CN1046139C - Pre-dephosporizing method for molten iron - Google Patents

Abstract

The present invention mainly relates to a processing method of molten iron pre-dephosphorization, particularly to a preprocessing method of the dephosphorization of medium phosphorus molten iron, which belongs to the field of pig iron refining. The molten iron pre-dephosphorization process is carried out in a converter type container, and an oxygen top blowing and nitrogen bottom blowing technology is used. Synthetic slag of which the chemical components comprise CaO or CaCO3, iron oxides and CaF2 is used as a dephosphorization agent, and the synthetic slag can be shaped by sintering at high temperature or by cooling and solidifying. The pre-dephosphorization processing method can reach the following index: the dephosphorization rate is no less than 85 to 95 %, and the dephosphorization amount is no greater than 0.7 %.

Description

Molten iron pre-dephosphorization method

The invention belongs to the field of refining of pig iron. Mainly relates to the dephosphorization in advance of molten iron.

In general, converter steelmaking uses blast furnace molten iron or cupola molten iron as a raw material, and if the molten iron contains high phosphorus, dephosphorization pretreatment of the molten iron is required before the molten iron enters the converter steelmaking. Otherwise, certain difficulties will be brought to the steelmaking operation. Such as increasing the consumption of raw materials (slag), prolonging the smelting time, etc. When the medium-phosphorus molten iron with the phosphorus content of 0.2-0.6% is adopted for steelmaking, pre-dephosphorization is generally required to be carried out, so that the phosphorus content of the molten iron before entering a converter is controlled in a proper range, and the dephosphorization load during converter smelting is reduced.

At present, the typical dephosphorization pretreatment is powder spraying treatment in a molten iron tank. Because the volume of the hot metal ladle is limited and the shape is not beneficial to the full reaction between slag and metal, the slag overflow is serious, the temperature drop is large and the dephosphorization effect is not ideal during the powder spraying treatment.

In the prior art, the dephosphorization of medium-phosphorus molten iron is also carried out in a steel converter by a double slag methodTetsu-to-Hagane, Vol.69(1983), S959; the third book of the "oxygen converter steelmaking Top and bottom blowing technology", P95-103]. The slagging material usually adopts different single slag materials. The addition is carried out in portions. The method causes large amount of slag in the smelting process, high content of ferric oxide in the slag and serious steel peroxidation tapping, thereby not only increasing lime consumption and prolonging smelting period, but also influencing the quality of molten steel and reducing furnace order. The main reasons are that the slag-making material has high lime content and high lime melting point; in addition, 2CaO. SiO with high melting point is easily formed on the surface in the lime melting process₂And the hard shell is not easy to melt at low temperature, so that the continuous melting of lime is hindered, the slagging speed is slow, and the dephosphorization efficiency is reduced.

The invention aims to provide a molten iron pre-dephosphorization method with a remarkable dephosphorization effect.

According to the experimental and theoretical analysis, the thermodynamic conditions for satisfying the dephosphorization of the molten iron are as follows: (1) high-alkalinity slag with good fluidity is quickly formed; (2) the [ P]in the molten iron is simultaneously contacted with CaO and FeO in the slag; (3) the temperature of the treatment process must be kept low; the dynamic conditions for molten iron dephosphorization are as follows: the slag and the molten metal are required to be well mixed at all times, i.e., the molten metal bath and the molten slag are sufficiently mixed and stirred.

According to the above experimental and theoretical analysis and the purpose of the invention, the technical implementation scheme of the molten iron pre-dephosphorization method of the invention is as follows:

the molten iron pre-dephosphorization is carried out in a converter type container with top and bottom combined converting function, and the technology of top oxygen blowing and bottom nitrogen blowing is adopted.

When the molten iron pre-dephosphorization treatment is started, firstly, a dephosphorization agent is added into a molten pool, the dephosphorization agent adopted by the invention is synthetic slag, and the synthetic slag comprises two types, namely synthetic slag A and synthetic slag B. The chemical composition (Wt%) of the synthetic slag A is as follows: 50-70% of CaO, 15-35% of iron oxide and CaF₂5-15％

The chemical components (Wt%) of the synthetic slag B are as follows: CaO 55-70%, iron oxide 15-30%, CaF₂4-10％,Na₂CO₂4-9％；

Of the above components, CaCO may be used as CaO₃Substitution or partial substitution; the iron oxide is FeO and Fe₂O₃Or FeO, Fe₂O₃Any one of the above; the iron oxide can be steel rolling sheet iron or converter smoke dust containing iron oxide more than or equal to 60 percent.

In the implementation, the dephosphorization agent can adopt any one of or the mixture of two of the synthetic slag A or the synthetic slag B during the pre-dephosphorization treatment. The total adding amount of the synthetic slag is determined according to the silicon content of the dephosphorized molten iron, and the alkalinity R of the final processed slag is required to be more than or equal to 3.0. And the alkalinity of the synthetic slag per se requires that R is more than or equal to 10. The synthetic slag forming method can adopt cold consolidation forming or high-temperature sintering forming. Cold consolidation forming adopts a ball press to extrude and form the bulk material; the high-temperature sintering temperature is 1180-1240 ℃ during high-temperature sintering molding.

In the dephosphorization pretreatment of molten iron, besides adding the dephosphorization agent into a molten pool in batches within seven and eight minutes from the beginning, the following technological parameters of the dephosphorization pretreatment need to be controlled. Namely: the oxygen supply intensity at the top is 0.75-1.20Nm³/min.t；

The stirring intensity of nitrogen supply at the bottom is as follows: 0.10-0.60Nm³T is/min; the alkalinity of the slag at the converting end point is controlled to be more than or equal to 3.0. The bath temperature should not exceed 1350 ℃.

In the implementation of the technical scheme, the application of the synthetic slag technology ensures that the molten iron dephosphorization pretreatment is carried out under the low-temperature condition (1300-. The synthetic slag has low melting point and good fluidity, and the synthetic slag contains higher CaO and proper amount of oxidants FeO and Fe₂O₃And (3) the iso-iron oxides promote the following dephosphorization reaction to rapidly occur on the interface of molten iron and molten slag in a molten metal pool:

the technical measures can meet the basic requirements of molten iron dephosphorization, which is the obvious technical characteristic of the invention different from other dephosphorization methods. And can achieve the following dephosphorization technical indexes:

when the synthetic slag sintered at high temperature is adopted:

the dephosphorization rate of molten iron in the converter type container is more than or equal to 85-90 percent;

the decarbonization amount delta C at the molten iron treatment end point is less than or equal to 0.7 percent;

the final slag alkalinity is controlled to be more than or equal to 3.0;

the purification treatment time is less than or equal to 18 min.

When the cold-concretion formed synthetic slag is adopted:

the dephosphorization rate of molten iron in the converter type container is more than or equal to 85-90 percent;

the decarbonization amount delta C = 0.5-0.7% of the molten iron treatment end point;

the alkalinity R of the final slag is more than or equal to 3.0;

the pure treatment time is 20 min.

Compared with the prior art, the invention has the following advantages:

(1) by using the mature technology of converter combined blowing, the required dynamic conditions in the molten iron dephosphorization process are fully ensured;

(2) the synthetic slag technology is adopted, so that the problem of quick melting of lime-based slag during dephosphorization under low temperature is properly solved;

(3) the dephosphorization efficiency of the molten iron dephosphorization is high, the dephosphorization effect is stable, and the method is suitable for the dephosphorization pretreatment of low-phosphorus and medium-phosphorus molten iron;

(4) the dephosphorizing agent has wide source of raw materials and low price, and can be conveniently obtained in large quantity.

Example 1

The treatment container is a medium frequency induction furnace, the weight of molten iron is 70Kg, the high temperature sintering synthetic slag with the slag amount of 5.6Kg is adopted, and the slag is added in three batches.

The chemical components (Wt%) of the synthetic slag are as follows: 60% CaO, FeO + Fe₂O₃30％,CaF₂10％。

Firstly, pouring molten iron into a medium-frequency induction furnace, electrifying and heating, and controlling the temperature of the molten iron

Namely, the mixed blowing of top-blown oxygen and bottom-blown nitrogen is started. And adding the synthetic slag in batches. Timing temperature measurement

The sampling is carried out along with the lapse of the converting time, and the components of the molten iron are continuously changed. Composition,temperature, top of molten iron

The changes over time in the oxygen partial blowing strength and the nitrogen bottom-blown strength are shown in Table 1. .

As shown in Table 1, the dephosphorization ratio was η_p= 88%, decarbonization amount Δ C =0.59, and final slag basicity R = 3.4.

The final slag composition (Wt%) was: CaO37.41%, SiO₂11％,P₂O₅6.43％,TFe17.90)％,MnO9.87％。

Table 1 example 1 variation of molten iron temperature, molten iron composition and blowing parameters with blowing time

Time (min) Parameter(s)		Start of converting	6	12	15	18	20
								The temperature of molten iron is lower		1328	1360	1344	1346	1349	1350
Strength of top blown oxygen Nm3/min.t		1.06	1.06	0.8	0.8	0.8	0.8
								Strength of bottom blown nitrogen Nm3/min.t		0.18	0.26	0.26	0.26	0.26	0.26
Composition of molten iron (Wt) ％)	C	4.31	4.11	3.98	3.81	3.72	-
								Si	0.32	0.13	0.02	＜0.01	＜0.01	＜0.01
	P	0.21 6	0.198	0.077	0.040	0.025	0.015
								Mn	1.03	0.61	0.38	0.33	0.29
	S	0.028	0.024	0.020	0.018	0.018	0.017
								Fe	Surplus	Surplus	Surplus	Surplus	Surplus	Surplus

Example 2

The treatment container is a medium frequency induction furnace, the weight of molten iron is 70Kg, and the synthetic slag formed by cold consolidation is 6.5 Kg.

The chemical components (Wt%) of the synthetic slag are as follows: CaCO₃64 percent, 30 percent of converter smoke and dust and CaF₂6 percent. Pouring molten iron into a medium-frequency induction furnace, electrifying and adding, controlling the temperature of the molten iron, immediately starting mixed blowing of bottom blowing nitrogen and top blowing oxygen, and simultaneously synthesizingAnd adding the slag into the furnace in batches, measuring the temperature of the molten iron at regular time and taking out a molten iron sample after blowing begins, and recording the mixed blowing parameters. Table 2 lists the change in molten iron temperature, molten iron composition and mix blow parameters with time.

The pretreatment results were as follows:

dephosphorization ratio of molten iron η_p=93.2％，

The molten iron terminal decarburization quantity delta C = 0.64%,

and (3) final slag alkalinity R = 3.04.

The final slag composition (Wt%) was: CaO44.84%, SiO₂14.75％,∑FeO25.58％,P₂O₅2.27％,MnO1.16％。

Table 2 example 2 variation of molten iron temperature, molten iron composition and mix blow parameters with time

Time (min) Parameter(s)		Start of converting	5	10	15	20
							The temperature of molten iron is lower		1335	1326	1346	1356	1348
Strength of top blown oxygen Nm3/min.t		1.22	1.20	1.00	0.85	0.90
							Strength of bottom blown nitrogen Nm3/min.t		0.155	0.18	0.18	0.21	0.218
Composition of molten iron (Wt) ％)	C	4.28	4.24	4.18	3.90	3.64
							Si	0.35	0.20	0.083	0.014	0.01
	P	0.074	0.059	0.042	0.011	0.005
							Fe	Surplus	Surplus	Surplus	Surplus	Surplus

Example 3

The treatment container is a medium frequency induction furnace, the weight of molten iron is 70Kg, and the amount of slag is 5.7Kg after high temperature sintering slag is prepared.

The chemical components (Wt%) of the high-temperature sintering synthetic slag are as follows: 55% CaO, FeO + F₂O₃27％,CaF₂9％，Na₂CO₃9％

Firstly, the pig iron material in the intermediate frequency induction furnace is heated and melted, and the temperature of the molten iron is controlled to be about 1300-1360 ℃. Then top blowing oxygen, bottom blowing nitrogen and 1/3 all slag (2.0Kg) are added simultaneously, the rest slag is added into the melting bath in two-three batches, temperature measurement and sampling are carried out at certaintime intervals.

Table 3 shows the change in the temperature, composition and amount of molten iron supplied during the treatment.

The final pretreatment results were as follows:

dephosphorization ratio of molten iron η_p=91.8％，

The decarburization quantity of the molten iron is delta C = 0.37%,

and (3) final slag alkalinity R = 3.3.

The chemical composition (Wt%) of the final slag is as follows: CaO 34.49%, SiO₂10.45％,P₂O₅8.0％,TFe18.10％,MnO 11.4％。

Table 3 example 3 variation of molten iron temperature, molten iron composition and mix blow parameters with time

Time of day (min) Parameter(s)		Start of converting	5	10	15	20
							The temperature of molten iron is lower		1328	1354	1316	1349	1346
Strength of top blown oxygen Nm3/min.t		1.14	1.06	0.87	0.87	0.87
							Strength of bottom blown nitrogen Nm3/min.t		0.32	0.42	0.60	0.53	0.50
Composition of molten iron (Wt) ％)	C	4.07	3.91	4.03	4.00	3.70
							Si	0.39	0.14	0.03	＜0.02	＜0.01
	Mn	1.06	0.64	0.42	0.33	0.27
							P	0.255	0.1 66	0.127	0.053	0.021
	S	0.025	0.020	0.018	0.016	0.015
							Fe	Surplus	Surplus	Surplus	Surplus	Surplus

Claims (6)

1. The utility model provides a molten iron dephosphorization method in advance to have the converter type container of top bottom combined converting function as the processing container, adopts the technology of top blowing oxygen and bottom blowing nitrogen gas, its characterized in that:

(1) either the synthetic slag A or the synthetic slag B is adopted as a dephosphorizing agent or a mixture of the two;

the chemical components (Wt%) of the synthetic slag A are as follows: CaO 50-70%, iron oxide 15-35%, fluorite CaF₂5-15％；

The chemical components (Wt%) of the synthetic slag B are 55-70% of CaO, 15-30% of iron oxide and fluorite CaF₂4-10％，Na₂CO₃4-9％；

(2) The pre-dephosphorization temperature range of the molten iron is 1300-1360 ℃;

(3) oxygen supply intensity at the top: 0.75-1.20Nm³/min.t；

(4) Bottom nitrogen supply strength: 0.10-0.60Nm³/min.t；

(5) The silicon content of the pretreated molten iron is required to be less than or equal to 0.4 percent;

(6) and controlling the alkalinity of the slag at the end point of the pre-dephosphorization blowing to be more than or equal to 3.

2. The method according to claim 1, wherein the CaO in the chemical composition is CaCO₃Instead of or in part.

3. A process according to claim 1, characterized in that the iron oxide in the dephosphorising agent chemistry is FeO and Fe₂O₃Or FeO, Fe₂O₃Any of the above.

4. The method as claimed in claim 1 or 3, wherein the iron oxide is mill scale containing iron oxide of 60% or more or converter dust.

5. The method of claim 1, wherein the synthetic slag is formed by cold consolidation

Molding or high-temperature sintering molding.

6. The method according to claim 1, wherein the basicity R of the synthetic slag is 10 or more.