Brake disk having high temper softening resistance

Abstract

A brake disk including, by mass, 0.1% or less of C, 1.0% or less of Si, 2.0% or less of Mn, 10.5% to 15.0% of Cr, 2.0% or less of Ni, greater than 0.5% to 4.0% of Cu, 0.02% to 0.3% of Nb, and 0.1% or less of N and further including N, Nb, Cr. Si, Ni, Mn, Mo, and Cu, the remainder being Fe and unavoidable impurities, such that the following inequalities are satisfied: 5Cr+10Si+15Mo+30Nb−9Ni−5Mn−3Cu−225N−270C<45  (1) 0.03≦{C+N−(13/93)Nb}≦0.09  (2) and having a martensitic structure having prior-austenite grains with an average diameter of 8 μm or more, a hardness of 32 to 38 HRC, and high temper softening resistance.

1 . A brake disk comprising, by mass, 0.1% or less of C, 1.0% or less of Si, 2.0% or less of Mn, 10.5% to 15.0% of Cr, 2.0% or less of Ni, greater than 0.5% to 4.0% of Cu, 0.02% to 0.3% of Nb, and 0.1% or less of N and further comprising N, Nb, Cr, Si, Ni, Mn, Mo, and Cu, the remainder being Fe and unavoidable impurities, such that the following inequalities are satisfied:
   5Cr+10Si+15Mo+30Nb−9Ni−5Mn−3Cu−225N−270C<45  (1)     0.03≦{C+N−(13/93)Nb}≦0.09  (2) and   
     having a martensitic structure having prior-austenite grains with an average diameter of 8 μm or more, a hardness of 32 to 38 HRC and high temper softening resistance. 
   
   
       2 . The brake disk according to  claim 1 , wherein a precipitated Nb-to-total Nb ratio that is defined as the ratio of the amount of precipitated Nb to the amount of total Nb is less than 0.75 and the following inequalities are satisfied:
   5Cr+10Si+15Mo+30Nb−9Ni−5Mn−3Cu−225N−270C<45  (1)     0.03≦{C+N−(13/93)Nb}≦0.09  (2).   
   
   
       3 . The brake disk according to  claim 1 , wherein the square root (√ρ) of the density ρ of dislocations present in the martensitic structure is within a range from 0.8×10 8  to 1.3×10 8  m −1 . 
   
   
       4 . The brake disk according to  claim 1 , having a hardness of 30 HRC or more after being tempered at 650° C. for one hour. 
   
   
       5 . The brake disk according to  claim 1 , having fine Cu precipitates formed at dislocations present in the martensitic structure, wherein the square root (√ρ) of the density ρ of the dislocations present in the martensitic structure tempered at 650° C. for one hour is within a range from 0.6×10 8  to 1.3×10 8  m −1 . 
   
   
       6 . The brake disk according to  claim 1 , further comprising one or both of 0.01% to 2.0% of Mo and 0.01% to 1.0% of Co on a mass basis. 
   
   
       7 . The brake disk according to  claim 1 , further comprising one or more selected from the group consisting of, by mass, 0.02% to 0.3% of Ti, 0.02% to 0.3% of V, 0.02% to 0.3% of Zr, and 0.02% to 0.3% of Ta. 
   
   
       8 . The brake disk according to  claim 1 , further comprising, by mass, one or both of 0.0005% to 0.0050% of B and 0.0005% to 0.0050% of Ca. 
   
   
       9 . The brake disk according to  claim 2 , wherein the square root (√ρ) of the density ρ of dislocations present in the martensitic structure is within a range from 0.8×10 8  to 1.3×10 8  m −1 . 
   
   
       10 . The brake disk according to  claim 2 , having a hardness of 30 HRC or more after being tempered at 650° C. for one hour. 
   
   
       11 . The brake disk according to  claim 3 , having a hardness of 30 HRC or more after being tempered at 650° C. for one hour. 
   
   
       12 . The brake disk according to  claim 9 , having a hardness of 30 HRC or more after being tempered at 650° C. for one hour. 
   
   
       13 . The brake disk according to  claim 2 , having fine Cu precipitates formed at dislocations present in the martensitic structure, wherein the square root (√ρ) of the density ρ of the dislocations present in the martensitic structure tempered at 650° C. for one hour is within a range from 0.6×10 8  to 1.3×10 8  m −1 . 
   
   
       14 . The brake disk according to  claim 3 , having fine Cu precipitates formed at dislocations present in the martensitic structure, wherein the square root (√ρ) of the density ρ of the dislocations present in the martensitic structure tempered at 650° C. for one hour is within a range from 0.6×10 8  to 1.3×10 8  m −1 . 
   
   
       15 . The brake disk according to  claim 4 , having fine Cu precipitates formed at dislocations present in the martensitic structure, wherein the square root (√ρ) of the density ρ of the dislocations present in the martensitic structure tempered at 650° C. for one hour is within a range from 0.6×10 8  to 1.3×10 8  m −1 . 
   
   
       16 . The brake disk according to  claim 9 , having fine Cu precipitates formed at dislocations present in the martensitic structure, wherein the square root (√ρ) of the density ρ of the dislocations present in the martensitic structure tempered at 650° C. for one hour is within a range from 0.6×10 8  to 1.3×10 8  m −1 . 
   
   
       17 . The brake disk according to  claim 2 , further comprising one or both of 0.01% to 2.0% of Mo and 0.01% to 1.0% of Co on a mass basis. 
   
   
       18 . The brake disk according to  claim 3 , further comprising one or both of 0.01% to 2.0% of Mo and 0.01% to 1.0% of Co on a mass basis. 
   
   
       19 . The brake disk according to  claim 4 , further comprising one or both of 0.01% to 2.0% of Mo and 0.01% to 1.0% of Co on a mass basis. 
   
   
       20 . The brake disk according to  claim 5 , further comprising one or both of 0.01% to 2.0% of Mo and 0.01% to 1.0% of Co on a mass basis.