Pneumatic bit repair

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We've transfered a old pneumatic bit tip from an old demo hammer by welding the tip onto a new shank. The weld has failed 2 times so far just outside of the weld (there is good penetration - the weld is not poor). It's as if the original shank is brittle just outside the weld because of the cooling process. We are using supermissleweld but we may just use 110. We air cooled the weld previously and are now considering using ashes to slow the cooling down even more.Anyone have any experience or know what's causing the failure?Lance
Reply:Your preheat should be at least 200 F  You don't want to lose temper if the tip is carbon steel.  If it is carbide tipped then I would preheat up around 300 F++ (spit dances)  After welding do the dry ashes, warm dry sand or vermiculite.
Reply:It might help to grind the weld smooth with the rest of the shank to avoid a stress concentration.