O.N. Mohanty

Understanding the complexities of bake hardening

Abstract The basic science behind bake hardening steels is well understood in terms of the interactions between interstitial solutes and dislocations. However, the manufacture of such alloys involves a variety of other variables, the interactions between which are influential in controlling the extent of hardening. In the present work, a model which includes the chemical composition of the steel, the strain before aging and the annealing and aging conditions is developed and used to explore certain anomalies in the published literature. It is found that whereas the roles of deformation and aging can be rationalised, the generic effect of niobium is associated with large uncertainties and warrants further experimental work.

Strain induced transformation of retained austenite in TRIP aided steels: a neural network model

Abstract A neural network model has been developed to predict the strain induced transformation behaviour of retained austenite in transformation induced plasticity aided steels, as a function of the driving force for martensitic transformation, initial retained austenite content, matrix microstructure and forming conditions. The model was found to make realistic predictions that generally agree with established metallurgical principles and other published data.

Aging response and strength formability parameters of hot rolled copper alloyed interstitial free steel

Abstract Laboratory investigations have been carried out on a copper alloyed interstitial free steel to develop a high strength steel for automotive applications in hot rolled conditions. The aging characteristics for a wide range of temperature and time have been documented and discussed in terms of diffusivity and solubility of copper in α iron. Coiling temperature, in general, influences the strength formability parameters of the hot rolled steel owing to its effect on copper precipitation. A high strength hot rolled steel for automotives with high strain hardening rate can be developed by adopting low temperature coiling at 550°C, without using any additional step in the normal processing schedule of interstitial free steels. Deep drawability or the Lankford parameter appears not to be influenced much by the coiling temperature.

Characteristics of forming limit diagram of copper alloyed interstitial free steel

Abstract Forming limit diagram of a promising high strength copper alloyed interstitial free steel has been determined by Nakazima tests under various processing conditions. Various parameters such as limiting strain, shear strain and strain ratio have been derived from the diagrams and analysed. The results have been compared with those of two traditional high strength interstitial free steels. It is observed that the formability parameters of copper alloyed interstitial free steel are lower than those of high strength interstitial free steels due to the effect of copper. Copper alloyed interstitial free steel in continuous annealed condition exhibits the highest limiting strain values among all the processing conditions and is comparable to traditional high strength interstitial free steels.