Martensitic stainless steel for brake disk and method for producing said steel

Abstract

A martensitic stainless steel used for a brake disk of a two-wheeled vehicle includes: in % by mass, C of 0.025% to 0.080%, Si of 0.05% to 0.8%, Mn of 0.5% to 1.5%, P of 0.035% or less, S of 0.015% or less, Cr of 11.0% to 13.5%, Ni of 0.01% to 0.50%, Cu of 0.01% to 0.08%, Mo of 0.01% to 0.30%, V of 0.01% to 0.10%, Al of 0.05% or less, and N of 0.015% to 0.060%; a DFE value defined by a formula (1) ranging from 5 to 30; and a δ ferrite fraction observed in a cross section structure ranging from 5% to 30% by an area ratio. Ti, B, Nb, Sn and Bi may be added. DFE =12(Cr+Si)−430C−460N−20Ni−7Mn−89  (1)

1 . A martensitic stainless steel used for a brake disk of a two-wheeled vehicle, the martensitic stainless steel comprising:
 in % by mass, C of 0.025% to 0.080%, Si of 0.05% to 0.8%, Mn of 0.5% to 1.5%, P of 0.035% or less, S of 0.015% or less, Cr of 11.0% to 13.5%, Ni of 0.01% to 0.50%, Cu of 0.01% to 0.08%, Mo of 0.01% to 0.30%, V of 0.01% to 0.10%, Al of 0.05% or less, and N of 0.015% to 0.060%;   the balance being Fe and inevitable impurities;   a DFE value defined by a formula (1) ranging from 5 to 30; and   a δ ferrite fraction observed in a cross section structure ranging from 5% to 30% by an area ratio,
     DFE =12(Cr+Si)−430C−460N−20Ni−7Mn−89  Formula (1)
 
   
       where: Cr, Si, C, N, Ni and Mn in the formula (1) respectively indicate contents. 
     
     
         2 . The martensitic stainless steel according to  claim 1 , further comprising: in % by mass, one or two of Ti of 0.03% or less and B of 0.0050% or less. 
     
     
         3 . The martensitic stainless steel according to  claim 1 , further comprising: in % by mass, Nb 0.30% or less. 
     
     
         4 . The martensitic stainless steel according to  claim 1 , further comprising: in % by mass, one or two of Sn of 0.1% or less and Bi of 0.2% or less. 
     
     
         5 . A manufacturing method of the martensitic stainless steel according to  claim 1 , comprising:
 heating a rough bar at a temperature ranging from 10 degrees C. to 50 degrees C. between a rough hot rolling and a finish hot rolling.   
     
     
         6 . The martensitic stainless steel according to  claim 1 , wherein
 the martensitic stainless steel is a hot-rolled steel plate that is not subjected to hot-rolling-and-annealing.   
     
     
         7 . The martensitic stainless steel according to  claim 1 , wherein
 the martensitic stainless steel is a hot-rolled and annealed steel plate.   
     
     
         8 . The martensitic stainless steel according to  claim 2 , further comprising: in % by mass, Nb 0.30% or less. 
     
     
         9 . The martensitic stainless steel according to  claim 2 , further comprising: in % by mass, one or two of Sn of 0.1% or less and Bi of 0.2% or less. 
     
     
         10 . The martensitic stainless steel according to  claim 3 , further comprising: in % by mass, one or two of Sn of 0.1% or less and Bi of 0.2% or less. 
     
     
         11 . The martensitic stainless steel according to  claim 8 , further comprising: in % by mass, one or two of Sn of 0.1% or less and Bi of 0.2% or less. 
     
     
         12 . A manufacturing method of the martensitic stainless steel according to  claim 2 , comprising:
 heating a rough bar at a temperature ranging from 10 degrees C. to 50 degrees C. between a rough hot rolling and a finish hot rolling.   
     
     
         13 . A manufacturing method of the martensitic stainless steel according to  claim 3 , comprising:
 heating a rough bar at a temperature ranging from 10 degrees C. to 50 degrees C. between a rough hot rolling and a finish hot rolling.   
     
     
         14 . A manufacturing method of the martensitic stainless steel according to  claim 4 , comprising:
 heating a rough bar at a temperature ranging from 10 degrees C. to 50 degrees C. between a rough hot rolling and a finish hot rolling.   
     
     
         15 . A manufacturing method of the martensitic stainless steel according to  claim 8 , comprising:
 heating a rough bar at a temperature ranging from 10 degrees C. to 50 degrees C. between a rough hot rolling and a finish hot rolling.   
     
     
         16 . A manufacturing method of the martensitic stainless steel according to  claim 9 , comprising:
 heating a rough bar at a temperature ranging from 10 degrees C. to 50 degrees C. between a rough hot rolling and a finish hot rolling.   
     
     
         17 . A manufacturing method of the martensitic stainless steel according to  claim 10 , comprising:
 heating a rough bar at a temperature ranging from 10 degrees C. to 50 degrees C. between a rough hot rolling and a finish hot rolling.   
     
     
         18 . A manufacturing method of the martensitic stainless steel according to  claim 11 , comprising:
 heating a rough bar at a temperature ranging from 10 degrees C. to 50 degrees C. between a rough hot rolling and a finish hot rolling.   
     
     
         19 . The martensitic stainless steel according to  claim 2 , wherein
 the martensitic stainless steel is a hot-rolled steel plate that is not subjected to hot-rolling-and-annealing.   
     
     
         20 . The martensitic stainless steel according to  claim 3 , wherein
 the martensitic stainless steel is a hot-rolled steel plate that is not subjected to hot-rolling-and-annealing.   
     
     
         21 . The martensitic stainless steel according to  claim 4 , wherein
 the martensitic stainless steel is a hot-rolled steel plate that is not subjected to hot-rolling-and-annealing.   
     
     
         22 . The martensitic stainless steel according to  claim 8 , wherein
 the martensitic stainless steel is a hot-rolled steel plate that is not subjected to hot-rolling-and-annealing.   
     
     
         23 . The martensitic stainless steel according to  claim 9 , wherein
 the martensitic stainless steel is a hot-rolled steel plate that is not subjected to hot-rolling-and-annealing.   
     
     
         24 . The martensitic stainless steel according to  claim 10 , wherein
 the martensitic stainless steel is a hot-rolled steel plate that is not subjected to hot-rolling-and-annealing.   
     
     
         25 . The martensitic stainless steel according to  claim 11 , wherein
 the martensitic stainless steel is a hot-rolled steel plate that is not subjected to hot-rolling-and-annealing.   
     
     
         26 . The martensitic stainless steel according to  claim 2 , wherein
 the martensitic stainless steel is a hot-rolled and annealed steel plate.   
     
     
         27 . The martensitic stainless steel according to  claim 3 , wherein
 the martensitic stainless steel is a hot-rolled and annealed steel plate.   
     
     
         28 . The martensitic stainless steel according to  claim 4 , wherein
 the martensitic stainless steel is a hot-rolled and annealed steel plate.   
     
     
         29 . The martensitic stainless steel according to  claim 8 , wherein
 the martensitic stainless steel is a hot-rolled and annealed steel plate.   
     
     
         30 . The martensitic stainless steel according to  claim 9 , wherein
 the martensitic stainless steel is a hot-rolled and annealed steel plate.   
     
     
         31 . The martensitic stainless steel according to  claim 10 , wherein
 the martensitic stainless steel is a hot-rolled and annealed steel plate.   
     
     
         32 . The martensitic stainless steel according to  claim 11 , wherein
 the martensitic stainless steel is a hot-rolled and annealed steel plate.