Analysis of minor hysteresis loops in plastically deformed low carbon steel

We have measured minor hysteresis loops with increasing magnetic-field amplitude Ha step by step and have analyzed them in connection with lattice defects such as dislocations in deformed low carbon steel. We define several magnetic parameters in the minor loops: pseudocoercive force HC*, pseudoremanence MR*, pseudosusceptibility at pseudocoercive force H*, pseudohysteresis loss WF*, and pseudoremanence work WR*. We find several simple relations between the pseudomagnetic properties, namely, MR*/Ma*=9/10 and 3/5, and WR*/WF*=1/6 and 1/8, before and after plastic deformation, respectively. These relations are due to the similarity of minor loops. Six magnetic coefficients that are sensitive to lattice defects and are independent of Ha, as well as of the magnetic field, are obtained from the pseudomagnetic properties. These coefficients are effective parameters for nondestructive evaluation of degradation before the initiation of cracking. The minor-loop method has several advantages for nondestructive evaluation compared with the traditional method using major loops. The coefficients can give us much information about lattice defects with high accuracy. The measurements can be done at low magnetic fields less than 20 Oe and the Ha step does not necessarily have to be fine to obtain detailed information because of the similarity of minor loops.