• PDF / 314,796 Bytes
• 7 Pages / 584.957 x 782.986 pts Page_size
• 64 Downloads / 205 Views

DOWNLOAD

REPORT

---

The local mechanical properties of ferritic and austenitic domains in a duplex stainless steel are locally studied by nanoindentation. The elastic and plastic properties of the two phases are determined. Without any specific surface treatment (chemical or electrochemical), the austenitic and ferritic domains present in the duplex stainless steel are distinguished using magnetic force microscopy. The magnetic scans allow nanoindentation results to be assigned to the respective phase, yielding the local mechanical properties of the duplex steel. The magnetic scans also show a sharp transition between the phases that is maintained even inside indentations. The ferrite phase is found to supersede austenite in the elastic modulus, hardness, and strain-hardening exponent, while both phases possess similar yield strength. Interface properties are a weighted average of the phase properties.

I. INTRODUCTION

Duplex stainless steel is a class of materials that attracts great interest due to its improved resistance to general and localized corrosion, stress corrosion cracking, abrasion, and wear.1– 4 In addition, it shows higher strength than the austenitic grades while also carrying a lower cost due to the decreased concentration of alloying elements, mainly molybdenum and nickel.5 Consequently, duplex stainless steel has become a typical material of choice in chemical, petrochemical, and nuclear industries,6 as well as in desalination plants.5 Duplex stainless steel is generally composed of equal volume fraction of two phases austenite c and ferrite a. Due to such inhomogeneities, each phase will respond differently for a given applied load.7 The correct prediction of the macroscopic properties of this material requires a local description of its properties taking into account the interaction between its constituents and their geometric arrangement.8 While several stereological parameters were proposed to describe the microstructure and phase distribution,9 the understanding will not be complete without knowing the local phase features. Nanoindentation can provide valuable information on the local elastic and plastic properties in dual phases materials with higher spatial resolution and minimal influence of geometric or texturing effects.10,11 Ahn et al.12 combined nanoindentation with Electron Backscattered Diffraction to study the nanohardness of statically and dynamically a)

Address all correspondence to this author. e-mail: [email protected] DOI: 10.1557/jmr.2012.99 J. Mater. Res., Vol. 27, No. 12, Jun 28, 2012

http://journals.cambridge.org

Downloaded: 23 Nov 2014

transformed ferrite in supercooled austenite. Campos et al.13 utilized nanoindentation to study the duplex stainless steel prepared by powder metallurgy to understand the effect of alloying elements and sintering conditions on the mechanical properties of their material. It is interesting to obtain quantifiable distinct properties of the phases using the same technique given that the phases can be clearly discerned. Studying the microstructure of duplex s