INTERACTIONS AND EFFECTS OF HYDROGEN ON HIGH STRENGTH STEELS

GRACIELA A. MANSILLA; ELENA BRANDALEZE; MARIANO N. INÉS

High Strength Steels - New Trends in Production and Applications

Ricardo Branco

Lugar: New York; Año: 2018; p. 89 - 114

Many steel components used in engineering in automotive transmissions require good machining capability, among other important mechanical properties. It ensures good in-service performance because structural applications require high resistance levels. However, these responses may be compromised by the presence of trapped hydrogen (H) in the product. Hydrogen embrittlement mechanisms are closely linked to the mobility and the segregation of hydrogen in the material. In this sense, microstructural defects, such as trapping sites (grain boundary, inclusions, dislocations, etc.), are sometimes reservoirs of diffusible hydrogen (low energy reversible traps). In this sense, microstructural defects, as trapping sites (grain boundary, inclusions, dislocations, etc.), sometimes are reservoirs for diffusible hydrogen (low energy reversible traps) known as high energy irreversible traps. Specifically, hydrogen atoms size allows to its high mobility in ferrite, specially in interstitial sites or interacting with inclusions. Probable H sources, besides those corresponding to iron making stages, are working atmospheres, electroplating processes, welding, and localized corrosion. One of the most damaging effects caused by these atoms in low carbon steel and low alloy is the reduction in the fatigue life and Hydrogen Induced Cracking (HIC). In general, HIC resistance may be correlated with some microstructural aspects. This behavior corresponds to the embrittlement mechanisms associated mainly to irreversible hydrogen trapping at ferrite-cementite interfaces, precipitates and inclusions. However, H can also be occluded in vacancies and dislocations, and in this case the literature refers to reversible or diffusible hydrogen, i.e. traps where hydrogen has a short residence time at the temperature of interest.This Chapter is devoted to hydrogen?steel interactions during low cycle fatigue of high strength steel. Differential scanning calorimetry and silver microprint decorating techniques are employed to detect H presence and to help to understand its influence on mechanical response.