Patent Publication Number: US-2016230242-A1

Title: Regenerative heat treatment method for heat-resistant metal member suffering from creep damage

Description:
TECHNICAL FIELD 
     The present invention relates to a regenerative heat treatment method for a heat-resistant metal member suffering from creep damage. 
     BACKGROUND ART 
     Hitherto, as a method to regenerate locations degraded by creep damage in high temperature members, such as those employed in thermal or nuclear power plants, or chemical plants (for example, high temperature resistant welds of boilers and turbines, and base material for high temperature pipes, headers, nozzles and the like), a method has been developed in which, for example, the high temperature member is secured by clamps, and regenerative heat treatment is then performed by heating a creep degraded section in a state in which thermal expansion at the creep degraded section between the clamps is restricted in the directions towards clamp secured sections (see JP 2003-253337 A). 
     SUMMARY OF INVENTION 
     Technical Problem 
     However, there is a problem with a method such as that described above, in that thermal expansion in the creep degraded section, occurring when the creep degraded section is heated, cannot be restricted in a direction toward the outer periphery of the above member. 
     An object of the present invention is to provide a method capable of restricting thermal expansion in a direction toward an outer periphery of a member occurring when a heat-resistant metal member suffering from creep damage is heated, and capable of performing efficient regenerative heat treatment on the heat-resistant metal member suffering from creep damage. 
     Solution to Problem 
     In order to address the above problem, a regenerative heat treatment method for a heat-resistant metal member suffering from creep damage according to the present invention includes the following configuration. More specifically, the present invention is: 
     (1) a regenerative heat treatment method for a heat-resistant metal member suffering from creep damage, the method including covering the heat-resistant metal member by a heat-resistant covering member and securing so as to contact an outer periphery of the heat-resistant metal member, and heating the heat-resistant metal member covered by the heat-resistant covering member to a temperature of 1000° C. or greater; and 
     (2) the method described in (1), wherein, after heating the heat-resistant metal member covered by the heat-resistant covering member to a temperature of 1000° C. or greater, the heat-resistant metal member covered by the heat-resistant covering member is cooled and re-heated to a temperature of an A 1  transformation point or greater. 
     Advantageous Effects of Invention 
     The present invention enables provision of a method capable of restricting thermal expansion in a direction toward an outer periphery of a heat-resistant metal member suffering from creep damage occurring when the member is heated, and capable of performing efficient regenerative heat treatment on the heat-resistant metal member suffering from creep damage. 
    
    
     
       BRIEF DESCRIPTION OF DRAWINGS 
         FIG. 1  is a schematic diagram illustrating a regenerative heat treatment method for a heat-resistant metal member suffering from creep damage, to explain an embodiment of the present invention. 
         FIG. 2  is a schematic cross-section illustrating a cross-section of  FIG. 1  to explain an embodiment of the present invention. 
     
    
    
     DESCRIPTION OF EMBODIMENTS 
     Detailed explanation follows regarding preferable embodiments of the present invention, with reference to the appended drawings. Note that the objects, features, advantages, and ideas of the present invention will be clear to a person of ordinary skill in the art from the content of the present specification, and a person of ordinary skill in the art would easily be able to reproduce the present invention from the present specification. The following embodiments, drawings, and the like of the present invention illustrate preferable embodiments of the present invention, and are there to give examples and for the purpose of explanation; however, the present invention is not limited thereto. It will be obvious to a person of ordinary skill in the art that various modifications may be implemented based on the content of the present specification within the intention and scope of the present invention disclosed in the present specification. 
       FIG. 1  is a schematic diagram illustrating a regenerative heat treatment method for a heat-resistant metal member suffering from creep damage, to explain an embodiment of the present invention.  FIG. 2  is a schematic cross-section illustrating a cross-section of  FIG. 1  to explain an embodiment of the present invention. Explanation follows of an example of the present embodiment in which a high temperature pipe, which has been manufactured using a heat-resistant metal material and damaged by creep with use, serves as a heat-resistant metal member  10 ; however, there is no limitation thereto. The heat-resistant metal member  10  may be another high temperature member, such as a turbine, which has been manufactured using a heat-resistant metal material and damaged by creep with use. 
     As illustrated in  FIG. 1  and  FIG. 2 , in the regenerative heat treatment method of the heat-resistant metal member  10  suffering from creep damage according to the present invention, first the heat-resistant metal member  10  (including a weld  20  therein; similar applies below), which has been manufactured using a heat-resistant metal material and damaged by creep with use, is covered by a heat-resistant covering member  30  so as to contact the outer periphery of the heat-resistant metal member  10 , and the heat-resistant covering member  30  is secured. The heat-resistant metal member  10  covered by the heat-resistant covering member  30  is then heated for a specific duration at a temperature of 1000° C. or greater using a heater  40 . 
     Covering and securing the heat-resistant metal member  10  suffering from creep damage, by the heat-resistant covering member  30 , and heating to a temperature of 1000° C. or greater, as described above, enables compressive force to act on the heat-resistant metal member  10  undergoing thermal expansion in a direction toward the outer periphery, and enables efficient regenerative heat treatment to be performed on the heat-resistant metal member suffering from creep damage, while restraining thermal expansion in the direction toward the outer periphery of the heat-resistant metal member  10 . More specifically, any creep voids or cracks are efficiently repaired using the force from thermal expansion toward the outer periphery of the heat-resistant metal member  10  and the structure of the heat-resistant metal member  10  is returned to a new material state (for example, an austenitic structure), thus enabling the lifespan of the heat-resistant metal member  10  to the extended. 
     In the method for regenerative heat treatment of a heat-resistant metal member suffering from creep damage according to the present invention, etching treatment, or shot peening and etching treatment, may be performed on the section to be covered by the heat-resistant covering member  30  prior to covering the heat-resistant metal member  10  by the heat-resistant covering member  30  and securing. Such processing enables work hardening of the surface layer of the heat-resistant metal member  10  to be performed by plastic deformation, enables residual compressive stress to be imparted to the surface of the heat-resistant metal member  10 , and enables any oxidized film on the surface of the heat-resistant metal member  10  to be removed. 
     In the regenerative heat treatment method for a heat-resistant metal member suffering from creep damage according to the present invention, processing to remove (reduce) residual stress, such as stress relief or tension annealing, may be performed after the heat-resistant metal member  10  covered by the heat-resistant covering member  30  has been heated to a temperature of 1000° C. or greater using the heater  40 . More specifically, after the heat-resistant metal member  10  covered by the heat-resistant covering member  30  has been heated to a temperature of 1000° C. or greater using the heater  40 , the heat-resistant metal member  10  may be first cooled to room temperature, then reheated to a temperature of an A 1  transformation point or greater (preferably from 10° C. to 100° C. above 1000° C.) for a specific duration (for example, from approximately several hours to approximately 24 hours). 
     Moreover, in the regenerative heat treatment method for a heat-resistant metal member suffering from creep damage according to the present invention, in order to restrict thermal expansion toward the outside in the length direction of the heat-resistant metal member  10  (in directions toward the ends of the heat-resistant metal member  10 ) occurring when a creep degraded section of the heat-resistant metal member  10  is covered by the heat-resistant covering member  30  and heated by the heater  40 , the heat-resistant metal member  10  may be secured in sections not being heated by the heater  40 , by, for example, two clamps so as to sandwich the section being heated by the heater  40 . This thereby enables any creep voids, cracks, or the like to be efficiently repaired. 
     In the cases in which the section heated by the heater  40  is small compared to the overall heat-resistant metal member  10 , there is no need to secure the heat-resistant metal member  10  in sections not being heated by the heater  40  with clamps or the like, since thermal expansion toward the outside in the length direction of the heat-resistant metal member  10  in the section being heated by the heater  40  is restricted by the sections not being heated by the heater  40 . 
     Examples of the heat-resistant metal of the member  10  include 0.3Mo steel, 0.5Mo steel, 0.5Cr-0.5Mo steel, 1Cr-0.2Mo steel, 1Cr-0.5Mo steel, 1.25Cr-0.5Mo steel, 2.25Cr-1Mo steel, 5Cr-0.5Mo steel, 7Cr-0.5Mo steel, 9Cr-1Mo steel, 0.3Cr—Mo—V steel, 0.5Cr—Mo—V steel, 9Cr—Mo—V steel, 12Cr—Mo—V steel, 1Cr-1.25Mo-0.25V steel, 9Cr-1Mo—W steel, SUS304, SUS304L, SUS316, SUS316L, SUS316TI, SUS317, SUS321, SUS347H, SUS310S, Super304, SUS904L, NCF600, NCF601, NCF800, and NCF800H; however, there is no limitation thereto. Any known material used for members employed in thermal or nuclear power generation units or other high temperature plants may be employed as the heat-resistant metal for the member  10 . 
     There are no particular limitations to the heat-resistant covering member  30 , as long as it is capable of covering the heat-resistant metal member  10  so as to make contact with the outer periphery of the heat-resistant metal member  10  suffering from creep damage, as long as it is made from a heat-resistant material that restrains thermal expansion in the direction toward the outer periphery of the heat-resistant metal member  10  occurring when heated to the heating temperature mentioned above, and is able to maintain the approximate profile of the heat-resistant metal member  10 . A material having a lower thermal expansion coefficient than the heat-resistant metal member  10  at temperatures of the heating temperature mentioned above or greater is preferably employed for the heat-resistant covering member  30 . In the cases in which the heat-resistant covering member  30  is configured from a heat-resistant material different from that of the heat-resistant metal member  10 , yet having a thermal expansion coefficient of about the same as the heat-resistant metal member  10 , or from a heat resistant material having a higher thermal expansion coefficient than the heat-resistant metal member  10 , in order to restrain the thermal expansion of the heat-resistant covering member  30  occurring when heated to the heating temperature mentioned above, the outer periphery of the heat-resistant covering member  30  may be secured by a member of a heat-resistant material having a lower thermal expansion coefficient than the heat-resistant metal member  10  at or above the heating temperature mentioned above, so as to maintain the profile of the heat-resistant covering member  30 . 
     Examples of the heat-resistant material of the heat-resistant covering member  30  include ceramics such as alumina, zirconia, aluminum nitride, silicon carbide, silicon nitride, cordierite, sialon, zircon, and mullite, and alloys such as Alloy 903, Alloy 909, and HRA 929. 
     The form of the heat-resistant covering member  30  is, for example, of a cord, plate, or clamp form. Securing of the above may be accomplished by, for example, wrapping a cord-shaped or plate-shaped heat-resistant covering member  30  around the outer periphery of the heat-resistant metal member  10  suffering from creep damage, by attaching a clamp-shaped heat-resistant covering member  30  to the outer periphery of the heat-resistant metal member  10  suffering from creep damage, or by attaching a heat-resistant covering member  30  formed in a plate shape or the like to the outer periphery of a heat-resistant metal member suffering from creep damage using fasteners, such as clamps or screws. In the present embodiment, the heat-resistant covering member  30  is made from fittings including two substantially semi-circular arc cross-section shapes. The heat-resistant covering member  30  is then secured to the surface of the heat-resistant metal member  10  using threaded members  35  attached to flanges of these fittings, such that the inner face of the fittings contact the outer periphery of the heat-resistant metal member  10  suffering from creep damage. The threaded members  35  are manufactured, for example, from the same material as the heat-resistant covering member  30 . 
     The heating temperature of the heat-resistant metal member  10  covered by the heat-resistant covering member  30  is not particularly as long as it is a temperature of 1000° C. or greater. Preferably the heat-resistant metal member  10  is heated to a temperature of, or greater than, an A 3  transformation point of the component of the heat-resistant metal of the member  10  having the highest A 3  transformation point (preferably from 10° C. to 100° C. above 1000° C.) for a specific duration (for example, from approximately several hours to approximately 24 hours). Note that although in the present embodiment, as a heating device, the high frequency heater  40  with capability to heat the heat-resistant metal member  10  covered by the heat-resistant covering member  30  from the outer periphery is employed, there is no particular limitation thereto, as long as a heating device capable of heating the heat-resistant metal member  10  at a section covered by the heat-resistant covering member  30  is employed. 
     REFERENCE SIGNS LIST 
       10  heat-resistant metal member 
       20  weld 
       30  heat-resistant covering member 
       35  threaded member 
       40  high frequency heater