| 摘要 |
PURPOSE:To provide superior resistance to sulfide stress corrosion cracking to a high tension steel sheet by rapidly cooling the steel sheet to a specified temp., suspending the cooling to form ferrite in the surface layer part, rapidly cooling the steel sheet again and tempering it at the Ar1 point or below when the steel sheet is heat treated by hardening or direct hardening and tempering. CONSTITUTION:When a high tension steel sheet is heat treated by hardening or direct hardening and tempering, the steel sheet is rapidly cooled until the surface layer part attains to 300-600 deg.C. The cooling is suspended at the temp. to form ferrite in the surface layer part and the steel sheet is rapidly cooled again until the central part attains <=300 deg.C. The steel sheet is then tempered at the Ar1 point or below.
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