JPS60115306A - Thick plate manufacturing installation - Google Patents

Abstract

PURPOSE:To obtain a product of high-tensile steel plate excellent in shape by arranging levelers for hot and cold leveling and a cooling bed for natural cooling and making a plate sufficiently flat even in the case of online rapid cooling. CONSTITUTION:A blank material 20 is subjected to thickness-reduction rolling by a plate mill 1 and is cooled by a rapid cooling device 2. This rolled and cooled plate is leveled by a leveler 3 used for hot leveling, and is transferred to a cooling bed 4 and is cooled gradually. Thereafter the plate is precisely leveled into sufficient flatness by a leveler 6 used for cold leveling. By said installation, a high-tensile thick-plate product excellent in shape is obtained.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Application of the Invention] The present invention relates to plate production equipment for producing high-strength steel plate products with excellent shapes.

[Background of the invention]

Pipes, storage tanks, steel plates for shipbuilding, etc. are manufactured in plate rolling equipment (plate mills).

The plate products manufactured with this equipment are required to have high toughness and high strength. Such products, ie, plate products called high-strength steel, have been manufactured using conventional methods (1).

That is, after being rolled in a plate rolling facility, it is straightened at a high temperature of 800 degrees Celsius, then allowed to cool down to room temperature, and then sheared into a predetermined length. Thereafter, it was transported to a heat treatment line, where it was reheated and then subjected to quenching treatment to ensure a predetermined quality of high-strength steel.

However, due to the need to save energy these days, even after hot plate rolling, the temperature of the steel plate is as high as 850°C or higher, so this thermal energy is used to perform heat treatment immediately after rolling to achieve the desired properties. Techniques have been developed to obtain the quality of high-strength steel.

This method is called an online heat treatment method.

That is, a rapid cooling device is installed on the exit side of the plate rolling mill, and in order to obtain a plate product with the desired mechanical strength from the steel plate temperature of 850 to 900°C immediately after rolling, the A1 transformation point is 730°C.
The crystal grain size is adjusted by rapid cooling to the following temperature.

Temperature T for online rapid cooling of a hot steel plate from 850 to 900°C. Table 1 shows the relationship between the mechanical strength of the steel plate at room temperature (2) after cooling.

Table 1 That is, by rapidly cooling on-line, a tensile strength steel plate with desired strength can be obtained.

However, the material that has been rapidly cooled in this way is then flattened using a hot straightening leveler. It was found that the flatness of the steel plate was significantly inferior to all conventional methods without rapid cooling.

That is, the flatness is significantly inferior to that of the conventional method, which is flattened by a straightening leveler at a high temperature of about 800° C. without on-line rapid cooling, and then cooled by air.

[Purpose of the invention]

(3) An object of the present invention is to provide a straightening equipment that can obtain sufficient flatness even in equipment that uses the online rapid method.

[Summary of the invention]

We will discuss the results of a study on why superior flatness can be obtained compared to the method of straightening steel sheets at high temperatures and the online rapid cooling method.

It has been found that the reason for this is due to the temperature of the steel plate during straightening, and the details will be explained below.

That is, if the temperature differs by AT degrees in the width direction of the plate, even if the plate is flattened by a straightening leveler, the portion where the temperature is just 7 degrees higher will have an extra length distortion of 1 JEQ, as shown in the following equation.

AεΩ=AT・α(1) α,: Coefficient of linear expansion Even if it is flat immediately after straightening at a high temperature, the length distortion of Aε remains in the nucleus, so it will not change even at room temperature. When cooled, the entire plate has a uniform temperature, so AεQ
(4) Deterioration of the shape of the board corresponding to (4), that is, it occurs from the uneven state.

This deterioration of shape occurs during the cooling step after straightening.

The cooling step is carried out using a cooling bed device designed to uniformly cool the material, and if the temperature is 800° C., it will be uniformly cooled to approximately room temperature in about one hour.

In this cooling, the temperature distribution difference AT of the steel plate decreases as the temperature decreases, and eventually becomes uniform at room temperature.

In this way, in the cooling process, the amount of change, IIT, in which the temperature distribution difference ΔT gradually decreases occurs. Based on this, a thermal stress AαK expressed by the following formula is generated within the nucleus.

Aα, = E・α+AAT (2) Here, E: longitudinal elasticity number However, if the temperature of the plate is high, such thermal stress will be
It has the characteristic of being gradually released due to the creep phenomenon. The stress relaxation due to this creep phenomenon increases as the temperature of the material increases.
Occurs a lot. As for thermal stress, as shown in FIG. 6, compressive stress occurs where the length of the plate is long, and tensile stress occurs where the length of the plate is short. Therefore, when the plate is at high temperature, the plate expands and contracts due to the above stress due to the creep phenomenon, and the residual strain shown in equation (1) also becomes J.
EΩ is being released. Therefore, the flatness of the plate can be maintained even after the plate reaches room temperature due to cooling.

On the other hand, the creep phenomenon rarely occurs, especially in the case where cooling is performed by online cooling to a temperature as low as 300 to 400[deg.] C. because the temperature is low.

Therefore, even if the temperature distribution difference ΔT in equation (1) for the conventional high-temperature material that has been straightened is the same as that for the straightened material after online rapid cooling, the shape difference that occurs after the cooling process is large.

That is, for those that have been straightened after online rapid cooling, (1)
A shape defect occurs whose length in the equation corresponds to the strain difference AεQ.

Since the temperature distribution difference ΔT is about 100° C. after straightening, the strain difference AεQ is about 0112%.

On the other hand, in high-temperature material straightening, the strain is released by creep during cooling, so the strain that remains after cooling completely (6) is 1/3 to 115 or less of that in the case of the rapid cooling method, and is less than normal. Excellent loading accuracy is achieved.

In this way, in the online rapid cooling method, the temperature of the plate material is low during straightening, so if there is a temperature difference in the width direction of the plate, even if the flatness of the plate is good immediately after straightening, the shape will deteriorate due to air cooling.

In addition, in online rapid cooling, the temperature drops from a high temperature of 800 to 850°C to 300 to 600°C in a short time of 10 to 30 seconds, so it is difficult to uniformly cool the entire surface of the steel plate, and the temperature distribution is usually About 100 occur.

For this reason, straightening levelers require new and different equipment.

That is, in the present invention, as shown in FIG. 2, the precision leveling work for straightening the flatness is performed by a cold straightening leveler after the plate has been left to cool on the cooling work bed and has reached approximately room temperature.

However, since the steel material after rapid cooling is uneven due to the rapid cooling, transporting it onto the cooling bed may cause problems such as irregular movement of the sheet feeding level (7) on the cooling bed. occurs.

Therefore, the plate after rapid cooling is straightened by a hot straightening leveler for straightening the plate, which is sufficiently hotter than room temperature, before being conveyed to the cooling bed for cooling the plate.

Furthermore, the precision cold straightening leveler after the cooling bed is placed in front of the device that separates the steel material.

The reason for this is that unless the board is flattened, an error in the length of the divided board is likely to occur.

As described above, in the present invention, a hot straightening leveler is arranged in front of the cooling bed and a cold leveler is arranged behind the cooling bed, thereby producing a board with excellent flattening accuracy.

[Embodiments of the invention]

FIG. 1 shows a schematic diagram of the planar arrangement of the thick plate manufacturing equipment of the present invention. Material 20 has a thickness of 250m and a width of 2000~4500+
The thickness of the nn+ plate is reduced by reversible rolling in the thick plate rolling mill 1.

This thickness reduction rolling results in a plate thickness of 6 to 50 mm.

The length of the rolled plate is usually about 30 to 30 m (8) Ru.

The temperature of this plate is approximately 850 to 900°C, but it then advances in the direction of the arrow and is cooled to 300 to 500°C while being conveyed in the same direction at the rapid cooling conveyance station 2.

The cooling time required for this is 10 to 30 seconds.

After rapid cooling, the plate is straightened into a substantially flat surface by the leveler 3 during hot straightening. Thereafter, the material is transported across the cooling bed 4. The traverse distance of this cooling 4 is about 50 m, and about 20 plates are placed on this bed and are gradually cooled by air cooling as they are not traversed in the direction of the arrow.

Cross-transfer time is approximately one hour.

Thereafter, the material is sent to a cold straightening leveler 6 which performs precise straightening, and the material at a temperature close to room temperature is straightened.

The straightened board is then sent to a tentering side shear 7 for width adjustment of the board. Next, it is shredded into regular lengths by a regular shearer 8.

FIG. 3 shows a front view from thick plate rolling 1 to cooling 4.

The plate rolling mill 7 has a pair of work rolls 15 and an auxiliary roll (9). A four-high rolling mill consisting of strong rolls 16 is used.

In the rapid cooling device 2 for rolled plates, a large amount of cooling water is spouted from the top and bottom of the plate using spray nozzles 13 and 14.

A hot leveler having rollers arranged in a row is arranged behind it. The plate straightened in the hot state is sent to a cooling bed 4. Here, the plate material 12 is transported laterally by the chun conveyor 11.

The cold straightening leveler uses a quadruple leveler as shown in FIG. 4 to repeatedly bend a board strongly and straighten the board to a highly accurate flatness. The leveler shown in FIG. 4 is arranged vertically in a staggered manner while holding a material 33 therebetween, and is composed of a working roller 30 and reinforcing rollers 31 and 32 that reinforce and support these rollers.

By straightening the rapidly cooled steel plate using a hot straightening leveler before performing the cooling operation using the cooling bed, smooth operation can be achieved without impairing the cooling performance and workability of the cooling bed (10) I can do it.

In addition, by cold straightening after cooling on a cooling bed,
The flatness of the board can be perfected.

The flatness accuracy of the board is expressed by the steepness shown in the following equation using the height of the waves on the board and the pitch Q of the waves in FIG.

λ= (q/Q) The shape was as bad as .20 nun, but with the thick plate manufacturing method of the present invention, it was possible to even reduce λ to 0.2% or less, resulting in a significant improvement in flatness accuracy.

〔Effect of the invention〕

According to the present invention, a sufficient degree of flatness can be obtained even in equipment using an online rapid cooling method.

[Brief explanation of drawings]

Fig. 1 is a schematic diagram showing the arrangement of the thick plate manufacturing equipment of the present invention, Fig. 2 is a diagram showing the relationship between temperature and deformation resistance of the thick plate material, (11) Fig. 3 is a front view of the entrance side equipment of Fig. 1. , FIG. 4 is a side view of the cold straightening leveler used in the thick plate manufacturing equipment of the present invention,
FIG. 5 is an explanatory diagram showing the steepness of a steel plate straightened by the equipment shown in FIG. 4, and FIG. 6 is an explanatory diagram showing the state of thermal stress P acting on the steel plate. 6... Leveler for cold straightening. Agent Patent attorney Akio Takahashi (12) 2 & (0ri 3rd flash 4-(¥1 50th 6th interlude)

Claims (1)

[Claims] 1. A hot steel plate that has been rolled to reduce its thickness by a thick plate rolling mill,
In equipment that manufactures high-strength steel sheets by rapid cooling to a certain temperature, a leveler for hot straightening and a cooling bed for cooling are arranged after rapid cooling, and then a cold leveler is installed to straighten the steel sheet after it has been cooled by air. Thick plate manufacturing equipment characterized by having a leveler installed for straightening the gaps.