Steels_ Metallurgy and Applications, Third Edition

334 Steels: Metallurgy and Applications

Table 4.10

Streicher 18)

Commercial grades of low interstitial ferritic stainless steels (After

Alloy Limits for carbon, Melting and

nitrogen and stabilizers (%) refining processes

I Fe-18 Cr-2 Mo-Ti C - 0.0250 max.

N - 0.0250 max.

II Fe-26 Cr-1 Mo

C + N < 0.030 desirable

Ti + Nb = 0.20 + 4 (C + N) min.

= 0.80 max.

C - 0.0050 max.

N - 0.0150 max.

Nb = 13 to 29 (N)

II-A Fe-26 Cr- 1 Mo-Ti C - 0.0400 max.
N - 0.0400 max.
0.2 to 1.0 Ti
C + N = 0.050 typical
III Fe-28 Cr-2 Mo C + N < 0.0100
Desirable C + N < 0.050

III-A Fe-28 Cr-2 Mo-4 C - 0.0150 max.
Ni-Nb N - 0.0350 max.
C + N < 0.0400 with
Nb > 12 (C + N) + 0.2
IV Fe-29 Cr-4 Mo C - 0.0100 max.
N - 0.0200 max.
C + N = 0.0250 max.
IV-A Fe-29 Cr-4 Mo-2 Ni Same

Argon-oxygen

decarburization

or

vacuum-oxygen

decarburization

Electron beam

hearth refining

or

vacuum induction

melting

Argon-oxygen

decarburization

Vacuum melting

followed by

arc remelting

Vacuum-oxygen

decarburization

Argon-oxygen

decarburization

Vacuum induction

melting or electron

beam refining

Vacuum induction

melting

2% Mo 4% Ni-Nb and 29% Cr 4% Mo 2% Ni is beneficial in improving the
corrosion resistance in reducing acids. It is also claimed 18 that nickel improves
the toughness of ferritic stainless steels.
Low interstitial ferritic stainless steels have enjoyed some commercial success
in Sweden and the United States but failed to make much impression in the UK.
However, the author recalls one trial, involving an 18% Cr 2% Mo steel, for
the manufacture of a brewery vessel. This trial proved to be unsuccessful due
to fabrication problems and poor impact properties in the heat-affected zones
of welds.

Welding of stainless steels

A very high proportion of stainless steels is welded in the fabrication of pressure
vessels, storage tanks, chemical plant and domestic appliances. In each case, the
welds are required to be of high integrity and to provide corrosion resistance or