| 摘要 |
PURPOSE:To obtain a steel for an oil well, etc. having high resistance to sulfide cracking by subjecting a high-strength steel contg. particularly a limited amt. of C and Nb to hot working at adequate reduction of area then to hardening and tempering treatment. CONSTITUTION:A steel consisting, by wt%, of 0.15-0.45 C, <=0.80 Si, >=0.01- <0.30 Mn, 0.20-1.50 Cr, 0.05-0.80 Mo, 0.01-0.10 Nb and 0.01-0.10 Al and if necessary 0.0005-0.0050 B, 0.05-0.50 Cu and >=1 kind among 0.01-0.10 V, 0.001-0.030 Ca and 0.001-0.05 REM and the balance Fe with inevitable impurities is melted. The P in the impurities is limited to <=0.015% and S to <=0.010%. Such steel is austenitized and is subjected to hot rolling at <=1,100 deg.C, by which the reduction of area RA expressed by the equation attains >=20%. The steel is then subjected to >=1 time of a hardening treatment after heating at Ac3-(Ac3+ 200 deg.C) followed by a tempering treatment at Ac1 or below. The steel having high strength and resistance to sulfide cracking is thus obtd. at a low cost. |
