Decuprization and Purification of molten steel by ammonia gas

本研究的目的是回收废钢，通过除铜二次精炼获得冷轧级钢。我们通过一些实验，从技术角度证实了在较高温度下的氨液被吹到钢液中的工业适用性。以含铜1.0%的普通钢SS41为例，在连续抽气（约10Torr）和强搅拌条件下吹气30min后，除铜至100ppm，除碳至10ppm，除氧和硫至10ppm，除磷至150ppm。然而，氮含量高达150ppm，我们判断需要进行后真空处理。氨顶吹后伴随脱气，氮降至5ppm。氨脱铜的速度比真空处理快10倍。由于界面面积对反应速率的影响较大，目前的小型坩埚在实验室使用时达到了一个极限。通过安排速率决定方程来调整工业操作，得到了较好的计算结果，即假设RH法的反应界面较宽，可以在与现有二次精炼工艺相同的时间内脱除铜和净化钢液。用激光闪蒸法观察了纯铜液中氨蒸发现象，并对其机理进行了探讨。用氨气吹法对纯铜、锗、锡熔液进行了异常蒸发。讨论了这些金属与分解后的氨气相互作用产生不稳定氢化物或氮化物的机理。在合金浓度较高的情况下，合金熔体中氮过饱和导致的飞溅形成是主要原因。

The purpose of this research is to recycle the steel scrap and to pbtain the cold-rolling grade steel by the secondary refining with copper removal. We confirmed an industrial applicability from the technical view by some experiments that the ammonia nustavle at the higher temperatures was blown to the molten steel. After blowing against the normal steel SS41 containing 1.0%Cu, for example, for 30min. under the continuous evacuation (about 10Torr) and strong stirring condition, copper was removed to 100mass ppm, carbon to 10ppm, oxygen and sulfur to a 10ppm level, and phosphor to 150ppm. However, nitrogen content was so high as 150ppm that we judged that a post-vacuum treatment was required. Accompanying degassing after ammonia top blowing, nitrogen decreased to 5ppm. The ammonia decuprization proceeded at 10 times faster rate than vacuum treatment. It reached to a limit when the present small crucible was used at the laboratory scale, because the effect of interface area on the reaction rate was large. Arranging the rate determine equation to adjust the industrial operation, a good calculation result was obtained that it is possible to remove copper and purify the molten steel within the same time as the present secondary refining process, assuming the wider reaction interface at RH method.The evaporation phenomenon by ammonia from pure copper liquid was visualized by the laser flash method to discuss the mechanism. Abnormal evaporation by ammonia gas blowing on molten pure Cu, Ge and Sn was recorded. The mechanism was discussed that the unstable hydride or nitride is produced by the interaction between these metals and the decomposing ammonia gas. In the high concentration of alloys, in addition to this mechanism, the splash forming introduced by over-saturated nitrogen in the alloy melts was largely contributed.