The effects of martensite morphology on mechanical properties, corrosion behavior and hydrogen assisted cracking in A516 grade steel

A low carbon A516 steel (0.2% C) having 0.9% Mn content has been annealed at 760 °C with predominantly austenite and martensite input structure. This treatment lead to a dual phase (DP) ferrite–martensite microstructures with 50% martensite volume fraction in two morphologies, i.e. bulk martensite (BM) and fibrous martensite (FM) respectively. The ferrite–martensite DP steels exhibits much higher strength (~2 times) than ferrite–pearlite (FP) steel albeit with lower elongation (50%). The martensite morphology does not affect the uniform elongation but FM morphology exhibits higher strain to fracture. However, the corrosion rate is effected by the fraction of interfaces rather than the type of constituent phase. The BM condition with minimum interfaces has the least corrosion rate in weak acidic solution. The DP steels are more disposed to hydrogen embrittlement than FP steel. This phenomena causes a lowering of flow stress and strain fracture, the former is more progressive with rise in temperature than the latter. The crack nucleation is directly related to the corrosion rate, however despite twofold higher corrosion rate in BM condition, the extent of hydrogen embrittlement in both morphologies is similar because of the connected ferrite–martensite boundaries in BM morphology.