JPS6013048B2 - Cooling method for hot-rolled steel coils - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a coil cooling method for producing a hot-rolled steel coil having uniform mechanical properties and excellent workability.

In manufacturing hot-rolled steel strip coils and cold-rolled steel sheets made from the same, after hot-rolling a steel slab (steel billet), it is wound into a hot-rolled steel sheet coil at a predetermined winding temperature and left in the atmosphere. The current standard process is to let it cool.

In this case, even if the winding temperature is adjusted to be uniform over the length of the steel strip, the thermal history will be uneven along the length of the steel strip when the coil is cooled to near room temperature after winding. .

During gradual cooling after winding into a hot rolled steel sheet coil, growth of crystal grains, precipitation of ASON, MnS, iron carbides, etc., and coarsening progress. The rolled steel plate has a European quality and improves workability. In order to further enhance these effects, a new technique for winding hot-rolled steel coils at high temperatures is described in, for example, Japanese Patent Publication No. 50-1811.

However, since this technology has non-uniform thermal history as described above, the mechanical properties of the product also become non-uniform. In other words, the outer and inner circumferences of the hot-rolled steel coil are far from being cooled after winding, resulting in crystal grain growth, A〆N and M
The precipitation and coarsening of nS or iron carbides is delayed, and only those positions become partially hard, resulting in poor workability.
This is particularly undesirable from the viewpoint of manufacturing steel sheets with required properties and supplying homogeneous products to customers. The present invention is intended to eliminate such drawbacks of the prior art, and the gist of the present invention is to cover a hot-rolled steel coil coil wound in a temperature range of 60,000 or higher with a heat insulating cover, and to reduce the temperature of the outer circumference of the coil. , (winding temperature -250)
This is a method of cooling a hot-rolled steel coil, which is characterized by cooling the area until the temperature reaches 10°C at an average cooling rate of 5°C/min or less. The present invention will be explained in detail below.

In manufacturing hot-rolled steel coils with excellent workability and cold-rolled steel coils made from the same, hot-rolling is performed at high temperatures, and during the subsequent gradual cooling process, A〆N, Mn
It is extremely effective to promote coarsening of precipitation of S, iron carbides, etc.

The hot rolling temperature must be 600° C. or higher to allow the reactions such as AsoN→AsoN, Mn+S→MnS, etc. to proceed sufficiently. Since the diffusion rate of AZ and Mn is slow at low temperatures, when winding is performed at a low temperature of less than 600q0, the precipitation and coarsening of M〆N, MhS, or iron carbides will not proceed sufficiently even if the material is slowly cooled thereafter. Even after winding at a high temperature of 600 qo, if the coil is left in the atmosphere, the temperature will drop quickly because the inner and outer circumferential parts of the coil are in direct contact with the air, and only in those parts will the precipitation of A〆N, MnS, and iron carbides not become coarse. It will be enough.

In order to prevent the above-mentioned phenomenon, a heat-retaining device is required during cooling of the coil. That is, the present invention is to quickly cover a hot-rolled steel coil wound at a temperature of 60,030 degrees Celsius or higher and keep it warm in the region of 600 degrees Celsius or higher, where the temperature does not drop much. The winding temperature was set to Tc (00
), and the coil outer temperature Ta(00) changes from Tc to (Tc
-250)℃ temperature range, its average cooling rate is 5℃/m
It is characterized by cooling so that the temperature becomes less than 1000 m.

Since A and Mn do not have a sufficient diffusion rate unless the temperature is high, even if the heat insulating cover is set to a temperature below (Tc-250)C, no additional effect will be produced for the above purpose. However, even if the heat insulating cover is set until the temperature reaches (Tc-250)°C or lower, the promotion of coarsening of the precipitation of ASON, MnS, and iron carbides will not be inhibited. By applying this heat-insulating cover usage technology, we can not only produce hot-rolled steel sheets with uniform mechanical properties and excellent workability, but also cold-roll and dull them to produce workable steel sheets with uniform mechanical properties. It is also possible to obtain a cold-rolled steel sheet with excellent properties, and furthermore, even if surface treatment such as galvanization is performed, the effects of the present invention will not be diminished.

Next, an embodiment of the cooling method using the heat insulating cover according to the present invention will be described. The heat insulating cover shown in FIG. 1 is simply placed over the coil, and the example shown in FIG. 2 has a heating device provided inside the heat insulating cover.
Note that FIG. 3 shows a plan view of FIG. 2. In the figure, 1 is the ceiling of the heat insulation cover, 2 is the outer panel, 3 is the insulation material, 4 is the hook, 5 is the support twill, 6 is the coil, 7 is the fuel supply pipe, 8 is the combustion nozzle, and the inner diameter of the coil. , Part 2 is the outer diameter of the coil. The heat insulating cover shown in FIG. 1 has a heat insulating material 3 applied to the outer panel 2, and a supporting rod 5 is provided in the center of the cover at a position that enters the inner diameter of the coil.

An arbitrary cooling rate can be obtained by changing the material or thickness of the outer plate 2 and the heat insulating material 3. The support bar 5 prevents the cover from falling off the coil when the cover is used on a conveyor that moves the coil. The cover may be used on the conveyor or after being placed on the floor.
If the coils are placed on the same floor, the coils may be stacked. Also, instead of using a heat insulating cover as shown in the figure,
× Even if it is the outer cover or inner cover of Yodo Anchor,
This is fine as long as a predetermined cooling rate can be obtained.

The heat insulating cover shown in FIG. 2 has a heat insulating material 3 applied to the outer panel 2 and a fuel supply pipe 7 installed inside the cover.

The pipe 7 heats the inner and outer diameter sides of the coil, and the pipe 7 is provided with a suitable combustion nozzle 8 for burning fuel (for example, COG). Since heat dissipation from the coil is greater from the side surface than from the end surface of the coil (edge side toward the center of the coil), the inner diameter and outer light portion of the coil are heated.

In terms of equipment, it may be possible to use a simple system that uses only pipes to heat the system, but it goes without saying that it would be more efficient to install steel plates and heat insulating materials. Example 1 Steel component C: 0.02-0.07%
, Mn: 0.15-0.30%, P: 0.014-0,
018%, S: 0.012-0.023%, 0:0.0
Nine capped steel slabs consisting of 45 to 0.053% were used, each having a winding temperature (Tc) of 73 on the 3.2 side after hot rolling.
It was wound into a coil at 5:00 am.

After that, while recording the temperature of the outer periphery of the coil, set the heat insulating cover (shown in Figure 1) under the conditions shown in Table 1. After the entire coil has cooled to room temperature, unwind the coil and remove the outermost part of the coil and the coil. A tensile test piece was taken from a position corresponding to the central part, and the yield point (YP) was determined. In the case (No. 1) in which the heat-retaining device shown in Table 1 is not used, the outer circumferential portion of the coil is rapidly cooled after winding, so the YP is about 7k9/2 skin higher than that of the central portion of the coil, and the workability is significantly reduced.

On the other hand, in the case of the method according to the present invention, a heat insulating cover is used (No. 2, 4, 6, 7, and 8), the difference in YP depending on the position within the coil is about 2k9/skin2, and almost uniform mechanical properties can be obtained. In this invention, if the time for using the heat insulating cover is extended until the coil is cooled to room temperature (M.2, 4, 7), YP depending on the coil position
The difference disappears completely.

Even when using a thermal cover, if the time to set the thermal cover is delayed (M.3, 5) and (Tc-25)
0) If the cooling rate to ℃ exceeds 5℃/min (shame.9
), the YP at the outer periphery of the coil becomes high, so it is desirable to take these conditions into consideration when performing the work. Example 2 Steel composition C: 0.025-0.056%, Mn: 0.12
~0.25%, P:0.013~0.019%, S:0
．． 013-0.021%, T・A So: 0.022-0.
Four aluminum killed steel slabs made of 0% unevenness were prepared, each of them was rolled at a hot rolling temperature (Tc) of 750 and 0 (coil unit weight 21 tons) and a heat insulating cover was set on the 3.2 side. First, let them cool in the atmosphere, and for the other set, wait 3.08 minutes after winding up (coil temperature 625q○ when the heat-insulating cover is attached), then set the heat-insulating cover (as shown in Figure 1). The coil was cooled to room temperature.

The cooling rate at this time was 2.5 qo/mjn. After pickling, these hot-rolled steel strips were rolled at a rolling reduction of 72%, and
Continuous anchor racing was conducted for oo×1 minute. The thus wrinkled cold-rolled steel strip coils were unwound, and tensile test pieces were taken from each fake to measure the rankford value (r value). The results are shown in FIG. When a heat insulating cover is not used, the r value is extremely low at positions corresponding to the outer and inner periphery of the hot-rolled coil, but
When a heat insulating cover is used according to the present invention, the r value is high even at a position corresponding to the outer periphery of the hot-rolled coil, and therefore, the inside of the product coil is uniform and a high r value can be obtained, and a product with excellent deep drawability can be obtained. I understand. As described above in the embodiments, the method of the present invention can be applied not only to hot-rolled steel sheets shipped, but also to lined steel sheets (including plated steel sheets).
Even cold-rolled steel sheets have a great effect when applied to aluminum killed steel used in continuous dawn anchors, and the Y of the outer periphery and center of the coil
P deviation (ΔYP) can be kept below 2.0 [9/rigidity 2].

[Brief explanation of the drawing]

Figures 1, 2, and 3 show examples of the heat insulating cover used in the method of the present invention. FIG. 3 is a plan view of FIG. 2, and FIG. 4 is a diagram showing test data of Example 2. 1...Ceiling of heat insulation cover, 2...Outer panel, 3...Insulating material, 4
...Hook, 5. Support rod, 6. Coil, 7. Fuel supply pipe, 8. Combustion nozzle. Figure 1 Figure 2 Section 3 Figure 4

Claims (1)

[Claims] 1 A heat-retaining cover is placed on a hot-rolled steel coil that has been wound in a temperature range of 600°C or higher, and the area is cooled at an average cooling rate of 5°C/5°C until the outer peripheral temperature of the coil reaches (winding temperature - 250)°C. A method for cooling hot-rolled steel coils, which is characterized by cooling in less than a minute.