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In the present study, the effect of hot rolling reduction ratio on dynamic recrystallization (DRX) of Nb-V bearing high-strength low-alloy (HSLA) steel was investigated. The hot rolling process was simulated physically by performing single-and double-hit plane strain compression using a thermo-mechanical simulator under similar conditions as experienced in the plant. The austenite no-recrystallization temperature (T NR ) value of the steel was determined through multi-hit plane strain compression in Gleeble simulator as well as using the actual rolling mill log data. The T NR value (* 940-945°C) obtained from both the methods were found to be in good agreement. The rolling reduction was varied in the range of 40-50% in the initial two passes. The kinetics of DRX were evaluated using the Avrami relationship. The dynamic recrystallization behavior was characterized by microtexture analysis using electron backscattered diffraction. The critical strain required for the instigation of DRX in the Nb-V HSLA steel was found to be * 0.15. Furthermore, a true strain of * 0.8, equivalent to 50% reduction in thickness was required in first pass for complete recrystallization to occur in the chosen steel. The grain orientation spread (GOS) analysis confirmed the presence of recrystallized grains with GOS values less than 2°in the specimens deformed with 40-50% and 50-40% reduction schemes between first two passes of rolling.

Global warming and green house gas emissions are the major issues worldwide and their impacts are clearly visible as a record high temperatures, rising sea, and severe 'flooding and droughts'. Motor vehicles considered as a major contributor on global warming due to its green house gas emissions. Hence, the automobile industries are under tremendous pressure from government and society to reduce green house gas emission to maximum possible extent. In present work, Dual Phase steel with boron as microalloying is manufactured using thermo-mechanical treatment during hot rolling. Dual phase steel with boron microalloying improved strength by near about 200 MPa than dual phase steel without boron. The boron added dual phase steel can be used for manufacturing stronger and a lighter vehicle which is expected to perform positively on green house gas emissions. The corrosion resistance behavior is also improved with boron addition which would further increase the life cycle of the vehicle even under corrosive atmosphere.

API 5L grade steel is mainly used for oil and gas transportation. The economy of gas transportation via pipeline demands for high operating pressures and large pipe diameters in order to improve transportation capacity which requires heavy thickness and/or high grade of the steel. This pushed the steelmakers to develop high strength steels (HSS) with superior metallurgical and mechanical (strength, toughness and ductility) properties in order to allow exploitation in hostile environments. The technology of production of API 5L grade through conventional thick slab process is matured enough as it gives flexibility of using higher %C, lower casting speed, high slab thickness (200–250 mm), higher reheating temperature and time, high reduction etc. However due to slower cooling rate during liquid to γ transformation, possibilities of centerline segregation defect increases. Thin slab technology (TSCR), on the other side allows a reduction in energy consumption (because of lower slab thickness and elimination of reheating process), with consequent benefits in terms of production costs and pollution reductions. But producing API X65 and above though TSCR route with subzero impact and DWTT is a challenge because of the difficulties in achieving a refined and homogeneous microstructure due to lower reduction ratio from slab to finish sheet thickness. This paper aims to give an overview of recent developments of high strength pipe steel grades as API 5L X70 through TSCR route. Information regarding the metallurgy and processing, such as chemical composition, microstructural design, thermo-mechanical controlled process (TMCP) and accelerated cooling process (AcC), to achieve the target strength, ductility and toughness properties are discussed. Mechanical properties are well above the requirement of X70 at HR stage as well as after pipe formation. Excellent Impact and DWTT is achieved up to −40° C.