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Lead is NOT banned by the European Union's End of Life Vehicles (ELV) Regulations for machining purposes in steel, aluminum and brass.
PDF HERE
Not banned in every application . . .
Lead is NOT banned by the European Union's 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 (i.e.,
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
Editor's Note: CR4 would like to thank Milo for sharing this blog entry, which appeared originally here.
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Re: Leaded Steels - What You Should Know
