Dimension change after Heat treatment

[Shox Dr]

Bought some 19.05mm (measured at 19.07) silver steel. Heat treated - carrot hot>quench in water.

came out 19.05mm needed it to stay the same ie 19.07, so case hardened it. Blow me it shrinks again to 19.04.

so bought 19.50 silver steel, machined down to 19.10. Heat treated and its got f’in bigger 19.11


Arrrrrrh


What im i doing wrong

 

[Seadog]

Why are you case hardening silver steel?

 

[Shox Dr]

Why are you case hardening silver steel?

It was only to see if it increased in size. I wasn't intending to c/h the replacement machine part

 

[Agroshield]

What am I doing wrong

Expecting it to stay the same. You have to grind or lap after hardening.

 

[Seadog]

You have to grind or lap after hardening.

Except that you can't grind something up in size

 

[Shox Dr]

Expecting it to stay the same. You have to grind or lap after hardening.

I took that into consideration when machining the second part. The machined area is to be pressed in so does not require a ground surface, I just want it to end up at 19.07mm.
First time it shrunk, 2nd it grow. I dont understand

 

[Shox Dr]

Just to clarify.
Required dia 19.07mm
1st piece 19.07 before, 19.04 after (not machined)
2nd supplied at 19.50, machined to 19.10, after heat treatment 19.11.
As the first shrank by 0.03mm, machining the 2nd to 19.10mm should result in 19.07mm

 

[Shox Dr]

Left to right, original, 1st, 2nd

 

[Shox Dr]

Tried to remachine the 2nd, Worth a try, but didnt work, simply because I could get it better than 0.04mm. Once taken it out the collet, all was clear, it still had scale from annealing.


3rd go. <0.002mmTIR. So should have been possible to remachine the 2nd, if it have been clean. Oh well on wards and up wards

 

[Agroshield]

First time it shrunk, 2nd it grow. I don't understand.

Heat treatment is sometimes challenging. Look how they did it in the old days, with virgin's blood or something.

The two bits of material you started with were not from the same bar, possibly did not have the same chemical composition. Unless you have very sophisticated facilities, the heat treatment process you did will have varied a bit between the two.

If you want dimensional stability, maybe silver steel is not the correct material - there are lots on online resources that can point to a more appropriate one. Also for dimensional stability, heat treatment is not necessarily a preferred process, with something like nitriding being better.

Lapping does not have to be sophisticated or difficult. A wooden clothes peg with some Solvol on the jaws, a piece of wood with a hole bored in it, a saw kerf across it and a tensioning bolt with valve grinding paste will do for a one off.

 

[Shox Dr]

Heat treatment is sometimes challenging. Look how they did it in the old days, with virgin's blood or something.

The two bits of material you started with were not from the same bar, possibly did not have the same chemical composition. Unless you have very sophisticated facilities, the heat treatment process you did will have varied a bit between the two.

If you want dimensional stability, maybe silver steel is not the correct material - there are lots on online resources that can point to a more appropriate one. Also for dimensional stability, heat treatment is not necessarily a preferred process, with something like nitriding being better.

Lapping does not have to be sophisticated or difficult. A wooden clothes peg with some Solvol on the jaws, a piece of wood with a hole bored in it, a saw kerf across it and a tensioning bolt with valve grinding paste will do for a one off.

I agree with everything you say. I’d not taken in to account the different material batch, and at 0.4mm difference I assumed it would be about the same.

No loss, so long as I’m learning.

I’ll machine it to 19.07mm tomorrow, and see what it comes out at after heat treatment.