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EN24 Rockwell Hardness

EN24 Rockwell Hardness

EN24 Rockwell Hardness

Hi, I am soon going to be rolling some threads from EN24 bar before having them heat treated.  Looking at page 10 of this pdf http://www.landisthreadingsystems.com/ThreadRolling/Library/TechnicalSupport.pdf how should I know what column I should be referring to?  They refer to material hardness, which I am unsure of.  EN24 is equivalent of SAE 4340.  The threads will be 7/16 unf and unc.  

I am also getting myself confused between the difference in class 2 and class 3 shown on the same page.

RE: EN24 Rockwell Hardness

Looks to me like one of the columns labeled "30-50C or Alloy [whatever Rockwell C hardness range you have]" would be applicable. 30-50C must be referring to the carbon content in 1/100th of a percent (customary in US).

Thread Class refers to the tolerances and allowances (i.e. slop).  Class 1 thru 3 get progressively tighter.  Its all defined in American National Standard Institute (ANSI) B1.1, titled 'Unified Screw Threads'. There are probably online calculators, but here's an example.

.4375-14UNC-[what the class is]A  ('A' means external.)
EXTERNAL    Class 2                    Class 3        
Major Dia    0.4360    +.0000 -    0.0103        0.4375    +.0000 -    0.0103
Pitch Dia    0.3896    +.0000 -    0.0050        0.3911    +.0000 -    0.0050
Minor Dia    0.3587    Max, Ref            0.3602    Max, Ref

EXTERNAL    Class 2                Class 3        
Major Dia    0.4361    +.0000 -    0.0081        0.4375    +.0000 -    0.0081
Pitch Dia    0.4036    +.0000 -    0.0047        0.4050    +.0000 -    0.0047
Minor Dia    0.3820    Max, Ref            0.3834    Max, Ref    

RE: EN24 Rockwell Hardness

Bestwrench is correct, the 30-50 C means 0.30-0.50 mass % carbon, which is the category for EN24.  Depending on the exact processing history, it will either be "soft" or "15-25 RC".

RE: EN24 Rockwell Hardness

EN24 is a well known UK steel.  It is commonly available in "condition T", meaning it has been heat treated to give a tensile strength of 55/65 T/in2
Depending on ruling section and heat treatment it can achieve 100 T/in2, "condition Z".
We use condition T for shafts.

RE: EN24 Rockwell Hardness

Excellent thanks very much, I have been referring to http://www.westyorkssteel.com/EN24.html for information, and wondered about the carbon content but it was not on the same scale (0.4% where the thread rolling chart suggests only 30-50) but now I know.  I will be heat treating the studs to V condition to finalise, as suggested by an incredibly well respected person in the industry.

Can I assume that some of the information I will been and have been using is slightly complicated by the fact that the EN24 info is UK based whereas most of the thread rolling etc info is US based?

RE: EN24 Rockwell Hardness

Hi, sorry the first part was a statement, the 2nd part was just wondering if some of my confusion was because of the cross over between UK and US units and terminology, I am to be rolling imperial threads anyway so US is fine for measurements, just the hardness scales etc I wasn't sure about.  Thanks for all your help.

RE: EN24 Rockwell Hardness

Yes, units can be confusing, particularly in this field.

RE: EN24 Rockwell Hardness

It's not just me then!  I'm trying to remember all that I learned at college 8 years ago as since then I've been doing dirty engineering and automotive stuff!

RE: EN24 Rockwell Hardness

Unified threads aren't American, they are unified between US, Canada & GB as I recall.

There is a BS for unified threads, I was going to say 1936 but I think that's undercuts for unified threads.

www.boltplanet.com has a calculator for unified threads which can be useful to check your own calcs.

Posting guidelines FAQ731-376: Eng-Tips.com Forum Policies http://eng-tips.com/market.cfm? (probably not aimed specifically at you)
What is Engineering anyway: FAQ1088-1484: In layman terms, what is "engineering"?

RE: EN24 Rockwell Hardness

My memory is that UNC and UNF were post-WW2 standards when the UK was still looking West to the US and Canada.

However in the late 1960's the UK started looking East to Europe and metricated.

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