JP4441372B2 - High strength and high toughness gas shielded arc welding wire - Google Patents

Description

The present invention relates to a gas shielded arc welding wire for a high-strength steel sheet applied to uses such as for construction machinery and industrial machinery, and in particular, the strength is 1200 MPa or more in tensile strength TS, 1100 MPa or more in yield stress YP, and Further, the present invention relates to a high-strength, high-toughness gas shielded arc welding wire from which a weld metal having an absorption energy vE- ₄₀ of 27 J or more by a 2 mmV notch Charpy impact test at −40 ° C. can be obtained.

  In recent years, as the demand for larger and lighter steel structures has increased in construction machinery and industrial machinery, etc., the tensile strength of steel plates used has increased, and recently, the tensile strength TS is higher than 780 MPa class. Steel is generally used, and in the future, it is considered that the use of ultra high strength steel having a tensile strength TS of 950 MPa or more and further a tensile strength TS of 1200 MPa or more will increase. Further, as the strength of the steel sheet for steel structure, it is required to improve the yield stress YP in the same manner as the tensile strength TS, and the yield stress YP is 850 MPa or higher for the high strength steel plate having the tensile strength TS of 950 MPa or higher. In a high-tensile steel sheet having a strength TS of 1200 MPa or more, it is desired that the yield stress YP is 1100 MPa or more.

  When a steel structure is manufactured by welding such a high strength steel plate having a high tensile strength TS and a high yield stress YP, the tensile strength TS and yield of the welded joint, particularly the weld metal, as in the case of the high strength steel plate. Improvement of stress YP is required. In a welded part of a normal welded steel structure, the strength of the weld metal is often designed to be overmatched to the steel plate, so the strength of the weld metal needs to be at least equal to or greater than the strength of the steel plate. Moreover, depending on the use of the steel structure, high strength of the weld metal and low temperature toughness are required at the same time.

  In order to produce a high-strength and high-toughness welded joint using a high-tensile steel plate having a tensile strength TS of 950 MPa or higher, or 1200 MPa or higher, the welding method is limited.

When welding such high tensile strength steel plates with high tensile strength TS, there is concern about the occurrence of cold cracks in the weld metal, so the amount of hydrogen in the weld metal can be reduced, and high strength and toughness can be achieved. Gas shielded arc welding such as TIG welding, MIG welding, MAG welding (Ar + CO ₂ welding or CO ₂ welding) that can obtain a welded joint is preferable. Also, among gas shielded arc welding, TIG welding can reduce the amount of hydrogen in the weld metal, so it is suitable for making the weld metal high toughness, but it is more suitable for welding than MIG welding and MAG welding. Inefficient. Therefore, there is a demand for a method for producing a high-strength and high-toughness welded joint using MIG welding and MAG welding.

  Conventionally, many studies have been made on increasing the strength and toughness of a welded portion when gas shielded arc welding is performed on a high-tensile steel sheet having a tensile strength TS of 780 to 900 MPa.

Recently, when gas-shielded arc welding is performed on thick high-tensile steel sheets with a tensile strength TS of 900 MPa or more and a thickness of 50 mm or more, the shape of the weld metal, welding conditions, and the components of the welding wire are specified. Proposed method to obtain welded joint with excellent strength and toughness to form weld metal with tensile strength TS of 988MPa and Charpy absorbed energy (vE- ₂₀ ) at 20 ° C of 74J for steel plate with TS of 1070MPa (For example, refer to Patent Document 1). In this method, the toughness of the weld metal is improved by lowering the tensile strength TS of the weld metal relative to the tensile strength TS of the steel plate, and the tensile strength of the weld joint is defined by the specifications of the weld metal shape and welding conditions. The TS is maintained at the same level as the tensile strength TS of the steel sheet. For this reason, it is difficult to improve the tensile strength and toughness of the weld metal in the weld joint of the high-tensile steel plate having a tensile strength TS of 950 Mpa or more, and further 1100 MPa or more, while the welding construction efficiency is lowered due to the restriction of the welding conditions. .

Conventionally, for example, a high-strength steel plate having a tensile strength TS of 1200 MPa or higher is gas shielded arc welded, a tensile strength TS of 1200 MPa or higher, a yield stress of 1100 MPa or higher, and a 2 mmV notch at −40 ° C. No gas shielded arc welding wire has been found that can form a weld metal satisfying a toughness with an absorbed energy vE- ₄₀ of 27 J or more in a Charpy impact test.

JP 2001-1148 A

In view of the current state of the above-mentioned prior art, the present invention uses a gas shielded arc welding such as MIG welding, MAG welding (Ar + CO ₂ welding or CO ₂ welding) to tension a high strength steel plate having a tensile strength TS of 1200 MPa or more. High-strength, high-toughness gas shield capable of forming a weld metal having a strength TS of 1200 MPa or more, a yield stress YP of 1100 MPa or more, and an absorbed energy vE- ₄₀ of 27 J or more by a 2 mm V notch Charpy impact test at −40 ° C. It is an object to provide an arc welding wire.

The weld metal is formed by solidification after welding wire and some steel plates are melted by welding heat input, and the structure is basically affected by reheating, but is basically solidified structure. In many cases, such as a steel sheet having a rolled structure, no clear yield phenomenon is exhibited. For example, even if the content of the quenching component in the weld metal is increased to obtain a martensite-based structure and the tensile strength TS is improved, the yield stress YP is increased in proportion to the increase in the tensile strength TS like a steel plate. On the contrary, the yield stress YP occurs even when it is extremely reduced. In particular, in a weld metal having a tensile strength TS of 1200 MPa or more, the yield stress YP cannot be improved to 1100 MPa or more in the prior art.

In the gas shield arc welding of a high-strength steel sheet, the inventors have a tensile strength TS of 1200 MPa or more, a yield stress YP of 1100 MPa or more, and an absorbed energy vE ₋ by a 2 mmV notch Charpy impact test at −40 ° C. The component composition of the high-strength, high-toughness gas shielded arc welding wire capable of forming a weld metal having a J of ₄₀ J or more was examined in detail by experiments and the like. As a result, in order to ensure high tensile strength and toughness in the welding wire in order to achieve a high yield stress YP at the same time as the high tensile strength TS and to improve the toughness simultaneously in the weld metal, It has been found that it is essential to contain an appropriate amount of Mo that suppresses the increase in movable dislocation density and the generation of retained austenite, while containing a predetermined amount of Ni and ensuring a predetermined hardenability.
The present invention has been made on the basis of this new finding, and the gist thereof is as follows.

(1) The composition of the welding wire is mass%,
C: 0.06 to 0.2%,
Si: 0.2-1%,
Mn: 0.5 to 2.5%
Al: 0.002 to 0.1%,
Ti: 0.005 to 0.3%,
N: 0.001 to 0.015%,
Ni: 0.5-6%
Including
P: 0.02% or less,
S: 0.01% or less,
O: limited to 0.01% or less,
further,
Mo: 0.1 to 4%
W: 0.1 to 3%
Nb: 0.005 to 0.1%,
V: 0.005-0.5% and
Ta: 0.005 to 0.5%
Containing one or more of
The carbon equivalent (Ceq) represented by the following formula (1) is 0.8 to 2%, and the Nb equivalent (Nbeq) represented by the following formula (2) is 0.091 to 0.5%, and the balance A wire for high-strength, high-toughness gas shielded arc welding, characterized by comprising inevitable impurities and Fe.
Ceq = [C%] + [Mn%] / 6+ [Si%] / 24+ [Ni%] / 40+ [Mo%] / 4+ [W%] / 8 (1)
Nbeq = [Nb%] + [V%] / 5+ [Mo%] / 20+ [W%] / 10+ [Ta%] / 5 (2)
However, [C%], [Mn%], [Si%], [Ni%], [Mo%], [W%], [Nb%], [V%], and [Ta%] are C, Each content (mass%) of Mn, Si, Ni, Mo, W, Nb, V, and Ta is shown.

(2) In mass%,
Cu: 0.01 to 1.5%,
Cr: 0.01-2%
Co: 0.01-6%, and
B: 0.001 to 0.015%
1 or 2 or more of them, and the carbon equivalent (Ceq) represented by the following formula (3) is 0.8 to 2%. Wire for tough gas shielded arc welding.
Ceq = [C%] + [Mn%] / 6+ [Si%] / 24+ [Ni%] / 40+ [Cr%] / 5+ [Mo%] / 4+ [W%] / 8 (3)
However, [C%], [Mn%], [Si%], [Ni%], [Cr%], [Mo%], and [W%] are C, Mn, Si, Ni, Cr, Mo, Each content (mass%) of W is shown.

(3) In mass%,
Ca: 0.0002 to 0.01%,
Mg: 0.0002 to 0.01%, and
REM: 0.0002 to 0.01%
The wire for high strength and high toughness gas shielded arc welding as described in (1) or (2) above, comprising one or more of the above.

According to the gas shielded arc welding wire of the present invention, the yield stress in gas shielded arc welding in general, such as MIG welding and MAG welding (Ar + CO ₂ welding or CO ₂ welding) on a high-tensile steel sheet having a tensile strength of 1200 MPa or more. It is possible to obtain a weld metal having high strength and high toughness, and providing a welded joint having high strength and high safety in a high-tensile steel plate. The present invention is particularly useful for achieving a toughness in which the yield stress of a weld metal is 1100 MPa or more and the absorbed energy in a 2 mmV notch Charpy impact test at −40 ° C. is 27 J or more.

The weld metal structure for achieving the yield strength YP of 1100 MPa or more with respect to the tensile strength TS of the weld metal of the present invention, which is 1200 MPa or more, is a martensite-based structure, so The density increases and the retained austenite increases. Increasing the density of movable dislocations in the weld metal lowers the yield stress YP and toughness, and the residual austenite in the weld metal undergoes martensitic transformation when exposed to low-temperature environments or when stress is applied, degrading toughness. Cause. Further, precipitation strengthening by precipitation elements is known as a means for increasing the yield stress YP of a steel sheet, but unlike a steel sheet in which precipitation behavior can be easily controlled by rolling or heat treatment like a steel sheet, it is basically solidified without heat treatment. The conventional common sense is that the weld metal of the structure does not show the yield phenomenon similar to that of the steel plate. For this reason, even if the tensile strength TS of the weld metal is improved, the yield stress YP is not necessarily improved, and conversely, the yield stress YP may be significantly reduced.

Therefore, the inventors have absorbed energy by a 2 mmV notch Charpy impact test at −40 ° C. at a tensile strength TS of 1200 MPa or more, a yield stress YP of 1100 MPa or more in gas shielded arc welding of a high-strength steel plate. With the goal of forming a weld metal with a vE- ₄₀ of 27 J or more, the component composition of the high-strength, high-toughness gas shielded arc welding wire for achieving this was examined in detail by experiments and the like.

As a result of the examination, in a weld metal having a tensile strength TS of 1200 MPa or more, Ni is contained in a predetermined amount, and a predetermined hardenability by other components is ensured, and Mo, Nb, V, and Ta are further included. When one or more of these elements are contained in a predetermined amount, these precipitates are combined with carbon and / or nitrogen, and precipitates precipitated in the weld metal are introduced in large amounts mainly by martensitic transformation. It has been clarified that the effect of pinning the movement of is effective in improving the yield stress YP and toughness at the same time. It has also been found that the precipitated elements of Mo, Nb, V and Ta stabilize the ferrite phase of the weld metal, reduce the retained austenite which inhibits the toughness of the weld metal, and improve the toughness of the weld metal.

  In addition, the effect of improving the yield stress YP and toughness of the weld metal by the precipitation elements of Mo, Nb, V, and Ta includes a relatively large amount of Ni as a basic component element that can simultaneously achieve the tensile strength TS and toughness. It is effective for the first time in a weld metal structure containing a large amount of movable dislocations and retained austenite under the above conditions. That is, in a weld metal having a low tensile strength TS, a mixed structure of ferrite and pearlite, or a bainite-based structure, the Mo only acts as a precipitation strengthening element in the weld metal, and the yield strength of the weld metal The inventors have confirmed that the improvement effect is small and the effect of suppressing the toughness deterioration of the weld metal accompanying the increase in strength cannot be obtained. In addition, although the said effect of the precipitation element of Mo, Nb, V, and Ta is obtained by adding these precipitation elements within the content range which satisfies the parameter | index of Nb equivalent mentioned later, it adds independently. In this case, Mo is more preferable among these precipitation elements from the viewpoint of the balance between strength and toughness of the weld metal.

From the above knowledge, in the weld metal having a tensile strength TS of 1200 MPa or more, a martensite structure main structure having a high movable dislocation density, and residual austenite that inhibits toughness is likely to remain, the yield stress YP ( 1100 MPa or more) and toughness vE- ₄₀ (Charpy at −40 ° C .: 27 J or more) in order to improve the tensile strength and toughness in the welding wire in a predetermined amount, It is effective to effectively utilize the synergistic effect of the pinning effect due to the Mo precipitate and the retained austenite suppressing effect due to the stabilization of the ferrite after ensuring the predetermined hardenability. The present invention has been made based on these findings and technical ideas.

  The reason for limiting the component composition of the wire for gas shielded arc welding in the present invention will be described below.

  In the following description, “%” means “% by mass” unless otherwise specified.

  C is an essential element for improving the tensile strength TS of the weld metal to 1200 MPa or more and preventing the unbalance of the tensile strength TS of the high-strength steel plate. For this reason, C is contained in the welding wire. It is necessary to contain 0.06% or more. The higher the C content in the welding wire, the better the tensile strength TS of the weld metal, but the excessive content of C significantly deteriorates the toughness of the weld metal. In order to ensure the toughness of the weld metal at −40 ° C., the upper limit of the C content in the weld wire needs to be 0.2%. Therefore, in the present invention, the C content in the welding wire is 0.06 to 0.2%.

  Si is a deoxidizing element, and in order to reduce the amount of O in the weld metal and increase the cleanliness, the Si content in the welding wire needs to be 0.2% or more. On the other hand, when the Si content in the welding wire exceeds 1% and becomes excessive, a coarse oxide is generated and the toughness of the weld metal is significantly deteriorated. For this reason, in this invention, Si content in a welding wire shall be 0.2-1%.

  Mn is an element effective for improving the toughness by refining the structure so as to increase the strength by ensuring the hardenability of the weld metal and within a certain amount. In order to reliably exhibit the effect of improving the strength of the welding wire and refining the structure using the action of Mn, it is necessary to contain 0.5% or more of Mn in the welding wire. On the other hand, when Mn exceeds 2.5% in the welding wire, the susceptibility to grain boundary embrittlement increases, and the possibility of deterioration of the toughness and weld crack resistance of the weld metal increases. For this reason, in this invention, Mn content in a welding wire is limited to 0.5 to 2.5%.

  Al is a deoxidizing element and, like Si, is effective in reducing O in the weld metal and improving cleanliness, but in order to exert the effect, it is necessary to contain 0.002% or more in the welding wire. On the other hand, if Al exceeds 0.1% in the welding wire, a coarse oxide is formed in the weld metal, and this coarse oxide significantly deteriorates the toughness, which is not preferable. Therefore, in the present invention, the Al content in the welding wire is 0.002 to 0.1%.

  Ti is also effective as a deoxidizing element in the weld metal, and can fix the solid solution N in the weld metal as a nitride to mitigate the adverse effect on the toughness of the solid solution N. In the case of welding, there is also an effect of refining the heated austenite grains in the reheat region of the weld metal. In order to exhibit the effect of improving the toughness of the weld metal by the action of Ti, it is necessary to contain 0.005% or more of Ti in the welding wire. On the other hand, if the Ti content in the welding wire exceeds 0.3% and excessive, there is a great possibility that the formation of coarse oxides in the weld metal and the toughness deterioration due to excessive precipitation of TiN will remarkably occur. It becomes. For this reason, in this invention, Ti content in a welding wire shall be 0.005-0.3%. In order to more clearly exhibit the effect of improving the toughness of the weld metal by Ti, the Ti content in the welding wire is more preferably 0.01 to 0.1%.

  N has the effect of forming Ti and TiN in the weld metal and refining the heated austenite grains in the reheat region of the weld metal in the case of multi-layer welding, and in order to exert this effect, It is preferable to contain 0.001% or more of N. On the other hand, if N exceeds 0.015% in the wire, the amount of solute N in the weld metal increases and the toughness is remarkably deteriorated. The content is limited to 0.001 to 0.015%.

Ni is the only element that can stably improve toughness regardless of the other components and structure of the weld metal by solid solution toughening. In particular, the toughness of high-strength weld metal with a tensile strength TS of 1200 MPa or more is achieved. It is a particularly important element in the wire of the present invention for enhancing. In order to exhibit the solid solution toughening effect of Ni reliably in the weld metal, it is necessary to contain 0.5% or more of Ni in the welding wire. The higher the Ni content in the wire, the more advantageous in improving the toughness of the weld metal. However, if the Ni content in the welding wire exceeds 6%, the effect is saturated and the manufacturing cost of the welding wire Is excessively undesirable. Therefore, in this invention, Ni content in a welding wire is limited to 0.5 to 6%.

  P is an inevitable impurity element in the wire and needs to be reduced as much as possible in order to inhibit the toughness of the weld metal. If the P content in the welding wire is 0.02% or less, adverse effects on the toughness of the weld metal can be tolerated. Therefore, in the present invention, the P content in the welding wire is limited to 0.02% or less.

  S is also an inevitable impurity element in the wire, and if it is excessively present in the weld metal, it deteriorates both the toughness and ductility of the weld metal, so it is preferable to reduce it as much as possible. If the S content in the welding wire is 0.01% or less, adverse effects on the toughness and ductility of the weld metal can be tolerated. Therefore, in the present invention, the S content in the welding wire is limited to 0.01% or less. Especially in high-strength weld metal where the yield stress YP of the weld metal is 1100 MPa or more as in the present invention, the adverse effect on ductility and toughness of S appears more significantly. It is more preferable to limit it to 0.005% or less.

  O is also an inevitable impurity element in the welding wire, and if present in a large amount, the manufacturability of the welding wire is hindered, and the O content in the weld metal is excessively increased to deteriorate the ductility and toughness of the weld metal. Therefore, it is not preferable. In the present invention, the upper limit of the O content is limited to 0.01% as a range in which the weld wire manufacturability and the weld metal quality do not deteriorate.

In the present invention, in order to secure a yield stress YP of 1100 MPa or more commensurate with the target tensile strength TS of 1200 MPa or more, in addition to the above components, Mo, W, Nb, It is necessary to contain one or more of V and Ta within the following predetermined range.

  Mo, W, Nb, V, and Ta are ferrite stabilizing elements and precipitate forming elements, and qualitatively have the following effects in substantially the same manner.

Mo is a hardenability improving element for increasing the tensile strength TS of the weld metal, and is an element effective for reducing retained austenite that inhibits the toughness of the weld metal because it is a ferrite stabilizing element. In addition, Mo forms fine carbides in the weld metal to increase the yield stress YP by precipitation strengthening, and at the same time, the pinning action by the precipitates hinders the movement of movable dislocations generated mainly during the martensitic transformation, thereby yielding stress. It is also an effective element for improving YP and toughness. In order to fully exhibit these effects, it is necessary to contain 0.1% or more of Mo in the wire. On the other hand, when Mo exceeds 4% in the welding wire, coarse precipitates are generated in the weld metal to deteriorate the toughness of the weld metal, and the deformation resistance between hot and cold becomes excessive. As a result, workability deteriorates, making wire production difficult. For this reason, in this invention, Mo content in a welding wire shall be 0.1 to 4%.

  W, like Mo, acts as a hardenability improving element to increase the tensile strength TS of the weld metal and reduces the retained austenite which inhibits the toughness of the weld metal because it is a ferrite stabilizing element. It is valid. In order to improve the toughness by forming fine carbides in the weld metal and increasing the yield stress YP by precipitation strengthening, and at the same time, the pinning action by the precipitates hinders the movement of movable dislocations generated during martensitic transformation. It is effective for. In order to exhibit these effects, it is preferable to contain 0.1% or more even in consideration of combined effects with other elements having similar effects. On the other hand, if the wire contains more than 3% W, the deformation resistance between hot and cold becomes excessive and the workability deteriorates, resulting in difficulty in wire production. The content when W is contained in the wire is preferably 0.1 to 3%.

  Nb is also a ferrite stabilizing element, and is effective in reducing retained austenite that inhibits the toughness of the weld metal. In order to improve the toughness by forming fine carbides in the weld metal and increasing the yield stress YP by precipitation strengthening, and at the same time, the pinning action by the precipitates hinders the movement of movable dislocations generated during martensitic transformation. It is effective for. In order to exhibit these effects, it is preferable to contain 0.005% or more even if the combined effect with other elements having similar effects is taken into consideration. On the other hand, if Nb is excessively contained in the wire in excess of 0.1%, coarse precipitates are formed and the toughness of the weld metal is deteriorated, which is not preferable. Therefore, in the present invention, the content when Nb is contained in the welding wire is preferably 0.005 to 0.1%.

  V is also a ferrite stabilizing element, and is effective in reducing retained austenite which inhibits the toughness of the weld metal. In order to improve the toughness by forming fine carbides in the weld metal and increasing the yield stress YP by precipitation strengthening, and at the same time, the pinning action by the precipitates hinders the movement of movable dislocations generated during martensitic transformation. It is effective for. In order to exhibit these effects, it is preferable to contain 0.005% or more even if the combined effect with other elements having similar effects is taken into consideration. On the other hand, if V exceeds 0.5% in the wire and excessively contained in the welding wire, coarse precipitates are formed and the toughness of the weld metal is deteriorated. Therefore, in the present invention, the content when V is contained in the welding wire is preferably 0.005 to 0.5%.

  Ta is also a ferrite stabilizing element, and is effective in reducing retained austenite that inhibits the toughness of the weld metal. Also, in order to improve the toughness by forming fine carbides in the weld metal and increasing the yield stress by precipitation strengthening, and at the same time, the pinning action by the precipitates hinders the movement of movable dislocations that occurred mainly during martensitic transformation. It is valid. In order to exhibit these effects, it is preferable to contain 0.005% or more even if the combined effect with other elements having similar effects is taken into consideration. On the other hand, if Ta exceeds 0.5% in the wire and excessively contained in the welding wire, coarse precipitates are formed and the toughness of the weld metal is deteriorated. Therefore, in the present invention, the content when Ta is contained in the welding wire is preferably 0.005 to 0.5%.

The above is the reason for limiting the contents of the basic component elements of the welding wire and the inevitable impurities to be limited in the present invention. In addition to the limitation of the content of these components, in the present invention, in order to ensure the hardenability necessary for obtaining a weld metal having a target tensile strength TS of 1200 MPa or more, the following (1 ) It is necessary to limit the carbon equivalent Ceq represented by the formula.
Ceq = [C%] + [Mn%] / 6+ [Si%] / 24+ [Ni%] / 40+ [Mo%] / 4+ [W%] / 8 (1)
However, [C%], [Mn%], [Si%], [Ni%], [Mo%], and [W%] are the respective contents of C, Mn, Si, Ni, Mo, and W ( Mass%).

That is, in order for the tensile strength TS of the weld metal image to be 1200 MPa or more, it is essential that the hardenability is sufficiently secured and the transformation structure of the weld metal is martensite or a mixed structure of martensite and bainite. It is. For that purpose, the content of the basic component in the welding wire is limited to the above range, and further, the content of C, Si, Mn, Ni, Mo, W, which are quenching components in the welding wire, is reduced. It is necessary to limit the carbon equivalent Ceq of the hardenability index obtained by the above formula (1) to 0.8% or more. When the carbon equivalent Ceq is less than 0.8, the hardenability for ensuring that the tensile strength TS of the weld metal image is 1200 MPa or more cannot be ensured.

  Stable hardenability can be secured as the carbon equivalent Ceq determined by the above formula (1) increases, but when the carbon equivalent Ceq exceeds 2% and the hardenability becomes excessive, the tensile strength TS of the weld metal is improved. This is not preferable because the effect is saturated and the yield stress YP and toughness deteriorate due to an increase in the formation of retained austenite in the weld metal. For the above reason, in the present invention, the carbon equivalent Ceq of the welding wire obtained by the above equation (1) is limited to 0.8 to 2%.

Further, in addition to the limitation of the content of the components in the welding wire, in the present invention, a target weld metal of 1200 MPa or more, in order to ensure a high yield stress with YP of 1100 MPa or more, the following formula (2) It is preferable to limit the Nb equivalent Nbeq represented by the following predetermined range.
Nbeq = [Nb%] + [V%] / 5+ [Mo%] / 20+ [W%] / 10+ [Ta%] / 5 (2)
However, [Nb%], [V%], [Mo%], [W%], and [Ta%] indicate the respective contents (mass%) of Nb, V, Mo, W, and Ta.

When the Nb equivalent Nbeq represented by the above formula (2) is less than 0.091 %, even if the specified ranges of the respective contents of Mo, W, Nb, V, and Ta described above are satisfied, 1100 MPa or more It is difficult to stably improve the yield stress YP. On the other hand, if the Nb equivalent Nbeq represented by the above formula (2) exceeds 0.5%, it is not preferable because the toughness of the weld metal is greatly deteriorated or the manufacturability of the welding wire is hindered. Yield stress YP of 1100 MPa or more commensurate with the target tensile strength TS of 1200 MPa or more is secured, and further, yield ratio YR (yield stress YP (0.2% proof stress (PS)) / tensile strength TS) in order to ensure at least 0.8, you the Nb equivalent Nbeq represented by formula (2) and from 0.091 to 0.5%.

  The above is the reason for limiting the basic component elements of the welding wire of the present invention and the contents of unavoidable impurities to be limited. In order to adjust a specific mechanical property, one or more of Cu, Cr, Co and B can be further contained in the welding wire as necessary.

  Cu is inevitably contained in the wire and the weld metal when the welding wire is plated and used. Cu is an element effective for improving the strength, and in order to exert the effect, it is necessary to contain 0.01% or more. However, if it is contained excessively, deterioration of the toughness and hot cracking resistance of the weld metal is not preferable. In the present invention, the Cu content of the wire is the upper limit that does not cause deterioration of the toughness or hot cracking resistance of the weld metal, even if it is contained as plating or intentionally contained for strength improvement. The upper limit is 1.5%.

  Cr is an effective element for increasing strength by enhancing hardenability. Therefore, when it contains in a welding wire, 0.01% or more is required. On the other hand, when the content exceeds 2%, bainite and martensite are hardened unevenly and the toughness is remarkably deteriorated. Therefore, in the present invention, the upper limit of the content in the welding wire is set to 2%.

Co is an element effective in securing the yield stress through the adjustment of strength and the suppression of the formation of retained austenite by suppressing the extreme reduction of the transformation point in the bainite-martensite structure. In order to exhibit this effect reliably, it is necessary to make it contain 0.01% or more in a welding wire. On the other hand, if the content exceeds 6%, the effect is saturated and the manufacturing cost becomes excessive. Therefore, in the present invention, when Co is contained in the welding wire, the range is set to 0.01 to 6%.

When B is contained in an appropriate amount in the weld metal, it is combined with solute N to form BN, and has the effect of reducing the adverse effect on the toughness of solute N, and also improves hardenability and improves strength. It is an element that can contribute. In order to exert these effects reliably, the B content in the welding wire needs to be 0.001% or more. On the other hand, when the B content in the welding wire exceeds 0.015%, the B in the weld metal becomes excessive and forms coarse B compounds such as BN and Fe ₂₃ (C, B) ₆ to reverse the toughness. It is not preferable because it deteriorates. Therefore, in the present invention, when B is contained in the welding wire, the content is limited to 0.001 to 0.015%.

In the case where the welding wire contains one or more of Cu, Cr, Co and B in addition to the basic components described above, the hardenability represented by the above formula (1) or the following formula (3) If the carbon equivalent Ceq of the index is less than 0.8, the hardenability for making the tensile strength TS of the weld metal image 1200 MPa or more cannot be ensured. If the carbon equivalent Ceq exceeds 2%, the yield stress YP Further, it is not preferable because toughness deteriorates. For this reason, it is necessary to limit carbon equivalent Ceq to 0.8-2% or more like the above.
Ceq = [C%] + [Mn%] / 6+ [Si%] / 24+ [Ni%] / 40+ [Cr%] / 5+ [Mo%] / 4+ [W%] / 8 (3)
However, [C%], [Mn%], [Si%], [Ni%], [Cr%], [Mo%], and [W%] are C, Mn, Si, Ni, Cr, Mo, Each content (mass%) of W is shown.

  Further, for the purpose of adjusting the ductility and toughness of the weld metal, one or more of Ca, Mg, and REM can be further contained in the welding wire as necessary. Ca, Mg, and REM are all effective in improving the ductility and toughness by changing the sulfide structure and reducing the size of the sulfide and oxide in the weld metal. The lower limit content for exhibiting the effect is 0.0002%. On the other hand, excessive content causes coarsening of sulfides and oxides, leading to deterioration of ductility and toughness, and also may cause deterioration of weld bead shape and weldability. 0.01%.

  The chemical composition of the above welding wire is a value in the final wire form, and if the chemical composition satisfies the present invention, even if the welding wire is a solid wire, a metal or alloy is contained in the steel outer shell. Even a wire filled with a granular or powdery raw material such as flux does not impair the effects of the present invention.

The effects of the present invention will be described in more detail with reference to examples. 1 were prepared using solid wires for gas shielded arc welding with various chemical compositions, and the strength and toughness of the weld metal were evaluated by a round bar tensile test and a 2 mm V notch Charpy impact test. The steel plate is a steel plate of 25 mm thickness, yield stress YP: 1100 MPa, tensile strength TS: 1200 MPa class, V-shaped groove butt joint, and under the conditions of Table 1, the diameter of 1. Multi-layer welding was performed by Ar + 20% CO ₂ gas shielded arc welding using a 2 mm solid wire.

A specimen was taken from the weld metal of the joint after welding and investigated for mechanical properties. In the tensile test, a round bar tensile test piece having a parallel part diameter of 6 mm and a parallel part length of 32 mm was sampled from the steel plate thickness center and the weld metal width center so that the test piece longitudinal direction was parallel to the weld bead longitudinal direction. At room temperature. Since all the weld metals did not yield a clear yield point and yield elongation, 0.2% proof stress (0.2% PS) was adopted as the yield stress YP. The toughness was evaluated by the average absorbed energy vE- ₄₀ (average value of three) at −40 ° C. in a 2 mmV notch Charpy impact test. As shown in FIG. 1, the test piece was sampled so that the center of the test piece was at the position ¼ of the steel plate thickness and the notch was in the center in the width direction of the weld metal.

Table 2 shows the chemical composition and mechanical test results of the welding wire. Fittings A1~ joint A 11 is welded joints using the welding wire having the chemical composition of the present invention. Strength of the weld metal of the joint A1~ joint A 11 is a tensile strength TS of 1200 MPa or more, and the yield stress YP (0.2% proof stress PS) also 1100 MPa or higher and has achieved sufficient strength . Also, the toughness of the weld metal is a very high strength weld metal with a 0.2% proof stress PS of 1100 MPa or more, all of which are absorbed energy (vE- ₄₀ ) by a 2 mmV notch Charpy impact test at -40 ° C. or 40J are obtained, that has achieved sufficient low-temperature toughness.

  On the other hand, the joints B1 to B14 are comparative examples welded with a wire that does not satisfy the requirements of the present invention, and the composition of the welding wire does not satisfy the present invention, and therefore the strength and / or toughness is not sufficient.

In the joint B1, since the Mo content of the welding wire is excessive, coarse precipitates are generated, and the toughness vE- ₄₀ of the weld metal is 13J, which is remarkably deteriorated. In addition, the deformation resistance of the wire between hot and cold is excessive, the workability is deteriorated, and the wire production becomes difficult.

In the joint B2, since the C content of the welding wire is excessive, the toughness vE- ₄₀ of the weld metal is 15 J, which is greatly deteriorated compared to the example of the present invention.

In the joint B3, since the Cr content of the welding wire is excessive, bainite and martensite are hardened unevenly, and the weld metal has a toughness vE- ₄₀ of 20 J, which is extremely inferior.

In the joint B4, since the P content of the welding wire is excessive, the weld metal has a toughness vE- ₄₀ of 14J, and the deterioration of the toughness is remarkable.

In the joint B5, since the S content of the welding wire is excessive, the toughness vE- ₄₀ of the weld metal is 21 J, and the toughness is clearly inferior to the example of the present invention.

In the joint B6, since the Ti content of the welding wire is excessively small, the microstructure of the weld metal is not sufficiently refined. Therefore, the toughness vE- ₄₀ of the weld metal is 22J, and the toughness is inferior.

  In the joint B7, since the carbon equivalent Ceq and the Nb equivalent Nbeq of the welding wire are too small, the tensile strength TS and the yield stress YP (0.2% PS) of the weld metal are the target values (TS ≧ 1200 MPa, YS ≧ 1100 MPa), and sufficient strength of the weld metal is not achieved as a wire for welding high-strength steel having a tensile strength of 950 MPa or higher.

  In the joint B8, on the contrary, since the carbon equivalent Ceq of the welding wire is excessive, the yield stress YP (0.2% PS) is as low as 1015 MPa for the weld metal tensile strength TS, which is insufficient. The toughness is also as low as 17J. Moreover, since the yield stress YP (0.2% PS) was too low with respect to the tensile strength TS of the weld metal, the yield ratio YR of the weld metal was also as low as 0.69.

  In the joint B9, since the Nb equivalent Nbeq of the welding wire is too small, the yield stress YP (0.2% PS) of the weld metal is 741 MPa, which is lower than that of the example of the present invention. Moreover, since the yield stress YP (0.2% PS) was too low with respect to the tensile strength TS of the weld metal, the yield ratio YR of the weld metal was also as low as 0.70.

In the joint B10, the Nb equivalent Nbeq of the welding wire was excessive, the toughness vE- ₄₀ of the weld metal was 11 J, and the toughness was significantly deteriorated.

In the joint B11, since any of Mo, W, Nb, V, and Ta was not contained in the welding wire, the yield stress YP of the weld metal was 784 MPa, and the yield stress was significantly reduced.

  In the joint B12, although Mo was contained in the welding wire, the yield stress YP of the weld metal was 788 MPa because the content was too small, and the yield stress was significantly reduced.

  In the joint B13, although Nb was contained in the welding wire, the yield stress YP of the weld metal was 784 MPa because the content was too small, and the yield stress was significantly reduced.

  In the joint B14, although Mo and Nb are contained in the welding wire, since the contents of both elements are too small, the yield stress YP of the weld metal is 765 MPa, and the yield stress is significantly reduced.

Also from the above examples, according to the present invention, the tensile strength TS, the yield stress YP, in general in gas shielded arc welding in a high-tensile steel plate having a tensile strength TS of 1200 MPa class or higher and a yield stress YP of 1100 MPa class or higher, Weld metal with excellent yield ratio YR (YP / TS) and toughness vE- ₄₀ can be obtained, and the strength and toughness are high and the safety is excellent in the welding of high-tensile steel plates applied in steel structures. Obviously, it is possible to provide a welded joint.

It is a schematic diagram which shows the groove shape of the weld joint used for the Example, and the extraction | collection point of a 2mmV notch Charpy impact test piece.

DESCRIPTION OF SYMBOLS 1 Steel plate 2 Backing metal 3 Weld bead 4 2mmV notch Charpy impact test piece

Claims (3)

The composition of the welding wire is mass%,
C: 0.06 to 0.2%,
Si: 0.2-1%,
Mn: 0.5 to 2.5%
Al: 0.002 to 0.1%,
Ti: 0.005 to 0.3%,
N: 0.001 to 0.015%,
Ni: 0.5-6%
Including
P: 0.02% or less,
S: 0.01% or less,
O: limited to 0.01% or less,
further,
Mo: 0.1 to 4%
W: 0.1 to 3%
Nb: 0.005 to 0.1%,
V: 0.005-0.5% and
Ta: 0.005 to 0.5%
Containing one or more of
The carbon equivalent (Ceq) represented by the following formula (1) is 0.8 to 2%, and the Nb equivalent (Nbeq) represented by the following formula (2) is 0.091 to 0.5%, and the balance A wire for high-strength, high-toughness gas shielded arc welding, characterized by comprising inevitable impurities and Fe.
Ceq = [C%] + [Mn%] / 6+ [Si%] / 24+ [Ni%] / 40+ [Mo%] / 4+ [W%] / 8 (1)
Nbeq = [Nb%] + [V%] / 5+ [Mo%] / 20+ [W%] / 10+ [Ta%] / 5 (2)
However, [C%], [Mn%], [Si%], [Ni%], [Mo%], [W%], [Nb%], [V%], and [Ta%] are C, Each content (mass%) of Mn, Si, Ni, Mo, W, Nb, V, and Ta is shown. In mass%,
Cu: 0.01 to 1.5%,
Cr: 0.01-2%
Co: 0.01-6%, and
B: 0.001 to 0.015%
The high-strength, high-toughness according to claim 1, wherein the carbon equivalent (Ceq) represented by the following formula (3) is 0.8 to 2%. Gas shielded arc welding wire.
Ceq = [C%] + [Mn%] / 6+ [Si%] / 24+ [Ni%] / 40+ [Cr%] / 5+ [Mo%] / 4+ [W%] / 8 (3)
However, [C%], [Mn%], [Si%], [Ni%], [Cr%], [Mo%], and [W%] are C, Mn, Si, Ni, Cr, Mo, Each content (mass%) of W is shown. In mass%,
Ca: 0.0002 to 0.01%,
Mg: 0.0002 to 0.01%, and
REM: 0.0002 to 0.01%
The high-strength, high-toughness gas shielded arc welding wire according to claim 1, wherein the wire contains one or more of them.

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