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SAE 4041 Heat Treatment
2

SAE 4041 Heat Treatment

SAE 4041 Heat Treatment

(OP)
What Heat Treatment process(s) would best be used to treat SAE 4041 to an Ultimate tensile strength of around 150,000 psi?

RE: SAE 4041 Heat Treatment

No such animal as SAE 4041. Do you mean 4140?.But in order to answer your question we will need to know the section size you are interested in hardening.

RE: SAE 4041 Heat Treatment

(OP)
Nothing like a critical typo right in the title of the post.  Yes, I am interested in 4140.  It is a bar section 5' long and 1" x 1" square.  The square cross section will be machined to an octagon prior to heat treating.  

RE: SAE 4041 Heat Treatment

A 1" section size in 4140 will not fully harden with an oil quench. You will need to use 4150, 4340 or 5160. You might make it with a water quench, but you risk quench cracking and distortion.

RE: SAE 4041 Heat Treatment

(OP)
What tensile could 4140 achieve with an oil quench.

RE: SAE 4041 Heat Treatment

The web site below might be of help regarding comparison of mechanical properties for AISI Type 4140 alloy steel, oil quenched and tempered for 1" rounds. Keep in mind you are dealing with variations in hardenability characteristics for the same alloy composition, but for the most part it will give you some idea for comparison.

http://www.matweb.com/search/SpecificMaterial.asp?bassnum=M4140G

RE: SAE 4041 Heat Treatment

With a 3/4" dia round, austenitized at 1575F, you would quench out (oil quench ) at least Rc 51. This would be for the entire section. Rc 51 is equivalent to a UTS of 264ksi and you would temper at 800F to drop the hardness to around Rc 34 for an UTS of 150 ksi. BUT,with a 1" square section, you will NOT form the desired 90% martensite upon quenching and will have a softer core. With such a variation in structure, you can't predict what UTS you will end up with.

RE: SAE 4041 Heat Treatment

swall;
I believe this is one of those situations where you would almost have to try a sample heat treatment using the 1" square bar (versus hardenability projections using a 1" diameter round) and run a tensile test to see how close one could get by using an oil quench/temper heat treatment. The core hardness after oil quench and temper may still be sufficient to reach 150 Ksi. Sounds like fun……

RE: SAE 4041 Heat Treatment

Bethlehem Steel mass effect data for a 1" Rd gives a tensile strength of 156,000 after oil quenching from 1550°F and tempering at 1000°F.  

Instead of all the machining could you use a std 4140 hex bar?
If not standard but close to standard it would be lot easier to machine a hex down that a Rd.

Look at 4140 ann
http://www.frysteel.com/data/MeettheMetals/showmetal.cfm?metal=aircraft

RE: SAE 4041 Heat Treatment

Well, yeah, you can do an experiment or use some by guess and by gosh method, but why not just stick with sound metallurgical engineering and chose a steel with the necessary hardenability in the first place?

RE: SAE 4041 Heat Treatment

Agreed, if GTFiji can upgrade to a higher hardenability steel.  My preference would be AISI type 4340. Many times, the horse is let out of the barn before the cowboy (metallurgist) is consulted.

RE: SAE 4041 Heat Treatment

(OP)
Yes, the horse is running wild in the hills right now.  

My finished machined bar needs to be an octagonal (1" flat to flat) with shallow (0.09" deep) slots machined in 4 of the 8 sides.  The 62.5" long bar is for a fitness (gym)application.  I need to be able to machine a square (or other) bar to this shape, then heat treat it to my requirements.  Requirements are as close to 150,000 UTS as possible & a surface hardness greater than ~Rc 30.  I have bearings (Rc 58)riding on the bar flats so the ideal would be a bar as hard as the bearing (but not necassary).  The bar will be lifted so it must be strong (safe) and not fail if dropped accidentally (impact).  Up to 200 lbs of weight plates may be loaded on.

Any and all material selections are welcomed.  Cost as always is an issue.  I need the material machined and then hardened (strength/toughness).  I would also consider a thin dense chrome (Armaloy) lastly to bump the surface hardness up.

RE: SAE 4041 Heat Treatment

(OP)
I meant to also mention, se currenly us Stainless electro polished for cosmetic & corrosion purposes.  I think Steel would be OK if I plate/coat it.

RE: SAE 4041 Heat Treatment

So are you considering switching from stainless because of cost?

RE: SAE 4041 Heat Treatment

Sorry about the mention of hex bar as it would be hard to get form 6 to 8 sides.  I'll have to think square.

Riding into the sunset the sun sometime gets into your eyes.

swall,
Would you please define a "guess and by gosh method" based on sound metallurgical engineering practices?

RE: SAE 4041 Heat Treatment

unclesyd--you guess that it will work, even though you have forgotten the sound metallurgical engineering practices and by gosh it comes out O.K. Interrupted oil quenching of large D2 tool steel mill rolls comes to mind. See also, "rule of thumb".

RE: SAE 4041 Heat Treatment

(OP)
If I choose an AISI 4340 what heat treatment gets me to the 150ksi UTS I am looking for?

I am considering switching from SS to steel for cost savings.  I also now realize I may be able to get the appearance of electro polished SS and the corrosion protectionby adding a thin dense chrome coating to steel.  I am evaluating both alternatives against one another.

RE: SAE 4041 Heat Treatment

(OP)
metengr - what would the oil quench and temper you suggest on MatWeb do to the dimensions of the part?

RE: SAE 4041 Heat Treatment

If you use AISI Type 4340 alloy steel, which has noticeably increased hardenability over your original selection (4140), it should respond well to an oil quench for thru-hardening. I believe distortion should be minimal for this material.

RE: SAE 4041 Heat Treatment

For 4340, austenitize at 1550F, oil quench and temper at 1000F. This will give you an UTS well inexcess of 150ksi.

RE: SAE 4041 Heat Treatment

You can also marquench 4340 and temper at 800-850F to reduce distortion and still make your UTS.

RE: SAE 4041 Heat Treatment

GTFiji--something to consider if you are in the U.S. Chrome plating is likely to take a big price increase in the near future due to OSHA's just released lower workplace limit for hexavalent chrome. So,make sure you have current quotes for plating when you factor in the cost savings of a change to plated 4340 from stainless.

RE: SAE 4041 Heat Treatment

(OP)
Swall - would this price increase be applicable to Armaloy's "thin dense chrome"?

RE: SAE 4041 Heat Treatment

If the Armaloy process is the typical electrolytic plating, using chromic acid, the answer would be yes. But, (and I may be wrong on this) I was thinking that Armaloy is some kind of chromizing process, not plating. If that is the case, you might not see a price increase.

RE: SAE 4041 Heat Treatment

Armoloy and other Thin Dense Chromium processes are a plating process without all the normal problems of electrolytic planting chrome.  
The last time I was involved with TDC it was limited in deposited thickness so it will tend to reflect the properties of the base metal, the harder the base metal the better.  
Rolling contact from a bearing might be a problem though the higher hardness you are specifying will help.  A sliding sleeve bearing might be better.  

I would definitely get in touch with Armoloy and discuss you design parameters with them.
I've had my best luck with the Texas Bunch, but that was some time ago.  Their home office is in Illinois.

http://www.armoloy-tx.com/tdc-coating.html

RE: SAE 4041 Heat Treatment

150 ksi UTS is easy for a decent heat of 4140 even in a 2" bar.  Unfortunately some heats are on the low side of the hardenability elements (C, Mn, Mo, and Cr) so they don't harden worth a dam*.  But if you have the time and a little hardenability knowledge, you can save some $$$.  

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