Dipti Samantaray

Assessing Constitutive Models for Prediction of High-Temperature Flow Behavior with a Perspective of Alloy Development

The utility of different constitutive models describing high-temperature flow behavior has been evaluated from the perspective of alloy development. Strain compensated Arrhenius model, modified Johnson–Cook (MJC) model, model D8A and artificial neural network (ANN) have been used to describe flow behavior of different model alloys. These alloys are four grades of SS 316LN with different nitrogen contents ranging from 0.07 to 0.22%. Grades with 0.07%N and 0.22%N have been used to determine suitable material constants of the constitutive equations and also to train the ANN model. While the ANN model has been developed with chemical composition as a direct input, the MJC and D8A models have been amended to incorporate the effect of nitrogen content on flow behavior. The prediction capabilities of all models have been validated using the experimental data obtained from grades containing 0.11%N and 0.14%N. The comparative analysis demonstrates that ‘N-amended D8A’ and ‘N-amended MJC’ are preferable to the ANN model for predicting flow behavior of different grades of 316LN. The work provides detailed insights into the usual statistical error analysis technique and frames five additional criteria which must be considered when a model is analyzed from the perspective of alloy development.

Hot Deformation and Microstructural Characteristics of Nitrogen Enhanced 316L Stainless Steel

Dynamic recrystallization (DRX) in 316LN austenitic stainless steel with 0.14wt% nitrogen has been studied using hot isothermal compression tests carried out in temperature range 1073-1423K and strain rate range 0.001 - 10 s-1. Critical strain and stress for DRX has been characterized using experimental data. Analysis of results shows that for the entire domain the critical stress is directly proportional to peak stress. However, no clear relationship between εc and εp prevails over the entire tested domain. Dynamic Recrystallized (DRX) grains are quantified by GOS and KAM maps. The four stages of DRX progression have been identified using the correlation between GOS and critical strain at different deformation conditions.

Microstructure Mapping: An Approach to Quantitative Interpretation of Microstructural Evolution in Indian Fast Reactor Advanced Clad Material during Hot Forging

In this paper, microstructural evolution of Indian Fast Reactor Advanced Clad (IFAC-1) steel during thermo-mechanical processing has been investigated. Hot isothermal forging has been simulated in a Gleeble® thermo-mechanical simulator in the temperature range 1173-1473K and true strain rate range 0.01-100s-1. Instability map has been developed using the stress-strain data obtained. Effect of major forging parameters on various microstructural features has been studied quantitatively. Results from this study have been used to construct various maps (‘μ-maps’) representing different aspects of microstructural evolution. An analogy between the μ-maps and instability maps provides essential insights into possible instability mechanisms operative in the material. The μ-map analysis shows potential as a tool for optimisation of industrial-scale forging parameters.

Thermally activated deformation of a high-nitrogen grade 316LN stainless steel under compressive loading

In this paper, the deformation behaviour of a high-nitrogen grade 316LN stainless steel (with 0.14%N) has been studied over a wide range of temperatures (1123-1423K) and strain rates (0.001-10 s-1). The key deformation controlling mechanisms have been investigated using thermal activation parameters, such as activation volume and activation enthalpy. The chromium nitride precipitates, dislocation intersections, both conservative and recovery, are found to be the key deformation controlling mechanism at different temperature–strain-rate domain during hot deformation of this material.

Atypical transitions in material response during constant strain rate, hot deformation of austenitic steel

Work hardening, dynamic recovery and dynamic recrystallization (DRX) occurring during hot working of austenitic steel have been extensively studied. Various empirical models describe the nature and effects of these phenomena in a typical framework. However, the typical model is sometimes violated following atypical transitions in deformation mechanisms of the material. To ascertain the nature of these atypical transitions, researchers have intentionally introduced discontinuities in the deformation process, such as interrupting the deformation as in multi-step rolling and abruptly changing the rate of deformation.In this work, we demonstrate that atypical transitions are possible even in conventional single-step, constant strain rate deformation of austenitic steel. Towards this aim, isothermal, constant true strain rate deformation of austenitic steel has been carried out in a temperature range of 1173–1473 K and strain rate range of 0.01–100 s−1. The microstructural response corresponding to each deform...

Characterization of Hot Workability of Boron-Added Modified 9Cr-1Mo Steel (P91B) Using Dynamic Materials Model

Elevated temperature workability of Boron added modified 9Cr-1Mo steel is studied in temperature range 1223-1473K and strain rates of 0.001-10s-1 using Dynamic Materials Model. Towards this end hot isothermal compression tests are carried out and the experimental results are used to obtain processing map. Extensive microstructural investigation is carried out to validate different domains of processing map. On the basis of the microstructurally validated processing map, parameters for the thermomechanical processing of P91B are recommended.