Effect of temperature on the hot formability of ductile iron in the semisolid state

Abstract

Macroporosity, microporosity and inclusions are the most common defects in ductile iron. Proper feeder design, gating system and use of filters can reduce macroporosity and inclusion defects. However, microporosity is intrinsic to solidification of ductile iron due to its dendritic solidification. Microporosity volume fraction is a function of nodule count, chemical composition and cooling rate. Obviously, the mechanical properties of ductile iron depend on the nature and volume fraction of defects. The effect of hot forging on the graphite structure and formability of ductile iron has been investigated. Alloyed ductile irons inoculated with two different inoculants were used. The blank irons were forged at three different temperatures in a die to make cap shape specimens.

An image analyser was used to measure the liquid volume fraction as a function of forging temperature and also nodularity of graphite in different regions of irons. In addition, specific gravity of irons before and after forging was measured to evaluate the effect of hot forging on the reduction of microporosity. The results show that this process not only can tremendously reduce the volume fraction of porosities but also it is possible to make precision iron casting with a minor graphite deformation.

Keywords:

• Ductile iron
• hot deformation
• semisolid state
• porosity