JP5556472B2 - Steel bar manufacturing method - Google Patents

Description

  The present invention relates to a method of manufacturing a steel bar used as a part material of, for example, an automobile or a construction machine.

Steel bars used as parts for automobiles and construction machinery are usually formed by heating a steel slab (bloom), which has been cast into a rectangular cross section with a continuous casting machine, to a predetermined temperature in a heating furnace, and then using a rough rolling mill with a rectangular cross section. And then rolled into a circular cross section with a finishing mill.
In this case, in order to improve the mechanical properties such as toughness, the finish rolling temperature is lowered by leaving the steel slab rolled into a square cross section with a roughing mill until it cools to a predetermined temperature. Yes. Therefore, it is expected that cooling efficiency can be improved by cooling to a predetermined temperature with a water cooling device. However, as a water-cooling device for cooling a steel slab rolled into a square cross-section with a rough rolling mill, when using a system that cools the steel slab by blowing cooling water over the entire surface of the steel slab, Is overcooled by the cooling water, which makes it difficult to produce a steel bar having a uniform material.
Such a problem also occurs when the hot-rolled steel sheet is water-cooled in the hot rolling process, and Patent Document 1 discloses that the cooling water from the spray header is sprayed only on the center of the upper surface of the hot-rolled steel sheet. A technique for preventing overcooling of an edge portion of a hot-rolled steel sheet by masking the upper edge portion of the rolled steel sheet with an edge mask is described.

JP-A-10-137832 (0010-0013)

However, when the technique described in Patent Document 1 is applied to cool a steel slab rolled into a rectangular cross section with a rough rolling mill with a water cooling device, the steel slab after rough rolling is obtained as shown in FIG. Although it is possible to prevent the upper corners 4a and 4b of the intermediate rolled material 4 from being overcooled, the lower corners 4b and 4c of the intermediate rolled material 4 are formed by the cooling water 8 from below and the cooling water 8 from the left and right directions. There is a problem of being overcooled.
The present invention has been made in view of the above-described circumstances. The purpose of the present invention is to reduce the corner of the steel slab when the steel slab rolled into a square cross section by a roughing mill is cooled to a predetermined temperature by a water cooling device. An object of the present invention is to provide a method of manufacturing a steel bar that can suppress the excessive cooling by cooling water and manufacture a steel bar having a uniform material.

  In order to solve the above-mentioned problem, in the invention according to claim 1 of the present invention, a steel slab is heated to a predetermined temperature, and then roughly rolled into a square cross section, and then the steel slab is cooled to a predetermined temperature by a water cooling device. Then, a method of producing a steel bar by finish rolling into a circular cross section, wherein the cooling water is sprayed on the entire upper and lower surfaces of the steel slab by the water cooling device, and the cooling water having a pressure that rebounds on the surface of the steel slab The steel slab is cooled to a predetermined temperature by spraying on the left and right side central portions of the steel slab.

  The invention according to claim 2 of the present invention is the method of manufacturing a steel bar according to claim 1, wherein the water cooling device is a plurality of cooling water jets that spray the cooling water from the left and right directions and spray the left and right side surface central portions. Water cooling having a plurality of water supply shut-off valves arranged vertically and shutting off water supply to the plurality of cooling water injection nozzles, and a control device for controlling opening / closing of the water supply shut-off valves in accordance with the thickness of the steel slab The steel slab is cooled to a predetermined temperature using an apparatus.

According to the first aspect of the present invention, when cooling a steel slab rolled into a square cross section with a roughing mill to a predetermined temperature by a water cooling device, the cooling water is sprayed on the entire upper and lower surfaces of the steel slab, By blowing cooling water with a pressure that bounces on the surface to the center of the left and right sides of the steel slab, the cooling water sprayed to the center of the left and right side of the steel slab rebounds in the left and right direction on the side of the steel slab. It is possible to manufacture a steel bar having a uniform material while suppressing excessive cooling by cooling water.
According to the invention which concerns on Claim 2, the injection area | region of the cooling water injected from the cooling water injection nozzle of a water-cooling apparatus to the right-and-left side surface of a steel slab is made into the thickness of the steel slab rolled into the cross-sectional square shape with the rough rolling mill. It can be arbitrarily adjusted accordingly.

It is a figure which shows an example of a steel bar manufacturing facility. It is a figure which shows the AA cross section of FIG. It is a figure which shows the result of having calculated | required the temperature change from the cooling of the intermediate rolling raw material which is the steel slab after rough rolling to finish rolling by heat-transfer analysis. It is a figure which shows the injection area | region of the cooling water in case the steel piece thickness after rough rolling is large. It is a figure for demonstrating the subject which this invention tends to solve.

Hereinafter, an embodiment of the present invention will be described with reference to FIGS.
In the figure, reference numeral 1 denotes a heating furnace for heating a steel slab (bloom) 2 cast in a rectangular cross section by a continuous casting machine. The steel slab 2 heated in the heating furnace 1 is roughened by a conveying roller table (not shown). It is conveyed to the rolling mill 3.
The rough rolling mill 3 rolls the steel slab 2 heated in the heating furnace 1 into a square cross-sectional shape, and the steel slab 2 rolled by the rough rolling mill 3 becomes an intermediate rolling material 4 having a square cross section. The water cooling device 5 installed in the subsequent stage of the rough rolling mill 3 is supplied.

The water cooling device 5 cools the intermediate rolling material 4, which is a steel slab rolled by the rough rolling mill 3, to a predetermined temperature. The intermediate rolling material 4 cooled by the water cooling device 5 is supplied to the finishing mill 6. Here, the steel bar 7 is formed by finish rolling into a circular cross section.
As shown in FIG. 2, the water cooling device 5 has a plurality of cooling water injection nozzles 9A and 9B for injecting cooling water 8A and 8B from the vertical direction and the horizontal direction on the surface of the intermediate rolling material 4, and these cooling water injections. Among the nozzles 9 </ b> A and 9 </ b> B, the cooling water injection nozzle 9 </ b> B is configured such that a plurality of cooling water injection nozzles are arranged in the vertical direction and the cooling water 8 </ b> B having a pressure that rebounds on the surface of the intermediate rolling material 4 is ejected.

The water cooling device 5 has a plurality of water supply shutoff valves 10 that shut off the water supply to the coolant injection nozzle 9B, and a control device 11 that controls the opening and closing of these water supply shutoff valves 10, and the control device 11 is an intermediate rolling material. The water supply shutoff valve 10 is controlled to be opened and closed according to the thickness of 4.
As a water-cooling device that cools the intermediate rolling material 4 that is a steel piece rolled into a square cross section by a roughing mill 3 when the steel piece 2 heated in the heating furnace 1 is hot-rolled to produce a bar steel 7. When the water cooling device 5 shown in FIG. 2 is used, the cooling water 8A ejected from the cooling water injection nozzle 9A of the water cooling device 5 is sprayed on the entire upper and lower surfaces of the intermediate rolling material 4, and the cooling water injection nozzle 9B of the water cooling device 5 is used. The cooling water 8 </ b> B ejected from the center is sprayed to the center of the left and right side surfaces of the intermediate rolling material 4. At this time, the cooling water 8B sprayed from the cooling water injection nozzle 9B to the center of the left and right side surfaces of the intermediate rolling material 4 bounces in the left and right directions on the side surface of the intermediate rolling material 4 as shown in FIG. The corners 4a, 4b, 4c, 4d of the intermediate rolled material 4 are not excessively cooled by the cooling water 8A, 8B from the nozzles 9A, 9B.

FIG. 3 shows the result of obtaining the temperature change from the cooling of the intermediate rolling material 4 to the finish rolling by heat transfer analysis. As is clear from FIG. 3, the intermediate rolling material 4 cooled by the water cooling device 5 is Finish rolling starts with a uniform temperature distribution on each surface.
Therefore, as in the above-described embodiment of the present invention, the cooling water 8A is sprayed on the entire upper and lower surfaces of the intermediate rolling material 4 by the water cooling device 5, and the cooling water 8B having a pressure that rebounds on the surface of the intermediate rolling material 4 is intermediate-rolled. By spraying the central part of the left and right side surfaces of the material 4, the corners 4 a, 4 b, 4 c and 4 d of the intermediate rolled material 4 are excessively cooled when the intermediate rolled material 4 is cooled to a predetermined temperature by the water cooling device 5. Therefore, the steel bar 7 having a uniform material can be manufactured.

Moreover, as a water-cooling device for cooling the intermediate rolling material 4, a plurality of cooling waters that inject cooling water 8 </ b> A, 8 </ b> B onto the surface of the intermediate rolling material 4 from the vertical direction and the horizontal direction as in the above-described embodiment of the present invention. Injection nozzles 9A, 9B, a plurality of water supply cutoff valves 10 for blocking water supply to cooling water injection nozzles 9B for injecting cooling water 8B from the left and right directions among these cooling water injection nozzles 9A, 9B, and these water supply cutoffs When the water cooling device 5 having the control device 11 that controls the opening and closing of the valve 10 according to the thickness of the intermediate rolling material 4 is used, as shown in FIG. 2 and FIG. The spray region of the cooling water 8B sprayed on the surface can be arbitrarily adjusted according to the thickness of the intermediate rolling material 4.
Next, referring to Table 1, examples of the present invention and comparative examples will be described.

In the examples of Table 1, the surface temperature immediately after finishing rolling of a steel bar (diameter: 180 mm) obtained by performing finish rolling after cooling the intermediate rolling material with the water-cooling device shown in FIG. 2 is measured by a radiation thermometer. And the result of investigating the mechanical properties of steel bars is shown.
Moreover, the comparative example of Table 1 measures the surface temperature immediately after completion | finish of finish rolling of the steel bar (diameter 180mm) obtained by performing finish rolling after cooling an intermediate rolling raw material by the method shown in FIG. In addition, the results of the investigation of the mechanical properties of steel bars are shown.

Comparing the examples in Table 1 with the comparative examples, the surface temperature immediately after the finish rolling of the steel bar is 610 to 750 ° C. in the comparative example, whereas the surface temperature immediately after the finish rolling of the steel bar is 650 in the working example. It is ˜750 ° C., and it can be seen that the variation in temperature distribution is smaller than that of the comparative example.
Further, in the comparative example, the tensile strength of the steel bar is 877 to 950 MPa, whereas in the example, the tensile strength of the steel bar is 881 to 902 MPa, which shows that the variation in tensile strength is smaller than that of the comparative example.

DESCRIPTION OF SYMBOLS 1 ... Heating furnace 2 ... Steel slab 3 ... Rough rolling mill 4 ... Intermediate rolling raw material 4a, 4b, 4c, 4d ... Corner part of intermediate rolling raw material 5 ... Water cooling device 6 ... Finishing rolling mill 7 ... Bar steel 8A, 8B ... Cooling water 9A, 9B ... Cooling water injection nozzle 10 ... Feed water shutoff valve 11 ... Control device

Claims (2)

  The steel slab is heated to a predetermined temperature, and then roughly rolled into a square cross section, and then the steel slab is cooled to a predetermined temperature with a water-cooling device, and then finished and rolled into a circular cross section to produce a bar steel, Cooling water is sprayed on the entire upper and lower surfaces of the steel slab by the water cooling device, and cooling water having a pressure that rebounds on the surface of the steel slab is sprayed on the left and right side central portions of the steel slab to cool the steel slab to a predetermined temperature. The manufacturing method of the steel bar characterized by the above-mentioned.   In the manufacturing method of the steel bar according to claim 1, as said water cooling device, a plurality of cooling water injection nozzles which inject the cooling water from the left-right direction and spray the cooling water on the center of the left and right side surfaces are arranged up and down. Using a water cooling device having a plurality of water supply shutoff valves for shutting off water supply to the water injection nozzle and a control device for opening and closing the water supply shutoff valve according to the thickness of the steel billet, the steel slab is heated to a predetermined temperature. A method for producing a steel bar, characterized by being cooled.

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