JP2698006B2 - Method for producing H-beam with excellent toughness - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for producing an H-section steel having excellent toughness used as a structural member of a building.

[0002]

2. Description of the Related Art H-section steels used for beams and columns are required to have higher strength and higher toughness due to stricter safety standards for buildings. In order to solve such required characteristics, conventionally, a heat treatment such as a normalizing process has been performed after the rolling. The addition of heat treatment causes a significant increase in cost such as a decrease in heat treatment cost and production efficiency, and there is a problem in economy. To solve this problem, it was necessary to develop a new alloy design and manufacturing method so that high-performance material properties could be obtained as-rolled.

Generally, a section steel having a flange, for example, H
When a section steel is manufactured by universal hot rolling, toughness is significantly reduced in a fillet portion. There are two reasons for this. One is that the processing temperature is higher in the fillet part than in the parts such as the web and the flange due to the limitations on the molding in universal rolling and the peculiarity of the shape. This is because the cooling of the steel material after the end of the rolling is gradually cooled and the microstructure is coarsened. Another reason is that in the rolling using the continuous cast slab, the central segregation portion of the material is accumulated during the rolling, This is because impurity elements such as P and S are concentrated at ferrite grain boundaries and become brittle as compared with a case where a portion where macrosegregation does not appear is rolled. As a result, for example, a portion that does not meet the standard such as a rolled steel material for a welding structure (JIS G3106) is generated.

[0004] Among them, the second reason for countermeasures against the accumulation of segregation is described in, for example, Japanese Patent Application Laid-Open No. 2-4696.
No. 0, Japanese Patent Application Laid-Open No. 2-15857, etc., there is a method for suppressing the generation of macrosegregation at the center during continuous casting, which is a material production stage. There is a problem in economical efficiency such as an increase in manufacturing cost due to the necessity of installing a screw-down device.

[0005]

SUMMARY OF THE INVENTION In order to solve the above-mentioned problems, the present invention provides a novel manufacturing means for the rolling process, in which the production efficiency is maintained without reducing the production efficiency. An object of the present invention is to provide a method for producing a rolled section steel with reduced macro segregation and excellent toughness.

[0006]

The gist of the present invention is that the mass%
C: 0.04 to 0.20%, Si: 0.05 to 0.5
0%, Mn: 0.50 to 1.80%, with the balance being F
e, and molten steel consisting of unavoidable impurities are cast into slabs by continuous casting, and the slabs are heated to a temperature range of 1100 to 1300 ° C. and rough-rolled to H-shaped rough shaped steel slabs, and then roughed again. After heating to the temperature before rolling and holding at the heating temperature for 3 minutes or more, intermediate rolling and finish rolling are performed, and after finishing rolling,
The present invention relates to a method for producing an H-section steel excellent in toughness, which is cooled to 800 to 500 ° C. at a cooling rate of 0.1 to 30 ° C./sec.

A feature of the present invention is that a number of dislocations are introduced into austenite grains by hot working in a rough rolling stage after the slab is heated, and at the same time, austenite grains are deformed and refined. By increasing the area of the austenite grain boundary, and then maintaining the high temperature,
It promotes the diffusion of atoms inside the base material as compared with before the working, promotes homogenization in the base material, and achieves improvement in toughness.

That is, the present invention provides an economical, efficient, and proper normalizing process which does not require any special equipment, as compared with conventional means for normalizing a slab before rough rolling at a constant temperature and time. Is what you do.

[0009]

Hereinafter, the operation of the present invention will be described in detail based on embodiments. First, the reasons for limiting the range of the basic components of the section steel to which the present invention is applied will be described. C is added as an effective component for improving the strength of steel. If it is less than 0.04%, the strength required for structural steel cannot be obtained.
An excessive addition exceeding 20% significantly reduces the base metal toughness, weld cracking resistance, weld heat affected zone toughness, etc., so the lower limit was made 0.04% and the upper limit was made 0.20%.

[0010] Next, Si is necessary for securing the strength of the base material, preliminary deoxidation of the molten steel, etc. If it exceeds 0.50%, high carbon martensite of a hardened structure is generated in the heat affected zone of the weld, and welding is performed. Significantly reduces joint toughness. If the content is less than 0.05%, the necessary preliminary deoxidation of molten steel cannot be performed, so the Si content is limited to the range of 0.05% to 0.50%. Mn must be added in an amount of 0.5% or more to ensure the strength and toughness of the base material, but the upper limit is set to 1.8% within an allowable range of the toughness, cracking, and the like of the welded portion.

The amounts of P and S contained as unavoidable impurities are not particularly limited. However, since the toughness is reduced by macrosegregation during solidification, the amount of P and S should be reduced as much as possible. It is respectively less than 0.02% that can be reduced to the target amount. After smelting the above components, deoxidation is performed by a normal deoxidation method, and then the cast slab produced by the continuous casting machine is reheated to a temperature range of 1100 to 1300 ° C. The reason for limiting the reheating temperature to this temperature range is that the production of shaped steel by hot working requires heating at 1100 ° C. or higher to facilitate plastic deformation, and also from the performance and economy of the heating furnace. The upper limit was 1300 ° C.

[0012] The heated steel material is roll-formed in each of rough rolling, intermediate rolling and finish rolling. The characteristic of the rolling process of the present rolling method is that after the rough rolling process, the rolling process between the rough rolling mill and the intermediate rolling mill is performed. With a simple heating device installed between,
Alternatively, the material is returned to the heating furnace again and the material is returned to 1100 again.
Heating to a temperature range of １1300 ° C. In this case, the operation is the same between the case where heating is performed by the simple heating device and the case where heating is performed by returning to the heating furnace, and there is no particular limitation. The time maintained at high temperature is the time required to homogenize sufficiently to improve toughness,
It is necessary to maintain the atmosphere temperature of 00 ° C. for 3 minutes or more. If it is less than 3 minutes, homogenization is insufficient, and the toughness does not improve. In the present invention, the longer the holding time, the more
Since the homogenization proceeds, the upper limit of the holding time is not particularly limited. The steel material reheated after the rough rolling undergoes intermediate rolling and finish rolling. After the finish rolling, the 0.1 mm
The reason for cooling to 800 to 500 ° C. at a cooling rate of 1 to 30 ° C./sec is that, in the process according to the present invention, the steel is cooled after finishing rolling, or accelerated to secure the strength and toughness of the base material. The above-mentioned temperature range was set because both are applicable when cooling is performed.

Next, a mechanism for improving the toughness of the fillet portion of the H-section steel will be described. The diffusion of atoms is a thermal activation process and requires diffusion activation energy, the lower the energy, the easier the diffusion. On the other hand, this activation energy has a different value in the crystal grain and in the crystal grain boundary, and it is known that the activation energy of diffusion at the crystal grain boundary is lower than that in the crystal grain. Atom diffusion at the crystal grain boundaries becomes easy. By performing the rough rolling, the structure of the steel material is refined, the grain boundary area is increased, and diffusion is facilitated. Since the diffusion proceeds in a direction in which the steel material becomes homogeneous, the diffusion is facilitated, so that the steel material is homogenized in a relatively short holding time. Therefore, the normalizing process can be efficiently performed by heating and holding after the rough rolling in the present invention, and the macro segregation portion is easily reduced, and as a result, H
The toughness of the fillet portion of the section steel does not decrease, and it is possible to obtain almost the same mechanical property values as the base metal.

[0014]

EXAMPLE A prototype steel was melted from a converter, the components were adjusted, and then cast into a slab of 240 to 300 mm thick by continuous casting.
Was heated in a heating furnace 1 shown in FIG. 1 or in a layout shown in FIG.
Thereafter, the heat is returned to the heating furnaces 1 and 2 again in the direction indicated by the broken line in FIG. 1 in the layout shown in FIG. 1 and heated, or the rough rolling mill 2 and the first intermediate rolling mill 4 as shown in FIG.
And the above-mentioned H-shaped crude steel slab was reheated by the simple heating device 3 installed between the two. Subsequently, the first intermediate rolling mill 4, the second intermediate rolling mill 5, and the finishing rolling mill 6 form the H-shaped steel having a predetermined size. The cooling rate after the rolling is controlled by allowing the water to cool or adjusting the amount of water in the flange water cooling device 7.

The mechanical properties of the H-shaped steel 8 shown in FIG.
Thickness t of J9_TwoCenter (1 / 2t _Two) With full flange width
1/4 width (1 / 4B), 1/2 width (1/2) of the length (B)
B) and at the center of the web 10, the web height
A test piece was sampled from 1/2 part (1 / 2H) and determined. What
The characteristics of these locations were determined by using the flange 1/4
B part and web 1 / 2H part are flange part and web part respectively
The average mechanical properties of the
It is equivalent to the fillet part where the
It is said that the mechanical test characteristics of the H-section steel can be represented by three places
That's why.

Table 1 shows the chemical composition values of the prototype steel, and Table 2
Indicates mechanical test characteristics for rolling and cooling conditions. In addition,
It is well known that the heating temperature is adjusted to 1280 ° C., in general, it is well known that the reduction of the heating temperature improves the mechanical properties, and it is estimated that the high-temperature heating condition shows the lowest value of the mechanical properties. This is because it has been determined that the characteristics at the following heating temperatures can be represented.

[0017]

[Table 1]

[0018]

[Table 2]

As shown in Table 2, steels 1 to 6 according to the present invention
Fully satisfies the target base material strength (JISG3106) and the Charpy impact absorption energy value at 0 ° C. of 47 (J) or more. On the other hand, the steel 7 of the comparative steel satisfies the standard strength because the macrosegregation is not sufficiently homogenized, but the toughness of the flange thickness equivalent to the fillet part and the width 1/2 part toughness is the target value. Not satisfied. Steel 8 has a flange plate thickness of 24 mm, 7 mm larger than the steel 7 flange plate thickness of 17 mm.
Thick size, but half flange thickness and half width
The toughness of the part does not meet the target. Further, in the case of steel 9, when the flange thickness is as large as 60 mm, the toughness of the flange thickness of 1/2 and the width of 1/2 is further reduced, and the difference from the target value is increased.

That is, when all the requirements of the present invention are satisfied, the steel sheet has sufficient strength even in a fillet portion which hardly satisfies the mechanical test characteristics of the rolled section steel, such as steels 1 to 6 shown in Table 2. Thus, it is possible to produce a rolled section steel having excellent toughness. The rolled section steel to which the present invention is applied is applicable not only to the above-mentioned H-section steel, but also to section steels having flanges such as I-section steel, angle steel, channel steel, and unequal thickness angle steel. Of course, you can.

[0021]

According to the present invention, H having excellent toughness even in a fillet portion where mechanical test characteristics are hardly guaranteed.
Efficient production is possible without the need for an off-line process for the production of shaped steel, and there are extremely remarkable industrial effects such as improved reliability, safety, and economic efficiency of large buildings. .

[Brief description of the drawings]

FIG. 1 is an explanatory schematic diagram of an example of a device arrangement row for implementing the method of the present invention.

FIG. 2 is a diagram showing a cross-sectional shape of an H-section steel, showing names of respective parts and a sampling position of a mechanical test piece.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 ... Heating furnace 2 ... Rough rolling mill 3 ... Simple heating device 4 ... 1st intermediate rolling mill 5 ... 2nd intermediate rolling mill 6 ... Finish rolling mill 7 ... Finish rolling mill rear flange cooling device 8 ... H-shaped steel 9 ... Flange 10 ... Web

 ──────────────────────────────────────────────────の Continuing on the front page (72) Inventor Takatoshi Hiroguchi 1 Chikko Yawatacho, Sakai City, Osaka New Nippon Steel Corporation Sakai Works (72) Inventor Yasushi Takeshima 1 Chikuko Yawatacho Sakai City, Osaka New Nippon Steel Corporation Sakai Works (56) References JP-A-62-253721 (JP, A) JP-A-61-159202 (JP, A) JP-A-6-122922 (JP, A)

Claims (1)

(57) [Claims] 1. C: 0.04 to 0.20% by weight, S
i: 0.05 to 0.50%, Mn: 0.50 to 1.80
%, With the balance being Fe and unavoidable impurities, and cast molten steel into a slab by continuous casting.
After being heated to a temperature range of 300 ° C. to perform rough rolling to an H-shaped rough shaped billet, it is heated again to a temperature before the rough rolling and maintained at the heating temperature for 3 minutes or more, and then subjected to intermediate rolling and finish rolling. And after the finish rolling, cooling to 800 to 500 ° C. at a cooling rate of 0.1 to 30 ° C./sec.