Alloy MP35N, 2.4999, UNS R30035 - nickel alloy

Alloy MP35N, 2.4999, UNS R30035 - nickel alloy according to AMS 5844 and API 6ACRA

MP35N, 2.4999 – description

Alloy MP35N (UNS R30035) is an Ni-Co-Cr-Mo high-performance, age-hardened superalloy, combining ultrahigh low-temperature strength, high ductility, and high corrosion resistance to the wide range of corrosive environments, including resistance to stress-corrosion cracking in the high-strength condition. MP35N is strengthened by cold work and age-hardening. Cold working causes the solid-state phase transformation of part of the matrix from a face-centered cubic (fcc) crystal structure to a hexagonal closed-packed (hcp) structure, which is possible due to the high cobalt content. The reaction is called the MultiPhase reaction, since MP in the alloy's designation. Age-hardening stabilizes the two phases, further strengthening the alloy. It is the highest strength material approved by NACE MR0175/ISO 15156 and API 6ACRA for structural components in aggressive, sour well environments.

There are two main versions of this alloy:

• AMS 5844 and AMS 5845 - for the aircraft industry
• NACE MR0175 / ISO 15156 and API 6ACRA - for the Oil&Gas industry

Please note that AMS 5844 materials are supplied in the cold-drawn condition and to achieve the final properties they need to be aged, whereas AMS 5845 and NACE MR0175 / ISO 15156 materials are supplied cold-drawn and aged.

Further, MP35N alloy products are differentiated by their tensile strength. Examples are version designated as 220ksi / 1517MPa or 265ksi / 1827MPa (both the American notation in ksi and the European notation in MPa are common). The tensile strength depends on the cold deformation and the heat treatment.

MP35N is produced by vacuum induction melting followed by vacuum arc remelting to provide control of chemistry and proper ingot solidification.

Applications

Alloy MP35N is used in the aircraft industry for fasteners, springs, airframes and tie rods (AMS 5844, 5845) and in Oil&Gas industry for high-strength structural components, drive shafts for downhole oil pumps and tubular goods. Additionally, it's for surgical implants and in medical marine applications.

Physical and Tensile Properties

Room temperature physical properties:

• Density: 8.43 g/cm³
• Melting Temperature: 1315-1440 °C

High-temperature Coefficient of thermal expansion, from 20°C to:

• 100°C: 12.8 μm/m⋅K
• 200°C: 13.7 μm/m⋅K
• 315°C: 14.8 μm/m⋅K
• 425°C: 14.9 μm/m⋅K
• 540°C: 15.7 μm/m⋅K

Thermal Conductivity:

• -184°C: 6.5 W/m · K
• -73°C: 9.1 W/m · K
• 20°C: 11.2 W/m · K
• 100°C: 12.7 W/m · K
• 200°C: 15.0 W/m · K
• 315°C: 17.0 W/m · K
• 425°C: 19.2 W/m · K
• 540°C: 21.3 W/m · K
• 650°C: 23.4 W/m · K

Electrical Resistivity:

• -184°C: 0.986 μΩ·m
• -73°C: 1.011 μΩ·m
• 20°C: 1.033 μΩ·m
• 100°C: 1.051 μΩ·m
• 200°C: 1.078 μΩ·m
• 315°C: 1.104 μΩ·m
• 425°C: 1.129 μΩ·m
• 540°C: 1.154 μΩ·m
• 650°C: 1.179 μΩ·m

Young's Modulus of annealed MP35N:

• 20°C: 232.8 GPa
• 232°C: 216 GPa
• 482°C: 201 GPa

Young's Modulus of cold worked and aged MP35N:

• 20°C: 234.8 GPa
• 232°C: 219 GPa
• 482°C: 201.3 GPa

Shear Modulus of annealed MP35N:

• 20°C: 83.36 GPa
• 232°C: 77.84 GPa
• 482°C: 70.60 GPa

Shear Modulus of cold worked and aged MP35N:

• 20°C: 80.95 GPa
• 232°C: 74.74 GPa
• 482°C: 67.78 GPa

Room-Temperature Tensile Properties of MP35N as a function of cold work reduction and heat treatment:

• Cold work reduction: 0 %
  • Tensile strength: 931 MPa
  • Yield strength: 414 MPa
  • Elongation: 70 %
  • Reduction of area: 70 %
  • Hardness: 8 HRC
• + aged (4h w 540°C, AC)
  • Tensile strength: 931 MPa
  • Yield strength: 414 MPa
  • Elongation: 68 %
  • Reduction of area: 77 %
  • Hardness: 7 HRC
• Cold work reduction: 15 %
  • Tensile strength: 1069 MPa
  • Yield strength: 814 MPa
  • Elongation: 41 %
  • Reduction of area: 70 %
  • Hardness: 29 HRC
• + aged (4h w 540°C, AC)
  • Tensile strength: 1089 MPa
  • Yield strength: 862 MPa
  • Elongation: 70 %
  • Reduction of area: 33 %
  • Hardness: 7 HRC
• Cold work reduction: 25 %
  • Tensile strength: 1172 MPa
  • Yield strength: 1034 MPa
  • Elongation: 28 %
  • Reduction of area: 65 %
  • Hardness: 34 HRC
• + aged (4h w 540°C, AC)
  • Tensile strength: 1282 MPa
  • Yield strength: 1207 MPa
  • Elongation: 24 %
  • Reduction of area: 65 %
  • Hardness: 39 HRC
• Cold work reduction: 35 %
  • Tensile strength: 1336 MPa
  • Yield strength: 1062 MPa
  • Elongation: 22 %
  • Reduction of area: 67 %
  • Hardness: 42 HRC
• + aged (4h w 540°C, AC)
  • Tensile strength: 1400 MPa
  • Yield strength: 1344 MPa
  • Elongation: 21 %
  • Reduction of area: 62 %
  • Hardness: 43 HRC
• Cold work reduction: 45 %
  • Tensile strength: 1572 MPa
  • Yield strength: 1303 MPa
  • Elongation: 17 %
  • Reduction of area: 62 %
  • Hardness: 47 HRC
• + aged (4h w 540°C, AC)
  • Tensile strength: 1772 MPa
  • Yield strength: 1731 MPa
  • Elongation: 12 %
  • Reduction of area: 52 %
  • Hardness: 46 HRC
• Cold work reduction: 53-55 %
  • Tensile strength: 1827 MPa
  • Yield strength: 1413 MPa
  • Elongation: 12 %
  • Reduction of area: 50 %
  • Hardness: 47 HRC
• + aged (4h w 540°C, AC)
  • Tensile strength: 2068 MPa
  • Yield strength: 1999 MPa
  • Elongation: 10 %
  • Reduction of area: 48 %
  • Hardness: 50 HRC
• Cold work reduction: 65 %
  • Tensile strength: 1931 MPa
  • Yield strength: 1620 MPa
  • Elongation: 11 %
  • Reduction of area: 49 %
  • Hardness: 50 HRC

Stress-Rupture Properties - stress causing rupture in:

• 220 ksi (1517 MPa) version, according to AMS 5844/5845
  • 540°C, 10h: 1288 MPa
  • 540°C, 200h: 1151 MPa
  • 540°C, 1000h: 951 MPa
  • 590°C, 10h: 1137 MPa
  • 590°C, 200h: 916 MPa
  • 590°C, 1000h: 661 MPa
  • 650°C, 10h: 916 MPa
  • 650°C, 200h: 641 MPa
• 265 ksi (1827 MPa) version, according to AMS 5844/5845
  • 540°C, 10h: 1440 MPa
  • 540°C, 200h: 1233 MPa
  • 540°C, 1000h: 985 MPa
  • 590°C, 10h: 1219 MPa
  • 590°C, 200h: 951 MPa
  • 590°C, 1000h: 661 MPa
  • 650°C, 10h: 944 MPa
  • 650°C, 200h: 641 MPa

R.R. Moore bending fatigue strength:

• 220 ksi (1517 MPa) version, according to AMS 5844/5845
  • 10⁶h: 689 MPa
  • 10⁷h: 620 MPa
  • 10⁸h: 606 MPa
• 265 ksi (1827 MPa) version, according to AMS 5844/5845
  • 10⁶h: 744 MPa
  • 10⁷h: 682 MPa
  • 10⁸h: 668 MPa

Charpy V-notch impact strength of 49% cold drawn and aged (4h, 650°C) alloy MP35N:

• 20°C: 25.6 J
• -73°C: 23.2 J
• -129°C: 20.7 J
• -196°C: 21.8 J
• -253°C: 18.3 J

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.

Weldability

Very good weldability, similar to 304 stainless steel. However, the weld's heat-affected zone is weakened, and it is not possible to recover the strength simply by using post-weld heat treatment, because MP35N gains strength through cold work.

Heat Treatment, Working and Machining

Cold working is a crucial step in the production process, determining the strength of the final product. As a rule, products are delivered in a cold-worked condition. Cold deformation reaches as high as 65%.

Heat treatment according to AMS 5844 / 5845 (max stress-rupture strength):

• Solution-treatment: 1040-1050°C 4-8h; AC
• Age-hardening: 540-650°C 4-4.5h; AC

Age-hardening according to NACE MR0175 / ISO15156 - the standard describes 6 following aging treatments:

• For springs: 649°C; 4h
• For any equipment 1: 704°C; 4h
• For any equipment 2: 732°C; 4h
• For any equipment 3 (best SCC resistance. lowest tensile strength): 774°C; 6h
• For any equipment 4: 788°C; 4h
• For any equipment 5: 802°C; 2h
• For any equipment 6: 816°C; 1h

Every aforementioned treatment is improving resistance to stress corrosion cracking (SCC) at the cost of the tensile strength. The best SSC resistance is provided by 6h treatment in 744°C.

We deliver this steel alloy as:

• Cold drawn bars according to AMS 5844
• Cold drawn and aged bars according to AMS 5845
• Cold drawn and aged bars according to NACE MR0175 / ISO 15156
• Centerless ground bars according to AMS 5758
• Fittings according to AMS 7468
• Surgical implants according to ASTM F 562

Replacements, equivalents and other designations:

MP35N, 2.4999, Haynes MP35N, Latrobe MP35N, SPS MP35N, 35N32KChM, AMS 5844 (R30035), AMS 5845 (R30035), AMS 7468 (R30035), AMS 5758 (R30035), ASTM B 1011 (R30035)/ASME SB1011 (R30035)