JP5218440B2 - Test method for evaluation of cracking susceptibility of weld metal - Google Patents

Description

  The present invention relates to a test method for evaluating crack susceptibility of a weld metal, and more specifically, a steel plate-like test material that is easier to manufacture than a weld wire is used for a component system that is relatively difficult to manufacture a weld wire. Thus, the present invention relates to a test method capable of efficiently performing a crack susceptibility evaluation test of a weld metal.

  The reliability of the welded joint is an important factor that determines the reliability of the welded structure. In particular, when there is a weld crack, the reliability of the entire structure is greatly affected.

  For these reasons, it is necessary to evaluate in advance the cracking susceptibility of the material to be used before selecting welding conditions. As a typical test method for weld cracks, the y-type weld crack test defined in Non-Patent Document 1, the U-shaped weld crack test defined in Non-Patent Document 2, and the like have been actively used. In particular, recently, since the resistance to weld cracking of steel materials has improved, cracks occurring in welded joints have often occurred in weld metals. Therefore, as a method for evaluating the weld crack sensitivity, a method capable of efficiently evaluating the crack sensitivity of the weld metal is desirable.

  In general, a method often used as a method for evaluating the cracking susceptibility of a weld metal is the aforementioned U-shaped weld crack test. This is a method for examining the presence or absence of cracking by placing a test bead along a U-shaped groove using a welding wire or a welding rod whose crack sensitivity is to be evaluated on a test body in which a U-shaped groove is processed. In this case, the component of the weld metal is affected by the component of the steel plate forming the test body, but the welding material such as a welding wire has the most influence. As a matter of course, the welding material for producing the joint of the actual welded structure and the welding material used for the crack sensitivity evaluation test need to be the same material.

  In the state where the welding material has already been manufactured or manufactured as a prototype, the above test method is a very effective test method. However, at the stage where the design of the welding material has not yet been fully studied, and at the stage where the candidate component system is narrowed down from the viewpoint of weld cracking susceptibility, the conventional test method is extremely efficient due to the difficulty in prototyping the welding material. It may be bad. In particular, recently, the strength of steel materials is high, that is, the tendency to use high-tensile steel is increasing, and the properties of weld metal are required to be as high as steel materials accordingly. The welding material for forming such a weld metal often contains a lot of alloying elements in order to ensure strength. In such a case, for example, in the case of manufacturing a welding wire, the wire is broken during wire drawing. It becomes easy to cause. At the stage of studying the component system of the welding material, not only wire drawability is necessarily discussed, but rather, it is more efficient to narrow down the candidate component system from the viewpoint of weld crack sensitivity, so that the welding material can be developed more efficiently.

  So far, crack test methods other than those in Non-Patent Documents 1 and 2 have been studied as weld crack test methods. In Patent Document 1, as a technique aimed at providing a crack test method in place of Non-Patent Documents 1 and 2, in a weld crack test method using a test piece in which a straight groove is formed in the central portion. A welding crack test method is disclosed, in which test welding is performed while supplying a welding rod in a straight line from the outside of the test piece on the extension line of the weld line to the weld portion of the groove. However, in these conventional technologies, a crack sensitivity test cannot be performed unless a welding material is prototyped. That is, in the prior art, when it is difficult to prototype a welding material, there is a problem that an efficient welding material cannot be developed.

Japanese Patent Laid-Open No. 06-180278

JIS Z3158 “y-type weld cracking test method” (1993) JIS Z3157 “U-shaped weld cracking test method” (1993)

Since weld crack susceptibility tends to increase as the strength of steel increases, an efficient crack susceptibility evaluation test method is desired. On the other hand, trial manufacture becomes difficult as the welding material for high-tensile steel. For this reason, the conventional evaluation method could not develop an efficient welding material.
Therefore, an object of the present invention is to provide a test method that can evaluate the cracking susceptibility of weld metal without trial manufacture of a welding material.

  From the above viewpoint, the present inventors have intensively studied a test method that can evaluate cracking susceptibility without trial manufacture of a welding material. Then, a steel plate that is easier than a prototype of welding material is prototyped, the steel plate has the same components as the weld metal, and TIG welding (hereinafter referred to as TIG tanning welding) that does not use a filler metal is performed. The present inventors have found a method capable of evaluating the cracking sensitivity of metals. This invention is made | formed by such a research, The summary is as follows.

(1) In the test method for evaluating the cracking susceptibility of weld metal,
Using a steel plate having the same component as the weld metal, processing a slit-shaped groove from the back surface of the steel plate, constraining the steel plate processed the slit-shaped groove with a restraining plate, and processing the slit-shaped groove A weld metal crack susceptibility evaluation test method comprising forming a weld metal reaching the slit-like groove by performing TIG welding without using a filler material from the surface.

(2) Examples shielding gas TIG welding, characterized by using an Ar gas containing 0.1% to 5% of _{H 2} gas in mass%, cracking susceptibility evaluation test method of the weld metal according to claim 1 .

  According to the present invention, the cracking susceptibility of the weld metal can be efficiently evaluated, so that the development speed of new welding materials can be greatly increased, and thus the industrial significance is extremely great.

It is a figure which illustrates the weld crack test method which this invention provides conceptually with sectional drawing. It is a figure which illustrates conceptually the test method employ | adopted in the Example of this invention with a perspective view and sectional drawing.

  The present invention is described in detail below.

  The component of the weld metal is determined as a mixture of the steel material and the component of the welding material, and the ratio is almost determined by the welding conditions. In general, as an index for expressing this influence, there is a contribution ratio from a steel material in a weld metal, and this is called a base material dilution ratio. That is, the base material dilution rate is substantially determined by the welding conditions, and conversely, if the welding conditions are determined in advance, the weld metal component can be calculated from the components of the steel material and the welding material. For example, when considering the welding condition where the base material dilution ratio is 20%, when the Ni of the steel material is 1% and the Ni component of the welding material is 2%, 1 × 0.2 + 2 × (1-0. 2) = 1.8, and the Ni component of the weld metal can be calculated as 1.8%.

  If the welding conditions are determined in advance, the base material dilution rate is determined, but the welding material that can be used when determining this base material dilution rate does not necessarily need to be a weld material whose crack sensitivity should be evaluated. Therefore, the base material dilution rate can be determined in advance through experiments or the like.

  Therefore, calculate the weld metal component using the base material dilution ratio obtained in advance from the component of the welding material to be evaluated for cracking susceptibility and the component of the steel plate to be welded. Prototypes can be made in advance. The reason for doing this is that even with the same components, it is easier to make a steel plate as a prototype than when making a prototype of a welding material such as a welding wire.

  However, even if the components are the same, the microstructures of steel sheets and weld metals differ greatly, which affects crack sensitivity. Therefore, it is necessary to give the steel sheet the same microstructure as the weld metal. Then, it decided to give a weld metal structure to a steel plate by constructing TIG tanning welding to a steel plate. As a result, a weld metal having the same composition and microstructure is introduced, and it can be considered as a test of a welding material whose crack sensitivity is to be evaluated.

  Next, the reason why the present invention is limited to the case where the steel plate has slit-like grooves will be described.

  As an influencing factor of cracks occurring in the weld metal, it is known that stress concentration is also a large influencing factor in addition to the weld metal component, the amount of hydrogen, and the degree of restraint. Therefore, in the present invention, a stress concentration portion is prepared to facilitate the comparison of crack sensitivity. FIG. 1 shows the procedure. That is, a steel plate 3 having the same components as the weld metal is prepared, and a slit-like groove having a predetermined slit width 1 and slit height 2 is prepared therein. This is shown in FIG. FIG. 1 shows an example in which a straight groove is produced. Further, as can be seen from FIG. 1A, the groove does not necessarily have to penetrate to the surface side. When TIG tanning welding is performed, it is sufficient that the penetration depth reaches the tip of the slit machined from the back surface so that a stress concentration portion can be formed in the weld metal portion. This is because the depth of the slit and the penetration depth when TIG tanning welding is performed are problematic. However, since the penetration depth can be determined in advance by experiments, determining the required slit height is not appropriate. If it is a trader, it is not particularly a problem. Thus, when TIG tanning welding 4 is performed, as shown in FIG. 1B, the weld metal structure 5 is introduced on the surface of the steel sheet, and the stress concentration portion 6 can be formed on the weld metal. Thereby, an actual weld metal can be reproduced, and crack sensitivity evaluation can be performed.

  Next, the reason why the present invention is limited to TIG tanning welding as a welding method will be described.

  In the present invention, a component system in which trial manufacture of a welding material cannot be performed efficiently is targeted. Therefore, it is necessary to assume a process that does not use a welding material. TIG tanning welding does not use a welding material (in this case, the welding material is also referred to as a filler metal). TIG welding generates a welding arc between a tungsten electrode and a steel material and melts the steel surface. Is a process. This process is limited to this method because it meets the object of the present invention and can be performed using a normal TIG welder.

  The above are essential requirements in the present invention.

In the present invention, it advance restrain the steel plates by constraining plate.

This is because the weld crack sensitivity is affected by how much the weld is constrained from the surroundings. In particular, regarding cold cracking susceptibility, the concept of restraint has been used as an index for evaluating the influence of restraint. Thereby, the comparison with an actual structure and a crack test body became easier. Also in the present invention, it is very practical to control the degree of restraint using a restraint plate in order to facilitate comparison with an actual structure. Me other, it was decided to accurately control the degree of restraint with captive plate. The degree of restraint is defined as the load per unit groove length required when the groove width is reduced by the unit length. When a restraint plate that is sufficiently larger than the test plate is used, the restraint degree can be calculated by RF = E × h ÷ W, where W is the width of the test plate, h is the plate thickness, and E is the Young's modulus. .

In the present invention, if necessary, Ar gas containing 0.1 to 5% by mass of H ₂ gas can be used as a shielding gas for TIG tanning welding. In general, when performing TIG tanning welding, it is common to use 100% Ar gas as the shielding gas. Even in the present invention, when the influence of hydrogen is not examined, for example, when examining hot cracking, 100% Ar is used. It is desirable to use gas as the shielding gas. On the other hand, with 100% Ar gas, hydrogen is not sufficiently introduced into the weld metal, and therefore, there is a risk of performing a crack susceptibility evaluation different from the actual one regarding the low temperature crack among the weld cracks. Therefore, in order to reproduce the influence of hydrogen, H ₂ gas was mixed into the shield gas, thereby introducing hydrogen into the weld metal. The lower limit of 0.1% was set to this value because the effect of hydrogen on cracking could not be sufficiently evaluated with an amount of hydrogen gas below the lower limit. The upper limit of 5% is set to 5% in consideration of the property of introducing an excessive amount of hydrogen when the amount of hydrogen exceeds the upper limit and the explosive nature of the hydrogen gas itself.

  Examples of the present invention will be described below.

  Table 1 lists the components of the welding wire used in this example. The diameter of the welding wire was unified to 1.2 mm. In the example of Table 1, especially Ni, Cr, and Mo are greatly changed. When drawing a wire rod to which these elements are added to a welding wire, the wire becomes too hard due to work hardening, and there is a possibility of disconnection. In order to prevent disconnection, annealing may be performed to soften the hardened wire, but the material that must be annealed is a material that is difficult to manufacture. Therefore, regarding the welding wire, the difficulty of trial manufacture of the wire can be evaluated by the number of annealing performed during wire drawing. In this example, the case where the number of times of annealing was 3 times or more was determined to be a component system in which the wire trial production was difficult.

Using a wire having the component system shown in Table 1, a U-shaped weld crack test, which is a normal weld crack test method, was performed. The steel used was SM490 steel in accordance with JIS G3106, and the main components are C: 0.12%, Si: 0.25%, and Mn: 1.45%. The plate thickness of SM490 steel is 50 mm. As shown in Table 1, depending on the component, when the wire was drawn to 1.2 mm, annealing had to be performed to prevent wire breakage. In this example, the minimum number of annealings necessary to prevent disconnection was adopted as a parameter representing the difficulty of wire manufacture. Since general welding wires are annealed less than 3 times, the case where the number of annealing times is 3 times or more is determined to be a difficult-to-manufacture wire component system. On the other hand, Ar gas containing 20% CO ₂ was used as a shielding gas for welding during the crack test. In addition, the oil component adhering to the wire surface at the time of a gentle wire exists in a welding wire, and it becomes a diffusible hydrogen source and becomes one of the factors which generate | occur | produce a weld crack. The welding conditions are 270A-29V-25 cm / min. Preheating is not performed. After welding, the sample was allowed to stand for 7 days, and then a five-section macro test piece was taken from one test specimen, and the presence or absence of cracks was judged by microscopic observation. In addition, the crack observation by a five-section macro is a method according to the measurement procedure described in JIS Z3157.

  A U-shaped weld cracking test was performed using the wires shown in Table 1, and cracks were judged by microscopic observation. Samples for component analysis were taken from the weld metal, and component analysis of the weld metal was performed. In the case of a weld metal, since the steel material is partially diluted with the weld metal, the wire component and the weld metal component do not necessarily match. Table 2 lists the weld metal component analysis results. It can be understood that the weld metal component and the wire component are different due to the influence of dilution from the base material.

  Next, in order to carry out the weld crack test of the present invention, a steel material having the same components as the weld metal components shown in Table 2 was prepared, and a weld crack test body shown in FIG. 2 was prepared. That is, a steel plate having a thickness of 5 mm and a size of 100 mm × 100 mm having the components shown in Table 2 was prepared, and a slit-like groove 8 having a width of 2 mm was produced from the back side. At this time, the depth of the slit-shaped groove is 4 mm, and the bottom of the groove is located 1 mm below the surface of the steel plate. This is the test steel plate. Next, a SM490 steel material having a width of 600 mm and a length of 600 mm and a thickness of 50 mm was prepared. The reason why the plate thickness is set to 50 mm is that a steel plate having a plate thickness of 50 mm was used in the U-shaped weld crack test method described above. A square hole of 100 mm × 100 mm is machined in the central portion of the SM490 steel. A test steel plate was inserted into the hole, the periphery was welded (restraint welding 7), and the test steel plate was attached to the SM490 steel plate. FIG. 2 also shows a cross-sectional view (A-B cross section) of a portion including the test steel plate.

Such a test body was produced with respect to all the steel plates (plate thickness 5mm) which have a component system shown in Table 2, and the weld cracking test was implemented. The weld cracking test was performed by TIG tanning welding. TIG tanning welding is a method of welding without using a filler metal, that is, a welding wire, and is often performed for the purpose of melting a steel sheet with a TIG arc. In order to reproduce the crack test, Ar gas containing 5% H ₂ gas was used as the shielding gas. The welding conditions are 240A-13V-10 cm / min. In addition, preheating is not performed in order to make it the same conditions as the U-shaped weld crack test method which is a conventional weld crack test method. The presence or absence of cracks was determined after standing for 7 days after TIG tanning welding, and by taking 5 cross-section macros per test piece from the weld and observing the cracks with a microscope. .

Table 3 lists the results of investigating the presence or absence of cracks in the test method of the present invention and the U-shaped weld crack test method. The restraint degree of the U-crack test is almost the same as that of the y-crack test, and is expressed as a plate thickness (mm) × 70 (kg / mm ² ). The test results in Table 3 are the results when the plate thickness is 30 mm. In the test method of the present invention, both test method 1 in which the test plate thickness and test plate width are adjusted so that the degree of restraint is the same as that of the U crack test method, and test method 2 in which the degree of restraint is reduced by 30%. Carried out. ○ in Table 3 indicates that no cracks occurred, and ● indicates that cracks occurred. As can be seen from Table 3, the results obtained by the test method of the present invention and the results obtained by the U-shaped weld crack test method, which is a conventional test method, are very good in Test Method 1 in which the degree of constraint is matched. You can see that they match. Further, in Test Method 2 in which the degree of restraint was relaxed, cracks could not be reproduced in Component System 4, but they were consistent with other component systems. This means that the test method of the present invention can sufficiently evaluate the influence of the degree of restraint. On the other hand, as can be seen from Table 1, depending on the component system, it can be seen that there are also component systems in which the number of annealing is 3 or more during wire production. In such a component system, problems such as an increase in wire manufacturing cost and a long development period occur. In the method of the present invention, a test steel material having a component equivalent to the weld metal component calculated from the base metal dilution rate can be used using a wire component that can be assumed in advance and a steel component to be welded. Problems such as disconnection troubles at the time of wire drawing can be avoided, and the development period can be significantly shortened.

Table 4 also compares the results of the U-shaped weld cracking test, which is a conventional weld cracking test performed under substantially the same conditions as in Table 3, and the cracking test provided by the present invention. As shown in Table 3, the test methods 1 and 2 of the present invention are implemented both when the degree of restriction is matched (test method 1) and when the degree of restriction is loosened (test method 2). Furthermore, the test conditions are the same as the test conditions in Table 3 except that in the U-shaped weld crack test, each welding wire was washed before the test and oil on the wire surface was removed. In the weld cracking test provided by the present invention in Table 4, the test conditions in Table 3 except that a gas containing 0.4% H ₂ in Ar was used as the shielding gas for TIG tanning welding. Is the same. As can be seen from Table 4, it can be seen that the results of the conventional weld crack test method and the results of the weld crack test method provided by the present invention are in good agreement. For this reason, the welding crack test method provided by the present invention can avoid problems such as wire breakage troubles during wire drawing, and can greatly shorten the development period.

  In Table 1, there is also a component system in which the wire drawing is completed after the number of annealing times is less than 3, but in such a case, the weld crack test method provided by the present invention is necessarily used. There is no. In addition, depending on the component system, it can be predicted in advance whether the wire is difficult to manufacture. Therefore, whether to examine the wire component candidates using the weld crack test provided by the present invention or to examine the wire component candidates using the conventional weld crack test method is involved in the welding material development. It is not a particularly difficult choice for those involved.

  As described above, by using the welding crack test method of the present invention, it is possible to significantly shorten the development period related to narrowing of wire component candidates in welding wire development. As a result, it has become clear that the present invention has an extremely large industrial advantage.

DESCRIPTION OF SYMBOLS 1 Slit height 2 Slit width 3 Steel plate 4 with slit-shaped groove TIG tanning welding 5 Weld metal 6 Stress concentration part 7 Restraint welding 8 Slit-shaped groove

Claims (2)

In a test method for evaluating the susceptibility of weld metal to cracking,
Using a steel plate having the same component as the weld metal, processing a slit-shaped groove from the back surface of the steel plate, constraining the steel plate processed the slit-shaped groove with a restraining plate, and processing the slit-shaped groove A weld metal crack susceptibility evaluation test method comprising forming a weld metal reaching the slit-like groove by performing TIG welding without using a filler material from the surface. The weld metal crack sensitivity evaluation test method according to claim 1, wherein Ar gas containing 0.1 to 5% by mass of H ₂ gas is used as the shielding gas for TIG welding.

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