Detection of Segregation in a High Carbon Steel by Non-Destructive Techniques

In high carbon steel manufacture, segregation is a common problem that compromises the quality and performance of cast products. When they are rolled or forged, hard metallurgical phases can develop, promoting material embrittlement. To detect the segregation presence, traditionally, it is analyzed by macro-attack (according to the ASTM 381 standard). However, this methodology is limited to the subjective interpretation of the quality inspector, and also it is dangerous. Non-destructive means represent an agile alternative for quality control because they are sensitive to the chemical composition and microstructure of the steel. Through conventional ultrasound technique, an increase in attenuation coefficient was detected in the area of greater segregation and lower values in regions with greater chemical homogeneity. On the other hand, the longitudinal wave velocity was lower in the segregated region and higher in the zone with less segregation. Furthermore, by some mathematical relationships and wave speeds, Poisson’s ratio Young’s and shear modulus were obtained, which are related to the ease of rolling in steel. Finally, Eddy currents and impedance plane determined that the segregation region has a lower phase angle, and therefore, a higher electrical conductivity concerning the zones of less segregation.