KR102602081B1 - H-beam having protrusions, and manufacturing method for same - Google Patents

Abstract

An H-beam with protrusions that can secure tensile strength and suppress the occurrence of surface cracks during continuous casting, thereby dramatically improving manufacturability, is provided along with its manufacturing method. C: 0.05 to 0.20 mass%, Si: 0.05 to 0.60 mass%, Mn: 1.20 to 1.70 mass%, P: 0.035 mass% or less, S: 0.035 mass% or less, Nb: 0.005 to 0.050 mass%, V: 0.005 to 0.005 mass% 0.050 mass%, Ti: 0.005 to 0.030 mass%, and N: 0.0020 to 0.0100 mass%, ([%S]/32)/([%Ti]/48)+4×([%N]/14)/( [%Ti]/48) ≤ 15.0, and the steel composition is made up of Fe and inevitable impurities, with a tensile strength of 490 MPa or more and a yield strength of 355 MPa or more at 0°C. The shock absorption energy vE0 is set to 27J or more.

Description

H-beam steel with protrusions and manufacturing method thereof {H-BEAM HAVING PROTRUSIONS, AND MANUFACTURING METHOD FOR SAME}

The present invention relates to a protruding H-beam steel and a manufacturing method thereof. In addition to excellent mechanical properties such as tensile strength and elongation, it is an alternative to reinforcing bars used as reinforcing materials for large structures such as bridges, and has excellent toughness. , relates to protruding H-beam steel and its manufacturing method.

Reinforced concrete using reinforcing bars as reinforcement is widely used in large structures such as bridge piers. In general, construction of a reinforced concrete structure is performed by assembling the reinforcing bars, installing a form, and pouring concrete into the form. Here, when excessive installation of reinforcing bars is necessary for strength reasons, the fillability of concrete decreases, not only deteriorating construction quality, but also prolonging construction, which is a major problem. In addition, the number of skilled workers engaged in construction tends to decrease every year, and there is a greater need for the development of structural steel that contributes to labor saving in field work and shortening the construction period.

In response to such requests, various studies are being conducted on protruding H-beam steel, which has greater cross-sectional rigidity than reinforcing bars and makes it possible to reduce the number of members required in the same structure. This protruded H-beam steel has protrusions formed on the outer surface of the flange, and is known to have high concrete adhesion performance equal to or higher than that of rebar. For H-beams with protrusions used in large structures as a replacement for rebar, in order to guarantee performance as a structure, guarantee of toughness is required in addition to mechanical properties such as tensile strength and elongation.

In order to satisfy these requirements, for example, Patent Document 1 discloses an H-beam steel with protrusions in which the tensile strength and toughness are improved in a good balance by adjusting the addition amounts of Nb, V, and Ni in the steel. In addition, Patent Document 2 discloses a technique for setting the optimal cooling stop temperature according to the flange thickness and appropriately adjusting the amount of coolant on the inner and outer surfaces of the flange for the purpose of improving the toughness of protruding H-beam steel. It is done.

Japanese Patent No. 4045977 Publication Japanese Patent Publication No. 2006-75883

However, the protruding H-beam steel described in the above-mentioned Patent Documents 1 and 2 aims to achieve both high tensile strength and toughness by adding Nb or V, which forms carbonitride, but it is impossible to manufacture a rolled material by continuous casting. At this time, there was a problem that defects on the surface of the cast steel, called continuous casting cracks, were likely to occur, which lowered manufacturability. The present invention was made to advantageously solve the above-mentioned problem, and manufactures a protruded H-beam steel that can dramatically improve manufacturability while securing tensile strength equivalent to or higher than that of conventional protruded H-beam steel. The purpose is to provide along with the method.

The present inventors produced protrusive H-beam steel with varying contents of C, Si, Mn, P, S, Nb, V, Ti, and N, and intensively investigated its tensile properties and toughness. As a result, it was found that when Nb or V was contained in the steel, the rate of occurrence of continuous casting cracks was high. In addition, by optimizing the amounts of S, Ti, and N contained in the steel, continuous casting cracking can be stabilized and suppressed even when Nb and V are included, and intragranular ferrite transformation with TiN as the nucleus can be achieved. It was discovered that excellent toughness was obtained by acceleration.

The present invention, based on the above recognition, has its main structure as follows.

1. C: 0.05 to 0.20 mass%, Si: 0.05 to 0.60 mass%, Mn: 1.20 to 1.70 mass%, P: 0.035 mass% or less, S: 0.035 mass% or less, Nb: 0.005 to 0.050 mass%, V: Contains 0.005 to 0.050 mass%, Ti: 0.005 to 0.030 mass%, and N: 0.0020 to 0.0100 mass% in a range that satisfies the following formula (1), the balance has a steel composition of Fe and inevitable impurities, and the tensile strength is H-beam steel with protrusions having a strength of 490 MPa or more, a yield strength of 355 MPa or more, and an impact absorption energy vE0 at 0°C of 27 J or more.

energy

([％S]/32)/([％Ti]/48)+4×([％N]/14)/([％Ti]/48)≤15.0… (One)

Here, [%S], [%Ti], and [%N] are the contents (% by mass) of S, Ti, and N in the steel, respectively.

2. The steel composition further includes 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, and B: 0.010 mass%. Hereinafter, the protruded H-beam steel described in 1 above, containing one or two or more types selected from Ca: 0.10 mass% or less, Mg: 0.10 mass% or less, and REM: 0.10 mass% or less.

3. The protrusion is an H-beam having the protrusion described in 1 or 2 above and having a height of 1.5 mm or more.

4. A method for manufacturing a protruded H-beam steel, which involves hot rolling a steel material having the steel composition described in any one of 1 or 2 above to form the protruded H-beam steel,

Protrusions are formed on the outer surface of the flange of the H-beam steel by the finish rolling of the hot rolling, and after the finish rolling, the temperature is cooled from a cooling start temperature of 750°C or higher to 500°C under the condition of an average cooling rate of 0.1 to 30°C/s. Manufacturing method of H-beam steel with cooling protrusions.

5. The method for manufacturing the protruded H-beam steel according to 4 above, wherein the finish rolling is performed at a temperature of 800°C or higher.

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

Figure 1 shows a cross-sectional view of an H-beam with protrusions.
Figure 2 is a view showing an H-beam with protrusions, where (a) is a side view seen from the opposite direction of the web, (b) is a top view seen from the opposite direction of the outer surface of the flange, and (c) is a top view of the outer surface of the flange. , respectively.

(Best mode for carrying out the invention)

Hereinafter, the present invention will be described in detail. First, in the present invention, the reason why the steel composition is limited to the above range will be explained. In addition, “%” in the following description shall represent “mass%” unless otherwise specified.

C: 0.05 to 0.20%

C is an element necessary to ensure base material strength and must be contained at least 0.05%. However, if the C content exceeds 0.20%, not only does the base material toughness decrease, but also weldability decreases. Therefore, in the present invention, the C content is set to 0.05 to 0.20%. Additionally, the C content is preferably 0.10% or more. Additionally, it is preferable that the C content is 0.15% or less.

Si: 0.05 to 0.60%

Si needs to be contained at 0.05% or more to ensure base material strength and as a deoxidizing agent, but if the Si content exceeds 0.60%, in addition to a decrease in toughness, weldability deteriorates due to the high bonding power of Si with oxygen. Therefore, in the present invention, the Si content is set to 0.05 to 0.60%. Additionally, the Si content is preferably 0.20% or more. Additionally, it is preferable that the Si content is 0.40% or less.

Mn: 1.20 to 1.70%

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 the Mn content is less than 1.20%, the effect of its addition is small, while if it exceeds 1.70%, upper bainite transformation is promoted and toughness is lowered, which is not preferable. Therefore, in the present invention, the Mn content is set to 1.20 to 1.70%. Additionally, the Mn content is preferably 1.40% or more. Additionally, 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 in steel is set to 0.035% or less. Preferably it is 0.020% or less. On the other hand, since the smaller the amount of P, the more preferable it is, 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 excessive P reduction causes an increase in refining time and an increase in cost, so it is desirable that the P content is 0.005% or more. do.

S: 0.035% or less

When S is contained in steel, it mainly exists in the steel in the form of A-type inclusions. When the S content exceeds 0.035%, the amount of inclusions increases significantly, and at the same time, coarse inclusions are generated, which greatly reduces the toughness of the steel. Therefore, in the present invention, the S content in steel is set to 0.035% or less. Preferably it is 0.020% or less. On the other hand, since the smaller the amount of S, the more desirable it is, the lower limit of the S content is not particularly limited and may be 0%. In addition, S is usually an element that is inevitably contained in steel as an impurity, and excessive reduction of S leads to an increase in refining time and an increase in cost, so it is preferable that the S content is 0.002% or more.

Nb: 0.005 to 0.050%

Nb is an element that has the effect of improving tensile strength and yield point by precipitating as carbonitride. In order to obtain this effect, the Nb content needs to be 0.005% or more. On the other hand, when the Nb content exceeds 0.050%, in addition to promoting precipitation embrittlement, it also promotes upper bainite transformation, so continuous casting cracks are likely to occur and toughness also decreases. Therefore, in the present invention, the Nb content is set to 0.005 to 0.050%. Additionally, the Nb content is preferably 0.010% or more. Additionally, the Nb content is preferably 0.030% or less.

V: 0.005 to 0.050%

V is an element that has the effect of improving tensile strength and yield point by precipitating as carbonitride. In order to obtain this effect, the V content needs to be 0.005% or more. On the other hand, if the V content exceeds 0.050%, precipitation embrittlement is promoted and continuous casting cracks are likely to occur. Therefore, in the present invention, the V content is set to 0.005 to 0.050%. Additionally, the V content is preferably 0.010% or more. Additionally, it is preferable that the V content is 0.030% or less.

Ti: 0.005 to 0.030%

Ti is a useful element that is effective in preventing surface cracks during bending and bending return during continuous casting, and is actively added in a range of 0.005% or more. In addition, Ti is an element that is effective in forming TiN in steel to refine austenite grains, further refining the microstructure by promoting intra-grain ferrite transformation with TiN as the nucleus, and improving toughness. On the other hand, it is not preferable that the Ti content exceeds 0.030% because coarse TiN is generated and the toughness of the steel is reduced. Therefore, in the present invention, the Ti content is set to 0.005 to 0.030%. Additionally, the Ti content is preferably 0.010% or more. Additionally, the Ti content is preferably 0.020% or less.

N: 0.0020 to 0.0100%

N is a useful element that forms carbonitrides in steel and improves the strength of steel, and its content must be 0.0020% or more. However, when the N content exceeds 0.0100%, the formed carbonitride coarsens and reduces the toughness of the steel. Additionally, if the N content exceeds 0.0100%, it is not preferable because surface cracks of the cast steel occur and the quality of the cast steel deteriorates. Therefore, in the present invention, the N content is set to 0.0020 to 0.0100%. Additionally, the N content is preferably 0.0030% or more. Additionally, it is preferable that the N content is 0.0070% or less.

In addition, in the present invention, it is not enough for each element to simply satisfy the above range, and for S, Ti, and N, [%S], [%Ti], and [%N] are respectively defined as S in steel. , it is important to satisfy the relationship of the following equation (1) when considering the content (mass %) of Ti and N.

([％S]/32)/([％Ti]/48)+4×([％N]/14)/([％Ti]/48)≤15.0… (One)

The inventors investigated the causes of cracks in steel during continuous casting and found that precipitation of coarse carbonitrides of MnS, V, and Nb into ferrite formed at austenite grain boundaries during continuous casting. , it was recognized that it was the cause of the crack. Therefore, studies were conducted to suppress the precipitation of MnS, V, and Nb-based carbonitrides in the ferrite, and as a result, by adjusting the contents of S, Ti, and N in the steel, MnS, V, and Nb-based carbonitrides in the grain boundary ferrite were removed. It was found that precipitation could be suppressed and cracking during continuous casting could be suppressed. That is, by ensuring that the value calculated from the left side of equation (1) above, which is a parameter based on the contents of S, Ti, and N, does not exceed 15.0, S is precipitated as Ti carbosulfide and N is precipitated as TiN during continuous casting. Precipitation of coarse MnS, V, and Nb-based carbonitrides into ferrite generated at austenite grain boundaries can be suppressed, and continuous casting cracks can be stably suppressed. In addition, it is more preferable that the right-hand side in the above equation (1) is set to 10.0 or less, that is, satisfying the following equation (1)'.

([％S]/32)/([％Ti]/48)+4×([％N]/14)/([％Ti]/48)≤10.0… (One)'

The steel composition of the protruded H-beam steel used in the present invention consists of Fe and inevitable impurities other than the components described above.

In addition, in the protruding H-beam steel of the present invention, in addition to the components described above, for the purpose of improving strength, ductility, toughness, and weld zone characteristics, 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, B: 0.010% or less, Ca: 0.10% or less, Mg: 0.10% or less, and REM: 0.10% or less. good night.

Hereinafter, the reason for specifying the content of the above elements will be explained.

Cr: 1.0% or less

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

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 cracks are likely to occur. Therefore, when the component composition of the steel contains Cu, the Cu content is set to 1.0% or less. More preferably, it is 0.005% or more and 0.5% or less.

Ni: 1.0% or less

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

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 is generated in the steel, and toughness tends to decrease. Therefore, when the component composition contains Mo, the Mo content is set to 1.0% or less. More preferably, it is 0.005% or more and 0.5% or less.

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-based inclusions are generated in the steel due to the high bonding force of Al with oxygen, and as a result, the ductility of the steel decreases. Therefore, when the steel composition contains Al, the Al amount is preferably set to 0.10% or less. Meanwhile, the lower limit of the Al content is not particularly limited, but for deoxidation, it is preferably set to 0.001% or more. More preferably, it is 0.001% or more and 0.03% or less.

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. In addition, it is an element that is effective in improving toughness by forming complex precipitates with TiN, which becomes the nucleation site of ferrite in the grains, and refining the microstructure. On the other hand, if its content exceeds 0.010%, toughness decreases due to grain boundary precipitation of coarse carbonitrides. Therefore, when the steel composition contains B, the B content is set to 0.010% or less. More preferably, it is 0.001% or more and 0.003% or less.

Ca: 0.10% or less

Ca has the effect of transforming oxides and sulfides in sulfide-based inclusions into ones with high stability at high temperatures and forming sulfide-based inclusions into particle shapes. And, the shape control effect of this Ca can improve the toughness and ductility of the steel. However, if the Ca content exceeds 0.10%, the cleanliness decreases and the toughness tends to decrease. Therefore, when the steel composition contains Ca, the Ca content is set to 0.10% or less. More preferably, it is 0.0010% or more and 0.0050% or less.

Mg: 0.10% or less

Mg has the effect of transforming oxides and sulfides in sulfide-based inclusions into particles with high stability at high temperatures. And, the shape control effect of this inclusion by Mg can improve the toughness and ductility of the steel. However, when the Mg content exceeds 0.10%, cleanliness decreases and toughness tends to decrease. Therefore, when the steel composition contains Mg, the Mg content is set to 0.10% or less. More preferably, it is 0.0010% or more and 0.0050% or less.

REM: 0.10% or less

REM (rare earth metal) has the effect of transforming oxides and sulfides in sulfide-based inclusions into ones with high stability at high temperatures and shaping sulfide-based inclusions into particles. And, the effect of controlling the shape of inclusions by this REM can improve the toughness and ductility of the steel. However, when the REM content exceeds 0.10%, cleanliness decreases and toughness tends to decrease. Therefore, when the steel composition contains REM, the REM content is set to 0.10% or less. More preferably, it is 0.0010% or more and 0.0050% or less.

The remainder other than the elements described above is Fe and inevitable impurities.

The protruding H-beam of the present invention will be described in detail. That is, as shown in FIG. 1, the protruding H-beam steel is formed by connecting a pair of flanges 2 with a web 3, like a general H-beam steel. And the protruded H-beam steel has protrusions (4) on the outer surface of the flange (2). This projection 4 is formed to provide concrete adhesion performance. In the protruding H-beam 1 in which the protrusion 4 is formed for this purpose, the location where the protrusion 4 is formed is the outer surface of the flange 2, as shown in FIG. 2(a). In the illustrated example, the entire outer surface of the flange 2 extends in the width direction of the flange 2 in the cross-sectional shape shown in the same figure (b), which is an enlarged view of the portion surrounded by a square in Figure 2 (a). It is formed by arranging protrusions 4 as ridges in the longitudinal direction of the flange 2.

In addition, the shape, size, number, etc. of the protrusions can be arbitrarily set according to the specifications required for H-beam steel with protrusions. Therefore, although it is not limited to the illustrated example, for example, it is preferable that the height h of the protrusion 4 is 1.5 mm or more considering concrete adhesion performance. On the other hand, the upper limit of the height (h) is preferably set to 6 mm from the viewpoint of preventing roll damage. In addition, considering the concrete adhesion performance, the spacing d between the protrusions 4 preferably satisfies the relationship of h/d ≥ 0.05 with the height h.

Next, the manufacturing method of the protruding H-beam steel of the present invention will be described. There are no particular restrictions on the melting method and casting method of steel (slab or beam blank), and all conventionally known methods are suitable. Additionally, the hot rolling conditions for forming H-beam steel are not particularly limited, and may be performed according to general methods. In hot rolling finish rolling, projections can be formed by using a roll that presses down the portion (outer surface of the flange) on which projections are to be formed, and grooves corresponding to the projections to be formed are formed on the roll surface. After finish rolling, it is necessary to perform cooling that satisfies the following conditions.

Flange temperature at start of cooling: 750℃ or higher

In the present invention, it is intended to prevent a decrease in production efficiency by starting cooling of the steel material immediately after finish rolling, and the flange temperature at the start of cooling is set to 750°C or higher. On the other hand, if the flange temperature at the start of cooling is lower than the Ar ₃ temperature, it becomes difficult to obtain sufficient strength, so it is preferable to further set the flange temperature at the start of cooling to the Ar ₃ temperature or higher. In addition, the Ar ₃ transformation temperature is simply expressed in relation to the steel components, for example, by equation (2) below.

Ar ₃ = 910-310×[％C]+25×([％Si]+2×[％Al])－80×[Mneq]… (2)

Here, [Mneq] is a value calculated using the following equation (3).

[Mneq]=[％Mn]+[％Cr]+[％Cu]+[％Mo]+[％Ni]/2＋10×([％Nb]－0.02)… (3)

In addition, in the above equations (2) and (3), [%M] means the content (mass%) of element M in the steel. Here, when calculating Ar ₃ using equations (2) and (3) above, the content of element M (analysis value) contained as an inevitable impurity is used for the content of element M that is not actively included. It is calculated by doing so.

Average cooling rate from cooling start temperature to 500℃: 0.1∼30℃/s

If the average cooling rate from the cooling start temperature to 500°C does not meet 0.1°C/s, it is difficult to secure the desired tensile properties and toughness, so the cooling rate is set to 0.1°C/s or more. On the other hand, if the cooling rate exceeds 30°C/s, negative effects such as a decrease in toughness and an excessive increase in tensile strength may occur due to the formation of bainite or martensite, so the average from the cooling start temperature to 500°C The cooling rate is in the range of 0.1 to 30°C/s. A preferable average cooling rate is in the range of 0.5 to 10°C/s.

By adjusting the composition to the above-mentioned composition and performing rolling and cooling according to the above-described conditions, the H-beam steel with protrusions has a tensile strength of 490 MPa or more, a yield strength of 355 MPa or more, and shock absorption at 0°C. Excellent mechanical performance can be obtained, with an energy vE0 of 27J or more. There is no need to specify an upper limit for any characteristic, but in practical terms, the tensile strength is 640 MPa, the yield strength is 475 MPa, and the impact absorption energy vE0 at 0°C is about 350 J.

Here, the flange thickness of the protruded H-beam targeted by the present invention is not particularly limited. The projections on the outer surface of the flange are formed using a grooved roll in the finish rolling process. That is, in order to provide the desired protrusion height, it is necessary to increase the reduction amount of the flange portion as much as possible. Therefore, protruding H-beams with thick flanges require greater reduction. In the present invention, as described later, by controlling the rolling temperature to an appropriate range, sufficient protrusion height can be provided even in thick H-beam steel with a flange thickness of 16 mm or more, where the formation efficiency of protrusion height is said to be reduced.

In finish rolling, which involves forming protrusions during hot rolling, it is desirable to set the finish rolling temperature to 800°C or higher from the viewpoint of forming protrusions with sufficient protrusion height. If the finish rolling temperature does not meet 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, so toughness tends to decrease. Therefore, it is preferable that the finishing temperature is 1050°C or lower.

Example

Hereinafter, the configuration and operational effects of the present invention will be described in more detail according to examples. However, the present invention is not limited by the following examples, and appropriate changes can be made within the scope suitable for the purpose of the present invention, and all of them are included in the technical scope of the present invention.

Steel materials with the composition shown in Table 1 were used as beam blanks with a cross section of 400 mm × 560 mm × length of 8000 mm in a continuous casting machine, and the presence or absence of cracks on the surface was examined. That is, the surface of the beam blank was observed in the longitudinal direction and the presence or absence of cracks of 10 mm or more in length was investigated. Surface cracks are evaluated by calculating the number of cracks per 1 m2 and using the following indices: A: no cracks, B: 1 to 4 cracks/m2, C: 5 or more cracks/m2, and based on these indices, an A or B decision is made. I passed it. Table 1 also shows the determination results of surface cracks. For steels whose compositions satisfied the formula (1) above, the surface crack determination result was A or B.

Next, among these beam blanks, those with a surface crack determination result of A or B were heated at 1250°C for 2 hours, then hot rolled and cooled under the conditions shown in Table 2 to obtain the cross-sectional shape shown in FIG. 1, that is, An H-beam steel (1) having a protrusion shaped like 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 manufactured. In the finish rolling, a rolling roll for pressing the outer surface of the flange, with grooves corresponding to the protrusions to be formed on the outer surface of the flange, is used to form a groove corresponding to the shape of the protrusion to be formed on the outer surface of the flange, in the width direction of the flange 2 as shown in FIG. 2. A protrusion (6) extending in series was formed. Here, grooves capable of forming protrusions of a protrusion width (w) of 15 mm and a protrusion height (h) of 1.5 mm or more are formed in the finish rolling roll for pressing the outer surface of the flange. The cooling rate after finish rolling is calculated by measuring the temperature of the outer surface of the flange with a radiation thermometer and converting the temperature change from the start of cooling to the stop of cooling into per unit time (seconds) to calculate the cooling rate (°C/s). did.

For the obtained H-beam with protrusions, protrusion height evaluation, tensile test, and toughness test were performed. Below, each evaluation content is explained in detail.

<Evaluation of protrusion height>

For the obtained protruded H-beam, the protrusion height (h) 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 protruded H-beam after finish rolling: the leading end, the central part, and the tail end, and the average value was adopted. In addition, the lower limit of the required performance of the protrusion height was set to 1.5 mm, and the appropriate range for the protrusion height (h) was set above this value. In addition, the manufacturing conditions under which a protruded H-beam steel with a protrusion height (h) equal to or greater than this value can be evaluated as particularly preferable conditions from the viewpoint of ease of protrusion formation.

<Tensile test>

From the flange 1/6B portion (flange width direction length 60 mm with 1/6B sandwiched between 1/6B) shown as symbol 5 in FIG. 1, a JIS1A test piece (flange) specified in JIS Z2201 is formed so that the tensile direction is in the flange longitudinal direction of the H-beam steel. A full thickness test piece) was taken, a tensile test was performed according to JIS Z2241, and the yield strength (yield stress YS or 0.2% proof stress) and tensile strength were measured.

<Toughness test>

Centering on the position of 1/4t (t is the flange thickness) from the back surface of the flange of the flange 1/6B portion (5) shown in Figure 1, a 2 mm V notch Charpy impact test piece specified in JIS Z2202 was taken, and the test piece was tested in JISZ2242. A Charpy impact test was performed accordingly to measure the absorbed energy at 0°C.

Table 2 also shows the results of the above survey. Test results of protruded H-beam steel manufactured by a manufacturing method within the scope of the present invention (the average cooling rate of the outer surface of the flange is within the scope of the present invention) using a suitable steel that satisfies the steel composition of the present invention (Test No. 2 in Table 2). 1 to 19 and 31) all satisfied the desired characteristics (tensile strength: 490 MPa or more, yield strength: 355 MPa or more, and impact absorption energy vE0 at 0°C: 27 J or more). Additionally, test no. 33 satisfies the desired properties for tensile strength, yield strength, and impact absorption energy at 0°C, but because the finish rolling temperature was below the lower limit of 800°C, the protrusion height was 1.4 mm, which was within the suitable range. (1.5 mm or more) was not met.

On the other hand, in the comparative examples (Test Nos. 20 to 30 and 32 to 34 in Table 2) in which the steel composition of the H-beam did not satisfy the conditions of the present invention or did not apply the manufacturing method within the scope of the present invention, the tensile strength was , any one of the yield strength and toughness does not satisfy the required characteristics.

1: H-beam steel with protrusions (rolled H-beam steel)
2: Flange
3: web
4: protrusion
5: Flange 1/6B part (test specimen collection location)

Claims (5)

C: 0.05 to 0.20 mass%, Si: 0.05 to 0.60 mass%, Mn: 1.20 to 1.70 mass%, P: 0.035 mass% or less, S: 0.035 mass% or less, Nb: 0.005 to 0.050 mass%, V: 0.005 to 0.005 mass% Contains 0.050% by mass, Ti: 0.005 to 0.030% by mass, and N: 0.0020 to 0.0100% by mass in a range that satisfies the following formula (1), the balance has a steel composition of Fe and inevitable impurities, and the tensile strength is 490%. A protruding H-beam steel having a protrusion on the outer surface of the flange, having a yield strength of 355 MPa or more and an impact absorption energy vE0 at 0° C. of 27 J or more, wherein the height of the protrusion is 1.5 mm or more and 6 mm or less. , an H-beam steel with protrusions in which the height h of the protrusions and the distance d between the protrusions satisfy the following equation (1A).
energy
([％S]/32)/([％Ti]/48)+4×([％N]/14)/([％Ti]/48)≤15.0… (One)
Here, [%S], [%Ti], and [%N] are the contents (% by mass) of S, Ti, and N in the steel, respectively.
h/d≥0.05... (1A) According to paragraph 1,
The steel composition further includes 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, B: 0.010 mass% or less, H-beam steel with protrusions containing one or two or more types selected from Ca: 0.10 mass% or less, Mg: 0.10 mass% or less, and REM: 0.10 mass% or less. delete A method of manufacturing an H-beam steel with protrusions according to claim 1 or 2,
A method for manufacturing a protruded H-beam steel, wherein a steel material having the steel composition according to any one of claims 1 or 2 is subjected to hot rolling to form a protruded H-beam steel,
In the finish rolling of the hot rolling, protrusions are formed on the outer surface of the flange of the H-shaped steel by using a roll that presses down the portion (outer surface of the flange) on which the protrusions are formed, and grooves corresponding to the protrusions to be formed are formed on the roll surface. A method of manufacturing H-beam steel with protrusions in which, after the finish rolling, cooling is performed from a cooling start temperature of 750°C or higher to 500°C under the conditions of an average cooling rate of 0.1 to 30°C/s. According to paragraph 4,
A method of manufacturing H-beam steel with protrusions, wherein the finish rolling is performed at a temperature of 800° C. or higher.