UNS R30035 (MP35N™ / ATI 35N™) and UNS N07718 (Alloy 718) are often seen as “competing” alloys, although the reality is that the choice between which to use is not a simplistic one versus the other. Each has specific properties that make it ideal for particular applications. This article will consider the strengths of each alloy.
First of all, it is important to know what you are comparing. Both UNS R30035 and UNS N07718 have “Oil & Gas” (respectively known as “NACE” and API 6A 718) and “Aerospace” (known by their AMS designations – UNS R30035 as AMS5844 and AMS5845, and UNS N07718 as AMS5662 and AMS5663) variants. Each variant has different mechanical properties (and the NACE variant of UNS R30035 has several according to the cold work / ageing temperature combination used). I will not go into these as they have been covered in depth in other articles and will instead concentrate on the advantages each alloy has.
MP35N is a nickel-cobalt alloy that contains 33-37% Nickel, 19-21% Chrome, and 9-10.5% Molybdenum, small additions of Titanium and Iron (1% max each), Carbon, Manganese, Silicon, Phosphorous and Sulphur (all less than 0.15% each). Cobalt is the balancing element (around 33%). It is known for its high tensile strength and ductility, making it a popular choice for Oil & Gas, Aerospace and Automobile fastener and nozzle / pin projects, and as medical and dental devices. However, the chemistry and manufacture also emphasise one of the most important properties of this alloy: resistance to corrosion. UNS R30035’s ability to resist corrosion from sources like hydrogen sulphide or saltwater mean that it is widely used in valve and pump applications as well as marine projects. Innate strength, toughness and corrosion resistance makes a superb combination.
UNS N07718 / alloy 718 is a nickel-chromium alloy that contains smaller amounts of iron, niobium, and molybdenum. In recent years, this alloy has become the” workhouse” of the Oil & Gas industry particularly in surface and down-hole applications. It is strong, easy to weld and resistant to corrosion – not as much as UNS R30035 but still impressive. It is especially durable at high temperatures, withstanding creep rupture even at temperatures up to 700° C. As a result, Alloy 718 is often also used in applications where heat tolerance is crucial, including Aerospace, Nuclear, Rocket and Turbines.
Both Alloy 718 and UNS R30035 are said to feature high tensile strength and ductility in a variety of different environments. However, MP35N definitely has the edge on tensile strength in all variants over Alloy 718, with Yield Strength values of 175-260 ksi compared to Alloy 718’s best of 130-150 ksi. Alloy 718 can also suffer significant losses of ductility at high Yield Strengths. For applications requiring very high tensile strength, then, MP35N has the advantage.
In specific environment settings as well, the two alloys compare well. Alloy 718 has a recommended temperature range of anywhere between -200°C and 550°C. By contrast, UNS R30035 has a range of between -200°C and 315°C. However, these operating temperatures need to be modified with consideration of the operating environment: in environments where the product may be exposed to saltwater or other corrosive substances, UNS R30035’s higher corrosion resistance makes it the superior product.
Making the Right Choice
Of course, the chemistry of each product makes the intrinsic cost significantly different, while manufacturing constraints limit UNS R30035 to relatively small bar sizes (3” or 76.2 mm dia). These undoubtedly need to be taken into account when considering the particular application being considered. Each alloy therefore has its own specific advantages. For help choosing the best metal for your application, please give us a call.
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