Welding of Carbon Steels

There are three broad categories of carbon steels:

(i) low carbon steels (carbon up to 0.3%),

(ii) medium carbon steels (carbon up to 0.5%) and

(iii) high carbon steels (carbon up to about 1.5%).

Welding Carbon steel

Welding of low carbon steels 

These are easily weldable by any common method of welding, e.g. flux shielded metal-arc welding, submerged arc welding, TIG, MIG, CO, welding, plasma arc welding, thermit welding, resistance welding processes, oxy-acetylene welding, brazing and soldering.

Flux shielded manual metal-arc welding is the most common method of welding mild steels. Mild steel and low hydrogen electrodes are used. Oxy-acetylene welding is frequently used. No flux is needed. A neutral flame is employed and filler rod is of mild steel. No pre-heating or post-heating is needed.

Welding of medium carbon steels

Welding of medium carbon steels poses problems as the weld joint tends to harden when mastensite is formed in the heat-affected zone (HAZ) due to rapid cooling. Pre-heating at 150 to 260°C is recommended to eliminate and reduce the hard and brittle areas. 

Post-heating is also done between 595 and 675°C. Medium carbon steels can be welded by flux shielded metal-arc welding, resistance welding, submerged arc welding, thermit welding and oxy-acetylene welding. With arc welding, low hydrogen electrodes should be used. In case of oxy-acetylene welding, an excess of acetylene should be used in the flame. No flux is used. High tensile steel rods are recommended.

Welding of high carbon steels

Flux shielded metal-arc welding, resistance welding, thermit welding and oxy-acetylene welding are often used for welding high carbon steels. In case of oxy-acetylene welding, a carburizing flame is used. Filter metal is of high carbon steel. 

When flux shielded metal-arc welding is done, pre-heating up to 205°C before welding is essential and post-heating after welding is required between 700 and 790°C. Electrodes used may be mild steel electrodes, austenitic electrodes or low hydrogen electrodes. Flash and upset butt welding and spot welding are also used for welding high carbon steels.

See More: Radiography Test for Welding

See More: Gas Welding and Its Types

See More: Solid State Welding

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