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

Eliza Romanczuk,Krzysztof Perkowski,Zbigniew Oksiuta

doi:10.3390/ma12203416

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.

Highlights

The most popular grade of the austenitic stainless steels used for medical applications has been the 316LV and an improved version of the REX 734, with the chemical composition described in the International Standards ISO 5832-1 Implants for surgery—Metallic materials, Part 1 and ISO 5832-9 Implants for surgery—Metallic materials, Part 9
In the powder mechanical alloying process (MA) in argon the peaks of both austenitic and ferritic phases were detected. This indicates that with the MA process parameters applied in this work, it is difficult to obtain a fully austenitic phase structure using argon atmosphere
High nitrogen content measured in the powder after MA, about 1%, as presented in Table 1, ensured the austenitic structure

Summary

Introduction

The most popular grade of the austenitic stainless steels used for medical applications has been the 316LV and an improved version of the REX 734, with the chemical composition described in the International Standards ISO 5832-1 Implants for surgery—Metallic materials, Part 1 and ISO 5832-9 Implants for surgery—Metallic materials, Part 9. Due to the low costs of production, well established manufacturing process, and good mechanical and corrosion properties, these steels are used for biomedical applications such as: implants, bone plates and screws, spinal stabilizers, cardiovascular application (stents), surgical instrumentations, and more [1]. It is characterized by the relatively low yield to tensile strength ratio and high formability [1,2]. The essential problem is a negative charge of the alloying ions, especially of the toxic nickel, that can be released from the steel during implantation [5,6]

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