The 1922 V-C catalog has 13 pages dedicated to their gun barrels, including an extensive discussion of the four steel grades they used. "Acier Diamant" is used for all four grades (in increasing order):

Acier Diamant
Acier Diamant/Acier Jacob Holtzer
Acier Diamant/Acier Jacob Holtzer (Qualite Superieure)
Acier Diamant/Acier Jacob Holtzer Trempe.

The only mention I can find in the catalog that seems to discuss Acier Diament's significance directly is the following (and you are on your own for translation!):

Quote:
Les aciers au creuset que nous employons depuis longtemps et que nous designons sous la denomination d'<<Acier Diamant>> donnent a resistance egale par millimetre des allongements, des resilences et des limites elastique bien superieures aux aciers Martin et electriques.

Last edited by Doverham; 08/26/13 02:36 PM.
Such a long, long time to be gone, and a short time to be there.