阅读说明：本技术 一种短流程中停留时间大于60min在炉铸坯氧化铁皮的控制方法 (Method for controlling iron scale of casting blank in furnace with retention time of more than 60min in short process ) 是由 高智 田军利 王毅 陈猛 谢斌 李波 赵强 王成 刘义涛 李国全 于 2020-06-19 设计创作，主要内容包括：一种短流程中停留时间大于60min在炉铸坯氧化铁皮的控制方法：故障原因导致铸坯在加热炉内停置时间＞60min；当故障排除后准备恢复生产时,除加热炉外其它按照正常进行启动操作；对于加热炉按照以下方式处理：对加热炉各段炉温的操作；空气过剩系数控制；进行炉压控制调整操作；高压除鳞水压力调整操作；加热炉步入正常运行；后工序步入正常运行。本发明通过对铸坯加热系统的调整,以及对除鳞水参数的调整,使氧化铁皮得以控制,使钢板降级量处理率由原来的0.32%降低至0.064%,判废率由原来的0.080%降低至0.0064%,且无需增加设备,操作简单,易实施。(A method for controlling the iron scale of a casting blank in a furnace with the retention time of more than 60min in a short flow comprises the following steps: the casting blank is stopped in the heating furnace for more than 60min due to the fault; when the production is to be recovered after the fault is eliminated, starting operation is performed normally except for the heating furnace; the following treatment was performed for the furnace: operating the furnace temperature of each section of the heating furnace; controlling the air excess coefficient; carrying out furnace pressure control and adjustment operation; adjusting the pressure of the high-pressure descaling water; the heating furnace is stepped to normal operation; and the subsequent process steps into normal operation. According to the invention, through the adjustment of the casting blank heating system and the adjustment of the descaling water parameters, the scale is controlled, the treatment rate of the degradation amount of the steel plate is reduced to 0.064% from the original 0.32%, the waste judgment rate is reduced to 0.0064% from the original 0.080%, and the method does not need to increase equipment, is simple to operate and is easy to implement.)

1. A method for controlling the iron scale of a casting blank in a furnace with the retention time of more than 60min in a short flow comprises the following steps:

1) conditions are as follows: the short-flow operation causes the situation that the time of the casting blank stopping in the heating furnace is more than 60min due to the fault of the production line;

2) when the fault is discharged and the production is to be recovered, starting operation is performed normally except for the heating furnace; the furnace phase is treated in the following way:

A. operation of the temperature of the furnace sections

After the furnace is shut down, firstly, the temperature of each section is reduced and adjusted:

the preheating section is reduced by 50-60 ℃ on the basis of the originally set temperature of the section;

the heating section is reduced by 30-50 ℃ on the basis of the originally set temperature of the heating section;

the temperature of the second heating section is reduced by 28-32 ℃ on the basis of the originally set temperature of the second heating section;

the temperature of the soaking section is reduced by 18-22 ℃ on the basis of the originally set temperature of the soaking section;

after receiving the production recovery notification time, the normal recovery time of the heating furnace is carried out according to the following requirements:

when the furnace shutdown time T is more than or equal to 60 minutes and less than 120 minutes, the normal operation temperature is recovered within 12-18 minutes before rolling;

when the furnace shutdown time T is not less than 120 minutes and less than 240 minutes, the normal operation temperature is recovered within 18-22 minutes before rolling;

when the furnace shutdown time T is more than 240 minutes, the normal operation temperature is required to be recovered within 28-33 minutes before rolling;

B. air excess factor control

After the furnace is shut down, the air excess coefficient of each section is adjusted according to the following parameters:

when the furnace shutdown time T is informed to be more than or equal to 60 minutes, the air surplus coefficients of the preheating section, the first heating section, the second heating section and the soaking section are reduced by 0.1-0.15 on the basis of normal setting;

after receiving the time for recovery starting: the air excess coefficients of the preheating section and the heating section are required to be recovered to normal set values within 14-16 minutes before rolling, and the air excess coefficients of the heating section and the soaking section are adjusted to 1.45-1.5;

C. performing furnace pressure control and adjustment operation

After the furnace is stopped, the pressure in each section of furnace is operated according to the adjustment requirement as follows:

when the furnace shutdown time T is informed to be more than or equal to 60 minutes, on the basis that the preheating section, the first heating section, the second heating section and the soaking section are set according to the target pressure of each steel type, each section is respectively subjected to pressurization operation, and the increase is 0.2-0.3 dpa;

after receiving the time for recovery starting: recovering to a normal set pressure value within 14-16 minutes before rolling, wherein the recovery procedure in the period is carried out from a highest pressure section to a minimum pressure section;

3) adjusting the pressure of high-pressure descaling water

After receiving the time for recovery starting: adjusting the inlet pressure of the descaling water to 249-253 bar and the outlet pressure of the descaling water to 300-330 bar within 3-5 minutes before rolling;

4) the heating furnace is stepped to normal operation;

5) and the subsequent process steps into normal operation.

2. The method for controlling the furnace casting blank iron scale with the retention time of more than 60min in the short process as claimed in claim 1, wherein the method comprises the following steps: when the fault is vented and production is ready to be resumed, the operation of the temperature of each section of the furnace:

after the furnace is shut down, firstly, the temperature of each section is reduced and adjusted:

the preheating section is reduced by 53-57 ℃ on the basis of the originally set temperature of the section;

the temperature of the first heating section is reduced by 35-45 ℃ on the basis of the originally set temperature of the section;

the temperature of the second heating section is reduced by 30 ℃ on the basis of the originally set temperature of the second heating section;

the temperature of the soaking section is reduced by 20 ℃ on the basis of the originally set temperature of the soaking section;

after receiving the production recovery notification time, the normal recovery time of the heating furnace is carried out according to the following requirements:

when the furnace shutdown time T is more than or equal to 60 minutes and less than 120 minutes, the normal operation temperature is recovered within 14-18 minutes before rolling;

when the furnace shutdown time T is not less than 120 minutes and less than 240 minutes, the normal operation temperature is recovered within 18-21 minutes before rolling;

when the furnace shutdown time T is more than 240 minutes, the normal operation temperature is recovered within 29-31 minutes before rolling.

3. The method for controlling the furnace casting blank iron scale with the retention time of more than 60min in the short process as claimed in claim 1, wherein the method comprises the following steps: after receiving the time for recovery starting: and adjusting the pressure of the descaling water outlet to 305-325 bar within 3-5 minutes before rolling.

Technical Field

The invention relates to a metal rolling method, in particular to a method for controlling iron scale of a casting blank in a furnace with the retention time of more than 60min in a short process.

Background

Under the continuous oxidation of the short-flow casting blank in a high-temperature heating furnace with different air excess coefficients, the upper surface and the lower surface of the casting blank are easy to form compact scaly iron oxide skins. For example, in a short-flow CSP production line, a continuous casting slab directly enters a soaking furnace to be heated, the furnace time is generally 20-40min, an iron scale formed on the surface of the slab is thinner than that of the traditional process, and the slab is removed by high-pressure water when passing through a high-pressure descaler between the soaking furnace and a finishing mill group.

The iron scale is the product of oxidation reaction of iron and oxygen in air at high temperature, and is mainly made of Fe₂O₃、Fe₃O₄The inner layer of the scale is loose and porous fine crystalline structure FeO, and the middle is compact, non-porous and fractured Fe with a vitreous fracture₃O₄The outermost layer being Fe of crystalline structure₂O₃。

The existence of the iron scale has great influence on the surface quality of the steel plate, and if the iron scale on the surface cannot be removed before rolling, the iron scale on the layer can be pressed into the surface of the strip steel by the acting force of the roller to generate the iron scale, thereby influencing the surface quality of the strip steel.

CSP short process production line process route: desulfurization → converter → LF furnace (RH) → conticaster → pendulum shear → soaking pit → high pressure descaling → finish rolling and tandem rolling → laminar cooling → coiler → transportation chain → baling and warehousing.

Under normal conditions, the molten steel of the CSP short-flow production line is cast into a slab, the slab is cut into single slabs by swing shearing, the single slabs enter a soaking pit for heating, the charging temperature of the slab is generally 700-.

The short-flow long-time in-furnace casting blank means that the heating time of the slab in the furnace exceeds the normal process standard time by more than 20 minutes (namely the in-furnace time is more than 60 minutes).

Because the short-flow production line belongs to rigid connection, once rolling line equipment is abnormal and cannot continuously produce, a plate blank can only be subjected to oscillation heating in a furnace, when the plate blank is heated in a soaking furnace for too long time, compact iron oxide scales which are difficult to remove by high-pressure descaling are easily formed, after the plate blank is rolled into a finished product, the pressed iron oxide scales on the surface of the strip steel are serious, so that the requirement of delivery standards cannot be met, degradation treatment is generally adopted, and waste judgment treatment is carried out when the plate blank is serious. Not only can the goods not be delivered to the user in time, but also the production cost is greatly improved and the resources are wasted. In 2016, because the time of the slab in the furnace exceeds 60min, the degradation treatment reaches 2530 tons and accounts for 0.321% of the specific yield, and the waste treatment accounts for 632 tons and accounts for 0.0811% of the specific yield. In 2017, as the slab time exceeds 60min, the degradation treatment reaches 2463 tons accounting for 0.32 percent of the specific yield, and the waste treatment reaches 568 tons accounting for 0.080 percent of the specific yield. For the present enterprises, how to reduce the degradation and the judgment of the waste treatment amount to the maximum extent is a technical issue. The skilled person also has many aspects to explore and study.

Disclosure of Invention

Aiming at the defects of the prior art, the invention provides a method for controlling the iron scale of the casting blank in the furnace, which controls the iron scale by adjusting a casting blank heating system and descaling water parameters after the short-process casting blank is in the furnace for more than 60min, so that the degradation processing rate of a steel plate is reduced from 0.32% to 0.064%, and the waste judgment rate is reduced from 0.080% to 0.0064%.

The technical measures for realizing the purpose are as follows:

a method for controlling the iron scale of a casting blank in a furnace with the retention time of more than 60min in a short flow comprises the following steps:

1) conditions are as follows: the short-process rolling line has the condition that the time for the casting blank to be stopped in the heating furnace is more than 60min due to the fault;

2) when the fault is eliminated and the production is to be recovered, starting operation is carried out normally except the heating furnace; for adding

The hot furnace stage is treated in the following way:

A. operation of furnace temperature of each section of heating furnace

When the estimated furnace time is more than 60 minutes, firstly, the furnace temperature of each section is cooled and adjusted at the first time:

the preheating section is reduced by 50-60 ℃ on the basis of the original set furnace temperature;

the heating stage is reduced by 30-50 ℃ on the basis of the original set furnace temperature;

the second heating section is reduced by 28-32 ℃ on the basis of the original set furnace temperature;

the temperature of the soaking section is reduced by 18-22 ℃ on the basis of the original set furnace temperature;

in the case of different furnace time, the following treatment is carried out before the production is recovered:

when the furnace shutdown time T is more than or equal to 60 minutes and less than 120 minutes, the temperature is recovered to the normal set temperature within 12-18 minutes before production is recovered;

when the furnace shutdown time T is not less than 120 minutes and less than 240 minutes, the temperature is recovered to the normal set temperature within 18-22 minutes before production recovery;

when the furnace shutdown time T is more than 240 minutes, the normal set temperature is recovered within 28-33 minutes before production recovery;

B. air excess factor control

After the furnace is shut down, the air excess coefficient of each section is adjusted according to the following parameters:

when the furnace shutdown time T is informed to be more than or equal to 60 minutes, the air in the preheating section, the first heating section, the second heating section and the soaking section is passed through

The residual coefficient is reduced by 0.1-0.15 on the basis of normal setting;

after receiving the time for recovery starting: the air excess coefficient of the preheating section and the heating section is set before rolling

Adjusting the air surplus coefficient of the heating second section and the soaking section to 1.45-1.5 when the normal set value is recovered within 14-16 minutes;

C. performing furnace pressure control and adjustment operation

After the furnace is stopped, the pressure in each section of furnace is operated according to the adjustment requirement as follows:

when the furnace shutdown time T is informed to be more than or equal to 60 minutes, on the basis that the preheating section, the first heating section, the second heating section and the soaking section are set according to the target pressure of each steel type, each section is respectively subjected to pressurization operation, and the increase is 0.2-0.3 dpa;

after receiving the time for recovery starting: recovering to a normal set pressure value within 14-16 minutes before rolling, wherein the recovery procedure in the period is carried out from a highest pressure section to a minimum pressure section;

3) adjusting the pressure of high-pressure descaling water

After receiving the time for recovery starting: adjusting the inlet pressure of the descaling water to 249-253 bar and the outlet pressure of the descaling water to 300-330 bar within 3-5 minutes before rolling;

4) the heating furnace is stepped to normal operation;

5) and the subsequent process steps into normal operation.

Further: when the fault is removed and the production is to be restored, the operation of the temperature of each section of the heating furnace is as follows:

after the furnace is shut down, firstly, the temperature of each section is reduced and adjusted:

the preheating section is reduced by 53-57 ℃ on the basis of the original set furnace temperature;

the heating temperature is reduced by 35-45 ℃ on the basis of the original set furnace temperature in the first heating stage;

the second heating section is reduced by 30 ℃ on the basis of the original set furnace temperature;

the soaking section is reduced by 20 ℃ on the basis of the original set furnace temperature;

after receiving the production recovery notification time, the normal recovery time of the heating furnace is carried out according to the following requirements:

when the furnace shutdown time T is more than or equal to 60 minutes and less than 120 minutes, the normal operation temperature is recovered within 14-18 minutes before rolling;

when the furnace shutdown time T is not less than 120 minutes and less than 240 minutes, the normal operation temperature is recovered within 18-21 minutes before rolling;

when the furnace shutdown time T is more than 240 minutes, the normal operation temperature is recovered within 29-31 minutes before rolling.

Further: after receiving the time for recovery starting: and adjusting the pressure of the descaling water outlet to 305-325 bar within 3-5 minutes before rolling.

Mechanism and action for adjusting main process parameters in the invention

The present invention operates the following for the temperature of each section of the heating furnace

After the furnace is shut down, firstly, the temperature of each section is reduced and adjusted:

the preheating section is reduced by 50-60 ℃ on the basis of the original set furnace temperature;

the heating stage is reduced by 30-50 ℃ on the basis of the original set furnace temperature;

the second heating section is reduced by 28-32 ℃ on the basis of the original set furnace temperature;

the temperature of the soaking section is reduced by 18-22 ℃ on the basis of the original set furnace temperature;

after receiving the production recovery notification time, the normal recovery time of the heating furnace is carried out according to the following requirements:

when the furnace shutdown time T is more than or equal to 60 minutes and less than 120 minutes, the normal operation temperature is recovered within 12-18 minutes before rolling;

when the furnace shutdown time T is not less than 120 minutes and less than 240 minutes, the normal operation temperature is recovered within 18-22 minutes before rolling;

when the furnace shutdown time T is more than 240 minutes, the normal operation temperature is recovered within 28-33 minutes before rolling.

If the recovery is carried out in advance, the iron scale can be penetrated too deeply, and the iron scale is difficult to remove. If the recovery time is delayed, the surface of the plate blank can not form a shell-shaped thick iron sheet layer, and the plate can not be effectively turned up after high-pressure descaling and striking.

The invention therefore controls the air excess factor during this period as follows

After the furnace is shut down, the air excess coefficient of each section is adjusted according to the following parameters:

when the furnace shutdown time T is informed to be more than or equal to 60 minutes, the air surplus coefficients of the preheating section, the first heating section, the second heating section and the soaking section are reduced by 0.1-0.15 on the basis of normal setting;

after receiving the time for recovery starting: the air excess coefficients of the preheating section and the heating section are required to be recovered to normal set values within 14-16 minutes before rolling, and the air excess coefficients of the heating section and the soaking section are adjusted to 1.45-1.5;

the reason is that the smaller the control process coefficient is, the better the control process coefficient is, under the condition of ensuring the full combustion in the soaking pit furnace. The slab is heated in the furnace for a long time, the excess air coefficient is properly reduced, so that a hearth is relatively 'oxygen deficient', the oxygen content in the furnace is effectively reduced, the chemical reaction speed of air oxygen molecules and the Fe atoms of the slab is reduced, and the generation amount of iron scale on the surface of the casting blank is reduced. Aiming at a casting blank with longer furnace time, two key factors need to be firmly grasped, the infiltration depth of the iron scale is reduced as much as possible when the machine is stopped, a larger excess air coefficient is needed before production is recovered, the ferrous oxide layer infiltrated to the surface of the slab is completely oxidized into a shell-shaped iron scale, and the shell-shaped iron scale is directly and effectively removed after high-pressure descaling.

The furnace pressure is controlled during the period, namely, the furnace pressure in each section is operated according to the adjustment requirement after the furnace is stopped as follows:

when the furnace shutdown time T is informed to be more than or equal to 60 minutes, on the basis that the preheating section, the first heating section, the second heating section and the soaking section are set according to the target pressure of each steel type, each section is respectively subjected to pressurization operation, and the increase is 0.2-0.3 dpa;

after receiving the time for recovery starting: recovering to a normal set pressure value within 14-16 minutes before rolling, wherein the recovery procedure in the period is carried out from a highest pressure section to a minimum pressure section;

because the furnace pressure and the distribution thereof are important means for organizing the flame shape, adjusting the temperature field and controlling the atmosphere in the furnace, the heating speed and the heating quality of the plate blank are influenced. The furnace pressure is adjusted by adjusting the opening degree of a flue gate, micro-positive pressure setting is generally adopted, and when a plate blank is heated in the furnace for a long time, the furnace pressure is properly increased, so that the aim of not forming serious fire and effectively preventing cold air suction is fulfilled, a blank is tightly wrapped by high-temperature furnace gas, and the interference of low-temperature air flow is prevented. Keeping the weak oxidizing atmosphere in the furnace, and reducing free oxygen ions in the furnace gas so as to reduce the thickness of iron scale in the steel. Meanwhile, the pressure of the hearth is micro-positive pressure, so that the phenomenon that the oxidizing atmosphere in the furnace is increased due to the fact that cold air is sucked into the furnace when the furnace door is opened is avoided.

The invention controls the pressure of the inlet and the outlet of the high-pressure dephosphorization water, namely after the time for recovering and starting is received: adjusting the inlet pressure of the descaling water to 249-253 bar and the outlet pressure of the descaling water to 300-330 bar within 3-5 minutes before rolling; because the high-pressure dephosphorization water forms high-speed jet flow through the nozzle, the scale on the surface of the plate blank quickly falls off from the surface of the plate blank under the action of erosion and stripping of water flow and thermal explosion effect. For a long time, the iron scale Fe on the surface layer of the furnace slab₂O₃、Fe₃O₄The FeO components are thicker than the normal plate blank, and the FeO and the Fe close to the steel matrix of the plate blank₃O₄The scale is invaded into the steel matrix of the plate blank in a wedge shape, and a complicated scale layer with a special structure is formed at the interface of the scale and the steel. Under the jetting of high-pressure water, the surface of the iron scale is locally supercooled and greatly contracted, so that the cracks of the iron scale are expanded, the dephosphorization pressure of the plate blank is properly increased through the impact of the high-pressure water, the dynamic pressure of the high-pressure water is increased in the cracks to become hydrostatic pressure which invades the bottom of the iron scale, and the iron scale is peeled off from the surface of the plate blank, so that the aim of removing the iron scale is fulfilled.

Compared with the prior art, the method has the advantages that the scale scales are controlled by adjusting the casting blank heating system and the descaling water parameters, the treatment rate of the degradation amount of the steel plate is reduced to 0.064% from the original 0.32%, the waste judgment rate is reduced to 0.0064% from the original 0.080%, no equipment is required to be added, and the method is simple to operate and easy to implement.

Drawings

FIG. 1 is a surface view of a steel sheet according to the present invention;

fig. 2 is a surface view of a steel sheet before the present invention.

Detailed Description

The present invention is described in detail below: