The Benefits of Weld Preheating and Reducing Thermal Stress
- Thermal Stresses Occur as Molten Weld Pools Cool
- Cracking Can Occur Both During and After Welding
- Colder Parent Metal Resists the Inevitable Contraction of the Weld Metal
- Preheating reduces the temperature difference between the Weld Metal and the Parent Metal and Minimizes Potential Cracking
Pre Weld Heat Treating and High heat Loss
- Heavy Wall Materials and Aluminum Alloys with higher thermal conductivity can act as a heat sink, drawing heat away from a weld and cooling at an accelerated rate.
- Preheat Heat treatment will reduce the cooling rate of the deposited weld material and allow a proper fusion with the parent metal
Pre Weld Heat Treatment will Reduce Weld Porosity
- If moisture is present at a welded joint, the high heat of the welding arc will break the water down into its elements, hydrogen and oxygen. The hydrogen by-product easily dissolves into the weld metal and causes weld porosity during weld solidification.
- Performing a pre weld heat treat drives away moisture from the welded joint.
Pre Weld Heat Treatment will Reduce Weld Hardening
- During and after completing of the welding process, both the weld pool and the Heat Affected Zone (HAZ) can harden and crack when cooling at a rapid pace
- By preheating the weld and the Heat Affected Zone (HAZ) the rate of cooling can be controlled and reduced thereby eliminating problems associated with weld hardening
Pre Weld Heat Treating Prevent Hydrogen Cracking
- Electrode Coatings and Fluxes can often introduce moisture directly to the arc and weld pool. The increase in moistures increases the possibility of weld or Heat Affected Zone (HAZ) cracking.
- Preheating slows down the weld cooling rate which allows hydrogen to escape
Pre Weld Heating Improves Material Microstructure
- Low Alloy Steels containing elements such as chromium, nickel, molybdenum, and vanadium are susceptible to cracking in the Heat Affected Zone (HAZ)
- Preheating improves the microstructure inside the HAZ by reducing the post weld cooling rate. The reduced cooling rate produces:
- A more desirable and ductile microstructure to be formed
- Minimizes Under Surface Cracking