Why Low Carbon Steel can be Welded, High Carbon Steel can not be Welded

Why Low Carbon Steel can be Welded, High Carbon Steel can not be Welded

Why Low Carbon Steel can be Welded, High Carbon Steel can not be Welded

According to chemical composition, steel can be divided into carbon steel and alloy steel two categories. According to the chemical composition of steel can be divided into carbon steel and alloy steel two categories. Carbon Steel is divided into:

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  1. Low carbon steel, carbon content less than 0.25% ;
  2. Medium carbon steel, carbon content of 0.25% ~ 0.6% ;
  3. High carbon steel, carbon content more than 0.6%.

Mild steel is a kind of carbon steel whose carbon content is less than 0.25% . It is called soft steel because of its low strength and hardness. It consists of zero ordinary carbon structural steels and a portion of high-quality carbon structural steels.

Medium Carbon Steel has good hot working and cutting properties and poor welding properties. Can not be heat-treated, direct use of cold-rolled, cold-drawn material, can also be used after heat treatment. The medium carbon steel after quenching and tempering has good comprehensive mechanical properties. The highest hardness is HRC55(HB538) and σb is 600-1100MPa.

High Carbon Steel commonly known as tool Steel, Carbon content from 0.60% to 1.70% , quenching and tempering, poor weldability.

Comparison of weldability between low carbon steel and high carbon steel

The weldability of steel mainly depends on its chemical composition. The most influential element is carbon, which means the amount of carbon in a metal determines its weldability. Most of the other alloying elements in steel are also unfavorable to welding, but their influence is generally much less than that of carbon.

General Low-carbon steel weldability, general do not need to use special measures, only in low temperature, thick plate or have higher requirements, only need to use basic electrode welding, and appropriate preheating. When the content of carbon and sulfur in low carbon steel is more than the upper limit, it is necessary to select groove form and reduce the fusion ratio, besides adopting high quality low hydrogen electrode, adopting pre-heating and post-heating measures, to prevent thermal cracking.

The higher the carbon content, the bigger the hardening tendency of HAZ, the bigger the cold cracking tendency and the worse the weldability. With the increase of the carbon content in the base metal, the carbon content of the weld metal will increase correspondingly. Therefore, the welding of medium carbon steel should use good crack resistance alkaline electrode, and take measures such as pre-heating and post-heating to reduce the crack tendency.

In the welding of high carbon steel, due to its high carbon content, great welding stress will be produced during welding, and the tendency of hardening and cold cracking in the Haz of welding is greater, and the weld is also more likely to produce hot cracks, high carbon steel is more likely to produce hot cracks than medium carbon steel, so this kind of steel is the worst weldability, it is not used in general welding structure, only for casting repair welding or surfacing. The post-weld parts should be tempered to eliminate stress, fix structure, prevent cracks and improve the properties of the weld.

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