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

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.

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.

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.

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.

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.

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.