Brine quench

J

Jared Stenoien

Joined
Dec 4, 2005
Messages
1,025
I asked this in the other thread but people probably didn't see it. I was wondering why people use water quenches over brine quenches, what are the advantages/disadvantages?
 
Brine is fastest quench and the fastest brine is 10 %NaCl in water. .The problem is - speed of quench vs risk !! The faster the quench the more the risk. You should always match the quench speed to the type of steel and never quench faster than necessary .Typical knife steels ,even 1095, don't really require anything but water. BTW heating water reduces the quench speed.
 
I know that brine is faster than water, but I thought it was less stressful due to reduced vapor jacketing. I thought I'd read that somewhere...
 
Reduceing the vapor jacket speeds the quench. Think about it. For a fraction of a second the water is not acually touching the steel. With brine, the jacket is gone even faster before contact, hence faster quench, hence more risk of cracking.
 
Heating the water seems to make things less severe for many folks, but we need to ask why? I would submit that it reintroduces the vapor jacket into the equation. The closer you get to 212F the greater the vapor jacket with H2O, and less face it, when cooling from 1450-1500F going from cool water to warm water, perhaps less than 100F, really isn't all that significant.

This last weekend I shared some images from the microscope with the crowd that made it very clear what mete is talking about when he says to quench fast enough to get the job done and no more. Lots of tiny little quench cracks unseen by the naked eye but potentially fatal later on. You see I quench my metallography samples in water in order to assure I have no other undersireable products, so they are often afflicted with quench cracks. Folks need to get out of this mindset that the fastest possible quench is going to make better martensite.
 
Kevin, Mete,

Could either of you discuss quench rate and carbide formation in high carbon, high alloy steel. Specifically chromium carbide and effects on corrosion resistance and carbide partial size due to different quench rates.

Thanks,
Nathan
 
Carbides do not form on quenching. When HTing a high carbon steel austenitizing dissolves the carbides [soaking] from the original structure but when austenite is saturated with carbon there will still be carbide left. This austenite on quenching forms martensite which again is saturated with carbon. On tempering some of that carbon will come out of the martensite and form fine carbides. As the tempering temperature increases the carbides increase in size. .....The carbides remaining after soaking are infuenced by the prior treatment .The finer , evenly distributed CPM type carbides are much better. The worst situation is to have continuous carbides in the austenite grain boundaries .This makes for a brittle steel.
 
if you multiple quench to refine grain, how important are the quench speeds before the final austenization?
 
The prior quench speeds are not as critical as the rate of heating to critical. If you are only dong one quench and do it at the proper temperature, you will be dissolving carbide and putting carbon into solution and then finally feezing it there with the quench. But upon reheating it will be important not to spend too much time around Ac1 as temperatures leading up to it allow things to segregate and spheroidize which will take longer to dissolve. If one lacks the ability to soak multiple quenches could be a desperation method of getting more pro-eutectoid products into solution by taking several shorter whacks instead of one good one, however if you cannot heat through the lower temperatures fast enough you will defeat this idea and cause more seperation than solution.

I will quench during normalizing for refinement, and all I am concerned about is getting it cooled fast enough to make either very fine pearlite, bainite or martensite, anything but course pearlite or spheroidal carbide. Martensite will produce the finer austenite grains on reheating, and will also spheroidize the easiest.

I am ever more vigilant about what mete said regarding grain boundary carbide, however. Having thick, carbide heavy grain boundaries is very bad and fairly easy to do if you are not careful with heat.
 
Kevin R. Cashen said:
Having thick, carbide heavy grain boundaries is very bad and fairly easy to do if you are not careful with heat.
Click to expand...

Kevin,

Could you go into this a bit more please? What causes that? How do I prevent it?

When I get a stick of D2, it comes fully spheroidized so it can be machined. What is the optimum way for me to heat treat this? If it matters, my furnace ramps up pretty fast.

Thanks,
Nathan
 
When you pull carbon into solution at the high end soak it will separate out on slow cooling. When you reach Ar1 this will be in the form of fine lamellae which will make up pearlite and any in excess of .8% will be in the form of coarser carbides, if cooling is slow enough to allow it all to move to the grain boundaries, there is where you will have it. One way to deal with it is to avoid hypereutectoids, which is another good reason for me to recommend 1084 for folks with simpler equipment. You can also avoid it by timing your cooling out so that you go right to the formation of a less coarse pearlite, and definitely avoid it by going spheroidal.

But most important is to get everything into solution and evenly distributed before hand. Many of the simple steels come with nasty bands and segregation right for the mill and if we don't get it hot enough to move this stuff around it will be a magnet for grain boundary carbides. I have great micrograph examples of this but do not have the time to upload them for this post. This irrational obsession bladesmiths have with low temperature forging seriously contributes to this problem and does nothing to alleviate it. When you add this to the easiest annealing methods, i.e. stuffing the blade into a forge and walking away for the day, there will be plenty of carbide in the grain boundaries and you will not have enough time at temperature in the final hardening to fix it.
 
I was going to start a new thread, but this seems a good place to ask my question. Will oil quenching 3/32" 1095 result in full hardness and minimize any warping? I tried quenching a 1095 kiridashi in water and it warped. It was kinda cool, as the point came up and the edge rippled a little from the expansion of the edge, but it makes all the work I did to get things nice and straight before quenching seem kinda pointless. I quenched my last one before grinding the edge, so this didnt happen then, but couldnt grind it as thin without heating up.
 
You can heat it to the tempering temperature [~ 400 F ?] without problems.
 
With respect to heat during edge regrinding, I turned it blue near the tip a couple of times, and had to grind that off and start over. I also temper at about 325 F, so turning the edge a light straw color is higher than my tempering temperature.

As for oil quenching, I saw the quenched wedge in Verhoevens on line book, where the 1080 (iirc) hardened fully up to about 0.09" in thickness in oil, with the wedge tapering from 0.03 up to 0.25 inches or so. I have some other issues regarding my finishing ability, and my latest kiridashi is going to a friend for free as a landscape utility knife, where finish wont be an issue after about 2 days. At any rate, if oil will do the trick, I may try it one more time and see if I can get the edge I'm after. The concrete drop test didnt break the tip, but edge holding left something to be desired in the first test. I have to resharpen and try again to make sure the as sharpened edge is the same as the comparison knife.
 
You must log in or register to reply here.
Back
Top