What is hot cracking Why may hot cracking occur during a ste

What is hot cracking? Why may hot cracking occur during a steel welding process? Where in the weld microstructure would you expect hot cracks to initiate? Where inside the weld microstructure would you expect to find weaknesses (low-ductility, low-toughness regions) that could lead to failure by other mechanisms? Briefly explain one of those other mechanisms in the context of either a steel or an aluminum alloy.

Solution

Hot cracking is a defect in which cracks occurs in the fusion zone or heat affected zone of a welded joint at elevated temperatures. Its occurrence is dependent on the existence of a relativity high tensile stress, developed by contraction of the welded joint, and lack of ductility due to the presence of a discontinuous intergranular liquid film.

Stainless steel and combinations of stainless steel, low alloy steels and nickels alloys can be a problem with certain compositions of weld metal. Presence of elements such as sulphur, phosphorus (which should be less than 0.025% to minimize risk) and copper which promote cracking.

Centreline cracking:It is characterised as separation in the in the centre of given weld bead.It is result og either segregation induced cracking,bead shape induced cracking, or surface profile indiced cracking