Detection of plastic deformation in low carbon steel by SQUID magnetometer using statistical techniques

In order to non-destructively detect the amount of plastic deformation accumulated in low carbon steel of S25C, the distribution of localized magnetism has been measured for plate-type S25 tensile specimens with plastic strains up to 6.45% by ultrahigh sensitive magnetic probes using superconducting quantum interference device (SQUID). The slope value obtained from the SQUID signal pattern, which means the ratio of the change in SQUID output voltage to the change in AC current flow in the superconducting magnet, was chosen as a candidate indicator to detect plastic strains in the present study. For quantitative assessment, statistical processing was performed for determining the datum of the distribution of the slope value. As a result of the statistical approach, small-scale plastic deformation could be detected on S25C tensile specimens. It was suggested that the magnetic measurement using SQUID magnetometer supported by the statistical techniques was a promising non-destructive evaluation method to detect the amount of plastic deformation accumulated in low carbon steel.