JP2010046678A - Friction stir welding method, method of manufacturing friction stir welded joint, and friction stir welded joint - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a friction stir welding method, a method of manufacturing a friction stir welded joint and a friction stir welded joint preventing the occurrence of blowholes. <P>SOLUTION: The friction stir welding method performs friction stir welding of high-nitrogen steel containing ≥0.08 mass% and ≤1.4 mass% nitrogen while controlling the friction heat generated between the high-nitrogen steel and a welding tool. The method of manufacturing the friction stir welded joint has a step of manufacturing the friction stir welded joint of the high-nitrogen steel containing ≥0.08 mass% and ≤1.4 mass% nitrogen by using the friction stir welding method. The friction stir welded joint is manufactured by the method of manufacturing the friction stir welded joint. <P>COPYRIGHT: (C)2010,JPO&INPIT

Description

  The present invention relates to a friction stir welding method, a friction stir welding joint manufacturing method, and a friction stir welding joint, and more particularly, a friction stir welding method for high nitrogen steel, a friction stir welding joint for high nitrogen steel. And a friction stir welded joint of high nitrogen steel.

  High nitrogen steel has excellent mechanical properties and corrosion resistance. Among high nitrogen steels, in particular, high nitrogen content austenitic stainless steel is desired to be used as a next-generation structural material. However, when high-nitrogen steel is joined, blowholes and chromium nitride (nitride), etc. resulting from nitrogen in the supersaturated solid solution are formed in the thermal cycle at the time of joining, so that it is difficult to obtain a good joint joint There is. As a joining method for solving such a problem, application of friction stir welding has been studied, but problems such as the occurrence of blowholes have been pointed out, and the present situation is that it has not been successful.

  Several techniques related to friction stir welding have been disclosed so far. For example, Patent Document 1 discloses a process of heating two metal materials that are austenitic stainless steel tempered by cold working to a predetermined temperature of 400 ° C. or higher and 550 ° C. or lower, and a metal heated by this step. There is disclosed a friction stir welding method including a step of abutting end portions of a material and performing friction stir welding along the end portions.

JP 2007-61885 A

  However, since the technique disclosed in Patent Document 1 is a technique for a normal austenitic steel, it cannot be immediately applied to high nitrogen steel. The main reasons are as follows. 1) High nitrogen steel has extremely high mechanical strength. Therefore, the control conditions are severely limited because it is necessary to prevent damage to the joining tool during joining. 2) When it is kept at a predetermined temperature in the range of 400 ° C. or more and 550 ° C., there is a concern about adverse effects such as precipitation of chromium nitride, and therefore the technique disclosed in Patent Document 1 is not applicable at all.

  The present invention has been made in view of the above problems. An object of the present invention is to provide a friction stir welding method, a friction stir welding joint manufacturing method, and a friction stir welding joint capable of preventing the occurrence of blowholes.

  The present inventors have found that by performing friction stir welding of high nitrogen steel under heat input control, it is possible not only to prevent the occurrence of blowholes but also to prevent softening of the joints, The present invention has been completed. The present invention will be described below.

  The first aspect of the present invention is to control the frictional heat generated between a high nitrogen steel containing 0.08 mass% or more and 1.4 mass% or less of nitrogen and the joining tool, A friction stir welding method characterized by performing friction stir welding.

  Here, in the present invention, “high nitrogen steel” is a concept including austenitic stainless steel, ferritic stainless steel, and duplex stainless steel having a duplex structure of austenite and ferrite. In the case of austenitic stainless steel, those containing 0.4 mass% or more of nitrogen, and in the case of ferritic stainless steel, those containing 0.08 mass% or more of nitrogen are classified as high nitrogen steel. The

  In the first aspect of the present invention, one or more selected from the group consisting of the shape of the joining tool, the rotational speed of the joining tool, the load applied to the high nitrogen steel through the joining tool, and the joining speed The frictional heat is preferably controlled by controlling at least two or more.

  In the first aspect of the present invention, it is preferable that the rotation speed of the welding tool is controlled to be not less than 100 revolutions per minute and not more than 600 revolutions per minute.

  In the first aspect of the present invention, it is preferable that the joining speed is controlled to be 50 mm / min or more and 300 mm / min or less.

  A second aspect of the present invention is a friction stir of high nitrogen steel containing 0.08% by mass or more and 1.4% by mass or less of nitrogen using the friction stir welding method according to the first aspect of the present invention. It is a manufacturing method of a friction stir welding joint characterized by having the process of manufacturing a joint joint.

  A third aspect of the present invention is a friction stir welded joint manufactured by the method for manufacturing a friction stir welded joint according to the second aspect of the present invention.

  According to the first aspect of the present invention, since friction stir welding of high nitrogen steel is performed while controlling frictional heat, it is possible to prevent the occurrence of blowholes in the stirring portion or precipitation of chromium nitride. In addition, a friction stir welding method can be provided.

  According to the second aspect of the present invention, there is provided a method for producing a friction stir welded joint capable of producing a good joint by preventing occurrence of blowholes or precipitation of chromium nitride. Can do.

  According to the third aspect of the present invention, it is possible to provide a friction stir welded joint in which generation of blowholes or precipitation of chromium nitride is prevented.

  Hereinafter, embodiments of the present invention will be described with reference to the drawings. The following embodiments are examples of the present invention, and the present invention is not limited to the illustrated embodiments.

1. Friction Stir Welding Method FIG. 1 is a diagram schematically showing an example of a friction stir welding method (hereinafter referred to as “the friction stir welding method of the present invention”) according to the first aspect of the present invention. As shown in FIG. 1, the friction stir welding method of the present invention uses a welding tool 1 and high nitrogen steels 2 and 2 (in the following, containing 0.08 mass% or more and 1.4 mass% or less of nitrogen). "High Nitrogen Steel 2a", "High Nitrogen Steel 2b", etc.) are joined by friction stir welding. In the friction stir welding method of the present invention, for example, the high nitrogen steels 2a and 2b arranged so as to abut end faces are brought into contact with the joining tool 1, and the joining tool 1 and the high nitrogen steels 2a and 2b are contacted via the joining tool 1. The welding tool 1 rotated at a predetermined rotational speed is moved along the abutting surface while applying a load toward. In this way, frictional heat is generated between the rotating joining tool 1 and the high nitrogen steels 2a and 2b, and the high nitrogen steels 2a and 2b can be softened by the generated frictional heat. Then, by moving the rotating joining tool 1, the joining portions of the high nitrogen steels 2a and 2b can be integrated by the plastic flow of the material, thereby joining the end faces of the high nitrogen steels 2a and 2b. can do.

  Thus, in the friction stir welding method, since the materials are joined without melting, the generation of blow holes can be suppressed as compared with arc welding, laser welding, or the like. However, the friction stir welding method of the present invention uses a high nitrogen steel containing 0.08% by mass or more and 1.4% by mass or less of nitrogen as a bonding material. If this is applied as it is, there is a concern that blowholes may be generated in the stirring section due to nitrogen in the supersaturated solid solution or chromium nitride may be precipitated. Therefore, in the friction stir welding method of the present invention, the generation of blow holes is prevented by controlling the amount of heat input generated between the welding tool 1 and the high nitrogen steels 2a and 2b. In the friction stir welding method of the present invention, the amount of heat input (friction heat) is controlled by the shape of the welding tool 1, the rotational speed of the welding tool 1, and the load applied to the high nitrogen steels 2a and 2b via the welding tool 1. And it controls through controlling at least one or two or more selected from the group which consists of the speed (joining speed) which joins high nitrogen steel 2a and high nitrogen steel 2b. Here, when the temperature of the high nitrogen steels 2a and 2b to which frictional heat is applied becomes equal to or higher than the melting point of the high nitrogen steels 2a and 2b (for example, 1200 ° C. or higher), bubbles (blow holes) are generated. Therefore, in the friction stir welding method of the present invention, the upper limit of the temperature of the high nitrogen steels 2a and 2b to which frictional heat is applied is less than the melting point of the high nitrogen steels 2a and 2b, and chromite is induced by heat input. In order to avoid the precipitation of the ride, the heat input is controlled to be appropriate.

  In the friction stir welding method of the present invention, the shape of the welding tool is a common shape as a welding tool for friction stir welding, and high nitrogen steels 2a and 2b can be friction stir welded without generating blow holes. If it is a shape, it will not specifically limit. In the friction stir welding method of the present invention, a shape having a probe (see FIG. 4 to be described later) or a shape having no probe (see FIG. 3 to be described later) depending on the thickness of the high nitrogen steels 2a and 2b to be joined. ) Can be selected as appropriate. Although the effect of the probe is not certain, it is considered that the interface can be intensively joined by stirring the metal in the thickness direction over a wide range using a joining tool having a probe immediately above the joining line. Although it is considered that the stirring motion by the probe at the time of heat input control contributes to the promotion of the heat generation, by controlling the heat input, it is possible to prevent the occurrence of blowholes. The probe is for propagating the stirring force of the welding tool in the depth direction of the bonding material, and the progress of the stirring region in the depth direction can be confirmed even in the case of high nitrogen steel. In the friction stir welding method of the present invention, when joining high nitrogen steels 2a and 2b having a thickness that can be joined even using a joining tool having no probe, it is possible to prevent the occurrence of holes corresponding to the probe or to join them. From the viewpoint of extending the tool life, it is preferable to use a joining tool having a shape that does not have a probe.

  In the friction stir welding method of the present invention, the material of the welding tool 1 is not particularly limited as long as it can withstand the environment when the high nitrogen steels 2a and 2b are friction stir welded. In addition to ceramic materials such as boron nitride (PCBN), known refractory metal materials and cemented carbides can be used. However, cemented carbide is advantageous from the viewpoint of keeping the heat input low.

  In the friction stir welding method of the present invention, the rotation speed of the welding tool 1 is not particularly limited as long as it is a rotation speed capable of friction stir welding the high nitrogen steels 2a and 2b without generating blowholes. However, for example, it is preferable that the rotation speed is 100 to 600 revolutions per minute.

  In the friction stir welding method of the present invention, the load applied to the high nitrogen steels 2a and 2b via the welding tool 1 can friction stir weld the high nitrogen steels 2a and 2b without generating blowholes. If it is a load, it will not specifically limit. The load applied to the high nitrogen steels 2a and 2b by the friction stir welding method of the present invention is preferably, for example, 2500 kg or more and 5000 kg or less.

  Further, in the friction stir welding method of the present invention, the high nitrogen steel 2a and the high nitrogen steel 2b can be joined at a speed (joining speed) by which the high nitrogen steel 2a and 2b can be friction stir welded without generating a blowhole. The speed is not particularly limited. The joining speed in the friction stir welding method of the present invention is preferably, for example, 50 mm / min or more and 300 mm / min or less.

2. Friction stir welded joint manufacturing method and friction stir welded joint FIG. 2 is a diagram schematically showing an example of a friction stir welded joint 3 manufactured by the friction stir welded joint manufacturing method of the present invention. The manufacturing method of the friction stir welded joint according to the present invention and the friction stir welded joint according to the present invention will be described with reference to FIGS.

  The friction stir welded joint manufacturing method of the present invention is a form shown in FIG. 2 by friction stir welding of high nitrogen steels 2a and 2b while controlling frictional heat by the friction stir welding method of the present invention shown in FIG. The step of manufacturing the friction stir welded joint 3 is provided. As described above, according to the friction stir welding method of the present invention, by controlling the frictional heat, it is possible to prevent the occurrence of blowholes and precipitation of chrome nitride in the stirring portion. Blow holes are not generated in the stirring portion 3a of the friction stir welding joint 3 manufactured by the method for manufacturing a joint joint, and chromium nitride is not precipitated. If the generation of blowholes and the precipitation of chromium nitride are prevented, it becomes possible to suppress the decrease in mechanical strength and the deterioration of crevice corrosion. According to the present invention, the occurrence of blowholes and chromium It is possible to provide a method for producing a friction stir welded joint that can produce a good friction stir welded joint 3 by preventing precipitation of nitride. And since the friction stir welded joint manufactured by the manufacturing method prevents the generation of blowholes and the precipitation of chromium nitride, according to the present invention, the generation of blowholes and the precipitation of chromium nitride are prevented. The friction stir welded joint 3 can be provided.

  The present invention will be further described with reference to the results of the examples.

1) Specimen and friction stir welding 1 mass% nitrogen-containing austenitic stainless steel produced by a pressure ESR method (Pressurized Electro-slag remelting) was used as a specimen. Table 1 shows the composition of the test material.

  The shape of the specimen before processing was length × width × thickness = 247 mm × 77 mm × 7 mm. After cutting this specimen, it was adjusted to a predetermined thickness by hot rolling and cold rolling. Thereafter, the test material adjusted to a predetermined thickness was subjected to a solution treatment under the condition of 1230 ° C. × 30 min using a stainless steel pack. Thereafter, the sample material that had undergone the solution treatment was cooled with water and brushed to completely remove the scale. Through this process, a plate of length × width × thickness = 300 mm × 30 mm × 1 mm or 2 mm was taken out and used for the friction stir welding test. The joint shape was butt. A joining tool made of a hard metal (tungsten carbide (W, C)) and a ceramic material (silicon nitride (N, Si)) was used. As for the shape of the joining tool, the former (tungsten carbide) has two types, with and without a probe. The latter (silicon nitride) was one type with a probe. Friction stir welding was performed using argon gas (flow rate: 20 L / min) as a shielding gas in order to prevent oxidation of the welding tool and the joint surface. Fig. 3 shows the cross-sectional configuration of the welding tool and the test material when the test material is friction stir welded using a welding tool without a probe, and Fig. 4 shows the friction of the test material using a welding tool with a probe. The cross-sectional forms of the welding tool and the test material at the time of stir welding are shown. Table 2 shows the friction stir welding conditions. The friction stir welding is not shown in FIGS. 3 and 4, but a backing plate was placed on the test material, and both ends of the test material were fixed with a restraining jig.

In Table 2, condition A corresponds to a condition using a bonding tool without a probe. Conditions B to D correspond to conditions for using a bonding tool with a probe, and “φ6 × 1.8” and “φ6 × 1.9” in Table 2 indicate the dimensions of the probe. Conditions A to D in Table 2 are all included in the technical scope of the present invention.

2) Macro observation In FIG. 2 shows a photograph of a friction stir welded joint (Example) obtained by friction stir welding 2 and a friction stir welded joint (Reference Example) obtained by friction stir welding under the conditions described below. FIG. 5A is a photograph showing the surface of the friction stir welded joint according to the example (the surface to which a load is applied via the joining tool; the same applies hereinafter), and FIG. It is a photograph which shows the back surface (surface on the opposite side of the said surface. The following is the same) of the friction stir welding joint concerning an example. FIG. 5C is a photograph showing the surface of the friction stir welded joint according to the reference example, and FIG. 5D is a photograph showing the back surface of the friction stir welded joint according to the reference example. In addition, the conditions at the time of manufacturing the friction stir welding joint concerning a reference example were set to the rotational speed of 500 rpm, the joining speed of 100 mm / min, and the load of 2000 kgf or less (a joining tool is the same as the conditions C).

3) Microstructure observation After the friction stir welded joint manufactured by friction stir welding under the above conditions is cut along a plane whose joining direction is the normal direction, wet polishing using emery paper (up to # 1500) is performed. Then, buffing using a diamond abrasive (up to a diamond paste having a particle size of 1 μm) was performed. Thereafter, the cut surface was etched using aqua regia, and the cut surface was observed using an optical microscope. FIG. 6 shows a structure photograph of the cut surface. FIG. 6A shows a friction obtained by friction stir welding of a test material having a thickness of 1 mm (the test material No. 1) under the condition A using a joining tool (tungsten carbide) without a probe. It is a photograph which shows the cross-sectional structure of a stir weld joint. Further, FIG. 6B is obtained by friction stir welding a test material having a thickness of 2 mm (the test material No. 2) under the condition B using a joining tool (tungsten carbide) with a probe. 3 is a photograph showing a cross-sectional structure of a friction stir welded joint. Moreover, FIG.6 (c) is obtained by carrying out friction stir welding of the test material of 2 mm thickness (the said test material No. 2) on the said conditions C using the joining tool (tungsten carbide) with a probe. 3 is a photograph showing a cross-sectional structure of a friction stir welded joint. Further, FIG. 6D is obtained by friction stir welding of a test material having a thickness of 2 mm (the test material No. 2) under the above condition D using a bonding tool with a probe (silicon nitride). 3 is a photograph showing a cross-sectional structure of a friction stir welded joint.

4) Hardness test JIS Z 2244: 2003 “Vickers hardness test-test method” with a maximum measurement interval of 25 mm from the advance side (Advancing Side) to the retreat side (Retreating Side) centering on the joint interface The Vickers hardness test specified in Section 1 was performed, and the Vickers hardness of the cross section was measured. The test force was 4.9 N, and the indenter spacing was 500 μm. FIG. 7 shows the results of the Vickers hardness test. “Condition A” in FIG. 7 means the test result of the friction stir welded joint shown in FIG. 6 (a), and “Condition B” in FIG. 7 indicates the friction stirrer shown in FIG. 6 (b). 7 indicates that the result is a test result of the joint joint, and “Condition C” in FIG. 7 indicates the test result of the friction stir weld joint illustrated in FIG. 6C, and “silicon nitride” in FIG. Means a test result of the friction stir welded joint shown in FIG.

5) Nitrogen measurement By measuring the nitrogen content of the base material and the stirring part, the presence or absence of denitrification in the stirring part was investigated. The results are shown in FIG. The vertical axis | shaft of FIG. 8 is nitrogen content (mass%). In addition, “X” in FIG. 8 means a base material, “Y” in FIG. 8 means a joint, and “Condition B”, “Condition C”, and “Condition D” in FIG. Means a friction stir welded joint obtained by friction stir welding under conditions B, C and D. Further, the “accepting material” in FIG. 8 means a test material that is not subjected to friction stir welding.

6) Results As shown in FIGS. 5 (a) and 5 (b), the friction stir welded joint according to the example was completely joined, but is shown in FIGS. 5 (c) and 5 (d). As described above, the friction stir welded joint according to the reference example was not completely joined. 6 (a) to 6 (d), the friction stir welded joint manufactured using the friction stir welding method of the present invention has a very fine structure in the stirrer in any joining condition. The occurrence of blow holes and cracks was not confirmed. That is, according to the present invention, it was confirmed that it is possible to provide a friction stir welding method, a friction stir welding joint manufacturing method, and a friction stir welding joint capable of preventing the occurrence of blowholes. Moreover, from FIG.6 (b)-FIG.6 (d), the stirring amount could be increased by using a joining tool with a probe with respect to the high nitrogen steel whose plate | board thickness is 2 mm. In addition, in this example, it was confirmed that blowholes, cracks, and the like do not occur when 1 mass% nitrogen-containing austenitic stainless steel is used as the bonding material. Furthermore, as shown in FIG. 8, when the amount of nitrogen in the stirrer of the friction stir welded joint according to the example was measured, the nitrogen content of the base material and the nitrogen content of the stirrer were similar, It was confirmed that no denitrification occurred in the stirring portion of the friction stir welded joint. Since the upper limit of nitrogen that can be contained in the high nitrogen steel at 1 atm is considered to be 1.4% by mass, the technical idea of the present invention in which denitrification does not occur in the stirring section is as follows. It is considered that the present invention can be applied to high nitrogen steel containing 4% by mass or less of nitrogen. On the other hand, as described above, as the amount of nitrogen contained in the high nitrogen steel increases, it is considered that blowholes are likely to occur. From the results of the examples, austenitic stainless steel containing 1% by mass of nitrogen. It was confirmed that by applying the present invention to steel, the occurrence of blow holes and cracks can be prevented. Therefore, it is considered that even if the amount of nitrogen contained in the high nitrogen steel is reduced to 0.08% by mass, it is possible to prevent the occurrence of blow holes and cracks by applying the present invention. That is, the technical idea of the present invention can be applied not only to austenitic stainless steel containing 1% by mass of nitrogen but also to high nitrogen steel containing 0.08% by mass to 1.4% by mass of nitrogen. It is believed that there is.

On the other hand, the phenomenon that the friction welding part of high nitrogen steel softens under the influence of sensitization by heat input has been reported so far. However, from FIG. 7, the friction stir welded joint manufactured according to the present invention does not change in hardness significantly when the joint is cured (conditions B, C, and silicon nitride) due to the difference in heat input. The case (condition A) was divided and no softening of the joint was observed.
Since the softening of the joint is considered to be a phenomenon suggesting elemental segregation or sensitization accompanying the precipitation of chromium nitride, it is also a result confirming that the joint of the present invention is good. As described above, according to the present invention, the friction stir welding method, the friction stir welding joint manufacturing method, and the friction stir welding joint capable of preventing the softening of the joint in addition to preventing the occurrence of blowholes, and the friction stir welding joint It was confirmed that it was possible to provide.

It is a figure which shows roughly the example of a form of the friction stir welding method of this invention. It is a figure which shows schematically the example of a form of the friction stir welding joint manufactured by the manufacturing method of the friction stir welding joint of this invention. It is a conceptual diagram which shows the cross-sectional form of the joining tool without a probe, and the test material joined. It is a conceptual diagram which shows the cross-sectional form of the joining tool with a probe, and the test material joined. It is a figure which shows the photograph of a friction stir welding joint. Fig.5 (a) is a photograph which shows the surface of the friction stir welding joint concerning Example. FIG.5 (b) is a photograph which shows the back surface of the friction stir welding joint concerning an Example. FIG.5 (c) is a photograph which shows the surface of the friction stir welding joint concerning a reference example. FIG.5 (d) is a photograph which shows the back surface of the friction stir welding joint concerning a reference example. It is a figure which shows the structure | tissue photograph of a cut surface. FIG. 6A is a photograph showing a cross-sectional structure of a friction stir welding joint that has been friction stir welded using a welding tool (tungsten carbide) without a probe. FIG. 6B is a photograph showing a cross-sectional structure of a friction stir welding joint that has been friction stir welded using a welding tool with a probe (tungsten carbide). FIG. 6C is a photograph showing a cross-sectional structure of a friction stir welding joint that has been friction stir welded using a welding tool with a probe (tungsten carbide). FIG. 6D is a photograph showing a cross-sectional structure of a friction stir welding joint that has been friction stir welded using a welding tool with a probe (silicon nitride). It is a figure which shows the result of a Vickers hardness test. It is a figure which shows a nitrogen measurement result.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 ... Joining tool 2a, 2b ... High nitrogen steel 3 ... Friction stir welding joint 3a ... Stirring part

Claims (6)

The friction stir welding of the high nitrogen steel is performed while controlling the frictional heat generated between the high nitrogen steel containing 0.08% by mass to 1.4% by mass of nitrogen and the welding tool. Friction stir welding method. Controlling at least one or more selected from the group consisting of the shape of the joining tool, the rotational speed of the joining tool, the load applied to the high nitrogen steel via the joining tool, and the joining speed. The friction stir welding method according to claim 1, wherein the frictional heat is controlled by. The friction stir welding method according to claim 2, wherein the rotation speed of the welding tool is controlled to be not less than 100 revolutions per minute and not more than 600 revolutions per minute. The friction stir welding method according to claim 2 or 3, wherein the joining speed is controlled to 50 mm / min or more and 300 mm / min or less. The process of manufacturing the friction stir welding joint of the high nitrogen steel containing 0.08 mass% or more and 1.4 mass% or less of nitrogen using the friction stir welding method of any one of Claims 1-4. A method for producing a friction stir welded joint, comprising: A friction stir welded joint manufactured by the method for manufacturing a friction stir welded joint according to claim 5.