Technical Diagnostics and Non-Destructive Testing #4, 2019, pp. 12-24
Diagnosis of damage in austenitic steel AISI 304 at mechanical loading by measurements of coercive force
O.P. Gopkalo1, V.O. Nekhotiashchiy2, G.Ya. Bezlyudko3, Yu.P. Kurash1, R.M. Solomakha3
G.P. Pisarenko Institute for Problems of Strength of the NAS of Ukraine. 2 Timiryazevskaya Str., 01014, Kyiv.
E.O. Paton Electric Welding Institute of the NAS of Ukraine. 11 Kazymyr Malevych Str., 03150, Kyiv. E-mail: firstname.lastname@example.org
CC «Spetsialni naukovi rozrobky», PO box 12036, 61184, Kharkiv, Ukraine
The paper gives the results of experimental studies of applicability of coercimetric control for assessment of the degree of metal damage at mechanical loading by measuring the coercive force. It is shown that the differences in the reaction of the coercive force on mechanical loading of ferromagnetic and austenitic steels consist in differences of physical nature of these phenomena. For ferromagnetic steels the changes of coercive force values at mechanical loading are related to ordering of the orientation of metal domain structure (from the chaotic to directional). Reaction of the coercive force on mechanical loading of paramagnetic (in the initial state) unstable austenitic steel AISI 304 (08Kh18N9) is related to structural transformations during deformation of initial austenite into deformation martensite with final ferrite-pearlite decomposition. Mechanical loads result in the change of the ratio of ferromagnetic and paramagnetic metal phases, which cause an increase of coercive force values up to a certain level that is followed by lowering of these values at fracture. It was found that increase of the values of the coercive force corresponds to elastic and elasto-plastic deformation (crack initiation stage), while lowering of their values is associated with loss of metal integrity at appearance of pores or cracks (crack propagation stages). For unstable austenitic steels it becomes possible to considerably simplify determination of the endurance limit and establishing the stages of damage accumulation process, by the change of the direction of coercive force kinetics during loading, with plotting of irreversible damage line (by French). Coercimetric monitoring of the surface of real structures allows determination of the direction of principal stresses and detection of initiation of surface and subsurface cracks, as well as assessment of the obtained damage level. 18 Ref., 18 Fig.
Keywords: structuroscope, coercive force, loading, damage, stress, deformation, fracture
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