H-beam with projections and its manufacturing method

Abstract

To provide an H-beam with protrusions that exhibits improved toughness while ensuring high tensile strength.SOLUTION: An H-beam with protrusions comprises C: 0.05-0.20 mass%, Si: 0.05-0.60 mass%, Mn: 1.20-1.80 mass%, P: 0.035 mass% or less, S: 0.035 mass% or less, V: 0.050-0.200 mass%, Ti: 0.005-0.040 mass% and N: 0.0100-0.0200 mass% (excluding 0.0100 mass%), satisfying 0.0085≤[%N]-{(14 / 48)×[%Ti]}≤0.0150, with the balance being Fe and inevitable impurities.SELECTED DRAWING: Figure 1

Description

[Technical Field]

[0001] The present invention relates to a protruding H-beam having a protrusion on the flange portion of the H-beam, and a manufacturing method thereof. [Background technology]

[0002] Reinforced concrete, which uses rebar as a reinforcing material, is widely used in large structures such as bridge piers. Construction of reinforced concrete structures typically involves assembling the rebar, setting up formwork, and pouring concrete into the formwork. However, when the rebar needs to be placed too densely for strength reasons, the concrete's ability to fill the concrete decreases, not only deteriorating construction quality but also lengthening the construction period, presenting a major challenge. In addition, the number of skilled workers engaged in such construction work is declining year by year, creating an even greater demand for the development of structural steel that can contribute to labor-saving on-site work and shortening construction periods.

[0003] Given this background, various studies have been conducted on protruding H-shaped steel beams, which have greater cross-sectional rigidity than rebar and can reduce the number of components required in the same structure. These protruding H-shaped steel beams have protrusions on the flanges, and have been reported to have high concrete adhesion performance equal to or greater than that of rebar. To ensure structural performance, protruding H-shaped steel beams used in large structures as a replacement for rebar are required to have guaranteed toughness in addition to mechanical properties such as tensile strength and elongation.

[0004] To satisfy these requirements, for example, Patent Document 1 discloses a protrusion-equipped H-section steel in which the amounts of Nb, V, and Ni added are adjusted to improve tensile strength and toughness in a well-balanced manner. Also, Patent Document 2 discloses a technology for setting an optimal cooling stop temperature according to the flange thickness and for appropriately adjusting the amount of cooling water on the inner and outer surfaces of the flange.

[0005] Furthermore, Patent Document 3 discloses a finish rolling technique for forming protrusions on the inner surface of the flange of an H-shaped steel, in relation to a manufacturing method for an H-shaped steel having protrusions on the flange portion of the H-shaped steel. [Prior art documents] [Patent documents]

[0006] [Patent Document 1] Japanese Patent Application Laid-Open No. 2004-256834 [Patent Document 2] Japanese Patent Application Laid-Open No. 2006-075883 [Patent Document 3] Japanese Patent Application Laid-Open No. 2003-136102 Summary of the Invention [Problem to be solved by the invention]

[0007] However, while the projection-equipped H-section steels described in Patent Documents 1 and 2 contain Nb and V, which form carbonitrides, the amount of N in the steel is not specified, leaving room for improvement. For example, if the N content is low, the amount of carbonitrides may be insufficient, and conversely, if the N content is high, the carbonitrides may become coarse. Therefore, there has been a demand for a steel that can stably provide high tensile strength and excellent toughness. Patent Document 3 is a published patent publication relating to a rolling technique for forming protrusions on the inner surface of a flange of an H-shaped steel, and does not particularly disclose the tensile strength or toughness of the H-shaped steel.

[0008] The present invention has been made to advantageously solve the above-mentioned problems, and aims to provide a protruding H-shaped steel beam that has improved toughness while maintaining a tensile strength equal to or greater than that of conventional protruding H-shaped steel beams, along with a manufacturing method thereof. [Means for solving the problem]

[0009] To solve the above problems, the inventors produced H-section steel with projections containing various amounts of C, Si, Mn, P, S, V, Ti, and N, and thoroughly investigated the tensile properties and toughness. As a result, they discovered that optimizing the amounts of Ti and N contained in the steel suppresses the coarsening of gamma grains during heating due to TiN precipitation and promotes intragranular ferrite transformation nucleated by TiN, thereby improving toughness. Furthermore, they discovered that ensuring a sufficient amount of solute N effectively causes VN to precipitate in ferrite, resulting in high strength and excellent toughness. The present invention is based on the above findings, and the gist and configuration thereof are as follows.

[0010] 1.C:0.05~0.20% by mass, Si:0.05~0.60% by mass, Mn: 1.20~1.80% by mass, P: 0.035% by mass or less, S: 0.035% by mass or less, V:0.050~0.200% by mass, Ti: 0.005 to 0.040 mass% and N: Over 0.0100% by mass to 0.0200% by mass in a range satisfying the following formula (1), with the remainder consisting of Fe and unavoidable impurities, and having protrusions on the flanges. Note 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.

[0011] 2. The protruding H-section steel according to 1 above, wherein the chemical composition further contains one or more elements selected from Cr: 1.0 mass% or less, Cu: 1.0 mass% or less, Ni: 1.0 mass% or less, Mo: 1.0 mass% or less, Al: 0.10 mass% or less, Nb: 0.10 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.

[0012] 3. A method for manufacturing a protruding H-shaped steel beam, comprising hot rolling a steel material having the component composition described in either 1 or 2 above to form a protruding H-shaped steel beam, The method for producing H-beam steel with projections comprises heating the steel material to a temperature T that satisfies the following formula (2), and then subjecting it to the hot rolling. Protrusions are formed on the flanges of the H-beam steel by finish rolling of the hot rolling. After the finish rolling, the steel is cooled 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 the common logarithm. [Effects of the Invention]

[0013] According to the present invention, it is possible to stably manufacture protruding H-shaped steel beams that have high strength and excellent toughness, which contributes to the rapid construction of large structures and the improvement of the quality of concrete construction products, thereby bringing about industrially beneficial effects. [Brief explanation of the drawings]

[0014] [Figure 1] A cross-sectional view of a protruding H-shaped steel beam. [Figure 2] 1A and 1B are diagrams showing an H-shaped steel beam with projections, in which (a) is a side view seen from the opposite side of the web, (b) is a plan view seen from the opposite side of the flange outer surface, and (c) is a top view of the flange outer surface. [Figure 3] This is an oblique view of an H-shaped steel beam with a protrusion. BEST MODE FOR CARRYING OUT THE INVENTION

[0015] The present invention will be described in detail below. First, the reasons for limiting the chemical composition of the steel to the above ranges in the present invention will be explained. In the following description, "%" represents "mass %" unless otherwise specified.

[0016] C: 0.05 to 0.20% C is an element necessary to ensure the strength of the base metal, and at least 0.05% must be added. However, adding more than 0.20% not only reduces the toughness of the base metal, but also reduces weldability. Therefore, in the present invention, the C content is set to 0.05 to 0.20%. The C content is preferably 0.10% or more. Furthermore, the C content is preferably 0.15% or less.

[0017] Si: 0.05 to 0.60% Si is necessary at 0.05% or more to ensure the strength of the base metal and as a deoxidizer, but if the Si content exceeds 0.60%, not only does toughness decrease, but weldability also deteriorates due to the high bonding strength of Si with oxygen. Therefore, in the present invention, the Si content is set to 0.05 to 0.60%. The Si content is preferably 0.20% or more. Furthermore, the Si content is preferably 0.40% or less.

[0018] Mn: 1.20 to 1.80% Like Si, Mn is a relatively inexpensive element that has the effect of increasing the strength of steel, making it an important element for increasing strength. However, if its content is less than 1.20%, the effect of its addition is small, while if its content exceeds 1.80%, it promotes upper bainite transformation and reduces toughness, which is undesirable. Therefore, in the present invention, the Mn content is set to 1.20 to 1.80%. The Mn content is preferably 1.40% or more. Furthermore, the Mn content is preferably 1.60% or less.

[0019] P:0.035% or less If the P content exceeds 0.035%, the ductility of the steel deteriorates. Therefore, in the present invention, the P content is set to 0.035% or less, preferably 0.020% or less. On the other hand, since the lower the P content, the better, there is no particular restriction on the lower limit of the P content, and it may be 0%. However, since P is an element that is usually inevitably contained in steel as an impurity, and excessively reducing the P content leads to increased refining time and costs, the P content is preferably set to 0.005% or more.

[0020] S: 0.035% or less When S is contained in steel, it exists in the steel material mainly in the form of A-type inclusions. If the S content exceeds 0.035%, the amount of these inclusions increases significantly, and at the same time, coarse inclusions are formed, significantly reducing the toughness of the steel. Therefore, in the present invention, the S content in steel is set to 0.035% or less, preferably 0.020% or less. On the other hand, since the lower the S content, the better, there is no particular restriction on the lower limit of the S content, and it may even be 0%. Note that S is usually an element that is inevitably contained in steel as an impurity, and excessively low S content leads to increased refining time and costs, so the S content is preferably set to 0.002% or more.

[0021] V: 0.050 to 0.200% V is an important element that precipitates in austenite as VN during rolling or cooling after rolling, becoming ferrite transformation nuclei and having the effect of refining crystal grains. V also plays a role in increasing the strength of the base material through precipitation strengthening, and is an essential element for ensuring tensile strength and toughness. To achieve this effect, the V content must be 0.050% or more. On the other hand, a V content exceeding 0.200% is undesirable because it promotes precipitation embrittlement and significantly impairs the toughness of the base material. Therefore, in the present invention, the V content is set to 0.050 to 0.200%. The V content is preferably 0.060% or more. The V content is preferably 0.120% or less.

[0022] Ti: 0.005 to 0.040% Ti is an important element that has the effect of suppressing grain coarsening by existing in austenite as TiN during heating. Furthermore, Ti precipitates in austenite as TiN during rolling or cooling after rolling, becoming ferrite transformation nuclei and having the effect of refining grains, making it an essential element for ensuring toughness. To achieve this effect, the Ti content must be 0.005% or more. On the other hand, a Ti content exceeding 0.040% is undesirable because it promotes precipitation embrittlement and significantly impairs the toughness of the base material. Therefore, in the present invention, the Ti content is set to 0.005 to 0.040%. The Ti content is preferably 0.010% or more. The Ti content is preferably 0.035% or less.

[0023] N: Over 0.0100% to 0.0200% N is a useful element that bonds with Ti and V in steel to form TiN and VN, improving the strength and toughness of the base material, and needs to be added in an amount exceeding 0.0100%. However, an N content exceeding 0.0200% is undesirable because the carbonitrides formed become coarse and significantly impair the toughness of the base material. Therefore, in the present invention, the N content is set to more than 0.0100% to 0.0200%. The N content is preferably 0.0120% or more. Furthermore, the N content is preferably 0.0180% or less.

[0024] Furthermore, in the present invention, it is not sufficient for each element to simply satisfy the above ranges; it is important that Ti and N satisfy the relationship of the following formula (1). 0.0085≦[%N]-{(14 / 48)×[%Ti]}≦0.0150 ··· (1) The inventors evaluated the strength and toughness of various H-section steels with projections having steel compositions within the above ranges. They found that ensuring the amount of available solute N, taking into account the amount of TiN formed, is important for achieving high strength and excellent toughness. Specifically, they found that when the value calculated by [%N] - {(14 / 48) × [%Ti]} is less than 0.0085, the precipitation strengthening and ferrite refinement effects of precipitated VN are insufficient, resulting in degraded strength and toughness. In other words, by controlling the value calculated by the above formula, which is a parameter based on the Ti and N content, to 0.0085 or greater, sufficient amounts of TiN and VN can be ensured to contribute to high strength and improved toughness. On the other hand, when the value of [%N] - {(14 / 48) × [%Ti]} exceeds 0.0150, the amount of precipitated VN becomes excessive, promoting precipitation embrittlement and significantly impairing the base material toughness. Therefore, in the present invention, the value calculated by [%N]-{(14 / 48)×[%Ti]} is set to the range of 0.0085 to 0.0150. Furthermore, the value calculated by the above formula is preferably set to 0.0090 to 0.0120%.

[0025] The component composition of the projection H-section steel used in the present invention contains the components explained above, with the balance being Fe and unavoidable impurities.

[0026] In addition to the components described above, if necessary, for the purpose of further improving strength, ductility, toughness, and weld characteristics, one or more selected from 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 may be optionally contained. The reasons for specifying the contents of each of the elements above will be explained below.

[0027] Cr:1.0% or less Cr is an element that can further increase the strength of steel through solid solution strengthening. However, a Cr content exceeding 1.0% is undesirable because it promotes upper bainite transformation and reduces toughness. Therefore, when the steel composition contains Cr, the Cr content is preferably 1.0% or less, and more preferably 0.005 to 0.5%.

[0028] Cu: 1.0% or less Cu is an element that can further increase the strength of steel through solid solution strengthening. However, if its content exceeds 1.0%, Cu cracking becomes more likely to occur. Therefore, if the steel composition contains Cu, the Cu content is preferably 1.0% or less, and more preferably 0.005 to 0.5%.

[0029] Ni: 1.0% or less Ni is an element that can increase the strength of steel without deteriorating ductility. Furthermore, when added in combination with Cu, it can suppress Cu cracking, so it is desirable for the steel composition to also contain Ni. However, if the Ni content exceeds 1.0%, the hardenability of the steel increases and the toughness tends to decrease. Therefore, if the steel composition contains Ni, the Ni content is preferably 1.0% or less. It is more preferably 0.005 to 0.5%.

[0030] Mo: 1.0% or less Mo is an element that can further increase the strength of steel through solid solution strengthening. However, if its content exceeds 1.0%, a large amount of upper bainite will be formed in the steel, which tends to reduce toughness. Therefore, if the composition of steel contains Mo, the Mo content is preferably 1.0% or less, and more preferably 0.005 to 0.5%.

[0031] Al: 0.10% or less Al is an element that can be added as a deoxidizer. However, if the Al content exceeds 0.10%, a large amount of oxide-based inclusions is formed in the steel due to the strong 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, although there is no particular lower limit for the Al content, it is preferably 0.001% or more for deoxidation. A range of 0.001 to 0.03% is more preferable.

[0032] Nb: 0.10% or less Nb is an element that has the effect of increasing tensile strength and yield point by precipitating as carbonitrides in steel. However, if its content exceeds 0.10%, it promotes precipitation embrittlement and accelerates upper bainite transformation, which tends to reduce toughness. Therefore, if the steel composition contains Nb, the Nb content is preferably 0.10% or less, and more preferably 0.01 to 0.05%.

[0033] 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 also forms complex precipitates with TiN, which serve as nucleation sites for intragranular ferrite, refining the microstructure and thereby improving toughness. On the other hand, if the B content exceeds 0.010%, the toughness tends to decrease due to the precipitation of coarse carbonitrides at grain boundaries. Therefore, when the steel composition contains B, the B content is preferably 0.010% or less, and more preferably 0.001 to 0.003%.

[0034] Ca: 0.10% or less Ca has the effect of transforming sulfide-based inclusions into oxysulfides, which are highly stable at high temperatures, and granulating the sulfide-based inclusions. This morphology control effect of Ca can improve the toughness and ductility of steel. However, if the Ca content exceeds 0.10%, cleanliness tends to decrease and toughness tends to decrease. Therefore, if the steel composition contains Ca, the Ca content is preferably 0.10% or less, and more preferably 0.0010 to 0.0050%.

[0035] Mg: 0.10% or less Mg has the effect of transforming sulfide-based inclusions into oxysulfides, which are highly stable at high temperatures, and granulating the sulfide-based inclusions. This morphology control effect of Mg can improve the toughness and ductility of steel. However, if the Mg content exceeds 0.10%, cleanliness tends to decrease, resulting in a decrease in toughness. Therefore, if the steel composition contains Mg, the Mg content is preferably 0.10% or less, and more preferably 0.0010 to 0.0050%.

[0036] REM: 0.10% or less REM (rare earth metals) transform sulfide-based inclusions into oxysulfides, which are highly stable at high temperatures, and act to granulate the sulfide-based inclusions. This morphology control effect of REM can improve the toughness and ductility of steel. However, if the REM content exceeds 0.10%, cleanliness tends to decrease, resulting in a decrease in toughness. Therefore, if the steel composition contains REM, the REM content is preferably 0.10% or less. It is more preferably 0.0010 to 0.0050%.

[0037] W: 1.0% or less W is an element that improves the strength of the base material of the protruding H-section steel by precipitating as carbides during and after hot rolling to form the steel into a protruding H-section steel. However, if its content exceeds 1.0%, it promotes precipitation embrittlement and accelerates upper bainite transformation, which tends to reduce toughness. Therefore, when the steel composition contains W, the W content is preferably 1.0% or less, and more preferably 0.5% or less. There is no particular lower limit for the W content, but in order to achieve the above-mentioned effect of improving the base material strength, it is preferably 0.001% or more.

[0038] Sb: 0.10% or less Sb is an element that has a significant effect of preventing decarburization of steel during reheating of a projection-equipped H-beam steel material in a heating furnace before hot rolling. However, an Sb content exceeding 0.10% adversely affects the ductility and toughness of the steel. Therefore, when the steel composition contains Sb, the Sb content is preferably 0.10% or less, and more preferably 0.05% or less. There is no particular lower limit for the Sb content, but in order to achieve the effect of reducing the decarburized layer, it is preferably 0.001% or more.

[0039] Sn: 0.10% or less Sn is an element that has a significant effect of preventing decarburization of steel during reheating of a projection-equipped H-beam steel material in a heating furnace before hot rolling. However, if the Sn content exceeds 0.10%, it has a negative effect on the ductility and toughness of the steel. Therefore, when the steel composition contains Sn, the Sn content is preferably 0.10% or less, and more preferably 0.05% or less. There is no particular lower limit for the Sn content, but in order to achieve the effect of reducing the decarburized layer, it is preferably 0.001% or more.

[0040] The balance other than the elements described above is Fe and unavoidable impurities. In other words, it is permissible for the balance to contain unavoidable impurities resulting from the conditions of raw materials, materials, or manufacturing facilities. Examples of raw materials include iron ore and scrap. Here, an example of an unavoidable impurity is O (oxygen). O is permissible up to 0.004%. Other unavoidable impurities include Zn, Pb, As, Bi, Co, Ta, Zr, and H. The inclusion of these impurities is permissible as long as it does not impair the objectives of the present invention.

[0041] The protruding H-shaped steel beam of the present invention will be described in detail below. That is, as shown in an example in FIG. 1 , the protruding H-shaped steel beam is formed by connecting a pair of flanges 2 with a web 3, similar to a general H-shaped steel beam. The protruding H-shaped steel beam has protrusions 4 on the flanges 2. In the example in FIG. 1 , the protrusions 4 are provided on the outer surfaces of the flanges 2. These protrusions 4 are provided to impart concrete adhesion performance. In the protruding H-shaped steel beam 1 provided with the protrusions 4 for this purpose, the protrusions 4 are provided on the outer surface of the flange 2, as shown in FIG. 2( a). In the illustrated example, the protrusions 4 are formed as ridges extending in the width direction of the flange 2 and arranged in the longitudinal direction of the flange 2 over the entire outer surface of the flange 2, with a cross-sectional shape shown in FIG. 2( b), which is an enlarged view of the area surrounded by a square in FIG. 2( a).

[0042] Furthermore, the protrusion-equipped H-shaped steel of the present invention may have protrusions 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, protrusions 4 may be provided as ridges extending in the width direction of the flange 2 on the inner surface of the flange 2, including the joint with the web 3. Furthermore, the protrusion-equipped H-shaped steel of the present invention may have protrusions 4 on both the outer surface and inner surface of the flange 2.

[0043] The shape, dimensions, and number of the protrusions can be set as desired depending on the specifications required for the protruding H-section steel. Therefore, although not limited to the illustrated example, it is preferable that the height h of the protrusions 4 be 1.5 mm or more, taking into account 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. Furthermore, it is preferable that the spacing d between the protrusions 4 and the height h satisfy the relationship h / d ≥ 0.05, taking into account concrete adhesion performance.

[0044] Next, a method for manufacturing a protrusion-equipped H-beam steel according to the present invention will be described. There are no particular limitations on the melting and casting methods for the steel material (slab or beam blank), and any conventionally known method is suitable. When hot-rolling the steel material to form an H-beam steel, if protrusions are to be formed on the outer surface of the flange during the finish rolling of the hot rolling, the protrusions can be formed by using vertical rolls that roll down the outer surface of the flange, with grooves formed on the circumferential surface of the vertical rolls that correspond to the protrusions. Furthermore, if protrusions are to be formed on the inner surface of the flange, similar to the technology disclosed in Patent Document 3, the protrusions can be formed by using horizontal rolls that roll down the inner surface of the flange, with grooves formed on the side surfaces of the horizontal rolls that correspond to the protrusions. In this case, the heating temperature of the steel material and the cooling after finish rolling must satisfy the following conditions.

[0045] 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 the 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 process will remain, making it difficult to ensure the effective amount of solute N, and as a result, it becomes difficult to ensure the desired tensile strength and toughness. Therefore, the heating temperature is set to a temperature range that satisfies the above formula (2). On the other hand, the upper limit of the heating temperature is preferably set to 1400°C or less from the viewpoint of preventing a decrease in toughness due to excessive coarsening of austenite grains.

[0046] 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 to 750°C or higher, with the aim of preventing a decrease in production efficiency by starting cooling of the steel material immediately after finish rolling. On the other hand, if the flange temperature at the start of cooling is below the Ar3 temperature, it becomes difficult to obtain sufficient strength, so it is preferable that the flange temperature at the start of cooling be set to the Ar3 temperature or higher. The Ar3 transformation temperature can be simply expressed in relation to the steel composition, for example, by the following equation (3). Ar3=910-310×[%C]+25×([%Si]+2×[%Al])-80×[Mneq] ···(3) Here, [Mneq] is a value calculated using the following equation (4). [Mneq]=[%Mn]+[%Cr]+[%Cu]+[%Mo]+[%Ni] / 2+10×([%Nb]-0.02)... (4)

[0047] In the above formulas (3) and (4), [%M] means the content (mass%) of element M in steel. When calculating Ar3 in the above formulas (3) and (4), the content of element M that is not intentionally added is calculated using the content (analytical value) of element M that is contained as an unavoidable impurity.

[0048] Average cooling rate from the cooling start temperature to 500°C: 0.2 to 30.0°C / s If the average cooling rate from the cooling start temperature to 500°C is less than 0.2°C / s, it is difficult to ensure the specified tensile properties, so the cooling rate is set to 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 will cause 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 set to a range of 0.2 to 30.0°C / s.

[0049] As a specific cooling method after finish rolling, spray cooling in which cooling water is sprayed onto the outer surface of the flange using a spray nozzle, mist cooling in which mist-like water is sprayed using a mist cooling nozzle, air blast cooling in which air is sprayed using an air nozzle, or convection cooling that utilizes air convection accompanying the transportation of the material can be appropriately selected.

[0050] By adjusting the chemical composition as described above and rolling and cooling under the conditions described above, it is possible to obtain a projection H-section steel with excellent mechanical properties, such as a tensile strength of 520 MPa or more, a yield strength of 355 MPa or more, and an impact absorption energy vE0 at 0°C of 47 J or more. There is no need to specify upper limits for any of these properties, but practical upper limits are approximately 720 MPa for the tensile strength, 580 MPa for the yield point, and 350 J for the impact absorption energy vE0 at 0°C.

[0051] Here, the flange thickness of the protrusion-equipped H-section steel targeted by the present invention is not particularly limited. The flange protrusions are formed using grooved rolls in the finish rolling process. That is, in order to impart the desired protrusion height, it is necessary to maximize the reduction ratio of the flange portion. Therefore, protrusion-equipped H-section steel with a thick flange requires a larger reduction ratio. In the present invention, as described below, by controlling the rolling temperature within an appropriate range, it is possible to impart sufficient protrusion height even to thick H-section steel with a flange thickness of 16 mm or more, which is considered to have a low efficiency in forming protrusion height.

[0052] In finish rolling, which includes forming protrusions during hot rolling, the finish rolling temperature is preferably 800°C or higher from the viewpoint of forming protrusions with sufficient 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, although there is no particular upper limit for the finishing temperature, if it exceeds 1050°C, the austenite grain size becomes coarse, which tends to reduce toughness. Therefore, the finishing temperature is preferably 1050°C or lower. [Example]

[0053] The following examples will explain the structure and effects of the present invention in more detail. However, the present invention is not limited to the following examples, and appropriate modifications can be made within the scope of the present invention, and all such modifications are within the technical scope of the present invention.

[0054] Steel material with the chemical composition shown in Table 1 was cast in a continuous casting machine to form a beam blank with a cross section of 400 mm x 560 mm x 8000 mm in length. After heating at a predetermined temperature for two hours, the blank was hot-rolled and cooled under the conditions shown in Table 2 to produce the protruding H-beam 1 shown in Figure 1, i.e., a shape having a web 3 and a pair of flanges 2 disposed at both ends of the web. The protruding H-beam was produced with one of four cross-sectional dimensions (web height x flange width x web thickness x flange thickness): 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 35 x 40 mm. In the finish rolling, a rolling roll with grooves corresponding to the protrusion shape to be formed on the outer flange surface was used to reduce the flange outer surface, forming protrusions 4 extending in the width direction of the flange 2 on the outer flange surface, as shown in Figure 2.

[0055] Here, the vertical rolls for finish rolling that roll down the outer surface of the flange were provided with grooves that could 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 was calculated by measuring the surface temperature of the outer surface of the flange at 1 / 6B part of the flange (see Figure 1) with a radiation thermometer and converting the temperature change from the start to the end of cooling into a value per unit time (seconds) to determine the cooling rate (°C / s).

[0056] [Table 1]

[0057] The obtained H-section steel with projections was subjected to projection height evaluation, tensile testing, and toughness testing. Each evaluation is explained in detail below.

[0058] <Protrusion height evaluation> The projection height h on the outer surface of the flange of the obtained projection H-section steel, shown in Figure 2, was measured. This value was measured at three locations in the rolling direction of the projection H-section steel after finish rolling: the tip, center, and tail, and the average value was used. The lower limit of the required performance for projection height was set at 1.5 mm, and values ​​above this value were defined as the preferred range for projection height h. Furthermore, the manufacturing conditions under which projection H-section steel with a projection height h of this value or more was obtained can be evaluated as particularly preferred conditions from the perspective of ease of projection formation.

[0059] <Tensile test> A JIS 1A test piece (full flange thickness test piece) specified in JIS Z2201 was taken from the flange 1 / 6B portion (60 mm in length in the flange width direction sandwiching 1 / 6B) shown as reference numeral 5 in Figure 1 so that the tensile direction was the longitudinal direction of the flange of the H-shaped steel. A tensile test was conducted in accordance with JIS Z2241 to measure the yield strength (yield stress YS or 0.2% proof stress) and tensile strength.

[0060] <Toughness test> A 2 mm V-notch Charpy impact test specimen as specified in JIS Z2202 was taken from the flange 1 / 6B part 5 shown in Figure 1, centered at a position 1 / 4t (t is the flange thickness) from the back surface of the flange. A Charpy impact test was performed in accordance with JIS Z2242, and the absorbed energy at 0°C was measured.

[0061] The results of the above investigation are also shown in Table 2. Test results (Test Nos. 1 to 17 and 39 to 42 in Table 2) of H-beams with projections, which were fabricated using suitable steel satisfying the steel composition of the present invention and by manufacturing methods within the scope of the present invention (heating temperature and average cooling rate on the flange outer surface within the scope of the present invention), all satisfied the desired properties (tensile strength: 520 MPa or more, yield strength: 355 MPa or more, and impact absorption energy at 0°C vE0: 47 J or more). Test No. 34 satisfied the desired properties for 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 projection height was 1.4 mm, which was below the preferred range (1.5 mm or more).

[0062] On the other hand, in the comparative examples (Test Nos. 18 to 33, 35 to 38 in Table 2) in which the steel composition of the H-shaped steel did not satisfy the conditions of the present invention or the manufacturing method within the scope of the present invention was not applied, the values ​​of any of the tensile strength, yield strength, and toughness did not satisfy the required properties.

[0063] Furthermore, although this embodiment is an example of a case where a protrusion is formed on the outer surface of the flange of an H-shaped steel, it has been confirmed that similar results can be obtained by following the present invention when a protrusion is formed on the inner surface of the flange of an H-shaped steel.

[0064] [Table 2] [Explanation of symbols]

[0065] 1: H-beam with projections (rolled H-beam) 2: Flange 3: Web 4: Protrusion 5: Flange 1 / 6B (test specimen collection position)

Claims

1. C: 0.10 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 0.120% by mass, Ti: 0.005 to 0.040 mass% and N: over 0.0100 mass% to 0.0200 mass% in a range that satisfies the following formula (1), with the remainder consisting of Fe and unavoidable impurities, and has a component composition including protrusions on the flanges, and has a tensile strength of 520 MPa or more, a yield strength of 355 MPa or more, and an impact absorption energy vE0 at 0°C of 47 J or more. Note 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.

2. 2. The protruding H-section steel according to claim 1, wherein the chemical composition further contains one or more selected from Cr: 1.0 mass% or less, Cu: 1.0 mass% or less, Ni: 1.0 mass% or less, Mo: 1.0 mass% or less, Al: 0.10 mass% or less, Nb: 0.10 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.

3. A method for manufacturing a protruding H-shaped steel beam, comprising hot rolling a steel material having the component composition according to claim 1 or 2 to form a protruding H-shaped steel beam, The method for producing protrusion-equipped H-section steel includes heating the steel material to a temperature T that satisfies the following formula (2), and then subjecting it to the hot rolling. Protrusions are formed on the flanges of the H-section steel by finish rolling of the hot rolling. After the finish rolling, the steel is cooled 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 the common logarithm.

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