JP2011152571A - Method for manufacturing flux-cored welding wire - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a method for manufacturing a flux-cored welding wire, which can remarkably reduce the amount of diffusible hydrogen generated from a constituent of a lubricant existing on the surface of the flux-cored welding wire. <P>SOLUTION: A liquid mixture produced by making a volatile liquid lubricant contain 5-40 mass% of a solid lubricant is used as a lubricant in a part or the whole of a wire drawing step of a flux-cored welding wire manufacturing process. The volatile liquid lubricant constituent of the liquid mixture is volatilized, after the wire drawing step. <P>COPYRIGHT: (C)2011,JPO&INPIT

Description

  The present invention relates to a method for manufacturing a flux-cored welding wire, and more particularly, to a method for manufacturing a flux-cored welding wire that can advantageously achieve a reduction in the amount of diffusible hydrogen, which is the main cause of low-temperature cracks occurring in welds. Is.

  It is no exaggeration to say that the reliability of the welded structure is determined by the reliability of the welded joint. Therefore, when a defect exists in the welded part, it greatly affects the reliability of the entire structure. Therefore, much attention has been paid to prevent the occurrence of the defect.

  One of the typical defects occurring in the weld zone is cold cracking. One of the main causes of cold cracking is diffusible hydrogen introduced during welding. As a source of the amount of diffusible hydrogen, there is a lubricant present on the surface of the welding wire. Therefore, from the viewpoint of preventing cold cracking, it is desirable to reduce this lubricant as much as possible. However, if the lubricant of the welding wire is completely removed, there will be a problem in wire feedability during welding, which may cause defects other than low temperature cracks. Therefore, a method that can reduce the amount of diffusible hydrogen without sacrificing wire feedability is desired.

  The reduction of the amount of diffusible hydrogen has an important meaning especially in the welding of high-strength steel. In general, high-strength steel is a steel material that is more susceptible to cold cracking than mild steel, and is often preheated to prevent cold cracking. However, since preheating has a large work load and increases the manufacturing cost of the welded structure, a method for reducing preheating as much as possible is desired. From such a background, many solid wires that easily reduce the amount of diffusible hydrogen are used in welding high-strength steel. On the other hand, flux-cored welding wires that are difficult to take measures to reduce hydrogen are not applied as much as solid wires when welding high-strength steel.

  On the other hand, the flux-cored welding wire has characteristics that are not found in solid wires, such as good welding workability and easy achievement of all-position welding. Such welding workability comes from the structural feature of the flux-cored welding wire that the wire is filled with flux. Although the flux itself contains a hydrogen source, the merit of the flux-cored wire over the solid wire is ensured by the location of the flux, so pay attention to the lubricant present on the wire surface, which is a hydrogen source other than the flux. This is considered to be a natural flow at present when the welded structure is moving in the direction of high-tensile steel.

  As a hydrogen reduction technology for flux-cored wires, as shown in Patent Document 1, a sulfur-based solid lubricant is used in the wire drawing process, and the applied lubricant is physically removed in-line. The technique which makes the process to perform an essential condition is disclosed. According to this technology, since the process of physically removing the applied lubricant is set, a reduction in the amount of hydrogen is achieved, but the wire manufacturing cost is increased due to more wire manufacturing processes, and Since the lubricant is limited to a sulfur-based solid lubricant, there is a problem that a problem arises in the fluidity of the lubricant during wire production.

  Regarding the combined technology of solid lubricant and liquid lubricant, Patent Document 2 discloses a technique of applying a liquid lubricant on a solid lubricant. Patent Document 3 discloses that a solid lubricant is used in a large diameter region and a small diameter. A technique is disclosed in which a liquid lubricant is used in the region and a solid or liquid lubricant is arbitrarily selected in the intermediate diameter region. However, in the techniques of Patent Documents 2 and 3, there is no description of how much low hydrogenation is achieved.

  As described above, in the prior art, a wire manufacturing method that can efficiently achieve low hydrogenation of flux-cored wires has not yet been realized.

Japanese Patent Laying-Open No. 2005-074438 JP 2001-179482 A Japanese Patent Laid-Open No. 06-015485

  Since reduction of diffusible hydrogen is a very important problem when considering application to high-strength steel, the present inventors have intensively studied methods for reducing the amount of diffusible hydrogen in flux-cored welding wires. . The present invention focuses not on the amount of diffusible hydrogen contained in the flux in the wire (essential for ensuring workability) but on the wire surface lubricant, and on the method for reducing the amount of increase in the amount of diffusible hydrogen due to this. did. If the amount of flux contained in the flux-cored welding wire is reduced, the amount of diffusible hydrogen can be reduced, but this method also means sacrificing workability. This is the reason why the lubricant present on the wire surface is focused.

  Accordingly, the present invention provides a method for manufacturing a flux-cored welding wire that can significantly reduce the amount of diffusible hydrogen that is a cause of generation of wire lubricant without sacrificing wire feedability and wire manufacturing efficiency. With the goal.

  From the above viewpoint, the present inventors have intensively studied the relationship between the wire lubricant and the amount of diffusible hydrogen. As a result, the inventors have found a method for producing a flux-cored welding wire that dramatically reduces the amount of diffusible hydrogen that is a cause of the generation of wire lubricant and does not sacrifice wire feedability and wire production efficiency. The present invention has been made by such research, and the gist of the invention is as follows.

  (1) In the manufacturing method of a flux-cored welding wire for welding, in which a steel outer sheath is filled with a flux, a volatile liquid is applied to part or all of the wire drawing step when wire drawing is performed to the wire diameter. Apply a lubricant solution containing 5 to 40% by weight of solid lubricant to the lubricant, and if there is a remaining wire drawing process, apply a volatile liquid lubricant to the wire for the wire drawing process. A method for producing a flux-cored welding wire, wherein the wire drawing process is terminated, and then only the volatile liquid lubricant component is volatilized from the wire surface, and the solid lubricant remains on the wire surface.

  (2) The method for producing a flux-cored welding wire according to the above (1), wherein a wire drawing step using at least one roller die is included in the wire drawing step.

  (3) The flux-cored welding wire according to (1) or (2) above, wherein the solid lubricant is a mixture of one or two of molybdenum disulfide and graphite. Manufacturing method.

  (4) Any of the above (1) to (3), wherein the wire before applying the lubricating solution in which the volatile liquid lubricant and the solid lubricant are mixed is Cu plated. A method for producing a flux-cored welding wire according to claim 1.

  According to the present invention, the amount of diffusible hydrogen in a flux-cored welding wire can be significantly reduced, and a flux-cored welding wire for high-strength steel that has been difficult to apply can be realized.

  The present invention is described in detail below.

  The function of the lubricant applied to the flux-cored welding wire is roughly classified into two types. That is, a reduction in wire drawing resistance at the time of wire manufacture and a reduction in feeding resistance generated when feeding the wire during welding.

  On the other hand, the lubricant on the surface of the wire is classified into a liquid lubricant represented by a lubricating oil and a solid lubricant represented by molybdenum disulfide. Some solid lubricants do not contain hydrogen, which is preferable from the viewpoint of reducing the amount of diffusible hydrogen. However, since solid lubricants are not liquids, it is difficult to apply them to wires, and since fluidity is not as high as liquid lubricants, the lubricants are efficiently used for dicing during wire drawing. In many cases, it is more efficient to use a liquid lubricant when manufacturing the wire. However, if the liquid lubricant remains on the wire surface, there arises a problem that a reduction in the amount of diffusible hydrogen cannot be achieved.

  Therefore, in the present invention, a mixed solution in which a solid lubricant is mixed into a volatile liquid lubricant is applied to a flux-cored welding wire. As a result, only the liquid lubricant component is volatilized after the wire drawing step, so that the solid lubricant remains on the surface of the wire, and with this solid lubricant, the wire feedability during welding can be ensured. Moreover, by using a volatile liquid lubricant, it is not always necessary to degrease the wire in order to achieve low diffusible hydrogen after wire drawing, which is also preferable from the viewpoint of improving the wire manufacturing efficiency. In addition, since the fluidity is higher than when a solid lubricant is used alone, the lubricant can be efficiently introduced between the wire and the die in the wire drawing process, thus solving the problem of disconnection during wire manufacture. be able to. In addition, the volatile liquid lubricant in the present invention is not particularly limited to a substance to be selected as a lubricant from the application. Moreover, the volatility in this invention means what does not remain | survive on the conditions hold | maintained in room temperature environment, but dissipates from the wire surface. The volatile liquid lubricant may be any volatile liquid lubricant that is dissipated by normal temperature or low temperature heating, and volatile liquid lubricants commercially available from many companies can be used.

  On the other hand, in order to simply ensure the efficiency of the wire drawing step, a volatile liquid lubricant that does not contain a solid lubricant is used, and the mixed liquid may be applied after the wire drawing step. However, the present invention is characterized by using a mixed solution in which a solid lubricant is mixed in a volatile liquid lubricant for some or all of the wire drawing processes. The reason is that the solid lubricant is embedded in the wire surface due to the rolling effect in the wire drawing process. Thereby, even after the liquid lubricant is volatilized, the solid lubricant is fixed on the surface of the wire, and the wire feedability at the time of welding can be ensured. When there is no rolling effect, the force for fixing the solid lubricant to the wire surface is lost after the liquid lubricant volatilizes. In this case, the solid lubricant may be peeled off from the wire, which causes a problem from the viewpoint of securing the wire feedability.

  In the present invention, the ratio of the solid lubricant is set to 5 to 40% by mass. The lower limit of 5% was set to this value because the addition of less than this amount was not much different from the case where the liquid lubricant was used alone, and the wire feeding property could not be secured. There are two reasons for setting the upper limit of 40%. Many solid lubricants contain many components such as molybdenum disulfide and graphite that cause problems of weld cracking and toughness when introduced into a weld metal. For this reason, the amount of solid lubricant used should be such an amount that does not cause these problems. The second problem is that when the content ratio of the solid lubricant becomes too high, the fluidity of the mixed solution becomes insufficient, and the lubricant does not sufficiently enter the gap between the die and the wire in the wire drawing process. The upper limit of 40% was set as the maximum value that can avoid such a problem.

  In the present invention, the die used in the wire drawing process is preferably a roller die. The reason for this is that by using a roller die, a lubricating solution containing a solid lubricant can be introduced into the gap between the wire and the die more efficiently than a normal wire drawing die, and the solid lubricant remains efficiently on the wire surface. It is because it can be made.

  In the present invention, it is desirable to use a solid lubricant obtained by mixing either molybdenum disulfide or graphite, or both. Generally, as a solid lubricant, in addition to molybdenum disulfide and graphite, powders such as tungsten disulfide and boron nitride are known. However, many of these solid lubricants are expensive, and the function of the solid lubricant in the present invention is only to ensure wire feedability. Therefore, either molybdenum disulfide, graphite, or both are used. It is desirable to use a mixture.

  In the present invention, it is desirable that Cu plating is applied to the wire surface before a mixed solution containing a solid lubricant in a volatile liquid lubricant is applied to the wire. The reason for this is that the liquid lubricant component on the surface of the wire is volatilized in order to reduce the amount of diffusible hydrogen, so that the wire may be rusted. If welding is completed before rusting occurs, there is no concern that the amount of diffusible hydrogen will increase. However, depending on the manufacturing schedule of the welded structure, the timing for performing the welding is not necessarily determined from the viewpoint of preventing rust of the wire. In addition, it is possible to solve this problem by tightening the wire storage management so that rust does not occur. However, tightening the storage management leads to an increase in the manufacturing cost of the welded structure. As a means for solving these problems, it is desirable to perform Cu plating on the wire.

  Examples of the present invention will be described below.

  The manufacturing process of the flux-cored welding wire is as follows.

  A thin steel plate having a plate thickness of 1.0 mm and a width of 15 mm is prepared, and this is sequentially formed from a flat plate into a U shape by a rolling roller. When the U-shaped state was reached, the flux was filled. The flux at this time is a flux for general-purpose 570 MPa class steel, and conforms to JIS Z3313 YFW-C60FR. The flux was heat-treated at 750 ° C. in advance, and the humidity in the flux was eliminated as much as possible so that the influence of the lubricant could be compared with high accuracy. Then, it shape | molded with the rolling roller further, and when it became a tube state, the mating surface was joined by TIG welding. Thereafter, wire drawing was performed until the diameter reached 3.6 mm. When the thickness reached 3.6 mm, Cu plating was performed. Thereafter, the wire drawing step was further performed until the diameter became 1.2 mm. In the same process, a flux-cored welding wire was also produced by a manufacturing process in which Cu plating was omitted.

  The lubricant used at the time of producing the flux-cored welding wire was obtained by adding a commercially available solid lubricant to a commercially available volatile liquid lubricant, and the types of lubricants and their mixing ratios are shown in Table 1. In Table 1, S-106J manufactured by Sugimura Chemical Co., Ltd. was used as the volatile liquid lubricant, and JOMO silicon grease manufactured by Japan Energy was used as the non-volatile lubricant. In addition, the mixing ratio in this invention is the mass% of the solid lubricant with respect to the whole mixed solution.

  Table 2 shows the results of gas chromatographic measurement using the mixed solution of Table 1 according to the diffusible hydrogen content measuring method described in JIS Z3118.

  In Table 2, the case where the mixed solution shown in Table 1 was used as a lubricant for the entire wire drawing process at the time of wire production was designated as circle 1. Also, a liquid lubricant before mixing the solid lubricant for the wire drawing process up to a diameter of 3.6 mm, that is, a 100% liquid lubricant is used, and then the solid lubricant is added according to the mixing ratio in Table 1. The case where the mixed solution is used is indicated as circle 2. The reason for this is that the purpose of leaving the solid lubricant on the wire surface is to ensure the feedability after the wire is manufactured, and not necessarily to improve the efficiency of the wire manufacturing process. That is, the manufacturing process that finally leaves the solid lubricant comes from the fact that it is not always necessary to use the mixed lubricant from the beginning. In addition, as a method of dissipating only the volatile liquid lubricant after the wire is manufactured, it is not necessary to take special measures if it is left for about one day. . In this example, it was left for one day.

  When measuring the amount of diffusible hydrogen, welding is performed with the length of the conduit cable fixed at 6 m and the conduit cable wrapped around a 50 cm diameter column once, and the amount of diffusible hydrogen at that time is measured. It was measured. The reason why the conduit cable is wound around the column is to intentionally increase the friction between the wire in the conduit cable and the conduit cable so that it is easy to observe whether the wire feedability is good. When the wire feedability is poor, appropriate wire feed cannot be performed with respect to the welding conditions, so that the weld bead is disturbed. Thereby, wire feeding property was evaluated.

As can be seen from the test results in Table 2, it can be understood that in the example of the present invention, the amount of diffusible hydrogen is all below 2 ml / 100 g. In contrast, test no. In No. 1, the mixing ratio of the solid lubricant is lower than the range of the present invention, and the amount of the solid lubricant present on the wire surface after the liquid lubricant is volatilized is insufficient. This is the case when a problem occurs and the bead is disturbed. Test No. 11 and no. No. 12 is a case where the mixing ratio exceeds the range of the present invention, and a problem occurs in the fluidity of the mixed liquid. Test No. 11, the wire drawing process could pass, but the solid lubricant component having poor fluidity did not efficiently enter between the wire and the die, so that the solid lubricant did not sufficiently adhere to the wire surface, and the wire feed There was a problem with sex. Test No. No. 12 was broken during wire drawing. Test No. Regarding Nos. 13 to 19, the wire drawing process at the time of wire production and the wire feedability at the time of welding were both good, but since the liquid lubricant was non-volatile, the amount of diffusible hydrogen exceeded all 3 ml / 100 g. The value is much higher than that of the example of the present invention. Test No. 23 and no. No. 26 is an example when a non-volatile liquid lubricant is used when the solid lubricant is changed from MoS ₂ to graphite and WS ₂ . Similar to 13-19, the amount of diffusible hydrogen is higher than in the present invention. The lower limit of the range of the solid lubricant is preferably 10% or more in order to further secure the lubricity after volatilizing the volatile lubricant, and the upper limit is in wire production. In consideration of efficiency, it is desirable to set it to 30% or less.

  As described above, according to the wire manufacturing method of the present invention, the amount of diffusible hydrogen can be made lower than that of the conventional manufacturing method, and the amount of diffusible hydrogen, which has a great influence on prevention of cold cracking susceptibility of the welded portion, is reduced. be able to. As a result, it has become clear that the present invention has an extremely large industrial advantage.

Claims (4)

  In the method of manufacturing a flux-cored welding wire for welding, in which a steel outer sheath is filled with flux, volatile liquid lubrication is applied to a part or all of the wire drawing process when drawing to a predetermined wire diameter in the wire drawing process. Apply a lubricant solution in which 5 to 40% solid lubricant is mixed with the agent, and if there is a remaining wire drawing step, apply a volatile liquid lubricant to the wire for the wire drawing step. A method for producing a flux-cored welding wire, characterized in that the wire drawing step is terminated, and then only the volatile liquid lubricant component is volatilized from the wire surface and the solid lubricant remains on the wire surface.   The method for producing a flux-cored welding wire according to claim 1, wherein a drawing step using at least one roller die is included in the drawing step.   The method for producing a flux-cored welding wire according to claim 1 or 2, wherein a mixture of one or two of molybdenum disulfide and graphite is used as the solid lubricant.   The wire before applying the lubricating solution in which a volatile liquid lubricant and a solid lubricant are mixed is subjected to Cu plating, according to any one of claims 1 to 3. Manufacturing method of flux-cored welding wire.