If you have ever ordered lead for a project and felt a little lost in the alphabet soup of alloy names, you are not alone. Pure lead, Pb-Sb, Pb-Sb-Sn, hardness ratings, percentage breakdowns… it can feel like a foreign language until you understand what each piece actually does. So let’s walk through it together, in plain terms, so you can order exactly what your application needs.
Why Pure Lead Isn’t Always the Answer
Pure lead is soft. Really soft. So soft you want to bite it (DON’T). That softness is actually one of its most valuable properties for certain jobs, which is why we wrote an entire post about purified lead and what makes it worth specifying. Pure lead, sometimes called chemical lead or corroding lead, has a Brinell hardness of roughly 4 to 5 BHN. That low hardness is exactly what you want for radiation shielding, chemical tank linings, and roofing applications where you need lead to conform to a surface rather than resist deformation.
But softness becomes a liability the moment you need lead to hold a shape under stress, resist wear, or maintain structural rigidity. That is where alloying comes in.
What Antimony Does: The Pb-Sb Story
Adding antimony to lead is one of the oldest tricks in metallurgy, and it remains one of the most useful. Antimony is a hardening agent. Even small percentages, in the 1 to 6 percent range, dramatically increase the hardness and tensile strength of the base lead. This is why Pb-Sb alloys, often called antimonial lead or hard lead, show up everywhere from battery grids to cable sheathing to counterweights.
The relationship is fairly linear at lower percentages. A 2 percent antimonial lead alloy might land around 8 to 10 BHN, while pushing up to 6 percent antimony can get you into the 14 to 18 BHN range depending on how the alloy is cast and cooled. Higher antimony content also improves fluidity when the alloy is molten, which matters a lot for casting complex shapes with fine detail.
The tradeoff is ductility. As antimony content climbs, the alloy becomes more brittle. That is a fine tradeoff for a stationary counterweight. It is a much bigger deal if the part will flex or experience impact.
Bringing Tin Into the Mix: Pb-Sb-Sn Alloys
This is where things get interesting for anyone casting detailed shapes. Tin does two things that antimony alone cannot. First, it improves fluidity even further, letting molten alloy flow into fine mold details before it solidifies. Second, tin helps offset some of the brittleness that comes from higher antimony content, giving you a tougher final product.
A typical Pb-Sb-Sn alloy might run somewhere around 2 to 6 percent antimony and 1 to 3 percent tin, though the exact ratio depends entirely on what you are casting and what hardness target you need to hit. These ternary alloys are the backbone of a lot of specialty casting work because they give you a controllable middle ground between soft pure lead and hard, brittle high-antimony lead.
Reading Hardness Specs Like a Pro
When someone tells you an alloy is “12 BHN” or references a hardness spec, they are talking about resistance to indentation, usually measured with a Brinell hardness test. Higher numbers mean harder metal. For most industrial lead applications, here is a rough guide:
Pure lead sits around 4 to 5 BHN, ideal for shielding and conformable applications. Light antimonial lead in the 1 to 3 percent range lands around 8 to 10 BHN, good for general casting and moderate wear resistance. Higher antimony or Pb-Sb-Sn blends can reach 15 BHN and beyond, suited for parts that need to hold tight tolerances and resist deformation under load.
Choosing the Right Composition
There is no universal “best” lead alloy. The right composition depends on your casting method, the finished part’s function, whether it needs to machine cleanly, and what kind of stress it will face in service. If you are not sure where to start, the honest answer is usually to talk through your application specifics with a supplier who can walk you through antimony and tin ratios rather than guessing off a generic spec sheet.
We work with customers across the hardness spectrum, from pure lead ingots for shielding work to custom Pb-Sb-Sn blends tailored to a specific casting job. If you want a deeper dive into pure lead specifically, check out our post on purified lead. Otherwise, reach out and tell us what you are building. We will help you land on a composition that actually fits.