Another heat treat question

S.Knowles

S.Knowles

I've finally got a good hold on maintaining constant temp in my forge so I want to start working more w/ hamon. I've read(when the search was working) ALOT about it and know from sunfishman,longrifle,burchtree, tictok and others its all in the time and temp. What I remember is Low temp on heat and raise quenchant temp. My question is: When i slowly bring blade to 1400 I know it been said 1095 needs approx 4 min soak, At 1400 the blade is still magnetic. Do i let soak from the moment it goes to 1400 or let it get to non-mag at 1400 then let soak for 4 mins? Next question is I just piced up some Brownells tough Quench, What temp is good for this? I;ve previously been using olive oil @ 130. Thanks for taking the time to read all this. Shawn
 
1400 is too low.The hardening temp is 1475 to 1550.I use 1500 to 1525 for 1095.
Bring it up to 1300-1400 slowly to equalize.Then raise to 1500 and soak for 4-5 minutes for a bigger knife 3-4 for a small one.Quench in 130-140 oil.Temper immediately at 450 twice,cooling to room temp between tempers.
 
Thanks guys, I thought it was 1400 but I probably mis-read. I've done some experimenting and it seem as though you can bring a blade to non-mag at lower temp with a longer soak. What i'm trying to achieve is bringing out the sublties in the hamon with a clay coat of satanite.
 
The Currie temp of iron is 1414F, you will begin to nonmagnetic there every time despite time to do it. The important part is that obtaining sufficient solution in austenite is a whole different ball game; this is one of theose cases where the magnet is not all that accurate. You can effect the Ac points by rate of heating due to more or less opportunity for diffusion. Heating very slow will allow one to reach Ac1 and Acm at a lower temp. I have myself tried the low temp soaks, as has been suggested to you, and I have tried it every way I can think of with the same results, which I have posted before but it is striking enough to show again:
1084salt.jpg

10min.jpg


The bottom is quenched in oil, vs. the top in salts but I am still dissapointed in the difference from what the Rockwell tester and microscope tells me vs. what I have heard. If you were quenching into water perhaps the top structures may be of use to you as they would help keep the steel from blowing itself apart, but if you are working with oil, I would stick to the higher temps and more complete solution, but that's just me.
 
Thanks Kevin, I have seen those before around here. Forgive me for asking but I am a little confused, What exactly am I looking at? ( grain structure, Amounts of dissolved carbon?) Please excuse my Ignorance I would normally not even be posting but just seaching fo my questions. Thanks Shawn
 
Please excuse the micrographs, but a very common reaction to pointing out the recommended temps and methods is “What I am doing is working fine for me”. But working fine is usually determined by a quick skate with a file, bending in a vice or some other test that reveals practically nothing about actual results. This topic is one of those that has some very credible believers, so to present just opinion to counter it is not good enough. Actual images of the inside of the steel allows me to completely remove myself and my opinions and just present what it is in the realest way possible.

What you are seeing is whole fields of martensite, which etches very light and crystally looking, but mixed in there are varying degrees of undissolved prior microstructure from incomplete solution at the austenitizing temperature that etches out very dark. To the right of the bottom image you will see little dark gray patches mixed in there. That is left over undissolved cementite in some segregated strings that were in the parent bar. Other images of the same piece heated at lower temps or shorter times show a lot more of the gray.

The top image is a slightly different story; it is not patches but islands of martensite surrounded by moats of pearlite. From either incomplete Austenitizing, insufficient hardening or a little of both. But to the left of the bottom image you have a solid field of total martensite from total austenization and a #50 oil quench fast enough to avoid any pearlite. Proper time+ proper temperature+ proper quenchant= success!
 
kevin

Since higher temps and longer soak times (above austenizing temp) promote grain growth, I assume the coarser looking grain of the upper pair of micrographs is because the magnification is higher than the lower pair?

Jim A.
 
O.K. now the pictures make sense.Great info and point of view. Cant argue with results you can actually see. Thanks again Kevin, Shawn
 
There has always been a great concern about grain growth amongst 'smiths.However there are a number of things that must happen before grain growth occurs. When we get above the critical temperature austenite grains start to form - nucleation. Then the structure becomes all austenitic.But we then must do something with the carbides in the typical higher carbon knife steels.Those carbides must dissolve [partly or fully] to saturate the austenite, then the dissolved carbon must diffuse uniformly through the austenite. When that is done we can then quench. If we heat beyond that point we will start to get grain growth which is a process of a grain absorbing an adjacent grain [hostile take over] .This requires grain boundary movement which things like vanadium will slow down. ..What Kevin is trying to show with his photos is that insufficient time and temperature will prevent the austenite from being saturated with carbon resulting in a less than optimum structure even though it appears to be "file hard". Proper time , temperature , quench must be followed to give optimum performance....The photos on top show an insufficiently austenitized structure , a mixed structure .I believe they are the same magnification....Now I'm getting as verbose as Kevin !!
 
yes the upper photo is much greater magnification. mete explained it so well, I can be brief;) . soak times below the grain growth temp (much higher than necessary ) can be as long as you like without much worry. Smiths experience grain growth so much because it is so easy to exceed proper temps with a forge. But those temps are actually quite high. Higher than necesarry for any hardening operation.
 
As kevin has pointed out,the correct temperature is critical to HT.
Turning the gas pressure down in the forge to get the temperature at a more controlled level will cure the problem of grain growth for those not using a HT oven.Having a pyrometer will tell you what temperature the forge chamber is at.After 5 min.the blade and the chamber will be the same.
If gun control is hitting your target - then temperature control is hitting your target temperature.
If optimum HT is 1525 with a 5min. soak - and you soak at 1525 for 5 min. you will get the optimum results - plain and simple!
Stacy
 
Typically they are written, 2+2 , that is two tempers each for two hours [a bit more if you like ].

For the rest of the questions I still have the same answers 6 years later !!!
 
As much as things have changed in six years ....... the specs for HT are still the same.
As mete said, two hours at temper, twice.
 
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