Non-destructive evaluation of material degradation in RPV steel by magnetic methods

The minor hysteresis loops are measured with increasing magnetic field amplitude, Ha, step by step and analyzed in connection with the lattice defects such as dislocations in deformed and neutron irradiated A533B steels. We have defined several new magnetic parameters in the minor loops: they are a pseudo coercive force Hc*, a pseudo remanence BR*, a magnetic susceptibility at pseudo coercive force χ H*, pseudo hysteresis loss Wf*, pseudo remanence work Wr*. Hc* is the magnetic field where the magnetization becomes zero in the minor loop. Six coefficients sensitive to lattice defects are obtained by the pseudo magnetic properties and they are independent of Ha as well as the magnetic field. These coefficients are effective parameters for nondestructive evaluation of degradation before the initiation of cracking. The minor loops have several advantages for the nondestructive evaluation compared with the major loop. The coefficients have much information about lattice defects and the high accuracy. The measurement is available for low magnetic field of 20 Oe and the Ha step is not necessarily fine for the detailed information because of the similarity. (orig.)