JP6589503B2 - H-section steel and its manufacturing method - Google Patents

Description

  The present invention relates to an H-section steel having a flange thickness of 40 mm or more used for a structural member of a building and the like, and a method for manufacturing the same.

  In recent years, buildings such as high-rise buildings have been increased in size and height, and thick steel materials are used as main structural strength members. However, in general, as the thickness of a product increases, it is difficult to ensure the strength of the steel material, and the toughness tends to decrease. In addition, when manufacturing thick steel plates by hot rolling, if accelerated cooling is applied after hot rolling, the cooling rate inside the steel plate will be slower than the surface of the steel plate, and the temperature history between the surface and inside of the steel plate will increase. A large difference occurs, and mechanical properties such as strength, ductility, and toughness may vary depending on the portion of the steel sheet.

  Furthermore, when a thick steel plate is welded, the heat input increases, and the toughness of the weld heat affected zone (hereinafter sometimes referred to as HAZ) may be reduced. To solve this problem, after hot rolling, even if it is allowed to cool, uniform mechanical properties can be obtained, and in order to ensure the toughness of HAZ, the amount of C is reduced, and B is added to improve the hardenability. Has been proposed to obtain a metal structure mainly composed of bainite (see, for example, Patent Documents 1 and 2).

  By the way, for large buildings, it is desired to use H-shaped steel with a flange thickness of 40 mm or more. However, H-shaped steel has a unique shape, and when rolling by universal rolling, rolling conditions ( Temperature, rolling reduction). Therefore, especially when manufacturing H-section steel, compared with a thick steel plate, the difference of the mechanical characteristics in each site | parts, such as a web, a flange, a fillet, may become large.

  For such a problem, there is a method of reducing the amount of C, hot rolling a steel piece to which Nb, Ti, and B are added and then allowing it to cool to ensure uniform mechanical properties and excellent HAZ toughness. Have been proposed (see, for example, Patent Document 3). In addition, the amount of Mn is increased, B is added, and the pinning effect that suppresses the growth of austenite crystal grains due to fine MgS is utilized. After hot rolling, air cooling is performed to produce bainite. A method of increasing strength and toughness has been proposed (see, for example, Patent Document 4).

JP-A-8-144019 JP-A-11-269602 JP-A-11-172373 JP, 2015-117386, A

  Conventionally, in the H-section steels of Patent Documents 1 to 4 mentioned above, the H-section steel having a flange thickness of 40 mm or more has been required to have toughness at room temperature or at most 0 ° C. Considering use on the ground, toughness at a lower temperature may be required. Moreover, in order to utilize the pinning effect, advanced manufacturing technology is required. This invention is made | formed in view of such a situation, and makes it a subject to provide H-section steel manufactured by standing to cool as it is after hot rolling, and a manufacturing method.

  The present inventors have studied so that strength can be secured even when the cooling rate is low. As a result, when the amount of C is suppressed and the hardenability is increased by adding an alloy element, a metal structure mainly composed of bainite is obtained even after cooling after hot rolling, and a mixture of martensite and austenite, which are hard phases, is obtained. It was found that the production of products (hereinafter sometimes referred to as MA) is suppressed. In addition, the present inventors have studied to ensure the strength without reducing the toughness of the H-section steel. As a result, it has been found that by containing Ni, B and V, the effect of increasing the strength can be obtained without greatly reducing the toughness.

This invention is made | formed based on such knowledge, and according to a certain viewpoint of this invention, it is H-section steel, Comprising: By mass%, C: 0.005-0.03%, Si: 0 0.01 to 0.50%, Mn: 0.80 to 1.60%, V: 0.02 to 0.12%, Ni: 0.50 to 1.00%, Al: 0.005 to 0.10 %, Ti: 0.001 to 0.025%, N: 0.0001 to 0.0050%, B: 0.0003 to 0.0020%, and the balance is Fe and impurities. The carbon equivalent C _eq determined by the following formula (1) is 0.33 to 0.50 mass%, the flange thickness is 40 to 150 mm, and the length of the flange in the H-shaped cross section of the H-shaped steel is a position of 1/6 from the surface in the direction, have you from the surface in a thickness direction of the flange at the position of 1/4 State, and are bainite area ratio of the metal structure is 80% or more, and, at room temperature yield strength or 0.2% proof stress than 385MPa, a tensile strength of not less than 490 MPa, the Charpy absorbed energy at -20 ° C. An H-section steel that is 100 J or more is provided.

  The H-shaped steel is, by mass%, Nb: 0.050% or less, Cr: 0.50% or less, Cu: 0.50% or less, Mo: 0.50% or less, W: 0.50% or less, You may contain 1 type (s) or 2 or more types among Ca: 0.0050% or less and Zr: 0.0050% or less.

Moreover, in order to solve the said subject, according to another viewpoint of this invention, it is a manufacturing method of H-section steel, Comprising: The steel piece of 1100-1350 degreeC is hot-rolled, and the thickness of a flange is 40-150 mm. The end temperature of the hot rolling is 750 ° C. or more at the surface temperature of the H-shaped steel, and the steel slab is in mass%, C: 0.005 to 0.03 %, Si: 0.01 to 0.50%, Mn: 0.80 to 1.60%, V: 0.02 to 0.12%, Ni: 0.50 to 1.00%, Al: 0.00. 005 to 0.10%, Ti: 0.001 to 0.025%, N: 0.0001 to 0.0050%, B: 0.0003 to 0.0020%, and the balance from Fe and impurities comprising a steel composition, Ri carbon equivalent C _eq is from 0.33 to 0.50% by mass as determined by the following formula (1) In the H-shaped cross section, in the H-shaped cross section, the area of the bainite of the metal structure is at a position 1/6 from the surface in the length direction of the flange and at a position 1/4 from the surface in the thickness direction of the flange. H-section steel having a rate of 80% or more, yield strength at room temperature or 0.2% proof stress of 385 MPa or more, tensile strength of 490 MPa or more, and Charpy absorbed energy at −20 ° C. of 100 J or more. A manufacturing method is provided.

  The steel slab is in mass%, Nb: 0.050% or less, Cr: 0.50% or less, Cu: 0.50% or less, Mo: 0.50% or less, W: 0.50% or less, Ca : 0.0050% or less, Zr: You may contain 1 type (s) or 2 or more types among 0.0050% or less.

  The method for manufacturing the H-section steel may include a cooling step in which the H-section steel is allowed to cool as it is after the hot rolling step.

  ADVANTAGE OF THE INVENTION According to this invention, the flange thickness applicable to a large-scale building can provide the H-section steel whose thickness is 40 mm or more, and its manufacturing method. More specifically, the flange thickness is 40 to 150 mm, the yield strength or 0.2% proof stress is 385 MPa or more, the tensile strength is 490 MPa or more, and the Charpy absorbed energy at −20 ° C. is 100 J or more. High strength H-section steel can be obtained.

It is a figure which shows the manufacturing line of the hot rolling process in an Example. It is sectional drawing of the H-section steel manufactured in the Example.

When manufacturing H-section steel without performing accelerated cooling after hot rolling, both the surface cooling rate and the internal cooling rate are small values. For example, in a H-section steel having a flange thickness of 100 mm, the cooling rate is 0.1 ° C./s or less when the steel is allowed to cool after hot rolling. The present inventors have studied so that strength can be secured even when the cooling rate is low. As a result, when the content of C is suppressed to 0.03% or less, B is added, the amount of Ni is increased, and the carbon equivalent C _eq is controlled within the range of 0.33 to 0.50 by addition of the alloy element, It was found that a metal structure of 80% or more in area fraction becomes bainite, the formation of MA as a hard phase is suppressed, and good toughness can be secured.

  Furthermore, the present inventors have found that it is effective to add V forming a nitride to improve the strength without reducing the toughness of the H-section steel having a flange thickness of 40 mm or more. . V is a particularly important element, and the present inventors presume that V nitride, which is a nucleation site of bainite transformation, precipitates in austenite grains and contributes to improvement of toughness.

  Hereinafter, embodiments of the present invention will be described in detail.

  The steel composition of the H-shaped steel of the present invention is mass%, C: 0.005 to 0.03%, Si: 0.01 to 0.50%, Mn: 0.80 to 1.60%, V : 0.02-0.12%, Ni: 0.50-1.00%, Al: 0.005-0.10%, Ti: 0.001-0.025%, N: 0.0001-0 .0050%, B: 0.0003 to 0.0020%, with the balance being Fe and impurities. Below, the component of the steel composition which the H-section steel of this invention has is demonstrated. Here, “%” of the content means mass% unless otherwise specified.

(C: 0.005-0.03%)
C is an element effective for strengthening steel, and the lower limit of the content is 0.005%. Preferably, the C content is 0.01% or more. On the other hand, if the C content exceeds 0.03%, the amount of MA produced becomes excessive, which may lead to a decrease in yield strength and a decrease in toughness. Therefore, the upper limit of the C amount is set to 0.03%. In order to improve toughness, the upper limit value of the C content is preferably 0.02%.

(Si: 0.01-0.50%)
Si is a deoxidizing element and contributes to the improvement of strength. In order to obtain such an effect, in the present invention, the lower limit value of the Si amount is set to 0.01%. On the other hand, the excessive Si content promotes the formation of MA and may lead to a decrease in yield strength and a deterioration in toughness. Therefore, the upper limit value of the Si content is set to 0.50%. In order to ensure toughness, the upper limit of the Si content is preferably 0.40%, and more preferably 0.30% or less.

(Mn: 0.80 to 1.60%)
Mn is an element that enhances hardenability, promotes the formation of bainite, and contributes to the improvement of the strength of the H-section steel. In order to obtain such an effect, the Mn content is set to 0.80% or more. In order to increase the strength, the Mn content is preferably 1.00% or more, more preferably 1.30% or more. On the other hand, if the content of Mn exceeds 1.60%, the formation of MA may be promoted and the toughness may be impaired. Therefore, the upper limit value of the Mn content is set to 1.60%. A preferable upper limit of the Mn content is 1.50%.

(V: 0.02-0.12%)
V is an important element and contributes to the improvement of toughness by forming a nitride. V nitrides precipitated in austenite grains act as transformation nuclei, and as a result of refining the effective crystal grains of bainite, it is presumed to contribute to the improvement of toughness. In order to obtain such an effect, the V content needs to be 0.02% or more, and preferably the V content is 0.04% or more. However, excessive addition of V may impair toughness due to coarsening of precipitates. Therefore, the upper limit value of the V content is set to 0.12%. Preferably, the upper limit of the V content is 0.10%.

(Ni: 0.50 to 1.00%)
Ni is an important element and has a great effect of increasing the hardenability and increasing the strength of the H-section steel. Moreover, the bad influence which reduces toughness is small. In order to obtain the effect of increasing the strength, the Ni content needs to be 0.50% or more. On the other hand, when the content of Ni is excessive, the formation of MA may be promoted and the toughness may be reduced. Therefore, the upper limit of the Ni content is set to 1.00%, preferably 0.90% or less. More preferably, the upper limit of the Ni content is 0.80%.

(Al: 0.005-0.10%)
Al is a deoxidizing element. In the present invention, the Al content is set to 0.005% or more. Preferably, the content is 0.01% or more. However, if the Al content is excessive, the oxide becomes coarse and becomes the starting point of brittle fracture, and the toughness of the H-section steel may be reduced. Therefore, the upper limit value of the Al content is 0.10%. Preferably, the upper limit of the Al content is 0.050%.

(Ti: 0.001 to 0.025%)
Ti is an element that forms TiN and fixes N in the steel, and suppresses precipitation of BN to increase solid solution B and improve hardenability. In order to obtain such an effect, the Ti content is set to 0.001% or more. TiN also has the effect of refining austenite by the pinning effect. In order to obtain such an effect, the Ti content is preferably 0.008% or more. On the other hand, if the Ti content exceeds 0.025%, coarse TiN is generated, and the toughness may be impaired. Therefore, the upper limit of Ti content is set to 0.025%. Preferably, the upper limit of the Ti content is 0.020%.

(N: 0.0001 to 0.0050%)
N is an element that forms TiN or VN and contributes to refinement of the structure and precipitation strengthening, and its content is set to 0.0001% or more. In order to obtain such an effect, the N content is preferably 0.0010% or more. However, when the N content is excessive, the toughness of the base material is lowered, which may cause surface cracks during casting and material defects due to strain aging of the manufactured steel. Therefore, the upper limit is set to 0.0050%. Preferably, the upper limit value of the N amount is 0.0040%.

(B: 0.0003 to 0.0020%)
B is an element that increases the hardenability by adding a small amount, promotes the formation of bainite, and improves the strength. In order to obtain such an effect, the B content is set to 0.0003% or more. Preferably, the B content is 0.0008% or more, and more preferably 0.00010% or more. On the other hand, if the content of B exceeds 0.0020%, MA formation may be promoted and toughness may be reduced. Therefore, the upper limit of the B content is set to 0.0020%. More preferably, it is 0.0015%.

  P, S and O are impurities and may be included in the steel composition. The content of these elements is not particularly limited, but P and S may cause weld cracking due to solidification segregation and a decrease in toughness. Therefore, it is preferable to reduce the content of these elements. The P content is preferably limited to 0.03% or less, more preferably 0.02% or less, and still more preferably an upper limit of 0.01%. The S content is preferably limited to 0.02% or less, more preferably 0.01% or less, and still more preferably an upper limit of 0.005%. If O is contained excessively, the toughness may be lowered due to the influence of solid solution oxygen or the coarsening of oxide particles. Therefore, the upper limit value of the O content is preferably 0.005%. The upper limit of the O content is more preferably 0.0030%, and still more preferably 0.0020%.

  The H-section steel of the present invention can contain one or more of Nb, Cr, Cu, Mo, W, Ca, and Zr in order to increase strength and toughness.

(Nb: 0.050% or less)
Nb is an element that enhances hardenability and contributes to improvement in strength. In order to obtain the effect of improving the strength, the Nb content is preferably 0.001% or more, more preferably 0.010% or more. However, if the Nb content is excessive, the toughness may be significantly reduced. Therefore, the upper limit of Nb content is 0.050%. A more preferable upper limit of the Nb content is 0.040%.

(Cr: 0.50% or less)
Cr is an element that improves the hardenability and contributes to the improvement of the strength of the H-section steel. In order to improve the hardenability, the Cr content is preferably 0.01% or more, and more preferably 0.10% or more. When the content of Cr exceeds 0.50%, the formation of MA may be promoted, or coarsening of Cr carbide may be caused and the toughness may be lowered. Therefore, when adding Cr, the upper limit of content of Cr shall be 0.50%. More preferably, the upper limit of the Cr content is 0.30%.

(Cu: 0.50% or less)
Cu is an element that improves hardenability and contributes to strengthening of the steel material by precipitation strengthening. In order to obtain these effects, the Cu content is preferably 0.01% or more, more preferably 0.10% or more. However, if the Cu content is excessive, the production of MA may be promoted, or the strength may be excessive and the toughness may be reduced. Therefore, when adding Cu, the upper limit of the content of Cu is set to 0.50%. More preferably, the upper limit value of the Cu content is 0.30%.

(Mo: 0.50% or less)
Mo is an element that improves the hardenability by forming a solid solution in the steel, and contributes to improving the strength of the H-shaped steel. In particular, in the H-section steel of the present invention to which B is added, the synergistic effect of B and Mo on the hardenability is remarkable. In order to obtain this synergistic effect, when adding Mo, the lower limit of the Mo content is preferably set to 0.01%. More preferably, the Mo content is 0.05% or more. However, if the Mo content exceeds 0.50%, MA formation may be promoted and toughness may be reduced. Therefore, the upper limit value of the Mo content is set to 0.50%.

(W: 0.50% or less)
W is an element that improves the hardenability by solid solution in the steel and contributes to the improvement of the strength of the H-section steel. In order to obtain this effect, the lower limit of the W content is preferably set to 0.01%. More preferably, the W content is 0.10% or more. However, if the W content exceeds 0.50%, the formation of MA may be promoted and the toughness may be reduced. Therefore, the upper limit value of the W content is 0.50%.

(Ca: 0.0050% or less)
Ca is an element effective for controlling the form of sulfide, suppresses the formation of coarse MnS, and contributes to the improvement of toughness. In order to obtain this effect, the Ca content is preferably 0.0001% or more. More preferably, the Ca content is 0.0010% or more. On the other hand, if the Ca content exceeds 0.0050%, the toughness of the H-section steel may be lowered. Therefore, the upper limit of Ca content is set to 0.0050%. The content of Ca is more preferably 0.0030% or less.

(Zr: 0.0050% or less)
Zr precipitates as carbides and nitrides and contributes to precipitation strengthening of steel. Further, precipitation as a nitride contributes to the reduction of solid solution N in the steel, and is effective in improving the hardenability by securing the solid solution B. In order to obtain these effects, the Zr content is preferably 0.0001% or more. The content of Zr is more preferably 0.0010% or more. On the other hand, if the content of Zr exceeds 0.0050%, Zr carbide and nitride are coarsened, and the toughness may be lowered. Therefore, the upper limit value of the Zr content is preferably 0.0050%.

  In addition, in the present invention, one or more of Mg and rare earth elements (REM) can be added for the purpose of improving the toughness of the base metal and the welded HAZ. These elements have the effect of contributing to control of the form of oxides and sulfides. In order to acquire such an effect, it is preferable to contain 0.0001% or more of these elements in total. The upper limit of the content is preferably 0.0050%.

  The H-section steel of the present invention has a chemical composition composed of the above elements (where P, S, and O are impurities), the balance Fe, and impurities. In the production process, elements other than the above may be inevitably mixed as impurities due to raw materials such as scrap, refractory materials, etc., but if the content does not affect the characteristics of H-section steel, it is acceptable. Is done.

In the present invention, enhance the hardenability, in order to accelerate the formation of bainite, the carbon equivalent C _eq which is obtained by the following formula (1) is from 0.33 to 0.50 wt%. When C _eq is less than 0.33, the formation of bainite becomes insufficient, and the strength and toughness of the H-section steel are lowered. Preferably, C _eq is 0.40% by mass or more. On the other hand, when C _eq exceeds 0.50% by mass, the strength of the H-section steel becomes too high and the toughness decreases. Preferably, C _eq is 0.45 mass% or less.

The carbon equivalent C _eq is an index of _{hardenability and} is obtained by the following formula (1). Here, C, Mn, Cr, Mo, V, Ni, and Cu are the contents (mass%) of each element in the steel, and the elements that are not contained are 0.

  In the H-section steel of the present invention, in the H-shaped cross section of the H-section steel, at a position 1/6 from the surface in the length direction of the flange and at a position 1/4 from the surface in the thickness direction of the flange, Evaluate the microstructure, strength and toughness of the metal. If it is the said position of H-section steel, the average intensity | strength and toughness of H-section steel can be evaluated.

  The microstructure of the metal can be determined by observation with an optical microscope. The area ratio of bainite was determined by arranging the measurement points in a lattice shape with a side of 50 μm using a micrograph taken with an optical microscope taken at 200 times, and determining whether the bainite is 400 bainite. Calculated as a percentage of the number of measurement points counted.

  To ensure sufficient strength in the H-shaped cross section of the H-shaped steel at a position 1/6 from the surface in the length direction of the flange and 1/4 from the surface in the thickness direction of the flange It is necessary that the metal structure contains bainite in an area fraction of 80% or more. The balance of the metal structure is one or more of ferrite, pearlite, and MA. When the area ratio of bainite is less than 80%, the strength of the H-shaped steel is lowered when the balance is a large amount of ferrite that is a soft phase. Moreover, when there are many pearlite and MA which are hard phases in remainder, toughness falls. Since the increase in the bainite area fraction contributes to the improvement of the strength of the H-section steel, the upper limit of the bainite area fraction is not particularly defined and may be 100%.

  Next, the shape and mechanical characteristics of the H-shaped steel of the present invention will be described. The flange of the H-shaped steel of the present invention has a thickness of 40 to 150 mm. The reason why the flange has a thickness of 40 mm or more is that it is required to be a strength member having a flange thickness of 40 mm or more as an H-shaped steel used for a high-rise building structure or the like. If an H-section steel with a flange thickness exceeding 150 mm is manufactured, the flange becomes too thick to obtain a sufficient cooling rate when cooling after rolling, and it is difficult to ensure the strength and toughness of the H-section steel. Therefore, the upper limit of the flange thickness is set to 150 mm. The thickness of the H-shaped steel web is not particularly specified, but there is no problem as long as it is 20 to 150 mm.

  With respect to the ratio of the flange of H-shaped steel to the thickness of the web (flange / web), assuming that the H-shaped steel is manufactured by hot rolling, the ratio is 0.5 to 2.0. If the thickness ratio exceeds 2.0, the web may be deformed into a wavy shape. On the other hand, when the thickness ratio is less than 0.5, the flange may be deformed into a wavy shape. Considering that deformation of the H-section steel may occur due to the difference in cooling rate between the flange and the web after hot rolling, the ratio of the thickness of the flange to the web is 0.7 to 1.5. It is more preferable that

  The target values of the mechanical properties of the H-shaped steel in the present invention are a yield strength or 0.2% yield strength at room temperature of 385 MPa or more, and a tensile strength of 490 MPa or more. In the stress-strain curve, when the yield phenomenon appears, the yield strength is obtained, and when the yield phenomenon does not appear, the 0.2% yield strength is obtained. If the yield strength or tensile strength is too high, the toughness of the H-shaped steel may be impaired. Therefore, the yield strength or 0.2% proof stress at room temperature is preferably 530 MPa or less, and the tensile strength is preferably 690 MPa or less. Moreover, the Charpy absorbed energy at −20 ° C. is 100 J or more. If it is lower than 100 J, it cannot be said that the toughness of the H-section steel is sufficient.

Next, the manufacturing method of the H-section steel of this invention is demonstrated.
The manufacturing method of the H-section steel of this invention includes the hot rolling process which hot-rolls the steel slab of 1100-1350 degreeC, and makes the thickness of a flange 40-150 mm. A hot rolling process is a process of performing rough rolling, intermediate rolling, and finish rolling. In each rolling, a breakdown rolling mill can be used for rough rolling, a universal rolling mill and an edging rolling mill for intermediate rolling, and a universal rolling mill for finishing rolling.

  If the temperature of the steel slab is less than 1100 ° C., the deformation resistance during finish rolling may increase. Therefore, the temperature of the steel slab is set to 1100 ° C. or higher so that the deformation resistance does not increase. On the other hand, when the temperature of the steel slab becomes higher than 1350 ° C., the scale of the surface of the steel slab, which is a raw material, may be liquefied, which may hinder manufacturing. Therefore, the upper limit of the temperature of the steel slab is 1350 ° C. so as not to hinder the production.

In the present invention, the temperature of the steel slab during hot rolling is preferably lowered from the viewpoint of improving toughness. However, if rolling is performed at a temperature lower than the Ar ₃ point at which ferrite transforms, toughness may be reduced. In consideration of the toughness of the H-section steel, the end temperature of the hot rolling is set to 750 ° C. or more at the surface temperature of the H-section steel. The upper limit of the end temperature of hot rolling is preferably 850 ° C. in consideration of improvement of toughness due to refinement of the structure.

  In the hot rolling step in the method for producing the H-section steel of the present invention, the steel slab is primarily rolled and cooled to 500 ° C. or lower, and then heated again to 1100 to 1350 ° C. to perform secondary rolling. You may employ | adopt the process which manufactures H-section steel, what is called 2 heat rolling. In the primary rolling, the steel slab (box-shaped slab) can be roughly shaped into an H shape, and in the secondary rolling, the steel can be rolled to the exact target shape of the H shape steel. If such two-heat rolling is used, the amount of plastic deformation in hot rolling is small, and the temperature drop in the rolling process is small, so the temperature of the steel slab during secondary rolling is lowered. Can do. In order to sufficiently dissolve elements forming carbides and nitrides such as Nb, it is preferable that the lower limit of the temperature of the steel slab at the time of secondary rolling is 1150 ° C. or higher.

  After completion of the hot rolling process, the H-section steel is cooled to room temperature. Since the H-shaped steel flange is thick, cooling inside the H-shaped steel is slower than the surface, which may cause a large difference in temperature history between the inside and the surface. May cause large differences in mechanical properties such as strength, ductility and toughness. Therefore, it is preferable to pay attention to the difference in the temperature history until the temperature of the H-shaped steel reaches room temperature. In order not to increase the difference in the temperature history, for example, cooling can be controlled by air cooling, mist cooling, or the like, or a cooling process for cooling the H-shaped steel after the hot rolling process can be provided.

  A hot rolling process can include processes other than the above. For example, in order to set the temperature of the steel slab to 1100 to 1350 ° C., a heating step of heating the steel slab by a heating furnace or the like can be provided before hot rolling. However, this is not the case when the cast slab is directly fed and rolled at a high temperature. Moreover, in the manufacturing method of the H-section steel of this invention, not only a hot rolling process but another process can be included. For example, it is possible to provide a sawing process for cutting the H-shaped steel after the hot rolling process to adjust the length in the longitudinal direction, a correcting process for correcting distortion and deformation of the H-shaped steel after cooling, and the like.

  The steel slab is prepared by a normal procedure. For example, it can be obtained by adjusting the chemical composition of the molten steel in the steelmaking process to steel that has passed through a blast furnace or converter, and then casting it. The casting is preferably continuous casting from the viewpoint of productivity, but may be a beam blank having a shape close to the H-shaped steel to be manufactured. In addition, the thickness of the steel slab is preferably 200 mm or more from the viewpoint of productivity, considering the segregation reduction, the uniformity of the heating temperature when the steel slab is heated before the hot rolling process, and the like. The thickness is preferably 350 mm or less.

  In the manufacturing method of the H-section steel of the present invention, the steel slab is in mass%, C: 0.005 to 0.03%, Si: 0.01 to 0.50%, Mn: 0.80 to 1.60. %, V: 0.02 to 0.12%, Ni: 0.50 to 1.00%, Al: 0.005 to 0.10%, Ti: 0.001 to 0.025%, N: 0.00. It has a steel composition containing 0001 to 0.0050%, B: 0.0003 to 0.0020%, and the balance being Fe and impurities. The steel composition is as described in the H-section steel according to the present invention. The steel slab is in mass%, Nb: 0.050% or less, Cr: 0.50% or less, Cu: 0.50% or less, Mo: 0.50% or less, W: 0.50% or less, Ca : 0.0050% or less and Zr: 0.0050% or less can contain 1 type (s) or 2 or more types.

In the method of H-shaped steel of the present invention, the steel pieces, carbon equivalent C _eq is from 0.33 to 0.50 wt%. The carbon equivalent is as described in the H-section steel according to the present invention.

  Hereinafter, based on an Example, this invention is demonstrated in detail.

Steel having the composition shown in Table 1 was melted, and steel pieces having a thickness of 240 to 300 mm were produced by continuous casting. The steel was melted in a converter, subjected to primary deoxidation, an alloy was added to adjust the components, and vacuum degassing was performed as necessary. The steel pieces (Nos. 1-42) thus obtained were heated using a heating furnace and hot-rolled to produce an H-section steel. The H-shaped steel after hot rolling was allowed to cool to room temperature. Table 1 shows the steel component composition and carbon equivalent C _eq . The steel component composition shown in Table 1 is obtained by chemical analysis of a sample collected from the manufactured H-section steel.

  FIG. 1 is a diagram showing a production line for a hot rolling process. The hot rolling was performed in the production line 1 of the universal rolling apparatus row including the heating furnace 2, the rough rolling mill 3a, the intermediate rolling mill 3b, the finishing rolling mill 3c, and the water cooling apparatus 4. The hot rolling is water cooling between passes, and water cooling between rolling passes is performed by using a water cooling device 4 provided on the front and rear surfaces of an intermediate rolling mill (intermediate universal rolling mill) 3b, and spray cooling and reverse rolling on the flange outer surface. went. Table 2 shows the types of steel slabs used, the plate thickness of the flanges, the heating temperature of the steel slabs heated by the heating furnace 2, and the surface temperature (end temperature) of the H-section steel when hot rolling is completed. The temperature shown by finish rolling is the surface temperature of the H-section steel after finish rolling.

  FIG. 2 is an H-shaped cross-sectional view of the H-section steel manufactured in the example perpendicular to the longitudinal direction. The H-section steel 10 includes a flange 11 and a web 12. F is the length of the flange in the cross section, and H is the height of the H-section steel. Moreover, t1 is the thickness of the web in a cross section, and t2 is the thickness of the flange in a cross section. Regarding the evaluation of the strength, toughness, and metal structure of the manufactured H-section steel, the evaluation part 13 is located at a position 1/6 from the surface in the length direction of the flange and 1/4 from the surface in the thickness direction of the flange. It was. A sample used for measurement of the tensile test, Charpy test and bainite fraction was taken from the evaluation site 13. Yield strength or 0.2% proof stress, tensile strength and toughness were evaluated and the bainite fraction was measured.

  The tensile test was performed in accordance with JIS Z 2241. When the yield behavior was exhibited, the yield point was obtained. When the yield behavior was not exhibited, the 0.2% yield strength was obtained and evaluated as the yield strength (YS). The Charpy impact test was performed at −20 ° C. in accordance with JIS Z 2242.

  The area fraction of bainite with an optical microscope is determined by arranging the measurement points in a lattice shape with a side of 50 μm using a structure photograph taken with an optical microscope taken at 200 times and determining whether the bainite is bainite at 400 measurement points. And calculated as a ratio of the number of measurement points counted as bainite.

Table 2 shows the results of yield strength (YS), tensile strength (TS), Charpy absorbed energy (vE _-20 ) at _-20 ° C, and bainite fraction. The target values of mechanical properties were such that the yield strength at room temperature or the 0.2% yield strength (YS) was 385 MPa or more, and the tensile strength (TS) was 490 MPa or more. The Charpy absorbed energy (vE _-20 ) at -20 ° C was 100 J or more.

  As shown in Table 2, the production No. of the present invention. The H-section steels of 1 to 8, 10, 11, 13, 14, 16 to 24, 26, and 27 satisfied the target lower limit values of 385 MPa and 490 MPa, respectively. Furthermore, the Charpy absorbed energy at −20 ° C. was 100 J or more, which sufficiently satisfied the mechanical property target.

  On the other hand, production No. The 9 and 25 H-section steels did not satisfy any mechanical properties as a result of the insufficient bainite fraction due to the low end temperature of hot rolling. Production No. No. 12 H-section steel had a low heating temperature and an insufficient solid solution of alloy elements. As a result, the yield strength and tensile strength did not meet the targets. Production No. In No. 15 H-section steel, the plate thickness of the flange was too thick, the cooling rate for cooling was slow, and the bainite fraction was insufficient, so the yield strength and tensile strength did not meet the targets.

Production No. H-beam of 28 to 47 is any one or more of the steel chemical composition and _{C eq} is outside the range of the present invention (Table 1). Therefore, in these H-shaped steels, any one or more of yield strength, tensile strength, and Charpy absorbed energy at −20 ° C. did not satisfy the target of the mechanical characteristics.

  According to the present invention, advanced steelmaking technology and accelerated cooling are not required, and the production load can be reduced and the construction period can be shortened. Therefore, it is industrially useful, for example, the reliability of a large building can be improved without impairing the economy.

DESCRIPTION OF SYMBOLS 1 Production line 2 Heating furnace 3 Rough rolling mill 3b Intermediate rolling mill 3c Finish rolling mill 4 Water cooling device of front and rear surfaces of intermediate rolling mill 10 H section steel 11 Flange 12 Web 13 Evaluation part F Length of flange in cross section H flange thickness of the thickness t ₂ the cross section of the webs at the height t ₁ section

Claims (5)

H-shaped steel,
% By mass
C: 0.005 to 0.03%,
Si: 0.01 to 0.50%,
Mn: 0.80 to 1.60%,
V: 0.02 to 0.12%,
Ni: 0.50 to 1.00%,
Al: 0.005 to 0.10%,
Ti: 0.001 to 0.025%,
N: 0.0001 to 0.0050%,
B: 0.0003 to 0.0020%
And the balance has a steel composition consisting of Fe and impurities,
The carbon equivalent C _eq calculated by the following formula (1) is 0.33 to 0.50% by mass,
The thickness of the flange is 40 to 150 mm,
In H-shaped cross-section of the H-shaped steel, a position from the surface 1/6 the length direction of the flange, and have contact the surface in a thickness direction of the flange at the position of 1/4, the metal structure of bainite Ri der area of 80% or more, and, at room temperature yield strength or 0.2% proof stress at least 385MPa, and a tensile strength of 490MPa or more, Charpy absorbed energy at -20 ° C. is at least 100 J, H Shape steel.

The H-shaped steel is in mass%,
Nb: 0.050% or less,
Cr: 0.50% or less,
Cu: 0.50% or less,
Mo: 0.50% or less,
W: 0.50% or less,
Ca: 0.0050% or less,
The H-section steel according to claim 1, containing one or more of Zr: 0.0050% or less. It is a manufacturing method of H-section steel, Comprising: The hot rolling process which hot-rolls a steel piece of 1100-1350 degreeC, and makes the thickness of a flange 40-150 mm,
The end temperature of the hot rolling is 750 ° C. or more at the surface temperature of the H-section steel,
The billet is mass%,
C: 0.005 to 0.03%,
Si: 0.01 to 0.50%,
Mn: 0.80 to 1.60%,
V: 0.02 to 0.12%,
Ni: 0.50 to 1.00%,
Al: 0.005 to 0.10%,
Ti: 0.001 to 0.025%,
N: 0.0001 to 0.0050%,
B: 0.0003 to 0.0020%
And the balance has a steel composition consisting of Fe and impurities,
Carbon equivalent C _eq obtained by the following formula (1) Ri 0.33 to 0.50% by mass,
In the H-shaped cross section, the area of the bainite in the metal structure is 1/6 position from the surface in the length direction of the flange and 1/4 position from the surface in the thickness direction of the flange. H-section steel having a rate of 80% or more, yield strength at room temperature or 0.2% yield strength of 385 MPa or more, tensile strength of 490 MPa or more, and Charpy absorbed energy at −20 ° C. of 100 J or more. Manufacturing method.

The billet is mass%,
Nb: 0.050% or less,
Cr: 0.50% or less,
Cu: 0.50% or less,
Mo: 0.50% or less,
W: 0.50% or less,
Ca: 0.0050% or less,
The manufacturing method of the H-section steel of Claim 3 which contains 1 type (s) or 2 or more types among Zr: 0.0050% or less. The manufacturing method of the H-section steel of Claim 3 or Claim 4 including the cooling process which cools the said H-section steel as it is after the said hot rolling process.

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