I found an old car spring at the side if the road (spring steel yes?) Heated it up in forge formed a decent shape as a start for a knife then when I took it out again only half of the knife came out I didn’t give up and began to shape a smaller knife but another bit broke off again!! Is it possible there was a fracture in the steel before I even began or is there something I could be doing wrong?
Either previously fractured or you could be hammering too cold.
Seen this happen a few time lately on Forged in Fire 
that’s the limit of my knowledge base.
Possibly you got it too hot in the fire (burned it up)
Another possibility; did you quench the steel to temper it? Don’t use water to do that use oil and take the appropriate safety precautions like wearing gloves etc.
Yet another possibility: did you drop the knife billet on the ground when it was hot, that is a no-no.
Yet another possibility; you did not achieve sufficient temperature of the material before working it as the previous person suggested, that can result in cracks and voids in the material. If you were doing a damascus or canister or fold method to form the knife, that would be referred to not making a good ‘weld’ of the metal.
Near as I can tell, if the metal had fractures in it to start with, the ‘weld’ process 9taking the metal to a molten state) should take care of that issue, but if you have impurities in the metal (rust or dirt) that could create some serious problems.