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

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 & DEG;C, and strain rates of 0.1,1, and 10 s-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 & DEG;C to 1200 & DEG;C, while increasing by approximately 32% on average from 0.1 s-1 to 10 s-1 in strain rate. The elongation exhibited an increase from 16.5% at 800 & DEG;C to 33% at 1200 & DEG;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 1 s-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.

Automated summary

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 results show that the flow stress decreases with increasing temperature and increases with increasing strain rate. The inclusion and porosity levels affect the elongation and ultimate tensile strength of the steel.