Leaf springs, coil springs, files and lawnmower blades are already high-carbon steel and make cutting tools and scrapers, while rebar, steel pipe and angle iron are mild steel suited to bars, hooks, handles and frames. Tell them apart with a file, which skates across hard steel and bites into mild steel, and treat spring steel as stored energy and hardened steel as brittle until it has been cut, shaped and heat-treated correctly.
Part of Tool Identification & Repair
When finished tools run out, raw steel becomes tools, and the main question is whether a piece is hard enough to hold an edge or soft enough to bend into a bar.
Spring And File Steel Make Edges, Mild Steel Makes Bodies
The parent article lists these sources and their uses:
- Leaf springs from vehicles: high-carbon steel, excellent for forging into knives, chisels and scrapers.
- Car coil springs: high-quality spring steel; small springs become arrow points or trap components.
- Files and rasps: already hardened steel; old files can be reground into chisels, scrapers or knife blanks.
- Lawnmower blades: hardened steel, already blade-shaped; good machete or chopping tool stock.
- Rebar: mild steel, easily bent into hooks, pry bars and handles.
- Steel pipe: cheater bars for wrenches, handles and structural support.
- Angle iron: shelving brackets and bed frames; drill and bolt into jigs and frames.
The practical difference is hardness. High-carbon steel can be hardened and tempered to hold an edge. Mild steel cannot be hardened usefully, so it is for structure, levers and handles, not edges.
What You Need
- A file, to test hardness.
- A hacksaw, cold chisel or grinder to cut stock; see Basic Repair of Hand Tools for sharpening and fitting.
- A hammer and anvil substitute (a heavy flat steel block) if you will forge.
- Eye protection, gloves, a face shield and a dust mask for cutting and grinding.
Method: Test, Identify, Then Match The Steel To The Job
Step 1: Clean the surface where you will test, down to bright metal at an edge or end.
Step 2: File test. Draw a file across the clean spot with moderate pressure. If it bites and takes a curl of metal, the steel is soft, mild steel. If it skates and leaves little mark, the steel is hard. A hardened file will not mark hardened steel at all.
Step 3: Sort. Hard stock goes to the edge-tool pile. Soft stock goes to the bar, hook and frame pile.
Step 4: Match the job. Cutting and chopping tools come from the hard pile; levers, handles and fixtures come from the soft pile. To harden and temper an edge tool, follow Heat Treatment and Forging; spring steel from a vehicle is usually already hard, so file-test it before and after working it.
Step 5: Cut with the right method. Use a hacksaw or cold chisel on soft stock. Hard stock resists a saw; you may need a grinder or a hot cut.
Common Mistakes
- Treating an old file as ordinary iron. It is hard and brittle, and shatters if hammered or bent sharply.
- Making a lever from spring steel. It springs back or snaps; use mild steel.
- Ignoring what the stock was used for. A bent coil spring may be fatigued or cracked.
- Skipping the test. Two pieces that look identical can behave very differently.
Safety
Spring steel stores energy, hard steel shatters, galvanised steel gives off fume
A compressed coil spring or a loaded leaf spring released by cutting or grinding can fly with force; clamp it and keep clear of its line of release. Hardened files and spring steel can shatter if struck or bent, throwing fragments, so wear eye and face protection. Galvanised (zinc-coated) stock gives off toxic zinc fume when heated or cut with heat; work in the open air with the wind carrying fume away, or strip the coating first. Quenching oil is flammable: keep it away from the forge flame and have a lid ready. If any fuel is around, see the warnings on Fire & Vapor Safety.
What’s Next
- Learn next: Assessing Tool Condition — judging finished tools you find
- Combine with: Forging — turning raw stock into shape