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).
Highlights
Spheroidal graphite cast iron is a superior cast iron with high tensile strength, good ductility and high toughness properties which are comparable to those of steel
This study aims to clarify the influence of external notch on impact characteristics of high toughness ductile cast irons prepared by austempering heat treatment
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)
Summary
Spheroidal graphite cast iron is a superior cast iron with high tensile strength, good ductility and high toughness properties which are comparable to those of steel. As the graphite of cast iron can behave as the supplier or the absorber of C content to the matrix when heat treated, cast iron has a very valuable metallurgical characteristic that the matrix can be modified widely and by heat treatment in order to satisfy various engineering requirements, e.g. ferritic matrix for good ductility, pearlitic matrix high tensile strength, and austempered matrix for high tensile-strength/toughness/hardness at a same time. Cast iron has various superior characteristics as mentioned above, the presence of graphite causes some undesirable affection to various mechanical properties due to the decrease of the effective sectional area of matrix and producing internal notch effect [4] [5] [6], cast iron is regarded as a material with a less anti-impact characteristic than that of steel. In order to expand the usage of cast iron in more various industrial fields, the influences of outer-notch effect on various impact characteristics and bending characteristics of cast iron are very important and need to be qualified systematically [9] [10]
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