Shafts: 4140 vs 4150?

[sprintcar]

For large pump shafts (12" diameter range) the published specifications on 4140 and 4150 appear to be very close in terms of yield, etc. IF material costs were equal, does anyone have a preference for either alloy in terms of machining or durability in service? I can't seem to find a quantitative difference so I'm asking you experts!
Thanks for the advice!

Keep the wheels on the ground
Bob
showshine@aol.com

 

[NickE]

the only difference I see in these two steels chemistry is the carbon content: 0.38-0.43 vs 0.48-0.53 for an nominal increase in carbon of .1%wt. The differences btw the steels in service is: additional carbon causes: less machinable, stronger, better quenching response (hardneability), harder martensite,lower corrosion resistance.

Obviously as the difference in carbon content gets bigger the differences btw the steels will be greater also.


Nick
I love materials science!

 

[sprintcar]

Thanks Nick
So in a real world situation, looking a nominal 110ksi ultimate and 85ksi 2% yield (this was the spec I found for 9" bar stock) the 4150 would be just a bit harder to machine, (not heat treated after machining) and a little bit stronger. Any way to define a percentage difference in strength? From what I can see cyclic endurance should be the same.
Thanks!

Keep the wheels on the ground
Bob
showshine@aol.com

 

[NickE]

I guess I have to say it all depends. If the material as specd from the producer at 110ksi UTS then thats its strength. Usually from lot/heat testing. Teh strength difference I mentioned is in the quenched and tempered condition. (same for each chemistry). The only good physical indicator of fatigue life is ultimate tensile strength since thats what governs the crack propagation speed. (Surface finish and geometry are really important too just not a result of chemistry/heat treat).

<opinion follows>
If you are'nt concerned about heat treated shaft then there wont be a significant difference in these materials. The additional carbon really plays a role when Quenched and tempered.

nick
(keep the wheels in the dirt you mean)
Viva Pro-Le-Ralliat

 

[EdDanzer]

Actually most 4150 has sulfur added to improve machining characteristics. It has a better machinability rating than 4140. This sulfur addition will effect corrosion in some atmospheres, makes it very poor to weld to and do not try bonding rubber to it. I have never used it in a high fatigue application, but do not believe the sulfur is a good thing.

 

[NickE]

Shouldn't 4150 with extra sulfur be denoted w/ some sort of modifier to the spec... IE: UNS# G4150x where x is 1 for boron, 4 for lead etc...

Doesnt the sulfur also impact the fatigue performance? (or is it completely iin solution?)

nick

 

[sprintcar]

Sulfur will reduce performance and can lead to premature failure vs non-resulfurized 4150. It does improve machining slightly, but we found it detrimental to long term operation in high load conditions. 4140 is supposed to have about a 3% cost advantage.

Nick - I try and keep at least ONE wheel in the dirt ...usually the fronts are just hanging there when the car is really hooked up!!

Keep the wheels on the ground
Bob
showshine@aol.com

 

[alexit]

Resulfurized materials also change size/shape more in heat treat processing. 4150 has a dramatically different Q&T process the ramp, soak, etc. (and higher hardenability of course.) Look not only at material or pre-machining costs, but heat treat processing and post-heat-treat machining operations in your costing...


Alex

 

[NickE]

you should be able then to order non-resulfurized 4150. thou as you state cost may not be worth it...

(Rally drivers do it sideways)
nick

 

[sprintcar]

Current spec IS non-resulfurized for the endurance and corrosion reasons. If 4140 will support the same operational properties, then the cost advantage would be worth looking at.

(Rally drivers go one at a time.... there's 24 of us on a 4/10 mile dirt oval at 130mph - all trying to be in front)


Keep the wheels on the ground
Bob
showshine@aol.com

 

[MOB1]

For a shaft of 12 inch diameter I believe that you would be better served using a higher alloy steel such as 4340 or better. This steel has superior hardenability response during heat treatment compared to either 4140 or 4150, that is, it will give superior tensile&yield strengths and other mechanical properties in larger diameters. This is important if you are doing considerable machining after final heat treatment.
There is some argument that the leaner alloy steels such as 4140 and 4150 give desirable compressive surface stresses after quenching and tempering. I have doubts about this because of the generally high tempering temperatures to bring these steels back to the strength level required for optimum machinability and fatigue resistance. The tempering acts as a stress relief and any benefits from compressive surface residual stresses are negated.

 

[sprintcar]

MOB1 raises an excellent point - the only problem is Engineering spec vs the bid price of the job (We all know how Sales and Purchasing are!)
I'd spec 4340 for most of the work (except corrosive) but the competition uses the cheap stuff.

I'd like to mention that everytime I get into EngTips it's VERY educational - Thanks!

Keep the wheels on the ground
Bob
showshine@aol.com