抄録
In charpy machine, the low-temperature impact test was carried out on a series of carbon steels in their various heat treated conditions, and the cause of low-temperature brittleness was systematically investigated.
It was found in the test that the sub-zero temperature brittleness is caused by iron carbide in steels, and the critical temperature (the temperature at which the brittleness sets in) varies in a wide range in accordance with the form as well as the quantity of the carbide. An extremely low carbon steel, in the quenched and tempered states, shows the critical temperature below -120°C. The low-temperature brittleness of this steel is an inherent characteristic of ferrite itself, and not due to the carbide which is so small in quantity and exists in an uninfluential form.
Steels containing a comparatively higher amount of oxygen show a greater susceptibility to subzero temperature brittleness. The effect of oxygen is particularly remarkable in low carbon steels.
