Use of Magnetic Barkhausen Noise (MBN) to Follow Up the Formation of Sigma Phase in Saf2205 (UNS S31803) Duplex Stainless Steel

Abstract

Duplex stainless steels have a structure normally composed of austenite and ferrite in approximately equal proportions. In order to attain control of its fabrication processes and performance, it is important to understand its microstructural evolution, due to the formation of intermetallic phases such as sigma (σ) and chi (χ), which may cause a severe deterioration of mechanical properties. In the present study, the evolution of sigma phase during heat treatments at temperatures in which intermetallic phases can be formed (800ºC-900°C) was studied using magnetic analyses on a SAF2205 (DIN 1.4462/UNS S31803) steel. A significant reduction of the intensity of Magnetic Barkhausen Noise (MBN) was observed with the increase of heat treatment time, indicating a decrease in the quantity of ferromagnetic phases. For 24-hour-long treatments, the Barkhausen Noise signal is almost completely enclosed by the background noise, indicating the existence of a very small volume fraction of ferrite. If proper calibration samples are to be produced, this technique may be a viable method for non-destructive evaluation of field components working under thermal conditions that may cause the formation of intermetallic phases.

A New methodology of Nondestructive Testing for Quantitative Evaluation of Sigma Phase in Duplex Stainless Steels

“…The effect of deleterious phases on the mechanical and corrosion properties on the Duplex Stainless Steels (DSSs) is well known and studied by many researchers. [1][2][3][4][5][6] These phases may be formed during hot rolling process, components operation at certain temperatures and welding, which constitute a broad application of DSSs. 7,8 Therefore, not only the knowledge of the effect of the intermetallic phases on the DSSs properties is necessary.…”