Metallurgical Factors Influencing the Performance of Medium Carbon Hot Rolled Coils Developed in Underpowered Mill

Medium carbon steels are having large demand for wide range of engineering applicat ions. Selected difficult-to-cast med iu m carbon grades e.g. MC 40, M C 55 & M C 60 have been successfully developed and subsequently commercialized at integrated steel plant. MC 40 grade have good market demand for application like t wo wheeler chain links, industrial chain links, hair clips, binder clips, stapler parts, sprockets etc. whereas MC 55 grade have demand for application like hacksaw b lade, d rop pin for textile industry, dowel pins, clutches, seat buckles etc. Similarly, M C 60 grade is used for manufacturing circlips, spring washers, band saw blades for wood cutting, circular saws, cross cut saws etc. The identified med iu m carbon grades have been developed by optimizing casting and hot rolling parameters. The mill load was maintained well within the finishing mill capacity i.e. 25 MN at hot strip mill by maintain ing adequate slab soaking time in the reheating furnace. The application of these steel demands good internal soundness and cleanliness to arrest the cracking susceptibility of the finished products during cold ro lling/ forming operations. The metallurgical factors contribute for develop ment of these grades are control of Al (< 0.04 %) & N content (~ 60 pp m) along with control of excessive segregation of carbon in the steel and presence of inclusions like alu miniu m o xide and MnS which are main ly responsible for inadequate cold reducibility.