I'm just getting in to knife making.  I am a passable smith, and just got a new grinder (Bader BIII).  There is a wrecking yard down the road, and I thought I would go by there and ask about buying some leaf springs.  I understand they are good for making knives.  But, which ones are good?  Car or truck?  Old or new?  Which ones should I look for?  Thanks in advance.

GMoore,

Springs are "mystery" steel.  Good knife making steel is really the least expensive thing on the list of materials to make a knife.  Leaf springs can make a good knife...........and would be fine "if" you knew exactly what material they are so you could follow proper heat treating instructions.  You'll be kind of hit and miss if you don't have that information.  That said, leaf springs can make a good knife.

I started with leaf springs because I had a couple full packs given to me from a family friend when I started. As Chris said, they are a mystery steel. Free steel is good if you take the time to do some test samples from each pack to see how they react to quenching and tempering to dial them in so to speak.

If you are buying them, you would honestly be better off just buying knife steel. You get a known alloy with known baselines for heat treat, and you don't have to worry about hidden stress fractures.

In addition to the above; leaf spring only appears to be attractive for forging blades because it's already sort of blade shape. However, Forging flat bar requires a higher level of skill than round or square stock. Drawing the cheeks down without flat rolling itself into a tight scroll takes more steps and isn't always successful. It can end up looking like a bacon roll. 

If however you use coil spring the round stock is much less effort managing it's tendency to curve away from the cheeks. Also being as a coil is a much longer spring it typically suffers significantly less micro fracture damage than leaf. If you buy from a scrapper be selective, don't buy a broken coil. Yes? Better still check automotive spring shops and see if they'll sell you spring they've removed from new vehicles. Lots of guys want their new pickemup trucks lifted. Spring shops can NOT install the old springs in another vehicle so it goes to the scrapper. OR YOU!! 

No matter you REALLY need to cut test coupons and do the tests to determine what steps you have to follow: Forging and heat treating to produce a functional blade. Even a wall hanger should be functional, you never know when someone will use it and if it fails and causes injury the maker is on the hook. Hmmm?

However, I highly endorse the advice to just buy new known steel and skip the headaches and risks involved in using salvage. Save that till you have the skill sets to evaluate what you have on the anvil, they'll come don't worry. Your patience WILL be rewarded.

Frosty The Lucky.

Sage advice, Frosty.  Also, I didn't realize the coiled spring would have less tendency to curve away than leaf spring.  Very interesting.

I've had a bunch of leaf springs that make for good blades, once you discover the right HT. 

Its not unusual  for that steel to have internal micro fractures, which  can only been seen when you getting ready to polish the blade. 

Which is why you want springs of either type: coil/leaf, with as few miles on them as possible and DON'T want one of either type with a known failure as the failure mode is for multiple micro cracks to form and then *1* to propagate catastrophically.---Leaving the rest to be discovered by blademakers *after* many hours of work have been done!

Sourcing springs from places that do lifts and lowers can result in getting springs with very low miles---I was once given a pack that had 19 miles on them. The distance from the rail car delivery point to the dealership to the place that replaced them with a different pack.