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Properties, designations and what they mean for the work.
Material knowledge is the foundation of all good blacksmithing. The same tool and the same method can give widely different results depending on which metal you have in hand. Being able to read a material designation and understand what it tells you is therefore a core skill.
Steel is an iron-carbon alloy where the carbon content greatly determines the properties. A low carbon content gives a soft, tough and easily weldable steel, while a higher content gives a harder but more brittle material that often requires special consideration during welding and heat treatment. Alloyed steel has added other elements that change strength, hardness or corrosion resistance.
Stainless steel is alloyed with chromium, which forms a thin, self-healing protective layer on the surface. This makes the material corrosion-resistant, but also tough and heat-sensitive to machine. Stainless conducts heat poorly compared to unalloyed steel, which means that the heat collects locally — something to take into account in both cutting and welding.
Aluminium is light, has good corrosion resistance and conducts heat well. It is soft to machine, but can stick to the tool, and it quickly forms a hard oxide layer on the surface that melts at a far higher temperature than the metal itself. This oxide layer must be taken into account when welding, where it has to be broken down to achieve a clean joint.
Metals have standardised designations that indicate type and composition. Once you know the system, you can read from the designation which material group a workpiece belongs to and thus how it should be treated. Material certificates and delivery notes also provide the material's documented properties.
The choice of material is about requirements for strength, weight, corrosion resistance, appearance and price, but also about how easy it is to process and weld. A skilled metal fabricator thinks about material selection early — because it propagates through the entire task from cutting to surface treatment.