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Aviation History
1963
1963 - 0275.PDF
Fl IGHT International, 21 February 1963 Flying Steel 25 Years of Stainless Steel in the Jet Age ON April 12 last, a dinner at Lancaster House, presided over by the then Minister of Aviation, Mr Peter Thorneycroft. was held to honour Sir Frank Whittle and mark the 25th anniversary of the initial run of the world's first turbojet on the same day in April 1937. That first day was dramatic for, very early on in the proceedings, the engine—the "WU"—soon went out of control. Technical personnel fled to nearby cover, but Whittle stayed at the controls and managed to subdue the shrieking, red- hot machine. Development proceeded, and before very long Sqn Ldr Whittle (as he then was) was able to write to Firth-Vickers Stainless Steels Ltd telling them "Your Rex 78 [steel] proved to be the first material capable of standing up to the necessary combination of stress and temperature." From that original steel has been deve loped a whole family of materials which are now vital to the air craft industry. But turbine engines were not the first field of appli cation for stainless steel in the air. For all practical purposes, the stainless-steel story started in 1913, when a Sheffield metallurgist called Brearley noted the corro sion-resisting properties of an experimental cast of steel containing 13 per cent chromium and about 0.30 per cent carbon. It was also observed that, during hot rolling and forging, this steel offered considerably more resistance to deformation than ordinary steels, and that at high temperatures comparatively little scaling or oxida tion occurred. Brearley suggested that steel of this type "might be suited for the manufacture of ventilators and valves in gas engines and for certain types of cutlery," and it is probably in the form of table knives that stainless steel is best known to the public. Brearley's other forecast also soon proved correct for, during the 1914-18 war, almost the whole production of the new steel was "called-up" for the manufacture of aero-engine valves. During the following years, several versions of the original stain less were developed, including one with 16 to 17 per cent chro mium and 2 to 3 per cent nickel. Suitably treated, this had a yield point of about 45 tons/sq in, with a maximum tensile strength of 50/60 tons/sq in. High-tensile stainless bolts, studs, pump spindles and drive shafts for use in aircraft are still produced in this useful material, which is best known as S.80. The famous Supermarine Schneider Trophy seaplanes used S.80 extensively for highly stressed components, but several of these machines incorporated an important newcomer to the family— 18/8. This steel, first produced in about 1923, was called "Stay- brite" and incorporated 18 per cent chromium and 8 per cent nickel. It is completely different from its predecessors. It is softer dnd more ductile, and does not harden when cooled from a high temperature. Its arrival opened the gate to large-scale production of stainless steel in thin sheets and strips, much better suited to the many forms of mechanical manipulation which had been difficult or even impossible with the earlier types. Further steel "cocktails" including small percentages of titanium md other metals, and subsequent permutations with various alloy elements. These produced a range of corrosion- and heat-resisting steels which have been essential to many great aviation develop ments. During World War 2, centri-spinning techniques were rapidly ieveloped and used for the production of sleeve valves for hundreds of thousands of Bristol and Napier engines. Poppet valves in the 'volls-Royce Merlin and many other units were another applica- 261 Over 90 per cent of the structure of the Bristol 188 consists of Firth- Vickers high-strength stainless steels tion, and stainless steel was also extensively used in the production of exhaust systems. When Whittle started work in earnest on his first engine in 1936, the best stainless-steel could not withstand temperatures above 500°C without excessive creep deformation under even quite low stress. Firth-Vickers "Stayblade" was better, and it was used for the turbine disc in the W.l engine which powered the Gloster E.28/39 on its first flight in 1941. On account of its higher creep strength, it continued to be used in discs for practically all jet development work until the end of 1943. From 1937 to 1939 Whittle's engines were run hotter and hotter, and the conditions imposed on the turbine blades became increas ingly severe. The introduction of FV Rex 78 steel in 1939 consider ably speeded-up development. Rex 78 was used for the blades in the W. 1 and W. 1X engines, as it had considerably improved proper ties at high temperatures and could work 100 C higher than other materials under trial at this time. The turbine and nozzle blades in the E.28/39 engine were made of this steel. In 1945 Whittle himself said "At the time of the design of the experimental engine, the best available material appeared to be Stayblade and we used this both for the disc and blades of the first engine. Had the temperatures of the gases passing through the Much of the structure of Blue Streak—including the very thin outer skin—is made of Firth-Vickers stainless steel
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