Effect of Nitrogen Addition on Microstructure and Mechanical Properties of As-Cast High-Chromium Cast Iron Containing Niobium

This work was conducted to study the effect of four different nitrogen additions on as-cast microstructure, hardness and impact toughness as well as abrasion wear resistance of high-Cr cast iron containing niobium. The results showed that as nitrogen content increased, the austenitic dendrites matrix became less elongated and the eutectic M(7)C(3)carbides were gradually refined in size. EDS analysis demonstrated that N element preferentially accumulated in the NbC particles and substitute part of C to form Nb nitrides (NbN) or Nb cabonitrides Nb(C,N). Such nitrides or carbonitride particles were relatively hard compared to matrix and eutectic carbides resulting in an increase in hardness with increasing N content. The optimum toughness (12 J) was obtained for the iron containing 0.093 wt%N with an enhancement of 33%. The wear resistance increased with increasing N addition, in which the maximum wear resistance was reported for the alloy containing 0.15 wt% N. There was an enhancement in wear resistance of 47% by adding 0.15 wt%N to HCCI at low applied load (30 N), and it decreased to 17.5% at high applied load (60 N). Hence, the highest wear resistance and moderate toughness of HCCI could be achieved by adding 0.15 wt%N.