Galling is when two metal surfaces join unintentionally, caused by micro-welding at localised points of contact. It is influenced by surface roughness, the type of metal, the environment, temperature and the load on the surface. The term usually refers to the damage done when the parts are pulled apart and the surface tears. The damage can repeat over time, and the debris generated can make it worse during later movements.

Limiting the occurrence of galling

  • Use coatings or lubricants to keep the bare metal surfaces apart and reduce the coefficient of friction between moving surfaces.
  • Reduce surface roughness. A ground or polished surface has fewer, less pronounced peaks at the microscopic level; those peaks encourage galling because of the high load over the small contact area at each point.
  • Use dissimilar metals. Bearings pair a relatively hard metal with a relatively soft one; the softer metal quickly conforms to the harder surface, removing large peaks.
  • Select alloys with particularly good resistance to galling.

Where components move or slide repeatedly, or need occasional disassembly, galling is a serious problem. We stock many alloys, and several stand out for their excellent galling resistance.

Galling-resistant alloys we stock

Hiduron® 130 (2.1504, DTD900/4805) and Hiduron® 191 (NES835, DEFSTAN 02-835) are high-strength copper nickel alloys invented by Langley Alloys. They resist galling well, particularly against super duplex stainless steels. They are also non-magnetic, highly resistant to seawater corrosion, resist marine fouling and stay tough down to low temperatures, which suits them to long-term seawater exposure - subsea connectors are a common application. Variations on the original Hiduron® 130 are produced by other manufacturers, such as Nibron Special.

Nitronic 60 (UNS S21800, Fermonic® 60) is an austenitic stainless steel with a unique composition, containing significant additions of both manganese and silicon. Manganese usually raises strength, but here, with silicon, it greatly improves the surface properties. Its galling resistance is extremely good, whether self-coupled or against a dissimilar metal, and it also has very good wear resistance for a corrosion-resistant alloy. That makes it well suited to specialist couplings, and it is also used selectively for valve seats, trim and stems, fasteners, couplings and break-away connectors, pins and bushes.

A more detailed exploration of galling is provided in a technical paper we presented at Duplex World.