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Revision as of 17:51, 18 September 2014 by Smokefoot (talk | contribs) (expand on the method, with a secondary ref (Ullmann's))(diff) ← Previous revision | Latest revision (diff) | Newer revision → (diff)Boriding, also called boronizing, is the process by which boron is introduced to a metal or alloy. It is a type of surface hardening, also called case hardening. In this process boron atoms are diffused into the surface of a metal component. The resulting surface contains metal borides, such as iron boride, nickel boride, and cobalt borides, As pure materials, these borides have extremely high hardness and wear resistance. Their favorable properties are manifested even when they are a small fraction of the bulk solid. Boronized metal parts are extremely wear resistant and will often last two to five times longer than components treated with conventional heat treatments such as hardening, carburizing, nitriding, nitrocarburizing or induction hardening. Most borided steel surfaces will have iron boride layer hardnesses ranging from 1200-1600 HV. Nickel-based superalloys such as Inconel and Hastalloys will typically have nickel boride layer hardnesses of 1700-2300 HV. Boride layer depths can range from .001" to .015" inch depending on base material selection and treatment.
Methods
Boriding can be achieved in several ways, but commonly the metal piece is packed with a boriding mixture and heated ca. 900 °C. Typical boriding mixture consists of boron carbide powder diluted with other refractory materials such as alumina or silicon carbide]]. Potassium tetrafluoroborate (KBF4) is used as a flux. The process converts some of the Fe to iron boride (FeB), which is concentrated near the surface, and diiron boride (Fe2B).
Materials
It is often used on steel, but is applicable to a variety of alloys and cermet materials. A wide range of materials suitable for treatment including plain carbon steels, alloy steels, tool steels, nickel-based super alloys, cobalt alloys, and stellite. The following materials not compatible with boronizing: stainless steels, nitrogen, aluminum or silicon containing grades.
Properties conferred
Borodizing gives the material the following desirable properties: wear resistance, improved hardness (1300-2000HV is possible), thermal stability, resistance to corrosion by acids, reduced coefficient of friction, and increased galling/cold-welding resistance.It is possible to combine with other heat treatments such as carburizing, hardening or induction hardening to create deeper wear layers or high core hardness.
Applications for borided components
- High wear agricultural machinery components
- Ground engaging tooling
- Oil field drilling tools
- Ball valves for severe service
- High wear pumps
- Gears
- Valves
- Thread guides
- Coffee grinding disks
- Burner nozzles
- Plastic injection molding components
- Tools and dies
- Aluminum extrusion dies
- Aluminum die-casting shot sleeves
- Coring tines for turf management
- Steam turbine components
- Glass cutting and forming tools and dies
- Any steel components that wear quickly due to abrasion or adhesive wear and require frequent replacement
References
- ^ Helmut Kunst, Brigitte Haase, James C. Malloy, Klaus Wittel, Montia C. Nestler, Andrew R. Nicoll, Ulrich Erning and Gerhard Rauscher "Metals, Surface Treatment" in Ullmann's Encyclopedia of Industrial Chemistry, 2006, Wiley-VCH, Weinheim. doi:10.1002/14356007.a16_403.pub2
- http://www.bodycote.com/services/heat-treatment/case-hardening-with-subsequent-hardening-operation/boriding.aspx
- https://www1.eere.energy.gov/manufacturing/intensiveprocesses/pdfs/ultra-fast_boriding.pdf
See also
- http://bluewaterthermal.com/boronizing/
- http://www.asminternational.org/portal/site/www/AsmStore/ProductDetails/?vgnextoid=121b7e0e64e18110VgnVCM100000701e010aRCRD
- http://www.bortec.de/en/boronizing
- Matuschka, Alfred (1980). Boronizing. Hanser. ISBN 9783446131767.
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