Analysis of the Thermomechanical Flow Behavior of Carburized Sheet Metal in Hot Stamping

The reduction of fuel consumption due to restrictions regarding CO₂ emissions is one of the major driving forces for lightweight design in the automotive industry. In this context, hot stamping of ultra-high-strength steels has developed to a state of the art process for manufacturing safety-relevant components. With regard to passenger safety and weight reduction, further potential lies in the functional optimization of the parts. Prior local carburization followed by hot-stamping is a new process variant for tailored properties, which overcomes the limitations of established processes. Due to the varying carbon content after carburization, the sheets have graded mechanical properties. Within this contribution, the influence of temperature, strain rate and carburization on the flow behavior will be investigated. For this purpose, tensile tests at elevated temperatures are carried out in a physical simulator of type Gleeble. The resulting flow curves of the carburized complex phase steel are modeled with a modified Norton-Hoff hardening law and the influence of the carburization process is analyzed by means of the initial yield stress. Furthermore, the results from tensile tests are correlated with the phase transformation behavior obtained by a laser ultrasonic sensor.