Novel and Cost Effective Process for Production of High Mn Medium C Steel
Abstract
The automotive industry is constantly searching for lighter, stronger and cheaper materials in an effort to create safer and more fuel efficient vehicles. In recent years, the introduction of aluminum alloys and polymer composite materials in automotive applications has been eroding what is traditionally one of the most lucrative portions of the iron and steel business. The steel industry responded to this challenge with Advanced High Strength Steel (AHSS) – a family of manganese containing steels with exceptional strength and ductility.
The significant growth in AHSS usage and its eventual and inevitable replacement of conventional steels in automotive application is now more or less a consensus among steelmakers and market analysts. ArcelorMittal predicted in 2014 that the usage of AHSS in cars to increase from the current level of about 10% to approximately 35% by 2020-20251. McKinsey & Co. predicts that between 2010 and 2030, the usage of conventional steel in automotive will fall by 75%, while that of High Strength Steel (HSS) will increase by 250% 2. World Steel Dynamics’ analysis claims that between 2014 and 2025, mild steel sheet deliveries will drop by 63%, mid-strength (High-Strength Low Alloy, HSLA) will drop by 14% and AHSS deliveries will rise by 330% 3.
Despite favorable market outlook and popularity within the industry, many existing technical and financial challenges prevent the widespread, large-scale commercial production of AHSS, making it a niche product of sorts. High-manganese AHSS are notoriously challenging to continuously cast and roll, requiring precise control and complex processing, to the point where entirely new continuous casting processes have sometimes been developed to produce AHSS sheets. On the other hand, the high cost of manganese alloy addition (usually low carbon ferromanganese, LC-FeMn) coupled with the low recovery of manganese to steel (sometimes as low as 50%) make it prohibitively expensive to produce AHSS economically for the automotive sector.
The present study provides an innovative approach for the production of mid- and high-manganese steels by addressing the economic challenges during manganese addition through the direct injection/charging of the pre-reduced, self-fluxed, manganese-ore micro-pellet into the furnace or LMF, instead of the traditional method of ferromanganese addition. The pre-reduction using H2 and CO (and potentially CH4) ensures the partial metallization of manganese and iron, while direct injection reduces volatilization/emission and improves manganese recovery. Furthermore, the composition of the pre-reduced pellets has been optimized through the use of mass and energy balance, and thermodynamic calculations of the process is performed to evaluate both the technical and economic feasibility of this technology.