Abstract:
Dissimilar metal welds including a buttering portion with a small variation in strength distribution in a plate thickness direction are formed by welding two parent materials having at least one of different compositions and different refining conditions through a buttering for alleviating mismatch between one of the different compositions and the different refining conditions of the two members and through a welded metal for joining one of the parent materials and the buttering. The buttering is formed of welding metals laminated in a plate thickness direction, and a dilution ratio of the buttering with the parent materials is 50% or less. The manufacturing method includes performing butt welding on a dummy material formed by increasing a groove depth by providing a member on a bottom side of a welding groove and on parent materials by using the buttering; and processing a groove within a welding metal formed of the buttering.

Description:
BACKGROUND OF THE INVENTION 
       [0001]    1. Field of the Invention 
         [0002]    The present invention relates to dissimilar metal welds and its manufacturing method, and more particularly, to a product obtained by welding and integrating two different materials of large welded structures such as the turbine rotor, and its manufacturing method. 
         [0003]    2. Background Art 
         [0004]    Some large welded structures are laterally placed and welded due to limitations of deformation of their shapes, work space, and the like. Examples of the structures include a turbine rotor to be welded. In general, a large steam turbine rotor has a large shaft length. In addition, a high-pressure-side rotor is required to have a high-temperature creep rupture strength, and a low-pressure-side rotor is required to have a tension strength and toughness. Therefore, in the case of forming a steam turbine rotor using one member, it has been difficult to obtain characteristics that satisfy these demands. In this regard, there is known a manufacturing method in which a high-pressure-side rotor is made of a material excellent in high-temperature creep rupture strength; a low-pressure-side rotor is made of a material excellent in tension strength and toughness; and these materials are integrated by welding. 
         [0005]    However, when the rotor is welded, a heat affected zone (HAZ) is formed in the parent material of the rotor. This HAZ includes a rapid cooling structure region with a high hardness and an over aging region with a low hardness. Accordingly, a strength uneven region is generated in the HAZ. In the case where the rotor is formed of a combination of the same materials by welding, the unevenness of the strength is alleviated by performing stress relief annealing after welding. Meanwhile, in the case where the rotor is formed of a combination of dissimilar metals, heat treatment temperatures required for the stress relief of the rotor are different. For this reason, the effect of alleviating the unevenness of the strength caused by heat treatment cannot be expected. 
         [0006]    Accordingly, as disclosed in JP Patent Application Publication No. 2001-123801, JP Patent Application Publication No. 2000-64805, and JP Patent Examined Application Publication No. 6-78721, for example, there are known methods of forming a buttering portion to achieve relaxation of the chemical composition of each of a rotor and a weld on a groove face of the rotor, before welding the rotor in the case of welding the rotor made of dissimilar metals. These methods use a weld having a chemical composition located between the rotor and the welding material, and perform padding welding on the buttering portion by tungsten inert gas arc (TIG) welding, metal inert gas (MIG) welding, submerged arc welding (SAW), or the like. 
         [0007]    JP Patent Application Publication No. 2007-278064 proposes a method of performing butt welding using a buttering material and forming a buttering portion from a welding metal. 
         [0008]    In the dissimilar metal welds including the buttering portion disclosed in JP Patent Application Publication No. 2001-123801, JP Patent Application Publication No. 2000-64805, and JP Patent Examined Application Publication No. 6-78721, a laminated direction of a buttering is perpendicular to the plate thickness of the parent material and thus coincides with a stress loading direction, leading to deterioration in strength reliability. Further, the buttering is applied to an end (plane) of a parent material. As a result, the shielding effect is reduced and the oxygen concentration of the welding metal is increased, leading to deterioration in strength. 
         [0009]    Further, in the dissimilar metal welds including a buttering layer disclosed in JP Patent Application Publication No. 2007-278064, the bottom of the buttering is located in a butt portion with great dilution between the welding metal and the parent material, which deteriorates the strength reliability. Furthermore, the outer peripheral end of the buttering portion is located in the vicinity of an opening of a welding groove, which produces the same conditions as those for the buttering to be subjected to padding welding on the plane as disclosed in JP Patent Application Publication No. 2001-123801, JP Patent Application Publication No. 2000-64805, and JP Patent Examined Application Publication No. 6-78721. Thus, there is a problem of deterioration in strength due to an increase in oxygen concentration of the welding metal. 
         [0010]    To solve the above-described problems, the present invention has an object to provide dissimilar metal welds which are formed by welding two parent materials having at least one of different compositions and different refining conditions and which include a buttering portion with a small variation in strength distribution in a plate thickness direction, and a manufacturing method of the dissimilar metal welds. 
       SUMMARY OF THE INVENTION 
       [0011]    To achieve the above-described object, the present inventor(s) has (have) researched the composition distribution of butt welding metals to obtain a buttering portion. As a result, it has turned out that a butt portion corresponding to the bottom of the buttering portion is formed by mixing two parent materials to be butted against the welding metals, and has a high dilution ratio. Further, it is obvious that in a welding opening corresponding to a surface layer portion of the buttering portion, the oxygen concentration is higher than that of a central portion and the strength reliability is lowered. 
         [0012]    On the basis of the above results, according to an aspect of the present invention, dissimilar metal welds are formed by welding two parent materials having at least one of different compositions and different refining conditions, through a buttering for alleviating mismatch between one of the different compositions and the different refining conditions of the two members and through a welded metal for joining one of the parent materials and the buttering. The buttering is formed of welding metals laminated in a plate thickness direction, and a dilution ratio of the buttering with the parent materials is equal to or less than 50%. 
         [0013]    According to another aspect of the present invention, there is provided a manufacturing method of dissimilar metal welds formed by welding two parent materials having at least one of different compositions and different refining conditions, through a buttering for alleviating mismatch between one of the different compositions and the different refining conditions of the two members and through a welded metal for joining the buttering and one of the parent materials, the manufacturing method including at least the steps of performing butt welding on a dummy material formed by increasing a groove depth by providing a member on a side of a bottom of a welding groove, and on the parent materials, by using the buttering; and processing a groove within a welding metal formed of the buttering. 
         [0014]    According to the present invention, buttering is formed of welding metals laminating in a plate thickness direction, and the dilution ratio of the bottom of the buttering portion and the oxygen concentration of the surface layer portion of the buttering portion are low, which makes it possible to set the dilution ratio to 50% or less. Consequently, it is possible to provide an effect of preventing the deterioration in strength of the welding metal due to an increased in oxygen concentration, and improving the strength reliability of large welded structures such as the turbine rotor. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0015]      FIG. 1  schematically shows a side surface of a tungsten-inert gas welding apparatus when dismissal metals of an exemplary turbine rotor are welded. 
           [0016]      FIG. 2 , (A) to (E) schematically show a manufacturing flow of welding two members made of different materials according to Example 1. 
           [0017]      FIG. 3 , (A) to (E) schematically show a manufacturing flow of welding two members made of different materials according to a related art method. 
           [0018]      FIG. 4 , up and down, shows an impact test result showing an effect of welding metals in a laminated direction as an example of a mechanical characteristic evaluation result of a buttering  22 . 
           [0019]      FIG. 5A  shows a case of performing padding welding on a plane in a welding method using a buttering material, and  FIG. 5B  shows a case of butt welding on a groove in the welding method using the buttering material. 
           [0020]      FIG. 6 , (A) to (E), is schematic diagrams showing a flow of manufacturing dissimilar metal welds of another related art method. 
           [0021]      FIGS. 7A and 7B  show schematic diagrams of a model for estimating an dilution ratio. 
           [0022]      FIG. 8 , (A) to (E), shows a flow of manufacturing welding two members made of different materials according to Example 2. 
           [0023]      FIG. 9 , (A) to (E), shows a flow of manufacturing dissimilar metal welds according to Example 3. 
           [0024]      FIG. 10 , (A) to (E), shows a flow of manufacturing dissimilar metal welds according to Example 4. 
       
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
       [0025]    Examples will be described below as embodiments for carrying out the present invention. 
       Example 1 
       [0026]    Example 1 of the present invention will be described below with reference to  FIGS. 1 to 6 . Though Example 1 illustrates dismissal metal welds of a turbine rotor as dissimilar metal welds, dissimilar metal welds of other product may also be used. The specifications and composition ranges of two dissimilar metals forming the welds are shown in the following Table 1. Example 1 uses an Ni-base superalloy and 12%-Cr steel from Table 1, and these components constitute the dissimilar metal welds. 
         [0000]    
       
         
               
               
               
               
               
               
               
               
               
               
             
               
               
               
               
               
               
               
               
               
             
           
               
                 TABLE 1 
               
               
                   
               
             
             
               
                 Kinds of steels 
                 C 
                 Mn 
                 Ni 
                 Cr 
                 Mo 
                 W 
                 Nb 
                 Co 
                 B 
               
               
                   
               
               
                 Ni-base superalloy 
                 0.05~0.20 
                   
                 bal. 
                     13~15.5 
                 0.1~2.0 
                 4.5~10  
                 0.1~1.0 
                 5~15 
                 0.001~0.03 
               
               
                 Ni—Fe-base 
                 ≦0.05 
                   
                 bal. 
                 14~16 
                   
                   
                 1.9~2.7 
               
               
                 superalloy 
               
               
                 12% Cr steel 
                 0.1~0.2 
                 0.3~1.0 
                 ≦1 
                  9~13 
                 0.1~1.5 
                 0.2~5.0 
                 0.02~0.1  
                 ≦3 
               
               
                 1% Cr—Mo—V steel 
                  0.25~0..35 
                 0.5~1     
                 ≦1 
                 0.8~1.5 
                 1.0~1.5 
               
               
                 3~4% Ni—Cr—Mo—V- 
                 0.17~0.32 
                 0.2~0.4 
                 3~4 
                 1.25~2.0  
                 0.25~0.60 
               
               
                 based steel 
               
               
                   
               
             
          
           
               
                   
                 Kinds of steels 
                 V 
                 Ti 
                 Al 
                 Ta 
                 Hf 
                 Zr 
                 Fe 
               
               
                   
                   
               
               
                   
                 Ni-base superalloy 
                   
                 0.1~2.0 
                 4.0~5.5 
                 0.1~3.0 
                 0.1~2.0 
                 0.01~0.1 
               
               
                   
                 Ni—Fe-base 
                   
                 1.2~1.7 
                 1.1~1.5 
                   
                   
                   
                 30~40 
               
               
                   
                 superalloy 
               
               
                   
                 12% Cr steel 
                   
                   
                   
                   
                   
                   
                 bal. 
               
               
                   
                 1% Cr—Mo—V steel 
                 0.2~0.3 
                   
                   
                   
                   
                   
                 bal. 
               
               
                   
                 3~4% Ni—Cr—Mo—V- 
                 0.05~0.15 
                   
                   
                   
                   
                   
                 bal. 
               
               
                   
                 based steel 
               
               
                   
                   
               
               
                   
                 (mass %) 
               
             
          
         
       
     
         [0027]      FIG. 1  schematically shows a side surface of a tungsten-inert gas welding apparatus when dissimilar metals of a steam turbine rotor are welded, for example. This welding apparatus includes at least a drive unit  5 , a welding unit  6 , a control unit  10 , a signal cable  8  for transmitting and receiving signals between the drive unit  5  and the control unit  10 , and a signal cable  9  for transmitting and receiving signals between the welding unit  6  and the control unit  10 . The drive unit  5  is at least configured to be able to move in the vicinity of a weld  3  in a shaft direction and a circumferential direction of a turbine rotor  1 . The welding unit  6  is configured to form the weld  3  by inputting heat into a parent material  1 . The drive unit  5  shown in  FIG. 1  is an autonomous-type unit that moves in contact with a welding structure (turbine rotor). Alternatively, the drive unit  5  may be moved by an external force of an operation arm or the like, for example. 
         [0028]    Example 1 uses a tungsten-inert gas (TIG) welding with a heat input amount of 20 KJ/cm. Alternatively, other methods such as submerge ark welding (SAW), shielded metal ark welding (SMAW), metal inert gas (MIG) welding, laser welding, and CMT (Cold Metal Transfer) may also be used. 
         [0029]      FIG. 2  schematically shows a manufacturing flow of welding two members made of different materials according to Example 1. The flow will be described below with reference to (A) to (E). 
         [0030]      FIG. 2  (A) shows the step of butting a parent material  20  and a dummy material  21 . The heat capacity of the dummy material  21  is preferably set to the same level as that of the parent material  20  so that unevenness of the cooling rate during welding can be suppressed. It is more preferable that the material of the dummy material  21  is the same as the parent material  20 . The plate thickness of the dummy material  21  is set to be greater than that of the parent material  20 . 
         [0031]    The bottom of the dummy material  21  extends beyond an end of the parent material  20  so as to overlap the parent material  20 . In Example 1, the plate thickness of the bottom of the dummy material  21  extending to the side of the parent material  20  is 3 mm, but the plate thickness may be equal to or more than 3 mm. When the plate thickness is less than 3 mm, a portion having a high dilution ratio unfavorably remains in the buttering  22  to be subsequently processed. In this case, however, the plate thickness of the bottom of the dummy material  21  is preferably as small as possible as long as the plate thickness is 3 mm or more, and a maximum length of 10 mm is sufficient. 
         [0032]    The length of the bottom of the dummy material  21  extending to the side of the parent material  20  is 10 mm from the center of the groove, but a length of 3 mm or more is sufficient. A bottom length of less than 3 mm is not favorable, because there is a problem in that a hole is generated in the shape of the butting groove portion, or the thickness of the groove portion is reduced with the result that the groove portion is melted down. Note that the bottom length of the dummy material  21  is preferably as small as possible as long as the bottom length is equal to or larger than 3 mm from the center of the groove, and a maximum length of 15 mm from the center of the groove is sufficient. 
         [0033]      FIG. 2  (B) shows the state of the step of performing butt welding on the groove of each of the parent material  20  and the dummy material  21  by using a welding metal material for the buttering  22 . 
         [0034]      FIG. 2  (C) shows the state of the step of processing the groove of the buttering  22  by removing a part of each of the dummy material  21  and the buttering  22 . By this step, the buttering  22  is formed of welding metals laminated in the same direction as the plate thickness direction of the parent material  20 . 
         [0035]      FIG. 2  (D) shows the state of the step of butting the parent material  23  and the buttering  22 . The buttering  22  is obtained so that the dilution ratio of the butt portion becomes 50% or less, and the groove is processed with respect to the end thereof. 
         [0036]      FIG. 2  (E) shows the state of the step of performing butt welding using a welded metal  24  with respect to the groove of each of the parent material  23  and the buttering  22 . 
         [0037]      FIG. 3  schematically shows a manufacturing flow of welding two members made of different materials by a related art method, for comparison with the present invention. The related art method illustrated herein greatly differs from the method of Example 1 in the step of forming the face of the parent material  20  shown in  FIG. 3A  into a plane and in the step of performing padding welding using the buttering  22  on the face of the parent material  20  shown in  FIG. 3B . In the step of forming the face of the parent material  20  shown in  FIG. 3A  into a plane, butting against the dummy material  21  shown in  FIG. 2A  is not carried out. In the step of performing padding welding using the welding material of the buttering  22  on the face of the parent material  20  shown in  FIG. 3B , padding welding is performed such that the laminated direction of the padding welds made of the welding material of the buttering  22  becomes perpendicular to the plate thickness direction of the parent material  20 , and the laminated direction of the padding welds is different by 90 degrees from the plate thickness direction of the parent material  20  shown in  FIG. 2B , as compared to layers laminated in the same direction. 
         [0038]    Referring next to  FIGS. 4 , and  5 A and B, an advantageous effect of the dissimilar metal welds of Example 1 will be described.  FIG. 4  shows an impact test result as an example of the mechanical characteristic evaluation result of the buttering  22 . In the upper figure of  FIG. 4 , (a) illustrates that a notch direction of an impact test piece is perpendicular to the laminated direction and (b) illustrates that the notch direction of the impact test piece coincides with the laminated direction. As a result of the impact test, the value of the impact absorption energy of the impact test piece (b) is about ten times higher than the value of the impact test piece (a). Thus, it has turned out that in the welding structure in which a stress is applied in the plate thickness direction, when the laminated direction of the buttering  22  coincides with the plate thickness direction, the anti-shock property is excellent and more favorable in view of the strength reliability, as compared to the case where the laminated direction of the buttering  22  is perpendicular to the plate thickness direction. Accordingly, in Example 1 according to the present invention, the laminated direction of the buttering  22  is set to coincide with the thickness direction of the parent material based on the same idea of the impact test piece (b), which contributes to an improvement in the strength reliability. 
         [0039]      FIGS. 5A and 5B  schematically show a welding method using the material of the buttering  22 .  FIG. 5A  schematically shows a method of performing padding welding on a plane by a related art method.  FIG. 5B  schematically shows a method of performing butt welding on a groove according to Example 1 of the present invention. 
         [0040]    In the case of performing padding welding on the plane shown in  FIG. 5A , a shielding gas for TIG welding spreads, which deteriorates the shielding performance with respect to the welding metal. On the other hand, in the case of performing butt welding on the groove shown in  FIG. 5B , the shielding gas is concentrated in the groove, leading to an improvement in the shielding performance with respect to the welding metal. The shielding performance affects the strength based on the oxidation degree of the welding metal. As a matter of course, the strength increases as the oxidation degree decreases, and the strength decreases as the oxidation degree increases. Accordingly, in Example 1 of the present invention, the method of obtaining the buttering  22  is set based on the same idea as that shown in  FIG. 5B , which contributes to an improvement in the strength. 
         [0041]      FIG. 6 , (A) to (E), shows a flow of manufacturing dissimilar metal welds in another related art method for comparison with Example 1 of the present invention. Example 2 differs from Example 1 of the present invention in the plate thickness of the dummy material  21  shown in  FIG. 6  (A) and in the dilution ratio of the butt portion of the buttering  22  shown in  FIG. 6  (C). In the case of manufacturing the dissimilar metal welds in accordance with the manufacturing flow shown in  FIG. 6 , the dilution ratio of the bottom of the weld using the buttering  22  becomes 50% or more by dilution of the parent material  20  and the dummy material  22  as shown in  FIG. 6  (B). The dilution ratio is defined as in Formula 1. 
         [0000]      (dilution ratio)=1−(volume of welding metal for first layer welding)/(volume of fusion zone by first layer welding)  (1)
 
         [0042]    According to Formula 1, the dilution ratio is determined by the welding metal for the first layer welding and the volume of the fusion zone obtained by the first layer welding. Here, the dilution ratios in various groove shapes are estimated. 
         [0043]      FIGS. 7A and 7B  show a model for estimating a dilution ratio.  FIG. 7A  shows an object of a model, and  FIG. 7B  shows a simple model. In  FIG. 7B , “x” represents the width of a fusion zone obtained by the first layer welding; “y” represents the depth of the welding metal for the first layer welding, and “z” represents a butt height. The model formula shown in Formula 2 was used as an estimating method. 
         [0000]      (dilution ratio)=1 −y /(2 z+y )  (2)
 
         [0044]    In Formula 2, since “x” has no relation with the estimation of the simple model, the dilution ration was estimated using “y” and “z” as variables. The actual “y” is in the range of 1 to 3 mm under the conditions for forming the welding metal. Further, the actual “z” is in the range of 1 to 3 mm under the condition of forming a sound penetration. As a result of estimating the dilution ratio within the variance range of the actual “y” and “z”, the range was 0.6 to 0.7. Thus, when the dilution ratio is high, the characteristics of the buttering portion deteriorate to be lower than the originally intended value. Therefore, it is preferable that the dilution ratio be at least 50% or less, and preferably 25% or less. 
         [0045]    On the other hand, the buttering  22  shown in  FIG. 6  (C) needs to be obtained from a portion having a dilution ratio of 50% or more as shown in  FIG. 6  (B), so that the deterioration in characteristics is unavoidable. In view of the above, Example 1 eliminates the need to obtain the buttering from a portion having a dilution ratio of 50% or more, thereby avoiding the characteristic deterioration. 
       Example 2 
       [0046]    Example 2 according to the present invention will be described with reference to  FIG. 8 , (A) to (E). Example 1 has characteristics involving the shape on the bottom side of the weld in the manufacturing method of the dissimilar metal welds, whereas Example 2 has characteristics involving the bottom side as well as the opening side of the weld in the manufacturing method of the dissimilar metal welds. The description of the characteristics identical with those of the Example 1 is herein omitted and only the differences from Example 1 will be described below. 
         [0047]      FIG. 8 , (A) to (E), shows a manufacturing flow of welding two members made of different materials according to Example 2. Example 2 differs from Example 1 only in  FIGS. 8 , (A) and (B).  FIG. 8  (A) shows the state of the step of butting the parent material  20  and the dummy material  21 . In the vicinity of the opening of each of the parent material  20  and the dummy material  21 , a shielding plate  25  is mounted to increase the depth of the welding groove. The shielding plate of Example 2 has a height of 10 mm and a width of 3 mm. Although the shielding plate may have a height of more than 10 mm and a width of more than 3 mm from a functional point of view, a minimum height and a minimum width are desirable in terms of cost. When the height is less than 10 mm, the concentration effect of the shielding gas within the welding groove is not exerted. Accordingly, oxygen is included in the weld in the vicinity of the shielding plate opening, which causes the characteristic deterioration. Further, when the shielding plate  25  has a width of less than 3 mm, the rigidity of the shielding plate which is necessary for scanning of the welding apparatus is insufficient. 
         [0048]      FIG. 8  (B) shows the state of performing butt welding on the shielding plate by using the material of the buttering  22 . The weld in the vicinity of the opening of the shielding plate includes oxygen because the concentration effect of the shielding gas is low. However, in the case of processing the groove in the buttering  22  shown in  FIG. 8  (C), the weld in the vicinity of the shielding plate opening are cut off, because the weld is not located in the shape of the buttering  22 . As a result, the buttering portion  22  shown in  FIG. 8  (C) does not include any portion including oxygen, which prevents occurrence of the characteristic deterioration. 
       Example 3 
       [0049]    Example 3 according to the present invention will be described with reference to  FIG. 9 , (A) to (E). An Ni-base superalloy and 1%-Cr—Mo—V-based steel are used as two dissimilar metals in Example 3. Example 2 relates to the shape on the bottom side of the weld in the manufacturing method of the dissimilar metal welds, whereas Example 3 relates to the material on the bottom side. The description of the characteristics identical with those of the Example 2 is omitted, and only the differences from Example 2 will be described below. 
         [0050]      FIG. 9 , (A) to (E), shows a manufacturing flow of welding two members made of different materials according to Example 3. Example 3 differs from Example 2 only in  FIGS. 9  (A) and (B).  FIG. 9  (A) shows the step of butting the parent material  20  and the dummy material  21 . In the vicinity of the weld bottom, the dummy material  21  and the parent material  20  have the same plate thickness. At a position apart from the vicinity thereof, the dummy material  21  and the parent material  20  do not necessarily have the same plate thickness. In Example 1, the bottom of the dummy material  21  extends beyond an end of the parent material  20  so as to overlap the parent material  20 , while in Example 3, the bottom in the vicinity of the weld of the parent material  20  are formed of the same material as the parent material  20  (see  FIG. 9  (B)). In Example 3, the difference in thickness between the region in the vicinity of the weld of the parent material  20  and the other region is 3 mm, but the difference may be more than 3 mm. When the plate thickness is less than 3 mm, a portion having a high dilution ratio is left in the buttering  22  to be subsequently processed. In this case, however, the plate thickness of the bottom of the dummy material  21  is preferably as small as possible as long as the plate thickness is 3 mm or more, and 10 mm is sufficient. Thus, the same effect as that of Example 2 can be obtained. 
       Example 4 
       [0051]    Example 4 according to the present invention will be described with reference to  FIG. 10 , (A) to (E). An Ni—Fe-base alloy and 12%-Cr-based steel are used as two dissimilar metals in Example 4. In Example 1 illustrates the characteristics related to the shape on the bottom side of the weld in the manufacturing method of the dissimilar metal welds. Example 4 illustrates the characteristics related to the shape on the bottom side of the weld in the manufacturing method of the dissimilar metal welds. The description of the characteristics identical with those of Example 1 is omitted, and only the differences from Example 1 will be described below. 
         [0052]      FIG. 10 , (A) to (E), shows a manufacturing flow of welding two members made of different materials according to Example 4. Example 4 differs from Example 2 only in  FIGS. 10 , (A) and (C).  FIG. 10  (A) shows the step of butting the parent material  20  and the dummy material  21 . The parent material  20  and the dummy material  21  may have the plate thickness. In Example 2, a part of the dummy material  21  extends beyond an end of the parent material so as to overlap the bottom of the parent material  20 , while in Example 4, a part of the dummy material  21  does not extend to overlap the bottom of the parent material  20 .  FIG. 10  (C) shows the step of processing the plate thickness of the weld to be smaller than the plate thickness of the parent material  20 , and the step of processing the groove in the buttering  22 . According to Example 4, a part of the weld bottom is cut off to remove a portion having a dilution ratio of the weld, thereby obtaining the same effect as that of Example 2. 
         [0053]    Next, the following table shows exemplary materials of the two different parent materials of the dissimilar metal welds according to the present invention. Here, Examples 1, 3, and 4 described above, as well as Examples 5 to 8 are illustrated. 
         [0000]    
       
         
               
               
               
             
           
               
                 TABLE 2 
               
               
                   
               
               
                   
                 Base material 
                 Base material 
               
               
                 Examples 
                 on high temperature side 
                 on low temperature side 
               
               
                   
               
             
             
               
                 1, 2 
                 Ni-base superalloy 
                 12% Cr-based steel 
               
               
                 3 
                 Ni-base superalloy 
                 1% Cr—Mo—V-based steel 
               
               
                 4 
                 Ni—Fe-base superalloy 
                 12% Cr-based steel 
               
               
                 5 
                 Ni—Fe-base superalloy 
                 1% Cr—Mo—V-based steel 
               
               
                 6 
                 12% Cr-based steel 
                 1% Cr—Mo—V-based steel 
               
               
                 7 
                 12% Cr-based steel 
                 3~4% Ni—Cr—Mo—V-based 
               
               
                   
                   
                 steel 
               
               
                 8 
                 1% Cr—Mo—V-based steel 
                 3~4% Ni—Cr—Mo—V-based 
               
               
                   
                   
                 steel 
               
               
                   
               
             
          
         
       
     
         [0054]    Examples of a combination of parent materials in the dissimilar metal welds according to the present invention may include a combination of an Ni-base superalloy and 12%-Cr-based steel according to Examples 1 and 2, a combination of an Ni-base superalloy and 1%-Cr—Mo—V-based steel according to Example 3, and a combination of an Ni—Fe-base alloy and 12%-Cr-based steel according to Example 4, as well as a combination of an Ni—Fe-base alloy and 1%-Cr—Mo—V-based steel (Example 5), a combination of 12%-Cr-based steel and 1%-Cr—Mo—V-based steel (Example 6), a combination of 12%-Cr-based steel and 3-4%-Ni—Cr—Mo—V-based steel (Example 7), and a combination of 1%-Cr—Mo—V-based steel and 3-4%-Ni—Cr—V-based steel (Example 8). The manufacturing flows shown in Examples 1 to 4 are also applicable to Examples 5 to 8, and the same operation and effect can be achieved. 
       DESCRIPTION OF SYMBOLS 
       [0000]    
       
           1  STEAM TURBINE ROTOR 
           3  WELD 
           5  DRIVE UNIT 
           6  WELDING UNIT 
           8  SIGNAL CABLE 
           9  SIGNAL CABLE 
           10  CONTROL UNIT 
           11  TORCH 
           14  GAS BOMBE 
           15  POSITIONER 
           17  GAS HORSE 
           18  GAS HORSE 
           19  EARTH CABLE 
           20  PARENT MATERIAL 
           21  DUMMY MATERIAL 
           22  BUTTERING 
           23  PARENT MATERIAL 
           24  WELDED METAL 
           25  SHIELDING PLATE 
           26  SIGNAL CABLE