Effects of Micro-Sized Ferrite and Austenite Grains on the Pitting Corrosion Behavior of Lean Duplex Stainless Steel 2101

Yadi Hu,Jian Wang,Xinglong Liu,Yan He,Yuping Li,Yong Zhang,Peide Han

doi:10.3390/met7050168

Abstract

The connection between the austenite transformation and pitting corrosion of lean duplex stainless steel LDX 2101 was investigated at different annealing temperatures in the range 950–1200 °C. Optical microscopy, scanning electron microscopy, and electrochemical techniques were employed in the present work. Results indicated that micro-sized ferrite and austenite grains, formed with the increase of annealing temperature, influenced the pitting corrosion resistance of the studied stainless steel. As the austenite phase transformed into ferrite, the micro-sized ferrite grains were produced in austenite domains with temperature increase from 1000 °C to 1100 °C, especially at 1050 °C. In these conditions, the corrosion resistance of LDX 2101 was reduced by the micro-sized ferrite grains. A further increase of annealing temperature to 1150 °C produced the presence of micro-sized austenite grains in the ferritic phase, due to an incomplete transformation of austenite to ferrite. They represent new sites for severe pitting attacks and therefore the corrosion resistance of LDX 2101 was the weakest. The sample annealed at 1200 °C, with few micro-sized austenite grains in the ferritic matrix, exhibited excellent corrosion resistance. Moreover, a schematic was used to illustrate the pitting corrosion of the samples annealed at different temperatures.

Highlights

Duplex stainless steel (DSS) with nearly equal proportions of ferrite (α) and austenite (γ) phases, has exhibited excellent mechanical properties, corrosion resistance, and weldability, compared with the traditional austenitic and ferritic stainless steel varieties
The γThe phase was uniformly distributed in the matrix microstructure of the samples annealed at different temperatures for ferritic
The microstructure of the samples was elongated along the rolling direction and few the γ phase was uniformly distributed in the ferritic matrix precipitatesspecimens

Summary

Introduction

Duplex stainless steel (DSS) with nearly equal proportions of ferrite (α) and austenite (γ) phases, has exhibited excellent mechanical properties, corrosion resistance, and weldability, compared with the traditional austenitic and ferritic stainless steel varieties. A relatively low-cost DSS, the lean duplex stainless steels LDX 2101 with low additional amounts of Ni, are attracting more and more attention [1,2]. Owing to its complicated structures and uneven distribution of the alloy elements in each phase, studying the corrosion resistance of LDX 2101 is complicated. The localized corrosions—including pitting, intergranular corrosion, and selective corrosion—occur at the weakest parts in the LDX 2101 matrix. It is generally accepted that pitting is one of the most detrimental and concealed forms and usually influences localized corrosion [3]. Investigating the pitting corrosion resistance of LDX 2101 is necessary

Methods

Results

Conclusion