 Mr. P. P. Mitragootri, Associate Professor in Mechanical Engineering Department of Walchand Institute of Technology, Sholapur. In the earlier session, we discussed about stainless steels and martensitic stainless steel. Today, we are going to discuss regarding further variety, one more variety of stainless steel and outcome of this session will also be the same that is you will be able to select a proper variety of stainless steel for a given application. Now, in this session, we are focusing on group B variety of stainless steels that is ferritic stainless steels and these ferritic stainless steels are cheaper varieties of stainless steel, I will tell you. Finally, these are plain chromium steels, why plain chromium steels? Because along with carbon, they contain only chromium as an alloying element. They do not contain anything other than chromium and chromium being cheaper alloying element, these ferritic stainless steels are called as cheaper varieties of stainless steel. But even though they are cheaper, they have excellent properties and they find very wide use in engineering and in these group B varieties of stainless steel, amount of chromium in solid solution exceeds 13 percent. That is percentage chromium minus 17 into percentage C is greater than 13 percent. Now, what is happening in this case? Chromium even though it is a carbide former, strong carbide former, it is also a ferrite stabilizer. Ferrite stabilizing property of chromium becomes important or dominant over here. What is meant by ferrite stabilizing? It lowers the A4 temperature and raises the A3 temperature due to which at around 13 percent chromium with little carbon content in steel, A4 and A3 temperatures will merge into one another in FEP3C diagram and region in which austenite is present will disappear and in that region we will find ferrite and due to which we have very good formability, excellent corrosion resistance, these properties are converted to these steels and this is the effect of ferrite stabilizing effect of chromium you can see. These steels containing more than 13 percent chromium in solution have ferrite at room temperature to high temperature as a result of which at room temperature they have ferrite up to solidus temperature they have ferrite. So we cannot harden them by hardening because unless and until we form austenite above A3 temperature and we under cool austenite to MS temperature we are unable to get martensite. So ferrite stainless steels can never be thought of hardening so they are non hardenable steels as these steels that is that has been explained already as these steels don't form austenite as they have ferrite at temperature these steels cannot be hardened by heat treatment but due to presence of ferrite they can be very very very easily cold work and they are used in work hardened condition and they get strain hardened and their strength and hardness increases due to work hardening. Now grain refinement of these steels can be done by cold working and recrystallization on a laying they have higher chromium to carbon ratio as compared to group A steel because they have very low carbon. Carbon content of these steel doesn't exceed generally 0.2 percent more than 0.2 percent and chromium content is much higher and these steels are also magnetic in nature. All of you all of we people have one misconception that is stainless steels are non magnetic but martensitic stainless steel as well as ferritic stainless steel both are magnetic in nature and ferritic stainless steels are also designated in AISI 400 series means martensitic stainless steels are also designated in AISI 400 series and ferritic stainless steels then how to identify this we will come to that little later. What are the properties of martensitic sorry ferritic stainless steel as these are ferritic stainless steel as these content ferrite at room temperature as well as high temperature high temperature they are soft ductile malleable as they contain very little carbon and have high chromium they have very high corrosion resistance because chromium in solid solution is very high they are low cost as only chromium is present as alloying element this is one of the important thing which once again I emphasize now before moving forward I will ask you one question what is the difference between group A that is martensitic stainless steel and group B that is ferritic stainless steels then what are the applications of ferritic stainless steel ferritic stainless steels find their applications to manufacture of vessels in food and chemical industry very widely used in chemical industry as well as in food industry juice carrying pipes in sugar mills pans and pots in sugar mills are invariably made of ferritic stainless steels and ferritic stainless steels have very good formability very good weldability and they have very good heat resistance to furnace parts and stoves and burners can also be made of ferritic stainless steel those our gas gas stoves we use at home they are nowadays made of ferritic stainless steels earlier they were made of cast iron nowadays they are made of ferritic stainless steel heat exchangers used in industry they also are manufactured from ferritic stainless steel due to good formability good weldability and good corrosion resistance then typical composition of ferritic stainless steel if you try to understand you find that 405 varieties of variety of ferritic stainless steel you find that carbon content is 0.08 it contains some amount of manganese and silicon invariably and if carbon content is less chromium content is also around 14 percent while if carbon content increases slightly in 4 as in 430 AISI steel we find that chromium content has also increased while in 446 variety of stainless steel we find that carbon content is 0.2 percent manganese content is also little more while chromium content is 23 to 27 percent and little amount of nitrogen is also present this steel will have better corrosion resistance as compared to 430 and 405 variety and now looking at these compositions and looking at the compositions of martensitic stainless steel you will definitely understand that martensitic stainless steel containing 0.15 percent carbon was containing around 13 to 14 percent chromium while ferritic stainless steel containing 0.2 percent carbon is containing 23 to 27 percent carbon chromium means carbon content and chromium content chromium content of ferritic stainless steel is much higher as compared to martensitic stainless steel and carbon content of martensitic stainless steel is higher for a given chromium content as compared to ferritic stainless steel and this is the basic difference while ferritic stainless steel find their applications where higher corrosion resistance resistance is there while martensitic stainless steel finds application where normal corrosion resistance is tolerable but what is required more is good hardness good wear resistance and that good hardness and good wear resistance to martensitic stainless steel is conferred due to hardening while good formability and very good corrosion resistance to ferritic stainless steel is given due to good formability for further reading I will suggest you to read material science and metallurgy by Dr. Kodgire engineering metallurgy 1 and 2 by A.S. Golub and M.S. Kulkarni introduction to engineering materials by B.K. Agarwal thank you