Metal Secrets Demobbed!
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IT is becoming possible to tell something of the story of war-time developments in metals and their application, particularly in regard to the commercial-motor industry and their bearing upon it. The necessities of war made it essential to pursue important investigations into the welding properties of the low-alloy steels, with the result that the value of depositing sustenitic material in welds was fully proved. Moreover, it is now becoming possible to specify weldability of steels according to a hardenability test and to the notch-bend performance of the quenched bar, the test-pieces being taken at various distances.
Seldom can engineers and designers specify, with confidence, steels having a tensile strength of over 67 tons per sq. in. for ordinary use in parts of machines or automobiles. Much knowledge and experience have, 'however, been gained during the war years, in both engineering and ordnance steels, with the result that there is no longer any difficulty in manufacturing and using steels with sufficient ductility at levels of strength well above this tonnage. figure. It is said that sttengths of even as high as 90 tons per sq. in. may, in the near future, be uniformly and regu_larly obtained.
Scheme of Standardization For Steels of this design strength, much will depend on the content of alloy and the kind of alloy needed to provide the necessary structure when
quenched. Steels suggested as ultimately being standardized for this class of work include nickel-chromium, chromium-molybdenum, nickel-chromiummolybdenum, and chromium-vanadium compositions. It is assumed that special addition .agents will be introduced and. that tolerances on residual elements will be broadened, which will be essential, because of the necessity of making the best possible use of scrap, of which there will be large quantities available.
In general, the tendency appears to be the employment of the already wellknown types of alloy constructional steel at increasingly higher design stresses, and the introduction Of newer steels meeting requirements in smaller sections and with intermediate ranges of strength.
The experiments that have been froceeding for some time in the use of boron as an alloying element (referred to more than once in this journal) appear now to have indicated that, whilst boron is extremely advantageous in combination with other alloying elements, it is not of great value in steels that have not been fully quenched and hardened throughout. It appears, therefore, that boron.will most likely be confined as an additional alloying element to the alloy steels.•
Silicon ie becoming -mach more important than it used to be in engineering steels. Steels are now being used in which the silicon content has risen to as much as 0.35 per cent., and this figure is often expressed to-dsay as a maximum; actually, higher percentages are being introduced into steel compositions for special purposes. It is, however, doubtful whether a -percentage of 0.4 will be exceeded, because of manufacturing difficulties that present themselves to the steel maker and roller.
Nevertheless, high silicon within the limits indicated is becoming increasingly common, and this trend is likely. to continue. The special advantages obtained by this increase in the silicon content include better deoxidation, higher hardenability, and greater facility in obtaining a fine grain structure. These advantages are particularly obtained when special deoxidizers are employed.
Many experiments have been carried out in the attempt to find case-hardening steels superior to the standard types, but it can be stated categorically that thernickel and chromium-base casehardening steels show no sign of being superseded, particularly when small percentages of molybdenum or vanadium are added to them. Research has not yet produced any startling advance in these steels.
Mn/Cr versus Ni/Cr Stainless Another fact emphasized by war-time experience is that, up to now, no really satisfactory substitute has been found for chromium and nickel in stainless steels. Many claims have been made for manganese, but it is plain that this element, whilst useful, is really only a substitute when nickel is difficult to -obtain and cannot be regarded as a rival . to it. It has, however, been shown that as a supplementary alloying element to nickel and chromium, it has advantages, and there is a definite trend towards increasing the manganese content of the standard austenitic stainless steels. Nitrogen is also proving useful in connection with these steels.
Electrodes for arc welding are being made of austenitic-steel core wire containing from 10 to 25 per cent, chromium and 6 to 15 per cent, nickel, with a protective coating containing enough molybdenum to produce a weld deposit containing approximately 1.25 to 5.0 per cent, molybdenum. An alloy for cutting and hot-working steels invented during the war by Krupp contained 0.1 to 1.0 per cent. carbon; 10 to 35. per cent tungsten, Or 2 to 12 per cent. molybdenum, singly or in combination; 25 tb 50 per cent. cobalt; 3 to 15 per cent, chromium, with additions of 10 to 20 per cent, iron, and either titantium, vanadium or tantalum. The alloy was quenched from 800 to 1,000 degrees C., then annealed at 400 to 700 degrees C.
A new die steel contains 0.3 to 1.1 per cent. carbon, 0.25 to 1.25 per cent. chromium, 0.6 to 1.0 per cent. manganese, 0.15 to 2.0 per cent. molybdenum, and silver in excess of its solid solubility in steel, but not above 2 per cent. The addition of silver is designed to give the steel superior machinability when heat-treated and hardened.
Argon arc welding is a new development and is replacing heliarc welding for alloys of magnesium base. A similar torch is needed and a flowtneter is generally employed. Sound and consistent joints are claimed, irrespective of design, by reason of the absence of fluxing. The argon used is 98 per cent. pure, the presence of nitrogen reducing welding speed.
Boosting Leaded Steels Striking improvements in machinability are claimed for leaded steels. The machinability constants of these steels are claimed to be 24 to 35 per cent. higher than for types without lead, and increases of feed from 36 to 60 per cent. are obtainable. Remarkable gains in tool life are also said to be feasible. Magnesium welds are being cleaned by means of immersion in 5 to 10 per cent, caustic soda at 65 degrees C. for five minutes, thorough rinsing In cold water, immersion in 20 per cent. chromic acid at 65 degrees C. for two minutes, further thorough rinsing In cold running water, and, finally, airblast drying.
Plated plastics are one of the latest developments, and may be of great usefulness. They cost rather more than plated metals, but have certain advantages, such as resistance to corrosion. An adherent, uniform, copper plating is seing_given to aluminium and its alloys by a simple preliminary dip at normal temperature. The dipping solution can be used in a steer', wood, or ceramic container and, as no fumes are said to I e produced, no venting is necessary. The solution has a long life, is stable, and is not sensitive to drag-out, normal contamination, or dilution.
In nitriding some chromium-containing steels, the hardness of the cask if greatly affected by the previous heat-. treatment to which the steel has been subjected. This is specialty true of the pre-nitriding tempering treatment. It has been found that, whilst the chromium-molybdenum and chromium.
molybdenum-vanadium steels are much influenced in this way, a chromiummolybdenum steel containing a notable amount of aluminium is barely affected, .To reduce wear and prolong life of piston heads of steel, flame hardening of the walls of the piston-ring grooves is being adopted.
Continuous induction heating is being applied to. the annealing of stainlesssteel tubes. These steels may be
quenched in oil, after they emerge from the beating coil, without any risk of fire,
A new design for an engine mount ring comprises an assembly of several curved channels of stainless steel.
Various nickel alloys are being extruded in larger tubes, usually of mane! metal up to 7i ins., and are thereby opening out new possibilities for designers needing corrosion-resistant and strong cylinders.
Spinning of light metals is becoming increasingly 'important as a forming method for certain purposes. Ease of forming high quality and economy, are likely to make spun parts more widely used in the near future.
. In mass production of precision form parts, the method of forming the grinding *heel by crushing is proving inCreasingly popular, as it combines accuracy with simplicity of producing the form, and cuts out costly diamonds and special equipment.
Round straight holes in dies and gauges are being produced more quickly with a mandrel charged with the correct grade of diamond dust than by the use of small mounted wheels.
Copper-cushioned Toot Tips The use of copper cushions under the carbide tips of cutting tools is said to have doubled the output between grinds. A new technique for the employment of silver solder and other low-melting-point alloys in production has virtually eliminated the main nonproductive finishing operations. Flux is supplied automatically. to the joint in the correct quantity and at a uniform rate.
A miniature welding, appliance has been developed in Germany and, is r to replace soldering originally used in the making of instruments. It leads to a considerable economy in tin, and work is speeded up because the somewhat intricate cleaning of the joint is greatly simplified.
A welding procedure has been developed whereby diecastings can be satisfactorily joined to a section of aluminium tubing. This has I:revel-been done previously, and is a method now being studied for many new products 'going on the drawing boards. High. 'frequency induction heating is economizing man-hours and heattreating equipment in the hardening of
rivet heads. Placed in an "elongated induction heating coil, three seconds are required to heat the rivet properly, as against three minutes. The rivets drop automatically into an oil bath, where they are cooled Cleaner work and closer control of hardening operations are advantages claimed.
Sound waves transmitted through water are being employed to test tyres for flaws The wearing properties and resistance to heavy loads of white-heart malleable iron are being considerably improved by suitable hardening, and, in .ome instances, a later simple tempering operation. Material manufactured from tiny metallic spheres is now being produced to specified and controlled porosity. It has already been widely applied to breathers, filters, flame arresters, and fluid meters.
The development of a two-million volt sealed-off X-ray tube makes practical for the first time the radiographing of thick metal sections by reducing the exposure time from, for example, a week with a million-Volt X-ray system, to less than an hour.
Radio-frequency energy makes it possible to produce thin case-hardening of finished ground metal parts without scaling or distortion. Megacycle heating by-induction reduces oxidation and scaling to negligible values even in the ordinary atmosphere, and prevents alteration of the physical characteristics of the metal underlying the hardened case.
High cutting. speeds in machining may set Up a welding action between chip and tool, combined with a softening of the tool edge. This produces a poor finish, excessive tool wear, and loss of production. To reduce these high
temperatures, refrigeration of the coolant or cutting oil has been successfully employed. Designed originally for the aircraft industry, the master tooling dock is proving of service in the automobile field, or wherever economical production depends upon the development of precise and co-ordinate tools and gauges. Addition of accessories for precision boring adds -to its practical possibilities.
Methods of comparing surface finishes have been invented, including a new lost cost comparison roughness gauge made of plastic material. These promote surface quality control, not only in the plant machine shop, but also among parts' suppliers scattered over . wide areas. Intense heat (above 4,500 degrees F.) is generated by the reaction of granular metals when correctly ignited, The heat alone can be applied to many uses, or the resulting metallic mass can be used for construction or repair purposes. Thermiting, as the process is known, is therefore branching out.
Towards Lighter Designing Rigiclized sheet metal is another interesting development. This is a method of substantially increasing flexural strip rigidity of sheet metal in. all directions by impressing carefully designed patterns of beads and ridges. It offers a new approach to weight reduction of panel structures.
Silver, lead and indium make up a combination that, so far, is claimed not to have been excelled for bearings subjected to high speeds and hea.Vy loads. A new high-strength aluminium alloy is a lightweight material with corrosion resistance comparable to that of pure aluminium, but with mechanieal properties superior to those of conventional pure aluminium-clad metals. It is also easy to fabricate, can be heat-treated, and introduces no contaminationin.the usual scrap-handling systems.