Martensitic stainless steel material

Abstract

A martensitic stainless steel material contains, in mass %, C: 0.030% or less, Ni: 5.00 to 7.00%, Cr: 10.00 to 14.00%, and Cu: more than 1.00 to 3.50%. On two line segments LS of 1000 μm extending in a wall thickness direction with arbitrary two points as a center located at positions at a depth of 2 mm from the inner surface, respectively, a degree of Cr segregation ΔCr defined by Formula (1) described in the description, a degree of Mo segregation ΔMo defined by Formula (2) described in the description, and a degree of Cu segregation ΔCu defined by Formula (3) described in the description satisfy Formula (4): ΔCr+ΔMo+ΔCu≤A  (4) where, when the yield strength is 758 to less than 862 MPa, A in Formula (4) is 0.70, and when the yield strength is 862 MPa or more, A in Formula (4) is 0.50.

1 . A martensitic stainless steel material that is a seamless steel pipe or a round steel bar, having a chemical composition consisting of, in mass %:
 C: 0.030% or less,   Si: 1.00% or less,   Mn: 1.00% or less,   P: 0.030% or less,   S: 0.0050% or less,   Ni: 5.00 to 7.00%,   Cr: 10.00 to 14.00%,   Mo: 1.50 to 3.00%,   Al: 0.005 to 0.050%,   V: 0.01 to 0.30%,   N: 0.0030 to 0.0500%,   Ti: 0.020 to 0.150%,   Cu: more than 1.00 to 3.50%,   Co: 0.50% or less,   B: 0 to 0.0050%,   Ca: 0 to 0.0050%,   Mg: 0 to 0.0050%,   rare earth metal (REM): 0 to 0.0050%,   Nb: 0 to 0.15%, and   W: 0 to 0.20%,   with the balance being Fe and impurities,   wherein:   a yield strength is 758 MPa or more;   in a case where the martensitic stainless steel material is the seamless steel Pipe,   when, in a cross section including a rolling direction and a wall thickness direction of the seamless steel pipe, an arbitrary two points at positions at a depth of 2 mm from an inner surface are defined as two center points P1, and two line segments of 1000 μm extending in the wall thickness direction with each center point P1 as a center are defined as two line segments LS, energy dispersive X-ray spectroscopy is performed at measurement positions at a pitch of 1 μm on each line segment LS, and a Cr concentration, a Mo concentration, and a Cu concentration at each measurement position are determined;   in a case where the martensitic stainless steel material is the round steel bar,   when, in a cross section including a rolling direction and a radial direction of the round steel bar, an arbitrary two points on a central axis of the round steel bar are defined as two center points P1, and two line segments of 1000 μm extending in the radial direction with each center point P1 as a center are defined as two line segments LS, energy dispersive X-ray spectroscopy is performed at measurement positions at a pitch of 1 μm on each line segment LS, and a Cr concentration, a Mo concentration, and a Cu concentration at each measurement position are determined; and   when:   an average value of all of the Cr concentrations determined at all of the measurement positions on the two line segments LS is defined as [Cr] ave ,   a sample standard deviation of all of the Cr concentrations determined at all of the measurement positions on the two line segments LS is defined as σ Cr ,   among all of the Cr concentrations determined at all of the measurement positions on the two line segments LS, an average value of the Cr concentrations included within a range of [Cr] ave ±3σ Cr  is defined as [Cr*] ave ,   among all of the Cr concentrations determined at all of the measurement positions on the two line segments LS, a maximum value of the Cr concentrations included within a range of [Cr] ave ±3σ Cr  is defined as [Cr*] max ,   among all of the Cr concentrations determined at all of the measurement positions on the two line segments LS, a minimum value of the Cr concentrations included within a range of [Cr] ave ±3σ Cr  is defined as [Cr*] min ,   an average value of all of the Mo concentrations determined at all of the measurement positions on the two line segments LS is defined as [Mo] ave ,   a sample standard deviation of all of the Mo concentrations determined at all of the measurement positions on the two line segments LS is defined as σ Mo ,   among all of the Mo concentrations determined at all of the measurement positions on the two line segments LS, an average value of the Mo concentrations included within a range of [Mo] ave ±3σ Mo  is defined as [Mo*] ave ,   among all of the Mo concentrations determined at all of the measurement positions on the two line segments LS, a maximum value of the Mo concentrations included within a range of [Mo] ave ±3σ Mo  is defined as [Mo*] max ,   among all of the Mo concentrations determined at all of the measurement positions on the two line segments LS, a minimum value of the Mo concentrations included within a range of [Mo] ave ±3σ Mo  is defined as [Mo*] min ,   an average value of all of the Cu concentrations determined at all of the measurement positions on the two line segments LS is defined as [Cu] ave ,   a sample standard deviation of all of the Cu concentrations determined at all of the measurement positions on the two line segments LS is defined as σ Cu ,   among all of the Cu concentrations determined at all of the measurement positions on the two line segments LS, an average value of the Cu concentrations included within a range of [Cu] ave ±3σ Cu  is defined as [Cu*] ave ,   among all of the Cu concentrations determined at all of the measurement positions on the two line segments LS, a maximum value of the Cu concentrations included within a range of [Cu] ave ±3σ Cu  is defined as [Cu*] max , and   among all of the Cu concentrations determined at all of the measurement positions on the two line segments LS, a minimum value of the Cu concentrations included within a range of [Cu] ave ±3σ Cu  is defined as [Cu*] min ,   a degree of Cr segregation ΔCr defined by Formula (1), a degree of Mo segregation ΔMo defined by Formula (2), and a degree of Cu segregation ΔCu defined by Formula (3) satisfy Formula (4):
   ΔCr=([Cr*] max −[Cr*] min )/[Cr*] ave   (1)
 
   ΔMo=([Mo*] max −[Mo*] min )/[Mo*] ave   (2)
 
   ΔCu=([Cu*] max −[Cu*] min )/[Cu*] ave   (3)
 
   ΔCr+ΔMo+ΔCu≤A  (4)
 
   where, in a case where the yield strength is 758 to less than 862 MPa, A in Formula (4) is 0.70, and in a case where the yield strength is 862 MPa or more, A in Formula (4) is 0.50.   
     
     
         2 . The martensitic stainless steel material according to  claim 1 , wherein the chemical composition contains one or more elements selected from the group consisting of:
 B: 0.0001 to 0.0050%,   Ca: 0.0001 to 0.0050%,   Mg: 0.0001 to 0.0050%,   rare earth metal (REM): 0.0001 to 0.0050%,   Nb: 0.01 to 0.15%, and   W: 0.01 to 0.20%.