SURFACE RING COARSE GRAIN STRUCTURE AND CONTROL MEASURES OF ULTRA-LOW CARBON STEEL HOT-ROLLED WIRE ROD
The causes of surface ring coarse grain structure of hot-rolled low carbon steel wire rod were analyzed.The ring depth of coarse grain structure reached about 1 000 μm and the grain size reached 60～ 80 μm on the wire rod surface evenly,no specific orientation abnormal grain growth characteristics.Through the annealing simulation analysis,a hereditary surface ring coarse grain structure was found which would seriously deteriorate the plastic properties.Based on the theoretical analysis and experiment,the main cause of ring coarse grain was that the pre-finishing intensity was too large,the temperature was lower than the dynamic phase transition temperature,lots of energy stored in the wire rod surface grain,which promoted the ferrite phase transformation and the specific orientation of the grain growth,eventually forming the coarse grain structure.By adjusting the water-cooled pre-finishing process,the finishing temperature controlled at above 920 ℃ on the ultra-low carbon steel wire rods,which could significantly reduce the occurrence of coarse grain structure.
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