Speaking of Precision Blog

Speaking of Precision

Speaking of Precision is a knowledge preservation and thought leadership blog covering the precision machining industry, its materials and services. With over 36 years of hands on experience in steelmaking, manufacturing, quality, and management, Miles Free (Milo) Director of Industry Research and Technology at PMPA helps answer "How?" "With what?" and occasionally "Really?"

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Leaded Steels - What You Should Know

Posted November 09, 2010 8:38 AM by Milo

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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#1

Re: Leaded Steels - What You Should Know

11/09/2010 1:18 PM

on the lead note , you would not believe how much water main and water services in use today are maid up of lead joints and fittings. also a lot of water main in use installed around the 50s and 60s are made out of asbestos.

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#2
In reply to #1

Re: Leaded Steels - What You Should Know

11/09/2010 1:41 PM

On second thought, not on this blog.

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#3

Re: Leaded Steels - What You Should Know

11/09/2010 1:50 PM

Milo,

I really appreciate your blog, it is always spot on with my concerns.

I was wondering, is there an easy test to distinguish the difference between 10L14 and 1018 cold rolled shaft. We have some mixed up. We use the 1018 when welding is involved in our products and machine mostly 12L14 when there will not be any welding.

Thanks,

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#4
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Re: Leaded Steels - What You Should Know

11/09/2010 2:06 PM

Thanks dgibson.

Presuming you are trying to sort 1018 from 12L14, you can sort based on sulfur content.

Get some filings or saw chips (free of oil!) from the steel and put them on a sheet of silver halide black and white photo paper. (Old develop in a darkroom process, NOT INKJET!)

Add a drop or two of dilute Hydrochloric (muriatic acid). Say 1-2% strength.

Let work for a minute or so.

The sulfur in the 12L14 will leave a dark brown stain, the 1018 with standard sulfur will not.

FS and MNS + 2HCL <_> FeCl2 and MNCl2 +H2S The H2S attacks the silver salts in the photo paper precipitating dark silver sulfide

I use chips or filings; We used to do this with whole slices of a billet which we would then fix conventionally and called them "sulfur Prints".

Happy Sorting.

Milo

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Re: Leaded Steels - What You Should Know

11/09/2010 2:31 PM

Thanks, just the information I needed.

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