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I Forge Iron

Boiling water quench.

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I forged a knackered old hammer head down into a little kindling splitter/axe/chopper thingy yesterday.

I have not yet got a tub of oil - so remembering Frosty's reworked hammer thread, I brought a cauldron of water up to a rolling boil, and did the quench in that. Tempered to purple and all seems well and good.

I was just wondering how does boiling water compare to oils on the quenchant scale?

Does it make the water a significantly more 'gentle' quenchant - anywhere near oil or still a world apart?

Im wondering whether I was just lucky with the steel, as the advice in all the other thread seems to be try oild first and water if necessary.

I dont think this has been asked before, but I appologise for starting yet another heat treat thread.


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Bob, good question. I would expect the hot water to be a very slow quench since you already have it to a rolling boil. It would not accept much more heat from a second source. My concern would be that the steam that is evolving in the water, especially around the part being quenched, would cause erratic heat removal. This could lead to distortion and cracking. However, if the part stayed together and you got it as hard as it needs to be, well, it's hard to argue with success.

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Hey Quench, not to question your judgement or anything, but I seem to remember from chemistry that there is a jump in absorbed energy right at the point of phase change. With all the water at a rolling boil, it would be right at the point of phase change. What do you think?

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On the subject of the quenching medium one will use, the number one most important thing to remember is consistency - do not not use one kind of oil this time and something else the next, you will not be familiar with either. Number two : Do not use old motor oil as it contains high amounts of sulphur - very bad for you. Number three: understand what is going on with your quenching medium when immersing hot metal into it.
There are several stages of cooling when immersing hot metal - in our case it will normally be steel or iron.
First is the rapid cooling stage - this is when the hot steel is first immersed in the quench. The steel will cool rapidly until the next stage.
Vapour covering stage - at this point, the qunching medium has began to boil violently and has formed a barrier of vapour between the steel and the qunching medium, there is very little cooling at this stage due to the impeded transfer of heat from the steel to the quench.
Last stage (there are many different terms used here and I won't use any) is the last rapid cooling stage - here the vapour barrier has lifted and the transfer of heat from the steel is occurring rapidly.
The different quenches that can be used are plenty. Everyone has a favorite. What is most important is using a quench that can minimise the vapour covering stage and cool the material rapidly enough to retain the best qualities of your steel. For any tool work, I simply use mineral oil; this is my own personal favorite though I have been very impressed with the results some of my aquaintances have had with stuff they use.

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This from the book -"Quenching and Martempering" american society for metals

" Water at a temp. of 55-75 F. will provide uniform quenching speed and reproducable results. As indicated in fig. 6, the surface cooling power of water decreases rapidly as water temp. increases. ( a graff shows cooling power percent X water temp. At 40-80F. cooling power is 90% from 80F. to 120F. it dives to 20% and less to 212F.)

It goes on to say "Hot water has a low cooling power because, as the boiling point is approched, the cooling action resembles that of steam. What Steve said.

AlsoThree stages of cooling

A. "vapor blanket cooling stage""
is charactorized by the Leidenfrost phenomenon- the formation of an unbroken vapor blanket that surrounds the piece. This stage is one of slow cooling.

B. the "vapor transport cooling stage" which produces the the highest rates of heat transfer, begins when the temp. of the surface metal has been reduced somewhat and the continuos vapor film collapses; violent boiling of the quench then occurs and heat is removed from the metal at a very rapid rate, largly as heat of vaporization.

C. the "liquid cooling stage": the cooling rate in this stage is slower than in stage B. Stage C begins when the temp. of the metal surface is reduced to the boiling point of the quenching liquid.

Hope this is helpful.

Edited by markb
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When I quenched that hammer head I didn't have enough decent oil so I used hot water to soften the chill. The hammer head brought it to a rolling boil fairly quickly though.

I wasn't recommending it, just relating what I did on that hammer. I think I mentioned it was a little soft for my taste but still good. It's been better than a year (I think) since I made it and it's working just fine, used it today in fact.

Lastly, I have a bucket of clean oil now.


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  • 10 years later...

Skoitch:  I assume that you are using a brine of salt mixed with water.  What concentration do you use?  A saturated salt solution of water only raises the boiling point to about 227 degrees at sea level.  That does not strike me as making a significant difference in quenching steel.  Or am I missing something entirely and you are doing something exotic like using molten salt as a quenchant?

"By hammer and hand all arts do stand."

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Hi temperature and low temperature salts are a standard modern way of heat treating. Using the high temperature salts at austenising Temp (800C up to 1050 for some stainless steels) and then quenching into low temperature salts (often preheated to 200+ centegrade) . the low temp salts can also be used for tempering or banite formation. there is very little oxidisation and internal circulation gives a very even heating....however there are associated dangers with liquid salts.....liquids at high temp being a lot more dangerous than the solids we are so used to dealing with.

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