JP2024040124A - H-shaped steel with protrusions and its manufacturing method - Google Patents

Abstract

An object of the present invention is to provide a protruded H-beam steel with improved toughness while ensuring high tensile strength. [Solution] C: 0.05 to 0.20 mass%, Si: 0.05 to 0.60 mass%, Mn: 1.20 to 1.80 mass%, P: 0.035 mass% or less, S: 0.035 mass% or less, V: 0.050 to 0.200 mass%, Contains Ti: 0.005 to 0.040 mass% and N: more than 0.0100 mass% to 0.0200 mass% within the range satisfying 0.0085≦[%N]−{(14/48)×[%Ti]}≦0.0150, and the remainder The composition consists of Fe and unavoidable impurities. [Selection diagram] Figure 1

Description

The present invention relates to a protrusion-equipped H-section steel having a protrusion on the flange portion of the H-section steel, and a method for manufacturing the same.

Reinforced concrete using reinforcing bars is widely used in large structures such as bridge piers. Generally, construction of reinforced concrete structures is carried out by assembling reinforcing bars, installing formwork, and pouring concrete into the formwork. Here, when it is necessary to place reinforcing bars in a dense manner for strength reasons, the filling properties of the concrete are reduced, which not only deteriorates construction quality but also prolongs the construction period, which is a major problem. In addition, the number of skilled workers engaged in construction work is decreasing year by year, and there is an increasing need for the development of structural steel that contributes to labor-saving on-site work and shortening construction periods.

Against this background, various studies are being conducted on H-beams with protrusions, which have greater cross-sectional rigidity than reinforcing bars and can reduce the number of required members in the same structure. This H-shaped steel with protrusions has a protrusion on the flange, and is reported to have high concrete adhesion performance equal to or higher than that of reinforcing steel. H-shaped steel with protrusions used in large structures as a replacement for reinforcing bars is required to have guaranteed toughness in addition to mechanical properties such as tensile strength and elongation in order to guarantee performance as a structure. .

In order to satisfy these demands, for example, Patent Document 1 discloses a protruded H-beam steel that has improved tensile strength and toughness in a well-balanced manner by adjusting the amounts of Nb, V, and Ni added. Further, Patent Document 2 discloses a technique for setting an optimal cooling stop temperature according to the flange thickness and appropriately adjusting the amount of cooling water on the inner and outer surfaces of the flange.

Further, Patent Document 3 discloses a finish rolling technique for forming a protrusion on the inner surface of the flange of the H-section steel, with respect to a method for manufacturing an H-section steel with a protrusion, in which the flange portion of the H-section steel has a protrusion.

Japanese Patent Application Publication No. 2004-256834 Japanese Patent Application Publication No. 2006-075883 Japanese Patent Application Publication No. 2003-136102

However, while the protruded H-beam steels described in Patent Documents 1 and 2 mentioned above have Nb and V added to form carbonitrides, there are no regulations regarding the amount of N in the steel, and improvements are needed. There was room. For example, if the amount of N is low, the amount of carbonitrides may be insufficient, and conversely, if the amount of N is large, the carbonitrides may become coarse. There was a need to stably provide toughness.
Note that Patent Document 3 is an open patent publication regarding a rolling technique for forming protrusions on the inner surface of a flange of an H-section steel, and does not particularly disclose the tensile strength or toughness of the H-section steel.

The present invention has been made to advantageously solve the above-mentioned problems, and provides a projection-equipped H-section steel with improved toughness while ensuring a tensile strength equal to or higher than that of conventional projection-equipped H-section steel. The purpose is to provide it together with the manufacturing method.

In order to solve the above-mentioned problems, the inventors created H-shaped steel with projections with varying contents of C, Si, Mn, P, S, V, Ti, and N, and carefully improved the tensile properties and toughness. investigated. As a result, by optimizing the amount of Ti and N contained in steel, coarsening of γ grains during heating due to TiN precipitation is suppressed, and intragranular ferrite transformation with TiN as the core is promoted, improving toughness. I came to know that it can be improved. Furthermore, we have also discovered that by ensuring the amount of solid solute N, VN precipitation in ferrite occurs effectively, resulting in high strength and excellent toughness.
The present invention is based on the above-mentioned knowledge, and the gist of the invention is as follows.

1. C: 0.05 to 0.20% by mass,
Si: 0.05 to 0.60% by mass,
Mn: 1.20 to 1.80% by mass,
P: 0.035% by mass or less,
S: 0.035% by mass or less,
V: 0.050 to 0.200% by mass,
Ti: 0.005 to 0.040 mass% and N: More than 0.0100 mass% to 0.0200 mass%
An H-shaped steel with a protrusion, which contains the following formula (1) within a range that satisfies the following formula (1), and has a composition in which the remainder is Fe and unavoidable impurities, and has a protrusion on the flange.
Record
0.0085≦[%N]－{(14/48)×[%Ti]}≦0.0150... (1)
Here, [%Ti] and [%N] are the contents (% by mass) of Ti and N in the steel, respectively.

2. The component composition further includes Cr: 1.0% by mass or less, Cu: 1.0% by mass or less, Ni: 1.0% by mass or less, Mo: 1.0% by mass or less, Al: 0.10% by mass or less, Nb: 0.10% by mass or less, B. : 0.010 mass% or less, Ca: 0.10 mass% or less, Mg: 0.10 mass% or less, REM: 0.10 mass% or less, W: 1.0 mass% or less, Sb: 0.10 mass% or less, and Sn: 0.10 mass% or less. 1. The H-section steel with protrusions described in 1 above, which contains one or more selected types.

3. A method for producing an H-section steel with projections, comprising hot rolling a steel material having the composition according to any one of 1 or 2 above to form an H-section steel with projections,
The steel material is heated to a temperature T that satisfies the following formula (2) and then subjected to the hot rolling, a protrusion is formed on the flange of the H-beam steel by finish rolling of the hot rolling, and after the finish rolling, A method for producing H-beam steel with projections, which involves cooling from a cooling start temperature of 750°C or higher to 500°C at an average cooling rate of 0.2 to 30.0°C/s.
Note T[℃]≧−16000/{log([%Ti] [%N])−5.09}−673 ・・・ (2)
Here, [%Ti] and [%N] are the contents (mass%) of Ti and N in the steel, respectively, and log is a common logarithm.

According to the present invention, it is possible to stably manufacture a protruded H-beam steel with high strength and excellent toughness, contributing to the rapid construction of large structures and improving the quality of concrete construction products, and contributing to industrial beneficial effects.

It is a sectional view of the H-shaped steel with a protrusion. It is a figure which shows the H-section steel with a protrusion, (a) is a side view seen from the opposing direction of a web, (b) is a top view of the flange outer surface seen from the opposing direction, (c) is a top view of the flange outer surface, It is. FIG. 2 is a perspective view of an H-shaped steel with a protrusion.

The present invention will be specifically explained below. First, the reason why the composition of steel is limited to the above range in the present invention will be explained. In addition, "%" in the following description shall represent "mass %" unless otherwise specified.

C: 0.05-0.20%
C is an element necessary to ensure the strength of the base material, and needs to be added in an amount of at least 0.05%. However, addition of more than 0.20% not only reduces base metal toughness but also reduces weldability. Therefore, in the present invention, the C content is set to 0.05 to 0.20%. Note that the C content is preferably 0.10% or more. Further, the C content is preferably 0.15% or less.

Si: 0.05~0.60%
At least 0.05% of Si is required to ensure the strength of the base metal and as a deoxidizing agent. However, if the Si content exceeds 0.60%, not only will the toughness decrease, but due to the high bonding strength with oxygen that Si has, weldability will deteriorate. deteriorates. Therefore, in the present invention, the Si content is set to 0.05 to 0.60%. Note that the Si content is preferably 0.20% or more. Further, the Si content is preferably 0.40% or less.

Mn: 1.20-1.80%
Like Si, Mn is a relatively inexpensive element that has the effect of increasing the strength of steel, so it is an important element for increasing strength. However, if it is less than 1.20%, the effect of its addition is small, while if it exceeds 1.80%, it promotes upper bainite transformation and reduces toughness, which is not preferable. Therefore, in the present invention, the Mn content is set to 1.20 to 1.80%. Note that the Mn content is preferably 1.40% or more. Further, the Mn content is preferably 1.60% or less.

P: 0.035% or less When the content of P exceeds 0.035%, the ductility of the steel deteriorates. Therefore, in the present invention, the amount of P is set to 0.035% or less. Preferably it is 0.020% or less. On the other hand, the lower the P content, the more preferable it is, so the lower limit of the P content is not particularly limited and may be 0%. However, P is usually an element that is unavoidably contained in steel as an impurity, and excessively low P causes an increase in refining time and cost, so the P content should not be less than 0.005%. preferable.

S: 0.035% or less When S is contained in steel, it mainly exists in the steel material in the form of A-based inclusions. When the S content exceeds 0.035%, the amount of inclusions increases significantly, and at the same time coarse inclusions are generated, which significantly reduces the toughness of the steel. Therefore, in the present invention, the S content in the steel is set to 0.035% or less. Preferably it is 0.020% or less. On the other hand, the lower the S content, the more preferable it is, so the lower limit of the S content is not particularly limited and may be 0%. Note that S is normally an element that is unavoidably contained in steel as an impurity, and excessive reduction in S content increases refining time and costs, so the S content should be 0.002% or more. preferable.

V:0.050~0.200%
V is an important element that precipitates in austenite as VN during rolling or during cooling after rolling, becomes ferrite transformation nuclei, and has the effect of refining crystal grains. Further, V also has the role of increasing the strength of the base material through precipitation strengthening, and is an essential element for ensuring tensile strength and toughness. In order to obtain the above effect, the V content must be 0.050% or more. On the other hand, if the V content exceeds 0.200%, precipitation embrittlement is promoted and the toughness of the base material is significantly impaired, which is not preferable. Therefore, in the present invention, the V content is set to 0.050 to 0.200%. Note that the V content is preferably 0.060 or more. Further, the V content is preferably 0.120% or less.

Ti: 0.005-0.040%
Ti is an important element that exists in austenite as TiN during heating and has the effect of suppressing coarsening of crystal grains. In addition, Ti precipitates into austenite as TiN during rolling or during cooling after rolling, becomes ferrite transformation nuclei, and has the effect of refining crystal grains, making it an essential element for ensuring toughness. . In order to obtain the above effect, the Ti content needs to be 0.005% or more. On the other hand, if the Ti content exceeds 0.040%, it is not preferable because it promotes precipitation embrittlement and greatly impairs the toughness of the base material. Therefore, in the present invention, the Ti content is set to 0.005 to 0.040%. Note that the Ti content is preferably 0.010% or more. Further, the Ti content is preferably 0.035% or less.

N: More than 0.0100% to 0.0200%
N is a useful element that combines with Ti and V in steel and improves the strength and toughness of the base metal as TiN and VN, and needs to be added in an amount exceeding 0.0100%. However, if the N content exceeds 0.0200%, the carbonitrides formed will become coarse and the toughness of the base material will be significantly impaired, which is not preferable. Therefore, in the present invention, the N content is set to exceed 0.0100% to 0.0200%. Note that the N content is preferably 0.0120% or more. Further, the N content is preferably 0.0180% or less.

Furthermore, in the present invention, it is not sufficient for each element to simply satisfy the above range; it is important for Ti and N to satisfy the relationship of the following equation (1).
0.0085≦[%N]－{(14/48)×[%Ti]}≦0.0150... (1)
The inventors evaluated the strength and toughness using various protruded H-beam steels having steel compositions in the above range, and found that in order to obtain high strength and excellent toughness, the amount of TiN produced was taken into account. It was found that it is important to ensure the amount of effective solid solution N. Specifically, when the value calculated by [%N] - {(14/48) x [%Ti]} is less than 0.0085, the precipitation strengthening and ferrite refinement effects due to precipitated VN are not sufficient, and the strength and It was found that the toughness deteriorated. In other words, by controlling the value calculated by the above formula, which is a parameter based on the content of Ti and N, to 0.0085 or more, it is possible to secure a sufficient amount of TiN and VN that contribute to improving high strength and toughness. I can do it. On the other hand, if the value of [%N] - {(14/48) x [%Ti]} exceeds 0.0150, the precipitated VN becomes excessive, which promotes precipitation embrittlement and significantly impairs the toughness of the base metal. Become. Therefore, in the present invention, the value calculated by [%N]-{(14/48)×[%Ti]} is set in the range of 0.0085 to 0.0150. Furthermore, the value calculated by the above formula is preferably 0.0090 to 0.0120%.

The composition of the H-section steel with protrusions used in the present invention includes the components described above, and the remainder is Fe and inevitable impurities.

In addition to the above-mentioned components, if necessary, Cr: 1.0% or less, Cu: 1.0% or less, Ni: 1.0% or less, Mo : 1.0% or less, Al: 0.10% or less, Nb: 0.10% or less, B: 0.010% or less, Ca: 0.10% or less, Mg: 0.10% or less, REM: 0.10% or less, W: 1.0% or less, Sb: 0.10 % or less and Sn: 0.10% or less.
The reasons for specifying the contents of each of the above elements will be explained below.

Cr: 1.0% or less
Cr is an element that can further increase the strength of steel through solid solution strengthening. However, if the content exceeds 1.0%, it is not preferable because it promotes upper bainite transformation and reduces toughness. Therefore, when the composition of steel contains Cr, the Cr content is preferably 1.0% or less. More preferably 0.005 to 0.5%.

Cu: 1.0% or less
Cu is an element that can further increase the strength of steel through solid solution strengthening. However, if the content exceeds 1.0%, Cu cracking tends to occur. Therefore, when the chemical composition of steel contains Cu, the Cu content is preferably 1.0% or less. More preferably 0.005 to 0.5%.

Ni: 1.0% or less
Ni is an element that can increase the strength of steel without deteriorating its ductility. Further, since Cu cracking can be suppressed by adding Cu in combination, when the steel composition contains Cu, it is desirable to also contain Ni. However, when the Ni content exceeds 1.0%, the hardenability of the steel increases and the toughness tends to decrease. Therefore, when the steel composition contains Ni, it is preferable that the Ni amount is 1.0% or less. More preferably 0.005 to 0.5%.

Mo: 1.0% or less
Mo is an element that can further increase the strength of steel through solid solution strengthening. However, if the content exceeds 1.0%, a large amount of upper bainite will be generated in the steel, and the toughness will tend to decrease. Therefore, when the composition of steel contains Mo, the Mo content is preferably 1.0% or less. More preferably 0.005 to 0.5%.

Al: 0.10% or less
Al is an element that can be added as a deoxidizing agent. However, when the Al content exceeds 0.10%, a large amount of oxide inclusions are generated in the steel due to the high bonding strength of Al with oxygen, resulting in a decrease in the ductility of the steel. Therefore, when the steel composition contains Al, the Al content is preferably 0.10% or less. On the other hand, the lower limit of the Al content is not particularly limited, but it is preferably 0.001% or more for deoxidation. More preferably 0.001 to 0.03%.

Nb: 0.10% or less
Nb is an element that has the effect of increasing tensile strength and yield point by precipitating as carbonitride in steel. However, if its content exceeds 0.10%, it not only promotes precipitation embrittlement but also promotes upper bainite transformation, which tends to reduce toughness. Therefore, when the steel composition contains Nb, the Nb content is preferably 0.10% or less. More preferably, it is 0.01 to 0.05%.

B: 0.010% or less B is an element that segregates at grain boundaries in steel and has the effect of improving grain boundary strength. It is also an effective element for improving toughness by forming composite precipitates with TiN, which serve as nucleation sites for intragranular ferrite, and refining the microstructure. On the other hand, if the content exceeds 0.010%, toughness tends to decrease due to grain boundary precipitation of coarse carbonitrides. Therefore, when the steel composition contains B, the B content is preferably 0.010% or less. More preferably it is 0.001 to 0.003%.

Ca: 0.10% or less
Ca has the effect of transforming sulfide-based inclusions into oxysulfides that are highly stable at high temperatures and granulating the sulfide-based inclusions. The shape control effect of Ca can improve the toughness and ductility of steel. However, if the Ca content exceeds 0.10%, the cleanliness tends to decrease and the toughness tends to decrease. Therefore, when the composition of steel contains Ca, the Ca content is preferably 0.10% or less. More preferably, it is 0.0010 to 0.0050%.

Mg: 0.10% or less
Mg has the effect of transforming sulfide-based inclusions into oxysulfides that are highly stable at high temperatures and granulating the sulfide-based inclusions. The shape control effect of Mg can improve the toughness and ductility of steel. However, if the Mg content exceeds 0.10%, the cleanliness tends to decrease and the toughness tends to decrease. Therefore, when the steel composition contains Mg, the Mg content is preferably 0.10% or less. More preferably, it is 0.0010 to 0.0050%.

REM: 0.10% or less
REM (rare earth metal) has the effect of transforming sulfide-based inclusions into oxysulfide, which is highly stable at high temperatures, and granulating the sulfide-based inclusions. The shape control effect of this REM makes it possible to improve the toughness and ductility of steel. However, if the REM content exceeds 0.10%, the cleanliness tends to decrease and the toughness tends to decrease. Therefore, when the steel composition contains REM, the REM content is preferably 0.10% or less. More preferably, it is 0.0010 to 0.0050%.

W: 1.0% or less W is an element that improves the strength of the base material of the H-shaped steel with protrusions by precipitating as a carbide during and after hot rolling to form the H-shaped steel with protrusions. However, if its content exceeds 1.0%, it not only promotes precipitation embrittlement but also promotes upper bainite transformation, which tends to reduce toughness. Therefore, when the composition of steel contains W, the W content is preferably 1.0% or less. More preferably, it is 0.5% or less. Although the lower limit of the W content is not particularly limited, it is preferably 0.001% or more in order to exhibit the above-mentioned effect of improving the strength of the base material.

Sb: 0.10% or less
Sb is an element that has a remarkable effect of preventing decarburization of the steel during reheating when an H-shaped steel material with projections is reheated in a heating furnace before hot rolling. However, if the Sb content exceeds 0.10%, it will have a negative effect on the ductility and toughness of the steel, so when the steel composition contains Sb, the Sb content is preferably 0.10% or less. More preferably, it is 0.05% or less. Although the lower limit of the Sb content is not particularly limited, it is preferably 0.001% or more in order to exhibit the effect of reducing the decarburized layer.

Sn: 0.10% or less
Sn is an element that has a remarkable effect of preventing decarburization of the steel during reheating when a protruded H-beam steel material is reheated in a heating furnace before hot rolling. However, if the Sn content exceeds 0.10%, it will have a negative effect on the ductility and toughness of the steel, so when the composition of the steel contains Sn, the Sn content is preferably 0.10% or less. More preferably, it is 0.05% or less. Although the lower limit of the Sn content is not particularly limited, it is preferably 0.001% or more in order to exhibit the effect of reducing the decarburized layer.

The remainder other than the elements explained above is Fe and unavoidable impurities.
That is, it is permissible for the remainder to contain unavoidable impurities originating from the raw materials, materials, or conditions of manufacturing equipment. Examples of raw materials include iron ore or scrap. Here, O (oxygen) is mentioned as an unavoidable impurity. O is allowed up to 0.004%. Other unavoidable impurities include Zn, Pb, As, Bi, Co, Ta, Zr, H, and the like. The above-mentioned impurities may be mixed in as long as they do not impede the object of the present invention.

Below, the H-section steel with projections of the present invention will be explained in detail. That is, as an example of the H-section steel with protrusions is shown in FIG. 1, the H-section steel with projections is formed by connecting a pair of flanges 2 with a web 3 like a general H-section steel. The H-shaped steel with a projection has a projection 4 on the flange 2. In the example shown in FIG. 1, the flange 2 has a protrusion 4 on its outer surface. This protrusion 4 is provided to provide concrete adhesion performance. In the H-section steel 1 with projections provided with projections 4 for this purpose, the location where the projections 4 are provided is on the outer surface of the flange 2, as shown in FIG. 2(a). In the illustrated example, a protrusion extending in the width direction of the flange 2 is formed on the entire outer surface of the flange 2 with a cross-sectional shape shown in FIG. The protrusions 4 are arranged in the longitudinal direction of the flange 2.

Moreover, the H-section steel with projections of the present invention may have projections 4 not only on the outer surface of the flange 2 but also on the inner surface of the flange 2. For example, as shown in FIG. 3, a protrusion 4 as a protrusion extending in the width direction of the flange 2 can be provided on the inner surface of the flange 2 at a portion including the joint with the web 3. Furthermore, in the H-shaped steel with projections of the present invention, projections 4 may be provided on both the outer and inner surfaces of the flange 2.

Note that the shape, size, number, etc. of the protrusions can be arbitrarily set according to the specifications required of the H-section steel with protrusions. Therefore, although not limited to the illustrated example, it is preferable that the height h of the protrusion 4 is, for example, 1.5 mm or more in consideration of concrete adhesion performance. On the other hand, the upper limit of the height h is preferably 6 mm from the viewpoint of preventing roll breakage. Further, in consideration of concrete adhesion performance, it is preferable that the distance d between the protrusions 4 satisfies the relationship h/d≧0.05 with the height h.

Next, a method for manufacturing a protruded H-section steel according to the present invention will be explained. Note that there are no particular restrictions on the melting and casting methods for the steel material (slab or beam blank), and any conventionally known methods are suitable. When hot-rolling the steel material to form an H-beam, if a protrusion is formed on the outer surface of the flange during the finish rolling of the hot rolling, a groove corresponding to the protrusion is used as a vertical roll to roll down the outer surface of the flange. Protrusions can be provided by using a material in which a vertical roll is formed on the circumferential surface of the vertical roll. Furthermore, when forming protrusions on the inner surface of the flange, a horizontal roll with grooves corresponding to the protrusions formed on the side surface of the horizontal roll for rolling down the inner surface of the flange is used, similar to the technique disclosed in Patent Document 3 mentioned above. By doing so, protrusions can be provided. At that time, the heating temperature of the steel material and the cooling after finish rolling must satisfy the following conditions.

Heating temperature T: T[℃]≧-16000/{log([%Ti] [%N])-5.09}-673... (2)
Here, [%Ti] and [%N] are the contents (mass%) of Ti and N in the steel, respectively, and log is a common logarithm.
If the heating temperature of the steel material (slab or beam blank) does not satisfy the above formula (2), a large amount of coarse TiN precipitated during the casting stage will remain, making it difficult to secure an effective solid solution N amount. It becomes difficult to ensure the desired tensile strength and toughness. Therefore, the heating temperature is set within a temperature range that satisfies the above equation (2). On the other hand, the upper limit of the heating temperature is preferably 1400° C. or less from the viewpoint of preventing a decrease in toughness due to excessive coarsening of the austenite grain size.

Flange temperature at the start of cooling: 750°C or higher In the present invention, the flange temperature at the start of cooling is set at 750°C or higher in order to prevent a decrease in production efficiency by starting cooling the steel material immediately after finish rolling. do. On the other hand, if the flange temperature at the start of cooling becomes less than the Ar ₃ temperature, it becomes difficult to obtain sufficient strength, so it is preferable that the flange temperature at the start of cooling is set to the Ar ₃ temperature or higher. Note that the Ar ₃ transformation temperature is simply expressed in relation to the steel components, for example, by the following equation (3).
_Ar3 = 910-310×[%C]+25×([%Si]+2×[%Al])-80×[Mneq]...(3)
Here, [Mneq] is a value calculated by the following equation (4).
[Mneq]=[%Mn]+[%Cr]+[%Cu]+[%Mo]+[%Ni]/2+10×([%Nb]-0.02)... (4)

In addition, in the above formulas (3) and (4), [%M] means the content (% by mass) of element M in the steel. Here, when calculating Ar ₃ using the above formulas (3) and (4), the content of element M that is not actively included is determined by the content of element M that is included as an unavoidable impurity ( It shall be calculated using the analysis value).

Average cooling rate from cooling start temperature to 500℃: 0.2 to 30.0℃/s
If the average cooling rate from the cooling start temperature to 500°C is less than 0.2°C/s, it will be difficult to secure the desired tensile properties, so the cooling rate should be 0.2°C/s or more. On the other hand, if the cooling rate exceeds 30.0° C./s, the formation of bainite or martensite causes problems such as a decrease in toughness and an excessive increase in tensile strength. Therefore, the average cooling rate from the cooling start temperature to 500°C is in the range of 0.2 to 30.0°C/s.

Specific cooling methods after finish rolling include spray cooling, which involves spraying cooling water onto the outer surface of the flange using a spray nozzle, mist cooling, which sprays atomized water using a mist cooling nozzle, and shock cooling, which sprays air using an air nozzle. Wind cooling, convection cooling that utilizes air convection accompanying the conveyance of the material, etc. can be selected as appropriate.

By adjusting the composition to the above and rolling and cooling under the above conditions, the H-section steel with projections has a tensile strength of 520 MPa or more, a yield strength of 355 MPa or more, and a shock absorption energy vE0 of 47 J at 0°C. As described above, excellent mechanical performance can be obtained. Although there is no need to define upper limits for any of the properties, practical upper limits are about 720 MPa for tensile strength, 580 MPa for yield point, and about 350 J for impact absorption energy vE0 at 0°C.

Here, the flange thickness of the H-section steel with projections targeted by the present invention is not particularly limited. The protrusions on the flange are formed using a grooved roll in the finish rolling process. That is, in order to provide a desired protrusion height, it is necessary to increase the rolling reduction ratio of the flange portion as much as possible. Therefore, a protruded H section with a thick flange requires a greater reduction. As described later, in the present invention, by controlling the rolling temperature within an appropriate range, sufficient protrusion height can be achieved even in thick H-beam steel with a flange thickness of 16 mm or more, where the efficiency of forming protrusion height is said to decrease. can be granted.

In finish rolling, which involves forming protrusions during hot rolling, the finish rolling temperature is preferably 800° C. or higher from the viewpoint of forming protrusions with sufficient protrusion height. If the finish rolling temperature is less than 800°C, it is difficult to stably form protrusions of sufficient height. On the other hand, the upper limit of the finishing temperature is not particularly limited, but if it exceeds 1050° C., the austenite grain size becomes coarse and the toughness tends to decrease. Therefore, it is preferable that the finishing temperature is 1050°C or less.

Hereinafter, the configuration and effects of the present invention will be explained in more detail according to Examples. However, the present invention is not limited by the following examples, and can be modified as appropriate within the scope that fits the spirit of the present invention, and all of these are included within the technical scope of the present invention. It will be done.

A steel material with the composition shown in Table 1 was made into a beam blank with a cross section of 400 mm x 560 mm x length of 8000 mm using a continuous casting machine, heated at a predetermined temperature for 2 hours, and then hot rolled and cooled under the conditions shown in Table 2. Thus, a protruded H-beam 1 having a cross-sectional shape shown in FIG. 1, that is, a shape having a web 3 and a pair of flanges 2 disposed at both ends of the web, was manufactured. Here, the cross-sectional dimensions (web height x flange width x web thickness x flange thickness) are 320 x 323 x 25 x 25 mm, 328 x 322 x 24 x 29 mm, 348 x 332 x 34 x 39 mm and 350 x 333 x H-beams with protrusions were produced in one of four types measuring 35 x 40 mm. In finish rolling, a roll with grooves corresponding to the shape of the protrusions to be formed on the outer surface of the flange is used as a rolling roll for rolling down the outer surface of the flange. The existing protrusions 4 were formed.

Here, the vertical rolls for finish rolling that roll down the outer surface of the flange are provided with grooves that can form protrusions with a protrusion width w of 15 mm and a protrusion height h of 1.5 mm or more. The cooling rate after finish rolling is determined by measuring the surface temperature of the outer surface of the flange 1/6B (see Figure 1) with a radiation thermometer, and calculating the temperature change per unit time (seconds) from the start of cooling to the stop of cooling. The cooling rate (°C/s) was calculated by converting into .

The obtained H-shaped steel with projections was subjected to evaluation of projection height, tensile test, and toughness test. The content of each evaluation will be explained in detail below.

<Evaluation of protrusion height>
Regarding the obtained H-shaped steel with projections, the height h of the projections on the outer surface of the flange shown in FIG. 2 was measured. These values were measured at three locations in the rolling direction of the H-section steel with projections after finishing rolling, namely the tip, center, and tail end, and the average value thereof was adopted. The lower limit of required performance for the protrusion height was set at 1.5 mm, and a value equal to or greater than this value was defined as the preferred range for the protrusion height h. Further, the manufacturing conditions under which a protrusion-equipped H-beam steel having a protrusion height h equal to or greater than this value was obtained can be evaluated as particularly preferable conditions from the viewpoint of ease of protrusion formation.

<Tensile test>
JIS 1A specified in JIS Z2201 so that the tensile direction is in the longitudinal direction of the H-beam flange from the flange 1/6B section (flange width direction length 60 mm sandwiching 1/6B) shown as reference numeral 5 in Fig. 1. A test piece (flange full thickness test piece) was taken and subjected to a tensile test according to JIS Z2241 to measure yield strength (yield stress YS or 0.2% proof stress) and tensile strength.

<Toughness test>
A 2mm V-notch Charpy impact test piece specified in JIS Z2202 was taken from a position 1/4t (t is the flange thickness) from the back surface of the flange 1/6B section 5 shown in Figure 1, and was tested in accordance with JIS Z2242. A Charpy impact test was conducted to measure the absorbed energy at 0°C.

Table 2 also shows the results of the above investigation. Test results of H-beam steel with protrusions manufactured by the manufacturing method within the scope of the present invention (heating temperature and average cooling rate of the outer surface of the flange within the range of the present invention) using compatible steel that satisfies the steel composition of the present invention (Table 2) Test Nos. 1 to 17, 39 to 42) all satisfied the desired properties (tensile strength: 520 MPa or more, yield strength: 355 MPa or more, and impact absorption energy vE0 at 0°C: 47 J or more). Test No. 34 satisfied the desired properties in terms of tensile strength, yield strength, and impact absorption energy at 0°C, but because the finish rolling temperature was below the preferred lower limit of 800°C, the protrusion height was The length was 1.4 mm, which was below the preferable range (1.5 mm or more).

On the other hand, comparative examples (Test Nos. 18 to 33 and 35 to 38 in Table 2) where the steel composition of the H-beam steel did not satisfy the conditions of the present invention or where the manufacturing method within the scope of the present invention was not applied , tensile strength, yield strength, and toughness do not satisfy the required properties.

Furthermore, although this example is an example in which protrusions are formed on the outer surface of the flange of H-section steel, similar results can be obtained by following the present invention in the case of forming protrusions on the inner surface of the flange of H-section steel. I'm sure you can get it.

1: H-shaped steel with protrusions (rolled H-shaped steel)
2: Flange 3: Web 4: Protrusion 5: Flange 1/6B section (test piece collection position)

Claims (3)

C: 0.05 to 0.20% by mass,
Si: 0.05 to 0.60% by mass,
Mn: 1.20 to 1.80% by mass,
P: 0.035% by mass or less,
S: 0.035% by mass or less,
V: 0.050 to 0.200% by mass,
Ti: 0.005 to 0.040 mass% and N: More than 0.0100 mass% to 0.0200 mass%
An H-shaped steel with a protrusion, which contains the following formula (1) within a range that satisfies the following formula (1), and has a composition in which the remainder is Fe and unavoidable impurities, and has a protrusion on the flange.
Record
0.0085≦[%N]－{(14/48)×[%Ti]}≦0.0150... (1)
Here, [%Ti] and [%N] are the contents (mass%) of Ti and N in the steel, respectively. The component composition further includes Cr: 1.0% by mass or less, Cu: 1.0% by mass or less, Ni: 1.0% by mass or less, Mo: 1.0% by mass or less, Al: 0.10% by mass or less, Nb: 0.10% by mass or less, B. : 0.010 mass% or less, Ca: 0.10 mass% or less, Mg: 0.10 mass% or less, REM: 0.10 mass% or less, W: 1.0 mass% or less, Sb: 0.10 mass% or less, and Sn: 0.10 mass% or less. The H-shaped steel with protrusions according to claim 1, containing one or more selected types. A method for producing an H-section steel with projections, comprising hot rolling a steel material having the composition according to claim 1 or 2 to form an H-section steel with projections,
The steel material is heated to a temperature T that satisfies the following formula (2) and then subjected to the hot rolling, a protrusion is formed on the flange of the H-beam steel by finish rolling of the hot rolling, and after the finish rolling, , a method for manufacturing H-beam steel with projections, in which cooling is performed from a cooling start temperature of 750°C or higher to 500°C at an average cooling rate of 0.2 to 30.0°C/s.
Note T[℃]≧−16000/{log([%Ti] [%N])−5.09}−673 ・・・ (2)
Here, [%Ti] and [%N] are the contents (% by mass) of Ti and N in the steel, respectively, and log is a common logarithm.

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