Rolled material for fracture split connecting rod excelling in fracture splittability, hot forged part for fracture split connecting rod excelling in fracture splittability, and fracture split connecting rod

Abstract

The present invention provides a rolled material having excellent fracture splitting characteristics and suitable for the manufacture of a connecting rod in which a through-hole section for assembly in a crankshaft is fracture split in substantially semicircles. Prescribed components are contained, an average aspect ratio of a sulfide-based inclusion as observed in a D/4 portion (D is the diameter of the rolled material) in a cross-section parallel to a longitudinal direction of the rod-shaped rolled material is not more than 10.0, a Pc indicated in Equation (1) below is between 0.41 and 0.75, and a Veq indicated in Equation (2) below is not less than 0.18 mass % Pc =C(1−α/100)  (1) {In Equation (1), C represents the carbon content in steel (mass %) and α represents the ferrite fraction (area ratio %)} Veq =V+Ti/2+Si/20  (2) {In Equation (2), V, Ti and Si represent the content of each element in steel (mass %)}.

1 . A rolled material for a fracture splitting-type connecting rod characterized in that its chemical composition comprises, by mass % (hereinafter the same for each component),
 C: 0.25 to 0.60%,   Mn: 0.5 to 2%,   S: 0.05 to 0.2%,   Si: 0.05 to 1.5%,   V: 0.05 to 0.3%,   P: 0.010 to 0.15%,   Al: 0.0010 to 0.06%,   N: 0.03% or less and   Cr: 0.1 to 2%,   and further comprises at least one type selected from the group consisting of   Zr: 0.005 to 0.2%,   Ti: 0.005 to 0.1%,   Mg: 0.0003 to 0.01%,   Ca: 0.0005 to 0.01%,   Te: 0.0010 to 0.1%, and   REM: 0.0005 to 0.3%,   and a balance of iron and unavoidable impurities,   wherein ferrite and pearlite occupies in total an area ratio to the whole of not less than 95%,   an average aspect ratio of a sulfide-based inclusion is not more than 10.0 when observed in a D/4 portion (D being the diameter of the rolled material) in a cross-section parallel to a longitudinal direction of a rod-shaped rolled material, and   a Pc indicated in Equation (1) below is between 0.41 and 0.75 and a Veq indicated in Equation (2) below is not less than 0.18 mass %
     Pc =C(1−α/100)  (1) 
   with C representing in Equation (1) a carbon content in steel (mass %) and α represents a ferrite fraction (area ratio %)
     Veq =V+Ti/2+Si/20  (2) 
   with V, Ti and Si representing in Equation (2) the content of each element in the steel (mass %).   
   
   
       2 . The rolled material for a fracture splitting-type connecting rod according to  claim 1 , further comprising a Ceq of not less than 0.80 mass % as indicated in Equation (3) below and a PM of not more than 500 mass % as indicated in Equation (4) below
     Ceq =C+0.28Mn−1.0S+0.32Cr+1.7V+1.3Ti  (3)       PM= 554C+71Mn−262S+82Cr+429V  (4)   with C, Mn, S, Cr, V and Ti representing in Equations (3) and (4) the content of each element in the steel (mass %).   
   
   
       3 . The rolled material for a fracture splitting-type connecting rod according to  claim 1 , further comprising at least one type selected from the group consisting of
 Se: 0.0010 to 0.1%, and   Bi and Pb: 0.01 to 0.2% in total.   
   
   
       4 . The rolled material for a fracture splitting-type connecting rod according to  claim 1 , further comprising B: 0.0005 to 0.004%. 
   
   
       5 . A hot-forged part for a fracture splitting-type connecting rod with excellent fracture splitting characteristics, obtained by hot forging the rolled material for a fracture splitting-type connecting rod according to  claim 1 . 
   
   
       6 . A fracture splitting-type connecting rod, obtained using the hot-forged part according to  claim 5 .