Steel-grading by micromagnetic techniques

In the present investigation attempts have been made to identify the steel grade in the nondestructive way using micromagnetic techniques (3MA: Micromagnetic-, Multiparameter-, Microstructure- and Stress-Analysis). Tube samples of steel grade ST 35, St 45, ST 52, St 55, ST 65 and 10 CrMo 9 10 (acc. DIN-standards) and with three different heat treatment histories (cold worked, cold worked and annealed, cold worked annealed and drawn) were tested using the 3MA laboratory set up. The micromagnetic parameters like the maximum of the magnetic Barkhausen noise (Mmax), the coercivity (Hcm), corresponding to the maxima of the Barkhausen noise, distortion factor (K) and coercivity (Hco), both derived from the analysis of magnetic tangential field strength have been estimated at five different locations at each tube for each steel grade. From the analysis of these four magnetic quantities taking into account the standard deviation it has been posible to identify each steel grade on the basis of composition and heat treatment history.