Supersolidus liquid-phase sintering of ultrahigh-boron high-carbon steels for wear-protection applications

Highlights: ► Fe–C–B steels can be fully densified by SLPS and HIP. ► HIP-temperature is limited due to a low-melting eutectic in the ternary Fe–C–B system. ► SLPS processing produced specimens with a density close to the bulk value. ► Liquid phase of 30–50 vol.% was required to reach fully compacted specimens. ► Specimens in the SLPS state had a higher wear resistance than HIP-densified specimens. - Abstract: Powder metallurgy (PM) represents an alternative to conventional casting processes for the production of wear-resistant materials. PM hard alloys for wear-protection applications feature both higher strength and fracture toughness compared to cast hard alloys due to their more finely grained microstructure. However, densification by hot-isostatic pressing (HIP), the conventional PM-compaction method, is relatively expensive and thus partially counteracts low-cost processing. To increase the economic efficiency of the processing route, supersolidus liquid-phase sintering (SLPS) was investigated. In addition, expensive Ni- and Co-base hard alloys were substituted by boron-rich Fe-base hard-facing alloys. In this study, three ultrahigh-boron hard-facing alloy powders were densified by SLPS and HIP. The sintering temperatures were optimized by means of sintering experiments that were supported by thermodynamic calculations. Both densification states were investigated and compared with respect to the microstructure and the tribological and mechanical properties of the compacted hard-facing alloys. It was shown that the mechanical and tribological properties are strongly influenced by the microstructure. Although the microstructure is affected by the chemical composition, it can also be adapted by the densification process. SLPS-densified hard-facing alloys have a coarse microstructure that imparts not only a high wear resistance but also a detrimental effect on the mechanical properties.