Abstract
Hydrogen embrittlement susceptibility of steels and its mechanism were evaluated in terms of environmental and metallurgical aspects.
Hydrogen entry and its effects on embrittlement susceptibility were investigated under atmospheric exposure and gaseous hydrogen environments. Investigations on hydrogen entry under atmospheric exposure by hydrogen permeation tests indicate that environmental factors such as temperature, humidity and sea salts on the steel surface strongly affected hydrogen entry and delayed fracture susceptibility of high strength steels. Evaluation by Slow Strain Rate Test (SSRT) in both gaseous hydrogen environments and electrochemical cathodic charging shows that hydrogen embrittlement susceptibility depended upon surface hydrogen contents.
Hydrogen embrittlement mechanism of high strength low alloy steels and the countermeasures were investigated from the viewpoints of precipitations (secondary phases) in the steel. Nano-scale carbides increased trapped hydrogen content. Carbides along grain boundary accelerated intergranular hydrogen cracking. Inclusions on the steel surface played pitting initiation sites, at which hydrogen cracking occurred. Controls of such secondary phases enabled developments of high strength steels withstanding hydrogen embrittlement.
