Potential pH diagram for iron based on [10
Schematic representation of a hydrogen permeation test based on [13
Schematic representation of an idealized permeation curve with the significant points.
Hydrogen absorption during austenitisation under different conditions and sample geometry.
Structure of the double cell for permeation measurements.
G8 Galileo, coupled with a quadrupole mass spectrometer.
Influence of NaCl and CH4N2S content on hydrogen absorption at a current density of 100 mA/dm2.
Impact of the pH value on the hydrogen concentration (above) at a current density of 100 mA/dm2 and (below) the calculated pH-value from the respective molarity of the solution.
Influence of current density on hydrogen absorption.
(a) Comparison of the measured currents, adjusted for corrosion current, at different pH-values on the loading side for the press-hardened 22MnB5, (b) normalized current of (a) and (c) sample after measurement.
Comparison of the determined diffusion coefficients (mean value of tb, tlag and tWP) for the quenched and tempered steels 22MnB5 and 37MnB4 for alkaline and acid solutions at a current density of 100 mA/dm2.
Impact of sample thickness on permeation measurement 22MnB5 in untempered and tempered condition.
Impact of the surface quality of the samples on the permeation measurement (22MnB5-press-hardened condition).
Thermal desorption analysis on 22MnB5 sheets with different coating concepts and varying heating rates (left), representation of the results according to Equation (2) (right).
Hydrogen desorption of 22MnB5 during isothermal heating at 200 °C (right) and temperature curve (left).
Comparison of diffusion coefficients.
Representation of desorption times at different temperatures and desorption stages.
Calculated Ea, D0 (left) and D (right) for different stages of desorption.
The procedure of the iteration.
Calculated desorption curves at the beginning (left) and after completion of the iteration (right) by means of an isothermal 200 °C—measurement.
Representation of the standard deviation.
Summary and comparison of the determined diffusion velocities for 22MnB5.
Calculated desorption times for the quenched and tempered steel 22MnB5 (left) and their coating concepts (right) under various conditions.
List of variables for the diffusion equations.
|c(x,t)||Hydrogen at location “x” at time “t”|| |
|Average hydrogen concentration at time “t”|
|cR||Hydrogen boundary concentration|
|c0||Initial hydrogen concentration|
|X||Position/location of hydrogen in the workpiece|
|N||Running number of the infinite sum|
Measured chemical composition in % by weight of 22MnB5 and 37MnB4, min/max values taken from [20
|37MnB4|| || || || || || || || || |
Dimensions of the sample.
|Material||Permeation||Thermal Desorption Analysis|
|22MnB5||Ø 25 mm, d = 1–1.2 mm||60 mm × 20 mm × 1.3 mm|
|37MnB4||Ø 25 mm, d = 1–1.2 mm||Ø 4.5 mm, l = 100–120 mm|
Measurement parameters of the TDA for the characterization of hydrogen uptake, the determination of Ea and D0 and the empirical verification of the desorption time.
| ||Ea/D0||Desorption Time|
|Analysis temperature and heating rate||0.2; 0.4; 0.6; 0.8; 1.0 °C/s (ΔT from 50 to 900 °C)||150–300 °C for the empirical Validation of desorption time|
|Analysis time||ΔT/q||20–30 min|
Determined activation energies and pre-exponential diffusion coefficients from the desorption curves as well as the calculated diffusion coefficients at room temperature.
| ||22MnB5||22MnB5 + Z140||22MnB5 + AS150||37MnB4|
|D0 [m2/s]||4.29 × 10−6||9.28 × 10−5||3.01 × 10−3||1.27 × 10−5|
|D (22 °C) [m2/s]||3.51 × 10−11||1.36 × 10−11||4.46 × 10−13||4.54 × 10−11|
Extract from the iteration.
|D0 [× 10−6 m2/s]||1.00||2.08||2.38||3.00||4.08||4.23||5.00|| |
|150 °C||24.02||26.34||26.78||27.51||28.48||28.60||29.13||Ea [kJ/mol]|
|standard deviation||0.3528||0.2626||0.2580||0.2629||0.2834||0.2934||0.3259|| |
|D (22 °C) [× 10−11 m2/s]||6.64||4.82||4.54||4.12||3.60||3.54||3.29|| |