Mechanism and estimation of porosity defects in ductile cast iron

Abstract

Although there are many works on the formation mechanism of porosity defects due to solidification in ductile cast iron, the formation mechanism is still not clear and decreasing the porosity defects is still a main issue in the industry. This paper critically reviews conventional explanations for the porosity formation including estimation methods. Based on the discussion the authors propose a formation theory where it considers gas and oxide entrapment during mould filling, expansion of outer part of casting due to graphite formation and pressure decrease in the inner part, followed by the growth of entrapped small gas bubbles. This mechanism can explain various facts in practice and be usable to estimate the defects. It also gives a good way to design effective risers. Future challenges are also discussed including the effect of inoculation on the fluidity of the mushy region.

Keywords:

• DUCTILE CAST IRON
• POROSITY DEFECTS
• FORMATION MECHANISM
• POROSITY ESTIMATION
• EXPANSION OF CASTING
• GAS ENTRAPMENT