Abstract

Nanoflex stainless steel is a promising material for medical applications. However, improvement of its mechanical properties without compromising its corrosion resistance is still a challenge. In order to investigate the effect of the nitriding process on the corrosion and wear resistance of Sandvik NanoflexTM steel, a number of processes were carried out in a gas atmosphere with differing ammonia contents in the temperature range of 425–475 °C for 4 h. The mechanical properties and wear resistance of the layers were tested using the nanoindentation and pin-on-disc methods, respectively. In order to assess corrosion resistance, potentiodynamic tests were carried out in Ringer’s artificial body fluid and in a 3% aqueous solution of sodium chloride. The results are discussed herein with respect to the microstructural characteristics of the layers studied using light and scanning electron microscopy, X-ray diffraction phase analysis and wavelength dispersive X-ray microanalysis. The structure of nitrided layers included three zones: the subsurface zone composed of nitrides and the zones composed of metastable phases, i.e., the S phase (γN) and expanded martensite (αN) with possible precipitates of nitrides. The third zone adjacent to the steel core was enriched with carbon. The nitrided samples showed significant improvement in the wear rate while maintaining good corrosion resistance in comparison to the non-treated steel. We concluded that nitriding should be carried out at a temperature below 450 °C and in an atmosphere containing no more than approximately 50% ammonia in order to avoid nitrides precipitation.

Highlights

  • We present results of research on nitrided layers of precipitationhardening stainless steel Sandvik NanoflexTM

  • Medicine is a significant field of application for Nanoflex steel, and it is used for manufacturing of various skin-piercing applications and surgical or microsurgical instruments

  • The nitriding kinetics and the structure of the layers produced under conditions A and B were described in previous works [27,28,40]

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Summary

Introduction

We present results of research on nitrided layers of precipitationhardening stainless steel Sandvik NanoflexTM. This is an ultra-high-strength steel with very good corrosion resistance. 1100 ◦C, and ageing at 475 ◦C for 4 h Achieving such good mechanical properties is possible thanks to very fine nanometric precipitates of intermetallic phases, such as η-Ni3(Ti, Al), Fe2Mo, ε-Cu and R [1,2,3,4,5,6], precipitating in martensitic matrix. Due to its special properties, this steel is suitable for production of durable mechanical parts, such as turbine blades and bearings. Medicine is a significant field of application for Nanoflex steel, and it is used for manufacturing of various skin-piercing applications (surgical staples, retractable syringes and needles for vaccination and acupuncture) and surgical or microsurgical instruments (including blades, saws, bone drills, biopsy punches and screwdrivers)

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