Forging steel, and forged products obtainable therefrom

Abstract

Disclosed is a forging steel characterized in that prescribed composition of components must be satisfied. In particular, any one of the below-mentioned (I)-(IV) need be complied with in regard to dissolved Ca and dissolved Mg. (I) Dissolved Ca: 2-500 ppb (meaning “mass ppb” hereafter) and dissolved Mg: 0.04-5 ppm (meaning “mass ppm” hereafter); (II) Dissolved Ca: 2-100 ppb and dissolved Mg: 5-ppm; (III) Dissolved Ca: 2 ppb or less (0% not included) and dissolved Mg: 0.04-5 ppm; (IV) Dissolved Ca: 2-500 ppb and dissolved Mg: 0.04 ppm or less (0% not included).

1 . Forging steel satisfying the following requirements concerning component composition:
 C, 0.2-0.6% (hereafter, % denotes ‘% by mass’),   Si: 0.05-0.5%,   Mn: 0.2-1.5%,   Ni: 0.1-3.5%,   Cr: 0.9-4%,   Mo: 0.1-0.7%,   Al: 0.005-0.1%,   S: 0.008% or less (0% not included),   O: 0.0025% or less (0% not included),   Total Ca: 0.0030% or less (0% not included), and   Total Mg: 0.0015% or less (0% not included);   and simultaneously, said forging steel also satisfying any one of the following (I) to (IV) in regard to dissolved Ca and dissolved Mg (hereafter, ppb and ppm denote respectively “ppb by mass” and “ppm by mass”):   (I) Dissolved Ca: 2-500 ppb, and
 Dissolved Mg: 0.04-5 ppm; 
   (II) Dissolved Ca: 2-100 ppb, and
 Dissolved Mg: 5-10 ppm; 
   (III) Dissolved Ca: 2 ppb (0 ppb not included), and
 Dissolved Mg: 0.04-5 ppm; or 
   (IV) Dissolved Ca: 2-500 ppb, and
 Dissolved Mg: 0.04 ppm or less (0 ppm not included). 
   
     
     
         2 . The forging steel according to  claim 1 , also comprising at least one out of the following groups (A), (B), and (C)
 (A) One or more elements selected from the group consisting of V, Nb, Ta, and Hf, in an amount within the range of 0.005-0.2% for all selected elements added together;   (B) Ti: 0.05% or less (0% not included); and/or   (C) Cu: 1.0% or less (0% not included).   
     
     
         3 . The forging steel according to  claim 2 , wherein the diameter of an assumed circle equivalent area-wise to the largest piece of inclusion existing in said forging steel is less than 100 μm. 
     
     
         4 . Forged products (including parts) manufactured from the forging steel according to  claim 3 . 
     
     
         5 . The forged products according to  claim 4 , wherein crankshafts are particularly referred to as said forged products.