JPH09118926A - Manufacture of cold rolled and galvanized steel sheet having little material deterioration in coil end - Google Patents

Abstract

PROBLEM TO BE SOLVED: To obtain a cold rolled and galvanized steel sheet having little material deterioration in the coil end by cleaning with an acid and crop-cutting the inferior range of a mechanical property as a product after annealing, including bulky crystal grains in the end part of the inner and outer peripheral surface of a hot rolled coil. SOLUTION: Barkhausen signals of a hot rolled coil are continuously measured with a non-contact way using a magnetic head before the acid cleaning, the measured value is compared with the relationship between the voltage value of Barkhausen signals and the size of bulky crystal grains which are previously obtained every the kind of steels, whereby the range including bulky crystal grains in the inner and outer peripheral surfaces of the coil is recognized on line and the cold rolling and annealing are performed after the acid cleaning and crop-cutting of the inferior range.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a cold-rolled steel sheet and a method for producing a plated steel sheet in which a coil end portion produced in a continuous annealing or continuous hot dip galvanizing line has little material deterioration.

[0002]

2. Description of the Related Art Cold-rolled steel sheets and plated steel sheets used for automobiles, electric appliances, furniture, etc. are usually ultra-low carbon steel containing C: 0.0010 to 0.0600% by weight% continuously cast or ingot. It is manufactured by hot rolling a slab of low carbon steel, pickling, cold rolling, and annealing, but in recent years annealing has been continuous annealing because it requires shortening the manufacturing period and uniformity of material and surface cleanliness. Or it is often performed by a continuous plating line. In a continuous line, the annealing time is short, and heating and cooling are quick, so when severe workability is required, it is necessary to coarsely agglomerate carbonitrides in advance. Therefore, as disclosed in Japanese Patent Laid-Open No. 63-72829, it is common practice to wind the coil at a relatively high temperature of 700 ° C. or higher after the hot rolling is completed.

However, deterioration of the material is recognized at the inner and outer ends of the coil, which are cooled more quickly after winding than at the center of the coil. In this case, the winding temperature may be further increased at the coil end. When the coil is wound at a high temperature, especially when the amount of C, Mn, S, etc. is reduced in order to improve the workability, coarse crystal grains of 50 to 100 μm or more around the surface of the coil end are centered. May occur, which may lead to deterioration of mechanical properties in the product sheet after cold rolling and annealing, and in a particularly remarkable case, it may cause rough skin and impair the aesthetics of the product.

Conventionally, it is difficult to determine the change in the structure of such a hot-rolled coil from the appearance of the steel sheet, and after the product is finished, a test piece is sampled and subjected to a mechanical test and an appearance test to determine that it is not suitable for the intended use. If so, the range was truncated. For this reason, it is necessary to cut off the inner peripheral portion and the outer peripheral portion of the coil to a range suitable for the use range, and in addition to the inconvenience, the cost is increased due to a decrease in yield. In particular, when the coiling temperature is high and an abnormal material is predicted in the product sheet, the possible range is cut off with a hot rolling coil in advance, and then pickling, cold rolling, and annealing are also performed. However, it was difficult to accurately determine the range, and it became necessary to cut off the product once it was made into a product, and in some cases, it also led to the loss of cutting off the range that could withstand the intended use.

[0005]

DISCLOSURE OF THE INVENTION The present invention relates to a cold-rolled steel sheet or a plated steel sheet produced by continuous annealing or a continuous plating line by winding a coil at a relatively high temperature of 700 ° C. or more after hot rolling, When pickling and cropping the range containing coarse crystal grains on the inner and outer circumferences of the coil, make the range accurate without excess or deficiency, and do not have the coil end deterioration that was previously recognized. Is intended to provide.

[0006]

When the coil is wound at a high temperature of 700 ° C. or higher after hot rolling for the purpose of improving workability, the coiling temperature at the inner and outer ends of the coil is too high. And, since the crystal grain size becomes coarse in the metal structure after hot rolling and before cold rolling, the crystal grain size becomes small in the metal structure after cold rolling and annealing, and the accumulation in the {111} orientation becomes weak,
Since the workability deteriorates rather, it is necessary to crop it. At this time, it is effective to measure the crystal grain size of the hot-rolled coil and compare and compare the change in the crystal grain size of the inner and outer circumferences of the coil with the center of the coil to determine the range for pickling and crop cutting. Then, the present inventors have found that there is a good correlation between the Barkhausen noise and the crystal grain size that occur when the steel sheet which is a ferromagnetic material is magnetized, and actually, a test piece is taken from the hot rolled coil to obtain a metal structure. By developing a method that can measure Barkhausen signals accurately and at high speed without contacting the coil using a magnetic head without investigating
The present invention has been accomplished.

That is, in order to detect the Barkhausen signal generated from the hot-rolled sheet, the hot-rolled sheet is magnetized with an alternating current by an exciting head, and the change in the magnetization is detected by the detecting head.
A voltage signal (voltage-time waveform) is induced in the detection head with respect to the change in magnetization. After amplifying the voltage signal, a Barkhausen signal can be obtained by extracting only a signal in a predetermined frequency range through a bandpass filter. After passing the voltage signal through a bandpass filter,
A Barkhausen signal can be similarly obtained by amplification.

In order to actually detect the crystal grain size distribution of the hot rolled sheet, the following is done. That is, a magnetic head composed of an exciting head and a detection head is installed so as to be separated from the hot-rolled plate by a predetermined distance, and the hot-rolled coil is continuously detected in the plate to obtain a signal. The distribution of the crystal grain size in the longitudinal direction of the hot-rolled coil can be known by comparing the obtained voltage signal with the relationship between the crystal grain size for each steel type and the voltage of the Barkhausen signal, which has been obtained in advance. After that, the hot-rolled coil is pickled and cold-rolled according to a predetermined schedule to be a product by continuous annealing or annealing in a continuous hot-dip galvanizing line. The material of the product coil, especially the r value and the crystal grain size of the hot-rolled coil. Since there is a certain correlation between steel types, the deterioration of the material at the coil end can be reduced by pre-pickling and cropping the range containing coarse crystal grains at the coil end.

[0009]

EXAMPLE Steels having the chemical composition shown in Table 1 were tapped in a converter and made into slabs by continuous casting, and then 1150 to 118
After heating to 0 ° C. and hot rolling to a finishing temperature of 920 to 960 ° C. and a plate thickness of 4.0 mm, the sheet was cooled on a runout table and wound at 700 to 770 ° C. Prior to pickling, the Barkhausen signal was measured online using a magnetic head in a non-contact manner. The results are shown in FIGS. 1 and 2. That is, FIG. 1 shows barkhausen noise of a hot-rolled coil of A steel and r when the coil was pickled, cold rolled and annealed.
It is a figure which shows the change of the coil value in the coil longitudinal direction, and FIG.
This is the case with steel. The range where the Barkhausen signal is measured and the pickling crop is cut is indicated by the diagonal lines.

As shown in FIGS. 1 and 2, Barkhausen noise was obtained, and the pickling crop length as indicated by the hatched lines in FIG. 1 was determined. In the case of steel material A, the voltage value of the Barkhausen signal is 50 mV or less, and in the case of steel material B, 4
It has been confirmed in advance in the laboratory that the hot rolled coil contains coarse crystal grains whose r value of the product after cold rolling and annealing is 3 mV or less and which does not meet the standard. After pickling, cold rolling was performed at a reduction rate of 80%, the entire coil length was annealed at 820 ° C., and 1% temper rolling was performed to obtain a product coil. JIS No. 5 tensile test piece is sampled from the quarter width of the product coil, and it is r at 15% tensile strain.
When the value was measured, the change in the coil longitudinal direction as shown in FIGS. 1 and 2 was shown. As a result, the minimum allowable r value was 1.7 for steel A and 1.6 for steel B, whereas according to the present invention, the pickling crop length was determined based on the Barkhausen signal continuously measured. It can be seen that the product yield is improved and at the same time, unnecessary pickling crop cut can be avoided by adjusting.

[0011]

[Table 1]

[0012]

As described in detail above, according to the present invention,
Before pickling, the Barkhausen signal of the hot-rolled coil was measured in a non-contact manner, and coarse crystal grains were contained at the inner and outer edges of the hot-rolled coil. By washing and cropping, it is possible to manufacture cold-rolled steel sheets and plated steel sheets with little deterioration of the material at the coil ends with continuous annealing or a continuous plating line with good yield, and waste of defective parts in product sheets and energy consumption are saved. Since it can be reduced, the effect that can be expected in industry is extremely large.

[Brief description of the drawings]

FIG. 1 is a diagram showing Barkhausen noise of a hot rolled coil of A steel and a change in r value in the longitudinal direction of the coil when the coil is pickled, annealed after cold rolling and made into a product.

FIG. 2 is a diagram showing Barkhausen noise of a hot rolled coil of B steel and a change in r value in the coil longitudinal direction when the coil is pickled, annealed after cold rolling and made into a finished product.

Front page continuation (72) Inventor Toru Inakuma 1618 Ida, Nakahara-ku, Kawasaki-shi, Kanagawa Nippon Steel Corporation Technology Development Division (72) Hiroaki Sakamoto 1618 Ida, Nakahara-ku, Kawasaki-shi, Kanagawa Steel Engineering Co., Ltd.

Claims (1)

[Claims] 1. A Barkhausen signal of a hot-rolled coil is continuously measured in a non-contact manner before pickling using a magnetic head, and the relationship between the voltage value of the Barkhausen signal of each steel type and the grain size obtained in advance is compared. By doing this, the range including coarse crystal grains on the inner and outer circumferences of the coil is recognized online, and this range is pickled and crop-cut, then cold rolled and annealed. Manufacturing method of steel sheet and plated steel sheet.