Magnetic structurescopy (Coercimetry) basis is correlation between physicochemical properties or mechanical characteristics of metal and one or more magnetic characteristics.
Its application in NDT started from new steel product quality assessment. Development of coercimetrical equipment enables distinction of structural inhomogeneity assessment of hardened layer conformity to required parameter (from 1 mm depth deviation) or Hard Spot detection (from 10 mm diameter and Δ <50 HV). The method is applicable for steel mills and in pipe manufacturing as well as on pipelines in operation.
At the video below is a demonstration of hardening depth and coercivity correlation at the example of crankshaft. Shaft’s necks are hardened with different hardening depth.
Coercivity of not-hardened parts is 6.8-7.2 A/cm.
The same principle is used for Hard Spot detection. Measurement on the steel plate shows the hardened areas.
Advantage of coercimetrical testing is resistance to scale, air gap, temperature up to +100°C, pollution or other imperfections of the surface inherent to heavy plates at steel mills.