Welding Preheat Temp

Pre‑heat is a critical step in many welding procedures because it reduces the cooling rate of the weld metal, limiting the formation of hard, brittle micro‑structures such as martensite. By raising the base‑metal temperature before welding, the thermal gradient is softened, which helps to control residual stresses and prevents cracking, especially in high‑strength steels.

The required pre‑heat temperature is most often expressed as a function of the material’s carbon equivalent (CE) and the joint thickness. Carbon equivalent combines the effects of carbon and alloying elements into a single value that predicts hardenability. A common empirical relationship is:

Increasing either the CE or the thickness raises the heat‑input needed to keep the cooling rate low, so the pre‑heat temperature must be raised accordingly. Adjustments are also made for different material groups because alloying elements change the hardenability response.