Microstructure formation and abrasive wear resistance of a boron-modified superduplex stainless steel produced by spray forming

The microstructure formation and wear resistance of a superduplex stainless steel modified with the addition of 3 wt% boron produced by spray forming were investigated. Thermodynamic simulations were used as comparison basis and to explain the experimentally observed microstructure, which was composed by primary M2B-type borides, an austenitic-ferritic matrix, and eutectic M3B2-type borides. The predicted solidification sequence started with the precipitation of primary M2B boride, followed by ferrite/austenite formation and a final eutectic reaction resulting in M3B2borides. A good correlation with the simulations and final microstructure was found. The abrasive wear resistance was investigated with the dry sand/rubber wheel test and the results indicated an outstanding performance, similar to the cobalt-based Stellite 1016 alloy. The excellent wear resistance resulted from the presence of a significant amount (about 35 vol%) of hard borides homogeneously dispersed in the microstructure, which was effective at increasing hardness and protecting the duplex matrix against abrasion.