Anjana Deva

Assessment of Formability of Hot-Rolled Steel through Determination of Hole-Expansion Ratio

Hole expansion ratio has been designed in recent past to characterize formability/stretch flangeability of hot-rolled high-strength steel. Various factors influencing the determination of hole-expansion ratio has been discussed. Parameters such as yield strength, ultimate tensile strength, elongation, carbon equivalent have been correlated with the hole-expansion ratio of various grades of hot-rolled steel. It is found that the ultimate tensile strength of steel is the most important criterion that correlates with hole expansion ratio provided the strengthening mechanism in the steel is the same.

Strain Hardening Behavior and Cold Reducibility of Boron-added Low-carbon Steel

Addition of boron in low carbon (0.06% max) hot rolled steel has improved its formability. A unique combination of properties with low strain hardening exponent (n) and high total elongation has resulted into higher percentage of cold reducibility of hot rolled coils.

Optimization of Annealing Parameters for Improvement in Formability of Extra Deep Drawing Quality Steel

A number of annealing cycles were investigated in an attempt to find the optimum cycle that results in an attractive combination of mechanical and formability properties of an extra deep drawing (EDD) quality steel. It was found that the cycle that involved an intermediate anneal at 600 °C followed by further soaking at 700 °C resulted in the best combination of mechanical and formability properties. It was also found that the rate of heating up to 600 °C can be kept at 50 °C/h while the heating has to be done at a rate of 30 °C/h from 600 °C to the final annealing temperature of 700 °C. The desirable combination of mechanical and formability properties has been correlated with the microstructure that shows pancaking of the annealed grains accompanied by precipitation of carbides. Precipitates of carbides are more in number and smaller in size in the case of samples annealed by the cycle mentioned above compared to the ones annealed by other cycles. They are spherical in shape, which is desirable for forming applications.

Microstructural Control in Aluminium-Killed Low C-Mn Boron Containing Steel for Improved Formability and Cold Reducing Properties

Microstructural control through thermo-mechanical simulation has been attempted in aluminum-killed low carbon-manganese boron containing steel. The results from dilatometric studies were used to explain austenite decomposition characteristics under different soaking temperatures and cooling rates. A significant lowering in Ar3 temperature was observed when the steel was soaked at 1200°C followed by rapid cooling (20°C/sec). On the contrary, no appreciable change in Ar3 temperature was noticed when soaking temperature was brought down to 950°C. Hot rolling simulations were carried out both in austenitic and ferritic regions to understand microstructural evolution. Ferritic hot rolling at 750°C followed by coiling at 650°C exhibited formation of coarse recrystallized ferrite grains of 30 micron, which is ideally suited for cold forming and reducing applications.

Microstructural Evolution in Boron-Added Advanced High-Strength Steel Suitable for Hot Stamping

Fuel cost, dwindling resources, and exponentially increasing traffic density have brought about a sea change in thinking of automotive designers, manufacturers, and end users. Though number of recently developed advanced high-strength steels fulfill the expectation of automobile component manufacturers in terms of weight reduction and safety norms, it suffers the inherent problem of spring back phenomena and limited formability. This problem can be addressed if the component is formed at high temperature where it has adequate formability and subsequently it is controlled cooled to get the desired combination of strength and ductility; the process is commonly known as hot stamping. As C (0.2–0.3 wt%)- Mn (1.2–1.3%)- Cr (0.1–0.2 wt%)- B (25–35 ppm) alloyed steels have been the point of focus for the choice of materials in hot stamping, study has been carried out on effect of concurrent deformation and cooling on hardening behavior and associated microstructural changes of C–Mn–Cr–B steel. Further, effect of molybdenum (~0.1 wt%) in influencing the microstructure and thereby hardening in conventional C–Mn–Cr–B steels has also been evaluated. The present study reveals that a range of tailored properties can be achieved through locally controlling strain, strain rate, cooling rate, and resultant microstructure within the stamping die.