Proof stress of tool steels in compression

Abstract

1. There is a direct relationship between the hardness of steels, the amount of residual austenite, and the proof stress in compression. The proof stress increases proportionately with hardness in the presence of residual austenite; the highest hardness (HRC 65-68) corresponds to the highest proof stress (250–280 kg/mm2). In the presence of residual austenite the proof stress decreases; small amounts of residual austenite (10–15%) have the greatest effect. 2. The stresses resulting from quenching also reduce the proof stress, but their effect is small; a lower cooling rate in quenching (cooling in air) has a favorable effect if it results in a higher hardness and higher proof stress. 3. The proof stress in compression does not depend on the austenite grain size. 4. To obtain a high proof stress in compression (200–230 kg/mm2) for steels with low and medium heat resistance the quenching temperature should be as low as possible and the tempering temperature should be as high as possible (with retention of sufficient hardness). 5. Heat resistant steels, which after tempering at 560\dgC have a high hardness and no residual austenite, have the highest proof stress in compression (250–280 kg/mm2).