Deformation Behavior and Plastic Instability of Ultra-High Strength Low Alloy Steel over Wide Temperature and Velocity Range

Ultra-high strength low alloy (UHSLA) steels are one of pivotal materials used in industrial sector. Its diversified compositions and characteristic mechanical properties as per service requirement have created an inevitable place for this steel class. The current study has been carried out on the deformation behavior and plastic instability of newly developed (UHSLA steel) XF1700 over a wide temperature range T_r to near T_m (298-1673 K) and at quasi-static (0.01-1/s) as well as dynamic (10-10⁴/s) conditions. Such a wide range of data were obtained by utilizing chemical composition of this alloy system in JMatPro (an efficient software based on CALPHAD module). The effect of temperature with increasing strain and strain rate has been quantified in terms of a four-parameter exponential model based on two Z (Zener–Hollomon) parameters Z_m and Z_n, as such to predict cold, warm and hot deformation mechanism by a subsection method. The novelty of this work lies in its simple mathematical model that can describe the deformation behavior of a material for temperature range T_r to near T_m, considering the temperature compensated strain and strain rate factors. EBSD analysis was carried out for microstructural analysis to support the deformation behavior and plastic instability mechanism. Based on four-parameter exponential model, the deformation stability criteria have also been elucidated for all the three zones: Zone I, cold forming zone (298-673 K); Zone II, warm forming zone (673 < T ≤ 973 K) and Zone III, hot forming zone (973 < T ≤ 1673 K). Through non-linear regression model in SPSS software, material parameters describing deformation behavior and plastic instability were segregated in parts and the four-parameter exponential model has been verified which is found to be in excellent agreement with available data. The AARE obtained was 2.03% (zone I), 7.17% (zone II) and 4.07% (zone III), respectively, while the overall AARE was 4.42%. Graphical abstract: (Figure presented.).