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2H vs Gr.7 differences from CCT curves

2H vs Gr.7 differences from CCT curves

2H vs Gr.7 differences from CCT curves

thread725-460863: A193 B7 studs with A194 L7 nuts

Quote (Rogue909)

2H material (1045) does not always effectively through harden during quenching. This results in uneven or un-attainable material characteristics. As your diameters get large (What diameter are you using?) grade 7 (4140, typically) becomes the go to. You can look in to the CCT (continuous cooling transformation) curves in 1045 vs 4140 for a bit more detail.

Question for all: how can I understand the difference between the materials from their CCT curves?

I've found these 2 diagrams:


Where do I see "uneven or un-attainable material characteristics"?

Thank you

RE: 2H vs Gr.7 differences from CCT curves

Large diameters have large differences in cooling speed (= different end structures).
This often results in a hard outer shell, but less hardening in the center.
The links don't work for me though.

RE: 2H vs Gr.7 differences from CCT curves

Apart from CCT curves, you can look through the MTCs to get an idea of the inclusion content of the steel, i.e. %S & %P.

Then, go thru the mill certificates to find out about the steel-making process and subsequent secondary steel-making.

Kolkata, India

RE: 2H vs Gr.7 differences from CCT curves

Look at the time required for cooling to maintain 100% martensite.
For 1045 this is about 3 sec, for 4140 this about 11sec. If you had one for 4340 you would find it out near 1 min.
This directly translates to how thick the material can be and still through harden.
Maybe Jominy end quench data would show you better. There is even a way to convert this into hardenability for various size bar.

= = = = = = = = = = = = = = = = = = = =
P.E. Metallurgy, consulting work welcomed

RE: 2H vs Gr.7 differences from CCT curves

It should not be necessary for a non-metallurgist to have to dive that deeply into the nuts and bolts (sorry) of hardenability concepts. Knowledge of the product characteristics should suffice.

"Everyone is entitled to their own opinions, but they are not entitled to their own facts."

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