| 摘要 |
PURPOSE:To prepare a low carbon seamless steel pipe having high strength and high toughness, by hot processing steel having a specific composition containing C, Si, Mn, Al, B, Ni, Cr, Mo, Cu, V, Nb, Ca, P, S, N and Ti before direct hardening. CONSTITUTION:Steel, which contains, on a wt. basis, 0.06-0.20% C, 0.10-0.50% Si, 0.5-2.0% Mn, 0.01-0.1% Al, 0.0005-0.0050% B, further, Tr-5% Ni, Tr- 1% Cr, Tr-1% Mo, Tr-0.5% Cu, Tr-0.1% V, Tr-0.1% Nb, Tr-0.0010% Ca, 0.03% or less P and 0.015% or less S and follows formula 3.42N-0.008<=Ti<= 3.42N+0.008, Ti>0 in 0.0010-0.0060% N and comprises the remainder of Fe and inevitable impruties, is heated to 1,200-1,300 deg.C and hot processed to mold a steel pipe having a predetermined shape. After this hot processing, the steel pipe is immediately hardened at 750 deg.C or more followed by tempering at a temp. of Ac1 or less to obtain a low carbon seamless steel pipe having excellent strength and toughness. |
