steel - Nouvelle page 1 - Free

MMPDS-01
31 January 2003
2.4.3 9Ni-4Co-0.30C
2.4.3.0 Comments and Properties — The 9Ni-4Co-0.30C alloy was developed specifically
to have high hardenability and good fracture toughness when heat treated to 220 to 240 ksi ultimate tensile
strength. The alloy is through hardening in section sizes up to 4 inches thick. The alloy may be exposed to
temperatures up to 900EF (approximately 100EF below typical tempering temperature) without
microstructural changes which degrade room temperature strength. This grade must be formed and welded
in the annealed condition. Preheat and post-heat of the weldment is required. The steel is produced by
consumable electrode vacuum melting.
The heat treatment for this alloy consists of normalizing at 1650 ± 25EF for 1 hour per inch of cross
section, cooling in air to room temperature, heating to 1550 ± 25EF for 1 hour per inch of cross section but
not less than 1 hour, quenching in oil or water, subzero treating at -100EF for 1 to 2 hours, and double
tempering at 975 ± 10EF (sheet, strip, and plate) or 1000 ± 10EF (bars, forgings, and tubings) for 2 hours.
Material specifications for 9Ni-4Co-0.30C steel are presented in Table 2.4.3.0(a). The room
temperature mechanical and physical properties are shown in Table 2.3.4.0(b). The effect of temperature on
thermal expansion is shown in Figure 2.4.3.0.
Table 2.4.3.0(a). Material Specifications for
9Ni-4Co-0.30C Steel
Specification
AMS 6524 a
AMS 6526
a Noncurrent specification.
Form
Sheet, strip, and plate
Bar, forging, and tubing
2.4.3.1 Heat-Treated Condition — Effect of temperature on various mechanical properties
is presented in Figures 2.4.3.1.1. through 2.4.3.1.4. Typical stress-strain and tangent-modulus curves are
presented in Figures 2.4.3.1.6(a) through (d). Notched fatigue data at room temperature are illustrated in
Figure 2.4.3.1.8.
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