alloying elements on AISI 4140

[epanabdullah]

Dear experts,
I've just done re-heat the AISI 4140 with the hardness result still didn't reach the maximum. The investigation found that the chrome is 0,7% which is should be on the range 0,9 to 1,2 % as the standard for AISI 4140. Is there any explanation or relation between the alloying element (with a little bit less form the standard range such as 0,7 of 0,9%) to the material properties?

Thanks in advance,
epan

 

[arunmrao]

Section thickness, hardening temperature, quenching media, any surface decarb are some of the details you need to provide,before getting a meaningful response.

_____________________________________
"It's better to die standing than live your whole life on the knees" by Peter Mayle in his book A Good Year

 

[redpicker]

The standard composition range for Chromium in AISI 4140 is 0.80-1.10.

Where are you getting the 0.90-1.20 range?

For AISI 4140H, the Cr range is 0.75-1.20.

If you consider a check analysis tolerance of 0.05% on Chromium, you result may not be out of range.

As arunmrao posted, we need more information.

rp

 

[mrfailure]

Since chromium increases hardenablity (among other functions), I can see how insufficient chromium could cause low hardness. You should check to see if 4140H (as opposed to 4140) is specified and if actual Cr content is in the tolerance band. It looks to me like your alloy has too little. Also, most steel makers shoot for the center of the range so even if you are in the tolerance band this may still be an indicator of lax quality and the degree of hardenibility.

Also, I noticed you only reported Cr content to one digit. Did you get composition using a quantitative method (such as OES) or from a semiquantitative method such as EDS or portable XRF? I would not trust values obtained using semi-quant methods for this purpose.

Aaron Tanzer

http://www.lehightesting.com

 

[epanabdullah]

Thank a lot for all the responses,
For the re-heat I do follow the step as referenced from ASM handbook vol.4 heat treating for ultra high-strength steels, with the section thickness 25mm, hardening to 870 degC, with oil quenching.
For Cr, some references said it's 0.9-1.2 and 0.8-1.1 I just pick the bigger one to have the different one.
I had the composition by OES method, the actual Cr is 0,734%, and the rest of the element is on the range even some is on the lowest range.

 

[gearcutter]

"with the hardness result still didn't reach the maximum"
Was the hardness test performed at the surface?
If not, at what depth were the readings taken from?

Ron Volmershausen
Brunkerville Engineering
Newcastle Australia

http://www.aussieweb.com.au/email.aspx?id=1194181