JP5218201B2 - Weld metal and weld material - Google Patents

Description

  The present invention relates to a weld metal and a weld material. Specifically, it is used for welding high-strength materials suitable as materials for various members such as high-pressure gas pipes in energy transportation equipment, and a weld metal with high strength and excellent “weld crack resistance” can be obtained. The present invention relates to a welding material and a weld metal of the welded member.

  In recent years, research on practical application of transportation equipment using hydrogen, natural gas, or the like as energy has been actively promoted. For practical use, it is necessary to prepare an environment in which these gases can be stored and transported at high pressures, and the materials used are required to have high strength. Has been made.

  For example, with respect to the base material, an austenite-based material has been proposed in which the solubility of N is increased by increasing the Mn content, V is added, and an appropriate heat treatment is performed as necessary to increase the strength. Yes. Specifically, Patent Document 1 and Patent Document 2 disclose a high-strength material having a tensile strength of 1 GPa or more that can be used as a material for a high-pressure gas storage and transport member.

  In general, when used as a structure, the above-described high-strength austenitic material is assembled by welding. And it is possible to use a base material as it is as a welding material in the case of welding.

  However, austenitic weld metals generally have high hot cracking susceptibility during welding. For this reason, the weld metal is required to prevent hot cracking. In addition, in the case of a base material, the structure is adjusted by rolling and heat treatment after melting, and high temperature strength is ensured. On the other hand, weld metal is almost always used in a solid structure.

  Therefore, when the base material is used as a welding material as it is, not only the hot cracking resistance is sufficient, but it is extremely difficult to obtain a high strength equivalent to that of the base material. For this reason, it is necessary to reinforce the weld metal at least as much as the base material by precipitating fine particles by performing “post heat treatment” after welding.

  As a welding material having a tensile strength of 1 GPa or more, for example, ERNiFeCr-2 of AWS A5.14-2005 has already been put into practical use. Patent Document 3 and Patent Document 4 propose a welding material (welded metal) having a tensile strength exceeding 800 MPa by actively utilizing Al, Ti, and Nb. Patent Document 4 also shows that solidification cracking can be prevented by containing an appropriate amount of Ti and / or Al.

  However, in order to increase the strength of these welding materials as well, it is necessary to perform “post heat treatment” for at least 120 minutes after welding. Therefore, when an actual large structure is considered, the long-time post-weld heat treatment as described above is greatly restricted in its application and the manufacturing cost is extremely increased.

WO 2004/083476 WO2004 / 083477 JP-A-5-192785 WO2004 / 110695 publication

  The present invention has been made in view of the above situation, and forms a weld metal having high strength obtained by a short post-weld heat treatment and also having excellent weld crack resistance, and such a weld metal. In particular, a weld metal in a welded structure using a high-strength material having a tensile strength of 1 GPa or more, which is being developed in recent years, and the above-described base material. It aims at providing the welding material used for welding of this.

  The present inventors have conducted various studies in order to solve the above-described problems. As a result, the following knowledge (a) was obtained.

(A) In order to achieve high strength in the weld metal, the content of Cr and Ni is regulated within a predetermined range, Al is contained, and post-weld heat treatment is performed, thereby strengthening precipitation by Ni ₃ Al. It is effective to utilize. However, even when Al is contained alone in a large amount, a long post-weld heat treatment is required to achieve high strength.

  Therefore, in order to achieve both high strength in post-weld heat treatment in a short time, in particular, a short time of 120 min or less and “weld crack resistance” as weldability, the present inventors first include Al. Investigation and examination were conducted with various amounts. In addition, about the weld metal in this case, while containing 50 to 68% of Ni in mass%, it was supposed to contain 20 to 30% Cr in mass%.

  As a result, the following items (b) and (c) were clarified.

(B) When Al is contained in an amount of 2.0 to 7.0% by mass, when heat treatment after welding is performed, Ni ₃ Al is finely precipitated in the matrix and the strength is increased.

(C) When Al is contained alone, long-time heat treatment is required to obtain the precipitation strengthening effect by Ni ₃ Al described above. In addition, “solidification cracks” and “ductility degradation cracks” tend to occur in the weld metal.

  Therefore, various investigations and investigations were performed on the influence of various elements when Al is contained in an amount of 2.0 to 7.0% by mass. As a result, the following important knowledge (d) was obtained.

  (D) For weld metals containing 50 to 68% Ni and 20 to 30% Cr in mass%, both high strength in short-time post-weld heat treatment and “weld crack resistance” as weldability are achieved. In order to make it contain 2.0 to 7.0% of Al by mass%, the contents of C and Nb are respectively mass%, and C: 0.06 to 0.18% and Nb. : It should be 0.55 to 1.50%.

  The reason for the above (d) is considered as the following <1> to <7>.

When heat treatment after welding is performed when Nb of <1>% by mass and 0.55% or more is contained, Al and Nb in Ni ₃ Al are slightly substituted to become Ni ₃ (Al, Nb). As a result, the driving force for the deposition increases and the deposition occurs in a short time.

  <2> However, when only the above-described amount of Nb is contained, Nb is an element that easily solidifies and segregates during solidification of the weld metal, so that the solidification cracking sensitivity is greatly increased.

  <3> By containing C in combination with Nb, the amount of harmful Nb that causes eutectic solidification of NbC and austenite during the solidification process of the weld metal and solidifies and segregates in the liquid phase to lower the melting point. Since it is reduced, solidification cracking can be prevented.

  <4> However, when the content of C becomes excessive, conversely, the amount of harmful C that solidifies and segregates in the liquid phase to lower the melting point increases, thereby increasing the susceptibility to solidification cracking.

  <5> NbC crystallized during solidification exists after a solidification by forming an austenite and a lamellar structure at the dendrite boundary. For this reason, the segregation of impurity elements is reduced by increasing the final solidification interface area. In addition, since stress concentration on a specific surface is also reduced, it has an effect of preventing ductile deterioration cracks caused by stress acting on the grain boundaries where the impurity elements are segregated and weakened.

When <6> C and Nb are contained in a large amount, solidification cracking and ductile degradation cracking can be prevented, but a large amount of NbC is formed at the grain boundaries. Since this NbC is poor in ductility as compared with the austenite phase as a matrix, the ductility of the weld metal is reduced. In particular, when 2.0% to 7.0% Al is contained by mass%, since the inside of the grain is strengthened by Ni ₃ (Al, Nb), thermal stress and external stress are concentrated on the grain interface. As a result, the decrease in ductility of the weld metal becomes significant.
<7> From the above-described viewpoint, the C and Nb contents are adjusted in a specific range, that is, in mass%, in a range of C: 0.06 to 0.18% and Nb: 0.55 to 1.50%. There is a need to.

  The present invention has been completed based on the above findings, and the gist thereof lies in the weld metal shown in the following (1) and the weld material shown in (2).

  (1) By mass%, C: 0.06-0.18%, Si: 0.5% or less, Mn: 2.0% or less, Ni: 50-68%, Cr: 20-30%, Al: 2.0 to 7.0%, Nb: 0.55 to 1.50% and N: 0.04 to 0.15%, the balance being Fe and impurities, and O, P and impurities in the impurities A weld metal, wherein S is O: 0.02% or less, P: 0.01% or less, and S: 0.01% or less, respectively.

  The “impurities” in the remaining “Fe and impurities” refer to materials mixed by raw materials such as ores and scraps and other various factors when industrially producing metal materials.

  The weld metal preferably has a Vickers hardness (hereinafter referred to as “HV hardness”) of 320 or more.

  The “welded metal” refers to a portion where a part of the base metal and the welding material are melted and solidified during welding.

  (2) By mass%, C: 0.06-0.18%, Si: 0.5% or less, Mn: 2.0% or less, Ni: 50-68%, Cr: 20-30%, 0 to 7.0%, Nb: 0.55 to 1.50% and N: 0.04 to 0.15%, with the balance being Fe and impurities, and O, P and S in the impurities being O: 0.02% or less, P: 0.01% or less, and S: 0.01% or less, respectively.

  Here, welding is performed on a member to be welded using the “welding material” in (2) above (in other words, the base material of the “welded structure”) or the base material of the “welded structure”. A high strength material having a tensile strength of 1 GPa or more is suitable for the base material when the “welded metal” of the above (1) is formed, and the shape thereof is a plate shape, a rod shape, a tubular shape, etc. Any shape can be used as long as it can be used for welding.

  Since the weld metal of the present invention can ensure high strength by a short post-weld heat treatment and has excellent weld cracking resistance, the welded structure having the weld metal of the present invention is energy transport. It can be suitably used as various welding members such as high-pressure gas piping in equipment. The weld metal of the present invention can be obtained by welding using the welding material of the present invention.

It is a figure explaining the groove shape given to the longitudinal direction of the alloy plate for welding base materials used in the Example.

  Hereinafter, the effect of each component element contained in the weld metal and the weld material of the present invention and the reason for limiting the content thereof will be described without distinguishing between the weld metal and the weld material. In the following description, “%” display of the content of each element means “mass%”.

C: 0.06 to 0.18%
C is an element related to the basis of the present invention together with Al and Nb, and has an effect of preventing solidification cracking and ductile deterioration cracking. That is, C combines with Nb during solidification to produce eutectic carbides when the weld metal solidifies, thereby accelerating the disappearance of the liquid phase, and the structure of the final solidified portion is the lamellar structure of NbC and austenite. And As a result, the residual form of the liquid phase changes from a planar shape to a point shape, stress concentration on a specific surface is suppressed, and the final solidification interface area that becomes a segregation site of impurities increases, so that solidification cracking and ductility Decline cracking can be prevented.

  In order to sufficiently obtain the above C effect, a C content of 0.06% or more is required. However, if the content of C becomes excessive, and particularly exceeds 0.18%, C that does not become carbide during solidification increases, and on the contrary, the melting point of the liquid phase decreases and the solidification cracking susceptibility increases. Therefore, the C content is 0.06 to 0.18%. The desirable lower limit of the C content is 0.07%, and the desirable upper limit is 0.14%.

Si: 0.5% or less Si is added as a deoxidizer. However, if the Si content increases and exceeds 0.5%, it segregates at the columnar grain boundaries during solidification of the weld metal, lowers the melting point of the liquid phase, and increases the susceptibility to solidification cracking. Therefore, the Si content is 0.5% or less. The Si content is desirably 0.4% or less, and more desirably 0.3% or less.

  In addition, although it is not necessary to set a minimum in particular about content of Si, excessive reduction leads to the increase in manufacturing cost while the deoxidation effect is not fully acquired but the cleanliness of an alloy falls. Therefore, the desirable lower limit of the Si content is 0.01%. If at least 0.01% of Si is contained, a deoxidizing effect can be obtained.

Mn: 2.0% or less Mn is added as a deoxidizer in the same manner as Si. However, if the Mn content increases and exceeds 2.0%, ductility and toughness are reduced. Therefore, the Mn content is set to 2.0% or less. The Mn content is desirably 1.8% or less, and more desirably 1.6% or less.

  In addition, although it is not necessary to set a minimum in particular about content of Mn, excessive reduction leads to the increase in manufacturing cost while the deoxidation effect is not fully acquired but the cleanliness of an alloy falls. Therefore, the desirable lower limit of the Mn content is 0.01%. If at least 0.01% of Mn is contained, a deoxidizing effect can be obtained.

Ni: 50-68%
Ni is not only an essential element for obtaining a stable austenite structure, but also finely dispersed as Ni ₃ (Al, Nb) and has the effect of greatly improving the strength of the weld metal. In order to sufficiently obtain the above effect, a Ni content of 50% or more is necessary. However, since Ni is an expensive element, the addition of a large amount causes an increase in cost. In particular, when the Ni content exceeds 68%, the increase in cost becomes significant. Therefore, the Ni content is 50 to 68%. The desirable lower limit of the Ni content is 55%, and the desirable upper limit is 65%.

Cr: 20-30%
Cr is an essential element for ensuring the corrosion resistance under the use environment, and a content of 20% or more is necessary to sufficiently obtain the effect. However, if the Cr content is excessive and exceeds 30%, the austenite structure becomes unstable, and embrittlement occurs depending on the type of gas contact environment. Therefore, the Cr content is 20-30%. The desirable lower limit of the Cr content is 22%, and the desirable upper limit is 28%.

Al: 2.0 to 7.0%
Al is an element related to the basis of the present invention together with Nb and the like. That is, Al combines with Ni and precipitates as a fine precipitate phase, and is an essential element for increasing the strength of the weld metal. In order to obtain the effect by heat treatment after welding for a short time, it is necessary to contain it in combination with Nb and to have a content of at least 2.0%. However, if the Al content becomes excessive and exceeds 7.0%, it will float as oxidized slag during welding, so the effect will be saturated, and the aesthetics and welding workability of the weld bead will be impaired. become. Therefore, the Al content is set to 2.0 to 7.0%. The desirable lower limit of the Al content is 3.0%, and the desirable upper limit is 6.0%.

Nb: 0.55 to 1.50%
Nb is an element related to the basis of the present invention together with C and Al. That is, Nb replaces Al in Ni ₃ Al to form a solid solution and becomes Ni ₃ (Al, Nb), thereby increasing the driving force of the precipitation, and the strength of the weld metal by a short post-weld heat treatment. It is an element that has the effect of increasing. Nb contributes to the strengthening of the weld metal not only by being precipitated in the grains as fine carbonitride. In addition, by containing it in combination with C, eutectic carbide is formed with C at the time of solidification, and the disappearance of the liquid phase at the time of solidification is accelerated, and the structure of the final solidified portion is changed to a lamellar structure of NbC and austenite. By doing so, the remaining form of the liquid phase is changed and the segregation sites are increased, thereby making it possible to prevent solidification cracking and ductile deterioration cracking.

  In order to obtain the Nb effect described above, an Nb content of 0.55% or more is required. However, if the Nb content becomes excessive and exceeds 1.50%, the weld metal ductility is deteriorated due to an increase in the amount of NbC produced. Therefore, the Nb content is 0.55 to 1.50%. The desirable lower limit of the Nb content is 0.70%, and the desirable upper limit is 1.40%.

N: 0.04 to 0.15%
N is an element effective for ensuring the strength of the weld metal by forming a fine nitride while forming a solid solution in the matrix. In order to sufficiently obtain this effect, the N content needs to be 0.04% or more. However, if the N content becomes excessive and exceeds 0.15%, it precipitates as AlN, which suppresses the precipitation of Ni ₃ (Al, Nb) necessary for increasing the strength and causes embrittlement. Become. Therefore, the N content is 0.04 to 0.15%.

  The weld metal of the present invention has a chemical composition in which the balance is composed of Fe and impurities in addition to the elements described above. The welding material of the present invention also has a chemical composition in which the balance is composed of Fe and impurities in addition to the elements described above.

  In addition, in the weld metal and welding material of this invention, it is necessary to regulate the content of O, P, and S in impurities as follows.

O: 0.02% or less O exists as an impurity, and when it is contained in a large amount, the workability of the welding material and the ductility of the weld metal are deteriorated. Therefore, it is preferable to reduce the O content as much as possible. However, if the content is 0.02% or less, no remarkable deterioration is observed in the characteristics of the weld metal or the weld material of the present invention. Therefore, the content of O is set to 0.02% or less.

P: 0.01% or less P is contained as an impurity, and lowers the melting point of the final solidified portion during solidification of the weld metal, and remarkably increases the susceptibility to solidification cracking. Furthermore, it segregates at the grain boundaries and increases the susceptibility to ductile drop cracking. Therefore, it is preferable to reduce the P content as much as possible. However, extreme reduction of the P content leads to an increase in steelmaking cost, and if it is 0.01% or less, the weld metal or welding material of the present invention. There is no noticeable deterioration in the characteristics. Therefore, the P content is 0.01% or less.

S: 0.01% or less S is contained as an impurity in the same manner as P, and lowers the melting point of the final solidified portion during solidification of the weld metal, and remarkably increases the susceptibility to solidification cracking. Furthermore, it segregates at the grain boundaries and increases the susceptibility to ductile drop cracking. Therefore, it is preferable to reduce the S content as much as possible. However, as in the case of P, the extreme reduction of the S content leads to an increase in steelmaking costs. There is no noticeable deterioration in the characteristics of the weld metal or welding material of the invention. Therefore, the S content is 0.01% or less.

  In addition, as a welded structure, the chemical composition of the “welded metal” obtained as a result of melting and mixing a part of the base material and the welding material only needs to satisfy the above-described requirements. For this reason, the chemical composition of the “welding material” needs to be selected according to the chemical composition of the “base metal” used, but the “base metal dilution” defined as “the ratio of the base metal composition in the composition of the weld metal” The “rate” varies depending on the groove shape, welding method and welding conditions, but is generally about 30 to 60%. Therefore, in the chemical composition range of the welding material described in (2) above, it is desirable to select the composition of the welding material in consideration of dilution by the base material.

  As the base material, a high-strength material having a tensile strength of 1 GPa or more is suitable, and the shape may be any shape as long as it can be used for welding joining such as a plate shape, a rod shape, or a tubular shape. It is as already mentioned that there is nothing.

  EXAMPLES Hereinafter, although an Example demonstrates this invention more concretely, this invention is not limited to these Examples.

  An alloy plate having a thickness of 10 mm, a width of 50 mm, and a length of 100 mm is welded from an ingot in which a material having the chemical composition shown in Table 1 is melted and cast in a laboratory by hot forging, hot rolling, heat treatment and machining. It was produced for the base material.

  Further, from the same ingot, a welding wire (welding material) having an outer diameter of 1.2 mm and a length of 1000 mm was produced by hot forging, hot rolling and machining.

  The groove plate shown in FIG. 1 is subjected to the groove processing shown in FIG. 1 in the longitudinal direction of the above-mentioned alloy base plate for welding, and is described in JIS Z 3224 (1999) on a commercially available SM400A steel plate having a thickness of 25 mm, a width of 200 mm, and a length of 200 mm. Four rounds were restrained and welded using the prepared “DNiCrFe-3” coated arc welding rod.

  Next, using the above-described welding wire having an outer diameter of 1.2 mm having the same chemical composition as that of the alloy plate for the weld base metal in the groove formed on the alloy plate for the weld base material, an average insertion is performed by TIG welding. Multi-layer welding was performed at a heat of about 10 kJ / cm. In addition, since it is restrained in the case of this TIG welding, the thermal stress by welding arises and it becomes easy to generate | occur | produce a crack.

  After welding, a micro test piece, a side bend test piece and an aging hardness test piece having a weld metal part at the center were collected and used for each test.

  The micro test piece was mirror-finished by buffing, and then all the weld metal parts were observed with an optical microscope at a magnification of 100 to 500 times, and the occurrence of "solidification cracking" and "ductility-reducing cracking" was observed. . The target was that neither “solidification cracking” nor “ductility degradation cracking” occurred.

  The side bend specimen was bent 180 ° with a bending radius twice the plate thickness, and the presence or absence of cracks in the weld metal and the ductility were examined. The goal was to prevent cracking.

  In addition, an aging heat treatment simulating post-weld heat treatment was performed using an aging hardness test piece, and an HV hardness test was performed with a test force of 98N. The aging heat treatment is performed at a temperature of 750 ° C. for 1 to 180 minutes, and it is necessary to reach the HV hardness 320 corresponding to 1 GPa which is the target tensile strength of the weld metal from the conversion formula described in ASTM E140. Aging time was investigated. And it aimed at aging time being 120 min or less.

  Table 2 shows the observation results of occurrence of “solidification cracks” and “ductility-reducing cracks” in micro test pieces, observation results of occurrence of cracks in side bending test pieces, and HV hardness 320 when aging heat treatment is performed at 750 ° C. Indicates the time required to reach.

  In addition, in the case of test number 8 in Table 2, since it was not possible to discriminate between “solidification cracking” and “ductility-reducing cracking” by observing the micro test piece, “Yes” is entered in the “solidification cracking” column. "-" Is written in the "Ductility reduced cracking" column.

  Moreover, about the test numbers 4-7, since "a fine crack" arose in the side bending test, it described as "present" in the crack column.

  From Table 2, in the case of an alloy whose chemical composition in Test No. 1 and Test No. 2 is within the range specified in the present invention, a sound welded joint free from solidification cracking and ductile deterioration cracking is obtained, and sufficient bending ductility is also obtained. It is clear to have. In addition, the HV hardness of the weld metal becomes 320 or more by a short aging heat treatment of 60 min or less, and it can be seen that the weld metal can be strengthened by a short post-weld heat treatment.

  On the other hand, in the case of an alloy in which the contents of C and Nb in Test No. 3 are both out of the upper limit of the range defined in the present invention, excess NbC is generated, so that the weld metal is poor in ductility and side bending. The test piece was cracked and inferior in bending ductility.

On the other hand, in the case of the alloys with test numbers 4 to 7 where the C and Nb contents are both below the lower limit of the range defined in the present invention, the amount of NbC produced is small and the dispersion of impurity elements due to the increase in segregation sites is sufficient. Because of this, ductile drop cracking occurred. Furthermore, since the content of Nb is not sufficient, the driving force for precipitation of Ni ₃ (Al, Nb) is small, and the target hardness of HV320 was not obtained for the weld metal even after aging heat treatment for 180 minutes.

  In the case of the alloy of test number 8, since the C content is lower than the lower limit of the range specified in the present invention, and the Nb content is lower than the upper limit of the range specified in the present invention, solidification cracking occurs. Since the Al content is below the lower limit of the range defined in the present invention, the target hardness of HV320 was not obtained for the weld metal even after 180 minutes of aging heat treatment.

  The weld metal of the present invention can ensure high strength by a short post-weld heat treatment and has excellent weld crack resistance. For this reason, the welding structure which has the weld metal of this invention can be used suitably as various welding members, such as high-pressure gas piping in an energy transport apparatus. The weld metal of the present invention can be obtained by welding using the welding material of the present invention.

Claims (3)

  In mass%, C: 0.06-0.18%, Si: 0.5% or less, Mn: 2.0% or less, Ni: 50-68%, Cr: 20-30%, Al: 2.0 -7.0%, Nb: 0.55-1.50% and N: 0.04-0.15%, the balance is Fe and impurities, and O, P and S in the impurities are respectively O: 0.02% or less, P: 0.01% or less, and S: 0.01% or less.   The weld metal according to claim 1, wherein the Vickers hardness is 320 or more.   In mass%, C: 0.06-0.18%, Si: 0.5% or less, Mn: 2.0% or less, Ni: 50-68%, Cr: 20-30%, Al: 2.0 -7.0%, Nb: 0.55-1.50% and N: 0.04-0.15%, the balance is Fe and impurities, and O, P and S in the impurities are respectively O: 0.02% or less, P: 0.01% or less, and S: 0.01% or less.

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