Method for smelting low-phosphorus steel in converter under the condition of ultra-high steel scrap ratio

Abstract

The invention relates to a method for smelting low-phosphorus steel in a converter under the condition of an ultra-high ratio of steel scrap to steel. It adopts a 130t top-bottom double-blown converter for smelting, and the molten iron turnover mode is one tank to the bottom. 112-115t, the temperature of molten iron after desulfurization is 1310-1360°C, the mass percentage of silicon is 0.3-0.6%, and the amount of scrap steel is 38-48t. The specific smelting process includes: (1) Implementing the slag retention operation system, ( 2) scrap loading system, (3) slag adding and oxygen supply system, (4) bottom blowing system, (5) end point control system, to realize the smelting of low-phosphorus steel under the condition of ultra-high steel scrap ratio; the method of the present invention is On the basis of the existing high scrap steel ratio process practice, through the optimization of converter smelting operation, large penetration specific oxygen lance, reblowing process, etc., a complete and effective control method is formed to realize the high scrap steel ratio of 130t converter when entering the furnace, smelting The purpose of process stability, cost reduction, controllable end point and low phosphorus tapping.

Description

technical field [0001] The invention relates to the technical field of iron and steel metallurgy and converter smelting, in particular to a method for converter smelting low-phosphorus steel under the condition of ultra-high scrap steel ratio. Background technique [0002] In the current and foreseeable future decades, China will remain the world's largest steel producer and seller. At the same time, due to geological and economic reasons, in the current and future period, China needs to import 100 million tons of iron ore from abroad every year to meet the survival and development needs of the steel industry. Due to the lack of voice in the iron ore trade, Chinese steel companies have to pay hundreds of billions of dollars for the price increase of iron ore every year, and their ability to resist the risk of fluctuations in iron ore supply is seriously insufficient. Contrary to the reality of the overall shortage of iron ore production capacity, after years of accumulation...

AI Technical Summary

Problems solved by technology

[0005] The core of the ultra-high scrap ratio process is still focused on the significant increase in the proportion of incoming scrap (ratio of incoming scrap ≥ 25%), which has a decisive impact on converter smelting, which is mainly reflected in several aspects: (1) Large amount of scrap Existence, forming a local relatively low temperature zone, the temperature in the furnace is uneven, the melting process of scrap steel is affected, and there may even be a situation where the scrap steel is not yet melted when the steel is tapped; It is difficult to quickly and effectively dephosphorize; (3) The stability of the converter smelting process is seriously insufficient, and the existence of solid and semi-solid scrap steel makes the depth of the effective molten pool smaller, and the probability of splashing during the process increases significantly; (4) Due to the low temperature Even, scrap melting is not complete, and the automatic steelmaking based on the sub-lance system is seriously affected. The sub-lance 1 (TSC) is prone to temperature deviation, inaccurate sampling components, etc., which interferes with the dynamic adjustment near the end of smelting, resulting in side effects at the end. Gun 2 (TSO) carbon temperature target control is inaccurate, manual intervention is required to remedy, automatic steelmaking is meaningless, converter smelting efficiency will be correspondingly significantly reduced, process cost will increase instead, and the cost reduction target of high scrap steel ratio will be difficult to achieve

(5) Due to the influence of the overall heat balance, the addition of lime-based slagging materials is limited, the melting speed slows down, and the binary alkalinity of the final slag is generally within 3.2, which is unfavorable for dephosphorization

In order to achieve the heat balance in the converter, some methods are mentioned in the existing literature, such as the patent "a high scrap steel ratio smelting process for converters" (CN20180853321.4) mentions that in addition to reducing heat loss in a tank to the bottom, coal is also added to the converter The problem of this method is that the melting of the coal block takes time, which has a serious adverse effect on the rapid slag formation in the initial stage of smelting, and the initial stage is the most favorable stage for dephosphorization, which will directly affect the end point Dephosphorization rate, and the coal contains more S, which is not good for the control of S content in molten steel. If high-quality steel is smelted, it will increase the subsequent refining time and cost

The document "Low Iron Consumption, High Scrap Steel Ratio Technical Review and Suggestions" mentions the method of using a secondary combustion oxygen lance in the converter to increase the secondary combustion rate of C in molten iron, thereby increasing the heat source. The secondary combustion oxygen lance was developed in the late 20th century It has indeed been studied in depth, and it has a definite role in improving the secondary combustion rate and reducing the oxygen lance nozzle sticking to the gun. However, the secondary combustion oxygen lance has not been fully promoted and applied so far, which is also determined by its obvious disadvantages. On the one hand , the nozzle holes are poorly set on different planes of the nozzle. Under the same oxygen supply intensity, the overall jet flow intensity will directly decrease, and the stirring ability of the molten pool will be weakened, which is not conducive to the rapid melting of excess scrap steel in the early stage of smelting, and the initial slag steel reaction The speed is correspondingly slower, and the overall smelting cycle becomes longer. Although the secondary combustion rate can be increased by about 10%, it is not enough to offset the adverse consequences caused by the reduction in smelting efficiency. On the other hand, the internal structure of the secondary combustion oxygen lance is complex and difficult to maintain. The frequency and cost are relatively high, and it does not meet the overall goal of cost reduction and efficiency increase. In addition, there are few experimental studies on the dephosphorization effect of the secondary combustion oxygen lance, and the promotion prospect of smelting low-phosphorus steel is limited.

Therefore, the above two methods have adaptability problems and cannot be promoted in a wider range.