Filler Metal Selection Basics When it Comes to Weathering Steel

Swanton Welding welder in action working on steel project

A weathering effect is produced by the alloying of small amounts copper, nickel and chromium to a steel substrate. Not only does the underlying steel take on a pleasing brownish tinge but also develops a corrosion resistant patina. Weathered steel is used extensively in outdoor applications where rain, sleet and snow are expected and where the finished steel product will be visible to the naked eye. In addition, the weld joints between the steel components and the associated metal filler must also be subjected to the weathering process to match or complement the steel base metal. Here is a quick rundown on how it works:

Filler Metal Selection Basics

Building codes and specification requirements will be the overriding concern when choosing filler metals for a weathering steel application. The location of the weld, its size and whether or not it will be painted will also figure in the decision process. Typically, any type of filler metal chosen will need to meet the same minimums as that of the base material.

It is extremely important to confirm the exact specification and grade of the substrate before choosing the filler metal as well as to what the final finish will be on the structure. To this end, consider the following two factors. What corrosion resistance does the weld need to provide and will the weld be expected to match the color of the substrate or will it be painted over. Once these decisions are made, you can make a choice from among the following filler materials:

Carbon Steel Filler Metals

Carbon steel filler metals are the most cost-effective option due to the fact that fewer alloying elements are incorporated into their formulations. A high amount of base metal dilution takes place and the alloys are deposited by using a number of single-pass welds. This dilution means that the weld inherently approximately mimics the strength, corrosion resistance and color of the steel substrate without any undue effort on the part of the welder. In addition, this alloy allows for the least labor intensive work and thus reduces overall cost.  

Low Alloy Filler Metals

Multi-pass welds are less invasive on the substrate and therefore do not dilute the base metal as much as single pass ones. Therefore they require fillers with a lower concentration of the expensive alloys but can still provide the proper amount of corrosion resistance. Still, it should be remembered that low alloy filler metals may not always provide the same inherent strength and toughness to match that of the steel substrate. For this reason, these types of welds are only used on non-critical seams that can fail without causing too much damage.


All outdoor welds will eventually adopt a patina similar to weathered steel substrate. In some cases, it is preferred that the the weld match the color and texture of base material in a far more expeditious manner. In this case, weathered are the preferred material of choice for welds. In addition, smaller welds can often be made with less than optimal filler materials because the high dilution rate of the base metal will conceal any lack of a color match.

Corrosion Resistance

All metals will degrade and weather to a certain extent over time. Sometimes this weathering is desired from an aesthetic point of view and sometimes it is not. For this reason, filler materials must be chosen carefully to either mimic the weathering of the base metal or to complement it. Filler materials are quite versatile in this respect and they comprise a small part of the total project. They can be designed and affordably manufactured with more expensive alloys that are far more corrosion-resistant than the base metal. The result is a weld that will highlight the structure of the base metal. Alternatively, filler metals can be created that completely blend in with the substrate.  

Finding the proper balance of strength and looks in a filler metal factors in science and the process. The science will take you a good part of the way but an experienced eye is also necessary when the process is actually begun. For all your structural steel needs, contact our team at Swanton Welding Company. We’ve been serving Ohio as one of the state’s largest metal fabricators since 1985. We’ve got the service and expertise to exceed all your metal fabricating expectations.

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