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Ebook Welding metallurgy and weldability: Part 2

(BQ) Part 2 book "Welding metallurgy and weldability" has contents: Hydrogen-Induced cracking, corrosion, fracture and fatigue, failure analysis, weldability testing. Invite you to reference | 5 Hydrogen-Induced Cracking 5.1â• Introduction The presence of hydrogen in the weld metal or HAZ may lead to a form of cracking known as hydrogen-induced cracking (HIC). This form of cracking is also commonly referred to as “hydrogen-assisted cracking” (HAC) or “cold cracking” since it occurs at or near room temperature after the weld has cooled. The loss of ductility associated with the presence of hydrogen is often referred to as hydrogen embrittlement. This form of cracking is most often associated with steels, but the presence of sufficient hydrogen can lead to cracking or embrittlement in other materials. Although hydrogen is present at some trace level in virtually all materials, it is the introduction of hydrogen during the welding process that allows hydrogen to be present at some threshold level to promote cracking. Atomic hydrogen is very mobile in the microstructure even at room temperature, allowing it to diffuse to regions of stress concentration and susceptible microstructure. While HIC normally occurs almost immediately upon cooling to room temperature, it may also occur after a delay. This form of HIC is referred to as “delayed” cracking. This suggests that an incubation time is necessary for the hydrogen to diffuse, and accumulate, in a location where cracking occurs after a threshold level of hydrogen is reached. Despite the fact that hydrogen cracking and its variants have been studied for over 60â•›years, there is still no universally accepted mechanism. This is due in part to the fact that hydrogen is very difficult to detect using analytical tools. Unlike other trace Welding Metallurgy and Weldability, First Edition. John C. Lippold. © 2015 John Wiley & Sons, Inc. Published 2015 by John Wiley & Sons, Inc. � 213 214� Hydrogen-Induced Cracking elements (P, S, B, O) that lead to cracking or embrittlement, hydrogen is effectively undetectable within the microstructure. Computational modeling tools have improved the understanding of hydrogen