels

Abstract

To investigate the effect of flame cutting on notch sensitivity of two high tensile and one mild ship steels, tests were performed with Kahn Test specimens of which the notches were machined or flame cut.
The conclusions may be summarised as follows:
(a) A flame cut notch raised transition temperatures by 30 to 60°C higher than that of machine-notched.
(b) Flame-notched specimens showed 19 to 25% lower load carrying capacity than machine-notched, and very poor ductility at notch root when measured by lateral contraction, only 1/6 to 1/2 times that of machine-notched.
The energies up to the maximum load in flame-notched specimens were only 2/3 to 1/7 times that of machine-notched, at higher and lower temperatures, respectively.
(c) The hardening of base metal was considerably greater at the root of a flame-notch than at a straight flame-cut edge.
(d) A flame-nothch is very dangerous in a mild steel as well as in a high tensile steel.
(e) The notch sensitivity of tested high tensile steel with lower carbon content, 0.14%, was similar to that of a mild steel, while the high tensile steel with higher carbon content, 0.19%, was embrittled seriously by flame cutting.
Thus, a miss cut in flame cutting or a notch which has been caused by flame interruption during cutting is considered very dangerous and should be carefully avoided from the standpoint of notchbrittle fracture. It is more so in high tensile steels.