Influence of the Local Hydrogen Concentration in Multi-Phase Steels on their Tendency to Hydrogen Induced Cracks

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Increasing technological high-quality standards of car body- and power plant engineering lead to an increased use of high-strength steels. Due to the usage of these steels it is possible for example in car body construction to reduce the weight and thus the fuel consumption. Operation conditions however have to be adapted to these new demands. With increasing strength the sensibility for hydrogen induced cracking rises, too. It is known that even low amounts of hydrogen can lead to damage. This hydrogen concentrates to a higher level in areas of high lattice expansion, e.g. near notches. If a limiting concentration has been met sudden component failure will occur.There does not exist any knowledge so far about the influence of specific microstructure constituents as e.g. ferrite, perlite, bainit or martensite on hydrogen induced cracking at conditions which other from that are constant. As these mirostructures are adjusted specifically to increase the strength, this knowledge however would be relevant for a safe usage of high-strength steels.Previous projectwas able to prove the increasing concentration of hydrogen in areas of high stress. The analysis of local hydrogen showed evidence of different behavior of various structure modifications. As we see high potential for successful research we decided not to propose a third year of support but to propose this new application.The aim of the project is to characterize single structure parts of stressed high-strength multi-phase steels concerning their critical hydrogen concentration and to evaluate their impact on the tendency to hydrogen-induced cracking of a steel. The obtained insights finally are supposed to significantly promote further development of high-strength steels with controlled hydrogen-induced cracking.