Leaded Steels-What You Should Know

Lead is NOT banned by the European Union’s End of Life Vehicles Regulations for machining purposes in steel, aluminum and brass.

PDF HERE

Not banned in every application...

Lead is NOT banned by the European Unions Restriction of Hazardous Substances (RoHS) Directive.

The exemption for “Lead as an alloying element in Steel containing up to 0.35% lead by weight, aluminum containing up to 0.4% lead by weight, and as a copper alloy containing up to 4% by weight.” This exemption is located in article 4.2 and Annex, line 6.

UK link to RoHS exemptions

If even the European Union recognizes that additions of Lead in materials for machining is worthy of exemption, Lead must provide some significant benefits…

  • “Boosts machinability 25% at lower cost”- Pat Wannell, La Salle Steel April 1994, quoted in Modern Metals Magazine
  • “Cutting Speeds can normally be increased from 15-25% above those employed for the standard grade”- Monarch  Turning Manual
  • “Lead, found mainly enveloping manganese sulfide inclusions, promotes machinability in two ways, possibly three. By forming a layer of liquid lubricant at the tool chip interface, it reduces the stress required to overcome friction. By acting as an initiator of microcracks and, possibly, by causing some liquid metal embrittlement, it reduces the deformation stress.” American Machinist Special Report 790.
  • In our experience we have found leaded steels to  lower cutting temperatures and reduce wear rates on tools, resulting in greater up time. Surface finish on leaded materials  is superior to those on non leaded equivalents.

Increasing speeds and production, reducing power needed (and thus greenhouse gas emissions), and improving surface finish are some powerful advantages that are provided by the addition of lead to materials for precision machining.

What’s the down side?

In this photo lead is visible as tails (pointed out by arrows.)

1) Lead is not soluble in iron.  It is therefore a separate phase in the steel, usually visible enveloping the manganese sulfides as tails, though sometimes appearing as small particles.

2) Lead has a greater density than iron. This means that it will tend to segregate given enough time while the metal is liquid.

3) Lead has a relatively low melting point (liquidus) compared to steel. This can mean that at processing temperatures for heat treatment, leaded steel parts can ‘exude’ lead

These three factors mean that if you ABSOLUTELY MUST HAVE parts that are free from possible segregation, parts that will not have potential hollows or porosity after being exposed to high temperatures, and absolutely no visible indications of a separate phase in the steel (ie. what the shop guys call  “lead stringers,” you probably ought to forego the leaded grade.

And forego  the 25-30 % savings that it gives you on the piece part machining cost…

You want highest machinability or highest product integrity?

Take your pick.

Periodic

Photo of Lead on Manganese sulfides from L.E. Samuels Optical Microscopy of Steels.

Coin Flip

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