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 metal- lurgist 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 proper- ties are to a great extent controlled by the carbon content. Low carbon, or mild steel, as we know it, contains approxi- mately .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. elonga- tion 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 man- ganese 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 appli- cations 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 contain- ing 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 applica- tion 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 quali- ties, 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.