Study on the effect of micro-shrinkage porosity on the ultra-low temperature toughness of ferritic ductile iron

Abstract

In this study, the ductile iron ingots are cast using a metal mold, and the riser neck diameter is changed to control the micro-shrinkage porosity, which can affect the ultra-low temperature toughness of ferritic ductile iron. The metallographic structure and micro-shrinkage porosity were observed by an Axiovert200 MAT measurer metallographic microscope and an MLA 250 (FEI quanta) scanning electron microscope, and the number and diameter of graphite nodules and micro-shrinkage porosity size were measured by Nano Measurer 1.2 software. The effect of micro-shrinkage porosity on the ultra-low temperature toughness of ferritic ductile iron was studied. It is found that the impact energy of ductile iron decreases with the increase of micro-shrinkage porosity size, and the influence of micro-shrinkage porosity is more obvious with the decrease of temperature. The results point out that the micro-shrinkage porosity becomes the key factor affecting the ultra-low temperature impact toughness of ductile iron when the spheroidization rate of ferritic ductile iron is greater than 98% and the number of graphite nodules is more than 810 mm−2. The impact energy of ferritic ductile iron can still reach more than 12 J at −70°C when the length of micro-shrinkage porosity is less than 3.7 μm.

Keywords

• ferritic ductile iron
• micro-shrinkage porosity
• ultra-low temperature
• impact toughness