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).
Special hardened steel from Krupps of Essen, used for crankshafts.
| Identifier | ExFiles\Box 154a\1\ scan0077 | |
| Date | 14th June 1928 | |
| Referring to the special crank in Bentley's possession with a hardened surface, which could not be touched with a file, of which Hs. {Lord Ernest Hives - Chair} informed you at his recent visit, the steel from which the crankshaft is produced is a special production, patented by Krupps of Essen. I have known of the existence of this steel for some little time, but have been waiting developments before submitting the matter to you, as Messrs. Firth & Sons had an option upon the production of the steel in this country. The steel in question is an alloy steel containing aluminium and chromium, an approximate analysis is :- 2% aluminium. 1.3 chromium. .40 carbon. The steel in question has had very little work done upon it, and there is not any quantity of reliable information available at the moment as to its possibilities for commercial use. The piece can be finished completely to size, ground and polished. It is then heated to quite a low temperature in an atmosphere of ammonia. The temperature is approximately 500°C or somewhere thereabouts. After being maintained at this temperature for a certain length of time in an ammonia atmosphere a hard skin is formed upon the material which gives a hardness of approximately 700 brinell, a very much higher figure than anything obtainable by normal case hardening process. There is no quenching operation necessary. The excessive hardness of the skin necessarily involves great possibilities of brittleness, and herein lies the possibilities of danger in the use of the steel, as obviously special precautions would have to be taken to eliminate any sharp corners in the pieces for which this particular steel is intended. I have further information on the subject which I will forward you later on, but at the moment I thought in view of the fact that the steel had been brought to your notice it would be better to let you have some general information upon the subject. The crank in Bentley's possession was produced for them in the Firth Derihon Forge. BY. {R.W. Bailey - Chief Engineer} | ||