Hardness of 1020 case hardnening 1

[SeasonLee]

A simple question on case hardening.

A part casted with 1020 steel, but need carburize ( .012 MIN DP) to HRC 30~45 in case. My questions are:
1. Can we test the hardness with HRA or superficial scale and convert it to HRC?
2. The size in section is 3/8” square, if hardness in surface measured at HRC 40, what is the hardness in core ?
3. If the hardness measured at HRC 15 in core, is this a carburizing process ? If not, what is the possible processing in heat treatment.

Thanks for all inputs

SeasonLee

 

[metman]

For .012 min depth, Rockwell I think will give too much penetration of the indenter even for the superficial scale. You need to use Diamond Pyramid or Vickers which are microscopic scales.

It appears that your test of the surface is punching thru the case and giving you a low reading of the actual case hardness. HRC 15 for the core sounds about right even though below about HRC 20 is off the C scale.

So yes it appears to be case hardened by carburizing.

 

[SeasonLee]

Thanks for the comments, metman.

May I ask again : Can we test it with superficial or HRA scale if the case hardening is deep enough, say .060” hardneing layer. If we can measure the hardness with HRC scale, for example HRC 40, then what is the minimum thickness of the case hardening.

SeasonLee

 

[redpicker]

What you are asking is can you use the Rockwell hardness test in a non-standard method. Sure, you can. Will the results be meaningful? That depends on what you want them to mean.

Years ago, I saw some research that tried to use the difference between the Rockwell "C" hardness and a superficial (I think it was 15N) hardness (converted to HRC) to indicate case depth. The theory is relatively sound; if you get the equivilent of 60 HRC on the surface using HR15N but only a 52 using a HRC, then that would show you have a case depth of 0.0xx. The problem was that there are too many variables. Most importantly, you have to know what the core hardness is, and you can't measure that accurately without cutting the part. If you are going to cut the part, you might as well do a proper hardness traverse rather than guess at the case depth.

Yes, you can test using a superficail scale on the surface. In fact, that is what these scales were developed for. But, if you are going to try to use the difference between the superficial hardness and the Rockwell "C" hardness, you will find that it is not very accurate.

rp

 

[metman]

I agree with redpicker and yes with .06" case depth you can accurately measure surface hardness with Rockwell superficial scale.

 

[blacksmith37]

Yeah Red, I did that. We were making 10,000+ (small) 8620 parts per month, with 5 -8 mil case. With that many parts we were able, and needed to, cut many dozens to get hardness/case depth corrolation. The surface was 15N 90 min. As I remember we had a Ra scale min/max to get preliminary case confirmation. (All final case depth was done metallographically).
However with the low hardenability of 1020, it may be more of a challange.

 

[emxhps06]

If you intend to measure the carburized layer, perhaps using a Knoop indenter for microhardness testing(ASTM D1474 standard)would be more useful.

 

[mrfailure]

Besides carburizing, you may be seeing such surface hardening from either nitriding or carbonitriding (microstructure can confirm).

I also agree that you would have no idea what the core hardness would be based only on measuring surface hardness if parts were given a hardening treatment.

Aaron Tanzer

http://www.lehightesting.com

 

[SeasonLee]

Thanks for all inputs.

Now, I am wondering what material casted on this part since I can tested it on HRC scale and the reading between 51 and 62.

SeasonLee

 

[unclesyd]

My Bethlehem Steel data book for a .505 round bar gives a case depth of 0.065 a hardness of Rc 61 and a core hardness of 20 Rc. Using the approximate conversions given in the Uconeer software linked below gives an 82 Ra hardness for the case. These numbers agree with my American Chain and Cable Handbook.

The Uconeer software has approximate conversion between most hardness scales.

http://www.katmarsoftware.com/?referrer=Uconeer24A

 

[SeasonLee]

unclesyd, Thanks for the valuable information on my judgement.

SeasonLee