Detection of the Ductile-Brittle Transition Temperature of an Ausformed Steel by Means of Hardness Testing

Abstract

The effects of ausforming on the ductile-brittle transition temperature of SKD 61-steel (H 11-steel) were examined by measuring the hardness and determining the transition temperature from the intersection of the straight line parts of the plot of the logarithmic Vickers hardness vs. the reciprocal of absolute temperature.
The results are summarized as follows:
(1) In the measured range from 60°C to -196°C, the ausformed steel has two transition temperatures T_* and T_** in the hardness test.
(2) The ductile-brittle transition temperature of the ausformed steel when plotted as a function of rolling ratio changes a little (within 20°C), having a slight maximum.
Among several factors influencing the ductile-brittle transition temperature of ausformed steels, the grain size and the dislocation density are considered to be very important. As a rule, these two factors in the ausforming give opposing influences on the ductile-brittle transition temperature, so that the ductile-brittle transition temperature of this ausformed steel remains almost unchanged as compared with that of a conventional heat-treated steel. Therefore, the ausforming is considered to be a strengthening treatment without having embrittlement rather than a treatment to improve toughness.