The process of dynamic strengthening of Hadfield steel, currently widely used for cast railway frogs, was studied. Continual dislocation hardening up to the depletion of plasticity and creation of surface microcracks presents the specific limited state under rolling contact in this application. The narrow affected zone and intensive mechanical and structural heterogeneity on the loaded surface are restrictive for standard mechanical testing.To study the different states of this process, instrumented indentation tests were performed. The results showed the possibility of comparative evaluation of the elastic-plastic behaviour of this steel, which is typical with high dynamic durability, but also with the significant sensibility to the ratio of normal impact loading vs. tangential slip. Because of this, an important parameter of fatigue life is the primary state of dynamic strengthening. The influence of explosion hardening, as a prospective way to improve the wear resistance of Hadfield steel, was included in the test. Each step of the degradation process was simulated using the special rolling contact stand at a defined loading condition. The measured hardness gradient of loaded surface layers displayed the depth and intensity of the induced changes. Martens hardness was measured in thus identified layers for each representative state of material. The elastic-plastic capacity of the surface layer was evaluated as a ratio elastic to the global energy of indentation. The metallography evaluation, focused on the contact surface, documented an increase of elastic response as a result of the dislocation hardening process.Keywords: rolling contact testing, Hadfield steel, surface layer, deformation hardening, indentation test
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