13th International Conference on Fracture June 16–21, 2013, Beijing, China -4- b) Figure 1. SEM-micrographs of surface nanostructured specimen 2.3. Static tension tests 2.3.1. Mechanical properties During tensile tests the loading diagram of 12Cr1MoV steel for dog-bone shape specimens was registered. It was found that for untreated specimens the presence of sharp yield point (yield tooth) is evident like it takes place for low carbon steels. Yield point of such specimens makes σ0.2= 270 ± 25 MPa, ultimate strength –σu= 494 ± 36 MPa and elongation – ε = 20 ± 3 % which is close by values to the reference book data for this steel [4]. After the surface nanostructuring the value of ultimate strength is increased up to σu = 570 ± 17 MPa while elongation becomes lower ε = 16 ± 0.7 %. In doing so, there is no formation of the yield plateau at the diagram of the processed specimens. 2.3.2. Optical microscopy Microscopic investigations of specimens surface near the area of the main crack at a certain distance from the fracture edge were performed (fig. 2). It is found that the specimen without surface treatment has the pronounced grain strain induced relief (fig. 2, a). At the same time undermore detailed observationit is seen that the surface of the nanostructured layer has small microcracks characterized by variation in their orientation in the modified layer (fig. 2, b). Whether, presence of the nanostructured layer on the surface of 12Cr1MoV steel hinders the formation of the grain relief that results in lower surface roughness of such specimens. The fracture surface of specimens after treatment shows signs of ductile fracture except for surface layer where the fracture was brittle. It is obvious that the thickness of the layer is not strictly constant which is manifested in the form of varying width of subsurface layer characterized by brittle fracture.
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