Hydrogen transport and embrittlement in 300M and AerMet100 ultra high strength steels

Abstract

This paper describes how hydrogen transport affects the severity of hydrogen embrittlement in 300M and AerMet100 ultra high strength steels. Slow strain rate tests were carried out on specimens coated with electrodeposited cadmium and aluminium-based SermeTel 1140/962. Hydrogen diffusivities were measured using two-cell permeation and galvanostatic charging methods and values of 8.0x10-8 and 1.0x10-9 cm 2 s-1 were obtained for 300M and AerMet100, respectively. A two-dimensional diffusion model was used to predict the hydrogen distributions in the SSR specimens at the time of failure. The superior embrittlement resistance of AerMet100 was attributed to reverted austenite forming around martensite laths during tempering.

Strain Gradient Plasticity-Based Modeling of Damage and Fracture

“…The upper bound is also given by (8.6) for E APP less than -0.750 V SCE , with the following relationship accurate for higher E APP [173] C H−Diff (wppm) = −739.24E The applied potential dependence of K T H is predicted by relating E APP to C Hσ using (8.5) for Monel K-500, or (8.6) and (8.7) for the steels in (8.4) with the relevant C Hσ from SGP FE analysis, then fitting the single-unknown parameter, α, in (8.1) to K T H measured for any E APP . A similar procedure is employed to predict the E APP dependence of da/dt II using (8.2), with measured D H−Eff [176] and independently determined x crit [36,179]. Critically, da/dt II is predicted without adjustable parameters since C Hσ appears in (8.1) and (8.2).…”

“…Electrochemistry measurements and modeling yielded crack tip H concentration versus applied potential (E APP ) [102,173], as well as trap-affected effective hydrogen diffusivity (D H−EFF ) for each alloy [174][175][176]. The E APP dependencies of K T H and the hydrogen-diffusion limited Stage II crack growth rate (da/dt II ) were originally modeled [92,102,171,172] using crack tip stress from a continuum blunt-crack formulation [91].…”

“…However, the precise Griffith toughness for a lath or packet inter-face in the martensitic microstructure of AerMet T M 100 is not known [172]. Each SGP prediction is given by a solid plus dashed curve, and compared to experimental measurements for AerMet T M 100 and Ferrium T M M54 [173,174] Ferrium M54 AerMet100 0.6M NaCl PSGP model Ferrium M54 AerMet100 0.6M NaCl PSGP model The E APP dependence of da/dt II is predicted without any adjustable constants using independently established D H−EFF [176] and x crit [179]; results are shown for upper bound (Figure 8.7) and lower bound (Figure 8.8 Crack tip stresses are substantially elevated, and the crack opening profile is reduced, due to a high-GNDs density.…”

Failure Analysis of Engine Crankcast Bolts Treated by Alodine Anodic Technology

“…When steels are protected by corrosion resistance coating of sacrificial metallic, it is increasing risk of hydrogen embrittlement for two reasons [4]. First, if the coating process is electrodeposition a small proportion of the plating current produces hydrogen, it will trapped into the coating and absorbed by the matrix steel slowly.…”

“…In this case, exposed portions of the steel substrate act as cathodic sites where hydrogen is generated by the reduction of water. If this hydrogen is absorbed in sufficient quantities it can also lead to failure of high strength steel and this process is termed hydrogen re-embrittlement [4].…”