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The present study aims to examine the deformation and annealing behaviour of Fe–0.07C–20Mn–2.6Si–1.6Al TWIP steel in the viewpoint of microstructural characterisation, fault analysis, triaxial residual stress measurement and mechanism of twin formation. 50% cold deformation results in improvement of hardness and tensile strength (428 HV and 1419 MPa, respectively), whereas annealing at 900 °C of the same leads to improvement in ductility (61%) with the decrease in strength (873 MPa). The residual stress is maximum and compressive in nature in deformed sample which has been diminishing after annealing. Hot rolled and hot rolled-solution treated samples develop dual phase microstructure along with annealing twins, whereas fine nano twins and high dislocation density with dual phase microstructure are apparent after 50% cold deformation. The presence of Shockley partial dislocation, overlapping of stacking faults, Lomer-Cottrell lock, intrinsic and extrinsic stacking faults affect the mechanical properties as obstacles of dislocation movements or assisting twin formation. Goss and Brass components of texture are dominating after rolling, whereas annealing results in weakening of rolling texture components. The nucleation mechanism of twin has been consistent with the pole mechanism along with the deviation process. Hence the present work amplifies the present understanding of deformation and annealing behaviour on low carbon dual phase TWIP steel from different characterisation perspectives. [ABSTRACT FROM AUTHOR]

The present study deals with the influence of cold rolling on microstructure, texture and mechanical properties of low carbon high Mn TWIP steel. It is noticed that the hardness, yield strength and tensile strength of the specimens increase whereas percentage elongation decreases as the amount of cold rolling reduction increases. The fully austenite phase with the average grain size of about 55 µm along with annealing twins became fragmented and flattened when subjected to 10–50% cold deformation. The cold deformation results in the evolution of sub-structure, comprising dislocations, twins as well as interaction of dislocations and twins. The hot rolled and air cooled sample (0% cold deformation) reveals γ-fibre (〈111〉//ND) texture, whereas cold rolled samples shows Goss texture ({110}〈001〉) and Brass texture ({110}〈112〉) components, which are expected after cold deformation of austenitic steels having lower stacking fault energy in the range of 15–40 mJ/m 2 . X-ray line profile analysis through extended convolution multiple whole profile fitting method is utilised to quantify the dislocation density and planar fault (twin) probability for the cold rolled samples with different degree of reduction. Fractography shows that with the increase in cold deformation, fractures become more and more brittle in nature. [ABSTRACT FROM AUTHOR]

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]

Abstract: The present study concerns the influence of Cu addition on the synergistic effects of Ti–B in low carbon thermomechanically processed steels. Effective retardation of the γ→α transformation due to the combined addition of Ti and B is known to enhance the hardenability of a wide range of low carbon microalloyed steel. On the other hand, addition of Cu in low carbon age hardenable steel suppresses the pearlitic transformation resulting into a microstructure constituted by interspersed islands of martensite in ferritic matrix. Therefore, it may be of interest to examine the role of Cu on the synergistic contribution of Ti and B in respect of increasing hardenability of austenite. In the present study, effects due to the addition of Ti, B and Cu in different steels are interpreted in respect of microstructure–property correlation. It is demonstrated that the addition of 1.5wt% Cu perceptibly enhances the synergistic effect as manifested by lowering the transformation temperature of austenite. Addition of 0.8wt% Ni in Cu–Ti–B steel does not alter the transformation temperature of austenite to any appreciable extent. However, Cu–Ni–Ti–B steel has resulted into the enhancement of strength–ductility combination. [Copyright &y& Elsevier]

The present study aims to investigate the evolution of microstructure of 304 austenitic stainless steel (SS) due to reversion annealing of cold deformed samples under different schedules. Evolution of phases in selected samples was identified and quantified by X-ray diffraction analysis along with corresponding microstructural characterisation through optical, scanning and transmission electron microscopy. Mechanical properties of the samples were determined by carrying out tensile test. Electron microscopy of selected samples has revealed that, while strain induced martensite, deformation twins, ε-martensite and high dislocated structures are the dominant microstructural features of the cold deformed samples, reversion annealing of the same results into ultrafine-grained reverted austenite, cell type dislocation sub-structures with some amount of untransformed martensite. The maximum tensile strength of 1589 MPa with an elongation of 9% has been obtained after 20% deformation at −196 °C (20LND), whereas 40% deformation at 0 °C (40ZCD) results into a tensile strength of 1225 MPa with 13% elongation. Annealing of 40ZCD and 20LND specimens at 300 °C results in significant improvement in tensile strength, while annealing at 725 °C increases the elongation with a decrease in tensile strength. During reversion annealing, strain induced martensite transforms to austenite through shear and diffusional processes. However, the reversion is essentially diffusional in nature at a higher temperature. [ABSTRACT FROM AUTHOR]

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]

Abstract: Surface hardening of low carbon hot rolled C–Mn steel has been successfully performed by high power diode laser with an achievable case depth of about 300μm. The laser treated samples have been characterised using optical microscope, scanning electron microscope, transmission electron microscope, and X-ray diffraction techniques. Higher hardness level is achieved in laser surface hardened zone (≈300HV) than in the base alloy region (≈140HV). The variation in hardness as a function of distance across the laser tracks is observed during multi-track laser hardening. Laser hardened steel sheets show enhanced mechanical strength (YS: 383–443MPa, UTS: 476–506MPa) with the lowering of percentage total elongation (23–28%) compared to the base alloy (YS: 351MPa, UTS: 450MPa and total elongation is 32%). Strain hardening exponent (‘n’) has been evaluated from true tensile stress–strain diagram and it shows a similar nature for both base alloy and laser treated steels. The microstructure in the base alloy region consists of a mixture of ferrite and pearlite, whereas predominantly lath martensite is present in the laser hardened surface layer. The improvement of mechanical strength is discussed in terms of the formation of this hardened layer on the surface. [Copyright &y& Elsevier]

Two C-Mn-Si steels with and without Nb micro-alloying are selected in the present study. Both these high carbon steels have been thermo-mechanically processed using Gleeble 3800 simulator. Optical microscope (OM), scanning electron microscope (SEM), transmission electron microscope (TEM), atomic force microscope (AFM) were utilised for microstructural characterisation. The austenitising temperature was varied from 1150 °C to 1200 °C followed by hot compression and subjected to free cooling to evaluate the influence of austenite grain size on transformed microstructure and mechanical properties. It is evident that higher austenite grain size is obtained for both types of steels subjected to higher austenitising temperature. The refinement of pearlite interlamellar spacing (<0.20 μm) with degenerated morphology as well as finer prior austenite grain size (<40 μm) is found to be more prominent for Nb micro-alloyed sample. The average hardness values of both the steels are higher for the specimens, treated at a higher austenitising temperature which is attributed to finer interlamellar spacing. Finally, the correlation between the evolving microstructure and resulting mechanical properties (hardness and yield strength) has been made. [ABSTRACT FROM AUTHOR]