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In general, most of
the cracking life of hot work dies is spent in the
fatigue crack growth. Therefore, the fatigue crack
propagation properties ( FCPP ) analyzed by using
fracture mechanics technique are useful to evaluate
the performance of die steels. The aim of this study
is to clarify the effects of heat treatment and
test temperature on the FCPP of hot work die steels.
The tests were carried out with a Δ
K < control servohydraulic test machine. It was
found that at high hardness levels the FCPP were
improved by raising the austenitizing temperature,
but at low hardness levels high austenitizing temperature
caused the deterioration of the FCPP.
Also the FCPP deteriorated
with a decrease in cooling rate, but the suppression
of bainite formation by the rapid cooling below
400°C caused the improvement of the FCPP. The effect
of test temperature up to 300°C on the FCPP was investigated.
The result showed that at high hardness levels the
FCPP improved dramatically with increasing test
temperature, but at low hardness levels the FCPP
was little affected by test temperature. Furthermore,
in this paper the FCPP of five hot work die steels
were compared.
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