JP4207843B2 - Method of using steel material for steel structure member and steel structure - Google Patents

Description

The present invention is, for example, buildings and steel structure such as bridges used as a material of the steel structure members constituting, for example section steel and the use of steel structural members steel materials such as steel pipes or planks buildup layers and steel structure Related to things. More specifically, the present invention is a steel structure member in which the mechanical properties (mainly strength) of the part subjected to the heat treatment are improved more than the mechanical properties of the other parts by performing a partial heat treatment. to methods and steel structure using the use steel.

  For example, a member obtained by cutting a shape steel, a steel pipe, a thick plate build-up material, or the like into a predetermined length is used as a steel structure member such as a column or a beam constituting a steel structure such as a building or a bridge. When an external force is applied to the steel structure, the stress generated in the steel structure member that forms a column or a beam is usually not uniform in the longitudinal direction. In general, this stress is greatest at the end of the steel structure member and is smallest at the center. Since steel structure members that have been used so far have uniform strength in the longitudinal direction, high strength is sufficient as long as it is inherently only included in the vicinity of the critical section where the bending stress that occurs in the steel structure member is maximum. Is provided over the entire length of the steel structure member, and an excessive specification is given in most regions of the steel structure member.

  Therefore, by performing heat treatment at the construction site of the building structure only in the vicinity area including the dangerous section of the steel structure member, the strength of the vicinity area including the dangerous section is partially increased, and the safety of the steel structure is increased. It has been proposed to secure without waste. For example, in Patent Document 1, a high temperature is obtained by performing a heat treatment in which a nearby region including a dangerous cross section within a predetermined length range of a steel structure member is partially heated by high frequency induction heating and then rapidly cooled and baked at a construction site. An invention for enhancing the safety of a steel structure by strengthening is disclosed.

Even in the case of a normal steel structure member that does not have such a stress gradient in the longitudinal direction, the strength of a specific part such as a panel zone that is surrounded by the end of a brace or a column and a beam. It is also known to use a steel structure member having an increased amount. For example, Patent Document 2 discloses an optimum component that does not decrease the toughness of the heat-treated portion even if it is partially heat-treated by locally increasing and reinforcing the plate thickness of the steel structure member.
Japanese Patent Laid-Open No. 10-266340 JP 2002-212669 A

  Patent Document 1 discloses that quenching is performed at a construction site. However, Patent Document 1 does not disclose any composition of steel to be subjected to quenching. For this reason, depending on the composition of the steel to be subjected to the quenching treatment, the toughness may be remarkably deteriorated although the strength is increased. For example, if a steel having a high weld cracking susceptibility index Pcm and a particularly high carbon content is subjected to quenching, the amount of martensite is excessively increased, resulting in a significant increase in strength and a deterioration in toughness. On the other hand, when the quenching treatment is performed on steel having a weld crack sensitivity index Pcm that is too low, a mixed structure mainly composed of ferrite and pearlite is formed, and a desired strength cannot be obtained. In some cases, the toughness may even deteriorate.

  On the other hand, in order to implement the invention disclosed in Patent Document 2, not only a local heating device but also a powerful compression device is required to partially increase the plate thickness. For this reason, in practice, the present invention cannot be surely carried out at the enforcement site, and the cost required for a powerful compression device increases.

The purpose of the present invention is not to require special processing as in the thickening method, and by performing a partial heat treatment on the steel structure member, not only the strength of the heat treatment part is increased, but also the toughness of the heat treatment part is ensured. It is another object of the present invention to provide a method of using a steel material for a steel structure member and a steel structure that can be sufficiently achieved.

In the present invention, C: 0.04 to 0.18% (in this specification, “%” means “% by mass” unless otherwise specified), Si: 0.02 to 0.50% , Mn: 0.5 to 2.0%, sol. Al: 0.06% or less, Ti: 0.003 to 0.030%, N: 0.008% or less, 2Nb + 3Ti + Al: 0.05% or more, Pcm = C + (Si / 30) + ( The weld cracking sensitivity index (Pcm) defined by Mn / 20) + (Cu / 20) + (Ni / 60) + (Cr / 20) + (Mo / 15) + (V / 10) + 5B is 0.12. a steel structure formed by using at least as one of ～0.27% der Ru steel structural members steel material constituent materials, the part including the risk section of steel structural member comprising the steel structural member for steel On the other hand, a heat treatment is performed by heating from 800 ° C. to 500 ° C. at an average cooling rate of 3 ° C./second or more after heating to 800 ° C. or more, and the heat treatment part has a 0 ° C. Charpy absorbed energy of 70 J or more. Give a fine veina It is a steel structure, characterized by a tissue bets mainly.

In the steel structure according to the present invention, the length (Lj) in the longitudinal direction of the portion to be heat-treated satisfies Lj / D ≧ 0.0308 (L / D) · (σyj / σy) +0.039. It is desirable. However, L in this formula shows the length of half of the total length of the steel structure member, and D shows the member fault of this steel structure member.

In these steel structures according to the present invention, it is desirable that the yield strength (σyj) of the portion to be heat-treated is 1.25 times or more the yield strength (σy) of the portion other than the portion to be heat-treated.

These steel structures according to the present invention preferably further contain at least one of B: 0.0003 to 0.003% or Nb: 0.003 to 0.05%.
In these steel structures according to the present invention, Cu: 0.05 to 1.5%, Ni: 0.05 to 2.0%, Cr: 0.03 to 1.0%, Mo: 0.00. It is desirable to contain one or more of 03 to 1.0% and V: 0.005 to 0.1%.

These steel structures according to the present invention have a cleanliness degree defined by JIS G 0555 of 0.040% or less at dA60 × 400, 0.030% or less at dB60 × 400, or 0.030% at dC60 × 400. The following is desirable.

Furthermore, in these steel structures according to the present invention, the segregated portion located at the center in the thickness direction is C: 0.29% or less, P: 0.30%, and Mn: 3.5% or less. It is desirable to have a composition.

  From another viewpoint, the present invention relates to C: 0.04 to 0.18%, Si: 0.02 to 0.50%, Mn: 0.5 to 2.0%, sol. Al: 0.06% or less, Ti: 0.003 to 0.030%, N: 0.008% or less, 2Nb + 3Ti + Al: 0.05% or more, and Pcm = C + (Si / 30) The weld cracking sensitivity index (Pcm) defined by + (Mn / 20) + (Cu / 20) + (Ni / 60) + (Cr / 20) + (Mo / 15) + (V / 10) + 5B is 0. .A heat treatment for cooling a portion including a dangerous cross section of a steel structure member of 12 to 0.27% from 800 ° C. to 500 ° C. at a cooling rate of 3 ° C./second or more after heating to 800 ° C. This is a method of using a steel material for a steel structure member characterized in that, by performing partially, the heat treatment part has a structure mainly composed of fine bainite that gives 0 ° C. Charpy absorbed energy of 70 J or more.

  In this method of using the steel material for steel structure members according to the present invention, the length (Lj) in the longitudinal direction of the portion to be heat-treated is Lj / D ≧ 0.0308 (L / D) · (σyj / σy) +0 It is desirable to satisfy .039. However, L in this formula shows the length of half of the total length of the steel structure member, and D shows the member fault of this steel structure member.

According to the present invention, by performing a partial heat treatment on the steel structure member without performing special processing such as a thickening method, not only the strength of the heat treatment portion is increased, but also the toughness of the heat treatment portion is improved. it is possible to provide that the use of the steel for steel structural members which can, and a steel structure using the steel for the steel structural members.

Hereinafter, the best mode for carrying out a method of using a steel material for a steel structure member and a steel structure according to the present invention will be described in detail with reference to the accompanying drawings. In the following explanation, the case where the steel material for the steel structure member is a steel plate is taken as an example, but the present invention is not limited to the steel plate, and other than the steel plate, it is a shape steel, a steel pipe, a thick plate build-up material, or the like. The same applies to the same.

  By performing partial heat treatment on the steel structure members that make up the steel structure at the construction site, sufficient toughness is ensured while increasing the strength of the heat treatment part without special processing such as thickening. In order to achieve this, it is important to reduce the hardness of the heat treatment part and to refine the structure.

  Since the heat treatment part of the steel structure member has a structure mainly composed of bainite or martensite by cooling after heating, (a) lowering the C content to lower the hardness of the structure, (b) brittle carbon concentration When the phase is formed, the C content is decreased to reduce the hardness and amount of the carbon-enriched phase, and (c) the microalloy such as Ti is added to the austenite grain size and the bainite packet of the heat treatment part. We focused on preventing any coarsening.

  In a steel structure member that has been partially heat-treated at the construction site, in order to ensure the mechanical properties of this heat-treated part, particularly strength and toughness, the heat-treated part has a structure mainly composed of fine bainite. It is effective to reduce the hardness of the heat treatment part. However, if the hardness of the heat treatment part is excessively lowered, the strength of the heat treatment part does not increase, and the original purpose cannot be achieved.

  In the present invention, “structure mainly composed of bainite” means that the area ratio of massive ferrite and pearlite is 20% or less, and the balance is bainite, or bainite and martensite and islands whose area ratio is 15% or less. An organization consisting of martensite.

  In this embodiment, in order to obtain the desired strength and toughness of the heat-treated portion subjected to the heat treatment in the field, the structure of the heat treatment in the field is a bainite-based structure, and the structure is refined. The composition of the steel structure member is adjusted so that it can be achieved. Then, the reason for limiting the composition will be described next.

C: 0.04% or more and 0.18% or less C is an element that greatly affects the hardness and toughness of the heat-treated portion. If the C content exceeds 0.18%, the hardness increase at the end of the steel sheet, which is the heat-treated portion, becomes excessive and the toughness deteriorates. From the same viewpoint, the upper limit of the C content is preferably 0.15%, and more preferably 0.12%. On the other hand, if the C content is less than 0.04%, the strength increase of the heat treatment part is insufficient. From the same viewpoint, the lower limit of the C content is preferably 0.06%.

Si: 0.02% or more and 0.50% or less Si contains 0.02% or more, and thereby exhibits both a deoxidizing action and a strength increasing action. Conversely, if the Si content is less than 0.02%, deoxidation becomes insufficient, so Si is contained by 0.02% or more. However, if it exceeds 0.50%, the toughness of the heat-treated part deteriorates. In particular, when the purpose is to increase the strength of the end portion of a steel plate that is a steel structure member, the lower limit of the Si content is preferably 0.3%, and more preferably 0.2%.

Mn: 0.5% or more and 2.0% or less Mn is contained for improving the strength. Mn is particularly effective among alloying elements because it has a high hardenability improving effect. If the Mn content is less than 0.5%, the effect of increasing the strength is insufficient. From the same viewpoint, the lower limit of the Mn content is desirably 1.0%, and more desirably 1.2%. On the other hand, when the Mn content exceeds 2.0%, the hardness of the heat-treated portion is excessively increased and the toughness is lowered. From the same viewpoint, the upper limit of the Mn content is preferably 1.6%.

sol. Al: 0.06% or less Al is an essential element for obtaining a slab having no defects, particularly when producing a slab as a raw material by continuous casting or the like. An amount exceeding about 0.005% remains as Al. However, sol. Al combines with N to become AlN, and the toughness is improved by refining the austenite grain size of the heat-treated portion. For this reason, sol. It is desirable to contain 0.01% or more of Al. On the other hand, sol. If the Al content exceeds 0.06%, the toughness of the heat-treated part deteriorates. sol. The upper limit of the desirable content of Al is 0.04%, more preferably 0.02%.

Ti: 0.003% or more and 0.03% or less Ti combines with N to precipitate TiN, and prevents the deterioration of toughness by making the austenite grain size of the heat treatment portion fine. In order to have a bonding effect with N, Ti is added by 0.003% or more. From the same viewpoint, the lower limit of the Ti content is desirably 0.01%. However, if Ti is contained in excess of 0.03%, Ti carbide precipitates in the heat treatment part, and conversely, the toughness of the heat treatment part deteriorates. From the same viewpoint, the upper limit of the Ti content is desirably 0.017%.

N: 0.008% or less N is contained in the steel as an impurity, but N is combined with Ti to become TiN, which is effective for improving the toughness by making the structure of the heat treatment portion fine. However, if the N content exceeds 0.008%, the toughness of the heat-treated part deteriorates. From the same viewpoint, the upper limit of the N content is desirably 0.006%, and more desirably 0.004%.

2Nb + 3Ti + Al: 0.05% or more In order to refine the structure of the heat treatment part of the steel sheet that is a steel structure member, the pinning effect of austenite grains by precipitated carbides and nitrides, and carbonitrides can be used. It is valid. For this purpose, it is effective that Nb, Ti, and Al, which are elements forming carbide, nitride, or carbonitride, satisfy the relationship of 2Nb + 3Ti + Al: 0.05% or more.

Weld cracking susceptibility index Pcm: 0.12% or more and 0.27% or less In order to reduce the hardness of the heat treatment part of the steel sheet which is a steel structure member, it is necessary to limit the content of additive elements including C . Welding specified as Pcm = C + (Si / 30) + (Mn / 20) + (Cu / 20) + (Ni / 60) + (Cr / 20) + (Mo / 15) + (V / 10) + 5B If the cracking sensitivity index Pcm exceeds 0.27%, the hardness of the heat treatment part becomes excessive and the toughness deteriorates. From the same viewpoint, the upper limit is preferably 0.22%. On the other hand, if the weld crack susceptibility index Pcm is less than 0.12%, the hardness of the heat-treated portion is insufficient and the original purpose cannot be achieved. From the same viewpoint, the lower limit is preferably 0.16%.

B: 0.0003% or more and 0.003% or less B is an optional additive element added as necessary. B is not only effective for increasing the strength of the heat-treated portion, but is also effective for improving the toughness of the heat-treated portion by making the structure of the heat-treated portion fine by precipitating as BN. When added to increase the strength of the heat treatment part, 0.0003% or more is added. From the same viewpoint, the lower limit is preferably 0.0005%. On the other hand, even if the B content exceeds 0.003%, an increase in strength sufficient for the addition cannot be obtained. From the same viewpoint, the upper limit is preferably 0.002%.

Nb: 0.003% or more and 0.05% or less Nb is an optional additive element added as necessary. When Nb is contained in an amount of 0.003% or more, not only is there an effect in increasing the strength of the heat-treated portion, but it is effective in improving the toughness of the heat-treated portion by reducing the austenite grain size in the heat-treated portion. However, even if it contains more than 0.05%, such an effect is saturated and only the cost increases. From the same viewpoint, the lower limit is desirably 0.01%, and the upper limit is desirably 0.04%.

Cu: 0.05% or more and 1.5% or less Cu is an optional additive element added as necessary. By containing 0.05% or more, Cu is effective in improving the hardenability of the heat treatment part, and the strength of the heat treatment part is increased. However, if the Cu content exceeds 1.5%, the toughness of the heat-treated part deteriorates. From the same viewpoint, the upper limit of the Cu content is desirably 0.8%, and more desirably 0.3%.

Ni: 0.05% or more and 2.0% or less Ni is an optional additive element added as necessary. Ni containing 0.05% or more is effective in improving the hardenability of the heat treatment part, and the strength of the heat treatment part is increased. However, even if the Ni content exceeds 2.0%, it is not possible to expect an increase in strength to meet the cost increase.

Cu: 0.05% or more and 1.5% or less Cu is an optional additive element added as necessary. By containing 0.05% or more, Cu is effective in improving the hardenability of the heat treatment part, and the strength of the heat treatment part is increased. However, if the content exceeds 1.5%, the toughness of the heat-treated part deteriorates. From the same viewpoint, the upper limit is desirably 0.8%, and more desirably 0.3%.

Cr: 0.03% or more and 1.0% or less Cr is an optional additive element added as necessary. When Cr is contained in an amount of 0.03% or more, it is effective in improving the hardenability of the heat treatment part, and the strength of the heat treatment part is increased. However, if added over 1.0%, the toughness of the heat-treated part deteriorates. From the same viewpoint, the lower limit is desirably 0.3%, and the upper limit is desirably 0.6%.

Mo: 0.03% or more and 1.0% or less Mo is an optional additive element added as necessary. When Mo is contained in an amount of 0.03% or more, it is particularly effective in improving the hardenability of the heat treatment part, and the strength of the heat treatment part is increased. However, if added over 1.0%, the toughness of the heat-treated part deteriorates. From the same viewpoint, the lower limit is preferably 0.2%, and the upper limit is preferably 0.5%.

V: 0.005% or more and 0.1% or less V is an optional additive element added as necessary. It is effective to add 0.005% of V from the viewpoint of increasing the strength. However, if added over 0.1%, the toughness of the heat-treated part deteriorates. From the same viewpoint, the lower limit is desirably 0.01%, and the upper limit is desirably 0.05%.

Other than the above are Fe and inevitable impurities.
Steel plates as steel structural members are required to have high reliability as structural members of steel structures such as buildings and bridges, so the cleanliness of steel and the degree of central segregation are to ensure this reliability. It becomes an important management item. Therefore, the cleanliness and center segregation of the steel plate as the steel structure member of the present embodiment will be described.

Cleanliness The steel plate as the steel structure member of the present embodiment is used after water cooling after heat-treating a part including a dangerous section such as an end portion at a construction site. For this reason, if there is a portion exhibiting excessive hardenability due to segregation or a portion where excessive inclusions exist, the toughness of the steel sheet deteriorates. Therefore, the cleanliness of the steel is 0. When the dA60 × 400, the cleanliness of the steel measured by the microscopic test method based on the point calculation method of “Microscopic test method of non-metallic inclusions in steel” defined in JIS G 0555 is set. Desirably, it is 040% or less, dB60 × 400 is 0.030% or less, or dC60 × 400 is 0.030% or less.

In the present embodiment, the number of inclusions used when determining the cleanliness is measured by means described below. Using an eyepiece with 20 grid lines in the vertical and horizontal directions on the steel surface, 60 fields of view were randomly observed at 400 times, and the number n of grid point centers occupied by inclusions was counted, and the cleanliness d = (n / p × f) × 100. Here, p: the total number of lattice points in the visual field f: the number of visual fields n: the number of lattice point centers occupied by inclusions in the f visual fields.

The steel piece such as continuous cast slab, which is the material of the steel structure member with the concentration of segregation part, inevitably accompanies center segregation. This center segregation is the center in the thickness direction of each flange and web of the steel structure member To significantly deteriorate the toughness of the steel sheet. When the C concentration in the segregation part is more than 0.29%, the hardness of the segregation part after the heat treatment becomes excessively large and the toughness is deteriorated. For this reason, it is desirable that the C concentration in the segregation part is 0.29% or less. Similarly, if the P concentration in the segregation part is more than 0.30% and the Mn concentration is more than 3.5%, the hardness of the segregation part after heat treatment becomes excessively large and the toughness deteriorates. Therefore, the segregation part is desirably C: 0.29% or less, P: 0.30% or less, and Mn: 3.5% or less.

  In order to manufacture a steel structure member having the above composition, cleanliness, and segregation part concentration, it is desirable to avoid that Al deoxidation mostly proceeds at the initial stage of refining, for example. It is desirable to adjust the composition other than Al together with Mn, Si, and the like, and after deoxidation proceeds with Ti and the like, Al is introduced into a small amount of molten steel immediately before the outgoing steel, and the obtained molten steel is cast.

  In casting, continuous casting or ingot casting is performed, but it is preferable to perform continuous casting in terms of solidification speed. Further, in the case of ingot casting, prior to hot rolling, an extra step of producing a steel slab by partial rolling has to be performed, resulting in an increase in cost and a decrease in yield.

  Continuous casting of steel having the above-described composition, cleanliness, and segregation concentration is performed, for example, by performing an inert gas blowing process from the converter to the molten steel in the ladle for the purpose of reducing inclusions in the melting stage. This can be realized. The refining conditions and continuous casting conditions in the present embodiment are listed and summarized below.

[Refining conditions]
Treatment method: Inert gas blowing treatment into molten steel in ladle Process: Inverter → Inert gas blowing treatment into molten steel in ladle → Continuous casting Refining treatment time: 1 to 15 minutes Refining treatment atmosphere / vacuum degree: atmospheric pressure [Continuous casting conditions]
Casting speed: 0.4 to 2.0 m / min Tundish molten steel temperature: ΔT (difference between calculated liquidus temperature and tundish molten steel temperature; 20 to 35 ° C.)
Specific water volume: 0.2-2.0 liters / kg of molten steel
In addition to these conditions, an electromagnetic brake is applied at 1000 to 5000 gauss by an electromagnetic braking device provided in the vicinity of the continuous casting mold as a discharge flow rate control during casting, or electromagnetic solidification treatment is applied to unsolidified molten steel at 250 to 1000 gauss. Alternatively, the final solidified portion may be squeezed with a gradient of about 1 mm / m to squeeze out the concentrated segregated molten steel from the final solidified portion.

In the present embodiment, the steel slab thus manufactured is heated to a predetermined temperature, subjected to hot rolling, and then subjected to water cooling or air cooling to obtain a steel plate.
The heating temperature of the steel slab is desirably 950 ° C. or more and 1200 ° C. or less, and the hot rolling finishing temperature is desirably 700 ° C. or more. When the heating temperature is less than 950 ° C., the transformation to austenite is not sufficient, and both strength and toughness after rolling and cooling are deteriorated. On the other hand, when the heating temperature exceeds 1200 ° C., the austenite grain size becomes coarse, so that the toughness of the portion where heat treatment is not performed deteriorates.

  Further, if the finishing temperature of hot rolling is less than 700 ° C., the amount of reduction in the two-phase region of ferrite and austenite becomes large, and the anisotropy of the characteristics of the steel sheet to be produced is prominent. The finishing temperature is preferably 700 ° C. or higher. Further, the amount of reduction at 900 ° C. or lower is desirably 10% or more in order to refine the structure.

Cooling after hot rolling is air cooling or water cooling. In the case of water cooling, it is desirable to cool to 450 ° C. or less at the surface temperature of the steel plate. In some cases, the water-cooled steel sheet can be tempered in a temperature range of Ac ₁ point or less. By tempering at less than Ac ₁ point, the toughness is improved although the strength is reduced.

The steel sheet for steel structure members of the present embodiment is manufactured as described above. This steel structure member has the following characteristics.
[Characteristics] A part including a dangerous section as a steel structure member is partially heated by heating from 800 ° C. to 500 ° C. at an average cooling rate of 3 ° C./second or more after heating to 800 ° C. or more. In this case, the heat-treated portion has a structure mainly composed of fine bainite that gives 0 ° C. Charpy absorbed energy of 70 J or more.

  Here, the “average cooling rate” is calculated as 300 / t (° C./second), where t (second) is the cooling time when cooling from 800 ° C. to 500 ° C. at the surface temperature of the steel material. In the case of a shape steel, the temperature at the surface at a location 1/4 of the flange width from the flange tip is used. In the case of a square steel pipe, cooling is performed from the outside or the outside and the inside, and this “average cooling rate” uses the temperature of the outer surface portion.

The reason why the heat treatment conditions are such that the portion where the strength is desired to be increased is heated to 800 ° C. or higher, and then the temperature between 800 to 500 ° C. is limited to an average cooling rate of 3 ° C./second or higher.
When the heating temperature is 800 ° C. or lower, the fraction of the hardened structure in the region where the heat treatment is applied becomes less than necessary, and an increase in strength due to the heat treatment cannot be expected. On the other hand, if the average cooling rate is less than 3 ° C./second, the cooling rate is too low and quenching becomes insufficient, and an increase in strength cannot be expected. A desirable range is to heat at a temperature of 900 ° C. or higher for 2 seconds or more, and to set the average cooling rate to 5 ° C./s or higher.

Next, the case where this steel structure member is applied to a steel structure will be described with reference to the accompanying drawings.
FIG. 1A to FIG. 1C are explanatory views showing a steel structure member 1 according to the present embodiment applied to the steel structure 0.

  In Fig.1 (a) and FIG.1 (c), it is the state which welded the steel structure member 1 of this Embodiment which is a beam, and the steel structure member 2 which is a pillar with the welding part 3, Comprising: 1 shows a state in which a heat treatment for heating and water cooling the heat treatment region 4 including the end portion of 1 is performed. FIG. 1B shows a state in which the steel structure member 5 that is a beam, the steel structure member 2 that is a column, and the steel structure member 1 of the present embodiment that is a brace are welded by a welded portion 3. Then, a situation is shown in which the heat treatment part 4 including the end of the steel structure member 1 is subjected to heat treatment for heating and water cooling. In FIG. 1A to FIG. 1C, reference numeral 6 denotes a through diaphragm, reference numeral 7 denotes an inner diaphragm, and reference numeral 8 denotes a panel zone.

  In the steel structure member 1, when an external force is applied to the steel structure 0, a moment gradient (stress gradient) is generated in the material axis direction (longitudinal direction). Since the stress is generally maximum at the end portion, in the example shown in FIGS. 1A to 1C, the region including the end portion of the steel structure member 1 is defined as the heat treatment portion 4, and this portion is subjected to heat treatment. Reinforce with increased strength.

By the way, in the brace which is the steel structure member 1 shown in FIG. 1B, the stress generated when an external force acts on the steel structure 0 is basically constant in the material axis direction. However, by making the plasticized region generated when the brace yields into a region other than the heat treatment portion 4, it is possible to prevent the end portion from being destroyed early (welded portion).

  In addition, when the present invention shown in FIG. 1C is applied to the panel zone 8, when an external force acts on the steel structure 0, the panel zone 8 is prevented from being broken before the columns and beams. In addition, there is a case where the part is reinforced. As shown in FIGS. 1 (a) and 1 (b), when the panel zone 8 is a through-diaphragm column formed by welding, only the panel zone 8 is made of high-strength steel or a plate thickness. By using an increased steel material, heat treatment can be performed relatively easily. However, as shown in FIG. 1C, in the case of the inner diaphragm type column 7, the panel zone reinforcement by this construction method is reasonable.

  That is, in order to improve the yield strength characteristics and plastic deformation capacity of the steel structure member 1, it is important to prevent premature breakage in the region including the dangerous cross section existing at the end portion (welded portion) in the longitudinal direction. (I) It is necessary to ensure the toughness of the region including the dangerous cross section and other regions and prevent the occurrence of a brittle fracture phenomenon. In addition to this, it is desirable to (ii) advance the plasticization region mainly in the region not including the dangerous section by yielding the other region before the region including the dangerous section.

  In this Embodiment, with respect to the heat processing part 4 containing the edge part containing the dangerous cross section as this steel structure member 1, after heating to 800 degreeC or more, from 800 degreeC to 500 degreeC, the average cooling of 3 degrees C / sec. This heat treatment part 4 is made into a structure mainly composed of fine bainite that gives 0 ° C. Charpy absorption energy of 70 J or more by partially performing heat treatment that is allowed to cool at a rate. Thus, the above item (i) is achieved.

Next, means for achieving the above item (ii) will be described.
FIG. 2 shows a steel structure member 1 of a steel plate member or a square steel pipe member, in which half of the total length (2L) is simplified to a cantilever (full length L), and the yield strength σyj of the heat treatment part 4 subjected to heat treatment and the heat treatment part 4 It is explanatory drawing for examining the relationship between the ratio (σyj / σy, hereinafter referred to as “yield strength ratio”) with the yield strength σy of the removed non-heat treated portion 9 and the length Lj of the heat treated portion 4.

The condition for the non-heat treated portion 9 to reach the total plastic moment before the heat treated portion 4 is given by equation (1).
hMp / cMp> ν (1)
Here, hMp represents the total plastic moment (= σyj · Zp) of the heat-treated portion 4, and cMp represents the total plastic moment (bMp = σy · Zp) of the non-heat treated portion 9 converted to a beam end moment.
cMyp = φ · bMp, φ = L / (L−Lj) (2)
As given. In the equation (2), Lj represents the length of the heat treated portion 4, Zp represents the plastic section modulus, σyj represents the yield strength of the heat treated portion 4, σy represents the yield strength of the non-heat treated portion 9, and , Ν is a safety factor and is a value of 1.0 or more.

Here, equation (3) is obtained from equations (1) and (2).
hMp / bMp (1-Lj / L)> ν (3)
FIG. 3A shows a case where heat treatment is performed on the entire cross-sectional area of the steel structure member 1 such as a steel plate member and a square steel pipe member, and FIG. 3B shows one of the steel structure members such as the steel plate member and the square steel pipe member. The case where heat processing is performed to the cross-sectional area | region of a part is shown.

As shown in FIG. 3A, since heat treatment is performed on the entire cross section of the heat treatment portion 4 and the entire cross section increases in strength uniformly, hMp / bMp = σyj / σy. ,
σyj / σy (1-Lj / L)> ν (4)
It becomes.

However, as shown in FIG. 3B, when heat treatment is performed on a part of the cross section of the heat treatment portion 4, hMp / bMp <σyj / σy is satisfied, so that the non-heat treatment portion 9 is surely preceded. In order to yield, it is necessary to set the safety factor ν larger than that shown in FIG. For example, in the case where the heat treatment part 4 where σyj / σy = 1.40 is provided at the end of a steel plate member having dimensions of H900 × B250 × tw19 × tf25, as shown in FIG. When performing on a region, hMp / bMp = σyj / σy = 1.40 (A)
Thus, as shown in FIG. 3 (b), hMp / bMp = 1.26 (B)
It becomes. In order to yield the non-heat treated portion 9 in advance in the case shown in FIG. 3 (b), the safety factor ν in the equation (4) is set to the ratio (A / B, above case) of the above (B) and (A). Therefore, it is necessary to set the value to 1.40 / 1.26 = 1.11) or more.

  Further, in order to prevent the preceding fracture of the welded portion at the end under the condition that the expression (4) is established, the maximum yield strength ratio hMu / bMu is set to be equal to or greater than the total plastic yield strength ratio (hMp / bMp). There is a need. The ratio of maximum proof stress (hMu / bMu) generally corresponds to the ratio of tensile strength (σuj / σu) of the cross-sectional material. Therefore, in the case of σuj / σu <σyj / σy, it is desirable to set the safety factor ν in the equation (4) to a value exceeding (σyj / σy) / (σuj / σu).

From the above viewpoint, the safety factor ν is
σyj / σy (1-Lj / L)> 1.2 (5)
According to the equation (5), the yield strength ratio (σyj / σy) may be smaller as the length Lj of the heat treatment portion 4 is smaller.

However, if the heat treatment part 4 is small, harmful strain concentration occurs at the end of the steel structure member 1, leading to early destruction of the end of the steel structure member 1.
Therefore, the model shown in Figs. 2 and 3 for steel beams and box columns is subjected to a total of 178 cases of three-dimensional finite element analysis (FEM analysis), and the optimum heat treatment part that minimizes the end strain value. The length Ljopt of 4 was examined.

  4 (a) to 4 (d) all show the material axial strain (hε at the maximum strength) obtained by FEM analysis, hε / εy normalized by the yield strain εy in FIG. It is a graph which shows the example of a relationship between length Lj of the heat processing part 4 (Lj / D normalized by the height D of the member was plotted on the horizontal axis). Note that σyj / σy = 1.26 unless otherwise specified. From the graphs shown in FIGS. 4A to 4D, it can be seen that in any case, there exists an optimum reinforcing length Ljopt that minimizes distortion at the end.

  FIG. 4E shows the product of the optimum length Ljopt of the heat treatment part 4 obtained from the diagrams shown in FIGS. 4A to 4D and the length of the steel structure member 1 and the yield strength ratio. It is a graph which shows the relationship with ((L / D) * ((sigma) yj / (sigma) y)). These correlations are regressed to obtain equation (6). Since the error is within ± 0.1D, Equation (7) is obtained as the minimum length Ljmin of the heat treatment part 4. The length Lj of the heat treatment part 4 is desirably set to be equal to or longer than the minimum reinforcement length Ljmin obtained by the equation (7).

Ljopt / D = 0.0308 (L / D) · (σyj / σy) +0.139 [median value] (6)
Ljmin / D = 0.0308 (L / D) · (σyj / σy) +0.039 [Lower limit value] (7)
The yield strength ratio (σyj / σy) required when the heat treatment part 4 has the minimum length Ljmin is obtained. Substituting Ljmin in equation (7) into Lj in equation (5), equation (8) is obtained.
L / D> 0.039 / [1-0.0308 (σyj / σy) −1.2 (σy / σyj)] (8)
When the equation (8) is illustrated, the graph of FIG. 5 is obtained. From the graph shown in FIG. 5, it is understood that the yield strength ratio (σyj / σy) is preferably 1.25 or more. In general, the value of L / D is 2 or more.

  Thus, in the present embodiment, when the steel structure member 1 having the steel composition described above is applied to the steel structure 0, (i) the yield strength ratio (σyj / σy): 1.25 or more, and (Ii) Strong length Lj: Ljmin / D = 0.0308 (L / D) · (σyj / σy) + Satisfying not less than the minimum reinforcement length Ljmin calculated by 0.039 has a sufficient reinforcing effect. It is possible to reliably prevent the end of the steel structure member 1 from being welded to the end of the steel structure member 1 as in the prior art, and to prevent the end of the steel structure member 1 from being destroyed at an early stage.

  As described above, according to the present embodiment, by performing a partial heat treatment on the steel structure member without performing special processing such as a thickening method, not only an increase in strength of the heat treatment portion, The steel material for steel structure members which can also aim at the toughness of a heat processing part, the usage method of this steel material for steel structure members, and the steel structure using this steel material for steel structure members can be provided.

Further, the present invention will be described in detail with reference to examples.
Table 1 shows the composition (mass%), Pcm value, and plate thickness (mm) of the sample used in this example.

  These samples 1 to X13 are all melted as a steel plate for trial tests, and all of samples 1 to 14 satisfy the range defined by the present invention. On the other hand, for samples X1 to X13, at least one of the chemical components is not within the scope of the present invention.

  For dissolution, an experimental melting apparatus was used, raw iron was charged, and degassing was performed for 15 minutes after melting. At this time, the initial charge carbon may or may not exist. Additive elements such as C, Si, and Mn were added, and the amount of the additive component was finely adjusted by additional addition, and then stirring and homogenization were performed. Thereafter, Al and Ti were added to obtain a molten steel in a final state. Molten steel was cast in a mold.

  These were heated to 1150 ° C. and then hot rolled to finish at 900 ° C., rolled to the plate thickness shown in Table 1, and then air-cooled to obtain steel plates. Table 2 shows the C, P, Mn concentration (%) and the number of inclusions in the segregated portion of the steel sheet.

  The steel sheet thus obtained was subjected to a strengthening test in which heat treatment was locally performed. Each steel material was heated to 1000 ° C. with a high-frequency heating device, held for 30 seconds, and then cooled to room temperature at a cooling rate of 10 ° C. to 15 ° C./second. Test specimens were collected from the heat-treated parts and subjected to a tensile test and a Charpy impact test. Table 3 shows the tensile test results (YS, TS (MPa)) and the Charpy impact test results (J, 0 ° C.). Table 4 shows the heating temperature (° C.) and the cooling rate (° C./s) under the heat treatment conditions A to E in Tables 2 and 3.

  As shown in Table 3, the sample numbers 1 to 14 show the results when the steel plates of the present invention were heat treated. Characteristics other than the heat treatment part (base material part) are YS: 350 MPa or more, TS: 450 MPa or more, and Charpy absorbed energy at 0 ° C .: 70 J or more.

  Furthermore, in the heat treatment part (TQ part), it is strengthened to YS: 450 MPa or more, TS: 550 MPa or more, and Charpy absorbed energy at 0 ° C .: 70 J or more is given.

  On the other hand, in Comparative Examples X1 to X13, either strength or toughness cannot be satisfied. In X1 and X4 where the amount of C and the amount of Mn are too small, the portions other than the heat treatment portion and the strength of the heat treatment portion are insufficient. On the other hand, in other examples, the amount of components is inappropriate, or the amount of segregation and inclusions is excessive, so that the toughness of the base material and the heat treatment part is insufficient.

  In this example, for example, in Mark 4 (σy = 449 MPa, σu = 518 MPa, σyj = 601 MPa, σuj = 606 MPa) in Table 3, σuj / σu = 1.17, σyj / σy = 1.34, In order to prevent destruction before the base metal part, it is necessary to set the safety factor ν to a value of (σyj / σy) / (σuj / σu) = 1.14 or more.

A three-point bending test was performed assuming the steel structure member 1 used as shown in FIG. FIG. 6 shows the shape of the test body, and FIG. 7 shows the details of the reinforcing part, which is an experimental parameter.
The test body of FIG. 6 is a three-point bending H-shaped cross section beam having a total length of 4000 mm, and a partition plate having a plate thickness of 25 mm in the center with both ends as fulcrums is used as a loading point. The test body is provided with four buckling stops for the purpose of preventing lateral buckling. This experiment is an experiment in which the right portion (test beam) is broken across the central partition plate. The H-section steel cross section beam (force beam) on the left side is designed so that the cross section is larger than the beam on the right side, and the cover plate is welded to the beam flange near the partition plate so that the left side portion does not break. Yes. In the beam end reinforcement portion where the range of Lj from the right partition plate is an experimental parameter, reinforcement as shown in FIG. 7 and Table 5 is performed. A total of eight displacement meters (δ1 to δ8) were attached to the test body, and the vertical displacement of each part was measured.

  Loading on the test body was repeated loading on the center part of the test body, and was controlled by the member angle on the test beam side (R = δc / L, δc is the vertical displacement of the center part of the test body, L is 1987.5 mm). The control is repeated once at R = ± 1/400, then R = ± 1/60 (about 1.67 δp), R = ± 2/60 (3.33 δp), R = ± 3/60 (about 5δp) and R = ± 4/60 (about 6.67δp) were repeated twice.

  Table 5 shows the steel materials used and the cross-sectional dimensions, and Table 6 shows the mechanical properties of the steel materials used.

  The BHH test body in FIG. 7 and Table 5 is a test body corresponding to the example of the present invention, and a part corresponding to non-heat treatment (hereinafter referred to as “base metal part”) is a built-in H of SM490A steel plate and corresponds to a heat treatment part. For the portion (hereinafter referred to as “reinforcement portion”), the strength increase due to the heat treatment was simulated by welding the built-in H of the SA440 steel plate to the base metal portion.

  The SA440 steel plate uses a steel plate having the same thickness as the base material portion, and is welded and joined to the SM490A material that is the base material portion at the stage of the flat plate before assembly, and then the surface is finished smooth. BHH1 to BHH3 are test bodies corresponding to FIG. 3A, and the value of Lj is changed from 125 mm (BHH3) to 275 mm (BHH1). The BHH4 specimen is a specimen corresponding to FIG. 3 (b), in which an SA440 steel plate is welded and joined only to the beam flange of the reinforcing portion (Lj is 275 mm). On the other hand, the SPH test body in Table 5 is a side plate test body for comparison, and the end portion is reinforced by widening the flange width of the end portion from 166 mm to 254 mm. In all the test bodies, the beam end and the partition plate were joined with a non-scalloped specification, and the end of the beam flange was smoothly finished with R10.

  The yield strength ratio (σyj / σy) of the BHH specimen was 1.395 when evaluated by the strength of the flange portion. On the other hand, the length Ljopt of the optimum reinforcing part (corresponding to the heat treatment part) and the length Ljmin of the minimum reinforcing part (corresponding to the heat treatment part) of the BHH specimen are as follows. Is also set to a value equal to or greater than Ljmin.

Ljopt = (0.0308 × (L / D) × (σyj / σy) +0.139) × 440 = (0.0308 × (1987.5 / 440) × 1 where L = 1987.5 mm and D = 440 mm .395 + 0.139) × 440 = 147 mm, Ljmin = (0.0308 × (L / D) × (σyj / σy) +0.039) × 440 = (0.0308 × 1987.5 × (1987.5 / 440) ) × 1.395 + 0.039) × 440 = 103 mm
The test results are summarized in Table 7. In Table 7, eMp represents the total plastic yield strength according to the general yield method, eMu represents the maximum yield strength (positive or negative, whichever is greater), Σθ represents the cumulative plastic rotation angle (positive or negative total value) until fracture, θ is a value obtained by dividing the deflection at the center of the specimen by the material length L, and Σθ was evaluated based on the point that the yield strength decreased by 5% from the maximum yield strength at the time of fracture.

  In the present invention example (BHH), the end portions of the test specimens were all healthy, and the maximum yield strength was determined by the destruction of the base material portion in the vicinity of the reinforcing portion. All of the BHH specimens are locally buckled in the base material portion to reach the maximum proof stress, and still retain the energy absorbing ability while causing a gentle load decrease after the maximum proof stress. It can be said that this is a failure mode that fully demonstrates the performance of the base metal part.

  On the other hand, in the SPH specimen as a comparative example, a ductile crack was generated at the starting portion of the side plate, causing a sudden decrease in yield strength.

FIG. 1A to FIG. 1C are explanatory views showing a steel structure member of the present embodiment applied to a steel structure. Yield strength σyj of the heat-treated portion after heat treatment is performed by simplifying half of the total length (2L) of the steel structure member of the steel plate member or square steel pipe member to the cantilever (full length L), and the yield of the non-heat-treated portion excluding the heat-treated portion It is explanatory drawing for examining the relationship between ratio with intensity | strength (sigma) y, and the length Lj of a heat processing part. FIG. 3A is an explanatory view showing a case where heat treatment is performed on the entire cross-sectional area of a steel structure member such as a steel plate member and a square steel pipe member, and FIG. 3B is a steel structure member such as a steel plate member and a square steel pipe member. It is explanatory drawing which shows the case where it heat-processes to some cross-sectional area | regions. 4A to 4D are graphs showing examples of the relationship between the strain in the axial direction of the end portion at the maximum proof stress obtained by FEM analysis and the length Lj of the heat treatment portion. (8) It is a graph which illustrates a relationship with Formula. FIG. 6 is an explanatory view showing the shape of a test body in Example 2. It is explanatory drawing which shows the detail of the reinforcement part (equivalent to the heat processing part in Example 2) of a test body.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Steel structure member 2 Steel structure member 3 Welding part 4 Heat treatment part 5 Steel structure member 6 Through diaphragm 7 Inner diaphragm type pillar 8 Panel zone 9 Non-heat treatment part

Claims (9)

In mass%, C: 0.04 to 0.18%, Si: 0.02 to 0.50%, Mn: 0.5 to 2.0%, sol. Al: 0.06% or less, Ti: 0.003-0.030%, N: 0.008% or less, 2Nb + 3Ti + Al: 0.05% or more, welding defined by the following formula (1) crack sensitivity index (Pcm) is a steel structure comprising been used at least as one of the constituent material of the steel product for 0.12 to 0.27% der Ru steel structural members,
Heat treatment for cooling a portion including a dangerous cross section of a steel structure member made of steel for the steel structure member from 800 ° C. to 500 ° C. at an average cooling rate of 3 ° C./second or more after heating to 800 ° C. A steel structure characterized in that the heat treatment part is made into a structure mainly composed of fine bainite that gives 0 ° C. Charpy absorbed energy of 70 J or more.
Pcm = C + (Si / 30) + (Mn / 20) + (Cu / 20) + (Ni / 60)
+ (Cr / 20) + (Mo / 15) + (V / 10) + 5B (1) The length (Lj) of the longitudinal direction of the part to which the said heat processing is performed is a steel structure described in Claim 1 which satisfies the following (2) Formula.
Lj / D ≧ 0.0308 (L / D) · (σyj / σy) +0.039
(2)
However, L in Formula (2) shows the length of the half of the full length of the said steel structure member, and D shows the member fault of this steel structure member. The steel structure according to claim 1 or 2, wherein a yield strength (σyj) of a portion subjected to the heat treatment is 1.25 times or more of a yield strength (σy) of a portion other than the portion subjected to the heat treatment. Thing . The steel frame according to any one of claims 1 to 3, further comprising, in mass%, B: 0.0003 to 0.003% and / or Nb: 0.003 to 0.05%. Structure . Furthermore, by mass%, Cu: 0.05-1.5%, Ni: 0.05-2.0%, Cr: 0.03-1.0%, Mo: 0.03-1.0% and V: The steel structure according to any one of claims 1 to 4, which contains one or more of 0.005 to 0.1%. The cleanliness defined by JIS G 0555 is 0.040% or less at dA60 × 400, 0.030% or less at dB60 × 400, or 0.030% or less at dC60 × 400. The steel structure described in any one of the above. The segregation part located in the center of the thickness direction has a steel composition in which C: 0.29% or less, P: 0.30%, and Mn: 3.5% or less in mass%. The steel structure described in any one of the items up to 6. In mass%, C: 0.04 to 0.18%, Si: 0.02 to 0.50%, Mn: 0.5 to 2.0%, sol. Al: 0.06% or less, Ti: 0.003 to 0.030%, N: 0.008% or less, 2Nb + 3Ti + Al: 0.05% or more, and further defined by the following formula (1) Weld cracking susceptibility index (Pcm) is 0.12 to 0.27%. The part including the dangerous cross section of the steel structure member is heated to 800 ° C or higher and then from 800 ° C to 500 ° C, 3 ° C / second. By partially performing the heat treatment for cooling at the above average cooling rate, the heat treatment part has a microstructure mainly composed of fine bainite capable of giving 0 ° C. Charpy absorbed energy of 70 J or more. How to use steel materials for steel structure members.
Pcm = C + (Si / 30) + (Mn / 20) + (Cu / 20) + (Ni / 60)
+ (Cr / 20) + (Mo / 15) + (V / 10) + 5B
・ ・ ・ ・ ・ ・ ・ (1) The method for using a steel material for a steel structure member according to claim 8, wherein a length (Lj) in a longitudinal direction of a portion to be subjected to the heat treatment satisfies the following expression (2).
Lj / D ≧ 0.0308 (L / D) · (σyj / σy) +0.039
(2)
However, L in Formula (2) shows the length of the half of the full length of the said steel structure member, and D shows the member fault of this steel structure member.

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