Effect of Hot Working on the Hardenability of Steels

Abstract

The effect of hot working on the hardenability of steels was investigated. 0.4%C-1%Cr steels were used and hot working was carried out by means of rolling. The following results were obtained.
The heating temperature for hot working affected the hardenability of steels. An increase in the temperature from 1050°C to 1250°C decreased the Vickers hardness by about 50 in the cooling condition in which the hardness after cooling from the austenitizing temperature decreased most steeply with a decrease of cooling rate. Effect of the working temperature and working ratio was small.
These results were due to the change of austenite grain size in relaition to the condition of hot working. When the heating temperature for hot working is higher and all aluminum nitrides dissolve into austenite, fine aluminum nitrides precipitate in the heating for normalizing after rolling and suppress the growth of austenite grain. When the heating temperature is lower and a part of aluminum nitrides does not dissolve, large particles of aluminum nitride distribute scatteringly and austenite grain grows larger. The hardenability of steels is varied according to the austenite grain size.