Hydrogen Absorption during Case Hardening of Steels EN20MnCr5 (SAE5120) and EN18CrNiMo7-6 (SAE4820)

Abstract

Damages to case-hardened components are often associated with the phenomenon of hydrogen embrittlement due to their specific fracture pattern. In the present work, the effects of the case hardening process on the hydrogen content in the material were investigated and the effects of hydrogen on the mechanical properties were examined. In order to determine not only the influence of the heat treatment process but also the influence of the material, the case-hardening steels EN20MnCr5 (SAE5120) and EN18CrNiMo7-6 (SAE4820) with different degrees of purity were investigated. From the results it can be deduced that the sulphidic and oxidic inclusions have no significant influence on the hydrogen content. When checking the mechanical properties, it was shown in the incremental step loading technique according to ASTM F1624 that a purely case-hardened condition only has a slight tendency to hydrogen embrittlement. However, if the material is additionally loaded with hydrogen, the material fails significantly below the maximum expected load in the incremental step loading test, which is to be interpreted as a clear indication of failure due to hydrogen embrittlement. However, the fracture patterns of these two states do not show any significant differences. Therefore, it does not seem possible to attribute damage to a case-hardened component to hydrogen embrittlement on the basis of the fracture pattern alone.

Keywords

• hydrogen embrittlement
• case-hardening
• carburising
• diffusible hydrogen
• residual hydrogen
• high-strength steel