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).
Article on French experimental research into different compositions of valve steels, including a data table of their properties.
| Identifier | ExFiles\Box 54\3\ Scan210 | |
| Date | 1st July 1926 | |
| 6 VALVE STEELS Automotive Industries July 1, 1926 creased number of seats made possible by the lengthening of the wheelbase, and economy of fuel and oil due to the reduced resistance on curves. This new type of underframe is said to be specially adapted for use in rail cars. It permits of carrying the power plant on the central truck, so that absolutely no vibration from it will be transmitted to the car body. A drawing of a 180 hp. rail car submitted with this article shows, besides a compartment for baggage and mail, seats for 66 passengers. The engine, change speed gear, reversing gear, fuel tank and air reservoir are all installed on the central truck and do not project into the car body. French Experimental Work on Valve Steels IN order that steels which are required to pass through numerous working cycles within an extended thermal range, may withstand for a long time the stresses to which they are exposed, it is necessary that their characteristics should return to the same values after each cycle, and that, in consequence, there are no critical points in the thermal zone. Under these conditions the “reversibility” of the steel is assured; that is to say, when the steel has cooled one finds the austenitic or sorbitic structure to the exclusion of the trossititic structure in a more or less accentuated coalescense, the heterogeneity of which has often given rise to great disappointment. Some experimental work bearing on the application of the above principle to valve steels, and particularly steels for valves for “forced” aircraft engines, has been done in France and was reported upon in a note to the French Academy of Sciences by Charles Grard, presented by M.{Mr Moon / Mr Moore} Leon Guillet. It is stated in this “Note” that the principal requirements in respect to these steels, and which extend over the entire temperature range of the working cycle, are as follows: Reversibility of the metal, the highest possible thermal conductivity, resistance to the corrosive action of the burnt gases, resistance to repeated shocks, sufficient resilience and hardness, and lightness. Results of Research Admitting that important improvements can be made by suitable mechanical design, metallurgical research has led to the following results: High nickel alloys, which are very resilient, sometimes seize at high temperatures; the so-called high speed steel are hard, particularly when hot, but brittle and not very resistant to repeated shocks; moreover, both of these steels are relatively heavy. Silicon chromium steels permit of lightening the valves by as much as 30 grams (about one ounce) as compared with the steels previously mentioned, in the case of a 450 hp. Lorraine engine, which materially cuts down the inertia forces due to the reciprocating motion. It is thus in this research work, seeking first of all, by methodically varying the components, to force the critical points beyond the maximum temperature reached by the valves in service. He specially covered the ranges of alloys of which the compositions are given in the following table. This table gives the critical points of transformation and the resistances to repeated shock, and it will be noted that the silicon content has a very important influence on the critical points. No. of the Steel | Carbon Content | Silicon Content | Chromium Content | Ac Point Deg. F.{Mr Friese} | Res'st.{Capt. P. R. Strong} to R'p't'd shock ------------------|----------------|-----------------|------------------|----------------|-------------------- First Group 1 | 0.570 | 1.565 | 13,140 | 1,598 | 18,570 2 | 0.395 | 1.960 | 11,610 | 1,630 | 20,300 3 | 0.560 | 1.920 | 14,210 | 1,652 | 20,300 4 | 0.470 | 1.775 | 11,800 | 1,652 | 18,790 Second Group 5 | 0.580 | 2.445 | 13,140 | 1,688 | 15,600 6 | 0.535 | 2.830 | 14,000 | 1,742 | 16,710 7 | 0.390 | 2.800 | 12,060 | 1,742 | 18,140 8 | 0.490 | 2.870 | 11,740 | 1,778 | 18,107 Third Group 9 | 0.540 | 3.885 | 13,130 | 1,868 | 15,570 10 | 0.355 | 4.030 | 11,610 | 2,022 | 9,473 11 | 0.345 | 4.020 | 12,020 | 2,060 | 6,918 12 | 0.410 | 4.100 | 14,080 | 2,138 | 3,498 Of the three groups of steels thus obtained the first one was discarded, because the temperatures of its critical points are too low, the third was also discarded, because the precipitation of graphite, due to the excessive silicon content and revealed by micrographic examination, entails too low a resistance to repeated shock and too low resilience; in the second group the compositions 5, 6 and 8 gave insufficient resilience (less than 2), by reason of their too high carbon content. Selection was made, therefore, of composition No. 7 (C, 0.40 per cent., Si., 2. 5 per cent, Cr.{Mr Cra???ster / Mr Chichester}, 12 per cent) which, after being air-hardened at 2200 deg. F.{Mr Friese} and drawn at 1,650 deg. has the following mechanical properties: Critical point on the rise in temperature, beyond 1650 deg.; specific gravity, 7.8; tensile strength when cold, greater than 130,-000 lbs. per sq. in. elongation when cold, greater than 12 per cent resilience when cold (what is evidently meant is notched bar test result) greater than 4; Brinell hardness when cold, greater than 280; Brinell hardness at 1650 deg. F.{Mr Friese}, a little less than 40 (this latter figure was slightly raised by the addition of 1.5 per cent of tungsten. Chromium silicon steel valves of the above composition, fitted to a Lorraine 450 hp. engine, passed through a 50-hr. endurance test without giving the least trouble—a case of sufficient rarity to merit mention. After the test the valves retained the same polish and texture as at the beginning. HEALTHY growth of the automobile movement in Tunisia, northern Africa, is reported in a commercial notice just published by the Regence of Tunisia. The number of automobiles in service on May 30, 1925, was 3,324, of which 2,611 were private cars, 236 trucks and 126 automobiles for public conveyance. The greatest volume of business is being done by French manufacturers. Returns, which give automobile importations in kilogrammes, show 953,171 last year from France, followed by 159,023 from the United States and 63,788 from Italy. Importations from other countries were small. The types of automobile having the biggest sales are of 5, 10 and 15 hp. (European rating). The use of trucks, particularly of 3-tons capacity, has extended considerably since the war. The use of light trucks of 1-ton to 1½ tons capacity is not as extensive as it might be, for there is opposition from cheap native haulage. Automobiles and parts are not affected by the new import tariff bill recently passed by the Japanese Diet and put into force March 29. Many changes, mostly increases, were made in the rates applying to other products imported from America, however. Ball bearings, for instance, are now subject to a duty of 20 yen ($10 at normal rate of exchange) per 100 kin. (A kin is equivalent of about 1 1/3 lb. avoir.) A duty of 25 per cent ad valorem has been placed on gearing chains. The rates on mineral oils are slightly decreased. | ||