STRUCTURE PROPERTY CORRELATIONS IN INTERSTITIAL FREE (IF) STEEL.

Abstract

Interstitial Free (IF) steel was firstly introduced in Japan in the 70's. Nowadays, IF steel has world widely known as the best affordable high quality material for deep drawing applications.It has been used for broad applications ranging from automotive body to electronic components. In the present work two types of IF steels have been procured from TATA steel and• BHUSHAN steel. The as received sample was studied in hot rolled condition and its microstructure was taken which consists of equiaxed ferrite matrix. In the present work we focused on mechanical properties of IF steel which depends upon thermo-mechanical treatment of IF steel. A combination of cold rolling followed by sub-critical annealing helps in obtaining high ductility and formability together with good strength. The as received two types of IF steel having different chemical composition had been given cold reductions of 20%, 40%, 60% and 80% followed by sub-critical annealing at 680°C for 10 minutes,20 minutes, 30 minutes and 40 minutes followed by furnace cooling. Tensile test specimens are prepared according to ASTM standards. The optimum combination of cold working and annealing cycle was found which gives us maximum elongation and strength. With the increase in annealing cycle time strength and hardness decrease and elongation increase. It has been observed that at 40 minutes of annealing we get the maximum elongation of 54 % but moderate strength. Fracture surface was studied using scanning electron microscopy (SEM) which shows brittle fracture in case of cold rolled sample- and ductile fracture in annealed sample. Electron dispersion analysis (EDS) analysis was done with field emission scanning electron microscopy (FESEM) to identify the precipitate. Two types of precipitates were found TiN and A1203 while the nano size precipitate is only visible in TEM.