Hydrogen trapping in ferritic steel weld metal

A brief overview is given of the role of hydrogen trapping in hydrogen management of steel welding. The concept of hydrogen trapping is introduced in conjunction with efforts in reducing hydrogen cracking in steel welding. Appropriate selection of hydrogen traps offers the potential to control the content and distribution of hydrogen in steel weldments. The effectiveness of hydrogen traps through selective alloying in reducing the concentration of diffusible hydrogen during welding thermal cycles is evaluated, particularly in its use as a substitute for costly weld heat treatment practices. The relationship of weld metal microstructure and hydrogen contents to the effective use of hydrogen trapping elements is discussed. The fundamental aspects which control hydrogen content as well as hydrogen distribution in steel are discussed, such as the statistical thermodynamics and the transport of hydrogen in steel containing traps. As tools for investigating potential hydrogen traps, several experimental methods are discussed in relation to their applicability to characterise the physical nature of hydrogen traps. These methods include the hydrogen permeation technique and hydrogen thermal desorption analysis. Recent efforts to prevent hydrogen cracking in steel weldments through numerical computations require consideration of hydrogen trapping in the weld microstructure, and hence knowledge of applicable data of hydrogen trapping parameters is necessary for welding engineers to improve hydrogen management in steel welding.