High strength steel pipe of api x65 grade or higher and manufacturing method therefor

Abstract

A high-strength steel pipe having a strength of API X65 grade or higher consisting essentially of, by mass %, 0.02 to 0.08% of C, 0.01 to 0.5% of Si, 0.5 to 1.8% of Mn, 0.01% or less of P, 0.002% or less of S, 0.01 to 0.7% of Al, 0.005 to 0.04% of Ti, 0.05 to 0.50% Mo, at least one element selected from 0.005 to 0.05% of Nb and 0.005 to 0.10% of V, and the balance being Fe, in which the volume percentage of the ferritic phase is 90% or higher, and complex carbides containing Ti, Mo, and at least one element selected from the group consisting of Nb and V are precipitated in the ferritic phase. The high-strength steel pipe has excellent HIC resistance and good toughness of a heat-affected zone, and can be manufactured stably at a low cost.

1 - 12 . (canceled) 
     
     
         13 . A method for manufacturing a high-strength steel pipe having a strength of API X65 grade or higher comprising:
 heating, to a temperature of 1000 to 1250° C., a steel slab consisting essentially of, by mass %, 0.02 to 0.8% of C, 0.01 to 0.5% of Si, 0.5 to 1.8% of Mn, 0.01% or less of P, 0.002% or less of S, 0.01 to 0.07% of Al, 0.005 to 0.04% of Ti, 0.05 to 0.50% Mo, at least one element selected from the group consisting of 0.005 to 0.05% of Nb and 0.005 to 0.10% of V, optionally at least one element selected from the group consisting of Ca, Cu, Ni and Cr, and the balance being Fe, in which the volume percentage of a ferritic phase is 90% or higher, and complex carbides containing Ti, Mo, and at least one element selected from the group consisting of Nb and V are precipitated in said ferritic phase;   hot rolling said steel slab at a finish temperature not lower than the Ar3 transformation temperature to make a steel plate;   cooling said steel plate at a cooling rate not lower than 2° C./sec to provide a cooled steel plate;   coiling said cooled steel plate at a temperature of 550 to 700° C. to provide a coiled steel plate; and   forming said coiled steel plate into a steel pipe.   
     
     
         14 . A method for manufacturing a high-strength steel pipe having a strength of API X65 grade or higher comprising:
 heating, to a temperature of 1000 to 1250° C., a steel slab consisting essentially of, by mass %, 0.02 to 0.08% of C, 0.01 to 0.5% of Si, 0.5 to 1.8% of Mn, 0.01% or less of P, 0.002% or less of S, 0.01 to 0.07% of Al, 0.005 to 0.04% of Ti, at least one element selected from the group consisting of 0.005 to 0.05% of Nb and 0.005 to 0.10% of V, W and Mo, and meeting the condition that the content of (W/2 +Mo) is 0.05 to 0.50%, wherein the content of Mo can be 0%, optionally at least one element selected from the group consisting of Ca, Cu, Ni and Cr and the balance being Fe, in which the volume percentage of a ferritic phase is 90% or higher, and complex carbides containing Ti, W, Mo, and at least one element selected from the group consisting of Nb and V are precipitated in said ferritic phase;   hot rolling said steel slab at a finish temperature not lower than the Ar3 transformation temperature to make a steel plate;   cooling said steel plate at a cooling rate not lower than 2° C./sec to provide a cooled steel plate;   coiling said cooled steel plate at a temperature of 550 to 700° C. to provide a coiled steel plate; and   forming said coiled steel plate into a steel pipe.   
     
     
         15 . A method for manufacturing a high-strength steel pipe having a strength of API X65 grade or higher comprising:
 heating, to a temperature of 1000 to 1250° C., a steel slab consisting essentially of, by mass %, 0.02 to 0.8% of C, 0.01 to 0.5% of Si, 0.5 to 1.8% of Mn, 0.01% or less of P, 0.002% or less of S, 0.01 to 0.07% of Al, 0.005 to 0.04% of Ti, 0.05 to 0.50% Mo, at least one element selected from the group consisting of 0.005 to 0.05% of Nb and 0.005 to 0.10% of V, optionally at least one element selected from the group consisting of Ca, Cu, Ni and Cr, and the balance being Fe, in which the volume percentage of a ferritic phase is 90% or higher, and complex carbides containing Ti, Mo, and at least one element selected from the group consisting of Nb and V are precipitated in said ferritic phase;   hot rolling said steel slab at a finish temperature not lower than the Ar3 transformation temperature to make a steel plate;   cooling said steel plate to a temperature of 600 to 700° C. at a cooling rate not lower than 2° C./sec to provide a cooled steel plate;   cooling said cooled steel plate to a temperature of at least 550° C. at a cooling rate not higher than 0.1° C./sec; and   forming said steel plate into a steel pipe.   
     
     
         16 . A method for manufacturing a high-strength steel pipe having a strength of API X65 grade or higher comprising:
 heating, to a temperature of 1000 to 1250° C., a steel slab consisting essentially of, by mass %, 0.02 to 0.08% of C, 0.01 to 0.5% of Si, 0.5 to 1.8% of Mn, 0.01% or less of P, 0.002% or less of S, 0.01 to 0.07% of Al, 0.005 to 0.04% of Ti, at least one element selected from the group consisting of 0.005 to 0.05% of Nb and 0.005 to 0.10% of V, W and Mo, and meeting the condition that the content of (W/2+Mo) is 0.05 to 0.50%, wherein the content of Mo can be 0%, optionally at least one element selected from the group consisting of Ca, Cu, Ni and Cr and the balance being Fe, in which the volume percentage of a ferritic phase is 90% or higher, and complex carbides containing Ti, W, Mo, and at least one element selected from the group consisting of Nb and V are precipitated in said ferritic phase;   hot rolling said steel slab at a finish temperature not lower than the Ar3 transformation temperature to make a steel plate;   cooling said steel plate to a temperature of 600 to 700° C. at a cooling rate not lower than 2° C./sec to provide a cooled steel plate;   cooling said cooled steel plate to a temperature of at least 550° C. at a cooling rate not higher than 0.1° C./sec; and   forming said steel plate into a steel pipe.   
     
     
         17 . A method for manufacturing a high-strength steel pipe having a strength of API X65 grade or higher comprising:
 heating, to a temperature of 1000 to 1250° C., a steel slab consisting essentially of, by mass %, 0.02 to 0.8% of C, 0.01 to 0.5% of Si, 0.5 to 1.8% of Mn, 0.01% or less of P, 0.002% or less of S, 0.01 to 0.07% of Al, 0.005 to 0.04% of Ti, 0.05 to 0.50% Mo, at least one element selected from the group consisting of 0.005 to 0.05% of Nb and 0.005 to 0.10% of V, optionally at least one element selected from the group consisting of Ca, Cu, Ni and Cr, and the balance being Fe, in which the volume percentage of a ferritic phase is 90% or higher, and complex carbides containing Ti, Mo, and at least one element selected from the group consisting of Nb and V are precipitated in said ferritic phase;   hot rolling said steel slab at a finish temperature not lower than the Ar3 transformation temperature to make a steel plate;   cooling said steel plate to a temperature of 550 to 700° C. at a cooling rate not lower than 2° C./sec to provide a cooled steel plate;   heating said cooled steel plate immediately after being cooled and maintaining said steel plate at a temperature of 550 to 700° C. for three minutes or longer; and   forming said steel plate into a steel pipe.   
     
     
         18 . A method for manufacturing a high-strength steel pipe having a strength of API X65 grade or higher comprising:
 heating, to a temperature of 1000 to 1250° C., a steel slab consisting essentially of, by mass %, 0.02 to 0.08% of C, 0.01 to 0.5% of Si, 0.5 to 1.8% of Mn, 0.01% or less of P, 0.002% or less of S, 0.01 to 0.07% of Al, 0.005 to 0.04% of Ti, at least one element selected from the group consisting of 0.005 to 0.05% of Nb and 0.005 to 0.10% of V, W and Mo, and meeting the condition that the content of (W/2 +Mo) is 0.05 to 0.50%, wherein the content of Mo can be 0%, optionally at least one element selected from the group consisting of Ca, Cu, Ni and Cr and the balance being Fe, in which the volume percentage of a ferritic phase is 90% or higher, and complex carbides containing Ti, W, Mo, and at least one element selected from the group consisting of Nb and V are precipitated in said ferritic phase;   hot rolling said steel slab at a finish temperature not lower than the Ar3 transformation temperature to make a steel plate;   cooling said steel plate to a temperature of 550 to 700° C. at a cooling rate not lower than 2° C./sec to provide a cooled steel plate;   heating said cooled steel plate immediately after being cooled and maintaining said steel plate at a temperature of 550 to 700° C. for three minutes or longer; and   forming said steel plate into a steel pipe.   
     
     
         19 . The method for manufacturing a high-strength steel pipe having a strength of API X65 grade or higher according to  claim 17 , wherein the heating for maintaining said steel plate at a temperature of 550 to 700° C. for three minutes or longer is accomplished by using two or more induction heating apparatuses provided in series on the same line as rolling equipment and cooling equipment. 
     
     
         20 . The method for manufacturing a high-strength steel pipe having a strength of API X65 grade or higher according to  claim 18 , wherein the heating for maintaining said steel plate at a temperature of 550 to 700° C. for three minutes or longer is accomplished by using two or more induction heating apparatuses provided in series on the same line as rolling equipment and cooling equipment.