| 摘要 |
PURPOSE:To improve the strength of a steel and the resistance to sulfide stress corrosion cracking by hardening the steel contg. prescribed percentages of C, Si, Mn, Cr, Mo, Zr, etc. and restricted percentages of P, S and Ni. CONSTITUTION:A steel contg., by weight, 0.2-0.4% C, 0.05-1% Si, 0.05-0.3% Mn, 0.1-1.5% Cr, 0.1-0.8% Mo, 0.01-0.15% Zr, 0.0003-0.003% B, 0.01-0.1% Al and <=0.2% in total of one or more among 0.01-0.1% each of Nb, V and Ti is produced. The amounts of P, S and Ni as impurities in the steel are restricted to <=0.02% P, <=0.005% S and <=0.03% Ni. The steel is hardened to form austenite having a grain size represented by ASTM grain size No. >=8.5. The austenite is then tempered to form a martensite-base structure.
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