连铸板坯快冷试验分析Q345D包晶钢板坯角部横裂成因和工艺改进

Analysis on Formation of Transverse Corner Cracks of Slab of Peritectic Steel Q345D by Slab Quenching Test and Process Improvement

通过对220 mm包晶钢板坯进行在线快冷试验,取冷却后板坯角部样,进行热酸浸及金相分析。从零段到矫直段的角样结果表明,角部横裂纹在矫直段内弧出现,随着板坯从结晶器往后延伸,奥氏体晶界的铁素体膜不断增厚,晶界越清晰,奥氏体晶粒度尺寸1.0~1.5 mm。由于奥氏体晶粒粗大,并且奥氏体晶界铁素体膜脆弱,矫直段铸坯角部温度偏低,进入第Ⅲ脆性区后,导致角部横裂沿着晶界展开。通过结晶器窄面水量由原30~32 m^3/h增加至34~36 m^3/h,关闭矫直段内弧边部喷嘴,使板坯角部横裂得到有效控制。

220 mm steel blocks were cut at the edge of quenching testing slab of peritectic steel from curving section to straightening section,and then its surface quality and microstructure is anlysized.The result shows that transverse comer cracks appear at straightening section.With the extending of strand from curving section to straightening section,ferrite film at grain boundary of austenite become thicker and clear,and the grain size of austenite is in the range of 1.0 mm to 1.5 mm.Owing to the coarse grain of austenite and thick fragile ferrite film,transverse corner cracks spread along the grain boundary of austenite.With increasing cooling water in single narrow side of mould from original 30~32 m^3/h to 34~36 m^3/h,and shut the side sprayer of inner arc of straightening sections,transverse corner cracks slab is effectively controlled.