In this work, a further study on boronizing using compression method called superplastic boronizing (SPB) was conducted. This process was conducted on duplex stainless steel (DSS) that exhibited superplasticity. Efforts were being put in obtaining ultra hard surface through SPB by focusing on the boron powder particle size. The microstructure, hardness, and layer thickness of the boronized materials were investigated. Comparison using as-received DSS with coarse microstructure also was performed. The overall results from the study showed that the SPB process can produced a very hard surface of close to 4000 HV and significantly improved the surface properties of the DSS.