BDCS Notes - Welding

Welding: A technique for joining two metal pieces by applying heat to fuse the pieces together.

Filler Metal: used to facilitate process of welding.

Arc Welding: Uses an arc between the electrode and the grounded base metal to bring both the base metal and the electrode to their melting points.

Shielded Metal Arc Welding (Stick Welding): Most common form of arc welding, limited to short welds in bridge construction. A consumable electrode, which is covered with flux, is used. The flux produces a shielding atmosphere at the arc to prevent oxidation of the molten metal. The flux also traps impurities in the molten weld pool.

Submerged Arc Welding: Semiautomatic or automatic arc welding process. A bare wire electrode is automatically fed by the welding machine while a granular flux is fed into the joint ahead of the electrode. The arc takes place in the molten flux, which completely shields the weld pool from the atmosphere. The molten flux concentrates the arc heat, resulting in deep penetration into the base metal.

Gas Welding: No flux is used. An external shielding gas is used, which shields the molten weld pool and provides the desired arc characteristics. Typically used for small welds.

Care must be taken during welding to consider the distortion that is the result of the non-uniform heating of the welding process.

When the molten weld metal cools, it shrinks, causing deformation of the material and introducing residual stresses into the structure.

Welding Zones – Determine the relative ease with which steel can be welded when compared to the hardness of the steel.

1. Zone I – Cracking unlikely, but may occur with high hydrogen or high restraint. Use hydrogen control method to determine preheat.

2. Zone II – The hardness control method and selected hardness used to determine minimum energy input for single-pass fillet welds without preheat.

3. Zone III – The hydrogen control method is used.

Hardness and Hydrogen Control Methods are means of determining the level of energy used to preheat the weld area before the weld is performed.

Whenever metal is welded, the base material adjacent to the weld is heated to a temperature that may be sufficient to affect its metallurgy. The material affect in this manner is termed the heat-affected zone, HAZ. This material is a high-risk area for failure, especially if proper preheating and cooling procedures are not followed.