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MX | Off-Road Gear Info & Reviews
New rear sprocket???
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[QUOTE="motometal, post: 760477, member: 24727"] Right on track with the Brinell test. Two basic situations on the surface, oxides or decarb, or a mixture of both. Unless it's really heavy, oxide will have less effect on hardnes testing. Heat treated parts shouldn't have any significant decarb on the surface unless they are processed in a furnace with poor atmosphere control. On a part like a chain, the dark color may vary well be from a tempering process, and in this case the oxide layer may be more of a visual thing (little effect on mechanical properties). So, the grinding before testing is most helpful on a part that 1. Is cast or forged with a rough surface 2. Has mill scale which hasn't been corrected with heat treat 3. Has been hardened in a furnace with a poor or no atmosphere 4. Has been tempered at a high temp with poor or no atmosphere, perhaps 1050-1250 F Regarding the rollers cracking, this could be a result of consumer abuse, out-of-spec material chemistry, incomplete or improper hardening, or "cold" tempering. To state that all steels share the same properties, regardless of which specific property we happen to be talking about, is a sweeping generalization. Exception: "A 10 pound chunk of steel will hurt if you drop it on your toe, regardless of it's specific chemistry". Four most common microstructures, dependant on the steel's chemistry and heat treatment, in no particular order: 1. Pearlite/Ferrite (soft, magnetic, annealed) 2. Austenitic (soft, nonmagnetic, 304 SS etc.) 3. Martensitic (medium to hard depending on temper, magnetic, chains sprockets, 440C SS, etc.) 4. Bainitic (medium hardness, magnetic, spring steel, 1080, mower blades etc.) Each microstructure has it's own properties relative to the others, but again two alloys even if they both have the same apparent microstructure can have significantly different mechanical properties. Also, higher carbon steels (tool steels and others) may have carbides in the structure as well, further complicating issues. [/QUOTE]
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MX | Off-Road Gear Info & Reviews
New rear sprocket???
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