The paper investigates the impact of the degree of plastic strain on the values of hardness HV5 and on the values which describe the Barkhausen noise and the residual magnetic field (RMF) quantitatively. Tests were performed on plastically deformed samples with a noticeable local narrowing – a neck. An analysis was carried out of the possibility of developing diagnostic relations that would allow an evaluation of mechanical quantities by means of magnetic characteristics. It is found that the differences in the degree of plastic deformation are well reflected by hardness values, the energy of Barkhausen noise E_BN, the number of counts N_BN and the gradients of the RMF components. The sensitivity of these diagnostic signals is similar. It is possible to develop quantitative diagnostic relations that could be used to evaluate the degree of plastic deformation based on the quantities mentioned above as well as dependences to determine other mechanical properties by means of magnetic measurements.