wwwmsmcamacuk phasetrans Facts Hydrogen dissolves in ferrite austenite Okamoto2004 Facts Hydrogen embrittles iron both single and polycrystalline forms Pfeil 1926 normal pickled ID: 594377
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Slide1
Hydrogen in complex microstructures in steels
www.msm.cam.ac.uk
/phase-transSlide2
FactsHydrogen dissolves in ferrite, austenite
Okamoto:2004Slide3
FactsHydrogen embrittles iron both single and polycrystalline forms
Pfeil 1926
normalpickledW. H. Johnson: ‘On some remarkable changes produced in iron and steel by the action of hydrogen and acids’, Proceedings of the Royal Society of London, 1875, 23, 168–179.Slide4
FactsIt is diffusible hydrogen that embrittles
it is atomic hydrogen that embrittlessubmerging H-containing steel causes frothing
stronger steel more susceptibleW. H. Johnson: ‘On some remarkable changes produced in iron and steel by the action of hydrogen and acids’, Proceedings of the Royal Society of London, 1875, 23, 168–179.Slide5
FactsHobson, 1951Slide6
FactsTendency to embrittle scales with strength
Hobson & Sykes, 1951
or does it in fact scale with ductility in the absence of hydrogen?Slide7
FactsFrohmberg, 1954Slide8
Factshydrogen diffuses faster in ferrite, but there are complications
Coe, 1973Slide9
MechanismsReduction in surface energy of iron, making it easier to cleave (Oriani, 1960)Song,
Bhadeshia, Suh 2013Slide10
Song, Bhadeshia, Suh 2013Slide11
MechanismsAccumulation of internal stress due to diffusible hydrogen precipitating at defects (Zapffe, 1941)Slide12
MechanismsHydrogen enhanced plastic instabilityincreased dislocation mobility due to H segregation
microscopically ductile fracturerequires a heterogeneous distribution of hydrogenSlide13
MechanismsHydrogen enhances vacancy concentrationsvacancies agglomerate
enhances ductile nucleation and linking of cracks
Terasaki et al. 1998Slide14
Facts: summaryAll evidence points to easily diffusible or weakly trapped hydrogen embrittlesTrapped molecular hydrogen irrelevantStrongly trapped hydrogen irrelevantSlide15Slide16Slide17
HydrogenSlide18
Yamasaki and
Bhadeshia, 2006Slide19Slide20
Song, Bhadeshia, Suh, 2013Slide21
Composition following transformationSlide22Slide23
200 Å
g
g
a
a
a
Caballero, Mateo, BhadeshiaSlide24Slide25
Sherif, 2005, Ph.D. thesis, CambridgeSlide26
Above percolation threshold
Below percolation thresholdSlide27
Geometrical percolation threshold of overlapping ellipsoidsSlide28Slide29
Fielding, Song, Han, Bhadeshia, Suh, unpublishedSlide30
Fielding, Song, Bhadeshia, Suh, unpublishedSlide31Slide32Slide33
Ryu
, Chun, Lee, Bhadeshia, Suh, 2012Slide34
Hydrogen embrittlement of austenite
B. C. De
Cooman
, O. Kwon and K.-G. Chin,
Materials
Science & Technology, 2012Slide35
Hydrogen embrittlement of austeniteSlide36
Hydrogen embrittlement of austeniteFe-0.6C-18Mn
wt% Fe-0.6C-18Mn-1.5Al Ryu, Kim, Lee,
Suh, Bhadeshia, 2012Slide37
Hydrogen embrittlement of austeniteRyu, Kim, Lee, Suh,
Bhadeshia, 2012
Combination of inter- and trans-granular fractureSlide38
Hydrogen embrittlement of austeniteRyu, Kim, Lee, Suh,
Bhadeshia, 2012Slide39
Hydrogen embrittlement of austeniteSlide40Slide41Slide42Slide43
Methods for mitigating consequences of hydrogenProvide traps for infused hydrogenRetard the infusion of hydrogen
Must not compromise other propertiesFerritic
Control stacking fault energyControl phase transformations
AusteniticSlide44
Open questions:How much hydrogen will enter steel over service life?Any long-term ex-service samples that we can test for hydrogen content?Can void formation at stress concentrations be observed directly using “large facilities”?
How can we suppress enhanced vacancy generation due to H?