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 mechanical properties and characteristics between 'N' Steel and Standard Nickel Chrome steel.
| Identifier | ExFiles\Box 154a\1\ scan0080 | |
| Date | 19th June 1928 | |
| - 2 - 1419 Brinell Hardness. "N" Steel - 340. Standard Nickel Chrome - 302. Tensile Tests. Yield Point. Max. Stress. Elong. % R.A.% "N" Steel 44.00 tons 55.6 tons 22.0 58.0 Standard Nic. Chrome 55.0 tons 62.0 tons 19.0 52.0 Izod Impact. "N" Steel 60 ft. lbs. Standard Nickel Chrome 45 ft. lbs. It will be seen that the general characteristics of the steel are quite good, and if one judged by these alone it would appear to be a very useful addition to our list of steels, particularly when one remembers that it has a skin hardness of approximately 700 Brinell - this skin is approximately .005" thick after a 48 hours treatment with a somewhat softer but still actually very hard second layer of approximately .008" thick - its weakness, however, lies in the fact that the skin produced is very brittle, and from an examination of a number of micrographs appears to contain a large number of what seem to be incipient cracks produced by the penetration of the steel by nitrogen and the formation of iron nitride Fe₄N, the secondary surface being apparently Fe₂N - the former compound is known as Nitride 1, the latter as Nitride 11. The steel after casehardening is extremely resistant to corrosion in running water, and from this point of view is an advance on present practice. I should consider the steel to be very subject to fatigue failure effects as the result of its apparent incipient cracking during "Nitrogenisation", and to elucidate this I am as pointed out in my previous memo inaugurating a series of Stanton tests to check just how it compares with our standard alloy steels and our 5% casehardening nickel. I have been in touch with the new steel for about eighteen months, and had expected to obtain samples for testing some time ago, but Firths have not been very satisfied, | ||