Effect of Alloying Elements on Structure and Mechanical Properties of Bainite Ductile Iron in the Step Austempering in Machine Oil at Room Temperature

A low alloy Bainite ductile cast iron had been obtained by using a new heat treatment technique of the step austempering in room temperature machine oil.The effects of elements B,Cu and Mn on structure and mechanical properties of the Bainite ductile cast iron in above-mentioned process were investigated.The phenomenon of hardness lag of the alloyed Bainite ductile cast iron has been discussed.This phenomenon showed that after the step austempering,the hardness increased with the time.Both elements B and Mn could increase the hardness and reduce the impact strength;element Cu could increase the impact strength.Reasonable alloy elements could improve mechanical properties of the Bainite ductile cast iron.Essentially,hardness lag of the alloyed Bainite ductile cast iron resulted from solute drag-like effect.