Waukesha Metal 88, also known as “WM88”, “Alloy 88”, ASTM A494 CY5SnBiM, and UNS N26055 is an
alloy invented and previously patented by Waukesha Foundry in 1954 (US5242657A). Its main purpose is to prevent galling during metal-on-metal contact while being resistant to corrosion, especially in food processing industries where the use of liquid lubricants is prohibited. It is approved by the FDA (and 3-A sanitary standards) for contact with food and works well in conjunction with stainless steels, Inconel, Monel, and chromium plated parts where daily cleaning or sterilization is needed.
WM88 is a nickel-base alloy, despite frequently being called a “non-galling stainless steel”. It prevents
galling without the use of liquid lubricants due to its unique microstructure and chemical composition. Bismuth and tin are the main contributors to solid lubrication phases within the alloy’s microstructure, which help to prevent galling and seizing when sliding against another hard metal’s surface (even more so than other non-galling alloys, such as Nitronic 60 / CF10SMnN). Galling in food processing is especially undesirable, due to the potential for steel particles to end up in food or metal folds to harbor bacteria growth.
Corrosion resistance is another important property of Waukesha Metal 88, since many food processing
facilities prefer to use a “clean-in-place” (CIP) method to clean their pumps. This method can help reduce downtime, but sometimes utilizes acids or bases to remove potential buildup and prevent bacteria growth. Fortunately, thanks to chromium and molybdenum, WM88 can withstand most of these chemicals and match the resistance of austenitic stainless steels, except for some nitric acids (contact Waukesha Foundry for questions regarding chemical compatibility). If nitric acid is to be used to passivate new installations of stainless steel in pump systems, it is recommended that any WM88 parts be removed and cleaned by hand. WM88 additionally offers good machinability, comparable to 304 stainless steel, and matches 304 in its thermal expansion rate.
Although Waukesha Foundry keeps many sizes of cylindrical bars in stock for quick machining, WM88 is
also a very castable alloy and much of Waukesha Foundry’s 88 volume is near-net-shape castings. In most cases, these near-net-shape castings are more desirable from a design standpoint, rather than large cylindrical shapes. Contact Waukesha Foundry for the best approach to suit your application.
Although it has many benefits, Waukesha Metal 88 is not without drawbacks. Due to the small phases of
bismuth and tin and their low melting points compared to the surrounding nickel matrix, the alloy has operating temperature limitations. At elevated temperatures, these phases begin to expand and even melt, causing microcracking throughout the metal. Thus, it is important to note that WM88 is not repairable by welding, or weldable in any fashion. WM88’s properties also tend to degrade at temperatures near and below freezing, like those needed for ice cream and other dairy processing.
Waukesha Foundry has introduced some solutions to WM88’s shortcomings by offering some other alloys
with similar applications. Some applications outside of food processing require high temperature galling resistance or better wear resistance, such as in polymer processing, atomic energy, and aerospace manufacturing. Conversely, some manufacturing requires lower temperature food processing such as with ice cream. These gaps in WM88’s operating range can be filled with different, more niche alloys. Please contact Waukesha Foundry with questions regarding anti-galling needs outside of the operating ranges listed here.
Despite several attempts at copies to replicate WM88’s success across the industry, Waukesha Foundry
remains the quality authority for ASTM A494 CY5SnBiM and anti-galling alloys in general. Gall testing is performed on-site and results are available to all of Waukesha’s WM88 customers upon request. Waukesha Metal 88 can be difficult to cast defect-free and many indications can be undetectable by traditional NDT methods, but Waukesha Foundry’s experience and knowledge regarding its own alloy is unmatched.