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.

In this work, a mathematical model to characterize the ageing degree on 12Cr1MoV steel used on main steam pipes from power plants is developed. This model start from Bertotti´s model about the variation of magnetic flux with the time, obtaining different mathematics expressions which relate the induced voltage on the coil and known as Magnetic Barkhausen Noise (MBN) with grain and carbides size, which constitute, among others parameters, one that can be used to evaluate the ageing process on the analyzed steel, with the developed model a decreasing and increasing later of voltage with the increasing of grain and carbide size respectively for the same magnetic field applied is verified, with this result it is possible to corroborate the magnetic measurements which be developed using MBN on practice applications.

En el presente trabajo se desarrolla, a partir del efecto Barkhausen, un modelo matemático que permite caracterizar el grado de envejecimiento del acero 12Cr1MoV empleado en las Líneas Principales de Vapor (LPV) de las Centrales Termoeléctricas de Cuba. El modelo parte de las ecuaciones del modelo de Bertotti sobre la variación del flujo magnético en el tiempo, con el cual se obtienen expresiones matemáticas que correlacionan el voltaje inducido en la bobina, conocido como ruido magnético Barkhausen (RMB), con el tamaño del grano y de los carburos que son, entre otros, parámetros microestructurales que definen el grado de envejecimiento del acero estudiado, el modelo desarrollado describe una disminución y un aumento del voltaje de la señal con el incremento del tamaño de grano y carburos respectivamente para un mismo valor del campo aplicado, este resultado permite corroborar las mediciones que se desarrollen del mencionado efecto en aplicaciones prácticas.