Best heat treat method for 300M 3

[Steinoff]

I have made some shafts from 300M material. Before heat treating I contacted the mill and asked them for the best method of heat treat,we went over the cert papers etc and they said renormalize 1700F for 1 hour followed by air cool. Then 1600F for 1 hour ,oil quench and temper 575F for 4-6 hours and your good to go with a 53-55 Rc part. Well after this ordeal on only 1 piece I have a distorted piece of soft maple,possibly oak at 46Rc and they have no answers other than "ask your heat treater to tweek it a little" . Can anyone refer me to the correct procedure and give some insight on an alternate method which will possibly reduce distorsion.

Thanks in advance,Stein

 

[diamondjim]

How quickly did you get the material
into the quench cycle?

 

[Steinoff]

The quench was done immediately

 

[unclesyd]

Unless we have two different materials I've never seen a heat treatment for 300M such as yours. I can’t say that there aren’t other heat treatments but none of my literature has anything like yours. I certainly would change my supplier and possibly my heat treater if I get that kind of advice.

We usually get the material (300M) in the annealed/solution treated condition and the do a simple low temperature age hardening at either 800°F or 900°F after machining.

Anneal and solution treat if we do it ourselves.
1500°F for 30 minutes. We require a fairly rapid heat up (500°F/hr) of the material to 1500°F.
Air cool

We age at 800°F for 9 hrs. Air cool. 900°F for 4 hrs., a minimum of 3 hrs. Air cool.
We prefer the 900°F treatment as we get somewhat better properties. This gives a 52 Rhc.

 

[TVP]

Steinoff,

The heat treat schedule that was recommended is a standard one for 300M. Timken Latrobe has some excellent information on their website regarding this alloy, heat treatment, etc.:

http://www.timken.com/products/spec...ech_info/PDF_Files/Lescalloy_300M_VAC-ARC.pdf

There are several areas to investigate when low hardness is obtained. diamondjim already mentioned the quench. What type of oil was used? Temperature of the oil? Was the part agitated in the oil? Any smoke or fire?

Another problem area is decarburization. 300M is particularly sensitive to this, due to the elevated Si levels. What type of furnace atmosphere was used? Were any precautions taken to eliminate oxygen? Again, Timken Latrobe has some excellent information on this topic, available by clicking on the following:

http://www.timken.com/products/specialtysteel/engineering/tech_info/html/T-T 102.htm

These are the first two items I would investigate. Feel free to post again if this information does not assist you in solving the problem.

unclesyd,

I think perhaps you are confusing one of the maraging grades like Marvac 300 (Timken Latrobe), Nickelvac 300 (Allvac), or NiMark 300 (Carpenter) with the medium carbon alloy steel 300M (SAE AMS 6419, UNS K44220).

 

[unclesyd]

TVP,
You are right, as the steel we used is definitely a maraging type steel. Another confusing set of nomenclature as we always talked about 300M as a maraging steel. That is why I worded my response as the heat treatments were so different. It is a wonder we never encountered a problem when we called out 300M.

Stienoff
Sorry for my confusion on the materials. My comments on the supplier still stand.

 

[Steinoff]

No problem unclesid , im already confused enough.

 

[Steinoff]

TVP thanks for the link ,checked it out and the treat is the exact same as what i have done except for the 2+2 hour double temper ,I wonder if that would have made that much difference?

Thanks again ,Stein

 

[unclesyd]

The 2 + 2 wouldn’t make any significant difference in the hardness if both temperatures are the same.
Low hardness can result from several things though 2 stand out, the austenizing temperature and the quench rate. The austenizing temperature and associated soak time is the first thing to verify. The next thing is the quenching system. Does it have the capacity to quench your part without heating the oil too much?

Come back with the size of your shaft.

 

[Steinoff]

The shaft is 1" diameter by approx 14" long and the oil temperature is unknown. Also we did not record the Rc after quench ,that was a mistake. I will try again on moday with another sample part and record the Rc after all the steps . If you can think of any other information that will help ,let me know.

 

[unclesyd]

There should be no problem quenching the a shaft of that size and you should have no mass effect problems. As TVP mentioned there could be some problem with decarb that could be quickly checked by doing a little grinding on your test shaft and a hardness test. Examination of the cross section and quick etch, either micro or macro. If there any sign of decarb check the furnace atmosphere.
If you find the quench adequate then look at the austenizing conditions. Check the temperature and soak times. Is the austenizing furnace of adequate size?
Check and see if your shaft was piggybacked with a big load of material.
I would leave out the normalizing step unless there is an absolute need. We very seldom normalized 4340 material, which is quite similar to 300M.

 

[Steinoff]

We were going to try another piece on monday and that was the method we were going to try as well with leaving out the normalize step. Would you still use the double temper method as mentioned by the manufacturer or just go with a 4 hour temper. We tempered at 575F would that be ok or would you try lower or higher temps.
Thanks,Stein

 

[unclesyd]

Looking at data I would look for hardness of 57-58 HRc on quenching. You can adjust the tempering temperature down say 25°F if the hardness is below 57 HRc.

Are if go with 2 tempers you can drop your first temper down 50°F check the hardness and then do the second temper at or near 575°F to the desired hardness. I would go with 2 tempers myself.
Make sure you quench to below 120°F, warm to the hand, before coming out of the oil. Cool on to RT and immediately do the first temper.

Make sure you lets us know the outcome and if you have any more questions please post.

 

[Steinoff]

Well i have some information, we tested the piece a little more thoroughly today and considered your thoughts of decarb. I think your dead on with that. With the surface being approx 46Rc I ground down about .010" and rechecked and it was 51Rc. The ovens that we used were no vacuum .The recommended procedure 1700 for 1 hour followed by air cool then 1600 for 1 hour we feel decarbed the alloy.
Also with the material only being 1" diameter I was thinking that 1 hour may be way too long and we cooked it to death.
We were going to try 1550F for a total oven time of 45 minutes ,quench and double temper and skip the 1700F air cool deal and just go with a stress relieve instead.
What do you think of these thoughts (be critical I can take it) and do you think Im on the right track .
Thanks again ,Stein

 

[unclesyd]

Lets not get off track or change too many things at this juncture. I would stay with the austenizing temperature of 1600°F using an atmosphere in the furnace. It doesn't have to be a vacuum type furnace. Also I would stay with the 1 hr at temperature to ensure a thorough soak.
As mentioned in previous posts you can tweak the final hardness by the adjusting the tempering temperature. It is usually bad business to try to adjust the hardness in austenizing step unless you are well versed in the art and have a compelling reason to do so. Staying at the recommended austenizing temperatures allows you to ask the producer of the material for assistance. You should always strive for the as-quenched hardness numbers posted by the producer or recognized handbooks for the material being heat treated.

 

[TVP]

Steinoff,

I would not change the austenitizing temperature from 1600 F. Since the section is only one inch in diameter perhaps you could austenitize for less time, but again, I would be inclined to keep it at one hour, especially if you don't have a normalized structure prior to austenitizing.

Now, I think it is apparent that decarburization occurred, with two excursions to elevated temperature without a proper atmosphere. As unclesyd mentioned, it does not have to be a vacuum-- just not an oxidizing environment. The following is copied from the Timken Latrobe heat treating suggestions that I previously linked:

1. Use a furnace which produces either a vacuum or an oxygen-free atmosphere inside a sealed heating chamber.

3. Use an air furnace which contains an interior muffle that can be filled with inert gas. Some special muffles generate an inert gas as they are heated.

4. Insulate the workpiece from the air by one of several methods:
A. Wrapping in an air-tight envelope of stainless steel foil.
B. Painting or plating the surface with high-temperature paint or metallic plating.
C. Packing the tool in box of inert material.

Option 4A is a very common method to avoid decarburization when heat treating small batches. You can buy these stainless steel foils/foil bags from McMaster-Carr. A reputable heat treating supplier should already be aware of this technique if they cannot create a neutral atmosphere or do not have a vacuum furnace. I recommend you stick with the suggested times and temeperatures, and use one of the above techniques to improve the heat treat process. Use the following link for more information on the foil bags:

http://www.mcmaster.com/param/asp/p...n=desc=Foils;stainlesssteel,130=1611;128=9815

 

[NickE]

Just an aside on the SS foil for preventing de-carb. I just did a batch of small parts of 17-7 cond. C. wrapped in foil well, the H900 ageing treatment produced almost no visible scale on the parts.

(I've also heard that you can pack the part in Grey Iron Chips)


nick

 

[unclesyd]

NickE,
Cast Iron shavings work very well but there is one thing one needs to do with the part being treated. The part should be wrapped in several layers of plain paper towels prior to burying it in the chips with at least 1" coverage top and bottom. The paper prevents the chips from sticking to the part but has to be removed while quenching, especially in air. We always tie a S/S wire to the part to facilitate removal from the chips.
Along with CI we used spent pitch coke which also generated a very good atmosphere. I have also used moth balls, napthelene, as the atmosphere when using a ceramic kiln generator.

 

[EdDanzer]

Your long part should be vertically heated and quenched to reduce distortion.

 

[funnelguy]

EdDanzer is 110% right about hanging the shaft for both heating and quenching. This is where the distortion comes from.

I made 4 shafts from 300M years ago and had the copper plated to avoid the decarb issue. My material supplier handled the HT at the time and there were no problems.

Steinhoff, my suggestion to you is to get a new HT house for this work. I'd look into vacuum with a nitrogen atmosphere and direct quench if I was running similar sized parts. But I'd really have a hard look at the quench rates they claim. Vacuum houses generally have better quality and methodology in my experience. More $$$ though. My 2c.