Abstract
A nondestructive testing method based on magnetic Barkhausen noise (MBN) detection is developed to evaluate the microstructural and mechanical properties of hot stamping boron steel with martensite/bainite mixed microstructures. Firstly, boron steel specimens are heat treated by Gleeble thermo-mechanical simulator to prepare mixed microstructures with different bainite fractions. Based on the analysis of MBN signals of these specimens, the relation between MBN characteristics and bainite fraction is investigated. The results indicate that the MBN intensity firstly decreases and then increases with the increasing bainite fraction. The MBN peak shows a positive linear correlation with bainite fraction above 30%. The bainite fraction could be simply evaluated when MBN peak is above 65 mV. Furthermore, according to the assessed bainite fraction by MBN detection, the ultimate tensile strength (UTS) and yield tensile strength (YTS) of hot stamping steel sheets treated by heated tools are calculated and compared with tensile tests. It is suggested that it could be feasible to evaluate the mechanical properties especially UTS of hot stamping parts with martensite/bainite mixed microstructures based on MBN detection.
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