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Heat treat AISI 4142 material

Heat treat AISI 4142 material

Heat treat AISI 4142 material

(OP)
I have to heat treat AISI 4142 material and meet a minimum tensile of 143,000 and (here's the kicker) we need to run charpy tests at -40 and obtain 25-mils lateral expansion. In the AISI 4142 range of chemistry allowed by ASTM A-540 B22, what elements will give me a better chance of meeting this (High C, low P & S, High Mo etc.) ?
 The finished material specification A-540 requires a minimum tempering temp of 850 F.
 If any one has performed a heat treat and met this I'd like to correspond w/you.  Thanks in advance for your time.

RE: Heat treat AISI 4142 material

QAFitz;
I would not change a thing regarding chemistry ( one exception; lower carbon is better because of the direct affect on notch toughness), expect make sure you have a tempered martensite structure throughout.  Quench in oil and temper at 1100 deg F. The tempered martensite structure of 4142 should meet the impact requirements.

For 4140  Q&T

1100 deg F
148 UTS Ksi
132 YS Ksi
19.0 % E (2" gage)
58% RA

311 BHN
69  ft-lbs at RT

RE: Heat treat AISI 4142 material

How thick? I'd try to get a heat with the Cr, Mn and Mo near the high limits if it's over ~1" thick, and as Metengr says, as low C as possible.  You should also check the grain size before you HT--you want it as small as possible.  Assuming it's a thick piece, quench from 1525 deg max. into cool oil or polymer with as much circulation as possible.  You may find an 1125 deg. temper will be right on.

"When the eagles are silent, the parrots begin to jabber."
    Winston Churchill

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