inal chromium contents of 12, 17, and 27% corresponding
to alloys 405, 430, and 446, respectively
(Table 1 and Fig. 13). The carbon content
is 0.12% maximum for type 430. This steel is
normally supplied in the annealed condition
and, with the exception of the rapid cooling
such as may occur after welding, type 430 is
considered a nonhardenable material. By comparison,
martensitic alloy 410 with 12% Cr and
0.12% C is fully air hardenable, while 12% Cr
ferritic alloy 405 with 0.08% C is not (Ref 24).
Similar to standard 18Cr-8Ni austenitic stainless
steels, chromium and carbon in these
chromium-iron ferritic alloys react to form
chromium carbide precipitates when heated to
315 to 925 °C (600 to 1700 °F). Precipitates
form both at grain boundaries and within the
grains. Sensitization develops as chromium is
depleted from the areas surrounding the precipitates
(Ref 24). Toughness is also reduced by
carbide precipitation. Between 370 and 480 °C
(700 and 900 °F), precipitation of α prime, a
bcc, chromium-rich phase, also occurs and
reduces overall toughness. The time required
for precipitation of α prime is much longer than
the time required for sensitization; therefore, α-
prime precipitation is generally associated with
in-service exposure, while sensitization may
develop during short-term exposure, such as
welding. The combined effect of these precipitates
results in 475 °C (885 °F) embrittlement
(Ref 25).
inal chromium contents of 12, 17, and 27% correspondingto alloys 405, 430, and 446, respectively(Table 1 and Fig. 13). The carbon contentis 0.12% maximum for type 430. This steel isnormally supplied in the annealed conditionand, with the exception of the rapid coolingsuch as may occur after welding, type 430 isconsidered a nonhardenable material. By comparison,martensitic alloy 410 with 12% Cr and0.12% C is fully air hardenable, while 12% Crferritic alloy 405 with 0.08% C is not (Ref 24).Similar to standard 18Cr-8Ni austenitic stainlesssteels, chromium and carbon in thesechromium-iron ferritic alloys react to formchromium carbide precipitates when heated to315 to 925 °C (600 to 1700 °F). Precipitatesform both at grain boundaries and within thegrains. Sensitization develops as chromium isdepleted from the areas surrounding the precipitates(Ref 24). Toughness is also reduced bycarbide precipitation. Between 370 and 480 °C(700 and 900 °F), precipitation of α prime, abcc, chromium-rich phase, also occurs andreduces overall toughness. The time requiredfor precipitation of α prime is much longer thanthe time required for sensitization; therefore, α-prime precipitation is generally associated within-service exposure, while sensitization maydevelop during short-term exposure, such aswelding. The combined effect of these precipitatesresults in 475 °C (885 °F) embrittlement(Ref 25).
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