The Influence Of Phosphorous On Phase Transformation And Microstructure In Strip Casting Weathering Steel

Twin roll strip casting (TRSC) process is an advanced technology in the field of metallurgy and materials. By using the TRSC technology, the harmful effects of impurity elements (P, S) are thought to be prevented to some extent due to high cooling rate during the solidification. The research about the effects of phosphorous on weathering steel of strip casting will have important significance, especially for the use of scraps and the development of new steel grades.In the present paper, the effects of phosphorous and cooling rate on theδâ†'γphase transformation and microstructure in weathering steel were studied by means of Thermo-calc, Optical Microscope, Differebtial Scanning Calorimetry, Confocal Laser Scanning Microscope (CLSM), Auger Electron Spectroscopy. The experimental results show that:Phosphorous is shown to decrease the finishing and starting temperatures of theδâ†'γtransformation. With the increasing P content, the transformation process was greatly retarded.Based on the CLSM observation, someδwere retained to a lower temperature, even some retainedδis kept until theγ/a phase transformation in steel containing high phosphorus. The retainedδphase could retard theγgrain growth and theγgrains could be refined.The microstructuresof the casting strips are largely different from that of the continuously cast slabs.Irregular polygonal ferrites, Widmanstatten ferrites and Acicular ferrites are observed in casting strips. The Phosphorous addition changes the a-grain structure dramatically. With the increasing P content and cooling rate, there will be more Acular ferrite appeared.The results of the AES show that the Phosphorous exists in the form of solid solution in steel. In the samples containing more than 0.07 mass% P, the Phosphorous contents near surface region are higher than that in the centre through the thickness of the strips.