PITA Fiscal Year 2008 Projects - Product and Process Design and Optimization

Decreasing Hot Shortness and Increasing Recycling of Steel

Principal Investigators: Sridhar Seetharaman, Richard J. Fruehan

Copper is a problem in steel scrap because it leads to a cracking defect known as hot shortness. Good surface quality is obviously an important requirement and this causes in a large amount of scrap being downgraded as low grade scrap. At the present time, in EAF operations producing higher quality products where copper and other elements must be controlled, up to 40% of the scrap charge must be replaced with virgin iron units such as pig iron or hot briquetted iron. This undermines many of the inherent energy and materials efficiencies of EAF steelmaking and adds significant cost to this process route. Furthermore, in the near future, the result of tramp element accumulation in the scrap supply may make it impossible to recycle much of the scrap supply via technologies available today.

The central hypothesis to be tested in this work is whether processing conditions can be tailored to control oxidation and micro-structural evolution in such a way that the amount of grain boundary penetrated Cu is decreased whereas the Cu occluded into the oxide phase is increased and thereby the occurrence of hot shortness cracking defects is avoided. Process conditions refer in this case to (i) the temperature and gas atmosphere variation with time for the two processes (DHC and conventional reheating) and (ii) the near surface microstructure after casting in the case of DHC. The approach is to perform high temperature oxidations and subsequently characterize the samples. If we can tolerate higher copper contents we can upgrade the scrap currently denoted as low grade scrap.