Microstructural Transition
Formation of a ferromagnetic phase in certain stainless steel alloys during cold plastic deformation alters their overall physical properties. The accumulation of strain induced martensite changes the material from a non-magnetic state to a magnetic one. When austenitic stainless steel is stretched, bent, or drawn, the mechanical energy triggers a crystal lattice transformation.
This localized magnetic phase causes a major shift in the impedance of nearby inductive sensors.
Phase Measurement
Non-destructive eddy current testing is used to quantify the volume fraction of the magnetic phase in the deformed metal. High-frequency probes measure the change in magnetic permeability caused by the strain induced martensite. This approach is highly effective for monitoring the structural integrity of formed components.
Process Validation
Metrology labs calibrate the test equipment using reference standards with certified martensite content. These standards are verified using magnetic balances or X-ray diffraction to ensure high measurement accuracy.
Structural Outcome
Uncontrolled martensite formation can lead to stress corrosion cracking and hydrogen embrittlement in industrial components. Detecting these localized zones before they lead to mechanical failure is critical for high-reliability systems. The sensor must be calibrated to ignore surface roughness while remaining sensitive to the magnetic phase fraction.
