TITLE:
Impact Properties of Austempered Spheroidal Graphite Cast Irons
AUTHORS:
Tohru Nobuki, Minoru Hatate, Toshio Shiota
KEYWORDS:
Spheroidal Graphite Cast Irons, Austempering, Impact Characteristics, Charpy Impact Value, High Toughness
JOURNAL NAME:
Materials Sciences and Applications,
Vol.8 No.13,
December
8,
2017
ABSTRACT: This
study aims to clarify the influence of external notch on impact characteristics
of high toughness ductile cast irons prepared by austempering heat treatment. We
produced ductile cast irons samples with various matrix microstructure tested
by Charpy impact within five kinds of external notches whose stress
concentration factors (α), with
values taken from 1.0 (Un-notched)
to 4.8. In addition, to clarify the initiation process of impact characteristics,
we observed the evolution of microstructure surface during bending tests with a
slow loading speed for the un-notched and the notched impact samples. The
results showed that the impact fracture energy decreases strongly in the range
of α from 1 to 2.3 but decreases
slightly for α larger than 3.
Moreover, the impact value of samples with austempered microstructure is
sensitive to the external notch shape. The impact transition temperature
increases with increasing the stress concentration factor. The fracture energy
is decreasing with the external notch from the impact test since the crack
initiation energy is directly affected by this later. This work contributes to
get a better understanding in the basic theories of external notch effect on
impact characteristics of austempered spheroidal graphite cast irons (ADI).