Heat treatment of novel low-carbon multi-alloyed anti-wear marine steel

A low-carbon anti-wear steel, multi-alloyed with Si-Cr-Mn-Al-Ni-Mo-(Nb, RE), was designed for vane pumps of ships. The novel cast steel after various heat treatments was characterized by microstructure observations and mechanical properties measurement in order to achieve an optimal process correlated with good abrasive resistance for a long marine service. Differential scanning calorimetry and hardness analyses deduced a complete austenitizing temperature of 1 000 °C, based on the alloying element homogenization and defective structure elimination without grain coarsening. An optimal austempering process (austenitized at 1 000 °C, quick cooled for holding at 350 °C for 1.5 h and then air-cooled to room temperature) produced a uniform mixture structure of fine carbide-free aciculate bainites and few lath martensites, resulting in the tensile strength increase of 34% and impact toughness increase of 50% compared with that of the as-cast steel. The abrasive wheel tests show that the austempered steel has good wear resistance with a mass-loss rate of 170 mg/(km·cm2) under applied load of 70 N in acidic slurry. The new grade steel (containing anti-corrosion elements of Cr and rare earth) can find wide application in marine engineering, with further enhanced comprehensive properties via melting process improvement.