Ferritic stainless steel
A ferritic stainless steel suited for use as a member for heat exchangers to be brazed with Ni-based filler metal or Cu-based filler metal, comprising, on the basis of mass percent, C: 0.03% or less, Si: 3% or less, Mn: 2% or less, P: 0.05% or less, S: 0.03% or less, Cr: from 11 to 30%, Nb: from 0.15 to 0.8%, and N: 0.03% or less, wherein the balance is composed of Fe and incidental impurities, and wherein a value A determined by the following equation is 0.10 or greater: A=Nb−(C×92.9/12+N×92.9/14).
1. A process for producing a ferritic stainless sheet, which comprises a ferritic stainless steel, the process comprising:
preparing the ferritic stainless steel;
carrying out hot rolling at a take-up temperature less than 750° C.;
carrying out finishing annealing under the condition that the average heating rate from 600° C. to a maximum attained temperature Tm in a heating procedure is 10° C./s or greater and that the average cooling rate from the maximum attained temperature Tm to 600° C. in a cooling procedure is 10° C./s or greater; and
brazing the ferritic stainless steel sheet and a brazing filler metal to form a stainless steel joint, wherein
the ferritic stainless steel comprises, on the basis of mass percent,
C: 0.03% or less,
Si: 3% or less,
Mn: 2% or less,
P: 0.05% or less,
S: 0.03% or less,
Cr: from 11 to 30%,
Nb: from 0.15 to 0.8%,
N: 0.03% or less, and
the balance is Fe and incidental impurities, and
the ferritic stainless steel has a value A determined by the following equation that is 0.10 or greater:
A=Nb−(C×92.9/12+N×92.9/14)
a maximum diameter (d) of Nb-precipitates in the ferritic stainless steel is 0.25 μm or less, and the volume fraction (f) of the precipitates in the ferritic stainless steel is 0.05% or greater.
2. The process for forming a ferritic stainless steel sheet according to claim 1 , the ferritic stainless steel further comprising at least one of Mo, Cu, V, and W in a total amount of 4% or less.
3. The process for forming a ferritic stainless steel sheet according to claim 1 , the ferritic stainless steel further comprising at least one of Ti and Al in a total amount of 0.4% or less.
4. The process for forming a ferritic stainless steel sheet according to claim 1 , the ferritic stainless steel further comprising at least one of Ni and Co in a total amount of 5% or less.
5. The process for forming a ferritic stainless steel sheet according to claim 1 , the ferritic stainless steel comprising a total content of C and N that is 0.01% or greater.
6. The process for forming a ferritic stainless steel sheet according to claim 1 , the ferritic stainless steel comprising from 0.1% to 3% Si.
7. The process for forming a ferritic stainless steel sheet according to claim 1 , the ferritic stainless steel being for use in the manufacture of a member of heat exchangers or a member to be torch brazed.
8. The process for forming a ferritic stainless steel sheet according to claim 1 , wherein the stainless steel sheet is brazed by the brazing filler metal.
9. The process for forming a ferritic stainless steel sheet according to claim 1 , the ferritic stainless steel comprising at least one of Cu, Ni, and Co in an amount of 0%.
10. A process for producing a ferritic stainless sheet, which comprises a ferritic stainless steel, the process comprising:
preparing the ferritic stainless steel;
carrying out hot rolling at a take-up temperature less than 750° C.;
carrying out finishing annealing under the condition that the average heating rate from 600° C. to a maximum attained temperature Tm in a heating procedure is 10° C./s or greater and that the average cooling rate from the maximum attained temperature Tm to 600° C. in a cooling procedure is 10° C./s or greater; and
brazing the ferritic stainless steel sheet comprising the ferritic stainless steel and a brazing filler metal, to form a stainless steel joint, wherein the ferritic stainless steel comprises, on the basis of mass percent,
C: 0.03% or less,
Si: 3% or less,
Mn: 2% or less,
P: 0.05% or less,
S: 0.03% or less,
Cr: from 11 to 30%,
Nb: from 0.15 to 0.8%,
N: 0.03% or less, and
the balance is Fe and incidental impurities,
and the ferritic stainless steel has a Ti content (mol) that is greater than the total content (mol) of C and N, a value A′ determined by the following equation that is 0.10 or greater:
A′=Nb−C ×(92.9/12)/2,
a maximum diameter (d) of Nb-precipitates in the ferritic stainless steel is 0.25μm or less, and a volume fraction (f) of the precipitates in the ferritic stainless steel is 0.05% or greater.
11. The process for forming a ferritic stainless steel sheet according to claim 10 , the ferritic stainless steel being for use in the manufacture of a member of heat exchangers or a member to be torch brazed.
12. The process for forming a ferritic stainless steel sheet according to claim 10 , the ferritic stainless steel comprising at least one of Cu, Ni, and Co in an amount of 0%.
13. The process for forming a ferritic stainless steel sheet according to claim 10 , the ferritic stainless steel further comprising at least one of Mo, Cu, V, and W in a total amount of 4% or less.
14. The process for forming a ferritic stainless steel sheet according to claim 10 , the ferritic stainless steel further comprising at least one of Ti and Al in a total amount of 0.4% or less.
15. The process for forming a ferritic stainless steel sheet according to claim 10 , the ferritic stainless steel further comprising at least one of Ni and Co in a total amount of 5% or less.
16. The process for forming a ferritic stainless steel sheet according to claim 10 , the ferritic stainless steel comprising a total content of C and N that is 0.01% or greater.
17. The process for forming a ferritic stainless steel sheet according to claim 10 , the ferritic stainless steel comprising from 0.1% to 3% Si.