Development and verification of a new mathematical model of hydrogen solubility and permeation in structural steels

European Commission Directorate-General For Research And Innovation

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Industrial research and development

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• Publié par: EUROPEAN-COMMISSION-DIRECTORATE-GENERAL-FOR-RESEARCH-AND-INNOVATION
• Nombre de lectures: 10
• Langue: English
• Poids de l'ouvrage: 4 Mo

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ISSN 1018-5593
EUROPEAN
COMMISSION
SCIENCE
RESEARCH
DEVELOPMENT
technical steel research
roperties and in-service performance
Development and
verification of a new
mathematical model
of hydrogen solubility
and permeation in
structural steels
Report
EUR 18293 EN
STEEL RESEARCH EUROPEAN COMMISSION
Edith CRESSON, Member of the Commission
responsible for research, innovation, education, training and youth
DG XII/C.2 — RTD actions: Industrial and materials technologies —
Materials and steel
Contact: Mr J.-L. Martin
Address: European Commission, rue de la Loi 200 (MO 75 1/10),
B-1049 Brussels — Tel. [phone]; fax [phone] European Commission
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Properties and in-service performance
Development and verification of a new
mathematical model of hydrogen solubility
and permeation in structural steels
K. Randerson, H. C. Carey, S. Haykin, E. Riecke, K. Schomberg
British Steel pic
9 Albert Embankment
London SE1 7SN
United Kingdom
Contract No 7210-KB/125/818
1 July 1992 to 30 June 1995
Final report
Directorate-General
Science, Research and Development
EUR 18293 EN 1998 LEGAL NOTICE
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Luxembourg: Office for Official Publications of the European Communities, 1998
ISBN 92-828-3856-0
© European Communities, 1998
Reproduction is authorised provided the source is acknowledged.
Printed in Luxembourg
PRINTED ON WHITE CHLORINE-FREE PAPER PAGE CONTENTS
Work at British Steel PARTI
Project No. 7210.KB/818
Authors: H.C. Carey
S. Haykin
K. Randerson
89 PART 2 Work at MPI
Project No. 7210.KB/125
Authors: E. Riecke
K. Schomberg
PART 3 A Comparison of the BS and MPI Results 125
Authors: H.C. Carey
K. Randerson SUMMARY
PARTI
The complex behaviour of Ti in structural steels, identified in previous work, was resolved on the
basis of composition and processing. In C-Mn-AI-Ti steel the influence of Ti is independent of
rolling conditions and there is a strong interaction with hydrogen. When Nb and Ti are present
together in a C-Mn-AI steel the effect of Ti is reduced and varies with slab reheat condition, low
slab reheat producing a weaker Ti/H interaction.
The effect of Β in QT steels was found to be more complex than expected. Free Β diffuses to
grain boundaries and reduces the available traps for hydrogen. Any residual BN in the structure
provides additional trap sites and increases safe hydrogen level. In the present samples the aim
was to study the filling of traps by B, but the presence of more BN at higher Β levels produced an
increase in safe hydrogen levels.
Work on QT steels demonstrated the increase in solubility of hydrogen in both bainite and
martensite due to quenching, with lower levels of safe hydrogen after tempering. The solubility
could be explained in terms of subgrain size in well tempered steels but a satisfactory
metallographic description in quenched steels or steelsd at low temperatures was not
possible.
On some laboratory steels there were problems with low results, thought to be due to subsurface
inclusions.
Fracture toughness tests of a high strength steel in high pressure hydrogen showed a minimum
level of fracture toughness of 10 MPa Vm. It was not possible to explain the onset of hydrogen
cracking with this data because the stress intensity of inclusions is generally <1 MPa Vm.
A preliminary study of stresses and strains at an inclusion using FE showed that effects were fully
contained within a segregation band at > 10 μιτι thickness. The location of maximum stress and
maximum strain did not coincide.
SUMMARY
Part 2
Permeation coefficients were measured on a series of iron alloys ex MPI and laboratory and
commercial steels ex BS. The permeability of all samples increased with test temperature as
expected. In most cases performance was close to that of pure iron but in the cases of fine
lamellar pearlite and QT samples the permeability was reduced to a greater extent.
Diffusion coefficients varied over about 2 orders of magnitude. Iron-carbon alloys and coarse
grained steel had coefficients close to that for pure iron but the coefficient was reduced
substantially by alloy traps (S, Ti) and by heat treatment (QT).
The number of deep and shallow traps and the respective binding energies were calculated for
each sample. The blocking of deep traps by the presence of boron was confirmed. SUMMARY
Part 3
The solubility model described in Part 1 was linked to a diffusion model to calculate the diffusion of
hydrogen in a permeability test in the presence of traps. To get good agreement then
equation had to be amended to give faster diffusion than values reported in the literature.
The predictive capability of the model was reasonable for ferrite pearlite steels and steels with
globular carbides. Diffusion in fully pearlitic steels was slower than predicted and this is thought to
be due to slower diffusion through the carbide lamellae or to a reduction in cross-sectional area
available for diffusion. The model did not work well on high titanium steels where the predicted
diffusion rate was faster than that observed, or the programme failed to give a result. QT steels
were not assessed reliably by the model and the error was higher in the high carbon steel.
The BS model has fewer traps than the normal calculation procedure by 2 orders of magnitude.
This is thought to be due to different initial assumptions about the proportion of traps filled by
hydrogen. The binding energy decreases as the number of traps increases and increasing the
number of traps in the BS model gives binding energies for shallow traps in the normally accepted
range. Part 1 Work at British Steel
Project No. 7210.KB/818
H.C. Carey
S. Haykin
K. Randerson