双辊薄带连铸低碳微合金钢的铸态组织

采用双辊薄带连铸技术制备了低碳微合金钢薄带,利用OM,SEM和TEM对铸态凝固组织、室温组织、析出及位错进行观察和分析.结果表明:低碳微合金钢铸带的凝固组织中二次枝晶间距约为12~15μm,相对于传统厚板坯和薄板坯连铸,铸带组织得到了明显细化.铸带的原奥氏体晶粒尺寸比较粗大,约为250~410μm,其组织由魏氏铁素体、珠光体和不规则铁素体组成.铸带组织中存在纳米级TiC析出和短棒状的渗碳体.TiC析出没有被薄带连铸的凝固过程及二次冷却过程明显抑制.铸带组织由于铸轧力及二次冷却速率不均匀导致大量位错的产生.

As-Cast Microstructures of Low-Carbon Microalloyed Steel Produced by Twin-Roll Strip Casting

Low-carbon microalloyed steel was produced via twin-roll strip casting in the laboratory. The solidification structure, microstructure at room temperature, precipitate and dislocation of the as-cast strip were analyzed by OM, SEM and TEM. The results showed that the secondary dendrite arm spacing of the solidification structure is in the range of 12~15μm, which is much finer than that of the slab produced by the traditional process. The prior austenite grain of the as-cast strip is quite coarse with a size range of 250~410μm. The microstructure of the as-cast strip consists of Widmanstatten ferrite, pearlite and irregular ferrite. The nano-sized TiC precipitate and rod-like cementite are observed in the as-cast structure. The TiC precipitate in the as-cast strip is not obviously suppressed by the rapid solidification rate and secondary cooling rate (cooling in air) of the twin-roll strip casting. Furthermore, a large amount of dislocations in the as-cast strip are also observed, formed by rolling force among the casting rollers and nonuniform cooling rate of the second cooling process.