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A-897
Grade 3
The ASTM A-897 ductile
iron casting specification is based on demonstrated mechanical
properties which depend on the proper cast iron microstructure.
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The
austempering heat treatment is the primary factor in determining the
microstructure and
mechanical properties of the A-897 ductile iron casting. |
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The
austempering process
produces a matrix microstructure that is substantially ausferrite (a mix of
high carbon austenite and acicular ferrite).
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Controlled
changes in the austempering process (temperatures and times) are used to tailor the ratio of austenite
and ferrite and to control the scale of the microstructure (fineness).
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The
different ADI grades reflect differences in microstructure which
produce the defined mechanical properties..
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For a
given cast iron alloy, the chemistry (carbon, silicon, manganese,
copper, nickel, molybdenum) is precisely controlled so
that the austemper process will consistently give the desired
microstructure and
mechanical properties.
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The
Grade 3 casting meets and exceed the requirements for tensile
strength, yield strength, and hardness, but it falls
short on ductility/elongation and impact strength. The
Grade 3 is not the best choice.
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