Welding of carbon steels: Standard codes and classifications

Welding of carbon steels

Carbon steel is a type of steel that is most widely used for welding in industries today, due to its flexibility, strength, and workability under the fabricating method and relatively low price.

Carbon steels are classified as follows:

Low carbon steel

Medium carbon steel

High carbon steel

Although carbon steel is a metal that is welded over a wide range, it has some grades that are not easily welded. Carbon steel is grouped with different percentages of "carbon". This percentage of carbon also affects weldability.
Carbon steels are classified with different ASTM codes and grades for different types of products :
ASTM code for carbon steels pipes:
ASTM A53 Gr. A/B, ASTM A106 Gr. A/B/C, ASTM A333 Gr.1/Gr.6
ASTM code for carbon steels tubes:
ASTM A178/179/192, ASTM A334 Gr.1/6.
ASTM code for carbon steels plates: -
ASTM A285, ASTM A515, ASTM A516.

Welding of carbon steels

Low carbon steel

Low carbon steel can be easily welded due to the low percentage of carbon content in the metal. The melting point of low carbon steel is about 1539-1515 ͦC. Low carbon steel may be welded by any of the commonly used welding processes, the choice depending upon the section the thickness, and quality requirements.

Welding of Low carbon steels

The most commonly used welding processes for low carbon material are as follows:
1- Oxy-acetylene welding 2- Flux shielded metal arc welding 3- Submerged arc welding 4- Gas tungsten arc welding 5- Gas metal arc welding 6- Plasma arc welding 7- Thermit welding 8- Resistance welding 9- Electroslag welding 10- Brazing etc.
Low carbon steel is easy to weld and machine. Basically, it is applied to make rivets, screws, press sheets, pipes, nails, and chains when the carbon content is between (0.05-0.015%)and plate, structural shapes, and bars with the carbon content between (0.15-0.30%)

Medium carbon steel

Medium carbon steels are not so easily weldable as low carbon steels due to the higher carbon content (0.30-0. 50%). the higher carbon content may lead to brittleness. The melting point of medium carbon steel is about 1492 to1515 ͦC.

Welding of Medium carbon steels

Medium carbon steels may be welded with some special care and precautions, for that need to care some facts, such as:

Martensite is formed in the heat-affected zone due to rapid cooling and may lead to cracking due to its hardness and brittleness. Moreover, its hardened zone is not easily Machinable.

Weld cracking may be avoided by using low hydrogen-type electrodes.

Pre-heating is recommended to eliminate and reduce the hard and brittle areas.

For thicker sections, post-heat (595-675 ͦC) for one hour/25 mm of section thickness should be performed after welding to improve the metallurgical structure and increase the ductility, also reducing residual welding stresses.

Medium carbon steel may be welded by the following welding processes:
Flux shielded metal arc welding, Oxy-acetylene welding, Resistance welding, Thermit welding, Submerged arc welding.
Medium carbon steels are harder and stronger than low carbon steels. Medium carbon steels are usually applied for Shafts, axles, connecting rods, etc.

High carbon steels

High carbon steels are high carbon content metal where the percentage of carbon is (0.50-1.5%), that percent of carbon creates limit weld quality. The melting point of high carbon, steels is about 1405-1492 ͦC. This metal is seldom welded except for repair purposes.

Welding of High Carbon steels

High carbon steel may be welded by the following welding processes:
Oxyacetylene welding, Flux shielded metal arc welding, Thermit welding, Resistance welding.

High carbon steels are basically used for making crankshaft, scraper blades, automobile springs, anvils, band saws, etc. Oxy-acetylene welding with carbon steel

When welding Medium carbon steel with Oxyacetylene welding, An excess of acetylene is used in the gas flame to obtain sufficient heat,

No flux is needed when employing oxy-acetylene welding.

A Carburizing flame should be used when welding of high carbon steel, to obtain welds strong and free from defects.