1. Hydrogen Embrittlement: Causes, Effects & Prevention Sidheshwar Kumar 107MM024 Department of Metallurgical and Materials Engineering NIT – Rourkela, 769008

2. Contents Introduction Causes Mechanism Effects Prevention Techniques References

3. Introduction Embrittlement is a loss of ductility of a material, or making it brittle. If embrittlement occurs due to the effect of hydrogen absorption then it known as Hydrogen Embrittlement. It is more susceptible to BCC and HCP structured metals as compare to FCC structured metals. As Little as 0.0001 weight percent of hydrogen can cause cracking in steel.

4. Hydrogen may be introduced during : [1] During Melting & Entrapped during Solidification, [2] Anodic Reaction during Corrosion, [3] Hydrogen Gas Welding & Moistured Electrode

5. The Chief characteristics of Hydrogen Embrittlement : [1] Strain Rate Sensitivity increases, [2] Susceptibility to Delayed Fracture increases. Hydrogen Embrittlement is enhanced by slow strain rates. At low temperatures and high temperatures hydrogen embrittlement is negligible, but it is most severe at Room Temperature for example steel. Slow bend test and Notched and Unnotched tension tests will detect hydrogen Embrittlement by a drastic decrease in ductility, but notched–impact tests are of no use for detecting the phenomenon.

6. Mechanism The exact mechanism of hydrogen embrittlement is not well known. The initial causes is the same: penetration of atomic hydrogen into the metal structure. Most of the mechanisms that have been proposed for hydrogen embrittlement are based on slip interference by dissolved hydrogen. This slip interference may be due to accumulation of hydrogen near dislocation sites or microvoids, but the precise mechanism is still in doubt.

7. Proposed Mechanism Hydride-Induced Embrittlement, HIE (Second-phase mechanism) Hydrogen-Enhanced Decohesion Mechanism, HEDE (brittle fracture) Hydrogen Enhanced Localized Plasticity-Mechanism, HELP (ductile fracture)

16. Prevention Techniques Reducing Corrosion Rate Hydrogen embrittlement occurs frequently during pickling operations where corrosion of the base metal produces vigorous hydrogen evolution. By careful inhibitor additions, base-metal corrosion can largely be eliminated during pickling with a susequent decrease in hydrogen pickup.

17. Prevention Techniques UsingClean Steel Rimmed steels tend to have numerous voids, and the subtitution of killed steel greatly increases the resistance to hydrogen interstitials for embrittlement because of the Less number of voids in this material.

18. Prevention Techniques Baking Hydrogen embrittlement is an almost reversible process, especially in steels. That is, if the hydrogen is removed, the mechanical properties of the treated material are only slightly different from those of hydogen-free steel. A common way of removing hydrogen in steels is by baking at relatively low temperatures at 200-300 F.

20. Prevention Techniques Practicing Proper Welding Low-hydrogen welding rods should be specified for welding if hydrogen embrittlement is a problem. Also, it is important to maintain dry conditions during welding since water and watervapor are major sources of hydrogen.

21. Prevention Techniques Substituting Alloys The materials most susceptible to hydrogen embrittlement are the very high-strength steels. Alloying with Ni or Mo reduces susceptibility. Because, Nickel-containing steels and Nickel-base alloys have very low hydrogen diffusion rates and best way to prevent from hydrogen embrittlement.

22. References [1] George E. Dieter and David Bacon, “Mechanical Metallurgy,” McGraw-Hill Book Company, ISBN 0-07-100406-8. [2] Mar G. Fontana, “Corrosion Engineering,” McGraw-Hill Book Company, ISBN 978-0-07-060744-6. [3] G. Alefeld and J. Volkl (eds.), "Hydrogen in Metals,“ Springer-Verlag, Berlin, Vols. 1 and 2, 1978. [4] R. Kirchheim, E. Fromm, E. Wicke, eds., Verlag, Munchen, "Metals-Hydrogen Systems," 1989. [5] A.M. Brass, J. Chêne, “Hydrogen Uptake in 316L Stainless Steel: Conseq- uences on Tensile Properties,” Corrosion Science 48 (2006) 3222-3242. [6] C. L. Briant and S. K. Banerji (eds.), “Embrittlement of Engineering Alloys,” Academic Press , New York, 1983. [7] R. Gibala, R. F. Hehnemann (eds.), “Hydrogen Embrittlement and Stress Corrosion Cracking,” American Society for Metals, Metals Park, Ohio, 1984.

23. Cont.. [8] I. M. Bernstein and A. W. Thompson (eds.), “Hydrogen in Metals,” Amer Soc. For Metals, Metals Park Ohio, 1974. [9] L . W. Tsay, T. Y. Yang, “Reduction of hydrogen embrittlement in an ultra-high-strength steel by laser surface annealing,” Fatigue FractEngng Mater Struct, 23, p325–333. [10] H. Kamoutsi, G.N. Haidemenopoulos, V. Bontozoglou, S. Pantelakis, “Corrosion-induced hydrogen embrittlement in aluminum alloy 2024,” Corrosion Science, 48 (2006), p1209–1224. [11] R.A. Siddiqui, H.A. Abdullah, “Hydrogen embrittlement in 0.31% carbon steel used for petrochemical applications”, Journal of Materials Processing Technology, 170 (2005) ,p430–435. [12] C. Pan, Y.J. Su, W.Y. Chu, et al, “Hydrogen embrittlement of weld metal of austenitic stainless steels”, Corrosion Science, 44 (2002), p1983. [13] P. Sofronis, I.M. Robertson, “Viable Mechanisms of Hydrogen embrittlement-A Review,” American Institute of Physics, 2006, p837. [14] C. D. Beachem, Met. Transactions, volume -3, page 437, 1972.

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