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White Irons and Ni-Hard BS4844 ASTM A532 BS 4844 ASTMA532 White Irons These irons, on fracture appear as white silvery fractures. The carbon in the iron is no longer free grey coloured graphite but is locked in chemical compositions of hard wearing carbides. The unalloyed White Irons have a hardness of 200-350 BHN the lower end of the hardness scale can be machined but generally are used as cast. The use of white irons is generally in low impact abrasive situations such as liner plates and abrasive material pump cases. Ni-Hard
In these irons a development of iron-chromium carbides produce a tougher more abrasion resistant iron. The variation of carbon content effects the toughness and abrasion resistance. Greater carbon increases the resistance to abrasion, however at the loss of toughness and vice versa lowering the carbon increases toughness but decreases the resistance to wear. Hardness ranges dependent on section thickness can be between 450-600 BHN The use for Ni-Hards is in pulverising, crushing and impact wear plates also in heavy duty pump casings and impellers for slurry and gravel applications. High Chromium Alloys These irons produce a more continuous structure
of iron-chromium carbides.
All the white irons are difficult to machine, however advances in ceramic machining tips have vastly improved the prospects. |
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