An Introduction to SMAW and SAW Consumables
Quality shielded metal arc welding (SMAW) and submerged arc welding (SAW) welds typically start with using a quality consumable. For both of these commonly-used processes, choosing the right consumable for the application is key.
Knowing the appropriate consumable for the job will support the development of the ideal welding procedure. Good input variables (welding consumables) are a key to good output variables (products). A handy online tool (lincolnelectric.com/en/Welding-and-Cutting-Resource-Center/Welding-Guides) lists consumables compatible with specific base metals for both processes.
Welding consumables are often manufactured and classified to AWS A5 filler metal specifications. The electrode classification makes for easier selection and comparison of electrodes. AWS A5.1, Specification for Carbon Steel Electrodes for Shielded Metal Arc Welding, was the first filler metal specification, issued more than 80 years ago by a joint committee of ASTM International and AWS. The A5 Committee revised this document many times, and another revision is planned for 2023.
AWS currently has nine different A5 filler metal specifications for SMAW electrodes. Each alloy (mild steel, stainless steel, etc.) has its own specification, including one for underwater wet welding electrodes. For Excalibur® 7018 MR® to have the AWS classification of E7018 H4R, the test details and requirements listed in AWS A5.1 must be met. These include the chemical composition, mechanical properties, diffusible hydrogen level, and moisture pickup. There are also requirements for usability, sizing, packaging, and labeling.
When determining the appropriate SMAW electrode for a job, consideration must be given to base metal selection, thermal conditions, joint design, machine parameters, and welding code requirements. Many SMAW electrodes are similar to each other, but certain characteristics make specific electrodes more desirable for a particular application. SMAW electrodes for carbon steel can be broken down into four electrode groups based on their usability characteristics.
Fast-freeze electrodes (for example, E6010 and E6011) have the ability to deposit weld metal that solidifies rapidly, providing advantages when welding joints with poor fitup or when welding in the vertical/overhead positions. These electrodes typically provide deep joint penetration and maximum admixture while also requiring a high degree of operator skill.
Fast-fill electrodes (for example, E7024-1 and E7028) have the ability to deposit metal rapidly in the heat of the arc and are thus capable of making very large welds on flat and horizontal surfaces. They are well suited to new welders since they are very easy to use. The coverings of fast-fill electrodes contain approximately 50% iron powder, yielding high deposition rates.
Fill-freeze electrode characteristics fall between fast-freeze and fast-fill electrodes. Fill-freeze electrodes provide medium joint penetration and medium deposition. These electrodes are particularly suited for welding sheet metal and are typically used in all welding positions. These are the go-to electrodes for home or farm welding. Examples are E7014 and E6013.
Low-hydrogen electrodes have either fast-fill or fill-freeze characteristics. They typically produce x-ray-quality welds with excellent notch-toughness properties. These electrodes reduce the risk of underbead cracking and are desirable for higher-carbon and low-alloy steels. Low-hydrogen electrodes may also lessen steel preheat requirements. Even though low-hydrogen electrodes should arrive in a hermetically sealed container, once the container is open, they are susceptible to moisture pickup. Proper low-hydrogen electrode storage and handling is key to preserving their unique properties. Electrodes designated H4—for example, E7018 H4 and E7016-1 H4R—are designed, manufactured, and tested to be resistant to moisture pickup.
SAW uses two separate consumables (flux and electrode) to make a weld deposit. The weld metal is a combination of both, so the flux/electrode combination is classified. AWS A5.17, Specification for Carbon Steel Electrodes and Fluxes for Submerged Arc Welding; A5.23, Specification for Low-Alloy and High Manganese Steel Electrodes and Fluxes for Submerged Arc Welding; and A5.39, Specification for Flux and Electrode Combinations for Submerged Arc and Electroslag Joining and Surfacing of Stainless Steel and Nickel Alloys, relate to SAW consumables. AWS A5.17 and A5.23 cover carbon and low-alloy steel, while A5.39 covers stainless steel and nickel-alloy SAW consumables.
Techniques to Classify SAW Consumables
There are two methods for SAW consumables classification in the AWS specifications: a multiple-pass technique and a two-run technique (used only in A5.23). The two-run method uses a single pass made from each side of the plate. This is common in the manufacture of pipe sections, wind towers, and various other industries.
Due to having two different recognized techniques, the same flux/wire combination may be certified to multiple classifications, each with significantly different strength and toughness designators. This is due to substantial differences in the amount of base metal dilution, the weld metal geometry, and the amount of microstructural grain refinement between the different welding conditions. An easy way to distinguish a two-run classification is the presence of a T following the number for the strength designator.
Many real-world applications with SAW fall somewhere between the two-run and the multiple-pass conditions. The push for increased productivity often results in a designed multiple-pass weld being only 3-4 passes. The weld metal toughness in this situation will be often closer to the two-run condition. It is recommended that both the multiple-pass and two-run classifications reported by the manufacturer be considered to determine if the chosen flux/wire combination will likely meet the required mechanical properties. An easy way to do this is by using an online certificate site (such as lincolnelectric.com/en/Certificate-Center).
This article was written by Charlie Cross (welding technical specialist) and Jennifer Peverelle (customer solutions development engineer), both of The Lincoln Electric Co., Cleveland, Ohio, for the American Welding Society.