High-strength steel pipe of API X65 grade or higher and manufacturing method therefor

Abstract

The present invention provides a high-strength steel pipe 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 0.07% 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 ferritic phase is 90% or higher, and complex carbides containing Ti, Mo, and at least one element selected from Nb and V are precipitated in the ferritic phase. The high-strength steel pipe in accordance with the present invention has excellent HIC resistance and good toughness of heat-affected zone, and can be manufactured stably at a low cost.

What is claimed is:  
     
         1 . A high-strength steel pipe 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 0.07% 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 ferritic phase is 90% or higher, and complex carbides containing Ti, Mo, and at least one element selected from Nb and V are precipitated in said ferritic phase.  
     
     
         2 . The high-strength steel pipe of API X65 grade or higher according to  claim 1 , wherein the content of Ti is 0.005 to less than 0.02%.  
     
     
         3 . A high-strength steel pipe 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 0.07% of Al, 0.005 to 0.04% of Ti, at least one element selected from 0.005 to 0.05% of Nb and 0.005 to 0.10% of V, W and Mo meeting the condition that the content of (W/2+Mo) is in the range of 0.05 to 0.50% (however, a case where the content of Mo is 0% is included), and the balance being Fe, in which the volume percentage of ferritic phase is 90% or higher, and complex carbides containing Ti, W, Mo, and at least one element selected from Nb and V are precipitated in said ferritic phase.  
     
     
         4 . The high-strength steel pipe of API X65 grade or higher according to  claim 3 , wherein the content of Ti is 0.005 to less than 0.02%.  
     
     
         5 . The high-strength steel pipe of API X65 grade or higher according to  claim 1 , wherein said steel pipe further contains 0.0005 to 0.0040% of Ca.  
     
     
         6 . The high-strength steel pipe of API X65 grade or higher according to  claim 3 , wherein said steel pipe further contains 0.0005 to 0.0040% of Ca.  
     
     
         7 . The high-strength steel pipe of API X65 grade or higher according to  claim 1 , wherein said steel pipe further contains at least one element selected from 0.5% or less of Cu, 0.5% or less of Ni, and 0.5% or less of Cr, by mass %.  
     
     
         8 . The high-strength steel pipe of API X65 grade or higher according to  claim 3 , wherein said steel pipe further contains at least one element selected from 0.5% or less of Cu, 0.5% or less of Ni, and 0.5% or less of Cr, by mass %.  
     
     
         9 . The high-strength steel pipe of API X65 grade or higher according to  claim 1 , wherein the ratio of the C content to the total content of Mo, Ti, Nb, V and W, R=(C/12)/[(Mo/96)+(Ti/48)+(Nb/93)+(V/51)+(W/184)], expressed by mass %, is in the range of 0.5 to 3.0.  
     
     
         10 . The high-strength steel pipe of API X65 grade or higher according to  claim 3 , wherein the ratio R is in the range of 0.5 to 3.0.  
     
     
         11 . The high-strength steel pipe of API X65 grade or higher according to  claim 9 , wherein the ratio R is in the range of 0.7 to 2.0.  
     
     
         12 . The high-strength steel pipe of API X65 grade or higher according to  claim 10 , wherein the ratio R is in the range of 0.7 to 2.0.  
     
     
         13 . A manufacturing method for a high-strength steel pipe of API X65 grade or higher, comprising the steps of: 
 heating a steel slab having chemical composition described in  claim 1  to a temperature in the range of 1000 to 1250° C.;    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./s;    coiling said cooled steel plate at a temperature in the range of 550 to 700° C.; and    forming said coiled steel plate into a steel pipe.    
     
     
         14 . A manufacturing method for a high-strength steel pipe of API X65 grade or higher, comprising the steps of: 
 heating a steel slab having chemical composition described in  claim 3  to a temperature in the range of 1000 to 1250° C.;    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./s;    coiling said cooled steel plate at a temperature in the range of 550 to 700° C.; and    forming said coiled steel plate into a steel pipe.    
     
     
         15 . A manufacturing method for a high-strength steel pipe of API X65 grade or higher, comprising the steps of: 
 heating a steel slab having chemical composition described in  claim 1  to a temperature in the range of 1000 to 1250° C.;    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 in the range of 600 to 700° C. at a cooling rate not lower than 2° C./s;    cooling said cooled steel plate to at least 550° C. at a cooling rate not higher than 0.1° C./s; and    forming said steel plate into a steel pipe.    
     
     
         16 . A manufacturing method for a high-strength steel pipe of API X65 grade or higher, comprising the steps of: 
 heating a steel slab having chemical composition described in  claim 3  to a temperature in the range of 1000 to 1250° C.;    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 in the range of 600 to 700° C. at a cooling rate not lower than 2° C./s;    cooling said cooled steel plate to at least 550° C. at a cooling rate not higher than 0.1° C./s; and    forming said steel plate into a steel pipe.    
     
     
         17 . A manufacturing method for a high-strength steel pipe of API X65 grade or higher, comprising the steps of: 
 heating a steel slab having chemical composition described in  claim 1  to a temperature in the range of 1000 to 1250° C.;    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 in the range of 550 to 700° C. at a cooling rate not lower than 2° C./s;    heating said cooled steel plate immediately after being cooled and keeping it at a temperature in the range of 550 to 700° C. for three minutes or longer; and    forming said steel plate into a steel pipe.    
     
     
         18 . A manufacturing method for a high-strength steel pipe of API X65 grade or higher, comprising the steps of: 
 heating a steel slab having chemical composition described in  claim 3  to a temperature in the range of 1000 to 1250° C.;    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 in the range of 550 to 700° C. at a cooling rate not lower than 2° C./s;    heating said cooled steel plate immediately after being cooled and keeping it at a temperature in the range of 550 to 700° C. for three minutes or longer; and    forming said steel plate into a steel pipe.    
     
     
         19 . The manufacturing method for a high-strength steel pipe of API X65 grade or higher according to  claim 17 , where in the heat treatment for keeping said steel plate at a temperature in the range 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 manufacturing method for a high-strength steel pipe of API X65 grade or higher according to  claim 18 , where in the heat treatment for keeping said steel plate at a temperature in the range 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.