Powder Technology, Vol.335, 103-113, 2018
An integrated approach for production of stainless steel master alloy from a low grade chromite concentrate
As an alternative process, the production of stainless steel master alloys in blast furnace (BF) exhibits high economic efficiency and great potential to use low-grade chromite resources. To produce desirable sinter products required by the blast furnace smelting process, sintering tests of ore mixtures made from a low grade South African chromite concentrate (Cr2O3/FeO = 1.99) and Chinese magnetite concentrate were performed in a sinter pot in terms of various sintering parameters including coke dosage, mix moisture, sinter basicity and proportion of magnetite concentrate, etc. An integrated process comprising "high pressure grinding rollers (HPGR) pretreatment, pelletizing, coke coating, pre-drying and non-fluxed sintering" steps was proposed based on the pellet sintering technique. The quality of Cr-bearing sinters was evaluated. The results show that high quality Cr-bearing sinters can be obtained through the proposed process. Addition of 40% or more magnetite concentrate in ore blends promises to yield desirable sinters of proper chemical composition and good metallurgical properties required by the blast furnace smelting process. The smelting performance of the Cr-bearing sinter made from the 40% chromite and 60% magnetite mixture was assessed under simulated blast furnace smelting conditions. It is feasible to use the Cr-bearing sinters in blast furnace for stainless steel master alloy production. A stainless steel master alloy containing 71.75% Fe, 19.52% Cr and 7.84% C with phosphorus and sulfur contents (<0.015%) is obtained at Fe and Cr recovery rates of 92.55% and 87.53%, respectively, when smelting at 1550 degrees C for 60 min with slag compositions (10% Al2O3, 10% MgO and R-2 = 1.0). The bonding mechanism of Cr-bearing sinters and the formation mechanism of liquid phase were further revealed by X-ray diffraction analysis (XRD), scanning electron microscopy (SEM) and energy-dispersive spectrometer (EDS). Both slag bonding (10 to 20% silicate) and solid bonding (recrystallization of spinel phase) contribute to the consolidation of the Cr-bearing sinters. Increasing the basicity of sinter made from 100% chromite concentrate or addition of magnetite concentrate in the ore blend at natural basicity lead to the formation of low-strength slag bonds, which generally reduces the sinter strength. (C) 2018 Elsevier B.V. All rights reserved.