SD40 Reinforcing ribbed steel | C=0.25%

The production was carried out as a continuous casting ingot of approx. 150×150 mm, which was then directly rolled. From the rolling heat, the edge zone is quenched. The residual heat of the core, which is still present, re-tempers the hardened edge zone. Some profiles show longitudinal cracks; however, the specified minimum strength of 400 MPa is always safely achieved. In addition to a crack, the unetched images show a (further) non-metallic inclusion line. By means of EDS analysis, these were identified as iron oxide and aluminum (Mg) oxide. Due to the round shape, rolled-in scale is excluded. The cause of the cracks is therefore the steel mill and not the rolling mill.