What is it about?
Landing gear steels are high performance materials which have a martensitic microstructure and are heat treated to extremely high strength levels. Up to the present, low alloyed steels have been applied which have to be extensively protected by respective coatings against corrosion. As an alternative, new type of high alloyed martensitic steels has been developed. The material properties evaluated dependent on the hydrogen concentration level in the fully saturated specimens have been evaluated for the new UHSS as compared to the legacy steel in the as-received condition as well as in service-applied condition. In addition , the alteration of fracture topographies dependent on the hydrogen concentration level has been elucidated.
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Why is it important?
Most aircraft failures in the past 50 years are related to mal-functioning landing gears which are made of ultra high strength steels that have to show a respectively high performance on a daily basis. Ultra high strength steels might become very susceptible to brittle failure by hydrogen assisted cracking, but the extent of degradation of the mechnical properties by hydrogen has not been investigated in Detail. For the first time, the material properties, i. e. the yield and tensile strength and , in particular, the ductility in terms of area reduction and true fracture strain have been evaluated dependent on the absorbed hydrogen concentration for landing gear materials with their the service-applied microstructure after several years of usage. The evaluated data not only just show the variation of the mechanical properties dependent on the absorbed hydrogen concentration, but also provide potential input to life time engineering and might also serve as respective crack criteria for numerical simulations. In addition, it has been evidenced again that increasing hydrogen concentrations might cause not only transgranular, but also extremely brittle intergranular cracking in martensitic microstructures.
Perspectives
This paper continues a series of papers that provide hydrogen dependent material properties for various kinds of steels, like structural steels, HSLA steels, creep resistant baoiler steels and supermartensitic stainless steels. The highly acknowledged contribution of the co-authors is highly acknowledged represents an evidence for a fantastic international collaboration.
Thomas Boellinghaus
BAM Federal Institute for Materials Research and Testing
Read the Original
This page is a summary of: Hydrogen Assisted Stress Corrosion Cracking Related Material Properties of Service-Applied Landing Gear Ultra-High Strength Steels, CORROSION, March 2019, NACE International,
DOI: 10.5006/3028.
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