Chapter 8 Manual Welding Techniques
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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.
Excessive penetration. Formed when excessive heat is applied to the upper part of the joint.
How to correct:
• Change torch angle to lower plate.
• Decrease bead size.
• Increase welding speed.
• Use chill bar behind joint to remove
excessive heat.
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.
Concave root surface. The molten weld penetration has retracted from the root surface.
How to correct:
• Increase welding speed.
• Decrease amperage.
• Increase arc length.
• Increase fi ller metal feed.