molten salt

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Posted · Report post

could someone tell me why i should/would use hot salt to temper my blades?
i plan to make a hot bed with 1 1/4 plate to heat ,place blade onto plate then cover with insulation and alow to cool slowly from temper heat. This is after first quench and to set the temper of steel

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Posted · Report post

Molten salt is very effective at heat transfer. It will bring a part to the temperature of the molten salt quickly. When quenching into salt, it will allow thin parts to reach the martensite or bainite start temperature while missing the pearlite nose. It will temper parts very uniformly. It is not something you should be doing in your garage or shop as salts are EXTREMELY dangerous and highly controlled by OSHA and the EPA. I am not sure why you want to slow cool from tempering, though. It only allows continued precipitation of the carbides in the BCT structure and that is not what you want. It will end up too soft. If little or none of what I just wrote makes sense, I would encourage you to read BP0078 on heat treating.

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Posted · Report post

yes lot of what you just said makes sense. the thing that confuses me is severall statments about holding the tempering temp for extended times to alow the heat to "soak" into the core of the thicker portions of the blade. with the melt. temp at 500deg the temper would be about right

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Meinhoutexas, tempering is the precipitation of carbides in the martensite. It requires time for the carbon to diffuse to the carbides to make them grow. Yes, you need to soak the piece to make sure the inside is as hot as the outside, too. BTW, do you belong to Houston Area Blacksmith Association? If not, we invite you to join us, go to HABA Houston Area Blacksmith's Association. I am in the Cypress Area, NW of Houston.

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Posted · Report post

Quenchcrack, if i understand your answer just molten salt will allow you to temper. when i say just molten i mean salt that has heated to the fluid state. that said i would prefer to heat a heavy piece of plate to the tempering temp and then introduce the blade to the "stove top " cover with ko wool and alow to temper that way. and yes i have taken you advice and am trying to avoid the use of salts. As far as joining the HABA i havent thought of that and i thank you for the invite. Please be advised i am verry new to th feld of blacksmithing and am learning from a blacksmith down in SantaFe and we both are learning to make blades

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Posted · Report post

Santa Fe NM? If so which one?

Thomas, just elected President of South West Artist Blacksmith Association, the ABANA affiliate for NM and El Paso.

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Posted · Report post

sorry SantaFe Texas Just south of Houston. Sorry when two texans start to talk we think everyone knows where we are talking about

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Posted · Report post

MHT, Yes, I meant salt heated to the melting point, not a salt/water solution. I have used heat sinks to temper, too. I heat two fairly heavy blocks of steel in the forge and set them just far enough apart to put the blade in. I used a small block of refractory with a groove in it to hold the blade upright. Shine up the blade and set it in the forge (now I am talking about a gas forge, not a coal forge), turn the gas off and let the blocks radiate heat to the blade. Pull it out when it turns golden brown and quench it. Putting a thick plate on a coal forge will do much the same thing but if you cover it, it gets tricky to know when to pull it out.

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Posted · Report post

thanks quench that helps i have read in some places that it is better to alow the blade to "soak" at the tempering stage for a better tempering of thicker steels. i would assume you could get the same results if you were to return to the "golden brown "stage severall time to deep draw the temper.

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Posted · Report post

Pshhhhh...OK, I just opened a fresh can of worms. You will usually get little or no tempering if you just re-heat to the same temperature and hold it for the same time. To get additional tempering, increase the temperature slightly or the time. This does not apply to the transformation of retained austenite where a second identical temper will get you some EXTRA hardness.

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Posted · Report post

Sorry for jumping in here. Are we talking about common salt (NaCl)? There are carburizing salts that contain cyanide and these are very dangerous to breathe.
These salts are heated under a ventilation hood and are used in manufacturing. There are neutral salts that do not case harden but are used for controlled heating and preventing exposure to oxygen. Does heating in common salt decarburize the steel? Are there any chlorine emissions from disassociation of the NaCl molecule?
Happy New Year all
Warren

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Posted · Report post

wow warren i thought i had some questions now you are asking some big ones. I was thinking of common salt .....Not now the process is too risky for to small reward i will look at some other ways to temper the steel. All the questions you have are the reason i walked away from the idea!!!!

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Posted · Report post

the low temp salts are NOT sodium, some are calcium based. much safer that NaCl.

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