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Speaker 1: Protect your photos, music and documents and access to them

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Speaker 1: today at m o z y dot com. Welcome to

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Speaker 1: brain Stuff from how Stuff works dot com where smart Happens.

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Speaker 1: Hi Marshall Brain with today's question, what does case harden mean?

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Speaker 1: When it's stamped on a piece of metal? Steel is

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Speaker 1: an amazing substance. By mixing in different elements and heating

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Speaker 1: and cooling it in different ways, you can create surprisingly

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Speaker 1: different properties. Some steels are easily bent, while others are

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Speaker 1: so brittle that they shatter some rust, and others don't.

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Speaker 1: The huge variety of steels means that they work in

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Speaker 1: many different situations. Everything from a surgical scalpel to a

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Speaker 1: skyscraper's massive metal frame can be made of steel. The

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Speaker 1: idea behind case hardening is to have two different types

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Speaker 1: of steel in this same piece. During manufacturing, what you

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Speaker 1: would like is a relatively soft steel that's easy to

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Speaker 1: bend into machine for a lock shank. However, a soft

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Speaker 1: steel is not good because it's easy to cut with

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Speaker 1: a metal saw, so after the piece is formed, you

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Speaker 1: harden it to make it very difficult to cut. Case

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Speaker 1: hardened steel is usually formed by diffusing carbon or nitrogen

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Speaker 1: into the outer layer of the steel at very high temperature.

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Speaker 1: The carbon combines with the steel to make it nearly

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Speaker 1: glass like and its hardness. The core of the metal

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Speaker 1: stays soft. This gives you a piece of metal that

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Speaker 1: cannot be cut with a saw, but also will not shatter.

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Speaker 1: Do you have any ideas or suggestions for this podcast?

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Speaker 1: If so, please send me an email at podcast at

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Speaker 1: how stuff works dot com. For more on this and

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Speaker 1: thousands of other topics, go to how stuff works dot com.

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Speaker 1: Your photos, music and documents are irreplaceable. Protect them with

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