The effect of steel strip on the quality of cold-formed hollow sections

摘要

The quality of steel strip is essential for tube quality. Conventional C-Mn steels are commonlyrnused for hollow sections. These steels are susceptible to strain ageing, thus questioning their lowrntemperature ductility in welded structures. To ensure good low temperature characteristics Ruukki shiftedrnto thermomechanically-rolled steels. This study compares hollow sections from the early 1990s with currentrnRuukki hollow sections made of thermomechanically-rolled fine grain steels. Ageing is noticeable in conventionalrnS355J2H hollow sections. In cold-formed areas, flat faces and in corners there is a risk that the toughnessrndoes not fulfill 27 J/−20℃ after welding. Ageing in Ruukki double grade S420MH/S355J2H hollow sections isrnstill noticeable, but virtually insignificant. After ageing, the transition temperature T40J remains around −70℃rnon the wide face, around −50℃ in corners and around −40℃ on the narrow face. There is only minor risk ofrntoughness not conforming to the EN 10219 requirement of 40 J/−20℃ after welding.