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MIL-A-12560H (MR)
w/INT. AMENDMENT 4
Plates shall not be stress relieved in a temperature range of 600-800 F. After stress relieving, the
plates shall be tested for hardness and shall meet the requirements of table II.
TABLE II. Hardness requirements.
Specified nominal thickness
Brinell hardness
Brinell
Rockwell C
of plate, inches
range, BHN,
indentation
hardness
From
To and incl.
Armor class
3000 kg load
diameters, mm
range, HRC
0.250
0.499
1&3
341-388
3.30-3.10
36.6-41.8
0.500
0.749
1&3
331-375
3.35-3.15
35.4-40.5
0.750
1.249
1&3
321-375
3.40-3.15
34.3-40.5
1.250
1.990
1&3
293-331
3.55-3.35
30.9-35.4
2.000
3.990
1&3
269-311
3.70-3.45
27.7-33.0
4.000
6.000
1&3
241-277
3.90-3.65
22.7-28.7
6.001
6999
3
241-277
3.90-3.65
22.7-28.7
7.000
8.999
3
223-262
4.05-3.75
19.2-26.7
9.000
12.000
3
212-248
4.15-3.85
16.4-24.2
0.250
1.250
2
277-321
3.65-3.40
28.7-34.3
3.2.4.2 Repairing. Unless otherwise approved by the procuring activity, weld repairs shall not be
made on any plates.
3.2.4.3 Forming. Forming after the final quenching and tempering operations shall not be done
except when authorized by the procuring activity.
3.2.4.4 Grinding. Grinding is not required but shall be performed to remove minor defects not
affecting the serviceability of the material provided that, unless otherwise authorized by the
procuring activity, the grinding does not result in the reduction of the plate thickness in the
ground area to less than the tolerances specified in tables III, IV, or V as applicable.
3.2.5 Mechanical properties.
3.2.5.1 Surface hardness. The average surface hardness of each plate including first article
samples shall be within the Brinell hardness range shown in table II for the applicable class and
thickness. The diameters of Brinell hardness impressions on any individual plate shall not vary
by more than 0.15 mm.
3.2.5.1.1 Class 4 armor plate. Surface hardness is required on every plate to insure quality and
uniformity of product. In addition, first article samples shall be tested for through hardness to
verify that they are within the HB range specified in 1.2.5 and 1.2.6. Respective diameters of the
Brinell hardness impression taken on an individual plate shall not vary by more than 0.15 mm.
Each lot shall be tested for through hardness. Acceptance for Class 4a material requires a
minimum through hardness of HRc 47 (BHN 442). Acceptance for class 4b material requires a
maximum through hardness HRc 41 (BHN 381).
6

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