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Abstract: An ultra-low carbon Ti-containing microalloyed steel has been thermo-mechanically controlled rolled and water-quenched. Microstructural characterization of the samples finish rolled in the temperature range of 750–850°C revealed the presence of polygonal ferrite, quasi-polygonal ferrite, acicular ferrite and granular bainite. Micro-texture study showed the dominance of random texture and cube orientation at higher deformation temperatures, whilst, α-fiber and γ-fiber components intensified with the decrease in finish rolling temperature. Characteristic ferrite-bainite microstructure with fine ferrite grain size (<4µm) and a uniform distribution of fine TiC particles (<100nm) offered decent combination of strength (yield strength: 478–497MPa, ultimate tensile strength: 557–571MPa), ductility (total elongation: 20–26%), and impact toughness (110–114J at −40°C). Such a combination of mechanical properties makes the steel a potential choice for pipeline application. [Copyright &y& Elsevier]

Abstract: A new low carbon titanium and niobium microalloyed steel has been thermomechanically processed in a pilot plant unit. Phase transformation phenomenon of the above steel during continuous cooling has been assessed. Evolution of microstructure and mechanical properties has also been studied at different finish rolling temperatures. A mixture of intragranular ferrite with granular bainite and bainitic ferrite along with inter-lath and intra-lath precipitation of (Ti, Nb)CN particles are the characteristic microstructural feature of air cooled steel. However, mixture of lower bainite and lath martensitic structure along with similar type (Ti, Nb)CN precipitate is observed in water quenched steel. High yield strength (896–948 MPa) with high tensile strength (974–1013 MPa) has been achieved with moderate ductility (16–17%) for the selected range of finish rolling temperature for air cooled steel. However, the water quenched steel yields higher yield strength (1240–1260 MPa) as well as higher tensile strength (1270–1285 MPa) but with lower ductility (13–14%) for the selected range of finish rolling temperature. Fairly good impact toughness values in the range of 50–89 J are obtained for the air cooled steel which are marginally higher than those of water quenched steel (42–81 J). [Copyright &y& Elsevier]

Abstract: In the present study, copper bearing low carbon microalloyed ultrahigh strength steel has been produced on a pilot scale. Transformation of the aforesaid steel during continuous cooling has been evaluated. The steel sample has been thermomechanically processed followed by either air cooling or water quenching. Variation in microstructure and mechanical properties at different finish rolling temperatures has been studied. A mixture of granular bainite, bainitic ferrite and precipitation of nano-sized (Ti, Nb)C particles is the characteristic microstructural feature of air cooled steel. On the other hand, predominantly lath martensitic structure along with the similar type of microalloying precipitates of air cooled steels and Cu precipitates are obtained in case of water quenched steel. The best combination of strength (1364–1403MPa) and ductility (11–14%) has been achieved for the selected range of finish rolling temperature of water quenched steel. [Copyright &y& Elsevier]

Ultrahigh strength steel is designed for light-weight cost-effective parts with improved safety by dint of high strength coupled with better fuel efficiency for automotive and aerospace applications. The current steel with medium carbon (0.28 wt%) and alloying elements (∼8%) such as Mn, Ni, Mo along with micro-alloying of Ti and Nb has been processed by thermo-mechanical controlled processing with different finish rolling temperature (FRT) followed by air cooling and water quenching. Microstructure of air cooled specimen consists of lower bainite with a few amount of lath martensite, whereas a mixture of lath martensite and lower bainite in prior pan-caked austenite grains has also been obtained on water quenching. It is observed that microstructure becomes gradually finer with reduction of FRT for both cooling conditions and fine-scale carbide/carbonitride precipitates, enriched with Ti/Nb along with dislocation sub-structures within bainite and martensite laths have performed as strengtheners. Ultrahigh strength (1991–2032 MPa) with lower elongation (5–7%) is obtained in water quenched samples, whereas air cooled samples show comparatively lower strength (1841–1928 MPa) with marginally higher elongation (8–9%). Different strengthening mechanisms have been quantified which cumulatively contribute to the yield strength of the current steels. [ABSTRACT FROM AUTHOR]

A low-carbon microalloyed steel containing high Ni and Cu content has been developed and subjected to thermo-mechanical processing by varying the finish rolling temperature (FRT∼850–750 °C) and cooling rates (air cooling and water quenching). Microstructures of air cooled samples consist of granular bainite and lath or plate-like bainite, whereas, water quenched samples exhibit a mixture of lower bainite and lath martensite. A refinement in microstructure has been noticed with the decrease in FRT and increase in cooling rate. Transmission electron microscopy demonstrates the presence of coarse (Ti, Nb)C precipitates (~90–160 nm) and fine Cu precipitates (<20 nm). Macro-texture and micro-texture results reveal the dominance of Goss and rotated Goss texture components, which strengthened with the decrease in FRT and increase in cooling rate. The proposed steel composition and TMCP schedule have offered YS ∼ 1000 MPa, UTS ∼ 1400 MPa, total elongation greater than 10% maintaining a low YS: UTS ratio (0.68–0.80). Such a satisfactory combination of tensile properties achieved in as-cooled or as-quenched conditions (without the need of any tempering treatment) makes the steel suitable for automotive application. [ABSTRACT FROM AUTHOR]