JP5986705B2 - Bright steel plate with excellent spot rust resistance and method for producing the same - Google Patents

Description

The present invention relates to a bright steel plate excellent in spot rust resistance and a method for producing the same.

  Conventionally, bright steel plates made of low carbon steel have been manufactured in the following steps. That is, the steel sheet is cold-rolled through a cold rolling apparatus using various small-diameter non-rolling rolls in addition to the rolling roll. And the fats and oils at the time of rolling are removed from this steel plate with an electrolytic cleaning apparatus, and it anneals with an annealing apparatus next. Thereafter, temper rolling is performed by a temper rolling apparatus using a bright roll.

JP-A-7-258733 JP-A-8-333654 JP-A-9-262603

  However, due to the roughness of the non-rolling roll that comes into contact with the steel sheet during rolling, minute pinhole wrinkles are generated on the surface of the steel sheet after rolling, particularly on the edge where tension is applied. Then, the rolling oil adhering to the steel plate surface is cleaned with an electrolytic cleaning line. At that time, dirt such as rolling oil adhering to the pinhole flange of the edge is sent to the next annealing step without being sufficiently cleaned.

  In general, the annealing process uses continuous annealing equipment from the viewpoint of productivity, but in the case of bright products, in order to exhibit its beautiful luster, it is necessary to pass through a continuous annealing process that contacts a large number of rolls. Is not appropriate and batch annealing is used. However, when a strip steel product is applied to batch annealing, a cooling time of about several days is required after the annealing is completed in order to cool to a temperature at which the plate can be passed through in the subsequent pressure adjusting process. In the meantime, if it keeps storing in the retort for annealing all the time, in order to remarkably inhibit the capacity of the batch annealing equipment, after cooling to a temperature around 100 ° C., it is discharged from the retort for annealing.

  And it is common to wait for cooling to the temperature which can be plate | boarded in a rust prevention chamber etc. and can be plate-passed in a pressure regulation process. Some anti-corrosion chambers are sealed, but when a large number of products are manufactured sequentially, the sealed type is not suitable. For this reason, a simple rust prevention chamber is applied, but in that case, the rust prevention ability is limited, and rust may be generated at the edge of the steel plate during cooling. In particular, in the case of a bright product, since it is applied to a reflector of an automobile headlamp or the like, even a minute rust that is not obvious by visual observation significantly deteriorates the quality. In addition, the minute rust cannot be detected on the surface as it is cold-rolled, but is detected after the pressure adjustment process and the product inspection stage, not only in terms of yield loss but also in terms of work efficiency. But the loss will be tremendous. Here, the atmosphere of the rust prevention chamber is dry air, and the humidity is 70% or less, more preferably 60% or less.

The problem to be solved by the present invention is to provide a bright steel sheet excellent in spot rust resistance and a method for producing the same, which can prevent the occurrence of pinhole rust in a cold rolled steel sheet as much as possible. And

  The bright steel sheet, which is the first means for solving the problems of the present invention, is made of low carbon steel having a surface with a gloss (Gs) of 350 to 500 and a center line average roughness (Ra) of 0.01 to 0.09 μm. It is a bright steel plate with excellent spot rust.

The method for producing a bright steel sheet made of low carbon steel, which is the second means for solving the problems of the present invention, is excellent in spot rust resistance . The center line average roughness (Ra) is 0.20 to 0.40 μm and the maximum surface height is as follows. A cold rolled steel sheet made of low carbon steel having a surface with (Rmax) of 5.0 μm or less is annealed, and then a bright roll having a centerline average roughness (Ra) of 0.1 μm or less is used. The temper rolling process is performed .

The method for producing a bright steel plate made of low-carbon steel and having excellent spot rust resistance, which is the third problem solving means of the present invention, is provided at the final stage of the multi-stage rolling roll stand and the outlet of the stage in front of it. As a non-rolling roll, the deviation index (Rsk) in the height direction of the roughness curve is −0.5 or less, the centerline average roughness (Ra) of the surface is 2.5 to 3.0 μm, and the maximum surface height ( Rmax) is finished and polished to 25 μm or less, and a steel plate made of low carbon steel is cold-rolled through the apparatus, then the steel plate is annealed, and then the steel plate is subjected to centerline average roughness. (Ra) is one that uses the following bright roll 0.1 [mu] m, to temper rolling process.

Here, the reason for limiting the numerical values of the present invention is as follows.
The bright steel sheet is used as a reflector for a headlight of a car or a reflector for a stove as an application, and is intended to satisfy a predetermined function in those products.

  This is because the cold-rolled steel sheet satisfies a certain degree of workability and the specifications (specifications / numerical values) of the bright steel sheet when making the final bright product. If the roughness of the original plate is too rough, it is necessary to increase the rolling rate (elongation) in order to obtain a predetermined gloss, but in that case, the steel sheet becomes hard and the predetermined workability cannot be obtained. There is.

  When finish polishing is performed on a non-rolled roll, the deviation index (Rsk) in the height direction of the roughness curve is −0.5 or less, and the centerline average roughness (Ra) of the surface is 2.5 to 3.0 μm. The reason why the maximum surface height (Rmax) is 25 μm or less is that the index (Rsk) is −0.5 or less while maintaining a certain roughness (Ra), so that the convex surface of the roll is This is to reduce the amount of indentation (pinhole) in the board. The reason for limiting Ra is that if the roll is too low, the roll slips, and if it is too high, the Rmax value cannot be entered (pinhole wrinkles appear).

Here, the index (Rsk) is related to JIS B 0601: 2001.
(Revised January 20, 2001) and defined as (4.2.3 Skewness of contour curve).

By this invention, generation | occurrence | production of pinhole-like rust of a cold-rolled steel plate can be prevented as much as possible.

It is explanatory drawing of the process in connection with manufacture of the steel plate of this invention, and is explanatory drawing of the non-rolling roll use location of cold rolling equipment. It is explanatory drawing of the process in connection with manufacture of the steel plate of this invention, and is explanatory drawing of the process after the process of FIG. It is a diagram of the profile of the non-rolling roll (4th stage exit) roughness with pinhole flaw generation. It is a diagram of the non-rolling roll (fourth stage exit) roughness profiling without pinhole flaw generation. It is a graph which shows transition of the generation | occurrence | production weight and generation | occurrence | production rate of pinhole-like rust.

  An embodiment of the present invention will be described below with reference to the drawings. As shown in FIG. 1a, in the cold rolling equipment 10 used for manufacturing bright steel plates, the steel plate A has four stages of rolling roll stands S1, S2, S3, S4 (having work rolls WR1, WR2, WR3, WR4). , And is wound on a winding roll 9 via a bridle roll 8. A plate pressing roll 1, a tension meter roll 2, and a billy roll 3 (final fourth stage stand S4) are provided at the exit of each stand.

  Further, between the final fourth stage stand S4 and the bridle roll 8, there are provided a shape detection roll (including a tension meter function) 4, a bridle front pinch roll (up and down) 5, a continuous single switching roll 6, and the bridle roll 8 A continuous switching roller 6 and a shear front pinch roll (upper and lower) 7 are provided between the winding roll 9 and the winding roll 9.

  Here, in the cold rolling step, the work roll (rolling roll) WR reduces the plate thickness. However, other rolls such as plate press roll 1, tension meter roll 2, billy roll 3, shape detection roll 4, bridle front pinch roll (up and down) 5, continuous single switching roll 6, shear front pinch roll (up and down) 7, etc. (Hereinafter referred to as a non-rolling roll) is in contact with the plate. In the present invention, the original sheet was investigated by paying attention to such a non-rolling roll.

  That is, in FIG. 2, a peak of a dull eye was observed, which generated pinhole wrinkles. Further, in FIG. 3, the non-rolled roll when pinhole wrinkles are not generated has few peaks and is not sharp. As a result, a pinhole wrinkle on the original sheet was found, and it was found that this was due to a dull eye peak of the non-rolled roll during cold rolling.

A possible reason for this is that the rolls of the non-rolling rolls are concentrated on the edge (where the tension is most applied) to generate a very small indentation flaw (hereinafter referred to as pinhole flaw). Then, in the subsequent process, extremely minute spot rust (hereinafter referred to as pinhole rust) due to this pinhole flaw is generated, and there is a case where rust is not generated even in the same mechanism.

  From this, the present invention attempts to prevent pinhole flaws by reviewing the specifications of the non-rolling roll and changing the building process as the countermeasure.

  In the conventional processing method, first polishing and shot processing are performed on the non-rolling roll so that the center line average roughness (Ra) of the surface becomes 3.2 ± 0.2 μm. On the other hand, hard chrome plating was applied, and then the surface center line average roughness (Ra) was 2.5 to 3.0 μm and the maximum surface height (Rmax) was 25 μm or less.

  Therefore, in the present invention, with respect to the non-rolling roll, the deviation index (Rsk) in the height direction of the roughness curve is −0.5 or less, and the centerline average roughness (Ra) of the surface is 2.5-3. Final polishing is performed so that the maximum surface height (Rmax) is 0.0 μm and 25 μm or less.

  The steel sheet is cold-rolled through the cold-rolling apparatus 10 using such a non-rolling roll. Then, as shown in FIG. 1 b, this steel sheet is subjected to removal of oil and fat during rolling with an electrolytic cleaning device 20, and then annealed with a tight coil annealing device 30. Then, the temper rolling process is performed by the temper rolling apparatus 40 using a bright roll having a center line average roughness (Ra) of 0.1 μm or less. Thus, the bright steel plate excellent in the spot rust resistance which consists of low carbon steel was obtained through the said process.

(1) Plate holding roll 1
・ Diameter 230 ~ 223mm
・ Surface roughness (μm)
Third stage Rsk-1.148, Ra 2.782, Rmax 23.85
4th stage Rsk-1.008, Ra 2.725 Rmax 18.90
(2) Tension roll 2
・ Diameter 230 ~ 223mm
・ Surface roughness (μm)
Rsk-0.548, Ra 2.656, Rmax 16.25
(3) Billy Roll 3
・ Diameter 230 ~ 223mm
・ Surface roughness (μm)
Rsk-1.587, Ra 2.579, Rmax 18.50
(4) Bright roll-Diameter 530-560mm
・ Surface roughness (μm) Ra 0.06 μm or less (5) Surface roughness of cold-rolled steel sheet (μm)
WS CN DS
Ra 0.24 0.20 0.23
Rmax 1.81 1.73 2.50
Here, WS: a position 10 mm from the working side end of the steel sheet rolling mill CN: a position of the central part of the coil width of the steel sheet DS: a position 10 mm from the driving side end of the steel sheet rolling machine (6) Surface roughness of the bright steel sheet (Μm)
WS CN DS
Ra 0.028 0.025 0.040
(7) Average value of surface roughness Ra (μm) and glossiness (Gs) of bright steel plate Maximum value (MAX), minimum value (MIN), average value of bright steel plate of coil according to samples No. 1 to 24 ( AVE) is shown in Table 1. Here, the glossiness (Gs) was measured using a handy gloss meter PG-1M manufactured by Nippon Denshoku Industries Co., Ltd. at a light projecting / receiving angle of 60 °.

（８）ストリップのピンホール状錆の発生状況（図４に示す）。

(8) The state of occurrence of pinhole rust on the strip (shown in FIG. 4).

  Figure 4 shows the occurrence of pinhole rust. The number of lots on the horizontal axis, the weight of the lot with pinhole rust on the left side, and the rate of pinhole rust on the right side (the weight of each lot) The ratio of the weight of rust generated relative to the As can be seen from this graph, as a result of using the non-rolling roll according to the present invention from lot 7, as the number of lots increases, the occurrence of rust decreases, and the occurrence rate in lots 11 to 17 is almost 0%. I understand that.

  The present invention is not limited to the above-described embodiments and embodiments, and includes various modifications without departing from the scope of the claims.

  The present invention is used for bright steel plates.

A Steel plate 10 Cold rolling equipment 20 Electrolytic cleaning device 30 Tight coil annealing device 40 Temper rolling device S1, S2, S3, S4 Rolling roll stand WR1, WR2, WR3, WR4 Work roll 1 Holding roll 2 Tension meter roll 3 Billy roll 4 Shape detection roll 5 Pinch roll in front of bridle 6 Single-unit switching roll 7 Pinch roll in front of shear 8 Bridle roll 9 Winding roll

Claims (3)

A bright steel sheet excellent in spot rust resistance comprising a low carbon steel having a surface with a gloss (Gs) of 350 to 500 and a center line average roughness (Ra) of 0.01 to 0.09 μm. After annealing a cold-rolled steel plate made of a low carbon steel having a surface with a center line average roughness (Ra) of 0.20 to 0.40 μm and a maximum surface height (Rmax) of 5.0 μm or less. A method for producing a bright steel sheet having excellent spot rust resistance comprising low carbon steel subjected to temper rolling using a bright roll having a center line average roughness (Ra) of 0.1 μm or less. As a non-rolling roll provided at the exit of the last stage and the preceding stage of a multi-stage rolling roll stand, the deviation index (Rsk) in the height direction of the roughness curve is −0.5 or less, the center of the surface A steel sheet made of low carbon steel is cold-rolled through the above equipment using a line average roughness (Ra) of 2.5 to 3.0 μm and a surface polished to a maximum surface height (Rmax) of 25 μm or less. Next, the steel sheet is annealed, and then the steel sheet is subjected to temper rolling using a bright roll having a center line average roughness (Ra) of 0.1 μm or less and subjected to temper rolling treatment. A bright steel sheet manufacturing method with excellent properties.

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