Barkhausen noise- and eddy current-based measurements for online
detection of deformation-induced martensite during flow forming of
metastable austenitic steel AISI 304L
Abstract
This paper deals with micromagnetic measurements for online detection of
strain-induced α’-martensite during plastic deformation of metastable
austenitic steel AISI 304L. The operating principles of the sensors are
Barkhausen noise (MBN) and eddy currents (EC), which are suitable for
detection of microstructure evolution due to formation of ferromagnetic
phases. Nevertheless, the description of the calibration and
transformation models of the micromagnetic measurements into
quantitative α’-martensite fractions is beyond the scope of this paper.
The focus will be put on the qualification of different micromagnetic
methods as well as of different measurement systems under conditions
similar to the real ones during production, which is crucial for
implementation of a property-controlled flow forming process. The
investigation was carried out on tubular specimens produced by flow
forming, which have different content of α’-martensite. To characterize
the sensitivity of the sensors, different contact conditions between
sensors and workpieces were reproduced. MBN sensors are suitable for
detecting amount of α’-martensite, but the measurements are affected by
the surface roughness. This entails that the calibration models for MBN
sensors must take account of these effects. EC sensors show a closer
match with the amount of α’-martensite without having major affectation
by other effects.