JPS6026608A - Method for dephosphorizing molten iron - Google Patents

Abstract

PURPOSE:To increase the rate of utilization of oxygen and quick lime and to carry out efficient dephosphorization by adding oxygen sources to slag floating on molten iron so as to regulate the weight ratio of CaO/O2 in the slag. CONSTITUTION:Molten iron is dephosphorized while maintaining 1.5-2.5weight ratio of CaO in a flux to be blown into the molten iron to oxygen in iron oxide and gaseous oxygen reacting with CaO, that is, CaO/O2. Oxygen and iron oxide are added to top slag produced by the floating of the flux to maintain <=2.5 weight ratio of CaO/O2 in the slag. By this method the necessary dephosphorization level can be attained with a reduced amount of the flux.

Description

[Detailed Description of the Invention] <Industrial Application Field> The present invention relates to a method for dephosphorizing hot metal. <Prior Art> Conventionally, dephosphorization of hot metal was carried out using 7 lacs mainly composed of quicklime. A method has been adopted in which oxidized phosphorus is stably maintained in the reaction atmosphere by adding iron oxide or gaseous oxygen, or both, together with quicklime, to the hot metal as an oxidizing agent.

In general, the appropriate addition ratio of quicklime and oxygen is unknown;
The conditions for addition are still being explored based on field experiments and experience, and the reality is that various addition conditions are being used. Therefore, problems such as a decrease in CaO dephosphorization utilization efficiency and unexpected decarburization have occurred.

In order to solve the above problem, the inventor of the present invention conducted various experiments and repeated studies, and as a result, as proposed in Japanese Patent Application No. 56-114974, when quicklime and oxygen are added to hot metal to dephosphorize it, quicklime and oxygen are added to hot metal. The weight ratio of CaO/02 and oxygen is 1.
It has been found that when the ratio is set to 5 to 2.5, the dephosphorization utilization efficiency of quicklime and oxygen becomes maximum, and as a result, a high dephosphorization rate can be obtained. However, CaO102 weight ratio 1.5~
When 2.5 was satisfied and quicklime and oxygen were actually injected into hot metal to dephosphorize it, the dephosphorization ability of 7six was lower than that in the experiment, and the slag and slag during the process of floating after CaO injection were found to be lower than in the experiment. It has been found that there is a problem in that a rephosphorization reaction occurs after the layer is formed, resulting in a decrease in the CaOO dephosphorization utilization efficiency.

As a result of repeated experiments, the diagram shown in Figure 1 was obtained. This diagram shows that after the dephosphorization flux has floated to the top of the yc hot metal (in the floated slag, the ratio of CaO content to oxygen content in the slag is 1.5~
It has been learned that the above problem can be solved by supplying an oxygen source at a voltage of 2.5 vc.

Therefore, an object of the present invention is to provide an efficient dephosphorization method based on this knowledge.

(Structure and operation of the invention) The present invention was made by VC based on the above knowledge, and its gist is that flux blown into hot metal is used in the process of dephosphorizing hot metal by adding quicklime and oxygen. Ca0 inside
The ratio between the weight and the weight of gaseous oxygen and/or oxygen in iron oxide that reacts with CaO102 is 1.5 to 2.5.
A hot metal dephosphorization method characterized by maintaining K and flux flotation (adding oxygen and/or iron oxide to top slag produced from C to maintain a CaO102 weight ratio in the slag of 2.5 vcm or less. be.

The theoretical yc of oxygen that reacts with CaO is the total amount of supplied oxygen minus the amount of oxygen that reacts with silicon in the hot metal, which is easier to oxidize than phosphorus.

<Example> The dephosphorization rate according to Example yc of the method of the present invention and the dephosphorization rate according to a comparative example are shown in Table 1 below to clarify the effects of the present invention.

Hot metal containing the following components (wt%) was dephosphorized in a pot under the conditions listed in Table 1.

C4, 5-4.8%, Sio, t~o, s%, MnO
, 3-o, 5a10. P O,10~O112o10
．． 80.02-0.04%.

Above table. As an example, oxidation, yakkeya (...) and iron ore or sintered ore (F e 20s ) were used.

As is clear from Table 1, Ca of the blown flux
In Comparative Examples All and 12 in which Olo 2 was outside the range of 15 to 2.5 and there was no oxygen supply to the top lag, the dephosphorization decreased rapidly and the dephosphorization rate did not reach 65 degrees.

CaO10□ of blown flux is 1.5 to 2.5
In Comparative Examples A 6, 8, and 13, which were outside the range, the dephosphorization rate did not reach 70% even if oxygen was supplied to the top slag. In addition, CaO10□ of the blown flux was added to 1
．． 5 to z5, but the dephosphorization rate did not reach 90 in comparison products No. 1, 9, and 10.14, which did not supply oxygen to the top slag. On the other hand, by setting Ca102 in the blown flux to 1.5 to z5 and supplying oxygen to the top slag, CaO102 in the top slag
A 2, 3 of the present invention example in which □ is smaller than 2.5,
In samples 4, 5, and 7, a dephosphorization rate of 94% or more was stably obtained.

Incidentally, in the examples of No. 43 and AIO, iron oxide was used as the oxygen source in the blown 7 lux, but there was no difference in the dephosphorization rate compared to the case of oxygen gas. Furthermore, in the 7 and 8 υ cases, iron oxide was used as the oxygen source to be supplied to the top slag, but there was no difference in the dephosphorization rate compared to the case of oxygen gas.

<Effects of the Invention> As explained above, according to the method of the present invention, when dephosphorizing hot metal, the weight ratio of CaO102 of 7 lux of blown iron is reduced to 1.
．． 5 to 2.5, and the CaO10□ ratio of the top slag is 2.
．． 5 or less, the utilization efficiency of oxygen and quicklime can be kept high, and the required level of dephosphorization can be achieved with less flux compared to conventional methods, making it possible to significantly reduce the basic unit of oxygen and quicklime. Therefore, a large economic effect can be obtained.

[Brief explanation of the drawing]

FIG. 1 is a diagram showing the relationship between the CaO/02 weight ratio in the slack and the dephosphorization rate when an enzyme is supplied to the top slag and when no enzyme is supplied. Agent: Patent attorney Masaaki Akizawa, Mitsugai (2 people)

Claims (1)

[Claims] (1) In the process of dephosphorizing hot metal by adding quicklime and oxygen, the ratio of the weight of CaO in 7 lux injected into hot metal to the weight of gaseous oxygen and/or oxygen in iron oxide that reacts with CaO CaO10t is maintained at 1.5 to 2.5, and oxygen and/or iron oxide is added to the top slag produced by the floating of Norax to remove CaO in the slag.
10□ A method for dephosphorizing hot metal, characterized by maintaining a weight ratio of 2.5 or less.