Applications for plasma transferred arc welded tools during hot steel tube making

Abstract

This paper describes applications of a tool reinforcement technology, using plasma transferred arc (PTA) welding, in hot metal rolling. The coating of large NbC particles shows a remarkable performance in the suppression of galling. As the rolling temperature increases, a matrix material with high temperature resistance to deformation is recommended. The tool life is slightly longer when a thick scale layer exists on the hot metal surface, but when the scale is eliminated the new tool demonstrates excellent capability. The new tool also shows a higher level of performance when rolling hot titanium and hot stainless steel. The application philosophy of PTA welded tools is demonstrated.     

Reduction swelling behaviour of haematite/magnetite agglomerates with addition of MgO and CaO

Abstract

The influence of three kinds of CaO and MgO additives (dolomite, burnt lime and serpentine) on the reduction swelling behaviour of haematite–magnetite (H–M) concentrates pellets was studied. Burnt lime and dolomite increased the reduction swelling index of H–M oxidised pellets, while the reduction swelling index was able to be reduced when serpentine was added. CaO accelerated the formation and growth of metallic iron whiskers and led to abnormal swelling of the magnetite briquettes, while MgO was able to be dissolved in wüstite and reduced the migration rate of Fe²⁺; therefore, there was no catastrophic swelling in either the haematite or magnetite briquettes. As far as H–M concentrate pellets were concerned, because the solubility of CaO in magnetite was greater than that in the primary haematite and the secondary haematite generated from magnetite during the oxidation was easy to be reduced to wüstite, there was abnormal swelling in the reduced H–M pellets with CaO addition.