JPS5849621B2 - Manufacturing method of cold rolled steel sheet - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a cold-rolled steel sheet, and more particularly, to a method for producing a cold-rolled steel sheet by directly cold rolling without descaling, followed by continuous annealing.

Conventional cold rolled steel sheets are usually manufactured through the following steps: hot rolling → descaling → cold rolling → electrolytic cleaning → box or continuous annealing → temper rolling.

The descaling process requires a good surface quality of the steel sheet, and currently it is mainly processed by pickling, but it not only requires a large amount of equipment, but also increases the equipment cost and running cost. , it is necessary to dispose of the waste acid that is discharged in large quantities.

The cleaning process is necessary to remove contaminants such as iron powder and residual rolling oil generated during rolling, and is usually carried out by electrolytic cleaning, but like the descaling process, it requires a lot of equipment costs and running costs. It takes.

Furthermore, regarding conventional annealing methods, box-type annealing, which is carried out to produce cooled steel sheets for drawing, etc., requires a long time, several days, for the entire process of heating, holding, and cooling, making it extremely inefficient. It is efficiency, and to solve this problem, 1
Many continuous annealing methods have been proposed that can complete the process in just a few minutes.
Some examples are actually in operation.

Although the processing using this apparatus is more efficient than the box-type annealing described above, there has recently been a strong demand for even greater efficiency, and a technology that completes the annealing process within a few minutes is in demand.

In the current continuous annealing equipment, each process such as uniform heating, primary cooling, (reheating) temporary aging treatment, secondary cooling, and temper rolling is adopted, but in order to meet the above requirements, , it is necessary to develop a technology that shortens the heating and soaking time, efficiently performs the primary cooling, eliminates the reheating step before the overaging treatment, and shortens the overaging treatment time.

If it were possible to realize an innovative manufacturing method that omitted the descaling and cleaning steps mentioned above in the manufacturing process of cold-rolled steel sheets, and also made it possible to shorten and improve the efficiency of the annealing process, the benefits would be truly great. I can say that.

The present invention focuses on these points, and eliminates the descaling and electrolytic processes that were conventionally considered essential technologies in the production of cold-rolled steel sheets, and uses a continuous annealing process in an extremely short time, within a few minutes, to reduce drawing. , provides a method for producing cold-rolled steel sheets for deep drawing, which is characterized by at least heating, soaking, primary cooling, over-aging treatment, secondary cooling and When performing continuous annealing treatment in a method that includes each step of cost rolling, a hot rolled steel strip with scale attached is cold rolled to produce a cold rolled steel strip with scale attached, and then this cold rolled steel strip is produced with scale still attached. After rapidly heating the rolled steel strip from the recrystallization temperature of the steel sheet to 860°C in a jet-flow direct-fired heating furnace where the atmosphere can be controlled without performing a cleaning treatment, it is heated in a non-reducing atmosphere or a weakly oxidizing atmosphere for 55 minutes. The oxide film on the copper strip is removed during the process of holding the copper strip for more than 2 seconds, followed by rapid cooling from a temperature range of 600°C or higher to near the overaging treatment temperature, and then overaging treatment and further cooling to room temperature or after cooling. This is a method for producing cold rolled steel sheets characterized by temper rolling.

In addition to ordinary cold-rolled steel sheets, the steel sheets to which the present invention is applied may be surface-treated steel sheets that are coated with metal plating or the like as the case may be.

Hereinafter, in the present invention, these will be collectively simply referred to as cold rolled steel sheets.

Next, the manufacturing process of the cold rolled steel sheet of the present invention (hot rolling→cold rolling→continuous annealing→surface oxide film removal→temper rolling) will be sequentially described in detail.

Direct cold rolling of scaled hot-rolled steel sheets can be carried out without problems using conventional rolling methods, although the rolling load may be slightly higher.

In order to reduce the rolling load, it is effective to apply a composition containing no emulsifier and whose main component is an organic polar substance to the surface of the steel sheet prior to rolling, and then roll the sheet in the conventional manner.

The thickness of the scale remaining after rolling is significantly reduced compared to before rolling, and unless a scale removal operation is performed especially during the cold rolling process, the surface of the steel plate after rolling will be almost completely covered with black scale with a thickness of 1 μm or less. Evenly coated.

Also, there are no defects in the steel plate due to direct cold rolling.

Conventionally, iron powder mixed in the cold rolling coolant has been separated and removed in order to suppress the adhesion of iron powder generated by rolling, but according to the present invention, this is not necessary.

Furthermore, the electrolytic cleaning process conventionally carried out for the purpose of removing surface stains on the steel sheet before annealing can be omitted in the present invention, which ultimately prepares the surface of the steel sheet.

Next, the method of the present invention for continuously annealing scaled steel plates will be described.

Recent continuous annealing methods for steel sheets aim to significantly shorten the furnace length and therefore significantly reduce equipment costs and running costs. Rapid heating → recrystallization treatment in a reducing atmosphere → rapid cooling → overaging treatment in a reducing atmosphere → The process of rapid cooling → temper rolling is being adopted.

Rapid heating is performed using a direct-fire furnace method that heats the steel plate with the gas generated by burning fuel gas with air.However, with the conventional method, the heating rate is insufficient for steel plates with metallic luster, so black bodies are heated before annealing. A method of annealing after chemical treatment has also been proposed.

In contrast, in the present invention, this is not necessary at all, and not only can a high heating rate be achieved due to the thin and uniform black scale that has an endothermic effect that exists in the steel sheet before annealing, but it is also possible to achieve a high heating rate. If instead, a jet direct-fire heating method in which a jet of combustion generated gas is actively collided with the steel plate is adopted, even more rapid heating is possible and more efficient.

Regarding the surface properties of steel sheets, in the case of conventional methods, it is necessary to reduce and eliminate the oxide film generated in the heating process in the next process, but excessive oxidation may require a long time for reduction, and the oxide film may remain unreduced. Since problems such as surface roughness of the steel sheet occur, heating conditions such as heating atmosphere and oil must be controlled to a low oxidation side.

On the other hand, according to the method of the present invention, new oxidation is suppressed by the scale present on the steel plate, so operation can be performed under combustion conditions with the highest combustion efficiency, which is a great benefit in terms of effective use of fuel gas. Not only that, but there is no need to reduce the oxide film, so there is no need to use expensive reducing gas.
Recrystallization treatment using a radiant heating furnace or a direct-fired furnace using N2 gas is also possible.

As mentioned above, the steel plate after rapid heating has a temperature higher than the recrystallization temperature86
Temperature range up to 0℃ for a short time, preferably 5 seconds or more 30
Hold for less than seconds.

The holding temperature varies depending on the characteristics (composition and target material) of the steel plate to be treated, but in any case it is not necessary to maintain a uniform temperature, and a heat cycle selected within the above temperature range can be adopted.

Thereafter, the steel plate is cooled (primary cooling) to near the overaging temperature, and the cooling is started from any temperature within the holding temperature range of 600° C. or higher.

For cooling from the holding temperature to 600°C, slow cooling (for example, 50°C/sec or less) is preferable from the viewpoint of the material, but there are cases where slow cooling is not necessary, and 600°C is the lower limit temperature for slow cooling. be.

Conventionally, various quenching methods have been proposed for this primary cooling, such as immersion in water or boiling water, but these methods do not allow water vapor to form again even if the surface oxide film is completely reduced and disappeared in the previous step. This is not preferable from the standpoint of thermal efficiency and equipment, as it is difficult to control cooling near the overaging temperature and requires reheating means.

In the present invention, by using a gas-liquid mixture, controlled cooling to near the overaging temperature is possible, and
There is no need to take preventive measures against the occurrence of temper color.

Such a cooling treatment makes it possible to ensure a cooling rate of 100° C./sec or more on average, and to enable controlled cooling without reheating to bring the steel plate to the overaging treatment temperature.

If the over-aging treatment is carried out within a temperature range of 300 to 500° C. for 20 seconds to 2 minutes, the steel sheet will be sufficiently non-aged.

There is no need for the processing atmosphere at this time to be reducing.

After the over-aging treatment, the steel plate is cooled to room temperature, and the conditions for this treatment may be appropriately selected from conventionally known conditions.

Thereafter, in the present invention, the film remaining on the surface of the steel sheet is removed, and temper rolling is performed by normal means.

As mentioned above, the thickness of the scale layer remaining on the steel plate after continuous annealing is significantly reduced by cold rolling, and it becomes porous. The surface properties after painting (paint adhesion, paint corrosion resistance) are comparable to those of conventional methods.

The residual scale removal treatment is preferably acid treatment, and cooling from the overaging treatment temperature may be performed by immersion in acid solution or spraying with acid solution, or immersion in acid solution before temper rolling.

Moreover, it is more effective to use electrolysis together. The acid used may be an inorganic acid such as hydrochloric acid, sulfuric acid, or phosphoric acid, or an organic acid such as formic acid or oxalic acid.

Under normal processing conditions, mechanical treatments such as wet polishing such as brushing, liquid honing, and shot blasting may cause deterioration of the steel plate surface due to the abrasive grains biting into the steel plate surface and the generation of surface linear flaws. Since the surface properties are restored by skin pass rolling, it is possible to use such a mechanical treatment method.

Normally, steel sheets are surface-treated before use, but galvanization and phosphate treatment, which is a base treatment for painting, are processed on separate lines.

In contrast, in the present invention, these processing devices can be installed successively after temper rolling to improve processing efficiency.

As described above, the present invention eliminates the pickling and electrolytic cleaning steps from the conventional manufacturing process of cold-rolled steel sheets, and also shortens the steps not found in the conventionally implemented or proposed continuous annealing process. Treatment time is 10 minutes or less, preferably 5 minutes.
Gives desired material properties to cold-rolled steel sheets in an ultra-short time of minutes or less,
Moreover, it has become possible to produce cold-rolled steel sheets with many new advantages in the annealing process.

In addition, the present invention also makes it possible to achieve the energy saving effects that the current state of the art is aiming for.

The present invention will be described below based on Examples, but it is clear that the present invention is not necessarily limited thereto.

In Examples 1 to 6 in Table 1, the descaling process was omitted and cold rolling was performed, and the electrolytic cleaning process was also omitted, and continuous annealing was subsequently performed, which enabled rapid heating. As a result, soaking and heating can be completed in a short time, and by using air-water cooling for the next primary cooling, rapid cooling is achieved and supercooling is prevented, eliminating the need for reheating for over-aging treatment. For this reason, the time from the start of temperature rise to the end of secondary cooling is 90 seconds or less.

Compared to the conventional manufacturing method for cold-rolled steel sheets (Comparative Examples 1 and 2), in addition to omitting steps, it is possible to save energy by significantly shortening annealing time and saving fuel and atmospheric gas.

Although cold-rolled steel sheets have been described above, the method of the present invention can of course be applied to various types of plated and surface-treated steel sheets, and can also be applied to the production of high-strength steel sheets, silicon steel sheets, and plates, which are different from the annealing heat cycle of ordinary cold-rolled steel sheets. can also be applied.

stainless steel

Claims (1)

[Scope of Claims] 1. When continuously annealing a cold-rolled copper strip by a method including at least the steps of heating, soaking, primary cooling, overaging treatment, secondary cooling, and temper rolling, A hot rolled steel strip with scale still attached is cold rolled to produce a cold rolled steel strip with scale still attached, and then this cold rolled steel strip is subjected to a jet flow that can control the atmosphere without having to perform a cleaning treatment. After rapidly heating the steel plate from the recrystallization temperature to 860°C in a direct-fired heating furnace, it is placed in a non-reducing atmosphere or a weakly oxidizing atmosphere for 5 minutes.
After holding for more than 2 seconds and then rapidly cooling from a temperature range of 600°C or higher to near the overaging treatment temperature, overaging treatment is performed.
A method for producing a cold-rolled steel sheet, which further comprises removing an oxide film on the steel strip during or after cooling to room temperature, and subjecting it to temper rolling. 2. The method according to claim 1, wherein at least one of the heating zone, soaking zone, and overaging zone is heated by a jet direct flame heating method. 3. The method according to claim 1, wherein cooling to near the overaging temperature is performed using a gas-liquid mixture. 4. The method according to claim 1, wherein the oxide film is removed by a pickling method before temper rolling. 5. The method according to claim 1, wherein the oxide film is removed by mechanical treatment such as wet polishing or liquid honing before temper rolling. 6. The method according to claim 1, wherein a surface treatment device is installed in series.