Calcium treatment modification of inclusions in pipeline steel and its continuous casting slabs
The calcium treatment technology is widely used in the production of pipeline steel.The effect of calcium treatment degree on the modification of non-metallic inclusions in the molten steel and continuous casting slab was studied.It is indicated that as the mass fraction of TCa in the molten steel increases from 0.000 5%to 0.002 0%,the average composition of non-metallic inclusions in the steel initially approaches the liquid phase region and then a-way from it.Moreover,the mass fraction of Al2O3 inclusions in the steel decreases from 68.14%to 48.89%,while the mass fraction of CaO inclusions increases from 21.8%to 27.8%.The average size of non-metallic inclusions in the continuous casting slab decreases from 4.02 μm to 3.83 μm,and the number density of non-metallic inclusions reaches a minimum value of 6.61/mm2 when the mass fraction of TCa in the steel is 0.002 0%.Thermodynamic calculations were performed by Factsage to investigate the transformation of inclusions during the solidification process.It is showed that the mass fraction of MnS in the continuous casting slab of pipeline steel decreases from 10.65%to 4.84%as the calcium content in the molten steel increases.Additionally,the precipitation temperature of MnS inclusions decreases from 1 340 ℃ to 1 220 ℃.The results obtained from thermochemical calculations are consistent with those from industrial experiments.