Parameters of load-displacement curves and their correlation with the fracture surface in medium-carbon steel

V.A. Khotinov ORCID logo , A.B. Ovsyannikov, A.A. Andreev, V.M. Farber show affiliations and emails
Received 28 September 2021; Accepted 16 November 2021;
This paper is written in Russian
Citation: V.A. Khotinov, A.B. Ovsyannikov, A.A. Andreev, V.M. Farber. Parameters of load-displacement curves and their correlation with the fracture surface in medium-carbon steel. Lett. Mater., 2021, 11(4) 514-518
BibTex   https://doi.org/10.22226/2410-3535-2021-4-514-518
Ductile-brittle transition behavior of medium-carbon steel with 0.32 %C-1,35 %Mn-0,003 %B by instrumented impact testing and fracture analysis was studied. On the load-displacement curves the periods corresponding to different zones of crack propagation are distinguished. Each period can be quantitatively described by a set of strength, plastic and gradient parameters.Impact tests are mandatory for a wide range of structural steel products to evaluate the required service life and operational safety. This test is especially relevant for products used in operation in climatic areas with a cold climate, since it allows one to determine the temperature range of the ductile-brittle transition. Depending on the structural-phase state of a metal, the type of the temperature relationship of impact toughness and its displacement on the temperature axis may differ significantly. For ductile materials, the temperature range of the ductile-brittle transition is shifted towards ultra-low negative temperatures whereas for materials in the embrittled condition it lies in the region of higher temperatures. Ductile-brittle transition behavior of medium-carbon steel with 0.32 % C-1.35 % Mn-0.003 % B in two conditions (after normalization and after quenching and tempering) by instrumented impact testing and fracture analysis was studied. On the descending branch of the force-displacement curves the periods corresponding to different zones of propagation of the main crack are distinguished: period I is the ductile zone of pure shear, period II is the zone of brittle fracture, period III is the ductile zone of break fracture. Each period can be quantitatively described by a set of strength, plastic and gradient parameters. It is established that the displacement to the beginning of linear period II (SIIb) and slope of the curve on it (ΔF / ΔS)II have a better correlation with shear fracture zone percentage (B) than the other distinguished parameters of force-displacement curves.