| 摘要 |
<p>A case hardened steel with excellent cold forgeability and excellent impact properties after case hardening processing contains C, Si, Mn, S, Cr, Al, Ti, Nb, B, and N, with the balance being iron and unavoidable impurities. Of precipitates containing Ti and/or Nb, precipitates having a size of not less than 20 µm 2 are at a number density of not more than 1.0/mm 2 . Of precipitates containing Ti and/or Nb, precipitates having a size of more than 5 µm 2 and less than 20 µm 2 and containing Mn and S are at a number density of more than 0.7/mm 2 and not more than 3.0/mm 2 . The ferrite fraction is more than 77% by area.</p> |
