阅读说明：本技术 一种罩式退火炉保护气氛的控制方法 (Control method of protective atmosphere of bell-type annealing furnace ) 是由 齐建群 孟凡月 王浩宇 刘春波 张选峰 张茜 于 2021-06-04 设计创作，主要内容包括：本发明涉及一种罩式退火炉保护气氛的控制方法,属于冶金行业罩式退火工艺技术领域。技术方案是：按照以下步骤进行操作：(1)内罩冷密封测试；(2)安全吹扫：退火加热开始前,采用N-2对内罩内的空气进行吹扫；(3)安全吹扫结束后,扣上加热罩,按照设定的退火工艺进行加热,在加热过程中,用H-2进行吹扫,将炉内N-2全部赶走,达到全氢退火目的；(4)在加热结束前,进行内罩热密封测试,确保内罩热密封测试试验合格；(5)当炉台温度冷到出炉温度时,采用保护气体N-2对炉内H-2进行吹扫置换。本发明的有益效果是：能够抑制钢中Mn、Si元素在弱氧气氛下在表面富集并形成颗粒状聚集物覆盖在带钢表面,从而达到消除钢卷边部色差缺陷的目的。(The invention relates to a control method of a cover type annealing furnace protective atmosphere, belonging to the technical field of cover type annealing processes in the metallurgical industry. The technical scheme is as follows: the method comprises the following steps: (1) testing the cold seal of the inner cover; (2) and (4) safe purging: before the annealing heating is started, N is adopted 2 Blowing air in the inner cover; (3) after the safe purging is finished, a heating cover is buckled, heating is carried out according to a set annealing process, and H is used in the heating process 2 Purging to remove N in the furnace 2 The whole is removed, so that the aim of full hydrogen annealing is fulfilled; (4) before heating is finished, carrying out heat sealing test on the inner cover to ensure that the heat sealing test of the inner cover is qualified; (5) when the temperature of the furnace platform is cooled to the tapping temperature, the furnace is adoptedWith protective gas N 2 To furnace H 2 And (5) carrying out purging replacement. The invention has the beneficial effects that: the method can inhibit Mn and Si elements in the steel from enriching on the surface under the weak oxygen atmosphere and forming granular aggregates to cover the surface of the strip steel, thereby achieving the purpose of eliminating the edge color difference defect of the steel coil.)

1. A method for controlling the protective atmosphere of a hood-type annealing furnace is characterized in that: the method comprises the following steps:

(1) testing cold sealing of the inner cover: ensuring that the cold sealing test of the inner cover is qualified;

(2) and (4) safe purging: before the annealing heating is started, protective gas N is adopted₂Purging the air in the inner cover to ensure that the residual oxygen concentration of the atmosphere in the inner cover of the cover type annealing furnace is less than or equal to 1 percent;

(3) after the safe purging is finished, a heating cover is buckled, heating is carried out according to a set annealing process, and H is used in the heating process₂Purging to remove N in the furnace₂The whole is removed, so that the aim of full hydrogen annealing is fulfilled;

(4) before heating is finished, carrying out heat sealing test on the inner cover to ensure that the heat sealing test of the inner cover is qualified;

(5) when the temperature of the furnace platform is cooled to the tapping temperature, protective gas N is adopted₂To furnace H₂And (5) carrying out purging replacement.

2. The method of claim 1, wherein the control of the atmosphere in the hood-type annealing furnace is performed by: the oxygen content of the hydrogen is less than or equal to 5ppm, the dew point is less than or equal to-50 ℃, and the purity is more than or equal to 99.999 percent; the oxygen content of the nitrogen is less than or equal to 5ppm, the dew point is less than or equal to minus 40 ℃, and the purity is more than or equal to 99.999 percent.

3. A method of controlling a protective atmosphere of a hood-type annealing furnace according to claim 1 or 2, characterized in that: the step (2) is safe in purging: the purging pressure of nitrogen is 3-7 bar, and the flow rate is 120Nm³/h。

4. The method of claim 1, wherein the control of the atmosphere in the hood-type annealing furnace is performed by: the purging pressure of the hydrogen in the step (3) is 2-4 bar, and the flow is 30-40 Nm³And h, the purging time is more than or equal to 8 h.

5. The method of claim 1, wherein the control of the atmosphere in the hood-type annealing furnace is performed by: and (3) heating according to a set annealing process, and maintaining the pressure in an inner cover of the cover type annealing furnace at 4-6 KPa in the heating process.

6. The method of claim 1, wherein the control of the atmosphere in the hood-type annealing furnace is performed by: the purging amount of the nitrogen in the step (5) is 80-120 m³Flow 120Nm³/h。

Technical Field

The invention relates to a control method of a cover type annealing furnace protective atmosphere, belonging to the technical field of cover type annealing processes in the metallurgical industry.

Background

Hood annealing generally refers to the annealing of cold rolled strip in a stack in a hood furnace. At present, all-hydrogen hood type annealing is mostly adopted, a cold-rolled steel coil is sent into a hood type annealing furnace for annealing treatment without degreasing in a state with a small amount of residual emulsion, and is cooled in a hydrogen atmosphere, so that the production period is long, but the product specification and the yield have strong flexibility.

Because the production period of the cover annealing is long, Mn and Si elements in steel are easy to enrich on the surface under the weak oxygen atmosphere when the steel coil is in a high-temperature state for a long time, and granular aggregates are formed to cover the surface of strip steel to form a color difference defect, so that the use of users is influenced. And because the middle part of the steel coil is still in a packing state during the cover annealing, the end face of the steel coil is easy to contact with the weak oxygen atmosphere, so that most of color difference defects are concentrated on the edge part of the steel coil. Therefore, to eliminate such edge color difference defects, the control of the annealing atmosphere is particularly critical.

At present, patent CN101760606B discloses a method for controlling the protective atmosphere of a stainless steel hood-type annealing furnace, which mainly aims at reducing the consumption of hydrogen in the annealing cycle and does not have explicit requirements on indexes such as oxygen content of protective gas; patent CN108913852B discloses a method for producing a tin plate substrate based on a hood-type annealing process, but no clear requirements are made on the protective atmosphere; patent CN102994708A discloses an annealing process method for bell-type furnace, but does not make clear requirements for key indexes of protective atmosphere, purging pressure and other processes; patent CN110055381A discloses a nitrogen protection annealing process for light-weight tool and die steel, which is only specified for steel grades under nitrogen protection.

The method of the invention optimizes the atmosphere control aiming at the edge color difference defect caused by improper atmosphere control in the production of the steel coil under the all-hydrogen cover type annealing process, so as to achieve the purpose of eliminating the defect, and no clear atmosphere control solution is available at present.

Disclosure of Invention

The invention aims to provide a control method of a protective atmosphere of a hood-type annealing furnace, which can inhibit Mn and Si elements in steel from being enriched on the surface under a weak oxygen atmosphere and forming granular aggregates to cover the surface of strip steel, thereby achieving the purpose of eliminating the edge color difference defect of a steel coil and solving the problems in the background technology.

The technical scheme of the invention is as follows:

a method for controlling the protective atmosphere of a hood-type annealing furnace comprises the following steps:

(1) testing cold sealing of the inner cover: ensuring that the cold sealing test of the inner cover is qualified;

(2) and (4) safe purging: before the annealing heating is started, protective gas N is adopted₂Purging the air in the inner cover to ensure that the residual oxygen concentration of the atmosphere in the inner cover of the cover type annealing furnace is less than or equal to 1 percent;

(3) after the safe purging is finished, a heating cover is buckled, heating is carried out according to a set annealing process, and H is used in the heating process₂Purging to remove N in the furnace₂The whole is removed, so that the aim of full hydrogen annealing is fulfilled;

(4) before heating is finished, carrying out heat sealing test on the inner cover to ensure that the heat sealing test of the inner cover is qualified;

(5) when the temperature of the furnace platform is cooled to the tapping temperature, protective gas N is adopted₂To furnace H₂And (5) carrying out purging replacement.

The oxygen content of the hydrogen is less than or equal to 5ppm, the dew point is less than or equal to-50 ℃, and the purity is more than or equal to 99.999 percent; the oxygen content of the nitrogen is less than or equal to 5ppm, the dew point is less than or equal to minus 40 ℃, and the purity is more than or equal to 99.999 percent.

The step (2) is safe in purging: the purging pressure of nitrogen is 3-7 bar, and the flow rate is 120Nm³/h。

The purging pressure of the hydrogen in the step (3) is 2-4 bar, and the flow is 30-40 Nm³And h, the purging time is more than or equal to 8 h.

And (3) heating according to a set annealing process, and maintaining the pressure in an inner cover of the cover type annealing furnace at 4-6 KPa in the heating process.

The purging amount of the nitrogen in the step (5) is 80-120 m³Flow 120Nm³/h。

The invention has the beneficial effects that: the method can inhibit Mn and Si elements in the steel from enriching on the surface under the weak oxygen atmosphere and forming granular aggregates to cover the surface of the strip steel, thereby achieving the purpose of eliminating the edge color difference defect of the steel coil.

Drawings

FIG. 1 is a microscopic morphology image of a scanning electron microscope for edge chromatic aberration before the implementation of the present invention;

FIG. 2 is a microscopic morphology image of the edge of the steel strip under a scanning electron microscope without chromatic aberration after the implementation of the invention.

Detailed Description

The invention is further illustrated by way of example in the following with reference to the accompanying drawings.

A method for controlling the protective atmosphere of a hood-type annealing furnace comprises the following steps:

(1) testing cold sealing of the inner cover: ensuring that the cold sealing test of the inner cover is qualified;

(2) and (4) safe purging: before the annealing heating is started, protective gas N is adopted₂Purging the air in the inner cover to ensure that the residual oxygen concentration of the atmosphere in the inner cover of the cover type annealing furnace is less than or equal to 1 percent;

(3) after the safe purging is finished, a heating cover is buckled, heating is carried out according to a set annealing process, and H is used in the heating process₂Purging to remove N in the furnace₂The whole is removed, so that the aim of full hydrogen annealing is fulfilled;

(4) before heating is finished, carrying out heat sealing test on the inner cover to ensure that the heat sealing test of the inner cover is qualified;

(5) when the temperature of the furnace platform is cooled to the temperature of the furnace platformWhen the furnace temperature is high, protective gas N is adopted₂To furnace H₂And (5) carrying out purging replacement.

The oxygen content of the hydrogen is less than or equal to 5ppm, the dew point is less than or equal to-50 ℃, and the purity is more than or equal to 99.999 percent; the oxygen content of the nitrogen is less than or equal to 5ppm, the dew point is less than or equal to minus 40 ℃, and the purity is more than or equal to 99.999 percent.

The step (2) is safe in purging: the purging pressure of nitrogen is 3-7 bar, and the flow rate is 120Nm³/h。

The purging pressure of the hydrogen in the step (3) is 2-4 bar, and the flow is 30-40 Nm³And h, the purging time is more than or equal to 8 h.

And (3) heating according to a set annealing process, and maintaining the pressure in an inner cover of the cover type annealing furnace at 4-6 KPa in the heating process.

The purging amount of the nitrogen in the step (5) is 80-120 m³Flow 120Nm³/h。

Example 1:

and a DC04 product is produced by adopting bell-type furnace annealing, and the thickness of the product is 1.0 mm. Wherein, the oxygen content of the hydrogen is 5ppm, the dew point is-50 ℃, and the purity is 99.999 percent; the nitrogen contained 4.5ppm of oxygen, had a dew point of-45 ℃ and a purity of 99.999%.

The control method specifically comprises the following steps:

1) testing and checking the cold seal of the inner cover: when the pressure of the inner cover is 5KPa and the time is 15min, the pressure is reduced to 950Pa, and the cold sealing test is qualified;

2) and (4) safe purging: before the annealing heating is started, protective gas N is adopted₂The air in the inner cover on the furnace platform is purged with the nitrogen flow of 120Nm³Per, nitrogen purge amount 81m³Blowing pressure is 3bar, and the residual oxygen concentration of the furnace atmosphere is 1 percent;

3) after the safe purging is finished, a heating cover is buckled, an annealing program is started to heat according to a set annealing process, and H is used for heating in the heating process₂Purging to remove N in the furnace₂All are removed to achieve the aim of hydrogen-full annealing. Within 0 to 8 hours, H₂Purge pressure 2bar, flow 40Nm³H; the furnace pressure is always maintained at 4-6 KPa in the heating process;

4) before the end of the heating, a heat-seal test was carried out: when the pressure is 5KPa and the time is 15 minutes, the pressure is reduced to 900Pa, the heat sealing test is qualified;

5) when the temperature of the furnace platform is cooled to the tapping temperature, protective gas N is adopted₂To furnace H₂And (5) carrying out purging replacement. Purging requirement: flow 120Nm³Per, nitrogen purge amount 80m³。

The implementation effect is as follows: the edge of the strip steel has no color difference. The microscopic morphology of the lower part of the scanning electron microscope is shown in fig. 2, the microscopic morphology of the chromatic aberration defect at the lower part of the scanning electron microscope is shown in fig. 1 before the method is implemented, and the contrast shows that the chromatic aberration defect has a plurality of white bright points in morphology and the content of Mn element at the bright points is higher in energy spectrum analysis.

Example 2:

the HC340LA product is produced by adopting bell-type furnace annealing, and the thickness of the product is 1.2 mm. Wherein, the oxygen content of the hydrogen is 4ppm, the dew point is-60 ℃, and the purity is 99.9997%; the nitrogen contained 5ppm of oxygen, had a dew point of-40 ℃ and a purity of 99.9996%.

The control method specifically comprises the following steps:

1) testing and checking the cold seal of the inner cover: the pressure of the inner cover is 5KPa, the pressure is reduced to 800Pa within 15min, and the cold sealing test is qualified;

2) and (4) safe purging: before the annealing heating is started, protective gas N is adopted₂The air in the inner cover on the furnace platform is purged with the nitrogen flow of 120Nm³Per, nitrogen purge amount 81m³Blowing pressure is 7bar, and the residual oxygen concentration of the furnace atmosphere is 0.5%;

3) after the safe purging is finished, a heating cover is buckled, an annealing program is started to heat according to a set annealing process, and H is used for heating in the heating process₂Purging to remove N in the furnace₂All are removed to achieve the aim of hydrogen-full annealing. Within 0 to 12 hours, H₂Purge pressure 4bar, flow 30 Nm³H; the furnace pressure is always maintained at 4-6 KPa in the heating process;

4) before the end of the heating, a heat seal test was carried out: when the pressure is 5KPa and the time is 15 minutes, the pressure is reduced to 720Pa, and the heat sealing test is qualified;

5) when the temperature of the furnace platform is cooled to the tapping temperature, protective gas N is adopted₂To furnace H₂And (5) carrying out purging replacement. Purging requirement: flow 120Nm³Per, nitrogen purge amount 120m³。

The implementation effect is as follows: the edge of the strip steel has no color difference.

Example 3:

and a DC01 product is produced by adopting bell-type furnace annealing, and the thickness of the product is 0.8 mm. Wherein, the oxygen content of the hydrogen is 3ppm, the dew point is-55 ℃, and the purity is 99.999 percent; the nitrogen contained 4ppm of oxygen, had a dew point of-48 ℃ and a purity of 99.9992%.

The control method specifically comprises the following steps:

1) testing and checking the cold seal of the inner cover: the pressure of the inner cover is 5KPa, the pressure is reduced to 400Pa within 15min, and the cold sealing test is qualified;

2) and (4) safe purging: before the annealing heating is started, protective gas N is adopted₂And blowing air in the inner cover on the furnace platform. Nitrogen flow 120Nm³Per, nitrogen purge amount 81m³The blowing pressure is 5bar, and the residual oxygen concentration of the furnace atmosphere is 0.3 percent;

3) after the safe purging is finished, a heating cover is buckled, an annealing program is started to heat according to a set annealing process, and H is used for heating in the heating process₂Purging to remove N in the furnace₂All are removed to achieve the aim of hydrogen-full annealing. Within 0 to 10 hours, H₂Purge pressure 4.5bar, flow 35 Nm³H; the furnace pressure is always maintained at 4-6 KPa in the heating process;

4) before the end of the heating, a heat seal test was carried out: when the pressure is 5KPa and the time is 15 minutes, the pressure is reduced to 220Pa, and the heat sealing test is qualified;

5) when the temperature of the furnace platform is cooled to the tapping temperature, protective gas N is adopted₂To furnace H₂And (5) carrying out purging replacement. Purging requirement: flow 120Nm³Per, nitrogen purge 100m³。

The implementation effect is as follows: the edge of the strip steel has no color difference.