词条 | Free machining steel | |||||||||||||
释义 |
The disadvantages of free machining steel are: ductility is decreased; impact resistance is reduced; copper-based brazed joints suffer from embrittlement with bismuth free machining grades; shrink fits are not as strong.[2] TypesThere are four main types of free machining steel: leaded, resulfurized, rephosphorized and super. Super free-machining steels are alloyed with tellurium, selenium, and bismuth.[3]
MechanicsFree machining steels are carbon steels that have sulfur, lead, bismuth, selenium, tellurium, or phosphorus added. Sulfur forms the compound manganese sulfide, which is soft and acts as a chip-breaking discontinuity. It also acts as a dry lubricant to prevent a built up edge on the cutting tool. Lead works in a similar way to sulfur. Bismuth achieves a free machining steel by melting into a thin film of liquid for a fraction of a microsecond to lubricate the cut. Other advantages to bismuth include: more uniformly distributed because of its similar density to iron; more environmentally friendly, as compared to lead; still weldable.[1] References1. ^1 Degarmo, p. 117. 2. ^Degarmo, p. 118. 3. ^1 {{Citation|title=Carbon steel |url=http://www.steelforge.com/ferrous/carbonsteel.htm |accessdate=2010-02-28 |archiveurl=https://www.webcitation.org/5ntWIDrKc?url=http://www.steelforge.com/ferrous/carbonsteel.htm |archivedate=2010-03-01 |postscript=. |deadurl=yes |df= }} Bibliography
1 : Steels |
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