冷却速度对含铌、钛微合金钢铸坯表层组织结构的影响

铸坯出结晶器后的冷却速度是影响和决定铸坯表层组织结构(0~5 mm)及第2相析出物分布的关键因素.在开发重熔凝固冷却实验装置的基础上,模拟铸坯在垂直段的凝固冷却条件,研究不同冷却速度对铸坯表层组织与第2相析出物分布的影响.研究表明,在0.8 m·min^-1拉速下,以5℃.s-1的冷却速度,使铸坯在出结晶器后表面温度下降到A₃温度以下,得到的表层组织均匀,晶界无膜状先共析铁素体,微合金元素析出物在晶内分布均匀,有利于提高铸坯热塑性及降低裂纹敏感性.

Effect of cooling rate on the slab surface microstructure of microalloyed steel containing Nb and Ti

Cooling rate is a key factor which affects the surface(0 to 5 mm) microstructure of a slab and the distribution of the second phase precipitates after the slab leaves the mould.In order to simulate the thermal cycle when a slab is drawn to the vertical segment,a remelting and solidification cooling experimental device was designed.The influences of cooling rate on the surface microstructure of a slab and the distribution of the second phase precipitates were investigated.It is shown that when the slab is drawninto the vertical segment at a speed of 0.8 m· min^-1 and the slab surface is cooled to less than the A₃ transformation temperature by intensive cooling at a cooling rate of 5℃·s^-1, the surface microstructure of the slab is uniform, the second phase precipitates containing Nb and Ti are well-distributed, and film-like proeutectoid ferrite does not precipitate along the austenite grain boundaries. These help to improve the hot ductility and to alleviate the cracking susceptibility of the slab.