Engineering Alloys

96 VICTORIAN INSTITUTE OF ENGINEERS.

PAPER ENGINEERING ALLOYS. By R. W. Ruddle. The subject matter of this lecture covers such a wide range of materials that it is impossible to treat completely each indi- vidual class of alloy. The present-day engineer has at his com- mand a range of alloys that has been developed by the metallurgist so overwhelming that, to appraise the value of them, more than an elementary knowledge of metallurgy is necessary. In large organisations, where a metallurgical department, is in exis- Y° tence, the engineer can approach the metallurgist with his Lii problem, and very often can be advised, but where this service ~à is not available, he has to wade through reams of sales propa= ganda and textbooks, which in most cases only further confuses him. The object of this paper, which was prepared at very x short notice, is to summarise the various classes of present-day alloys and to convey some idea of their application in engineer- 4; ing. The alloys with which we deal may be broadly classified into two groups, ferrous and non-ferrous, and these groups may .l be further subdivided. Ferrous Alloys. Ferrous alloys cover a wide field, and include plain. steel, alloy steels, wrought iron, malleable cast iron, plain cast iron, and alloy cast irons. Plain carbon steel, containing a range of carbon contents from _1% to 1.5%, are commercially produced, and the physical properties are to a great extent controlled by the carbon content. Low carbon, or mild steel, as we know it, contains approximately .1-.2% of carbon, is ductile and soft, and we are familiar with it in merchant bars and to a certain extent in structural steel. Mild steel has a tensile strength of 26-28 tons per square inch, with an elongation figure of 30-40%. The next class of this material, containing .25-.3% carbon, has a tensile strength of 32-34 tons per square inch, with an. elongation of 30%, and is designed to meet B.S.S. 32/2. This material has a considerably higher elastic limit than mild steel, and is often preferred to mild steel for this reason. A medium carbon grade of steel known also as shell steel contains from .40-.50% carbon, and is widely used for shafts, etc. It has a tensile strength of 40 tons, and an elongation figure of 25-30%. ENGINEERING ALLOYS. !)

With a small percentage of nickel and chromium (under 0.5%) , this steel has good toughness after heat treatment.. Shear steel contains from .70%-.90% carbon, and is used in the heat-treated condition for certain classes of dies, and for i:G cutting knives in the timber industry. In the foregoing steels the silicon and manganese content remain reasonably `constant '(manganese .4-.6%, and silicon .1-.2%). A pearlitic manganese steel is in use, where a high yield point is necessary, accompanied by a good impact figure. A typical composition would be carbon .25-.45%, with manganese 1.3-1.7%. With suitable heat treatment, a high yield point with good impact figures is obtained. These steels are known as pearlitie manganese, to distinguish them from the austenitic type manganese steels, which contain 11-13% of manganese. A typical application would be the knuckles in the automatic coupling gear on rail cars. Corten is an American trade name for a steel for sheet or structural applications and combines improved corrosion resistance properties with improved physical properties over those of mild steel. The composition of an average grade of corten is carbon 0.1%, manganese 0.1-0.3%, phosphorus 0.1-0.2%, silicon 0.5-1.0%, copper 0.3-0.5%, with chromium 1.0-1.5%. Physical properties are yield point 26 tons per sq. in., tensile strength 32 tons per sq. in., elongation 25%, Izod impact 60 FP. This material, on account of its much higher yield point as compared with mild steel, effects a considerable saving in weight and has a life of at least 22 times that of mild steel. A typical application is for railroad car bodies, etc. While dealing with carbon steels, mention may be made of wrought iron. This material was the forerunner of mild steel. It contains the lowest percentage of carbon of any commercial ferrous material, and for this reason is widely used for applications involving slightly corrosive conditions, such as chains, etc., in marine work. Wrought iron has a fibrous structure, and is extremely tough. Although wrought iron has been supplanted by mild steel for many purposes on account of cost, it still has many applications, and a method has been used in the U.S.A. to produce it synthetically by pouring liquid mild steel into a ladle of specially prepared slag. After thorough mixing, the mix is then put through squeezers and rolls, and the product is similar to wrought iron made in the puddling furnace. 98 VICTORIAN INSTITUTE OF ENGINEERS. Alloy Cast Irons. These cast irons have become widely used in industry for special purpose applications. The major alloying metals are chromium, nickel, copper and molybdenum. By varying the composition, the iron can be made heat resisting, corrosion resisting, abrasion resisting, and non-magnetic for electrical purposes. Certain alloy cast irons respond to heat treatment, and may be oil quenched and tempered to produce special physical properties. For special abrasion resistance applications, an alloy containing nickel and chromium, known as Ni Hard, is widely used, and depending on composition and method of casting, Brinell Hard- ness numbers up to 600 are readily obtained. Malleable Cast Iron. This material is produced by subjecting white cast iron to an annealing process for from 3-4 days at 900° C., this process rendering the material malleable. Two processes are in use- (a) the White Heart process, and (b) the Black Heart process. The chief difference between these annealing processes is the packing medium used to malleabilise the metal. The White Heart process is used for thin, sectioned castings under in., while the Black Heart process is for thicker sections. The iron, after malleabilising, somewhat resembles mild steel, and is used widely in the agricultural implement and automobile industry. Plain Cast Irons are too well known to be included in these notes, and, due to improvements in foundry technique, it is not unusual for present-day cast irons to have a tensile strength of 16-1$ tons per sq. in., as compared with 9-12 tons of a few years ago. Alloy Steels may be broadly classified into two groups, low alloy and high alloy. Before detailing the alloy steels, brief mention will be made of the effects of the alloying elements. Nickel—This element dissolves in the ferritic matrix of the steel, increasing its toughness, i.e., an increased izod impact figure. For this reason, it is used in conjunction with low carbon steel for case hardening steel where a tough core is required, surrounded by a hard martensitic case after carburising and quenching. Chromium produces fineness of structure, giving static strength with little corresponding loss in toughness and ductility. It produces double or complex carbides of unique hardness and strength, making chromium steels distinctive in their application to bearing and tool purposes. It increases the sluggishness ENGINEERING ALIOYS. 99 of austenite, giving greater depth hardness on quenching. It also has a marked effect on magnetic properties and resistance to corrosion. Molybdenum tends to produce free scaling properties and has a profound effect on density of structure, carbide constituents, austenitic decomposition and critical range occurrence. The presence of molybdenum permits and requires higher drawing temperatures to develop, equivalent physical properties, and for an equivalent elastic limit produces greater toughness. It is a constituent of non-creep steels, such as linen cylinder heads and pistons in diesel work. Copper increases the tensile strength, slightly lowers the ductility, improves fatigue properties, and increases corrosion resistance. Vanadium in small amounts raises the yield point and increases toughness. Tungsten forms carbides, which are stable at temperatures up to 700° C., by acting as a strong obstructing agent to the transi- tion of austenite to pearlite. It also induces additional hardness imparted by the double carbide of tungsten and iron. Plain Nickel Steels with nickel contents up to 3.5% are used for applications requiring toughness without a high tensile strength, such as before mentioned, in a case hardening steel. The carbon content is varied slightly to suit the section of metal in the particular application. With a carbon content of .35-.40% and 3.5% nickel, this steel complies with B.S.S. 5005/402 after heat treatment, and with 3% nickel to B.S.S. 5005/401. The presence of .5% chromium in nickel case hardening steel confers homogeneity, greater strength, and wear-resisting qualities, due to the much finer grain size throughout after double quenching. Chromium is alloyed with carbon steel up to 1% to give wear- resisting qualities and increased tensile strength. A steel with .35%-.40% carbon alloyed with .5% chromium responds readily to heat treatment, and after normalising and tempering, will give an elastic limit of 26-30 tons per sq. in., tensile strength 45-55 tons per sq. in., with an elongation of 15-25%. With a carbon content of 1% combined with 1% chromium, normalising will give a tensile strength of 65-75 tons per sq. in., with an elongation of 10%. Steel of this class is used for crushing rolls and abrasion resistance applications in the mining industry. 100 VICTORIAN INSTITUTE OF ENGINEERS.

Low Alloy Nickel Chrome Steels. As before mentioned, the introduction of chromium produces hardness and loss of ductility, but this is counteracted by the addition of nickel. The usual ratio of nickel to chromium is 3-1. Heat treatment by oil quenching and tempering produces a high tensile strength steel, having good ductility and impact value. Various compositions have become standard for automobile components, shafts, bolts for reciprocating big ends, etc. The Nickel Chrome Steels Covered by the S.A.E. Specifications. 3300, 3400 and 3100 range in composition from nickel 3.5%- 1.5%, and chromium 1.5%-.75%. The carbon varies from .15% -.55%. The lower alloy range may be water quenched, while the higher range require oil quenching. Chromium Vanadium Steels. The addition of vanadium to chromium steels reduces grain size and produces homogeneity. The percentage of vanadium is generally under 0.2%, and two grades are in popular use, the low carbon case hardening grade, containing carbon .2%, chromium 1%, and vanadium 0.15%, and the oil hardening grade, containing carbon .5%, chromium 1%, and vanadium 0.15%. While vanadium is classed as an alloy, it is only added as a grain refiner, and cannot be considered as an alloy of the same category as may be considered nickel and chromium. Vanadium is also added to plain carbon, plain nickel, chro mium, molybdenum and tungsten steels as a grain-refining medium. Molybdenum is usually present in conjunction with chromium or nickel, and is added to give some particular property, such as hardness or in an application where a liquid quench would be dangerous. It induces in the steel a marked ability to retain the complex carbides in solid solutions upon cooling from above the critical temperatures. .It imparts strength, high elastic limit, resistance to wear, and high impact value. It inhibits grain growth as steel is heated to high temperatures, and enables it to show resistance to creep under sustained loads at these temperatures. Molybdenum produces depth hardening properties, due to the fact that it uniformly disseminates and does not segregate. The molybdenum content is usually between .15% .25% or .25%-.5%. A nickel molybdenum steel was developed during the World War in an effort to discover a steel suitable for light armour- plate for tanks, which would develop higher and more uniform ballistic properties and, if possible, greater machineability than ENGINEERING ALLOYS. 101

the chrome nickel or nickel steels then under production. This steel has a high elastic limit and a high reduction in area, necessary for a satisfactory armour-plate. As the diameter of the armour-piercing bullet is greater than the thickness of the plate, it is necessary to build up more metal in front of the bullet, as when it starts to enter the plate it prevents full penetration. A typical steel would contain .3%-.35% carbon, .6% molybdenum, and 4.5% nickel. A typical S.A.E. steel, No. 4130, for such parts as drive shafts, steering knuckles and bolts, contains approximately, carbon .30%, chromium .65%, and molybdenum .15%. This is a water-quenching steel. By increasing the carbon to .35% and the chromium to 1.0%,. the steel may be oil quenched, and greater resistance to wear is obtained. Typical applications would be gears, roller bearings, etc. Silicon Steels. Silicon up to .2% is found in practically all steels, and is incidental to the manufacture of the same. It is sometimes introduced as an alloy for steel for special purposes such as electrical purposes of corrosion resistance. Acid resisting steel contains 13%-15% of silicon, but is extremely brittle and unmachineable. Silicon increases the electrical resistivity of iron 11.4 microhms per cubic centimeter for each per cent. of silicon added. Trans- former sheets are rolled from steel containing 4%-4.5% silicon. Grain size in the rolled sheet is important, and this is governed by the rolling temperature. Silico maganese steels, with a medium carbon content, and about 1.5% silicon and .75% maganese are made for use in the manufacture of gears and springs. Silicon chromium steels are used for valves and .springs in automotive service, and contain carbon 0.5%, chromium 1.0%, and silicon .5%. This alloy in the cast condition is used for dipper teeth and similar applications. For this particular application extreme hardness is undesirable, as in service it has been found that actually small pieces chip off, which erosion is far greater than if the steel is softer and wears off. Tungsten is widely used as an alloying element in steels, and may be divided into five grades—(1) Plain tungsten steel with a tungsten content of 170-270. (2) Magnet steels. (3) Drawing die steels. (4) Pneumatic, battering and hot work steels. (5) I igh-speed steels. Chromium is added to tungsten steers up to .4%-.5% to assist the response to heat treatment. Tungsten produces hard carbides, use of which is made in the production of tools. The range containing 1-2.5% W. is suitable 102 VICTORIAN INSTITUTE OF ENGINEERS.

for chisels and keen-edged tools, valves for • gasoline motors, threading dies, broaches, reamers, taps, drills, etc. Magnet steels contain 5%-6% of tungsten, with .65%-.75% of carbon, but in recent years the patented nickel-aluminium alloys have largely supplanted the tungsten alloys. Tungsten alloyed with chromium and vanadium give depth hardening, strength and shock resisting properties for pneumatic tools, hot work dies, etc. High-speed steels contain carbon 0.65%, tungsten 18%, chromium 4%, and vanadium 1%, and are sometimes referred to as 18-4-1 or 14-4-2, etc:, the numbers signifying the main alloy content. Tungsten alloyed with chromium is used for drawing dies, a typical composition being chromium 30%, tungsten 2%, carbon 3.0%. Tungsten steel containing carbon .9%, manganese 1%, chromium .5%, tungsten 0.5%, and vanadium .1%, are known as non-shrinking or non-deforming steels, and are essentially oil-hardening steels. Typical applications would be for taps, reamers, broaches, blanking dies, master tools and gauges.. Tungsten Carbide, an extremely hard material, is now used as a cutting tip brazed to a carbon steel shank for high machining speeds. These sintered carbide tips require to be carefully ground to avoid cracking.

Aluminium Steels. This range of steels is produced for nitriding treatment for ease hardening, and is marketed under the name of "Nitralloy." The nitriding process consists of subjecting the steel to the action of a nitrogenous substance, commonly ammonia gas, whereby remarkable surface hardness is obtained without further treatment, as is necessary when carburising with :+ carbonaceous material. It is necessary for the steel to contain at least 1% of aluminium. An average composition of Nitralloy would be carbon 0.2%-0.3%, manganese 0.4%-0.6%, aluminium 0.9%-1.4%, chromium 0.9%-1.4%, and molybdenum .25%-.5%. The process consists, as before mentioned, of subjecting the machined part to the action of ammonia gas at temperatures ranging from 935°-1000° F. The nitrogen of the gas combines with the alloying elements in the steel to form nitrides, imparting great hardness to the surface of the metal. The advantages of nitriding over carburising are :- (1) Low temperature necessary for nitriding prevents the formation of scale on the parts, so that they may be finished to size before hardening. (2), Lack of distortion, since the temperature is low. ENGINEERING ALLOYS. 103

(3) Higher skin hardness than that obtainable by carbonaceous hardening. Material for the nitriding containers is usually enamelled low carbon steel, the coating presenting an inert surface. Stainless steel has been used with success, also the higher nickel chrome alloys (62% nickel, 12% chromium).

Chromium Steels. As previously mentioned, low carbon chromium steel is widely used in engineering components. The special high chromium alloys commonly used are as follow—Chromium, 5%,12% ; cutlery grade, 17% and 27%. In addition to these straight chromium alloys, high chromium with the addition of nickel, molybdenum, titanium, columbium, titanium and silicon. The 5% chromium steel, containing .1%-.2% carbon is used for the manufacture of rolled steel tubes, widely used in the petroleum industry. It has good heat-resisting properties at 1000° F., with high resistance to sulphide corrosion, as under conditions as would be encountered in petroleum cracking. This alloy can be annealed to give similar properties to those of mild steel where severe cold work is applied during fabrication. It can be air hardened and tempered to produce a tensile strength of 100 tons per sq. inch, with an elongation of 10%. The alloy containing 11%-13% chromium, with .12% carbon, is used for forgings and rolled bars. This alloy was similar to the original type of cutlery steel except that the carbon content is lower. It is a mortensitic type of steel, i.e., it may be hardened, and after oil hardening will develop a Brinell hardness of 450-550. It has a wide application in industry for valves, valve seats, valve stems and other parts subjected to high and low pressure steam conditions. Shafting operating under steam, mine-water and moist air conditions has given satisfactory service. For any applications for a non-rusting steel where corrosive conditions are not severe these straight chromium alloys are satisfactory, such as cutlery, golf clubs, rifle barrels and interior ornamental work. Chromium steels containing 11%-16% chromium and .12% chromium are used in place of the foregoing where corrosive conditions are more severe and for rolling into sheet and strip. They have good cold working properties, due to excellent ductility. Castings in this alloy are used in the wood pulp industry to resist the corrosive action of tannic acid. Modern types of cutlery steel contain 16.5% chromium, with carbon .7%, and are heat treated to give a Brinell hardness number of 500-600. It is forged at 17000-2000° F., annealed at 1400°- 104 VICTORIAN INSTITUTE OF ENGINEERS.

1500° F., and hardened at 1850° F. Failures in cutlery can usually be traced to faulty heat treatment rather than faulty steel. An alloy containing 13% chromium with 1% carbon is used for forged parts which will be subjected to severe corrosion and heat, such as is encountered in oil refineries. Higher carbon high chromium alloys are used for gauges and dies, etc., where abrasion resistance is required. A typical composition would be carbon 2%, chromium 13%, and is suitable for blanking dies, shear blades, punches, etc. It can be hardened to give a Brinell hardness number of 750, or Rockwell C 67. One commercial material widely used, and known as chrome iron or stainless iron, contains 16%-18% of chromium, with carbon under .10%-12%. It has good corrosion resistance, and is produced for rolling into sheets, plates and bars. It cannot be appreciably hardened by heat treatment, and has a tensile strength of 40 tons per sq. inch. and 30% elongation. Large tonnages of this material are used in the production of nitric acid. Owing to the low impact value of this alloy, it is unsuit- able for rivetted fabrication, and welding must be used. Cast- ings and tubing can be readily produced for fittings such as flanges, valves, pipe fittings, etc. Stainless steel in general use usually contains approximately Cr. 18%-20%, and Ni. 8%-10%, with small percentages of molybdenum, silicon, titanium and columbium to suit special requirements. These alloys are on the market under the name of Staybright, F.D.P., Weldanka, etc. The addition of the foregoing - modifying elements is to prevent weld decay or intergranular corrosion where the material is required for welded fabrication. The straight 18% chromium, 8% nickel alloys, commonly known as 18/8, is used for domestic stainless applications where the corrosive conditions are slight, i.e., not in direct contact with acids, etc. A grade containing chromium 20%, nickel 10%, molybdenum 3% is specially made for components requiring welded fabrication. The alloys molybdenum, titanium and columbium are modifiers to prevent intergranular corrosion in welded construc- tion. These stainless steels are austenitic and non-magnetic, and readily work harden; therefore special machinery technique is necessary to satisfactorily machine them. For a combination of corrosion resistance and abrasion resistance an alloy containing 18% chromium with 2% nickel is widely used. This material is martensitic, i.e., it can be hardened after machining. One of these grades is marketed under the name of Twoscore. ENGINEERING ALLOYS. 105

Plain chromium steels containing 27%-30% chromium are used for heat-resisting applications. They will give continuous service at 1000°-1100° C., provided that the furnace atmosphere is not reducing. For reducing atmospheres the chromium is reduced to 20%, and 40% of nickel introduced. This material can be cast and hot worked, and is particularly suited for hearth plates, etc., of heat treatment furnaces. It is produced locally in the cast condition. Higher nickel chromium alloys are used for electrical resistance applications, one well-known alloy being Nicrome, containing 60% nickel with 40% chromium. These alloys are ductile, and may be rolled and drawn. Cobalt steel, having a cobalt content of 4%-6% Co. with .8% carbon, is used for cutting tools, but is extremely sensitive to temperature changes, and care should be used in grinding it. Manganese steels, containing 11%-13% of manganese with 1%-1.3% carbon, are widely used in the mining industry for such parts as jaws, rollers, swing hammers, etc. This material is austenitic and work hardens readily, thus making it almost unmachinable. Use of this work-hardening property is made when the parts are placed in service. In the heat-treated condition manganese steel has a Brinell hardness number of 170-180, which is indicative of a soft material. By subjecting the working face of the part to hammer blows, this hardness can be increased to 500-600 very readily. When a manganese steel part is put into service the first work develops this hard surface, provided that the material being handled is hard, but if the material being handled is soft, the part must be processed or hammered before installing to obtain a reasonable life.

Non-ferrous Alloys. Copper base alloys are collectively referred to as bronzes, although the composition of the various bronzes cover a wide range. Gunmetals are alloys of copper, tin and zinc, and the most well-known example is the Admiralty gunmetal containing 88% Cr., 10% Sn., and 2% Zn. It gives excellent service for many duties, and casts readily. Several modifications of the 88.10.2 alloy are employed, the object being to increase its suitability for some special purpose. Thus, for castings to withstand pressure, the zinc may be increased at the expense of the tin. For corrosion resistance the zinc may be replaced by lead, and this gives a range of leaded bronzes. 106 VICTORIAN INSTITUTE OF ENGINEERS.

Of the most popular grades of zinc bronzes, the following cover a useful field :— A B CD Tin .. 10 8 5 6 Copper ...... 88 84 85 88 Zinc . .. . .. 2 4 5 6 Lead.. .. — 4 5 Tensile Strength .. 14-20 13-19 13-18 16-19 tons per sq. in. Elongation ...... 10-25 18-26 20-30 30-60% Izod Impact .. .. 24-34 90-120 70-120 120 A—Standard gunmetal, hard, strong and sound alloy for general work. B—Good general purpose gunmetal, where greater toughness and better machineability than A are required. Suitable for pump bodies where no great resistance to corrosion is required. C—Lead zinc bronze suitable for bushes, etc. D—Soft zinc bronze of great value for thin-sectioned work where extreme toughness is required. Gunmetal cannot be cold worked, and therefore is almost always found in the cast condition.

Phosphor Bronzes are nearly true bronzes, being alloys of copper and tin, with comparatively small quantities of phosphorus, usually .15%-.5%. They sometimes contain a small amount of nickel to prevent segregation of the lead. Phosphor bronze may be forged and rolled for pump spindles, bushes, turbine blades, etc., for which the chief requirements are strength and ductility, and where the alloys, while showing mechanical quality comparable with that of mild steel, are much superior to steel in corrosion resistance. The composition of the various grades are varied to suit special purposes in service. The B.S.S 421 calls for 14 tons tensile strength, 7% elongation, with a phosphorus content of 0.15%. Copper in cast form is specified for duties demanding high electrical conductivity. A small percentage of phosphor copper is added as a deoxidiser to molten copper, to prevent porous castings. In some cases 1% of zinc is added where the presence of phosphorus is undesirable. Where, however, high electrical conductivity is required, neither phosphorus nor zinc is permis- sible, and .3%-.4% of silicon copper (10% Si.) will produce good results. Copper in the rolled condition will respond to heat treatment. It may be hardened by heating and being allowed to cool slowly ENGINEERING ALLOYS. - 107 or softened by water quenching. • Being ductile; it is readily spun and formed into intricate shapes. Brasses are composed of copper and zinc, the most common composition being 70% copper and 30% zinc. Alloys containing 61%-100% of zinc are soft and ductile, increasing both in strength and ductility with zinc. These alloys are very amenable to cold working by rolling and drawing, being annealed and pickled from time to time in the process to correct the brittleness due to work hardening. These alloys are seldom worked hot. Alloys containing more than 39% of zinc, owing to their brittleness, cannot be cold worked. As the percentage of zinc is increased, the alloys become more brittle. A standard 70-30 brass has a tensile strength of 1245 tons per sq. inch, with an elongation of 50%, whereas a brass containing 50% copper and 50% zinc will have a tensile strength of eight tons per sq. inch, with an elongation of 1%. These figures vary with the method of manufacture. Lead up to 1% has no effect on the strength of brass, but when present in excess of this amount reduces both strength and ductility, but considerably improves machineability, and 1.5%- 3.0% of lead is sometimes specified for stampings. Brass, containing 2% aluminium is used for extension and stampings, this alloy being more ductile than that containing the lead. High Tensile Brasses—The addition of various metals to 60-40 brasses has produced a range of alloys known as high tensile brasses. The metals commonly used are aluminium, iron, manganese, nickel and tin, several being frequently used together. The metals are used to replace portion of the zinc, and have the following values :—Aluminium 6, tin 2, lead 1, iron .9, manganese ,5, and nickel 1.3. Thus 1% of tin has the same effect as 2% of zinc. Aluminium is added up to 9%, and the product is known as aluminium bronze. It increases strength and hardness, and reduces ductility. From the foregoing list of equivalents, it will be seen that 9% of aluminium will replace all of the zinc; therefore it actually becomes an alloy of copper and aluminium. An average composition of aluminium bronze contains 7%-9% aluminium, up to 4% iron, and the balance copper, which will give the following physical properties- Tensile strength 30 tons per sq. inch, and elongation 20%. This alloy has good corrosion-resisting properties, and is readily machineable. Manganese bronzes have been developed for high tensile strength applications and tensile strengths of the order of 40 tons per sq. inch, with elongations of 25%-30% are readily 108 VICTORIAN INSTITTJTE OF ENGINEERS.

obtained. These alloys have good corrosion resistance and machineability, and may be extended and rolled for special sections. This alloy is widely used in the cast condition, and the foundry technique is similar to that used for steel castings. Manganese bronze is suitable for contact with sea water for pump spindles, propeller tail shafts, valve rods, etc. The propellers of the "Queen Mary" were cast in this material. It may be hot worked, and lends itself to die casting. The average composition would be copper 55%-65%, manganese .1%- 3.5%, aluminium .10%-5.0%, iron .1%-2.0%, tin .1%-1.'%, and zinc the balance. Silicon Bronzes. These alloys usually contain 2%-4% of silicon, and are used to replace gunmetal where forging or cold working are necessary, when their strength is equivalent to that of mild steel, and the resistance to corrosion very much greater. These alloys are sold under the proprietary names of Everdur, Herculoy and P.M.G. Metal. The composition would be copper 94%-96%, silicon 3%-4%, manganese 1%. The tensile strength of Everdur is 28.6 tons per sq. inch, with an elongation of 54%. Silicon Brasses. These alloys contain approximately copper 82%, silicon 5%, and zinc 12%, and are commonly used for aircraft tubes and sheets, being covered with D.T.D. specifications. They may be readily rolled and drawn, and are particularly suited for casting. One trade name for a patented silicon brass is Tungum, and is used for annealed sheets and medium pressure tubes. The composition of Tungum is copper 81%-86%, silicon .8%-1.30, aluminium .7%-1.%, nickel .8%4.4%, zinc 14%. Nickel silver, German silver and white brass are copper base alloys. Nickel brasses contain a maximum of 10% of nickel and nickel silver, a minimum of 15% nickel, and these compositions divide the classification of these alloys. Corrosion resistance increases with increase in nickel content. By careful alloying a wide variety of colours is obtainable for decorative applications. For nickel silver for commercial use a minimum nickel content of 15% will insure that the alloy will be white, but for positive anti-corrosive properties a minimum of 18% is necessary. Nickel silver containing 20%-22% nickel is widely used in the cast and wrought state, and can be employed without electroplating. The average physical properties of nickel silver would be yield point 7-9 tons per sq. inch, tensile strength 20-30 tons per sq. inch, with an elongation of 35%. Further increase in nickel increases the strength and lowers the ductility. Proprietary ENGINEERING ALLOYS. 109 names of nickel silver are Albatsor, Ambrac, Malloydium, Nicke- lene, Silvore. Copper nickel alloys are characterised by high strength and ductility, with excellent resistance to corrosive conditions and high temperatures. Precipitation hardening in copper nickel alloys involves the solution in copper at high temperatures of a constituent which is less soluble at lower temperatures, and is thereby precipitated on cooling or by tempering after quenching in the form of minute particles which are comparatively hard, but not brittle. Silicon is often used in the copper nickel alloys for this purpose, and hardening is obtained by the precipitation of nickel silicide. "Tempaloy" is a proprietary alloy containing copper 95%, nickel 4%, and silicon 1%. This alloy can be readily worked hot or cold if quenched from temperatures above 750° C. By tempering at 450° C. hardening occurs by precipitation, so that a tensile strength of 50. tons per sq. inch, with an elongation of 16%, can be readily obtained. Kuprodur is another such alloy. For motor slip rings, where the material must have resistance to abrasion and good conductivity, cast copper-low nickel alloys are used. The nickel is usually kept below 4.0%. Motel Metal is an alloy containing approximately 66% nickel and 33% copper, and is produced by smelting a Canadian ore. The composition of this range of alloys varies for different purposes. Monel metal possesses high strength and resistance to elevated temperature and corrosion. For valve seats in steam valves for superheated steam.monel metal gives excellent results. The alloy can be . readily forged and hot rolled, and shows a marked increase in strength after cold working. Recently metals such as silicon or aluminium have been added to monel metal to give it precipitation hardening properties. Monel "H" is a modified alloy containing 2.75%-3% silicon, where hardness must be combined with strength and ductility. It will not gall or size under most severe conditions. Monel S" contains 3.75%-4% silicon,. and is suitable for applications requiring a higher tensile strength than that obtainable with Monel "H." Monel "K," containing 2.75% aluminium, forged and heat treated, will have a tensile strength of 60 tons per sq. inch, elongation 20%, with an Izod impact figure of 70 foot pounds. Light Alloys. Aluminium is alloyed with several metals to produce a wide range of alloys for particular purposes. Zinc-aluminium alloys contain up to 15% of zinc. The most popular metal in this 110 VICTORIAN INSTITUTE OF ENGINEERS.

class is known as 3L5, containing 12.5%-14.5%0 of zinc and 2.5%-3.0% copper, with aluminium the remainder. It is mechanically superior to many other aluminium alloys, and is largely used for crankcases, gear boxes, etc. Owing to it being a cheap alloy to produce, it is popular, but for more severe services it has been superseded by other alloys. Aluminium Copper Alloys contain 4%-7% or 12% of copper. The density and hardness increase pro rata with the copper content. The 7% alloy is often used for gravity die casting, usually known as L8. Some copper aluminium alloys respond to heat treatment, but usually age harden if left in the heat-treated condition. The 4% copper aluminium alloy is the basis of an important series of wrought alloys responsive to heat treatment such as Duralumin, Y Alloy, and Lantal. These alloys contain alloys other than copper, such as magnesium and silicon, when a further age-hardening effect can be obtained. Y Alloy is the 4 :2 :1.5 copper nickel magnesium aluminium alloy developed specifically as a piston alloy. It has good strength at working temperatures of 250°- 300° C. It has excellent conductivity (thermal), and in the heat-treated condition tensile strengths of 20 tons and over are obtained. Silicon aluminium alloys are important because of their low density. The average silicon content is about 8%, and the alloys are marketed under the trade names of Alpax, Silumin, Wilmil, etc. These alloys have good fluidity and low shrinkage, thus lending themselves to either pressure or gravity die casting. Lo-Ex Alloy contains 11%-14% silicon, 1% magnesium, 2.5% copper. It is responsive to heat treatment, and has a very low expansion. It has a tensile strength of 16-19 tons per sq. inch, and is widely used for automobile pistons. Magnesium aluminium alloys containing up to 10% of magnesium are produced under the name of Birmabright, and contain 3%-6% magnesium and .5% manganese. It has excellent eastability, which makes it suitable for die casting, either pressure or gravity. It is mechanically strong, light, and has the property of being free from cracking, with excellent resistance to corrosion. It is widely used for various medium stressed aircraft components. The alloys known as R.R. are derivatives of the Y Alloy, containing copper, nickel and magnesium, with iron silicon and titanium. ENGINEERING ALLOYS. 111

R.R.50 contains copper 1.3%, nickel 0.9%, magnesium 01%, iron 1.270, silicon 2.25%, titanium 0.18%, and aluminium the remainder. Magnesium Alloys have an approximate density of 1.8, or about two-thirds that of aluminium alloys, with a tensile strength of the order of 15-20 tons per sq. inch. The chief industrial alloys are confined to those having an aluminium content of from 3.5%-10%, with zinc up to 3.5%. Alloys of this class are used for die castings, forgings, extension, etc., and respond to heat treatment. Heat treatment is usually carried out in a muffle furnace filled with an atmosphere of sulphur-dioxide, or in a salt bath consisting of a mixture of 72% sod. bichromate, 24% pot. dichromate, and 370 pot. chromate. The temperature of treatment varies with the composition of the alloy, and is generally between 380°-425° C. for a period of 12-16 hours. These alloys are known as Electron, and are produced to comply with D.T.D. specifications. The metal is melted in low carbon steel pots, which have been calorised on the outside to prevent scaling. A. large quantity of flux is used, one commonly used. containing 60% antydrom magnesium chloride and 40% sod. chloride. Electron alloys can be forged, rolled or extruded successfully, and air screws are now being forged from this material. Lead Alloys are mostly used as bearing metals when alloyed with tin and antimony. Various alloys are used for special applications, and these mixtures are known as lead base or tin base alloys, depending on whether lead or tin is the major constituent. Lead base alloys in use contain up to 80% lead with tin 5%, and antimony 15%. This composition, sometimes containing a small percentage of bismuth, is suitable for medium load bearings functioning at higher temperatures than those suitable for tin base alloys. Tin Base Alloys are more widely used than the lead base alloys, and contain from 6070-90% tin, 370-10% antimony, with 270-370 copper, and in,some cases up to 4% lead. A standard composition contains tin 83%, antimony 10.5%, copper 2.570, lead 4%, and is widely used for main bearings for automobiles, aero engines, and similar services. The design of the bearing indicates the composition required for successful operation. Cadmium Base Bearing Alloys have good strength, heat conductivity, and excellent anti-frictional properties. A modern type of copper base alloy has been developed, containing copper with 2.5% beryllium, and is being used on the 112 VICTORIAN INSTITUTE OF ENGINEERS. intermediate sleeve between the shaft and the blade of variable pitch propellers. The lead-tin-antimony range of alloys are plastic, and consist of hard grains of entectic embedded in a soft matrix, whereas in bronze or gunmetal the position is reversed, the matrix being hard with plastic crystallites of copper spread throughout the mass. Bronzes therefore have a greater tendency to cut than the lead-tin-antimony alloys. Antimony is chiefly added to increase the compressive strength of the alloy, but, owing to its embrittling effect, the proportion of antimony should never exceed 15%. Lead or zinc should be kept low in white metal alloys, which are lubricated with oils containing free fatty acids, as these acids readily form metallic soaps with those two elements, and therefore corrode badly. '

Library Digitised Collections

Author/s: Ruddle, R. W.

Title: Engineering alloys (Paper)

Date: 1941

Persistent Link: http://hdl.handle.net/11343/24876

File Description: Engineering alloys (Paper)