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).
Hardness test results on American Spring material after various cyanide and heat treatments.
| Identifier | ExFiles\Box 154a\4\ scan0058 | |
| Date | 9th December 1937 | |
| -3- With a furnace atmosphere of carbon monoxide or one which is approximately neutral, or again, by quenching direct from a cyanide bath, the endurance limit is maintained at ± 47 tons/sq.in. In these experiments the tests were limited to specimens which had been machined and polished to remove any decarburisation produced prior to heat-treatment. The points raised in your memo BY.16/G.9.12.37, are covered by the results of some experiments we have made, using test pieces cut from the decarburised American Spring. For these tests the specimens were not machined, so that the cyanide bath had to replace the carbon in a decarburised layer .004" thick. The hardening shop bath used contains 12 to 15% cyanide. As Messrs. Firth's use a special jig for holding the spring to the correct camber during quenching, it is possible that quenching direct from the salt bath might give trouble owing to the accumulation of salt in the parts of the jig. We have therefore included tests in which the spring is cooled in air after leaving the salt bath and is subsequently reheated for hardening. Preliminary tests showed that quenching direct from the cyanide bath gives a surface hardness equal to that of the "core" or greater, whereas reheating forhardening results in the surface hardness being again reduced by partial decarburisation. Hardness Tests on American Spring. Before Cyanide Treatment. 30Kg/1mm. Decarburised Surface 313 "Core" 415 Surface -102 After 15 mins. Cyanide Treatment, air cooling, and re-heat treatment. Surface 404 "Core" 485 Surface -81 After 1 hour Cyanide treatment, air cooling, and re-heat treatment. Surface 445 495 Surface -50 | ||