Detection of a milling-induced surface damage by the magnetic Barkhausen noise

• We study applicability of magnetic Barkhausen noise for evaluation of milled surfaces.
• Parameters based on envelope integrals over specific field intervals are proposed.
• Shape of the Barkhausen noise rms profile strongly correlates with the dH/dt waveform.
• Surface rehardening leads to a distinct two-peak envelope for the soft 50 HRC steel.

The potential of the magnetic Barkhausen noise method for a non-destructive evaluation of the steel surface damage cased by milling was comprehensively investigated. A typical bearing steel was heat treated to three different hardnesses and then machined using the cutting tools with different degrees of the flank wear. The magnetic low-frequency measurements with a high reading depth were performed using a unique laboratory system providing a full control of the magnetization process. The high-frequency measurements were performed using a commercial Rollscan device. To study the induced magnetic anisotropy, the measurements were performed in two magnetization directions. In the feeding direction, the Barkhausen noise profiles showed a second high-field peak ascribed to an induced hardened surface layer, a so-called white layer. The most reliable results were obtained with the controlled waveform of the surface magnetic field measured directly by Hall sensors. In the perpendicular rotation direction, formation of the preferentially oriented matrix resulted in an enormously high Barkhausen noise activity. Based on these results, new magnetic parameters were proposed for the non-destructive evaluation of the white layer formation.