材料期刊网

针对S355J2钢连铸坯角部横裂纹,现场取样,利用扫描电镜、能谱仪等检测手段分别从裂纹形貌、夹杂物的组成及分布等方面进行分析;同时采用辐射温度计对连铸坯矫直段角部温度进行现场测量.结果表明,裂纹主要分为非封闭的主裂纹和许多细小的封闭裂纹,主裂纹内含有Al、Ca、Mg等氧化物夹杂,且裂纹已经被氧化;细小的封闭裂纹中有保护渣成分,说明钢液在凝固过程有保护渣卷入.夹杂物聚集导致连铸坯在矫直阶段因内弧受到拉应力作用而产生应力集中,成为横裂纹出现的内因.铸坯矫直段角部及其附近温度为850℃左右,处于第三脆性区,成为横裂纹产生的主要原因.优化保护渣制度和炼钢工艺可避免卷渣行为的发生;采用倒角结晶器可使角部温度避开第三脆性区.

Aming at the transverse cracks formed in S355J2 steel slab comer,through field sampling,the crack morphology,composition and distribution of inclusions were analyzed using scanning electron microscopy and energy spectrum analyzer.The comer temperature at flattener part of continuously cast slab was measured using a radiation thermometer.The results showed that the cracks were divided into the unenclosed main cracks and many tiny closed cracks.The main cracks contained the oxide inclusions of Al,Ca and Mg,and cracks have been oxidized,and the tiny closed cracks contained protecting slag composition,which indicated that the protecting slag had involved in the liquid steel.The inclusions gathered leading to the stress concentration occured when the inner arc was subjected to tensile stress in the straightening stage,which become the internal reason of transverse cracks appearing.The corner temperature of the slab straightening section and the region near it was about 850 ℃,and was in the third brittle zone,which become the main reason of transverse cracks appearing.By optimizing the protecting slag and steelmaking process,the slag entrapment can be avoided,and using the chamfer mold can make the temperature of slab corner to avoid the third brittle zone.