Destructive testing method for specimen and crystal structure on maximum solubility

From non-destructive testing, we have found various flaws in both specimens so no method in the universe is perfect but we can rectify the defects but cannot be removed completely. From destructive testing we have found that First specimen MS (MS) sustain stress without failure due its similar crystal structure (BCC) on the other hand second specimen have failed within the lower stress range due to lack of cohesion, adhesion between the dissimilar metals MS and SS, and also both have different crystal structures BCC and FCC respectively. Thus, to gain maximum strength of weld bead, welding should be done using similar metals with maximum solubility