利用金相观察、扫描电镜及能谱分析和透射电镜等手段,对热装热轧微合金钢板出现的表面裂纹进行分析研究,并与使用同批次连铸坯冷装热轧无裂纹的钢板进行比较,分析产生表面裂纹的原因。试验结果表明热装热轧微合金钢板产生表面裂纹的原因是铸坯冷却或加热过程中Cu、As低熔点元素在奥氏体晶界的偏聚。与热装热轧板相比,冷装热轧板晶粒尺寸小,直径在10μm左右,而热装热轧板晶粒尺寸大且不均匀。热轧板析出物尺寸在15～25nm之间,裂纹源处较基体多,大量细小的Nb（C,N）化合物在奥氏体晶界析出,降低了晶界强度。
In order to find out the cause of surface cracks for the same batches slab,surface crack on micro-alloyed steel plate produced by direct hot charging process was investigated by means of metallographic analysis,scanning electron microscopy,energy spectrometer analysis and transmission electron microscopy,and compared with crack-free plate produced by cool charging process.The results show that the main factors of surface crack on micro-alloyed steel plate produced by direct hot charging process are the segregation of low melting point elements such as Cu,As in slab＇s cooling or heating process.Compared with hot-rolled plates produced by hot charging,the grain size of cold charged rolled plate about 10 μm in diameter,while the grain size of hot-rolled plates by hot charging are large and uneven.Precipitates of hot plate are between 15-25 nm in size,the crack source are more than the matrix and a large amount of fine Nb（CN） precipitate at the boundary of the austenite grains,which decreases the strength of the grain boundary sharply.
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