Investigations into the nature of relation between magnetic properties and the structure of cold-and hot-deformed steels after different kinds of annealing have enabled us to recommend that magnetic methods should be applied for evaluating the structural state and mechanical properties of the rolled steel. At many metallurgical plants of Russia magnetic nondestructive instruments are being used for production acceptance.

In many cases the changes occurring in the structure and phase composition of steel during hardening and tempering adequately affect its magnetic and mechanical properties, therefore one can use magnetic methods to determine mechanical properties of steel after hardening or tempering. For instance, the wearability of thermally hardened drill bits can be checked by measuring coercive force (H_c). However, there is an extensive class of problems in controlling the quality of hardening and tempering for medium-and high-carbon steels, which cannot be solved with the use of classical magnetic characteristics, e. g. H_c. To Solve these problems, we suggest using the analysis of stability of magnetic states against external actions: electromagnetic fields, elastic deformations and temperature.

Proceeding from the analysis of the stability of magnetic states against electromagnetic fields, together with the quality control of hardened and tempered products, one can diagnose service changes in the physicomechanical properties of products. Investigation into the stability of magnetic states against temperature have enabled us to propose both new methods for testing the quality of heat treatment and methods for active control of the heat treatment process by comparing the thermokinetic dependence of magnetic characteristics of the article being heat treated with those of the standard one. The methods for analysing the stability of magnetic states against elastic deformations have enabled us to apply this principle to developing various sensors memorising external attacks and to creating methods for evaluating microstresses and fatigue damage accumulation in structure elements. For surface-hardened products, due to different stability of the layers differing in their magnetic properties, one can achieve perfectly trustworthy inspection of the depth and hardness of the hardened layer, since the action of electromagnetic fields first ruins the remanent magnetism of soft magnetic components and then that of harder ones.

The level of internal macro-and microstresses is an important characteristic of structures. This problem can be solved by several methods. One of them was mentioned above. Another technique is the use of magnetoelastic acoustic emission parameters. There is one more technique implying evaluation of microstress by separating of contributions from reversible of displacements of 180° and 90° domain boundaries and the analysis of the permeability change stipulated by the reversible displacement of 90° domain boundaries. If we compare the microstress measurement results obtained by magnetic methods with those obtained for thermally treated and plastically deformed steels by the X-ray diffraction analysis or through of dislocation density, we can establish a high degree of correlation.

Thus, one can use magnetoelastic acoustic emission parameters and effective magnetic permeability ensuring from the reversible displacement of 90° domain boundaries to analyse dislocation distribution in materials and to evaluate internal stresses in products. For example, the study of the magnetoelastic properties of some samples of a bend wrecked after 90 thousand hours of working in a steam pipe at the steam temperature of 540° C and the pressure of 14MPa has proved that the level of microstresses in the sample taken from the tension zone of the bend near the fracture spot (a zone of different dislocation structure) is about 25% lower than that in the sample taken from the neutral zone.

The division of magnetization and remagnetization into reversible and irreversible processes allows one to solve various problems in the structure inspection of ferromagnetic materials. Thus, we have found that irreversible magnetic characteristics measured in weak magnetic fields are more sensitive to neutron irradiation of steels than coercive force.

Magnetic methods are widely used for evaluating the quality of sintering in powder metallurgy. We suggest using saturation magnetization to evaluate residual porosity and using coercive force to evaluate the structural state. We have developed a two-parameter magnetic structuroscope for checking industrial products. Magnetic methods have also found an application for nondestructive quality control and evaluation of the cutting properties of tungsten-cobalt-alloy tools.