Dephosphorization of Steels Aug15

Dephosphorization of Steels...

Dephosphorization of Steels  The effects of phosphorus (P) on the properties of steels are summarized in Tab 1. It can be seen that P has both positive and negative effects on the steel’s properties. Tab 1 Effects of phosphorus on properties of steels Sl.No. Property Effect of phosphorus 1 Strength Strong positive (strengthens ferrite) 2 Bake hardenability Positive 3 Ductility Strong negative 4 Galvanneal Can improve resistance to powdering 5 Phosphatability Positive 6 Enameling a. Fish scaling Negative b. Pickling Positive 7 Weldability Not harmful for contents less than 0.1 % 8 Core loss in motor lamination Strong negative 9 Fracture toughness Strong negative   Steels having low content of P are necessary for applications where high ductility is needed, such as thin sheets, deep drawn steel, and pipelines etc. In the earlier days, P control was not considered a big challenge in steel production since iron ores with low P contents were readily and cheaply available. However, in the recent past, because of high iron ore prices, lower priced iron ores from sources which normally have higher P content are being used and this has made P control an important activity during the steelmaking. In addition to P from in the iron ores, P also enters the liquid steel due to the recycling of the BOF (basic oxygen furnace) slag. The recycling of the BOF slag is being done through the sinter plant or directly into the blast furnace in order to retrieve the iron and lime content of the slag and to minimize the issues related to slag disposal. The sinter or the BOF slag fed to the blast furnace inevitably increases the P content of the hot metal and hence the P loads on the steelmaking process. In integrated steel plants,...