Evaluation of Embrittlement of Construction Steels by Microindentation

The mechanical characteristics of a metal are determined by a combination of three groups of factors: the chemical composition, the structural features, and the deformation ability of the structure, i.e., the ability of elements to relax internal stresses during deformation through dislocation sliding which does not lead to the crack formation and destruction. The possibility of using microindentation to assess the deformation ability of the structure of structural steels with a relatively high ductility is the goal of the study. The theoretical analysis revealed that an increase in the stiffness and a decrease in the plasticity of a metal leads to a change in the deformation model during indentation and, in particular, to the occurrence of deformation effects of various morphologies on the surface near the imprint, which can be indicative of the metal plasticity. Experimental studies performed on pipe steels of various strength and types of structure confirmed that, as the deformation ability of the metal decreases (primarily as a result of deformation hardening), a system of localized shears is formed near the imprint along the lines of action of maximum tangential stresses. A scale for ranking data of localized shears is proposed, and the optimal load value and shape of the indenter which provide gaining maximum information by microindentation are determined. A methodology for assessing the embrittlement of plastic construction steels on the basis of the results of microindentation has been developed, which can form a basis for creating an effective technology of nondestructive evaluation of the metal state.