The influence of steelmaking processes on the hydrogen embrittlement of a tempered martensitic steel

High strength low alloy (HSLA) steels with tempered martensite microstructure are widely applied in the offshore industry such as fasteners. The subsea environment conditions are quite favorable for severe hydrogen embrittlement (HE). Their good hardenability influences the achievement of excellent mechanical properties. Three different steelmaking routes such as continuous casting (CC), conventional ingot casting (CIC) and electroslag remelting (ESR) were investigated to verify the influence on the AISI 4140 steel microstructure and the HE susceptibility. Electrochemical hydrogen permeation tests were correlated with the microstructure obtained from each route that presented different levels of segregation bands. The CC process was responsible for the appearance of a high density of non-metallic inclusions (NMIs) like manganese sulfide (MnS) and impurities in segregation regions that increased the HE degree. The ESR route presented the best mechanical behavior due to the lowest reduction in ductility for hydrogenated uniaxial tensile test conditions and, consequently, the highest resistance regarding the HE.