Influence of austempering process on microstructures and mechanical properties of V-containing alloyed ductile iron

Abstract

The influence of austempering time and vanadium addition on microstructure and mechanical properties of the alloyed ductile iron has been investigated. The 0.30 wt% V-containing and V-free alloyed ductile irons were firstly austenitized at 850 °C for 1 h and then austempered in a salt bath at 300 °C for 2, 3 and 4 h, respectively. For the 0.3 wt% V-containing alloyed ductile iron, the transformation product (ausferrite) was finer, and a small amount of martensite and a large amount of stable austenite were obtained after austempering for 2 h, while higher hardness and compressive strength of 62.8 HRC and 3000 MPa were achieved. For the V-free alloyed ductile iron, lower hardness and compressive strength were measured to be 56.8 HRC and 2320 MPa. As the austempering time increases, the amount of stable austenite decreases in the V-containing ductile iron, typically for the start of the second stage formation (retained austenite (γr) → α + carbide). Based on this, it is assumed that the optimal processing window (OPW) was narrowed due to the addition of 0.30 wt% V as compared to the V-free ductile iron. When the hardness of 0.30 wt% V-alloyed ductile iron was higher than 59 HRC, the highest wear resistance was obtained. The mechanical cutting plays a dominant role in abrasive wear process.