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Thread: lead in brass?

  1. #1
    Member ryuen's Avatar
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    lead in brass?

    need help with this question:

    Why is there lead in free-cutting brass?

  2. #2
    Member ckj's Avatar
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    The lead in free-cutting brass gives the brass a higher machinability. This is important, because this type of brass is known for its ease of machinability.

    I hope that's enough, in my low division courses (where I was asked this question) my answer was sufficient. You can also google "lead in free cutting brass" (no ") and get a more in depth answer there.
    Last edited by ckj; 05-24-07 at 01:14 AM.

  3. #3
    Senior Something Moto7451's Avatar
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    Looking it up online, it seems that that type of alloy is used to make tool and machine parts (gears, etc). I would assume its either to make the brass harder or softer.

    Pure elements in many cases are poor performers depending on the intended use. For example, pure aluminum will oxidize into nothingness while aluminum oxide is a lightweight material that creates a protective oxide and in many cases can be as strong as a mild steel. Pure iron (wrought iron) is best used in decorative items because it is too weak to support any considerable load as its carbon content is too low (.2%). Adding more carbon and silicon can allow you to turn the iron into cast iron or steel, suitable for engine, steel girders, and other more useful items.

    Elements are usually introduced into metals in small quantities to increase a property of the metal. .0007% Boron for example has the same effect as .7% chromium in hardening but allows for fast hardening and doesn't affect the tempering ability of the steel. However, Boron doesn't prevent oxidation and after 7x10^-3% it isn't nearly as affective at hardening as chromium. High chrome contents in many types of steel prevent major shifts in tempering (this is why a good sword is never made from stainless steel, carbon and semi-stainless tool steel are the materials of choice). Carbon allows for a harder metal, but at the cost of more difficult machining and a greater rate of oxidation.
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  4. #4
    Member ckj's Avatar
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    Lead makes the brass softer.

  5. #5
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    Well, if you want to get technical, lead is not soluble in solid copper and it tends to fill in the voids between the crystals, thus it helps to make the resulting alloys less brittle and more easily machinable. A couple of links for you:

    A short discussion with some micrographs of common lead copper alloys:

    http://www.copper.org/resources/prop...d_brasses.html

    Images and links to some common copper alloys:

    http://www.metalreference.com/Forms_Copper_Alloy.html

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