High-temperature toughness of structural steels

Overview

It is well known that ordinary or unalloyed structural steels can fail brittlely at low temperatures. By contrast, it is assumed that these steels fail ductilely at room temperature – the so-called ‘high-temperature range’ – meaning that failure does not occur without warning. However, the latest findings show that the assumption of ductile failure does not always hold true for the structural steels used in building construction. Damage has been observed in steel structures that could be attributed to non-ductile failure of structural steels at room temperature. Furthermore, it was found that the product standards for unalloyed structural steels define limit values for notched impact energy which are insufficient to ensure ductile failure in the high-temperature range. Against this background, when the technical guidelines for steel construction were revised, the minimum required notched impact energy for steel structures subjected to dynamic loads was significantly increased, as this is the only way to fulfil the fundamental principles of the design of steel structures. As a result of this change, the structural steels used to date may no longer be used; instead, only high-alloy thermomechanically rolled or normalised structural steels may be used in future. Their production and the alloying elements required for this process must be regarded as highly problematic from both an economic and an environmental perspective. For steel suppliers, the change to the standard means that existing product and process chains cannot be maintained and that certain established structural steels are no longer permitted. It is noteworthy that the change to the standard has been implemented without any freely accessible scientific studies. The planned project will therefore experimentally investigate the influence of temperature on the toughness of two commercially available, unalloyed structural steels. The results will be incorporated into existing numerical calculation models and will enable the findings to be applied to other structural steel grades and types.