Reduction of phosphorus from ferrous scrap during induction melting

Abstract

The phosphorus (P) content in carbon steel is generally kept below 0.05 percent. This small quantity tends to dissolve in ferrite, increase the strength and hardness slightly. In larger quantities, phosphorous reduces ductility, thereby increasing the tendency of the steel to crack when cold worked. During the production of steel, P removal can be achieved by maintaining a basic oxidizing environment in the melt which is ensured by the constituents of slag. This dephosphorization as well as refining is generally done using basic oxidizing steel making processes viz. Linz-Donawitz process (LD) and electric arc furnace (EAF). In Bangladesh steelmaking is done mainly using the silica based acid lining induction furnace where acid oxidizing environment exists during melting. While for P removal from steel, basic oxidizing environment is required which cannot be applied in induction furnace as acid lining is chemically attacked during the operation. Thus, induction melting cannot remove P from high P content raw materials known as low cost materials and produced high P content steel. The production of low P steel from high P scraps by induction furnace is the challenge in the present day in Bangladesh. Although, the P removal in induction furnace using basic oxidizing process has been found in a very few open literatures, there is still no efficient development of the method has been reported yet. In this thesis work, melting has been performed to reduce the phosphorus content from high phosphorus containing steel scrap in induction furnace using mill scale as oxidizing source with addition of different amount of lime as flux material to maintain the proper refining of steel in induction furnace with neutral lining. The main purpose of this study is to find out optimum ratio of mill scale to CaO and basicity of molten metal for best refining of phosphorus from steel. The starting steel scrap used in the present study contains 0.175%P. From the experiment, minimum P content 0.044% was found at the mill scale to CaO ratio 3.7: 1 with the basicity of 1.58.