Steel for fracture splitting type connecting rod

Abstract

The present invention provides a steel for a fracture splitting type connecting rod, in which: the steel contains C: 0.25-0.5% (in mass %, the same is applied hereunder), Si: 0.01-2.0%, Mn: 0.50-2.0%, P: 0.015-0.080%, S: 0.01-0.2%, V: 0.02-0.20%, Cr: 0.05-1.0%, Ti: 0.01-0.10%, and N: 0.01% or less; an f-value represented by the expression shown below is in the range of 0.003 to 0.04; and the average aspect ratio of sulfide system inclusions is 15 or less, f =[Ti]−[N]×48/14 (in the expression, [Ti] and [N] represent the contents (mass %) of Ti and N in a steel, respectively).

1 . A steel for a fracture splitting type connecting rod, containing
 C: 0.25-0.5% (in mass %, the same is applied hereunder),   Si: 0.01-2.0%,   Mn: 0.50-2.0%,   P: 0.015-0.080%,   S: 0.01-0.2%,   V: 0.02-0.20%,   Cr: 0.05-1.0%,   Ti: 0.01-0.10%, and   N: 0.01% or less,   with the remainder consisting of iron and inevitable impurities,
 wherein an f-value represented by the expression (1) shown below is in the range of 0.003 to 0.04; and 
 in a longitudinal section at a position of D/4 (D is the thickness or the diameter of the steel) from the steel surface, the number of sulfide system inclusions 1 μm or more in width is 100 to 4,000 pieces per 1 mm 2 , and the average aspect ratio (length/width) of the sulfide system inclusions 1 μm or more in width is 15 or less,
     f =[Ti]−[N]×48/14   (1), 
 
   
       (in the expression, [Ti] and [N] represent the contents (mass %) of Ti and N in a steel, respectively). 
     
     
         2 . A steel for a fracture splitting type connecting rod according to  claim 1 , wherein Ti is 0.08% or less. 
     
     
         3 . A steel for a fracture splitting type connecting rod according to  claim 1 , wherein V is 0.10% or less. 
     
     
         4 . A steel for a fracture splitting type connecting rod according to  claim 1 , further containing at least one kind selected from the group consisting of
 Zr: 0.15% or less,   Ca: 0.005% or less,   Mg: 0.005% or less,   Te: 0.1% or less, and   REM: 0.3% or less.   
     
     
         5 . A steel for a fracture splitting type connecting rod according to  claim 1 , further containing at least either one of
 Al: 0.05% or less, or   Nb: 0.05% or less.   
     
     
         6 . A steel for a fracture splitting type connecting rod according to  claim 1 , further containing at least one kind selected from the group consisting of
 Cu: 1.0% or less,   Ni: 1.0% or less, and   Mo: 1.0% or less.   
     
     
         7 . A steel for a fracture splitting type connecting rod according to  claim 1 , further containing
 Bi: 0.1% or less.