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

Job Knowledge 86

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/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/ISO 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. (In the EN/ISO specifications, the classification may indicate either yield or ultimate tensile 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/ISO specification for non-alloyed steel solid wires is BS EN ISO 14341. This specification classifies wire electrodes in the as-welded condition and in the post weld heat-treated condition, based on classification system, strength, Charpy-V impact strength, shielding gas and composition. The classification utilises two systems based either on the yield strength (System A) or the tensile strength (System B):

• System A - based on the yield strength and average impact energy of 47J of all-weld metal.
• System B - based on the tensile strength and the average impact energy of 27J of all-weld metal.

In most cases, a given commercial product can be classified to both systems. Then either or both classification designations can be used for the product.

The symbolisation for mechanical properties is summarised in Table 1A for classification system A and Table 1B for classification system B. For classification system B, the 'X' can be either 'A' or 'P', where 'A' indicates testing in the as-welded condition and 'P' indicates testing in the post weld heat-treated condition. The symbol for chemical composition is summarised in Table 3A and 3B of BS EN ISO 14341 based on each classification system. For classification system A, the standard lists eleven compositions, too many to describe completely here. Six 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 1A Symbols for mechanical properties based on classification system A

Table 1B Symbols for mechanical properties based on classification system B

A full designation could therefore be ISO 14341-A-G 46 5 M G3Si1 where the '-A' designates the classification system A, the '-G' designates solid wire electrode/or deposits, and the 'M' designates a mixed gas. An example of a System B designation could be ISO 14341-B-G 49A 6 M G3, where 'A' indicates testing in the as-welded condition.

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 'E' or 'ER'. 'E' designates an electrode. 'ER' indicates that the filler metal may be used either as an electrode or a rod. The next two digits designates the tensile strength in either 1000s of psi.(ksi) or N/mm² eg ER70 (70ksi UTS) or ER48 (480N/mm² UTS). However, note that there is only 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% CO₂, the cored wires with argon/CO₂ or as agreed between customer and supplier, in which case there is a final letter 'C' designating CO₂ 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, CO₂ gas shielded and with minimum Charpy-V energy of 27J at -20°C. E70C-3M identifies the wire as a solid wire 70ksi UTS metal cored filler metal, 27J at -20°C and tested with an argon/CO2 shielding gas.

The EN/ISO specification for non-alloy steel flux and metal cored wires is BS EN ISO 17632. This covers gas shielded as well as self-shielded wires. The standard identifies electrode based on two systems in a similar way as BS EN ISO 14341, indicating the tensile properties and the impact properties of the all-weld metal obtained with a given electrode. Although the specification claims that the wires are all non-alloy, they can 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 1A&B and a somewhat similar method to describe the composition as BS EN ISO 14341. 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 electrode core composition. Table 2 summarises the symbols for electrode core type and welding position in accordance with classification system A. Classification system B uses Usability Indicators as oppose to a one-letter symbol for electrode core type, which can be found in Table 5B of BS EN ISO 17632.

Table 2 Symbols for electrode core type and position based on classification system A

In addition, there are symbols for gas type. These are 'M' for mixed gases, 'C' for 100% CO₂ and 'N' for self-shielded wires and 'H' for hydrogen controlled wires. A full designation may therefore be ISO 17632-A -T46 3 1Ni B M 1 H5 in accordance with classification system A. For classification system B, an example may be ISO 17632-B -T55 4 T5-1MA-N2-UH5, where 'T5' is the usability designator, 'A' indicates test in the as-welded condition, 'N2' is the chemical composition symbol, and 'U' is an optional designator.

The American Welding Society classification scheme for carbon steel flux cored wires is detailed in the specification AWS A5.36. This also contains information from A5.18, but does not officially supercede it. The full designation is ten characters in length beginning 'E' for an electrode then designators for strength, welding position, cored wire, usability, shielding gas, toughness, heat input limits and diffusible hydrogen, the last four 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, requirements for external shielding, 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 shielding gas used for the classification, 'C' being 100% CO₂, 'M' for argon/CO₂, 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 AWS A5.36 designation could therefore be E71T-2M-JQH5. This identifies the wire as a cored, all positional wire to be used with argon/CO₂ shielding gas on electrode positive polarity. The weld metal should achieve 70ksi tensile strength, 27J at -40°C, 58 to 80ksi yield strength at high heat input, a maximum 90ksi at low heat input, and a diffusible hydrogen content of less than 5ml of H2/100g of deposited weld metal.

This article was written by Gene Mathers, reviewed and modified by Runlin Zhou.