I'm a bit embarrassed to post this as I absolutely cooked this joint but something has gone drastically wrong and I want to learn from this.

I was brazing in this dropout when I realised things were not going well and so I decided to pull the pin. I began to heat up the whole joint so I could pull the dropout out of the slot when suddenly it came loose and the fork blade split in this unusual way. I don't understand how a non hardened steel could crack like this. It appears to have come from the ends of the slot so I'm assuming it's something I've done. I slotted the blade on the mill with a slitting saw and I'm thinking maybe I went to fast here and that has caused a fracture or something? Thoughts?

Also another question, the blade is Columbus Max, and I had the shop I ordered from bend the blades for me as I don't have a bender. They have heated the blades up to bend them, is this normal/ok? I've never seen anyone use heat to bend a fork blade.

Thanks
Scott CundyIMG_0636 copy.jpgIMG_0639 copy.jpg