阅读说明：本技术 一种基于热送热装工艺的板坯表面氧化铁皮加热控制方法 (Plate blank surface iron scale heating control method based on hot-conveying and hot-charging process ) 是由 魏兵 尹云洋 张扬 梁文 张鹏武 谭佳梅 徐峰 王立新 王世森 于 2020-06-29 设计创作，主要内容包括：一种基于热送热装工艺的板坯表面氧化铁皮加热控制方法,所述方法包括步骤：将加热炉内部依次划分为预热段、加热段和均热段；获取所述加热段对应的抛物线氧化规律公式和所述均热段对应的直线氧化规律公式；根据所述抛物线氧化规律公式和所述直线氧化规律公式计算临界氧浓度；向所述预热段中通入第一加热气氛,向所述加热段中通入第二加热气氛,向所述均热段中通入第三加热气氛；将板坯输送至所述预热段中以对其进行预加热；将所述板坯输送至所述加热段中以对其进行第一氧化；将所述板坯输送至所述均热段中以对其进行第二氧化。本发明无需对现有产线进行改造,只需优化加热工艺参数,控制炉内气氛及相应段的加热温度,简单易行,具有普遍推广意义。(A slab surface iron scale heating control method based on a hot-feeding and hot-charging process comprises the following steps: dividing the interior of the heating furnace into a preheating section, a heating section and a soaking section in sequence; acquiring a parabolic oxidation rule formula corresponding to the heating section and a linear oxidation rule formula corresponding to the soaking section; calculating the critical oxygen concentration according to the parabolic oxidation law formula and the linear oxidation law formula; introducing a first heating atmosphere into the preheating section, introducing a second heating atmosphere into the heating section, and introducing a third heating atmosphere into the soaking section; conveying the slabs into the preheating section to preheat the slabs; conveying the slab into the heating section for a first oxidation thereof; transporting the mat into the soaking section for a second oxidation thereof. The invention does not need to modify the existing production line, only needs to optimize the heating process parameters and control the heating temperature of the atmosphere in the furnace and the corresponding section, is simple and easy to implement and has general popularization significance.)

1. A slab surface iron scale heating control method based on a hot-feeding and hot-charging process is characterized by comprising the following steps:

dividing the interior of the heating furnace into a preheating section, a heating section and a soaking section in sequence;

acquiring a parabolic oxidation rule formula corresponding to the heating section and a linear oxidation rule formula corresponding to the soaking section;

calculating the critical oxygen concentration according to the parabolic oxidation law formula and the linear oxidation law formula;

introducing a first heating atmosphere into the preheating section, introducing a second heating atmosphere into the heating section, and introducing a third heating atmosphere into the soaking section;

conveying the slabs into the preheating section to preheat the slabs;

conveying the slab into the heating section for a first oxidation thereof;

transporting the mat into the soaking section for a second oxidation thereof.

2. The slab surface scale heating control method based on the hot-delivery hot-charging process as claimed in claim 1, wherein the parabolic oxidation law formula is:

wherein, W represents the scale oxidation increment, Kp represents the speed constant of the parabolic oxidation law, and t represents time.

3. The method for controlling the heating of the scale on the surface of the slab based on the hot-feeding and hot-charging process as claimed in claim 1, wherein the linear oxidation law formula is as follows:

W＝K1*P_o2*t

where W represents the scale increase, K1 represents the linear oxidation rate constant, Po2 represents the oxygen concentration, and t represents time.

4. The method for controlling the heating of the scale on the surface of the slab based on the hot-feeding and hot-charging process as claimed in claim 1, wherein the formula of the critical oxygen concentration is as follows:

P_o2lin＝7.519*Kp/(2*G*K1)

wherein, it represents critical oxygen concentration, Kp represents parabolic oxidation rate constant, G represents thickness of iron scale, and K1 represents linear oxidation rate constant.

5. The method for controlling the heating of the scale on the surface of the slab based on the hot-feeding hot-charging process as claimed in claim 1, wherein the step of conveying the slab into the preheating section for preheating the slab comprises the steps of:

keeping the charging temperature of the plate blank to be more than or equal to 400 ℃;

the plate blank is heated by using the flue gas to recover the waste heat;

keeping the heating time of the preheating section at 40-60 min;

the temperature of the end section of the preheating section is maintained at 700-1000 ℃.

6. The method for controlling the heating of the scale on the surface of the slab based on the hot charging process as claimed in claim 5, wherein the method further comprises the following steps before the step of keeping the charging temperature of the slab to be more than or equal to 400 ℃:

connecting the heating section and the soaking section with the preheating section respectively;

recovering the flue gas waste heat generated in the heating section and the soaking section into the preheating section;

and heating the plate blank in the preheating section by using the residual heat of the flue gas.

7. The method for controlling the heating of the scale on the surface of the slab based on the hot-charging process as claimed in claim 1, wherein the step of conveying the slab into the heating section for carrying out the first oxidation comprises the steps of:

introducing the second heating atmosphere into the heating section;

keeping the heating time of the heating section at 65-80 min;

keeping the end temperature of the heating section at 1200-1300 ℃;

and keeping the temperature of the slab uniform, wherein the temperature gradient in the slab is less than or equal to 20 ℃.

8. The slab surface scale heating control method based on the hot-delivery hot-charging process as claimed in claim 7, wherein the second heating atmosphere comprises: the air-fuel ratio is 1.05-1.25, the oxygen content is more than or equal to the critical oxygen concentration, H₂O content of 15% or more, CO₂Content of not less than 8%, N₂The content is 71-74%.

9. The method for controlling the heating of the scale on the surface of the slab based on the hot charging process as claimed in claim 1, wherein the step of conveying the slab into the soaking section to carry out the second oxidation comprises the steps of:

introducing the third heating atmosphere into the soaking section;

keeping the temperature gradient between the soaking section and the tail end of the heating section to be less than or equal to 20 ℃;

keeping the heating time of the soaking section at 25-40 min;

keeping the end temperature of the soaking section at 1200-1300 ℃;

and keeping the temperature of the slab uniform, wherein the temperature gradient in the slab is less than or equal to 20 ℃.

10. The slab surface scale heating control method based on the hot-delivery hot-charging process as claimed in claim 1, wherein the third heating atmosphere comprises: the air-fuel ratio is 0.90-1.0, the oxygen content is less than or equal to the critical oxygen concentration, H₂O content of 10-15%, CO₂Content of 6-8%, N₂The content is 71-74%.

Technical Field

The invention belongs to the technical field of steel manufacturing for hot rolled strips, and particularly relates to a slab surface iron scale heating control method based on a hot-feeding hot-charging process.

Background

The continuous casting billet hot-feeding hot charging and direct rolling are a new process and a new technology which are developed by integrating the latest technical achievements of steel making, continuous casting and steel rolling in recent years, promote the integrated process of the production management of steel making, continuous casting and steel rolling, can obtain the comprehensive benefits of energy conservation, consumption reduction, product quality and productivity improvement and the like, and are continuously improved in proportion of application in steel enterprises. According to the introduction of data, only the hot-feeding and hot-charging process is adopted, the fuel consumption can be reduced by 45%, and the production cost can be reduced by about 30-60 yuan/ton. In the continuous low-level steel market and the current situation that various large steel plants fight for survival, energy conservation, consumption reduction, cost reduction and efficiency improvement are particularly important, so that a plurality of steel enterprises carry out deep research and integrated innovation on heating furnace process technologies and equipment for hot charging and direct rolling. The heating furnace has the advantages that the heating furnace is flexible to operate and accurate to control, can be used for reheating high-temperature casting blanks and directly heating cold blanks by combining the characteristics of key factors such as continuous casting, steel-making plane arrangement, equipment configuration and the like, meets the requirements of direct rolling continuity and quick passing performance of slabs, and realizes energy conservation and consumption reduction.

The hot charging or direct charging process has higher requirements on the overall coordination capacity of steel enterprises, and manufacturing management departments, hot rolling plants, steel mills and sales centers are often required to be in seamless connection, but the process is difficult to achieve in the actual production organization process, and a large part of steel billets still enter a furnace in a cold charging mode. The hot history of the plate blank charged into the furnace by cold charging is completely different from that of hot charging, the heating requirements are different, meanwhile, the temperature of the cold charging plate blank is above 400 ℃, a layer of thicker iron oxide scale exists on the surface of the plate blank, and if the subsequent heating process is not proper, the serious quality problem of the final product can be caused. Therefore, a system research of a slab heating process needs to be carried out aiming at the hot-feeding hot-charging process, a proper heating process needs to be formulated, the problem of surface defects of the slab is solved, and the surface quality of the slab is improved.

Disclosure of Invention

In view of the above problems, the present invention provides a method for controlling the heating of scale on the surface of a slab based on a hot-charging process, which overcomes or at least partially solves the above problems.

In order to solve the technical problem, the invention provides a slab surface iron scale heating control method based on a hot-delivery hot-charging process, which comprises the following steps:

dividing the interior of the heating furnace into a preheating section, a heating section and a soaking section in sequence;

acquiring a parabolic oxidation rule formula corresponding to the heating section and a linear oxidation rule formula corresponding to the soaking section;

calculating the critical oxygen concentration according to the parabolic oxidation law formula and the linear oxidation law formula;

introducing a first heating atmosphere into the preheating section, introducing a second heating atmosphere into the heating section, and introducing a third heating atmosphere into the soaking section;

conveying the slabs into the preheating section to preheat the slabs;

conveying the slab into the heating section for a first oxidation thereof;

transporting the mat into the soaking section for a second oxidation thereof.

Preferably, the formula of the parabolic oxidation law is as follows:

wherein, W represents the scale oxidation increment, Kp represents the speed constant of the parabolic oxidation law, and t represents time.

Preferably, the linear oxidation law formula is as follows:

W＝K1*P_o2*t

where W represents the scale increase, K1 represents the linear oxidation rate constant, Po2 represents the oxygen concentration, and t represents time.

Preferably, the formula of the critical oxygen concentration is:

P_o2lin＝7.519*Kp/(2*G*K1)

wherein, it represents critical oxygen concentration, Kp represents parabolic oxidation rate constant, G represents thickness of iron scale, and K1 represents linear oxidation rate constant.

Preferably, said conveying of slabs into said preheating section for preheating thereof comprises the steps of:

keeping the charging temperature of the plate blank to be more than or equal to 400 ℃;

the plate blank is heated by using the flue gas to recover the waste heat;

keeping the heating time of the preheating section at 40-60 min;

the temperature of the end section of the preheating section is maintained at 700-1000 ℃.

Preferably, before the step of maintaining the charging temperature of the slab to be more than or equal to 400 ℃, the method further comprises the following steps:

connecting the heating section and the soaking section with the preheating section respectively;

recovering the flue gas waste heat generated in the heating section and the soaking section into the preheating section;

and heating the plate blank in the preheating section by using the residual heat of the flue gas.

Preferably, said conveying of said slabs into said heating section for a first oxidation thereof comprises the steps of:

introducing the second heating atmosphere into the heating section;

keeping the heating time of the heating section at 65-80 min;

keeping the end temperature of the heating section at 1200-1300 ℃;

and keeping the temperature of the slab uniform, wherein the temperature gradient in the slab is less than or equal to 20 ℃.

Preferably, the second heating atmosphere comprises: the air-fuel ratio is 1.05-1.25, the oxygen content is more than or equal to the critical oxygen concentration, H₂O content of 15% or more, CO₂Content of not less than 8%, N₂The content is 71-74%.

Preferably, said conveying of said slab into said soaking section for a second oxidation thereof comprises the steps of:

introducing the third heating atmosphere into the soaking section;

keeping the temperature gradient between the soaking section and the tail end of the heating section to be less than or equal to 20 ℃;

keeping the heating time of the soaking section at 25-40 min;

keeping the end temperature of the soaking section at 1200-1300 ℃;

and keeping the temperature of the slab uniform, wherein the temperature gradient in the slab is less than or equal to 20 ℃.

Preferably, the third heating atmosphere comprises: the air-fuel ratio is 0.90-1.0, the oxygen content is less than or equal to the critical oxygen concentration, H₂O content of 10-15%, CO₂Content of 6-8%, N₂The content is 71-74%.

One or more technical solutions in the embodiments of the present invention have at least the following technical effects or advantages:

(1) according to the invention, the critical oxygen concentration in the heating furnace is determined according to the oxidation rule of the plate blank, the oxygen concentration of each section in the heating process is reasonably controlled, the plate blank is subjected to oxidation according to the designed oxidation rule, and finally, an iron scale structure mainly comprising FeO is realized;

(2) the invention does not need to modify the existing production line, only needs to optimize the heating process parameters and control the heating temperature of the atmosphere in the furnace and the corresponding section, is simple and easy to implement and has general popularization significance.

Drawings

In order to more clearly illustrate the technical solutions in the embodiments of the present invention, the drawings needed to be used in the description of the embodiments are briefly introduced below, and it is obvious that the drawings in the following description are some embodiments of the present invention, and it is obvious for those skilled in the art to obtain other drawings based on the drawings without creative efforts.

Fig. 1 is a schematic diagram of surface scale on a discharged plate blank obtained by using a plate blank surface scale heating control method based on a hot charging process provided by an embodiment of the invention;

FIG. 2 is a schematic diagram of the surface scale of the discharged plate blank obtained by the conventional heating process in the prior art.

Detailed Description

The present invention will be described in detail below with reference to specific embodiments and examples, and the advantages and various effects of the present invention will be more clearly apparent therefrom. It will be understood by those skilled in the art that these specific embodiments and examples are for the purpose of illustrating the invention and are not to be construed as limiting the invention.

Throughout the specification, unless otherwise specifically noted, terms used herein should be understood as having meanings as commonly used in the art. Accordingly, unless defined otherwise, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this invention belongs. If there is a conflict, the present specification will control.

Unless otherwise specifically stated, various raw materials, reagents, instruments, equipment and the like used in the present invention are commercially available or can be prepared by existing methods.

In the embodiment of the application, the application provides a slab surface iron scale heating control method based on a hot-delivery hot-charging process, and the method comprises the following steps:

dividing the interior of the heating furnace into a preheating section, a heating section and a soaking section in sequence;

acquiring a parabolic oxidation rule formula corresponding to the heating section and a linear oxidation rule formula corresponding to the soaking section;

calculating the critical oxygen concentration according to the parabolic oxidation law formula and the linear oxidation law formula;

introducing a first heating atmosphere into the preheating section, introducing a second heating atmosphere into the heating section, and introducing a third heating atmosphere into the soaking section;

conveying the slabs into the preheating section to preheat the slabs;

conveying the slab into the heating section for a first oxidation thereof;

transporting the mat into the soaking section for a second oxidation thereof.

When the plate blank is in the heating section, sufficient oxygen required by oxidation reaction is contained in the atmosphere gas in the furnace, the oxidation speed of the plate blank is determined by the diffusion of iron ions at high temperature, the oxidation speed is high at the moment, and the oxidation is carried out according to a parabolic oxidation rule formula, wherein the parabolic oxidation rule formula is as follows:

wherein, W represents the scale oxidation increment, Kp represents the speed constant of the parabolic oxidation law, and t represents time.

Further, Kp can be calculated by the following formula:

where Kpo is 0.60g2/(cm2 · s), E represents activation energy, R represents a gas constant, and T represents temperature.

Under the condition of high oxygen concentration, the surface of the slab can obtain a typical three-layer iron scale structure (the outermost layer of Fe)₂O₃Middle layer Fe₃O₄Innermost layer, most preferably a layer of a thermoplastic resinFeO)。

When the slab is in the soaking section, along with the continuous oxidation of slab, its surface scale thickness is more and more thick, can't supply sufficient oxygen from outermost scale to the innermost scale (being close to the base member), and high temperature scale is under the low oxygen concentration condition, and the oxidation rate mainly is supplied with the decision by the oxygen in the iron sheet, and the oxidation rate is slower, and the oxidation law goes on with mild straight line oxidation law formula, straight line oxidation law formula is:

W＝K1*P_o2*t

wherein W represents the scale increase, K1 represents the linear oxidation rate constant (9.6 x 10-6 g/(cm-2. cndot. s)), Po2 represents the oxygen concentration, and t represents time.

In the process, the high-valence oxides continuously lose oxygen, and finally, an iron scale structure mainly containing FeO is obtained, and little Fe304 and Fe203 or no Fe304 and Fe203 exist in the iron scale.

The transition from high oxygen concentration to low oxygen concentration is critical and requires accurate calculation of the critical oxygen concentration. The oxygen concentration critical point is calculated by equalizing the high oxygen concentration atmosphere condition in which oxidation is performed according to the parabolic oxidation law formula and the low oxygen concentration atmosphere condition in which oxidation is performed according to the linear oxidation law formula, as shown below,

the following relationship exists between the thickness of the iron scale and the oxidation increment:

W＝G/7.519，

wherein G represents the thickness (um) of the scale.

Therefore, the critical oxygen concentration at the intersection of the high oxygen concentration and the low oxygen concentration atmosphere can be calculated by the above formula:

P_o2lin＝7.519*Kp/(2*G*K1)

wherein, it represents critical oxygen concentration, Kp represents parabolic oxidation rate constant, G represents thickness of iron scale, and K1 represents linear oxidation rate constant.

This formula shows that the critical oxygen concentration depends not only on the oxygen supply in the furnace but also is closely related to the thickness of the scale and the temperature of the furnace. Therefore, during the actual rolling process of the slab, the heating process parameters are established according to the principle, and a thin and single iron oxide scale structure is generated on the surface of the slab.

Firstly, calculating the critical oxygen concentration in the heating furnace according to the formula so that the oxygen concentration of the heating section and the soaking section meets certain requirements: in the heating section, the oxygen content is required to be not more than equal, and in the soaking section, the oxygen content is required to be not more than equal. And then, according to the specific requirements of each section such as temperature, time and the like, reasonably setting the process parameters of each heating stage to meet the final requirements. Meanwhile, certain water vapor is generated in the heating oxidation process, the oxygen concentration of the water vapor can affect the surface of the plate blank, and the concentration of the water vapor in the furnace also needs to be strictly controlled.

In an embodiment of the application, said conveying the slabs into said preheating section for preheating thereof comprises the steps of:

keeping the charging temperature of the plate blank to be more than or equal to 400 ℃;

the plate blank is heated by using the flue gas to recover the waste heat;

keeping the heating time of the preheating section at 40-60 min;

the temperature of the end section of the preheating section is maintained at 700-1000 ℃.

In the embodiment of the application, before the step of maintaining the charging temperature of the slab to be more than or equal to 400 ℃, the method further comprises the following steps:

connecting the heating section and the soaking section with the preheating section respectively;

recovering the flue gas waste heat generated in the heating section and the soaking section into the preheating section;

and heating the plate blank in the preheating section by using the residual heat of the flue gas.

In the embodiment of the application, the slab in the preheating section can be preheated by using the waste heat of the tail gas generated by heating in the heating section and the soaking section, so that on one hand, the waste heat of the tail gas can be utilized to improve the utilization efficiency of energy; on the other hand, resources such as heating gas can be saved.

In an embodiment of the present application, said conveying said slab into said heating section for a first oxidation thereof comprises the steps of:

introducing the second heating atmosphere into the heating section; wherein the air-fuel ratio of the second heating atmosphere is 1.05-1.25, the oxygen content is greater than or equal to the critical oxygen concentration, and H₂O content of 15% or more, CO₂Content of not less than 8%, N₂The content is 71% -74%;

keeping the heating time of the heating section at 65-80 min;

keeping the end temperature of the heating section at 1200-1300 ℃;

and keeping the temperature of the slab uniform, wherein the temperature gradient in the slab is less than or equal to 20 ℃.

In the embodiment of the application, the conveying the slab into the soaking section to carry out the second oxidation comprises the following steps:

introducing the third heating atmosphere into the soaking section; wherein the air-fuel ratio of the third heating atmosphere is 0.90-1.0, the oxygen content is less than or equal to the critical oxygen concentration, and H₂O content of 10-15%, CO₂Content of 6-8%, N₂The content is 71% -74%;

keeping the temperature gradient between the soaking section and the tail end of the heating section to be less than or equal to 20 ℃;

keeping the heating time of the soaking section at 25-40 min;

keeping the end temperature of the soaking section at 1200-1300 ℃;

and keeping the temperature of the slab uniform, wherein the temperature gradient in the slab is less than or equal to 20 ℃.

The present application is described in detail below with specific examples.