Is this a CJP butt weld? My fist inclination would be to think that he failure is due to the difference in coefficient of expansion, but Inconel woud do better at than than the 309 since its coefficient is half way in-between the two. Where is the cracking taking place? Weld, HAZ of CS, HAZ of sst? How is it being heated and at what rate? Slow is obviously better.