Degradation of nuclear pressure vessel steel material (15H2NMFA) was investigated by a novel magnetic nondestructive testing method, so called Magnetic Adaptive Testing (MAT), which is based on systematic measurement and evaluation of minor magnetic hysteresis loops. The measured samples were thermally treated by a special step cooling procedure, causing embrittlement of the material. It was found that this type of degradation can be easily followed by magnetic measurements. Results of Charpy impact tests were compared with the magnetic parameters. A good, reliable and nearly linear correlation was found between magnetic descriptors and transition temperature. Some results suggest that MAT testing of cladded block samples is possible even through the relatively thick cladding