JP5742507B2 - Manufacturing method of hot-rolled steel sheet - Google Patents

Description

  The present invention relates to a method for producing a hot-rolled steel sheet.

  In recent years, it has become necessary to increase the strength of steel sheets in order to reduce the weight of automobiles. And when manufacturing a high-strength hot-rolled steel sheet, low-temperature winding at 600 ° C. or less is frequently performed in order to stabilize the material and improve workability.

  However, as the strength of the steel sheet increases, the load on the hot rolling mill increases, and at the same time, the steel sheet thickness is reduced for weight reduction, making it difficult to stabilize the shape of the steel sheet. In particular, this problem is significant when the plate thickness is 2.3 mm or less.

  In low-temperature winding, a slight temperature difference appears as a large material difference, and when the steel sheet is subjected to press working, cracks may occur depending on the width direction and longitudinal direction parts. Need to be controlled within a narrow tolerance.

  Therefore, when trying to produce a hot rolled steel sheet with high strength by conventional batch-type hot rolling in units of slabs, it takes time until the steel sheet shape and winding temperature are stabilized, and the steel sheet rolled during that time The part was discarded as nonconforming product. In particular, the amount of cut-off was large when manufacturing thin objects.

  On the other hand, it is conceivable to manufacture a high-strength hot-rolled steel sheet by a hot rolling method called endless rolling.

  In endless rolling, for example, as described in Patent Documents 1 and 2, the slab is roughly rolled, the sheet bar which has been roughly rolled is wound up and rewound, and then the leading end is joined to the tail end of the preceding sheet bar. This is a hot rolling method in which finish rolling is performed, and it is possible to suppress instability phenomena at the tip and tail ends of the steel sheet.

  However, when producing high strength hot-rolled steel sheets, usually, a method of adding additive elements such as Si and Mn is used to achieve high strength, thereby inhibiting weldability and endless rolling. In this case, there is a problem that the welding of the seat bar becomes unstable.

JP 2003-211214 A JP 2006-239777 A

  This invention is made | formed in view of the above situations, and it aims at providing the manufacturing method of the hot-rolled steel plate which can manufacture a high strength hot-rolled steel plate stably with favorable quality. To do.

  As a result of intensive studies to solve the above problems, the present inventors have conceived a manufacturing method in which endless rolling and cooling with rod-shaped cooling water are combined.

  That is, based on the above idea, the present invention has the following features.

  [1] After hot rolling the steel material to a sheet thickness of 2.3 mm or less, winding the steel material at a coiling temperature ≦ 600 ° C. to form a hot rolled steel sheet, hot rolling, rough rolling the slab, and rough rolling After winding and unwinding the sheet bar, the end of the sheet bar is joined to the tail end of the preceding sheet bar, and finish rolling is used for endless rolling, and cooling is performed on the run-out table after finishing rolling. A hot-rolled steel sheet characterized by spraying bar-shaped cooling water on the upper surface side of the steel sheet to be inclined toward the traveling direction of the steel sheet and draining the cooling water by a draining means provided on the downstream side thereof Manufacturing method.

  [2] The method for producing a hot-rolled steel sheet according to [1], wherein the coiling temperature is 400 ° C. or lower.

  In the present invention, a high-strength hot-rolled steel sheet can be stably produced with good quality.

It is a figure which shows the hot rolling installation in one Embodiment of this invention. It is a figure which shows the upper surface cooling device of the strong cooling device in one Embodiment of this invention. It is a figure which shows the upper surface cooling device main body of the strong cooling device in one Embodiment of this invention.

  An embodiment of the present invention will be described with reference to the drawings.

  FIG. 1 shows a hot rolling facility in one embodiment of the present invention.

  As shown in FIG. 1, the hot rolling facility 10 in this embodiment includes a roughing mill (not shown), an endless rolling facility 11, a finishing mill 12, and a conventional type installed on a runout table 13. A cooling device 14 and a strong cooling device 15 and a winding device (coiler) 16 are provided.

  Here, the endless rolling equipment 11 includes a joining device, a coil box, and a joining crop shear in order to join the tail end portion of the preceding sheet bar and the leading end portion of the following sheet bar. Further, a deburring device, a sheet bar heater, an edge heater, a joint cooling device, a high-speed plate device, and the like may be installed as appropriate.

  The conventional cooling device 14 includes an upper surface cooling device 14a having a plurality of circular laminar nozzles for supplying cooling water as a free fall flow to the upper surface of the steel plate 1 transported on the run-out table 13, and the steel plate 1 The lower surface cooling device 14b having a plurality of spray nozzles for supplying spray-like cooling water to the lower surface of the liquid is provided.

  The strong cooling device 15 includes an upper surface cooling device 15 a that supplies cooling water to the upper surface of the steel plate 1 conveyed on the run-out table 13, and a lower surface cooling device that supplies cooling water to the lower surface of the steel plate 1. 15b.

  First, as shown in FIG. 2, the upper surface cooling device 15a of the strong cooling device 15 inclines the bar-shaped cooling water on the upper surface side of the steel plate 1 conveyed on the run-out table 13 by inclining it toward the traveling direction of the steel plate 1. It consists of an upper surface cooling device main body 21 to be sprayed and a draining means 25 provided on the downstream side thereof.

  As shown in FIG. 3, the upper surface cooling device main body 21 has circular pipe nozzles 23 arranged in a row at a predetermined pitch (for example, 60 mm pitch) in the steel plate width direction on the cooling header 22 in a predetermined direction in the steel plate traveling direction. A predetermined number of columns (for example, 100 columns) is provided at a pitch (for example, 100 mm pitch). The circular tube nozzle 23 is connected to the cooling water supply pipe 24 via one cooling header 22 for each row, and each cooling water supply pipe 24 can be controlled on and off independently. .

  The circular tube nozzle 23 is a straight tube nozzle having a predetermined inner diameter (for example, 8 mmφ) and a smooth inner surface, and the cooling water supplied from the circular tube nozzle 23 is a rod-shaped cooling water. And this circular pipe nozzle 23 is inclined and arrange | positioned so that rod-shaped cooling water may be injected in the advancing direction of the steel plate 1 with predetermined | prescribed injection angle (theta) (for example, (theta) = 50 degrees).

  Here, the rod-shaped cooling water in the present invention is cooling water injected in a state of being pressurized to some extent from a circular (including elliptical or polygonal) nozzle outlet, and is cooled from the nozzle outlet. The water injection speed is 7 m / s or more, and it refers to cooling water of continuous and straight water flow in which the cross section of the water flow from the nozzle outlet to the steel plate is maintained in a substantially circular shape. That is, it is different from a free fall flow from a circular tube laminar nozzle or a liquid ejected in a droplet state such as a spray.

  Further, as the draining means 25, a nozzle (in this case, a nozzle for ejecting rod-shaped cooling water) 26 for ejecting a draining fluid is installed. This rod-shaped cooling water for draining is not intended for cooling, but is used in the same manner as the rod-shaped cooling water from the circular tube nozzle 23 of the upper surface cooling device body 21, and is injected in a pressurized state, Since a continuous and straight water flow in which the cross section of the water flow from the nozzle outlet to the steel plate 1 is maintained in a substantially circular shape is used, it is referred to as rod-shaped cooling water here.

  The rod-shaped cooling water injection nozzle 26 is arranged on the downstream side of the upper surface cooling device main body 21 with a predetermined nozzle diameter (for example, an inner diameter of 5 mm), a nozzle pitch (for example, 30 mm), and the number of rows (for example, three rows). In addition, the rod-shaped cooling water inclined toward the upper surface cooling device main body 21 side is sprayed so as to face the rod-shaped cooling water from the upper surface cooling device main body 21. The angle η formed by the rod-shaped cooling water sprayed from the rod-shaped cooling water spray nozzle 26 and the steel plate 1 is approximately the same as the spray angle θ of the rod-shaped cooling water from the upper surface cooling device body 21, and is preferably 60 ° or less, 55 More preferably, it is less than 0 °.

  In addition, as the draining means 25, it may replace with said rod-shaped cooling water injection nozzle 26, and may use the draining roll of a pinch roll system.

  On the other hand, the lower surface cooling device 15b of the strong cooling device 15 is the same as the lower surface cooling device 14b of the conventional cooling device 14, and includes a plurality of spray nozzles that supply spray-like cooling water to the lower surface of the steel plate 1. Have.

  In this way, the strong cooling device 15 faces the rod-shaped cooling water from the upper surface cooling device main body 21 and the plurality of circular tube nozzles 23 that inject the rod-shaped cooling water at the injection angle θ toward the traveling direction of the steel plate 1. Since the rod-shaped cooling water injection nozzle 26 for spraying the rod-shaped cooling water is provided on the upper surface of the steel plate 1, the cooling water (residual water) after being supplied from the circular tube nozzle 23 to the upper surface of the steel plate 1 is directed toward the traveling direction of the steel plate 1. In addition, the accumulated water that has flowed is blocked by the rod-shaped cooling water from the rod-shaped cooling water injection nozzle 26 for draining, so that the cooling area by the cooling water becomes constant. And since rod-shaped cooling water is injected from the circular tube nozzle 23, the water film of the staying water on the upper surface of the steel plate 1 can be broken, and fresh cooling water can reach the steel plate 1. This makes it possible to perform strong cooling that is uniform and has a high cooling rate.

  And in the hot rolling equipment 10 comprised as mentioned above, when manufacturing a high intensity | strength hot-rolled steel plate with a plate | board thickness of 2.3 mm or less, it carries out as follows.

  That is, first, hot rolling is performed, a slab (steel material) is roughly rolled by a roughing mill, and the roughly rolled sheet bar is taken up and rewound by the endless rolling equipment 11, and then the leading end portion is set as a preceding sheet. The runout table 13 is joined to the tail end of the bar, and is subjected to endless rolling in which the finish bar 12 finish-rolls the sheet bar to a target plate thickness (2.3 mm or less). The conventional cooling device 14 and the strong cooling device 15 installed on the winding device 16 are wound around the winding device (coiler) 16 at a winding temperature of 600 ° C. or lower (400 ° C. or lower if necessary).

  Thereby, in this embodiment, a high-strength hot-rolled steel sheet having a thickness of 2.3 mm or less can be stably manufactured with good quality.

  That is, a strong cooling device 15 (a plurality of circular pipe nozzles 23 for injecting a rod-shaped cooling water at an angle and a rod shape for draining) capable of performing strong cooling at a uniform and high cooling rate for cooling for low-temperature winding. By using the cooling water injection nozzle 26), the steel plate 1 can be uniformly cooled even in the low temperature winding as described above, and high strength can be realized without increasing additive elements such as Si and Mn. Therefore, it is easy to perform endless rolling that can suppress the instability phenomenon at the front end portion and the tail end portion of the steel plate 1 by preventing the weldability from being hindered. It becomes possible to improve the shape variation and material variation of the leading end.

  In addition, the cooling temperature and the coiling temperature can be changed by using / not using the strong cooling device 15 or changing the number of nozzles used, and a plurality of mechanical properties (for example, the same tensile strength and high elongation can be obtained). There is also an effect that it is possible to realize a high-elongation flange and the production of a tensile strength of 370 MPa and 440 MPa.

  As an example of the present invention, a high-strength hot-rolled steel sheet having a thickness of 1.6 mm was manufactured.

  At that time, as Example 1 of the present invention, based on the above embodiment, after performing hot rolling by endless rolling, the conventional cooling device 14 is used from a steel plate temperature of 850 ° C. at the exit of the finishing mill 12. Then, it was cooled to 700 ° C. and cooled to 400 ° C. by the strong cooling device 15. As a result, the temperature variation over the entire width of the steel plate 1 at this time could be within ± 10 ° C.

  On the other hand, as Comparative Example 1, hot rolling was performed by conventional batch-type rolling in units of slabs. As a result, the temperature variation over the entire width of the steel plate 1 at this time was ± 30 ° C.

  Moreover, as Comparative Example 2, hot rolling was performed by conventional batch-type rolling in units of slabs, and cooled to 400 ° C. using only the conventional cooling device 14. As a result, the coiling temperature was 300 to 420 ° C.

  Further, in Example 1 of the present invention, the tensile strength of the steel sheet 1 was equivalent to 440 MPa. However, as Example 2 of the present invention, when the coiling temperature was set to 550 ° C. by setting the strong cooling device 15 to a half cooling capacity. The tensile strength of the steel plate 1 was equivalent to 370 MPa.

  Further, as Example 3 of the present invention, when the strong cooling device 15 was used in another component system, the tensile strength of the steel sheet 1 was equivalent to 590 MPa, but the elongation was 25% and the stretch flangeability was 100%. On the other hand, as Example 4 of the present invention, when the conventional cooling device 14 was cooled to 550 ° C. and the strong cooling device 14 was cooled to 400 ° C., the elongation was 28% and the stretch flangeability was 80%.

DESCRIPTION OF SYMBOLS 1 Steel plate 10 Hot rolling equipment 11 Endless rolling equipment 12 Finishing mill 13 Runout table 14 Conventional cooling device 14a Conventional cooling device upper surface cooling device 14b Conventional cooling device lower surface cooling device 15 Strong cooling device 15a Strong cooling device Upper surface cooling device 15b Lower surface cooling device of strong cooling device 16 Winding device 21 Upper surface cooling device body 22 Cooling header 23 Circular pipe nozzle 24 Cooling water supply pipe 25 Draining means 26 Drained rod cooling water jet nozzle

Claims (2)

When the steel material is hot-rolled to a thickness of 2.3 mm or less and then wound at a coiling temperature ≦ 600 ° C. to obtain a hot-rolled steel sheet,
After hot rolling, roughly rolling the slab, winding the roughly rolled sheet bar, rewinding, joining the tip to the tail end of the preceding sheet bar, performing endless rolling to finish rolling,
Cooling from finish rolling to winding is performed using conventional cooling equipment and strong cooling equipment,
The conventional cooling device includes a top surface cooling device having a plurality of circular laminar nozzles for supplying cooling water as a free fall flow to the upper surface of the steel sheet conveyed on the run-out table, and a spray form on the lower surface of the steel sheet. A lower surface cooling device having a plurality of spray nozzles for supplying the cooling water of
The strong cooling device injects the bar-shaped cooling water on the upper surface side of the steel sheet conveyed on the run-out table in an inclined direction toward the traveling direction of the steel sheet, and the cooling water is provided by a draining means provided on the downstream side. An upper surface cooling device for draining water, and a lower surface cooling device having a plurality of spray nozzles for supplying spray-like cooling water to the lower surface of the steel plate,
A hot-rolled steel sheet characterized in that a steel plate having a plurality of mechanical properties with the same component is produced by changing the cooling temperature and the coiling temperature by using / not using the strong cooling device or changing the number of nozzles used. Manufacturing method.   The method for producing a hot-rolled steel sheet according to claim 1, wherein the coiling temperature is 400 ° C or lower.

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