Steel for pipeline

Abstract

The present invention provides a steel for pipeline which has excellent strength and toughness at room temperature and high temperature without the necessity of adding expensive alloy elements. The steel for pipeline of present invention comprises 0.04 to 0.16% of C, not greater than 0.5% of Si, 0.8 to 1.7% of Mn, not greater than 0.015% of P, not greater than 0.003% of S, not greater than 0.04% of Ti, 0.001 to 0.07% of Al, not greater than 0.01% of N, simultaneously satisfying expression:Al(N−Ti/3.4)≦0.00015, and is constituted of structure comprising martensite or bainite with an austenite average grain size of 30 to 200 μm, or the tempered structure thereof. The steel for pipe of the present invention is suitably for the use as the flow line in severe environment such as seabed oil fields or the like, and can be produced at low cost.

1 . Steel for pipeline comprising, by mass percent, 0.04 to 0.16% of C, not greater than 0.5% of Si, 0.8 to 1.7% of Mn, not greater than 0.015% of P, not greater than 0.003% of S, not greater than 0.04% of Ti, 0.001 to 0.07% of Al, not greater than 0.01% of N, and simultaneously satisfying expression (1):  
       Al(N−Ti/3.4)≦0.00015  (1)  
     and said steel for pipeline being constituted of structure comprising martensite or bainite with an austenite average grain size of 30 to 200 μm, or the tempered structure thereof.  
   
   
       2 . The steel for pipeline according to  claim 1 , further comprising one or more, by mass percent, not greater than 0.6% of Cr, not greater than 0.3% of Mo, not greater than 0.4% of Cu, not greater than 0.4% of Ni, not greater than 0.01% of Nb, not greater than 0.08% of V and not greater than 0.001% of B.  
   
   
       3 . The steel for pipeline according to  claim 1 , further comprising, by mass percent, not greater than 0.005% of Ca.  
   
   
       4 . The steel for pipeline according to  claim 2 , further comprising, by mass percent, not greater than 0.005% of Ca.