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Cobalt - 188 Bar

Spec: AMS 5772

188 Bar

AMS 5772
UNS R30188
PDF: 188 Bar

Nominal Composition

  • Cobalt 40%
  • Nickel 22%
  • Chromium 22%
  • Tungsten 14%
  • Silicon 0.4%
  • Lanthanum 0.05%

Description

Alloy 188 is a cobalt-base austenitic alloy with excellent high temperature strength and good oxidation resistance to 2000°F (1093°C). The high chromium level coupled with small additions of lanthanum produce an extremely tenacious and protective scale. The alloy also has good sulfidation resistance and excellent metallurgical stability displayed by its good ductility after prolonged exposure to elevated temperatures. Good fabricability and machinability combine to make the alloy useful in typical gas turbine applications as well as airframe and chemical processing applications.

Properties

Non-magnetic. Alloy 188 has good high temperature strength up to 1800°F (982°C) and good oxidation resistance up to 2100°F (1149°C). This alloy performs well in continuous high temperature service and has excellent oxidation, spalling and corrosion resistance, achieved through the addition of chromium in combination with a minute amount of lanthanum. The lanthanum addition produces a tenacious, protective oxide scale at high temperatures. This alloy also maintains its ductility at cryogenic temperatures but strength levels are increased substantially. AMS 5772 requires minimum yield strength of 55,000 psi at room temperature.

Hardness

Hardness of Aerodyne stock is typically 240 BHN and never higher than 302 BHN by specification. Alloy 188 has a very high rate of work hardening and can be strengthened by cold deformation, with enhancement of strength achieved by aging at 1000°F (540°C) temperature for 4 to 16 hours. Cold working prior to aging significantly increases the response to precipitation hardening.

Machinability

RATING:
15% of B-1112

TYPICAL STOCK REMOVAL RATE:
25 surface feet/minute with high speed tools. 70 surface feet/minute with carbide tools.
Conventional machining techniques used for stainless steels may be used. This alloy does work-harden during machining and has higher strength and "gumminess" typical of stainless steels. Heavy duty machining equipment and tooling should be used to minimize chatter or work-hardening of the alloy ahead of the cutting. Water-base coolants are preferred for high speed operations such as turning, grinding, or milling. Heavy lubricants work best for drilling, tapping, broaching or boring.

Density:

0.324 lbs/in3, 8.98 g/cm3

Standard Inventory Specifications

  • AMS 5772
  • GE B50TF74
  • Line marked over 0.5 inch in diameter
  • Predominantly produced by AOD-ESR melt method. Hot rolled, solution heat treated (annealed), then centerless ground or rough turned.
  • Lengths: 10-12 feet