JP2012055904A - Liquid phase diffusion welding method and welded product - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a liquid phase diffusion welding method to weld members mutually to be welded having cylindrical portions at their ends while suppressing generation and inclusion of oxides at the welding portions.SOLUTION: Steel pipes 10A, 10B are welded mutually at opening end faces by disposing a low-melting point welding material 11 with a lower melting point than that of steel between the respective opening end faces of the steel pipes 10A, 10B and then welding the steel pipes 10A, 10B at their opening end faces by pressing the steel pipes 10A, 10B while heating the steel pipes 10A, 10B to a welding temperature which is the melting point of the low-melting point welding material 11 or higher. The oxides generated at the welding portions are pushed out around the welding portions. The material of the low-melting point welding material 11 is diffused in the steel pipes 10A, 10B by heating the steel pipes 10A, 10B to a diffusing temperature higher than the welding temperature while maintaining the pressing state. Then, the steel pipes 10A, 10B are pressed at a pressing force lower than the pressing force in a welding/extracting process while maintaining the heating state and the material of the low-melting point welding material 11 is further diffused in the members to be welded.

Description

  The present invention relates to a method of liquid phase diffusion bonding of a pair of steel members to be bonded and a bonded product manufactured by the method, and particularly, to-be-bonded members having cylindrical portions at their ends are preferably bonded. The present invention relates to a liquid phase diffusion bonding method and a bonded product manufactured by the method.

  Conventionally, a low-melting-point bonding material having a melting point lower than that of the material of the bonding member is sandwiched between the bonding surfaces of the bonded members, and in this state, the bonded members are heated while being pressed, A method of joining the joining members to each other by a liquid phase diffusion joining method may be employed (see, for example, Patent Document 1). According to this method, compared to the conventional welding method that involves partial melting of the members to be joined, it is possible to suppress thermal deformation, chemical structural change, and the like of the joined product.

  For example, as such a liquid phase diffusion bonding method, an insert material having a melting point equal to or lower than the liquidus temperature of the member to be bonded and containing B at 4% or less is inserted between the members to be bonded. Is heated and held between the liquidus temperature + 50 ° C and the liquidus temperature + 250 ° C of this insert, and the liquid phase diffusion bonding is completed by holding at that temperature for a predetermined time while pressing with a predetermined pressure. There has been proposed a method for joining steel materials (see, for example, Patent Document 2).

  Another aspect is a method in which a bonding material is interposed between the butted members to be joined and diffusion bonding is performed by heating the bonding portion. When the temperature rises, the temperature of the bonding layer reduces the melting point of the bonding material. The initial stress, which is the maximum value of the compressive stress, is 50 to 150 MPa when the temperature exceeds the melting point of the member to be joined, and the compressive stress is 10 to 45 MPa smaller than the initial stress when the temperature of the joining layer reaches the joining temperature. A liquid phase diffusion bonding method has been proposed in which the compressive stress is less than 10 MPa within 30 seconds after the temperature of the bonding layer reaches the bonding temperature (see, for example, Patent Document 3).

JP 2008-229647 A Japanese Patent Laid-Open No. 05-3181343 JP 09-267184 A

  However, using the liquid phase diffusion bonding method of Patent Documents 1 to 3 described above, as shown in FIG. 8 (a), a pair of steel members 10A and 10B having a cylindrical portion is used as a member to be joined. When the joining material 11 is disposed on the steel plates 10A and 10B by a pressing device through the pressing plates 41 and 41 and heated by the heater 32 made of a high-frequency coil in an oxidizing atmosphere, these are joined. As shown in FIG. 8B, since a considerable amount of oxide S is generated in the bonded portion including the bonding material, the bonding strength of the bonded product may be reduced.

  As the reason for the formation of the oxide S, the following reasons can be considered. Specifically, since the groove including the opening end face of the member to be joined opens in a morning glory shape (trumpet shape) as shown in FIG. 8C due to thermal deformation (plastic deformation), the facing joint surfaces are parallel. Do not touch. As a result, the open groove is plastically deformed by the joining stress, and this progresses. At this time, since the atmosphere is entrained, the joining portion including the joining material 11 is oxidized. Furthermore, this phenomenon becomes more prominent as the atmosphere of the joint portion diffuses from the outer periphery of the joint portion to grow an oxide and the temperature rises.

  The present invention has been made to solve such a problem, and the object of the present invention is to join with a cylindrical portion at the end while suppressing the formation and interposition of oxide in the bonded portion. An object of the present invention is to provide a liquid phase diffusion bonding method capable of bonding members together.

  As a result of intensive studies, the inventors, as described above, in order to prevent the groove including the opening end face of the member to be joined from being opened, joining the members to be joined, and joining the members to be joined. We thought that it was preferable to separate the diffusion of the bonding material under suitable conditions.

  That is, when performing bonding, if the heating temperature is set lower than the temperature at the time of diffusion of the bonding material and this is set as the bonding temperature so that the members to be bonded are not thermally deformed, it is caused by thermal deformation (plastic deformation). It was thought that the formation of oxide at the bonding interface was suppressed. Furthermore, if the oxide formed on the joined portion including the end face of the joined member and the joining material can be pushed out together with the joining material by the pressing force between the joined members at the time of joining, It was considered that the amount of product generated was suppressed, and the generated oxide was pushed out around the joint.

  Here, when shifting from the joining of the members to be joined to the diffusion of the joining material to the members to be joined, the heating temperature is raised in order to improve the diffusion rate. This increased temperature is taken as the diffusion temperature. When the temperature rises up to this diffusion temperature, the members to be joined are already partly joined, and it is considered that the positional displacement of the materials to be joined in the subsequent diffusion joining process does not normally occur. It is a general idea to lower the pressure of. However, the inventors have obtained the knowledge that the joint part opens due to the difference in thermal expansion amount at each part due to this temperature rise, and the predetermined time from the temperature rise is the pressure during joining. We thought that the bonding material should be diffused to the members to be bonded while maintaining the state.

  The present invention is based on such a series of ideas, and the liquid phase diffusion bonding method according to the present invention is performed between the open end faces of a pair of steel members to be joined having a cylindrical portion at the end. A step of disposing a low melting point bonding material having a melting point lower than that of the steel, and pressing the members to be bonded together while heating the members to be bonded to a bonding temperature equal to or higher than the melting point of the low melting point bonding material. The joined members are joined at the opening end faces, and at least the oxide generated at the joined portion is pushed out around the joined portion, while maintaining the pressed state at the time of the joined extrusion step In the first diffusion step, the first diffusion step of diffusing the material of the low-melting-point bonding material into the bonded member by heating the bonded member to a diffusion temperature higher than the bonding temperature; Keep heated However, it includes at least a second diffusion step of pressing with a pressing force lower than the pressing force of the bonding and extruding step to further diffuse the material of the low melting point bonding material into the member to be bonded. .

  According to the present invention, first, the low melting point bonding material is disposed between the open end faces of the non-bonding member. Next, in the bonding extrusion step, the members to be bonded are pressed to each other while the members to be bonded are pressed to a bonding temperature equal to or higher than the melting point of the low-melting-point bonding material. Join with. Thereby, to-be-joined members can be joined. Furthermore, the oxide produced | generated by the joining part (the end surface of a to-be-joined member, and a low melting-point joining material) is extruded around a joining part with a pressing force with the molten low melting-point joining material (it discharges | emits from a joining part). As a result, the oxide of the bonded portion pressed to a diffusion temperature higher than the bonding temperature is pushed out to the periphery together with the excess bonding material, so that the oxide of the bonded portion is suppressed from being interposed, Strength reduction can be reduced.

  Here, the bonding temperature is equal to or higher than the melting point of the low-melting-point bonding material and is lower than the diffusion temperature described later, and the oxide can be pushed out around the bonded portion by the pressing force at this temperature, Furthermore, it is the temperature which can suppress the thermal deformation (plastic deformation) of a to-be-joined member by pressing force, Preferably, the range from melting | fusing point of a low melting-point joining material to +60 degreeC is more preferable.

  Next, in the first diffusion step, the bonded portion of the member to be bonded is heated to a diffusion temperature higher than the bonding temperature while maintaining the pressed state during the bonding extrusion step (that is, keeping the pressing force constant). By doing so, the solid solution element which is the material of the low melting point bonding material can be accelerated and dissolved and diffused into the member to be joined, and the joint portion can be prevented from opening due to the thermal stress due to this temperature rise. However, if this state is kept, the members to be joined are plastically deformed by thermal deformation due to the pressing force, so that the process proceeds to the following second diffusion step.

  In the second diffusion step, while maintaining the heating state in the first diffusion step, the solid solution element which is a material of the low melting point bonding material is pressed to a pressing force lower than the pressing force of the bonding extrusion step. It can be further diffused in the member to be joined. Depending on the element contained in the low-melting-point bonding material, the material strength can be made higher than that of steel, which is the base material, so that it is possible to partially strengthen the bonded portion of the member to be bonded.

  In addition, since the joining member is joined by liquid phase diffusion joining, it can be joined with a relatively low pressing force compared to crimp joining or friction joining, etc., so that the residual stress at the joining portion or deformation of the joining member due to pressurization can be reduced. Even when it is made of high alloy steel or heat resistant steel that can be suppressed and welding of the joining member is difficult, these can be easily joined.

  In this way, the bonded product that has been subjected to liquid phase diffusion bonding is bonded at a temperature lower than the second heating temperature corresponding to the diffusion temperature in the bonding extrusion step. Since the tip is not easily deformed into a morning glory, the generation of oxide can be suppressed. Furthermore, since the oxide produced | generated slightly by the extrusion process is extruded, the oxide which intervenes in a junction part can also be reduced. Moreover, in this extrusion process, some elements in the low melting point bonding material diffuse into the members to be bonded.

  The “member to be joined” in the present invention is a member mainly composed of an iron element, and is a steel-based joining member, which may be subjected to heat treatment such as quenching and tempering. Surfaces other than the joint surface may be hardened by forging. For example, steel-based joining members include carbon steel, alloy steel, non-heat treated material, high carbon steel, bearing steel, heat resistant steel, or high Young's modulus steel using dispersed particles (dispersed high rigidity steel (HMS)). As long as liquid phase diffusion bonding can be performed, the components added, the heat treatment, the processing method including surface processing, and the like are not particularly limited.

  In addition, the “liquid phase diffusion bonding” referred to in the present invention is a method in which a low melting point bonding material is interposed and pressurized, and the low melting point bonding material (insert metal) is melted by heating to a temperature just above the liquidus line, It means joining the members to be joined. Further, in liquid phase diffusion bonding, since the bonding surface of the members to be bonded may be heated, it is more preferable to heat and bond by high frequency induction heating. Such a high-frequency induction heating enables rapid heating or local heating of the bonding surface, so that more suitable liquid phase diffusion bonding can be performed. Further, a groove portion such as a V groove for alignment for bonding or a stepped portion may be formed on the member to be bonded.

  As a more preferred embodiment, in the joining and extruding step, the joining member is heated at a temperature condition ranging from the melting point of the low-melting-point joining material to 1130 ° C., and the member to be joined is heated in the range of 10 to 25 MPa. By pressing the members to be joined together for 60 to 600 seconds under the condition of one pressing force, the members to be joined are joined to each other at the opening end face, and at least the oxide generated in the joining portion is joined to the joining portion. Extruding around the part, and in the first diffusion step, while maintaining the pressing state during the bonding extrusion step, the diffusion temperature is 1200 to 1250 ° C. for 2 to 20 seconds under the temperature condition. By heating the member, the material of the low-melting-point bonding material is diffused in the member to be joined, and in the second diffusion step, the first diffusion step By pressing the members to be bonded together for 200 seconds or more after reaching the diffusion temperature under the condition of the second pressing force in the range of 2 to 4 MPa while maintaining the heating state in the above, The material of the melting point bonding material is further diffused into the member to be bonded.

  That is, in the joining and extruding step, the groove including the opening end face of the joined member has a morning glory shape by applying pressure within the above-described time under the above-described joining temperature temperature condition and the first pushing pressure condition. The member to be joined can be suitably joined without being opened, and the oxide generated at the joined portion can be pushed out at least around the joined portion and suitably discharged from the joined portion.

  That is, even when heated at a temperature lower than the melting point of the low melting point bonding material, the low melting point bonding material does not melt, so liquid phase diffusion bonding cannot be performed, and when the temperature exceeds 1130 ° C., the groove opens. It becomes easy and the thermal deformation (plastic deformation) of the member to be joined proceeds easily. Further, when the first pressing force is less than 10 MPa, the oxide may not be sufficiently extruded, and when the first pressing force exceeds 25 MPa, the groove may be thermally deformed. In addition, when the pressing time is less than 60 seconds, the members to be bonded may not be sufficiently bonded. When the pressing time exceeds 600 seconds, the groove may be thermally deformed.

  Further, in the first diffusion step, the member to be bonded is heated within the above-described time under the temperature condition of the diffusion temperature while maintaining the pressing state with the pressing condition of the first pressing force at the time of the bonding extrusion step. Thus, the element of the material of the low-melting-point bonding material can be accelerated and dissolved in the member to be bonded without opening the bonding portion due to thermal stress due to temperature change.

  That is, even when heated at a temperature of less than 1200 ° C., the elements of the low melting point bonding material may not be sufficiently diffused into the steel of the member to be bonded. The joining members are easily deformed by heat. In addition, when the pressing time is less than 2 seconds, the joint portion may be opened due to plastic deformation due to the thermal stress of the joint portion due to the temperature rise, and the joint interface may be oxidized. On the other hand, when the time exceeds 20 seconds, the bonded portion may be thermally deformed (plastically deformed) by the pressing force, and similarly, the strength of the bonded portion may be reduced due to interface oxidation.

  In the second diffusion step, heating is performed for the above-described time or longer under the pressing condition of the second pressing force while maintaining the heating state. Thereby, the material of the low melting point bonding material can be efficiently diffused in the member to be bonded without deforming the bonding portion.

  That is, when the pressing force is less than 2 MPa, deformation due to thermal stress during cooling may not be suppressed. When the pressing force exceeds 4 MPa, the members to be joined are likely to undergo creep deformation. Further, when the diffusion time after reaching the diffusion temperature is less than 200 seconds, the material of the low-melting-point bonding material may not be sufficiently diffused to the member to be bonded. In addition, when the second diffusion step is performed in the atmosphere, the bonded product including the bonded portion may be oxidized, so that the diffusion time after reaching the diffusion temperature is less than 400 seconds. Is more preferable.

  The low-melting-point bonding material used as the insert material between the bonding members may be in the form of foil, powder, or a plating film on the bonding surface, and is particularly limited as long as it can be interposed between the bonding members. It is not something. Further, the low melting point bonding material is preferably made of a material having a eutectic composition having a lower melting point than that of the bonding member. The main material is silicon (Si), iron (Fe), nickel (Ni) or the like, and boron (B ) Or phosphorus (P) may be contained, and as long as liquid phase diffusion bonding can be performed, the element as the main material and the element to be added are not particularly limited.

  However, more preferably, a foil made of a Ni-based amorphous alloy containing B, Si, and V is used as the bonding material. According to the present invention, B can be diffused in the bonding portion and the vicinity thereof during the liquid phase diffusion bonding. Thus, the hardened property is improved at the bonding portion where B is diffused and in the vicinity thereof (diffusion layer) because B is dissolved in the iron structure. As a result, the diffusion layer has higher hardness and higher fatigue strength than the iron structure at other locations, so that the joined product can be partially strengthened. Furthermore, since the low-melting-point bonding material contains nickel element, the low-melting-point bonding material can be a nickel-based amorphous alloy, and liquid phase diffusion bonding is more suitably performed by using the amorphous alloy. be able to.

  And as a joined article manufactured by the above-mentioned liquid phase diffusion joining method, it is more preferred that the structure of steel other than the joined part is a bainite structure, and the tensile strength of the joined part is 500 MPa or more. . According to the present invention, by adopting a bainite structure, the hardness distribution of the joined product can be made uniform, and can be suitably used for a propeller shaft of a vehicle.

  ADVANTAGE OF THE INVENTION According to this invention, joining to-be-joined members which have a cylindrical part in the edge part can be performed, suppressing the production | generation and intervention of an oxide.

The apparatus block diagram for performing the liquid phase diffusion bonding method which concerns on this embodiment. It is a figure for demonstrating the liquid phase diffusion bonding method which concerns on this embodiment, (a) is the figure which showed the arrangement | positioning process, (b) is the figure which showed the joining extrusion process, (c) is The figure for demonstrating the state of the junction part before a diffusion process. The state line figure of the joining member concerning this embodiment. It is a figure for demonstrating the joining extrusion process shown in FIG.2 (b), (a) is a figure before extrusion, (b) is a figure after extrusion. The figure for demonstrating the heating temperature and pressing force (load stress) accompanying the time passage of each process of this embodiment. The figure for demonstrating the method to measure the quantity of the oxide which concerns on an Example. The figure for demonstrating the temperature distribution and pressing force (load stress) with time passage in the liquid phase diffusion bonding method which concerns on a comparative example. It is a figure for demonstrating the conventional liquid phase diffusion joining, (a) is a figure for demonstrating the apparatus structure, (b) is a figure for demonstrating the production | generation of an oxide, (C) is a figure for demonstrating the thermal deformation of the groove of a to-be-joined member.

  The liquid phase diffusion bonding method according to the embodiment of the present invention will be described below. FIG. 1 is an apparatus configuration diagram for performing the liquid phase diffusion bonding method according to the present embodiment, and FIG. 2 is a diagram for explaining the liquid phase diffusion bonding method according to the present embodiment. FIG. 4 is a diagram showing an arrangement process, FIG. 4B is a diagram showing a bonding extrusion process, and FIG. 4C is a diagram for explaining a state of a bonding portion before a diffusion process.

  FIG. 3 is a state diagram of the joining member according to the present embodiment, FIG. 4 is a diagram for explaining the joining and extruding process shown in FIG. 2 (b), and (a) is a view before extrusion, (B) is the figure after extrusion. Moreover, FIG. 5 is a figure for demonstrating the heating temperature and the pressing force (load stress) accompanying the time passage of each process of this embodiment.

  As shown in FIGS. 1 and 2 (a), in the liquid phase diffusion bonding method according to the present embodiment, a pair of steel pipes 10A and 10B are used as a pair of steel members having a cylindrical portion at the end. Prepare. Next, the low melting point bonding material 11 having a lower melting point than the steel of the steel pipes 10A and 10B is disposed between the open end faces of the one end of the steel pipes 10A and 10B, Push plates 41 and 41 are arranged.

  Further, a heater 32 made of a high-frequency coil is disposed so as to heat the portion where the low melting point bonding material 11 and the steel pipes 10A and 10B are joined, and the ends of the steel pipes 10A and 10B are covered with the heater 32 in the nitrogen gas chamber 33. . Further, in order to control the temperature of the heater 32, a thermocouple 30 is disposed in the vicinity of the low melting point bonding material 11. In this state, the joining members are pressed (pressurized) using the pressing device (not shown) through the pressing plates 41 and 41. Here, as the low melting point bonding material 11, a foil made of a Ni-based amorphous alloy containing B, Si, and V is used.

  As shown in FIG. 2B and FIGS. 4A and 4B, nitrogen gas is supplied to the nitrogen gas chamber 33 to bring it into a nitrogen atmosphere so that the bonding temperature is equal to or higher than the melting point of the low melting point bonding material 11. By pressing the steel pipes 10A and 10B while heating the steel pipes 10A and 10B, the steel pipes 10A and 10B are joined at the opening end faces, and further, the joined parts (the end faces of the steel pipes and the low melting point joining material 11). The oxide S produced in step 1 is extruded around the joint portion together with a part of the molten low melting point bonding material 11 (joint extrusion step).

  Here, when the low melting point bonding material 11 contains 3.6% by mass of B as shown in FIG. 3, the liquidus temperature is Tm1070 ° C., and specifically, as shown in FIG. 5. Thus, in this heating state, the steel pipes 10A and 10B are pressed for 60 to 600 seconds under the pressing conditions of the first pressing force in the range of 10 to 25 MPa, and the steel pipe 10A is brought to the joining temperature in the range of Tm 1070 ° C. to 1130 ° C. , 10B is heated to melt the low-melting-point bonding material 11, and the steel pipes 10A, 10B are joined at the opening end faces while suppressing thermal deformation of the steel pipes 10A, 10B. Furthermore, since the oxide of the joining portion is pushed out together with the excessive low melting point bonding material 11, it is possible to suppress the presence of the oxide of the joining portion and to reduce the strength reduction of the joining portion.

  Here, since the process is performed in a nitrogen atmosphere, no oxide is generated. However, when an oxide is generated on the surfaces of the steel pipes 10A and 10B, the extrusion of the oxide is effective. Further, it may be an air atmosphere or a mixed gas atmosphere having an oxygen concentration of 100 ppm or more. Under the conditions described above, since the groove including the opening end faces of the steel pipes 10A and 10B can be joined without being deformed (plastically deformed), there is little entrainment of air and the generation of oxide is suppressed. Moreover, even if it is generated, the generated oxide is pushed out by the pressing force, while some elements in the low melting point bonding material diffuse into the steel structure of the steel pipe, and as shown in FIG. The tissue will coagulate isothermally.

  In addition, when heating temperature exceeds 1130 degreeC, the groove | channel of steel pipe 10A, 10B may thermally deform, and plastic deformation of steel pipe 10A, 10B may advance, and when heating temperature is less than 1070 degreeC, it is low. The melting point bonding material 11 does not melt. Further, when the first pressing force is less than 10 MPa, the oxide may not be sufficiently extruded, and when the first pressing force exceeds 25 MPa, the plastic deformation of the steel pipes 10A and 10B is similar to the above. May progress. In addition, when the pressing time is less than 60 seconds, the members to be bonded may not be sufficiently bonded. When the pressing time exceeds 600 seconds, plastic deformation of the steel pipes 10A and 10B may proceed as described above.

  Next, as shown in FIG. 5, the first heating temperature (Tm 1070 ° C. to 1130 ° C. range) is maintained while maintaining the pressing state (first pressing force condition in the range of 10 to 25 MPa) during the bonding extrusion process. By heating the steel pipes 10A and 10B at a higher diffusion temperature (1200 ° C. to 1250 ° C.) for 2 to 20 seconds, the elements constituting the material of the low melting point bonding material 11 are diffused into the steel pipes 10A and 10B (first). One diffusion step). Thereby, the element (B) of the material of the low-melting-point bonding material can be accelerated and dissolved in the steel pipes 10A and 10B without opening the bonding portion due to thermal stress due to temperature rise.

  That is, even when heated at a temperature of less than 1200 ° C., the bonding material boron (B) may not be sufficiently diffused into the steel of the steel pipes 10A and 10B. The steel pipes 10A and 10B are easily plastically deformed by thermal deformation. In addition, when the pressing time is less than 2 seconds, the joint portion may be opened due to plastic deformation due to the thermal stress of the joint portion due to the temperature rise, and the joint interface may be oxidized. On the other hand, when the time exceeds 20 seconds, the bonded portion may be thermally deformed (plastically deformed) by the pressing force, and similarly, the strength of the bonded portion may be reduced due to interface oxidation.

  Further, as shown in FIG. 5, in the second diffusion step, the second pressing step in the range of 2 to 4 MPa is performed while maintaining the heating state in the first diffusion step (diffusion temperature is constant 1200 to 1250 ° C.). By pressing the steel pipes 10A and 10B for 200 seconds or more under the pressure condition, the material of the low-melting-point bonding material 11 is further diffused in the member to be joined (second diffusion step). Thereby, some elements in the low melting-point joining material 11 can be efficiently diffused in the steel pipes 10A and 10B without deforming the joining portion.

  That is, when the pressing force is less than 2 MPa, deformation due to thermal stress during cooling may not be suppressed, and when it exceeds 4 MPa, the steel pipes 10A and 10B are likely to undergo creep deformation. Further, when the diffusion time is less than 200 seconds, the material of the low melting point bonding material 11 may not be sufficiently diffused in the steel pipes 10A and 10B. In addition, when performing a 2nd spreading | diffusion process in air | atmosphere, since oxidation of the junction goods containing a junction part may arise, it is more preferable that it is less than 400 seconds.

  Thereafter, cooling is performed at a predetermined cooling rate. Thereby, as for the joined goods manufactured by the liquid phase diffusion joining method, the structure | tissue of steel other than the joined part is a bainite structure, and the tensile strength of the joined part becomes 500 Mpa or more. By making the steel structure a bainite structure, the hardness distribution of the joined product can be made uniform, and can be suitably used for a propeller shaft of a vehicle.

Examples will be described below based on the above embodiment.
Example 1
Liquid phase diffusion bonding was performed by the following method. Specifically, an amorphous foil (liquidus temperature Tm = 1070 ° C.) having a thickness of 30 μm and containing 3.5 mass% Si-3 mass% B-2.5 mass% V and the balance being Ni. Prepared as a low melting point bonding material. Two steel pipes of STKM-13B-E80 (JIS standard) having an outer shape of 60.5 mm, a wall thickness of 1.8 mm, and a length of 92 mm and having a steel structure of bainite were prepared as members to be joined.

  Next, using the apparatus of FIG. 1 described above, an amorphous foil is disposed between the open end faces of one end of the steel pipes, and a push plate is disposed at each other end. . Then, as shown in FIG. 5, the amorphous foil and the end of the steel pipe are heated by applying an initial stress that is a joining stress (first pressing force) in advance, and immediately above the liquidus line of the amorphous foil. Holding for a certain period of time at the temperature of the amorphous foil to finish the melting and isothermal solidification process (joining extrusion process), and then a diffusion treatment process (first diffusion process) of immediately raising the temperature and holding the temperature + Second diffusion step).

  Specifically, as shown in the column of the bonding treatment conditions in Table 1, the bonding extrusion process is performed under the atmosphere of atmospheric pressure, applying a pressing force (initial stress) of 25 MPa, with a bonding temperature of 1080 ° C. and a holding time of 600 seconds. I did it.

  Immediately thereafter, as shown in the column of diffusion treatment conditions in Table 1, the temperature was raised to 1200 ° C. while maintaining the initial stress (first pressing force) of 25 MPa, and the stress was maintained while maintaining this diffusion temperature. The first diffusion step was performed for a time of 10 seconds. Subsequently, with the diffusion temperature maintained at 1200 ° C., the final stress (second pressing force) is set to 3 MPa, and the total holding time from the first diffusion step to the second diffusion step is maintained for 300 seconds. (In other words, the second diffusion step was held for 290 seconds), and the second diffusion step was performed. In addition, although the heating rate until it reaches | attains joining temperature from room temperature is not specified, it controlled by the high frequency heating program so that it might become an average heating rate of 5 degree-C / s here. In addition, the cooling of the joint portion after the second diffusion step was controlled by a high-frequency heating program so that the average cooling rate was 1 ° C./s up to 400 ° C. In this way, a joined product in which steel pipes were joined by liquid phase diffusion joining was produced.

(Example 2)
In the same manner as in Example 1, liquid phase diffusion bonding was performed to produce a bonded product. The difference from Example 1 is that, as shown in Table 1, the bonding temperature under the bonding process conditions is 1130 ° C., the holding time is 60 seconds, and the initial stress is 15 MPa.

Example 3
In the same manner as in Example 1, liquid phase diffusion bonding was performed to produce a bonded product. The difference from Example 1 is that, as shown in Table 1, the -joining temperature was 1110 ° C., the holding time was 300 seconds, the initial stress was 20 MPa, and the stress holding time was 20 seconds, as shown in Table 1. It is.

(Examples 4 to 7)
In the same manner as in Example 3, liquid phase diffusion bonding was performed to produce a bonded product. The difference from the third embodiment is that the diffusion processing conditions are changed as shown in Table 1.

(Examples 8 and 9)
In the same manner as in Example 1, liquid phase diffusion bonding was performed to produce a bonded product. The difference from Example 1 is that the bonding atmosphere is changed to a nitrogen atmosphere of 100 ppm oxygen and the bonding treatment conditions and the diffusion treatment conditions are changed as shown in Table 1.

(Example 10)
In the same manner as in Example 1, liquid phase diffusion bonding was performed to produce a bonded product. The difference from Example 1 is that the atmosphere is changed to a nitrogen atmosphere and that the bonding process conditions and the diffusion process conditions are changed as shown in Table 1.

(Comparative Examples 1-5)
In the same manner as in Example 1, liquid phase diffusion bonding was performed to produce a bonded product. The difference between Comparative Example 1 and Example 1 is that the bonding temperature under the bonding processing conditions was set to less than 1080 ° C. (1040 ° C.). The comparative example 2 is different from the first embodiment in that the bonding holding time is less than 60 seconds (10 seconds), and other conditions are the conditions shown in Table 1. The comparative example 3 is different from the first embodiment in that the initial stress is over 25 MPa (30 MPa) and the other conditions are the conditions shown in Table 1. Comparative Example 4 is different from Example 1 in that the diffusion temperature is less than 1200 ° C. (1150 ° C.), and other conditions are the conditions shown in Table 1. The difference between Comparative Example 5 and Example 1 is that the diffusion temperature was increased to 1250 ° C. (1300 ° C.), and the other conditions were the conditions shown in Table 1. Comparative Example 6 is different from Example 1 in that the final stress is set to exceed 4 MPa (5 MPa), and the other conditions are the conditions shown in Table 1. The comparative example 7 is different from the first embodiment in that the stress holding time exceeds 20 seconds (30 seconds), and other conditions are the conditions shown in Table 1. Comparative Example 8 differs from Example 1 in that the total holding time was less than 200 seconds (30 seconds), the stress holding time was more than 20 seconds (30 seconds), and other conditions are shown in Table 1. It is the point made into the conditions shown.

(Comparative Examples 9-11)
In the same manner as in Example 1, liquid phase diffusion bonding was performed to produce a bonded product. The difference from the first embodiment is that a temperature and pressing force profile as shown in FIG. 7 is obtained. More specifically, the amorphous foil and the steel pipe end are heated to the diffusion temperature by heating while preliminarily applying an initial stress (15 to 25 MPa), which is a bonding stress (pressing force). After reaching the diffusion temperature, the initial stress is maintained for a predetermined time (5 to 15 seconds), and immediately thereafter, the final stress as the pressing force is set to 2 to 3 MPa in order to suppress plastic deformation due to creep, and the diffusion temperature is maintained. The time was 400 to 600 seconds in terms of the total holding time. In this way, isothermal solidification and diffusion treatment were performed. The detailed conditions are shown in Table 2.

<Evaluation test>
(Measurement of oxide area ratio)
The oxide area ratio was measured for the joined articles of Examples 1 to 10 and Comparative Examples 1 to 11. Specifically, as shown in FIG. 6, the joined portion of the joined product (steel pipe) was cut in parallel with the length direction, and the joint surface was cut into four sections. This cut sample was embedded in a resin and corroded with a nital etchant, and the oxide at the bonding interface and the structure in the vicinity thereof were observed. And the total length of the oxide which appeared on the joining interface and the total length of a junction part were measured, and the average value of the ratio of the total length of the oxide with respect to the total length of a junction part was made into the oxide area ratio. The results are shown in Tables 3 and 4 below.

[Tensile test]
Tensile test measurements were performed on the joined articles of Examples 1 to 10 and Comparative Examples 1 to 11. A tensile test piece was cut out from the steel pipe, which was a joined product, in parallel with the length direction. A tensile test piece was cut out from the joined product so that the parallel part had a width of 10 mm and a length of 50 mm, and the joined part was located at the center of the parallel part. The specimen was gripped with a jig having the same curvature as that of the steel pipe, a tensile test was performed, and the tensile strength was measured. The results are shown in Tables 3 and 4 below. In addition, as shown in the lower column of the table, A: the joint surface indicates a fracture starting from an oxide in the joint interface.

[Torsion test]
The torsion test was measured for the joined articles of Examples 1 to 10 and Comparative Examples 1 to 8. A flange having bolt holes was welded to both ends of a steel pipe as a joined product, and the bolt was fixed to a torsion tester. The torsion speed was 0.1 ° / s, and the torsion angle and the maximum torsion torque were measured from the data of torsion angle-torsion torque. The results are shown in Table 3.

[Result 1]
The joining interfaces (joining portions) of all the joined articles of Examples 1 to 10 and Comparative Examples 1 to 11 were improved in the hardenability by Ni contained in the joining material, and became a martensite structure. The base material continuous with the interface had a bainite structure, which was the same as the structure before joining.

[Result 2]
As shown in Table 3, in the joined products joined in the atmosphere of Examples 1 to 7, the oxide at the joint interface is 5% or less in area ratio, and in the tensile test, the joint breaks at the joint portion. There was something that broke except the part. When joining was performed in the nitrogen atmosphere containing 100 ppm of oxygen in Examples 8 and 9 and in the complete nitrogen atmosphere in Example 10, there was no fracture at the joint. It is apparent that the joined portion is alloyed with the joined foil and is harder than the base material. Therefore, the joined articles of Examples 8 to 10 joined in a low oxygen atmosphere in which almost no oxide is present at the joining interface are broken at the base material.

[Result 3]
As shown in Table 3, the tensile strength of the joined portion of the joined articles of Examples 1 to 10 was 585 MPa or more. Moreover, the tensile strength of the junction part of Examples 1-7 in which the oxide is not produced | generated has ensured the intensity | strength exceeding 82% compared with Examples 8-10 in which the oxide is not produced | generated. It can be said.

[Result 4]
As shown in Table 3, in the torsion test, all of the joined products joined in the atmosphere of Examples 1 to 7 were broken at the joined portion, but all were broken after exceeding the torsion angle showing the maximum torsion torque. ing. Further, as shown in Table 3, the joined product joined in a nitrogen atmosphere containing 100 ppm of oxygen in Examples 8 and 9 and the joined product joined in a complete nitrogen atmosphere in Example 10 did not break. The entire joint was plastically deformed. In addition, the maximum torsional torque of the joint portions of Examples 1 to 7 exceeds 88% compared to the maximum torsional torque of Examples 8 to 10.

[Result 5]
The joined articles of Comparative Examples 1 and 2 have a higher oxide area ratio and significantly lower tensile strength and torsional strength than the joined articles of Examples 1 to 10. Moreover, the starting point of destruction is an oxide produced | generated in the junction part.

  In the tensile test, the bonded products of Comparative Examples 3 and 5 to 7 were poor in balance between the heating temperature and the pressing force, caused plastic deformation, and were not suitable for strength evaluation. Although the bonded product of Comparative Example 4 has a low oxide area ratio, the fracture position is the bonded interface, and the alloy in the bonded foil was not sufficiently diffused, so it is considered that the bonded product was embrittled. In Comparative Example 8, the oxide area ratio is low and the plastic deformation is small, but as a result of shortening the diffusion treatment time, breakage occurred at the joint surface in the tensile test and the torsion test, compared with those in Examples 1 to 10, The tensile strength and the maximum torsion torque were small.

[Result 6]
As shown in Table 4, the bonded articles of Comparative Examples 9 to 11 bonded in the air have a larger oxide area ratio and tensile strength than the bonded articles of Examples 1 to 7 bonded in the air. It was low. In the joining conditions of Comparative Examples 9 to 11, as shown in Table 2, the initial stress and the final stress are substantially the same as those of Examples 1 to 10, and the initial stress holding time is the diffusion treatment of Examples 1 to 10 ( It is within the range of the stress holding time in the first diffusion step). That is, it can be considered that the conditions in Table 2 omit the joining and extruding step (joining process immediately above the joining foil melting temperature (liquidus)) in Examples 1 to 10. From this, it can be said that the conditions of the joining extrusion process of Examples 1 to 10 are effective in suppressing the generation of oxides and performing sound joining.

  10A, 10B: Steel pipe, 11: Low melting point bonding material, 32: Heater, 33: Nitrogen gas chamber, 41: Push plate

Claims (4)

A step of disposing a low melting point bonding material having a melting point lower than that of the steel between the open end faces of a pair of steel members to be joined having a cylindrical portion at the end, and
The members to be joined are bonded to each other at the opening end surfaces by pressing the members to be joined while heating the members to be joined at a joining temperature equal to or higher than the melting point of the low melting point joining material, A bonding extrusion step of extruding the generated oxide around the bonding portion;
First, the material of the low-melting-point bonding material is diffused in the bonded member by heating the bonded member to a diffusion temperature higher than the bonding temperature while maintaining the pressed state during the bonding extrusion step. The diffusion process of
While maintaining the heating state in the first diffusion step, the second diffusion is performed by pressing with a pressing force lower than the pressing force in the bonding extrusion step, and further diffusing the material of the low melting point bonding material into the bonded member Process,
A liquid phase diffusion bonding method comprising: In the bonding extrusion step, a first pressing force condition in the range of 10 to 25 MPa while heating the member to be bonded under the temperature condition in the range from the melting point of the low melting point bonding material to 1130 ° C. as the bonding temperature. Then, by pressing the members to be bonded for 60 to 600 seconds, the members to be bonded are bonded to each other at the opening end surfaces, and at least the oxide generated in the bonding portion is pushed out around the bonding portion,
In the first diffusion step, by maintaining the pressed state at the time of the bonding extrusion step, the member to be bonded is heated for 2 to 20 seconds under the temperature condition in the range of 1200 ° C. to 1250 ° C. as the diffusion temperature. , Diffusing the material of the low-melting-point bonding material into the bonded member
In the second diffusion step, while maintaining the heating state in the first diffusion step, for 200 seconds or more after reaching the diffusion temperature under the condition of the second pressing force in the range of 2 to 4 MPa. 2. The liquid phase diffusion bonding method according to claim 1, wherein the material of the low melting point bonding material is further diffused in the member to be bonded by pressing the members to be bonded to each other.   3. The liquid phase diffusion bonding method according to claim 1, wherein a foil made of a Ni-based amorphous alloy containing B, Si, and V is used as the bonding material. A bonded article manufactured by the liquid phase diffusion bonding method according to claim 1,
A bonded product, wherein the structure of the steel other than the bonded part is a bainite structure, and the tensile strength of the bonded part is 500 MPa or more.

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