Welding material and a method of producing welded joint

Abstract

In the present invention, an iron based alloy which contains by mass %: 0.20% or less of C; 6.0 to 16.0% of Cr; 6.0 to 16.0% of Ni and whose martensitic transformation starting temperature (Ms point temperature) is in the range of 0-170° C., inclusive of 0° C. and exclusive of 170° C., is used as a welding material. With respect to a weld metal, the weld metal has a iron alloy composition which contains by mass %: 0.20% or less of C; 3.0 to 13.0% of Cr; 3.0 to 13.0% of Ni and whose martensitic transformation starting temperature (Ms point temperature) is in the range of 50-360° C., inclusive of both 50° C. and 360° C.

What is claimed:  
     
         1 . An iron based alloy welding composition consisting essentially of, by mass %: 
 at most about 0.20% of C;    at most about 1% of Si;    at most about 2.5% of Mn;    from about 6.0 to about 16.0% of Cr;    from about 6.0 to about 16.0% of Ni;    balance Fe and inevitable impurities,    wherein the composition has a martensitic transformation starting temperature in a range of at least about 0° C. and less than about 170° C.    
     
     
         2 . The composition according to  claim 1 , having C, Si, Mn, Cr, Ni contents satisfying the following formula (1): 
       0≦719-795C-35.55Si-13.25Mn-23.7Cr-26.5Ni<170  (1) wherein C, Si, Mn, Cr, Ni represent a content of each element (mass %), respectively.    
     
     
         3 . An iron based alloy welding composition consisting essentially of, by mass %: 
 at most about 0.20% of C;    from about 6.0 to about 16.0% of Cr;    from about 6.0 to about 16.0% of Ni;    at most about 1.0% of Si;    at most about 2.5% of Mn;    at least one of (a) at most about 4.0% of Mo and (b) at most about 1.0% of Nb;    balance Fe and inevitable impurities,    wherein the composition has a martensitic transformation starting temperature in a range of at least about 0° C. and less than about 170° C.    
     
     
         4 . (new) The composition according to  claim 3 , having C, Si, Mn, Cr, Ni, Mo, Nb contents satisfying the following formula (1): 
       0≦719-795C-35.55Si-13.25Mn-23.7Cr-26.5Ni-23.7Mo-11.85Nb<170  (1) wherein C, Si, Mn, Cr, Ni, Mo, Nb represent a content of each element (mass %), respectively.    
     
     
         5 . The composition according to  claim 1 , wherein linear expansion occurs in a temperature range from (a) a temperature at which elongation turns into expansion due to martensitic transformation immediately after onset of transformation, to (b) 50° C. in a temperature-elongation curve, in an amount of 2×10 −3  to 8×10 −3  mm/(sample)mm.  
     
     
         6 . A method of producing a welded joint, in which materials to be welded are welded to each other using a welding material so as to form a welded joint, comprising the steps of: 
 employing a low alloy steel material as a material to be welded;    forming a weld metal by welding; and    adjusting composition and welding conditions of the welding material, according to the composition of the material to be welded, such that the weld metal is an iron alloy composition containing at most about 0.20 mass % of C, from about 3.0 to about 13.0 mass % of Cr, from about 3.0 to about 13.0 mass % of Ni and has a martensitic transformation starting temperature in about a range from about 50° C. to less than 360° C.    
     
     
         7 . The method of  claim 6 , wherein the composition of the weld metal satisfies the following formula (2): 
       50≦719-795C-35.55Si-13.25Mn-23.7Cr-26.5Ni-23.7Mo-11.85Nb<360  (2) wherein C, Si, Mn, Cr, Ni, Mo, Nb represent the content of each element (mass %), respectively.    
     
     
         8 . The method of  claim 6 , wherein the martensitic transformation starting temperature (Ms point temperature) of the weld metal is in a range of at least 50° C. and less than 170° C.  
     
     
         9 . The method of  claim 8 , wherein the weld metal is adjusted such that C, Si, Mn, Cr, Ni, Mo, Nb contents thereof satisfies a following formula (3): 
       50≦719-795C-35.55Si-13.25Mn-23.7Cr-26.5Ni-23.7Mo-11.85Nb<170  (3) wherein C, Si, Mn, Cr, Ni, Mo, Nb represent the content of each element (mass %), respectively.    
     
     
         10 . The method of  claim 6 , wherein the weld metal assumes martensitic characteristics during a cooling process after the welding and then reaches, at a room temperature, a state in which the weld metal is expanded as compared with a state thereof when martensitic transformation started.  
     
     
         11 . The method of  claim 6 , wherein the weld metal undergoes linear expansion in temperature range from (a) a temperature at which elongation turns into expansion due to martensitic transformation immediately after starting of transformation, to (b) 50° C. in a temperature-elongation curve, in an amount of 2×10 −3  to 8×10 −3  mm/(sample)mm.  
     
     
         12 . The method of  claim 6 , wherein the welding is multi-layered welding.  
     
     
         13 . The method of  claim 12 , wherein the composition of the weld metal, formed by first-layer welding or further by final-layer welding of the multi-layer welding, satisfies following formula (2) or formula (3): 
         50≦719 -795C-35.55Si-13.25Mn-23.7Cr-26.5Ni-23.7Mo-11.85Nb<170  (3)50≦719-795C-35.55Si-13.25Mn-23.7Cr-26.5Ni-23.7Mo-11.85Nb<360  (2) wherein C, Si, Mn, Cr, Ni, Mo, Nb represent the content of each element (mass %), respectively.    
     
     
         14 . A welded joint, in which materials to be welded are welded to each other by using a welding material, comprising: 
 a low alloy steel material as material to be welded; and    a weld metal formed by welding,    wherein the weld metal is an iron alloy composition containing at most about 0.20 mass % of C, from about 3.0 to about 13.0 mass % of Cr, from about 3.0 to about 13.0 mass % of Ni and has a martensitic transformation starting temperature in range of at least 50° C. and not more than 360° C., and the weld metal is a composition which exhibits a temperature-elongation curve in which the weld metal is in an expanded state, at room temperature, as compared with a state thereof when martensitic transformation started.    
     
     
         15 . The welded joint according to  claim 14 , wherein an amount of linear expansion of the weld metal, in a temperature range from (a) a temperature at which elongation turns into expansion due to martensitic transformation immediately after a starting of transformation, to (b) 50° C. in a temperature-elongation curve, is 2×10 −3  to 8×10 −3  mm/(sample) mm.  
     
     
         16 . The welded joint according to  claim 14 , wherein a composition of the weld metal is adjusted such that C, Si, Mn, Cr, Ni, Mo, Nb contents thereof satisfy the following formula (2): 
       50≦719-795C-35.55Si-13.25Mn-23.7Cr-26.5Ni-23.7Mo-11.85Nb<360  (2) wherein C, Si, Mn, Cr, Ni, Mo, Nb represent the content of each element (mass %), respectively.    
     
     
         17 . The welded joint according to  claim 14 , wherein martensitic transformation starting temperature of the weld metal is in a range of at least 50° C. and less than 170° C.  
     
     
         18 . The welded joint of  claim 17 , wherein the weld metal is adjusted such that C, Si, Mn, Cr, Ni, Mo, Nb contents thereof satisfy a following formula (3): 
       50≦719-795C-35.55Si-13.25Mn-23.7Cr-26.5Ni-23.7Mo-11.85Nb<170  (3) wherein C, Si, Mn, Cr, Ni, Mo, Nb represent the content of each element (mass %), respectively.    
     
     
         19 . The welded joint according to  claim 14 , wherein the composition comprises: 
 at most about 0.20 mass % of C;    from about 3.0 to about 13.0 mass % of Cr;    from about 3.0 to about 13.0 mass % of Ni; and further contains,    at most about 1.0 mass % of Si;    at most about 2.5 mass % of Mn; or further contains,    at least one of (a) at most about 4.0 mass % of Mo and (b) at most about 1.0 mass % of Nb; and    balance Fe and other inevitable impurities.