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.

 

[redpicker]

Having the threads hardened 4150 at 60 HRC scares me. Even with the constraints you mention, it is the sort of thing that will work...for a while. That is, you will go a year or two without any problem, then, all of a sudden, one will break and within days (perhaps even hours), you will have them all breaking, some that have never been put into service. The perverse ways of nature, I guess.

Being so small diameter, can you just flame harden the area where the seal will be? 4150 in that size would probably harden just fine with a strong air blast for a quench. A 350F temper and a polish after flame hardening and you're done.

rp

 

[dbooker630]

Or you can selectively soften the threads, flame or induction would work. I agree that any threads in the 55-60 HRC can cause a problem. I can also attest to having parts with hard threads break in the shipping container, long before assembly.

 

[fastline12]

I really thought we were close with nitriding because we could suspend the parts from the threaded end and get what we need but the case is ultra thin, the process leaves nasties on it the part, etc.

We previously 8620 and carburized it. We are getting closer to that I guess...

If we flame harden, I will need to design a device to do that or I supposed outsource but that will not be cheap due to lack of batch processing. I might like the idea of drawing back the threaded part though. I was also curious about threading something on the threads during HT? However, with this much carbon, and the dims, I bet through harden is a given...