The effect of austenite grain size and tempering temperature on the cold-brittleness threshold of steel

Abstract

1. We investigated the effect of the grain size and tempering temperature on the cold-brittleness threshold of steel by electron-microscopic examination of the fractures. Grain refining (from grade 5 to grade 9–11) lowers the cold-brittleness threshold of the steels investigated in different structural conditions. No definite relationship was found between the cold-brittleness threshold and the tempering temperature. 2. The shift of the cold-brittleness threshold with changes in the grain size and tempering temperature determined by the electron-microscopic method coincided with that determined by the change in the percentage of ductile components (%D) in the fracture. 3. The electron-microscopic method was used to study the fine structure of the fractures. A relationship was found between the true austenite grain size and the dispersity of the dimpled structure in the region of ductile failure.