On the Change of Quality of the High Tensile Steel by Water Cooling Operation

Abstract

In the production of high tensile weldable steels having the tensile strength over 60 kg/mm², the allowable ranges of the compositions are quite narrow or the no small scale of heat-treatment equipments are required for quenching and tempering after rolling. In order to avoid these troubles, the authors tried the cooling of materials within the range of Ar₃ to Ar₁ and from the temperature slightly above Ar₁ down to the room temperature. According to the results obtained by this experiment, the strength increases exponentially and the elongation decreases, with the increase of cooling rate. Impact value is restored within the range of the moderate cooling rate at Ar₃-Ar₁, but decreases continuously with decreasing the rate from the temperature slightly above Ar₁.
Consequently, the accelerated cooling at Ar₃-Ar₁ instead of air cooling during the normalizing operation is effective owing to the recovery of impact value.