Winner of the the Excellence in the Innovation of the Year Steelie Award 2023
The present invention provides a technological breakthrough in new product innovation through electric arc furnace (EAF) steelmaking and crude steel production (CSP) mini mills using 100% steel scrap in EAF for steelmaking and continuous production from casting to hot rolling and coiling.
The product is a single-phase, lean-alloyed ferritic steel with uniformly distributed nano precipitates of TiC (2-4nm in size), deriving a tensile strength of minimum 780MPa in the final hot rolled steel. The sheet steel manifests high formability indexes such as a hole expansion ratio of more than 40% and forming strain limits compared to equivalent strength Dual-phase 780, Multiphase 780 and Ferritic-Banitic 600 steel grades.
The steel can be supplied in both uncoated and coated conditions with similar product properties. The strength guarantee in hot rolled coil itself eliminates the need for cold rolling and high-temperature annealing. Performance trial at customer sites indicated outstanding steel and edge retention capability formability in stamped parts that
outsmarts highly costlier AHSS steels e.g., Dual phase 780.
High formability is imparted by a single-phase ferrite matrix, absence of second-phase Fecarbides at grain boundaries, extreme cleanliness of the matrix and absence of chemical segregation at the centre and microstructural banding. The weldability of the steel is outstanding due to the very low carbon equivalence value of the composition (CIIW <0.30).
The steel has nano-sized TiC in the matrix, which also imparts great resistance to hydrogen-induced cracking in H2-containing atmospheres. The steel composition is 0.06C-1.5Mn-0.30Si-0.15Ti-0.03Al (wt.% max).
The steel is made in EAF with almost 100% scrap and then continuously cast in a thin slab caster at high casting rates of 4.0-4.8m/min and then continuously hot rolled into coils.
The processing thus generates the lowest CO2 emissions per tonne of hot rolled steel made (scope 1 + scope 2) and is calculated to be a mere 410kg per tonne of hot rolled coil made, which is almost 83-85% lesser than that emitted by other conventional steel manufacturing.