December, ig4j Abstracts from the Scientific and Technical Press " (No. 117. October, 1943) AND Titles and References of Articles and Papers Selected from Publications (Reviewed by R.T.P.3) TOGETHER WITH List of Selected Translations (No. 63)' London : "THE ROYAL AERONAUTICAL SOCIETY" with which is incorporated "The Institution of Aeronautical Engineers" 4, Hamilton Place, W.I Telephone: Grosvenor 3515 (3 lines) ABSTRACTS FROM THE SCIENTIFIC AND TECHNICAL PRESS. Issued by the Directorate's of Scientific Research and Technical Development, Ministry of Air­ craft Production. (Prepared by R.T.P.3.) No. 117. OCTOBER, 1943. Notices and abstracts from the Scientific and Technical Press are prepared primarily for_ the information of Scientific and Technical Staffs. Particular attention is paid to the work carried out in foreign countries, on the assumption that the more accessible British work (for example that published by the Aeronautical Research Committee^ is already known to these Staffs. Requests from scientific and technical staffs for further information of transla­ tions should be addressed to R.T,P.3, Ministry of Aircraft Production, and not to the Royal Aeronautical Society. Only a limited number of the articles quoted from foreign journals are trans­ lated and usually only the original can be supplied on loan. If, however, translation is required, application should be made in writing to R.T.P.3, the requests being considered in accordance with existing facilities. ' NOTE.—As far as possible, the country of origin quoted in the items refers to the original source. The Effect of Nitrogen on the Properties of Certain Austenitic Valve Steels. (H. Cornelius and K. Fahsel, L.F.F., Vol. 20, No. 7, 20/7/43, PP- 210-216.) (117/1 Germany.) The valve steels commonly employed contain about 15 per cent. Cr, 13 per cent. Ni and 2 per cent. AV (Tungsten). Recently austenitic Cr>Mn steels of much smaller Ni content have been proposed as a satisfactory alternative and it was claimed that the heat stability of such steels could be still further improved by small additions of N2. To investigate this matter, the authors prepared 14 samples of austenitic steels covering the following ranges of per cent, composition :— C Si Mn Ni Cr W Ti N2 .43 1.7 I.I 3-1 11-7 o o .02 •59 3-5 6.7 9.1 18.3 1.2 .48 .23 The variation in N3 content was obtained by adding different amounts of Ferrochrome (containing up to 6 per cent. N2) to the melt (high frequency furnace). The specimens were hardened by air cooling after forging (i,oso°C.) and subse­ quently tempered at 8oo°C. for 3 hours and again air cooled. 676 ABSTRACTS FROM THE SCIENTIFIC AND TECHNICAL PRESS. 677 The tests were carried out both in this (so-called original) state and after a further annealing at 700°C. for 200 hours followed by air cooling. A comparison of the mechanical properties obtained in the original and annealed state enabled conclusions as to the stability of the austenitic structure to be drawn. The preliminary tests covered the elastic limit (.2 per cent, set), yield point (.2 per cent.), ultimate tensile, extension at fracture, contraction and impact strength, as well as magnetic saturation. The authors conclude that the stabilising effect of N2 on the austenitic structure of the steels is very small and that its introduction into the steel does not render possible any marked reduction in the Ni content as had been previously claimed. Under the most favourable circumstances the max. possible addition of N2. ('-' .25 per cent.) is equivalent to about 2 per cent. Ni, but in most cases con­ siderably less (.5 per cent.). (Some previous investigators had claimed the replacement value of .2 per cent. N2 to be the equivalent of 6 per cent. Ni.) In addition to the mechanical tests detailed above, the resistance of the steels to both rapid and slow rates of deformation was investigated. For the former, a special pendulum apparatus devised by the author was utilised, the experiments covering the temperature range up to 85o°C. For the slow rates of deformation, the D.V.L. creep test was carried out at 7oo°C. For high rates of deformation (pendulum test) the addition of Na is definitely beneficial at temperatures up to 4oo°C. At the working temperature of the valve (8so°C.), however, the N2 appears to have no effect. From the creep tests at 7oo°C, the authors conclude that the N2 produces only a very small effect. Further tests carried out on scale formation, thermal conductivity and thermal expansion all showed that the N2 content exerts only a very minor influence. In conclusion, the specimens were nitrided in an atmosphere of NH3 and tests carried out on the surface hardness and thickness of nitrided layer. It appeared again that the N2 content of the alloy affected the results only slightly. The final conclusion appears to be that the addition of N2 to austenitic steels of the type discussed seems scarcely justified. Such austenitic steels, especially when containing about .5 per cent.. Ti, are sufficiently stable to replace the commonly employed valve stgels of high nickel and tungsten contents, thus leading to a considerable saving in these two constituents.- The Effect of Welding Faults on the Static and Dynamic Strength of Welded Joints of Steel St. 52, with Notes on the Limits of Fault Detection by X-Ray Examination. (H. Keller and E. Klein, Schiff u. Werft, Vol. 44-24, No. 17-18, Sept., 1943, pp. 257-261.) (117/2 Germany.) The experiments refer to welded steel plates of St. 52 material such as used in ship building. (ABSTRACTOR'S NOTE.—This steel has the following average compositions :— C= .2% Cu=,55% Mn=i.2% P = .o5% Si=. -5% . S = .o5% Ultimate tensile of commercial product 52-64 kg./mm.2.) Thickness of plate 15-22 mm., standard butt weld, V seam. A selenium electrode was employed, type Bohler K.V.A. The test specimen (35 to 45 mm. wide) were obtained either from the hull itself (making use of such portions as had to be removed in order to provide room for certain fittings) or from samples of work supplied by the welder during his periodic examination for efficiency. 678 ABSTRACTS FROM THE SCIENTIFIC AND TECHNICAL PRESS. In addition, special samples incorporating intentional faults were prepared by the authors. In general, welding faults may be of the following types:— i. Slag inclusion, mainly due to electrode sheathing. 2. Pores, due to gas absorption (vapourisation of sheathing). 3. Cracks, due to shrinkage or local hardening. 4. Local burning, due to excessive welding current. 5. Adhesion and root faults, due to the current being too low or the electrode moving too rapidly. Slag and gas inclusions generally give rise to spherical cavities and if finely dispersed affect the strength of the weld only slightly (no notch effect). In the case of trained welders using modern equipment and suitable electrodes, the chance of producing large inclusions and thus weakening the weld, is practically negligible, and for this reason the authors rule out this source of trouble in the present investigation". On the other hand, faults 3 and 5 (crack and root faults) give rise to considerable notch effects and are considered by the authors as responsible for most of the subsequent failures, especially under fatigue. Since the samples obtained from the hull or submitted by the welder were generally of high quality and especially free from cracks, the authors prepared, additional test pieces in which these faults were exaggerated intentionally. Thus root or adhesion faults were induced by a quick pass of the electrode whilst artificial cracks were prepared by first forming a connection by means of welded- on straps. These were subsequently broken and the plates rewelded with a continuous seam in such a way that the- fractured strap -surfaces were retained as internal cracks. The position C*f these cracks was found by X-ray examination and the plate subsequently cut into strips of equal width each incorporating one crack. The extent of root (adhesion) or crack faults was estimated by projecting the area of such faults (as revealed after test) on a plane at right angles to the axis of the specimen and dividing by the nominal cross-section of test specimen. TENSILE TESTS. About 35 samples were tested, of which 2-29 (originating mainly from the ship's hull or from the specimen submitted by the welder) showed neither root faults nor internal cracks of the weld when examined after ultimate failure. These so-called " faultless " specimens had an average tensile strength of 54 kg./mm.2 (50 per cent, of samples) which is only very little less than average values for the original plate. The scattering of this " faultless " specimen was however relatively large, ranging from 45 to 61 kg./mm.2, whilst the ultimate for steel St. 52 falls between the limits 52-64 kg./mm.2. It is evident that even in the absence of visible root and crack faults, other factors such as the notch effect of the burn or local hardening in the transition zone influence the results. In this connection it should be pointed out that all the welds were tested " as finished " so as to reproduce practical conditions. No attempts were made to improve the weld subsequently, either by milling off the bead or burned zone or by annealing the joint. There is no doubt that such measures would have improved the consistency of the results appreciably. EFFECT OF ROOT FAULTS ON ULTIMATE TENSILE. After eliminating the " faultless " specimen, those showing adhesion or root faults after failure (45 specimens) were collected and their ultimate tensile plotted on a relative " fault size " basis, the latter being estimated from the projected area of the fault as already explained.