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).
Technical bulletin detailing the use and properties of various steel alloys in automotive components, including axles, steering, and the 'Golden Arrow' engine.
| Identifier | ExFiles\Box 154a\1\ scan0256 | |
| Date | 23th April 1932 guessed | |
| - 4 - Fig. 4 by courtesy of The Autocar. 3½ per cent. Nickel Steel was used for the Radius Arms. The extensive use throughout the whole automobile of the nickel steel just referred to indicates its dependability and the wide range of properties obtainable from it with the simplest of treatments. In the normalised condition it will give maximum stress figures of 35 tons per sq. inch and over, with elongation and reduction of area per cent. up to 25 and 45 respectively. The actual properties obtainable will, of course, depend on the size of the bar. Oil-hardening and subsequent tempering will naturally allow of the attainment of much better figures. Thus a 1¼ inch diameter bar, oil-hardened from 840° C. (1540° F.{Mr Friese}) and tempered at 550° C. (1020° F.{Mr Friese}), will have properties similar to those below:— Yield Point. Tons per sq. in. 42.4 Maximum Stress. Tons per sq. in. 53.6 Elongation. Per cent. 28.0 Reduction of Area. Per cent. 61.5 Izod Impact Figure. Ft. lbs. 56 On the “Golden Arrow” it was used both in the normalised condition and after quenching and tempering to various degrees of hardness. Front and Rear Axles. The axles were located in the frame by means of radius arms made of the same 3½ per cent. nickel steel, being supported on springs of which the shackles, shackle pins and spring carriers were of similar material, as were also the buffer housings and shock absorber brackets and pins. Fig. 4 shows one end of the front axle and includes a radius arm and spring housing. For the main parts (centre, ends and swivel) of the axles themselves a particularly strong, tough material was naturally needed and choice fell upon a nickel-chromium-molybdenum steel of approximately the following composition:— Carbon Per cent. 0.3 Manganese Per cent. 0.4 Nickel Per cent. 3.5 Chromium Per cent. 0.65 Molybdenum Per cent. 0.2 This was used in the heat-treated condition, a typical test result following the treatment being:— Yield Point. Tons per sq. in. 56.0 Maximum Stress. Tons per sq. in. 63.4 Elongation. Per cent. 20.5 Reduction of Area. Per cent. 60.4 Izod Impact Figure. Ft. lbs. 67 Besides its combination of strength and toughness, a steel of this type has the added advantage of giving exceptionally uniform properties throughout its length and cross section when properly heat-treated and this fact no doubt influenced the designer in selecting it. The driving shaft in the rear axle was made of the same material. 3½ per cent. nickel steel was used for a number of details, while the swivel pins and other parts subject to wear were made of a 5 per cent. nickel case hardening steel. This type of steel, which usually contains about 0.1 per cent. carbon, combines a high tensile strength in the core with exceptional toughness throughout its section. Thus a usual specification for this material after refining at 830° C. (1530° F.{Mr Friese}) and quenching from 760° C. (1400° F.{Mr Friese}) is:— Maximum Stress. Tons per sq. in. <55 Elongation. Per cent. <15 Reduction of Area. Per cent. <40 Izod Impact Figure. Ft. lbs. <20 Fig. 5 by courtesy of The Autocar. The Steering Control Mechanism. Steering Mechanism. Reference has been made to the difficulty of steering a heavy machine at high velocity, and a steering mechanism of unusual design had to be devised. As will be seen from the illustration, the steering arm was placed horizontally and operated two bevel gears (See Fig. 5), which in turn actuated specially constructed Marles steering gears situated at the ends of short shafts. The two drop arms were attached individually, by means of rods and bell-cranks, to each of the front stub axles, the wheels being thus controlled independently. For the track rod arms, steering arms and levers, where the stresses involved may be exceptionally high, use was made of a nickel-chromium-molybdenum steel containing a rather higher chromium and lower nickel and carbon contents than that referred to above. Its approximate composition was:— - 5 - Fig. 6 Napier Lion Aero Engine, as used in the “Golden Arrow.” By courtesy of Messrs. D.{John DeLooze - Company Secretary} Napier and Son. Carbon. Per cent. 0.25 Manganese. Per cent. 0.5 Nickel. Per cent. 3.0 Chromium. Per cent. 1.2 Molybdenum. Per cent. 0.2 and the following mechanical properties are typical of those which can be obtained from it in the quenched and tempered condition:— Yield Point. Tons per sq. in. 62.5 Maximum Stress. Tons per sq. in. 69 Elongation. Per cent. 19.5 Reduction of Area. Per cent. 61.5 The various worm shafts and bevels were made of 3½ per cent. nickel steel, this being employed in the heat-treated condition. Brake Equipment. The bringing of a heavy car to a standstill from travelling at 231 miles per hour naturally involved a considerable stress on the braking mechanism, while perfection of operation was essential, since any sharp braking effect would almost certainly lead to disaster. Both hand and foot brakes were fitted, the latter operating through a Dewandre vacuum servo motor. The 3½ per cent. nickel steel was largely used here again, the following parts being made of it:—hand brake lever, ratchet, stop and trigger rod, foot brake shafts, lever, draw bars and fork-ends, brake carriers, brackets, and shoes. For the brake cam, a 3½ per cent. nickel case-hardening steel was used. This steel has not the strength of the 5 per cent. nickel steel, but the following properties can easily be obtained in the core even after a single quench in oil from 760° C. (1400° F.{Mr Friese}) following carburising:—* Maximum Stress. Tons per sq. in. 36 Elongation. Per cent. 55 Reduction of Area. Per cent. 64 Izod Impact Figure. Ft. lbs. 90 The camshafts were made of the case-hardening nickel-chromium steel referred to below. (b) The Engine. The Napier Lion Engine which was employed in the “Golden Arrow” was similar to that fitted to Flight Lieut. D'Arcy Greig's seaplane which last autumn attained a speed of 319½ miles per hour, the highest then ever travelled by man. It has *For further details regarding this and other nickel case-hardening steels see our publication S1. “Case-Hardening and the Use of Nickel Steels.” | ||