The Use of Mild Steel for Service at Sub-zero Temperatures

Abstract

The paper describes an investigation undertaken to determine the limiting sub-zero temperature at which mild steel may safely be used, in relation to notch brittleness.

After a brief discussion of the literature on the subject, experimental work is described on the effects of variation in notch dimensions on impact value at sub-zero temperatures. Further work determines the effect on impact values of the surface cold-working resulting from grinding and machining, and indicates the beneficial effect of stress-relieving in removing the harmful effects of cold work on the surface. Practical experiments on small welded vessels in mild steel are then described, the vessels being tested to destruction at −80 deg. C. This work indicates that, while such vessels ultimately fail in a brittle manner, actual rupture is preceded by a considerable amount of plastic flow. It is argued, from these results, that the observed plastic flow gives adequate assurance that properly constructed mild-steel welded vessels will be able to absorb local overstressing to an appreciable extent without rupture, and this conclusion is supported by stress-strain diagrams taken at sub-zero temperatures.

The results of the investigation are the basis for the conclusion that, provided the recommended precautions as to quality of material and care in fabrication are taken, mild-steel welded equipment may safely be used at sub-zero temperatures down to −50 deg. C.