高性能中厚板钢中微小氧化物夹杂在凝固前沿行为研究

The behaviors of fine oxides produced in aluminium killed steel and precipitated in titanium killed steel during solidification of high performance steel plates will be studied with the help of confocal laser scanning microscope and Bridgeman solidfication equipment, especially focused on the influence of oxdies characteristics (morphology, type, size, amount) , chemical composition of steel and cooling rate on behaviors of primary inclusion aggregation and pushing/ engulfment in the solidifying interface, aiming to get the methods for preventing them aggregate and grow up in the solidifying interface. In additon, the behaviors of fine oxides precipitated during solidification of titanium killed steel will also be studied, the nucleation, growth and pushing/engulfment behaviors of secondary fine oxides will be in-situ observed by confocal laser scanning microscope,the effect of cooling rate on the diameters of fine oxides will be stuided by Bridgeman solidification experiment. The ruslts will help understand the phenomena of aggregation of fine oxides during solidification and how to get distributed uniformly fine oxides which are apt to induce acicular ferrtie during solidificaiton. The precipitation model considering the pushing/engulfment of fine oxides will be established to forcast the size of fine oxides preciptated during solidfication more precisely. All the resluts will help decrease the B-type stringer non-metallic inclusions of heavy plates, improve the toughness of heat affect zone(HAZ) and advance the development of oxide metallurgy technology.

采用高温激光共聚焦扫描显微镜、定向凝固等实验方法对中厚板铝脱氧钢中的一次微小氧化物夹杂、钛脱氧钢凝固过程中析出的二次微小氧化物夹杂在凝固前沿行为进行研究，重点研究夹杂物特征（形貌、类型、尺寸和数量）、钢液成分及冷却速率等因素对一次微小氧化物夹杂在凝固前沿聚集长大、被凝固前沿推动/捕捉行为的影响规律，提出防止凝固过程中一次微小氧化物夹杂聚集长大的控制方法；研究钛脱氧钢凝固过程中析出的二次钛氧化物夹杂在凝固前沿形核长大及被凝固前沿推动/捕捉行为的影响因素及规律，为控制钛脱氧钢凝固过程中形成尺寸细小、均匀分布且能诱导针状铁素体的钛氧化物夹杂提供理论指导；建立基于夹杂物被凝固前沿推动/捕捉行为的二次氧化物夹杂析出长大数学模型，对钛脱氧钢凝固过程析出的二次钛氧化物夹杂的大小进行预测。研究结果对于提高高性能中厚板钢中夹杂物控制水平，改善焊接热影响区韧性及推动氧化物冶金技术进步都具有重要意义。

为了提高国内高性能中厚板钢中夹杂物控制水平，改善大线能量焊接热影响区韧性及推动氧化物冶金技术进步，本项目采用高温激光共聚焦扫描显微镜对高性能中厚板钢中微小氧化物夹杂在凝固前沿行为进行了系统研究。通过对中厚板铝脱氧钙处理钢中的一次微小氧化物夹杂（直径≤5μm）在凝固前沿推动/捕捉行为的原位动态观察研究，发现夹杂物的类型和冷却速率对于其被凝固前沿推动/捕捉行为具有重要影响，冷却速率越大，微小夹杂物越容易被凝固前沿捕获；相同冷却速率下，液态夹杂物比固态夹杂物更容易被凝固前沿推动。通过对铝钛复合脱氧钢中的二次钛铝复合氧化物夹杂在凝固前沿形核长大及被凝固前沿推动/捕捉行为的原位动态观察研究，发现微小尺寸的钛铝复合氧化物夹杂在平面状凝固前沿易于被捕获，而较大尺寸的铝钛复合夹杂物则易于在凝固前沿聚集长大，同时还对微小铝钛复合夹杂物诱导针状铁素体的过程进行了初步的原位动态观察研究。建立了Ti脱氧钢中二次氧化物夹杂析出长大的数学模型和夹杂物被凝固前沿推动/捕捉行为的模型，并对钛脱氧钢凝固过程析出的二次钛氧化物夹杂的大小进行了预测，预测值与实验室观察结果吻合较好。为了能够更好的理论联系实际，本项目在大生产中系统研究了RH精炼过程中铝脱氧钙处理钢中一次非金属夹杂物的碰撞、聚集、长大和去除行为，发现RH循环过程中固态夹杂物比液态夹杂物更容易去除，基于此结论优化了热轧中厚板钢夹杂物控制工艺，大大提高了钢中微小夹杂物的去除效率，新工艺对提高高品质热轧中厚板产品性能和质量稳定性起到了重要作用。