Posted by Matt Wilson [172.69.69.79] on Sunday, April 07, 2019 at 02:49:18 :
In Reply to: Re: Calling All Engineers/Machinists posted by Vaughn [172.69.33.80] on Saturday, April 06, 2019 at 09:00:01 :
I doubt 1020 is a mix of leftover steels. That sounds like one of those rumors that someone starts and no one can justify. 1020 is just a spec for a steel, like any other spec. 1020 has 0.2% carbon and a certain amount of other elements (not much of those other elements though).
I'm a little surprised that the reverse gear shaft you mention makes use of the low-carbon steels you listed. Of course, maybe it's not a big deal since reverse gear is generally not used for any great length of time. Also, if those transmissions are anything like the ones I've dealt with, the reverse gear has a bushing inside, rather than a set of rollers, which would be harder on a soft steel like the ones you mentioned.
In any case, I must say I'm not a metallurgist, so all I can do at the moment is look up stuff online, but I just saw that you were leaning toward 1015 and I know that stuff won't get very hard unless you carburize it.
Reading a little bit on 4140 leads me to believe it might do what you want, although it might not get quite as hard as you'd like. 4340 may get to the hardness you want, but apparently is susceptible to other problems at such hardnesses, such as stress corrosion cracking. 8620 is a case hardening steel, meaning it will develop a good case hardness if it is carburized, but if it's just heated, quenched and tempered, I don't think it will.
I'm wondering if something like 1050 steel would be a decent candidate. It can be hardened to as much as Rc 61 at the surface and I didn't see anything to indicate it suffers from the same issues as 4340. Hopefully the machine shop you use has knowledge of heat treating and a way to heat it to a known temperature. These alloys usually require heating to somewhere between 1500 - 2000 deg F then quenching in water or oil, then stress relieving/tempering at 300 - 400 deg F. If you are wanting them to carburize the parts, then they will have to have a furnace with a carbon-rich environment. I doubt most machine shops have such capabilities, so I'm guessing they will be doing flame hardening (heating with a torch and quenching then stress relieving).
This may be ok for the shaft, but not sure how this will work for the hardened spacer you're talking about. How thick are you planning to make the spacer (wall thickness)? If it's fairly thin, it may get very hard all the way through, which may or may not be desirable. It seems like the sleeve as a whole might be brittle.
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