Comparison of Mechanical and Corrosion Properties for 17-4 PH Stainless Steel Fabricated by Metal Injection Moulding Using Varied Powder Sizes

Abstract

17-4 PH stainless steel is commonly used in several engineering applications because of the combined good mechanical properties and high corrosion resistance. Metal injection moulding (MIM) was used to fabricate 17-4 PH stainless steel specimen with three mean powder sizes (D50), which are 2.82, 4.04 and 12.65 µm. The rheology of three feedstocks were investigated using melt flow index (MFI) and viscosity analysis. Feedstocks were injected at 170 °C. Injected tensile specimens were sintered at 1325 °C for 2 h in argon atmosphere. Surface roughness (Ra) measurement, relative density measurement, tensile test and hardness test (HRC) were carried out. Corrosion properties were determined by cyclic polarisation tests. The results indicated that the relative density of sintered samples is higher than 98% (7.68-7.74 g/cm3). α-Fe (bcc-martensite), δ-Ferrite (delta ferrite) and also SiO2 were observed in all sintered samples, which were detected by scanning electron microscopy (SEM) with energy dispersive x-ray spectroscopy (EDS). As the mean powder size of injected specimens increases, the elongation and hardness increase, whereas the ultimate tensile strength (UTS) and surface roughness decrease. Moreover, the specimens using the smallest powder (2.82 µm) have shown better corrosion resistance than the specimens using the larger powders as the higher potentials in term of E-pit (the potential of pitting) and E-rep (the potential of repassivation) and the lower potential in term of E-cor (the potential of corrosion).