What a Filler Metal Designation Is Telling You

Why this matters

Most of a shop reads a filler metal classification as a strength number with some digits after it. It is closer to a compressed test report: every field records a property measured under a stated condition, and the condition is the part that gets dropped. "70" is not the strength of your weld, it is a specified minimum from an all-weld-metal tension test on an assembly built the way the filler metal specification says to build it. Drop the condition and you get the two mistakes that cost real jobs: buying a strength number that does not survive your position or your shielding gas, and telling an inspector a property your product never claimed.

Before the rod is in your hand: arc radiation burns unprotected eyes and skin at a distance, so use the filter shade for the process and current with screens per 29 CFR 1910.133 and 29 CFR 1910.252(b)(2). The fume constituents follow the consumable as well as the base metal: a stainless or hardfacing filler puts hexavalent chromium into the breathing zone, regulated at 29 CFR 1910.1026 in general industry and 1926.1126 in construction, and a plain carbon steel electrode puts manganese there. Both are inhalation routes needing local exhaust at the arc and respiratory protection under a written program meeting 29 CFR 1910.134. Read the consumable's safety data sheet for its own constituents before you open the carton, because the classification tells you about mechanical properties and says nothing about what you will be breathing.

Reading the fields

Four classifications a general fabrication shop meets constantly, decoded field by field. Each row names the condition that travels with the field, because that is what makes it usable.

The same reading applied to three more:

• E6010. 60 ksi minimum tensile on the same test basis, all-position, cellulosic coating on direct current electrode positive. Its coating is designed to contain moisture, which is why it is a deep-penetrating open-root electrode and why baking it destroys it.
• ER70S-6. Electrode or rod, solid, 70 ksi minimum tensile, with the trailing number designating the wire's chemistry class rather than a mechanical property. The 6 class carries higher deoxidizer content, which is what lets it run over mill scale with fewer defects.
• E71T-1. 70 ksi minimum tensile, all-position, tubular (flux cored), with the usability and polarity class following, and then a shielding gas designator. That gas designator is not decoration. A flux-cored wire classified with a specific gas produces a different deposit chemistry on a different gas.

What the strength number is and is not

The strength digit is a specified minimum from a test of the deposited metal alone. Three things it is not:

• It is not the strength of your joint. Your weld metal is the filler diluted by whatever parent metal melted into it, and its geometry, its fusion and the parent metal beside it are all load-carrying. The related card on what a welded joint changes about the parent metal owns that.
• It is not toughness. Unless the classification carries an impact designator with a test temperature, nothing has been claimed about how the deposit behaves under impact or at low temperature. A shop working outdoors in winter that needs toughness has to select for it explicitly.
• It is not necessarily the target. Filler is sometimes deliberately undermatched, meaning a lower specified minimum than the base metal, on heavily restrained joints where you would rather the weld metal yield than crack. That is an engineering decision the WPS or the engineer of record owns, not a shop substitution.

The fields that a job can invalidate without touching the label

Three fields are conditions, not properties, and the job changes them:

• Position. A 1 classification was tested in all positions. Running it out of position is not the issue; running it outside what your WPS qualified is, and the two are separate documents. The card on reading a welding procedure specification owns that boundary.
• Shielding gas. For gas-shielded wires, the gas is part of the classification. Change from the classified gas to another and the deposit's chemistry, its mechanical properties and its transfer behaviour all change. A WPS treats it as a variable whose change requires requalification.
• Condition of the consumable in your hand. An H4 designator is measured on the product in the condition its specification defines. A rod that has spent three days on a bench in a humid shop is no longer that product. The related card on electrode storage owns this, and it is the field most often assumed rather than checked.

The specification family behind the label

A classification is meaningless without the specification that defines it, because the same digits mean different things in different families. AWS A5.1 covers carbon steel covered electrodes, A5.5 low-alloy covered electrodes, A5.18 solid carbon steel wires, A5.20 carbon steel flux-cored wires, and A5.4 and A5.9 the stainless covered electrodes and bare filler respectively. Each binds through your WPS, your contract, or the code the project adopted, in the edition that document names, and none of them binds on its own.

Worked example: matching stock to one job, decoded

A fabricator has a drawing calling for a 50 ksi minimum yield structural steel whose specified minimum tensile is 65 ksi. The assemblies are outdoor field connections, some overhead, heavily restrained where a brace lands between two fixed members. The rack holds three products. The exercise is to fill in the fields and let the fields decide.

Working the job's constraints against the table.

1. Strength. 70 ksi minimum deposit tensile against 65 ksi minimum base metal tensile is a ratio of 70 divided by 65, or 1.08, so the deposit's specified minimum overmatches by about 8 percent. Both figures are specified minimums from tests, not measurements of the steel on the rack or the rod in the quiver, so this is a comparison of two floors and not a prediction of what either will actually do.
2. Wind. Both gas-shielded products lose their shielding to wind, and the field connections are outdoors. That eliminates ER70S-6 and the gas-shielded flux-cored wire unless the shop erects wind screening it can maintain all day, which on a connection at height it usually cannot.
3. Position. Overhead work needs a product whose classification claims all positions and a WPS that qualified overhead. E7018 clears the first half; the second half is a separate check against the procedure.
4. Restraint. The brace between two fixed members is the heavily restrained joint, so hydrogen is the factor to attack. H4 is the lowest designator on the rack, and the R suffix means the coating passed a moisture-resistance test, which matters in the field where a quiver is the only conditioning available.

Selection: E7018 H4 R, and the reasoning that decided it is wind and restraint, not strength, because all three products carried the same 70 ksi minimum.

Correction, printed. The 4 millilitres per 100 grams applies to the electrode in the condition its specification defines. The field crew is issued rods from a holding oven into quivers each morning and returns unused rods within the exposure limit for that classification. Without that, the selection above is a purchase record rather than a hydrogen control, and the joint gets whatever the weather gave it.

What would flip this. Move the same connections into the shop, out of the wind, and the flux-cored wire becomes the stronger choice on deposition rate for the same 70 ksi minimum, with its own gas and hydrogen designators checked. Change the base metal to a higher-strength grade and the whole table is rebuilt, because 70 ksi would then be an undermatch, and whether that is acceptable is a question for the engineer of record rather than for the rack.

Check it against the rules the siblings state

• Strength figures carry their basis every time they appear: 70 ksi and 65 ksi are both stated as specified minimums from defined tests, and the 1.08 ratio is labelled a comparison of two floors.
• Hydrogen figure carries its condition: the H4 designator is written as at most 4 millilitres per 100 grams on the specification's test, in the specification's defined condition, and the example prints the oven-and-quiver control that keeps it true.
• Selection reasoning matches the table it was drawn from: all three products show 70 ksi, so strength did not discriminate, and the decision is attributed to wind and restraint, which are the two rows that differ.
• Numbers in the example traced to their source: 70 ksi and the 4 millilitres per 100 grams designator are defined in the sections above; 65 ksi minimum tensile and 50 ksi minimum yield are the job's own base metal figures, taken from the drawing rather than derived here.
• Field count checked: three products compared, three eliminated or selected on stated grounds, and the four constraints worked in order are strength, wind, position and restraint.

References

• AWS A5.1 and A5.5 for covered carbon steel and low-alloy electrodes, A5.18 for solid carbon steel wire, A5.20 for carbon steel flux-cored wire, A5.4 and A5.9 for stainless, each in the edition invoked by your WPS, contract or adopted code
• AWS D1.1, structural welding code for steel, in the edition invoked by your project specification or the adopted building code, for filler metal grouping and matching requirements
• Filler metal manufacturer's data sheet and safety data sheet for the classified shielding gas, the conditioning requirements and the fume constituents
• 29 CFR 1910.134 for respiratory protection, 29 CFR 1910.1026 (general industry) and 1926.1126 (construction) for hexavalent chromium, 29 CFR 1910.133 and 1910.252(b)(2) for arc radiation
• See related: What Electrode Storage Has to Do With Cracking; How to Read a Welding Procedure Specification; What a Welded Joint Changes About the Parent Metal