Abstract
Four kinds of Si-Mn high strength low alloy steels were hot rolled into plates of 12 and 22 m/m in thickness. Schnadt impact test was carried out in the range of temperature from -80 to 97°C to investigate the effect of the degree of reduction in plate thickness, gas cutting, shearing, welding, and chemical composition on the transition temperatures and impact properties of these plates.
The results obtained are as follows;
1) Schnadt impact properties of the specimens taken from the thin plates are generally superior to those of the specimens taken from the thick plates.
2) Gas cutting seems to reduce the notch sensibility of the plates which is rather advantageous, while the sheared surface has the trend to be notch sensible. Weld metal used is excellent in toughness.
3) Suitable contents of aluminum and nitrogen in the form of aluminum-nitride seem to have a good effect on the impact properties of steel plates. Attention should be paid, therfore, in the deoxidation of molten steel to leave a small content of metallic aluminum in the steel.
4) The temperature of complete brittleness (i.e. Bifractance defined by Schandt) of the specimens is lower than -15°C when the Venant number is assumed to be 20, while that of full plasticity (Octafractance) lies in a relatively high temperature range. This tendency is more conspicuous in the thick plates.
5) Transition temperature is lowered as the number of Venant is increased. Transition temperature of the thin plates is lower than that of the thick plates.
6) These results show that the test plates belong to high or moderate class of high strength low alloy steels when compared with the various foreign types of steels of the same kind.
