Heat treating 01 water hardening?

[mcostello]

I have a shaft to make for a mower gearbox. It has been unavailable for 30 years. I bought a piece of 0-1 water hardening drill rod and hardened it at around 1700° and tempered at 325° for an hour. The middle was file hard, ends came out soft. After more research another site said to harden at 1400° and I tried again, it is anealing right now and the ends seem hard now. Would the extra heat bozo the job? Double heat treat is good or bad? How hard is file hard at the minumum? This shaft has to roll on needle bearings and 58rC seems adequate, specs say I should be able to get 62-64rC. Doea all this sound right?

[Steve Sells]

I may as well be the one to rain on your parade, because I dont know where you got the idea of using water, but you may have ruined that steel because O1 is not water hardening, its OIL hardening,  that is what the O means it could be fine, tho it could now have many micro fractures, time and hard use will tell

[Latticino]

O-1 is the canonical oil hardening steel, and has been in use for a relatively long time.  Please note that heat treatment "recipes" used for knife crossections are likely not appropriate for a 1" shaft used in a mower. For this kind of application you should be using industrial grade heat treatment services and quality tempering as the last thing you want is a brittle steel part rotating at high RPM.

I'm not sure why you chose O-1 in the first place.  I would expect a mower shaft would need more toughness than hardness.  I would be selecting needle bearings with an inner ring (or race) that is appropriately high chromium to limit corrosion (see below) and most likely use 1045 or 4140 shaft stock (that is water hardening) for toughness.  Honestly, even if the needle bearings were directly resting on the shaft, I would still probably go with 4140 or similar (though I would expect a machined and appropriately polished race would greatly increase the lifespan of the bearings and shaft).  Note there is a great, free, downloadable heat treatment app (Heat Treater's Guide Companion) that is sponsored by the Heat Treatment Society under the ASM International Umbrella.  They recommend austentizing O-1 between 1455 and 1500 deg F prior to oil quenching for 63-65 HRC, then tempering between 345 and 500 deg. F for hardness ranges between 62 and 57 HRC on a sliding scale.

To answer your direct questions:  Double heat treatment is typically bad, particularly if you don't control grain growth or have an accurate way to measure stock temperatures.  File hardness depends on the file being used to check the surface and the experience of the tester(and can be confused by the potential for surface decarbonization).  Also, "annealing" is to soften the stock so it can be machined.  This differs from tempering to remove brittleness after the hardening quench.

I would be very wary about using the shaft you have made.

[mcostello]

The industrial store I bought it from says They only buy water hardening drill rod. The second time it got hard, although the only change was lowering the temperature using the color chart provided from the book mentioned on this site. My bad the shaft was tempered. One source for hardening color temperature stated 1700° which looked like I should have been close to. The second try was 1400° going by the same chart. Maybe They are buying W-1, will ask next time I can.

[Randy Griffin]

Well if you quenched it twice in water, 1700 the first time, and then anealed it, you now have some soft micro fractures and oversized soft grain. If you want to make the shaft, machine it yourself and send it somewhere to be hardened correctly.

[ThomasPowers]

What happens if it "explodes" during use?  Your liability is quite high I believe.