 P. P. Mitravotri, Associate Professor in Mechanical Engineering Department of Valshan Institute of Technology, Swalapur. Today I am going to deal with the topic Unhealing and Normalizing. The learning outcome of this topic will be that is students shall be able to apply the unhealing and normalizing properly to get best set of properties in a component depending upon functional aspect of the component, means students will be able to understand where to apply unhealing and where to apply normalizing depending upon functional need of the component. Already discussed what is unhealing and in the session we will also discuss the differences or comparison between unhealing and normalizing. The treatment normalizing in its word normalizing indicates that to normalize the structure and to normalize the properties of the material this treatment is intended. Now normalizing and unhealing there are basic differences and first of all we will start with the basic difference that is range of temperature for heating the steel in unhealing and range of temperature for heating the steel in normalizing. Now in unhealing we heat the steel hypo eutectoid steel above A3 temperature while hyper eutectoid steel is heated above A1 temperature that is 20 to 30 degrees above A3 temperature for hypo eutectoid steel and 20 to 30 degrees Celsius above A1 temperature in hyper eutectoid steel. In this case if we heat the steel above hyper eutectoid steel above A3 temperature or ACM temperature due to slow cooling between A3 and A1 we may get coarsening of grains and sole purpose of unhealing treatment that is refinement in grain size will be totally defeated but in normalizing we heat all the steels 40 to 50 degrees above A3 temperature whether it is hyper eutectoid steel or whether it is hypo eutectoid steel. Now we may have a question that is heating in heating the steel in normalizing we are heating it above A3 temperature while in unhealing we are heating it above A1 temperature only to avoid grain coarsening then my question to all of you is whether grain coarsening occurs in normalizing of hyper eutectoid steel or grain coarsening is avoided. Now next factor for comparison is cycle time for unhealing and cycle time for normalizing. Now in unhealing we carry out cooling in furnace only that is slow cooling at the rate of 40 to 50 degrees Celsius per hour that is unhealing involves slow cooling while normalizing is carried out in air that is air cooling air cooling is much faster than furnace cooling as a result of which cycle time required for normalizing is much lesser as compared to that of unhealing in normalizing we find that furnace time consumed is much lesser as compared to that of unhealing. So in a given prescribed time we can carry out more number of cycles of unhealing normalizing than that of unhealing this is advantage and energy consumption in unhealing is greater than that of normalizing energy consumption of normalizing is lesser this is one of the advantages point of normalizing and surface finish of the component after unhealing is poor while surface finish is good after normalizing because of cooling in air these are general aspects of comparison between unhealing and normalizing but most important aspect of comparison is grain refining unhealing carries out refinement to the great extent normalizing also carries out grain refinement but grain refinement observed after normalizing is not to the extent that is observed after unhealing no doubt normalizing refines the grain size and that refinement in grain size is okay for most of the purposes but for critical applications if we require refinement in grain size one has to go for unhealing and for normal purposes if we want to refine the grain size we can go for normalizing and we can achieve economy then form of perlite that we get in unhealing is coarse perlite coarse perlite is obtained after unhealing as a result of which properties are lesser while perlite obtained after normalizing is fine perlite that is inter lamellar spacing between ferrite and cementite observed after normalizing is very less they are closer as a result of which strength after normalizing hardness after normalizing is much better than that of unhealing mechanical property improvement occurring after normalizing is much higher than that of unhealing unhealing generally softens the steel while normalizing hardens the steel to certain extent this is a basic difference then to improve the machinability of hyper u-tectoid steels and tool steels we generally employ spheroidizing unhealing but for economy for achieving economy and for improving machinability of medium carbon steels we can apply normalizing because normalizing also carry out globularization of perlite which will definitely improve the machinability to certain extent may not be to the extent that has been improved by unhealing but normalizing certainly helps in enhancing the machinability of medium carbon steel then after normalizing the toughness that we get in low carbon steel is greater than the toughness that we get in unhealing but in medium carbon steel it is always preferred to have unhealing if we want better toughness in short unhealing and normalizing are the two treatments which seem to be similar but they have basic difference and one has to judge when to apply unhealing and when to apply normalizing if we have steel castings we shall generally go for unhealing but if we have forging of low carbon steel it is always better to go for normalizing because normalizing will not only relieve the stresses to great extent may not be to the extent that has been relieved by unhealing but normalizing also improves hardness tensile strength as well as a toughness of the steel and normalizing in some cases is preferred over hardening and tempering because normalizing does not introduce a transformation stresses and temperature stresses developed in normalizing are generally negligible that is one of the greatest advantage and in forging industry to save the cycle time to save the furnace time to achieve the economy unhealing and normalizing are used hand in hand so in some cases double normalizing is also employed so that so as to improve or so as to get better set of properties so friends you might have understood the basics of normalizing and unable to material size and metallurgy metallurgy for engineers written by ec relation introduction to physical metallurgy by evner tmh publication thank you have a good day