Characterization of low-carbon steel after cold deformation based on Barkhausen noise

In recent years, the original aim of non-destructive testing, i.e. the detection of defects arising in components either during manufacture or during operation, has been added a mew task of assessing material state, e.g. with regard to mechanical properties. The non-destructive testing techniques used for this purpose must allow characterisation of the appropriate state of the polycrystalline material structure (grain size, different phases, precipitates, dislocations etc.). It is to be expected that mom-destructive analysis of microstructures and microstructures differences will attain considerable importance. In order to obtain information on microstructural state using non destructive methods, measurements must be used which result from physical processes dependent upon the material microstructure. It must be emphasised, that the influences of lending (operational and residual stresses) are often superimposed with equal intensity on the measurement. The Barkhausen noise associated with this, resulting from irreversible Bloh wall movements, can be used for such measurements after suitable amplification. Barkhausen noise signals and power spectrum of the Barkhausen noise signal have been measured for a structural steel over a range of plastic deformations up to 60%. The intercept or the power spectrum is seen to decrease with increasing deformation while the coercivitiy increases and both the permeability and remanence decrease.