Steel materials and welded joints

Abstract

The present invention provides steel materials and welded joints that ensure low-temperature toughness not only of the steel material but also of the welded joint. [Solution] Standard value of tensile strength TS (N / mm 2 ) is 400-550 N / mm 2 It is a grade, and the carbon equivalent C eq A steel material having a toughness value of 27J or more at 0℃ to -50℃, wherein the steel material has a tensile strength standard value TS w1 (N / mm 2 )(However, TS w1 ≥TS+60, and TS w1 Steel material having a toughness value of 27 J or more at 0°C to -50°C when gas-shielded arc welding is performed using welding material (≥1.05 TS) under welding conditions of a heat input of 40 kJ / cm or less and an interpass temperature of 350°C or less.

Description

[Technical Field]

[0001] This invention relates to steel materials in a steel frame structure, and to welded joints formed by welding such steel materials. [Background technology]

[0002] Steel frame structures for buildings and other structures are generally designed so that the column-beam joints undergo plastic deformation during earthquakes, thereby absorbing seismic energy. Therefore, the steel materials that make up these steel frame structures are required to have high yield strength and tensile strength, as well as high toughness and ductility from a safety perspective.

[0003] Furthermore, it is known that the toughness of steel decreases at temperatures below 0°C. For example, when constructing buildings such as refrigerated warehouses or low-temperature warehouses with steel frames, the ambient temperature of the steel frame falls below 0°C, raising concerns about a decrease in the toughness of the steel. Thus, steel used at low temperatures needs to possess properties that allow it to exhibit excellent toughness even at low temperatures.

[0004] In this regard, Patent Document 1 discloses a steel material that exhibits excellent low-temperature toughness by defining the steel composition and microstructure of the steel material. [Prior art documents] [Patent Documents]

[0005] [Patent Document 1] Japanese Patent Publication No. 2011-195883 [Overview of the Initiative] [Problems that the invention aims to solve]

[0006] Here, when the column-beam joint of the steel frame structure is configured in a general continuous diaphragm form, the diaphragm and the beam flange at the column-beam joint are welded, and the steel column and the diaphragm are welded. The diaphragm is a flat steel material provided in the direction transverse to the steel column in order to supplement the stress transmission at the column-beam joint and enhance the rigidity of the joint. If the steel material and the welded joint do not have sufficient toughness, early fracture may occur at these locations during an earthquake, the column-beam joint may not be able to exhibit sufficient plastic deformation performance, and the seismic resistance of the steel frame structure may be significantly impaired. Therefore, in addition to the low-temperature toughness of the steel material, it is necessary to ensure the low-temperature toughness of the welded joint.

[0007] In order to solve the above problems, an object of the present invention is to provide a steel material and a welded joint that can ensure the low-temperature toughness of the welded joint in addition to the low-temperature toughness of the steel material.

Means for Solving the Problems

[0008] In order to solve the above problems, the present invention has the following features.

[0009] [1] A steel material having a specified tensile strength value TS (N / mm 2 ) in the range of 400 to 550 N / mm 2 , a carbon equivalent C eq of 0.41 or less, and a toughness value of 27 J or more at 0°C to -50°C. When the steel material is gas shielded arc welded under welding conditions of a heat input of 40 kJ / cm or less and an interpass temperature of 350°C or less using a welding material with a specified tensile strength value TS w1 (N / mm 2 ) (where TS w1 ≧TS + 60 and TS w1 ≧1.05TS), the toughness value of the welded joint formed at 0°C to -50°C is 27 J or more.

[0010] [2] A specified tensile strength value TS (N / mm 2 ) in the range of 400 to 550 N / mm 2 , a carbon equivalent C eqA steel material having a toughness value of 27J or more at 0℃ to -50℃, wherein the steel material has a tensile strength standard value TS w2 (N / mm 2 )(However, TS w2 Steel material in which the toughness value of the weld formed when submerged arc welding is performed using welding material (≥TS+80) under welding conditions of 80 kJ / cm or less heat input is 27 J or more at 0°C to -50°C.

[0011] [3] A welded joint between a diaphragm and a beam flange at a column-beam joint of a steel frame structure, wherein the diaphragm and the beam flange are each made of the steel material described in [1], and the diaphragm and the beam flange are joined by gas shielded arc welding under welding conditions of a heat input of 40 kJ / cm or less and an interpass temperature of 350°C or less, and the yield strength of the diaphragm is specified as YS d (N / mm 2 ) and standard value of tensile strength TS d (N / mm 2 ), and the standard value YS of the yield strength of the beam flange g (N / mm 2 ) and standard value of tensile strength TS g (N / mm 2 ) is given by the following equations (1) and (2) below YS d ≧YS g ...(1) TS w1 ≥min(TS d , TS g ) + 60 ……(2) A welded joint that satisfies the following conditions.

[0012] Note that the min on the right-hand side of equation (2) above refers to the minimum value of the values ​​listed in parentheses.

[0013] [4] A welded joint between a steel column and a diaphragm at a column-beam joint of a steel frame structure, wherein the steel column and the diaphragm are joined by gas shielded arc welding under welding conditions of a heat input of 40 kJ / cm or less and an interpass temperature of 350°C or less, and the yield strength of the steel column is specified as YS c(N / mm 2 ) and standard value of tensile strength TS c (N / mm 2 ), and the standard value YS of the yield strength of the diaphragm. d (N / mm 2 ) and standard value of tensile strength TS d (N / mm 2 ) is given by the following equations (3) and (4) below YS d ≧YS c ...(3) TS w1 ≥ max(1.05TS) c , TS d ) ... (4) A welded joint that satisfies the following conditions.

[0014] Note that the 'max' on the right-hand side of equation (4) above refers to the maximum value among the values ​​listed in parentheses.

[0015] [5] A welded joint between the web and flange of a welded H-beam, wherein the web and the flange are each made of the steel material described in [2], and the web and the flange are joined by submerged arc welding under welding conditions of a heat input of 80 kJ / cm or less, and the tensile strength of the web is the standard value TS w (N / mm 2 ), and the standard value TS for the tensile strength of the flange f (N / mm 2 ) is given by the following equation (5) TS w2 ≥min(TS w , TS f ) + 80 ……(5) A welded joint that satisfies the following conditions.

[0016] Note that the min on the right-hand side of equation (5) above refers to the minimum value of the values ​​listed in parentheses. [Effects of the Invention]

[0017] According to the steel material and welded joint of the present invention, the toughness value of the steel material and welded joint is ensured at temperatures from 0°C to -50°C. As a result, in steel frame structures using the steel material and welded joint of the present invention, premature fracture during earthquakes is prevented even at low temperatures, and the steel frame structure can be provided with sufficient plastic deformation performance and seismic resistance. [Brief explanation of the drawing]

[0018] [Figure 1] Figure 1 is a graph showing the toughness value and brittle fracture surface ratio obtained by performing a Charpy impact test on one embodiment of the steel material of the present invention. [Figure 2] Figure 2 is a graph showing the toughness values ​​obtained by performing a Charpy impact test on one embodiment of the welded joint of the present invention. [Figure 3] Figure 3 is a graph showing the toughness values ​​obtained by performing a Charpy impact test on one embodiment of the welded joint of the present invention. [Figure 4] Figure 4 is a graph showing the toughness values ​​obtained by performing a Charpy impact test on one embodiment of the welded joint of the present invention. [Figure 5] Figures 5(a) and 5(b) are a plan view and a side view, respectively, showing the shape of a test specimen from a joint tensile experiment conducted on one embodiment of the welded joint of the present invention. [Figure 6] Figure 6 is a graph showing the load-deformation relationship obtained from a joint tensile experiment conducted on one embodiment of the welded joint of the present invention. [Modes for carrying out the invention]

[0019] Hereinafter, embodiments of the steel material and welded joint of the present invention will be described in detail with reference to the drawings.

[0020] [Steel] The steel material of one embodiment of the present invention has a tensile strength of the standard value TS(N / mm 2 ) is 400-550 N / mm 2 It is a grade, and the carbon equivalent C eqThe steel material has a toughness value of 27 J or more at 0°C to -50°C, with a hardness value of 0.41 or less. This toughness value is obtained by the Charpy impact test specified in the Japanese Industrial Standard JIS Z2242 "Charpy Impact Test Method for Metallic Materials".

[0021] Furthermore, the steel material of this embodiment has a tensile strength of the standard value TS (N / mm²). 2 ) is 400-550 N / mm 2 In grade steel materials, carbon equivalent C eq By making it 0.41 or less, the transition temperature of the toughness value v T rs It can be reduced to below -30°C. And the transition temperature v T rs If the temperature is below -30°C, the toughness value in the 0°C to -50°C range can be increased to 27J or higher.

[0022] Furthermore, the steel material of this embodiment has the characteristic that the toughness value of the weld formed when this steel material is welded is 27 J or more at 0°C to -50°C. The welding conditions for the above welding are one of the following: The first welding condition is the standard value of tensile strength TS w1 (N / mm 2 )(However, TS w1 ≥TS+60, and TS w1 This refers to gas shielded arc welding using welding material with a tensile strength of ≥1.05 TS, under welding conditions of a heat input of 40 kJ / cm or less and an interpass temperature of 350°C or less. The second welding condition is the standard value of tensile strength TS w2 (N / mm 2 )(However, TS w2 This refers to submerged arc welding performed using welding materials with a heat input of 80 kJ / cm or less.

[0023] By using the steel materials and welded joints of this embodiment to construct welded joints in column-beam connections and welded H-shaped steel sections of steel frame structures, premature fracture during earthquakes can be prevented even at low temperatures, providing the steel frame structure with sufficient plastic deformation performance and seismic resistance. [Welded joint between diaphragm and beam flange at column-beam connection] One embodiment of the present invention is a welded joint between a diaphragm and a beam flange at a column-beam joint of a steel frame structure, wherein the diaphragm and the beam flange are each made of the aforementioned steel material.

[0024] In welded joints between diaphragms and beam flanges, it is common practice to make the diaphragm thickness two sizes greater than the beam flange thickness, with the diaphragm thickness typically set to 12mm to 100mm and the beam flange thickness to 9mm to 50mm.

[0025] In the welded joint of this embodiment, the diaphragm and beam flange at the column-beam joint are joined by gas shielded arc welding, specifically CO2 welding, under welding conditions of a heat input of 40 kJ / cm or less and an interpass temperature of 350°C or less.

[0026] And the standard value YS for the yield strength of the diaphragm d (N / mm 2 ) and standard value YS for the yield strength of the beam flange g (N / mm 2 ) is given by the following equation (1) YS d ≧YS g ...(1) The relationship is satisfied.

[0027] Furthermore, the standard value TS for the tensile strength of welding materials w1 (N / mm 2 ) is given by the following equation (2) TS w1 ≥min(TS d , TS g ) + 60 ……(2) The relationship is satisfied.

[0028] However, TS d (N / mm 2 ) is the standard value for the tensile strength of the diaphragm, TS g (N / mm 2 ) is the standard value for the tensile strength of the beam flange.

[0029] Furthermore, the min on the right-hand side of equation (2) above means the minimum value of the values ​​listed in parentheses.

[0030] Specifically, the standard value for tensile strength is 400 N / mm². 2 When using graded steel materials for the diaphragm and beam flange to construct a welded joint, for example, the following can be done:

[0031] First, a 30° to 35° V-groove is made in the beam flange, and the root gap, i.e., the distance between the diaphragm and the beam flange, is set to 7 mm. Then, YGW11, as specified in the Japanese Industrial Standard JIS Z3312 "Mag and MIG welding solid wire for mild steel, high-tensile steel and low-temperature steel," is used as the welding material for welding. The diaphragm and the beam flange are then joined by multi-layer full penetration welding using CO2 welding under welding conditions of a heat input of 30 kJ / cm or less and an interpass temperature of 250°C or less.

[0032] The standard tensile strength of YGW11 is 490 N / mm². 2 Therefore, the standard value for the tensile strength of the diaphragm and beam flange is 400 N / mm². 2 The relationship in equation (2) above is satisfied.

[0033] By constructing the welded joint in this manner, the toughness value of the welded joint at low temperatures of 0°C to -50°C can be increased to 27 J or higher. This toughness value is obtained by the Charpy impact test specified in the Japanese Industrial Standard JIS Z2242.

[0034] Furthermore, the standard tensile strength value is 490 N / mm². 2 When using graded steel for the diaphragm and beam flange to construct a welded joint, the standard tensile strength value is 490 N / mm². 2 It is common to use YGW11, which has a tensile strength of 490 N / mm². In contrast, in this embodiment, the standard value of the tensile strength is 490 N / mm². 2When using graded steel materials for the diaphragm and beam flange to construct a welded joint, the standard value of YGW18 (tensile strength of 550 N / mm²) specified in JIS Z3312 is used. 2 Use the following standard value for tensile strength of YGW18: 550 N / mm². 2 The standard value for the tensile strength of the diaphragm and beam flange is 490 N / mm². 2 The relationship in equation (2) above is satisfied.

[0035] By constructing the welded joint in this manner, the toughness value of the welded joint at low temperatures of 0°C to -50°C can be increased to 27J or higher. YGW18 improves the tensile strength of the weld by refining the crystal grains of the weld metal through a high content of Mn and other elements. This refinement of the crystal grains improves the low-temperature toughness of the material, enabling the creation of a welded joint with high low-temperature toughness.

[0036] In addition, the diaphragm and beam flange have a standard tensile strength value of TS (N / mm²). 2 ) is 400-550 N / mm 2 Even when using various grades of steel, the relationships between equations (1) and (2) above should be satisfied. The diaphragm and beam flange are then joined by gas shielded arc welding under welding conditions of a heat input of 40 kJ / cm or less and an interpass temperature of 350°C or less. In this way, the reduction in toughness of the weld can be suppressed even at low temperatures where toughness decreases due to the refinement of the weld metal, and the toughness value of the welded joint at low temperatures of 0°C to -50°C can be made 27 J or more. [Welded joint between steel column and diaphragm at column-beam connection] Another embodiment of the present invention is a welded joint between a steel column and a diaphragm at a column-beam joint of a steel frame structure, wherein the steel column and the diaphragm are each made of the steel material described above. The steel column is made, for example, from a cold-formed square steel pipe.

[0037] In the welded joint between the steel frame column made of cold-formed square steel pipe and the diaphragm, the thickness of the cold-formed square steel pipe is set to be 6 mm to 50 mm, the column diameter is 250 mm to 1200 mm, and the thickness of the diaphragm is set to be 25 mm to 100 mm.

[0038] In the welded joint of this embodiment, the steel frame column and the diaphragm at the column-beam joint are joined by gas shielded arc welding under the welding conditions of heat input of 40 kJ / cm or less and inter-pass temperature of 350 °C or less.

[0039] And the specified value of the yield strength YS c (N / mm 2 ) of the steel frame column and the specified value of the yield strength YS d (N / mm 2 ) of the diaphragm satisfy the following formula (3) YS d ≧YS c ……(3) That is, they satisfy the relationship.

[0040] Furthermore, the specified value of the tensile strength TS w1 (N / mm 2 ) of the welding material satisfies the following formula (4) TS w1 ≧max(1.05TS c , TS d ) ……(4) That is, they satisfy the relationship.

[0041] However, TS c (N / mm 2 ) is the specified value of the tensile strength of the steel frame column, and TS d (N / mm 2 ) is the specified value of the tensile strength of the diaphragm.

[0042] Also, the max on the right side of the above formula (4) means the maximum value of the values listed in the parentheses.

[0043] When welding joints are formed using steel materials with a specified tensile strength of 490 N / mm 2 grade for the steel frame column and the diaphragm, the specified tensile strength is 490 N / mm2 It is common to use YGW11, which has a tensile strength of 490 N / mm². In contrast, in this embodiment, the standard value of the tensile strength is 490 N / mm². 2 When using graded steel materials for steel columns and diaphragms to construct welded joints, the standard tensile strength value is 550 N / mm². 2 Use YGW18. The standard tensile strength of YGW18 is 550 N / mm². 2 The standard value for the tensile strength of steel columns and diaphragms is 490 N / mm². 2 The relationship in equation (4) above is satisfied.

[0044] Then, a 35° V-groove is made in the steel column, and the root gap, that is, the distance between the steel column and the diaphragm, is set to 4 mm to 10 mm. The diaphragm and the beam flange are then joined by multi-layer full penetration welding using CO2 welding under welding conditions of a heat input of 30 kJ / cm or less and an interpass temperature of 250°C or less.

[0045] By constructing the welded joint in this manner, the toughness value of the welded joint at low temperatures of 0°C to -50°C can be increased to 27 J or higher. This toughness value is obtained by the Charpy impact test specified in the Japanese Industrial Standard JIS Z2242.

[0046] YGW18 improves the tensile strength of the weld by increasing the content of elements such as Mn, thereby refining the crystal grains of the weld metal. This refinement of crystal grains improves the low-temperature toughness of the material, enabling the creation of welded joints with high low-temperature toughness.

[0047] In addition, the standard tensile strength value TS (N / mm²) for steel columns and diaphragms is specified. 2 ) is 400-550 N / mm 2Even when using various grades of steel, the relationships in equations (3) and (4) above are satisfied. The steel column and the diaphragm are then joined by gas shielded arc welding under welding conditions of a heat input of 40 kJ / cm or less and an interpass temperature of 350°C or less. In this way, the reduction in toughness of the weld can be suppressed even at low temperatures where toughness decreases due to the refinement of the weld metal, and the toughness value of the welded joint at low temperatures of 0°C to -50°C can be made 27 J or more. [Welded joint between the web and flange of a welded H-beam assembly] A welded joint in yet another embodiment of the present invention is a welded joint between the web and flange of a welded H-shaped steel beam, wherein the web and flange of the welded H-shaped steel beam are each made of the steel material described above.

[0048] In the welded joint between the web and flange of a welded H-beam, the thickness of the web and flange is set to 9mm to 40mm.

[0049] In this embodiment, the welded joint is formed by submerged arc welding under welding conditions of a heat input of 80 kJ / cm or less, with the web and flange of the welded H-shaped steel joining together.

[0050] And the standard value TS for the tensile strength of the welding material. w2 (N / mm 2 ) is given by the following equation (5) TS w2 ≥min(TS w , TS f ) + 80 ……(5) The relationship is satisfied.

[0051] However, TS w (N / mm 2 ) is the standard value for the tensile strength of the web, TS f (N / mm 2 ) is the standard value for the tensile strength of the flange.

[0052] Furthermore, the min on the right-hand side of equation (5) above means the minimum value of the values ​​listed in parentheses.

[0053] The standard tensile strength is 490 N / mm². 2 When using grade S502-H steel for the web and flange of welded H-beams to form welded joints, the grade S502-H (with a tensile strength of 490 N / mm²) specified in Japanese Industrial Standard JIS Z3183 "Quality Classification of Submerged Arc Weld Metals for Carbon Steel and Low Alloy Steel" should be used. 2 It is common to use ). In contrast, in this embodiment, the standard value of tensile strength is 490 N / mm 2 When using grade S582-H steel for the web and flange of a welded H-beam to construct a welded joint, the standard tensile strength value is 570 N / mm² as specified in JIS Z3183. 2 Use the following standard value for tensile strength of S582-H: 570 N / mm². 2 The standard value for the tensile strength of the web and flange of welded H-beams is 490 N / mm². 2 The relationship in equation (5) above is satisfied.

[0054] Furthermore, if the thickness of the web of the welded H-beam is less than 19 mm, no groove is provided; if the thickness is 19 mm or more, a 45° to 60° K-groove is provided. The web and flange of the welded H-beam are then joined by fillet welding using submerged arc welding under welding conditions of a heat input of 80 kJ / cm or less.

[0055] By constructing the welded joint in this manner, the toughness value of the welded joint at low temperatures of 0°C to -50°C can be increased to 27 J or higher. This toughness value is obtained by the Charpy impact test specified in the Japanese Industrial Standard JIS Z2242.

[0056] S582-H improves hardenability and enhances the tensile strength of the weld by increasing the content of Mo, B, and other elements. Improved hardenability suppresses the formation of grain boundary ferrite, enabling the creation of welded joints with high low-temperature toughness.

[0057] In addition, the web and flange of welded H-beams have a tensile strength standard value TS (N / mm²). 2 ) is 400-550 N / mm2 Even when using various grades of steel, the relationship in equation (5) above should be satisfied. The web and flange of the welded H-beam are then joined by submerged arc welding under welding conditions of a heat input of 80 kJ / cm or less. In this way, the reduction in toughness of the weld can be suppressed even at low temperatures where toughness decreases due to the refinement of the weld metal, and the toughness value of the welded joint at low temperatures of 0°C to -50°C can be made 27 J or higher. [Examples]

[0058] The following describes embodiments of the steel material and welded joint of the present invention.

[0059] As an example of the steel material of the present invention, the standard value of tensile strength TS (N / mm) 2 ) is 490 N / mm 2 It is a grade, and the carbon equivalent C eq For steel materials with a coefficient of 0.40, a Charpy impact test as specified in JIS Z2242 was performed to investigate the toughness value and brittle fracture surface ratio.

[0060] Figure 1 shows the toughness values ​​and brittle fracture ratios of the steel material for each test temperature of 20°C, 0°C, -20°C, -40°C, -60°C, and -80°C, with three values ​​for each temperature. The toughness values ​​are shown as black circles and the brittle fracture ratios as white circles. Also in Figure 1, the transition curve drawn from the toughness values ​​is shown as a solid line, and the transition curve drawn from the brittle fracture ratios is shown as a dashed line.

[0061] From the transition curve shown in Figure 1, the transition temperature v T rs The temperature was -56°C, confirming that it was below -30°C. Furthermore, it was confirmed that the toughness value between 0°C and -50°C was 27J or higher.

[0062] Next, these two steel sheets are further processed according to JIS Z3312, which specifies YGW18 (with a tensile strength standard value of 550 N / mm²). 2Using a specific welding method, welded joints were fabricated by gas-shielded arc welding under welding conditions of a maximum heat input of 29.8 kJ / cm and a maximum interpass temperature of 210°C. The standard tensile strength of YGW18 is 550 N / mm². 2 The standard tensile strength of the two steel plates is 490 N / mm². 2 The relationship between equations (2) and (4) above is satisfied. The toughness value of this welded joint was investigated by performing a Charpy impact test as specified in JIS Z2242.

[0063] Figures 2 to 4 show three toughness values ​​for the weld metal, boundary, and heat-affected zone of the aforementioned welded joint for each test temperature of 0°C, -25°C, -40°C, -60°C, and -80°C, respectively. Figures 2 to 4 also show the transition curves drawn from these toughness values.

[0064] As shown in Figures 2 to 4, in this embodiment, it was confirmed that the toughness value at 0°C to -50°C was 27 J or higher in the welded joint, boundary, and heat-affected zone. [Examples]

[0065] As an embodiment of the present invention, the standard value of tensile strength TS(N / mm) 2 ) is 490 N / mm 2 It is a grade, and the carbon equivalent C eq Tensile joint tests were conducted on welded joint specimens of steel with a yield strength of 0.40. The yield strength and tensile strength (test values) of the steel used in this example were 365 N / mm², respectively. 2 , 528 N / mm 2 That is the case.

[0066] Figures 5(a) and 5(b) show the plan view and side view, respectively, of the welded joint test specimen.

[0067] As shown in Figures 5(a) and 5(b), two welded joint test specimens (JT25 and JT80) were fabricated by joining rectangular and trapezoidal pieces of the steel material using gas shielded arc welding. The welding used was YGW18 as specified in JIS Z3312 (with a tensile strength standard value of 550 N / mm²). 2 The welding conditions were set with a maximum heat input of 22.1 kJ / cm and a maximum interpass temperature of 245°C, using ( ). The standard tensile strength of YGW18 is 550 N / mm². 2 The standard tensile strength of the two steel plates is 490 N / mm². 2 The relationship between equations (2) and (4) above is satisfied. The cross-sectional area of ​​the welded joint of the welded joint test specimen is 5000 mm². 2 Since the dimensions are (25mm x 200mm), the calculated yield strength and tensile strength of the welded joint test specimen are 1825kN and 2640kN, respectively.

[0068] For one welded joint test specimen, JT25, the steel surface temperature around the weld was cooled to -25°C, and a joint tensile test was performed. For the other welded joint test specimen, JT80, the steel surface temperature around the weld was cooled to -80°C, and a joint tensile test was performed.

[0069] Specifically, welded joint test specimens JT25 and JT80 were mounted on a tensile testing machine. Then, the area around the weld was covered with a box made of synthetic resin material, and dry ice was introduced into the box. Tensile tests were then conducted while cooling the specimens so that the surface temperature of the steel around the weld reached -25°C or -80°C. During the tensile tests, the amount of dry ice was adjusted to ensure that the steel surface temperature remained consistently below -25°C or -80°C.

[0070] Figure 6 shows the load-deformation relationship obtained from the joint tensile experiment described above.

[0071] As shown in Figure 6, the fracture strength of the welded joint test specimens JT25 and JT80 both exceeded the calculated tensile strength of the welded joint, which was 2640 kN. This confirms that the welded joint in this embodiment has sufficient tensile strength even in low-temperature environments of -25°C and -80°C.

Claims

1. Standard value for tensile strength TS (N / mm) 2 ) is 400-550 N / mm 2 It is a class, Carbon equivalent C eq It is 0.41 or less, A steel material having a toughness value of 27 J or more at 0°C to -50°C, The aforementioned steel material has a tensile strength of the standard value TS w1 (N / mm 2 ) (However, TS w1 ≥TS+60, and TS w1 Steel material having a toughness value of 27 J or more at 0°C to -50°C when a weld is formed by gas-shielded arc welding using a welding material (≥1.05 TS) under welding conditions of a heat input of 40 kJ / cm or less and an interpass temperature of 350°C or less.

2. The standard value TS (N / mm 2 ) of the tensile strength is 400 to 550 N / mm 2 grade, and Carbon equivalent C eq It is 0.41 or less, A steel material having a toughness value of 27 J or more at 0°C to -50°C, The aforementioned steel material has a tensile strength of the standard value TS w2 (N / mm 2 ) (However, TS w2 A steel material in which the toughness value of the weld formed when submerged arc welding is performed using a welding material (≥TS + 80) under welding conditions of a heat input of 80 kJ / cm or less is 27 J or more at 0°C to -50°C.

3. A welded joint between a diaphragm and a beam flange at a column-beam joint in a steel frame structure, The diaphragm and the beam flange are each made of the steel material described in claim 1, The diaphragm and the beam flange are joined by gas shielded arc welding under welding conditions of a heat input of 40 kJ / cm or less and an interpass temperature of 350°C or less. YS, the standard value of the yield strength of the diaphragm. d (N / mm 2 ) and standard value of tensile strength TS d (N / mm 2 ), and the standard value YS of the yield strength of the beam flange. g (N / mm 2 ) and standard value of tensile strength TS g (N / mm 2 ) is given by the following equations (1) and (2) YS d ≧YS g ……(1) TS w1 ≧min(TS d 、TS g )+60 ……(2) A welded joint that satisfies the following conditions.

4. A welded joint between a steel column and a diaphragm at a column-beam joint in a steel frame structure, The steel column and the diaphragm are each made of the steel material described in claim 1, The steel column and the diaphragm are joined by gas shielded arc welding under welding conditions of a heat input of 40 kJ / cm or less and an interpass temperature of 350°C or less. YS, the standard value for the yield strength of the aforementioned steel column. c (N / mm 2 ) and standard value of tensile strength TS c (N / mm 2 ), and the standard value YS of the yield strength of the diaphragm. d (N / mm 2 ) and standard value of tensile strength TS d (N / mm 2 ) is given by the following equations (3) and (4) below YS d ≧YS c ……(3) TS w1 ≧max(1.05TS c 、TS d ) ……(4) A welded joint that satisfies the following conditions.

5. A welded joint between the web and flange of a welded H-shaped steel beam, The web and the flange are each made of the steel material described in claim 2, The web and the flange are joined by submerged arc welding under welding conditions of a heat input of 80 kJ / cm or less. The standard value TS for the tensile strength of the aforementioned web w (N / mm 2 ), and the standard value TS of the tensile strength of the flange f (N / mm 2 ) is given by the following equation (5) TS w2 ≧min(TS w 、TS f )+80 ……(5) A welded joint that satisfies the following conditions.

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