The Impact of Nb, Ti, Zr, B, V, and Mo on the Hydrogen Diffusion in Four Different AHSS/UHSS Microstructures

Abstract

Advanced and ultra-high strength steels (AHSS/UHSS) are susceptible to hydrogen embrittlement (HE), [1][2][3][4] for which diffusion of hydrogen is essential. [5,6] To obtain information on hydrogen diffusion in AHSS grades, the present work is focusing on the impact of AHSS grade microstructures and microalloying elements (Nb, Ti, Zr, V, B, and Mo) on the hydrogen diffusion coefficient and the density and energy of reversible traps. For this purpose hydrogen diffusion in non-and microalloyed dual-phase-, complex-phase, and tempered martensitic microstructures with tensile strength levels between 1200 and 1400 MPa was analyzed. The diffusion coefficient and trapping parameters were determined via electrochemical permeation measurements according to the works of Grabke et al. [7] and Gehrmann. [8] Generally, a dependence of the hydrogen diffusion coefficient on the microstructure was found with tempered martensitic microstructures showing the highest diffusion coefficents followed by dual-phase microstructures. Complex-phase microstructures reveal the lowest values for the diffusion coefficient. A significant dependence of the diffusion coefficient and trapping parameters on microalloying is not evident, except for substitutionally dissolved Mo and V-precipitates which tend to influence the density of reversible traps significantly.

The effect of microstructure on hydrogen permeability of high strength steels

“…However, the situation is complicated in the case of model samples with prevailing martensite and the AHSSs as not only prior austenite grain boundaries but all interfaces including lath/matrix boundaries should be taken into account. Rehrl et al associated higher diffusivity measured for DP1200 with less interfaces, that is, phase and grain boundaries, compared to CP1200 and CP1400. In this study, one of the largest interface area was revealed in DP1000, which is in agreement with the lowest diffusivity among the studied materials.…”

“…Favourable mechanical properties of AHSSs are achieved by combination of hard and soft phases in their microstructure. For instance, dual phase (DP) AHSSs consists of mostly ferrite and martensite, whereas complex phase (CP) AHSSs contain martensite, tempered martensite, bainite, ferrite and retained austenite …”

Hydrogen embrittlement of DP-1000 flat steel sheet: Influence of mechanical properties, specimen geometry, pre-damaging and electrolytically zinc galvanizing

“…Different testing methods to characterize hydrogen embrittlement resistance have been carried out in the last decades [3][4][5][6][7][8]. Well known test methods are, for example, constant load testing, slow strain rate testing, U-bend tests implying internal stress fields or electrochemical permeation techniques [9].…”

Critical Assessment of Techniques for the Description of the Phase Composition of Advanced High-Strength Steels

“…Over the last decades, the automotive industry has searched for new materials with improved mechanical properties in combination with low density. The aim is to decrease the weight of components and CO 2 emissions, to improve crash safety of automobiles and to reduce gasoline consumption [1][2][3][4][5][6]. Materials used in the automobile industry should be easily formable, weldable, coatable and repairable [7][8][9].…”