Abstract
Today’s manufacturing of structural car body parts faces several challenges, like forming accuracy and passenger safety. Besides these two requirements, lightweight design plays an important role. One possibility to fulfill these partially rivalling demands is the application of hot stamped parts. The combination of hot forming and in die quenching reduces not only springback, but also results in tensile strengths of up to 1500 MPa. This makes a simultaneous reduction of sheet thickness and therefore weight reduction possible. Further development enabled a tailored adjustment of mechanical properties, for example by applying different cooling conditions along the parts. One of the biggest issues of these state of the art processes is the formation of a transition zone due to heat transfer. A promising approach to adjust the mechanical properties with a minimized transition zone is the carburization of sheet metal. Therefore, the parts are coated with graphite, heat treated and subsequently quenched. In this work, the time variant process of carbon diffusion is investigated. Sheets with two different thicknesses are carburized and quenched. The resulting mechanical properties are analyzed using uniaxial tensile tests and microhardness measurements. The results are correlated with the carbon content measured by EDX-analysis.
Highlights
Ecological aspects as well as increasing safety standards are two reasons for growing importance of lightweight construction in automotive industries [1]
A promising approach to adjust the mechanical properties with a minimized transition zone is the carburization of sheet metal
Aim of this work is to investigate the influence of sheet thickness and several heat treatment parameters on mechanical properties, such as tensile strength or Vickers hardness and carbon content after carburization
Summary
Ecological aspects as well as increasing safety standards are two reasons for growing importance of lightweight construction in automotive industries [1]. By preventing a full austenitization of particular areas, or decreasing the heat transfer between tool and sheet below the critical value, it is possible to retain the original ferritic-pearlitic microstructure besides the martensitic structure [9] One challenge of these state of the art process variants is the formation of a transition zone due to heat transfer between areas of different temperatures. Aim of this work is to investigate the influence of sheet thickness and several heat treatment parameters on mechanical properties, such as tensile strength or Vickers hardness and carbon content after carburization. Depending on these influencing factors, a process window for carburization of sheet metal will be identified. The applicability of energydispersive X-ray spectroscopy to the analysis of carbon content is investigated
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