When is steel weldable?

The numerous steel grades (more than 2,500 alloys) with their many different properties often make it difficult to find out when steel is weldable, and when not. You will find some general technical guidelines and some more about the suitability for welding here.

Carbon content

A very important criterion for whether steel is weldable or not is the carbon content of the respective steel grade. Basically, it can be assumed that a steel with a carbon content of less than 0.22% will in most cases be weldable.

For steels with a carbon content of between 0.22% to around 0.3%, it may still be possible to weld a steel in a certain way by means of suitable additional measures.

Reason

For steels with high carbon content, changes and changes in the microstructure occur during welding (microstructure of the steel atoms). This can lead to either so-called hardness peaks or cracking in the material by welding. Both are not welcome.

hardness peaks

The term hardness peaks is the formation of martensite in the boundary between the so-called heat affected zone (where welding heats the steel) and the rest of the material.

cracking

Cracking can also be threatening if the microstructure changes at the weld or converts to harder martensite. However, the reason for cracks can also be internal stresses in the workpiece, which are caused by welding.

Measures to improve the weldability

With additional individual measures, steels with carbon contents between 0.22% and 0.3% can still be made weldable, or their suitability for welding can be increased. These measures are:

  • Preheat the weld
  • Preheating the workpiece
  • Change in the so-called cooling rate during welding
  • previous stress relief annealing

Carbon equivalent

Not only the carbon content but possibly also other alloy components can cause internal stresses in the workpiece during welding. Since consideration in detail is complicated, one uses the so-called carbon equivalent. It indicates the extent to which alloy components influence the suitability for welding.

Tips & Tricks

Welding can always lead to embrittlement of the workpiece at the weld, which should always be considered. Also, not all welds are always suitable for each alloy. This can be checked by looking up the weldability of the respective material under the respective material number.

Video Board: Lec 33 - Weldability of carbon and alloys steels: Fe-C, CCT