Recommendation for steel alloy for small shaft

[fastline12]

We currently make a small shaft that is approx .375" diam x 4" long. There is such minimal stresses on the shaft that any steel would do the job. However, due to an oil seal riding on it, the shaft surface must be hardened to HRC 58-62. What we have used in the past is 8620 and carburized it. However, we need to outsource this part and finding that the extra grinding and treatments are getting expensive.

Is there by chance a magic bullet for this that would have high enough carbon to reach HRC 58 with just quench and temper? Ideally only harden to this level on the surface? I never like to use parts as quenched but with really no stress on the parts, it could be an option.

 

[Tmoose]

What machining operations are necessary?

if none, how about starting with a drill or reamer blank?

http://www.vermontgage.com/Newprices/blanks/blanks.html

If many, I'd be thinking about ion beam nitriding, flame hardening, or something similar.

Looks like standard "speedi sleeves" start around 1/2 inch shafts.

 

[ornerynorsk]

Years ago I was manufacturing a proprietary manual hydraulic pump and I switched from a through hardened alloy to 12L14, carburize, and grind for the very reason of cost! In this case, the case-harden and grind only cost us 20 or 30 cents per part, whereas the through hardening caused more problems than it solved.

Could you use a hardchromed barstock and simply turn your part from it with no further treatments?

Just a couple of ideas.

It is better to have enough ideas for some of them to be wrong, than to be always right by having no ideas at all.

 

[fastline12]

LOL, it sounds like we may already be on the right track I guess. Actual material cost in this size is pretty minimal. These parts get some turned. Threaded end, other end has a taper and other features as well as cross hole. The cross hole really cannot be drilled practically at full hardness. Chrome plate we try to stay away from due to flaking. Probably would be much more expensive too.


We certainly are not getting our parts carburized and ground for 30C each though!

 

[ornerynorsk]

Hard chromed shafting is available stock in many sizes, but I don't know if your sealing surface is on the major OD. Your material cost may be secondary to your heat treat and grind.

http://www.scotindustries.com/inventory.php

It is better to have enough ideas for some of them to be wrong, than to be always right by having no ideas at all.

 

[fastline12]

One of the questions raised around here is if possibly a higher alloy steel such as 4140 or 4340 would still work for this but would just operate at full hard condition plus the carburize surface? Generally not a really great idea structurally but again, very little load on this shaft. I am just trying to keep the door open to other alloys. 1018 is not quite the structural good stuff as 8620 but could work I guess.

 

[ornerynorsk]

I don't think you'll hit your hardness requirement with 4140 or 4340 unless you go with flame hardening. Do you have any concern over warpage or distortion with no post heat-treat grinding?

Another idea . . . While developing the aforementioned hydraulic pump, I tried 2 other methods experimentally before settling on the case hardened and ground 12L14. I had aluminum hard coat anodized with a teflon fill, and also used a ground stock shafting and had it electroless nickel plated, but I never tested either to a million cycles, I just ran out of time with the project, and always wondered how it would have worked out.

Good luck on the project!

It is better to have enough ideas for some of them to be wrong, than to be always right by having no ideas at all.

 

[EdStainless]

Electroless high phos Ni that you then age harden (forms intermetallics in the plating). is quick and cheap.
But it does add steps.

= = = = = = = = = = = = = = = = = = = =
Plymouth Tube

 

[fastline12]

My thought in the 4140/4340 material was to ALSO use the carburizing method which should infuse enough carbon in the surface to get to HRC 58-65 pretty easy and the rest would stay at full hard of HRC55-ish...


There is concern of warpage in the part and we have always specified grind after heat treat. However, I just talked to a potential vendor that wants to grind BEFORE heat treat. I am a little nervous about that. If there is runout, there will be issues. 4140 for us has been extremely dimensionally stable in the size areas we work in. Love it. all diams and bores stay true. 8620 also seems a good alloy.

 

[dbooker630]

What about induction hardening? One option would be to use prehardened 4140 in the 30s HRC range, machine the shaft body and roll or cut the threads, then induction hardening the surface except for the threads. A temper around 300-325 should result in a surface of 55-58 HRC.

 

[TVP]

I concur with dbooker630. This is commonly used for hydraulic cylinder Piston Rods, etc. that require high pressure seals. Even lower cost is 1045 that is only induction hardened on the surface.

 

[swall]

Salt bath nitriding with a final polish would be an option. Something like the QPQ process.

 

[fastline12]

We work a lot wtih 4140 and find it to hit around HRC55. 58 is a minimum and probably only obtainable as full hard, no temper.

I might be curious about 1045 or 4150. Both have a little more carbon so guess could possible work?

I figure induction hardening to actually cost more than batch processing? Is there a major concern in hardness in the threads? The mating part is Aluminum and not under much torque. I could sure see though if we were torquing something down hard, there that could be an issue though!

 

[BrianE22]

Have you tried running the seal on a not-so-hard shaft?

 

[Maui]

An air hardening tool steel like A2 should work well in this type of application. It is readily available in a variety of diameters, and is not excessively expensive. If dimensional stability is a concern, during heat treatment I would suggest using a cold treatment at dry ice temperatures after the first tempering cycle has been completed, and then follow that with another normal tempering cycle. Obtaining a through hardness of 58 - 60 HRC with a corresponding Charpy C-notch toughness of 33 - 41 ft-lbs is readily achieved with this grade.

Maui

http://www.EngineeringMetallurgy.com

 

[dbooker630]

The intent of induction hardening would be to selectively heat the shaft body, keeping the threads at their existing hardness. We use pretreated 4140 for several shaft applications with threads at our facility.

If you were to use 1045 or 1050 the best induction hardening response would be with heats that have the manganese on the high end, or 0.80-0.90% Mn. Not always easy to find in a warehouse but it can be found with some extra effort.

 

[TVP]

4145 and 4150 are both commonly available instead of 4140 when surface hardness needs to be > 55 HRC. The cost of batch furnace vs. induction depends greatly on the details. For low volumes and/or irregular sizes, a new induction coil is needed, which requires up front money and time. I work for a company that produces large quantities for the automotive industry, hence induction is a low cost, high productivity process.

 

[fastline12]

It has been a day or two but forgot I created this thread. I am still working on this problem and we will have to make a decision in the next few weeks.

I am looking hard at just batch treatment if 4150 with a low temper. The two questions I have are:

1. If we have them vacuum treated, will we still have a low micro finish if we grind "before" treating them?
2. The 3/8" shaft has a 1/4 male thread on the end. Could we get away with heat treatment of the threads? I DO realize they will become brittle but they are really only used to mate an aluminum hub that is only fitted one time and glue is applied to the threads. All load on it is radial.

 

[ornerynorsk]

Two comments, for what it's worth. If you are going to grind them anyway, why not just grind after heat treat? Could you use female threads instead?

It is better to have enough ideas for some of them to be wrong, than to be always right by having no ideas at all.

 

[fastline12]

Grinding post heat treat really is probably the better way to go, I agree.

threads have to stay male and really need machined when the shafts are made. Hard turning threads can suck and it is one more operation that will cost us hours. If it is done when still in the machine, it will take 15 sec/part.