| Gallery, Projects and General > How do I?? |
| silver steel hardaning |
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| Lew_Merrick_PE:
Krv, 1) When a strong magnet is no longer attracted to a piece of steel (assuming enough carbon content to make it hardenable), you are at the correct temperature. You don't want to get it too much hotter than that or the crystal grains will get big and brittle. For anything less than (about) .50 inches (12 mm), you want to hold it at that temperature for a bit more than a minute. Larger pieces need to stay at temperature longer (look up "heat treating tool steel" on the McMaster-Carr website). Holding it at temperature too long also makes for big and brittle grains. 2) Salt water works better as a quench than tap water. Boiling water holds salt better and still makes a good quench (the key is getting the temperature of the part down to at least 360°F or 185°C). 8-10 drops per gallon (call it 2-3 drops per litre) of quench of (A) glycerine and (B) good grease-cutting dishwashing liquid detergent help the quenching process -- these are called surfactant wetting agents. 3) Whenever possible, put the part in the quench as quickly as you can and swirl it in a figure-of-eight pattern. This helps keep bubbles from sticking to the side of the part and reducing the quench effect. No matter what, full-hard untempered steel is brittle. Older editions of Machinery's Handbook had good, not-too-technical sections on tempering (also called stress relieving). I believe that the first of Guy Lautard's The Machinist's Bedside Reader books has a pretty good non-technical discussion of tempering (though it may be one of the others in that series). Basically, you polish up your part and then heat it from the "it can be softer" end and watch the change in oxide colors. When you hit the temperature (color) you want, you re-quench it. When I was an apprentice, heat treat instructions on drawings often read: Full harden & draw to straw or Full harden and draw to light blue. That is the level of practice described here. A modern metallurgist/heat treater would be aghast... |
| AdeV:
So, assuming we ignore those purple carrots for the time being (irrelevant fact: ALL carrots used to be purple...), does carrot come before or after cherry on the redness scale? I'm thinking after, but would prefer to be sure.... |
| andyf:
I never knew carrots used to be purple, Ade. Most cherries are basically red (I just know someone's going to tell me about striped ones). Carrot-hot is when the workpiece has gone a bit beyond red; a bit of yellow is beginning to creep in. Andy. |
| AdeV:
Thanks Andy, I guess it's obvious when you think about it... but I wanted to be sure. OT: It's true that carrots used to be purple. See http://www.carrotmuseum.co.uk/maroon.html (blame google for that one) |
| wongster:
Anyone has a colour chart of sort? I only get orange the last time I tried. Regards, Wong |
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