JPS60243226A - Method and device for controlling quality of hot rolled material - Google Patents

Abstract

PURPOSE:To improve the quality of hot rolled steel plate by controlling the cooling of steel plate immediately after its hot rolling. CONSTITUTION:A steel plate is rapidly cooled at the cooling speed of >=1,000kcal/m<2>-hr deg.C heat transfer coefficient within 0.5sec immediately after its hot rolling and is subjected to an alpha transformation from the condition of leaving rolling distortion. As a result, the quality can be improved by an alpha granulation owing to gamma-alpha transformation. For executing of the above rapid cooling, a water cooling nozzles 51-53, 61-63 of a direct rapid cooling device having >=1,000kcal/m<2>-hr deg.C heat transfer coefficient are provided on one or both sides of the roll outlet of the final and front stands 1, 2 of a hot finishing rolling machine. The length of a direct rapid cooling zone A is sufficient in about 1-5m and when an air cooling zone B is provided at the front of a zone cooling device 9 with providing a water remover of gas jet, etc. behind the zone A, the temp., plate thickness, plate width, plate shaped, etc. can be measured within the zone B.

Description

DETAILED DESCRIPTION OF THE INVENTION (Technical Field of the Invention) The present invention relates to hot rolling technology, and in particular to a method and apparatus for improving the quality of hot finish rolled steel.

(Prior art and its problems) Conventionally, when hot finish rolling a steel plate, for example, 1.2 to 51 RI is applied from the final stand of a 6 to 7-high hot finishing mill.
After the steel plate rolled to a thickness of It is usually passed through a cooling device and cooled with water.

Temperature of the hot-rolled steel sheet coming out of the final stand mentioned above1. The plate thickness, plate width, plate shape, etc. are measured using thermometers and x
Ii! Thickness gauge, board width gauge, four fill gauge 1. Measurements are performed using feedback control sensors or measuring devices such as shape detectors, and the presence of water and water vapor on the surface of the steel plate reduces measurement accuracy, so it is said that it is necessary to provide an air-cooled area. .

However, as a result of the hot-rolled steel sheet passing through such an air cooling area, there is not only the problem of scale generation, but also
There was a problem in that the internal strain caused by hot rolling disappeared and the structure became coarse.

As a method to solve the scale problem caused by providing the above-mentioned air cooling area, JP-A-58-157517
The publication describes a technique for blocking the atmosphere by placing a laminar water stream sprayed from a slit-shaped laminar nozzle over the entire area between the finishing rolling mill and the zone cooling device, covering the entire front and back surfaces of the m-plate moving between them. ing. This technology aims to reduce the formation of scale by completely placing the front and back surfaces of the steel plate in a stream of water to cut off contact with air. It is necessary to place the entire front and back sides of the steel plate in the entire area between the finishing rolling mill and the zone cooling device, so it is necessary to measure the plate condition by measuring the thickness of the steel plate after finishing rolling with an X-ray thickness gauge. There is a problem in that it cannot be carried out with a zone cooling device, and no consideration is given to the coarsening of the structure due to the disappearance of internal strain caused by hot rolling.

(Object and Structure of the Invention) The present invention was made in view of the above-mentioned points, and an object of the present invention is to improve the material quality of a hot rolled steel sheet by controlling the cooling of the steel sheet immediately after hot rolling.

Improvement of the material quality of hot rolled steel sheets is achieved by refining the structure.

Controlled rolling and controlled cooling are known as means for obtaining a fine structure. All of these methods reduce the grain size of γ, γ−
The basic idea is rapid cooling during α transformation and suppression of α grain growth.

The present invention is based on the recognition of the fact that it is possible to improve the quality of the material by making the α grains finer through the γ-α transformation by strongly water cooling immediately after hot rolling and causing the α transformation from a state where rolling strain remains. be.

Therefore, in the present invention, the heat transfer coefficient of the hot-rolled material immediately after rolling reaches 1000 Koaj/m within 0.5 seconds during hot rolling.
It is characterized by controlling the material quality of the hot rolled material by rapidly cooling it at a cooling rate of -hr 'C or higher and transforming it in a state where rolling strain is accumulated. By rapidly cooling the hot-rolled material immediately after rolling (hereinafter referred to as immediate quenching), a significantly fine grain structure can be obtained.

Further, the present invention provides a device for implementing the above-mentioned material quality control, in which a heat transfer coefficient of 1000 Ka is applied to the roll exit side of the final stage and/or the previous stage of a hot finishing tandem rolling mill.
It is characterized in that it is equipped with an immediate quenching device that has a cooling capacity of more than al/m''-hr'c.

(Example) FIG. 1 shows a schematic diagram of the exit side of a hot finishing mill according to the present invention.

In the drawing, 1 and 2 indicate the final stand and the front stage stand of the hot finishing rolling mill, and in the illustrated example, immediately after the final stand 1, there are strong water cooling headers 8□~88, 4□~ as the immediate quenching device. Water cooling nozzles/I15□-58, 6□-68 are attached to each header with their directions inclined to the roll bite 8 so as to strongly water-cool the hot-rolled steel plate 7 immediately after rolling.

The heat transfer coefficient of the water cooling nozzle of the immediate quenching device is 1000 [c
a//fn"-hr ℃ or above, and it is necessary to strongly water-cool the hot-rolled steel sheet at this cooling rate within 0.5 seconds immediately after rolling. Therefore, one or two of the most advanced quenching equipment For water-cooled nozzles 6□, 5g, 8□, and 6., set the injection pressure to 50
It is preferable to make it variable at ~200 kg/c-.

It is sufficient for the length of the immediate quenching area A by the immediate quenching device to be 1 to 6 m, and an air cooling area B is provided after the immediate quenching area A by providing a gas jet or other suitable water draining means. Necessary measuring devices can be installed in this air cooling area B to measure temperature, plate thickness, plate width, plate shape, etc.

Example 1 Steel containing 15% OO and 5% In O by weight was tapped from a converter, heated to 1260°C, rough rolled into a sheet bar with a thickness of 3511111 mm, and then rolled into a 7-stand hot finishing mill. At 8
Finished with a thickness of 4m. The rolling conditions and finishing temperature during hot rolling were the same, and those according to the present invention were immediately quenched with a water-cooled jet, while those of the comparative example were rolled without immediately quenching. The α grain size and hardness of the steel sheet after rolling are shown in Table 1. As is clear from Table 1, the α grain size can be significantly refined by performing the immediate quenching according to the present invention. In this example, the most recent quenching time using the water-cooled jet IOt was about 0.4 seconds, and the temperature drop during this time was about 8°O''C. Based on this cooling condition, the thermal conductivity coefficient of the water-cooled nozzle was It is approximately 2000 Kcal/m''-hr'c.

Furthermore, by changing the number of headers 8□ to 88, 4□ to ringing of the immediate quenching device on the exit side of the rolling m shown in Fig. 1, or by changing the threading speed, the time until the start of water cooling after pressing was changed, and the ferrite was Particle size was examined. The results are shown in the graph of FIG.

As is clear from FIG. 2, the grain refining effect appears when immediate quenching is started within 0.5 seconds immediately after rolling;
Even if strong water cooling is started with a delay of more than 5 seconds, no particle refining effect will appear.

In addition to the immediate quenching at the exit side of the final finishing stand, the above-mentioned granulation effect can be further improved by installing a similar immediate quenching device on the exit side of the pre-stage stand 2 or each stand before it and performing the same immediate quenching. A remarkable grain refinement effect can be obtained.

(Effects of the Invention) According to the present invention, by immediately quenching at a cooling rate with a heat transfer coefficient of 1000 Kcat/m"-'hr'C or more within 0.5 seconds immediately after hot rolling, α grain refinement is achieved. The effect is that the quality of the material can be improved.

[Brief explanation of drawings]

FIG. 1 is a schematic fs diagram of the apparatus according to the present invention, and FIG. 2 is a graph showing the relationship between the quenching start time after rolling and the ferrite grain size. l...Hot finishing mill final stand 2...Pre-stage stand 8□~88, 4□~48...Water cooling header 61~58, 6□~68...Water cooling nozzle 7 of the immediate quenching device・・・
Hot rolled steel plate 8... Roll bite 9... Zone cooling device. Patent applicant: Kawasaki Steel Corporation Figure 1 Figure 2

Claims (1)

[Scope of Claims] L During hot rolling, immediately after rolling, transformation occurs in a state where rolling strain is accumulated by rapid cooling at a cooling rate of at least 1000 KOaj/m"-hr"c with a heat transfer coefficient within 0.6 seconds. A method for controlling the material properties of a hot rolled material. a A heat transfer coefficient of 1000 KOa4/
1. A material quality control device for hot rolled material, characterized in that it is equipped with an immediate quenching device of m''-hr'c or more.