Effect of cooling rate during quenching on the structure and properties of steel R6M5

Previously abstracted from original as item 9206-56-0690. The effect of quenching in air, oil, and water from 1220 deg C on as-quenched and tempered hardness of R6M5 high speed steel was determined on samples of 12.0 mm diameter and 20.0 mm length. These hardness tests and metallographic examinations indicated that decreasing cooling rate during quenching in this steel, as is done in traditional heat treatments, does not produce optimal structure or hardness. Increasing the cooling rate by water quenching prevented excessive precipitation of carbides from supersaturated austenite and thereby raised hardness after exposure to 620 deg C for 4 h. Water quenching of R6M5 tool inserts was recommended to raise tool life in cutting operations.