Electric resistance welded steel pipe for mechanical structural components, and method for producing same

Abstract

An ERW steel pipe for a mechanical structural part, the pipe including a straight pipe portion includes a base metal portion and an ERW portion, wherein the base metal portion has a chemical composition including, in terms of % by mass: 0.30 to 0.38% of C, 0.05 to 0.40% of Si, 0.50 to 2.00% of Mn, 0.010 to 0.060% of Al, 0.005 to 0.050% of Ti, and 0.0003 to 0.0050% of B, wherein a microstructure of a wall thickness central portion of the base metal portion is tempered martensite, wherein, a de-C layer in which a concentration of C is 90% or less with respect to the concentration of C in the chemical composition has a thickness of less than 0.20 mm, and a de-B layer in which a concentration of B is 90% or less with respect to the concentration of B in the chemical composition has a thickness of less than 0.10 mm, at each of inner and outer surface sides of the base metal portion, and wherein each of a Vickers hardness at a position at a depth of 0.5 mm from each of the inner and outer surface sides is 420 Hv or more and less than 510 Hv.

1 . An electric resistance welded steel pipe for a mechanical structural part, the pipe comprising a straight pipe portion,
 wherein the straight pipe portion comprises a base metal portion and an electric resistance welded portion,   wherein the base metal portion has a chemical composition consisting of, in terms of % by mass:   from 0.30 to 0.38% of C,   from 0.05 to 0.40% of Si,   from 0.50 to 2.00% of Mn,   from 0.010 to 0.060% of Al,   from 0.005 to 0.050% of Ti,   from 0.0003 to 0.0050% of B,   from 0.0005 to 0.0040% of Ca,   from 0 to 0.0060% of N,   from 0 to 0.020% of P,   from 0 to 0.0200% of S,   from 0 to 0.0050% of O,   from 0 to 0.50% of Cu,   from 0 to 0.50% of Ni,   from 0 to 0.50% of Cr,   from 0 to 0.20% of V,   from 0 to 0.10% of Nb,   from 0 to 0.50% of Mo,   from 0 to 0.0500% of Mg,   from 0 to 0.0500% of REM, and   a balance consisting of Fe and impurities,   wherein a microstructure of a central portion in a wall thickness direction of the base metal portion is tempered martensite,   wherein, in a case in which a layer in which a concentration of C is 90% or less with respect to the concentration of C in the chemical composition of the base metal portion is defined as a de-C layer, and a layer in which a concentration of B is 90% or less with respect to the concentration of B in the chemical composition of the base metal portion is defined as a de-B layer, the de-C layer has a thickness of less than 0.20 mm and the de-B layer has a thickness of less than 0.10 mm, at each of an inner surface side and an outer surface side of the base metal portion, and   wherein each of a Vickers hardness at a position at a depth of 0.5 mm from an inner surface of the base metal portion and a Vickers hardness at a position at a depth of 0.5 mm from an outer surface of the base metal portion is 420 Hv or more and less than 510 Hv.   
     
     
         2 . The electric resistance welded steel pipe for a mechanical structural part according to  claim 1 , wherein the chemical composition of the base metal portion comprises one or more selected from the group consisting of, in terms of % by mass:
 from 0.01 to 0.50% of Cu,   from 0.05 to 0.50% of Ni,   from 0.05 to 0.50% of Cr, and   from 0.01 to 0.50% of Mo.   
     
     
         3 . The electric resistance welded steel pipe for a mechanical structural part according to  claim 1 ,
 wherein the straight pipe portion has an outer diameter of from 10 to 50 mm, and   wherein a value obtained by dividing a wall thickness of the base metal portion by the outer diameter of the straight pipe portion is from 0.04 to 0.25.   
     
     
         4 . The electric resistance welded steel pipe for a mechanical structural part according to  claim 1 , wherein, in the chemical composition of the base metal portion, F1 represented by the following Formula (1) is 0.50 or more: 
       
         
           
             
               
                 
                   
                     
                       F 
                       ⁢ 
                       1 
                     
                     = 
                     
                       Ca 
                       × 
                       
                         ( 
                         
                           1 
                           - 
                           
                             124 
                             × 
                             O 
                           
                         
                         ) 
                       
                       / 
                       
                         ( 
                         
                           1.25 
                           × 
                           S 
                         
                         ) 
                       
                     
                   
                 
                 
                   
                     Formula 
                     ⁢ 
                         
                     
                       ( 
                       1 
                       ) 
                     
                   
                 
               
             
           
         
         wherein each element symbol in Formula (1) represents a content of each element in terms of % by mass. 
       
     
     
         5 . A method of producing the electric resistance welded steel pipe for a mechanical structural part according to  claim 1 , the method comprising:
 a preparation step of preparing an as-rolled electric resistance welded steel pipe, wherein:
 the as-rolled electric resistance welded steel pipe comprises a base metal portion A and an electric resistance welded portion A; and 
 the base metal portion A has a chemical composition consisting of, in terms of % by mass: 
   from 0.30 to 0.38% of C,   from 0.05 to 0.40% of Si,   from 0.50 to 2.00% of Mn,   from 0.010 to 0.060% of Al,   from 0.005 to 0.050% of Ti,   from 0.0003 to 0.0050% of B,   from 0.0005 to 0.0040% of Ca,   from 0 to 0.0060% of N,   from 0 to 0.020% of P,   from 0 to 0.0200% of S,   from 0 to 0.0050% of O,   from 0 to 0.50% of Cu,   from 0 to 0.50% of Ni,   from 0 to 0.50% of Cr,   from 0 to 0.20% of V,   from 0 to 0.10% of Nb,   from 0 to 0.50% of Mo,   from 0 to 0.0500% of Mg,   from 0 to 0.0500% of REM, and   a balance consisting of Fe and impurities;   a quenching step of subjecting the as-rolled electric resistance welded steel pipe to quenching; and   a tempering step of subjecting the as-rolled electric resistance welded steel pipe that has been subjected to quenching to tempering, to obtain the electric resistance welded steel pipe for a mechanical structural part;   wherein, in the quenching step, an oxygen content in an atmosphere in which the quenching is performed is 1,000 volume ppm or less, and a cooling rate in the quenching is 10° C./sec or more.   
     
     
         6 . The method of producing the electric resistance welded steel pipe for a mechanical structural part, according to  claim 5 , further comprising a pipe-drawing step of subjecting the as-rolled electric resistance welded steel pipe to pipe drawing, after the preparation step and before the quenching step,
 wherein the as-rolled electric resistance welded steel pipe that has been subjected to pipe drawing is subjected to quenching, in the quenching step.   
     
     
         7 . The method of producing the electric resistance welded steel pipe for a mechanical structural part, according to  claim 5 , further comprising a step of subjecting the as-rolled electric resistance welded steel pipe to shot blasting, after the preparation step and before the quenching step. 
     
     
         8 . The method of producing the electric resistance welded steel pipe for a mechanical structural part, according to  claim 5 ,
 wherein a heating temperature in the quenching is from 900 to 1,050° C., and   wherein a heating temperature in the tempering is from 100 to 500° C.   
     
     
         9 . An electric resistance welded steel pipe for a mechanical structural part, the pipe comprising a straight pipe portion,
 wherein the straight pipe portion comprises a base metal portion and an electric resistance welded portion,   wherein the base metal portion has a chemical composition comprising, in terms of % by mass:   from 0.30 to 0.38% of C,   from 0.05 to 0.40% of Si,   from 0.50 to 2.00% of Mn,   from 0.010 to 0.060% of Al,   from 0.005 to 0.050% of Ti,   from 0.0003 to 0.0050% of B,   from 0.0005 to 0.0040% of Ca,   from 0 to 0.0060% of N,   from 0 to 0.020% of P,   from 0 to 0.0200% of S,   from 0 to 0.0050% of O,   from 0 to 0.50% of Cu,   from 0 to 0.50% of Ni,   from 0 to 0.50% of Cr,   from 0 to 0.20% of V,   from 0 to 0.10% of Nb,   from 0 to 0.50% of Mo,   from 0 to 0.0500% of Mg,   from 0 to 0.0500% of REM, and   a balance comprising Fe and impurities,   wherein a microstructure of a central portion in a wall thickness direction of the base metal portion is tempered martensite,   wherein, in a case in which a layer in which a concentration of C is 90% or less with respect to the concentration of C in the chemical composition of the base metal portion is defined as a de-C layer, and a layer in which a concentration of B is 90% or less with respect to the concentration of B in the chemical composition of the base metal portion is defined as a de-B layer, the de-C layer has a thickness of less than 0.20 mm and the de-B layer has a thickness of less than 0.10 mm, at each of an inner surface side and an outer surface side of the base metal portion, and   wherein each of a Vickers hardness at a position at a depth of 0.5 mm from an inner surface of the base metal portion and a Vickers hardness at a position at a depth of 0.5 mm from an outer surface of the base metal portion is 420 Hv or more and less than 510 Hv.   
     
     
         10 . The electric resistance welded steel pipe for a mechanical structural part according to  claim 9 , wherein the chemical composition of the base metal portion comprises one or more selected from the group consisting of, in terms of % by mass:
 from 0.01 to 0.50% of Cu,   from 0.05 to 0.50% of Ni,   from 0.05 to 0.50% of Cr, and   from 0.01 to 0.50% of Mo.   
     
     
         11 . The electric resistance welded steel pipe for a mechanical structural part according to  claim 9 ,
 wherein the straight pipe portion has an outer diameter of from 10 to 50 mm, and   wherein a value obtained by dividing a wall thickness of the base metal portion by the outer diameter of the straight pipe portion is from 0.04 to 0.25.   
     
     
         12 . The electric resistance welded steel pipe for a mechanical structural part according to  claim 9 , wherein, in the chemical composition of the base metal portion, F1 represented by the following Formula (1) is 0.50 or more: 
       
         
           
             
               
                 
                   
                     
                       F 
                       ⁢ 
                       1 
                     
                     = 
                     
                       Ca 
                       × 
                       
                         ( 
                         
                           1 
                           - 
                           
                             124 
                             × 
                             O 
                           
                         
                         ) 
                       
                       / 
                       
                         ( 
                         
                           1.25 
                           × 
                           S 
                         
                         ) 
                       
                     
                   
                 
                 
                   
                     Formula 
                     ⁢ 
                         
                     
                       ( 
                       1 
                       ) 
                     
                   
                 
               
             
           
         
         wherein each element symbol in Formula (1) represents a content of each element in terms of % by mass. 
       
     
     
         13 . A method of producing the electric resistance welded steel pipe for a mechanical structural part according to  claim 9 , the method comprising:
 a preparation step of preparing an as-rolled electric resistance welded steel pipe, wherein:
 the as-rolled electric resistance welded steel pipe comprises a base metal portion A and an electric resistance welded portion A; and 
 the base metal portion A has a chemical composition comprising, in terms of % by mass: 
   from 0.30 to 0.38% of C,   from 0.05 to 0.40% of Si,   from 0.50 to 2.00% of Mn,   from 0.010 to 0.060% of Al,   from 0.005 to 0.050% of Ti,   from 0.0003 to 0.0050% of B,   from 0.0005 to 0.0040% of Ca,   from 0 to 0.0060% of N,   from 0 to 0.020% of P,   from 0 to 0.0200% of S,   from 0 to 0.0050% of O,   from 0 to 0.50% of Cu,   from 0 to 0.50% of Ni,   from 0 to 0.50% of Cr,   from 0 to 0.20% of V,   from 0 to 0.10% of Nb,   from 0 to 0.50% of Mo,   from 0 to 0.0500% of Mg,   from 0 to 0.0500% of REM, and   a balance comprising Fe and impurities;   a quenching step of subjecting the as-rolled electric resistance welded steel pipe to quenching; and   a tempering step of subjecting the as-rolled electric resistance welded steel pipe that has been subjected to quenching to tempering, to obtain the electric resistance welded steel pipe for a mechanical structural part;   wherein, in the quenching step, an oxygen content in an atmosphere in which the quenching is performed is 1,000 volume ppm or less, and a cooling rate in the quenching is 10° C./sec or more.   
     
     
         14 . The method of producing the electric resistance welded steel pipe for a mechanical structural part, according to  claim 13 , further comprising a pipe-drawing step of subjecting the as-rolled electric resistance welded steel pipe to pipe drawing, after the preparation step and before the quenching step,
 wherein the as-rolled electric resistance welded steel pipe that has been subjected to pipe drawing is subjected to quenching, in the quenching step.   
     
     
         15 . The method of producing the electric resistance welded steel pipe for a mechanical structural part, according to  claim 13 , further comprising a step of subjecting the as-rolled electric resistance welded steel pipe to shot blasting, after the preparation step and before the quenching step. 
     
     
         16 . The method of producing the electric resistance welded steel pipe for a mechanical structural part, according to  claim 13 , wherein:
 a heating temperature in the quenching is from 900 to 1,050° ° C., and   a heating temperature in the tempering is from 100 to 500° C.