Method for predicting content of Al and Fe in equilibrium state through hot galvanizing aluminum increasing and iron removing operation

Abstract

The invention discloses a method for predicting the content of Al and Fe in an equilibrium state through aluminum-rising and iron-removing operation in hot galvanizing, which comprises the following steps: carrying out aluminum-rising and iron-removing operation on zinc liquid in the last production period, and adding a zinc ingot with higher aluminum content; the temperature T is kept unchanged, sampling is conducted, and the aluminum content Fe0 and the iron content Al0 in the zinc liquid in the aluminum rising and iron removing operation are measured; calculating to obtain Al and Fe contents in an equilibrium state; according to the method, the aluminum content and the iron content reaching a Zn-Fe-Al metallographic equilibrium line are calculated according to the aluminum content and the iron content in the zinc liquid in the aluminum rising and iron removing operation, the aluminum content and the iron content in the zinc liquid in the equilibrium state of the zinc liquid can be judged in advance, and the method is a conventional method for removing scum in the hot galvanizing process. Therefore, the GI product production process is quickly determined.

Description

Technical Field

[0001] The invention belongs to the technical field of hot-dip galvanizing, and particularly relates to a method for predicting Al and Fe contents in a balanced state during hot-dip galvanizing aluminum-addition and iron-removal operations. Background Art

[0002] Galvanizing on the surface of steel is the most commonly used, cheapest and most effective measure in steel corrosion protection. The process flow of hot-dip galvanizing mainly includes pre-treatment stage, hot-dip galvanizing stage and post-treatment stage. The galvanizing process of the strip surface is mainly completed in the hot-dip galvanizing stage. In the hot-dip galvanizing stage, the steel strip passes through the furnace nose and enters the zinc pot liquid zinc at a temperature of 450-470°C. Under the guidance of the zinc pot sinking roller and two stabilizing rollers, it is brought out vertically from the zinc liquid, and then passes through a pair of air knives to blow off the excess zinc liquid through gas impact, thereby obtaining a uniform surface coating.

[0003] The zinc pot contains not only molten zinc liquid, but also iron and aluminum dissolved in it. When iron and aluminum react in the zinc liquid, zinc slag is formed. The current GI zinc pot bottomless slag production process requires an aluminum content of 0.16% to 0.18%, and the aluminum content is required to reach 0.2% to 0.25% when producing high-quality GI products. In the aluminum content range required for GI production, slag Fe2Al5 is generated, which has a lower density than zinc liquid and generally floats on the surface of zinc liquid. However, due to the stirring of the roller system in the zinc pot, it flows to the vicinity of the steel strip and adheres to the surface, causing zinc slag defects in GI products. How to reduce the zinc slag defect rate of GI products has always been a research focus in the field of hot-dip galvanizing.

[0004] Those skilled in the art should know that zinc slag will precipitate when the iron and aluminum content values ​​exceed the Zn-Fe-Al metallographic equilibrium line and become oversaturated. Therefore, monitoring the iron and aluminum content in the zinc liquid is the key. The commonly used method is to take samples on-site, detect them by chemical methods, and install online real-time monitoring tools. On-site sampling and testing is time-consuming and has a lag of several hours. Installing online real-time monitoring tools has the problem of high investment and maintenance costs.

[0005] In addition, when producing high-quality GI products, the scum content in the zinc pot is generally reduced by increasing aluminum and removing iron from the zinc pot, and the aluminum content in the zinc liquid is adjusted to a suitable range to ensure the production requirements for the aluminum content of the zinc liquid. Before formal production, it is also necessary to judge whether the state of the zinc pot scum meets the conditions for producing outer plates by producing products with lower surface quality requirements such as inner plates. The specific process is generally carried out based on on-site operation experience, and the operation process is cumbersome, time-consuming and labor-intensive. Summary of the invention

[0006] The present invention aims to provide a method for predicting the Al and Fe contents in the equilibrium state in the aluminum-raising and iron-removing operation in the hot-dip galvanizing process, which can effectively predict the development trend of the aluminum and iron contents in the zinc pot and monitor the state of the slag in the zinc liquid, thereby quickly determining the on-site GI product production process and reducing production costs.

[0007] In order to achieve the above purpose, the technical solutions adopted are as follows:

[0008] The method for predicting the Al and Fe contents in the equilibrium state of hot-dip galvanizing aluminum-adding and iron-removing operation comprises the following steps:

[0009] (1) The zinc liquid from the previous production cycle is subjected to an aluminum-adding and iron-removing operation, and a zinc ingot with a high aluminum content is added;

[0010] (2) Keeping the temperature T constant, sampling and measuring the aluminum and iron contents Fe0 and Al0 in the zinc solution during the aluminum-raising and iron-removing operation;

[0011] (3) Calculate the Al and Fe contents in equilibrium:

[0012] Fe=0.041*Fe0-0.0342*Al0+0.00015*T-0.0527

[0013] Al=-1.148*Fe0+0.9576*Al0+0.0002*T-0.0644.

[0015] According to the above scheme, the aluminum content of the zinc ingot in step 1 ranges from 0.8wt% to 1.0wt%.

[0016] According to the above scheme, the temperature T in step 2 ranges from 450°C to 470°C.

[0017] According to the above scheme, the iron content Fe0 in the zinc liquid in the aluminum-raising and iron-removing operation in step 2 is in the range of 0.01wt%-0.025wt%.

[0018] According to the above scheme, the aluminum content Al0 in the zinc liquid in the aluminum-raising and iron-removing operation in step 2 is in the range of 0.16wt%-0.36wt%.

[0019] Compared with the prior art, the present invention has the following beneficial effects:

[0020] The operation of increasing aluminum to remove iron reduces the iron content in the zinc liquid through the reaction of Al and Fe. It is a conventional method for removing scum in the hot-dip galvanizing process. The present invention calculates the aluminum and iron content values ​​reaching the Zn-Fe-Al metallographic equilibrium line according to the aluminum and iron contents in the zinc liquid obtained by the operation of increasing aluminum to remove iron. The aluminum and iron contents in the zinc liquid when the zinc liquid is in equilibrium can be judged in advance, thereby quickly determining the production process of GI products. BRIEF DESCRIPTION OF THE DRAWINGS

[0021] Figure 1 : Zn-Fe-Al metallographic equilibrium line at 450℃ in hot-dip galvanizing process. DETAILED DESCRIPTION

[0022] The following examples further illustrate the technical solution of the present invention, but are not intended to limit the scope of protection of the present invention.

[0023] like Figure 1 As shown in the figure, during the process of increasing aluminum and removing iron, the aluminum content in the zinc liquid is adjusted from the equilibrium point A to point B. At this time, since the aluminum and iron content exceed the equilibrium state, the aluminum and iron will immediately react to precipitate slag Fe2Al5. The chemical reaction formula is: 2Fe+5Al=Fe2Al5. After several hours, the aluminum and iron content will fall to point C of the Zn-Fe-Al metallographic equilibrium line.

[0024] The calculation process of point C is as follows: Assume that there is any point B (Fe0, Al0) in the L+Fe2Al5 region. Due to supersaturation, Fe2Al5 is formed, in which the weight ratio of Al / Fe is 135 / 112.

[0025] Therefore, B→C can be expressed as:

[0026] (Al0-Al) / (Fe0-Fe)=135 / 112; Simplified arrangement:

[0027] Al-1.2*Fe=Al0-1.2*Fe0--------------Formula (1).

[0028] According to the Zn-Fe-Al metallographic equilibrium line diagram, when the zinc liquid temperature is 450°C, the solubility equilibrium line has two points with coordinates of (0.16, 0.01) and (0.30, 0.005), respectively. The slope of the solubility line is:

[0029] ΔFe / ΔAl=(0.01-0.005) / (0.16-0.30)=-0.0357.

[0030] Therefore, the equation for the dissolution line is:

[0031] (Fe-0.01) / (Al-0.16)=-0.0357; Simplified arrangement:

[0032] Al+28*Fe=0.44----------------------Formula (2).

[0033] According to research, the solubility of Al and Fe is also affected by the temperature T of zinc liquid. For every 10°C increase in temperature, their solubility increases by 10%.

[0034] Let L = Al + 28 * Fe = 0.44;

[0035] When T=450→460℃, L increases by 10% from 0.44→0.484;

[0036] ΔL / ΔT=(0.484-0.440) / (460-450)=0.0044;

[0037] (L-0.44) / (T-450)=0.0044;

[0038] L=0.0044*T-1.54-------------------------Formula (3).

[0039] Substituting formula (3) into formula (2), we can get:

[0040] Al+28*Fe=0.0044*T-1.54-------------Formula (4).

[0041] Substituting formula (4) into formula (1), we can obtain:

[0042] 29.2*Fe=1.2*Fe0-Al0+0.0044*T-1.54, after rearrangement, we can get:

[0043] Fe=0.041*Fe0-0.0342*Al0+0.00015*T-0.0527----------Formula (5).

[0044] Substituting formula (5) into formula (4), we can obtain:

[0045] Al=-1.148*Fe0+0.9576*Al0+0.0002*T-0.0644---------Formula (6).

[0046] Formula (5) and Formula (6) are the aluminum and iron content values ​​reaching the Zn-Fe-Al metallographic equilibrium line after any supersaturated Fe0 and Al0 form Fe2Al5 in the L+Fe2Al5 region.

[0047] The specific implementation method provides a method for predicting the Al and Fe contents in equilibrium state in hot-dip galvanizing aluminum-removal iron removal operation:

[0048] According to the aluminum and iron contents in the zinc liquid obtained by the aluminum addition and iron removal operation, the aluminum and iron contents reaching the Zn-Fe-Al metallographic equilibrium line are calculated by formulas (5) and (6). At present, when producing high-quality GI products, zinc ingots with a high aluminum content are first added to increase the aluminum content in the zinc liquid, and the iron content in the zinc liquid is reduced through the reaction of Al and Fe, thereby reducing the generation of scum. When the aluminum and iron contents reach the Zn-Fe-Al metallographic equilibrium line, no scum will be precipitated in the zinc liquid. According to the aluminum and iron contents at this time, the appropriate GI product production process can be determined.

[0049] As shown in Table 1, the Al and Fe contents at equilibrium predicted by the present invention in Examples 2, 3, 4, and 5 are suitable for the production of GI products of different qualities. The Al and Fe contents at equilibrium predicted by the present invention in Examples 1 and 6 are not suitable for the production of GI products and need further adjustment.

[0050] Table 1

[0051]

Claims

1. A method for predicting the Al and Fe contents in equilibrium state during hot-dip galvanizing and aluminum-removal operation, characterized in that The following steps are involved: (1) The zinc liquid from the previous production cycle is subjected to an aluminum-adding and iron-removing operation, and a zinc ingot with a high aluminum content is added; (2) Keeping the temperature T constant, sampling and measuring the aluminum and iron contents Fe0 and Al0 in the zinc solution during the aluminum-raising and iron-removing operation; (3) Calculate the Al and Fe contents in equilibrium: Fe=0.041*Fe0-0.0342*Al0+0.00015*T-0.0527; Al=-1.148*Fe0+0.9576*Al0+0.0002*T-0.0644.

2. The method for predicting the Al and Fe contents in equilibrium state during hot dip galvanizing and aluminum removal operation as claimed in claim 1, characterized in that The aluminum content of the zinc ingot in step 1 is in the range of 0.8wt%-1.0wt%.

3. The method for predicting the Al and Fe contents in equilibrium state during hot-dip galvanizing and aluminum-removal operation as claimed in claim 1, characterized in that The temperature T in step 2 ranges from 450°C to 470°C.

4. The method for predicting the Al and Fe contents in equilibrium state during hot-dip galvanizing and aluminum-removal operation as claimed in claim 1, characterized in that In the aluminum-raising and iron-removing operation in step 2, the iron content Fe0 in the zinc solution ranges from 0.01wt% to 0.025wt%.

5. The method for predicting the Al and Fe contents in equilibrium state during hot dip galvanizing and aluminum removal operation as claimed in claim 1, characterized in that In the aluminum-raising and iron-removing operation in step 2, the aluminum content Al0 in the zinc solution ranges from 0.16wt% to 0.36wt%.

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