Article Article
Implementation and Calibration of Nondestructive Determination of Mechanical Properties of Open-Die Forgings by 3MA-Technique

Nondestructive testing of open-die forgings is indispensable to guarantee high quality of such products. UT-testing has been implemented into the production chain as means of quality since the 1950’s. Furthermore, the detection of surface and subsurface defects can be performed by eddy current techniques. For the last 40 years, Fraunhofer Institute for Nondestructive Testing (IZFP) has been developing the 3MA-technique (Micromagnetic Multiparameter Microstructure and Stress Analysis), that combines four techniques of measuring electric and magnetic effects in the sample. By means of Barkhausen Noise, Eddy currents, harmonic analysis and electromagnetic interference permeability the correlations between magnetic properties such as coercitivity and magnetic permeability on one hand and hardness, tensile strength and residual stresses on the other hand are defined. The measurement of hardness by application of 3MA-technique has been standardized in several guidelines. Saarschmiede Freiformschmiede (SSF) is continuously developing and implementing NDT-techniques into its process chain to ensure highest product quality. The co-operation with Fraunhofer IZFP permitted to correlate 3MA-signals to mechanical properties measured destructively by tensile testing. High accuracies between destructive and non-destructive determination of tensile properties have been observed during first examinations. Implementation of 3MA-technique into SSF’s production chain permits shorter lead times due to fast pre-evaluation of mechanical properties before final inspection by destructive techniques. This paper deals with newest measurements on shafts made of creep-resistant steels and steel grades that are tough at low temperatures. Different calibration modes and both advantages as challenges in achieving a reliable calibration for this testing method will be presented.

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