Understanding Crankshaft journal hardness

[BRENT in 10-uh-C]

I am trying to work thru an issue, and so I have been comparing an aftermarket crankshaft in an engine we are working on to what the manufacturer says the hardness should be, ...and to what the original print says it was.

He is what I have so far;

The aftermarket crankshaft manufacturer gave me these specs for their crank:

......Web hardness 260-320
......The main and rod journals nitridation hardened to HV>500


The Ford crankshaft prints I have say:

......Heat Treatment:
......Heat Treat to 1560° F. Hold for 30 minutes
......Cool to 1200° F. in 30 minutes
......Air cool to room temperature - Brinell 149-179
......Center on the 3 main bearings and rough machine
......Heat to 1500° F. A Quench in Caustic Solution
......Anneal at 650° F. to meet a Brinell of 402-444
......Re-anneal Front End as indicated (Brinell 302-364)
......Brinell hardness of Flange from 228 to 402-444 as indicated
......Finish machine and grind.

So, ...in language I am familiar with, how do the two compare?

Also, does any of that tell how deep the treating is into the journal??

......

[MikeK]

OK, pretty simple.

The after market crank has a core hardness of 260-320 and a thin (a few thousanths) nitrogen penetration case hardness that is higher to resist frictional wear. Any regrind (even 0.010") will be through the nitrided layer and you have a crank with a journal surface of 260-320. At that point you have some choices: a) Have it re-nitrided and straightened. b) just run with the softer face. -This is OK as long as you are using babbitt or shell inserts with babbitt over copper and the journals are properly micro-polished in the direction of sliding contact. I don't know the alloy of the crank you refer to, but the spec'd web hardness suggests this crank will bend significantly before fracture . . . not that a bent crank is good for anything other than an anchor! Several years ago I had a Burlington crank that I cross-drilled and ground 20 under (removing all nitride surface hardness) running on inserts for someone that ran the hexx out of it with a R2P and it was fine 'till he decided to switch from Rotella diesel oil to brand-x non-detergent (idiot!) then it all seized up which was, of course, my fault!

Henry's crank has no added surface case hardness. It does, however, have a somewhat higher overall hardness in the journals, 402-444. You could grind it a quarter inch undersize or more (to model T size) and it would still be close to 402-444. Having the surface in this range will somewhat reduce the possibility of friction welding bearing material onto it, but this is more dependent on micropolish and oil film strength. The flange and front ends are further annealed to reduce the possibility of accumulated cyclic stress fracture. The disadvantage here is there is already 80+ years of accumulated cyclic stress, so all of Henry's wonderful heat-treat steps no longer give it an advantage over a lesser processed replacement.

All numbers (both cranks) are from the Brinell 3000Kg/10mm ball column or the Vickers (HV) on this conversion chart. For comparative reference, a quality (not chinese!) cobalt drill bit will be about 740 brinell, a hardware store bit about 550+, a wood boring bit ~ 375, hot rolled structural steel ~ 275, and chinese drywall screws either zero or infinity!

In any case, the ability to run against a bearing surface is far more dependent on surface prep and oil film than hardness.

Late Add: Someone emailed me and asked why the aftermarket crank used BOTH Brinell & Vickers- Did they do it just to confuse the victim (customer)? Well, no, not exactly. It's like this: If you want to know how hard a mattress is you lay your bum on it and measure the indent. Brinell uses a 3000kg load on a 10mm carbide ball to make the dent. Now, if I want to protect the mattress from my pussycat's scratchy claws I could put a sheet of window glass on top of it. I could not, however, again use my derriere indent as a hardness test as it would smash the glass. I would need a much lighter load to test the surface hardness. A Vickers test can be done with 6000X less load than the Brinell. The Vickers does not, however, do much to distinguish through hardness vs. thin surface hardness. Yes, you've got apples + oranges but in this case it makes an understandable fruit salad.

[SteveB31]

Great answer MikeK.!!!

[hardtimes]

Hey Mike,
Thanks for the lesson !
So, is it fair to say that what you are saying, in a way, is that if I have a NOS Ford produced B crank..with properly polished surfaces.. that would be a much better crank than a currently produced/available similar sized crank ?

Do you know how Ford got such high 'hardness' thru/thru his cranks and why that is not so with say available and much more expensive A/B cranks of today ? Is that due to cost of processes and/or metal make up ??

[Mike V. Florida]

Originally Posted by hardtimes

Hey Mike,
Thanks for the lesson !
So, is it fair to say that what you are saying, in a way, is that if I have a NOS Ford produced B crank..with properly polished surfaces.. that would be a much better crank than a currently produced/available similar sized crank ?

Do you know how Ford got such high 'hardness' thru/thru his cranks and why that is not so with say available and much more expensive A/B cranks of today ? Is that due to cost of processes and/or metal make up ??

I know I,m not the Mike you are referring to but I want to post my thought before those truly in the know chine in.

No, With all dimensional specs the same and the only difference being the method of hardness, they would work, and last just equals.

[C26Pinelake]

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Truly amazing! Us Guys that turn the key and drive down the road have no idea what degree of expertise was necessary for us to do so. It is also amazing what tremendous expertise is available on this site ! I am truly impressed ! Wayne

[Chris in CT]

Hi Guys,

First of all, let me say that Mike K's explanation above is excellent and very much to the point. I'd like to add a couple of observations to his remarks and to address Brent's initial question above.
1. Quenching in a caustic solution (sometimes arsenic!!) is part of a case-hardening process. Brent's recitation of the Ford process does indicate some level of case-hardening in the manufacturing process.
2. Nitridization is a modern form of case hardening. In vacuum nitridization, it is not necessary to exceed about 950 degrees Fahrenheit, not enough to warp a piece of forged steel unless there are captured stresses in the forging. Therefore, a reground crankshaft can safely be re-nitrided. There will be a light surface film on the journals and mains which will need to be carefully removed with crocus cloth. Ask the performance engine guys about this - they do it more than a little frequently...
3. In modern heat treating practice, it is common to do more than one level of body, or web hardening. Heat treat practice will often harden the outer section of the workpiece for stiffness and ridgidity, while leaving a core thickness much softer for toughness and resilience.
4. It is difficult to compare the hardness specifications for a modern crankshaft against the heat-treat process for an antique crankshaft. The best practice would be to hardness-test the antique crank and compare the specs with the specs for the modern crank. This would have to include core-samples from the antique crank. And yes, I get it, the best way to be sure about the modern crank would be to hardness-test it as well... Happy Motoring!

[BlueSunoco]

Originally Posted by C26Pinelake

Truly amazing! Us Guys that turn the key and drive down the road have no idea what degree of expertise was necessary for us to do so. It is also amazing what tremendous expertise is available on this site ! I am truly impressed ! Wayne

I'll second this. Very interesting thread I'm learning a lot!

[MikeK]

Chris,
Thank you for the additions. I do disagree with your statement #1. Although quenching is also done in case hardening treatments, the Ford process as stated does not, in any way produce any case as it does not specify any previous treatment to diffuse carbon or nitrogen into the matrix surface. No type of quench can do that. The caustic is specified simply because it has a heat transfer rate much greater than plain water. 10% caustic potash (KOH) has a 1.38 rate, 10% sodium hydroxide (NaOH) has a 2.06 rate. This is done to ensure through hardening with the relatively low alloy steel Ford used. The quench function is to rapidly form Martensitic structure from austenite before excess carbon has time to diffuse out and form cementite (Fe3C).

[SAJ]

MikeK. Is this a typo? Caustic soda is the common name for sodium hydroxide. Did you mean water is 1.38?
I am not familiar enough with these figures. What is the rate for brine quench, which I sometimes use and for oil quench?
Thinking some more, are these rates relative to oil which is 1? I would like to put these figures on file for ref. when I harden tools, parts etc
Thanks for the info.
SAJ in NZ

[MikeK]

SAJ- Yes, a bit of a brain freeze on my part. I should have said "caustic potash" (KOH) not caustic soda which is NaOH. I will correct it.

High to low, the heat transfer quench list goes something like this:
2.06 - 10% NaOH solution
1.96 - 10% Brine (NaCl) solution
1.38 - 10% KOH solution
1.00 - water @ 65F / 18C
0.40 - very light fuel oil
0.30 - diesel fuel
0.20 - 20wt straight non-det. oil
0.03 - circulated air
0.015 - still air

[SAJ]

Thanks MikeK. I will stay with brine for a fast quench, since my leather welding coat has holes from hot caustic splashes from the one time I tried it, and face protection is much more important than with 10% salt water, which is quite close to NaOH in heat transfer, from your table. Though less corrosive to steels than brine if not washed off, I guess.
The trouble with dilute solutions is they become concentrated as they dry and even vinegar eats skin too if not washed off before it concentrates - apropos my good leather welding coat!!.
That is a handy table to have near the welding bench. And the huge differences explain why brine cracks things much more easily than an oil quench if not done carefully and evenly.
SAJ in NZ

[BRENT in 10-uh-C]

Mike, I just finished picking up the aftermarket crankshaft from the machine shop in a neighboring city that had the Rockwell tester. The owner said he had 3 different readings beforehand on different journals and when I asked, he did one in front of me on the front journal that was at a tad over 50, but he said his three readings were all between 50-55. That appears to be a far cry from the 260-320 range doesn't it? Thoughts now? Any chance of salvaging this crank?


.

[d.j. moordigian]

Brent,

I think he gave you the Rockwell number....50-55 on the C scale..

[BRENT in 10-uh-C]

Originally Posted by d.j. moordigian

Brent,

I think he gave you the Rockwell number....50-55 on the C scale..

May be Dudley?? I know he grabbed a file and made a couple of passes on the throw and commented he felt it was soft material. Maybe he did not know how to read the silly machine?? I know I sure don't!!

In looking at a chart HERE does anything look like it corresponds to what the crank manufacturer specs listed above are??

[d.j. moordigian]

Originally Posted by BRENT in 10-uh-C

May be Dudley?? I know he grabbed a file and made a couple of passes on the throw and commented he felt it was soft material. Maybe he did not know how to read the silly machine?? I know I sure don't!!

In looking at a chart HERE does anything look like it corresponds to what the crank manufacturer specs listed above are??

If you go to "50 on the C scale" (Rockwell),...then follow the line across
to Brinnell, it reads "475". I think I'm reading that correctly. The thing that
bothers me is the "file" testing,...ya, a file will cut metal @ 50 on the C
scale....it's NOT carbide, that's hard..

[BRENT in 10-uh-C]

Originally Posted by d.j. moordigian

If you go to "50 on the C scale" (Rockwell),...then follow the line across
to Brinnell, it reads "475". I think I'm reading that correctly. The thing that
bothers me is the "file" testing,...ya, a file will cut metal @ 50 on the C
scale....it's NOT carbide, that's hard..

Yes, but '475' is WAY more than what is specified by the Manufacturer ( manufacturer's specs were to be 260-320 ).

[d.j. moordigian]

".Anneal at 650° F. to meet a Brinell of 402-444"...I think this
is the journals.

".Re-anneal Front End as indicated (Brinell 302-364)"...I think this is the snout of the
crank.

I don't think theirs enough information.....this is a bunch of "best guessing" and you
know what I think about guessing O'l buddy...

[johnneilson]

Brent,

Did I read this correctly? You picked up and Aftermarket crank?

I had one here some time ago that was cast Iron. Very soft compared to the original.

Can you enlighten us with who the mfg is?

John

[MikeK]

Brent, If the journals are at 50C Rockwell you are good to go for either babbitt, tri-metal, or Aluminum/Silicon bearings. Harder won't accomplish much. A typical file will be ~62C Rockwell or 700+ Brinell. If you are using AER's latest inserts they are Al/Si and will actually do best on a surface that is not glass-hard! The Silicon in the alloy actually micro-polishes a crank in the 400-500 Brinell range (42C-52C) and gives you the 100K mileage bearing life in today's production engines.