| 摘要 |
<p>A low alloy steel which has a chemical composition, in mass %: C: 0.2 to 0.5 %, Si: 0.05 to 0.5 %, Mn: 0.1 to 1 %, S: 0.0005 to 0.01 %, O: 0.0010 to 0.01 %, Al: 0.005 to 0.05 %, Ca: 0.0003 to 0.007 %, Ti: 0.005 to 0.05 %, Cr: 0.1 to 1.5 %, Mo: 0.1 to 1 %, Nb: 0.005 to 0.1 %, and balance: Fe and inevitable impurities, wherein the impurity component contains 0.03 % or less of P and 0.015 % or less of N, and contains composite inclusions which have a core of an Al-Ca based oxysulfide and, formed around it, an outer shell of a carbonitride of Ti, Nb and/or Zr and have a longer diameter of 7 μm or less, in a number of 10 pieces or more per 0.1 mm2. The low alloy steel is free from the induction of pitting corrosion by inclusions and that of SSC by pitting corrosion, and thus exhibits excellent resistance to pitting corrosion.</p> |
