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).
The heat treatment and tempering of steel, specifically concerning hardness and fatigue in valve springs.
| Identifier | ExFiles\Box 154a\1\ scan0060 | |
| Date | 21th November 1927 | |
| - 2 - crystaline state structurally and thereby enable the varying heat treatment to take effect as you suggest at the lowest possible temperature. In regard to (2), I concur, but this minimum hardening temper will not be effective throughout the steel unless the steel had previously been by a very thorough normalising brought into such a condition that it will readily respond to the minimum temperature. The reason why springs break under the condition you mention is generally that the steel :- a {Mr Adams} /- Does not carry the carbide in thorough solution. or b/- previous treatment givesit crystal growth. In regard to (3) tempering, I think there are two main factors in tempering. a {Mr Adams} /- The correct minimum temperature. b/- To temper for a sufficient length of time to ensure that the reluctance of the steel to change its state has been overcome. If a steel due to slight peculiarities in composition or any previous treatment shows itself reluctant to go thoroughly into solution at the high temperature it will be equally reluctant to take up its final state or condition during the tempering period. In the first place, that is at the high heat, the reluctance can be reduced by increasing the temperature at the expense of crystal growth. This again can be corrected by a further normalising or treatment like Mr. Pendlebury's, and secondly a long tempering period will ensure homogeneity in the state of the steel. We have endeavoured to keep the brinell on the low side of the mean figure when heat treating valve springs, since the fatigue curve falls off very much less rapidly on the low side of the mean than it does on the high. The figure we are aiming at is 379 to 402, but tests may prove that even these figures are somewhat on the high side, as we found that for road springs 379 was the best brinell for fatigue conditions. I regret that owing to my absence from the Works last week through feeling a little offside, I was unable to reply to R1/MAO.1.11.27. and R1/MA2.11.27. earlier. BY | ||