The lab has attached the following initial failure evaluatio

The lab has attached the following initial failure evaluation information for your use. These data show a macro image of the weld cross-section and the micro-hardness survey taken across the HAZ (Starting in the base metal and moving out towards the weld bead) as shown in the macro-photo above. What type of weld is specified in this design? (Type, size, location, GDT tolerance, etc.). What can be concluded from the lab data?

Solution

a) type of weld- fillet weld

b) Conclusion are:

The most probable cause for the crack are:

The residual stress in the HAZ because of the sudden heating and cooling which leads to the crack growth and propagation.

How to reduce the chances of crack: By preheating followed by slow cooling after welding. Preheating slows the cooling rate both in the weld and the HAZ during and after austenite transformation, thus reducing martensite formation to a minimum and limiting the hardness any martensite which does form.

Preheating also dissipates the shrinkage stress and reduces distortion.