 In the previous lectures, we have been learning about the principles involved in the green sand molding, the what is it properties of the green sand, design of the gating system, casting defects and so on. Next we were learning about the melting practices, next treatment of the molten metal. Now in the next few lectures, we will be learning about the important to cast metals and alloys. Now today we will see the cast irons and steels. First we will see the cast irons, next we will be learning about the steels. Now cast iron, cast iron is made by re-melting pig iron often along with substantial quantities of scrap iron and scrap steel. During melting of this cast iron, various steps are taken to remove undesirable contaminants such as phosphorus and sulphur because this phosphorus and sulphur are detrimental they can cause cracking to the castings that is why they should be minimized their proportion should be minimized and depending upon the application carbon and silicon contents are reduced to the desired levels. Cast iron in the cast iron carbon and silicon are also present but they should be within the prescribed limits. So we will take every measure so that if there is any excess carbon or silicon we will reduce it. Now cast irons can easily be cast into intricate shapes we can make complex shaped castings. Next one they have good wear resistance and they have high hardness and they possess good machinability. So these are the important features and characteristics of cast iron. Now there are mainly 4 types of cast irons. One is the grey cast iron, second one is the white cast iron, third one is the ductile cast iron and the fourth one is the malleable cast iron. Now we will be learning all these one by one initially we will see the grey cast iron. Now what is what are the characteristics and features of grey cast iron? If cast iron is cooled slowly what will happen graphiteization takes place and during this graphiteization graphite flakes will get a chance to form. Now this is the microstructure of grey cast iron and we can see here these are all the graphite flakes and several such flakes will be there all along the casting. So this is the what is a simple characteristic of the grey cast iron. Now this is the composition carbon will be present from 2.5 percent to 4 percent, silicon 1 percent to 3 percent, manganese 0.25 to 1 percent, sulphur 0.05 to 0.25 percent and phosphorus 0.05 to 1 percent. Remember what is a proportion of sulphur and phosphorus are extremely small. Now again we have to note that the carbon is present in a free form graphite in a matrix of ferrite and pearlite and here we can see these are the graphite flakes. This is one flake and this is another graphite flake, this is a graphite flake, this is a graphite flake likewise we can see several such graphite flakes. Now these are the advantages of grey cast iron, graphite acts as a chip breaker during machining. During the machining we require discontinuous chips because continuous chips would harm the tool as well as the surface finish of the job. Now we always discontinuous chips are preferred. Now what happens during machining when the graphite flakes come in contact with the tool immediately because this graphite flake is soft the chip will be breaking. That is how we get the discontinuous chips because of the presence of the graphite flakes. That way this graphite acts as a chip breaker during machining. Now not only that graphite acts as a lubricant during machining, this graphite is a what say good lubricant during machining of grey cast iron. Next one it has good dry bearing qualities due to graphite. Next one it has got the high castability means what is the meaning it is able to penetrate into all the what say what say intricate chips, minute chips of the cavity that is the high castability. Now these are the disadvantages or the limitations of the grey cast iron. High libretel right it has got the low impact strength which severely limits is used for critical applications. Next one graphite acts as a void and reduces the strength because graphite is soft it become it acts as a void and it reduces the strength. Next one changes in section size will cause variations in machining characteristics due to variation in microstructure. Next one higher strength grey cast irons are more expensive to produce right. So because of the presence of the graphite flakes there will be voids. So we have to overcome these difficulties we need to make certain treatments. So that way what say if we have to produce grey cast iron with higher strength that would become expensive. Now these are the applications of grey cast iron. Pump housings, engine heads, crankshafts, flywheels, machine tool bases, sanitary pipes these are the important applications in fact there will be many more applications of grey cast iron. Now here we can see this is the pump housing this is made up of grey cast iron. This is an engine head made up of grey cast iron this sanitary pipe and this is the machine tool structure and this is a flywheel all these are made up of grey cast iron. Next one let us see the white cast iron. Now what is the characteristic of white cast iron? If cast iron is cooled rapidly the graphite flakes do not get a chance to form. In the case of the grey cast iron we were cooling slowly that is how graphite flakes were forming. Now here we cool the what say cast iron very rapidly so that there is no chance for the graphite flakes to form. Now when the cast iron is melted the carbon will be present in the melt in the form of the in a chemically combined form that is the iron carbide or the cementite. Now during that state we are rapidly cooling means we are arresting the chemical combination of iron and carbon. Now what will happen when it is cooled down the white cast iron forms with cementite the what say chemically combined form that is the iron carbide or the cementite will continue to present even in the solid state. That way white cast iron is more hard compared to other cast irons. Now this is the typical composition of white cast iron carbon will be present from 1.8 to 3.6 percent, silicon 0.5 to 1.9 percent, manganese 0.25 to 0.8 percent, sulphur 0.06 to 0.2 percent and phosphorus 0.06 percent to 0.18 percent again we have to note that carbon is present in a combined form that is the Fe3C right and which is known as the cementite. Now this is the microstructure we can see everywhere we can see the cementite particles everywhere. So this cementite is very hard as hard as cementite that is how the entire cast iron the white cast iron becomes very hard. Now these are the mechanical properties of white cast iron very hard why because cementite is present cementite is very hard that is why the white cast iron is very hard next one it is very brittle and it has got good wear resistance white hard what say this cementite is very hard because of that there is a good wear resistance. Now these are the common applications in fact important applications of white cast iron break shoes, mining shovels, rolls for rolling mills, rail car break shoes, liners in machineries for processing abrasive materials we will see few pictures. So these are the mining shovels so these are made up of white cast iron these are the rolls for rolling mills again these are made up of white cast iron. Now this is the rail car break shoes here we can see this is the rail car break shoe now if it is the ordinary cast iron what will happen it will be what say undergoing wear but white cast iron has got the excellent wear resistance because of that nothing will happen even when we apply the break this break shoe will be very good its condition will be very good. Next one let us see the ductile cast iron what is the characteristic of ductile cast iron ductile cast iron also referred to as spheroidal cast iron or nodular cast iron was patented in the year 1948. Now what is its characteristic here in the case of the grey cast iron graphite flakes were present and here graphite nodules are present instead of flakes that is why we call it as the nodular cast iron. Now how we are able to get these nodules magnesium, selenium, calcium or other spheroidizing elements are added in a very small quantity to the molten cast iron then what will happen the elements that we are adding promote spheroidization and with this solute in the liquid to form heterogeneous nucleation sites. Now what will happen these magnesium or selenium or calcium elements that we are adding will be in a extremely small quantity. Now they are spread all over now these will be acting as the nucleating agents means a small particle of magnesium will be present around that some cast iron will be solidifying. Other magnesium particle will be there somewhere around that cast iron will be solidifying likewise there will be millions of what say magnesium particles and there will be millions of what say nodules will be there. Now the alloying elements are injected into the mould before pouring. So this is the simple characteristic or important characteristic of the ductile cast iron the graphite is present in the form of the nodules. Now this is the chemical what is a typical composition carbon is present 3 to 4 percent silicon 1.8 to 2.8 percent manganese 0.15 to 0.9 percent sulphur 0.03 percent and phosphorus 0.1 percent and again we must note that carbon is present in the form of spheroids or nodules. Now this is the microstructure everywhere we can see this is one nodule and this is one nodule this is one nodule this is one nodule this is one nodule means at the centre of each nodule there will be one magnesium particle or selenium particle around that cast iron is solidified. Now here we can see again so with ferrite matrix we can see these are the graphite nodules everywhere we can see graphite nodules and this is the pearlitic matrix and again here we can see these are the nodules. Now these are the advantages of ductile cast iron high ductility as the name implies name is ductile cast iron it has got high ductility. Now it has also got high mission ability next one it has got high wear resistance and it can be forged. Now these are the important applications of ductile cast iron engine connecting rods, truck axles, front wheel spindle supports, disc brake calipers, suspension system parts, power transmission yokes, the cast iron pipes and here we can see this is a connecting rod of what say internal combustion engine right. Next one here we can see this is the disc brake calipers next one these are the cast iron pipes all these are made up of ductile cast iron. Now you can see here this is the pump and valve components made up of ductile cast iron so all these are made up of ductile cast iron. Now there is another category of ductile cast iron that is known as the aus tempered ductile iron ADI what is that aus tempering is an isothermal heat treatment process applied to ferrous materials. Initially the component is heated to an optimum austenizing temperature then it is quenched into a liquid salt bath at a constant temperature between 310 degrees to 375 degrees centigrade means it is the temperature at which martensite transformation starts. After complete transformation of the microstructure the part is removed and air cooled to room temperature. Now we will see the diagram so this is the schematic diagram of the aus tempering process now what is happening so here the component will be heated so this is the austenite temperature range. Now we will be heating the component to an optimum austenizing temperature then what will happen it will be quenched in a salt bath at this temperature you can see at this temperature in this range it will be cooled down and you can see here this line this is cooled down quenched at a constant temperature. So this is the say optimum microstructure regarding wall thickness now this is the temperature range of the salt bath. So this is 400 degrees centigrade and this is say 232 something between that we what say quench the component. Now what is this what say austenizing temperature range let us see the phase diagram yes in the phase diagram you can see here the austenite will be starting at a temperature of 912 degrees centigrade. So this is the starting what say temperature for the formation of austenite. Now you see here this is the austenite temperature range yes 912 is somewhere in between in this range to that temperature we will be heating then we will be quenching at a constant temperature then we will be getting the austenpored ductile iron. Now what are the advantages of austenporing or the austenpored ductile iron it produces a structure that is stronger and tougher than the structures produced with conventional heat treatments thin walled net shape components can be produced why because within ordinary cast iron or with the grey cast iron if we produce thin walled sections they may not be strong enough to withstand whereas the what say austenpored ductile iron has got higher strength it is strong enough. So even a thin walled section will be strong enough to sustain next one components possess high hardness and excellent wear resistance. Now ADI means it is the short form for the austenpored ductile iron it is much easier to cast than steel it is approximately 9 percent lighter than steel even it is density is lesser. Nowadays what is the requirement for the castings we want lesser density. So that way austenpored ductile iron density is lesser than the density of steel. Now this is a typical example of ductile what say austenpored ductile iron application a wheel what say cassette part made up of austenpored ductile iron. Now finally we will see the mullible cast iron mullible cast iron is obtained from white cast iron but with improved mullibility it is obtained from white cast iron. What is mullibility ability of the component to be made into thin what say plates or thin sections that is the mullibility. So when we are making mullible cast iron from white cast iron this property is improved the mullibility property. Next one the white cast iron is reheated to about 927 degrees for a for a long periods of time in the presence of materials containing oxygen such as what say iron oxide. And what will happen at the elevated temperatures cementite decomposes into ferrite and free carbon. Then what will happen upon cooling the combined carbon further decomposes means the combined carbon from the cementite further decomposes to small what say compact particles of graphite instead of flakes like graphite in grey cast iron. So in the case of the grey cast iron we have seen what say graphite flakes further varies in the case of the ductile cast iron there were graphite nodules for there. Now here what will happen there will be what say graphite or the carbon packets will be there. This free carbon is referred to as temper carbon and the process is called mullibilizing. Now this is the typical composition of mullible cast iron carbon its proportion is from 1.8 to 3.6 percent, silicon 0.5 to 1.9 percent, manganese 0.25 to 0.8 percent, sulphur 0.06 to 0.2 percent and phosphorus 0.06 to 0.18 percent. Now we must note that carbon is present in the form of tempered carbon packets. Now this is the microstructure of mullible cast iron. So this is a tempered carbon packet this is another such packet this is another tempered carbon packet likewise there will be several such tempered carbon packets will be there and because of that the mullibility of cast iron is improved. Now we can see here again so this is the free carbon or the tempered carbon. Now again this is we can see the microstructure here the matrix is the ferrite we can see here this is the ferrite what say matrix and this is the graphite packet or the carbon packet this one and again we can see here we can see pearlitic matrix and this is the what say carbon packet and again here we can see this is the ferrite matrix and this is the carbon packet or the graphite packet and here it is partially malleable iron we can see and here we can see fully malleable iron. Now, these are the advantages of malleable cast iron one is the it has got excellent missionability next one it has got significant ductility next one good shock resistance properties and these are the demerits or disadvantages of malleable cast iron one is malleable cast iron undergoes excessive shrinkage during solidification. As a result larger feeders or the razors are required these are the applications of malleable cast iron universal joint yokes transmission gears differential cases crankshafts and hubs flanges pipe fittings and valve parts marine and other heavy duty applications all these are made up of malleable cast iron and here we can see few what say pictures. So, this is a differential in used in the automobiles. So, this is made up of malleable cast iron differential case and this is the pipe fittings and valve parts. So, these are made up of malleable cast iron next one. So, far we have completed the cast irons now let us see the cast steels the steels can be broadly classified into two categories one is the plain carbon steels and the other one is the alloy steels. Now, in the plain carbon steels yes several elements are present like carbon, silicon, manganese, sulfur, phosphorus are present but carbon is the principal alloying element whereas, in the case of the alloy steels carbon is also present along with carbon several elements like chromium, nickel, vanadium, molybdenum, tungsten, cobalt, copper, manganese, silicon, phosphorus, sulfur these are also present but what is the difference between plain carbon steels and the alloy steels is that in the case of the plain carbon steels carbon is the main alloying element or the principal alloying element whereas, in the case of the alloy steels though carbon is present some other element like chromium or nickel and several such elements one of these will be the principal alloying element rather than the carbon that way there are two categories. Now, first we will see the plain carbon steels next we will see the alloy steels plain carbon steels. Plain carbon steels among them again there are three categories one is the low carbon steels and another one is the medium carbon steels and the third one is the high carbon steels. Now, first we will see the low carbon steels it has less than 0.3 percent carbon usually ferrite and pearlite and it lacks hardenability what are the advantages it possess good weldability as carbon content increases there is a tendency for crack here the carbon content is lesser that is why the welding is good but as the carbon content is increasing it develops cracking during welding. Now, rated 55 to 60 percent machinability now what are the applications say among them when the carbon is present from 0.2 to 0.3 percent such what say low carbon steel is used for structural steels machine parts also used for case hardened machine parts and screws. Next one let us see the medium carbon steels in the medium carbon steels the carbon content is between 0.3 percent to 0.8 percent. Now, these are the special advantages better machinability good toughness and ductility good balance of properties and this is extremely popular and have numerous applications because the carbon content is neither less nor high it has got the moderate amount of carbon. Now, what are the applications when the carbon content is present from 0.3 to 0.5 percent it will be used for making crankshafts, gears, axles, mandals, tool shanks and heat treated machine parts and many more. So, these are the applications of medium carbon steels. Next one let us see the high carbon steels now when the carbon content is more than 0.8 percent to up to 2.1 percent this is the high carbon steel. Now, what are the advantages it has got high hardness why because carbon content is very high. Next one it has got high wear resistance fair formability. Now, what are the disadvantages because the carbon content is very high during welding it develops cracking. Now, what are the applications it is used for cutting tools milling cutters punching dyes and few other few such applications. Next one let us see the alloy steels. Now, what are the characteristics of alloy steels? In the alloy steels the principle alloying element is something other than carbon like chromium molybdenum tungsten etcetera. It does not mean that carbon is not present carbon will be present, but rather than the carbon the influence of some other element will be dominating. Stainless steels and tool steels are the common examples of alloy steels. Now, we can see here these are the typical applications of alloy steels. So, this is a pelton wheel blades made up of austenite stainless steel and here we can see this is a standard high speed what is a milling cutter made up of high speed steel. So, these are the applications of the alloy steels. Now, important elements of high alloy steels what are the elements or the principle alloying elements present in the high alloy steels? One is the carbon may not be the what is a primary element or the principle alloying element, but these are present carbon is present silicon manganese nickel chromium molybdenum cobalt tungsten and vanadium. Silicon is a principle alloying element, but carbon is not the principle alloying element in the high alloy steels. Now, we will see the alloying elements of steels and their functions one is the carbon what is it what are the functions of carbon it increases solid solution strength and also it increases hardenability. This element is the silicon it is used as a deoxidizer means it prevents oxidation. Now, it is an alloy for electrical and magnetic sheet metals improves oxidation resistance because if you what is a metal is about to undergo oxidation this silicon reacts with the oxygen and saves the metal instead this undergoes what is a oxidation that way what say it improves the oxidation resistance of the what say that alloy. Strengthens low alloy steels also prevents decarburization. Now, decarburization is another severe problem in the steels or in fact even in the casterins. What is this decarburization carbon has to be present in a what say particular range is both in the steels and also in the casterin. Now, because of this carbon right the casting will get a what say particular amount of strength, but if this carbon content is reduced this is the decarburization what will happen the strength of the casting comes down. At such times when they what say decarburization is about to takes place silicon prevents such decarburization. Next one next element is the manganese what are the functions of manganese contracts the effect of brittleness from sulphur. Now, sulphur has to be present in the both in the casterin and also in the steel. Now, it is sometimes it is intentionally allowed, but up to a extremely small amount may be 0.05 percent that improves the machinability of the casting. Sometimes by mistake if the proportion of the sulphur crosses that limit may be 0.05 is the limit the casting becomes brittle. Now, the casting develops cracking at such times this manganese reacts with sulphur and forms the manganese sulphide and contracts the effect of the brittleness from the sulphur. Next one manganese increases hardenability in expensively we do not have to spend so much. Next one high manganese and high carbon produces steels resistant to wear and abrasion because of the manganese and sulphur there will be wear and abrasion resistance. So, these are the functions of manganese. Next alloying element is the nickel what are its functions its strengthens unquenched steel or annealed steels. Next one it toughens the paralytic ferritic steels especially at low temperatures. Next one it renders high chromium high what say ferrous alloys austenitic. Next alloying element is the chromium it increases the corrosion and oxidation resistance that is why this is widely used in the stainless steel. Often we say that stainless steel is what say it has got the highest resistance against corrosion why it contains chromium. Next one it increases hardenability it increases strength at high temperatures. Now with higher carbon it also develops good wear and abrasion resistance for the component. So, these are the what say functions of chromium. Next one next alloying element is the molybdenum what are its functions it raises grain coarsening temperature of austenite. It increases depth of hardening it raises hot and creep strength and promotes red hardness especially this molybdenum is used in the high speed steel. Now what happens to the high speed steel during machining the high temperature will be developed at such times even the tool becomes red hot such times the tool should still possess the required hardness and because molybdenum is present in the high speed steel even if the when the tool is what say heated up to an what say elevated temperature it does not lose the strength because of molybdenum. Next one it enhances corrosion resistance in stainless steels it forms abrasion resistant particles. Because of the molybdenum the what say abrasion resistance of the casting will be higher. Next alloying element is the cobalt what are its functions contributes to red hardness by hardening ferrite. What is this red hardness means hardness of the cast component when its temperature is raised to an elevated temperature during its use. For example the best example is the what say a cutting tool made up of say high speed steel. Next one alloying element for high speed steel it is an alloying element for high speed steel. Next one is the tungsten what are its functions it is a strong carbide former once there is carbide there will be good wear resistance will be there. The carbides form hardened abrasion resistance particles in the steels. So once there is carbide formation there will be abrasion resistance to the casting and there will be wear resistance to the casting. It promotes red hardness and hard strength again. So this tungsten is again used in the high speed steel tungsten say tungsten series the tungsten will be present 18 percent why because it promotes the red hardness means even when the tool is heated to a red state red hot state the tool still contains still possess the hardness. So that is the red hardness it promotes the red hardness. Next one next element is the vanadium what are the functions it promotes fine green elevates the coarsening temperature of the austenite. Next one it increases hardenability when dissolved it resists tempering and causes mark what say secondary hardening and it is a strong carbide and nitrate former. Once it is a what say carbide former what is the advantage there will be good wear resistance there will be good abrasion resistance also there will be it will be a nitrate former. Now apart from these alloying elements there will be residual elements in the steels what are these residual elements and their functions. So these are the residual elements phosphorous is present in the steels. So what is the meaning of residual element means it comes into the what say cast metal or the alloy without our intention or without our knowledge that is the residual element. Now it strengthens low carbon steels it increases resistant to atmospheric corrosion it improves machinability in free cutting steel that is why though it is a what say residual element though it comes without our intentional knowledge we alloy it to a small proportion. Next one sulphur sulphur is another residual element but what is its use it improves machinability but if the sulphur content is more it makes the casting brittle and cracking takes place. Next one copper is also considered as a residual element in the steel. Now it improves corrosion resistance though it is a residual element means though it comes into the what say alloy without our knowledge and intention it does some favor to us what are they it improves corrosion resistance increases strength and hardness through heat treating edging. So these are the advantages of copper. Next tin tin is also considered as a residual element means it comes into the alloy without our knowledge and without our intention it promotes temper embrittlement. Now the SAI the Society for Automotive Engineers and AI SAI American Iron and Steel Institute system for classification of steels. The SAI AI SAI system classifies all other alloy steels using four digit index as follows right. One means one series these are the carbon steels. Two series means nickel steels means nickel is the principle alloying element other elements also will be present. Three series means nickel chromium steels. Four series means molybdenum steels. Five series means chromium steels. Six series means chromium vanadium steels. Seven series means tungsten chromium steels. And nine series means silicon manganese steels. Now there will be four digits will be there in this what is a coding. The first digit indicates the principle alloying element. The second digit of the series indicates the concentration of the major element in percentile right. And the last two digits of the series indicate the carbon concentration. Carbon is also present in all the steels. So last two digits indicate the carbon what is a concentration. And this is the we can see here SAI AI SAI system for classification of the steels. And here we can see few series one series we can see one zero and something one one and something one two and something. So these are all the carbon steels means carbon is the principle alloying element. And in the first series if the second digit is zero then these are the plain carbon steels and manganese maximum one percent. And if the second digit is one it is the resulphurized free machining. And if the second digit is two resulphurized or refosphurized free machining. Again in the one series if five is the second digit it will be plain carbon and manganese will be from one percent to one point six five percent. Next one in the one three series when the second digit is three what will happen so the manganese is one point seven five percent. Now here we can see these are the two series means the first element is the two means these are the the principle alloying element is the nickel. Again when the first second digit is three nickel proportion is three point five percent when the second digit is five the nickel is five percent. Again we see the three series means the first digit is three means it indicates the the principle alloying elements are nickel and chromium. Again when the first second digit is one it is nickel one point two four percent chromium point six five two point eight percent when the second digit is two nickel is one point seven five percent chromium is one point zero seven percent. When the second digit is three nickel is three point five percent chromium one point five percent to one point five seven percent. When the second digit is four nickel is three percent and chromium is point seven seven percent and here we can see these are the four series means what are they these are the what say molybdenum steels means the principle alloying element is molybdenum. Again among them when the second digit is zero molybdenum proportion is point two to point two five percent. When the second digit is four the molybdenum proportion is point four to point five two percent. When the second digit is one chromium proportion is point five two point nine five percent molybdenum point one two point three percent. When the second digit is three we can see nickel proportion is one point eight two chromium point five to 0.8 and molybdenum 0.25. When the second digit is 7, the nickel proportion is 0.1.05, chromium 0.45, molybdenum 0.2, 2.22, 0.35. When the second digit is 6, nickel 0.85 to 1.82, molybdenum 0.22, 0.25. When the second digit is 8, nickel will be 3.5, molybdenum 0.25. And again we see this is the 5 series, means the principal alloying element is chromium. Again the second digit can change, when the second digit is 0, the chromium content is 0.27 to 0.65 percent. When the second digit is 1, chromium proportion is 0.8 to 1.05 percent. When the second element is, digit is 0, again 0 and there will be through 3, what say digit will be there, then chromium will be 0.5 to 1 percent. Again when the second digit is 1 and another 3 digits will be there, means totally 5 digits, again chromium will be 1.02 to 1 percent, minimum carbon, carbon 1 percent. When the second digit is 2 and 3 more digits will be there, chromium will be 1.45 to 1 percent and carbon will be 1 percent. In this lecture, we have seen the, what say important cast steels and the cast irons. We have seen the cast irons are divided into broadly four types. One is the gray cast iron, second one is the white cast iron, third one is the nodular cast iron and fourth one is the malleable cast iron. And we have seen the applications of these types of cast irons. We have also seen different types of the steels. The steels are broadly classified into plain carbon steels and the alloy steels. In the plain carbon steels, carbon will be the principle alloying element, whereas in the alloy steels, though carbon is present, some other element like chromium, nickel, molybdenum or tungsten, such elements will be the principle alloying elements. And we have seen, again in the principle, what say plain carbon steels, there are three types, low carbon steels, medium carbon steels and high carbon steels. And we have seen the classification of the alloy steels according to the AISA. So, in the next class, we will be learning about the aluminum and magnesium cast irons. Until then, goodbye and thank you.