Type Analysis | Description | Applications | Corrosion Resistance
Physical Properties | Heat Treatment | Workability | Typical Mechanical Properties

Type Analysis

Description

Alloy M-252 is a precipitation hardening, nickel-based high temperature alloy designed for use in highly stressed parts operating at temperature up to 1600°F. The elements chromium, cobalt, aluminum, molybdenum, and titanium confer good high temperature strength, good corrosion resistance to jet engine gases, and continuous resistance to oxidation up to 1800°F.

Applications

Alloy M-252 has been used in jet engine and gas turbine buckets.

Corrosion Resistance

Alloy M-252 exhibits very good resistance to jet engine gases up to 1600°F (871°C). Room temperature resistance to normal corrosive atmospheres is superior to that of Type 316 stainless.

Physical Properties

Density                                                                                            Melting Range
  lb/cu in ............................. 0.298                                                   °F................................... 2400/2500
  kg/cu m ............................ 8249                                                    °C ................................. 1316/1371

Modulus of elasticity

Mean coefficient of thermal expansion

Thermal conductivity

Heat Treatment

Annealing
Heat to 1900/1925°F (1038/1050°C), hold at heat for 4 hours, then water quench. Hardness will vary between Rb 90 and Rc 30, depending upon section size or rapidity of quench.

Solution Treatment
Heat to 1950°F (1066°C), hold at heat for 4 hours, then air cool. Hardness Rc 27/30.

Precipitation Hardening Treatment
Heat to 1400°F (760°C), hold at heat for 15 hours, then air cool. Hardness Rc 36/42.

Workability

Hot Working
Alloy M-252 should be forged between an initial furnace temperature of 2150°F and an optical finishing temperature of 1800/1850°F.

Cold Working
Alloy M-252 work hardenss very rapidly and frequent anneals are required. An annealing treatment in the range of 1900/1025°F with water quench is desirable. Aging after cold working can result in strain age cracking. Cold worked sections should be heated through the aging temperature range of 1200/1600°F to the solution or annealing temperature as rapidly as possible. Sizable amounts of cold reduction-between anneals-are mandatory. Small reductions, such as sizing passes, must be avoided because strain age cracking may result.

Machinability
Alloy M-252 is very difficult to machine in the solution treated or age hardened conditions. Better tool life will be obtained by machining in the solution treated condition; however, a smoother finish will be obtained by machining in the age hardened condition.
Alloy M-252 has been satisfactorily machined in both the solution treated and age hardened conditions using a tungsten carbide grade with the following tool shapes:
0° back rake
6° side rake
7° clearance end and side
10° end cutting edge angle
45° side cutting edge angle
1/16" (1.59 mm) nose radius
The following general machining parameters are suggested when machine alloy M-252:
Feed: 0.005/0.11" (0.130/0.28 mm) per revolution
Depth of cut: 1/32-1/8" (0.79/3.18 mm)
Speeds: 60/70 ft per min (0.30/0.36 m/s) for solution annealed condition 48/56 ft per min (0.24/0.28 m/s) for age hardened condition.
Rigid, well powered machines should be used. Machined finishes are generally improved if the alloy is in the fully treated or partially aged condition. Air cooling from the solution treating temperature is adequate.
If solution treating is required after finish machining, the treating should be in protective atmosphere to prevent intergranular oxidation. Intergranular surface oxidation is minor at aging temperatures; thus machining followed by aging may be acceptable for many applications.

Typical Mechanical Properties

Typical Room Temperature and Elevated Temperature Mechanical Properities
Solution treated 1950°F (1066°C) 4 hrs, air cooled, + 1400°F (760°C) 15 hrs, air cooled.

Hot Hardness
Treated 1950°F (1066°C) 4 hrs, air cool + 1400°F (760°C) 16 hrs, air cool.(Rockwell hardness before and after the hot hardness tests -Rc 39/40.)

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