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Workshop and Production Section AIRCRAFT ENGINEERIN G June, 1941 URIN G recent years considerable attentio n has welding rod. This element is not burned out of a and advisable to weld from one side only. Care been given to the welding of alloy steels. Un rod of proper analysis t o any extent during welding. should be taken to fill the scam completely so that til recently a limiting factor in the use of 18-8 Th e result is tha t an analysis of the weld an d th e metal ther e will be no occasion to return to some point stainless steels was that certain service conditions adjacen t to it shows that nearly all the columbium which should have been finished as the weld pro ha d a tendency to lower their corrosion resistance by in the rod has been carried through the welding pro gressed. It. is importan t not to stop or retrace a hot producing a susceptibility to inter-granular corro cess to give a "treated " weld fully as capable of weld. If this must be done wait until the weld sion. Welding also was found to cause the same resisting corrosion as before manufacture. There cools entirely. susceptibility in narrow zones in the parent metal fore, the use of treated or "stabilized " 18-8 stain If it should become necessary to go back over a nea r the weld. In some cases, heat-treatment after less steel base material and the new columbium- weld, or if there is need for welding at the back of welding would restore the desired properties but treate d stainless steel welding rod allow the making th e seam (in order to eliminate severe stresses), the this was not always feasible. However, the recent of a welded article with all the desirable corrosion entire seam should be pre-heated before the flame introduction of a columbium-treated 18-8 stainless resistan t properties of th e base material and without is applied to the local area of the joint. Such pre steel welding rod is likely to mark an important th e need for subsequent heat-treatment. heatin g is frequently undesirable because of the advanc e in the fabrication of stainless steel. The Columbium is important in another way as it likelihood of warping of the metal and because slow use of this rod in conjunction with 18-8 base metal counteract s the harmful effect of th e slight carbon cooling is harmful to the stainless steel. In other treated or "stabilized" with columbium or titan pick-up which may occur during welding. The words, complete the weld in one pass, get thorough ium permits the manufacture of welded stainless welding rod contains sufficient columbium to main penetratio n in one pass, so tha t it is unnecessary to steel products which, in the as-welded condition, tain the proper ratio to carbon and other alloying work over or touch up a weld in an y way. have full resistance to corrosive and oxidizing in elements even after a small increase in carbon, to a Anothe r operation against which the operator fluences, particularly at elevated temperatures. maximu m of about 0·10 per cent, resulting from mus t be cautioned is welding away from an edge. Th e carbon conten t of 18-8 stainles s steel ha s a n im welding. If it is necessary to weld away from an edge, begin portan t effect on its corrosion resistance. Increase in While the columbium-treated welding rod was th e weld an inch or two in and return to the starting th e carbon content causes a rapid decrease in the developed primarily to meet the problems of success point later to complete the weld to th e edge, ability of this steel to resist corrosion at elevated fully welding the new treated or "stabilized " steel Th e operator should familiarize himself thorough temperature s or afte r it ha s been heated during manu withou t subsequent heat-treatment, distinct ad ly with the recommended procedure before any facture, as in welding. The so-called low-carbon 18-8 vantage s are found in using it for welding the work is attempted. The columbium-treated rod stainless steel, which is the type most generally ordinary untreated 18-8 steel. When it is used for flows easily and smoothly and very high quality used for high corrosion resistance, is usually specified welding straight 18-8 steel, its chief advantage lies welds may be expected. The welds will have good as maximum 0·10 or 0·07 per cent carbon, depend in the fact that the columbium in the rod counter strengt h and will be completely corrosion-resistant ing on th e severity of th e intended service. act s the effect of any possible pick-up of carbon in the as-welded condition. The completed struc durin g th e welding process. This results in a welded Th e metallurgical reasons for the development of tur e therefore may be used without the need of metal with better corrosion-resisting properties susceptibility to inter-granular corrosion can be subsequent heat-treatment. unde r service conditions than welds made with un explained in the following way. When an 18-8 I t has been found helpful to place th e parts being treate d rod. steel is cooled rapidly from high temperatures, as is joined so tha t the line of weld inclines slightly down normally done in its manufacture, the material re There is another important advantage. When ward in the direction of the welding. In this way, tains a homogeneous structure, with carbon and straigh t "untreated" 18-8 stainless steel is used th e flux, which fuses a t lower temperatures than the othe r constituents in solution with the iron base in crossed welds, tha t portion of th e first weld which steel, can flow forward and consequently provide metal. In this condition it is quite corrosion- adjoins the second is affected in exactly the same protection for the metal as it fuses. resistant . However, when this steel is reheated to a manne r as untreate d base material . In other words, As compared with ordinary steel, the 18-8 stain temperatur e within the approximate range of 500 a narrow zone of lowered corrosion resistant steel is less steels have a much higher coefficient of expan to 1,400 deg. F., a new constituent, a carbide, is created which crosses the first weld and is parallel sion, with, at the same time, lower thermal conduc precipitated or thrown out of solution. This tends with the second. When joining welds, as, for tivity. Because of these properties, welding, especi t o form at the boundaries of the individual grains example, in closing a circumferential weld, a similar ally when applied to thin material, may cause dis forming th e metal structure. The formation of this condition will occur in the cold portion of the weld tortion and warping unless suitable provision is made precipitat e lowers the corrosion resistance of the which was laid down at the beginning of the opera to prevent this action. Clamps, copper chill plates, material at this point to a degree. This allows tion. These effects are entirely eliminated by the an d jigs are used separately or in combination to th e destruction of the material by inter-granular use of a welding rod containing columbium. This, hold the plates in line until the weld has cooled. corrosion under conditions that it would normally as explained previously, is because the columbium Greater case and speed in welding are other advan resist. remains in the weld metal to give a treated weld tages obtained by the use of these appliances. unaffected by re-heating. I n welding, then, the critical 500 to 1,400 deg. F. Less absorption of hea t in th e par t welded, and more rang e is passed and exceeded. As the heat passes Th e procedure used in welding' 18-8 stainless steel rapid chilling, are also further advantages. thi s range slight precipitation may take place, but is essentially the same as in welding ordinary steel I n most instances, sheets 1/16in. or less in thick th e higher heat of welding permits complete solu except that certain precautions must be more care ness are flanged at the edge to a height of about tion to take place again. Cooling of th e weld metal fully followed. Greater care must be exercised, 1/16in. The flanged edges are painted with the flux is usually rapid enough to prevent precipitation as particularly with the treated or "stabilized" a t both the top and bottom and are held in place as th e metal passes through the critical range. Thus types , in order to obtain the most desirable results. th e flame melts down the flanges to form a smooth, th e weld itself retains to a large exten t th e corrosion- Th e properties of welds in stainless steels are moderatel y reinforced weld. resisting properties of the original base metal. greatly affected by the type of flame employed, so Slightly heavier sheets up to l/8in. in thickness Ther e is a zone parallel with the weld in the base tha t a neutral flame is essential. ma y have the edges butted and welded with some metal, however, tha t is brought to th e critical range Th e use of a (lux is strongly recommended for addition of metal from a welding rod. A backing because of the welding heat. The metal in this welding 18-8 steel, as it makes the control of the strip, generally of copper, is used beneath the joint zone remains healed within the critical range for a molten metal easier and also ensures a sound, t o prevent the liquid metal from flowing out of the sufficient length of time and cools at a slow enough clean weld of good appearance. The Mux is applied weld. l'"or plates heavier than l/8in., the edges rat e so tha t precipitation takes place and this zone to the seam or the welding rod in the usual way by should be chamfered to provide a vee so that is subject to inter-granular corrosion. Before the mixing the flux with water to the consistency of a complete fusion to the bottom of the weld can be adven t of the newer "treated " 18-8 steels or the thin paste and applying it with a brush. The use obtained easily. Welding rod is, of course, used in new welding rod, full corrosion resistance after of flux on the rod is particularly helpful when weld th e making of these welds. welding could be obtained only by re-heating the ing light gauge sheet. Advantages are also gained produc t to the high temperature necessary to put by painting the underside of the seam with flux, BOOKS RECEIVED all of the carbon into solution again and cooling it since this prevents oxidation and allows a more rapidly. perfect union to be made along the bottom of the Ho w to Dra w 'Planes. F. A. A. Wootton. seam. A great deal of study was given to this problem, 64 pp. , illustrated. [Studio. 2s. 6d.] Welding should be conducted in such a way as to with the result that certain elements were found Th e High-Speed Internal Combustion preven t or minimize any tendency to puddle the which, when added to ordinary 18-8 stainless steel, Engine . H. R. Ricardo ; revised by H. S. weld as this increases the tendency to oxidation and would eliminate the susceptibility to inter-granular removal of the valuable constituents. The welding Glyde . 434 pp. , illustrated . [Blackie. 30s.] corrosion. The elements of greatest value for this technique consists in holding the rod ahead of the purpose are columbium and titanium. When Plastics . V. E. Yarsley and E. G. Couzens. either of these elements is added in such quantity blowpipe so tha t the molten metal melts in place or is 160 pp., illustrated. [Penguin. 6d.] as to create the proper balance between it and the melted simultaneously with the base metal to form Aircraf t Identification. Part III. Italian carbon, formation of the precipitate is minimized or a union between the parts being welded. Fighters , Bombers and Seaplanes. 65 eliminated altogether. '1 his preserves the corrosion Th e heat used in welding stainless steel should be resistance of the alloy steel, even when it is heated th e minimum that will give the results desired. pp. , illustrated. [Temple Press. 2.?.] subsequently to within the critical range. This Excessive heat on molten columbium-treated 18-8 Electro-Platin g and Anodising. J. Ross- further eliminates the necessity of subsequent re steel increases the loss of columbium during welding. lyn . 224 pp., illustrated. [Newness. 6s.] heating or annealing to a temperature above that Th e normal heat keeps the loss of this element to a Aircraf t Production. 104 pp., illustrated. range followed by rapid cooling. This discovery small allowable percentage of that contained in the rod. [Newnes . 5s.] has led to the development of the so-called treated or "stabilized" 18-8 stainless steels, which are Th e choice between leftward and rightward Meta l Aircraft Construction. Fourth Edi likely to have a wide use in commercial applications welding depends chiefly on the skill of the operator tion . M. Langley. 443 pp., illustrated. when high corrosion resistance is necessary. in either method. In general, leftward welding [Pitman . 15s.] is preferable on light-gauge sheet, while rightward While the presence of either element in the base Pressworkin g of Metals. C. W. Hinman. welding is bette r on the heavier gauges. metal is effective in eliminating the "hea t effect," 44 3 pp. , illustrated. [McGraw-Hill. 28s.] columbium is more advantageous for use in the When working on stainless steel, it is customary
Aircraft Engineering and Aerospace Technology – Emerald Publishing
Published: Jun 1, 1941
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