Hydrogen-assisted damage in austenite/martensite dual-phase steel

For understanding the underlying hydrogen embrittlement mechanism in transformation-induced plasticity steels, the process of damage evolution in a model austenite/martensite dual-phase microstructure following hydrogenation was investigated through multi-scale electron channelling contrast imaging and in situ optical microscopy.  

Figure 1: Non-deformed steel microstructure and corresponding hydrogen distribution. (a) Optical micrograph. (b) ECC image showing twins in martensite. SEM images showing silver particles  (white) at (c) low and (d) high magnifications

Localized diffusible hydrogen in martensite causes cracking through two mechanisms: (1) interaction between {1 1 0}M localized slip and {1 1 2}M twin and (2) cracking of martensite–martensite grain interfaces. The former resulted in nanovoids along the {1 1 2}M twin. The coalescence of the  nanovoids generated plate-like microvoids. The latter caused shear localization on the specific plane where the crack along the martensite/martensite boundary exists, which led to additional martensite/martensite boundary cracking.

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