Weld metal excellent in low temperature toughness and SR cracking resistance used for high-strength Cr-Mo steel

Abstract

Disclosed is a weld metal which comprises 0.02 to 0.10% of C (% by mass; the same holds also hereinafter), 0.05 to 0.4% of Si, 0.3 to 1.3% of Mn, 0.8 to 3.25% of Cr, at most 2% (inclusive of 0%) of Mo, 0.30 to 1.0% of V, and at most 0.03% of N, wherein the contents of Al, Ti and Ni are suppressed to at most 0.03%, at most 0.03% and at most 0.40% respectively; sum total ([Mn]+[Ni]) of Mn content [Mn] and Ni content [Ni] is at most 1.2% the balance is Fe and inevitable impurities; the contents of P, S, Sn, As and Sb among the inevitable impurities are suppressed each to at most 0.01%; the content of O is suppressed to at most 0.040%; EV value as defined by related expressions satisfies EV≧0.00; and the number of carbides which have an equivalent circle diameter of at least 0.2 μm and which are present in non heat affected zone of the weld zone after being subjected to stress relieving annealing at 625° C. for 10 hours is at most 1.0 number/μm 2 . The weld metal, which is well suited for use in high—strength Cr—Mo steel, is improved in toughness, particularly low temperature toughness and SR cracking resistance as well, while maintaining high—temperature strength.

1 . A weld metal excellent in low temperature toughness and SR cracking resistance which is used for high-strength Cr—Mo steel, which is formed by an arc welding method, and which comprises 
 0.02 to 0.10% of C (% by mass; the same holds also hereinafter),    0.05 to 0.4% of Si,    0.3 to 1.3% of Mn,    0.8 to 3.25% of Cr,    at most 2% (inclusive of 0%) of Mo,    0.30 to 1.0% of V, and    at most 0.03% of N,    wherein    the contents of Al, Ti and Ni are suppressed to at most 0.03%, at most 0.03% and at most 0.40%, respectively;    sum total ([Mn]+[Ni]) of Mn content [Mn] and Ni content [Ni] is at most 1.2%;    the balance is Fe and inevitable impurities; the contents of P, S, Sn, As and Sb among the inevitable impurities are suppressed each to at most 0.01%;    the content of 0 is suppressed to at most 0.040%;    EV value as defined by the following formula (1) satisfies EV≧0.00; and    the number of carbides which have an equivalent circle diameter of at least 0.2 μm and which are present in non heat affected zone of the weld metal after being subjected to stress relieving annealing at 625° C. for 10 hours is at most 1.0 number/μm 2          EV =[V]−([C]/12+[N]/14)×50.9  (1)    where [V], [C] and [N] represent the contents (mass %) of V, C and N, respectively.    
   
   
       2 . The weld metal for high-strength Cr—Mo steel as set forth in  claim 1 , which further comprises at least one species selected from the group consisting of at most 0.10% (exclusive of 0%) of Nb, at most 0.10% (exclusive of 0%) of Zr, at most 0.10% (exclusive of 0%) of Hf and at most 0.10% (exclusive of 0%) of Ta.  
   
   
       3 . The weld metal for high-strength Cr—Mo steel as set forth in  claim 1 , which further comprises at least one species selected from the group consisting of at most 2.0% (exclusive of 0%) of W and at most 2.0% (exclusive of 0%) of Co.  
   
   
       4 . The weld metal for high-strength Cr—Mo steel as set forth in  claim 1 , which further comprises at most 0.015% (exclusive of 0%) of B.