JPH0657327A - Manufacture of h-shape steel having high toughness and strength - Google Patents

Abstract

PURPOSE:To provide a manufacturing method obtaining high toughness and strength and uniform characteristic even in the case of a large H-shape steel having thick flange part. CONSTITUTION:A cooling device capable of cooling both surfaces 2A, 2B at the inner and the outer parts of the flange 2 and both surfaces 3A, 3B at the upper and the lower parts of a web 3 is arranged at the front and the rear parts of a rough mill and a finish mill in a rolling line for H-shape steel 1. The rolling after cooling to just above Ms temp is repeated two times and cooling-reheating is executed one or more times before finish-rolling. After executing the finish-rolling at 750 deg.C or higher temp., the same cooling-reheating is repeated and the H-shape steel having high toughness and strength is manufactured.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION The present invention is made of H which is rich in toughness and strength.
Regarding the method of manufacturing shaped steel, especially when the plate thickness exceeds 40 mm H
The present invention relates to a method for manufacturing a shaped steel.

[0002]

2. Description of the Related Art Conventionally, as a method for producing a high-strength shaped steel having a complicated cross-sectional shape such as an H-shaped steel, it is disclosed in, for example, JP-A-62-253721 and JP-A-2-22414. There is something. The former is to increase the strength while preventing distortion (web wave) from occurring in the web when manufacturing thin H-section steel having a large flange thickness / web thickness ratio and a small web thickness by rolling. The aim is to make the rolling finish temperature of the thick flange part above the transformation point of the steel and below that of the thin web below the transformation point, and forcibly cool only the flange after rolling at a prescribed cooling rate to achieve uniform To produce H-section steel with high toughness and strength.

The latter is, for example, in an H-section steel in which the thickness of the web and the flange are different, when the thickness of the thin-walled portion is smaller than 15 mm, the thin-walled portion is air-cooled after low-temperature rolling, and the thick-walled portion is forcibly cooled after final finishing rolling. By doing so, when the plate thickness of the thin portion is 15 mm or more, high-strength products are manufactured by forced cooling after final finish rolling under different conditions for the thin portion and the thick portion.

[0004]

In recent years, there has been a marked tendency for H-section steels to increase in size due to the heightening of buildings, and the wall thickness also increases, for example, flange thicknesses exceeding 40 mm are extremely thick H-sections. The demand for steel is increasing. However, in all of the above conventional examples, the flange thickness is 40 mm or less, and even in the technology of forcibly cooling the steel material after rolling to obtain a high-strength product, the cooling site is outside the left and right flanges. Limited to the sides and the underside of the web. The reason why the forced cooling is applied to only one surface of the H-section steel is as follows. That is, in addition to the fact that the flange thickness is larger than the web thickness and the plate thickness ratio is 1.5 or more due to the characteristics of the H-section steel, the cooling rate is different and the web is naturally easier to cool than the flange. Since it has an H-shaped cross section, the top surface of the web becomes a "gutter" during rolling and transportation, which makes it easy to ride on water. Therefore, if the inner surface of the flange or the upper surface of the web is forcibly cooled with water, the cooling water rides on the web, resulting in a further decrease in the web temperature.

For this reason, conventionally, one-sided cooling has to be performed, which causes a large temperature difference between the inner and outer surfaces of the flange of the H-section steel, which causes thermal stress, which causes flange warpage and squareness defects. Although there is a tendency for shape defects to occur, the change in material properties on the inner and outer surfaces of the flange becomes even more pronounced with the extremely thick H-section steel whose flange thickness exceeds 40 mm, as already mentioned, and uniformity over the entire cross section There was a problem that could not be guaranteed.

Incidentally, in the case of H-section steel used as a column or a beam in the construction direction, it is common that stress is applied in the thickness direction because the flange is welded, but in addition, the size has increased in recent years. As the flange thickness increases, it is becoming essential to make the impact characteristics (toughness) and strength uniform in the thickness direction from the viewpoint of earthquake resistance. Therefore, the present invention has been made by paying attention to the above-mentioned conventional problems, in which cooling before rolling, cooling after rolling and recuperation are repeated, and the cooling is performed on both the inner and outer surfaces of the flange of the H-section steel. It is an object of the present invention to provide an H-section steel which is rich in toughness and strength with uniform characteristics even if the flange plate thickness is large by applying it to both upper and lower sides of the web.

[0007]

According to the present invention for achieving the above object, a cooling device which surrounds an H-shaped steel and can cool the inner and outer surfaces of a flange and the upper and lower surfaces of a web is provided on the front and rear surfaces of a rough mill and a finishing mill. Each of them is installed, and the material to be rolled is M
A step of cooling and recuperating a pattern in which the step of cooling to just above the s point and immediately performing rough rolling is repeated twice or more, and then the material to be rolled is cooled to just above the Ms point and reheated by the cooling device while being conveyed to the finishing mill. Is performed once or more, the surface layer temperature of the material to be rolled is set to 750 ° C. or more, finish rolling is performed, and after the finish rolling, the cooling and reheating step of the pattern is repeated one or more times. .

[0008]

The inventors of the present invention manufacture a web thin-walled H-section steel by hot rolling, as shown in the previous application by the present applicant (see Japanese Patent Laid-Open Nos. 3-271320 and 4-17622). In this case, water cooling from the outside of the flange and recuperation are repeated twice or more, and if the cooling stop temperature (cooling lower limit temperature) after the second is Ms point or more, the hardness of the product is included regardless of the recuperation temperature. We have obtained the knowledge that good mechanical properties can be secured. Then, based on this finding,
As a result of repeated studies on the possibility of guaranteeing the toughness and strength of the extremely thick H-section steel with the flange thickness exceeding 40 mm, the present inventors have forcibly cooled and reheated the flange and the web from both sides. The present invention was completed by finding that a product having high toughness and high strength can be obtained by repeating before and after rough rolling and finish rolling.

The forced cooling points of the H-section steel in the present invention are
As shown in FIG. 1, the left and right flanges 2 of the H-section steel 1 have both outer surfaces 2A and inner surfaces 2B, and the web 3 has both upper surfaces 3A and lower surfaces 3B. The inner and outer surfaces of the flange and the upper and lower surfaces of the web may be cooled at the same time, or may be cooled separately at different timings. In order to realize this cooling, according to the present invention, the front and rear surfaces of the rough universal mill, the conveying path from the rough universal mill to the finishing universal mill, and the front and rear surfaces of the finishing universal mill are respectively provided in the flanges of H-section steel. A double-sided cooling device having a cooling water nozzle is arranged so as to surround the outer surface and the upper and lower surfaces of the web.

The cooling and rolling of the present invention using these nozzles is performed in the following pattern. First, in the rough universal mill rolling, two steps of forcibly cooling the surface layer portions on both sides of the flange and the web to a temperature just above the Ms point (martensitic transformation start point) using the double-sided cooling device and immediately performing rolling are performed twice. Repeat above. Cooling only once results in significant hardening of the surface layer and makes the structure non-uniform, so it is necessary to repeat the cooling-rolling twice or more. In one of the plurality of forced coolings, the temperature may be immediately below the Ms point and then the heat may be recovered. Even if the initial cooling is too strong and a low-temperature transformation structure such as martensite is generated on the cooling surface, and as a result the surface hardness increases too much and the toughness deteriorates, the cooling stop temperature after the second cooling If the temperature exceeds the Ms point, the material properties of the product including hardness can be guaranteed regardless of the recuperation temperature.

The cumulative rolling reduction during the above rough rolling is 20 to 30.
% So that the reduction reaches the center of the flange or the web, but 30% to obtain a sufficiently satisfactory product strength.
It is preferable that After the rough universal mill rolling and before the material to be rolled is transported to the finishing universal mill, both the inner and outer surfaces of the flange of the material to be rolled and the upper and lower surfaces of the web are directly above the Ms point by the double-sided cooling device in the transport path. Forcibly cooling to the temperature, followed by recuperation is performed at least once. The water cooling at this time may be performed by cooling both the inner and outer surfaces of the flange and the upper and lower surfaces of the web independently or simultaneously. After the water cooling, it reheats to 750 ° C or higher. The recuperative means may be heat transfer from the inside of the material to be rolled, or a heating means from the outside may be used.

By setting the recuperation temperature to 750 ° C. or higher, the finish universal mill rolling temperature can be controlled to about 750 ± 30 ° C., which has a large strength improving effect. The reduction rate of finish rolling by the finish universal mill is 10% or less which is usually performed. After finish rolling, the inner and outer surfaces of the flange of the material to be rolled and the upper and lower surfaces of the web are forcibly cooled to a temperature just above the Ms point by using the double-sided cooling device, and then reheated. repeat. In this final cooling-reheat treatment, the reheat temperature of at least one of them must be 600 ° C. or higher in order to soften the low-temperature transformation product and precipitate the ferrite.

Thus, in the H-section manufacturing method of the present invention, the inner and outer surfaces of the flange of the material to be rolled and the upper and lower surfaces of the web are water-cooled, so that the temperatures of both the flange and the web are equalized. Therefore, it is possible to prevent the phenomenon that the temperature difference between the inner and outer surfaces of the flange and the upper and lower surfaces of the web as in the case of the conventional single-sided cooling is large, and the resulting thermal stress causes a shape defect such as a flange warp or a squareness defect. In the case of an extremely thick H-section steel with a flange thickness exceeding 40 mm, the effect of double-sided cooling is more remarkable, and the material properties are stable in the thickness direction of the flange and the thickness direction of the web, and as a result, uniformity over the entire cross section is achieved. It is possible to guarantee and it is possible to provide H-section steel rich in toughness and strength.

[0014]

EXAMPLES Examples of the present invention will be described below. Figure 2
FIG. 3 is a plan view showing the arrangement of rolling lines to which the method for producing H-section steel of the present invention is applied, and in order from the left, the front surface RU ₁ of the coarse universal mill, the first-stage coarse universal mill body U ₁ , the edging mill E ₁ , the first Two-stage coarse universal mill (this may be omitted) U ₂ , the rear surface RU ₂ of the coarse universal mill,
Cooling zone 1, cooling zone 3, finishing universal mill U
_F , cooling zone 4 is located. Each cooling zone 1,
3 and 4 are divided into smaller banks,
Cooling zone 1 is 3 banks, cooling zone 3 and cooling zone 4
Are set in 4 banks, respectively, and are installed on both sides of the transport path. For each of these banks, and on the front surface RU ₁ of the rough universal mill and the rear surface RU ₂ of the rough universal mill, the water cooling device described below is arranged.

FIG. 3 shows a schematic view of the water cooling device 10.
In addition, this figure shows only one side of those arranged on both sides of the rolling line. Reference numeral 11 denotes an H-shaped steel as a material to be rolled, which is placed on a table roller (not shown) in the rolling line. The nozzle guide wheel 12 placed on the side of the H-shaped steel 11 is provided with a plurality of flange outer surface cooling nozzles 13 facing the outer surface of the flange 11F, and cooling provided from the outer surface cooling nozzle header 14 is performed. Water flange 11
Spray on the outer surface of F to cool with water. According to the flange width which changes depending on the size of the H-shaped steel 11, the flange outer surface cooling nozzle 13 is moved up and down by the lifting motor 16 of the nozzle mounting support 15 to adjust the nozzle position. This nozzle guide car 1
2 、 Flange inner / outer surface nozzle guide spacing adjustment motor 1
A flanged inner surface upper cooling nozzle carriage 20A on which a connecting block 19 to which the output screw shaft 18a of No. 8 is screwed is mounted is connected. To the trolley 20A, a trolley 20B for lower flange inner surface cooling nozzle and web lower surface cooling nozzle is connected via a trolley connecting screw shaft 22. Both carriages 20A,
20B is movably mounted on a nozzle elevating beam 23, and the nozzle elevating beam 23 is movably supported by a lift lever 25 driven by a beam elevating motor 24. The carriage 20B is equipped with a lower flange inner surface cooling nozzle 26A and a water supply header 27 thereof, and a web lower surface cooling nozzle 28 and a water supply header 29 thereof.

Further, on the carriage 20A for the flange inner surface upper cooling nozzle, a flange inner surface upper cooling nozzle 26B, a water supply header 31 thereof, and a lifting motor 32 thereof are mounted via a support 30. The flange outer surface cooling nozzle 13, the flange inner surface lower cooling nozzle 26A, and the flange inner surface upper cooling nozzle 26 of the water cooling device 10 described above.
B, each nozzle of the web lower surface cooling nozzle 28 can move vertically and horizontally in a direction perpendicular to the rolling line. Therefore, the size of the H-section steel 11, that is, the web height,
The position is appropriately set according to changes in the flange width and the flange thickness, and the cooling water jetting region is kept optimum. Further, it has a function of independently controlling on / off of each nozzle and arbitrarily adjusting the timing of cooling water injection. In addition, the water cooling device arranged on the opposite side of the water cooling device 10 sandwiching the H-shaped steel 11 has a flange outer surface cooling nozzle 13 for cooling the inner and outer surfaces of the other flange 11F of the H-shaped steel 11 as well.
Although it has a flange inner surface lower cooling nozzle 26A and a flange inner surface upper cooling nozzle 26B, regarding the web cooling,
Instead of the web lower surface cooling nozzle 28, a web upper surface cooling nozzle (not shown) is provided.

Here, an explanation will be given of an H-section steel manufacturing experiment by the method of the present invention, which was carried out using the water cooling device 10 while omitting the second-stage coarse universal mill U ₂ in the line of FIG. First, by the water cooling device 10 installed on the front surface RU ₁ of the rough universal mill, the rough universal mill body U ₁ and the edging mill E _1, and the water cooling device 10 installed on the rear surface RU ₂ of the coarse universal mill, Reverse rough rolling and flange 11 immediately before each rolling process
The process of cooling both the inner and outer surfaces of F and the upper and lower surfaces of the web 11W to a temperature just above the Ms point was alternately repeated three times. Next, in the 1-1 bank of the cooling zone 1, the water cooling is interrupted to recover the heat. In the 1-2 bank, the same forced cooling as described above is performed. In the 1-3 bank, the water cooling is interrupted to recover the heat. Similarly, forced cooling is performed in 3-1 bank, water cooling is stopped and reheated in 3-2 bank, same forced cooling is performed in 3-3 bank, water cooling is stopped and reheated in 3-4 bank, and cooling is performed in the transfer route. After carrying out the recuperation pattern a plurality of times, finish rolling was carried out by the finish universal mill U _F. The surface temperature of the material to be rolled immediately before the finish rolling was 750 ° C. or higher (see Table 2). After the finish rolling, the material to be rolled is further sent to the cooling zone 4, and the forced cooling similar to the above is performed in the 4-1 bank, and the water cooling is interrupted in the 4-2 bank to recover the heat, 4-3.
Similarly, forced cooling was performed in the bank, and in bank 4-4, cooling-reheating was repeated twice through a process of interrupting water cooling and recovering heat. The surface temperature (water cooling stop temperature) of the material to be rolled immediately after water cooling with the 4-3 bank is 600 ° C. or higher (see Table 2).

The composition of the rolled material used in the above experiment is shown in Table 1.

[0019]

[Table 1]

Table 2 shows the condition of the treatment temperature of the product of the present invention and the result of the material test conducted after the above-mentioned manufacturing experiment, in comparison with the case of the conventional product manufactured without water cooling. The measurement items of the material test are yield strength (YP), tensile strength (TS), and elongation (E
1), the yield ratio (YR), and the hardness (Hv).

[0021]

[Table 2]

Further, FIG. 4 shows the result of the Charpy impact test performed on the product of the present invention obtained in the above manufacturing experiment, in comparison with the result of the conventional product obtained by the manufacturing method without water cooling. The sampling position and the longitudinal axis (L) direction of the test piece in the impact test are as shown in FIG. From the above test results, the following things became clear.

The hardness of the conventional product is flange 11F and web 1
There is a difference of 10 Hv from 1 W (the web that is cooled faster because the thickness is thin is harder) and non-uniform. On the other hand, the product of the present invention, which has been water-cooled on both sides, has a flange 11F having a large thickness, which is about 10 Hv higher than that of the conventional product.
There is no difference from the conventional product, and the flange and the web have the same hardness and are uniformized.
Mechanical properties such as S and El have also been improved at each measurement point compared to conventional products, no increase in YR is observed, especially the toughness of the flange is significantly improved, and it has reached the level where the product's entire cross section can be guaranteed. .

[0024]

As described above, according to the present invention,
The H-shaped steel was rolled while repeating water cooling and recuperation on both the inside and outside of the flange and both the top and bottom of the web. Originally, since the H-section steel has different plate thicknesses between the flange portion and the web portion and has a large heat capacity at the R portion, the impact resistance (toughness) is lower than other shape steels having different cross-sectional shapes, but the production of the present invention. According to the method, even for large H-section steel with a large flange thickness, strength and toughness can be increased without relying on complicated rolling methods such as controlled rolling, and weldability can be improved, leading to cost reduction and lead. The time can be shortened and a great effect can be obtained in practical use.

[Brief description of drawings]

FIG. 1 is an explanatory view of places where water is cooled in an H-section steel in a manufacturing process of the present invention.

FIG. 2 is a plan layout view showing an example of a manufacturing process of the present invention.

FIG. 3 is a cross-sectional view of the cooling device of the present invention.

FIG. 4 is a graph showing the impact test results of the product of the present invention and the conventional product.

FIG. 5 is a perspective view showing a sampling position of an impact test piece.

Claims (1)

[Claims] 1. A cooling device that surrounds an H-shaped steel and is capable of cooling the inner and outer surfaces of a flange and the upper and lower surfaces of a web is installed on the front and rear surfaces of a rough mill and a finishing mill, respectively, and a material to be rolled is cooled to the Ms point by the cooling device. 2 steps to cool directly above and rough rolling immediately
Repeat at least once, and then, while the rolled material is being conveyed to the finishing mill, the cooling reheating step of the pattern of cooling to just above the Ms point by the cooling device to reheat is carried out once or more, and the surface temperature of the rolled material is changed. A method for producing an H-section steel rich in toughness and strength, which comprises performing finish rolling after the temperature is 750 ° C. or higher, and further repeating the cooling reheating step of the pattern once or more after the finish rolling.