Sintering of a boron-doped injection moulded 17-4PH stanless steel

Abstract

Powder injection molding (PIM) is an attractive process to produce complex, near-net shaped components. The process overcomes the shape limitation of traditional powder compaction, the cost of machining, the productivity limits of isostatic pressing and slip casting, and the defect and tolerance limitations of conventional casting. Over 50% of the injection molded and sintered components are made from stainless steel composition [1–3]. The alloy 17-4 PH stainless steel powders—a precipitation-hardening martensitic stainless steel, shaped and processed via injection molding can achieve high complexity of part geometrical with mechanical and corrosion properties, similar or superior to wrought material. Due to its high strength and good corrosion resistance 17-4 PH has widespread applications, especially in medical, automotive, military, and aerospace instruments [4–6]. Earlier investigations on PM or PIM 17-4 PH focused on the effect of powder characteristics, sintering atmosphere, sintering temperature, sintering time, heat treatment, residual carbon content on microstructure, corresponding microstructural characterization, mechanical and corrosion properties [4–6]. In several investigations boron as a sintering additive has been used to achieve higher sintered density in stainless steels at lower sintering temperatures [7–9]. As a consequence, a noticeable improvement in the mechanical properties is obtained. Boron can be added either in its elemental form (both amorphous and crystalline) or as a compound (for example, Fe2B, BN, NiB, and CrB). A small particle size of the additive is desirable to obtain a uniform dispersion. Boron additions increase hardenability in steels, increase strength (via increase in sintered density), improve grain boundary cohesive strength, enhance corrosion resistance, and improve ductility [7, 9]. The aim of this study is to investigate the effect of added boron on the sintering behavior and final properties of powder injection molded 17-4 PH stainless steel. In this research, gas atomized 17-4 PH stainless steel powders (Fe-16.2Cr-4.6Ni-4.6Cu-0.54Mn0.30Nb-0.30Si-0.095Mo-0.038C-0.026P-0.002S) provided by Osprey Metals Ltd. were used. It has particle size distribution of D10 = 3.25 µm, D50 = 10.65