Calibration of the Johnson–Cook model at high temperatures for an Ultra-High Strength CrNiMoV Steel

Abstract

This paper presents a study on the thermo-mechanical behavior of an ultra-high strength CrNiMoV steel at high temperatures and medium strain rates through hot tensile tests. The material was examined in two conditions: as-cast/heat-treated (AC/HT) and as-rolled (AR). Tensile tests were conducted at temperatures of 800,900,1000,1100, and 1200°C, and strain rates of 0.1,1, and 10s−1. Inclusion and porosity analysis was also performed on the tensile specimens. The results revealed that the flow stress decreased by approximately 70% on average from 800°C to 1200°C, while increasing by approximately 32% on average from 0.1s−1 to 10s−1 in strain rate. The elongation exhibited an increase from 16.5% at 800°C to 33% at 1200°C. However, the ductility transition was slower than expected, particularly for the AC/HT conditions. The AC/HT samples exhibited higher levels of inclusions and porosity compared to the AR samples, with porosity significantly affecting the elongation to failure and ultimate tensile strength (UTS) at a strain rate of 1s−1. Furthermore, calibrated Johnson–Cook parameters were reported and compared, demonstrating excellent agreement between predicted and experimental values with less than 20% variation. The calibrated Johnson–Cook model can be effectively employed for modeling purposes within the studied temperature range, and its application can even be extrapolated for higher strain rates.