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DC

DC: Delayed Cracking
Definition:Material failure after an incubation time with or without external loading, caused by the interaction of stresses or residual stresses with hydrogen.
Explanation:DC is one kind of material failure frequently observed in advanced high strength steels (→AHSS) with the tensile strength above 800 MPa. The AHSS are strengthened by multiphase structure or deformation mechanisms such as TRIP, TWIP, etc. Therefore, the deformed components obtain high residual stress and high density of lattice defects. Then, hydrogen atoms are accumulated within the stress concentrated regions and also interacts with various lattice defects (hydrogen trapping) during the redistribution process (hydrogen diffusion). As a result, materials fail with a time delay, when the material strength is lowered by the local hydrogen concentration.

A deep drawing (→DD) test is a typical test to reveal the material susceptibility to DC. The successfully deformed specimens show DC after different incubation periods (varying from minutes to months), which indicate their DC susceptibility.
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Diagram:

Delayed cracking in high Mn steels. (a) Fractured cup. (b) SEM picture of fracture surface. (c) Incubation time until the first crack occurrence, the grade X60Mn22 shows delayed fracture
SFB-Link:High Mn steels are known to be susceptible to DC. The underlying fracture mechanisms have been investigated on specimens after mechanical testing in combination with ab initio calculation of hydrogen interactions with different lattice defects, deformation mechanisms and fracture analysis.
References:Xiaofei Guo, Influences of Microstructure, Alloying Elements and Forming Parameters on Delayed Fracture in TRIP/TWIP-Aided Austenitic Steels, RWTH Aachen, 2012 (Dr. -Ing. Diss).
J. Con Pezold, L. Lymperakis, J. Neugebauer: Hydrogen-enhanced local plasticity at ductile bulk H concentrations-The role of H-H interactions and the formation of local hydrides. Acta materialia 59(2011) 2969.