Hi Guys, I need some help to find out what I did wrong with a billet I welded the other day. After reading on the forum that pallet strapping was ok to use as a "spring steel" I decided to give it a go. I got some old power hacksaw blades and cleaned them up plus some strapping and made a billet of 21 layers (9 of hacksaw). I had some trouble getting it to stick together at the heat I normally use, so I kept it in the forge for longer and it finally all stuck together. I started to clean it up and noticed the cracking in the outside layers. What could have caused this?. The billet looks as if it is fully welded. I stuck it in some vinegar overnight to help clean up the flux. I put it in the vice and gave it a couple of good wacks with a hammer and it didnt crack. Any suggestions or help would be greatly appreciated.