AMS 5845 MP35N Cobalt Alloy
MP35N Known for its exceptional strength, MP35N is deployed in aerospace applications that demand robust performance, including landing gear and engine fasteners.
Cobalt MP35N is a Multiphase cobalt-based alloy with a high percentage of nickel, chromium, and molybdenum. Like similar alloys, MP35N is non-magnetic. Further, it is characterized by an ultra-high tensile strength of up to 300 ksi (2070 mPa), depending on the work-strengthening method used, good ductility, excellent toughness, and biocompatibility. This alloy can be used in the fully-hardened condition at service temperatures up to 750° F (400° C).
Lork Group offers Cobalt MP35N in three AMS and three ASTM sub-type specifications:
- AMS 5758 (Bar)
- AMS 5844 (Bar)
- AMS 5845 (Bar)
Note: The choice depends on subsequent processing requirements. If the customer intends to perform secondary operations-such as thread cutting or external grinding-AMS 5844 is recommended, as it provides a more generous machining allowance. Conversely, if the material is to be installed and used directly without further modification, AMS 5845 is the preferred choice due to its superior stability and strength.
Chemical Composition
| Element | min | max |
| Carbon, C | - | 0.025 |
| Manganese, Mn | - | 0.15 |
| Silicon, Si | - | 0.15 |
| Phosphorus, P | - | 0.015 |
| Sulfur, S | - | 0.010 |
| Nickel, Ni | 33.00 | 37.00 |
| Chromium, Cr | 19.00 | 21.00 |
| Iron, Fe | - | 1.00 |
| Molybdenum, Mo | 9.00 | 10.50 |
| Titanium, Ti | - | 1.00 |
| Cobalt, Co | Balance* | |
Mechanical and Physical Properties
| Property | Imperial | Metric |
| Density | 0.309 lb/in3 | 8.55 g/cm3 |
| Hardness, Rockwell B | 90 | 90 |
| Ultimate Tensile Strength (Annealed condition) | 130000 psi | 896 MPa |
| Tensile Strength, Yield 0.2% (Annealing at 1925 °F or 1052 °C) |
55000 psi | 379 MPa |
| Elongation at Break (Annealed condition in 4D) | 65 % | 65 % |
| Reduction of Area | 75 % | 75 % |
| Modulus of Elasticity (Annealed) | 33760 ksi | 232.8 GPa |
| Modulus of Elasticity (Cold worked and aged) | 34050 ksi | 234.8 GPa |
| Modulus of Elasticity (Annealed at 900 °F or 482 °C) |
29150 ksi | 201.0 GPa |
| Modulus of Elasticity (Cold worked and aged at 900 °F or 482 °C) |
29190 ksi | 201.3 GPa |
| Shear Modulus (Annealed at 900 °F or 482 °C) |
9830 ksi | 67.8 GPa |
| Shear Modulus (Cold worked and aged at 900 °F or 482 °C) |
10240 ksi | 70.60 GPa |
| Shear Modulus (Annealed at 78 °F or 25.6 °C) |
11740 ksi | 80.94 GPa |
| Shear Modulus (Annealed at 78 °F or 25.6 °C) |
12090 ksi | 83.36 GPa |
Heat Treatment
To achieve full strength of heavily cold-worked M35N alloy parts, an aging process of 4 hours at 1000° F to 1200° F (540° C to 650° C) is recommended. Better corrosion and sulfide resistance can be achieved by an aging process at 425° F (220° C), but in this case, the tensile strength will be much lower. Extremely high aging temperatures aren't recommended as they might reduce the strength that was achieved with cold working.
Corrosion Resistance
Excellent resistance to nitric, hydrochloric, sulfuric acids, hydrogen sulfide, seawater, and salt spray environments. Exceptional resistance to stress-corrosion cracking (SCC) and hydrogen embrittlement, even at very high strength levels in severe environmental conditions. High resistance to localized attacks such as pitting and crevice corrosion. In seawater, MP35N is nearly immune to corrosion.
According to NACE MR0175/ISO15156 for MP35N "any combinations of temperature pH2S, chloride concentration, and in situ pH occurring in production environments are acceptable."
Boiling 85-89% ZnCl2 is known to cause SCC in alloy MP35N.
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