DEVELOPMENT OF PROCESSING MAPS BY PHYSICAL SIMULATION OF LOW ALLOY MEDIUM CARBON STEEL

Abstract

There is leading applications and importance of steels continue in many critical areas even when the availability of ceramics, polymers, composites etc. with improved properties exists. “Nothing can replace a steel, only a steel having better property can replace the existing steel”. Low alloy medium carbon steel have very wide applications in automobile parts, railway rails, wheels, shafts, high tensile tubing, high tensile fasteners, pins, gear, connecting rods, crankshafts and many more. To produce quality products at low cost, new approach should be employed to optimize the processing parameters. Thermo-mechanical processing (TMP) is a technique that can control the hot deformation processing parameters (strain, deformation temperature and strain rate), due to which mechanical properties of material enhanced. In this study, the hot deformation behavior of low alloy medium carbon steel is studied by hot compression tests on Gleeble® 3800 thermo-mechanical simulator. The tests were carried out in temperature ranging from 800ºC to 1050ºC and strain rate from 0.01 s-1 to 10 s-1 for total true strain of 0.7 after austenitization at 1100ºC for 2 min. To model the flow behavior of this steel, constitutive analysis were done for calculation of Zener-Hollomon parameter and prediction of flow stress. For parameter optimization of forging and determining a safe working domain, processing maps were developed based on different materials models namely dynamic materials model (DMM), modified DMM and Poletti instability criteria. The microstructure of the deformed and water quenched specimens are obtained by light optical microscopy. The stable and instability domains of the processing map are correlated with the evolved microstructure. The flow behavior in a processing domain is also correlated with its power dissipation efficiency and values of strain rate sensitivity and Z-parameter. The deformation mechanisms are identified based on stress exponent value and further verified by micrographs.