Microstructure, Mechanical, and Corrosion Properties of Ni-Free Austenitic Stainless Steel Prepared by Mechanical Alloying and HIPping

Abstract

An influence of the powder metallurgy route on the phase structure, mechanical properties, and corrosion resistance of Fe–18%Cr–12%Mn–N nickel-free austenitic stainless steel as a potential material for medical applications were studied. The powder was mechanically alloyed in a high purity nitrogen atmosphere for 90 h followed by Hot Isostatic Pressing at 1150 °C (1423 K) and heat treatment at 1175 °C (1423 K) for 1 h in a vacuum with furnace cooling and water quenching. More than 96% of theoretical density was obtained for the samples after Hot Isostatic Pressing that had a direct influence on the tensile strength of the tested samples (Ultimate Tensile Strength is 935 MPa) with the total elongation of 0.5%. Heat treatment did not affect the tensile strength of the tested material, however, an elongation was improved by up to 3.5%. Corrosion properties of the tested austenitic stainless steel in various stages of the manufacturing process were evaluated applying the anodic polarization measurements and compared with the austenitic 316LV stainless steel. In general, the heat treatment applied after Hot Isostatic Pressing improved the corrosion resistance. The Hot Isostatic Pressing sample shows dissolution, while heat treatment causes a passivity range, the noblest corrosion potential, and lower current density of this sample.

Bioactivity, Cytotoxicity, and Tribological Studies of Nickel-Free Austenitic Stainless Steel Obtained via Powder Metallurgy Route

“…SBF solution was prepared through the dissolving in 1 L of deionised water of a reagent composed of sodium chloride (NaCl), potassium chloride (KCl), calcium chloride dihydrate (CaCl 2 •2H 2 O), magnesium chloride hexahydrate (MgCl 2 •6H 2 O), sodium hydrogen carbonate (NaHCO 3 ), dipotassium hydrogen phosphate trihydrate (K 2 HPO 4 •3H 2 O), and sodium sulphate (Na 2 SO 4 ). Then, the solution was buffered to physiological pH 7.4 at 37 • C (310 K) by both hydrochloric acid (HCl) and tris (hydroxymethyl)-aminomethane ((CH 2 OH) 3 CNH 2 ) [21]. The pH value of SBF, as obtained, was similar to that of human blood plasma, as shown in Table 1.…”

“…The HIP + HT microstructure consists of the homogeneous and small grain size 2.47 ± 0.49 µm, as well as annealing twins (red arrow in Figure 2b). The XRD analysis confirmed a fully austenitic phase structure, as presented in Figure 2c [21]. tested material groups, a one-way ANOVA followed by a test was used.…”

“…The MA process was conducted in a stainless steel high-energy planetary ball mill Pulverisette 6 (Fritsch, Idar-Oberstein, Rhineland-Palatinate, Germany), in an argon atmosphere (99.999 purity) with stainless steel balls (10 mm in diameter) and a ball-to-powder ratio (BPR) of 8:1 up to 90 h. The powder after MA was degassed in vacuum, hermetically closed in a low-carbon steel capsule and HIPped under a pressure of 200 MPa, at 1150 • C (1423 K) for 1 h. The material after consolidation was annealed at 1175 • C (1448 K) for 1 h in a vacuum with furnace cooling (denoted as HIP + HT). More details of the mechanical alloying and consolidation process are presented in the literature [21].…”

“…It can be noted that the heat treatment after HIP significantly affects the corrosion properties. The corrosion resistance of PM steels is related to the density and pore morphology of the HIP and HIP + HT samples [21]. Tissue fluids circulate constantly in the human body, so it can be assumed that a more appropriate method for testing bioactivity is the approach with regular replacement of the SBF solution.…”

Evolution of Microstructure and Elements Distribution of Powder Metallurgy Borated Stainless Steel during Hot Isostatic Pressing

“…Therefore, it is necessary to minimize the oxygen content of the powder to improve the properties of HIP sintering materials. A number of process parameters and material properties of powdered stainless steel were investigated after HIP [24][25][26][27][28].…”