Magnetic Barkhausen Noise Analysis for Microstructural Effects Separation during Flow Forming of Metastable Austenite 304L

This work deals with the analysis of the influence of different microstructural effects on non-destructive micromagnetic testing using magnetic Barkhausen noise (MBN) analysis, during flow forming of austenitic steel 304L tubes. This is necessary for the implementation of non-destructive MBN testing within the model of a soft sensor for closed-loop control systems. A characterization of the specimens was carried out by means of α'-martensite measurements, hardness tests, residual stresses and surface roughness. The aim is to establish the influence of the different microstructural effects on the measured MBN parameter, the maximum MBN amplitude Mmax. The strain-induced hardening, evolution of residual stresses and phase transformation during plastic deformation have a direct influence in the development of the Mmax parameter. However, a lower surface roughness triggers a mitigating effect on the MBN signals. This information is valuable to define the operation window of the sensor within the material modeling for property control.