SMAW, hardfacing electrode basics

You’d need a book to contain every piece of essential knowledge pertaining to electrodes for shielded metal arc welding (SMAW) and hardfacing. One thing for sure is that these consumables are not one size fits all. They have varying material coatings, fall into different categories, serve a variety of purposes, and even require specialized storage and care. Understanding these basics about your SMAW and hardfacing electrodes makes a world of difference in your end result.

Steel electrodes fall into three categories based on coating composition: cellulosic, rutile, and basic. Cast Iron Weld Fabrication

Cellulosic electrodes, such as E6010 and E6011, primarily feature wood pulp (cellulose) that generates hydrogen to create a digging/driving arc with deep penetration. The driving arc creates appeal for farm equipment repair and other applications with contaminated surfaces, as well as the V-grooves associated with open-root pipe joints. To control the weld puddle with a digging/driving arc, use a “whip and pause” technique with E6010 electrodes.

A rutile electrode, such as E6013 and E7014, has a coating comprising titanium dioxide (TiO2), silicon dioxide (SiO2), iron powder, and calcium carbonate (CaCO3). E7014 electrodes have elevated iron levels so they can run at higher currents and offer higher deposition rates. Rutile electrodes start easily, require no special manipulation, and create a soft arc with light penetration. They are said to have high welder appeal, but they do generate more spatter.

Basic electrodes have a coating comprising CaCO3, fluorspar (CaF2), ferromanganese, and iron powder. The word basic refers to the coating’s pH. E7018 is the most popular basic electrode and achieves an arc with medium dig/drive and medium penetration. Basic coatings also have low hydrogen and moisture absorption levels, which are essential for critical welds because hydrogen molecules can permeate the weld metal and cause cracking when they expand and try to escape. As a result, this electrode category is commonly referred to as low hydrogen.

Low-hydrogen electrodes also may carry additional designations, with E7018 H4R becoming more common. The H4 indicates less than 4 ml of diffusible hydrogen per 100 g of deposited weld when the electrodes are tested in the as-received condition, typically hermetically sealed foil packages or canisters. The R indicates moisture resistance. H4R electrodes will have less than 0.4 percent moisture absorption after nine hours of exposure at 80 to 85 degrees F and 80 to 85 percent relative humidity.

To preserve the H4R designation beyond nine hours, be sure to store open containers at 225 to 300 degrees F. If necessary, recondition them by baking for one hour at 700 degrees F. Additionally, store and bake low-hydrogen electrodes separately.

Not only can mixing electrodes in a rod oven cause contamination, but different coating types carry and require different moisture content for proper performance. For example, cellulosic electrodes require a certain amount of moisture to deliver the designed arc force; therefore, mixing basic and cellulosic electrodes in an oven will be detrimental for both.

An E7018 electrode also may carry a -1 designation, which means that it provides the promised Charpy V-notch impact properties at -50 degrees F compared to -20 degrees F for electrodes without a -1. These electrodes provide exceptional toughness at low temperatures. Note: An E7018-1 electrode can be used in place of an E7018 electrode, but the reverse is not true.

Stainless electrode coatings also come in three categories, EXXX-15, EXXX-16, and EXXX-17. The -15 after the base alloy indicates a lime basic coating, which contains considerable amounts of limestone and fluorspar, producing a fast-freezing slag that facilitates welding in the vertical and overhead positions. The bead is moderately rippled and slightly convex; the latter trait can provide the necessary margin of safety in highly stressed joints.

Lime basic coatings provide optimal mechanical properties. These electrodes commonly are specified for welding superaustenitic and very high-nickel grades of material in cryogenic applications such as LNG tanks and compressed gas systems.

Unfortunately, lime basic electrodes have the poorest weldability due to globular-like metal transfer that makes the puddle more challenging to control. Using a slight whipping technique—perhaps 1⁄8 in. of forward stepping and a pause—will help build up the puddle. Lime basics also require slag removal— always requiring chipping—and can run only on direct-current electrode-positive (DCEP).

A -16 indicates a basic rutile-type coating that contains dominant amounts of rutile, medium amounts of limestone, and limited amounts of fluorspar. Given a choice, most operators prefer to use a -16 electrode. It provides a stable, smooth spray-transfer arc and a convex to flat bead profile with fine ripples and good side-wall fusion. It also produces a low amount of fine spatter and a slag that usually self-releases.

The -17 electrodes have more silicon than the -16 electrodes, producing a more fluid weld puddle that works best for welding in the flat position. Vertical and overhead welding are possible, but they require more operator skill than a lime basic electrode because the slag does not freeze as quickly. These electrodes operate on DCEP or alternating current (AC).

Stainless steel electrodes typically do not exhibit hydrogen cracking, but porosity, excess spatter, and poor slag detachment may occur if the coating absorbs moisture. Be sure to store your stainless steel electrodes at 300 degrees F. If you leave them out for too long, you can recondition the electrodes by baking them at 600 to 800 degrees F for one to six hours.

The Hard Facts of Hardfacing

Do not confuse hardfacing with a joining process. Hardfacing is the process of applying a harder or tougher metal to the base material. Hardfacing electrodes are divided into three categories: iron base, nickel base, and cobalt base, which are then alloyed with carbide-forming elements such as chromium, tungsten, molybdenum, and other elements. They typically do not have specific AWS classifications except for the standard cobalt alloy range 1, 6, 12, and 21.

Unlike joining electrodes, hardfacing electrodes are a collection of proprietary alloy formulations geared toward meeting specific needs. They are produced three ways: a tubular rod filled with an alloy mix and then dipped in a coating or has a coating extruded over it; a carbon steel rod coated with a mix of alloys and deoxidizers; or a cast cobalt rod with a coating extruded over it.

Hardfacing electrodes, especially those with a tubular construction, are not designed for penetration. They require lower parameters for less dilution and more hardfacing efficiency. One common mistake with tubular electrodes is crowding the electrode into the workpiece, causing it to overheat. Remember, hardfacing electrodes run differently from an E7018 SMAW electrode. They have a more globular transfer and require a longer arc length.

Hardfacing electrodes, when applied with a stringer bead or weave bead pattern, develop a cross-cracking (cross-check) pattern because of carbides that form in the matrix of the weld pool during solidification. This is normal. The exception is if the electrode is designed specifically for crack-free deposits.

Halinson Campos is project business manager – filler metals at ESAB Welding & Cutting Products; Martin Denault is applications engineer and CWI at Exaton, an ESAB brand; Richard Cook is senior product manager at Stoody Co., an ESAB brand, 2800 Airport Road, Denton, TX 76207, 800-372-2123.