Start with the Steel, Not the Hammer

Walk into any smithy and the first thing that catches your eye is the forge, the anvil, the rack of hammers. But the real decisions begin at the steel rack. Two bars that look identical on the outside can behave completely differently under the hammer, and understanding which grade you are holding is the difference between a clean shoulder and a cracked billet. Most hand forgers work with a handful of grades: mild steel for general ironwork, medium and high-carbon steels for edges and tools, and the occasional alloy steel for jobs that need extra toughness. Here is how they behave in the fire and what each is good for.

Mild Steel: The Forge's Bread and Butter

Mild steel — often sold as EN3B, S275 or plain "bright mild" — carries somewhere between 0.1% and 0.25% carbon. It moves beautifully. At a bright yellow heat it flows under the hammer almost like clay, tolerates being worked at lower temperatures than most, and forge welds with very little fuss. It will not harden to any useful degree, so it is not the steel for a blade or a chisel, but it is perfect for the majority of decorative and structural work.

• Gates, railings, brackets, hooks and scrollwork
• Fire pokers, trivets, handle hardware and camp tools
• Tongs, punches, drifts and other tools you will re-forge constantly
• Practice pieces and joints for learners

It is cheap, widely available in round, square and flat bar, and unforgiving to nobody. If you can case harden it with a compound, a mild steel punch will survive light work. Beyond that, treat it as a structural material that happens to be a joy to forge.

Medium Carbon: Where Hardening Begins

Step up to EN8 (around 0.4% carbon), EN9 (0.5%) or 1045 and the rules change. These steels harden, but not to the brittle edge of a blade. They take an edge that is tough enough to survive impact, which makes them the natural choice for striking tools and anything that meets shock.

• Hammer heads, axes and hatchets
• Cold chisels, drifts, punches and bolster tools
• Striking ends of tooling and hardy tools

The forging range is narrower than mild steel's. Work above the point where the steel shows a dull red in shadow, and stop forging below a low red heat — working medium carbon cold invites hairline cracks. Quench in oil rather than water, and temper straight away. A hammer head wants to be tough rather than glass-hard, so temper it further back than a knife.

High Carbon: Edges, Blades and Bite

Above roughly 0.6% carbon you are in blade and cutting-tool territory: 1080, 1095, EN42, or the classic W1 and O1 tool steels at 0.9% to 1.2%. These take a keen, lasting edge, but they punish sloppy heat control. Overheat them and you grow the grain, leaving a blade that will not hold up no matter how carefully you temper it.

• Knives, drawknives, gouges and carving tools
• Woodworking chisels and plane irons
• Springs, scrapers and farrier tools

Forge at a lower heat than mild steel and stop early. Normalise the piece — heat to non-magnetic and let it cool in still air — once or twice before hardening to refine the grain. Then bring it evenly to just past non-magnetic, quench in the medium the grade wants (water for simple carbon steels, oil for O1), and temper immediately in an oven or with a torch. For most blades, 180°C to 220°C gives a usable balance of hardness and toughness; a straw colour on a polished surface is the traditional guide.

Alloy Steels and Silver Steel

Add a little chromium, vanadium or manganese and you get a steel that hardens more deeply and resists wear better. Silver steel (BS1407) is the blacksmith's favourite of this family: a 1% carbon, chromium-bearing bar ground to a fine tolerance, ideal for punches, drifts, small punches and precision tooling. It quenches in water or oil and takes a superb polish for tempering colours.

Reclaimed spring steel — leaf springs, coil springs and EN45 — is another gem. Tough, oil-hardening and forgiving of impact, it makes excellent axes, hammers and long blades. The higher-alloy tool steels such as D2 and the hot-work grades are stiffer under the hammer and far less pleasant to forge, so most hand forgers buy them finished and ground rather than fight them in the fire.

Reading Recycled Steel

Much of the joy of forging comes from scrap, but unknown steel demands respect. A spark test on a grinding wheel tells you a great deal: short, dark orange sparks that burst close to the wheel suggest mild steel, while long, bright, forking sparks that carry further indicate higher carbon. A file test confirms it — if a file skates, the steel is hard.

• Leaf and coil springs, lorry axles and plough shares: treat as medium to high carbon
• Farrier rasps, files and ball bearings: high carbon, superb for tools
• Galvanised, plated or painted stock: never forge it — the fumes are genuinely dangerous

When you cannot identify a steel, assume it is high carbon. Forge it gently, normalise it, oil quench a test coupon, snap it and read the grain. Fine, silky grey means good; coarse and bright means you overheated it.

Matching the Steel to the Job

The simplest rule is to choose the least exotic steel that will do the work. Mild steel for anything decorative or structural, EN8 or EN9 for tools that get struck, high carbon for anything that cuts, and alloy or spring steel where toughness under repeated shock matters most. Buy known stock for critical pieces, keep a notebook of every heat and quench, and test coupons before you commit a finished piece to the oil. Learn how three or four grades behave and you will forge better work than any rack of mystery steel will ever allow.