Influence of the heat treatment on the toughness of some hot-work tool steel grades

Abstract

The influence of heat treatment on the toughness of a number of hot-work tool steel grades used for e.g.
die-casting has been researched. The researched grades were X40CrMoV5-1, X37CrMoV5-1 and Dievar:
an improved hot-work tool steel grade developed by Uddeholm. The impact toughness was researched by
conventional Charpy V-notch testing and instrumented Charpy V-notch testing at various temperatures.
The fracture toughness was studied by KIc testing at room temperature and JIc testing at elevated
temperatures. The influence of the hardness and the cooling rate during quenching were examined.
Additionally, the toughness after austempering was measured and compared with the toughness after
quenching and tempering to equivalent hardness. The influence of preheating of the die on the toughness
was studied by impact and fracture toughness measurements at various temperatures.
The energy absorption in impact testing decreased throughout the whole temperature range with
increasing hardness and decreasing quenching rate. The fracture toughness decreased also with
increasing hardness and decreasing quenching rate. Austempering followed by tempering gave a lower
toughness than conventional hardening and tempering to equivalent hardness. Preheating of the die
increases the toughness considerably.