Please review my water quench plan 10

[knowlittle]

What is the practicality of heating the following clevis to 1500 F (815 C) and dropping it into a water bucket?

Dimension: 3"x3"x8" (75x75x200 cm)
Weight: 16 pounds (7.5 kg)
Material: 4340

Please don't ask why not oil quench. My buddy is all set to try water quench first unless there are compelling reasons not to. Thanks.

 

[swall]

I would think that the possibility of cracking the piece into small bits would be a compelling reason.

 

[Helicopterjunky]

Knowlittle,

You may crack your part upon quenching into water. You have too many sharp corners. A sixteen pound part into a bucket sounds real iffy. Without agitation it will not quench uniformly, soft spots and more chance to crack. Most compelling reason not to try this is it will probably fail miserably. If you insist, I would be interested in what happens.

 

[Jughandle]

Don’t do it – for several reasons
[1] Unnecessary in 4340. It defeats the purpose. 4340 is a deep (below the surface, that is) hardening steel, therefore only a slow quench (a good thing) is necessary for transforming the austenite to martensite. It all has to do with the way those expensive alloys in 4340 affect the thermodynamics of the transformation.
[2] Machine two pieces because the first one might crack. Quenching thick sections like this causes steep thermal gradients, internal stresses, and possible quench cracks from tensile forces, esp on the surface. Water is a faster quenchant than oil, so the cracking tendency is worsened.
[3] Also, investigate if an air-quench (i.e. Normalizing), rather than water quench & temper, would give you the desired mechanical properties.

Sorry, got carried away. To respond to your question, if you really must do this, put a big radius at the bottom of the slot and chamfer the exterior corners in order to attain a constant thickness throughout the cross section. Use a big bucket of very hot water, drop the part in – vertically constrained. NDI it afterward for cracks that you hope are not there. Letting it air-cool for a few minutes (check a CTT diagram for 4340), before the quench, probably wouldn’t hurt. If the center core gets to < 800F in < 10 minutes, or so, the part should be thru hardened. (Check a metals book, e.g., Reed-Hill – Physical Metallurgical Principles, 3rd Ed.)

Also fyi, spec AMS-H-6875 recommends Austenitizing at 1500-1550F, Oil Quench, then temper 850-1200F depending on toughness/strength requirements.

Good luck. Try it.

 

[TVP]

In addition to the substantial risk for cracking, there is also a substantial risk of distortion, meaning that it DEFINITELY will distort. Are the clevis legs supposed to be flat, parallel to each other, with a concentric axis for the through holes? What type of tolerance is this part supposed to have? If the expectation is for dimensions to be accurate to some decimal fraction of mm, then water quenching is unlikely to work. Has your buddy ever quenched a 16 pound part? Do you know how much volume of water will be necessary to safely quench a 16 pound part? Please post some photos for all of us to see after the part is water quenched.

 

[redpicker]

What hardness/strength are you trying to achieve?

Going with a water quench on the part shown made from 4340 will crack it. I've seen 4340 crack quenching in oil due to sharp fillets. I'd just machine it from heat treated material.

rp

 

[knowlittle]

Thanks.
The part has already been made. I hope your replies convinced my buddy not to attempt water quench and take the longer route of oil quench (due to complicated fund transfer).

Someone mentioned air quench. We will look into it.

I don't know what my buddy is targeting for hardness/strength. I would say about 50 should be good enough. It will be used as fatigue test adapter. And we only have a limited number of test samples. That's why air quench may actually work.

If my buddy has further questions, he will post here. By the way, he is a mechanical engineer and I am a used-to-be metallurgist, sidetracked to non-metals, knowing little of both fields, thus my login name knowlittle.
Thanks again.

 

[unclesyd]

I concur that quenching this part is water is extremely hazardous for the part and the quencher. If the high hardness is combat wear in pin holes you could use a tension bushing to take care of the wear instead of taking a chance on quench cracks.

What is the end use for this clevis?

Have you tapped the threads yet.

If it's for lifting you may fall under some specific rules and regulations depending on you jurisdiction.

 

[knowlittle]

END USE: It's an adapter for fatigue testing. Basically, a sample sits between 2 hydraulic cylinders. The cylinder rod threads into this adapter. We don't want this clevis adapter fail by fatigue before all fatigue samples are tested. Since we have a limited number of samples, moderate hardening may meet our need. It is a strictly a laboratory test device. No lifting.

THREADS: All machining has been done including the threads.

WEAR: Yes, the holes in the clevis are for pin connection to a test sample. For extended use of the clevis beyond our immediate test need, we will consider bushing approach.

Thank you.

 

[redpicker]

It's difficult to tell, but are those pin connection holes flat-bottomed as with a CT fracture mechanics specimen clevis? If so (I've been throught this before), you _will_ need to protect against decarburization during heat treatment, at least on these holes. Otherwise, the surfaces will not harden and you will get yielding from the pins and these holes will loose their flats.

You can try some stop-off methods (stop-off paints, copper plating, etc...) or stainless wrap, but your best bet in an atmosphere controlled intergral (oil) quench furnace.

As far as hardness is concerned, I wouldn't want to use 4340 in a fatigue application above about 45 HRC, and that is with excellent transformation during heat treatment. With questionable transformation, I think I'd try and hold it to below 38 HRC (I'd assume you'd get excellent transformation in an atmosphere controlled intergral quench furnace).

rp

 

[knowlittle]

Yes, it is for Compact Tension specimen testing.

Thanks for the advice to protect the pin mating area. Heat treatment will be done inhouse. I will bring it up to their attention.

Thanks for 38 HRC. I was way off.

I am not familiar with the term "integral quench furnace."

 

[TVP]

There are several different names for "integral quench furnace" but they all mean that the quench tank is integral with the heating furnace and its atmosphere, so that the parts are never exposed to outside air, contamination, etc. The following link is one manufacturer's description and equipment:

http://www.afc-holcroft.com/non-ferrous/batch-furnace

 

[CoryPad]

I would not limit hardness to 38 HRC. ASTM specifications like E 1820 require the following:

Clevises and pins should be fabricated from steels of sufficient strength (greater than 40 HRC) to elastically resist indentation of the clevises or pins.

Regards,

Cory

Please see FAQ731-376 for tips on how to make the best use of Eng-Tips Fora.

 

[unclesyd]

Here are the type tension bushings I was referring to.

Click on Spring Bushing at the bottom of the page for technical data.

http://www.connexusa.com/

http://www.rollpin.com/Usage_Guides/Tension Bushings/Section1.html

 

[Robertmet]

One rule of thumb for quenching is at least 1 gallon per pound of steel.Water quench for that shape will garantee cracking and /or warping. Air quench is a possibility.

 

[unclesyd]

Robertmet,
I believe your volume to weight ratio is way too small for any part this size. I would have a least three + gallons/per pound. Any less water and a part this size would blow all the water out of the container. I would also use agitated water or a moving basket to prevent steam blanketing, especially a blind hole.
That said I concur with all that this part should be oiled quenched at the same ratio or a least a slow polymer quench.
Aside from the yoke this part has a high potential for die cracking at the blind hole. The possibility is far less with agitated oil.

 

[Robertmet]

Unclesyd, I won't argue there .The 1 gal/lb is for parts less than 1 lb.Of course the proper way is slow oil or polymer and on a part without sharp corners.

 

[knowlittle]

Thanks for your replies. I am learning much.

I read a few articles on glycol+water quenching. My buddy has 1" diameter x 4" long (25 mm dia. x 100 mm) pin that weighs about 2 lbs (1 kg). Is this a good candidate for glycol+water quenching? Is glycol+water as good as oil? He has 2 pins. He asked me to post this question here. Thanks.

 

[CoryPad]

What material is used for the pins? Since the pins have the same requirement as the clevis (> 40 HRC), I assume they are 4340 also.

It isn't a question of water being as "good" as oil, it is a question of compatibility. Water and its solutions are capable of extracting heat very quickly from steels. The problem is that the quenching rate may be too high for higher carbon steels and they may crack. One of the reasons all of the alloying elements (Ni, Cr, Mo) are put into 4340 is to make it hardenable in oil quenchants.

The simple shape of the pin makes it less likely to crack than your clevis, but it still may crack. Also, dimensional change (diameter, straightness, etc.) may occur. It is best to use oil for alloy steels.

Regards,

Cory

Please see FAQ731-376 for tips on how to make the best use of Eng-Tips Fora.

 

[redpicker]

Make sure you aren't confusing (poly-alkylene) glycol quenchants with Ethylene Glycol anti-freeze. They are not the same and will not give similar results.

PA Glycol quenchants can be made to provide cooling rates either faster or slower than most oils (generally a bit faster, though), depending on concentration.

Using Ethylene Glycol (anti-freeze) as a quenchant is not recommended.

rp