Welding consumables Part 5 - MIG/MAG and cored carbon steel wires

Part 1
Part 2
Part 3
Part 4

The article in Issue 145 of Connect briefly described the characteristics of solid and cored wires.

To ensure that there is a consistency in composition and properties between wires from a variety of manufacturers, specifications have been produced that enable a wire to be easily and uniquely identified by assigning the consumable a 'classification', a unique identification that is universally recognised.

The two schemes that are dealt with in this article are the EN or EN ISO method and the AWS scheme. There are such a large number of specifications covering the whole range of ferrous and non-ferrous filler metals, both solid wire and cored, that it will not be possible to describe all of these here. This article therefore reviews just the carbon steel specifications.

The identification of the solid wires is relatively simple, as the chemical composition is the major variable although both the EN and the AWS specifications detail the strength that may be expected from an all-weld deposit carried out using parameters given in the specification. It should be remembered, however, that most welds will contain some parent metal and that the welding parameters to be used in production may be different from those used in the test. The result is that the mechanical properties of a weld can be significantly different from those quoted by the wire supplier, hence the need to always perform a procedure qualification test when strength is important. In addition, the mechanical properties specified in the full designation include the yield strength.

When selecting a wire remember that the yield and ultimate tensile strengths are very close together in weld metal but can be widely separated in parent metal. A filler metal that is selected because its yield strength matches that of the parent metal may not, therefore, match the parent metal on ultimate tensile strength. This may cause the cross joint tensile specimens to fail during procedure qualification testing or perhaps in service.

The EN specification for non-alloyed steel solid wires is BS EN 440. This specification identifies the wires by either the chemical composition alone, a four character designation, or a nine character designation that includes yield strength, Charpy-V impact strength, shielding gas and composition.

The symbolisation for mechanical properties is summarised in Table 1. The specification lists eleven compositions, too many to describe completely here. Five of the wires are carbon steel with varying amounts of deoxidants, two wires contain approximately 1% or 2.5% nickel and an additional two wires contain around 0.5% molybdenum. The designation of these wires is for example G3Si1, 'G' identifying it as a solid wire, '3' as containing some 1.5% manganese and Si1 as containing around 0.8% silicon; G3Ni1 is a wire with approximately 1.5% manganese and 1% nickel.

Table 1 Symbols for mechanical properties

A full designation could therefore be BS EN 440 G46 3 M G3Si1 where the 'M' designates a mixed gas and 'C' 100% CO ₂ .

The AWS specification AWS A5.18 covers both solid, composite stranded and cored wires comprising six carbon steel filler metals for MAG, TIG and plasma welding in both US and metric units.

The classification commences with the letters 'ER' that identify the consumable as an uncoated wire electrode, the next two digits the tensile strength in either 1000s of psi.(ksi) or N/mm ² eg ER70 (70ksi UTS) or ER48 (480N/mm ² UTS). However, note that there is only this one strength level in the specification.

The next two characters identify the composition, essentially small variations in carbon, manganese and silicon contents, the wire type )solid wire (S) or metal cored or composite wire (C)) and the Charpy-V impact values.

With one exception, the solid wires are tested using 100% CO ₂ , the cored wires with argon/CO ₂ or as agreed between customer and supplier, in which case there is a final letter 'C' designating CO ₂ or 'M', a mixed gas.

The permutations in these identifiers are too many and too complicated to be able to describe them all in sufficient detail but as an illustration, a typical designation would be ER70S-3, a 70ksi filler metal, CO ₂ gas shielded and with minimum Charpy-V energy of 27J at -20°C. ER70C-3M identifies the wire as a solid wire 70ksi UTS metal cored filler metal, 27J at -20°C and tested with an argon/CO ₂ shielding gas.

The European specification for non-alloy steel flux and metal cored wires is BS EN 758. This covers gas shielded as well as self-shielded wires. Although the specification claims that the wires are all non-alloy there is only one that contains no alloying apart from manganese, the remaining eight all contain molybdenum up to 0.6% and/or nickel up to 3.85%. The classification commences with the letter 'T', identifying the consumable as a cored wire.

The classification uses the same symbols for mechanical properties as shown in Table 1 and a somewhat similar method to describe the composition as BS EN 440. Thus MnMo contains approximately 1.7% manganese and 0.5% molybdenum; 1.5Ni contains 1% manganese and 1.5% nickel. In addition to the symbols for properties and composition there are symbols for flux composition as in Table 2.

Table 2 Symbols for flux core type and position

In addition there are symbols for gas type. These are 'M' for mixed gases, 'C' for 100% CO ₂ and 'N' for self-shielded wires and 'H' for hydrogen controlled wires. A full designation may therefore be BS EN 758 T42 4 2Ni B 2 H5.

The American Welding Society classification scheme for carbon steel flux cored wires is detailed in the specification AWS A5.20. The full designation is ten characters in length beginning 'E' for an electrode then designators for strength, welding position, cored wire, polarity, shielding gas, toughness, heat input limits and diffusible hydrogen, the last three designators being optional.

There are two strength levels - E7 (70ksi UTS) and E6 (60ksi UTS) followed by a designator for welding position,'0' for flat and horizontal and '1' for all positions, including vertical-up and vertical-down.

The next symbol 'T' identifies the wire as being flux cored and this is followed by either a number between 1 and 14 or the letter 'G' that identifies the usability. This number refers to the recommended polarity and whether the wire can be used to deposit single or multi-pass welds. 'G' means that the operating characteristics are not specified. The sixth letter identifies the shield gas used for the classification, 'C' being 100% CO ₂ , 'M' argon/CO ₂ , no letter indicating a self-shielded wire.

The non-compulsory part of the designation may include the letter 'J', confirming that the all-weld metal test can give Charpy-V values of 27J at -40°C; the next designator may be either 'D' or 'Q'. These indicate that the weld metal will achieve supplementary mechanical properties at various heat inputs and cooling rates. The final two designators identify the hydrogen potential of the wire.

A full A5.20 designation could therefore be E71T-2M-JQH5. This identifies the wire as a cored, all positional wire to be used with argon/CO ₂ shield gas on electrode positive polarity. The weld metal should achieve 70ksi tensile strength, 27J at -40°C; 58ksi yield strength at high heat input, 90ksi at low heat input and a diffusible hydrogen content of less than 5mlsH ₂ /100gms weld metal.

This article was written by Gene Mathers