Please use picture below to answer the following question b

Please use picture below to answer the following question:

b) What is the most probable cause for the crack? How would you change the weld process to reduce the chance for cracks in future welds or this design?

Question #6: Answer the following questions about a weld failure for the design shown below. (15 points) Lab Failure analysis Report The lab has attached the following initial failure evaluation information for your use. Weld Weld Hardness Profile Weld Weld HAZ 10 Base Metal 1 2 3 s 6 7 s 9 to 11 12 13 14 15 16 17 Base Metal Weld HAZ Measurement Number 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

Solution

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.