JPH1110204A - Method for preventing scale defects in hot rolled sheet - Google Patents

Abstract

PROBLEM TO BE SOLVED: To detect scale defects rapidly and to prevent such successive generation plomptly by controlling rolling temperature and/or draft of finish rolling based on the detected result of defects detector arranged between finishing mills consisting of a plurality of stands of hot rolling line and the coiler. SOLUTION: Control of rolling temperature and/or draft of finish rolling based on the detected result of defects detector 4 is executed. The temperature of sheet in finishing mill 1 falls through heat absorption by rollers at the time of biting to rolls and rises through working heat generation while rolling. The above procedure is repeated successively in the stands F1-F7. Under such circumstances, in the forestages of fimishing mill 1, the sheet temperature reaches peak point and the rolling load gets larger. In consequence, in order to prevent continuous generation of scale defects, it is essential to lower the rolling load of these forestage stands, and accordingly it is effective to lower the rolling temperature and/or the draft in the stands concerned.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for preventing scale flaws in a hot-rolled material, and more particularly to a method for detecting surface defects called scale flaws generated in a material to be rolled during hot rolling as quickly as possible. The present invention relates to a method for preventing scale flaws in a hot-rolled material for preventing continuous occurrence thereof.

[0002]

2. Description of the Related Art Inspection of defects on the front and back surfaces of a hot-rolled material has conventionally been performed by using a coil outer periphery after winding, a coil outer winding portion in a rewinding line, and a refining line (an pickling line, a skin pass line, a slit line, etc.). ) Was observed by observing the front and back surfaces of the coil.

[0003]

However, scale flaws caused by the secondary scale biting into the material to be rolled during hot rolling can be observed only after the winding or rewinding line where only the outer periphery of the coil or the outer winding portion can be observed. Is difficult to find, and it is almost always found on a refinement line downstream of these that allows observation of the front and back surfaces over the entire length of the plate, including the inner coiled portion and the intermediate portion. Was.

As described above, according to the conventional inspection method, the presence / absence and degree of scale flaws are firstly determined from the results of surface inspection in the refining line. Therefore, the rolling operation conditions of the scale flaw-generating material are retrospectively investigated and analyzed. Finding appropriate conditions for preventing recurrence, the rolling control measures to control the rolling so as to satisfy the proper conditions are delayed, and during this time, a considerable amount of the material to be rolled is subjected to the rolling conditions before the rolling reduction measures (the conditions under which scale flaws are likely to occur). ), Causing a large loss.

Accordingly, an object of the present invention is to propose a method of preventing scale flaws in a hot-rolled material, which can detect scale flaws as quickly as possible and can prevent the occurrence thereof continuously and effectively.

[0006]

SUMMARY OF THE INVENTION The present invention is directed to a flaw detecting device which is capable of detecting defects existing on the front and back surfaces of a material to be rolled between a finish rolling mill comprising a plurality of stands of a hot rolling line and a winding machine. And controlling the rolling temperature and / or the rolling reduction of the finish rolling based on the detection result of the flaw detection device.

Preferably, the control is performed so that the rolling temperature and / or the rolling reduction at the stand where the rolling temperature reaches a peak when a defect is detected and at the stands before and after the same are changed to a range lower than the current value.

[0008]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS As shown in FIG. 1, a method for preventing scale flaws in a hot-rolled material according to the present invention is described below. A flaw detection device 4 capable of detecting the presence or absence of a defect existing on the front and back surfaces of the material to be rolled (hot-rolled material) 3, and based on the detection result of the flaw detection device 4, the rolling temperature of finish rolling and / or Alternatively, the gist is to control the rolling reduction. The number of stands is not particularly limited, but is shown in FIG.
Shows a finishing mill 1 having a 7-stand configuration.
1 to F7 are stand numbers.

As the flaw detecting device 4, for example, Japanese Patent Publication No.
An apparatus as proposed in Japanese Patent No. 24503 may be used. The control of the rolling temperature and / or the rolling reduction is preferably performed as follows. FIG. 1 shows a change in the sheet temperature (rolling temperature) in the finishing rolling mill 1. The sheet temperature decreases due to heat removal from the rolls when the rolls are engaged, and rises due to processing heat (reheat) during rolling. This is sequentially repeated in F1 to F7. At this time, the first stage (F1 to F1) of the finishing mill 1
In F3), the sheet temperature reaches a peak and the roll load increases.

Therefore, in order to prevent the continuous occurrence of scale flaws, it is important to reduce the roll load at the preceding stand, and it is effective to reduce the rolling temperature and / or rolling reduction at the stand. Means. The rolling temperature has an allowable range of several tens of degrees, and when the occurrence of scale flaws is detected, the sheet temperature is gradually decreased to near the lower limit of the allowable range. In order to lower the sheet temperature, a method of increasing the amount of roll coolant in the former stand, increasing the amount of water in a cooling device such as a shower between the rough rolling mill and the finishing rolling mill 1, or delaying the biting into the finishing rolling mill 1 is performed. Can be adopted. Since the actual measurement of the sheet temperature between the stands is extremely difficult, the reduction rate, the rolling speed, and the like are taken into consideration based on the actual measured value of the exit side temperature (finish exit side temperature = FDT) or the entrance side temperature of the finishing mill 1. It is practical to estimate the plate temperature at the preceding stand to be controlled.

As for the rolling reduction, the rolling reduction of the entire finishing rolling mill may be changed to reduce the rolling reduction in the former stage, and the reduced amount may be directed to the latter stage. If the generation of scale flaws does not stop even after changing the rolling temperature and the rolling reduction within the allowable range, continuous generation of scale flaws is prevented by replacing the rolling roll.

Two typical types of scale flaws are (a) satin texture and (b) meteor shown in plan view in FIG. 2. In (a), the rolling temperature is reduced. It is effective to preferentially lower the rolling reduction in the case of (b). Of course, the rolling load is a function of the rolling temperature and the rolling reduction, and it is more effective to reduce both at the same time.

According to the present invention having the above-described structure, scale flaws generated in a hot-rolled material can be found immediately during or after rolling of the material, and the scale flaws can be found immediately after the next rolled material. Since the operating conditions can be quickly optimized, continuous generation of scale flaws can be effectively prevented. The present invention can be applied to any type and thickness of a material to be rolled as long as the material can be hot-rolled.

[0014]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS As shown in FIG. 1, an embodiment in which a flaw detection device 4 is arranged between a finishing mill 1 and a winding machine 2 of a hot rolling line to prevent continuous generation of scale flaws according to the present invention. explain. (Example 1) Table 1 finish thickness 2.0mm low carbon steel shown (C: 0.04%) in the finish rolling of A ₁ to A _4, the front and rear surfaces of the longitudinally intermediate portion after the flaw detection device A ₁ On the other hand, scale flaws (defects) having a pear-skin texture (see FIG. 2A), which are considered to be caused by secondary scale, were detected. At this time, finishing delivery temperature of the subsequent intermediate portion of A ₁ (FDT) was 870 ° C. As shown in the same table.

Therefore, according to the present invention, when the FDT of the continuous next rolled material A _{2 to} A ₄ is controlled in the range of 850 to 855 ° C. as shown in the same table, the FDT is detected at A ₁ as shown in the same table. scale defects degree is not detected in a ₂ to a ₄ in the, it could prevent continuous occurrence of scale defects.

[0016]

[Table 1]

(Example 2) Finished plate thickness 1.2 mm shown in Table 2
Low carbon steel: in (C 0.04%) finish rolling of B ₁ ~B _4, meteor-like flaws detection equipment appears to work roll surface roughening attributed finish on the back table over the entire length of the B ₁ (FIG. 2
(Refer to (b)). At this time, B ₁
As shown in the table, the rolling reductions at the F2 and F3 stands before finishing were 48% and 46%, respectively.

Therefore, according to the present invention, as shown in the same table, the rolling reduction of the continuous next rolled material B _{2 to} B _{4 in} the stand is controlled to 45 to 46% in F2 and to 43 to 44% in F3. As a result, as shown in the table, the medium scale flaw detected in B ₁ was reduced to a small extent in B ₂ , and was not detected in B ₃ and B ₄ , and continuous generation of scale flaws could be prevented. Was.

[0019]

[Table 2]

[0020]

According to the present invention, there is an excellent effect that scale flaws of a hot-rolled material can be detected at an early stage and continuous generation thereof can be effectively and promptly prevented.

[Brief description of the drawings]

FIG. 1 is an explanatory diagram showing an embodiment of the present invention.

FIG. 2 is a plan view showing aspects of scale flaws.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Finish rolling mill 2 Winding machine 3 Material to be rolled (hot rolled material) 4 Flaw detection device

Claims (1)

[Claims] 1. A flaw detection device capable of detecting a defect existing on the front and back surfaces of a material to be rolled is disposed between a finish rolling mill having a plurality of stands of a hot rolling line and a winding machine, Controlling the rolling temperature and / or the rolling reduction of the finish rolling based on the detection result of (1).