JP2012040584A - Method for bonding ferrous material - Google Patents

Abstract

An iron-based material joining method capable of improving the life of a rotary tool in friction stir welding is provided.
In a method for joining iron-based materials in which iron-based base materials 100 and 101 are joined by friction stir welding, the joining portion of the iron-based base materials 100 and 101 has a temperature higher than the temperature at which friction stir welding can be performed independently. After the preheating by the high frequency induction heating source 20 a, the joining parts are joined by friction stir welding using the rotary tool 10. Even if the joining sites of the iron-based base materials 100 and 101 are preheated so as to have a temperature at the time of friction stir welding exceeding the softening point, the joining sites become soft and the frictional heat with the iron-based alloy generated during the friction stir welding is reduced. Since it is greatly reduced, the amount of heat applied to the joint site as a whole does not change. The metal structure of the joined part after joining is not changed from the case where the friction stir welding is performed without preheating. The joining portion is softened by preheating, the load on the rotary tool 10 is reduced, and the life of the rotary tool 10 can be improved.
[Selection] Figure 1

Description

  The present invention relates to a method for joining ferrous materials, and more particularly, to a method for joining ferrous materials in which ferrous base materials are joined together by friction stir welding.

  In recent years, friction stir welding (hereinafter sometimes referred to as FSW (Friction Stir Welding)) for joining materials to be joined made of metal materials has attracted attention. In this friction stir welding, the ends of plate-shaped metal base materials are brought into contact with each other to form a joint, and the tip of a rod-shaped rotary tool is inserted into the joint and moved along the joint while rotating the rotary tool. By doing so, the metal base material is joined. Alternatively, in a technique called spot FSW, the plate-shaped metal base materials are overlapped with each other, and the bar-shaped rotary tool is pushed in from the surface of the front-side metal base material to reach the back-side metal base material. Join metal base materials together.

  In this FSW, a friction stir welding apparatus using a heating means other than frictional heat input has been proposed. For example, in Patent Document 1, in an apparatus that performs friction stir welding, heat input performed at a front position on a bonding line is performed by a heat input means that is equal to or lower than a softening point temperature that is performed by self-heating such as high-frequency induction heating. The different heat input means performed together with friction heat input is self-heating such as high-frequency induction heating or electric resistance heating applied to the base material side from the small diameter part of the rotary tool, and after joining by friction stir welding , An apparatus including means for cooling the thermal effect remaining position behind the joining position is disclosed.

JP 2004-154790 A

  By the way, when joining iron-type base materials by FSW, there exists a problem that the lifetime of a rotary tool becomes short from the hardness of an iron-type base material. Even in the above-described technique, the life of the rotary tool cannot be sufficiently improved, and improvement is desired.

  The present invention has been made in view of such circumstances, and an object thereof is to provide a method for joining ferrous materials capable of improving the life of a rotary tool in friction stir welding.

  The present invention is a method for joining ferrous materials in which an iron base material is joined by friction stir welding, and at least a part of the joining portion of the iron base material is at or above a temperature at which friction stir welding can be performed independently. This is a method for joining ferrous materials in which the joined parts are joined by friction stir welding after heating.

  According to this configuration, in the joining method of the iron-based material in which the iron-based base material is joined by friction stir welding, at least a part of the joining portion of the iron-based base material is equal to or higher than the softening temperature, that is, the friction stir welding can be performed independently. After heating (preheating) so as to be equal to or higher than the temperature, the joining parts are joined by friction stir welding.

  In the conventional friction stir welding that heats the joint part in advance, if the base material is heated so as to exceed the softening point, the advantage of the friction stir welding that can be joined at a low temperature is lost. The preheating is performed at a temperature below the softening point, and further cooling is performed.

  On the other hand, according to the knowledge of the present inventor, even when preheating the joining part of the iron-based base material to a temperature at the time of friction stir welding exceeding the softening point, the joining part becomes soft, and thus occurs at the time of friction stir welding. Since the frictional heat with the iron-based alloy is greatly reduced, it has been found that the amount of heat given to the joint as a whole does not change so much. Furthermore, it has been found that the metal structure of the bonded portion after bonding is not so different from that when the friction stir welding is performed without preheating. Thereby, since a joining part becomes soft by preheating, the load to a rotating tool reduces, and the lifetime of the rotating tool in friction stir welding can be improved. Note that the present invention is effective if at least a part of the joining portion is at or above the temperature at which the friction stir welding can be performed alone, but there is a range in which the temperature at or above the temperature at which the friction stir welding can be performed alone within the joining portion. The larger the effect, the greater the effect of reducing the load on the rotating tool.

  In addition, the “friction stir welding” in the present application refers to an FSW that moves the rotating tool in the processing direction while rotating the tool, a spot FSW that does not move at the processing site while rotating the rotating tool, and an iron-based base material at the joining site. There are included four modes of FSW to be matched, and four modes of FSW in which a rotating tool is inserted from the side of one iron-based base material to the overlapped portion, and a combination of these.

  In this case, it is preferable to join the joining portion of the iron base material by friction stir welding after heating the joining portion of the iron-based base material to a temperature at which the friction stir welding can be performed independently by high frequency induction heating.

  According to this configuration, the joining part of the iron-based base material is heated only to a temperature at which the friction stir welding can be performed by only high frequency induction heating, and then the joining part is joined by friction stir welding. By performing preheating by high frequency induction heating, preheating can be performed by a safe, clean and inexpensive method. Conventionally, when friction stir welding is performed on an iron-based alloy without using an auxiliary heating source, generally, the welding is performed at 600 ° C. or higher. Refers to above ℃.

  In this case, it is preferable that the joining portion of the iron base material is heated to a temperature of 600 ° C. or higher by high-frequency induction heating, and then the joining portion is joined by friction stir welding.

  Conventionally, when friction stir welding is performed on an iron-based alloy without using an auxiliary heating source, generally, the joining is performed at 600 ° C. or higher. According to this configuration, the joining of the iron-based base material is performed by high-frequency induction heating. By heating the part to a temperature of 600 ° C. or higher, the iron-based alloy can be preheated to a temperature at which friction stir welding is performed without using an auxiliary heating source.

  Further, it is preferable that the frequency of high-frequency induction heating is lowered as the thickness of the plate-shaped iron-based base material is increased, and the frequency of high-frequency induction heating is increased as the thickness of the iron-based base material is decreased.

  According to this configuration, the frequency of high-frequency induction heating is decreased as the thickness of the plate-shaped iron-based base material is increased, and the frequency of high-frequency induction heating is increased as the thickness of the iron-based base material is decreased. Thereby, it becomes easy for a high frequency current to penetrate | invade from the surface of a plate-shaped iron-type base material to a back surface, and it can improve the efficiency of preheating.

In this case, in the high frequency induction heating, the electrical resistivity ρ (μΩ), the relative magnetic permeability μ, and the frequency f (Hz) of the induction coil in the high frequency induction heating are equal to the thickness δ (cm) of the plate-like iron base material. On the other hand, it is preferable to carry out so as to satisfy δ ≦ 10.06 (ρ / (μ · f)) ^1/2 .

According to this configuration, the high-frequency induction heating is performed when the induction coil electrical resistivity ρ (μΩ), the relative magnetic permeability μ, and the frequency f (Hz) in the high-frequency induction heating are equal to the thickness δ ( cm), δ ≦ 10.06 (ρ / (μ · f)) ^1/2 is satisfied. Thereby, it will surely preheat from the surface of a plate-shaped iron-type base material to a back surface, and it can improve the efficiency of preheating.

  Moreover, it is suitable to use what consists of either ceramics or a cermet as a rotary tool used by friction stir welding.

  According to this structure, what consists of either ceramics or cermet is used as a rotary tool used by friction stir welding. When the rotary tool is made of ceramics or cermet, especially when preheating is performed by high frequency induction heating, the iron base material is heated but the rotary tool is not heated so much. Can be prevented, and the life of the rotary tool can be further improved.

In this case, it is preferable to use a rotating tool used in the friction stir welding that is made of PCBN, Si ₃ N ₄ , SiC, or ZrO ₂ .

According to this configuration, a rotating tool used in friction stir welding is made of PCBN, Si ₃ N ₄ , SiC, or ZrO ₂ having excellent characteristics. Therefore, the life of the rotary tool can be further improved.

  According to the method for joining ferrous materials of the present invention, the life of a rotary tool in friction stir welding can be improved.

It is a perspective view which shows the friction stir welding apparatus which concerns on 1st Embodiment. It is sectional drawing in the AA line of the high frequency induction heating source which concerns on 1st Embodiment. It is sectional drawing in the BB line of the high frequency induction heating source which concerns on 1st Embodiment. It is a side view which shows the high frequency induction heating in the friction stir welding apparatus which concerns on 2nd Embodiment. It is a side view which shows the spot friction stir welding in the friction stir welding apparatus which concerns on 2nd Embodiment. It is a bottom view of the high frequency induction heating source which concerns on 2nd Embodiment. It is sectional drawing of the high frequency induction heating source which concerns on 2nd Embodiment. It is a table | surface which shows the joining speed and joining state of normal FSW and high frequency FSW in an experiment example. It is a figure which shows the macro cross section and micro cross section of the coupling obtained by high frequency FSW. It is a figure which shows the macro cross section and micro cross section of the coupling obtained by normal FSW. It is a figure which shows the fine structure of the stirring part of the coupling obtained by high frequency FSW. It is a figure which shows the fine structure of the stirring part of the coupling obtained by normal FSW. It is the figure which compared the structure | tissue of the stirring part center part of high frequency FSW and normal FSW. It is a graph which shows the relationship between the joining speed and stirring part area in normal FSW and high frequency FSW. It is a figure which shows the hardness distribution of the joint cross section obtained by the high frequency FSW. It is a figure which shows the hardness distribution of the joint cross section obtained by normal FSW. It is a graph which shows the relationship between the joining speed and tensile strength in normal FSW and high frequency FSW. It is a top view of the junction part which joined SN490B of plate | board thickness 15mm with the high frequency FSW. It is sectional drawing of the junction part which joined SN490B of plate | board thickness 15mm with the high frequency FSW. It is a figure which shows the microstructure in the stirring part of the joint made into the joint speed 400mm / min in the case of the hybrid FSW which irradiated the laser beam to the site | part of 15 mm from the front of the rotation tool, and the case of normal FSW at low magnification. It is a figure which shows the microstructure in the stirring part of the joint made into the joint speed 400mm / min in the case of the hybrid FSW which irradiated the laser beam to the site | part of 15 mm from the front of the rotation tool, and the case of normal FSW at low magnification. In the hybrid FSW in which a laser beam is irradiated to a portion 15 mm from the front of the rotary tool, the bonding speed is 600 mm / min and 800 mm / min, and in the normal FSW, the bonding speed is 400 mm / min. It is a figure which shows the microstructure of a middle layer and a bottom layer. FIG. 6 is a graph showing the relationship between the bonding speed of 5-Center, 5-Adv side, and 5-Ret side and the agitation area. It is a top view shown about the flow form of the probe periphery in FSW. It is a top view shown about the flow form of the probe periphery of 5-Adv side. It is a top view shown about the flow form around the probe of 5-Center. It is a top view shown about the flow form around the probe of 5-Ret side.

Hereinafter, a first embodiment of the present invention will be described with reference to the accompanying drawings. As shown in FIG. 1, in the friction stir welding apparatus 1a of the present embodiment, plate-shaped iron base materials 100 and 101 are joined by friction stir welding. The friction stir welding apparatus 1a includes a rotary tool 10 and a high frequency induction heating source 20a. The rotary tool 10 and the high-frequency induction heating source 20a are arranged along the joining direction of the iron-based base materials 100 and 101. In the friction stir welding apparatus 1a, the rotary tool 10 can perform the friction stir welding after the high frequency induction heating source 20a preheats the iron base materials 100 and 101. During the friction stir welding, the relative positional relationship between the rotary tool 10 and the high-frequency induction heating source 20a is not changed, and the iron base materials 100 and 101 are relatively moved in the direction opposite to the joining direction. Friction stir welding can be performed. Further, as the back plate, the back side of the iron-based base material 100 and 101 may be disposed a ceramic plate such as _Si 3 _{N 4.} Further, in this case, members made of the same iron-based material may be disposed only on the back side of the joining portion of the iron-based base materials 100 and 101. As a result, the iron-based member on the back side of the bonded portion is heated by high-frequency induction heating, and the efficiency of heating the entire bonded portion of the iron-based base materials 100 and 101 can be improved.

The rotary tool 10 has a substantially cylindrical shape, and includes a substantially cylindrical probe portion having a smaller diameter than the shoulder portion at the tip. The material of the rotary tool 10 is preferably ceramic, cermet, or a material that is difficult to be heated by high frequency induction heating, and more preferably PCBN, Si ₃ N ₄ , SiC, and ZrO ₂ . SiC is weak against thermal shock, and ZrO ₂ is weak at high temperatures, but has properties of excellent strength and toughness. In this embodiment, since the temperature of the rotary tool 10 does not rise, it is possible to compensate for the disadvantages of these materials and take advantage of the advantages. Or as a material of the rotary tool 10, a cemented carbide alloy, W alloy, Ir alloy, Ni alloy, Co alloy, etc. can also be used.

  2 shows a cross-sectional view taken along the line AA in FIG. 1 and FIG. 3 shows a cross-sectional view taken along the line BB in FIG. 1, the high-frequency induction heating source 20a of the present embodiment In addition, the entire surface of the coil winding 21 is covered with the core 22 by being covered up to the side surface. By attaching the core 22 to the coil winding 21, the magnetic flux concentrates on the iron-based base materials 100 and 101, and the heating efficiency can be improved.

In the present embodiment, the electrical resistivity ρ (μΩ), the relative magnetic permeability μ, and the frequency f (Hz) of the high-frequency induction heating source 20a are relative to the thickness δ (cm) of the plate-like iron base materials 100 and 101. Thus, δ ≦ 10.06 (ρ / (μ · f)) ^1/2 is satisfied. That is, the frequency f is increased as the thickness of the iron-based base materials 100 and 101 is decreased, and the frequency f is decreased as the thickness of the iron-based base materials 100 and 101 is increased. Furthermore, after preheating the joining site | part of the iron-type base materials 100 and 101 so that it may become more than the temperature which can carry out friction stir welding independently, a joining site | part is joined by friction stir welding. The temperature of the iron-type base materials 100 and 101 at the time of preheating can be 600-800 degreeC, for example.

  In the present embodiment, in the method of joining ferrous materials in which the ferrous base materials 100 and 101 are joined by friction stir welding, the joining sites of the ferrous base materials 100 and 101 can be higher than the softening temperature, that is, the friction stir welding can be performed independently. After preheating with the high-frequency induction heating source 20a so that the temperature is higher than a certain temperature, the joined parts are joined by friction stir welding using the rotary tool 10.

  In the conventional friction stir welding that heats the joint part in advance, if the base material is heated so as to exceed the softening point, there is no point in applying heat to the base material in the friction stir welding, and friction stir can be performed at a low temperature. Since the advantage of joining is lost, as in Patent Document 1, preheating is performed at a temperature below the softening point, and further cooling is performed.

  On the other hand, according to the knowledge of the present inventor, even when the joining portion of the iron-based base materials 100 and 101 is preheated so as to have a temperature at the time of friction stir welding exceeding the softening point, the joining portion becomes soft. It was found that the amount of heat given to the joint as a whole does not change so much because the frictional heat with the iron-based alloy that is sometimes generated is greatly reduced. Furthermore, it has been found that the metal structure of the bonded portion after bonding is not so different from that when the friction stir welding is performed without preheating.

  Thereby, since a joining site | part becomes soft by preheating, the load to the rotary tool 10 reduces, and the lifetime of the rotary tool 10 in friction stir welding can be improved. Moreover, the joining speed in friction stir welding can be improved, and the plate | board thickness which can be joined can be increased. In addition, as will be described later, there are cases where the characteristics of the bonded portion can be improved. Note that this embodiment is effective if at least a part of the joining portion is at or above the temperature at which friction stir welding can be performed alone, but the range at which the temperature is at or above the temperature at which friction stir welding can be carried out independently within the joining portion. The greater the is, the greater the effect of reducing the load on the rotary tool 10.

  Moreover, in this embodiment, after heating the joining site | part of the iron-type base materials 100 and 101 so that it may become the temperature at the time of friction stir welding by the high frequency induction heating source 20a, a joining site | part is joined by friction stir welding. By performing preheating with the high frequency induction heating source 20a, preheating can be performed by a safe, clean and inexpensive method.

  When performing friction stir welding of an iron-based alloy without using an auxiliary heating source, generally, since the welding is performed at 600 ° C. or higher, according to the present embodiment, the iron-based base material 100, By heating the bonding portion 101 to a temperature of 600 ° C. or higher, the iron-based alloy can be preheated to a temperature at which friction stir welding is performed without using an auxiliary heating source.

  In the present embodiment, the frequency of the high frequency induction heating source 20a is decreased as the thickness of the plate-shaped iron base materials 100 and 101 is increased, and the frequency of the high frequency induction heating source 20a is set to be lower than that of the iron base materials 100 and 101. Increase as the thickness decreases. Thereby, it becomes easy for a high frequency current to penetrate | invade from the surface of the plate-shaped iron-type base materials 100 and 101 to a back surface, and it can improve the efficiency of preheating.

In particular, in the present embodiment, the high frequency induction heating source 20a has a plate-like iron base material 100, 101 in which the electrical resistivity ρ (μΩ), the relative magnetic permeability μ, and the frequency f (Hz) of the high frequency induction heating source 20a are the same. Is performed so as to satisfy δ ≦ 10.06 (ρ / (μ · f)) ^1/2 . Thereby, it preheats reliably from the surface of the plate-shaped iron-type base materials 100 and 101 to a back surface, and can improve the efficiency of preheating. In order to ensure that the high frequency current permeates from the front surface to the back surface of the plate-like iron base materials 100 and 101, δ ≦ 5.03 (ρ / (μ · f)) ^1/2 is satisfied. It is preferable to perform preheating. As a result, the high-frequency current will surely permeate from the front surface to the back surface of the plate-like iron base materials 100, 101, and the preheating efficiency can be further improved.

  Moreover, in this embodiment, what consists of ceramics is used as the rotary tool 10 used by friction stir welding. When the rotary tool 10 is made of ceramics, especially when the preheating is performed by high frequency induction heating, the iron base materials 100 and 101 are heated but the rotary tool 10 is not heated so much. It is possible to prevent the life of the rotating tool 10 from decreasing and further improve the life of the rotary tool 10.

In particular, in the present embodiment, the rotary tool 10 used in the friction stir welding is made of PCBN or Si ₃ N ₄ having excellent characteristics. Therefore, the life of the rotary tool can be further improved.

  Hereinafter, a second embodiment of the present invention will be described. As shown in FIG. 4, in this embodiment, the superposed iron base materials 100 and 101 are joined by a spot FSW. As shown in FIG. 4, the friction stir welding apparatus 1b of the present embodiment includes a high frequency induction heating source 20b, a matching box 30, and an air cylinder 40. The matching box 30 supplies power to the high frequency induction heating source 20b. The air cylinder 40 is extendable and moves the high-frequency induction heating source 20b and the matching box 30.

  As shown in FIGS. 6 and 7, in the high frequency induction heating source 20b, the coil winding 21 and the core 22 are arranged so as to form a spiral coil. By configuring the high frequency induction heating source 20b as a spiral coil, a coil having an inductance L larger than the area of the high frequency induction heating source 20b can be obtained. The core 22 is configured to cover the upper surface and side surfaces of the coil winding 21. The relationship between the electrical resistivity ρ, the relative magnetic permeability μ and the frequency f of the high frequency induction heating source 20b and the thickness δ of the plate-like iron base materials 100 and 101 is the same as that in the first embodiment.

  As shown in FIG. 4, at the time of joining, the high frequency induction heating source 20b is disposed above the joining portion and performs preheating. The rotary tool 10 stands by above the high frequency induction heating source 20b. Next, when the preheating is completed, as shown in FIG. 5, the air cylinder 40 moves the high-frequency induction heating source 20b and the matching box 30 from above the joining portion. After the high frequency induction heating source 20b and the matching box 30 are moved from above the joining portion, the rotary tool 10 is lowered to the joining portion, and friction stir welding is performed. Further, when there is no drive mechanism such as the air cylinder 40, it is necessary to produce a coil with a hole in the center and to have a structure in which the rotary tool 10 is inserted in the center of the coil.

  According to the present embodiment, even in the spot FSW, it is possible to improve the life of the rotary tool 10 and improve the joining speed. In addition, in the spot FSW, there are cases where the characteristics of the bonded portion can be improved.

  In the first and second embodiments, the preheating is performed by high frequency induction heating. However, in the present invention, the iron base materials 100 and 101 are preheated using a laser beam such as a YAG laser. May be. When the iron-based base materials 100 and 101 are preheated using laser light, it is desirable that the iron-based base materials 100 and 101 are once melted by the laser light. This is because the laser absorption efficiency is increased and heating up to the back surface is possible.

(Experimental example 1)
Hereinafter, Experimental Example 1 of the present invention will be described. A friction stir welding apparatus 1a as shown in FIG. 1 was prepared. In the friction stir welding apparatus 1a used in this experimental example, the diameter of the rotary tool 10 is 10 to 25 mm, the inclination angle of the rotary tool 10 is 0 to 5 °, and the rotational speed of the rotary tool 10 is 100 to 1000 rpm. The joining speed was 25 to 1000 mm / min, and the load could be changed in the range of 1 to 40 t. In the apparatus of Experimental Example 1, all of the rotary tool 10 and the high-frequency induction heating source 20a are arranged in a shield box, and the shield box is filled with Ar gas. Further, a Si ₃ N ₄ plate was used as the back plate.

  Regarding the high-frequency induction heating source 20a, in a separately conducted experiment, when a SN490 material having a thickness of 20 mm is heated at a frequency of 33 kHz and a heating power source capacity of 27.2 kW, the high-frequency induction heating source reaches a heating temperature of 800 ° C. in a heating time of 5 seconds. 20a was used.

As the iron base materials 100 and 101, S45C, which is a general medium carbon steel material, was used. The composition of S45C is as follows: C: 0.45 mass%, Si: 0.2 mass%, Mn: 0.58 mass%, P: 0.02 mass%, S: 0.01 mass%, Cu: 0.01 Mass%, Ni: 0.02 mass%, Cr: 0.04 mass%, and the balance is Fe. As a feature of S45C, since involving tissue transformation by the magnitude of cooling rate when it exceeds A ₁ point to (723 ° C.), by including hardness and elongation of the joint is changed depending on the conditions, a significant impact on the strength It is thought to give. The plate thickness was 3.2 mm. The size of the sample used for joining was 300 mm long × 50 mm wide.

  First, an experiment was performed with a normal FSW (hereinafter sometimes referred to as a normal FSW), and after confirming the bonding limit speed, friction stir welding (hereinafter referred to as a high frequency FSW) using the high-frequency induction heating source 20a of the present invention was used. Experiment). The rotational speed was 600 rpm, the joining speed was 100 to 800 mm / min, the load was 1900 to 4700 kgf, the tilt angle of the rotary tool 10 was 3 °, and the flow rate of Ar gas as the shielding gas was 25 L / min. The rotating tool 10 used was a shoulder part having a diameter of 15 mm, a probe part having a diameter of 6 mm, and a probe part having a length of 3.2 mm.

  Experiments were performed with normal FSW and high-frequency FSW, and the joining possible range was determined. FIG. 8 shows a surface photograph of the joint when the joining speed is 400 mm / min to 800 mm / min. The case where there is no defect that can be observed with the naked eye on the surface and the inside is indicated by ○, and the case where the probe (tool) is destroyed during joining is indicated by ×. As shown in FIG. 8, with the high frequency FSW, it was possible to achieve a bonding speed twice that of a normal FSW. When a defect occurred on the surface of the joint portion with normal FSW, it occurred on the advancing side. Generally, defects on the forward side are caused by insufficient heat input. However, when the high-frequency FSW is used, it is possible to join without defects at a joining speed of 800 mm / min.

  FIG. 9 shows a macro and micro observation of a cross section of a high frequency FSW, and FIG. 10 shows a normal FSW. In order to make it easy to observe areas such as TMAZ (Thermo-Mechanically Affected Zone) and HAZ (Heat Affected Zone, heat affected zone), the conditions for the maximum joining speed for both normal FSW and high frequency FSW A comparison was made. Therefore, a normal FSW was used with a joining speed of 400 mm / min, and a high frequency FSW was used with a joining speed of 800 mm / min. Both rotation speeds are 600 rpm.

  In the cross-sectional photographs of the joints shown in FIGS. 9 and 10, the right side is generally the advancing side and the left side is the retreating side. 9 (a) and 10 (a) are cross sections of the base material and the joint on the receding side, FIGS. 9 (b) and 10 (b) are the center of the joint, and FIGS. 9 (c) and 10 (c). Is a cross section of the base material on the forward side and the joint, and FIGS. 9D and 10D show the base material.

The base material had a ferrite-pearlite structure and showed a uniform appearance as a whole. 9 (a), 9 (c), 10 (a), and 10 (c), a clear boundary can be confirmed between the ferrite pearlite structure and the joint structure of the base material structure. A small amount of a deformed ferrite pearlite layer is present at the boundary, which is considered to be TMAZ. From this inner it has become a very fine ferrite-pearlite structure, the site is presumed to have joined with A ₁ or less. This boundary feature was found in both normal and high frequency FSW.

  FIG. 11 shows structural photographs of the upper, middle, and lower portions of the stirring section at high-frequency FSW joining speeds of 400, 600, and 800 mm / min. When the joining speed is 400 mm / min, the upper part and the middle part have a mixed structure of ferrite and pearlite. When the joining speed is 600 mm / min, the upper part and the middle part are martensite (white areas with streaks) and bainite (dark black grains).・ It was ferrite (white part of grain boundary) and pearlite (light black grain). At a joining speed of 800 mm / min, a martensite (white area with streaks) / bainite (black grains) structure was formed. Regardless of the bonding speed, the lower part had a fine ferrite (white part and white grain) and pearlite (thin black grain) structure.

That top, during FSW is in the middle, once becomes austenite beyond the _point A, it can be seen that transformed into a variety of tissues by various cooling rates depending on welding speed. Furthermore, at the same time, the dynamic recrystallization of austenite occurs due to the stirring effect of the rotary tool 10, resulting in a fine mixed structure. On the other hand, in the lower part, since the bonding was performed at a point A ₁ or less under all conditions, transformation does not occur, and a fine ferrite / pearlite structure is formed by dynamic recrystallization due to the stirring effect of the rotary tool 10.

A similar trend was seen in normal FSW. This is shown in FIG. In the upper part, a ferrite pearlite structure is formed at bonding speeds of 100 mm / min and 200 mm / min, but a bainite martensite structure is formed at a bonding speed of 400 mm / min. As the joining speed increases, the cooling speed increases and a bainite martensite structure is generated. Regardless of the joining speed, the fine ferrite pearlite structure is formed from the top to the bottom. The temperature lower of as welding speed becomes larger gradually approaches the _point A, the grain refinement for equal to or less than A ₁ point in the case welding speed of 400 mm / min is considered to become remarkable. Thus, the same tendency was observed for both normal FSW and high-frequency FSW.

  Next, comparison of the joint structure between the normal FSW and the high frequency FSW was performed. FIG. 13 shows the structure of the middle part of the joint in the range of 300 mm / min to 800 mm / min between the normal FSW and the high frequency FSW. When the joining speed was 400 mm / min, the structure was a ferrite / pearlite structure, and the presence of bainite could not be confirmed.

  Therefore, the high frequency FSW has a ferrite pearlite structure at bonding speeds of 300 mm / min and 400 mm / min, and it can be said that martensite bainite is generated from the bonding speed of 600 mm / min. On the other hand, normal FSW has a ferrite pearlite structure at a joining speed of 300 mm / min, but martensite bainite is observed at a joining speed of 400 mm / min. It can be seen that the occurrence of martensite bainite is shifted to a higher speed side in the high frequency FSW than in the normal FSW. When compared at the same 400 mm / min, it can be said that normal FSW is easier to burn.

  FIG. 14 shows the influence of the joining speed on the area of the normal FSW and high-frequency FSW stirring section. The flow amount of the high frequency FSW is increased as compared with the normal FSW. That is, it can be understood that the heat supplied from the high frequency is a heat amount corresponding to a difference of about 200 mm / min by increasing the flow amount. This is consistent with the result of temperature measurement. The high-frequency FSW has a flow rate that is shifted to the high speed side by approximately 200 mm / min compared to the normal FSW, but it can be joined at a joining speed of 800 mm / min. You can see that That is, the load on the rotary tool is reduced and the life is extended. These show that heating by high frequency is effective for reducing the load on the rotary tool 10 and improving the joining speed.

  FIG. 15 shows a vertical cross-sectional photograph and hardness distribution of a high frequency FSW joint, and FIG. 16 shows a normal cross-sectional photograph and hardness distribution of a normal FSW joint. In the cross-sectional photograph, there are a black portion and a slightly discolored portion, but the outside of the discolored portion and the range in which the hardness distribution has changed are the same regardless of the normal FSW and the high frequency FSW. That is, this is considered to correspond to a stirring part.

  From the measured hardness, mainly martensite (high frequency FSW, bonding speed 800 mm / min), martensite with a large proportion and bainite (high frequency FSW, bonding speed 800 mm / min), bainite with a large proportion and other martensite And pearlite (high frequency FSW, joining speed 600 mm / min), pearlite with a large proportion and bainite and ferrite (normal FSW, joining speed 400 mm / min), pearlite with a large proportion and other ferrite (normal FSW, joining speed) 300 mm / min) and a base material structure (ferrite / pearlite), which was also confirmed by observation of the structure.

  The hardness increased as the joining speed increased, and this tendency was particularly noticeable in the high frequency FSW. Further, in the normal FSW, an increase in hardness was observed at a joining speed of 400 mm / min, but in the high frequency FSW, an increase in hardness was observed at a joining speed of 600 mm / min or more, and the increase width was large. This may be due to the difference in cooling rate. In the high frequency FSW, by using a high frequency, a bonding speed that is impossible in a normal FSW is achieved. Therefore, the cooling rate increased. It is considered that as the cooling rate increases, a structure having high hardness such as martensite and bainite is likely to be generated. In general, when the bonding speed is high, a structure such as martensite and bainite is likely to occur. For this reason, it is considered that by using the high frequency FSW, the start of increase in the hardness of the joint is shifted to the high speed side, and the increase width is also increased. On the other hand, when compared at the same 400 mm / min, the high-frequency FSW having a higher temperature was lower in hardness. This is presumably because the cooling rate was reduced because the maximum reached temperature was slightly higher.

Moreover, the increase in hardness is observed from the upper part of the joint to the center. Normally, the temperature in the stirring section during FSW increases as it approaches the upper part, and the lower part is larger because the cooling rate is in contact with the back plate. Therefore, originally, the lower part tends to be a structure such as martensite or bainite, and an increase in hardness should be observed. In this experiment junction it is performed in the following _point A in the vicinity of the bottom because the increase of such hardness not observed, believed to have become a tissue of fine ferrite and spherical cementite. A similar phenomenon is also seen in the high frequency FSW, indicating that the temperature rise is small.

  Moreover, HAZ was not able to be confirmed from the junction cross-sectional photograph and hardness distribution. TMAZ is slightly present as ferrite pearlite crushed at the boundary between the base material and the stirring portion, and it was confirmed from the observation of the structure that it exists at the boundary between the light gray portion of the stirring portion and the base material.

  Next, the result of the tensile test of the stirring part is shown. The result is shown in FIG. Under all conditions, the tensile strength increased significantly over the base metal, but the values varied slightly. This is because when the bonding speed is increased, the maximum temperature is lowered, the structure is refined, and when the cooling rate is increased, martensite or bainite having a hard structure is generated. Generally, the tensile strength increases as the hardness of the material increases. On the other hand, the reason why the tensile strength varies is that the hardness becomes uneven as the cooling rate gradually increases as the distance from the center of the joint increases. By using the high frequency FSW, the peak in the tensile strength was shifted to the high speed side as the generation peak of the bainite / martensite structure was shifted to the high speed side.

From the above, medium carbon steel was joined by the method of preheating the FSW and the iron-based material to the temperature at the FSW by high frequency induction heating, and the following conclusions were obtained.
(1) By using a high frequency, it is possible to achieve a bonding speed twice that of a normal FSW for the same material.
(2) The joint strength exceeds the base material unless a defect occurs. Moreover, the joining speed which shows the maximum stirring part intensity | strength shifts to a high-speed side by using a high frequency together.
(3) Since the maximum temperature and the cooling rate can be changed by changing the high-frequency conditions, the structure of the joint after FSW and the amount of stirring can be controlled.
(4) In general, when the bonding speed is high, a structure such as martensite and bainite is likely to occur. Therefore, by using the high frequency FSW, the start of increasing the hardness of the joint is shifted to the high speed side, and the increase width is also increased. On the other hand, when compared at the same bonding speed, the high-frequency FSW having a higher temperature has lower hardness. This is because the cooling rate is decreased by slightly increasing the maximum temperature.
(5) A Joint joined at ₁ point or less has a fine ferrite and spherical cementite structure. Such a region exists regardless of the presence or absence of high-frequency induction heating.

  Further, in the same manner as described above, high frequency FSW was performed using SN490B having a plate thickness of 15 mm as the iron base materials 100 and 101. The rotational speed of the rotary tool 10 was 300 rpm, the joining speed was 80 mm / min, and the load was 5 ton. Moreover, the coil of the shape which surrounds the circumference | surroundings of the rotary tool 10 was used as a high frequency induction heating source. FIG. 18 shows a top surface of the joint, and FIG. 19 shows a cross section of the joint. From FIG. 18 and FIG. 19, it can be seen that good bonding is performed even in an iron-based material having a plate thickness of 15 mm.

(Experimental example 2)
Hereinafter, Experimental example 2 of the present invention will be described. In this experimental example, as a heat source for preheating, a YAG laser irradiator (model number: MW2000) manufactured by Sumitomo Heavy Industries, Ltd. was used to join an iron-based material by FSW (hereinafter referred to as hybrid FSW). Sometimes called). SS400 was used as the iron base material used as a sample. In the FSW method in this experimental example, the irradiation of the YAG laser used as a heating source immediately before the rotating tool is inserted into the sample is started with the irradiation angle of the laser beam being 45 ° from the horizontal, the output is 2 kW, and rotating simultaneously with the start of bonding. Joining was performed while continuing to irradiate locally with the laser beam irradiation angle maintained at 45 ° from the horizontal and the output at 2 kW. In addition, the relative position of the rotating tool and laser irradiation during bonding was always constant.

  As joining conditions, the tilt angle of the rotary tool was 3 °, and the rotational speed of the rotary tool was 400 rpm. The welding speed is 400 rpm, 500 rpm, 600 rpm, 700 rpm, and 800 rpm when a laser beam is irradiated to a 15 mm site from the front of the rotary tool, and 600 rpm and 800 rpm when a laser beam is irradiated to a 5 mm site from the front of the rotary tool. And 1000 rpm.

  With normal FSW, the joining speed was possible up to 400 mm / rpm, but when laser light was irradiated to a 15 mm site from the front of the rotary tool, joining was possible up to a joining speed of 700 mm / rpm.

  20 and 21, the surface layer of the microstructure in the stirring portion of the joint having a joining speed of 400 mm / min in the case of the hybrid FSW in which the laser beam is irradiated to a portion 15 mm from the front of the rotary tool and the case of the normal FSW, The middle and bottom layers are shown in comparison. FIG. 20 shows the microstructure at a low magnification, and FIG. 21 shows the microstructure at a high magnification.

  It can be seen that the structures obtained by the hybrid FSW and the normal FSW are almost the same in the surface layer, the middle layer, and the bottom layer. That is, a ferrite-pearlite-bainite mixed structure was formed in the surface layer and the middle layer, and a ferrite-pearlite microstructure was formed in the bottom layer, which was assumed to be joined in a region at a point A1 or less that is not accompanied by transformation. When the hybrid FSW was applied, a systematic change was expected due to an increase in heat input at the time of joining due to laser preheating. However, since the main factor for forming the joint was joining by the FSW, an equivalent structure was obtained. It is estimated that the temperature was comparable.

  FIG. 22 shows a case where the welding speed is 600 mm / min and 800 mm / min in the hybrid FSW in which the laser beam is irradiated to a portion 15 mm from the front of the rotary tool, and a case where the bonding speed is 400 mm / min in the normal FSW. The microstructure of the surface layer, middle layer and bottom layer of the part is shown. In the hybrid FSW, a fine mixed structure composed of ferrite, pearlite and bainite is obtained in the surface layer and middle layer with a joining speed of 600 mm / min, and a fine mixed structure composed of ferrite and pearlite is obtained in the surface layer and middle layer of 800 mm / min. It was. Further, the structure becomes finer as the bonding speed increases. This is because the heat input per unit length decreases and the temperature decreases. These are structural changes as if they were performed in the same process, with or without preheating. Since the bottom layer was joined at a point A1 or less that did not undergo phase transformation under any of the conditions, a fine ferrite and pearlite structure was formed. The size of the ferrite grains also decreased with increasing bonding speed. No martensite formation was observed under any of the conditions.

  When the laser irradiation position is 5 mm forward from the rotary tool and shifted to 5 mm on the joining center position and Advancing side (advance side) (hereinafter sometimes referred to as 5-Adv side), and 5 mm on the retreating side (retreat side) The temperature was measured for the case of shifting (sometimes referred to as 5-Ret side). When the difference in maximum temperature reached is measured at a joining speed of 600 mm / min, when the laser beam is irradiated to the center of the joining line (hereinafter sometimes referred to as 5-Center), the forward side is shifted by 5 mm. It was found that the temperature decreased by 83 ° C., and the temperature increased by 40 ° C. when irradiated with a shift of 5 mm toward the receding side.

  It is said that, generally, flow occurs from the backward side behind the rotating tool of the FSW, and no flow occurs on the forward side. On the front side of the rotary tool, the friction is large on the forward side, and frictional heat due to the probe rotation is generated most. On the other hand, the amount of heat obtained from the laser is the same regardless of the laser irradiation position. That is, when the laser beam is irradiated on the forward side, the sample is softened and the frictional heat generated by the probe may be reduced. Compared with other irradiation positions, the heat generated by the probe rotation decreased, and the total amount of heat input from the laser and the heat generated by the probe rotation during the hybrid FSW decreased. Conversely, when the laser is irradiated on the backward side, the heat from the laser is supplied after the heat is sufficiently generated by the frictional heat between the rotating tool and the material from the forward side to the center on the front of the tool. It is considered to be.

FIG. 23 shows the relationship between the joining speed of 5-Center, 5-Adv side, and 5-Ret side and the stirring portion area. The flow rate increased most when the 5-Ret side condition was used. The amount of flow increases in the order of 5-Adv side <5-Center <5-Ret side. This is consistent with the result of temperature measurement. The joining speed of 500 mm / min at 5-Center and the joining speed of 500 mm / min at 5-Ret side are the conditions under which the highest stirrer strength was obtained. It can be seen that the time of the stirrer region of about 29 mm ² is optimal as before.

  Although the load on the rotating tool decreases as the flow rate increases, the maximum joining speed is most improved at 5-Center. In other words, although the 5-Ret side has a high temperature and a large amount of flow, the load on the rotating tool is greater than that of 5-Center. To explain this, it is necessary to clarify the flow of FSW.

  First, as shown in the FSW normal flow section 202 in FIG. 24, when the FSW comes into contact with the front surface of the rotary tool, almost all of the sample on the progress of the rotary tool flows toward the retracted side of the tool when joined. After that, it is considered that the material flows from the backward side to the forward side behind the rotary tool and is joined. Further, a place where the load is most applied to the rotary tool is indicated by a maximum frictional force region 203. The maximum frictional force region 203 as the high load portion exists in front of the probe 11 from the forward side to the center. The temperature and flow due to the difference in laser irradiation position (direction perpendicular to the bonding interface 201) based on the FSW mechanism will be described below. Since the rotary tool breakage mainly occurs in the probe 11, the shoulder 12 is not considered, and only the probe 11 is considered.

  FIGS. 25 to 27 show the flow around the probe 11 during joining of the 5-Center, 5-Adv side, and 5-Ret side. Under these three conditions, since the same amount of heat is obtained from the laser at the laser irradiation point 301, the difference in the maximum temperature reached in the high temperature portion 302 is considered to be due to the difference in the frictional heat of the tool. On the 5-Adv side, the front of the maximum frictional force region 203 is softened, so the frictional heat generated by the probe 11 is reduced and the total amount of heat is considered to be greatly reduced. Therefore, the flow amount became small. On the 5-Ret side, since the front of the maximum frictional force region 203 is not softened, the heat generated by the friction of the probe 11 is the largest among the three conditions. Thereafter, since the same amount of energy is input by the laser, the flow amount is considered to increase most among the three conditions. In 5-Center, the front of the probe 11 softened, the load on the probe 11 decreased most among the three conditions, and the flow amount increased because it was close to the backward side. However, because the softening range was small, heat was generated by friction with the sample on the forward side. Thus, it was found that the flow greatly affected the change of the laser irradiation position.

  It should be noted that the present invention is not limited to the above-described embodiment, and it is needless to say that various modifications can be made without departing from the gist of the present invention. For example, in the above-described embodiment, not only the FSW that moves in the processing direction while rotating the rotary tool, but also the spot FSW that does not move at the processing site while rotating the rotary tool, and the iron-based base material are abutted at the bonding site. The FSW and four modes of the FSW in which the iron tools are overlapped and the rotating tool is inserted from the side of the one iron base material to the overlapped portion, and a mode in which these are combined are included.

DESCRIPTION OF SYMBOLS 1a, 1b ... Friction stir welding apparatus, 10 ... Rotary tool, 20a, 20b ... High frequency induction heating source, 21 ... Coil, 22 ... Core, 30 ... Matching box, 40 ... Air cylinder, 100, 101 ... Iron base material.

Claims (7)

  A method of joining an iron-based material in which an iron-based base material is joined by friction stir welding, wherein at least a part of the joint portion of the iron-based base material is heated to a temperature at which friction stir welding can be performed independently. A method for joining ferrous materials, in which the joining parts are joined by friction stir welding later.   The high-frequency induction heating is performed so that at least a part of the joining portion of the iron-based base material is heated to a temperature at which friction stir welding can be performed alone or more, and then the joining portion is joined by friction stir welding. The method for joining ferrous materials as described in 1.   The iron according to claim 2, wherein at least a part of the joining portion of the iron-based base material is heated to a temperature of 600 ° C. or higher by high-frequency induction heating, and then at least a part of the joining portion is joined by friction stir welding. Bonding method of system materials.   The frequency of the high-frequency induction heating is decreased as the thickness of the plate-shaped iron-based base material is increased, and the frequency of the high-frequency induction heating is increased as the thickness of the iron-based base material is decreased. The method for joining ferrous materials as described in 1. In the high-frequency induction heating, the electrical resistivity ρ (μΩ), the relative magnetic permeability μ, and the frequency f (Hz) of the induction coil in the high-frequency induction heating are equal to the thickness δ (cm) of the plate-like iron base material. On the other hand, the joining method of the iron-type material of Claim 4 performed by satisfy | filling (delta) <= 10.06 ((rho) / ((micro | micron | f))) ^1/2 .   The joining method of the iron-type material of any one of Claims 1-5 using what consists of either ceramics or a cermet as a rotary tool used by the said friction stir welding. The method for joining ferrous materials according to claim 6, wherein a rotating tool used in the friction stir welding is made of any one of PCBN, Si ₃ N ₄ , SiC, and ZrO ₂ .