Filler Metal Welding: Choosing the Right Consumables

Picture a shop on a Friday afternoon: a fabricator has to finish forty steel brackets before the truck leaves, grabs the nearest box of stick rods, and welds them all. On Monday, three brackets are cracked clean through. The steel was fine, the machine was fine, and the welder was good. The electrodes were simply the wrong filler metal for the job. That story plays out in shops, garages and hobby benches every week, and almost all of it traces back to one avoidable decision: choosing a consumable without knowing what the classification on the box actually means.

What Filler Metal Welding Actually Is, and Why the Consumable Decides the Joint

Those cracked brackets from the Friday afternoon job failed for one reason, and it was printed on the box: the consumable was wrong. That leads to the short answer. Filler metal welding is any welding process where the material being joined is added as a consumable (a wire, rod, electrode or strip) and that filler metal ends up as part of the finished weld. A bolt-up joint is held together by a fastener. In filler metal welding, the metal you feed into the arc holds the pieces together: it melts into the joint and solidifies as the load-carrying deposit.

A weld is not simply the base metal with some heat applied. It is a metallurgical composite of base metal that melted into the puddle and filler metal that melted in with it. Change the consumable and you change that mix, and with it the strength, toughness, corrosion resistance and cracking behaviour of the finished joint.

Electrode, Rod, Filler Metal: The Words on the Box

AWS A3.0, the American Welding Society’s standard terms and definitions for welding and brazing, keeps these separate, and the distinction explains why some consumables are coated and others are not:

• Welding electrode: ‘a component of welding circuit through which current is conducted and that terminates at the arc, molten conductive slag, or base metal.’
• Welding rod: ‘a form of welding filler metal, normally packaged in straight lengths, that does not conduct the welding current.’

Read those two definitions and consumable design makes sense. A stick electrode is not just filler metal with a coating. It is part of the electrical circuit: current runs down the core, arcs across the gap, and the coating melts to make slag and shielding. A TIG rod or a GMAW wire carries no current, so the shielding has to come from somewhere else: a gas blanket, or nothing at all in the case of self-shielded flux-cored wire. That self-contained design is why SMAW still wins on the job site.

Not everything that melts into a joint is welding filler metal. Brazing filler alloys (AWS A5.8) melt and flow into a joint but do not melt the base metal, the line that separates brazing from fusion welding. Consumable inserts (AWS A5.30) are placed in the joint before welding, often at the root of a groove, and they do become part of the weld, but they are never fed through the torch. Different products, different specifications, different rules.

Four Jobs a Consumable Does

1. Joins the pieces. Fusion across the interface is the primary job, and the one most people picture first.
2. Fills the joint. It bridges the gap, builds reinforcement on the face of the bead, and covers up fit-up variation in the parts.
3. Adds alloying elements. Deposit chemistry is where much of the strength comes from. Chromium builds stainless and wear resistance, nickel adds toughness and corrosion resistance, molybdenum adds creep and pitting resistance, and deoxidizers such as silicon and manganese clean the puddle. A look at alloy steel welding electrode selection shows how quickly that chemistry changes the product.
4. Carries deoxidizers and cleaning agents. The flux coating on a stick electrode, or the formulation inside a flux-cored wire, is a chemistry delivery system. It dissolves oxides, ties up nitrogen and hydrogen, and shapes the arc.

When a weld comes out soft, brittle, rusty or cracked, the cause is usually sitting in one of those four buckets.

The Families You Will Meet

Six product families cover nearly every shop on earth: SMAW electrodes (E7018 and friends), GMAW solid wire (ER70S-6), FCAW tubular wire (E71T-1C), GTAW rod (ER70S-2), SAW wire for submerged arc welding, and brazing filler. They differ in how they are fed, how they are shielded, how fast they deposit, and how much slag you have to chip off. If you are choosing between rod types for a vertical joint, the all position welding rod guide covers that choice in more detail.

The specifications are organised by material family and process, and the AWS A5 Committee on Filler Metals maintains them. A5.1 covers carbon steel SMAW electrodes, A5.18 carbon steel GMAW, A5.20 carbon steel FCAW, A5.9 stainless, A5.14 nickel alloys, and A5.8 brazing alloys and fluxes. The full catalogue is published by the American Welding Society, which has authored more than 350 welding standards, codes and specifications, and those documents decide what counts as a qualified weld.

Get the consumable right and most downstream problems get easier. The next section takes the mystery out of the biggest label on the box, and decodes E7018, ER70S-6 and E71T-1C one character at a time.

Reading the AWS Classification on the Box: E7018, ER70S-6, E71T-1C Decoded

Every box of stick electrode, spool of wire and tube of flux core carries a short code stamped on it, and for most shops that code is a mystery. It looks like a model number or a marketing code. It is actually a specification, written in a deliberately compact language by the AWS Committee on Filler Metals and Allied Materials, and once you can read it you can pick the right consumable for almost any job in the shop.

Start with stick electrode, because that is where the language began. The classification is a letter followed by four digits, such as E7018 or E6013.

What each digit of E7018 actually tells you

The E simply means electrode, the component of the welding circuit that carries current and terminates at the arc. The next two digits are the minimum tensile strength of the deposited weld metal, in thousands of pounds per square inch. In E7018, the 70 means the weld metal must meet a minimum of 70,000 psi (70 ksi) in tension. In E6013, the 60 means 60,000 psi minimum. These are floors, not averages, and they tell you nothing about yield strength, ductility or toughness.

The third digit is position capability. A 1 means all position, so the electrode can be run flat, horizontal, vertical and overhead. A 2 means flat and horizontal fillet welds only. A 4 means flat, horizontal, vertical down and overhead. That single digit is where a lot of cracked brackets come from, because a fabricator grabs an E70xx-2 for speed and then tries to run it vertical up.

The final digit describes the coating type and current. In practice, a suffix of 0 or 1 points to a cellulose coating, 2 or 3 to a titania or rutile coating, 4 to an iron powder coating, and 5, 6 and 8 to the basic low-hydrogen coatings. The trailing letter, when present, tells you the current type: AC, DC or both. The Hobart Brothers electrode classification guide breaks the same scheme down coating by coating.

The carbon steel families in AWS A5.1

Classification	Coating	Current	Character
E6010	Cellulose sodium	DC only	Deep digging penetration, DCEN, best root pass on pipe
E6011	Cellulose potassium	AC or DC	Deep penetration, forgiving on dirty or rusty metal
E6012	Titania	AC or DC	Gap bridging, shallow penetration, dense slag
E6013	Rutile	AC or DC	Soft arc, low spatter, easy slag, clean new sheet metal only
E7014	Iron powder and titania	AC or DC	General purpose, smooth bead, moderate deposition
E7015 / E7016 / E7018	Basic low hydrogen (sodium, potassium, or potassium plus iron powder)	DC or AC	Low diffusible hydrogen, code work, all position
E7024	Iron powder	AC or DC	Fast deposition, flat and horizontal only

AWS A5.1 covers shielded metal arc electrodes. Solid wire sits in A5.18 and flux core in A5.20, so the letters change between families but the logic does not.

Solid wire, flux core and the letters that change

Wire classifications use a slightly different pattern. ER means the product can be used as either an electrode or a rod, which is why the same ER70S-6 spool can feed a MIG gun or become TIG filler. S means solid, T means tubular, so all position rod selection and the wire designations share the same logic. In ER70S-6, the 70 is again the minimum tensile strength in ksi, and the 6 describes the deposit chemistry and properties, such as the higher ductility and impact toughness of ER70S-6 versus general purpose ER70S-3. Stainless grades follow the same pattern, with the chemistry doing the talking: ER308L means 308 chemistry at low carbon.

Flux core wires add a letter for the shielding gas. E71T-1C is designed for 100% CO2, while E71T-1M runs on a 75/25 argon and CO2 blend, and the 1 in E71T-1C flags single pass, all position capability. E71T-11 is self-shielded, carrying its own flux core and needing no gas bottle at all, which is why it is standard for site and structural work far from a gas supply. Miller’s guide to common electrodes and their classifications is a good free reference for the stick side of this.

Suffixes that flag special properties

• 1 in the position or coating field: improved toughness and ductility, commonly used for impact-tested applications.
• H: the coating has been tested for diffusible hydrogen.
• R: the electrode has passed the absorbed moisture test.
• M: meets military requirements.
• J: Charpy V-notch toughness of at least 20 ft-lb at -40 °F.
• D and Q: supplemental mechanical property requirements at low and high heat input respectively.

Why does any of this matter beyond curiosity? AWS classifications exist so a fabricator can buy a second supplier’s product with the same classification and get comparable chemical and mechanical properties, even though arc behaviour, wetting and handling feel different from the brand you are used to. That substitution is exactly what the case for stick welding depends on, and it lets a shop swap brands on an approved job without rewriting the whole procedure.

Read the code, match the code, and the box stops being a mystery. The current AWS filler metal specifications list is where to confirm the exact requirements behind any classification before you write it into a procedure or purchase order.

The Filler Metal Families Compared: Stick, Solid Wire, Flux-Cored, TIG Rod and SAW

Filler metal welding is not one product category, it is five. Each family delivers the consumable to the joint differently, demands different equipment and leaves a different bead behind, so the product form often matters more than the grade within it. Every family is covered by the AWS filler metal specifications, with the classification decoded in the Hobart Brothers electrode classification guide.

Family	Consumable	Needs	Deposition	Where it fails
SMAW (stick)	E7018 rod	No gas; rod oven for low-hydrogen	Moderate, all-position, slag to remove	Slag inclusions, grinding
GMAW (solid wire)	ER70S-6	Gas, dry wire, clean gun	Fast, slag-free, some spatter	Wind, dirty metal, gas cost
FCAW (flux-cored)	E71T-1C or E71T-1M	Feeder and gas; E71T-11 self-shielded	High feed speed, tolerates scale	Fume, gun cleaning, higher cost
GTAW (TIG rod)	ER70S-2	Argon, steady hand, back-purge	Slowest, cleanest deposit, root control	Thin material, labour cost
SAW	Wire + granular flux	Flux hopper, wire handling, shop	Highest deposition, one pass on long seams	Field work, thin plate, tight fit-up

Stick is self-contained, and that is its superpower

SMAW needs only a power source and a holder: the flux coating does the shielding, deoxidising and slag formation in one package, which is why it still wins for structural, pipeline and field work where machines cannot reach. The cost is slag to chip away and deposition speed well below a wire process. The advantages of stick welding is worth reading before you rule it out.

Solid wire is fast and clean but fussy about preparation

GMAW with ER70S-6 lays down a slag-free bead at high deposition and is the default for shop fabrication of carbon steel. The trade is preparation and shielding: gas costs money, the arc cannot be pushed into a dusty yard, and rust, mill scale or paint will drive porosity and lack of fusion. Wire must be stored dry and off the floor, and the gun liner and contact tip need regular cleaning. Aluminum MIG welding covers the different aluminium setup.

Flux-cored is the compromise that keeps improving

FCAW combines wire feed speed with the slag-forming benefits of a flux, so it handles rustier, less-prepared steel better than solid wire. E71T-1C runs on 100% CO₂, E71T-1M on a 75/25 argon blend, and self-shielded E71T-11 needs no gas at all, making it the site-work favourite. Against that it makes more fume than GMAW, needs frequent gun cleaning and costs more per pound. See our aluminum flux core welding guide for another context.

TIG rod buys control and pays in time

GTAW gives the cleanest, most controllable deposit of any family, so it dominates root passes, thin gauge, stainless and heat-sensitive alloys. It is also the slowest and most skill-intensive, needing inert gas plus a back-purge on stainless. Aerospace TIG welding shows the control tight-tolerance work demands.

SAW is a production-line process

Submerged arc welding deposits the highest volume of filler metal of any process with almost no visible fume, running on long straight seams in plate and pipe mills. It needs a flux hopper, a positioner and a flat shop, so it is not a repair-shop process.

Iron powder is the trade-off that rules out code-critical work

Electrodes such as E7024 carry extra iron powder, raising the deposition rate and making the weld pool more fluid. That pool spreads heat, and on a vertical-up or overhead joint it runs ahead of the puddle. High-deposition electrodes are used for flat and horizontal fillet welds on plate of at least 1/4 inch thick, and are ruled out of out-of-position work and code-critical pressure vessel or boiler fabrication. Miller’s guide to common electrodes covers coating types in depth.

Low hydrogen is a property of the process, not just the label

GTAW and GMAW are inherently low-hydrogen processes because they use no flux, so there is no coating or core moisture to add hydrogen to the deposit. FCAW and SMAW can be low or non-low hydrogen depending on the flux formulation, which is why the classification matters. Check any selection against the AWS A5 Committee on Filler Metals and Allied Materials specifications.

Storage rules differ family by family

Cellulose and rutile rods tolerate ambient conditions and need no dry storage. Low-hydrogen rods do not: they need hermetically sealed containers or a heated rod oven. ESAB’s shelf-life guide puts hermetically sealed cans of low-hydrogen electrodes at 5 years, hermetically sealed carbon steel at 2 years and other non-hermetic packages at about a year, kept unopened and dry. Wire is different again, because damaged or damp wire shows up as porosity rather than a failed coating. Formats are packaged and priced differently, as Airgas welding supplies shows.

I’ll rewrite this section, tightening the prose while keeping every fact and link intact.

Choosing Filler Metal by Base Metal, Joint Design and Position

Read a classification and the next question decides your weld: which filler metal belongs on this joint? The answer is a sequence.

Step 1: Identify the base metal specification

Start with the designation, not the shape of the part: A36, A572 Grade 50, A106 Grade B, 4130, 304L. Each carries minimum mechanical properties that define what the weld metal must deliver.

Low-alloy steels typically exceed 70 ksi tensile, some exceed 120 ksi; more alloy content means more chance of brittle microstructures after welding, so filler metal and heat input matter more than on plain carbon steel. Nickel, molybdenum and chromium typically make up more than 0.5 percent but less than 5 percent of the steel, and that small percentage changes welding behavior. For low-alloy steel, Hobart Brothers recommends preheat above 212 degrees Fahrenheit plus thorough removal of rust, scale, oil and grease to reduce weld metal hydrogen.

Step 2: Match weld metal strength to base metal strength

“Matching” means the weld metal meets or exceeds the base metal’s specified tensile strength. “Undermatching” means it falls below, yet it is a deliberate, often superior choice. As weld metal tensile strength increases, ductility tends to decrease, so a matching 100 ksi filler on HSLA makes the weld metal the weakest, least forgiving part of the assembly. Undermatching HSLA with a 70 ksi electrode maximizes weld ductility and fatigue life, provided stresses are not concentrated in the weld.

One caveat: few low-alloy filler metal classifications align perfectly with base metal compositions, because steelmaking and weld-metal production differ. That is why the code deals in strength thresholds, not exact chemistry matches.

Step 3: Check the code before you pick the rod

For code-governed work the classification is not your choice. AWS D1.1 Tables 3.1 and 4.9 and AWS D1.5 Table 4.1 list the classifications considered matching for code-recognized materials. Pick from that list, confirm the position rating, and document it in the WPS.

Step 4: Joint design, thickness and fit-up

Thickness and fit-up dictate arc character. Thin material with tight fit-up wants a short, concentrated arc that melts the base metal without burning through. Thick plate, a wide root gap or poor fit-up wants more penetration and a longer, forgiving arc, often with a weave or stringer.

Hot-rolled plate carries mill scale, a hard oxide layer that resists fusion. Rutile electrodes like E6013, with shallow penetration and a forgiving arc, work on clean sheet metal but fail on scaled or rusty plate. For dirty hot-rolled plate, the all-position welding rod guide lists cellulosic and low-hydrogen options.

Step 5: Position and available power source

The position rating must cover every position you will actually weld in. An E70xx-2 electrode is rated for flat and horizontal fillets only; in a vertical joint you get poor fusion, spatter and rework.

Power source follows from electrode and position. Cellulosic E6010 is DC electrode positive only. E6013 and E7018 run on AC or DC. An AC-only machine shrinks your consumable list considerably, while all-position electrodes like E7018 cover any position.

Step 6: Service conditions and production efficiency

• Low temperature: demand Charpy V-notch toughness. The “J” suffix means at least 20 ft-lb at -40 degrees F.
• High temperature or creep: the filler must be creep-resistant and match base chemistry, not just strength.
• Corrosive service: check nickel, chromium and molybdenum in the deposit, not the base metal grade.
• Pressure-retaining: the code governs; strength matching and toughness testing are mandatory.
• Shock loading: toughness and ductility matter more than raw strength.

Speed comes last. Deposition rate, travel speed and slag removal cost rank below fitness for the joint: a slightly slower electrode that produces a compliant weld beats a fast one that fails inspection.

Worked examples

Joint	Filler	Why
3/8-in A36 structural fillet, flat	E7024 iron powder	Volume is the driver: high deposition rate, good flat and horizontal fillet behavior, minimal slag. Details in the alloy steel welding electrode guide.
Same bracket, bridge joint, vertical-up	E7018	E7024 is out: iron powder electrodes are generally not permitted for out-of-position work or code-critical fabrication such as pressure vessels and boilers, and the fluid pool is hard to control going up. E7018 is all-position rated for vertical-up.
1/8-in hot-rolled plate repair, flat	E6013	Tight fit-up, thin material, no pressure service: soft arc, low spatter, easy slag, minimal heat input. On rusted or painted plate, clean it first or step up to a cellulosic electrode.
3/4-in pipe root pass	E6010 or E6011	Thick wall, real penetration, often a hot or dirty surface. E6010 has deep digging penetration on DC and is the standard pipe electrode; E6011 adds AC capability and a more forgiving arc.
4130 chrome-moly exhaust header	Matching low-alloy	Chrome-moly grades are air-hardening, so welding heat plus the chemistry can create hard, crack-sensitive microstructures in the heat-affected zone. Control interpass temperature and heat input, and consider post-weld heat treatment response. See our advantages of stick welding guide.

Low Hydrogen, Hydrogen Cracking and Why Filler Metal Storage Changes Your Weld

Pick up a box of E7018 electrodes and the first thing on the label is a designation that looks like a lab result: H4R. On a basic-fluxed electrode it appears in the AWS classification too, as in E7018-H4R. Those four characters are the most misunderstood information on the shelf, and the reason a weld can look perfect on the bench and still hide a time bomb.

Hydrogen-assisted cold cracking does not happen while the weld is hot. The joint has to cool below roughly 150 °C before damage develops. That is why a crack can appear hours, even a day, after the welder walks away, and why inspection plans on critical work include a delay before final acceptance.

The three ingredients of a crack

All three must be present at once, in the same joint. Miss one and the crack will not happen.

1. Hydrogen. Atomic hydrogen, dissolved in the weld metal while it is liquid and hot enough to absorb it.
2. A susceptible microstructure. Hard, brittle martensite and other hard transformation products form in the heat affected zone of higher-strength steels and tolerate very little hydrogen.
3. Tensile stress. The joint has to be pulling itself apart, from restraint, thermal contraction during cooling and the residual stress every weld leaves behind.

Stress comes from geometry, fit-up and thickness, not from the electrode. Swap a low-hydrogen electrode for a cellulose one and the hydrogen changes, not the stress, and with it goes the safety margin that kept hydrogen below the level the martensite could tolerate.

The CWB Group guidance on hydrogen-induced cold cracking lays out the same three-part logic if you weld higher-strength steels.

Where the hydrogen comes from

• Moisture in the electrode coating. The big one for stick. A coating out of a holding oven absorbs water from the air, and that water flashes to hydrogen during the arc.
• Rust, paint, oil and grease. Hydrocarbons and moisture on the base metal get dragged into the weld pool.
• Damp wire. Tubular and spooled wire pick up moisture in the carton, and shielding gas does nothing to stop it.
• Moisture in the base metal. A wet or cold joint that dries from the outside in releases hydrogen into the weld.

Reading the H and CH numbers

Two systems describe the same idea, and you will see both on the shelf.

System	What the number means	Typical example
AWS H suffix	The coating was tested for diffusible hydrogen, and the number is millilitres of hydrogen per 100 grams of weld metal. Lower is better.	H4R carries roughly 4 mL of hydrogen per 100 grams of weld metal, H8 about 8, and an ordinary non-designated coating is uncontrolled and can be far higher.
CSA CH class	Millilitres of hydrogen per 100 grams of deposited weld metal, where 16 mL/100 g is the line between low hydrogen and not low hydrogen.	A common basic-fluxed SMAW electrode sold in Canada under CSA W 48 as E4918 carries a maximum controlled hydrogen level of CH16.

Step up in strength and CH8 and CH4 classifications become available, and code work on higher-strength steels may require them rather than a plain CH16 electrode. The AWS filler metal specifications are the governing documents, maintained by the AWS A5 Committee on Filler Metals. When a drawing or code document says “low hydrogen” it may mean the low hydrogen family or a specific H or CH level, so read the requirement instead of assuming.

Storage: the part that actually decides your weld

Low-hydrogen electrodes arrive hermetically sealed. An unopened can has not seen atmospheric moisture, so the coating inside is still dry. The clock does not start when the box leaves the warehouse, it starts when the seal is broken. Opening a can does not restart anything, it starts the exposure.

Once opened, put electrodes straight into an electrode holding oven at roughly 250-300 °F (120-150 °C). The oven does not bake out moisture, it keeps electrodes dry while you use them. Shop rules of thumb for how long exposed electrodes can still be used:

• E8018 and E9018 series: swap them out after roughly three to four hours out of the holding oven.
• E10018 series: swap them out sooner, after about two to three hours.

Past those exposure limits the coating has absorbed too much water and the electrode is no longer reliably low hydrogen, so recondition it or throw it out. Reconditioning is not the same as holding. Bringing an exposed electrode back to a low-hydrogen condition needs a baking oven at a considerably higher temperature: industry guidance puts that bake in the 400-500 °F range, while other sources recommend 500-800 °F for one to two hours. Re-drying is limited to twice, because repeated baking degrades the coating until the electrode will not perform properly even though it looks fine.

Here is the warning that saves the most money: returning a long-exposed electrode to the holding oven does not restore its low-hydrogen properties. A holding oven is a moisture exclusion device; a baking oven is a moisture removal device. Electrodes left out overnight and dropped back in the holding oven give false comfort, and the weld quietly carries more hydrogen than the procedure assumes. Proper baking ovens are required, and The Fabricator and Lincoln Electric spell out the difference in practical terms.

What to do in practice

• Buy low-hydrogen product in hermetically sealed containers and open one can at a time, not the whole case.
• Put opened electrodes in the holding oven immediately, every time.
• Mark the oven or bin with a time so exposure limits are tracked, not guessed.
• Keep a separate labelled bin for electrodes past their exposure time, and do not mix them back into the rotation.
• Re-bake exposed product only in a real baking oven, and no more than twice.
• Keep moisture out of the wire side too. Wire sitting on a concrete floor is a hydrogen source whether or not the spool was sealed.

The Hobart Brothers electrode classification reference is a good side-by-side check on the hydrogen designation printed on a box, and the Hobart filler metal selection guide for low-alloy steel shows how those classifications tie into heat input limits on higher-strength material.

None of this is glamorous and none of it appears on the cut list. But when a low-hydrogen electrode has been sitting out, porosity and spatter show up in the first few inches of the bead and the weld improves as the rod warms, the clearest sign the deposit was already compromised. Get the storage right and hydrogen cracking stops being something you chase after the fact.

I’ll rewrite this section to fit the word count while keeping all the facts and links intact.

Seven Filler Metal Mistakes and How to Troubleshoot Them

Most filler metal problems do not announce themselves. The wire feeds, the arc is lit, the bead passes a visual glance. The failure shows up later: a crack that opens on the night shift, a bracket that snaps at the bolt hole, a stainless tank weeping rust at the seam. Nearly every filler metal mistake leaves a signature, so it can be caught early.

1. Ignoring the Position Rating

The third digit in a stick electrode classification is a position rating, not a suggestion. An E7018 is rated for all positions; an E70xx-2 covers flat and horizontal fillet welds only. In a vertical joint an E7024 or E70xx-2 runs too hot and too fluid for a vertical-up bead: poor fusion, a wandering puddle, spatter and a root that will not close. If the electrode says “2”, it stays on flat and horizontal. The all-position welding rod guide decodes position digits.

2. Confusing Matching With Over-Matching

Matching means the weld metal is at least as strong as the base metal; over-matching means it is much stronger. Welding 4130 chrome-moly header with an E7018 and expecting 4130 properties is the classic error. E7018 deposits a mild steel weld metal, without the base material’s strength, toughness or heat-treated response, and on a hot cycling exhaust application it can soften and creep. You need a matching low-alloy electrode, plus a decision on post-weld heat treatment. Our guide to alloy steel welding electrodes covers those classifications.

3. Using High-Deposition Electrodes On Code Or Out-Of-Position Work

High deposition electrodes such as E7024 have a high iron powder percentage, and they are faster. They lay down a fluid, hot pool a welder cannot control out of position, and they are not permitted for critical code-required work such as pressure vessel or boiler fabrication. The code cares about deposit properties and weld control, and E7024 gives less control, not more. Rule of thumb: high deposition for flat and horizontal production on non-code assemblies, E7018 for everything else.

4. Using E6013 On Dirty, Painted, Rusted Or Hot-Rolled Plate

E6013 is fast and easy, with a soft arc and moderate penetration, which suits clean new sheet metal. Put it on mill scale, rust, paint, oil or hot-rolled plate and you get porosity, slag inclusions and lack of fusion. For dirty work use an E6010 or E6011, cellulose electrodes with deep penetration that punch through rust, oil, paint and dirt. Catch: E6010 requires a direct current source, while E6011 works on AC or DC. Hobart Brothers covers the coating chemistry in its electrode classification reference.

5. Welding Stainless With Carbon Steel Consumables

A carbon steel electrode or contaminated carbon steel wire used on stainless introduces iron into the weld, promoting carbide precipitation and rust. The joint can look perfect and fail months later, rusting from the inside out. Keep stainless consumables physically separate: separate storage, dedicated contact tips and liners, a dedicated grinder with stainless-only discs, and never a carbon steel spool beside a stainless one. When in doubt about contamination, the prep discipline matters more than the product.

6. Storing Low-Hydrogen Electrodes Badly

Moisture is the enemy of a low-hydrogen electrode. Open a can, leave it in a humid shop for a few hours, and the coating absorbs water. Weld with it and you get porosity, spatter and cracking.

The other symptom of a wet electrode is a noisy, sputtering arc. Lincoln Electric does not recommend re-baking high-cellulose electrodes in the E6010 and E6011 group. With excessive moisture, cellulosic electrodes spatter heavily, rust the core wire at the holder end and blister their coating. They are consumed quickly and cheap to replace.

7. Mixing Brands And Lots Without Checking The Classification

Switching suppliers is fine; switching without reading the classification is not. Two boxes of “E7018” from different mills can differ in position rating, diffusible hydrogen level and suffix designators, and a job approved for one may not be approved for the other. Before a swap, confirm: identical AWS classification, mill test report and certification on file, and the lot number recorded for traceability. The AWS filler metal specifications list, maintained by the A5 Committee on Filler Metals and Allied Materials, defines each classification, so any product can be judged by the same yardstick.

Symptom To Cause: A Quick Diagnostic Table

Symptom	Likely Cause	Fix
Spatter, noisy arc	Moisture, wrong polarity, low voltage, long arc	Check storage, polarity and voltage; hold a short arc
Porosity	Dirty base metal, poor shielding, wrong polarity	Clean the joint, check gas flow and wind protection, confirm DCEP
Slag will not remove	Travel speed too high, bad weave, low amperage	Slow down, weave properly, raise amperage
Cracking hours later	Hydrogen-assisted cold cracking, restraint on cooling	Low-hydrogen electrode, control heat input, check fit-up and preheat
Undercut	Amperage too high, travel too slow, poor work angle	Trim amperage, speed up travel, fix work angle
Poor fusion out of position	Position rating mismatch, high-deposition rod used vertically	Use an all-position classification such as E7018

Hydrogen-assisted cracking deserves respect, because it is delayed and invisible until it is not. The CWB Group’s guide to preventing HICC explains the three requirements, hydrogen, a susceptible microstructure and tensile stress, and none can be met if the consumable pumps moisture into the weld.

A weld that looks good is not a weld that passed. The OSHA welding safety and health factsheet is a reminder that fume and gas control belongs to the same job as choosing the right consumable. No consumable choice compensates for a shop that ignores ventilation.

Catch the mistake in the first ten minutes, and the rework disappears.

Filler Metal for Stainless Steel, Aluminium, Nickel Alloys and Cast Iron

For carbon steel, filler metal choice is mostly strength matching. With stainless, aluminium, nickel alloys and cast iron, chemistry, contamination and thermal behaviour take over. The specs still sit in the AWS A5 family, so the decoding rules from earlier in this guide apply.

Stainless Steel: Chemistry and the Contamination Rule

Two AWS specifications cover stainless consumables. AWS A5.4 covers bare stainless electrodes for SMAW, and AWS A5.9 covers bare stainless electrodes and rods for GMAW, SAW and other fusion processes. A5.9 classifies stainless filler metal by chemical composition, not mechanical properties: at least 10.5 percent chromium, with iron exceeding any other single element in the deposit. That is why E/ER numbers carry chemistry, not strength.

Base material	Filler	Why
304/304L, 316/316L	ER308L (ER308LMo for chloride service)	Matches base chemistry plus a nickel margin; Mo grade for seawater and chemicals
304 to 316, or carbon steel to stainless	ER309L	Higher Cr and Ni tolerate carbon steel dilution
Duplex and super duplex	ER2209 / ER2594	Tuned for a ferrite-austenite balance near 40 percent ferrite

The “L” suffix means low carbon. Carbon combines with chromium to form chromium carbides at grain boundaries, draining chromium and killing the passive film that gives stainless its corrosion resistance.

For root passes, GTAW with a back purge is preferred, because the root side is where oxidation hides. Argon behind the root keeps oxygen off the hot metal, and the aerospace TIG welding guide covers shielding discipline. Without purging, a root-side gas cup or FCAW product are the alternatives.

Aluminium: Two Alloys Cover Almost Everything

AWS A5.3 covers aluminium and aluminium-alloy electrodes for SMAW, and A5.10 covers bare aluminium electrodes and rods for GMAW and GTAW. Aluminium filler metal is defined by composition, and two alloys do most of the work:

• ER4043 is the general-purpose choice for most sheet fabrication. Its silicon content lowers the melting point, improves fluidity and run, and makes the weld forgiving on thin material.
• ER5356 suits 6000 and 7000 series aluminium, giving higher strength and ductility than 4043, which should be avoided on these alloys because its high silicon content promotes hot cracking in strain-hardened material.

Aluminium has a tenacious oxide skin that must come off before welding, using a dedicated stainless wire brush kept for aluminium only. The guide to prepping aluminium for welding has the step-by-step, the aluminium MIG welding guide covers process detail, and aluminium flux-core welding covers self-shielded field options.

Polarity matters. AC reverses the arc, breaking the oxide film continuously, and is the general-purpose choice. DCEP-SP (direct current electrode positive, straight polarity) gives more penetration on thicker sections but puts more heat into the electrode. Keep wire and base metal clean and store aluminium wire dry, because moisture is a direct route to porosity.

Nickel Alloys, Copper Alloys and Cast Iron

Nickel consumables fall under three specifications: A5.14 for solid nickel-alloy electrodes for GMAW and GTAW, A5.34 for cored nickel-alloy electrodes, and A5.11 for nickel-alloy electrodes for SMAW. ERNiCrMo-3 is the classic workhorse, used for cladding and overlay on Inconel 625 and for welding Inconel 718.

Nickel alloys punish two things. Contamination with iron, sulfur, phosphorus or oxygen causes porosity and hot cracking, so nickel filler gets its own brushes, tools and storage, and carbon steel contamination is not acceptable in the sequence. Heat is the second: Inconel 718 is prone to liquation cracking in the heat-affected zone, so interpass temperature and heat input must be controlled deliberately. The Alloy 20 guide shows the same logic on a different nickel-iron alloy.

Copper alloys sit under A5.6 for copper and copper-alloy welding electrodes and A5.7 for the bare products. Copper conducts heat well and expands a lot, so preheat is the standard lever for distortion control. Silicon bronze (ERCuSi-A) is the common filler for steel-to-bronze joints and cast iron repair, because it tolerates ferrous base metal.

Cast iron is covered by AWS A5.15, which includes nickel-iron and nickel-alloy electrodes. These are designed for cold welding with no preheat, producing a deposit that is machinable and that accommodates grey iron’s lack of ductility. That combination is why nickel-iron is the standard repair answer for engine blocks and machine bases. The alloy wheel welding guide shows the same matching logic on aluminium wheel repair.

Titanium, Magnesium and Hardfacing

Titanium and magnesium alloys are covered by AWS A5.16 and A5.19, and both need total inert gas shielding. An incompletely shielded titanium weld absorbs nitrogen and oxygen and turns brittle, so the root side needs a purge as well. Magnesium has the opposite problem: the fume is a serious health hazard, so extraction matters more than on almost any other material. The OSHA welding safety fact sheet covers exposure controls, and NIOSH’s welding resources is worth bookmarking for any shop handling magnesium.

Surfacing alloys are their own category. AWS A5.13 covers surfacing alloys and A5.21 covers composite surfacing electrodes and rods. These consumables are not joining materials, they are wear materials, used to build up a worn die, a shaft or a wear plate so the part goes back into service instead of being scrapped.

Buying, Storing and Living With Filler Metals: A Shop-Floor Routine

This guide assumes the filler metal arrives in the condition the manufacturer intended. A textbook E7018 loses most of its advantage after a summer in a hot truck bed, and a qualified procedure can still make a bad weld when the rod throws porosity in the first two inches.

Buy the Classification First, the Brand Second

Start with the mechanical requirement, not the catalogue. On code work the classification table decides what is acceptable, and your favourite brand becomes a tiebreaker. Put the classification and the AWS specification number on the purchase order first. The box should carry AWS A5.1 for carbon steel electrodes, with A5.18 and A5.20 covering other consumable categories; the full set sits in the AWS filler metal specifications index. Reading the classification markings on a stick electrode settles most arguments before they start.

• Buy the smallest quantity that matches your consumption. A 50-pound box of E7018 in a shop that burns two pounds a week stays open long enough to matter.
• Pay for hermetically sealed or vacuum-sealed packaging on low-hydrogen product. It costs more per pound, but it decides whether the rod is still good next year.
• Buy on classification even for non-code work, then let brand decide last. Our Airgas welding supplies buyer guide covers the other ordering details.

Packaging Sets the Clock

Stick electrodes carry no printed expiration date, so nothing on the box tells you when the coating has taken on enough moisture to matter. Practical rule: do not keep opened electrodes beyond about a year, and some types go bad in six months depending on coating and storage. The Fabricator and Lincoln Electric both treat electrode condition as something you manage, not read off a label.

ESAB publishes product-specific shelf-life tables that differ sharply by pack type: hermetically sealed and vacuum-sealed product stays usable far longer than cardboard or non-sealed packages. For product in other containers, ESAB recommends keeping it unopened, protected from direct contact with water, at a steady temperature and humidity.

Storage Setup: Where the Consumables Live

Three zones, three rule sets:

• Low-hydrogen electrodes go in a rod oven or electrode holding oven at 250 to 300 °F (120 to 150 °C), rotated so the oldest stock leaves first. Most shops skip this and regret it.
• Cellulose and rutile electrodes belong in rod guards or sealed containers, dry and off the floor. No heat required, and heat is not their friend.
• Wire sits on a spool rack, off the floor and out of the weather, plastic still on. GMAW and FCAW wire picks up moisture fast, and you will spend an afternoon chasing the porosity that causes.

Clean the copper contact tip and gun liner on a schedule, because a contaminated liner arcs before the wire does. And check the shielding gas setup on mixed-gas GMAW, including the 75/25 argon-CO2 blend normally paired with E71T-1C, for leaks and correct flow. See our guide to air gas welding equipment and process for the details, and keep ventilation and fume control in the plan from day one, as set out in OSHA’s welding safety fact sheet.

Paperwork That Pays for Itself Later

Keep the certifications. Mill test reports tell you what the deposit is guaranteed to be, and lot numbers trace a problem back to one box on a job you already shipped. Before substituting another supplier’s product on an approved job, confirm the classification matches the procedure. Classification, not brand, makes a swap legitimate. The AWS A5 Committee on Filler Metals publishes the specifications behind those classifications, and Miller’s guide to common electrodes is a crib sheet for shops standardising on one or two classifications.

The Weekly and Monthly Routine

Every week:

• Check rod oven temperature with a thermometer, not the dial you set it with.
• Rotate stock so opened low-hydrogen electrodes are used first.
• Wipe the contact tip and gun liner, and check gas pressure and leaks.

Every month:

• Open a carton and look for damp electrodes, crumbling coating or broken rods.
• Review recent welds for spatter and porosity in the first inches, the tell-tale sign of a bad rod.
• File mill test reports and reconcile lot numbers against invoices.

None of this is glamorous, and all of it separates a shop that manages its consumables from one that simply burns through them.

Wrapping Up: The Filler Metal Decision Framework

If you take one idea away from this guide, make it the list below. Choosing filler metal well is not about memorizing electrode numbers. It is about asking the same questions in the same order every time, so the result is repeatable instead of lucky.

1. Know the base metal specification. Start with the ASTM or AISI/SAE grade and its minimum yield and tensile values, not the trade name on the invoice. A36 tells you far more than “mild steel” ever will.
2. Pick the process first, then the consumable form that process requires. SMAW needs stick, GMAW needs solid wire, FCAW needs tubular wire, GTAW needs rod, SAW needs wire. Your power source, shielding gas and welding position narrow the choice faster than the shelf does. If you are still weighing the trade-offs, why SMAW still wins on structural and field work is a useful starting point.
3. Match the AWS classification for strength and chemistry. Matching weld metal strength to base metal strength remains the most common selection approach for low-alloy and carbon steel fabrication, though undermatching is deliberate where ductility or fatigue life matters more than peak strength. Match on the classification, never on the brand.
4. Check position rating, polarity and coating type. E7018 is an all-position electrode; an E70xx-2 is flat and horizontal fillet only. Cellulosic coatings want DC, rutile is comfortable on AC, and basic low-hydrogen coatings work either way but demand dry storage.
5. Check the code and the welding procedure specification. AWS D1.1 and D1.5 list which classifications count as matching for code-recognised materials. The PQR backs the classification, so swapping E7018 for E7024 on an approved job means requalification.
6. Control hydrogen. Select a low hydrogen product when the strength level, the restraint or the code calls for it. An H4R coating carries roughly 4 mL of diffusible hydrogen per 100 grams of weld metal, and hydrogen plus a susceptible microstructure plus tensile stress is the classic cold cracking recipe.
7. Store low hydrogen product properly and rotate it. Opened electrodes belong in a holding oven at about 250-300 °F (120-150 °C), and 8018/9018 series should be swapped out after roughly three to four hours of exposure. A holding oven preserves what a baking oven removed; it cannot rescue a coating that has been open for a week. The storage rules are laid out in detail in our guide to all position welding rod types, uses and tips.
8. Verify the deposit, not the bead. A good-looking weld proves very little. Confirm the procedure is qualified, complete the required visual inspection, and add NDT when the code asks for it. Filler metal classification appears in both the WPS and the PQR, and that is where accountability lives.

The Mindset Shift

Most crack and porosity problems are not weld defects in the mysterious sense. They come from treating an engineered component like a consumable commodity. Filler metal has a specification, a classification, a defined strength and chemistry range, a required storage regime and a shelf life. It is a structural component that happens to melt, and it deserves the same respect as the plate it joins.

Run the framework consistently and filler metal welding stops being guesswork. It becomes a routine that produces repeatable welds, and the ones worth framing are the ones you never have to think about. For deeper dives, our guide to alloy steel welding electrodes, our complete practical guide to aluminum MIG welding and our look at aerospace TIG welding standards each show the same decision logic applied to specific materials and codes.

Frequently Asked Questions

What is the difference between filler metal and a welding electrode?

Filler metal is the broad category: any material added to the weld to join the pieces or build up the deposit. A welding electrode is one specific form of filler metal that also carries welding current to the arc. Bare rod, solid wire and tubular flux-cored wire are also filler metals, and some of them can serve double duty as electrode or rod.

What do the numbers on an E7018 electrode mean?

The E stands for electrode, 70 is the minimum tensile strength of the deposited weld metal in thousands of psi, 1 means the electrode is approved for all welding positions, and 8 identifies the coating type, in this case a low-hydrogen potassium coating with added iron powder. Optional suffixes carry extra promises, such as H for diffusible hydrogen testing and R for the absorbed moisture test.

Is a low-hydrogen electrode always the better choice?

No. Low-hydrogen consumables matter most on higher-strength steels, thick restrained joints and code-critical work where hydrogen-assisted cracking is a real risk. For clean sheet metal, non-low-hydrogen electrodes such as E6013 are easier to weld and far cheaper, and many fabricators keep them for exactly that reason.

How long can I keep stick electrodes before they go bad?

Stick electrodes carry no printed expiration date, but the practical rule is not to keep them longer than about a year, and some can deteriorate in six months depending on packaging and storage conditions. Hermetically sealed and vacuum-sealed low-hydrogen products carry published shelf lives of several years, while opened low-hydrogen product must be held in a rod oven at roughly 250-300 °F.

Why did my weld crack a day after I finished it?

Delayed cracking in carbon and low-alloy steel is very often hydrogen-assisted cold cracking, which can only occur once the joint cools below roughly 150 °C. Look at the consumable’s hydrogen level, whether the electrodes had been stored dry, whether the base metal was clean and free of rust, paint and oil, and whether preheat and interpass temperatures were specified.

Can I use ER70S-6 wire instead of an E7018 electrode on my structural job?

Only if your qualified procedure permits it. Filler metal classification is written into the welding procedure specification and the qualification record, and code work under AWS D1.1 or D1.5 has rules about which filler metals qualify for a given base material and joint design. Ask your welding engineer or inspector before swapping.

Which filler metal should I use for aluminium?

ER4043 is the general-purpose aluminium alloy and is the usual choice for sheet metal, while ER5356 is the better match for higher-strength 6000 and 7000 series alloys because of its higher strength and crack resistance. Aluminium is unforgiving of contamination, so use a dedicated stainless brush to break the oxide and keep filler metal dry and clean.

Is it safe to weld stainless steel with the same stick electrode I use on mild steel?

No. Carbon steel electrodes or contaminated carbon steel wire introduce dilution that promotes carbide precipitation and rust in the stainless weld. Use ER308L for 304/304L and 316/316L, ER309L for dissimilar joints or joining stainless to carbon steel, and a separate dedicated grinding setup to avoid cross-contamination.

What does the difference between solid wire and flux-cored wire mean for weld quality?

Solid wire such as ER70S-6 deposits faster with no slag, but it needs clean metal and reliable gas shielding. Flux-cored wire such as E71T-1C or E71T-1M handles rustier or less prepared surfaces, deposits at higher rates and offers lower hydrogen levels when the flux is designed for it, but you must clean the slag and it costs more per pound.