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).
Valve steel specifications, a failure analysis related to silicon content, and a recommendation to switch to austenitic steel.
| Identifier | ExFiles\Box 54\3\ Scan217 | |
| Date | 11th May 1928 | |
| - 2 - BY4/G.11.5.28. In regard to the reduction of the silicon content we immediately reduced our specification upper limit and arranged with Messrs. Firths to have no material of the higher limit delivered as there appeared to be some value in keeping lower. This may be open to question, as although the maximum tensile of the lower percentage silicon is higher, in some figures I have examined the elastic limit is very much lower, and it is this latter figure which determines whether a valve will stretch or not at the temperatures under discussion. In the engine where the valve failed, all the valves were of the same content viz. 4.1 silicon. It would appear that as R.{Sir Henry Royce} suggests the tulip was too thin and in the case of the valve that failed for some reason or other slight pre-ignition effects had probably happened in operation putting up the temperature of this valve considerably above normal. Hs{Lord Ernest Hives - Chair}'s report indicates this. As I have consistently pressed the need for abandoning the silicon chrome type of steel for an austenitic steel, preferably H.R. Crown (Firth's) which has a tensile approximately three times as great at 800°C as the silicon chrome, it is necessary to point out that my reasons for pressing the new steel are entirely connected with the manufacture of the material, it being a particularly difficult steel to deal with owing to the effects of slight temperature variations during the working of the steel, and the final forging operations on the valve. BY.{R.W. Bailey - Chief Engineer} | ||