Dear Ankur,
The cracking occurs due to formmation of Matenstitic structure, In welding SS-304 to SA 516 Gr.70 , the choice of the filler material is is the main area of concern. If you use ER-308 filler wire , the weld metal(SS+ CS) with the formation of martensite may contain cracking, because the filler metal cannot tolerate dilution by both base metals. A proper filler metal, inthis case, is Type E309, for applications below 800F in general. The procedure of estimating the microstructure of the E309-type diluted weld metal can be done by using a Schaeffler diagram , the diluted weld metal will contain about 4% of ferrite and no martensite in the austenitic matrix, which is resistible to cracking.
Vineet Kumar
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