UNIT 1: ENGINEERING METALS

METALLURGY

Introduction.

The significance of metals in the modern technics is immeasurably great. Metals are used in all branches of industry. For all that it is extremely important to chose the metal with required properties. The right choice of metal provides normal technological process of machining workpieces, high operation characteristics of machines and mechanisms and their long service life.

Quality of metal works is mainly determined by their phisical, chemical, mechanic and technological properties of materials, they are made of. Among metals and metal alloys, found in nature and known in industry, ferrous metals are the most important and widely used. There are two forms of ferrous metals: cast iron and steel. These two alloys are produced from pig iron. Pig iron is derived from iron ore by separating iron from impurities contained in the ore. For this the iron ore must be melted at high temperature, produced by burning coke in a furnace. Steel differs from cast iron in the quantity of carbon content. Steel contains less percentage of carbon than cast iron does. And also steel contains less quantity of harmful impurities: sulphur and phosphorus. Steel is melted out from cast iron. Thus for making steel it is necessary to reduce the concentration of carbon and harmful elements contained in cast iron. To improve the structure and to obtain high or specified mechanical properties steel undergoes heat treatment. Although ferrous metals are specified for more engineering applications than all non-ferrous metals combined, the large family of non - ferrous metals offers a wider variety of characteristics and mechanical properties. These characteristics are: high electrical and thermal conductivity, high corrosion resistance, light weight, non-magnetic qualities, etc. The metals most frequently used are: copper, tin, lead, nickel, aluminium, zinc, magnesium, gold, titanium, silver. The above-mentioned non-ferrous metals may be mixed in various proportions to form many alloys, chief among them are brasses, bronzes and aluminium alloys. One of the basic process of the metal-working industry is the production of metal casting. Casting may be described as the pouring of hot liquid or molten metal into a mould of a desired shape, where the metal solidifies and hardens.

For obtaining required shape and size metal billets undergo mechanical working processes, when metal is shaped by pressure. Mechanical working involves the plastic deformation of either cold or heated metal by external action of special tools such as mill rolls, forging dies, flat hammer, etc.

The science which studies processes, mentioned above, is called metallurgy.

UNIT 1: ENGINEERING METALS