Silicon Bronze Hot cracking?

[Matt 5.0]

Was welding a sump on a steel gas tank today for one of our race cars. Tried my hand at the Si Br filler. 1/16 filler, 45 amps, 2%thoriated, Miller dynasty 200DX, post flow 5sec, gas set at 15lbs. The first thing I noticed was that it looks real dirty in the puddle, then when I flipped the hood up, I noticed it was cracked back about 4 inches back from the crater. Any ideas? Thanx guys
Matt

[ASKANDY]

A couple things...

Either the two different base metals don't like the SiBr filler, wasn't enough base metal dillution in the filler for strength or the base metal cooled too quick and cause a quench crack. Might try a different filler or preheat slightly and cool slowly or post heat slightly.

The dirt look lends me to believe that my first guess may be right or that some contaminants from the underside came up.

Andy

[Matt 5.0]

Thanx Andy, I'm going to cut the sump off tomorrow and weld it on a new tank with some 70S2. Kind of hard to mess that up

Matt