Handbook - Wire Electrodes

3 Others – Nickel, chromium and molybdenum are often added to improve mechanical and/or corrosion resistance properties. In small amounts, they can be used in carbon steel wires to improve the strength and toughness of the deposit. They are used in larger amounts in stainless steel wires. Generally, when welding is done in Argon with 1% to 3% oxygen or with mixtures of argon containing low CO₂ content, the weld metal chemical composition will not vary greatly from the analysis of the wire electrode. However, when CO₂ is used for shielding, reductions in Si, Mn and other deoxidizing elements can be expected. Ni, Cr, Mo and carbon contents will remain quite constant. Wires with very low carbon contents (.04-.06 percent) will produce, with CO₂, a weld metal with a higher carbon content. CARBON STEEL ELECTRODES Table 5-1* lists the chemical requirements and designations for all mild steel wires covered under the American Welding Society Specification A5.18. The minimum as-welded mechanical properties of welds conforming to each classification appear in Table 5-2*. Although mechanical properties and service requirements do influence the wire selection in some cases, a more general consideration will be found most useful for the majority of applications and weld joint designs. As either the welding current, weld puddle size, amount of rust, mill scale and oil found on the base plate surface, or the O₂and CO₂ content of the shielding gas increases, the Mn and Si content of the wire electrode should also increase to provide the highest quality weld. The following is a description of the characteristics and intended use of the most common wire electrodes of each classification appearing in Table 5-2. ER70S-2 (Spoolarc 65) – This wire is heavily deoxidized and is designed for producing sound welds in all grades of carbon steel: killed, semi-killed and rimmed. Because of the added deoxidants (Al, Zr and Ti) in addition to Mn and Si, it is suited for welding carbon steels having a rusty surface. Ar-O₂, Ar-CO₂ and CO₂ shielding gases can be used. In general, an extremely viscous weld puddle will be produced, making it well suited for short-arc welding out of position. To improve the wetting, 0₂or CO₂ content should be kept relatively high. Continued on next page...