ASTM 668 Vs AISI 4340

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Main Question or Discussion Point

Please can anyone help me to understand, is ASTM 668 is equivalent with AISI 4340.
In AISI 4340 Hardness values are restricted upto 35 HRC , whereas ASTM 668 hardness values are upto 38 HRC.
waiting for replies. Please help me out.
 

Answers and Replies

  • #2
Astronuc
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ASTM is a standard which covers a particular form (and heat treatment schedule) of 4340, and perhaps other grades of steel.
http://www.astm.org/Standards/A668.htm

AISI 4340 is a particular grade with a particular composition with nominally 0.4% C (0.38-0.43) - Ref: http://www.suppliersonline.com/propertypages/4340.asp
Note the ranges of heat treatment and forging temperatures. The temperature and degree of work will affect final microstructure.
Note the many standards that apply to 4340, but each may represent a different geometry, e.g, wire, rod, plate, bar, strip, . . . , final heat treatment and degree of cold work.

Usually there is a range of ductility and hardness, part of which is dependent on the amount of carbon, and the amount of cold-work (dislocation density) remaining.

I'll try to find more information, but I don't have the ASTM 1.06 Standards book.
 

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