Effect of Grain Size and Heat Treatment upon Impact Notch Toughness of High Tensile Mn-Si Steels

Abstract

The effects of ferrite grain sizes and microstructures after various heat treatments on the V-Charpy transition temperatures were investigated with two high tensile Mn-Si steels, of approximately the same chemical comporition, but the one aluminum treated and the other not-treated.
The results obtained are summarized as follows ;
(1) The austenitic grain-coarsening temperature of the Al treated steel N3B was considerably higher than that of Al non-treated steel K1B.
(2) A close relationship was found between the ferrite and the austenite grain sizes after various heat treatments of test steels.
(3) Generally, the transition temperature increased with increasing the austenitizing temperature and with lowering cooling rate.
(4) The greatest difference in transition temperatures between these steels occured after heat treatment at about 950°C at which the difference of austenitic grain sizes was the most significant.
(5) A linear relationship exsisted clearly between the V-Charpy transition temperature and the ferrite grain size.