kb0fhp

I suspect that you got a hydrogen blister, and combined with your description, it is very likely. Where the starting materials completely dry, including the crucible? Even minute amounts of water can have a disastrous effect with hydrogen pick up.

That is OK Mike - no problems

As long as you keep to the "one pound of parts to one gallon of quenchant" rule of thumb, you will get long life and quality work. Just keep the water out of it, and filter it occasionally and you will be rewarded with repeatable results. It is like anything else - if you take care of something, and do occasional maintenance, things will last a long time.

Now we need to work on getting the final paptent and make it really official.!

I'm not personally aware that oil has a lifetime, but can imagine all the variety of stuff that would get into the oil bucket over time. Those could affect the process, but I've not noticed any significant problem to this point. Stuff still gets hard. This is the barrel into which all things get thermal cycled, so I expect a good deal of scale in the bottom someday, but that's about it. Now the quench-oil companies would be very happy to have us all believe there was a lifetime to their oils. That way we'd buy more. Hmm, seems like the car companies do that to us already.

Oils do have a lifetime, it depends on how it is used. For light use, like quenching an occasional blade, and not letting the oil get too hot - a good rule of thumb is one pound of parts to one gallon of oil, if it is a quality oil, it should last a long time, even years or decades. If you exceed this rule of thumb, the temperature of oil will go up, and the oil will start to break down. It will become oxidized. If there is a robust antioxidant package in the oil, it will be able to compensate for this oxidation - but only to a point. Eventually the additive package will become depleted, and the oil's properties will change. For instance, viscosity will increase, and staining will become apparent. The quench speed will also change - martempering oils will get faster (up to a point, then they will get slower because of the viscosity has greatly increased) because the vapor phase will become less stable, and cold oils (those used below about 180F) will become slower because of viscosity effects. Then you run the risk of missing properties.

For instance, I have a commercial shop that is making gears for automatic transmissions. They quench 5000 pounds in a 4000 gallon quench tank, and the oil is a quality martempering oil, and the temperature of the oil is maintained at 275F. They have a life of about 6 months before the oil starts staining and causing low properties. The oil has become severely oxidized.

If it gets contaminated with water, greater than about 500 ppm of water, then the shape of the cooling curve can change and you can get upper transformation products, or soft spots. You can also get cracking.

But again for the light use of occasional quenching small loads compared to the volume of oil - it could last a lifetime.

On the industrial/scientific side of the equation where they get paid to pay attention to details, there is a published effect. Can't argue much with that. I guess the question I have leftover is "does it really make a difference?" How long is the interval before an oil fails?

 

A part of me respects all the science that has refined this craft to a huge degree. I can't argue against being precise and controlling variables, I do it myself.

 

But realistically, practically, economically, does it matter that someone can hit a Rockwell C scale point of 60.35 every time? How will the customer be able to tell the difference in the field? It's one thing for me to do it, if I require that sort of precision from my efforts. It's quite another when this sort of thought process begins to dominate the whole craft and a bias develops against smiths/makers who don't adhere to the strict requirements of whatever the oil du jour is. We've been over this with the wide variety of wonderstahls and liquid nitrogen and you name it.

 

Whatever happened to making a knife that was "good enough," with simple tools that helped the juniors in this craft get off to a good start without feeling that there was no hope of ever catching up to the more experienced because they don't have exactly all the right tools?

 

I think that all this discussion is very helpful when it comes to troubleshooting all the little demons that interfere with our routines. I don't know if the detail work should drive the whole business.

Mike - it depends on the application. For instance, when I ran a heat treat shop for Boeing, we made landing gears. They had very stringent property and distortion requirements. In other applications, such as automotive, the requirements are just as tight. For instance, for heat treating cam shafts, they have very demanding requirements for the depth of case and the hardness profile at the surface and at the core, as well as a specific depth in the case. For instance, having a soft camshaft can wear down the lobes and have a very detrimental effect on the engine - Pinto engines failed because of a faulty heat treatment on the camshaft. Gears for transmissions also have very stringent requirements for distortion and properties. In one application, if a gear fails in a wind turbine - and those gears are 96 inches in diameter and 3 feet thick - it costs $250,000 to pull the gear from the transmission on top of the tower. This does not include the price of a new gear.

The journey man tests for knife making are very severe. It requires an attention to all aspects of the fabrication, one of the main parts is heat treatment and quenching. If it wasn't done properly, it will fail the tests. But for many applications, heating it to cherry red and throwing it in a bucket of oil will work just fine. It just depends on what you are trying to do. By controlling all factors, it helps repeatability so that the knife or camshaft or landing gear, is the same as the one you made one week ago, and the same that you will make 10 years from now.

Also, remember, something that you make for a customer or yourself, often has your name on it. It should reflect the producer. It the requirements are not stringent, then the process may not be stringent. But remember, most of the industrial stuff is made to perform in a given environment. The manufacturers want the customer to be happy, and not have a product that is variable in quality. It is also cheaper to make if they are all produced the same.

I finished reading the Houghton pdf. Not a bad summation of what could have been a lot of complicated metal quenching. I can't argue with the conclusions about the changing chemistry or contamination of the oils used in quenching. The factors mentioned are, from an industrial point of view, like effects that they would have noticed, given the volume of the work they are doing and the precision that the engineers have specified for the whole job. In my mind, for say a knife production shop, thousands of blades would all have to be identical at the end of the production line. With that kind of volume, I can't argue with their recommendations.

 

That being said, I'm a little put off that they leave this suggestion without any clear idea of how much of an effect the contaminants and chemistry changes will make. They leave it at saying there's an effect but do not give much of a degree of expected effect, nor do they suggest any length of time over which to expect such changes nor their magnitude. How fast does oil degrade? How much hardness change are they worried about over time? How many blades put through a typical oil bath before noticeable change in hardness values are seen? Things like that would be helpful.

 

Plus after all that discussion of the problems with oil, I get the distinct feeling that the desired outcome of the paper was to sell polymer quenchants.

 

Personally, I haven't noticed any difference in practice over the years. I did learn something. Glad I'm not dead yet.

Mike - standard metallurgist answer - "It Depends". BTW, in the interest of clarity, I work for Houghton. I am their technical person for quenchants. Regarding contaminants, a lot depends on the type of contamination. Different contaminants have different effects. For instance, organic acids tend to cause staining, and will slow down a cold oil, but speed up a martempering oil. A lot depends on how the oil is used and abused. If you don't exceed one pound of parts to one gallon of quenchant, you will get long life (months/years). A lot also depends on how much work you run through it - if you run a load of parts that exceeds the one pound - one gallon rule, life will be shortened because the oil will actually overheat and the antioxidants will be expended. Coolants from machining, can also cause staining, as well as the residue after heat treatment can cause non uniform effects. To give you an idea, most oils will last a LONG time in an industrial setting, as long as the oil is replenished from drag-out. Most oils are thrown away because of staining, before they start causing problems with metallurgical properties. That way you always add new additives (speed improvers and anti-oxidants). For the hobbyist, as long as you don't over heat the oil (one pound of parts to one gallon of quenchant), you will get very, very long life. Since the amount of oil is very large compared to the amount of parts in a typical hobbyist setting, and the oil temperature does not rise very much (probably less than 25-50 degrees or so) - you will get very long life - it will probably last you a lifetime, as long as you use a quality oil from the beginning. If you email me at smackenzie@houghtonintl.com, I can email you some papers on contamination and the specific effects.

That paper or booklet, is/was designed to be really non-commercial in nature. If you notice, not one time was a specific product mentioned. Regarding polymer quenchants, we describe a multitude of different quenchants - even those by our competitor. It was designed to be informational and not a tout on specific Houghton products. If you have any specific recommendations, I would be glad to hear them. I am looking at revising the document when I have time as it has not been revised in many years. But remeber, it is targeted at commercial or OEM heat treaters, and not the hobbyist.

I hope that helps - and don't be shy to ask me a question or post a comment.

Scott, aka KB0FHP

Hello Scott,

 

How would canola oil hold up as a quench oil?

 

Mike

It does well. There are several commercial heat treaters using a canola type - specifically our product Bio-Quench 600. It is a refined canola/vegetable oil. Excellent quenchant. It does tend to absorb water, and has a tendancy to cause staining (the type of burned on stained like frying something), but it is an excellent quenchant - very unstable vapor phase, high boiling temperature, high flash. Fast where it needs to be - and slow where it needs to be - I really like canola based quenchants.

Cool Bob - I will be down in Nashville for the FUrnaces North America show in September. Perhaps get together and bend an elbow? email me at kb0fhp@comcast.net

It can't hurt. It might be of some benefit for high carbon steels with some nickel.

Brian, you don't need to use known steels and commercial quenchants. A lot of good knives have been made from saw blade and veg oil. But like I said, a lot of folks read this stuff

 

I used to use warm olive oil and worked good with saw steel. But when one becomes obsessed with performance and makes a living at it, the known stuff is preferred

 

I have several saw steel knives in our kitchen that were quenched in veg oil and they are wonderful.

 

Do some experimenting and remember, your edge should be hard, no roll and no chipping. But most of all, have fun

Canola is an excellent quenchant. High flash, and excellent cooling curve. It tends to have a short lived vapor phase (good), and fast nucleate boiling (also good), and a very high transition between nucleate boiling and convection phase (also excellent for distortion control).

Personally, commercially I have excellent luck with reducing distortion with a sperodization just prior to my hardening. It removes any vestiges of residual stress in the material. A couple of people have tried it here, and have had good luck with it.

Regarding quenching, I recommend going strait down. Is there any agitation in the tank? If not, some agitation strait up will help. You could use a large PVC tube and a small pump directing the flow upwards. That will help keep the heat transfer equal on both sides.

The cause of warpage is from prior residual stresses that relieve them selves during heating, or differential temperature during quench - either surface to surface, or center to surface. I suspect the issue is because of differential heat transfer on the two sides. Agitation will help cure that - whether you are using oil or water.

Hope that helps

Scott

I was going to post something, but decided to do it later....

Any needed from PA - if so, PM me your address please....

One issue is that quenchants are designed to quench things. Brake fluid is designed to be a hydraulic fluid. As such, there is additional additives and the like (such as zinc) that may cause issues with controllability and the like. Brake fluid is not in any manner similar to the chemistry of some polymer quenchants. Entirely different species, and potentially different results. Canola and peanut oil are good quenchants. There are also excellent commercial quenchants available such as Houghto-Quench K, and others from Park, etc. The cost difference is nominal - and a lower risk for your hard work.

I get my pipe tobacco locally, so it isn't an issue. However some good cigar shops that also have pipe tobacco are www.coronacigars.com, www.mikescigars.com, I have bought from all of them.

Don't worry I am not going to go on a massive anti pipe-smoking rant here like on the nasty gross beer threads.

 

In fact, I have smoked cigs for awhile, only a full time habit when i was younger, now I only venture a puff at get togethers and stuff. I have always liked pipes, always wanted to find a good tobacco to go in them too, but never found one that tasted as sweet as they smell coming from someone else's. My little steel pipe I made works pretty good too, though nothing to go in it:(.

Actually Sam - I have found that the sweeter the smell - the hotter it burns and the worse it tastes. If if smells bad - then it generally tastes good.

So I pick something in the middle of the road

Howdy, Don!

 

Quick answer: warm alcohol, not rubbing or denatured as they're poisonous. Be careful, it'll strip the stain off the bowl.

 

Slow and better answer: soften with a little alcohol (wet cotton ball in the bowl left to soak overnight), and ream it all out with a pipe reamer/carefully applied sanding drum on a dremel/knife blade, then ream out the airway with a drill bit and pliers, not power.

 

Gotta go, be back in a bit...

Personally, I use Jack Daniels or George Dickel. I know some purist will blanch, but it works very well to clean the organic goo and stuff out of the pipe and stem. I leave it there for a few moments, and also use a pipe cleaner soaked in it - it does a good job.

From when I worked in a foundry.... drink milk before you melt zinc. It eliminates the zinc shakes....I did some study on it and not believing the wives tales. But it does work. Apparently the milk chelates the zinc, and ties it up so you don't get the shakes. All in all though - avoid doing it. From a practical matter, heating up galvanished steel to the point where rapid diffusion of the zinc occurs can lead to solid metal embrittlement or liquid metal embrittlement. Neither of which is good for the blade.

Many many years ago, I was smoking my pipe, with my daughter curled up next to me, while I was reading her a story. After the end of the story - I think it was "Fox in Socks" - her favorite...I caught my breath, and took a nice pull on my pipe. I blew a really nice series of smoke rings. My daughter was transfixed.... and after a few moments watching the smoke rings vanish, she looked at me and said "Daddy - can you blow triangles?"

The tobacco that I like now is called Professor's Blend. It can be found at a lot of different places....It has a touch of vanilla, but not so much that it burns hot. Just very pleasant. Now if I could just get my wife off my back about it....

I didn't know that - didn't notice it until now. Might be interesting to set up a time to have a quenching or heat treating time....some of the metallurgist here could get together and answer questions...kind of like a panel discussion and be open for questions from the "audience".. Could be a lot of fun!

The sand will circulate on its own. You set up nozzles at the bottom - about 3/8" in diameter in a circular pattern - think lots and lots of nozzles. Set them up on a series of circles inside one another. There are two type internally heated and externally heated. Check out Technomics and Procedyne - they make commercial fluidized beds. You may also want to check out some transport phenomena books to get the physics behind it. But you generally have the right idea. Just one set on nozzles at the bottom is adequate. You may want to go for a higher velocity using smaller nozzles, but more of them.

Regarding clumping and static buildup, probably the best idea is not to use extremely dry nitrogen. Because it is so dry, static electricity can build up. Add a small amount of natural gas or propane so you are below the flammability limit. That should help the amount of static electrictiy build up and provide a small measure of scaling protection.

So it sounds like you're gonna go for it. I was thinking that the internal combustion might be the way to go The same gas you use as an O2 barrier is heating the bed as well. That leaves the Nitrogen out of the picture.

You can also quench in fluidized beds - it gives similar quenching performance as quenching in molten salt. You have to watch how you design the nozzle plate to direct the fluidizing gas for any design of fluidizing beds. Typically they use small nozzles - say 3/8" diameter drill holes in a circular pattern.

As you increase the the flow of gas, the bed will expand. Gradually up to a point it will keep expanding. There is a point where the bed will become "fluidized" and there is rapid bubbling or rolling of the bed. Increase this gas flow rate further, and you start blowing the sand out of the bed. I have installed and operated larger (36" diameter beds) and they work very well with limitations. Probably the biggest limitation is the static charge build up when dry nitrogen is used. The sand starts to clump and fluidization is difficult or impossible to achieve.

Kevin - I believe you are right - it sounds a lot like a fluidized bed furnace. It has the same basic fast heat transfer as a salt bath, but few of the negatives. It is not as fast as a salt bath - but it does work quickly. One issue is static buildup on the sand, making it clump. You can also add a small bit of natural gas - about 1% to provide a reducing atmosphere to reduce decarb and scaling.

Kevin - that sounds like one of my customers down south...the used to sperodize anneal 52100 using nitrogen and a small amount of natural gas. Does the name Harry Walton ring a bell?

I have bought lots of stuff from Shapiro on Natural Bridge - even bought a nice 50 foot steel tower for cheap! You never know what you will find there. I used to live in STL before I moved to PHL.

You can get the thermite - it is called CadWeld and is used for welding large pieces of copper together for electrical type stuff