Evaluation of hydrogen diffusion and trapping in AHSS and effects of laser-welding

Abstract

In this study, different techniques are applied to measure diffusion coefficient D of three cold-rolled Advanced High-Strength Steels (AHSS): CR700Y-980T-DH, CR780Y980T-CH, and DR700Y980T-DP, and their laser-welded counterparts. By thermal desorption analysis (TDA) the hydrogen transport at elevated temperatures is investigated. This method allows the measurement of hydrogen quantities at different trapping sites and enables the determination of activation energies Ea and pre-exponential diffusion coefficients D0. The analysis is conducted under various temperature regimes using different heating rates φ. Additionally, the corresponding diffusion coefficients for the examined states are determined by electrochemical permeation (ECP) at room temperature. The findings indicate an increase in D after laser welding, with differences in microstructure and material chemistry being identified as the reasons behind this phenomenon. This study demonstrates that the employed method, along with the chosen sample geometries, holds significant potential for enhancing our understanding of hydrogen kinetics in AHSS and the effects of thermal heat treatments, such as laser-welding.

Keywords

• Laser welding
• AHSS
• Thermal desorption analysis
• Diffusible hydrogen
• Activation energy
• Diffusion coefficients