Evaluating of test methods for hydrogen embrittlement in UHS martensitic steel sheets
Independent thesis Advanced level (degree of Master (Two Years)), 20 credits / 30 HE creditsStudent thesis
Ultra high strength steel is very sensitive for hydrogen embrittlement and problem with hydrogen absorption occurs mainly when the material is corrosion protected by electro galvanizing. The purpose with this thesis work is to evaluate different test methods for detecting HE. Two main mechanical test methods, conventional strain rate test and slow strain rate test, was evaluated. Three martensitic high strength steel types was tested where both naked hydrogen charged samples and samples coated with zinc by electro galvanizing was evaluated. The different material had an ultimate tensile strength of 1300, 1500 and 1700 MPa respectively. The concept of increased amount of alloying the steel with boron was tested with the expectation of decreasing the susceptibility of HE. Heat treatment was also performed on punched samples before hydrogen charging to evaluate if the susceptibility of HE is decreasing when reducing stresses on the edge from the punching.
The hydrogen charging procedure was performed electrolytically and the naked samples were hydrogen charged for 24, 48 and 72 hours before mechanical testing and hydrogen analysis.
The result show that both CSRT and SSRT can be used to detect hydrogen embrittlement for all three materials at all charging times. Hydrogen charging the samples for 72 hours does not give more brittle fractures at lower load than the samples charged for 48 hours. The electro galvanizing process does not generate a big amount of absorbed hydrogen according to both hydrogen analysis and mechanical testing. Heat treatment does not improve the susceptibility for HE and neither does increased amount of boron as alloy in the material. Formation of a unknown deposition layer on the metal surface during the hydrogen charging procedure seems to act as a barrier preventing hydrogen to absorb in the metal lattice.
Place, publisher, year, edition, pages
2015. , 4 p.
Hydrogen embrittlement, test methods, conventional strain rate technique, electro galvanizing, ultra-high strength steel
Other Materials Engineering
IdentifiersURN: urn:nbn:se:kth:diva-179039OAI: oai:DiVA.org:kth-179039DiVA: diva2:879841
Master of Science in Engineering - Materials Design and Engineering