Effect of rolling conditions on ferrite refinement of low-carbon steel
Refinement of the ferrite grains provides a promising approach to simultaneously improving both the strength and the toughness of steels. Among recent techniques to obtain ultrafine ferrite, dynamic strain induced transformation (DSIT) is used. This type of treatment is sensitive to steel composition, deformation temperature, the prior austenite grain size, strain and cooling rate. This work is aiming to improve the mechanical properties of steels using ferrite grain refining through trials on industrial scale using a compact strip production plant (CSP) with hot strip mill (HSM) containing six stands F1-F6 in EZDK Steel Company. The chemical composition of the trials was C (~0.046), Si (0.073) Mn (0.50) and Ti (0.008). The effect of final deformation temperature of 750, 775, 800 and 815°C on the microstructure and mechanical properties was studied. In addition the effect of strain rate variation at the final two rolling stands was correlated with the ferrite refining mechanisms. The ferrite grain size attained after refining varies from 10 μm to be 6 μm. Yield and tensile strength increased slightly through changing deformation temperature, with the advantage of keeping almost the original high ductility. Toughness of the processed steel increased with ferrite grain refining.
Processing and Evaluation of Ferritic-Bainitic Multi-phase Steel
Production of bainite-ferrite multi-phase steels on industrial CSP scale provides approach to improve mechanical properties along with large cost reduction opportunity. In terms of hot-rolling conditions, chemical composition, and microstructure; characterizing ferritic-bainitic steels and their difference from ferritic-pearlitic steels regarding properties and cost becomes of a great importance to understand the optimum conditions for production. This work is aiming to improve mechanical properties of steels by producing bainite-ferrite steel through industrial scale runs on the  6 stands  hot strip mill (HSM) with at EZDK steel using low alloy Al-killed steel. The effect of hot rolling coiling temperature and alloy content on final properties was studied. In addition to characterizing differences between ferrite-bainite steels and conventional ferrite-pearlite steels. Ferrite-bainite steel has been successfully produced in different conditions, showing up to 27% (~100 MPa) improvement in yield strength, 8% (42 MPa) in tensile strength, 13% in total elongation, and 11% (27 J) in impact toughness. Vanadium microalloying has proven to have almost no effect on mechanical properties of ferrite-bainite steels upon its rising from 0.045% to 0.063% which is not the case in ferrite-pearlite steels. Ferrite-bainite steel offers a great margin for alloy cost saving compared to ultra-low carbon microalloyed steels (up to 56%) through replacing chemical strengthening with phase transformation strengthening. We expect this new approach to significantly reduce the cost of production without sacrificing the quality.
Ferrite grain refinement by controlled rolling of lovv-carbon and microalloyed steel
AbstractA C–Mn steel and two microalloyed steels, one containing niobium and the other vanadium, were subjected to controlled hot rolling followed by cooling in air or vermiculite. The experiments were designed to allow differentiation between cases in which transformation started after the end of rolling and those in which it started in the roll gap during deformation. When transformation began after the end of rolling, austenite grains of the C–Mn steel were refined by recrystallization, while in the microalloyed steels austenite grains were elongated due to the absence of recrystallization. In all three steels ferrite grain refinement originated wholly from changes in size or shape of austenite grains and constancy of the ratio of austenite to ferrite grain sizes. Significant change in the transformation mechanism need not be invoked in order to explain the observed degrees of ferrite grain refinement. On the other hand, when transformation began during rolling, more efficient grain refinement was obta...