 Hello friends, I am Mr. P. P. Mitragootri, Associate Professor in Mechanical Engineering Department of Walshchand Institute of Technology, Solapur. In earlier two sessions, we have studied about group A variety of stainless steels that is martensitic stainless steel and group B variety of stainless steels that is ferritic stainless steels. In this session, we are going to discuss about austenitic stainless steels. Outcome of this session will be, students will be able to apply their knowledge in selection of proper variety of stainless steel for given component. Now, with this, I will begin introduction to austenitic stainless steels. Their stainless steels were ferritic stainless steel and martensitic stainless steels and they were containing martensite and ferrite in their structure. So, austenitic stainless steels will contain austenite at room temperature as a result of which what will be the properties of these austenitic stainless steels? As austenite is an interstitial solid solution of carbon in iron having face centered cubic structure, this presence of austenite even at room temperature in such steels makes them much more ductile, much more malleable as compared to ferritic stainless steel because ferrite is BCC structure and austenite is FCC structure and FCC structure is supposed to have better ductility and malleability as compared to BCC structure. So, in general austenitic stainless steels are superior in all respect to ferritic stainless steels. How they are superior? We will try to learn them. In what respect they are superior? We will try to understand within next few minutes. What is austenitic stainless steel? These steel ferritic stainless steels were containing chromium along with carbon. While these steels contain at least 24 percent of chromium, nickel and manganese means along with chromium, nickel and manganese are essential constituents of these austenitic stainless steels. Along with chromium, it is nickel and manganese which makes these steel austenitic. Amount of chromium in these steels is at least 18 percent mind well. So chromium in solid solution is very high and carbon content varies between 0.03 to maximum 0.2 percent and we rarely observe maximum 0.2 percent carbon in 90 percent of varieties of austenitic stainless steel, our carbon content is less than 0.14, 0.15. So we find that these steels have excellent chromium to carbon ratio as a result of which they have very high corrosion resistance. As a result of which chromium in solid solution is very high, amount of chromium in solid solution is very high as a result of which their corrosion resistance is at par or excellence as compared to ferritic and martensitic variety. And as these steels have nickel or man or nickel and man both are present and as these are austenitic stabilizing element, these steels will have austenitic structure at room temperature as well as at high temperature that is up to solder's temperature means these steels also cannot be hardened by heat treatment. Similar to ferritic stainless steels, these steels are non-hardenable by heat treatment but these can be work hardened, these can be cold work hardened, work hardened and they have excellent ductility as already stated and due to presence of austenitic at room temperature they have better shock resistance and as already stated they have better corrosion resistance than group A and group B variety of stainless steels that is martensitic and ferritic varieties of stainless steels. And these steels as they are austenitic even at room temperature and even at high temperature they are non-magnetic. This is the only variety of stainless steel which is non-magnetic and as already discussed as these steels contain high chromium and low carbon, very low carbon, their chromium in solid solution is high and they contain nickel due to which they have better toughness and shock resistance but presence of nickel make these steels costly. These steels have excellent cold forming ability, they have excellent high temperature strength and some of these varieties can be precipitation hardened. Precipitation hardening treatment is the treatment which is known to us carried out on as the treatment carried out on beryllium bronzes and duralumine but some of the varieties of stainless steels can also be precipitation hardened and after precipitation hardening of some varieties of stainless steels they will yield excellent properties. And these steels if contain more than 0.03 percent carbon will present difficulty in welding that is one of the major drawback with these steels and in heavy manufacture of heavy vessels, heavy fabricated components from austenitic stainless steel we have to purposefully keep carbon content less than 0.03 percent, their welding properties are good, fabrication properties are good but carbon content has to be kept below 0.03 percent. So, in many of the stainless steels you will find two varieties, one normal variety another low carbon variety and these stainless steels are designated in 300 series if they contain nickel, nickel and manganese both and if these steels contain only very high manganese and very little nickel they are designated in AISI 200 series and many of the times we find that AISI 200 series steels can satisfy our requirement and as AISI 200 series steels contain higher manganese and lower nickel as they are cheaper and if they are able to satisfy our requirements we may not go for costly variety of austenitic stainless steel. Now, for example I will give you here one example that is we have a thermos flask, thermos flask has flask in flask one outside outer container and another inner container. Carries what you say fluid so inner container is made of AISI 300 series steel and outer container is made of AISI 200 series steel due to which cost of thermos flask is considerably reduced instead of making both the what you say containers of flask of AISI 300 series this type of things can be adopted and cost reduction can be done for that proper knowledge is essential and in some of the varieties of austenitic stainless steel molybdenum is added and it adds to acid corrosion resistance to acidic environment. Now, before moving forward I want to have one question over here that is what difference do you find in austenitic variety of stainless steels and ferritic stainless steels think over it. Now what are the applications of austenitic stainless steels austenitic stainless steels find wide spread applications in milk processing plants food and chemical industry these austenitic stainless steels are invariably used utensils and utensils in household applications are made of austenitic stainless steels dials of wrist watches are made of austenitic stainless steels costly sanitary fittings are made of austenitic stainless steels. Now we will study some of the typical we will have a look over some of the typical compositions of austenitic stainless steels AISI 200 series AISI 400 series now 304 and 304 YAL you observe everything is same only carbon content is less and 200 series will contain lesser nickel and higher manganese while 300 series will contain higher nickel and little manganese. Now for further reading related to all the varieties of stainless steels I will recommend material science and metallurgy by Dr. Kodigre engineering metallurgy 1 and 2 by A.S. Golub and M.S. Kulkarni introduction to engineering materials by B.K. Agarwal thank you all.