This paper discusses the condition in the magnetic and mechanical properties of metal materials near the edges of a fatigue crack (samples example - steel20). On the special samples with straight fatigue cracks, the coercive force and hardness were measured near the crack edges. The coercive force drop on the crack was 25%. Therefore, if the magnetic properties of ferromagnetic material fall during the survey, this means that there is a crack in the structure being examined, which is not always detected visually or by non-destructive testing methods with a different physical basis. The obtained results of hardness measurements allowed us to formalize the dependence of the straight crack depth on the drop in hardness near its edges relative to the same parameter in the defect-free section. By calculating and experimentally, the relationship angle between normal and the tangent to the surface of crack inclinationswas identified and formalized. The results of the work can be used in the technical diagnostics of engineering objects. © Published under licence by IOP Publishing Ltd.