JPS5935406B2 - Method for promoting dephosphorization in bottom-blown converter refining - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a method for promoting dephosphorization reaction in bottom-blowing converter refining, and utilizes the advantage that once molten slag powder melts easily and turns into slag quickly, We propose a method to accelerate dephosphorization by injecting fine powder of recycled converter slag obtained by adding iron oxide to converter slag into a steel bath.

In general, in the case of a bottom-blown converter, the refining gas is injected from the bottom of the furnace together with the protective gas, so the mixing characteristics are very good. It has the advantage of good yield rate and rapid progress of decarburization reaction.

On the other hand, in the case of the generated phosphorus oxide, it is reduced by carbon during the floating process, so the carbon content in the steel is 0.1%.
There is a drawback that dephosphorization does not proceed unless the carbon range reaches a certain level, and there is also a drawback that the oxidation of Fe is delayed and the formation of slag is delayed, so that the migration of P into the slag is delayed.

For this reason, in the case of conventional refining using a bottom-blown converter, the dephosphorization process occupies a large proportion of the steelmaking reaction, which has the disadvantage that re-blowing is often required for dephosphorization.

It is known that to promote such dephosphorization, it is effective not only to increase the basicity but also to generate slag with good fluidity as quickly as possible.

Therefore, the present invention is a method for promoting the dephosphorization reaction by speeding up the slag formation, using converter slag, which has a uniform composition, is easily remelted, and quickly turns into slag, as a slag forming material.
This method speeds up slag formation by feeding the steel into the steel bath again, which in turn promotes the dephosphorization reaction.

In short, the method of this invention involves adding iron oxide to converter slag, which is easy to remelt since it has been melted once, and pulverizing it to less than 100 meshes, thereby producing recycled converter slag. from the bottom tuyere of the bottom blowing converter,
This method involves injecting refining oxygen gas into a steel bath as a carrier gas.

The composition of the recycled converter slag largely depends on the original recycled converter slag used in the actual manufacturing process, but it is generally within the following composition range (wt%). Early high carbon region (carbon content:
4.5%), it is blown in together with oxygen gas.

Then, about half the amount of the slag is blown in until the carbon content reaches 1%.

After that, only oxygen is blown in, and the carbon content is approximately 0.3%.
After reaching a certain level, it is preferable to inject the remaining half of the recycled converter slag from the bottom tuyeres using oxygen gas as a carrier gas, in the same way as the above-mentioned regenerated converter slag.

In addition, recycled converter slag is usually used together with other auxiliary raw materials, such as iron oxide and lime.
30%, regenerated converter 20-60% for lime 25-50%
Use around %.

When the recycled converter slag exceeds 60%, the phosphorus oxide content in the slag increases, which is rather disadvantageous for dephosphorization.

On the other hand, as mentioned above, by using converter slag and mixed fine powder of iron oxide, the amount of iron oxide produced in the steel bath and slag increases, and the slag's tendency to slag increases. It is thought that dephosphorization improves as the temperature decreases.

Furthermore, in the case of the method of the present invention, even greater effects can be expected since the recycled converter slag powder is injected from the bottom tuyere.

This means that the phosphorus oxide generated directly above the tuyere returns to the molten steel in the form of phosphorus due to the reduction of carbon during the flotation process, but by injecting the fine slag powder according to the present invention from the bottom,
It is thought that the slag particles collide and coalesce with phosphorous oxide during the floating process, which has a positive effect on dephosphorization.

Furthermore, when converter slag is continuously regenerated, enrichment of phosphorus oxide occurs, but according to examples, even when the enrichment is close to 10%, the dephosphorization performance is good. was gotten.

In addition, as a source of iron oxide that exhibits the above-mentioned effect, specifically, iron ore, Mn ore, mill scale, etc. can be considered.

Next, embodiments of the invention will be described.

Table 1 shows the composition of converter slag produced after blowing ordinary low carbon steel in an oxygen bottom-blown converter.

Lime and iron oxide were added to and mixed with this converter slag, and this was pulverized (adjusted to a powder finer than 100 mesh) to obtain fine powder of recycled converter slag having the composition shown in Table 2.

The slag thus obtained was blown into a steel bath together with oxygen gas from the bottom tuyere of an oxygen bottom-blown converter (inner volume: 4.8 m'').

The operation results are shown in Table 3.

As is clear from this table, according to the present invention, dephosphorization, which was considered to be the biggest drawback of bottom-blown converters, was extremely effective.

This is because in the case of the conventional method, silicon is oxidized in the first half of the blowing process, but not enough to turn into slag, and slag with good fluidity is formed only in the second half of the blowing process. In contrast, in the method of the present invention, slag formation is performed from the first half of blowing.

In addition, the method of the present invention makes it possible to effectively utilize converter slag, which was conventionally discarded, and therefore has excellent effects such as saving the time and effort of disposal and greatly contributing to a reduction in steel manufacturing costs.

Claims (1)

[Claims] 1. From the tuyere provided at the bottom of the furnace, along with oxygen gas for refining,
A method for promoting dephosphorization in bottom-blowing converter refining, characterized in that fine powder of recycled converter slag mixed with iron oxide is placed at the bottom in a steel bath.