Page 142 - CITS - Welder - Trade Theory

WELDER - CITS

Fig 2 Fig 3

Fig 4

b temperature to which the part is to be post-heated

c holding time in the furnace
d the rate of cooling.
Post heating of carbon steels depends on the thickness of the base metal and its carbon content. (Fig 5)

Fig 5

Post heating retards the rate of cooling of a welded joint:

For plain carbon steels the joint is heated from 100°C to 300° C for general post heating. This treatment will
reduce the cracking tendency of carbon steel and cast iron. If they are not post heated, cracks may develop.
Also the welding heat can develop hardness and brittle- ness in some areas of the joint. In addition the grains of
the base metal in the heat affected zone and fusion zone will grow in size which will change the property of the
welded joint.

129

CITS : C G & M - Welder - Lesson 33 - 43