2001 Volume 41 Issue 1 Pages 25-30
To accurately satisfy the size tolerance of metallic parts, it is necessary to take into account the dimensional change (DC) caused by heat treatment, and the dispersion (ΔDC) of the DC values. The informationavailable on this topic for ADI is very scarce.
The present work aims to determine DC and ΔDC on ADI and SAE 4140 steel parts and to analyze its influence on the size tolerances. Ductile iron and SAE 4140 steel specimens were used to compare DC and ΔDC caused by austempering, and quenching and tempering heat treatments. DC and ΔDC were also measured for several industrial parts of different ADI grades, having different chemical compositions, shapesand sizes.
The results show that in average ADI suffer greater DC than SAE 4140 steel parts of similar mechanical properties, but, on the other hand, ΔDC is always lower for ADI than for steel.
A more accurate prediction of the DC is then possible on ADI than on steels. This would allow the use of less strict machining tolerances, under better machinability conditions, when final operations can be done before heat treatment, producing series of ADI parts. This represents a technical and economical advantage for ADI in comparison with steel.
The influence that the previous microstructure, the austempering temperature and the piece anisotropy, exert on the DC of ADI were also studied. The effects identified in this work are in agreement with previously reported results.
