Martensite morphology and volume fraction evaluation of dual-phase X70 steel using magnetic Barkhausen noise technique

• Published in: Journal of magnetism and magnetic materials 2022-08, Vol.555, p.169397, Article 169397
• Main Authors: Nebair, Hocine, Helifa, Bachir, Bensaid, Samir, Zidelmel, Sami, Khaldoun Lefkaier, Ibn
• Format: Article
• Language: English
• Subjects: Barkhausen effect; Direct quenching; Dual phase steels; Dual-phase steel; Engineering Sciences; Evaluation; Excitation; Hardness; Heat treating; Heat treatment; Heat treatments; High strength low alloy steels; Interrupted quenching; Magnetic Barkhausen noise; Martensite; Martensite volume fraction; Microstructure; Microstructure morphologies; Morphology; Non-destructive evaluation; Nondestructive testing; Optical microscopy
• ISSN: 0304-8853; 1873-4766
• DOI: 10.1016/j.jmmm.2022.169397

•The magnetic Barkhausen noise method is highly sensitive to changes in microstructure morphologies and martensite volume fraction.•The IQ treatment formed fine and fibrous martensite morphology uniformly distributed in the ferrite matrix.•The DQ treatment revealed hard martensite distributed in a ductile ferrite matrix.•The SQ treatment showed a banded morphology with a non-uniform distribution of the phases.•There are direct correlation between magnetic hardness (Hc) and mechanical hardness (HV) for each heat treatment. This paper aims to evaluate the martensite morphologies and volume fractions of dual-phase (DP) X70 microstructure (ferrite + martensite) using the Magnetic Barkhausen Noise (MBN) non-destructive technique. In order to develop different morphologies in X70 steel, three different heat treatments (intermediate quenching (IQ), direct quenching (DQ), and step quenching (SQ)) are done for half-hour. The inter-critical annealing temperature (IAT) ranges applied to the samples are from 740 °C to 820 °C. Measurements of MBN were carried out using the MikroMach instrument. Hardness measurements and microstructure examinations were conducted using a durometer and optical microscopy. Experimental results show that IQ treatment formed fine and fibrous martensite morphology uniformly distributed in the ferrite matrix. DQ treatment revealed hard martensite distributed in a ductile ferrite matrix. SQ treatment showed a banded morphology with a non-uniform distribution of the phases. Martensite Volume Fraction (MVF) and hardness get larger with IAT increases. These treatments permit obtaining the highest hardness in DQ treatment, and the lowest hardness has been identified in SQ treatment. Indeed, the MBN method has been proved to be highly sensitive to changes in microstructure morphologies and MVF. The highest MBN signal amplitude (MBNSA) for the SQ treatment has been identified at the lowest magnetic excitation field; in contrast, the lowest MBNSA for DQ treatment was located at the highest magnetic excitation field. The maximum MBNSA decreases whenever IAT increases. Finally, the direct correlation between magnetic hardness (Hc) and mechanical hardness (HV) for each heat treatment is established in this paper.