JP4273787B2 - H-shaped steel for multipass prime welding with high toughness of fillet part and high pass temperature, and manufacturing method thereof - Google Patents

Description

【００４２】
【表２】

【００４３】
【表３】

【００４４】
【発明の効果】
本発明により、フィレット部の靭性が70J以上と高く、かつ700℃以上の高パス間温度で多層盛り溶接を行なっても溶接熱影響部（HAZ）の靭性が70J以上を確保できる高パス間温度多層盛り溶接用Ｈ形鋼を提供することができる。それにより、建築構造物の建設能率を向上することができ、併せて梁端溶接部や柱一柱溶接部の高靭化により構造物の信頼性向上を図ることができる。
【図面の簡単な説明】
【図１】 Ti、N及びCeq（炭素当量）を変化させた組成を有する素材のフィレット部相当のシャルピー試験値を、素材スラブ組成の炭素当量の関係で整理したグラフである。
【図２】 Ti、N及びCeq（炭素当量）を変化させた組成を有する素材からＨ形鋼を圧延し、そのフランジ部から試験切り出した試験片についての再現HAZ試験結果である。[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a rolled H-shaped steel in which multilayer welding of carbon dioxide gas, EGW, and SAW is performed. In particular, multilayer welding can be performed at a high pass-to-pass temperature, and the viewpoint of brittle fracture resistance and welding work efficiency. To rolled H-section steel with high fillet part toughness.
[0002]
[Prior art]
Rolled H-section steel (hereinafter simply referred to as “H-section steel”) is an indispensable steel material for the development of social infrastructure. JIS SN400MPa class and JIS SN490MPa class H section steel is mainly used as a material for building structures. It is used as a beam material. In the SN standard of JIS, the upper limit of the yield point and the yield ratio is determined from the viewpoint of earthquake resistance of the building structural member, and the upper limit of the carbon equivalent is determined from the viewpoint of weldability.
[0003]
When assembling structures such as buildings and bridges using such H-shaped steel, multi-layer welding by various welding methods such as carbon dioxide welding, electrogas welding (EGW), submerged arc welding (SAW) is performed. Is called. In this multi-layer welding, the temperature between passes tends to be high, and the joint performance tends to be lowered. For this reason, in multi-layer welding of steel materials, the preheating temperature during welding, welding materials, etc. are optimally selected according to the grade, thickness, and welding method of the steel material used, and the upper limit of the interpass temperature is set, and strict work is performed accordingly. The strength and toughness of the weld metal and HAZ are secured under the management standards. Generally, the interpass temperature is required to be 350 ° C. or lower.
[0004]
In particular, column-diaphragm type multi-layer beam end welding by carbon dioxide arc welding is frequently used for column-beam welding of building structures made of H-shaped steel, but the temperature between passes tends to be high due to its structure. In many cases, the temperature between passes defined by the work management standard exceeds 350 ° C. For this reason, the welding operation must be interrupted, and then the welding must be resumed after waiting for a decrease in interpass temperature, resulting in a reduction in welding operation efficiency.
[0005]
Therefore, it is desired to provide an H-section steel that can be welded in a multi-pass manner at a high interpass temperature that does not cause such a decrease in welding work efficiency. In particular, when multi-layer welding is applied as reciprocal continuous welding to beam end joints or column-column joints, it is said that the construction man-hour will be reduced to 1/3 or less compared to the case of ordinary carbon dioxide arc welding. However, by performing reciprocal continuous welding, the interpass temperature rises to 500 ° C or higher, and in particular, at the flange under the beam, the weld length is about half of the flange length due to the presence of the web portion. There is a problem in that the temperature between passes increases to higher than or equal to ° C., and the demand for providing an H-section steel capable of multi-layer welding at the above-mentioned high pass temperature is further increased.
[0006]
On the other hand, when H-section steel is applied as the beam material of the structure, the H-section steel has a notch portion called scallop near the fillet portion where the flange portion and the web portion intersect to pass the backing metal. It is generally done. As a result, the possibility of brittle fracture from this scallop at the time of an earthquake has been pointed out, and there is a strong demand for increasing the toughness of the fillet part of the H-section steel adjacent to the scarp as well as the weld heat affected zone.
[0007]
In connection with the above technical requirements, research on welding materials has been advanced in order to increase the interpass temperature in multi-layer welding, such as Patent Document 1, Patent Document 2, and Patent Document 3, for example. This technique is disclosed in Japanese.
[0008]
[Patent Document 1]
Japanese Patent Laid-Open No. 10-230387 [Patent Document 2]
Japanese Patent Laid-Open No. 1-239892 [Patent Document 3]
JP 2000-288743 A [0009]
[Problems to be solved by the invention]
However, these techniques are directed to obtaining a weld metal with good performance, and attention has been focused on improving the base material side (that is, the H-shaped steel) which is the other member constituting the weld joint. Absent. In other words, due to high-pass welding, there was still a problem with regard to the toughness of the heat affected zone (HAZ) of the H-shaped steel on the base metal side. Specifically, for column-column welds that exceed 50 passes in the field when CO ₂ multi-layer welds at the beam end welds or extremely thick H-section steel are used for the column materials, Although the work efficiency improvement due to the allowance is extremely large, at present, there is a problem that the HAZ toughness near the melting line cannot be obtained sufficiently.
[0010]
In addition, H-section steel applied to beam end welds must be able to cope with the risk of brittle fracture of building structures from scallops during an earthquake, as described above. Therefore, it is required to increase the toughness of the fillet portion of the H-shaped steel, specifically, to satisfy the Charpy absorbed energy value at the fillet portion as vE ₀ > 70J.
[0011]
The present invention advantageously solves the above-mentioned problems, and can ensure the toughness of the heat affected zone (HAZ) even when performing multi-pass welding at a high interpass temperature, and at the same time fillets corresponding to the roots of the web portion and the flange portion. An object of the present invention is to provide an H-section steel for high pass temperature multi-pass welding with high fillet part toughness that can secure the toughness of the part.
[0012]
[Means for Solving the Problems]
The present inventor examined the cause of insufficient toughness of the fillet part, and in the fillet part, the austenite grains at the reheating temperature are maintained without being recrystallized by rolling, and the final microstructure is obtained from coarse austenite grains. It was found that coarse ferrite + pearlite or coarse ferrite + upper bainite was formed, and the toughness was insufficient compared to flanges and webs. In addition, HAZ toughness degradation when multi-pass welding is performed at a high pass temperature is due to the fact that the austenite in the heated part is coarsened, the HAZ microstructure is coarsened, and the microstructure is upper bainite. I knew that this was to increase island martensite (MA). And the cause of the lack of toughness of these fillets and the HAZ toughness reduction at the time of high-pass welding has a common point of the formation of coarse austenite, so in order to solve the above problem, first of all hot rolling To refine the austenite grains at the time, secondly to promote the formation of ferrite, thirdly to adjust the steel composition to control the amount of the second phase structure formed in the fillet part and HAZ part After confirming that it is important, we conducted intensive research on the component systems and processing conditions that can achieve such conditions, and concluded that the following component systems and processing conditions are suitable.
[0013]
The H-section steel for high pass temperature multi-pass welding according to the present invention is C: 0.07 to 0.18%, Si: 0.05 to 0.6%, Mn: 0.6 to 1.6%, P: 0.020% or less, S: 0.020% or less, Ti: 0.005 to 0.025%, N: 0.0030 to 0.0070 %, Al : 0.005 to 0.1% , Nb content is limited to 0.003% or less, the balance is Fe and inevitable impurities, and , Ceq (carbon equivalent): 0.42% or less, Ti / N: 2 to 4 steel composition, fillet part has a structure consisting of ferrite and pearlite, and its V- notch Charpy absorbed energy at 0 ° C is 70 J In addition, the HAZ toughness of the final pass part in multi-layer continuous welding at an interpass temperature of 720 ° C. is 70 J or more . Here, Ceq (carbon equivalent) is
Ceq = C + Si / 24 + Mn / 6 + Ni / 40 + Cr / 5 + Mo / 4 + V / 14 (mass%)
Say.
[0014]
The steel composition may further contain one or two of Ca: 0.0050% or less and REM: 0.03% or less. Moreover, Cu: 0.7% or less, Ni: 1.5% or less, Cr: 0.5% or less, Mo: 0.2% or less, V: 0.08% or less can be contained.
[0015]
High interpass temperature multi-layer welding for H-shaped steel according to above, a material having a steel composition described above, and after reheating to 1200 to 1350 ° C., the crude universal rolling finishing temperature Ar ₃ temperature or more universal It is advantageous to manufacture by forming into H-shaped steel by rolling and then applying post-rolling cooling selected from air cooling and accelerated cooling .
[0016]
DETAILED DESCRIPTION OF THE INVENTION
H-shaped steel is formed using a universal rolling mill. At that time, the left and right flange portions are pressed by horizontal and vertical rolls, and the web portion is pressed by vertical rolls to reduce the structure. Toughness is given. However, the fillet part is hardly expected to have a rolling reduction effect due to rolling, and has a feature that the cooling rate after rolling is smaller than that of the flange part or the web part. Therefore, at the reheating temperature, the austenite grains are maintained as they are without recrystallization by rolling, and coarse ferrite + pearlite or coarse ferrite + upper bainite is formed as the final microstructure from coarse austenite grains. And toughness is reduced. The present inventor conducted the following test to clarify the influence of the material chemical composition on the lack of toughness of the fillet portion due to the above cause.
[0017]
By mass ratio, C: 0.07 to 0.18%, Si: 0.05 to 0.6%, Mn: 0.6 to 1.6%, P: 0.020% or less, S: 0.020% or less, Ti: 0.005 to 0.025%, N: 0.0030 to 0.070% A 20mm-thick block is cut from steel consisting of Fe and the inevitable impurities, and this is heated to 1300 ° C for 1h, and then (without rolling), the cooling rate between 800-500 ° C is 0.4 ° C / s. As cooled. The block was subjected to a structure investigation and a V-notch Charpy test at 0 ° C. using a JIS Z 2202 No. 4 test piece. This test result gives an estimate of the structure and toughness of the fillet part with a small hot rolling effect.
[0018]
FIG. 1 is a graph in which the toughness (Charpy test value, vE ₀ ) equivalent to the fillet obtained in the above test is arranged in relation to the carbon equivalent of the material slab composition. The curve (1) in the figure does not contain Ti and N as steel components (excluding those inevitable impurities), and the curve (2) shows Ti: 0.010 to 0.018 mass%, N: 0.035. It contains ~ 0.065 mass%. In the figure, the ▲ marks are for steel materials containing Ceq: 0.039%, Ti: 0.015%, N: 0.0046%, Nb: 0.012%.
[0019]
As can be seen from FIG. 1, steel containing no Ti and N as a steel component has low toughness, but steel containing an appropriate amount of Ti and N has high toughness as a whole, especially when the carbon equivalent is 0.42 mass% or less. It turns out that the above high toughness is obtained.
[0020]
As a result of structural observation, steel components that do not contain Ti and N are coarsened to an average austenite grain size of about 500 μm by heating at 1300 ° C, so that coarse ferrite + pearlite structure or upper bainite structure during cooling process. It has been found that this is the cause of the above-mentioned decrease in toughness. On the other hand, the steel containing the proper amount of Ti and N is refined with an average austenite grain size of about 100μm even after heating at 1300 ° C, so the microstructure after cooling is mainly a dense ferrite + pearlite structure. It was found that if Ceq (carbon equivalent) is limited to 0.42 mass% or less, intermediate transformation structures such as upper bainite are hardly generated, and high toughness of 100 J or more can be obtained. However, even steels containing proper amounts of Ti and N have a low estimated value of the toughness of the fillet part when Nb is contained in an amount of 0.012 mass% (▲). This will be described later.
[0021]
As mentioned above, if steel compositions contain appropriate amounts of Ti and N, and Ceq (carbon equivalent) is limited to 0.42 mass% or less, sufficient toughness exceeding 70 J will be ensured even in the fillet where little reduction occurs. be able to. However, when H-shaped steel is used as a building material, it is necessary to clear the toughness value of the fillet part described above, and it has sufficient toughness even when performing multipass welding at a high interpass temperature. Required.
[0022]
FIG. 2 shows the welding heat corresponding to the case where the H-shaped steel was rolled from a material having the same composition as in Experiment 1 and the test piece cut out from the flange portion was subjected to the final bead at a temperature between passes of 550 ° C. This is the result of giving a history and examining its toughness. The component system indicated by the reference numerals in the figure is the same as in FIG. Figure 2 shows that steel components that do not contain Ti and N have low reproducible HAZ toughness, but those that contain suitable amounts of Ti and N have high reproducible HAZ toughness, especially when the carbon equivalent is 0.42 mass% or less, 70 J or more. It can be seen that high toughness can be obtained.
[0023]
Thus, when Ti and N are contained in proper amounts and Ceq (carbon equivalent) is 0.42 mass% or less, H-shaped steel is to be welded in multiple layers at a high interpass temperature with high toughness of the fillet part. Even if it carries out, it can have sufficient toughness. The present invention makes use of this finding and further provides an H-section steel having the necessary mechanical and structural conditions by satisfying the following chemical composition conditions. Hereinafter, the chemical composition of the H-section steel according to the present invention will be specifically described.
[0024]
C: 0.07 to 0.18% (mass%, the same applies below)
C is an effective element for obtaining the strength required for structural steel, and must be contained at least 0.07% or more. However, if the content exceeds 0.18 %, the fraction of the second phase increases in the microstructure, especially when Cr, Mo, etc. are alloyed, the second phase becomes upper bainite, and a large amount of MA is contained therein. (Island martensite) is generated and HAZ toughness is reduced during multi-pass welding at high interpass temperatures. Therefore, the upper limit of C content is set to 0.18%.
[0025]
Si: 0.05-0.6% or less
Si dissolves in steel and is effective in improving the strength, but 0.05% or more is necessary to obtain the effect. However, if it exceeds 0.60%, MA increases and HAZ toughness decreases. Therefore, it was made into the range of 0.05 to 0.6%.
[0026]
Mn: 0.6 to 1.6% or less
Mn is also an element effective in increasing the strength. However, if it is less than 0.6%, the effect is small, and if it exceeds 1.6%, the hardenability is improved and the weldability is lowered, so the content was made 0.6 to 1.6%.
[0027]
P: 0.020% or less, S: 0.020% or less
P improves strength by increasing hardenability, but segregates in the final solidified part during the solidification stage such as continuous casting, lowering the toughness of the base metal and lowering the toughness of the part subjected to repeated thermal history by multi-layer welding. Therefore, the upper limit is made 0.020%. On the other hand, S forms MnS and lowers the ductility and toughness of the H-section steel, so the lower amount is desirable, but if it is 0.020% or less, there is no practical problem, so the upper limit was made 0.020%.
[0028]
Al: 0.005-0.1%
Al is an element added as a deoxidizer, but if its amount is less than 0.005%, the effect is small, and conversely, if it exceeds 0.1%, the effect is saturated, but the amount of nonmetallic inclusions is rather Since it becomes a cause of increase, the content is set in the range of 0.005 to 0.1%.
[0029]
Ti: 0.005-0.025%
Ti forms TiN and is effective for refining the structure of the fillet part and refining the HAZ structure during multipass welding at high-pass temperature due to the refining function of austenite grains and the nucleation ability of ferrite. The effect appears at 0.005% or more, but saturates above 0.030%. Therefore, it is contained in the range of 0.005 to 0.030%.
[0030]
N: 0.0030 to 0.070%
N combines with Ti to form TiN. TiN is effective for refining austenite grains as described above, and also has the ability to nucleate ferrite, making the fillet part tougher and refining the structure of the HAZ part during multipass welding at high pass temperatures. It is effective for. However, if the amount of N is less than 0.0030%, the effect is small. On the other hand, even if added over 0.0070%, the effect is saturated, so the range was 0.0030 to 0.0070%.
[0031]
Ti / N: 2.0 to 4.0
When Ti / N is less than 2.0, N is stoichiometrically excessive, and free N that does not bind to Ti remains in the steel, resulting in strain aging embrittlement and increased yield point (YP). This will cause a drop in the seismic performance. On the other hand, when it exceeds 4.0, TiN becomes coarse and the number of TiN present per unit volume of the steel structure decreases, and the function of TiN is not sufficiently exhibited. Therefore, the upper limit is set to 4.0 and the lower limit is set to 2.0.
[0032]
Nb: 0.003% or less
If Nb is present in an amount of 0.003% or more, the effect of increasing the toughness of the fillet with TiN and refining the structure of the multipass welds with high interpass temperature will be drastically reduced (see ▲ marks in Figs. 1 and 2). It shall be the following.
[0033]
Ceq (carbon equivalent): 0.42% or less
If the Ceq (carbon equivalent) exceeds 0.42%, even when TiN is present in the proper amount of steel, the toughness of the fillet will not improve (see Fig. 1), and during high pass temperature multi-layer welding Since the toughness in the vicinity of the melting line (reproduced HAZ toughness) decreases (see FIG. 2), Ceq (carbon equivalent) is set to 0.42% or less.
[0034]
One or two of Ca: 0.0050% or less , REM: 0.03% or less These elements are added as a deoxidizer, and can be contained alone or in combination within the above range. In addition, Ca forms (Mn, Ca) (O, S) and granulates MnS to improve the toughness of the steel material, and also acts as a nucleus of ferrite transformation to improve the toughness of the fillet part, between high passes It also contributes to the improvement of HAZ toughness during temperature multilayer welding. Also, REM forms REM (O, S) and brings about austenite refinement, thereby contributing to improvement of toughness of the fillet part and improvement of HAZ toughness during multipass welding at high interpass temperature.
[0035]
Cu: 0.7% or less, Ni: 1.5% or less, Cr: 0.5% or less, Mo: 0.2% or less, V: 0.08% or less of one or more of these elements is an element improving the strength of the base material In particular, a thick flange H-shaped steel can be contained alone or in combination within the above range in order to ensure its strength. However, these excessive contents cause Cu to precipitate upon cooling and reduce toughness for Cu, and for Ni it is expensive and its effect is saturated, so Cr and Mo reduce weldability, In order to promote the upper bainite transformation and increase MA (island martensite), V precipitates as VN or VC and lowers the toughness of the fillet . Therefore, the content of these elements is limited to the above range.
[0036]
The H-section steel according to the present invention is subjected to breakdown rolling and roughing after reheating a material obtained by solidifying molten steel adjusted to a predetermined chemical composition into a slab or beam blank by continuous casting according to a conventional method. It is manufactured by hot rolling into a predetermined shape by universal rolling and finish universal rolling. After finishing universal rolling, the rolled H-section steel is air cooled or accelerated cooled. Accelerated cooling can be performed by water cooling the flange portion and / or the web portion.
[0037]
In the rolling step, the slab heating temperature is preferably in the range of 1200 to 1350 ° C. When the heating temperature is lower than 1200 ° C., the rolling load at the time of the hole-type rolling by the breakdown mill before the universal rolling becomes large and the number of rolling passes increases. As a result, the rolling temperature of the web portion decreases, the rolled structure of the web portion becomes extremely fine, and in some cases, rolling occurs in part of the ferrite region, which significantly increases the yield point (or proof stress) of the web portion. To do. This causes a deterioration in the seismic performance of the building. On the other hand, heating above 1350 ° C promotes scale loss.
[0038]
Further, the end temperature of rough universal rolling needs to be Ar ₃ temperature or higher. This is because the yield point (or proof stress) rises sharply when the rolling finish temperature during rough universal rolling is below the Ar ₃ point. In particular, the web part, which is thin compared to the flange part, has a large heat removal during rolling and tends to be low in temperature, so it is important to pay close attention to the rolling end temperature and maintain Ar ₃ or higher. It is.
[0039]
【Example】
Steel materials having the compositions shown in Table 1 were melted and rolled into H-shaped steel under the conditions shown in Table 2. The mechanical properties (yield point (YP), tensile strength (TS), yield ratio (YR), toughness (vE ₀ ) and toughness of the fillet part (vE ₀ )) of the manufactured H-section steel flange and web In addition, the final welding when a heat cycle test specimen was taken from the flange part of the manufactured H-section steel and CO ₂ multilayer welding was continuously welded under the conditions of a heat input of 40 kJ / cm and a welding length of 100 mm. A reproducible thermal cycle test corresponding to the heat history in the vicinity of the melting line of the part (corresponding to a temperature of 720 ° C.) was performed, and its reproducible HAZ toughness was evaluated.
[0040]
As can be seen from Table 3, the H-section steel according to the present invention has an excellent fillet portion toughness (vE ₀ ) of 100 J or more and a small strength difference between the web portion and the flange portion. On the other hand, in the case of the comparative example, the toughness of the fillet portion was about 50J. In addition, the reproduced HAZ toughness of the final pass portion in multi-layer continuous welding assuming an interpass temperature of 720 ° C. was as good as 70 J or more in the present invention example, but about 30 J in the comparative example.
[0041]
[Table 1]

[0042]
[Table 2]

[0043]
[Table 3]

[0044]
【The invention's effect】
With this invention, the toughness of the fillet part is as high as 70J or higher, and the high pass-to-pass temperature that can ensure the toughness of the weld heat affected zone (HAZ) to be 70J or higher even when performing multipass welding at a high pass temperature of 700 ° C or higher. An H-section steel for multi-layer welding can be provided. Thereby, the construction efficiency of a building structure can be improved, and at the same time, the reliability of the structure can be improved by increasing the toughness of the beam end welded portion and the column-one-column welded portion.
[Brief description of the drawings]
FIG. 1 is a graph in which Charpy test values corresponding to fillet portions of materials having compositions with varying Ti, N, and Ceq (carbon equivalent) are arranged in relation to the carbon equivalent of the material slab composition.
FIG. 2 is a reproduction HAZ test result for a test piece obtained by rolling an H-section steel from a material having a composition in which Ti, N, and Ceq (carbon equivalent) are changed, and cutting out from the flange portion.

Claims (4)

By mass ratio, C: 0.07 to 0.18%, Si: 0.05 to 0.6%, Mn: 0.6 to 1.6%, P: 0.020% or less, S: 0.020% or less, Ti: 0.005 to 0.025%, N: 0.0030 to 0.0070 % , Al : 0.005 to 0.1% , Nb content is limited to 0.003% or less, the balance is Fe and inevitable impurities, and Ceq (carbon equivalent): 0.42% or less, Ti / N: 2 to Multi-layer continuous welding with a steel composition of 4 and a fillet part with a structure consisting of ferrite and pearlite, with a V- notch Charpy absorbed energy at 0 ° C of 70 J or more and an interpass temperature of 720 ° C H-section steel for high pass temperature multi-pass welding with high fillet toughness, characterized by HAZ toughness of 70J or more in the final pass section . Here, Ceq (carbon equivalent) is
Ceq = C + Si / 24 + Mn / 6 + Ni / 40 + Cr / 5 + Mo / 4 + V / 14 (mass%)
Say. The steel composition further contains one or two of Ca: 0.0050% or less and REM: 0.03% or less, for high pass temperature multi-pass welding with high toughness of the fillet part according to claim 1 H-section steel. Steel composition further, Cu: 0.7% or less, Ni: 1.5% or less, Cr: 0.5% or less, Mo: 0.2% or less, V: claims, characterized in that it contains 0.08% or less of one or more Item H or H-shaped steel for high pass temperature multi-pass welding where the toughness of the fillet portion is high. The raw material having the steel composition according to any one of claims 1, 2, and 3 was reheated to 1200 to 1350 ° C and then formed into an H-shaped steel by universal rolling with a rough universal rolling finishing temperature of Ar ₃ or higher . Then, after-rolling cooling selected from air cooling and accelerated cooling is performed , and a method for producing a H-section steel for high pass temperature multi-layer welding with high fillet portion toughness.

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