Abstract
Effects of the quenching temperature on the mechanical properties at room temperature of two kinds of P/M hot work tool steels, AISI Hll standard grade and a newly developed grade, were investigated in comparison with conventional materials produced by ingot metallurgy. The tensile strength increased and the impact energy decreased with increasing the quenching temperature. However, the impact energy of P/M materials quenched from 1403K were much higher than that of I/M materials. It was found from the results of instrumented Charpy impact tests that the approximately 80% of impact energy was exhausted for crack initiation. The impact fracture modes at the root of the notch were divided into three groups as follows: 1) ductile fracture paralleled to the direction of maximum shear stress, 2) ductile fracture with stretched zone and 3) brittle intergranular fracture. It was also found that the anisotropy impact energy in P/M materials quenched from 1303K resulted from broken stringer inclusions of SiO2.
