4140 Surface Hardness

[MarSeb]

Hello,

I am trying to harden a 4140 bar to RC 52-55. Is there a reason why the surface hardness on this bar would be so low (RC 10) compared to the hardness at a depth of .050 in where the hardness reaches 52?

Any help will be appreciated.

Thanks!

 

[swall]

Decarb?

 

[dbooker630]

I suspect decarb also - but how much was on the incoming product.
Another possibility is the furnace atmosphere, if there was one at all.

 

[MarSeb]

I'm thinking decarb as well. I was talking to one of the heat treatment/hardening shops here in town and they suspect there's something wrong with the material itself.
We heat it up to 1600 and quenched it in water and it did not even crack or anything which you would expect for 4140. This was part of a project I'm working on.

dbooker630, what do you mean how much was on the incoming product?

 

[redpicker]

Sounds like Decarb to me. If the surface is very low, but at 0.050 it meets expectations, it just about seals it.

4140 can be water quenched without cracking; it might crack, but depending on variables, it may not. If you meet 52 HRC, you have enough carbon to crack if conditions are right.

Get a micorsturcture analysys done and you will see if decarb is the problem.

rp

 

[dbooker630]

When I mentioned incoming product, I am suggesting that the microstructure analsyis be performed on samples both before and after heat treatment. As redpicker has noted this should confirm whether the material or the furnace is the problem.

 

[MarSeb]

Thank you for your responses repicker and dbooker630. I will try a sample piece from a different bar. If this does not work, I will go ahead and look into the microstructure analysis. It might be that I'm not getting the correct material from my supplier.

Thank you!