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If a chisel or a plane blade has been overheated, or “blued,” and then the discoloring has been lapped away, all that you can practically do is grind/hone it and use it, recognizing that it will dull quickly, and then hone it again, and again, until the burned area is ground/honed away. Unless someone was extremely careless and burned it extensively, the burned area probably won’t go too deep into the blade.

CBN grinding wheels are far safer for avoiding a burned temper.

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When I worked in a Met Lab we made samples from gear teeth that had been surfaced hardened  and tempered to around 62 HRC. We cut them with a huge 14" carborundum blade flooding it with water as we cut. Still the heat generated tempered the sample neat the cut. After mounting in thermal-plastic mounts we hand ground the surface to get below the tempered area. No more that two seconds hand grinding before putting the sample in a can of water. Repeat this at least about 15 times. It the sample tested too low in hardness then do some more hand grinding to see if the tempered area had not been removed. You could do this on a tool that had been tempered in grinding and also do this always to avoid the problem. 

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1 hour ago, Greg Sigworth said:

When I worked in a Met Lab we made samples from gear teeth that had been surfaced hardened  and tempered to around 62 HRC. We cut them with a huge 14" carborundum blade flooding it with water as we cut. Still the heat generated tempered the sample neat the cut. After mounting in thermal-plastic mounts we hand ground the surface to get below the tempered area. No more that two seconds hand grinding before putting the sample in a can of water. Repeat this at least about 15 times. It the sample tested too low in hardness then do some more hand grinding to see if the tempered area had not been removed. You could do this on a tool that had been tempered in grinding and also do this always to avoid the problem. 

Usually over heating on the grinding wheel anneals the steel, leaving it in a soft state, and often with some of the carbon  burnt out of the steel which makes it impossible to harden properly.

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