Influence of the Dimensional Change, and Its Dispersion, on the Fabrication Size Tolerances of Austempered Ductile lron (ADI) Parts. Comparison with SAE 4140 Steel.

Abstract

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 (DDC ) of the DC values. The information available on this topic for ADI is very scarce.The present work aims to determine DC and DDC 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 DDC caused by austempering, and quenching and tempering heat treatments. DC and DDC were also measured for several industrial parts of different ADI grades, having different chemical compositions, shapes and 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, DDC 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.KEY WORDS: dimensional change; dispersion of dimensional change; ADI and SAE 4140 steel; fabrication and machining tolerances; fabrication steps.

Influence of nodule count on residual stresses and distortion in thin wall ductile iron plates of different matrices

“…The studies carried out by Moncada and Sikora (1996) have demonstrated that DC of conventional sized ADI parts mainly depend on heat treatment parameters and prior microstructure. Echeverría et al (2001) agree with this results working on ADI parts of thickness ranging from 10 to 40 mm. Nevertheless, to the best of the authors' knowledge RS, DC, distortion and surface hardening have not been reported for ADI parts of small thickness.…”

Comparison of High-Temperature Properties and Thermal Shock Resistance of Austempered Ductile Irons (ADI) with Those of Pearlitic Ductile Cast Irons

“…These can lead to the formation of elastic strains, which cause: a) heavy microstructural subsurface damage because of the graphite matrix interfaces and debonding, matrix microcracking, and void growth, b) a significant amount of austenite-martensite transformation, and c) decomposition of the reacted stable austenite, due to the localized increase in temperatures. [16][17][18][19][20] The reacted austenite matrix in ausferrite is thermodynamically stable down to liquid nitrogen temperatures. During the heating process, acicular ferrites in bainitic ductile cast iron break and the reacted austenite phase decomposes to carbide and ferrite.…”

Fatigue Strength Improvement by Replacing Welded Joints with Ductile Cast Iron Joints

“…Also DCI has high strength and toughness comparable to steel materials. [5][6][7] Furthermore, in the sand mold casting, DCI may reduce the residual stress by cooling gradually. Therefore, the DCI fatigue strength can be improved higher than the fatigue strength of welded structures.…”