Sensitivity of Barkhausen Noise in Monitoring the Surface Integrity of SAE 4340 Hardened Steel After Turning Process

This work investigates the feasibility of using the non-destructive testing technique based on the measurement of Magnetic Barkhausen Noise (MBN) to assess the surface integrity of SAE 4340 hardened steel after the turning process. The experiments were conducted using ceramic inserts and divided into two distinct experimental setups. In Experiment 1, the cutting parameters were kept within the levels recommended by the tool manufacturer. In Experiment 2, cutting parameters above these levels were applied. For the resulting samples, measurements of roughness, hardness, and residual stress were performed. MBN measurements were taken in the longitudinal direction to the cutting direction, and from the obtained signals, the MBN_rms e MBN_{peak−position} parameters were calculated and analyzed. The results showed that the MBN technique was unable to differentiate the hardness levels generated in the samples from both experiments, where a relatively low variation ( < ± 7,4%) was found. Regarding the roughness levels, it was found that, for the levels generated below Ra = 4, the MBN parameters were not influenced. However, when comparing the MBN results with the residual stress levels obtained by X-ray technique, the method demonstrated high efficiency for the analyzed conditions, showing a strong linear correlation (R² > 0,93). Finally, it was found that the presence of a white layer drastically influences the MBN signal, interfering with its sensitivity in measuring residual stress. Furthermore, this work suggests that the MBN technique also demonstrates sensitivity in detecting changes in the material induced by cutting tool wear.