CN110195202A - A method of hot rolled steel plate surface oxidation iron sheet crackle is repaired based on hydrogen reducing - Google Patents

Abstract

A method for repairing iron oxide scale cracks on the surface of a hot-rolled steel sheet based on hydrogen reduction, relates to a method for repairing the surface of a steel sheet. The cracks generated by the iron sheet during the hot rolling process, cooling process and leveling process can improve the surface roughness of the steel sheet; according to the structure of the iron oxide sheet on the surface of the hot-rolled steel sheet, the structure is Fe ₃ O ₄ in the outer layer and proeutectoid in the inner layer. Fe ₃ O ₄ and eutectoid structure, as well as residual FeO, after the hot-rolled steel sheet is reduced with different concentrations of hydrogen and nitrogen mixed gas, the newly formed reduced iron can be repaired by the previous processes (hot rolling, cooling , flattening, etc.) resulting in surface cracks. It can not only improve the surface quality of the hot-rolled steel sheet, but also reduce the surface roughness of the steel sheet, and at the same time, the hot-rolled steel sheet can be used as a galvanized substrate to improve the surface quality of the galvanized sheet.

Description

A method for repairing iron oxide scale cracks on the surface of hot-rolled steel sheets based on hydrogen reduction

technical field

The invention relates to a method for repairing cracks on the surface of steel plates, in particular to a method for repairing cracks in iron oxide scales on the surface of hot-rolled steel plates based on hydrogen reduction.

Background technique

Due to the high production temperature of hot-rolled steel sheets and the condition of air, iron oxide scale is inevitably generated during the hot-rolling process. Many surface quality problems of hot-rolled steel sheets are caused by iron oxide scale. For example: pitting, pitting, iron oxide scale pressing and red iron oxide scale, etc. The cracking and bubbling of scale on the surface of the steel sheet during hot rolling are the direct causes of surface defects.

Under the traditional process conditions, the iron oxide scale on the surface of the hot-rolled steel sheet is washed off after pickling. As a galvanized substrate, it is first subjected to reduction annealing and then enters a zinc pot for galvanizing. As a highly polluting link in the traditional hot-dip galvanizing process, pickling brings a series of quality problems while increasing costs and reducing efficiency, and urgently requires technological innovation and production process optimization to reduce energy and resource consumption, protect the ecological environment, and achieve green manufacturing. . At present, there are many methods for cleaning and removing iron oxide scale, such as mechanical descaling and descaling by reducing atmosphere. For example, the patent application with the application number of 201110158729.8 "Continuous reduction and descaling method and device for hot-rolled strip steel" provides a method of reducing the scale of the hot-rolled strip steel surface to metal iron by using reducing gas, and using a high-speed rotating wire brush The method of cleaning and brushing the surface of the strip, and then cooling to room temperature after smoothing to eliminate surface defects. The surface roughness of the strip treated by this method is high, which affects the surface quality of the subsequent galvanized sheet. The patent application with the application number of 201310714802.4 "A method of pickling-free hot-dip galvanizing of hot-rolled strip based on iron oxide scale reduction" provides a method for reducing iron oxide scale and galvanizing by heating and gas reduction. In this patent application, the iron oxide scale structure of the hot-rolled strip is adjusted by controlling the temperature rise, and the reduction-annealed hot-rolled strip is reduced in a hydrogen atmosphere, and then hot-dip galvanizing is performed to optimize the effect of reduction galvanizing while reducing environmental pollution. Although the iron oxide scale can be reduced by reduction annealing, the reduction is not complete. At the same time, the patent focuses on the transformation of the iron oxide scale structure and the surface quality after galvanizing, but does not pay attention to the surface cracks of the hot-rolled strip after reduction. and defect conditions on the surface quality of subsequent galvanized sheets. SUMMARY OF THE INVENTION

The object of the present invention is to provide a method for repairing cracks on the surface of the hot-rolled steel sheet based on hydrogen reduction. In the present invention, after the hot-rolled steel sheet is reduced by a mixed gas of hydrogen and nitrogen with different concentrations, the newly formed reduced iron is repaired by the previous steps. (hot rolling, cooling, leveling, etc.) generated surface cracks; not only improve the surface quality of hot-rolled steel sheet, reduce the surface roughness of the steel sheet, while hot-rolled steel sheet can be used as a galvanized substrate to improve the surface quality of galvanized sheet.

The purpose of this invention is to realize through the following technical solutions:

A method for repairing iron oxide scale cracks on the surface of a hot-rolled steel sheet based on hydrogen reduction. Cracks generated during the flattening process improve the surface roughness of the steel plate;

The method includes the following processes:

Heating: in the heating furnace, the hot-rolled steel sheet with iron oxide scale is raised to the target temperature of 900-1000°C at a heating rate of 5-20°C/min, and the atmosphere in the heating section is nitrogen;

Isothermal: After heating to the target temperature, fill in the mixed gas with a volume fraction of 10%-30% hydrogen, and the rest is nitrogen; the isothermal reduction time is 30-600s;

Cooling: After isothermal reduction, nitrogen is charged, and after the hydrogen in the furnace is exhausted, the hot-rolled strip is taken out of the furnace and cooled to room temperature naturally in the air.

In the method for repairing cracks in iron oxide scale on the surface of a hot-rolled steel sheet based on hydrogen reduction, the thickness of the iron oxide scale on the surface of the hot-rolled steel sheet is 7-15 μm.

In the described method for repairing cracks in iron oxide scale on the surface of a hot-rolled steel sheet based on hydrogen reduction, the iron oxide scale on the surface of the hot-rolled steel sheet has an outer layer of Fe3O4, an inner layer of pro-eutectoid Fe3O4 and an eutectoid structure, and simultaneously. There is residual FeO.

The method for repairing iron oxide scale cracks on the surface of a hot-rolled steel sheet based on hydrogen reduction, wherein the hot-rolled steel sheet is a galvanized substrate.

The advantages and effects of the present invention are:

The invention abandons the pickling process under the traditional process conditions, reduces the pickling cost and the discharge of waste acid, and has the process characteristics of energy saving and environmental protection.

According to the present invention, the hot-rolled steel sheet is subjected to different concentrations of Fe _{3 O 4 on the surface of the hot-rolled steel sheet according to the fact that the structure of the iron oxide scale on the surface of the hot-rolled steel sheet is Fe 3 O 4 in the outer layer, the Fe 3 O 4 and eutectoid} structure in the inner layer are pro-eutectoid, and at the same time there are residual FeO. After the reduction of the mixed gas of hydrogen and nitrogen, the newly formed reduced iron can repair the surface cracks generated by the previous processes (hot rolling, cooling, leveling, etc.). It can not only improve the surface quality of the hot-rolled steel sheet, but also reduce the roughness of the surface of the steel sheet. At the same time, as a galvanized substrate, the hot-rolled steel sheet can also improve the surface quality of the galvanized sheet. The iron oxide scale on the surface of the hot-rolled steel sheet is repaired by hydrogen reduction. Cracks generated in the process of hot rolling, cooling and leveling not only reduce the occurrence of surface defects of hot-rolled steel sheets, but also directly improve the surface quality of hot-rolled steel sheets. For the hot-rolled steel sheet as a galvanized substrate, the surface quality of the steel sheet is improved after the surface cracks of the iron oxide scale are repaired, thereby reducing the occurrence of surface defects of the galvanized sheet.

Description of drawings

1 is a photo of the surface morphology of the metallographic structure before the iron oxide scale on the surface of the hot-rolled steel sheet is not reduced in Example 1 of the present invention;

2 is a photo of the surface morphology of the metallographic structure after the reduction of iron oxide scale on the surface of the hot-rolled steel sheet in Example 1 of the present invention;

3 is a photo of the surface morphology of the metallographic structure before the iron oxide scale on the surface of the hot-rolled steel sheet is not reduced in Example 2 of the present invention;

4 is a photo of the surface morphology of the metallographic structure after the reduction of iron oxide scale on the surface of the hot-rolled steel sheet in Example 2 of the present invention;

5 is a photo of the surface morphology of the metallographic structure before the iron oxide scale on the surface of the hot-rolled steel sheet is not reduced in Example 3 of the present invention;

6 is a photo of the surface morphology of the metallographic structure after the reduction of iron oxide scale on the surface of the hot-rolled steel sheet in Example 3 of the present invention;

7 is a photo of the surface morphology of the metallographic structure before the iron oxide scale on the surface of the hot-rolled steel sheet is not reduced in Example 4 of the present invention;

8 is a photo of the surface morphology of the metallographic structure after the reduction of iron oxide scale on the surface of the hot-rolled steel sheet in Example 4 of the present invention;

9 is a photo of the surface morphology of the metallographic structure before the iron oxide scale on the surface of the hot-rolled steel sheet is not reduced in Example 5 of the present invention;

10 is a photo of the surface morphology of the metallographic structure after the reduction of iron oxide scale on the surface of the hot-rolled steel sheet in Example 5 of the present invention;

11 is a photo of the surface morphology of the metallographic structure before the iron oxide scale on the surface of the hot-rolled steel sheet is not reduced in Example 6 of the present invention;

12 is a photo of the surface morphology of the metallographic structure after the reduction of the iron oxide scale on the surface of the hot-rolled steel sheet in Example 6 of the present invention.

Detailed ways

The present invention will be described in detail below with reference to the embodiments.

The model of the tubular hydrogen furnace used in the embodiment of the present invention is SKGL-1200H.

The metallographic microscope model used in the embodiments of the present invention is BX53M.

The hydrogen and nitrogen used in the embodiments of the present invention are industrial products.

Example 1

(1) Heating up: In the heating furnace, the hot-rolled steel sheet with iron oxide scale is raised to the target temperature of 900°C at a heating rate of 5°C/min, and the atmosphere in the furnace in the heating section is nitrogen.

(2) Isothermal: After heating to the target temperature, the mixture is filled with hydrogen with a volume fraction of 30%, and the rest is nitrogen. The isothermal reduction time was 120 s.

(3) Cooling: After isothermal reduction, nitrogen is charged, and after the hydrogen in the furnace is exhausted, the hot-rolled strip is taken out of the furnace and cooled to room temperature naturally in the air.

Figure 1 shows the surface morphology of the metallographic structure before the iron oxide scale on the surface of the hot-rolled steel sheet is not reduced. As shown in the figure, there are a large number of cracks on the surface of the iron oxide scale. Figure 2 shows the surface morphology of the metallographic structure after reduction of the iron oxide scale on the surface of the hot-rolled steel sheet. The position of the morphology is the in-situ position shown in Figure 1. As shown in the figure, the surface cracks of the iron oxide scale are repaired.

Example 2

(1) Heating up: In the heating furnace, the hot-rolled steel sheet with iron oxide scale is raised to the target temperature of 960°C at a heating rate of 10°C/min, and the atmosphere in the heating section is nitrogen.

(2) Isothermal: After heating to the target temperature, the mixture is filled with hydrogen with a volume fraction of 30%, and the rest is nitrogen. The isothermal reduction time was 60 s.

(3) Cooling: After isothermal reduction, nitrogen is charged, and after the hydrogen in the furnace is exhausted, the hot-rolled strip is taken out of the furnace and cooled to room temperature naturally in the air.

Figure 3 shows the surface morphology of the metallographic structure before the iron oxide scale on the surface of the hot-rolled steel sheet is not reduced. As shown in the figure, there are a large number of cracks on the surface of the iron oxide scale. Figure 4 shows the surface morphology of the metallographic structure after reduction of the iron oxide scale on the surface of the hot-rolled steel sheet. The position of the morphology is the in-situ position shown in Figure 3. As shown in the figure, the surface cracks of the iron oxide scale are repaired.

Example 3

(1) Heating up: In the heating furnace, the hot-rolled steel sheet with iron oxide scale is raised to the target temperature of 1000°C at a heating rate of 20°C/min, and the atmosphere in the heating section is nitrogen.

(2) Isothermal: After heating to the target temperature, the mixture is filled with hydrogen with a volume fraction of 30%, and the rest is nitrogen. The isothermal reduction time was 30s.

(3) Cooling: After isothermal reduction, nitrogen is charged, and after the hydrogen in the furnace is exhausted, the hot-rolled strip is taken out of the furnace and cooled to room temperature naturally in the air.

Figure 5 shows the surface morphology of the metallographic structure before the iron oxide scale on the surface of the hot-rolled steel sheet is not reduced. As shown in the figure, there are a large number of cracks on the surface of the iron oxide scale. Figure 6 shows the surface morphology of the metallographic structure after reduction of the iron oxide scale on the surface of the hot-rolled steel sheet. The position of the morphology is the in-situ position shown in Figure 5. As shown in the figure, the surface cracks of the iron oxide scale are repaired.

Example 4

(1) Heating up: In the heating furnace, the hot-rolled steel sheet with iron oxide scale is raised to the target temperature of 900°C at a heating rate of 20°C/min, and the atmosphere in the heating section is nitrogen.

(2) Isothermal: After heating to the target temperature, the mixture is filled with a volume fraction of 10% hydrogen and the rest is nitrogen. The isothermal reduction time was 600 s.

(3) Cooling: After isothermal reduction, nitrogen is charged, and after the hydrogen in the furnace is exhausted, the hot-rolled strip is taken out of the furnace and cooled to room temperature naturally in the air.

Figure 7 shows the surface morphology of the metallographic structure before the iron oxide scale on the surface of the hot-rolled steel sheet is not reduced. As shown in the figure, there are a large number of cracks on the surface of the iron oxide scale. Figure 8 shows the surface morphology of the metallographic structure of the iron oxide scale on the surface of the hot-rolled steel sheet after reduction. The position of the morphology is the in-situ position shown in Figure 7. As shown in the figure, the surface cracks of the iron oxide scale are repaired.

Example 5

(1) Heating up: In the heating furnace, the hot-rolled steel sheet with iron oxide scale is raised to the target temperature of 960°C at a heating rate of 10°C/min, and the atmosphere in the heating section is nitrogen.

(2) Isothermal: After heating to the target temperature, the mixture is filled with hydrogen with a volume fraction of 20%, and the rest is nitrogen. The isothermal reduction time was 120 s.

(3) Cooling: After isothermal reduction, nitrogen is charged, and after the hydrogen in the furnace is exhausted, the hot-rolled strip is taken out of the furnace and cooled to room temperature naturally in the air.

Figure 9 shows the surface morphology of the metallographic structure before the iron oxide scale on the surface of the hot-rolled steel sheet is not reduced. As shown in the figure, there are a large number of cracks on the surface of the iron oxide scale. Figure 10 shows the surface morphology of the metallographic structure of the iron oxide scale on the surface of the hot-rolled steel sheet after reduction. The position of the morphology is the in-situ position shown in Figure 9. As shown in the figure, the surface cracks of the iron oxide scale are repaired.

Example 6

(1) Heating up: In the heating furnace, the hot-rolled steel sheet with iron oxide scale is raised to the target temperature of 1000°C at a heating rate of 20°C/min, and the atmosphere in the heating section is nitrogen.

(2) Isothermal: After heating to the target temperature, the mixture is filled with a volume fraction of 10% hydrogen and the rest is nitrogen. The isothermal reduction time was 240s.

(3) Cooling: After isothermal reduction, nitrogen is charged, and after the hydrogen in the furnace is exhausted, the hot-rolled strip is taken out of the furnace and cooled to room temperature naturally in the air.

Figure 11 shows the surface morphology of the metallographic structure before the iron oxide scale on the surface of the hot-rolled steel sheet is not reduced. As shown in the figure, there are a large number of cracks on the surface of the iron oxide scale. Figure 12 shows the surface morphology of the metallographic structure of the iron oxide scale on the surface of the hot-rolled steel sheet after reduction. The position of the morphology is the in-situ position shown in Figure 11. As shown in the figure, the surface cracks of the iron oxide scale are repaired.

Claims (4)

1. a kind of method based on hydrogen reducing repairing hot rolled steel plate surface oxidation iron sheet crackle, which is characterized in that the method Hot rolled steel plate surface oxidation iron sheet is reduced into iron by the method for hydrogen reducing, restores the iron repairing iron scale of formation in heat Generated crackle in process, cooling procedure and formation process is rolled, the surface roughness of steel plate is improved；

This method includes following procedure:

Heating: in heating furnace, the hot rolled steel plate with iron scale is increased to target with the heating rate of 5-20 DEG C/min 900-1000 DEG C of temperature, warming-up section furnace atmosphere is nitrogen；

Isothermal: after being heated to target temperature, being filled with volume fraction is 10%-30% hydrogen, remaining is the mixed gas of nitrogen；Isothermal Recovery time is 30-600s；

It is cooling: after Isothermal Reduction, to be filled with nitrogen, after hydrogen drains in furnace, hot-strip is taken out out of furnace in air certainly So it is cooled to room temperature.

2. a kind of method based on hydrogen reducing repairing hot rolled steel plate surface oxidation iron sheet crackle according to claim 1, It is characterized in that, the hot rolled steel plate surface oxidation iron sheet with a thickness of 7-15 μm.

3. a kind of method based on hydrogen reducing repairing hot rolled steel plate surface oxidation iron sheet crackle according to claim 1, It is characterized in that, the tissue of the hot rolled steel plate surface oxidation iron sheet is the Fe3O4 of outer layer, internal layer is pro-eutectoid Fe3O4 and Eutectoid structure, while there are also remaining FeO.

4. a kind of method based on hydrogen reducing repairing hot rolled steel plate surface oxidation iron sheet crackle according to claim 1, It is characterized in that, the hot rolled steel plate is zinc-plated substrate.