Strain aging in the surface layers of low alloy steel
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Investigation of the process of anomalous strain aging in the surface layers of low carbon, steel after grinding and lengthy aging confirmed the decisive role of carbon in the change of the mechanical properties of the surface layers and of their physical state.
The microhardness of steel (0.033% C; 0.010% N) after aging for one year more than doubles in the surface layers 6–8 μm thick. Across the layer it changes nonmonotonically; hardness changes most in the surface layer 1–2 μm thick.
The effect of strain aging of steel is associated with the gradual development of a mosaic structure in the crystal grains, caused by the redistribution of dislocations. The magnitude of misorientation of substructural elements of the grains, evaluated according to the size of the interference spots on the x-ray photograph, changes during aging from a few to tens of degrees.
The change of properties of the subsurface layers in time is apparently caused by hydrogenation that occurs when steel is ground, and by the subsequent process of redistribution of impurity elements, causing a high degree of lattice distortions in it.
KeywordsHydrogenation Mechanical Property Surface Layer Alloy Steel Decisive Role
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