Proceedings of the Third International Conference on Metals & Hydrogen P62

Hydrogen embrittlement mechanism in crack growth of micro-alloyed advanced high strength steels

P. Gong (1)1 , B. Wynne (1)1 , W.M. Rainforth (1)1

  • (1) 1

    Department of Materials Science and Engineering, Sir Robert Hadfield Building, Mappin Street, Sheffield, S1 3JD


It is known that as the strength of steels exceeds about 800MPa they become increasingly susceptible to hydrogen embrittlement. This is important in advanced high strength steels (AHSS) for automotive applications with a continuous push to increase strength to well above 1000MPa. In this work, model advanced high strength steels based on Ti-Mo, V, and V-Mo microalloyed chemistries were studied. The effects of hydrogen on tensile crack growth behaviour and ductility after slow strain-rate testing was investigated in detail. As expected, charging by hydrogen resulted in a loss in strength and ductility, although post yield work hardening rates were similar. By using double notched specimens, it was possible to undertake detailed investigation of the crack initiation and propagation around the notch site that did not fail. In the uncharged specimen the failure tended to be by conventional tensile necking. In the hydrogen charged specimens, multiple cracking was observed, with intergranular cracking in purely ferrite steel and transgranular cracking in dual phase steels. Cracks grew within the ferrite along the (100) plane, while cracks were preferentially along the martensite/ferrite phase boundary or along the (110) plane in the martensite. In addition, the hydrogen charging appeared to have modified the dislocation slip activity with a significant increase in dislocation density. The implication of these observations on the mechanism of hydrogen embrittlement in these steels is discussed.