Effect of grain size on mechanical electrochemical and hydrogen embrittlement behaviour of a micro-alloy steel

A fine grain micro-alloy steel subjected to various annealing treatments resulted in microstructure with different grain sizes. Optical, scanning and transmission electron microscopes are used for microstructural characterizations. Hardness measurement, tensile testing, electrochemical polarisation and hydrogen embrittlement (HE) studies have been carried out to assess the mechanical and corrosion behaviour of the steel. Annealing treatment resulted in increase of grain sizes with the increase of holding time, decrease of cooling rate; and an associated decrease of hardness and strength. TEM study of the steel showed the characteristics morphology and distribution of precipitates. Tensile specimens of different grain sizes of the steel cathodically charged in an electrochemical cell, followed by tensile testing did not exhibit appreciable loss of ductility. FESEM fractographs of hydrogen charged samples showed a few chain of voids along with the ductile cup-cone features for other states as well and a quasi-cleavage features in the coarse ferrite grains alloy.