From the Rolls-Royce experimental archive: a quarter of a million communications from Rolls-Royce, 1906 to 1960's. Documents from the Sir Henry Royce Memorial Foundation (SHRMF).
Comparison of different steel types (V.C.M., Hykro, Nitralloy) and the effects of aluminium in the nitriding process for aero engines and chassis.
| Identifier | ExFiles\Box 146\1\ scan0129 | |
| Date | 8th December 1937 | |
| - 2 - BY.10/G.8.12.37. We are quite satisfied with V.C.M. and Hykro for our aero engines and chassis, and we are satisfied from the experiments we did that we have for our purpose selected the steel which is the best all round compromise. The main difference between V.C.M. and Aubert & Duval's steel, which is known in this country as 'Nitralloy', is in the addition of aluminium in quantities of between 1.00 and 1.50%. The object of the addition of aluminium is to increase the rate and capacity for nitride hardening, but the addition of aluminium whilst increasing the rate at which nitriding is produced also increases the intensity, and there are a series of nitrides of iron with increasing quantities of nitrogen which are very similar to the C.H. products in organic chemistry, the higher the nitrogen content the harder the part, but the more loosely it remains secure to the base metal, and it is this effect which we have found most detrimental as it necessitates a grinding operation following the nitriding operation, whereas with V.C.M. in nitriding, the only further operation is a light lapping or polishing. In addition to the above, the aluminium present creats under certain conditions a seriously speckled skin to the steel, the speckling being the presence of aluminates of iron produced during the casting of the material which again are undesirable and create a constant discussion between the users of the steel and the makers of same, as the user rightly says, the steel is not clean, whereas the maker, knowing that he must have aluminium present in this type of steel has to excuse the appearance in the interests of the harder skin which, however, is not an altogether undisguised blessing. By BY.{R.W. Bailey - Chief Engineer} | ||