JPS6182901A - Working method of billet - Google Patents

Abstract

PURPOSE:To squash out perfectly the central pores existing in the inside of a billet by subjecting the billet to the rolling reduction specified in shape ratio at the time when the billet has a prescribed temperature difference between its surface and central part just after being perfectly solidified. CONSTITUTION:In a continuous casting process; a billet just after solidified, having the >=200 deg.C temperature difference between its surface and central part, is subjected to rolling reduction at a >=0.5 shape ratio by a press or rolls, etc.; where, the shape ratio is the effective contact length (mm) in the longitudinal direction of billet/the thickness (mm) of billet. By this rolling reduction, the compression in the longitudinal direction of billet, required for perfectly extinguishing the central pores in the billet, is produced. This rolling reduction is applied only in the thickness direction of billet, and the rolling reduction in the width direction is not always required.

Description

Detailed Description of the Invention (Industrial Field of Application) The present invention provides a method for efficiently and efficiently processing the cavity before rolling a steel billet having a cavity in the center (also referred to as center? center split). The present invention also relates to an economical crimping method.

(Prior art) As a technology in this field, for example, Japanese Patent Publication No. 44-24
There is a technique described in Publication No. 41.

In particular, in order to eliminate the shrinkage tubes and shrinkage cracks inherent in continuous cast billets, the cast slabs before complete solidification are transferred to multistage rolls, crawlers, etc.
This is a continuous casting method that uses a hydraulic press to pressurize and compress.

(Problem to be solved by the invention) In the continuous casting method, the conventional intention was to eliminate the occurrence of center porosity at the casting stage, and the remaining center porosity/tee was crimped during rolling in the next rolling process. The conventional wisdom was to set a certain level of tolerance as the limit and to control the process.

However, in reality, crimping also produced the expected results.
Center polo 7 tie may remain as a product defect. To make matters worse, the above-mentioned Special Public Interest Publication No.
Despite many years of efforts in the field after the proposal of the publication, there is still no technology to completely prevent the occurrence of center poronte, and the center poronte from the J, /j piece is still unresolved1.
Or not. Therefore, it can be said that a desirable method is to add processing to completely eliminate PC and then roll it into a product.

Based on the proposal of Japanese Patent Publication No. Sho dll-2441, the present inventor found that center porosity actually remains in any slab, and that the remaining center porosity is not necessarily completely crimped during the rolling process. As a result of searching for the reason why the crimp conditions for the center poronti do not hold, we found that the proposal in Japanese Patent Publication No. 44-2441 applies pressure compression that far exceeds the solidification shrinkage of the slab before it completely solidifies. , the stress disappears in the unsolidified part, and the reduction for crimping is not achieved, and the reduction not only does not exert the crimping effect, but also causes excessive flow of molten steel, which inevitably causes the occurrence of molten steel. It has been found.

The present invention provides a rolling method that completely compresses the center porosity inherent in a steel billet, and solves the unavoidable real problem of center porosity inherent in the steel billet supplied to the rolling process. .

(Means for Solving the Problems) In order to solve the above problems, the present invention has the following means. That is, 1. The gist of the present invention is to obtain a cast slab that has just been completely solidified and has a temperature difference of 200°C or more between the surface and the center with a shape ratio (effective contact length in the longitudinal direction of the slab n).
This is a method for processing a steel billet, characterized by applying a reduction at a ratio of 0.05 to 0.05. The reduction can be applied by a press or by rolling by a roll.

The reason why the present invention chooses the stage immediately after the complete solidification of the slab is that the effective propagation of the rolling edge and the lack of temperature conditions can be easily obtained, and the surface and core part of the slab can be heated to 200°C or more. The reason for the need for a temperature difference of This is to efficiently generate compressive stress.

In addition, the shape ratio is set to 0.5 or more, as shown in Figure 1, in order to stably generate the compressive stress necessary for crimping the center poro 7 tie at the center of the slab by working pressure. This is because 0.5 or more is required.

Note that the surface temperature is measured and calculated by a known method such as a radiation thermometer, and the center temperature is measured and calculated by a known method such as a riveting method or a thermotechnical calculation based on the surface temperature and hot water temperature history.

(Function) The present invention targets slabs that have just been completely solidified and have a temperature difference of 200°C or more between the surface temperature and the center temperature. Conditions are in place for the formation of compressive stress.

Under these conditions, rolling is carried out with the effective contact length in the longitudinal direction of the slab/the thickness of the slab, that is, the shape ratio, of 0.5 or more, so as shown in Figure 1, there is no tensile stress in the center of the slab, and the compressive A stress is formed, which wraps around the center poronti.

FIG. 1 shows the stress state formed at the center of the slab due to the temperature difference between the surface and center of the slab and the shape ratio during rolling.

FIG. 1 shows Example 1, which will be described later. For each steel slab of Il, [l and the steel slab of the comparative example, the horizontal axis represents the shape ratio and the vertical axis represents the stress distribution within the steel slab, and the relationship between the two is determined by the difference between the surface temperature and center temperature of the steel slab. 121. As is clear from the figure, within the range limited by the present invention, compression in the longitudinal direction of the steel billet necessary to eliminate the center voluntariness of the steel billet is generated.

Note that in carrying out the present invention, the reduction applied to the steel billet may be applied in the thickness direction of the steel billet.1 The reduction in the width direction is not necessarily required when the stress propagation efficiency to the center of the steel billet is poor, such as in width rolling of a slab. Not necessary.

(Example) ■...Immediately after solidifying the slab or the original metal using an anti-fouling fan, a piece of 01 was pressurized in the thickness direction with a press, and a center boron tie was punched.

■ Immediately after the section is completely solidified in the continuous casting process, pressure is applied in the thickness direction of the slab using horizontal rolls.

As a result, center polo/tee metals disappeared.

■1... Continuous casting process completely turns two Jj pieces into l'', (j
Immediately after -j + pressing t, press and roll the section in the thickness direction with a horizontal roll.

■...For comparison 11, why not apply the present invention to slabs? h
A piece was produced.

■...As a comparative example, 2J extracted from a rolling heating furnace
The surface of the J piece was instantly cooled and post-rolling was applied to produce a steel piece for rolling.

Each machining condition and each condition of the slab and steel slab, the slab,
Table 1 shows the results of turning steel slabs into rolled products in a rolling process. Note that the rolling reduction: i may be the amount that is formed to allow the rolling blade to reach the center of the steel billet.

As is clear from Table 1, there are 1 cases of 1 house and 1 leave.

In H1■, the purpose is itri3g in both cases,
JRN T of the present invention already? +, The center polo/tee of the steel billet had completely disappeared before rolling, and naturally the product after rolling had no residual defects based on the center polo/tee. The stress distribution inside the workpiece during processing according to the present invention is shown in FIGS. 2(a) and 2(b).

On the other hand, in the comparative examples IV and V, the center polo/tee cannot be expected to be eliminated even in the rolling process, residual defects exist, and the yield is low and poor. In the meantime, the temperature difference is 200% due to the reheating of the surface temperature of the steel piece after instantaneous cooling and before pressurization.
It seems that it was difficult to maintain the temperature above ℃, and that mere pressure reduction was not effective.

(Effects of the Invention) The present invention has 5. Immediately after completion of vertical hardening and 200% on the surface and center
Since a slab with a shape ratio of 0.5 or more is completely filled with oil under pressure, which forms a temperature difference of ℃ or more, compressive stress acts from all directions around the center hole/tee inherent in the slab.

The center volunteer was RJLJ IB. This eliminates the yield loss caused by this type of defect in rolled products, and not only reduces manufacturing costs.

Seedling production and operability, including post-processing involved in rolling product manufacturing, are greatly improved, reducing the amount of steel produced.

The industrial effects, such as improving the quality of the steel used, are extremely large.

[Brief explanation of the drawing]

FIG. 1 is a diagram showing the relationship between the shape ratio on the horizontal axis and the stress at the center of the steel slab on the vertical axis, and the temperature difference between the surface of the steel slab and the central part. FIGS. 2(A) and 2(B) are diagrams showing the stress distribution in the thickness direction of the steel slab in the example of the present invention. Agent Patent attorney Masamitsu Akizawa and 2 othersJ'-mtO size D ~ \ 5 \ ~
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Claims (3)

[Claims] (1) Immediately after complete solidification and at 200°C on the surface and center
A method for processing a steel billet, characterized by applying a reduction to a billet having the above temperature difference at a shape ratio (effective contact length in longitudinal direction of billet (mm) / billet thickness (mm)) ≧0.5. (2) The method according to claim 1, wherein the reduction is applied by a press. (3) The method according to claim 1, wherein the reduction is applied in a spreading manner by a roll.