Nitronic® 60 (UNS21800, Alloy 218) is an austenitic stainless steel that is used in a wide range of applications due to its exceptional wear and galling resistance. It was originally designed as a temperature alloy and has properties for temperatures of approximately 1800℉.
Due to the material’s good corrosion and wear resistance and its excellent high temperature oxidation resistance, Nitronic® 60 is used in a wide range of applications including military aircraft, deep-space exploration, bridge building and various medical applications. See below for a few specific examples:
- Surgical Scissors
- Wear Pins
- Pin and hanger expansion joints for bridges
- Marine shafts
- Valve trim
- Threaded assemblies
Medical Application Details
Due to the material’s resistance to fretting and galling with an ASTM F899 specification, the grade is used in a wide range of surgical instruments. It is important to note that Nitronic® 60 is not an implantable metal. Instead, it is primarily use for various surgical instruments includes but not limited to surgical scissors, ear pins, rollers and guides.
Other grades of Stainless Steel including 316 have better corrosion resistance than Nitronic® 60. However, the grade does have better chloride pitting resistance and stress corrosion cracking resistance. Additionally, in many applications wear and galling failure occurs first before corrosion failure. For these applications, this unique grade is an excellent choice. Also, its room temperature yield strength is nearly twice the levels found in stainless steel 304 and 316 grades.
You can find excellent wear and galling properties in various Nickel or Cobalt alloys, but these alloys come at a much higher price when compared to Nitronic® 60.
Galling Resistance Overview
Galling occurs when a metal surface is torn, rendering the component unserviceable. In threaded assemblies and valve trims, galling is a major concern which represents major application categories for Nitronic® 60. A button and block test is one way to rank alloys based on their galling resistance. In this test, a small button item and a large block are machined to provide parallel contacting surfaces. The smaller item is then rotated 360 degrees against the larger block. The material is then examined. If no damage is detected, the material is subjected to progressively higher stress levels.
Galling is important when dealing with stainless steels because most grades, with the exception of Nitronic steels, have fairly weak galling resistance compared to other steels.
Elevated Temperature Galling Applications
Nitronic® 60 can perform well in elevated temperature operating environments. Valve trim is one specific application where the grade performed consistently across a wide range of temperatures (800-1500℉). Other alloys galled within the range of (800-1500℉), illustrating the value that the grade can provide. Additionally, Nitronic 60® cannot be hardened by heat treatment. Annealing at 1950℉ followed by water quenching is what the mill producer AK Steel recommends.
- Bars and shapes – ASTM A276
- Stainless and heat-resisting steel billets and forging bars – ASTM A314
- Bars and shapes for use in boilers and other pressure vessels – ASTM A479
Nitronic® 60 Versus Nitronic® 50
Nitronic is an AK Steel registered trademark that includes a range of austenitic stainless steels. Nitronic® 50 (UNS S20910) is a widely used grade for pump and valve components.
Nitronic® 50 is similar to Nitronic® 60 in many ways. Nitronic® 50 is relied on more for its corrosion-resistant properties while Nitronic® 60’s primary benefits relate to its resistance to oxidation and its ability to tolerate extreme galling and wear.
Nitronic® 60 Summary Information
|ASTM A193, ASTM A194, ASTM A276, ASTM A479, AMS 5848-4||Medical, Aerospace, Industrial||Surgical Scissors, Cartilage Cutters, Wear Pins, Marine Shafts, Valve Trim, Threaded Assemblies||Bar, Wire, Plate, Sheet|
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