Heat treating 4140 round stock

[Jorville]

I was told when metal is heat treated it will shrink or get larger. not sure which. I want to harden a 3/4" piece of round stock. I also want to harden a piece of 1 1/4" round stock with a 3/4" hole through the center. After they are hardened I want the 1 1/4" piece to rotate on the 3/4" piece. with maybe .004 clearance, maybe a little more. Anyone have any ideas on this?

 

[ruffdog]

My experience is the solid piece will not grow as much as the hollow piece. Are you quenching in oil and drawing them back? Be sure to quench straight down into the liquid to keep it from warping like a banana.

 

[yomax4]

What is your application? 4140 is pretty tough stuff even without heat hardening.

 

[MickeyDBC]

Sometimes it will move a little but as long as your heat treater knows what they are doing it should not be bad. If you are doing it yourself, be careful because you can hurt yourself or start a nasty fire if you are using an oil quench.

 

[kthompson]

I worked in a tool shop area for a manufacturer few years back. Can not tell you more about the steel than we called it "tool steel" and used it for drill bushings and such with an oil quench and never had issue with the dimension changing. Now would 4 thousands had mattered, doubt it.

 

[Jorville]

what I want to do is fix the 3/4 round so it can not rotate,the larger piece will rotate like a bearing, slowly.

 

[Jorville]

kthompson how hot did you get the steel, red. red should be around 1,000 degrees, I think.

 

[metalbender]

Probably help to know the application of the pieces. Usually, rotating parts have bushings and lube. Why are hardened parts required?

 

[Jorville]

metalbender, Harding is not required, I just thought the parts would last longer, I plan on keeping the parts oiled or greased. I could get by with just cold rolled steel. I might go that route. I might experiment a little with my heat treating idea. If it does not work just go with cold rolled. Or 4140 with no heat treat.

 

[metalbender]

Guess it's because I have a pretty well equipped shop, that I look for ways to build things. Metal on metal will not wear if there is ample lube. The moment the lube film is broken, wear begins. In the case of a bronze bushing, they are porous and hold lube well. Many furnace blower motors lasted decades with a regular shot of 3 in 1 oil. In your project, try to utilize a bushing, but the center pin must be polished.