4140 Investment Cast Steel Strength Properties?

[farmer2]

What should the hardness be for 4140 investment cast steel? As cast, not heat treated.

One reference shows an Rb of 100. Checked some parts which show Rb 80-85 (converted from Rc scale). Having to check using Rc tester and getting Rc of 0 to 2. Looks like Rb 100 should convert to approx. Rc 22.

We have seen ususual wear on 2 parts hardness checked on.

Thanks,

 

[dbooker630]

If you are getting HRC values <20, you should switch to a lighter diamond load such as HRA or heavier ball load such as HRG (150 kg 1/16 ball).

Also need to know the chemistry of the parts and how they were cooled to ambient temp.

 

[redpicker]

As stated above, converting from Rockwell 'C' from values less than 20 is not going to be very accurate.

The hardness of 4140 investment castings in the as-cast condition can vary widely. The values you get are going to depnend on the cooling rate from the casting temperatures, the amount of surface decarburization you have, and the amount of surface preparation done prior to taking the hardness test.

I don't know why you would use 4140 investment cast without a specified heat treatment after casting. If you aren't interested in the mechanical properties (or, put another way, if 80-85 HRB is acceptable), there are steel chemistries that would be easier to process (read: cheaper to make). Depending on the size of the casting and the application, I suspect you should be specifying either a quench and temper or normalize and temper heat treatment.

rp

 

[SMF1964]

Agree with the rest of you - Rockwell C values below 20 are not valid numbers, just as Rockwell B values above 100 are not valid numbers. You should run a Rockwell B test on the samples to get an accurate hardness reading if your hardness numbers are coming in too low to be on the C scale.

Was there a hardness requirement in the original spec?

 

[farmer2]

Had 4 samples hardness tested. Range was HRBW 84 to 100. Converts to 81,000 to 114,000 psi.

Even though our dwg does not specify a hardness range, does this range look too broad?

Part is running against a steel part which has a hardness of Rc 33 with grease between the running surfaces, so may not want it heat treated so as to be closer to the hardness of the mating part.

 

[dbooker630]

I would section the low and high readings to examine the associated microstructures. If the structures are similar, perhaps the range is not too broad.

 

[TVP]

The range is probably reasonable for an investment casting that has variable section size leading to some variation in microstructure. Agree with dbooker630 regarding the method for verifying this scenario.