MIL-DTL-62567D(AT)
3.2 Design and construction.
3.2.1 Materials. The contractor shall select the material, but the material shall be capable
of meeting the operational requirements specified herein. It is recommended, but not mandatory,
that steel alloy 300M, class 3, condition optional, as specified in SAE AMS 6257 be used.
3.2.1.1 Billet material. The billet material shall meet both of the following requirements:
a. The billet material shall have a sufficient internal cleanliness as determined by
testing in accordance with 4.2a.
b. The billet material shall have a sufficient surface cleanliness as determined by
testing in accordance with 4.2b.
3.2.1.2 Bar stock. The bar stock shall meet both of the following requirements:
a. The finished bar stock (before hot upsetting) shall have a sufficient internal
cleanliness as determined by testing in accordance with 4.2c.
b. The finished bar stock shall be as follows:
1. The finished bar stock (before hot upsetting) shall have a sufficient surface
cleanliness as determined by testing in accordance with 4.2d. No laps or
seams shall be permitted, or,
2. The finished bar stock shall have a sufficient internal cleanliness as
determined by testing in accordance with 4.2e.
3.2.2 Processing.
3.2.2.1 Heat treatment. The torsion bar shall be quenched and double tempered to a
through hardness of Rockwell C51 minimum. This hardness is required for the bar to be
compatible with the design requirements of interfacing components (see 4.6.1).
3.2.2.1.1 Decarburization and retained austenite. Microscopic examination of a prepared
cross section of the torsion bar following final heat treatment at a magnification of 250 diameters
shall show no evidence of retained austenite or partial decarburization beyond a depth of
0.003 inches from the surface. Partial decarburization between the surface and a depth of
0.003 inches shall not result in a hardness reduction of more than 3 points Rockwell C as
determined by microhardness traverse comparison between that area and the core hardness
(see 4.6.1).
3.2.2.2 Surface indications. Magnetic particle inspection of the finished torsion bar
(after final heat treatment) shall disclose no indications in excess of the requirements of
SAE AMS 2300 and SAE AMS 6257. Laps, inclusions, and seams shall not be permitted. Nicks
and scratches less than four inches long shall be removed by blending the surface to a depth of
not greater than 0.010 inch. After removal of scratches, the torsion bar shall still meet
dimensional requirements of Drawing 12292010 (see 4.6.2 and 4.6.3).
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