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My understanding matches Doug -- that cryo converts retained austenite on high alloy steels (stainless, D2, 1V, 3V,...). The low alloy tool steels like 5160 won't have a bunch of retained austenite if heat treated correctly.

 

More importantly, the heat treat sheets from Carpenter, Crucible et al indicate that cryo has to be done on high alloy tool steels almost immediately after quench to be effective.

What will happen when you quench steel in liquid nitrogen is that the LN2 will immediately turn to vapor and you will get a very persistent vapor phase - it is a very slow quench. Only vigerous agitation will break up the vapor phase. Another thing to concern yourself with is that all the LN2 will also turn to gas and create a suffocation hazard. This was well documented about 30 years ago when several people died when a manufacturer tried it.

My oil certainly got faster! Then I discovered that the bottom 1/3 was now water! Once we got rid of the water, the "oil" went back to normal speed!

Canola will get faster if there is water present. It will not separate as canola or vegetable oil is hydrophillic (likes water).

Oil that contains more than 1000 ppm of water can be a serious fire hazard as the water turns to steam and pushes the oil out. Often the oil ignites from the hot part. Then you have a real mess with flaming oil over everything

Geez Ric, that alloy is older than you are! Same formula as 12C27 basically but manufactured by BU rather than Sandvik. I heard Soligen was working on something called "wunderstahl..."

Why not nitride the blade edge of the stainless?

Thanks Scott,

looking forward to seeing more

that one is a "small one" eh? It's cool to see how fast the technology has ramped up both in size and the "tech development" side of it...

Dick

Wind turbines are really a favorite of mine. They have to be forged, machined, heat treated and then assembled. Good solid manufacturing work. It is really cool when they are quenched and knowing that you had a part in it when you see them erected.

Maybe I should let one of the real metallurgists answere this but 5160 is not a real complex steel and I don't know if the real M_f point is below room temperature. None of the info I have from ASMI gives that data. Most ITT diagram only list the M₉₀point. It won't hurt anything if you do it but you might only be making the steel cold. It could help if you measured the HRC before and after the cryoquench to get an answere. Some heat treaters go from the normal quenchant to the cryoquench and then to tempering oven. I know from data on cryquenching a stainless steel that you cause less stress by going from the quenchant to the tempering oven, to the cryoquench, then back to the tempering oven.

 

Doug

Download Timken Practical Guide for Metallurgists - lots of good data there and free. There is a new edition out there - just go to the Timken site and download it.

Timken Practical Data for Metallurgist.pdf

Scott,

 

On further reflection, I was trying to figure out why that Ms for 15N20 was so high and I realized that we seem to be talking about different steels.

 

My contents as listed from the source, Admiral Steel, are as follows:

 

C .75

Mn .75

Si .25

Ni 1.5

 

I realized that in another forum you had compared it to 15B22, which reads really different, (notably missing carbon,) though still not the numbers above.

 

When I calculate the figures from Admiral, (here: http://calculations.ewi.org/cgi-bin/IgorCGI.exe/ ) including for various variables, I consistently come up with 350F - 400F numbers for the 15N20, which place near, again depending on exact composition, to the 1075 (Correction on my part, the material from Admiral is listed as 1070/1080, and the carbon may run as high as .88. I don't have the exact specs they sent on hand, but will find or obtain them.)

 

This leads me to conclude that the first heat treatment indeed suffered from the stiff decarb, OR that quenching into 450F and 475F worked better because of an actual alloy content as opposed to one on paper, i.e. if I had low carbon content within the specs of both of these alloys, the Ms is raised in one case to 404F, and the 400 quench could have just missed it. The high temp tank has a range from top to bottom, but the low temp one seems very consistent throughout.

 

Another variable I am considering is time spent in the low-temp tank, up to 10 minutes on the large piece, for "equalization." Should I think of this process more as a controlled interrupted quench with these alloys and quench into oil / water as soon as possible after inspecting & adjusting for warpage?

 

Am I missing something?

 

Edited to add: I found the specs on the 1075: C .74, Si .16, Mn .65, Ni .04, Mo .008, Cr .19, V .005, Co .008, B 0.0. The calculator says 399.88F for Ms. Now. For the 15N20. Phone calls have been made...

 

Further edited to add... according to the formula above, when I calculate the alloy contents that I have (specs, not actual certificate figures,) I come to a Ms of 475F for the 15N20...

No - you are not missing anything. I misread it - I was thinking that you had a laminate of low carbon steel with a high carbon steel. I goofed. Thank you for calling it to my attention. The Ms temperature that you determined empirically is about right.

Because the section size is small and the thermal mass of the salt is high, I would use a much shorter time at the martempering temperature.

Thanks for the condolences, Peter. I feel your pain.

 

Scott, thanks for the response and the resource, it's very helpful.

 

A few things I noticed and a follow up question, if I may borrow your expertise for a moment...

 

Peter's scenario seems plausible for this piece, but at the time I cracked it, it had been quenched in 400F salt. I thought it was unhardened enough to gently untwist it. The crack occurred in the edge material, which I'm 95% sure was laminated 15N20. Tiny chance it's possible it was laminated 1070.

 

In the meantime I quenched several small 15N20 / 1070 flawed blades for experiments. They were all 48 layer *tight* twists; effectively tight enough to count for higher layer counts... about 50-100. (Lucky for me I have a LOT of them. )

 

At 450F they were hard but bent a bit before breaking. At 475F they snapped clean, with no indication I could ascertain with regards to layers.

 

When I requenched the big blade at 475F, it definitely seemed harder, but also kind of "tough". Though I hear this is to be expected I have no physical reference point with which to compare it. It had a little bit of give and broke along layer lines after major torquing. Crunchy-like. I could even post pictures.

 

Is it possible that the low layer counts of this Migration style pattern welding hardened the layers differently since the Ms of the 15N20 is so much higher? (This would be a cool modern echo of the fable, see, all that "hard and soft layers" made it tougher stuff...)

 

Is it possible that the 15N20 is still hardening due to the quenching effect of the 450F curve getting it below the high Ms point regardless, and that basically only the 1070 is getting the martemper effect?

 

Either way the warpage is extremely reduced, and the big blade that broke only twisted, and mildly at that, after being normalized, quenched twice and bent a bit. These salts rawk!

That certainly makes sense. What you could have also done is created bainite in the 1070 - making it nicely tough, but still had martensite in the lower hardenability stuff. For grins - try a 1070 blade with only 1070 and austemper it, i.e., hold at Bs (°F) ~ 1526 - 486 x C - 162 x Mn - 126 x Cr - 67 x Ni - 149 x Mo for a period of time - then quench. You will end up with a baiitic structure - hard and tough. Maybe not real hard - maybe 53+ HRC but it will be real tough.

Well, I got to play around a lot this afternoon. The good news is that a 450F quench seems to be the trick. In my set up at least, with 15N20 / 1070 at a 1450-1500F high temp range.

 

The bad news is I was straightening out a rather nice blade I thought wasn't hardened.

 

It was.

 

However, as a result, I had a really typical long pattern welded piece to experiment on in ways I'd not try if I thought I had a perfect blade. All systems go!

 

Peter, I think you may have been right about a thin decarb layer on that piece, which is a cool thing to know. Thanks for that insight.

 

Sigh.

 

Back to the forge!

Ms temperature for 1065 is 525 and Ms for 1090 is 420F - so what you found empirically is about right. I have not found the Ms temperature for 15n20 but it is very high - much higher than 525F. I found the data on p 79 of "Practical Guide for Metallurgists" - very practical little booklet that is a freebie.

As an approximation:

Ms (°F) ~ 930 - 600 x C - 60 x Mn - 20 x Si - 50 x Cr - 30 x Ni - 20 x Mo - 20 x W from E. S. Rowland and S. R. Lyle, Trans. ASM, 37, 1946, p 27.

I agree that you probably have a slight decarb.

Scott, What is the personal and company (as a rep expert) pucker factor when you have gone all that way to "watch"?

 

Ric

There is always a "pucker" factor - Hopefully whenever I do a fill like that I have looked at all the mitigating factors like quench rate, part alloy, thickness, agitation, quenchant used - and how to control the concentration (if polymer). Luckily I have only had one failure and that was because of agitation issues. I thought it was stronger than it was - after we corrected it, it worked like a champ.

Regardless of what you are doing - there is always a risk - that is why they pay me the big bucks - to minimize risk to the company; the customer, and to the part.

One I get to the actual load - it is more of excitement and celebration than anything else.

BTW, I am trying to put together some additional pictures. But to give you an idea of the size of the wind turbines - here are some small blades for 1.5MW turbines:

Now each of these blades has a yaw and pitch bearing - that means numerous parts from rolled rings that bust be heat treated (typically either 52100 or carburized 9310). The rings, races and bearings (the balls) must be heat treated.

Scott,

what luck! I did not notice the author info because I never looked closely. Since its not my field, I did not expect to know the person in any way...

 

 

I had fun reading your paper. Impressive that a non-chemist can access and sort of understand your writing about such a complex topic. You write well. I struggle with writing my stuff so people (anyone) can read it. Sorry that I did not give a full cite in the beginning.

 

I guess you were pretty serious when you said you were interested in the performance of canola oil as a quenchant!

 

thanks for all of the info. I do appreciate it, and your general good nature.

 

kc

Thank you - I appreciate it. BTW, I am not a chemist but a simple metallurgist. I have chemist's for lunch.

thanks a lot for this.

 

How would one obtain a small (5 gallon) quantity of bioquench?

 

Kevin

Just call our customer service at 610-666-4000 (ask for customer service).

So, if I had some McMaster-Carr "11-second quench oil", would I be far off the mark assuming it would function similarly to Houghto-quench "G"? Like pre-heat about the same... figure it to be pretty well ideal for O1, L6, and the like... reasonably expect it to fully quench up to 1/4" of 10XX steels (maybe not use a knife maker's interrupted quench on 10xx steels)?

 

Mike

I would say that it would behave in a very similar manner

Depends on what you want (see - you can never get a straight answer from a metallurgist )

If you are looking to get the O1/O2 hard I would suggest using Houghto-Quench 100. The steel that you just cited has a very high hardenability because of the Cr and V. The V and W (Tungsten) will make nice carbides and help retain a nice edge. However, if you ever want to do lower hardenability alloys you will have a problem getting the lower hardenability parts hard. You may want to consider Houghto-Quench G - this is a medium speed oil that will get the high hardenability parts hard and should get your low hardenability parts hard too.

I use one part diesel fuel to 3 parts 30 weight motor oil. I got this from either a knife book or one of the knife making videos out there. Works just great on 5160 type steel!

 

Geno

I wouldn't use diesel fuel - the flash point is way too low. I also wouldnt use motor oil either because of the additives and stuff that is in the oil for lubrication. A straight mineral with low viscosity will get you the speed you want a lot safer.

An 11-sec quench oil refers to the GM Quenchometer test. It is a pretty cool test - essentially it measures the time it takes to cool a nickel ball that is 0.5 inches in diameter, from 1600F to the curie point. There is a lot of variability in the test, but it has been used in the US for years it is hard moving people to a better test like a cooling curve.

This would compare directly to Houghto-Quench G.

And yes I do know

Would Houghton Quench 100 be a good choice for steels like O1, O2 and 1.5052?

I am not familiar with DIN 1.5052 - is it similar to AISI 52100? Or could you give me a composition?

O1 and O2 should be hardenable in thin sections with Houghto-Quench 100. It is the extra V (O1) and Mn (O1 and O2) that makes it better than 1090 steel and more hardenable. It should work.

Scott,

 

Do you have a rough relationship on the longevity difference between canola oil and commercial quench oils (like Houghto-quench "K", for instance)?

 

Mike

It all depends on how hard you abuse them. As a general rule the oil would go rancid before it would not achieve metallurgical properties. A mineral oil, properly taken care of will last a very long time. Filter it occasionally using a good quality filter and mineral oil will last a long time. Even if it does get very oxidized, a mineral oil will tend to get faster because the shellac layer on the part. Vegetable oil would do the same thing.

Take care of it and they will both last - but I can't quantify how long each will last as it is so dependent on a whole bunch of things. But in general I would suspect that the mineral oil would last longer.

Could you have set the temp wrong and not noticed? For me oil tends to turn a turd brown in the oven or just burn off and turn black or, if it is my new HT oil it is red/purple (IDK why, but it seems the HT oil turned red). In my experiance the second temper at the same temp takes the hardness lower then the previous one (ie. the more tempers at X temp the softer it becomes).

I suspect that there is some residual moisture either in the atmosphere or on the steel.

I suspect that it more than likely Chinese steel. One of the real problems with Chinese steel is the tendency for low hardenability, uneven grain size and alloy banding.

Thank you for the input. I would like the information. I will contact you.

I can't recall - did I send the information to you?

For a blade I would recommend plunging it downward and agitating it by moving it up and down. As an alternative, you could try ultrasonics for agitation. Back and forth will cause uneven cooling on one side or the other. I would not expect it to relax when tempering unless you put a LARGE weight on it and tempered at a fairly high temperature.

Cool Scott.

 

Yes , I'd like to see more... Do you have any shots of them being forged? Thanks for showing ... it is really nice to have an industrial expert add his two cents to a bunch of bladesmiths.... we really appeciate your input and insight... it's invaluable.... Thanks,

 

Dick

I have the pictures on my work PC - I will try loading some from work.

Can you do me a favor and stick a few blades inside one of those things when no one's looking?

 

Thanks for posting that. I'd love to see a video of the actual quench. I bet that's exciting!

Next time I am there I will try and take some video. Lots of flames and stuff.

Nice to get some size perspective about "big" parts for quenching.

 

Are the gears case hardened and quenched with martensite on the surface, and pearlite cores ? Or is it something different ? I would think martensite hard to get with that large a mass unless it is a special alloy ?

That is basically correct - they use special alloys - think 4320 for the core, and carburized. Distortion can be an issue but is generally controlled by racking and control of agitation (they also use our oil for precision quenching).

It is very cool to see them quenching these gears, bearings and big shafts. It is the reason why I love heat treating.

Holly crap Scotty!!!!! beam me with some heat!!!!

 

are those windmill gears do you know? Very cool .... thanks for showing ... jaw dropping

 

Dick

Yes - they are the gears for the windmill transmission. These are 1.5MW wind turbines - the 5MW wind turbines are larger. The diameter of the blades is typically about 6+ feer in diameter - I can stand in the middle of the blades - they are also about 90 feet long. The pod at the top of the mast is about the size of a tractor trailer. Typical quench tank size is about 40,000 gallons, with many of the quench tanks being 60,000 gallons. These pictures were taken in the US, Brazil and China. One of the problems is that there is a shortage of qualified heat treaters with knowledge of quenching and control of distortion.

One thing I saw was quenching a 800T part into 1,000,000 gallons of quench oil - very impressive. The forges are amazing from the basic shaping of the billet to the actual forging of the blank. Typical weight of the hear treated gears is 25,000 pounds each. Ring rolling is used extensively for the large bearings used for yaw and pitch of the turbine blades. I have more pictures if anyone is interested. But I thought you would be interested in seeing how forging a small blade is related to larger industrial applications.