In recent years, there has been a substantial increase not only in the production of steel via the EAF route, but also the production of 'high-end' steel products by this route. The stringent quality requirements of flat products and special bar quality (SBQ) end users demands that steel nitrogen levels are kept to a consistent minimum. HBI and DRI are a suitable raw materials for dilution of residual elements, however they are often overlooked as a reliable means of reducing dissolved gases, especially nitrogen, in the final product. As well as a dilution effect there is evidence that melting of HBI and DRI results in lower nitrogen levels at low addition levels. The in situ carbon content of HBI/DRI (present as both finely dispersed free carbon, and as iron carbide particles) is much more efficient to promote carbon boil reactions than large batch additions of lump coke and similar materials. The manner in which nitrogen enters the steel in the EAF, and the strategies for minimising nitrogen levels are discussed. The effects of nitrogen on steel processing and product properties are also described. Results from various EAF plants using HBI/ DRI are presented and analysed, demonstrating improved nitrogen control, process efficiency and product properties. Further, it is shown that using HBI and DRI to achieve these improvements optimises productivity and cost of the EAF and downstream processes.
展开▼
