冷却速率对薄带连铸低碳钢微观组织的影响

摘要：为了探究冷却速率对薄带连铸低碳钢微观组织的影响，采用相变仪设备对铸带重新加热并进行不同冷却速率冷却，采用光学显微镜、场发射电子探针和电子背散射衍射等手段对微观组织和针状铁素体形核所利用的夹杂物进行了分析。结果表明，铸带经1200℃保温3min后，原奥氏体晶粒尺寸约为150～650μm，可以满足晶内针状铁素体形核对原奥氏体晶粒尺寸的需要。在2～5℃/s的冷却速率范围内，试样中得到了大量的针状铁素体组织，冷却速率为2℃/s的试样中大角度晶界所占比例约为60%；当冷却速率大于20℃/s，针状铁素体的形成受到抑制。铸带中针状铁素体形核所利用的夹杂物是Ti-Al-Si-Mn-O+MnS复合夹杂物。

Effect of cooling rate on microstructure of low-carbon steel produced by strip casting

In order to explore the effect of cooling rate on the microstructure of low carbon steel produced by strip casting， the reheating and continuous cooling process of the as cast strip was simulated using a dilatometer， and the microstructures and inclusions providing nucleation site for acicular ferrite were investigated by OM，EPMA and EBSD. The results showed that the prior austenite grain size of the as cast strip reheated at 1200℃ for 3min was in the range of 150-650μm， which can satisfy the requirements for the nucleation of acicular ferrite. When the cooling rate was in the range of 2-5℃/s， a large amount of acicular ferrite was formed. The high angle boundary proportion was about 60% when the cooling rate was 2℃/s. The formation of acicular ferrite was inhibited when the cooling rate was up to 20℃/s. Composite inclusions of Ti-Al-Si-Mn-O+MnS could be as nucleation sites for acicular ferrite formation.