Welding Characteristics of Carbon Steel Materials in Welding Material Companies

1. Carbon Steel Welding by a Welding Materials Company

(1) Low-carbon steel welding

Under normal conditions, welding does not result in severe microstructural hardening or the formation of quenched structures. Low-carbon steels have low carbon content and relatively low levels of manganese and silicon; consequently, welded joints made from these steels exhibit good ductility and toughness. They also demonstrate excellent ductility and impact toughness, and typically do not require preheating or post-weld heating, nor do they necessitate any special welding procedures to produce high-quality welds. Therefore, low-carbon steel boasts superior weldability among all steels and is characterized by outstanding welding performance.

(2) Welding of Medium-Carbon Steel

Among welding materials, medium-carbon steels exhibit poorer weldability than low-carbon steels due to their higher carbon content. When the carbon equivalent (CE) approaches the lower limit of 0.25%, the weldability is relatively good. However, as carbon content increases, the tendency for hardening intensifies, and the heat-affected zone is prone to forming low-plasticity martensitic microstructures, which can lead to cold cracking. Moreover, when the welded component has high structural stiffness or when inappropriate welding consumables and process parameters are selected, the proportion of base metal melted into the weld bead becomes significant. Under such conditions, multi-pass welding—particularly when a single pass is deposited—results in elevated carbon, sulfur, and phosphorus levels in the weld, thereby increasing the susceptibility to hot cracking. Additionally, higher carbon content correlates with greater porosity sensitivity.

(3) Welding of High-Carbon Steel

High-carbon steels with a carbon equivalent (CE) greater than 0.6% exhibit high hardenability, and weldments made from such steels are prone to the formation of hard, brittle high-carbon martensite. This microstructure can lead to cracking in the weld metal and heat-affected zone, resulting in significant welding challenges. Consequently, these steels are generally not used for fabricating welded structures; instead, they are employed in the manufacture of components or parts that require high hardness or wear resistance. In most cases, welding of such parts is carried out as repair work on damaged components. Prior to welding, these parts should be annealed to minimize the risk of weld cracking, followed by post-weld heat treatment.

2. Welding of low-alloy high-strength steel by welding material companies

Low-alloy high-strength steels generally have a carbon content of no more than 0.20% and a total alloying element content of no more than 5%. Precisely because low-alloy high-strength steels contain a certain amount of alloying elements, their weldability differs from that of carbon steel, and their welding characteristics are as follows:

Welding Cracks in Weld Joints

Low-alloy high-strength steels prone to cold cracking contain alloying elements such as carbon, manganese, vanadium, and niobium, which enhance the steel’s strength; however, these steels are susceptible to hardening during welding. The resulting hardened microstructures are highly sensitive. Consequently, under conditions of high structural stiffness or significant restraint stresses, improper welding procedures can readily lead to the formation of cold cracks. Moreover, such cracks often exhibit a delayed onset, posing substantial hazards.

Reheat cracking refers to intergranular cracks that develop in the coarse-grained zone near the fusion line of welded components during post-weld stress-relief heat treatment or prolonged high-temperature service. It is generally believed that carbides of elements such as vanadium, niobium, chromium, and molybdenum in the heat-affected zone dissolve into the austenite at the elevated welding temperatures. These carbides do not precipitate during post-weld cooling but instead disperse and precipitate during PWHT, thereby strengthening the grain structure and concentrating creep deformation at the grain boundaries during stress relaxation. For more information on welding materials and related industry news, please follow Phoenix New Materials.