Non-destructive characterization of martensite in AISI type 304 stainless steel using squid and MBN methods

Detection and characterisation of small amounts of strain induced martensite in AISI tape 304 steinless steel is useful for early detection of in-service degradation. Since mertensite is a magnetic phase, magnetic methods of NDE are very attractive. Two such methods namely Superconducting QUantum Interference Device (SQUID) and magnetic Barkhausen noise (MBN) signal are discussed in this paper. Specimens with different degree of cold work have been prepared and investigated. A monotonic increase in SQUID and MBN Signal output has been noticed with cold work. Martensite in even 10 % cold woked specimens has been unambiguously characterised. Experimental studies have shown that the SQUIDs and MBN methods are more sensitive to detection of mertensite as compared to the other methods such as eddy currents testing, X-ray diffraction (XRD) analysis, and use of magnetic hysteresis loop parameters