Comparison of the Notch-Sensitivity of Steels with their Tensile Test Results

A Simplified method to judge the notch-sensitivity of materials (No. 1)

Abstract

To specify the notch-toughness of materials, so-called transition temperature is, used as a criterion with the general belief that the characteristics of notch-toughness cannot be evaluated to ordinary mechanical tests such as tension test, etc.
In the factory, however, it will take great labor to obtain the transition temperature of materials. From this point of view the authors have carefully studied the relation between ordinary tensile test results and U-and V type standard Charpy test results within the temperature range -80°C to +200° using four Japanese representative rimmed steels (see Tables I and II).The characteristics of the tension test results at low temperatures are shown in Figs 7-13. From these, of course, it is difficult to specify the notch-toughness of materials. Then φ or φ' was defined which represents the measure of strain hardening to ultimate point from origin or yield-point as follows:
φ=actual ultimate point stress/ultimate point strain
φ'=(actual ultimate point stress) - (yield-point stress)/ultimate point strain
(see Fig.20), where actual ultimate point stress, ct and strain, εt are calculated by the area apart from local shrinkage portion after breaking, according to Mc Gregor (refer to the notations in Sect. 5).
As to the value of φ or φ' the following characteristics are notable:
a) φ or φ' value is constant within the temperature range of -80°C to +100°C and the value increases as the temperature is raised above +100°C (see Figs 18 and 19).
b) The relation between the transition temperature determined by Charpy test and φ or φ' within the temperature range of -80°C to +100°C is shown in Fig.22 or 23. From them, it is clear that the material of which φ or φ' value is the smaller shows the lower transition temperature.
Thus φ or φ' may be taken as an index of the notch-toughness of materials.