JP4879688B2 - Steel arc welded joint with excellent fatigue strength, its welding method and steel structure - Google Patents

Description

  The present invention relates to a steel arc welded joint excellent in fatigue strength among steel arc welded joints used in steel structures such as automobiles, home appliances, building structures, ships, bridges, construction machines, various plants and penstocks. And a steel structure having the steel arc welded joint.

  In general, the fatigue strength of a steel base material increases as the strength increases, but the fatigue strength of an arc welded joint (hereinafter also referred to as joint fatigue strength) does not improve even if the strength of the steel base material is increased. This has been shown by experiment. Therefore, the fatigue strength of joints arc welded with high-strength steel is approximately the same as the fatigue strength of joints arc-welded with low-strength steel. The design strength could not be improved even when used as a base material. For such a situation, techniques for improving the solidification structure of the weld metal and further the elements and structure of the weld metal have been studied and disclosed (for example, Patent Documents 1 to 5, Non-Patent Documents 1 and 2). reference.).

  First, Non-Patent Document 1 discloses in detail the solidification structure forms that differ depending on the relationship between the element concentration and the temperature distribution in the molten metal in relation to the solidification structure of the weld metal. Non-Patent Document 2 discloses an example of a solidified structure of a weld metal. Furthermore, Patent Document 1 discloses a repair welding method that defines the type and size of the solidified structure of the weld metal.

  On the other hand, in Patent Document 2, among the inventions related to the elements and structures of the weld metal, the elements and structures of the weld metal are defined, and the fatigue strength of the elements of the steel base material and the structure of the weld heat affected zone is excellent. A welding method in which a weld joint and welding conditions are defined is disclosed. Patent Document 3 specifies C, Si, Mn, S, Al, B, and N of the weld metal for the purpose of obtaining a weld metal having high toughness, and 90% or more of the structure of the weld metal. A manufacturing method and welded steel structure of an ultra-low carbon high-tensile steel weld joint having an ultra-low carbon bainite structure are disclosed.

  Furthermore, in Patent Document 4 and Patent Document 5, for the purpose of improving joint fatigue strength, the difference in the maximum hardness between the weld metal near the weld fusion boundary and the weld heat affected zone, and the elements of the weld metal and the base metal are defined. A structural steel weld joint is disclosed.

Japanese Patent Laid-Open No. 7-75893 JP-A-9-227987 JP 2002-180181 A JP-A-7-171679 JP-A-11-104838 Edited by Kunihiko Sato, “Welding Strength Handbook”, Science and Engineering, 1988, p. 2-27 to 2-33 Haruna Muneharu, Kondo Yasuhiro, “Research on Microstructure and Hardness Change of Laser Welds in Carbon Steel”, Annual Conference of the Japan Welding Society, Vol. 57, October 1995, p. 420-421

  However, none of the techniques described in Patent Documents 1 to 5 and Non-Patent Documents 1 and 2 have been studied on the solidification structure of the weld metal in the vicinity of the weld toe where fatigue cracks are easily generated. There is a problem that a steel arc welded joint having excellent fatigue strength cannot be obtained stably.

  The present invention has been made in view of the above-mentioned problems, and the purpose thereof is a fatigue strength that can stably obtain a high fatigue strength without requiring special consideration in terms of design and construction. To obtain an excellent steel arc welded joint, its welding method and steel structure.

  The steel arc welded joint having excellent fatigue strength according to the present invention is, in mass%, C: 0.0001 to 0.0600%, Si: 0.01 to 0.36%, Mn: 0.01 to 1.20. %, P: 0.030% or less, S: 0.009% or less and Al: 0.001 to 0.100%, with the balance being Fe and unavoidable impurities, and in mass%, C: 0.0001 to 0.0200%, Si: 0.01 to 0.12%, Mn: 0.01 to 0.40%, P: 0.030% or less, S: 0.003% or less, and Al: 0 0.001 to 0.100%, and the balance consists of a weld metal composed of Fe and inevitable impurities, and the weld metal has a solid interface structure in which at least a range from the weld toe to 0.1 mm is grown at a smooth interface. It is characterized by being.

  The weld metal in this steel arc welded joint is further, in mass%, Cu: 0.10 to 1.00%, Mo: 0.10 to 5.00%, Nb: 0.005 to 1.000%, V: 0.005 to 5.000%, Ti: 0.005 to 0.100%, B: 0.0001 to 0.0050%, Ni: 0.10 to 0.50%, and Cr: 0.10 One or two or more elements selected from the group consisting of 7.00% may be contained.

  Further, the steel is further mass%, Cu: 0.10 to 3.00%, Mo: 0.10 to 5.00%, Nb: 0.005 to 1.000%, V: 0.005. ˜5.000, Ti: 0.005 to 0.300%, B: 0.0001 to 0.0050%, Ni: 0.10 to 1.50% and Cr: 0.10 to 7.00% One or two or more elements selected from the group may be contained.

  The welding method of the steel arc welded joint excellent in fatigue strength according to the present invention is mass%, C: 0.0001 to 0.0600%, Si: 0.01 to 0.36%, Mn: 0.01 to 1.20%, P: 0.030% or less, S: 0.009% or less, Al: 0.001 to 0.100% contained, with the balance being Fe and inevitable impurities Welding to obtain the steel arc welded joint described above

  In the welding method of the steel arc welded joint, the welding material is further in terms of mass%, Cu: 0.10 to 3.00%, Mo: 0.10 to 5.00%, Nb: 0.005 to 1. 0.000%, V: 0.005 to 5.000%, Ti: 0.005 to 0.300%, B: 0.0001 to 0.0050%, Ni: 0.10 to 1.50%, and Cr: One or more elements selected from the group consisting of 0.10 to 7.00% may be contained.

  Also, welding can be performed at a welding speed of 10 to 50 cm / min. At that time, the arc welding torch or the welding rod may be swung at a frequency of 1 to 4 Hz and a width of 2 to 6 mm in a direction perpendicular to the welding line.

  The steel structure according to the present invention has the above-described steel arc welded joint.

  In addition, since the welding method of the present invention can be applied not only to welding to steel in one pass, but also to a welding pass in the middle of a multi-layer weld metal, the steel in the steel arc welded joint of the present invention includes: It shall include not only the steel base material but also the weld metal and weld heat affected zone during multi-layer welding.

  According to the present invention, the chemical composition of steel and weld metal is specified, and the solidified structure in the vicinity of the toe where fatigue cracks occur is a structure in which fatigue cracks are unlikely to occur. When used in welded joints and steel structures, high fatigue strength can be stably obtained without requiring special consideration in terms of design and construction, and it can be said that the invention has extremely high industrial value. Furthermore, the principle of the present invention can be applied over a wide range regardless of the type of joint type or the like.

  Hereinafter, the best mode for carrying out the present invention will be described in detail. When a fatigue load is applied to the steel arc welded joint, fatigue failure occurs from the weld toe. As described above, the cause of fatigue fracture from the weld toe is that the stress concentration and residual stress at the weld toe are large, and the weld metal cannot withstand the stress and easily generates fatigue cracks. .

  In view of this, the inventor first made extensive studies on the relationship between the structure of the arc welding toe and the fatigue crack initiation behavior. As a result, most fatigue cracks are generated from the weld metal and not from the heat affected zone, and the ease with which fatigue cracks are generated is closely related to the solidification structure of the weld metal. It was found that the fatigue crack initiation resistance was different. That is, if the solidification structure is a cellular interface growth structure, a cell dendritic interface growth structure, a columnar dendritic interface growth structure, and an equiaxed dendritic growth structure that grows with compositional supercooling, fatigue cracks It has been discovered that fatigue cracks are less likely to occur in the case of a smooth interface growth structure that occurs in the absence of compositional supercooling, whereas the occurrence of this is easy.

  Fig.1 (a) is a top view which shows the welding part of the steel arc welding joint of this invention, FIG.1 (b) is sectional drawing by the AA line shown to Fig.1 (a). The present inventor examined the range 14 from the weld toe of the structure that grows the smooth interface shown in FIGS. 1 (a) and 1 (b), and the range of 0.1 mm or more from the weld toe in the weld metal is the smooth interface. In the case of a growth structure, the joint fatigue strength is remarkably improved, and a cell-like interface growth structure, a cell dendritic interface growth structure, a columnar dendritic interface growth structure, and an equiaxed tree branch are within a range from the weld toe to 0.1 mm. It was found that the joint fatigue strength is less improved when the mixed growth structure is mixed. This greatly depends on the shape of the weld toe, and in turn, the welding conditions and orientation, the composition of the weld metal, etc., but the position where the stress is highest at the weld toe is at least 0.05-0. It was discovered that it was due to the presence of about 1 mm on the weld metal side.

  Next, based on this result, the present inventor examined the formation conditions of the solidified structure of the weld metal. The welding phenomenon is a rapid solidification phenomenon, and in the case of welding of normal carbon steel, low alloy steel and high alloy steel, cellular interfacial growth structure, cell dendritic interfacial growth structure, columnar shape with large compositional supercooling. In order to form dendritic growth structures, equiaxed dendritic growth structures, etc., and to prevent compositional overcooling and make smooth interface growth structures, the amount of additive elements that are likely to cause compositional overcooling is reduced as much as possible. Was found to be effective.

  And this inventor examined the upper limit of the addition amount which prevents composition supercooling about C, Si, Mn, P, S, and Al which are the main elements of a weld metal. In addition, in the state of smooth interface growth, when one or more of Cu, Mo, Nb, V, Ti, B, Ni, and Cr are contained in an appropriate range amount, the solid solution of the weld metal -It was also found that the fatigue strength improvement effect by the precipitation strengthening mechanism is manifested. Furthermore, the present inventor also examined arc welding conditions that affect the growth rate of the solidified structure, and the formation of the solidified structure is more affected by the welding speed than the welding heat input, and the structure of smooth interface growth is likely to crystallize. It was understood that there was a welding speed range.

  First, the reasons for limiting the components of the weld metal in a steel arc welded joint (hereinafter simply referred to as a steel arc welded joint) excellent in fatigue strength according to the present invention will be described. In the following description, mass% in the composition is simply described as%.

C: 0.0001 to 0.0200%
C has an effect of increasing strength, but when the content is less than 0.0001%, sufficient strength cannot be ensured. On the other hand, when the C content in the weld metal exceeds 0.0200%, a cellular interface growth structure, a cell dendritic interface growth structure, a columnar dendritic interface growth structure, an equiaxed dendritic growth structure, and the like are crystallized. . Therefore, the C content is set to 0.0001 to 0.0200%.

Si: 0.01 to 0.12%
Si is an element useful for ensuring the strength, but when the Si content is less than 0.01%, the effect cannot be obtained. On the other hand, when the Si content in the weld metal exceeds 0.12%, a cellular interface growth structure, a cell dendritic interface growth structure, a columnar dendritic interface growth structure, an equiaxed dendritic growth structure, and the like crystallize. . Therefore, the Si content is set to 0.01 to 0.12%.

Mn: 0.01-0.40%
Mn is useful as an element that increases strength at a low cost. However, when the Mn content in the weld metal is less than 0.01%, sufficient strength cannot be ensured. On the other hand, when the Mn content in the weld metal exceeds 0.40%, cellular interface growth structure, cell dendritic interface growth structure, columnar dendritic interface growth structure, equiaxed dendritic growth structure, and the like crystallize. . Therefore, the Mn content is set to 0.01 to 0.40%.

Al: 0.001 to 0.100%
Al is a deoxidizing element. However, when the Al content in the weld metal is less than 0.001%, a sufficient deoxidation effect cannot be obtained. On the other hand, if the Al content exceeds 0.100%, the toughness of the weld metal deteriorates. Therefore, the Al content is 0.001 to 0.100%.

P: 0.030% or less, S: 0.003% or less P and S are impurity elements unavoidably contained in a normal steelmaking process, and the P content in the weld metal exceeds 0.030%. When the S content exceeds 0.003%, the cell-like interface growth structure, the cell dendritic interface growth structure, the columnar dendritic interface growth structure, the equiaxed dendritic growth structure, and the like are crystallized and welded. Helps crack metal. Therefore, the P content is restricted to 0.030% or less, and the S content is restricted to 0.003% or less.

  In addition to the above components, the weld metal in the steel arc welded joint of the present invention is one or more selected from the group consisting of Cu, Mo, Nb, V, Ti, B, Ni and Cr. An element may be contained. Cu, Mo, Nb, V, Ti, B, Ni and Cr are all components that exhibit a solid solution strengthening mechanism and a precipitation strengthening mechanism and improve the fatigue characteristics of the steel welded joint. It is an active ingredient. However, when these elements are excessively present in the weld metal, a cellular interface growth structure, a cell dendritic interface growth structure, a columnar dendritic interface growth structure, and an equiaxed dendritic growth structure are crystallized, or Since the toughness of the weld metal is reduced, when these elements are added, Cu: 0.10 to 1.00%, Mo: 0.10 to 5.00%, Nb: 0.005 to 1.000% , V: 0.005 to 5.000%, Ti: 0.005 to 0.100%, B: 0.0001 to 0.0050%, Ni: 0.10 to 0.50%, and Cr: 0.10 ˜7.00%. In addition, the remainder in the weld metal of the steel arc welded joint of the present invention is Fe and inevitable impurities.

  Next, the reason for limiting the components of steel (base material) in the steel arc welded joint of the present invention will be described. During welding, the welding material is melted and a part of the steel is also melted, and these molten metals are stirred at a high temperature. As a result, a weld metal having a substantially uniform composition is formed. Therefore, the composition of the weld metal is highly dependent on the composition of the welding material and steel. For example, when the penetration of steel, that is, when the dilution ratio is small and the amount of additive elements in the welding material is small, the element of steel Even if the concentration is high, it is considerably diluted by welding to form a weld metal. Similarly, when the steel melts, that is, when the dilution rate is small and the amount of added elements in the welding material is large, a high concentration weld metal is formed even if the element concentration of the steel is low. As described above, the present inventor examined the dilution ratios in various types of joints, and then studied the component range of steel for obtaining a solidified structure of smooth interface growth at the toe of the weld metal.

C: 0.0001 to 0.0600%
C has an effect of increasing strength, but when the content is less than 0.0001%, sufficient strength cannot be ensured. On the other hand, when the C content in the steel exceeds 0.0600%, cellular interface growth structure, cell dendritic interface growth structure, columnar dendritic interface growth structure, equiaxed dendritic growth structure and the like are easily crystallized. . Therefore, the C content is set to 0.0001 to 0.0600%.

Si: 0.01 to 0.36%
Si is an element useful for ensuring the strength, but when the Si content is less than 0.01%, the effect cannot be obtained. On the other hand, when Si is added to the steel in an amount exceeding 0.36%, a cellular interface growth structure, a cell dendritic interface growth structure, a columnar dendritic interface growth structure, an equiaxed dendritic growth structure, and the like are easily crystallized. Therefore, the Si content is set to 0.01 to 0.36%.

Mn: 0.01-1.20%
Mn is useful as an element that increases the strength at a low cost, but if the content is less than 0.01%, sufficient strength cannot be ensured. On the other hand, when Mn exceeds 1.20%, cellular interface growth structure, cell dendritic interface growth structure, columnar dendritic interface growth structure, equiaxed dendritic growth structure and the like are easily crystallized. Therefore, the Mn content is set to 0.01 to 1.20%.

P: 0.030% or less, S: 0.009% or less P and S are impurities inevitably contained in a normal steelmaking process, and the P content in steel exceeds 0.030%, Alternatively, when the S content exceeds 0.009%, the cellular interface growth structure, the cell dendritic interface growth structure, the columnar dendritic interface growth structure, and the equiaxed dendritic growth structure are easily crystallized or welded. Metal toughness is significantly reduced. Therefore, the P content is regulated to 0.030% or less, and the S content is regulated to 0.009% or less.

Al: 0.001 to 0.100%
Al is a deoxidizing element, but when its content is less than 0.001%, a sufficient deoxidizing effect cannot be obtained. On the other hand, if the Al content in the steel exceeds 0.100%, the toughness of the weld metal is significantly reduced. Therefore, the Al content is 0.001 to 0.100%.

  Further, the steel in the steel arc welded joint of the present invention is one or more elements selected from the group consisting of Cu, Mo, Nb, V, Ti, B, Ni and Cr in addition to the above components. May be contained. Cu, Mo, Nb, V, Ti, B, Ni and Cr are all components that improve the fatigue properties of steel arc welded joints by exhibiting a solid solution strengthening mechanism and a precipitation strengthening mechanism. It is a synergistic ingredient. However, when these elements are added excessively to steel, cellular interface growth structure, cell dendritic interface growth structure, columnar dendritic interface growth structure, equiaxed dendritic growth structure, etc. crystallize or weld metal When these elements are added, Cu: 0.10 to 3.00%, Mo: 0.10 to 5.00%, Nb: 0.005 to 1.000%, V: 0.005 to 5.000%, Ti: 0.005 to 0.300%, B: 0.0001 to 0.0050%, Ni: 0.10 to 1.50% and Cr: 0.10 7.00%. In addition, the remainder in steel of the steel arc welding joint of this invention is Fe and an unavoidable impurity.

  Hereinafter, a welding method for obtaining the above-described steel arc welded joint, that is, a welding method for a steel arc welded joint excellent in fatigue strength of the present invention (hereinafter simply referred to as a welding method) will be described.

  During welding, the welding material is melted and part of the steel is also melted, and these molten metals are stirred at a high temperature, so that a weld metal having a substantially uniform composition is formed. Therefore, the composition of the weld metal greatly depends on the composition of the welding material and the steel. For example, when the penetration of steel, that is, when the dilution ratio is large and the amount of additive elements of the steel is small, the element concentration of the welding material is low. Even if it is high, it is thinned by welding to form a weld metal. Similarly, when the dilution ratio is large and the amount of added elements in steel is large, a weld metal having a high concentration is formed even if the element concentration of the welding material is low. As described above, the present inventor examined the dilution ratio in various joint types, and then examined a preferable component range of the welding material for obtaining a solidified structure of smooth interface growth at the toe of the weld metal. It came. First, the reasons for limiting the components of the welding material used in the welding method of the present invention will be described.

C: 0.0001 to 0.0600%
As described above, C has an effect of increasing the strength. However, when the C content in the welding material is less than 0.0001%, sufficient strength cannot be ensured. On the other hand, when the C content in the welding material exceeds 0.0600%, cellular interface growth structure, cell dendritic interface growth structure, columnar dendritic interface growth structure, equiaxed dendritic growth structure and the like are easily crystallized. Become. Therefore, the C content is set to 0.0001 to 0.0600%.

Si: 0.01 to 0.36%
Similar to C, Si is an element useful for securing the strength, but when the Si content in the welding material is less than 0.01%, the effect cannot be obtained. On the other hand, when Si is added to the welding material in an amount exceeding 0.36%, the cellular interface growth structure, the cell dendritic interface growth structure, the columnar dendritic interface growth structure, the equiaxed dendritic growth structure, and the like are easily crystallized. . Therefore, the Si content is set to 0.01 to 0.36%.

Mn: 0.01-1.20%
Mn is an element useful for increasing the strength at a low cost. However, when the Mn content in the welding material is less than 0.01%, sufficient strength cannot be ensured. On the other hand, when Mn is added to the welding material in an amount exceeding 1.20%, a cellular interface growth structure, a cell dendritic interface growth structure, a columnar dendritic interface growth structure, an equiaxed dendritic growth structure, and the like are easily crystallized. . Therefore, the Mn content is set to 0.01 to 1.20%.

P: 0.030% or less, S: 0.009% or less P and S are impurity elements inevitably contained in a normal steelmaking process. When the P content in the welding material exceeds 0.030% or the S content exceeds 0.009%, a cellular interface growth structure, a cell dendritic interface growth structure, a columnar dendritic interface growth structure In addition, the equiaxed dendritic growth structure or the like is easily crystallized, or the toughness of the weld metal is significantly reduced. Therefore, the P content is regulated to 0.030% or less, and the S content is regulated to 0.009% or less.

Al: 0.001 to 0.100%
Al is a deoxidizing element. However, when the Al content in the welding material is less than 0.001%, a sufficient deoxidation effect cannot be obtained, and when the Al content exceeds 0.100%, the toughness of the weld metal is significantly reduced. . Therefore, the Al content is 0.001 to 0.100%.

  In the welding method of the present invention, the welding material is one or more elements selected from the group consisting of Cu, Mo, Nb, V, Ti, B, Ni, and Cr in addition to the above components. May be contained. Cu, Mo, Nb, V, Ti, B, Ni and Cr are all components that exhibit the solid solution strengthening mechanism and the precipitation strengthening mechanism to improve the fatigue characteristics of the steel arc welded joint. Is a synergistic ingredient. However, when these elements are added in excess, cellular interface growth structure, cell dendritic interface growth structure, columnar dendritic interface growth structure, equiaxed dendritic growth structure, etc. are easily crystallized, or weld metal When these elements are added to the welding material because toughness decreases, Cu: 0.10 to 3.00%, Mo: 0.10 to 5.00%, Nb: 0.005 to 1.000% , V: 0.005 to 5.000%, Ti: 0.005 to 0.300%, B: 0.0001 to 0.0050%, Ni: 0.10 to 1.50%, and Cr: 0.10 ˜7.00%.

  In addition, components other than the above in the welding material used in the welding method of the present invention, that is, the balance is Fe and inevitable impurities. Further, various elements are added in the state of oxides and nitrides in the steel and welding material in the welding method of the present invention, and N and O are inevitably contained, but these elements are When the content is within the normal addition range, the influence on the fatigue strength is small, and therefore the component range is not particularly limited in the present invention.

  On the other hand, in the welding method of the present invention, it is considered that the temperature gradient in the weld pool changes due to the difference in arc welding method and welding heat input, which affects the solidification structure and the difference in fatigue strength improvement effect appears. The inventor examined the solidification structure near the toe by changing the welding conditions in arc welding in various ways. As a result, among the welding conditions, the influence of the welding current and the arc voltage is relatively small, but it has been found that the solidification structure changes depending on the welding speed, especially when the welding speed is in the range of 10 to 50 cm / min. It was found that the structure of smooth interface growth was easily crystallized.

  Although it greatly depends on the composition of the steel and the welding material, when the welding speed exceeds 50 cm / min, the temperature gradient in the molten pool near the toe becomes small, and compositional overcooling tends to occur near the toe. As a result, a cellular interface growth structure, a cell dendritic interface growth structure, a columnar dendritic interface growth structure, an equiaxed dendritic growth structure, and the like are easily crystallized. Also, if the welding speed is less than 10 cm / min, the temperature gradient is large and the possibility of compositional overcooling is small, but the welding speed is slow, so the weld metal rises and becomes a bead with a bad toe shape, Fatigue strength decreases. In the present invention, for such reasons, the preferred welding speed is 10 to 50 cm / min. However, even if the welding speed is out of the above-described range, the structure of smooth interface growth is obtained depending on the components of the steel and the welding material, and thus the effect of the present invention is not greatly reduced.

  The inventor has also studied a method for obtaining a bead having a good toe shape while maintaining a large temperature gradient. FIG. 2 is a diagram showing the locus of the position of the welding torch or welding rod during welding. As a result of the study by the present inventors, as shown in FIG. 2, welding is performed so that the position of the welding torch or the welding rod takes a locus 17 that intersects the welding line 15 at a frequency of 1 to 4 Hz and a width of 2 to 6 mm. That is, it is extremely effective to weld the welding torch or welding rod while swinging in a direction substantially perpendicular to the welding direction 18 with a frequency of 1 to 4 Hz and a swinging width 16 of 2 to 6 mm. I found out. By applying this method, the weld bead spreads in the width direction, and a good bead shape can be obtained without rising at the center of the weld. At that time, the frequency and the width of oscillation at the time of oscillation greatly depend on the composition of the steel and the welding material, and can be appropriately set according to these compositions. However, if the frequency is less than 1 Hz, the center of the bead If the frequency is higher than 4 Hz, the bead has a wavy shape corresponding to the frequency, so that the stress concentration at the toe may increase, and high fatigue strength is difficult to obtain. On the other hand, if the rocking width 16 is smaller than 2 mm, the bead central portion may be raised as in the case where the frequency exceeds 4 Hz. Further, if the swinging width is larger than 6 mm, the bead tends to spread and the temperature gradient becomes slightly large, so that solidification is promoted and compositional overcooling is likely to occur. As a result, a cellular interface growth structure, a cell dendritic interface growth structure, a columnar dendritic interface growth structure, an equiaxed dendritic growth structure, and the like are easily crystallized. In addition, the locus | trajectory at the time of rocking | fluctuating a welding torch and a welding rod is not specifically limited, In addition to the locus | trajectory 17 shown in FIG. 2, the locus | trajectory 17a as shown in FIG. 3 and the locus | trajectory 17b as shown in FIG. Etc.

Furthermore, the arc welding method in the present invention is not limited to TIG welding, covering arc welding, and gas shield welding using CO ₂ gas, Ar gas, and a mixed gas of Ar and CO ₂ as a shielding gas. It has been confirmed that the joint fatigue strength is improved by other arc welding methods such as submerged arc welding. However, in submerged arc welding, not only the consumable electrode, but also the amount and consumption of metals and metal compounds contained in the flux greatly affect the composition of the weld metal. By applying the present invention in consideration of the additive element, a joint with high fatigue strength can be obtained.

  Furthermore, the steel base material targeted in the present invention is not limited to thin steel plates and thick steel plates, and the same effect can be obtained for various steel materials such as steel pipes, bar steels and shaped steels, and welded joints such as cast steel and forged steel. It is done. Furthermore, according to the welding method of the present invention, fatigue strength can be improved regardless of the type of joint such as a turn welded joint, fillet joint, butt joint, and overlay welded joint.

  Furthermore, by applying the steel arc welded joint of the present invention described above and the welding method of the present invention to a steel structure, high fatigue strength can be stably stabilized without requiring special consideration in terms of design and construction. Obtainable.

  Of the conventional techniques described above, Non-Patent Document 1 describes in detail the relationship between the concentration distribution of the additive element during solidification of the weld metal and the solidification structure as described below. FIG. 5 is a diagram showing compositional supercooling. As shown in FIG. 5, when an element having an element concentration in the solid phase that is equilibrated at the same temperature is smaller than that in the liquid phase, an additive element concentration distribution 13 is generated in the liquid phase during the solidification process, The vicinity of the interface of the liquid phase is higher than the nominal concentration 10, and the temperature distribution 8 of the liquid phase that is in equilibrium with the concentration distribution 13 is determined based on the liquid phase line 11. A region where the temperature distribution 8 is higher than the actual temperature distribution 7 is called compositional supercooling 9, and it is shown that the solidified structure varies greatly depending on the size of the compositional supercooling 9.

  6 is a diagram showing a smooth interface growth solidified structure, FIG. 7 is a diagram showing a cellular interface growth solidification structure, FIG. 8 is a diagram showing a cell dendritic interface growth solidification structure, and FIG. 9 is a columnar dendrite. FIG. 10 is a diagram showing an equiaxed dendritic interface growth and solidification structure. As shown in FIGS. 6 to 10, the solidified structure forms smooth interface growth 3, cellular interface growth 3 a, cell dendritic interface growth 3 b, and columnar dendritic interface growth as the degree of compositional supercooling 9 increases. 3c and equiaxed dendritic growth 3d are shown in this order. The solidified structure 3 of smooth interface growth shown in FIG. 6 is a smooth structure that grows from the base material 1 on the condition that the above-described compositional supercooling 9 does not occur. The cellular interface growth structure of FIG. 7, the cell dendritic interface growth structure of FIG. 8, the columnar dendritic interface growth structure of FIG. 9, and the equiaxed dendritic growth structure of FIG. 10 are all compositions. This is a structure that occurs when there is a static supercooling 9.

  On the other hand, the structure of smooth interface growth defined in the present invention is conventionally shown in a very narrow region of a non-ferrous metal such as pure aluminum or a weld toe of an iron alloy, but is low carbon steel and low alloy steel. None of the weld toes are shown with a width of 0.1 mm or more.

  Further, as shown in Non-Patent Document 2, high energy density welding such as laser welding has a steep temperature distribution 7 in the liquid phase, so that a smooth interface growth structure is obtained in the weld of low carbon steel. It is done. However, Non-Patent Document 2 does not show a smooth interface growth structure having a width of 0.1 mm or more at the weld toe in the arc welding that is the subject of the present invention.

  Furthermore, Patent Document 1 discloses a method for solidifying a defect-remelted portion into a dendritic crystal as a repair method for a structure in which a crack-like defect has occurred, as shown in FIG. The structure of dendritic interface growth is a structure generated when the compositional supercooling 9 is larger than the structure of smooth interface growth in FIG. 6 defined in the present invention, and is different from the present invention in this respect. .

  Furthermore, in Patent Document 2, although the C content of the weld metal is as high as 0.02% or more, and the upper limit of the S content is specified from the viewpoint of preventing weld cracking, the addition amount shown in the examples is Since it is more than the S content specified in the present invention, the compositional supercooling 9 becomes large, and the solidified structure of the present invention cannot be obtained, which is an invention different from the present invention.

  Furthermore, in Patent Document 3, the upper limits of the contents of Si and Mn are defined from the viewpoint of lowering the toughness of the weld metal, but the contents shown in the examples are higher than the scope of the present invention, and the present invention. The coagulated tissue cannot be obtained. Further, since the preferable content of Mn is too much larger than the range of the present invention, only a structure having a larger compositional supercooling than that of the present invention can be obtained, which is an invention different from the present invention.

  In Patent Document 4 and Patent Document 5, the upper limit is defined for the C content from the viewpoint of uniform hardness distribution, and the Si and Mn contents from the viewpoint of ensuring weldability. The combination of the contents of C, Si and Mn in the weld metal is outside the scope of the present invention, and is different from the present invention in that only a solidified structure having a compositional supercooling greater than that of the present invention can be obtained.

  As described above, in the conventional techniques described in Patent Documents 1 to 5 and Non-Patent Documents 1 and 2, the solidification structure in the weld metal in the vicinity of the weld toe where fatigue cracks are easily generated is studied. Therefore, this portion does not always grow at a smooth interface, and a high fatigue strength cannot be obtained stably. On the other hand, in the present invention, the chemical composition of the steel and the weld metal is specified, and the weld metal in the vicinity of the weld toe where fatigue cracks are likely to occur has a solidified structure grown at a smooth interface. It can be obtained stably.

Hereinafter, the effects of the present invention will be specifically described with reference to Examples and Comparative Examples of the present invention. A steel plate having a thickness of 2.3 mm and a chemical composition shown in Tables 1 to 4 below as steel, and a welding material for CO ₂ arc welding having a diameter of 1.2 mm in the chemical composition shown in Tables 1 to 4 below. Were used, arc welding was performed at a welding speed shown in Tables 1 to 4 below with a welding layer number of 1, a welding current of 100 A, and a welding voltage of 15 V, and a lap fillet welded joint was manufactured. And about the weld metal of each joint, the solidification structure contained in the range from a weld toe to 0.1 mm was investigated. The observation of the coagulated structure was performed by using a saturated picric acid aqueous solution to which 5% by mass of a surfactant (Lybon F made by Lion) was used as a corrosive solution, corroding at room temperature for 10 to 30 minutes, and then using an optical microscope. The observation was performed at a magnification of ˜100 times. Next, a lap fillet welded joint fatigue test piece having the shape and dimensions shown in FIG. 11 was produced from each joint of the examples and comparative examples produced by the above-described method, and various stress ranges were obtained using this test piece. In other words, the fatigue life was determined by performing a fatigue test with bending loads in various ranges of the nominal bending stress at the toes. These data were subjected to linear regression to determine the fatigue strength at which the fracture life was 2 million times. The above results are also shown in Tables 1 to 4 below. In the chemical compositions shown in Tables 1 to 4 below, the upper stage is weld metal, the middle stage is steel, the lower stage is welding material, and the balance is Fe and inevitable impurities. Moreover, the underline in the following Table 3 and Table 4 shows that it is outside the scope of the present invention.

  As shown in Tables 1 to 4 above, no. 1-No. Each of the 32 joints is a joint of the embodiment of the present invention, in which the solidified structure of the weld metal in the range from the toe to 0.1 mm is a smooth interface growth structure. The joints of these examples are No. 33-No. The fatigue strength was improved by 20% or more as compared with the joint of 42 comparative examples, and it was found that the joint of the present invention and the joint by the welding method of the present invention are effective for improving the fatigue strength.

  Among the joints of the examples shown in Tables 1 to 3, No. 1 and no. The joint of No. 2 is a joint having a chemical composition in the range of claim 1. The joint of No. 3 to No. 22 is a joint in which the additive element specified in claim 2 is contained in the weld metal. These No. No. 3 to No. 22 joints are No. 1 and no. Compared to the joint of No. 2, the fatigue strength was further improved by about 10%, and it was confirmed that the addition of these elements was more effective for improving the fatigue strength. No. 1 and no. The joint of No. 2 uses the welding material specified in claim 4 and The joint of No. 3 to No. 22 uses a welding material specified in claim 5.

  On the other hand, Comparative Example No. 4 shown in Table 4 above. 33-No. In all of the joints of 42, the structure of the weld metal in the range from the weld toe to 0.1 mm is mixed with the columnar dendritic interface grown structure, the cell dendritic interface grown structure, and the smooth interface grown structure. Tissue, cellular interfacial growth tissue mixed with cell dendritic interfacial growth tissue, cell dendritic interfacial growth tissue mixed with columnar dendritic interfacial growth tissue, and columnar dendritic interface growth tissue equiaxed dendritic It was an organization with a growing organization. Among these joints, No. 33-No. Since the content of any one of C, Si, Mn, P, S and Al is out of the scope of the present invention, the joint No. 38 has a working example No. 38. 1 and no. Compared with the joint of No. 2, the fatigue strength was low. No. 33-No. Since the joint of No. 38 was a weld metal or steel and the range of the additive element was outside the scope of the present invention, the fatigue strength was lower than that of the joints of the above-mentioned examples. In particular, no. 36 and no. In the joints of 38, the contents of P and Al exceeded the range of the present invention, respectively, so the toughness of the weld metal was low, which was one factor that the fatigue strength was not improved.

  Example No. shown in Table 3 above. 23-No. The 32 joints compare the effects of welding speed. The welding speed deviated from the range defined in claim 6. 23, no. 31 and no. In the joint No. 32, the fatigue strength increased by 20% compared to the joint of the comparative example. 24, no. 29 and No. The joint of No. 30 is No. 23, no. 31 and no. A fatigue strength higher by about 10% than that of 32 joints was obtained, and it was confirmed that setting the welding speed within the range specified in claim 6 is more effective in improving the fatigue strength. No. 24, no. 29 and No. The weld metal of 30 joints has a smooth interface growth structure in a wider range than the range from the weld toe to 0.1 mm, specifically, from 0.5 to 1.0 mm from the weld toe. It was confirmed that it occurred. Furthermore, no. It was also confirmed that the joint of No. 23 was a toe-shaped joint with a large weld bead and a very large stress concentration.

  In addition, Example No. 11, no. 12, no. 16-No. 18 and no. 24-No. The joint of No. 28 is a comparison of the effects when the welding torch is swung in a direction perpendicular to the welding direction. The swing condition is No. in the range defined in claim 7. 12, no. 17 and no. Each of the joints of No. 18 is not swung. 11 and no. It was confirmed that the fatigue strength was further improved as compared with 16 joints. Further, when the swing condition is out of the range defined in claim 7, the No. 25, no. 27 and no. The joint of No. 28 is No. Although the effect of improving the fatigue strength for the joint of No. 24 is slight, No. 24 in which the rocking condition is within the range of claim 7. In the joint of No. 26, a further significant fatigue strength improvement effect was recognized. Thus, it was confirmed that setting the swing condition within the range defined in claim 7 is more effective for improving the fatigue strength.

  Thus, it was found that the steel arc welded joint and welding method of the present invention are effective in improving joint fatigue strength.

(A) is a top view which shows the welding part of the steel arc welding joint of this invention, (b) is sectional drawing by the AA line shown to (a). It is a figure which shows the locus | trajectory of the position of a welding torch or a welding rod. It is a figure which shows the other locus | trajectory of the position of a welding torch or a welding rod. It is a figure which shows the other locus | trajectory of the position of a welding torch or a welding rod. It is a figure which shows composition supercooling. It is a figure which shows a smooth interface growth solidification structure | tissue. It is a figure which shows a cell-like interface growth solidification structure | tissue. It is a figure which shows a cell dendritic interface growth solidification structure | tissue. It is a figure which shows a columnar dendritic interface growth solidification structure | tissue. It is a figure which shows an equiaxed dendritic interface growth solidification structure | tissue. It is a figure which shows the test piece shape and dimension of the lap fillet joint in the Example of this invention.

Explanation of symbols

1 Steel (base material)
2 Weld metal 3 Solidified structure (smooth interface growth structure)
3a Solidified structure (cellular interface growth structure)
3b Solidification structure (cell dendritic interface growth structure)
3c Solidification structure (columnar dendritic interface growth structure)
3d solidified tissue (equiaxial dendritic growth tissue)
4 Liquid phase 5 Solid phase-liquid phase interface 6 Weld toe 7 Temperature distribution in liquid phase 8 Temperature distribution of liquidus line in equilibrium with element concentration in liquid phase 9 Compositional supercooling region 10 Nominal concentration of additive element 11 Equilibrium Phase diagram liquid phase line 12 Equilibrium phase diagram solid phase line 13 Element concentration distribution in liquid phase 14 Distance from weld toe to weld metal direction (range)
15 Welding line 16 Oscillating width 17, 17a, 17b Trajectory of the position of the welding torch or welding rod

Claims (8)

In mass%, C: 0.0001 to 0.0600%, Si: 0.01 to 0.36%, Mn: 0.01 to 1.20%, P: 0.030% or less, S: 0.009 % And Al: 0.001 to 0.100% steel, the balance being Fe and inevitable impurities,
In mass%, C: 0.0001 to 0.0200%, Si: 0.01 to 0.12%, Mn: 0.01 to 0.40%, P: 0.030% or less, S: 0.003 % And Al: 0.001 to 0.100%, the balance consists of a weld metal consisting of Fe and inevitable impurities,
A steel arc welded joint excellent in fatigue strength, wherein the weld metal is a solidified structure having a smooth interface grown at least in a range from the weld toe to 0.1 mm.   Further, the weld metal is, in mass%, Cu: 0.10 to 1.00%, Mo: 0.10 to 5.00%, Nb: 0.005 to 1.000%, V: 0.005. 5.000%, Ti: 0.005 to 0.100%, B: 0.0001 to 0.0050%, Ni: 0.10 to 0.50% and Cr: 0.10 to 7.00% The steel arc welded joint excellent in fatigue strength according to claim 1, comprising one or more elements selected from the group.   Further, the steel is, in mass%, Cu: 0.10 to 3.00%, Mo: 0.10 to 5.00%, Nb: 0.005 to 1.000%, V: 0.005 to 5%. Group consisting of 0.000%, Ti: 0.005 to 0.300%, B: 0.0001 to 0.0050%, Ni: 0.10 to 1.50% and Cr: 0.10 to 7.00% The steel arc welded joint excellent in fatigue strength according to claim 1 or 2, comprising one or more elements selected from   In mass%, C: 0.0001 to 0.0600%, Si: 0.01 to 0.36%, Mn: 0.01 to 1.20%, P: 0.030% or less, S: 0.009 % Or less, Al: 0.001 to 0.100%, with the balance being welded using a welding material consisting of Fe and inevitable impurities, steel according to any one of claims 1 to 3 A method for welding a steel arc welded joint excellent in fatigue strength, characterized by obtaining an arc welded joint.   Further, the welding material is, in mass%, Cu: 0.10 to 3.00%, Mo: 0.10 to 5.00%, Nb: 0.005 to 1.000%, V: 0.005. 5.000%, Ti: 0.005 to 0.300%, B: 0.0001 to 0.0050%, Ni: 0.10 to 1.50% and Cr: 0.10 to 7.00% The welding method for a steel arc welded joint having excellent fatigue strength according to claim 4, comprising one or more elements selected from the group.   The welding method for a steel arc welded joint having excellent fatigue strength according to claim 4 or 5, wherein welding is performed at a welding speed of 10 to 50 cm / min.   The steel with excellent fatigue strength according to claim 6, wherein the arc welding torch or the welding rod is welded while being swung in a direction perpendicular to the welding direction at a frequency of 1 to 4 Hz and a width of 2 to 6 mm. Arc welding joint welding method.   A steel structure excellent in fatigue strength, comprising the steel arc welded joint according to any one of claims 1 to 3.

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