Copyright Goodheart-Willcox Co., Inc. Chapter 8 Manual Welding Techniques 151 Postweld Treatment Postweld treatment depends on the type of material welded, joint restraint, and the desired mechanical values. In postweld treatment, the cooling rate of the welded part is controlled, allowing the mechanical prop- erties of the metal to return to a normal condition. Cooling some materials too rapidly severely affects their mechanical properties, such as making the part very hard and brittle. Preweld and postweld heat treatments are used on steels with higher carbon content, castings, and other materials that are prone to cracking. A stress-relieving operation performed on carbon steels at approximately 1150°F (621°C) removes residual stresses caused by weld shrinkage. This can be done by local or furnace heating. The weld area is heated to 1150°F (621°C) and this temperature is maintained for one hour per inch of material thickness. The part can then be air-cooled. Low-alloy steels can be stress-relieved in the same manner however, the cooling period should be lengthened by covering the part with heat-resistant materials. Melt-through. Occurs when the molten pool melts through the base material and creates a hole. How to correct: • Change torch angle to lower plate. • Decrease bead size. • Increase welding speed. • Use chill bar behind joint to remove excessive heat.