Metals are classified into two maingroups depending upon presence of ironcontent.
(1) Ferrous metals:All those metals which contain ironas chief constituent are called ferrousmetals.Such as:(1) Pig iron(2) Wrought iron(3) Cast iron
(2) Non-Ferrous metals:All those metals which do not contain iron asprincipal constituent are called non-ferrous metals.Such as:– Zinc– Lead– Nickel– Chromium– Silver– Platinum– Gold and all other metals except steel and iron.
DUCTILE MATERIALS:A material which can undergo considerabledeformation without rupture is called ductilematerial. E.g. steel.(OR)A material that can be stretched, drawn orhammered thin without breaking.BRITTLE MATERIALS:A material which can not undergo any deformationis called brittle material. Brittle material hastendency to break into pieces easily, e.g. concreteand glass.
STEEL:Steel is an alloy (mixture of twoor more than two metals) ofcarbon and iron. It is mostimportant metal which is widelyused in RCC construction of civilengineering.
Types of Steel:Steel is classified into three maintypes depending uponcarbon content.
(1) Low / Mild / Soft /Plain Carbon Steel:In this type of steel, the carbon content is 0.15% to0.3%.Properties:(1) It is ductile and malleable.(2) It corrodes quickly.(3) It can be easily forged, welded and riveted.(4) It withstands shocks and sudden impacts well.(5) It is not much affected by saline water.(6) It is equally strong in tension, compression andin shear. Continued-------
Uses:Mild steel round bars are extensively usedas reinforcement in R.C.C construction.It is extensively used in the manufacturing ofvarious tools and equipments, machine parts,railway tracks , transmission towers andindustrial buildings.
(2) Medium carbon Steel:In this type of steel, the carbon content is0.3 to 0.8 %.Medium steel has characteristics betweenthose of low –carbon and high carbonsteel.It is widely used for boilers.
(iii) High- Carbon Steel (or) Hard Steel:In this type of steel, the carbon content is more than0.8 to 1.5 %. Higher %age of carbon in it renders itharder and tougher.Properties:(1) Its structure is granular.(2) It is more tough and elastic than mild steel.(3) It is easier to harden and to temper.(4) It is more difficult to forge and to weld.(5) Comparatively it is stronger in compression thanin tension or in shear.(6) It with stands shocks and vibrations better.
Uses of High carbon steel:(1) It is used in the pre-stressed concrete.(2) It is used for making tools such asdrills, files, chisels, fine types of cutlery.(3) It is also used in the manufacturing ofcutters,keys,knives,razers,etc.(4) It is used in the manufacturing of thoseparts of machinery that need a hard, tough,durable material capable of withstandingshocks and vibrations.
REINFORCED STEEL BARS:As plain cement concrete (PCC) is strong in compressionbut very weak in tension and shear. As mild steel bars arestrong in tension. Therefore, mild steel bars or high carbonsteel bars are embedded as reinforcement in the concrete tomake good that deficiency of the plain concrete. Therefore,round, flat or square bars too can be used for that purpose.Welded wire mesh and expanded metal too are used asreinforcement in cement concrete.Commonly deformed bars or twisted bars are used in cementconcrete.Therefore, RCC sections will carry compression as well astension safely without failure.In these sections compression will be taken by concrete andtension by steel.
(1) ALUMINUM:It is more commonly used non-ferrous metal. It is widelyused in every field of Engineering. Due to improved strengthand durability, aluminum is a versatile material for use byEngineers.Properties and Uses:(1) Its colour is silvery white.(2) It shows bright luster on a freshly broken surface.(3) It is ductile material,(4) It is very light in weight.(5) It also resists atmospheric corrosion,(6) It is very good conductor of electricity,(7) It is used for making door and window frames,(8) It is also used in roofing, piping, etc,(9) It is also used in electric wires, cables.
(2) COPPER:It is one of the most widely used non-ferrousmetals. It is not widely used in Engineering dueto its high cost.Properties:(1) It is crystalline in structure,(2) Its color is reddish brown,(3) It is highly ductile,(4) It is excellent conductor of electricity,(5) When exposed to sun, its colour turnsgreenish,Continued------
(6) It with stands corrosion,(7) It is soft and highly flexible,(8) It is light in weight,(9) Dents in copper can be hammered outwithout any damage to it.Uses:(1) It is used for winding electric motors,generators and for transmission of electricity,(2) Its sheets are used as damp proofing inbuildings.
(3) LEAD:It is widely used in building construction and has drawback of being poisonous.Properties:(1) It is bluish grey metal,(2) It is soft as it can be cut with a knife,(3) It is highly ductile,(4) It is a good conductor of heat and electricity,(5) It does not corrode,(6) Its specific gravity is 11.35.Uses:(1) It is used as a base in paints,(2) Lead pipes and lead joints in sanitary fittings areextensively used.
(4) TIN:It is one of the mostly used protective metalsused in construction activities.Properties:(1) It is lustrous silvery white metal,(2) It is highly ductile,(3) It is a good conductor of heat and electricity,(4) It is soft and has good plasticity,(5) Its specific gravity is 7.3.Uses:It is used to give protective coatings to iron andsteel sheets.
(5) ZINC:It is commonly used in building construction either as abase for paints or as protective coverings for metals.Properties:(1) It is bluish white crystalline metal,(2) It is brittle metal at ordinary temperature,(3) It becomes ductile between 100-1500C,(4) It is a good conductor of heat and electricity,(5) It resists corrosion.Uses:(1) It is used for galvanizing iron sheets and pipes, forbatteries and printing blocks,(2) It is also used for preparing paints.
(1) BRASS:Brass is an alloy of about 60-70 % copper andzinc. Hardness of this alloy depends upon theamount of zinc present in it.Properties:(1) It is very strong,(2) It is ductile alloy,(3) It resists corrosion,Uses:It is widely used for making house hold utensils,water pumps and other machine parts.
(2) BRONZE:Bronze is an alloy of 90 % copper and 10 % tin. Itcan be easily machined and cast.Properties:*It resists corrosion.*It takes a fine polish.Uses:(1) It is used for manufacturing of house holdutensils.(2) Phosphorous bronze is used for making radioaerials and certain other instruments.
CORROSION:Conversion of metals into various compounds bynatural means or agencies is described ascorrosion. Corrosion of ferrous metals appearsin the form of rusting.Corrosion of metals is explained in two ways.One is by the formation of oxides. As in case ofiron, reaction with oxygen, carbon dioxide andwater results in the formation of bicarbonate,which in turn alters into carbonate and finallychanges into hydrated oxide. Continued---
According to other explanation, themetal surface processes areas whichact as cathode and anodes. Thepresence of water or moisture etcprovides a contact between suchareas which results in corrosion.
Protection against Corrosion:Ferrous metals have tendency for corrosion.It is maximum for steel and least for castiron. Wrought iron has a moderate tendencyto rust. Therefore, all the products require aprotective cover to prevent the possibility ofcorrosion and thereby adding to itsdurability. Various methods which are incommonly used include Electroplating,Galvanizing, Tin plating, Metal spraying,Painting, etc.
(1) Electroplating:This method involves the use of electric current togive a coating of chromium or nickel which ishighly resistant to corrosion.(2) Galvanizing:In this method zinc is used to give a coating on theferrous metal products.(3)Tin Plating:This method is similar to the galvanizing process.The iron products are thoroughly cleaned andwashed. Then these are dipped into the hot moltentin and it will give protection against corrosion.
(4) Metal Spraying:This method involves the use of a special sprayerin which fuel gas, oxygen and air are used tomake flame. The wire of metal to be sprayed likezinc, tin, or aluminium is used in these sprayers.The wire metals and a thin layer is sprayed overthe ferrous metal items.(5) Painting:The iron made goods are often coated with paint.Care should be taken to first clean the iron surfacethoroughly and then give a good coating of goodquality paint.