转炉冶炼低磷洁净钢的工艺开发和实践

 转炉具备冶炼低磷钢的生产能力,但生产超低磷9Ni钢,转炉脱磷工艺仍然是主要难点和研究重点。分析了钢水温度、炉渣碱度、FeO和渣量等对转炉脱磷的影响规律,并结合现场工装设备条件,对转炉双联法、三渣法、双渣法3种脱磷模式进行试验对比。双联脱磷工艺半钢温降大、单炉周期长、生产组织难度大,三渣法操作过程复杂、终点磷控制优势不明显。双渣法冶炼周期短,通过优化转炉脱磷工艺,实现了采用双渣法冶炼工艺生产超低磷钢,简化了超低磷钢转炉冶炼流程,提高了生产效率。研究了转炉脱磷主要工艺参数,分析得出采用脱碳氧枪喷头时,供氧流量按脱碳吹炼流量的83.5%控制,可达到良好的脱磷效果并减少铁水碳的烧损;脱磷期半钢碳含量不宜控制过低,半钢碳质量分数为3.0%～3.5%时能保证前期的脱磷效果和脱碳期的热量。脱磷期温度控制在1 300～1 350 ℃,脱磷率较高也有利于炉渣熔化。炉渣碱度为1.8～2.2时,可保证较高的脱磷率和化渣效果。一次倒渣量40%以上,脱碳期终点温度按1 590～1 610 ℃控制,终渣FeO质量分数不小于20%,终渣碱度大于6,转炉终点磷质量分数可降低到0.002%以下。采用下渣检测系统和滑板挡渣操作,严格控制下渣量,出钢采用磷含量低的合金,炉后钢水增磷可控制在小于0.000 5%。通过工业试验,实现了铸机成品磷质量分数小于0.002%。

Process development and practice of converter smelting low phosphorus clean steel

The converter has the production capacity of smelting low phosphorus steel now, and the converter dephosphorization process is still the main difficulty and research focus in the production of ultra-low phosphorus 9Ni steel. The effects of molten steel temperature, slag basicity, FeO and slag amount on dephosphorization of converter were briefly analyzed. Combined the three modes of dephosphorization of the converter with the field tooling and equipment conditions, such as double-association method, three-slag method and double-slag method. Double-association method has large temperature drop, long cycle and difficult production organization. The operation process is complex and the end phosphorus is unstable with three-slag method. By optimizing the converter dephosphorization process, the production of ultra-low phosphorus steel by double-slag smelting process was realized, which simplified the converter smelting process of ultra-low phosphorus steel and improved the production efficiency. The main process parameters of converter dephosphorization were studied. By using the decarburization oxygen lance nozzle, the oxygen flow was controlled following by 83.5% of the decarburization blowing flow, which could achieve good dephosphorization effect and reduce the burning loss of hot metal carbon. The carbon content of semi-steel in dephosphorization stage could not be controlled too low, and the dephosphorization effect and heat control in dephosphorization stage were better when the carbon was 3.0%-3.5%. When the dephosphorization temperature was controlled between 1 300 ℃ and 1 350 ℃, the dephosphorization rate was higher. When the basicity of slag was 1.8-2.2, the dephosphorization rate and slagging effect were better. A pouring slag volume of more than 40%, decarburization period end temperature was controlled by 1 590-1 610 ℃, the mass percent of FeO of slag was more than 20%, and the basicity of final slag was more than 6, the end phosphorus of converter could be reduced to less than 0.002%. Under the condition of slag detection and tapping slide plate used to block slag, reducing the amount of slag and alloy with low phosphorus content adopted in tapping, the phosphorus increase of molten steel could be controlled within 0.000 5%. Through industrial tests, the phosphorus content of the finished castings was achieved to less than 0.002%.