TWI449792B - Method of steelmaking in reducing rephosphorization - Google Patents

Description

Steelmaking method for reducing the amount of phosphorus

The present invention relates to a steelmaking process, and more particularly to a steelmaking process for reducing the amount of phosphorus in a converter using slag.

The steelmaking process mainly removes impurities in the steel raw material by high-temperature oxidation reaction, and thereby adjusts the proportion of the constituent elements in the molten steel to prepare various steel products. The converter blowing process is a key step in removing impurities in the steel making process, and the impurities in the molten steel are converted into converter slag by introducing oxygen, an inert gas and a slagging agent. The activity of impurities in the converter slag also affects the stability of the impurities. The higher the impurity activity, the easier it is to return to the molten steel from the converter slag.

In general, phosphorus is considered a harmful element in steel and is liable to cause low temperature brittleness and temper brittleness of steel. High-quality steel has stricter requirements on the phosphorus content of steel, especially for low-temperature steel, marine steel, and hydrogen-resistant cracking steel (such as natural gas, petroleum pipeline and petroleum refining equipment). Below certain conditions. Since phosphorus cannot be removed in the secondary refining process in the steelmaking process, the converter blowing process is the main step in removing phosphorus in the molten steel for the preparation of low-phosphorus steel products (phosphorus content less than or equal to 100 ppm). By reducing the activity of phosphorus in the converter slag, the concentration of phosphorus returned to the molten steel is reduced.

In the prior art, the concentration of the phosphorus recovered from the converter slag to the molten steel is often controlled by the dephosphorization and dephosphorization step of the pre-treatment process, the blowing conditions of the converter blowing process, and the composition of the slagging agent. However, the sources of steel raw materials are often uneven, resulting in steelmaking conditions that must be changed in accordance with changes in the composition of steel raw materials, in order to produce low-phosphorus steel, resulting in increased manufacturing costs.

In addition, the prior art does not effectively reduce the activity of phosphorus in the converter slag, only to improve the phosphorus fixation capacity of the converter slag or to reduce the converter slag flowing into the molten steel by the slag blocking process, so that the phosphorus is still easily recovered from the converter slag. In the molten steel, increase the concentration of phosphorus in the molten steel.

Therefore, one aspect of the present invention provides a steelmaking method for reducing the amount of phosphorus which is obtained by using a calcium citrate (Calcium Trisilicate; CaO‧3SiO ₂ ) to adsorb molten steel by calcium trisilicate. The phosphorus in the middle reduces the activity of phosphorus in the converter slag, thereby reducing the amount of phosphorus, and thereby preparing the finished product of low-phosphorus steel.

According to the above aspect of the present invention, a steelmaking method for reducing the amount of phosphorus is proposed. In an embodiment, the steelmaking method comprises a pretreatment process, a top and bottom blowing furnace steelmaking process and a slag blocking process. The foregoing pretreatment process is for providing a first molten steel, wherein the first molten steel has a cerium concentration of 0.001% by weight (% by weight) to 0.015% by weight, and the first phosphorus concentration is 0.01% by weight to 0.045% by weight, and the first The temperature of a molten steel is from 1150 ° C to 1300 ° C.

The above-mentioned top and bottom and the converter steelmaking process pour the first molten steel into a converter to form a second molten steel, wherein the second molten steel has a second phosphorus concentration. The converter bottom end temperature of the top and bottom and the converter steelmaking process is 1550 ° C to 1680 ° C. The top and bottom of the rotary converter steelmaking process further comprises a slagging step, which introduces a slag forming agent into the converter, introduces oxygen at the top of the converter, and introduces an inert gas at the bottom of the converter to make the impurities in the second molten steel. Forming converter slag. The flow rate of oxygen is from 500 Nm ³ /min to 800 Nm ³ /min, and the flow rate of the inert gas is from 0.03 Nm ³ /min to 0.5 Nm ³ /min.

The above slagging agent comprises calcium oxide, a strontium iron compound and calcium fluoride. The amount of calcium oxide is 30 kg / ton of molten steel to 55 kg / ton of molten steel, the amount of strontium iron compound is 2 kg / ton of molten steel to 10 kg / ton of molten steel, and the amount of calcium fluoride is 0.1 kg / ton Steel liquid to 3 kg / ton of molten steel.

The above slag blocking process is for removing the converter slag having a thickness greater than 40 mm in the second molten steel and forming a third molten steel, and the third molten steel has a third phosphorus concentration. Wherein the first phosphorus concentration is greater than the third phosphorus concentration, and the third phosphorus concentration is greater than the second phosphorus concentration, and the calcium tribasic acid in the converter slag adsorbs phosphorus in the second molten steel, so that the third phosphorus concentration and the second phosphorus concentration The difference in phosphorus concentration is from 5 ppm to 10 ppm.

According to an embodiment of the invention, a solidification process is further selectively performed after the slag removal process, wherein the solidification process pours the third molten steel into the ingot mold to form a steel ingot.

According to another embodiment of the present invention, a casting process is further selectively performed after the slag blocking process, wherein the casting process pours the third molten steel into the casting machine to form a steel blank.

According to still another embodiment of the present invention, the pre-treatment process further comprises introducing a dephosphorization dephosphorization agent and oxygen into the molten steel to form the first molten steel. The flow rate of the oxygen system of 500Nm ³ / min to 800Nm ³ / min. The above dephosphorization dephosphorization agent comprises calcium oxide, iron oxide and calcium fluoride, wherein the content of calcium oxide is 38 wt% to 55 wt%, the content of iron oxide is 43 wt% to 60 wt%, and the content of calcium fluoride is 1 wt. % to 5wt%.

According to still another embodiment of the present invention, the converter slag comprises calcium oxide, cerium oxide, total iron (T-Fe) and phosphorus pentoxide, wherein the content of calcium oxide is 33% by weight to 52% by weight, and dioxide is oxidized. The content of cerium is 10% by weight to 20% by weight, the content of T-Fe is 20% by weight to 37% by weight, and the content of phosphorus pentoxide is more than 0% by weight and less than or equal to 4% by weight.

The steelmaking method for reducing the amount of phosphorus in the invention is applied by using a pretreatment process, a top and bottom blowing furnace steelmaking process and a slag blocking process, and introducing a slag forming agent to form a converter slag, by using a converter slag The calcium acid adsorbs the phosphorus in the molten steel and reduces the activity of the phosphorus of the converter slag, thereby preventing the phosphorus of the converter slag from returning to the molten steel to reduce the amount of phosphorus in the third molten steel.

The making and using of the present invention are discussed in detail below. However, it will be appreciated that the embodiments provide many applicable inventive concepts that can be implemented in a wide variety of specific content. However, the specific embodiments discussed are illustrative only and are not intended to limit the scope of the invention.

The invention provides a steelmaking method for reducing the amount of phosphorus. In one embodiment, the method of the present invention comprises a pretreatment process, a top and bottom blow converter steelmaking process, and a slag removal process to form a low rephosphorus amount of molten steel. The term "rephosphorization amount" as used herein means the difference between the concentration of phosphorus in the molten steel after the slag blocking process and the concentration of phosphorus in the molten steel at the end of the steelmaking process of the converter. In the conventional converter steelmaking process, when the activity of phosphorus in the converter slag is increased, the phosphorus is easily returned to the molten steel by the converter slag, causing the phosphorus concentration in the molten steel to increase, so that the amount of phosphorus is increased. Therefore, the steelmaking method for reducing the amount of phosphorus in the present invention reduces the amount of phosphorus in the converter slag by controlling the composition of the converter slag, adsorbing phosphorus in the molten steel, and reducing the activity of phosphorus in the converter slag.

In the pretreatment process, the molten steel material is melted and introduced into the demagnetization dephosphorization agent and oxygen in the molten steel to form the first molten steel. In one embodiment, the first molten steel has a cerium concentration of 0.001% by weight to 0.015% by weight, and the first phosphorus concentration (hereinafter referred to as [P ₁ ]) is 0.01% by weight to 0.045% by weight, and the first molten steel is The temperature is from 1150 ° C to 1300 ° C. In one example, the release agent comprises calcium dephosphorization silicon oxide, iron oxide and calcium fluoride and the flow of oxygen-based 500Nm ³ / min to 800Nm ³ / min.

In one example, the calcium oxide content is from 38 wt% to 55 wt%. When the content of calcium oxide is more than 55wt%, the fluidity of the molten steel is likely to be deteriorated, and the ability of the pretreatment process to remove phosphorus is inhibited, so that the converter slag of the top and bottom with the converter steelmaking process cannot contain an effective content of calcium tribasic acid. (Calcium Trisilicate; CaO‧3SiO ₂ ), so that it is unable to effectively adsorb phosphorus and reduce the activity of phosphorus. When the content of calcium oxide is less than 38% by weight, [P ₁ ] cannot be reduced to 0.01 wt% to 0.045 wt%, which affects the ability of the subsequent process to remove phosphorus.

In one example, the iron oxide content is from 43% to 60% by weight. When the content of iron oxide is more than 60% by weight, the formation of calcium tribasic acid in the converter slag is affected. When the content of iron oxide is less than 43% by weight, it is also impossible to effectively reduce [P ₁ ] to 0.01 wt% to 0.045 wt%.

In one example, the calcium fluoride is present in an amount from 1% to 5% by weight. When the content of calcium fluoride is more than 5% by weight, the gaseous fluorine released during the pretreatment process has an adverse effect on the environment. When the content of calcium fluoride is less than 1% by weight, [P ₁ ] cannot be effectively reduced.

After the pretreatment process, the top and bottom and the converter steelmaking process are carried out, wherein the first molten steel is poured into the converter, and oxygen, an inert gas and a slagging agent are introduced to form a second molten steel, wherein the second molten steel It has a second phosphorus concentration (ie, the concentration of phosphorus in the molten steel at the end of the top and bottom blowing steelmaking process; hereinafter referred to as [P ₂ ]). In one embodiment, the top end is the same as the blowing end temperature of the blow converter steelmaking process from 1550 ° C to 1680 ° C. In this embodiment, when the blowing end temperature of the converter steelmaking process is greater than 1680 ° C, the stability of phosphorus in the converter slag is lowered, so that phosphorus is easily returned to the molten steel.

The above-mentioned top and bottom and the converter steelmaking process further comprise a slagging step, which introduces the slag forming agent into the converter, introduces oxygen into the top of the converter, and introduces an inert gas at the bottom of the converter to make the second molten steel The impurities in the middle (for example, containing antimony and phosphorus) form converter slag. In one embodiment, the flow rate of the oxygen-based slag steps 500Nm ³ / min to 800Nm ³ / min, while the flow rate of the inert gas system 0.03Nm ³ / min to 0.5Nm ³ / min.

The above slagging agent comprises calcium oxide, a strontium iron compound and calcium fluoride. In one embodiment, the amount of calcium oxide is from 30 kg/ton of molten steel to 55 kg/ton of molten steel, and the amount of ferroniobium compound is from 2 kg/ton of molten steel to 10 kg/ton of molten steel, and calcium fluoride The dosage is 0.1 kg/ton of molten steel to 3 kg/ton of molten steel. When the amount of calcium oxide of the slag forming agent is more than 55 kg/ton of molten steel, the base degree of the subsequently formed converter slag is increased, resulting in deterioration of the fluidity of the converter slag; when the amount of calcium oxide is less than 30 kg/ton of steel When the liquid is used, the salt base degree of the subsequently formed converter slag is reduced, and the impurities in the second molten steel cannot effectively form the converter slag. Secondly, when the amount of the strontium iron compound is more than 10 kg/ton of molten steel, the base degree of the subsequently formed converter slag is increased, so that the impurities in the second molten steel cannot effectively form the converter slag; when the amount of the strontium iron compound is less than 2 In the case of kg/ton of molten steel, the base degree of the subsequently formed converter slag is reduced, and the fluidity of the converter slag is deteriorated. Furthermore, when the amount of calcium fluoride is more than 3 kg/ton of molten steel, the fluorine released from the slagging process will be increased, which will adversely affect the environment; when the calcium fluoride is less than 0.1 kg/ton of molten steel, The impurities of the second molten steel cannot effectively form the converter slag.

In one embodiment, the introduced slagging agent affects the salt base of the converter slag, wherein the term "salt base of the converter slag" refers to the weight ratio of calcium oxide to cerium oxide in the converter slag (CaO). /SiO ₂ ). In one embodiment, the base slag of the converter slag is from 3 to 4.5, so that the converter slag has better fluidity and the impurities in the second molten steel form converter slag.

In an example, the converter slag comprises calcium oxide, cerium oxide, total iron (T-Fe) and phosphorus pentoxide, the content of calcium oxide is 33% by weight to 52% by weight, and the content of cerium oxide is 10wt. % to 20% by weight, the content of T-Fe is 20% by weight to 37% by weight, and the content of phosphorus pentoxide is more than 0% by weight and less than or equal to 4% by weight.

The above slag blocking process is for removing the converter slag having a thickness of more than 40 mm in the second molten steel to form a third phosphorus concentration (ie, the concentration of phosphorus in the molten steel after the slag removal process; hereinafter referred to as [P3]) The third molten steel. By means of the slag blocking process, the converter slag flowing into the third molten steel can be reduced, and the unstable phosphorus in the converter slag can be reduced to return to the third molten steel. In one embodiment, [P ₁ ] is greater than [P ₃ ] and [P ₃ ] is greater than [P ₂ ].

It is worth mentioning that the steelmaking method for reducing the amount of phosphorus in the present invention is to reduce the concentration of bismuth and the concentration of phosphorus in the molten steel by the pretreatment of dephosphorization and dephosphorization of the pretreatment process, and then carry out the top and bottom blowing converter. The steelmaking process causes the impurities in the molten steel to form a converter slag containing calcium trisilicate. Compared with the prior art, the calcium dibasic acid contained in the converter slag is used to adsorb and reduce the activity of phosphorus, and the phosphorus content thereof is as high as 30 ppm to 40 ppm. The calcium tribasic acid contained in the converter slag of the present invention is more effective for adsorbing steel. Phosphorus in the liquid reduces the activity of phosphorus in the converter slag, improves the stability of phosphorus in the converter slag, and further reduces the amount of phosphorus in the subsequent steelmaking process, wherein the amount of phosphorus in the molten steel obtained by the method of the invention can be reduced to 5 ppm Up to 10ppm.

In addition, compared with the calcium bismuth citrate contained in the conventional converter slag, the calcium tribasic acid contained in the converter slag of the present invention can make the obtained molten steel have a lower amount of rephosphorization, and at the same time, calcium tricalcium citrate and Calcium dicitrate has a distinctly different crystalline form. Referring to Fig. 1, there is shown an electron micrograph of calcium tribasic acid in a converter slag according to an embodiment of the present invention, wherein the calcium citrate shown in Fig. 1 is a rod-like crystal. Please refer to Fig. 2, which is an electron micrograph showing the calcium disilicate in the conventional converter slag, wherein the calcium disilicate is a round crystal.

Comparing Fig. 1 and Fig. 2, it can be seen that the calcium citrate contained in the converter slag obtained by the method of the present invention has a distinct crystal form compared with the calcium dibasic acid contained in the conventional converter slag. . In other words, in the slagging step of the present invention, it is necessary to use the slag forming agent of the specific composition of the present invention to obtain the converter slag having calcium citrate under a specific process condition, so that the obtained molten steel has a lower rephosphorization. the amount.

In one example, a solidification process can be selectively performed after the slag removal process. This solidification process pours the third molten steel into an Ingot Module, and after it solidifies, it forms an ingot. Thereafter, a processing process (for example, steps such as rolling or forging) is performed to produce a finished product of low-phosphorus steel.

In another example, after the slag removal process, a casting process is selectively performed. The casting process is to pour the third molten steel into a continuous casting machine and cast into a steel shell (Slab) to form a low phosphorus. Steel.

It can be seen from the above embodiments of the present invention that the steelmaking method for reducing the amount of phosphorus in the invention has the advantages that the slag-forming agent is used to form the impurities in the molten steel into the converter slag containing calcium trisilicate, and the adsorption by the calcium citrate Phosphorus in the molten steel reduces the activity of phosphorus in the converter slag, thereby preventing the phosphorus of the converter slag from returning to the molten steel to reduce the amount of phosphorus in the molten steel.

Although the present invention has been disclosed in the above embodiments, it is not intended to limit the present invention, and the present invention can be modified and modified without departing from the spirit and scope of the present invention. The scope is subject to the definition of the scope of the patent application attached.

The above and other objects, features, advantages and embodiments of the present invention will become more apparent and understood.

Fig. 1 is an electron micrograph showing calcium tribasic acid in a converter slag according to an embodiment of the present invention.

Figure 2 is an electron micrograph showing the calcium disilicate in the conventional converter slag.

Claims (6)

A steelmaking method for reducing a phosphorus content, comprising: performing a pretreatment process, wherein the pretreatment process is for providing a first molten steel, wherein the first molten steel has a cerium concentration of 0.001 weight percent (wt%) Up to 0.015 wt%, the first phosphorus concentration of the first molten steel is 0.01 wt% to 0.045 wt%, and the temperature of the first molten steel is 1150 ° C to 1300 ° C; performing a top and bottom blowing furnace steelmaking process, The top and bottom and the converter steelmaking process pour the first molten steel into a converter to form a second molten steel, wherein the second molten steel has a second phosphorus concentration, and the top and bottom are the same as the rotary converter steelmaking The process of the converter blowing end temperature is 1550 ° C to 1680 ° C, and the top and bottom of the converter steelmaking process further comprises: a slagging step, the slagging step is to put a slag forming agent into the converter, the converter An inert gas is introduced into the top of the converter, and an inert gas is introduced into the bottom of the converter to form a converter slag. The flow rate of the oxygen is 500 Nm ³ /min to 800 Nm ³ /min, and the inert gas is the flow coefficient 0.03Nm ³ / min to 0.5Nm ³ / min, wherein the fluxing agent comprises: 30 kg / t Calcium oxide from liquid to 55 kg/ton of molten steel; bismuth iron compound from 2 kg/ton of molten steel to 10 kg/ton of molten steel; and calcium fluoride of 0.1 kg/ton of molten steel to 3 kg/ton of molten steel; Performing a slag process to remove the converter slag having a thickness greater than 40 mm in the second molten steel and forming a third molten steel, wherein the third molten steel has a third phosphorus concentration, and wherein the first phosphorus The concentration system is greater than the third phosphorus concentration, the third phosphorus concentration is greater than the second phosphorus concentration, and the converter slag calcium citrate (Calcium Trisilicate; CaO.3SiO ₂ ) adsorbs the phosphorus in the converter slag, so that The difference between the third phosphorus concentration and the second phosphorus concentration is 5 ppm to 10 ppm. The steelmaking method for reducing the phosphorus content according to claim 1, further comprising performing a solidification process after the slag removal process, wherein the solidification process is to pour the third molten steel into a steel ingot mold (Ingot Module). To form a steel ingot. The steelmaking method for reducing the phosphorus content according to claim 1, further comprising performing a casting process after the slag removing process, wherein the casting process is to pour the third molten steel into a continuous casting machine to form a Steel embryo. The steelmaking method for reducing the amount of phosphorus in the claim 1, wherein the pretreatment process further comprises introducing a dephosphorization dephosphorization agent and oxygen into a molten steel to form the first molten steel, and the flow of the oxygen It is 500 Nm ³ /min to 800 Nm ³ /min, and the dephosphorization dephosphorization agent comprises: 38 wt% to 55 wt% of calcium oxide; 43 wt% to 60 wt% of iron oxide; and 1 wt% to 5 wt% of calcium fluoride. A steelmaking method for reducing a phosphorus content according to claim 1, wherein the impurities comprise cerium and phosphorus. The steelmaking method according to claim 1, wherein the converter slag comprises: 33% by weight to 52% by weight of calcium oxide; 10% by weight to 20% by weight of cerium oxide; and 20% by weight to 37% by weight of total iron ( Total Iron; T-Fe); and more than 0% by weight and less than or equal to 4% by weight of phosphorus pentoxide.