Carburizing steel

Yep, I can help:
D = D0 * exp(-Qd/RT), where D = diffusion coefficient, Qd = activation energy, R = gas constant (8,31 J/mol*K), T = abs. temperature, D0 = a material constant.
Examples:
D0 for Carbon in alfa-ferrit: 6,2e-7 m^2/s and D0 for Carbon in gamma-ferrit: 2,3e-5 m^2/s.
Qd is respectively 80 kJ/mol and 148 kJ/mol.
Fick's first law: J = -D* dC/dx, where dC/dx is you concentration gradient, J = diffusion flux (kg/m^2*s or atoms/m^2*s)
Fick's second law: dC/dt = D * d^2C/dx^2 .... and you could probably also find use for the error function solution:
Cx - C0 / (Cs - C0) = 1 - erf(x/(2*sqrt(Dt)) ), where Cs = concentration at surface/interface, C0 = beginning concentration and C0 > Cx > Cs
I think we need some additional information in order to calculate your problem...
Med venlig hilsen / Best regards Martin Jørgensen

Thanks Martin,
I will take a good look at the information tomorrow.
Regards
Mark