Evaluation of thermal ageing conditions in 17-4 PH stainless steel by Fourier descriptor analysis of magnetic hysteresis loops

Fourier descriptor analysis of magnetic hysteresis loops has been used to assess the conditions of isothermal and isochronal ageing in quench-aged precipitation hardening 17-4 PH stainless steel. The Fourier descriptors (i.e. sine harmonic coefficients in the Fourier series expansion of the magnetic flux density as a function of current arc length value of the ascending branch of hysteresis loop) have been found to be suitable for assessment of aged conditions of this material. This technique serves as a reliable tool to distinguish (i) as-quenched specimenen from the quench-aged specimens and (ii) specimens with different ageing conditions. The results obtained indicate that the Fourier descriptor technique is a promising tool for assessment of ageing conditions in 17-4 PH steel.