JP2672236B2 - 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. In order 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 uses a novel manufacturing means for a rolling process, in particular, to effectively keep the rolling as it is without lowering the production efficiency. It is an object of the present invention to provide a method for producing a rolled steel having excellent toughness by reducing macro segregation.

[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 Fe and unavoidable impurities, molten steel was cast into a slab by continuous casting, and the slab was placed in a temperature range of 1200 to 1300 ° C. After heating and rough rolling to H type rough billet, 5 minutes or more 1
A method for producing an H-section steel with excellent toughness, in which it is left to cool for 0 minutes, then subjected to intermediate rolling and finish rolling, and after finishing rolling, cooled to 800 to 500 ° C at a cooling rate of 0.1 to 30 ° C / sec. It is in.

A feature of the present invention is that by hot working in a rough rolling stage after heating a slab, a large number of dislocations are introduced into austenite grains, and at the same time, austenite grains are deformed to form fine grains. As a result, the austenite grain boundary area is increased. After that, by holding, the diffusion of atoms in the base material is promoted more than before processing, homogenization in the base material is promoted, and improvement of toughness is achieved.

That is, according to the present invention, as compared with the conventional means for normalizing the slab before rough rolling at a constant temperature and time, economical and efficient proper normalizing treatment is required without any special equipment. It is something to 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 the above components are melted, deoxidized by a normal deoxidizing method, and then the slab produced by the continuous casting machine is reheated to a temperature range of 1200 to 1300 ° C. The reason why the reheating temperature is limited to this temperature range is that the plastic deformation due to the intermediate rolling and the finish rolling is facilitated even if it is left to cool for 5 minutes or more and 10 minutes after rough rolling as described later. Heating above ℃ is required, and the upper limit is 13 due to the performance and economy of the heating furnace.
It was set to 00 ° C.

The heated steel material is roll-formed by each step of rough rolling, intermediate rolling and finish rolling. The characteristic feature of the rolling step of this rolling method is that the raw material is allowed to cool as it is after the rough rolling step. . Although the raw material temperature after rough rolling is slightly lower than the heating temperature, it is a high temperature sufficient for homogenization, and by allowing to cool in this high temperature range, homogenization for improving toughness becomes possible. The time period for cooling is limited to 5 minutes or more and 10 minutes or less because the homogenization is insufficient and the toughness is not improved when the time is 5 minutes or less. The material temperature decreases and the homogenization is efficient when the time is 10 minutes or more. However, the upper limit was set due to the fact that it becomes low temperature rolling in subsequent intermediate rolling and finish rolling and the load on the rolling mill increases. The steel material reheated after the rough rolling undergoes intermediate rolling and finish rolling. After the rolling is finished, the cooling is continued to a temperature of 800 to 500 ° C. at a cooling rate of 0.1 to 30 ° C./sec, and it is said that in the process according to the present invention, when the material is left to cool after the rolling is finished or the base metal Since it can be applied both when accelerated cooling is performed to secure the strength and toughness of
The above temperature range was set.

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 the direction in which the steel material becomes homogeneous, the diffusion is facilitated and the homogenization is achieved in a relatively short time. Therefore, the normalizing process can be efficiently performed by heating and cooling after the rough rolling in the present invention,
The macrosegregated portion is easily mitigated, and as a result, it becomes possible to obtain mechanical property values almost the same as those of the base metal without lowering the toughness of the fillet portion of the H-section steel.

[0014]

[Example] A prototype steel was melted in a converter, adjusted in composition, and cast by continuous casting into 240 mm to 300 mm thick slabs, which were then heated in a heating furnace 1 having a layout shown in FIG. Was roughly rolled to produce an H-shaped coarse billet. After that, rough rolling machine 2
And the first intermediate rolling mill 3 is allowed to cool the H-shaped rough steel slab. Subsequently, the first intermediate rolling mill 3, the second intermediate rolling mill 4, and the finishing rolling mill 5 perform forming until an H-section steel having a predetermined dimension is obtained. The cooling rate after rolling is controlled by allowing cooling or adjusting the amount of water in the rear surface flange water cooling device 6 of the finishing rolling mill.

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
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]

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.

[0019]

[Table 2]

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.

[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 an explanatory view showing a cross-sectional shape of an H-section steel, showing names of respective parts and sampling positions of mechanical test pieces.

[Explanation of symbols]

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

 ─────────────────────────────────────────────────── ─── Continuation of the front page (72) Inventor Takatoshi Hiroguchi 1 No. 1 Tsukiko Hachiman-cho, Sakai City, Osaka Pref. Kai 60-200913 (JP, A) JP-A-6-57327 (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 inevitable impurities, is cast into a slab by continuous casting, and the slab is drawn from 1200 to 1
After heating to a temperature range of 300 ° C. and rough rolling to an H-shaped rough billet, it is left to cool for 5 minutes or more and 10 minutes, then intermediate rolling and finish rolling, and after finishing rolling, 0.1 ~ 30
A method for producing an H-section steel having excellent toughness, which comprises cooling to 800 to 500 ° C at a cooling rate of ° C / sec.