(Modeling of hydrogen long-range diffusion)

The development of steel, which is resistant against hydrogen embrittlement, is a major research focus and highly challenging since typical operation temperatures range from -150°C to 600°C.

H embrittlement can occur during manufacturing, welding or from services in an aqueous, corrosive or gaseous environment that charge H into the steel. Depending on the prevalent mechanism, several influencing factors must be considered, such as the varying hydrogen diffusivity as a function of the number and strength of traps, the yield stress of the material, the fracture toughness and the hydrogen potential at the sample surface.

 

 

 

 

 

                                                    Different types of hydrogen traps

 Our solution: A quantitative calculation of hydrogen redistribution would allow deeper understanding of hydrogen embrittlement in the materials and open the possibility of prediction and prevention of this type of material degradation.

By application of MatCalc it is possible to understand and analyze the evolution of the microstructure during processing and application. This, in combination with the cell simulation method gives us the opportunity to analyze the diffusion of H-atoms through the material and their trapping respectively. As a result, it is possible to optimize the production route, heat treatments and the alloying concept of the steels.

Typical applications

H-charging and –discharging behavior of different steels in the presence of traps, prediction of the optimal cooling rates from operating temperatures for maintenance to prevent H induced damage, parameter studies on the influence of trapping energies between H atoms and precipitate interfaces on the H-diffusion, evaluation of the relation between size and shape of precipitates and trapping capacity

Sketch of the simulation grid for the calculated hydrogen charging and discharging process

 

 

Parameter study: Case 1 – Influence of the trapping energy               Case 2 – Influence of a variation in the trap density

 

Example for vessel maintenance

Material: C-2.25%Cr-1%Mo – Mo2C as active traps

Vessel in operation at 400°C, traps are filled during operation

Discharging from operating temperature to room temperature for technical service is simulated at different cooling rates until 

 

 

 

       Free H content after cooling at different cooling rates (CR)